Nickel-catalyzed [2+2+2] cycloaddition of two alkynes and an ...

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Pure Appl. Chem., Vol. 80, No. 5, pp. 1115–1125, 2008.doi:10.1351/pac200880051115© 2008 IUPAC

Nickel-catalyzed [2+2+2] cycloaddition of twoalkynes and an imine*

Sensuke Ogoshi‡, Haruo Ikeda, and Hideo Kurosawa

Department of Applied Chemistry, Osaka University Suita, Osaka 565-0871, Japan

Abstract: The reaction of N-benzenesulfonylbenzaldimine with Ni(cod)2 and PCy3 gave thecorresponding η2-iminenickel complex quantitatively. Diphenylacetylene reacted with theη2-iminenickel complex to generate five-membered aza-nickelacycle. Insertion of secondalkynes into the five-membered aza-nickelacycle led to the formation of the correspondingseven-membered aza-nickelacycles. Heating the solution of the seven-membered aza-nickel-acycles induced the reductive elimination to give 1,2-dihydropyridine. In the presence of10 mol % of Ni(cod)2 and PMetBu2 at 100 °C, the intermolecular [2+2+2] cycloaddition ofN-benzenesulfonylbenzaldimine and 2-butyne occurred to give the expected 1,2-dihydro-pyridine in 87 % yield. In the presence of PCy3, the reaction also proceeded catalytically,however, PMetBu2 gave better results. Less bulky or less basic phosphine, PnBu3 or P(o-tol)3,was not efficient for the reaction. Although Ni(0)-NHC complex was a good catalyst for[2+2+2] cycloaddition of two alkynes and a ketone or an aldehyde, this reaction did not pro-ceed in the presence of an NHC ligand, 1,3-bis-(2,4,6-trimethylphenyl)imidazol-2-ylidene.

Keywords: nickel; oxidative cyclization; alkynes; imines; dihydropyridine.

INTRODUCTION

Oxidative cyclization with a transition metal is a very efficient method to form a C–C bond betweentwo unsaturated molecules. Especially, the oxidative cyclization of C≡C triple bond and C=X (X = O,NR) double bond with a transition metal can simultaneously form a C–C bond, a carbon–metal bond,and a metal–heteroatom bond to generate a hetero-metalacycle (Scheme 1) [1,2]. Therefore, a hetero-metalacycle can potentially act as a key intermediate in a late transition-metal-catalyzed reaction in-volving C–C bond formation between C≡C and C=X (X = O, NR). Nickel is a popular transition metalas a catalyst in these reactions. In fact, a variety of Ni-catalyzed reactions involving C–C bond forma-tion between an alkyne and an aldehyde, a ketone, or an imine have been reported. These reactionscould be classified into two types (Scheme 2). One is multicomponent coupling reaction [3]. The otherone is [2+2+2] cycloaddition of two alkynes and an aldehyde or a ketone [4]. Recently, we reported theformation of oxa-nickelacycles by the oxidative cyclization of aldehydes or ketones and an unsaturatedC–C bond with Ni(0) [5]. However, so far, [2+2+2] cycloaddition with imines has not been reported. Itis believed that a hetero-nickelacycle is the key intermediate for both reactions. Thus, the formation ofan aza-nickelacycle from an imine and an alkyne and its application to [2+2+2] cycloaddition of twoalkynes and an imine is a next logical step. Here, we report the formation of a five-membered aza-nickelacycle, nickelapyrroline, by oxidative cyclization of an imine and an alkyne with Ni(0). The in-

*Paper based on a presentation at the 14th International Symposium on Organometallic Chemistry Directed Towards OrganicSynthesis (OMCOS-14), 2–6 August 2007, Nara, Japan. Other presentations are published in this issue, pp. 807–1194.‡Corresponding author

sertion of the second alkyne to give a seven-membered aza-nickelacycle, nickeladihydroazepine, fol-lowed by the reductive elimination to give a 1,2-dihydropyridine is also reported. Furthermore, the cat-alytic application of these reactions to [2+2+2] cycloaddition of two alkynes and an imine is demon-strated.

RESULTS AND DISCUSSION

Formation of �2-iminenickel complex

The reaction of PhCH=NSO2Ph (1: N-benzenesulfonylbenzaldimine) with Ni(cod)2 and PCy3 gave(η2-PhCH=NSO2Ph)Ni(PCy3)2 quantitatively (Scheme 3). The molecular structure determined byX-ray crystallography shows that η2-coordination of C–N double bond to Ni(0) center and the geometryaround double bond is E (Fig. 1). The atom distance between carbon and nitrogen (1.389 Å) is slightlylonger than that of the known imine compound (1.30 Å), which might be due to back-donation fromNi(0) to C–N double bond having an electron-withdrawing group on the nitrogen atom. The imine hy-drogen and carbon in 2 are found far upfield in 1H and 13C NMR spectra compared to those of 1, whichis consistent with η2-coordination of 1 to a Ni(0) and the strong back-donation from the Ni(0) center tothe C=N group in a solution. N-Methylbenzaldimine did not react with Ni(0) under the same reactioncondition. N-Phenylbenzaldimine reacted with Ni(0) to give a trace amount of the correspondingη2-imine complex. An electron-withdrawing group on nitrogen is required for the formation ofη2-iminenickel complex, which suggests that η2-coordination of imine to Ni(0) is governed by back-donation from Ni(0) to imine.

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© 2008 IUPAC, Pure and Applied Chemistry 80, 1115–1125

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Scheme 1 Oxidative cyclization of C≡C and C=X with transition metal.

