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Application Progress of Recent Advances in Some Copper Catalyzed Coupling Reactions

Sunil U. Tekalea*, Vivekanand B. Jadhav

a, Vijay P. Pagore

a, Sushma S. Kauthale

b, Digambar D.

Gaikwadb and Rajendra P. Pawar

b

aDepartment of Chemistry, Shri Muktanand College, Gangapur - 431 109 (MS) India

bDepartment of Chemistry, Deogiri College, Station Road, Aurangabad - 431 005 (MS) India

Abstract: Different cross-coupling reactions for the formation of biologically important motifs and intermediates in or-

ganic synthesis using various suitable copper catalysts are reviewed. These include C-C, C-N, C-O, C-S heteroatom bond

forming, cyclization and other miscellaneous reactions catalyzed by elemental copper, copper salts, CuI, Cu (OTf)2, CuBr,

Cu2O etc. The use of copper reagents instead of palladium catalysts and ligands seems to be advantageous from the com-

mercial point of view. The methods described herein afford the products in excellent yield without using expensive and

moisture/air sensitive palladium catalysts, ligands and reagents.

Keywords: Copper catalysts, Cross coupling reactions, Ligands.

1. INTRODUCTION

The metal copper and its alloys are extensively used by

mankind since thousands of years. Copper (derived from the

Latin word cuprum) is a first-row transition metal that exists

mainly in (I) and (II) oxidation states. The Cu (II) (Cu2+

) ions

are soluble in water. In sufficient amounts, copper salts can

be poisonous to bacteria, fungi and higher living organisms

too. However, despite universal toxicity at higher

concentrations, the copper (II) ion at lower concentrations is

an essential trace nutrient to all higher plants and animal life.

In animals it is widely dispersed in tissues, liver, muscle and

bone. It serves as a co-factor in various enzymes and copper-

based pigments.

Copper is a coinage transition metal in the field of co-

ordination chemistry and catalysis that constitutes the heart

of organometallic chemistry. One of the most important

striking features of transition metals is the variable oxidation

states due to which they show efficient catalytic activity.

Many copper reagents are widely utilized as catalysts for

numerous organic reactions. Transition metal catalyzed

coupling reactions are the important tools in synthetic

organic chemistry to construct C-O, C-N, C-C and C-S

bonds and several other miscellaneous reactions.

Recently the copper reagents are replacing the palladium

catalysts which are limited for industrial applications mainly

due to high costs. The Pd catalyst and ligands have restricted

applicability due to their expensiveness, air and moisture

sensitiveness [1].

Nowadays, the copper mediated organic reactions have

become a significant and interesting area of research in the

scientific community due to versatile nature of the copper

*Address correspondence to this author at the Department of Chemistry,

Shri Muktanand College, Gangapur - 431 109 (MS) India; Tel: +91

(02433)221342; Fax: +91 (02433) 221342;

E-mail: tekale.sunil@rediffmail.com

catalysts. They are mainly employed in the Ullmann and

Buchwald type of protocols.

The classical Ullmann reaction which encompasses the

synthesis of diphenyl amines, diphenyl ethers and diphenyls

normally requires the conditions of high temperature under

which many functional groups are not tolerated hence has

limited utility. It also requires stoichiometric amounts of the

copper catalysts which on scale up process poses the

disposal problem. Further DMF is the conventional solvent

for this reaction whose removal from the reaction mass is

tedious. So attempts are being made by the scientific

community to use catalytic quantities of copper reagents

instead of stoichiometric amounts. Studies are directed

towards the investigation to develop novel protocols using

copper catalysts along with a combination of suitable base

and ligand under relatively mild reaction conditions. The

commonly used solvents in the copper catalyzed

transformations include THF, DMF, DMSO, acetonitrile,

toluene while DIPEA (N,N-Diisopropylethylamine), Et3N

(triethylamine), Cs2CO3, K2CO3, K3PO4 etc. are the

frequently used bases. The ligands employed also play a

crucial role in such reactions, normally labile i.e. those

which can be displaced easily are used. Though the ligand

plays no direct role in the reaction its presence is essential

for the reaction to occur. It protects the Cu ion from

interactions which may degrade the reactants or form side

products and also prevents the oxidation of the Cu (I) species

to the Cu (II). The ligand may act as a proton acceptor and

hence eliminating the requirement of a base.

2. COPPER CATALYZED ORGANIC TRANSFOR-MATIONS

In the present review we would like to focus attention on

certain synthetic strategies using copper catalysts. Herein we

have categorized the copper catalyzed reactions into six

classes:

282 Mini-Reviews in Organic Chemistry, 2013, Vol. 10, No. 3 Tekale et al.

i. C-Arylation (Ullmann protocol: C-C bond forming

reactions)

ii. N-Arylations/alkylation (Buchwald protocol: C-N

bond forming reactions)

iii. S-Arylation (C-S bond forming reactions)

iv. O-Arylation (C-O bond forming reactions)

v. Cyclization reactions and

vi. Miscellaneous reactions

2.1. C-Arylation (C-C Bond Forming Reactions)

Organic chemistry is the chemistry of carbon

compounds. Consequently; C-C bond forming reactions are

of much significance in synthetic organic chemistry. This

part of the present review concerns with different C-C bond

forming reactions catalyzed by various copper catalysts.

Dawei Ma et al. [2] developed an efficient method for the

arylation of active methylene compounds such as diethyl

malonate, ethyl acetoacetate etc using CuI/L-proline catalyst

(scheme 1). Among the various bases (Cs2CO3, K2CO3, NaH,

K3PO4) and solvents (toluene, dioxane and DMSO) used

for the optimization of reaction conditions; the base

Cs2CO3 in DMSO at 50 oC was highly useful. This protocol

was successful with aryl iodides as well as aryl bromides.

R

O

OEt

O

ArX CuI/L-proline

Cs2CO3, DMSO, 40-50oC

Ar

O R

O

OEt

X = I, Br,

R = Me, Ph, OEt

Scheme 1.

R X

-MgBr+

1) Cu(OTf)2

iPr2O, 25OC, 3h

2) H2, PtO2

R -

Scheme 2.

OAc n-BuMgI

14 mol% of (S)-1

Bu

S

Me

NMe2

Cu

(S)-1

*

(R)

Scheme 3.

Cu(OTf)2 was reported as a convenient catalyst for the

reaction between aryl halides and cyclopentadieny-

lmagnesium bromide reagent in isopropyl ether [3]. This

constitutes a method for the synthesis of substituted

cyclopentane ring systems (scheme 2). Allylic substrates are

important for many addition reactions. G. J. Meuzelaar et al. [4]

catalyzed asymmetric allylic substitution reaction with

Grignard reagent by a chiral arenethiolatocopper (I) complex

(scheme 3).

The cross coupling reaction between aryl iodides and

bromides with ethyl acetoacetate using CuI catalyst in the

presence of N-methyl glycine ligand is documented in

literature [5]. The various solvents (THF, toluene, dioxane)

and ligands (L-cystein, glycine, sacrocine etc) were tried for

the reaction (scheme 4). Jin-Heng Li et al. reported an

efficient protocol using Cu2O nanoparticles/ ionic liquid [6]

as a novel combination for the Stille coupling reaction. They

used various catalysts, ligands and ionic liquids for

optimizing the reaction and demonstrated Cu2O

nanoparticles/P(o-tol)3/TBAB system as the efficient and

reusable system for Stille coupling (scheme 5). The reagent

required for the present protocol being readily available and

inexpensive, the Cu2O nanoparticles/P(o-tol)3/TBAB system

is superior over the application of palladium catalysts in

Stille coupling. Regioselective and enantioselective allylic

alkylation using a catalytic amount of copper bromide (1 mol

%) and dialkylzinc in the presence of phosphoramidite

ligand was successfully developed by Ben L. Feringa and

coworkers [7] (scheme 6). The catalyst CuBr was generated

in situ during the reaction from CuBr·Me2S source. F. Y.

