An Experimentally Derived Model for Stereoselectivity in the Aerobic Oxidative Kinetic Resolution of Secondary Alcohols by (Sparteine)PdCl_2

摘要

Palladium-catalyzed aerobic oxidation of alcohols has a rich history that began with the first example by Schwartz in 1977. Recently, enantioselective aerobic oxidation of secondary alcohols by Pd and (-)-sparteine (sp) has emerged as a powerful method for the preparation of enantioenriched alcohols by kinetic resolution. While numerous improvements to oxidative kinetic resolution (OKR) have been made3b,c and the mechanism has been analyzed using kinetics, there have been no reports detailing a structural model for asymmetric induction by sp in these reactions. Herein, we describe experiments that probe the origins of stereoselectivity in the oxidation and present a nonintuitive model for the absolute stereochemical outcome. This model is based on the reactivity and solid-state structures of (sp)PdII complexes, including the first reported structure of a chiral Pd(II) alkoxide relevant to this problem.