Scheme 2 Ni-catalyzed reaction via hetero-nickelacycle.

Scheme 3 Formation of η2-iminenickel complex.

Formation of five-membered aza-nickelacyle and insertion of alkyne

The reaction of 2 with diphenylacetylene proceeded smoothly to give a five-membered aza-nickel-acycle (3) quantitatively along with the dissociation of 1 equiv of PCy3 (Scheme 4). The elementalanalysis of 3 showed the expected composition. The aza-nickelacycle 3 could also be prepared fromdiphenylacetylene, 1, Ni(cod)2, and PCy3 directly. The coordination of oxygen to nickel is inferredfrom the molecular structure of the seven-membered aza-nickelacycle determined by X-ray crystal-lography (see later). Hoberg has reported the only example of an analogous five-membered aza-nickel-acycle, nickelalactam, formed by the reaction of diphenylacetylene and phenylisocyanate with Ni(0)[6]. The treatment of 3 with carbon monoxide (5 atm) led to the formation of the corresponding lac-tam in 78 % yield, which is consistent with the structure depicted in Scheme 4. This observation sug-gests that a hetero-Pauson–Khand reaction might proceed via a hetero-metalacycle analog of 3 [7].The reaction of 3 with one more equivalent of diphenylacetylene proceeded much slower than the for-mation of 3 to give a seven-membered aza-nickelacycle (5a) quantitatively. On the other hand, the in-sertion of 2-butyne occurred much faster than the insertion of diphenylacetylene to give the expectedseven-membered aza-nickelacycle (5b) quantitatively. The molecular structure of 5a was determinedby X-ray crystallography. The molecular structure of 5a in Fig. 2 shows the square planar dimeric


Aza-nickelacycle 1117

Fig. 1 Molecular structure of η2-iminenickel complex 2.

Scheme 4 Formation of five-membered aza-nickelacycle and insertion of alkyne.

structure around Ni. The spatial relation between benzenesulfonyl group and phenyl group aroundN-C5 bond is trans. This geometry is consistent with N-benzensulfonylimine coordinated to Ni(0) incomplex 2. The coordination of oxygen to nickel might play an important role to isolate as a stablesquare planar complex 5.[8]

The reaction of N-benzenesulfonylbenzaldimine (1) with 2-butyne (1 equiv) in the presence ofNi(cod)2 and PCy3 at room temperature for 10 min gave an inseparable mixture of a five-memberedazanickelacycle (3c), seven-membered azanickelacycle (5c), and η2-iminenickel complex (2)(Scheme 5). The addition of an additional equivalent of 2-butyne (total 2 equiv) to the reaction mixturegenerated 5c as a sole product in 95 % yield. The molecular structure of 5c was also determined byX-ray crystallography. As mentioned above, the insertion of 2-butyne proceeded much faster than thatof diphenylacetylene, which might be a reason why 3c was obtained as a mixture with 5c.

Reductive elimination from 5a–c

Heating the solution of the seven-membered azanickelacycles 5a–c at 100 °C induced the reductiveelimination to give 1,2-dihydropyridine compounds (6a–c) (Scheme 6). Moreover, the formation of1,2-dihydropyridine by the reductive elimination suggests that the construction of the Ni-catalyzed[2+2+2] cycloaddition of two alkynes and an imine might be possible.

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Fig. 2 Molecular structure of seven-membered azanickelacycle 5a. (Cyclohexyl groups were omitted for clarity.)

Scheme 5 Rapid formation of seven-membered azanickelacycle from 2-butyne.

Scheme 6 Reductive elimination of 1,2-dihydropyridine from seven-membered azanickelacycles.

Ni(0)-catalyzed [2+2+2] cycloaddition of alkynes and imine

In the presence of 10 mol % of Ni(cod)2 and PMetBu2 at 100 °C, the intermolecular [2+2+2] cyclo-addition of 2-butyne and 1 occurred to give the expected 1,2-dihydropyridine (6c) in 87 % yield(Scheme 7). In the presence of PCy3, the reaction also proceeded catalytically, however, PMetBu2 gavebetter results. Less bulky phosphine, such as PnBu3, was not efficient for this cycloaddition. Less basicphosphine, such as P(o-tol)3, was neither efficient. Although Ni(0)-NHC complex was a good catalystfor [2+2+2] cycloaddition of two alkynes and a ketone or an aldehyde, this reaction did not proceed inthe presence of 1,3-bis-(2,4,6-trimethylphenyl)imidazol-2-ylidene. 3-Hexyne and trimethylsilyl-acetylene also gave the corresponding 1,2-dihydropyridine (6d, 6e). Although diphenylacetylene re-acted with 1 in the presence of Ni(0) species to give seven-membered aza-nickelacycle 5a, [2+2+2]cycloaddition of diphenylacetylene and 1 did not occur. This might be due to slow and inefficent re-ductive elimination from 5a. To the best of our knowledge, only one example to give 1,2-dihydro-pyridine from two alkynes and an imine catalytically had been reported [6], however, in which 1,2-di-hydropyridine was obtained as a byproduct. Thus, this catalytic reaction might be very attractive as anew method to prepare 1,2-dihydropyridine compounds. A plausible mechanism is depicted inScheme 8. The oxidative cyclization as Ni(0) gives rise to a five-membered aza-nickelacycle followedby insertion of a second alkyne to form a seven-membered aza-nickelacycle. Then, the reductive elim-ination gives 1,2-dihydropyridine and regenerate Ni(0). As mentioned above, we isolated both five-membered aza-nickelacyle and seven-membered aza-nickelacycle, thus, this reaction mechanism mightbe very likely. Reported Ni-catalyzed [2+2+2] cycloaddition of alkynes with an aldehyde or a ketonemight also proceed via a similar reaction path [4].



