Vinylidene Homologation of Boronic Esters and its Application to the Synthesis of the Proposed Structure of Machillene

Alkenylboronic esters are important reagentsin organic synthesis. Herein, we report that these valuable products can be accessed by the homologation of boronic esterswith lithiated epoxysilanes. Aliphatic and electron-rich aromatic boronic esters providedvinylideneboronic esters in moderate to high yields, while electron-deficientaromatic and vinyl boronic esters were found to give the corresponding vinyl silane products. Through DFT calculations, this divergence in mechanistic pathway has been rationalized by considering the stabilization of negative charge in the C-Siand C-Bbond breaking transition states. This vinylidene homologation was used ina short six step stereoselective synthesis of the proposedstructure of machillene, however, synthetic and reported data were found to be inconsistent.