Auxiliary Induced e-Stereocontrol in Acetaloxyalkyl Radical Addition Reactions

摘要

Radical-based C—C bond forming reactions offer a powerful alternative to their polar counterparts and, accordingly, occupy an increasingly prominent role in organic synthesis. Whereas early work in this area had focused on issues related to chemoselectivity and regioselectivity, attention has now shifted to the control of acyclic stereochemistry. Both substrate and auxiliary-derived chirality have been used to control the stereochemical course of radical addition and substitution reactions. However, a general approach to the control of acyclic stereochemistry during radical reactions still remains an elusive goal. Toward this end, the development of a readily available and easily recoverable chiral auxiliary for α-hydroxyalkyl radicals would be particularly valuable (1→ 2 → 3 and 4). We now report a conceptually simple solution to this problem wherein acetal-based chiral auxiliaries can be used to control acyclic e-Stereocontrol (see ref 2b for a description of this terminology) in addition reactions of hydroxyalkyl radical equivalents.