The mechanism of the Peterson reaction. Part 2. The effect of reaction conditions, and a new model for the addition of carbanions to carbonyl derivatives in the absence of chelation control

Abstract

The stereochemistry of the Peterson olefination reaction between PhHSiMe₃ and PhCHO has been studied under a wide variety of conditions with excellent reproducibility and extremely high yields. The effects of counterion, solvent, added salts, variation of the carbanion-forming base, and temperature have been investigated. The product stereochemistry is remarkably insensitive to the reaction conditions. The results lead to a new method of analysis of steric approach control based on the angle of approach as defined by Dunitz and Baldwin. The method involves analysis of ‘primary’ and ‘secondary’ transition-state interactions. This analysis should be generally applicable to carbanion additions in which chelation is insignificant.