Readily Synthesized Chiral Sulfides as Reagents for Asymmetric Epoxidation

Chiral oxathianes were designed, synthesized, and successfully used for asymmetric sulfur ylide mediated epoxidation. A considerable emphasis has been placed upon the design of sulfides with suitable architecture in a small number of steps (three or four). The use of (4aR,6S,8aR)-6-isopropenyl-8a-methyloctahydro-1,4-benzoxathiane in asymmetric epoxidation resulted in good diastereo- and enantioselectivity in the formation of stilbene oxide, and (2S,6S)-2-allyl-2,3,3,6-tetramethyl-1,4-oxathiane produced even better results. Moderate to good diastereoselectivities with essentially complete enantioselectivities were observed in the formation of alkyl-aryl-, vinyl-aryl-, and propargyl-aryl-substituted epoxides. The selectivities were rationalized and supported by density functional theory calculations.