Practical and Highly Selective Sulfur Ylide Mediated Asymmetric Epoxidations and Aziridinations Using an Inexpensive, Readily Available Chiral Sulfide. Applications to the Synthesis of Quinine and Quinidine

Abstract

Heating one of the most abundant naturally occurring inorganic chemicals (elemental sulfur) with one of the most readily available homochiral molecules (limonene) gives a one-step synthesis of a chiral sulfide which exhibits outstanding selectivities in sulfur ylide mediated asymmetric epoxidations and aziridinations. In particular reactions of benzyl and allylic sulfonium salts with both aromatic and aliphatic aldehydes gave epoxides with perfect enantioselectivities and the highest diastereoselectivities reported to date. In addition reactions with imines gave aziridines again with the highest enantioselectivities and diastereoselectivities reported to date. The reactions are scaleable, and the sulfide can be reisolated in high yield. The epoxidation has been used as the key step in a convergent and stereoselective synthesis of each of the diastereoisomers of the cinchona alkaloids, quinine and quinidine.