Synthesis of Sulfur-Substituted α-Stereogenic Amides and Ketones: Highly Enantioselective Sulfa-Michael Additions of 1,4-Dicarbonylbut-2-enes

Conjugate addition to 1,4-dicarbonylbut-2-enes will generate an alpha-stereogenic center with respect to one of the carbonyl groups, which informally, can be considered as an inversion of normal reactivity patterns or umpolung protocol. In this paper, the addition of tert-butyl mercaptan to 1,4-dicarbonylbut-2-enes including (E)-4-oxo-4-arylbutenamides and (E)-4-oxo-4-arylbutenones has been developed, to synthesize a series of chiral sulfur-substituted a-stereogenic amides and ketones in high regioselectivity and enantioselectivity (up to 98% ee).