Chiral Squaramide-Catalyzed Enantioselective Conjugate Michael Addition of Various Thiols to α,β-Unsaturated N-Acylated Oxazolidin-2-ones

A highly enantioselective sulfa-Michael addition (SMA) of various thiols to alpha,beta-unsaturated N-acylated oxazolidinones has been achieved with a chiral squaramide catalyst under very mild reaction conditions. In addition, the conversion of the beta-thio-substituted adduct to the corresponding methyl beta-tosylbutanoate was demonstrated in high yield through a methanolysis/oxidation sequence.