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

Abstract

With Bu^tNH₂ the anhydride R(PhNH)P(O)OS¹⁸O₂Bn 5 (R = Bu^t), like the hydroxylamine derivative R(Ph)P(O)NHOS¹⁸O₂Bn 4 (R = PhMeCH), gives Bu^tNHS¹⁸O₂Bn containing only a part (76–78%) of the available ¹⁸O label; this is a result of partial scrambling of the label in 5 (OS¹⁸O₂ ⇌ ¹⁸OSO₂) 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.