Kwong et al. [8] reported -arylation of malonate esters

using aryl iodides or bromides, a catalytic amount of CuI (5

mol%) in the presence of 2- picolinic acid as the ligand and

Cs2CO3 base at room temperature (scheme 7).

R

X

R'Sn(n-Bu)3

Cu2O, P(o-tol)3

KF,TBAB, 125-130 oC

R

R'

Scheme 5.

The effect of ligand was also studied during optimization

of the reaction conditions. Since mild reaction conditions

were used many functional groups such as methoxy, nitrile,

fluoro were found to be tolerated.

K. A. Jorgensen et al. [9] demonstrated an enantio-

selective and efficient nitro-aldol (Henry) reaction using a

catalytic amount of Cu(OTf)2 and triethyl amine base to form

the corresponding -nitro- -hydroxy esters in excellent yield

(scheme 8). Benzoxazoles can be arylated at the C-2 position

using CuI in DMF as a solvent in the presence of lithium or

potassium t-butoxide base [10]. Although it requires higher

temperature, the reaction is rapid for the arylation purpose

(scheme 9). Iron salt/ CuI catalyzed reaction of aryl iodides

with terminal alkynes was reported [11] (scheme 10). CuI

I O

O

O

RR

O

O

K2CO3, CuI

N-methyl glycine,

reflux, 48h

dioxane

Scheme 4.

Recent Advances in Some Copper Catalyzed Coupling Reactions Mini-Reviews in Organic Chemistry, 2013, Vol. 10, No. 3 283

was used as an efficient catalyst for the stereospecific

synthesis of ethyl (2Z)- 2, 3-difluoro-4-oxo-substituted 2-

butenoates from (E)-2,3-difluoro-3-stannylacrylic ester and

acid chlorides by D. Burton [12]. This was the first synthetic

route for cis-difluoro-substituted analogues of 4-oxo-2-

butenoates (scheme 11). G. Sekar reported the arylation of

alkynes from aryl halides and terminal alkynes using the

Sonogashira type cross-coupling reaction (scheme 12) [13].

2.2. N-Arylations/alkylation (Buchwald Protocol: C-N

Bond Forming Reactions)

N-aryl amines including many nitrogen containing

heterocycles such as imidazole, pyrazole etc motifs are

biologically and pharmaceutically interested compounds

[14]. Buchwald and others have reported several protocols

for the formation of C-N bonds [15, 16]. The C-N cross

coupling between aryl iodides and amines using the Buchwald

Br

Et2Zn

2 mol% L

1 mol % CuBr.Me2S

diglyme,

-40 oC, 18 h

Et

77% ee

L =

O

O

P

Ph

Ph

Scheme 6.

X

REtO

O

OEt

O

R

O OEt

O

OEt

5 mol % CuI

10 mol % L

Cs2CO3, dioxane

r.t.

X = I, Br

N

O

OH

L = 2-picolinic acid

Scheme 7.

R COOEt

O

R COOEt

OH

NO2

MeNO2

20 mol% Cu(OTf)2, L

20 mol % Et3N

N

OO

N

t-But-Bu

L =

Scheme 8.

O

N10 mol% CuI

PhX, DMF, base

140 oC,10 minO

N

Ph

Scheme 9.

I

Fe salt/CuI

Cs2CO3 (2 eq)

NMP, 140 oC

Scheme 10.

284 Mini-Reviews in Organic Chemistry, 2013, Vol. 10, No. 3 Tekale et al.

protocol under ligand free condition in the presence of

copper oxide nano particles is documented in literature [17].

The reaction can also be carried out in the atmosphere of air.

An important feature of this method is reusability of the

catalyst which is significant from economic point of view.

The catalyst showed remarkable activity without any much

loss of activity (scheme 13). CuBr was used as a catalyst for

the one pot synthesis of propargyl amines from aldehydes,

secondary amines and terminal alkynes using chiral (R)

Qinap ligand in toluene at room temperature [18]. However

the reactions required prolong time (scheme 14).

Anilinoanthraquinones can be obtained from the Cu (0)

catalyzed and microwave assisted synthesis from

bromaminic acid with aniline derivatives [19]. During the

reaction pH has to be maintained between 6-7 using

phosphate buffers. Initially the reaction was tried under two

conditions: i) CuCl, Na2CO3 and Na2SO3 in H2O at room

temperature for 8-24 h, or under reflux at 120 °C for 8-10 h

and ii) CuSO4 and Na2CO3 in H2O at 120 °C for 12-48 h. It

was observed that no products or only poor yields could be

obtained by these strategies. Further there was formation of

1-amino-4-hydroxy-9, 10-dioxo-9, 10-dihydroanthracene 2-

sulfonate as the undesirable product (scheme 15).

F. Y. Kwong and coworkers [20] reported N-arylation of

hydrazides using copper (I)-picolinic acid as an effective

catalytic system (scheme 16). Among the several solvents

(dioxane, THF, tert-amyl alcohol, toluene, DMF) and bases

(Na2CO3, K2CO3, LiCO3, NaOt-Bu etc.); the combination of

Cs2CO3/DMF provided the highest yield of the products.

Stephen L. Buchwald [21] described a highly efficient and

selective route for the N-arylation of amines using aryl

bromides. N, N-diethylsalicylamide was used as the effective

ligand and potassium phosphate as the base in this reaction

(scheme 17). Usually the cross coupling reactions carried out

by conventional methods require more reaction time which

can be reduced to few minutes using microwave irradiation.

Such a microwave promoted C-N cross coupling reaction of

aryl halides with amino acids was investigated by Sivan

Velmathi [22] using copper catalyst (scheme 18). The N-

arylation of azaheterocycles like benzimidazole with aryl

SnBu3

F

COOEt

FF

COOEt

F

O

RRCOCl

10 mol % CuI

DMF, r.t.

Scheme 11.

R R'I

R R'

Ligand-CuI (20 mol%)

K2CO3, DMF, 140 oC

NHBn

NHBn

Ligand

Scheme 12.

XN

R'

R1.26 mol% CuO nanoparticles

1.12 eq RR'NH

1 eq KOH, DMSO,

80-110 oC, air,1.2-29 h

Scheme 13.

R H

O R"

HNR2'5 mol % CuBr, MS 4A

5.5 mol % (R)-Quinap

toluene, r.t.1-6 days

R

NR'2

R"

N

PPh2

(R)-Qinap

Scheme 14.

Recent Advances in Some Copper Catalyzed Coupling Reactions Mini-Reviews in Organic Chemistry, 2013, Vol. 10, No. 3 285

halides can be performed with copper catalysts such as

Cu(I)I and Cu(II)(OAc)2·H2O using K2CO3 base and 4,7-

dichloro-1,10-phenanthroline as the ligand in NMP solvent

(scheme 19) [23].

