[2+2] Cycloaddition and ring expansion reactions of cyclic phosphonium and aminophosphonium salts: synthesis and structure of the first eight-membered ylide-type heterocycles

Abstract

A series of new eight-membered heterocycles, 4 and 6, was isolated from the reactions of simple six-membered aza-ylides with acetylene and nitrile derivatives. These structures were elucidated by X-ray crystal analysis. On the other hand, the reactions of five-membered ylides and aza-ylides with nitrile derivatives formed seven-membered ylides, which were hydrolyzed immediately during aqueous work-up to give phosphine oxide derivatives.