The reaction of diols with triphenylphosphine and di-isopropyl azodicarboxylate. Part 1. Formation of cyclic phosphoranes from 1,3- and 1,4- diols

Abstract

Triphenylphosphine and di-isopropyl azodicarboxylate react with propane-1,3-diol and butane-1,4-diol in tetrahydrofuran at 0 °C to give cyclic dioxytriphenylphosphoranes that appear to be oligomeric. Under conditions of high-dilution, however, the expected six- and seven-membered-ring phosphoranes are formed. Contrary to a previous report, propane-1,3-diol does not undergo cyclodehydration to give oxetane, but gives instead a pyrazolidine derivative. Substituted, and conformationally restricted, 1,3- and 1,4-diols form the expected six- and seven-membered-ring cyclic phosphoranes without recourse to high-dilution techniques. A¹³C n.m.r. method for distinguishing apical from equatorial phenyl groups in phosphoranes is reported: dialkoxytriphenylphosphoranes bearing an apical phenyl group exhibit much smaller one-bond coupling constants (¹J_P–C∼ 120 Hz) than those containing only equatorial phenyl groups (¹J_P–C > 170 Hz).