An enantioselective protonation of transient enolate generated
in sulfa-Michael addition was investigated. Various α-substituted
acrylic derivatives and thiols were examined as substrates. α-Benzyl acrylimide gave the
best results in terms of chemical yield and enantioselectivity (up
to 93% yield and 92% ee)
asymmetric protonation - enantioselective catalysis - squaramide - hydrogen bonding