BF₃-Promoted Ring Expansion of Iminylphosphiranes and Acylphosphiranes for Divergent Access to 1,2-Azaphospholidines and 1,2-Dihydrophosphetes

Abstract

Ring expansion of strained small rings provides an efficient method for the synthesis of various high-value carbocycles and heterocycles. Here we report BF 3 •Et 2 O as both an activating reagent and fluorine source, enabling ring expansion of phosphirane and P−F bond formation. Treatment of 1iminylphosphirane complexes with BF 3 •Et 2 O resulted in 1,2azaphospholidines, while the reaction of 1-acylphosphirane complexes with BF 3 •Et 2 O afforded 1,2-dihydrophosphetes. The reaction path was tuned by the nucleophilicity of the N and O atoms toward the intermediate phosphenium cation.