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

• DOI: 10.1073/pnas.0705809104
• Publication Date: 2007-08-14T00:54:28Z
• Authors: Vincent Lavallo; Guido D. Frey; Shazia Kousar; Bruno Donnadieu; Guy Bertrand
• Keywords: Alkadienes; Models, Molecular; Cross-Linking Reagents; Vinyl Compounds; Molecular Structure; Gold; Methane; 01 natural sciences; Catalysis; Hydrocarbons; 0104 chemical sciences

Addition of a sterically demanding cyclic (alkyl)(amino)carbene (CAAC) to AuCl(SMe 2 ) followed by treatment with [Et 3 Si(Tol)] + [B(C 6 F 5 ) 4 ] − in toluene affords the isolable [(CAAC)Au(η 2 -toluene)] + [B(C 6 F 5 ) 4 ] − complex. This cationic Au(I) 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 diastereoselective. 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.”