Scheme 7 Ni(0)-catalyzed [2+2+2] cycloaddition of alkynes and imine.

CONCLUSION

We isolated η2-iminenickel(0) complex and determined its molecular structure by X-ray crystallo-graphy. The oxidative cyclization of an imine and an alkyne with Ni(0) to give a nickelapyrroline andthe subsequent insertion of a second alkyne to give a nickeladihydroazepine was reported for the firsttime. This complex underwent the reductive elimination to give a 1,2-dihydropyridine. Moreover, thissequential reaction process was expanded to a Ni-catalyzed [2+2+2] cycloaddition of two alkynes andan imine to synthesize a 1,2-dihydropyridine. This is the first example of the selective formation of a1,2-dihydropyridine by a transition-metal catalyst.

EXPERIMENTAL SECTION

General: All manipulations were conducted under a nitrogen atmosphere using standard Schlenk or drybox techniques. 1H, 31P, and 13C NMR spectra were recorded on JEOL GSX-270S and JEOL AL-400spectrometers. The chemical shifts in 1H NMR spectra were recorded relative to Me4Si or residual pro-tiated solvent [C6D5H (δ 7.16) or CHCl3 (δ 7.27)]. The chemical shifts in the 13C spectra were recordedrelative to Me4Si. The chemical shifts in the 31P spectra were recorded using 85 % H3PO4 as externalstandard. Assignment of the resonances in 1H and 13C NMR spectra was based on 1H-1H COSY,HMQC, and HMBC experiments. HMQC and HMBC experiments are inverse detection heterocorre-lated NMR experiments recorded at the 1H frequency of the spectrometer, probing one-bond (CH) andmultiple-bond (CCH and CCCH) connectivity. Elemental analyses were performed at InstrumentalAnalysis Center, Faculty of Engineering, Osaka University. For some compounds, accurate elementalanalyses were precluded by extreme air or thermal sensitivity and/or systematic problems with ele-mental analysis of organometallic compounds. X-ray crystal data were collected by a Rigaku RAXIS-RAPID Imaging Plate diffractometer.

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Scheme 8 A plausible mechanism for Ni(0)-catalyzed [2+2+2] cycloaddition.

Materials: The degassed and distilled solvents (THF, toluene, and hexane) used in this work werecommercially available. C6D6, THF-d8 were distilled from sodium benzophenone ketyl. All commer-cially available reagents were distilled and degassed prior to use.

Caution: The treatment of Ni compounds with carbon monoxide can yield Ni(CO)4 (extremelytoxic) due to the addition of insufficient amounts of PR3, careless handling or an accident. The reactionmixture must be handled in a well-ventilated fume hood.

Isolation of Ni(�2-PhCH=NSO2Ph)(PCy3)2: Ni(cod)2 (272.4 mg, 0.99 mmol), PCy3 (577.2 mg,1.00 mmol) and 1 (246.2 mg, 1.00 mmol) were dissolved in 5 mL of toluene. The red solution wasstirred for 3 h. The reaction mixture was concentrated in vacuo to give red solids. The solids werewashed with cold pentane to give 762.9 mg of complex 2 (red solid) in 88 % yield. 1H NMR (270 MHz,C6D6): δ 0.85–2.58 (m, 66H, Cy), 4.49 (brt, J = 4.9 Hz, 1H, –CH=NSO2C6H5), 6.72–7.03 (m, 6H), 7.76(brd, JHH = 5.4 Hz, 2H), 8.16 (d, JHH = 7.1 Hz, 2H) 31P NMR (109.4 MHz, C6D6): δ 29.6 (d, JPP =26.2 Hz), 31.8 (d, JPP = 26.2 Hz). 13C NMR (67.5 MHz, C6D6): δ 27.3 (s, Cy), 27.5 (s, Cy), 28.3 (d,JCP = 10.4 Hz, Cy), 28.5 (d, JCP = 10.4 Hz, Cy), 28.8 (d, JCP = 5.8 Hz, Cy), 28.9 (d, JCP = 5.8 Hz, Cy),30.7 (s, Cy), 30.8 (s, Cy), 32.1(s, Cy), 35.9 (d, JCP = 11.9 Hz, Cy), 36.5 (d, JCP = 15.6 Hz, Cy), 52.8(dd, JCP = 22.9, 4.9 Hz, –CH=NSO2C6H5), 125.0 (s), 127.0 (s), 127.1 (s), 128.9 (s), 129.1 (s), 130.5(s), 146.5 (dd, JCP = 1.2, 0.6 Hz), 147.4 (s). Anal. calcd. for C49H77NNiO2P2S: C, 68.05; H, 8.97; N,1.62. Found: C, 67.62; H, 8.87; N, 1.83. X-ray data for 2. M = 864.86, brown, monoclinic, P21/n(No. 14), a = 10.8288(3) Å, b = 17.5527(4) Å, c = 25.9319(8) Å, β = 99.124(1)°, V = 4866.6(2) Å3, Z =4, Dcalcd = 1.180 g/cm3, T = 0 °C, R (Rw) = 0.060 (0.097).

