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.