Elimination from diastereoisomeric methyl 2-acetoxy-1-bromo- and 1,2-dibromo-2-phenylethylphosphonates

Abstract

The examination of the kinetics and stereochemistry of dehydroacetoxylation of erythro-and threo- PhCHOAcCHBrPO₃Me₂ promoted by triethylamine in various solvents, and comparison with those for erythro- and threo- PhCHOAcCHBrCO₂Me, leads to the conclusion that the acetoxybromophosphonates undergo elimination through a carbanion process of the irreversible type. The similarity of the elimination behaviour of the threo-PhCH BrCH BrPO₃Me₂ and that of threo-PhCHBrCH BrCO₂Me is interpreted as indicating that the concerted pathway is also operative for the former compound. In the case of erythro- PhCHBrCHBrPO₃Me₂ the kinetics suggest that elimination of the latter occurs viaa concerted mechanism.