Propargylsilanes as Reagents for Synergistic Gold(I) Catalyzed Propargylation of Carbonyl Compounds. Isolation and Characterization of σ‐Gold(I) Allenyl Intermediates

: Reported herein is the isolation and characterization, for the first time, of a σ-gold allenyl complex as an intermediate in gold catalysis. This intermediate was captured during the study of a novel gold(I)-catalyzed propargylation of carbonyl compounds with propargylsilanes. Notably, the gold-catalyzed propargylation reaction, which proceeds with aldehydes and ketones, can be driven to the formation of either homopropargyl silyl ethers or the in situ synthesis of corresponding 2-silyl-4,5-dihydrofurans.