Oxidative cyclization of 1 and diphenylacetylene: Ni(cod)2 (5.5 mg, 0.02 mmol), PCy3(5.5 mg, 0.02 mmol), 1 (4.9 mg, 0.02 mmol) and diphenylacetylene (3.8 mg, 0.02 mmol) were dissolvedinto 0.5 mL of C6D6. The reaction proceeded immediately to generate 2a quantitatively.

Isolation of 3a: Ni(cod)2 (276.0 mg, 1.00 mmol), PCy3 (289.1 mg, 1.00 mmol), 1 (245.9 mg,1.00 mmol) and diphenylacetylene (178.4 mg, 1.00 mmol) were dissolved into 9 mL of toluene andstirred for 0.5 h. The reaction mixture was concentrated in vacuo to give purple solids. The solids werewashed with hexane and cold pentane to give 3a (669.9 mg pale, purple solids) in 88 % yield. 1H NMR(400 MHz, C6D6, 70 °C): δ 0.87–2.21 (m, 33H, Cy), 5.91 (s, 1H, –CHPh–), 6.58–7.16 (m, 16H, Ph),7.36 (d, JHH = 7.2 Hz, 2H), 8.29 (brs, 2H). 31P NMR (109.4 MHz, C6D6, 70 °C): δ 28.5 (s). 13C NMR(100 MHz, C6D6, 70 °C): 27.0 (s, Cy), 28.2 (d, JCP = 3.8 Hz, Cy), 28.3 (d, JCP = 3.8 Hz, Cy), 30.8(s, Cy), 31.0 (s, Cy), 32.8 (d, JCP = 17.5 Hz, Cy), 73.8 (s, –CHPh–), 124.8 (s, Ph), 125.8 (s, Ph), 126.0(s), 127.3 (s, Ph), 127.5 (s, Ph), 127.6 (s, Ph), 128.1 (s, Ph), 128.3 (s, Ph), 128.7 (s, Ph), 128.9 (s, Ph),129.7 (s, Ph), 130.5 (s, Ph), 131.7 (s, Ph), 139.6 (s, ipso-Ph), 142.7 (s, ipso-Ph), 150.2 (d, JCP = 3.8 Hz,ipso-Ph), 156.4 (s, ipso-Ph). Anal. calcd. for C45H54NNiO2PS: C, 70.87; H, 7.14; N, 1.84. Found: C,70.47; H, 6.95; N, 1.88.

Reaction of 2 with diphenylacetylene: 2 (17.2 mg, 0.02 mmol) and diphenylacetylene (3.6 mg,0.02 mmol) were dissolved into 0.5 mL of C6D6. The reaction proceeded immediately to generate 3ain quantitatively concomitant with the dissociation of 1 equiv of PCy3.

Carbonylation of 3a: A pressure tight NMR tube containing a solution of 3a (15.1 mg,0.02 mmol) and a small amount of 2-methoxynaphthalene as an internal standard in 0.5 mL of C6D6was treated with carbon monoxide (5 atm). The solution changed from purple to colorless immediatelyto give 4 (78 %). 1H NMR (400 MHz, CDCl3): δ 6.10 (s, 1H, –CHPh–), 6.98 (d, JHH = 7.2 Hz, 2H,o-Ph), 7.11 (t, JHH = 7.2 Hz, 2H, m-Ph), 7.13 (d, JHH = 7.2 Hz, 2H, o-Ph), 7.18 (t, JHH = 7.2 Hz, 3H,m, p-Ph), 7.23 (t, JHH = 5.4 Hz, 1H, p-Ph), 7.26-7.28 (m, 3H, m, p-Ph), 7.27 (t, JHH = 6.9 Hz, 2H,m-SO2Ph), 7.32–7.34 (m, 2H, o-Ph), 7.47 (t, JHH = 7.4 Hz, 1H, p-SO2Ph), 7.50 (d, JHH = 7.2 Hz, 2H,o-SO2Ph). 13C NMR (100 MHz, CDCl3): δ 66.9, 128.1, 128.57, 128.61, 128.7, 128.77, 128.80, 128.9,128.97, 128.99, 129.8, 129.9, 130.1, 131.1, 131.8, 133.6, 134.7, 139.0, 155.9, 168.1. HRMS calcd. forC28H21NO3S 451.1242, Found m/z 451.1237.



Reaction of 3a with diphenylacetylene: 3a (11.4 mg, 0.015 mmol) and diphenylacetylene(2.7 mg, 0.015 mmol) were dissolved into 0.5 mL of C6D6. The reaction proceeded slowly to give 5aquantitatively after 24 h.

Reaction of 3a with 2-butyne: To a solution of 3a (11.4 mg, 0.015 mmol) in 0.5 mL of C6D6was added 2-butyne (0.8 mg, 1.2 µL, 0.015 mmol). The insertion reaction proceeded to give 5b quan-titatively.

Isolation of 5a: Ni(cod)2 (219.1 mg, 0.80 mmol), PCy3 (229.6 mg, 0.80 mmol), 1 (196.1 mg,0.80 mmol) and diphenylacetylene (285.0 mg, 1.60 mmol) were dissolved into 7 mL of toluene. The re-action mixture was stirred for 24 h. The reaction mixture was concentrated in vacuo to give purplesolids. The solids were washed with hexane and cold pentane to give 688.6 mg of complex 5a (red or-ange solids) in 92 % yield. Anal. calcd. for C59H64NNiO2PS: C, 75.32; H, 6.86; N, 1.49. Found: C,74.84; H, 6.93; N, 1.59. X-ray data for 5a. M = 940.89, brown, monoclinic, P21/n (No. 14), a =10.7809(3) Å, b = 19.1028(6) Å, c = 24.5928(7) Å, β = 101.1880(8)°, V = 4968.5(2) Å3, Z = 4, Dcalcd =1.258 g/cm3, T = 0 °C, R (Rw) = 0.052 (0.055).

