Rh-Catalyzed Asymmetric Hydrogenation of 2-Substituted 4-(Thio)chromenes for Synthesis of Chiral (Thio)chromanes.

Rh-catalyzed asymmetric hydrogenation of 2-substituted 4-thiochromenes and 4-chromenes was successfully developed. This method provided highly efficient access to a series of chiral 2-substituted thiochromanes and chromanes in high yields with excellent enantioselectivities (up to 99% yield, 86-99% ee). The obtained chiral 2-substituted thiochromane products were also successfully transformed to corresponding chiral substituted sulfoxides and sulfones with excellent enantioselectivities. Furthermore, this highly enantioselective hydrogenation process could be successfully applied to the concise and practical synthesis of the chiral pharmaceutical BW683C.