Phosphinidenes and related intermediates. Part II. Reactions of phosphonic or phosphonothioic dichlorides with benzil in the presence of an excess of magnesium. Formation of diphenylacetylene

Abstract

Phenylphosphonic and phenylphosphonothioic dichlorides, when treated with benzil and an excess of magnesium, gave diphenylacetylene, diphenylmethyl phenyl ketone, and 1,2,2-triphenylethanol. The formation of these products is attributed to reduction of 1,3,2-dioxaphosphole 2-oxide and 2-sulphide, the adducts from phenyl-phosphinoylidene (Ph–O) and phenylphosphinothioylidene (Ph–S) intermediates with benzil, respectively, in the magnesium dichloride–magnesium system. The corresponding cyclohexyl derivatives similarly gave diphenylacetylene under similar conditions. A reaction mechanism involving the dianions of 1,3,2-dioxaphosphole 2-oxide and 2-sulphide is suggested.