Isolation of 5b: To a solution of 3a (151.6 mg, 0.20 mmol) in 5 mL of toluene was added 2-bu-tyne (16.2 mg, 23.5 µL, 0.30 mmol). The insertion reaction proceeded to give 5b quantitatively. The re-action mixture was stirred for 1 h. The reaction mixture was concentrated in vacuo to give red solids.The solids were washed with hexane and cold pentane to give 128.5 mg of complex 5b (red orangesolids) in 79 % yield. 1H NMR (400 MHz, C6D6): δ 0.98 (s, 3H, Me), 1.05–1.35 (m, 9H, Cy), 1.56–1.97(m, 21H, Cy including 3H of Me at 1.85), 2.19 (brs, 3H, Cy), 2.46 (brs, 3H, Cy), 5.52 (s, 1H, –CHPh–),6.85-7.30 (m, 4H), 7.46 (t, JHH = 7.2 Hz, 2H), 7.64 (brs, 3H), 8.19 (brs, 2H). 31P NMR (109.4 MHz,C6D6): δ 31.5 (s). 13C NMR (100 MHz, C6D6): 17.0 (d, JCP = 3.0 Hz, Me), 26.6 (d, JCP = 7.6 Hz, Me),27.2 (s, Cy), 28.4 (d, JCP = 5.3 Hz, Cy), 28.5 (d, JCP = 6.1 Hz, Cy), 30.9 (s, Cy), 31.3 (s, Cy), 34.1(d, JCP = 17.5 Hz, Cy), 60.6 (s, –CHPh–), 125.5 (s), 126.5 (s), 127.5 (s), 127.7 (s), 128.3 (s), 128.5 (s),128.7 (s), 129.1(s), 131.3 (s), 135.5 (s), 135.9 (s), 146.0 (s). Anal. calcd. for C49H60NNiO2PS: C, 72.06;H, 7.40; N, 1.71. Found: C, 71.59; H, 7.38; N, 1.82.

Oxidative cyclization of N-benzenesulfonylbenzaldimine (1) and 2-butyne on Ni(0): To a so-lution of Ni(cod)2 (5.9 mg, 0.02 mmol), PCy3 (5.9 mg, 0.02 mmol), N-benzenesulfonylbenzaldimine(1) (5.4 mg, 0.02 mmol) in 0.5 mL of C6D6 was added 2-butyne (1.1 mg, 1.6 µL, 0.02 mmol) at roomtemperature. The reaction proceeded to give an inseparable mixture of five-membered nickelacycle (3c:21 %), seven-membered nickelacycle (5c: 32 %) and η2-iminenickel complex (2: 22 %). The additionof an additional equivalent of 2-butyne (1.6 µL, 0.02 mmol) to the reaction mixture led to the forma-tion of 5c (95 %). The isolation of 3c failed due to very rapid insertion of 2-butyne. Yield of 3c was cal-culated based on the resonance at δ 31.3 in 31P NMR spectrum.

Isolation of Ni(C(CH3)=C(CH3)C(CH3)=C(CH3)C(Ph)NSO2Ph)(PCy3) (3a): To a solution ofNi(cod)2 (274.8 mg, 1.00 mmol), PCy3 (288.4 mg, 1.00 mmol) and 1 (244.0 mg, 0.99 mmol) in 5 mLof toluene was added 2-butyne (276.4 mg, 400 µL, 5.11 mmol) at room temperature. The solutionchanged from red to dark red. The reaction mixture was stirred for 1 h. The reaction mixture was con-centrated in vacuo to give red solids. The solids were washed with hexane to give 467.5 mg of complex3a (orange solids) in 68 % yield. 1H NMR (400 MHz, C6D6): δ 0.87–1.96 (m, 39H, Cy including 3Hof –NiC(Me)=C(Me)C(CH3)= at 1.09, 3H of –NiC(CH3)= at 1.69 and 3H of –NiC(Me)=C(CH3)- at1.95), 2.38 (brs, 3H, Cy), 2.55 (brs, 3H, –NiC(Me)=C(Me)C(Me)=C(CH3)–), 5.07 (s, 1H, -CHPh-),6.97-7.02 (m, 4H), 7.11 (t, JHH = 7.6 Hz, 2H), 7.31 (brs, 2H), 8.29 (brd, JHH = 6.5 Hz 2H). 31P NMR(109.4 MHz, C6D6): δ 31.3 (s). 13C NMR (100 MHz, C6D6): 15.6 (s), 18.2 (s), 22.2 (s), 24.8 (d, JCP =6.1 Hz, Cy), 27.2 (s), 28.4 (d, JCP = 9.9 Hz, Cy), 28.5 (d, JCP = 9.9 Hz, Cy), 30.2 (s), 31.0 (s), 33.6 (d,JCP = 17.5 Hz, Cy), 60.2 (s, -CHPh-), 125.5 (s), 126.5 (s), 127.5 (s), 127.7 (s), 128.3 (s), 128.5 (s), 128.7(s), 129.1(s), 131.3 (s), 135.5 (s), 135.9 (s), 146.0 (s). Anal. calcd, for C39H56NNiO2PS: C, 67.63; H,8.15; N, 2.02. Found: C, 67.36; H, 8.21; N, 2.12. X-ray data for 3a. M = 692.61, brown, monoclinic,

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P21/n (No. 14), a = 10.1244(3) Å, b = 21.5519(6) Å, c = 17.5944(5) Å, β = 102.400(1)°, V = 3749.5(2)Å3, Z = 4, Dcalcd = 1.227 g/cm3, T = 0 °C, R (Rw) = 0.054 (0.069).

