The Role of Acyloxyphosphonium Ions and the Stereochemical Influence of Base in the Phosphorane‐Mediated Esterification of Alcohols

Intimate details of the Mitsunobu mechanism: The trapping of an acyloxytributylphosphonium ion with a chiral secondary alcohol leads to either retention or inversion of stereochemistry in the resulting ester depending on the exclusion or inclusion of a base (see scheme). Insight into the mechanism of phosphorane‐mediated esterification processes is presented.