The mechanism of the Clemmensen reduction: the substrates
Abstract
Product analysis and deuterium labelling experiments suggest that the critical intermediate in the reduction of ArCOCH2R with Zn/HCl is a zinc–carbene; this may be protonated to give ArCH2CH2R, converted into ArCHCHR by rearrangement, deprotonated to give a vinyl–zinc species, or captured by an alkene to give a cyclopropane.