Metal-Free Approach for Oxa-spirocyclohexadienones through [3 + 2]/[4 + 2] ipso -Cyclization of para -Quinone Methides with Halo Alcohols.

A facile one-pot metal-free, base-mediated formal [3 + 2] and [4 + 2] dearomative ipso -cycloaddition of para -quinone methides ( p -QMs) with halo alcohols has been designed for the efficient construction of 2-oxa-spirocyclohexadienones in excellent yield under mild reaction conditions. The commercial availability of the bases, reagents, and convenient reaction procedure makes it an attractive method for ipso -cyclization.