Organophosphorus-Catalyzed Borylative Ring-Opening of Vinylcyclopropanes: A Stereoselective Route to δ-Valerolactones

We report an operationally simple route to δ-valerolactones through an organophosphorus-catalyzed borylative ring-opening/allylation of vinylcyclopropanes providing δ-hydroxy esters stereoselectively. The δ-hydroxy esters were lactonized to obtain densely substituted δ-valerolactones. The present methodology exhibited enhanced functional group tolerance compared to the existing metal-mediated methods. A plausible mechanism for borylative ring-opening reaction has been suggested. 31P NMR studies indicated the involvement of a phosphonium zwitterionic species. The synthetic utility of the intermediate allyl boronates was demonstrated.