| Abstract: | The mechanism of the reaction of tributyl(trimethylsilyl)methylene]phosphorane with benzaldehyde and its p‐substituted analogues has been examined. It has been found that the electronic nature of the p‐substituents in aromatic aldehydes strongly influences the stereochemical and kinetic outcome of the Peterson olefination whereas temperature substantially affects their Hammett correlation. This indicates that the Peterson olefination is a multistep reaction involving the formation of at least an oxyanion/betaine and a carbanion as intermediates. In turn, moderate Z‐selectivity might be the result of “steric approach intermediate control”; however, E‐selectivity seems to result from the silicon–oxygen interaction and interactions of steric substituents in competing erythro‐ and threo‐betaines. |