The reductive amination of bromonaphthyridines can be

carried out at room temperature in the presence of copper-

catalysts in aqueous ammonia [24]. The effective method for

preparation of alkyl 2, 7-diaminonaphthyridine mono-amides

can be carried out by performing the amination in ethylene

glycol/aqueous ammonia solution at room temperature in the

presence of Cu2O. This provides an important access to the

synthesis of nonsymmetrical 2, 7-diamido-1, 8-

naphthyridines (scheme 20). A C-N cross coupling reaction

between aryl halides and amines using Cu (I) catalyst and

pyridine based ligand in DMF as the solvent was carried out

by Wanzhi Chen et al. [25]. Among the various ligands and

copper catalysts; the combination of CuI and 1,3-di(pyridine-

2-yl)propane-1,3-dione was found to be efficient for C–N

coupling reactions to afford various N-arylated products in

good to excellent yields (scheme 21).

O

O

NH2

Br

SO3NaNH2

R

O

O

NH2

HN

SO3Na

R

Cu(0), pH 6-7

MW, 2-20 min

Scheme 15.

Me

Me I

HN

Boc

NH2

Me

Me N

Boc

NH2

CuI (5 mol%)

2-picolinic acid (10 mol%)

Cs2CO3( 3 mol %)

N2, DMF, 80 oC,

24 h

Scheme 16.

Br

R HN

R'

R''

R

NR''

R'

NEt2

O

OH

CuI, L

K3PO4

L =

Scheme 17.

X

Y

R OH

OH2N

Y

HN COOH

R

CuI/K2CO3, DMF

MW, 15-25 min, 140 oC

Scheme 18.

NH

N

Br

NN

ClCl

Cu(I)I or Cu(II)(OAc)2·H2O

K2CO3, 125 oC, NMP

N

N

Scheme 19.

N N NH2NH

R

O

N NH

ONH

R

Oi) PBr3, 110 oC

ii) Cu2O

amination, r.t.

10-87%

Scheme 20.

286 Mini-Reviews in Organic Chemistry, 2013, Vol. 10, No. 3 Tekale et al.

ArX NuH ArNuCuI (10 mol %), L (10 mol%)

K2CO3, DMF, 110 oC

N

O O

N

L =

X = Br, Cl

Ar = aryl, heteroaryl

NuH = N- heterocycles

Scheme 21.

N

Br

HN

S

R2

OO

R1

CuI/L, K2CO3, DMF

110-120 oC, 40h

N

N

S

R1

R2O

O

N

O O

N

L =

Scheme 22.

HN O

YX

N O

Y

X

I

20 mol % CuI

40 mol % L

2 eq K3PO4

1,4-Dioxane, 110°C

16-24 h

Scheme 23.

S

IH NHR1R2

S

NR1R2

N,N-dimethyl ethanolamine

10 mol % Cu metal

2 eq K3PO4.H2O

Scheme 24.

Different bromopyridines were successfully coupled with

sulfonamides by using CuI (20 mol %) and 1, 3-di (pyridin-

2-yl) propane-1, 3-dione (20 mol %) with K2CO3 (2 eq). The

proper solvent used was DMF and the reactions were carried

out at 110–120 °C [26]. The reactions required prolong time

for completion, nearly 36–40 h (scheme 22). C. S. Li [27]

demonstrated an efficient protocol for the Buchwald

coupling reaction of pyridine-2-ones with aryl iodides. N,

N’-dimethyl ethylene diamine ligand and K3PO4 base were

conveniently used for the reactions (scheme 23). The

presence of substituent affects reactivity of the halides. It

was observed that aryl iodides having electron withdrawing

groups react readily than the substrate without substituent

which in turn reacts faster than the iodides possessing

electron-donating groups. Thiophene ring is the central core

of many optoelectronic materials. Halothiophenes can be

aminated using copper metal catalyst, N, N-dimethylethanol-

amine ligand and potassium phosphate base [28] (scheme

24). Different amines including cyclic, acyclic, aromatic

reacted smoothly with halothiophenes.

Ar I HNR1R2

CuI(10 mol %)

Ligand (10 mol %)

K3PO4 or Cs2CO3

Ar NR1R2

Scheme 26.

Ar X HNR1R2

CuI (5 mol %)

2 eq HO(CH2)2OH

2 eq K3PO4

Ar NR1R2

80 oC, i-PrOH

Scheme 27.

R1

N

EWG

HKHMDS, CuI

R2Br

pyr, r.t.

R1

N

EWG

R2

Scheme 28.

COOR

Ar

2-NsNCl2/2-NsNHNa(2:1)

CuOTf (10 mol %)

Ar

COORCl

NH S

O

O

O2N

Scheme 29.

Cu(PPh3)3Br complex was used as a catalyst for the cross

coupling reaction of amines and aryl iodides in toluene at

100 oC by D. Venkataraman and coworkers [29] (scheme

25). The complex was stable to air and is soluble in many

organic solvents. The coupling of aryl iodides with amines,

amide and various nitrogen heterocycles using CuI catalyst,

K3PO4 or Cs2CO3 base in dioxane solvent at 110 o

C

temperature was reported by S.-K. Kang et al. [30]. The

reaction was complete within around 24 h to afford the

NH

R2

R1

I

R3

Cu-complex

base, toluene

110-120 oC

N

R1

R2

R3

N N

RRCu

Ph3P Br

R = H Cu(phen)(PPh3)Br

R = Me Cu(neocup)(PPh3)Br

Cu- complex

Scheme 25.

Recent Advances in Some Copper Catalyzed Coupling Reactions Mini-Reviews in Organic Chemistry, 2013, Vol. 10, No. 3 287

products in 41-95% yield (scheme 26). The cross coupling of

alkyl amines and aryl halides utilizing CuI (5 mol %) in the

presence of ethylene glycol as the additive and potassium

phosphate base at 80 oC in isopropyl alcohol was reported by

Buchwald S. L. [31] (scheme 27). A common process for the

N-alkynylation of carbamates, ureas and sulfonamides using

copper iodide catalyst was reported by R. L. Danheiser [32].

Initially the amides were deprotonated with KHMDS and

then treated with CuI and an alkynyl bromide to afford the

corresponding alkynes in excellent yields (scheme 28). A

regioselective and stereo selective aminohalogenation of

cinnamates was successfully carried out [33]. The reactions

were carried out using 2-NsNCl2/2-NsNHNa as the nitrogen

and chlorine sources and copper (I) triflate as the catalyst

(scheme 29). The synthesis of 1, 2, 3-triazole derivatives of

2-indolones can be accomplished using a catalytic amount of

CuI (scheme 30) [34].

CuO/AB i.e. CuO nanospheres immobilized on acetylene

black (AB) was demonstrated as a versatile catalyst for the

N-arylation of different amines in excellent yield by Park

and coworkers [35] (scheme 31). Boshun Wan [36]

synthesized oxime-phosphine oxide ligand which was found

to be highly active in the copper-catalyzed N-arylation of

alkyl amines and various N–H heterocycles under mild

N

HOZ

O

R1

R2

N

HOZ

O

X

R2

N N

NBn

NaN3, BnBr, CuI, Et3N

tBuOH:H2O, 6 h

R1 = CH2CCH, CH2OCH2CCH

R2 = H, CH3, Br, F

Z = CN, CO2Me, CO2Et, CO2Bu

X= CH2, CHOCH3

Scheme 30.

X

R1HN

R2

R3

5 mol% CuO/AB

KOtBu, toluene

180 oC, 18 h

N

R1

R2

R3

Scheme 31.

