Competing sulfonylation and phosphonylation following rearrangement of an O-sulfonyl-N-phosphinoylhydroxylamine with tert-butylamine: demonstration of a phosphonamidic-sulfonic anhydride intermediate and 18O-labelling evidence on how it may be formed.
Reaction of R(Ph)P(O)N HOSO2Bn (R = PhMeCH) with Bu(t)NH2 in CH2Cl2 gives a mixture of RP(O)(NHPh)-NHBu(t) and Bu(t)NHSO2Bn, the proportion of the sulfonamide increasing steadily (14.6% to 32.9%) as the concentration of amine is reduced (8.0 to 0.2 mol dm(-3)). Apparently the phenyl and sulfonate groups in the substrate become transposed, giving a phosphonamidic-sulfonic anhydride RP(O)(NHPh)OSO2Bn which then reacts at the phosphorus or sulfur atom to give the final products; an authentic sample of the anhydride gives similar mixtures of products. Substrate labelled with 18O in the sulfonyl position (57 mol% one 18O atom) gives sulfonamide containing most but not all of the label (43.7 mol% one 18O atom with 2.0 mol dm(-3) amine). This implies partial equilibration of the three sulfonate oxygen atoms during rearrangement, or after the anhydride intermediate has been formed.
Harger
Martin J P
MJ
Department of Chemistry, The University, Leicester, UK LE1 7RH.