Synthesis of substituted dibenzophospholes. Part 1

Abstract

Approaches to the synthesis of 4,6-diaryl-5-hydroxydibenzophosphole 5-oxides are described. 3,5,7-Trihydroxydibenzophosphole 5-oxide and several of its O-substituted derivatives were made either from 5-hydroxydibenzophosphole 5-oxide (convenient preparation described) by dinitration, reduction and tetrazotization or from 2,2′-dibromo-4,4′-dimethoxybiphenyl via lithiation and reaction with dichloromorpholinophosphine with subsequent oxidation. 3,5,7-Trihydroxydibenzophosphole 5-oxide could be selectively blocked in the 2,8-positions by methyl groups generated via a Mannish reaction. The bis-2-iodobenzyl ethers of 3,7-dihydroxy-5-methoxydibenzophosphole 5-oxide and of its 2,8-dimethyl derivative were cyclized by photolysis to form 4,6-diaryl derivatives in poor yield.