I

R1

R2NH2

5 mol% Cu2O

20 mol% ligand

Cs2CO3

NHR2

R1

N

OH

P

O

PhPh

Ligand

Scheme 32.

Z

NH

X

Y

B(OH)2

Cu(OAc)2, Bipy

Na2CO3, DCM

70 oC, 2-6 hZ

N

X

Y

Scheme 33.

Br

R

N

HN

N

HN

NH

N

CuI, KF/Al2O3, 130-140 oC

1, 10-phenanthroline

N

RN

N

N

N

N

R

R

Scheme 34.

288 Mini-Reviews in Organic Chemistry, 2013, Vol. 10, No. 3 Tekale et al.

conditions (scheme 32). The ligand was stable and the

reaction was successful under solvent free conditions. The

construction of cyclopropyl ring is an important and much

difficult task. The N-alkylation of several nitrogen

containing heterocycles such as azoles, amides,

sulfonamides, pyrroles etc was carried out with cyclopropyl

boronic acids in excellent yield (scheme 33) [37].

R. Hosseinzadeh et al. [38] reported KF/Al2O3 as an

efficient base for the N-arylation of pyrazole, imidazole etc

with aryl bromides using 1, 10-phenanthroline ligand and

CuI catalyst (scheme 34). Mild reaction conditions, simple

and inexpensive catalyst and air insensitiveness of the

catalyst are the striking features of the catalyst. Further

strong basic character of the system makes this protocol

attractive to replace organic bases in synthesis. The

amidation of allylic and benzylic C-H bonds using copper

triflate catalyst can be carried out successfully [39] (scheme

35). The amidation was successful with both primary and

secondary amides in excellent yields. O-Acyl ketoximes can

be converted into N-substituted imines by treating them with

boronic acids or organostannanes in the presence of copper

catalysts [40] (scheme 36).

2.3. S-Arylation (C-S Bond Forming Reactions)

Diaryl sulfides constitute an important class of structural

units present in many valuable intermediates for organic

synthesis and biologically active compounds [41]. Aromatic

compounds with a C-S bond constitute a privileged class

those have attracted the attention of chemists in

pharmaceutical and medicinal chemistry. The cross coupling

reaction between aryl halides and thiols is a simple way for

C-S bond formation. Among the several approaches

suggested, transition metal catalyzed reactions are the

important routes for the synthesis of diaryl sulfides [42].

From literature survey; many copper catalysts are useful for

such reactions.

Synthesis of thioethers by the cross- coupling of

thiophenols with aryl halides using CuI catalyst,

benzotriazole ligand and potassium t-butoxide base was

reported by A. K. Verma and coworkers [43] (scheme 37).

The advantages of this method are tolerance of several

functional groups, simple work up and readily available low

cost catalyst. Jin-Heng Li et al. [44] reported the first silicon

reagent employed solvent-free protocol for the conversion of

disulfides into sulfides with aryltrimethoxysilanes in the

presence of CuI/TBAF/2-(di-tert-butylphosphino) biphenyl

(scheme 38). The reaction can be carried out even in the

presence of O2 atmosphere and moderate to good yields were

obtained by this method.

Ar S

S Ar

Ar'Si(OMe)3

CuI, L, air

TBAF, 100 oC

Ar S

Ar'

PtBu2

L =

Scheme 38.

The conversion of aryl boronic acids into alkyl-hetero

aryl sulfones using copper acetate can be easily carried out

[45]. Sulfinate salts were utilized as the coupling partners in

these reactions. Among the various ligands tried for

optimizing the reaction conditions, 1-benzyl-imidazole was

found to be the best ligand under these conditions (scheme

39).

The combination of copper iodide/ cis-1, 2-

cyclohexanediol was used as an effective system for the

cross-coupling of alkyl or aryl halides with thiols in

R2

R1

NH

SR3

R4

O O Cu(OTf)2

1,10-phenanthroline

t-BuOOAc

4A MS, DCE

R2

R1

NSR3

R4

O O

Scheme 35.

R1 R2

N

R1 R2

N

R3OR' R3B(OH)2

R3Sn(n-Bu)3

or

Cu(I) or Cu(II)

DMF, Ar or air

50-70 oC

R' = Ac, COC6F5

R1, R2 = aryl, heteroaromatic, alkyl

R3 = aryl, alkenyl

Scheme 36.

SH

R1

R2

Br S

R1 R2

CuI (0.5 mol %) / L (1 mol %)

KO-tBu, DMSO, 100 oC

10-18 h

NH

N

N

L =

Scheme 37.

Recent Advances in Some Copper Catalyzed Coupling Reactions Mini-Reviews in Organic Chemistry, 2013, Vol. 10, No. 3 289

excellent yield. The coupling was carried out using K3PO4

base and DMF solvent at 30 or 60 oC

(scheme 40) [46]. A

ligand-free synthesis of thioethers was carried out [47] using

a catalytic amount of Cu2O in DMSO/H2O solvent system.

Using this protocol, a number of diaryl sulfides and alkylaryl

sulfides were obtained in excellent yields (scheme 41). The

coupling reaction of disulfides and boronic acids was used

for an efficient synthesis of thioethers by N. Taniguchi [48]

using Cu metal catalyst and bipyridyl ligand. A major

disadvantage of this protocol is the requirement of excess of

boronic acid (3 eq) (scheme 42).

The synthesis of vinyl sulfides using the homogeneous

catalyst [Cu(phen)(PPh3)2]NO3 was described by D.

Venkataraman (scheme 43) [49]. The reactions proceeded

with retention of stereochemistry in good yield. The

synthesis of aryl sulfides from thiols and iodides was

reported [50] using 10 mol % CuI, 10 mol-% neocuproine

and NaOt-Bu base (scheme 44). Raul Martin et al. [51]

reported a method describing the S-arylation of arenethiols

with activated aryl chlorides using copper chloride catalyst

in the presence of ethylene diamine ligand as well as base.

The reaction required excess of ethylene diamine (4 eq).

Since the reactions were performed in water, it constitutes a

green and environment-friendly synthesis. This protocol also

allowed the coupling of sterically hindered aryl chlorides

(scheme 45).

The selective S-arylation of mercaptobenzimidazoles

using Cu(I) iodide catalyst and 1, 10-phenathroline ligand

was reported by Anandan Sambandam et al. (scheme 46)

[52]. A mild approach can be applied for the synthesis of

diaryl thioethers by the cross coupling reaction between aryl

halides and thiophenols catalyzed by CuI/L-proline in

biphasic system [53]. The reaction was carried out in the

presence of ATPS at 80 o

C to afford the corresponding

thioethers in excellent yields (scheme 47). An efficient

copper-catalyzed protocol was documented in literature for

the S-Arylation of thiols with aryl bromides and chloride

(scheme 48) [54].

A two step method for the synthesis of diaryl ethers

utilizing xanthate precursor instead of thiols was developed

by G. Sekar [55]. The strategy involves treatment of aryl

iodides and potassium ethyl xanthogenate in the presence of

copper acetate and ligand in DMF at 105 o

C followed by

reaction with another halide using KOH base (scheme 49).

The synthesis of alkyl-aryl thioethers through the copper

triflate catalyzed cross coupling reaction using BINAM

ligand and Cs2CO3 base (scheme 50) is reported in literature

[56].

