Direct observations of diastereoisomers in chiral oxazaphosphoranes [3-aryl-2,3-dihydro-1,3,2-benzoxazaphosph(V)oles] by 1H and 31P nuclear magnetic resonance spectroscopy

Abstract

Low- and variable-temperature studies of the ¹H and ³¹P n.m.r. spectra of 3-(2-substituted-phenyl)-2,3-dihydro-l,3,2-benzoxazaphosph(V)oles (1) show the presence of unequally populated diastereoisomeric forms (1) and (2) corresponding to two possible orientations of the N-aryl ring, interconversion of isomers occurring solely via ligand reorganisation (pseudorotation) about the phosphorus atom and not by rotation about the N-aryl bond, leading, in principle, to a resolvable phos-phorane system.