Use of an 18O-labelled phosphonamidic-sulfonic anhydride to learn more about the mechanism by which O-sulfonyl-N-phosphinoylhydroxylamines rearrange

Abstract

With Bu(t)NH2 the anhydride R(PhNH)P(O)OS(18)O2Bn 5 (R = Bu(t)), like the hydroxylamine derivative R(Ph)P(O)NHOS(18)O2Bn 4 (R = PhMeCH), gives Bu(t)NHS(18)O2Bn containing only a part (76-78%) of the available (18)O label; this is a result of partial scrambling of the label in 5 (OS(18)O2 <==> (18)OSO2) while it is reacting; there is no need to postulate scrambling in the rearrangement of 4 to 5 (R = PhMeCH) or to exclude a concerted mechanism.