Substrate-Directable Electron Transfer Reactions. Dramatic Rate Enhancement in the Chemoselective Reduction of Cyclic Esters Using SmI2–H2O: Mechanism, Scope, and Synthetic Utility

by Michal Szostak,* Malcolm Spain, Kimberly A. Choquette, Robert A. Flowers and David J. Procter*

Substrate-directable reactions play a pivotal role in organic synthesis, but are uncommon in reactions proceeding via radical mechanisms. Herein, we provide experimental evidence showing dramatic rate acceleration in the Sm(II)-mediated reduction of cyclic esters that is enabled by transient chelation between a directing group and the lanthanide center. This process allows unprecedented chemoselectivity in the reduction of cyclic esters using SmI2–H2O and for the first time proceeds with a broad substrate scope. Initial studies on the origin of selectivity and synthetic application to form carbon–carbon bonds are also disclosed.

Journal of the Americal Chemical Society
DOI: 10.1021/ja4078864