Synthetic and Mechanistic Aspects on the Competition between C–H Insertion and Hydride Transfer in Copper-Mediated Transformations of α-Diazo-β-Keto Sulfones

Competition between C–H insertion and hydride transfer is reported for the copper-catalysed reactions of a range of phenyl-substituted α-diazo-β-keto sulfones. Control of chemoselectivity is possible by alteration of the electronic properties of the diazo substrate. The production of enantioenriched cyclopentanones (up to 89% ee), formed via C–H insertion, and alkylidene tetrahydrofurans (up to 43% ee), produced via hydride transfer, is described. The isolation of products derived from hydride transfer provides mechanistic insight into the copper-mediated C–H insertion of α-diazo­carbonyl compounds.