Reductive elimination reactions of 5a–c: A solution of a seven-membered nickelacycle (5a–c,0.04 mmol) and a small amount of 2-methoxynaphthalene as an internal standard in 0.5 mL of C6D6(0.5 mL) was heated at 100 °C. After complete decomposition of the starting complex was confirmedby 31P NMR, the yield of the reductive elimination product (6a–c) was determined by 1H NMR.

1-Benzenesulfonyl-3, 4, 5, 6-tetramethyl-2-phenyl-1, 2-dihydropyridine (6c): 1H NMR(400 MHz, CDCl3): δ 1.23 (s, 3H, –CHPhC(Me)=C(CH3)–), 1.50 (s, 3H, –CHPhC(CH3)=), 1.63(s, 3H, –N(SO2Ph)C(Me)=C(CH3)–), 1.98 (s, 3H, –N(SO2Ph)C(CH3)=), 5.26 (s, 1H, –CHPh–),7.24–7.30 (m, 5H, Ph), 7.43 (t, JHH = 7.2 Hz, 2H, m-SO2Ph), 7.51 (t, JHH = 7.2 Hz, 1H, p-SO2Ph), 7.70(d, JHH = 7.2 Hz, 2H, o-SO2Ph). 13C NMR (100 MHz, CDCl3): δ 13.2, 14.6, 18.2, 19.9, 61.6, 125.0,125.3, 127.1, 127.93, 127.94, 128.1, 128.3, 128.5, 128.7, 132.5, 137.8, 138.7. HRMS calcd. forC21H23NO2S 353.1449, found m/z 353.1442.

1-Benzenesulfonyl-2, 3, 4, 5, 6-pentaphenyl-1, 2-dihydropyridine (6a): An inseparable mix-ture was obtained. Yield of 6b was calculated based on the resonance at d 5.88 in 1H NMR Spectrum.

1-Benzenesulfonyl-5, 6-dimethyl-2, 3, 4-triphenyl-1, 2-dihydropyridine (6b): 1H NMR(400 MHz, CDCl3): δ 1.40 (s, 3H, –N(SO2Ph)C(Me)=C(CH3)–), 2.09 (s, 3H, –N(SO2Ph)C(CH3)=),5.95 (s, 1H, –CHPh–), 6.53 (brs, 2H), 6.96 (t, JHH = 7.4 Hz, 2H), 7.02 (t, JHH = 7.2 Hz, 1H), 7.10–7.16(m, 3H), 7.36–7.46 (m, 5H), 7.58–7.62 (m, 3H), 7.69 (d, JHH = 7.4 Hz, 2H). 13C NMR (100 MHz,CDCl3): δ 16.0, 20.0, 61.8, 126.9, 127.2, 127.65, 127.68, 127.74, 127.74, 128.23, 128.25, 128.30,128.30, 128.6, 128.80, 128.84, 130.0, 132.7, 137.4, 138.6, 138.7, 138.9, 139.5. HRMS calcd. forC31H27NO2S 477.1762, found m/z 477.1768.

General procedure for Ni(cod)2/PtBu2Me-catalyzed cycloaddition of 2-butyne and 1: To asolution of 2-butyne (13.5 mg, 19.6 µL, 0.25 mmol) and PtBu2Me (3.2 mg, 3.9 µL, 0.02 mmol) in0.5 mL of C6D6 was added 1 (24.5 mg, 0.1 mmol) and Ni(cod)2 (2.8 mg, 0.01 mmol). The solution washeated at 100 °C. After 48 h, 6c was generated in 87 % yield. The reaction mixture was concentratedin vacuo. The residue was purified by preparative thin-layer chromatography of silica gel to give 6c(17.6 mg, 50 %).

Ni(cod)2/PCy3-catalyzed cycloaddition of 2-butyne and 1: The reaction was carried out ac-cording to the general procedure using PCy3 (5.5 mg, 0.02 mmol). After 24 h, 6c was generated in64 %.

Ni(cod)2/PnBu3-catalyzed cycloaddition of 2-butyne and 1: The reaction was carried out ac-cording to the general procedure using PnBu3 (4.0 mg, 0.02 mmol). After 24 h, 6c was generated in17 %.

Ni(cod)2/P(o-tol)3-catalyzed cycloaddition of 2-butyne and 1: The reaction was carried out ac-cording to the general procedure using P(o-tol)3 (6.3 mg, 0.02 mmol). After 29 h, 6c was generated in6 %.

