Rhodium/Silver Synergistic Catalysis in Highly Enantioselective Cycloisomerization/Cross Coupling of Keto-Vinylidenecyclopropanes with Terminal Alkynes

A rhodium/silver synergistic catalysis
has been established, enabling
cycloisomerization/cross coupling of keto-vinylidenecyclopropanes
(VDCPs) with terminal alkynes toward the regio- and enantioselective
formation of diversified tetrahydropyridin-3-ol tethered 1,4-enynes
in good yields and high ee values. In this synergistic catalysis,
Rh­(I) and Ag­(I) catalysts selectively activate keto-VDCP substrates
and terminal alkynes to generate the π-allyl Rh­(III) complex
of oxa-rhodacyclic intermediate and Ag alkynyl intermediate, respectively.
The rapid transmetalation of alkynyl groups from Ag to Rh is proposed
to play a key role in realizing the regioselective cleavage of the
distal bond of the three-membered ring in this transformation.