A simple and novel method for the methylthiolation of

aryl halides was developed using DMSO as the source of

sulfur and suitable copper catalyst (scheme 51) [57]. For aryl

iodides 10 mol % CuBr and for bromides, 10 mol % CuI

were used. During the reactions many functional groups

including formyl, nitro, chloro, fluoro, methoxycarbonyl etc

remained intact.

The S-arylation of thiophenols can be carried out in the

presence of strong basic condition such as KOH/DMSO

(scheme 52) [58]. Thioethers were also obtained under base

free conditions from the cross-coupling reaction between

boronic acids and N-thioimides in tetrahydrofuran at 45-50

oC (scheme 53) by Lanny Liebeskind et al. [59]. Palomo and

co-workers [60] described CuBr catalyzed efficient synthesis

Y

SH

R

Cl

EWG

NH2H2N

10 mol % CuCl

H2O, 1200C

Y = C, N

R

S

Y

EWG

Scheme 45.

Ar B(OH)2S

O

ONaR

Cu(OAc)2 (20 mol %)

1-Bn-imidazole (40 mol %)

4 A MS, DMSO

60oC, 22 h

R S Ar

O

O

Scheme 39.

R I HS-R'

0.1 eq CuI

0.2 eq L

1.5 eq K3PO4

DMF 30 or 60 oC

0.5-8 h

SR R'

OH

OH

L =

Scheme 40.

Ar I HS R

1.1 eq

5 mol % Cu2O

2 eq KOH

DMSO/H2O(4:1)

80 oC, 24 h

Ar S R

Scheme 41.

S

S

ArAr (OH)2B-R

5 mol % Cu

5 mol % bipyridine

air, DMSO/H2O (2:1)

100 oC, 12-48 h

S

Ar R

Scheme 42.

R SH I

R'

5 mol % [Cu(phen)(PPh3)2]NO3

1.5 eq K3PO4

toluene, 110 oC

4-24 h

S

R'R

Scheme 43.

10 mol % CuI

10 mol % neocuproine

1.5 eq NaOt-Bu

24 h

S

Ar RAr-I HS-R

toluene, 110 oC,

Scheme 44.

290 Mini-Reviews in Organic Chemistry, 2013, Vol. 10, No. 3 Tekale et al.

of diaryl ethers with phosphazene base in toluene under

reflux condition within 1-4 hours (scheme 54).

2.4. O-Arylation Reactions

The copper catalyzed Ullmann types of reactions are

traditional routes for the synthesis of diaryl ethers [61].

These normally require harsh conditions and stoichiometric

amount of the copper reagents. Here is a summary of certain

attempts conducted by different research groups to develop

mild reaction protocols using catalytic amounts of the copper

catalysts.

Dawei Ma [62] reported a simple CuI catalyzed and N,

N-dimethyl glycine promoted synthesis of diaryl ethers from

the Ullmann coupling of aryl halides and phenols as the

R N

HN

SH

R N

HN

S

R N

N

SH

i) CuI

ii) 1,10-phenanthroline

NR

R = H, OCHF2

X

(X = Br, Cl)

Scheme 46.

R1

XHS

R2 R1

S

R2

X = Br,Cl

CuI/L-Proline

ATPS, 80 oC

Scheme 47.

X

R1

HS

R2

20 mol % CuBr

20 mol % L

2 eq Cs2CO3

DMF, 130 oC, 48 h

S

R1 R2

Scheme 48.

R

I

KS

S

OEt

S OEt

S

R

S

Ar

NH2

NH2L =

Cu(OAc)2, L

DMF, 105 oC

KOH

ArXR

Scheme 49.

R

X

R

S

R'

NH2

NH2

BINAM, Cu(OAc)2,

Cs2CO3, DMF, 110 oCR'SH

BINAM

Scheme 50.

Recent Advances in Some Copper Catalyzed Coupling Reactions Mini-Reviews in Organic Chemistry, 2013, Vol. 10, No. 3 291

synthons. The reactions were carried out by using Cs2CO3

base and dioxane as the solvent under relatively mild

conditions (scheme 55). This protocol is applicable to a wide

range of compounds bearing different functional groups.

Cu(I)/1-butylimidazole was found to be an efficient catalytic

system for the practical synthesis of diaryl ethers through the

coupling reaction of aryl bromides and suitable phenols [63]

(scheme 56). Diaryl ethers were obtained in excellent yield

[64] from aryl iodides and phenols using copper iodide and

Cs2CO3 under microwave irradiation (scheme 57).

The utility of copper nano-particles for the Ullmann

protocol involving the synthesis of diaryl ethers in excellent

yields was made by Mazaahir Kidwai et al. [65]. This

protocol avoids the use of a heavy metal co-catalyst. The

copper nano-particles being reusable, it is an economic

process. Further the reactions were carried out without the

use of additives, the method needs low catalyst loading and

the conversions take short reaction-times (scheme 58).

Aryl iodides and phenols were cross-coupled through

Ullmann type coupling reactions using BINAM–Cu(OTf)2

complex [66] in catalytic amount under mild reaction

conditions (scheme 59).

2.5. Cyclization Reactions

Miquel A. Pericas et al. [67] described the synthesis of

1,2,3-triazoles using a copper catalyst based on Tris

(triazolyl)methanol-Cu(I) structure (scheme 60). 1,2,3-

triazoles can be synthesized from the 1,3-dipolar cycloaddition

reaction between aryl azides and calcium carbide by using

copper iodide as the catalyst. Calcium carbide was employed

as a source of acetylene in this reaction. The reaction was

carried out in acetonitrile-water solvent mixture (scheme 61)

[68]. Triazoles can be synthesized using Cu/AlO(OH) as an

efficient heterogeneous catalyst at room temperature [69].

The reaction can be performed even in the absence of any

additive (scheme 62). Copper nanoparticles supported on

activated charcoal were used as a novel heterogeneous

catalyst for the same purpose (scheme 63) [70].

The utility of heterogeneous catalysts predominates over

the homogeneous ones due to several advantages such as

simple recovery, their reusability etc. 1,2,3-Triazoles were

X

Y Y

HO

Z

O

Z

X= I, Br

CuI/ N,N-dimethyl glycine

Cs2CO3, dioxane, 90 oC

Scheme 55.

BrHO

O

Cu(I)/N-alkyl imidazole

Scheme 56.

OH I

But

CuI, Cs2CO3

MW

O

But

Scheme 57.

OH I

10 mol % Cu-np

Cs2CO3, CH3CN

50-60 oC, N2, 1 atm

O

Scheme 58.

R

X

Me

S

Me

O[Cu]

ZnF, 150 oC

R

SMe

Scheme 51.

XSH S

R KOH/DMSOR

130 oC

Scheme 52.

R1B(OH)2 N

O

O

R2S R1-SR2cat. Cu(I)

THF, 45-50 oC

R1 = aryl, alkenyl

R2 = alkyl, aryl, heteroaryl

Scheme 53.

Ar I

R1

SNa

CuBr ( 20 mol %)

R1

S

Ar

B ( 2eq), toluene

reflux,1-4 h

P

N

P

NMe2

NEt

Me2N

NMe2

Me2N NMe2

B =

Scheme 54.