General procedure for Ni(cod)2/PtBu2Me-catalyzed cycloaddition of 3-hexyne and 1: To asolution of 3-hexyne (20.5 mg, 28.4 µL, 0.25 mmol) and PtBu2Me (3.2 mg, 3.9 µL, 0.02 mmol) in0.5 mL of C6D6 was added 1 (24.5 mg, 0.1 mmol) and Ni(cod)2 (2.8 mg, 0.01 mmol). The solution washeated at 100 °C. After 70 h, 6d was generated in 64 % yield. The reaction mixture was concentratedin vacuo. The residue was purified by preparative thin-layer chromatography of silica gel to give 6d(22.3 mg, 55 %). 1H NMR (400 MHz, CDCl3): δ 0.34 (t, JHH = 7.4 Hz, 3H, –N(SO2Ph)C(CH2CH3)=),0.40 (t, JHH = 7.4 Hz, 3H, –CHPhC(Et)=C(CH2CH3)–), 0.81 (t, JHH = 7.6 Hz, 3H,–CHPhC(CH2CH3)=), 0.88 (t, JHH = 7.6 Hz, 3H, -N(SO2Ph)C(Et)=C(CH2CH3)–), 1.82–1.94 (m, 2H),1.96–2.12 (m, 3H), 2.22–2.37 (m, 2H), 2.68 (td, JHH = 14.8, 7.4 Hz, 1H, –N(SO2Ph)C(CH2CH3)=),5.55 (s, 1H, –CHPh–), 7.23–7.29 (m, 5H, Ph), 7.39 (t, JHH = 7.6 Hz, 2H, m-SO2Ph), 7.49 (t, JHH =7.6 Hz, 1H, p-SO2Ph), 7.74 (d, JHH = 7.2 Hz, 2H, o-SO2Ph). 13C NMR (100 MHz, CDCl3): δ 12.1,



13.2, 14.3, 14.9, 20.1, 24.3, 24.7, 59.5, 127.5, 127.96, 127.99, 128.5, 129.2, 131.1, 131.3, 132.4, 133.0,133.9, 137.7, 139.6. HRMS calcd. for C25H31NO2S 409.2075, found m/z 409.2066.

Ni(cod)2/PCy3-catalyzed cycloaddition of 3-hexyne and 1: The reaction was carried out ac-cording to the general procedure using PCy3 (5.5 mg, 0.02 mmol). After 24 h, 6d was generated in26 %.

Ni(0)-catalyzed cycloaddition of trimethylsilylacetylene and 1: To a solution of trimethylsilyl-acetylene (24.5 mg, 34.6 µL, 0.25 mmol) and PtBu2Me (3.2 mg, 3.9 µL, 0.02 mmol) in 0.5 mL of C6D6was added 1 (24.5 mg, 0.1 mmol) and Ni(cod)2 (2.8 mg, 0.01 mmol). The solution was heated at 100 °C.After 5 h, 2.5 equivalents of trimethylsilylacetylene were added to a reaction mixture. Heating more13 h, 6e was generated in 58 % yield. The residue was purified by preparative thin-layer chromato-graphy of silica gel to give 6e (16.7 mg, 38 %). 1H NMR (400 MHz, CDCl3): δ –0.18 (s, 9H,–CHPhCTMS=), 0.14 (s, 9H, –N(SO2Ph)CH=CTMS–), 5.66 (s, 1H, –CHPh–), 6.27 (s, 1H,–CHPhCTMS=CH–), 6.59 (s, 1H, –N(SO2Ph)CH=), 7.24–7.26 (m, 3H), 7.34–7.37 (m, 2H), 7.41 (t,JHH = 7.8 Hz, 2H, m-SO2Ph), 7.52 (t, JHH = 7.4 Hz, 1H, p-SO2Ph), 7.71 (d, JHH = 7.2 Hz, 2H,m-SO2Ph), 7.49 (t, JHH = 7.6 Hz, 1H, p-SO2Ph), 7.74 (d, JHH = 7.2 Hz, 2H, o-SO2Ph). 13C NMR(100 MHz, CDCl3): δ –1.75, –1.64, 58.2, 120.2, 126.7, 128.43, 128.45, 129.0, 130.3, 131.9, 132.8,133.1, 139.3, 140.7. HRMS calcd. for C23H31NO2SSi 441.1614, found m/z 441.1610.

Ni(cod)2/NHC-catalyzed cycloaddition of 2-butyne and 1: To a suspension of Ni(cod)2(2.8 mg, 0.01 mmol), 1,3-bis-(2,4,6-trimethylphenyl)imidazolium chloride (3.4 mg, 0.01 mmol) andpotassium tert-butoxide (1.1 mg, 0.01 mmol), 1 (24.5 mg, 0.1 mmol) and 2-methoxynaphthalene as aninternal standard in 0.5 mL of C6D6 was added 2-butyne (13.5 mg, 0.25 mmol). The solution was heatedat 60 °C for 19 h. However, 6c was not obtained.

ACKNOWLEDGMENTS

Partial support of this work through the Sumitomo Foundation and a Grant-in-Aid for ScientificResearch and a Grant-in-Aid for Scientific Research on Priority Areas “Advanced MolecularTransformations of Carbon Resources” from the Ministry of Education, Culture, Sports, Science andTechnology, Japan is gratefully acknowledged.

