Mechanistic complexity in organo-SOMO activation.

Singly occupied molecular orbital (SOMO) activation provides a pathway for asymmetric a-addition to aldehydes. The scope of SOMO activation includes the allylation, enolation, vinylation, styrenation, chlorination, polyene cyclization, and arylation of a range of aldehydes. This union of organocatalysis with single-electron oxidative coupling is an intricate process involving the complex balance of catalyst, oxidant, radicophile, base, temperature, heterogeneous reaction conditions, and H2O. To examine the role of each component in this complex process, a series of spectroscopic and kinetic studies were carried out to study the asymmetric allylation of 1 shown in Equation (1). The data described herein show three important features: 1) Oxidation of the intermediate enamine is rapid and preferential to oxidation of the catalyst, 2) H2O concentration is critical for catalytic efficiency, and 3) the kinetic role of ceric ammonium nitrate (CAN) is masked by a physical phase-transfer process.