Photochemical Ring Expansion of Cyclic Sulfoximines with Aryl Diazoacetates and Subsequent Diastereoconvergent Oxidation

A visible light-mediated ring expansion reaction of cyclic N-sulfenyl sulfoximines with aryl diazoacetates is presented. The protocol results in the formation of six-membered heterocycles through the formation of sulfur ylide intermediates and a subsequent [1,2]-sigmatropic rearrangement. The reaction proceeds well under ambient conditions and gives the desired heterocycles in moderate to good yields with a good functional group tolerance. Subsequent oxidation of the products with m-CPBA results in significant diastereomeric enrichment of the products. Density functional theory studies indicate that the diastereoconvergent oxidation is enabled by a ring opening and recyclization, which allow the diastereomeric ratio to adjust to a value governed by the differing thermodynamic stabilities of the diastereomers.