REFERENCES

1. Examples of isolated oxa-metalacycles, see: (a) H. G. Alt, G. S. Hermann. J. Organomet. Chem.356, C53 (1988); (b) D. F. Hewlett, R. J. Whitby. J. Chem. Soc., Chem. Commun. 1684 (1990);(c) V. B. Shur, V. V. Burlakov, A. I. Yanovsky, P. V. Petrovsky, Y. T. Struchkov, M. E. Vol’pin. J.Organomet. Chem. 297, 51 (1985); (d) C. Dales, H. Urabe, F. Sato. Chem. Commun. 272 (2002);(e) W. E. Crowe, A. T. Vu. J. Am. Chem. Soc. 118, 1557 (1996); (f) C. Lefeber, A. Ohff,W. Baumann, R. Kempe, V. V. Burakov, U. Rosenthal, H. Gorls. J. Organomet. Chem. 501, 179(1995); (g) N. Morlender-Vais, N. Solodovnikova, I. Marek. Chem. Commun. 1849 (2000); (h)G. Erker, R. Zwetteler. J. Organomet. Chem. 409, 179 (1991); (i) S. L. Buchwald, B. T. Watson.J. Am. Chem. Soc. 109, 2544 (1987); (j) R. M. Waymouth, K. R. Clauser, R. H. Grubbs. J. Am.Chem. Soc. 118, 6385 (1986); (k) J. R. Stricker, M. A. Bruck, P. A. Wexler, G. Erker,F. Rosenfeldt. J. Organomet. Chem. 224, 29 (1982); (l) D. E. Wigley. Organometallics 9, 266(1990); (m) D. Thomas, P. Arndt, N. Peulecke, N. Rhette, A. Spannenberg, R. Kempe,U. Rosenthal. Eur. J. Inorg. Chem. 1351 (1998); (n) N. Peulecke, A. Ohff, A. Tillack,W. Baumann, R. Kempe, V. V. Burlakov, U. Rosenthal. Organometallics 15, 1340 (1996); (o)T. Oshiki, K. Tanaka, J. Yamada, T. Ishiyama, Y. Kataoka, K. Mashima, K. Tani, T. K. Akai.Organometallics 22, 464 (2003); (p) R. Siebenlist, H.-W. Fruhauf, K. Vrieze, W. J. J. Smeets,A. L. Spek. Organometallics 21, 5628 (2002).

S. OGOSHI et al.


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2. Examples of isolated aza-metalacycles, see: (a) S. L. Buchwald, M. W. Wannamaker, B. T.Watson. J. Am. Chem. Soc. 111, 776 (1989); (b) S. L. Buchwald, B. T. Watson, M. W.Wannamaker, J. C. Dewan. J. Am. Chem. Soc. 111, 4486 (1989); (c) M. G. Thorn, J. E. Hill, S. A.Waratuke, E. S. Johnson, P. E. Fanwick, I. P. Rothwell. J. Am. Chem. Soc. 119, 8630 (1997); (d)H.-W. Fruehauf, F. Seils, C. H. Stam. Organometallics 8, 2338 (1989); (e) J. R. Strickler, D. E.Wigley. Organometallics 9, 1665 (1990); (f) J. E. Hill, P. E. Fanwick, I. P. Rothwell.Organometallics 11, 1775 (1992); (g) N. Coles, M. C. J. Harris, R. J. Whitby, J. Blagg.Organometallics 13, 190 (1994); (h) M. G. Thorn, P. E. Fanwick, I. P. Rothwell. Organometallics18, 4442 (1999).

3. Alkyne-aldehyde, ketone: (a) W. S. Huang, J. Chan, T. F. Jamison. Org. Lett. 2, 4221 (2000); (b)Y. Ni, K. K. D. Amarasinghe, J. Montgomery. Org. Lett. 4, 1743 (2002); (c) K. M. Miller, W. S.Huang, T. F. Jamison. J. Am. Chem. Soc. 125, 3442 (2003); (d) G. M. Mahandru, G. Liu,J. Montgomery. J. Am. Chem. Soc. 126, 3698 (2004); (e) K. M. Miller, T. F. Jamison. J. Am.Chem. Soc. 126, 15342 (2004); (f) M. Murakami, S. Ashida, T. Matsuda. J. Am. Chem. Soc. 127,6932 (2005); alkyne-imine: (g) S. J. Patel, T. F. Jamison. Angew. Chem., Int. Ed. 42, 1364 (2003);(h) S. J. Patel, T. F. Jamison. Angew. Chem., Int. Ed. 43, 3941 (2004).

4. (a) T. Tsuda, T. Kiyoi, T. Miyane, T. Saegusa. J. Am. Chem. Soc. 110, 8570 (1988); (b) T. N.Tekevac, J. Louie. Org. Lett. 7, 4037 (2005); (c) M. Murakami, S. Ashida, T. Matsuda. J. Am.Chem. Soc. 128, 2166 (2006).

5. (a) S. Ogoshi, M. Oka, H. Kurosawa. J. Am. Chem. Soc. 126, 11082 (2004); (b) S. Ogoshi,M. Ueta, T. Aral, H. Kurosawa. J. Am. Chem. Soc. 127, 12810 (2005); (c) S. Ogoshi, K. I.Tonomori, M. A. Oka, H. Kurosawa. J. Am. Chem. Soc. 128, 7077 (2006); (d) S. Ogoshi,M. Nagata, H. Kurosawa. J. Am. Chem. Soc. 128, 5350 (2006).

6. (a) H. Hoberg, B. W. Oster, J. Organomet. Chem. 234, C35 (1982); (b) H. Hoberg, B. W. Oster.J. Organomet. Chem. 252, 359 (1983).

7. (a) N. Chatani, T. Morimoto, Y. Fukumoto, S. Murai. J. Am. Chem. Soc. 120, 5335 (1998); (b)K. Fuji, T. Morimoto, K. Tsutsumi, K. Kakiuchi. Chem. Commun. 3925 (2005).

8. K. I. Fujita, M. Yamashita, F. Puschmann, M. M. Alvarez-Falcon, C. D. Incarvito, J. F. Hartwig.J. Am. Chem. Soc. 128, 9044 (2006).



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