Unexpected formation of 1,4-diphenylbutylphosphinic acid from 1,4-diphenylbuta-1,3-diene and elemental phosphorus via the Trofimov–Gusarova reaction

trans,trans -1,4-Diphenylbuta-1,3-diene reacts with elemental (red) phosphorus in the superbasic KOH / DMSO (H 2 O) system (120 °C, 3 h) to give, after acidic work-up, 1,4-diphenylbutylphosphinic acid in 48% yield.