292 Mini-Reviews in Organic Chemistry, 2013, Vol. 10, No. 3 Tekale et al.

regioselectivley synthesized from alkyl or benzyl halides,

sodium azide and terminal alkynes using silica supported

copper catalysts [71] (scheme 64). An important advantage

of the catalyst is the ease of separation by simple filtration

which can be studied for its catalytic reusability. Aromatic

amines can be efficiently converted into azides using t-butyl

nitrite and trimethyl silyl azide which on treatment with

terminal acetylene in the presence of CuSO4 and sodium

ascorbate cyclizes to yield the corresponding 1,4-

disubstituted-1,2,3-triazoles at room temperature [72]

(scheme 65). Kimberly D. Grimes [73] developed a method

for the synthesis of 1-heteroaryl substituted -1,2,3-triazole

derivatives from boronic acids and boronates or

trifluoroborate esters by converting them into azides as the

good leaving groups followed by cyclization to afford the

corresponding triazoles at room temperature (scheme 66). A

drawback of the present protocol is excess quantity of the

acetylene carboxylate ester required during the reaction. A

two step method was developed for the synthesis of several

heterocyclic compounds from Aza-Michael reaction based

on pyrazolone-triazole skeleton (scheme 67) [74]. The

thermal cyclization of azide and terminal alkynes results in

the formation of a regioisomeric mixture of anti and syn

1,2,3-triazoles which poses a separation problem whereas the

application for Cu(I) catalyst for the reaction gives

exclusively the anti isomer (scheme 68) [75, 76]. Stephen L.

Buchwald et al. [77] carried out the CuI catalyzed

conversion of 1, 4-dihalo-1, 3-dienes into pyrroles and

heteroaryl pyrroles using N,N’-dimethylethylenediamine

(DMEDA) at 80-100 oC (scheme 69). The reactions were

performed using K2CO3 or Cs2CO3 base. Under these

conditions several functional groups including esters, ethers, Boc-protected hydrazines, alkenes, heterocycles etc were

observed to remain intact.

Copper bromide was used as a catalyst for synthesis of

indoles and benzofurans by the cyclization reaction between

N-tosylhydrazones and terminal alkynes under ligand free

conditions [78] (scheme 70). X. Liu and coworkers [79]

reported heterocyclization of substituted ortho bromo/iodo

anilines with secondary amine, CS2 and CuCl2 as the

catalyst. With bromo substrates, the reaction required

slightly higher temperature as compared to the iodo (scheme

71). Different cyclic sulphonamides were synthesized by

copper-catalyzed intramolecular reaction of unsaturated

iminoiodinanes [80]. An important advantage of this method

is that the aziridines may be opened by various nucleophiles

such as methanol, thiophenol, allylmagnesium bromide,

benzylamine etc to give the corresponding substituted cyclic

sulfonamides (scheme 72). The first successful metal-

R X R'NaN3

catalyst

5 mol% Cu(I)

EtOH, reflux, 24h

N

N

N

R

R'

O

O

O

O

O

O

Si

Si

NH2

NH2

2g

1 mmole CuI, DMF, r.t., 4hX= Br,Cl

Catalyst preparation

Scheme 64.

Ar NH2

1.5 eq t-BuONO

1.2 eq TMSN3

CH3CN, r.t., 2 h

Ar N3

1 eq Ph

7 mol% CuSO4

14 mol % sodium ascorbate

CH3CN/H2O(10:1), r.t.

N

N

N

Ph

Ar

Scheme 65.

X OH

R R' R

O

R'

BINAM-Cu(OTf)2

(20 mol %)

Cs2CO3,

dioxane, 110 oC

X = I, Br

Scheme 59.

R N3 R'

N

N

NR

R'

0.25-.5 mol % catalyst

H2O, r.t., 4-18 h

R: Ar, alkyl, COOEt

R': Ph, Bn, C8H17

Scheme 60.

Ar N3 CaC2

0.3 eq CuI

0.3 eq Na ascorbate

MeCN/H2O (2:1)

r.t., 2-20 h

N

N

N

Ar

Scheme 61.

R N3R'Cu/ AlO(OH)

hexane,r.t.

1-24 h

N

N

N

R

R'

Scheme 62.

R N3 R'

N

N

N0.1 eq Cu/C

1.1 eq Et3N

dioxane 60 oC

10-120 minR'

R

Scheme 63.

Recent Advances in Some Copper Catalyzed Coupling Reactions Mini-Reviews in Organic Chemistry, 2013, Vol. 10, No. 3 293

catalyzed cyclization of heterocyclic system with

alkenyldiazo compounds was made by M. Tomas et al. [81].

NH2

X

Z

S

N

NRR'Z

CS2, HNRR', CuCl2.2H2O

K2CO3, DMF

X = I, 110 oC

X = Br, 140 oC

Scheme 71.

S

N

O

OIPh

n

n = 0,1, 2.....

CuI or II, CH3CN

S

N

O

O

n

Scheme 72.

Copper bromide was used as a catalyst for the synthesis

of indolizines via the [3+2] cycloaddition of alkylidene

diazoacetate over the pyridine ring (scheme 73). (Fig. 1)

illustrates mechanism for the copper (I)-catalyzed regio-

selective synthesis of indolizines form alkenyldiazoacetates

and pyridine involving the [3 + 2] cyclization. The diazo

compound (1a) interacts with copper bromide to form the

copper (I) alkenylcarbene (1b) which reacts with pyridine

(1c) resulting in the species (1d). The intermediate (1d)

undergoes cyclization to the desired indolizine product (1g)

via the formation of intermediate (1f).

R = H, Me

N

R

COOEt

N2

N

COOEt

RCuBr (5 mol%)

DCM, r.t.

Scheme 73.

Ar B(OH)2

1.5 eq NaN3

0.1 eq Cu(OAc)2

MeOH, 50 oC,1-3 h

Ar N3

3 eq COOMe

10 mol % sodium ascorbate

25 oC, 16 h

N

N

N

Ph

Ar

Scheme 66.

R1

N

N

R2

COR

ROC

R2 N

HN

R1

NN

N

R3

N

HN

N

O

R1

R2

NN

R3

3.CH3OH

K2CO3

4. Dowex

HCRS(E)

1. CH2Cl2

TMSN3

Cu(OAc)2.H2O

2. H2O

Na-ascorbate

R3

Scheme 67.

R1-N3 R2

Cu (I)

neat, 80 oC

N

N

N

N

N

N N

N

N

R1

R2

R1

R2

R2

R1

antisyn

Scheme 68.

X

R1

X

R4

R2 R3

NBoc

R3R2

R1 R4

X = Br, I

NH2Boc

CuI (5mol%)

DMEDA

solvent, base

80-100 oC

Scheme 69.

XH

NNHTsR

R'

X R'

X = O, NH, NAc

CuBr (10 mol%)

Cs2CO3 (3 eq)

MeCN, 100 oC

R

Scheme 70.

294 Mini-Reviews in Organic Chemistry, 2013, Vol. 10, No. 3 Tekale et al.

R

O

SO2Ph

N2

O

SO2Ph

R

CuCl, ligand,

NaBARF

CH2Cl2

Scheme 74.

The enantioselective (ee 82%) synthesis of

cyclopentanone derivatives can be carried out from -diazo-

-keto sulfones using copper catalyst (scheme 74) [82].

Benzoxazoles constitute an important class of organic

ring skeletons commonly observed in a number of

biologically active natural products and medicinally

significant compounds [83]. 2-Arylbenzoxazoles were

obtained from bisaryloxime ethers using copper triflate as a

catalyst in the presence of molecular oxygen (Scheme 75)

[84].

