Stereoselective organocatalytic synthesis of γ, γ -disubstituted butenolides

Abstract

A direct highly diastereo- and enantioselective asymmetric doubly vinylogous 1,6-Michael addition reaction of 3-methyl-4- nitro-5-alkenyl isoxazoles with g-substituted deconjugated butenolides has been successfully developed with the help of Cinchona derived squaramides. This novel strategy has been utilized to synthesize a range of enantiopure g,g-disubstituted butenolide molecules bearing remote contiguous quaternary and tertiary stereocenters in yield up to 76% with ee up to 98% and dr up to 20:1.