Metal-Catalyzed Oxa-[4+2] Cyclizations of Quinone Methides with Alkynyl Benzyl Alcohols

An
oxa-[4+2] cyclization of quinone methides with alkynyl benzyl
alcohols has been realized in the presence of a metal catalyst, and
the reaction afforded spiroacetal products in overall high yields
(up to 99%) and good diastereoselectivities (up to >95:5 dr). By
carrying
out the reaction under gold catalysis and utilizing alkynyl benzyl
alcohols as electron-rich reaction partners, this approach provides
a useful strategy for settling the challenges in oxa-[4+2] cyclization
of para-quinone methide derivatives. This reaction
serves as a good example for metal-catalyzed oxa-[4+2] cyclizations
of quinone methides. In addition, it also offers a useful method for
the construction of spiroacetal skeletons.