Synthesis of substituted dibenzophospholes. Part 7. Regiospecific synthesis of 4,6-diaryl-3,7-dioxydibenzophospholes from 2,2′4,4′-tetranitrobiphenyl

Abstract

3,3‴-Dimethyl -2′,2″,4″,6′-tetranitro-5,5‴-di-t-butyl-m-quaterphenyl did not undergo selective alkoxydenitration at the 2′ and 4″ positions, but when acetoxymethyl groups were placed at the 2 and 2‴ positions, treatment with sodium methoxide caused regiospecific cyclization at these positions and formation of a bibenzochromenyl. Other reagents led to a mixture of two regioisomers. The two remaining nitro groups were replaced via a diamine and a di-iodide by a phosphinic ester bridge. The pyran rings could then be opened by boron tribromide to afford a 4,6-diaryldibenzophosphole. The two bromomethyl groups in this intermediate were converted after acetylation into dimethylphosphonomethyl groups and one atropisomer (the meso isomer) was isolated. Some analogous experiments in the biphenyl series are reported.