Stereoselective Organocatalytic Synthesis of γ,γ-Disubstituted Butenolides

A direct highly diastereo- and enantioselective asymmetric doubly vinylogous 1,6-Michael addition reaction of 3-methyl-4-nitro-5-alkenyl isoxazoles with gamma-substituted deconjugated butenolides has been successfully developed with the help of Cinchona derived squaramides. This novel strategy has been CDATA[utilized to synthesize a range of enantiopure gamma,gamma-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.