The influence of α-coordinating groups of aldehydes on E / Z -selectivity and the use of quaternary ammonium counter ions for enhanced E -selectivity in the Julia-Kocienski reaction.

Modified reaction conditions for improved E -selectivity of olefins in the Julia-Kocienski reaction of aldehydes having α-coordinating substituents are demonstrated. The chelating groups in aldehydes are expected to stabilize the syn -transition state with metal ions, whereas the weakly coordinating quaternary ammonium ions are devoid of all possible chelating interactions to enhance E -selectivity. A systematic investigation is presented to study the size of the neighbouring protecting groups of aldehydes and their chelation effect on E / Z -selectivity in the Julia-Kocienski reaction.