Rapid Betaine Collapse in the Reactions of Six-Membered Ring Cyclic Phosphines with Styrene Oxide, and Rates of Alkaline Hydrolysis of Related Cyclic Phosphonium Salts

Abstract

The reactions of a series of six-membered ring cyclic phosphines (10-phenylphenoxaphosphine, 10-phenylphenothiaphosphine, and the related sulphone) with styrene oxide in ethanol result in the formation of styrene and the corresponding cyclic phosphine oxide, indicating that betaine collapse is rapid compared to alternative routes involving the formation of vinylphosphonium salts. This conclusion is supported by studies of the rates of alkaline hydrolysis of the related methylphosphonium salts which give rise to ringopened products. These salts undergo hydrolysis significantly faster than the acyclic salt methyltriphenylphosphonium iodide, due to the electron-withdrawing effect of the oxygen, sulphur or sulphone grouping in the six-membered ring