| Abstract
| - Diynes 1a−c [X(CH2C⋮CCO2Me)2: X = (CH2)2, 1a, X = CH2, 1b and X = O, 1c] undergo [2 + 2 + 2]ene−diyne cycloaddition reactions with a variety of allenes (n-butylallene 2a, phenylallene 2b,(4-chlorophenyl)allene 2c, (4-bromophenyl)allene 2d, (3-methoxyphenyl)allene 2e, 1-naphthylallene2f, cyclohexylallene 2g and cyclopentylallene 2h) in the presence of Ni(dppe)Br2 and Zn powder inCH3CN at 80 °C for 8 h to give the corresponding polysubstituted benzene derivatives 4a−l ingood to excellent yields. Under similar reaction conditions, unsymmetrical diynes 5a−c (HC⋮CCH2XCH2C⋮CCO2Me) react with allenes 2 to afford exclusively the corresponding meta-isomers 6a−gin 73−86% yields. The catalytic reaction is highly regioselective and completely chemoselective.This synthetic method is compatible with many functional groups such as Cl, Br, and OMe on thephenyl group of the allene moiety and an ether linkage in a diyne moiety. In this catalytic reaction,allenes are synthetically equivalent to terminal alkynes. Interestingly, unsymmetrical diyne 7(MeC⋮C(CH2)4C⋮CCO2Me) undergoes 2:1 cocyclotrimerization with allenes 2a and 2g to affordthe corresponding polysubstituted benzene derivatives 9a,b in 87% and 82% yields, respectively.A plausible mechanism involving a nickelacycloheptadiene intermediate is proposed to account forthis nickel-catalyzed reaction.
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