Selective Vinylogous Reactivity of Carbene Intermediate in Gold-Catalyzed Alkyne Carbocyclization: Synthesis of Indenols

A gold-catalyzed carbocyclization of alkynes with a pendant diazo group that is completed by reaction with a protic nucleophile for the synthesis of indenol derivatives with a tertiary center is described. Mechanistic studies and DFT calculations indicate that the transformation is initiated by a gold-promoted 5-endo-dig carbocyclization to form the key intermediate vinyl gold carbene, which is intercepted by an unprecedented vinylogous addition and followed by external protic nucleophile-assisted protodeauration. Furthermore, in this catalytic alkyne transformation, various nucleophiles, including water, commercially available 1°, 2°, and 3° alcohols, menthol, d-galactose, cholesterol, steroid, etc., all perform well under these mild conditions to produce the corresponding indenol derivatives in high yields with structural diversity.