Diastereoselective Radical-Mediated Hydrogen-Atom Abstraction

摘要

Radical reactions are becoming a very valuable tool for organic synthesis. The mildness of the reaction conditions, their complementary nature to ionic processes, and the possibility of carrying out sequential reactions (cascade reactions) are some of the key factors of their success. Radical reactions can be used for highly stereoselective bondforming reactions. The stereochemistry of radical cyclizations has been studied extensively and reliable stereoselectivity rules (the Beckwith-Schiesser-Houk model) have been proposed. Hydrogen-atom abstraction (also called radical translocation) is a bond-breaking-bond-forming process that is frequently encountered in radical reactions. With proper design of substrates, radical translocation represents a unique mode for remote functionalization of unreactive C-H bonds. Until now, stereoselective hydrogen-atom abstractions have been considered as curiosities. Herein we report examples of diastereoselective hydrogen-atom abstractions from chiral acetals and show that the stereochemical outcome is governed by rules similar to those developed for related cyclization processes.