Catalytic Asymmetric 1,6-Michael Addition of Arylthiols to 3-Methyl-4-nitro-5-alkenyl-isoxazoles with Bifunctional Catalysts

An enantioselective 1,6-Michael addition reaction of arylthiols to a wide range of 3-methyl-4-nitro-5-alkenyl-isoxazoles catalyzed by readily available Takemoto's thiourea catalyst has been developed. This reaction provides a useful catalytic method for the synthesis of optically active chiral sulfur compounds bearing a 4-nitroisoxazol-5-yl moiety in high to excellent yields (up to 97%) and high enantioselectivities (up to 91% ee). Significantly, the potential utilities of the protocol had been further demonstrated by gram-scale reaction and the versatile conversions of some resulting products into other functionalized and useful compounds.