A versatile synthesis of allenic hydrocarbons. Evidence for an organocopper(III) intermediate

A number of allenes RR1CCCHR2 2 have been prepared by interaction between acetylenic tosylates R1C≡CCHR2OTs, 1 (R1 = H, alkyl, aryl, H2CC(CH3) or CH3C≡C; R2 = H or t‐C4H9) and organocopper(I) compounds “RCu” (formed from Grignard compounds RMgCl or RMgBr with R = alkyl, aryl or 2‐thienyl and copper(I) bromide in tetrahydrofuran). If R = t‐C4H9 the reaction with catalytic amounts of CuBr also gives good results. Significant amounts of C6H5CHCCH2 or C6H5CDCCH, are formed if C6H5CCCH2OTs is reacted with “CH3Cu” (from CH3MgCl and CuI) at −60° in tetrahydrofuran and the reaction mixture is quenched at low temperatures with methanol or deuteriomethanol. This finding is considered as evidence for the intermediate occurrence of a copper(III) derivative.