1,6-Carbene Transfer: Gold-Catalyzed Oxidative Diyne Cyclizations

In the presence of a gold catalyst
an unprecedented oxidative cyclization
of diynes takes place. The reaction cascade is initiated by an oxygen
transfer from a N-oxide onto a gold-activated alkyne.
The formed α-oxo carbene is transferred across the second alkyne
yielding a stabilized vinyl carbene/cation. Alkyl migration or sp3-CH insertion then terminates the catalytic cycle by formation
of highly substituted functionalized indenones. A 1,6-carbene shift
could be supported by the oxidation of the vinyl carbene. This protocol
represents an attractive alternative to procedures which are based
on the metal-catalyzed decomposition of hazardous, not easily accessible,
diazo compounds.