The plausible mechanism for the copper (II)-catalyzed

transformation of bisaryloxime ethers into 2-

arylbenzoxazoles is depicted in (Fig. 2). Initially the

bisaryloxime ether (2a) undergoes chelation with the copper

(II) catalyst to form the intermediate (2c) which rearranges to

(2d) followed by reductive elimination of copper to afford

the 2-arylbenzoxazoles (2e).

S. Cacchi et al. reported a novel synthetic route for the

synthesis of 2-aryl and 2-heteroaryl indole moieties from

NN+

N CuBr

N

N

Me

CO2Et

CuBr

Me

CO2Et

N2

Me

Cu-Br

CO2Et

Me

CO2Et

CO2Et

Me

CuBr

CO2Et

Me

CuBr

(1a)

(1b)

(1c)

(1d)

(1e)

(1f)

(1g)

Fig. (1). Mechanism for the Cu(I)-catalyzed synthesis of indolizines (Scheme 73).

H

NO

R1

R1

H

N

O

CuH

O

R2

CuL2

R2

L2Cu -LH

L

N

R2R1

-LH

R2

O

N

Cu

O R1

R2

R1, R2 = EWG, EDG

L = OTf

-Cu

R1

(2a) (2b)

(2c)

(2d)(2e)

Fig. (2). Mechanism for copper (II)-catalyzed synthesis of 2-arylbenzoxazoles from bisaryloxime (scheme 75).

Recent Advances in Some Copper Catalyzed Coupling Reactions Mini-Reviews in Organic Chemistry, 2013, Vol. 10, No. 3 295

1-alkynes and o-iodotrifluoroacetanilide using the catalyst

[Cu(phen)(PPh3)2]NO3 in the presence of potassium

phosphate base (scheme 76) [85]. A one pot synthesis of 2,

3-disubstituted indoles via the intermolecular cyclization

between ortho-iodoanilines and -keto esters was reported

under mild conditions [86]. The reaction proceeds smoothly

at 50 oC in the presence of Cs2CO3 base and BINOL ligand

(scheme 77). Additives and base played important role

during the reaction.

Quinazolines are present in many biologically important

heterocyclic compounds [87]. An important method for the

synthesis of quinazolines from benzamidines and

monosubstituted arenes was developed [88]. The synthesis

was carried out in the presence of CuBr catalyst and K2CO3

base (scheme 78). The synthesis of benzodiazepine was

carried out by M. Nayaka and S. Batra [89] from 4-iodo-1,5-

diphenyl-1H-pyrazole-3- carbaldehyde and ortho-phenylene

diamine using a catalytic amount of CuI (10 mol %) and

potassium phosphate base in DMSO solvent under nitrogen

atmosphere at 90 oC (scheme 79). Stoichiometric amounts of

copper bromide was used for the construction of indole ring

[90] from N-tosylated 2-ethynylaniline, paraformaldehyde

and diisopropylamine in dioxane in 92 % yield (scheme 80).

S. Chang et al. [91] reported the use of copper catalyst for

the cycloaddition reaction of - aryldiazoesters and terminal

alkynes for the efficient synthesis of indenes in excellent

yield (scheme 81).

2-Boryl- and silylindoles were synthesized by copper-

catalyzed cyclization of 2-alkenylaryl isocyanides in high

yields [92] (scheme 82). Enantioselective synthesis of trans-

aryl and heteroaryl-substituted cyclopropyl boronates can be

achieved using CuCl catalyst [93] (scheme 83).

R2

O

N

R1

O

N

R1

R2Cu(OTf)2 (20 mol %)

Toluene, O2, 80 0C

1.5-4 h

Scheme 75.

I

NH

COCF3

R

NH

R[Cu(phen)(PPh3)2]NO3

K3PO4

toluene, 110 oC

Scheme 76.

I

NH2

R

O

OR'

O

NH

COOR'

R

10 mol % CuI

20 mol % BINOL

Cs2CO3 (1 eq)

DMSO

Scheme 77.

NH

Ph

NHO2N

O

I

O

TIPS

N

N

Ph

TIPS

CuBr, K2CO3

benzene, 80 oC

Scheme 78.

N

N

CHO

I

Ph

Ph

NH2

NH2

N

N

Ph

Ph

NH

N

10 mol % CuI

3 eq K3PO4, N2 atm

DMSO, 90 oC, 36 h

Scheme 79.

NHTs

(HCHO)n (i-Pr)2NH

NTs

N(i-Pr)2CuBr (1 eq)

dioxane

80 oC

Scheme 80.

296 Mini-Reviews in Organic Chemistry, 2013, Vol. 10, No. 3 Tekale et al.

Ar Br Ar I5 mol% CuI, 10 mol% L

2 eq NaI, Dioxane

110 oC, 22-24 hNHMe

NHMe

L =

Scheme 85.

O

R1 R3

R2 R4

Cu(OTf)2

acetone, r.t.O

O

R1

R2

R3

R4

O

R4(R3)

R3R4

R2

R1

Scheme 86.

2.6. Miscellaneous Reactions

Finally in this last part of the present review many

miscellaneous reactions catalyzed by different copper

catalysts; particularly oxidation reactions are described.

A versatile method for the synthesis of allylboronates

from allylic carbonates and bis(pinacolato)diboron involving

-substitution in the presence of achiral Cu(I) catalyst in

excellent optical purity was described by M. Sawamura et al.

[94] (scheme 84). Tolerance of different functional groups,

good selectivity, high yields etc are the advantages

associated with this protocol.

Aryl iodides are synthetically important substrates for

many cross coupling reactions such as Heck, Suzuki,

Ullmann etc. S. L. Buchwald [95] demonstrated that aryl

bromides can be converted into aryl iodides by using a

catalytic amount of CuI and suitable ligand (Scheme 85).

The copper(II)-catalyzed conversion of oxiranes into 1,3-

dioxolanes using copper (II) catalyst can be carried at

ambient temperature [96]. During these transformations, the

copper catalysts act as the Lewis acids (scheme 86).

T. Punniyamurthy and coworkers reported a method for

the conversion of sulfides to sulfoxides [97]

and alkyl

benzenes into the corresponding ketones using 30% H2O2 in

the presence of a recyclable copper complex (scheme 87 and

88). It was observed that yield of the transformation was

increased with the addition of TEMPO.

Normally the reductive deprotection of benzyl ethers

requires rigorous conditions. A regioselective and specific

oxidative cleavage of benzyl ethers in the presence of

diacetoxyiodobenzene and p-toluene sulfonamide using

copper (II) trifluoromethane sulfonate under mild conditions

was reported in literature [98] (scheme 89). A. J. Phillips

R1

N2

OR2

O

Ar H

R1

Ar

OR2

O

10 mol % Cu(Pr)Cl

12 mol % AgSbF6

12 mol % NaB(ArF)4

CH2Cl2, 25 oC, 30 min

Scheme 81.

COOMe

N

C:

cat.Cu(I)PPh3

B2(pin)2

MeOH

THF, 25 oCNH

COOMe

B(pin)

Scheme 82.

Ph OP(O)(OR)2 (pin)B-B(pin)

10 mol % CuCl

12 mol % Ligand

1 eq K(O-t-Bu)

toluene/THF

Ph

B(pin)

trans/cis 99:1

Scheme 83.

