Oxo-phospholes from the alkoxyphosphonium ylides formed in the reaction of trialkyl phosphites or dialkyl phosphonites with dimethyl acetylenedicarboxylate

Abstract

The cyclic ylides (3), formed by the reaction of trialkyl phosphites or dialkyl phosphonites with 2 mol equiv. of dimethyl acetylenedicarboxylate, undergo protonation and dealkylation in the presence of hydrogen bromide to give the 1-substituted 2,5-dihydrophosphole 1-oxides (4). The phospholes (4) undergo ready elimination of a molecule of alcohol on being heated to give the phosphole 1-oxides (5).