Allene formation by gold catalyzed cross-coupling of masked carbenes and vinylidenes

Addition of a sterically demanding cyclic (alkyl)(amino)carbene (CAAC) to AuCl(SMe2) followed by treatment with [Et3Si(Tol)](+) [B(C6F5)(4)](-) in toluene affords the isolable [(CAAQAu(eta(2)-toluene)](+) [B(C6F5)(4)](-) complex. This cationic Au(l) complex efficiently mediates the catalytic coupling of enamines and terminal alkynes to yield allenes and not propargyl amines as observed with other catalysts. Mono-, di-, and tri-substituted enamines can be used, as well as aryl-, alkyl-, and trimethylsilyl-substituted terminal alkynes. The reaction tolerates sterically hindered substrates and is diaste-reoselective. This general catalytic protocol directly couples two unsaturated carbon centers to form the three-carbon allenic core. The reaction most probably proceeds through an unprecedented '' carbene/vinylidene cross-coupling.''.