Ph

OCOOMe

Me

PhMe

B(pin)

Ph

Me

B(pin)

(pin = pinacolato)

B B

O

OO

O

MeMe

Me

Me

MeMe

Me

Me O

PPh2 PPh2

Me Me

Cu(O-t-Bu) (5 mol%)

Xantphos (5 mol%)

r.t., 3h

Bispinacolato diborane

Bispinacolato diborane

Xantphos

Scheme 84.

Recent Advances in Some Copper Catalyzed Coupling Reactions Mini-Reviews in Organic Chemistry, 2013, Vol. 10, No. 3 297

et al. [99] synthesized the precursor ketone from natural

trans-kumausyne, a marine natural product, using

stoichiometric amounts of Stryker’s reagent and phenylsilane

(scheme 90).

J. Xu [100] studied the selective synthesis of 4-hydroxy

benzaldehyde from p-cresol via the oxidation of methyl

group using carbon supported copper and magnesium

bimetallic oxide, CuMn/C (scheme 91). The catalyst worked

without loss of activity for subsequent runs. The

combination of Cu(NO3)2.5H2O and CuBr2 catalytic system

for the oxidation of sulfides into sulfoxides under mild

reaction conditions was made applicable by S. E. Martin

[101] (scheme 92). A copper acetate catalyzed asymmetric

sulfoxidation of aryl alkyl and aryl benzyl sulfides with

aqueous H2O2 is also reported (Scheme 93) [102]. Recently;

O

O

H

H

(Ph3P)CuH

PhSiH3

toluene, r.t. O

O

H

H

Scheme 90.

CH3

OH

CHO

OH

COOH

OH

7.4 % CuMn(5:1)

NaOH, MeOH, O2

75 oC, 3h

98.5%

Scheme 91.

S

O

SCu(NO3)2.5H2O-CuBr2

CH3CN , O2, r.t.

3 h

Scheme 92.

S R' S+

O-

R'

RRCu(acac)2 (2 mol%)

Ligand (4 mol%)

30% H2O2, r.t.

Scheme 93.

O OHN

Ts

PhI(OAc)2/TsNH2

CH2Cl2, 40 oC

Cu(CF3SO3)2

Scheme 89.

CuIIPhCH2OH

100 oC

Cu(OCH2Ph)2

H2O2

PhCH2OH

CuII

O

O

OH

C

H

H

PhH2O

CuII

H2O

O-

CuII

H2O

OH

O OH

H2O2

PhCH2OHH2O

(3a)

(3b)

(3c)

O

Ph

H

H2O

Fig. (3). Catalytic cycle for CuSO4 catalyzed oxidation of benzylic alcohols into carbonyl compounds (Scheme 95).

1 mol % Complex

5 mol % TEMPO

2 eq 30 % H2O2

4.5-24 h, 20 oC

ACN

R

S

O

R'R

S

R'

Cu

N N

OO

H H

Cu-complex

Scheme 87.

0.1 mol % Complex

10 eq 30 % H2O2

80 oC, 5-10 h

ACN

R

O

R'R R'

Cu

N N

OO

HH

Cu-complex

H2O

Scheme 88.

298 Mini-Reviews in Organic Chemistry, 2013, Vol. 10, No. 3 Tekale et al.

HNS

O

R2R1R3

R3 N

S

O

R1 R2

CuCl2 (10 mol%), O2 (1 atm)

pyridine, Na2CO3,

1,4-dioxane, 30 oC

Scheme 94.

OH

R

R'

O

R

R'

O

R

R'

CuSO4, H2O

H2O2, 100 oC

CuSO4, H2O

H2O2, 60 oC, Ligand

TEMPO, K2CO3

Ligand = 2-N-(p-fluorophenyl)-pyrrolecarbaldimine

Scheme 95.

ArCHO ArCN

Cu2+/ NH3 (aq.) /O2

ArCH2OH

Cu2+/TEMPO/NH3 (aq.) /O2

MeCH=NOH

one pot

Ar-CONH2

Scheme 96.

R

OH

R'

R

O

R'

nano CuO (10 mol%)

bipyridine, t-BOOH (70%)

CH2Cl2, r.t., 2-24 h

Scheme 97.

OH

Ph

R R

O

Ph

CuCl, K2CO3

DMF, 60 oC, air

Scheme 98.

R

B

OH

OHR

OHCuSO4 (10 mol%), Phen. (20 mol%)

KOH, H2O, r.t., 1-10 h

Scheme 99.

N N

H

H

R1R2

H

HR1

N

N

R2

[Cu] cat.,air or O2

H2O

Scheme 100.

an efficient synthesis of N-alkynylated sulfoximines from

sulfoximines and alkynes using copper chloride was reported

by Carsten Bolm et al. (scheme 94) [103]. CuSO4 can be

effectively used a catalyst for the oxidation of benzylic

alcohols into carbonyl compounds using 30% H2O2 as the

oxidant in the presence of 2-N-(p-fluorophenyl)-

pyrrolecarbaldimine ligand in combination with

TEMPO/K2CO3 (scheme 95). The reaction can be performed

under base free and ligand free conditions at 100 oC. Under

these conditions; primary benzylic alcohols were oxidized

into aldehydes (70–90%); remaining being the corresponding

carboxylic acids as the side products [104]. The mechanism

for the copper catalyzed oxidation is shown in (Fig. 3). A

direct oxidation of alcohols into amides via nitriles is

possible using NH3 as the nitrogen source, O2 oxidant and

TEMPO as the co-catalyst (scheme 96) [105]. Propargylic

alcohols can be oxidized to ynones by copper oxide

nanoparticles using TBHP or air as the oxidant (scheme 97)

[106]. It was observed that use of bipyridine ligand

significantly enhanced the reaction rate. The combination of

CuCl and K2CO3 can be effectively used for the ligand free

conversion of benzylic alcohols into ketones (scheme 98)

[107]. The reactions occur in the atmosphere of air. Y. Hu et

al. reported a room temperature method for the direct

oxidative hydroxylation of arylboronic acids in aqueous

medium (scheme 99) [108]. Aromatic azo compounds can be

obtained by the oxidative coupling of anilines using CuBr as

the simple catalyst. The reaction can be carried out by air or

oxygen as the oxidant (scheme 100) [109].

Recent Advances in Some Copper Catalyzed Coupling Reactions Mini-Reviews in Organic Chemistry, 2013, Vol. 10, No. 3 299

CONCLUSION

The copper reagents have low cost and are not

air/moisture sensitive in contrast to the palladium catalysts.

Hence they provide a broad platform for the cross coupling

reactions in synthetic organic chemistry using low cost and

readily available copper catalysts. The reactions discussed

herein indicate the application of copper catalysts in

numerous chemical processes. Improvements in activity and

scope of these catalysts will assist to reduce the

environmental impact and increase the sustainability of

synthetically useful catalytic transformations. Challenges for

future developments in this area will be to develop novel and

reusable heterogeneous copper catalysts with scope and

activity. Copper-catalyzed cross-coupling reactions and the

synthesis of various heterocyclic compounds are useful in

synthetic organic chemistry. We hope this review will be

helpful for the researchers in the field of copper chemistry to

develop novel reusable heterogeneous copper catalysts and

their utility in the exploration of new routes for different

organic transformations.

CONFLICT OF INTEREST

The author(s) confirm that this article content has no

conflict of interest.

ACKNOWLEDGEMENTS

The authors are thankful to the Principal, Shri.

Muktanand College, Gangapur (MS) India for encouraging

them.

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Received: January 02, 2013 Revised: May 06, 2013 Accepted: May 09, 2013