Generation of Endocyclic Vinyl Carbene Complexes via Gold-Catalyzed Oxidative Cyclization of Terminal Diynes: Toward Naphthoquinones and Carbazolequinones

Carbene
cascade reactions involving carbene/alkyne metathesis have
attracted much attention over the past decades because this chemistry
offers great potential to build complicated cyclic molecules. However,
the formed vinyl metal carbenoids in these reactions are limited to
exocyclic carbenes, and the generation of endocyclic vinyl carbene
complexes remains unexplored. Here, we report an unprecedented gold-catalyzed
oxidative cyclization of terminal diynes. Importantly, the generation
of endocyclic vinyl carbene complexes was involved in this oxidative
cyclization, which is distinctively different from previous protocols.
This method allows the facile synthesis of various valuable naphthoquinones
and carbazolequinones from readily available diynes under exceptionally
mild reaction conditions and features a broad substrate scope and
wide functional group tolerance. Moreover, theoretical calculations
provide further evidence on the divergent selectivity of this cyclization
reaction.