N-phosphinylhydroxylamines and rearrangements of their derivatives.

A range of N-phosphinylhydroxylamines and their o-sulphonyl derivatives has been prepared and characterised. Investigation of the chemistry of these compounds has focused particularly on the Lossen-like base-catalysed rearrangement of the sulphonyl derivatives. The rearrangement of N-(diphenylphosphinyl) hydroxylamine derivatives has been examined in detail using a variety of bases and nucleophiles, including mixtures of competing amines. The results, together with those for the reactions of sulphonyl derivatives of unsymmetrical N-(phenylarylphosphinyl) hydroxylamines, give considerable insight into the mechanism of the rearrangement. For the unsymmetrical compounds the effect of substituents on the rate of migration of the aryl group (p-XC6H4; X=Meo, Me, C1, NO2) relative to phenyl correlates with the substituent parameter o. Monomeric metaphosphonimidates, displaying low selectivity for competing nucleophiles, appear to be the initial products of these rearrangements. The rearrangements of o-sulphonyl derivatives of N-(phenylalkylphosphinyl)- hydroxylamines and N-(dialkylphosphinyl) hydroxylamines have also been examined. Alkyl migration (R=Me, Et, Pr1, PhCH2) occurs much less readily than phenyl migration and has been observed in only one case (R=PhCH2). Substituted amino groups (Me2N, PhNH) attached to the phosphorus centre migrate very readily and at a rate that far exceeds the rate of phenyl migration in unsymmetrical N-[phenyl(amino)phosphinyl] hydroxyamine derivatives. o-Sulphonyl derivatives of N-phosphinylhydroxylamines bearing an aryloxy group on the phosphorus atom rearrange without any aryloxy migration, while N-(diaryloxyphosphinyl) hydroxylamine derivatives do not rearrange at all. In the latter case (formal) nitrene products are obtained. The o-sulphonyl derivatives of N-phosphinylhydroxylamines are susceptible to nucleophilic attack at nitrogen by sulphides (Me2S, MeSCH2 CH=CH2) and triphenylphosphine, giving rise to protonated sulphilimines or phosphine imines by displacement of sulphonate anion. The free imines can be liberated by treatment with base, although those derived from allylmethylsulphide undergo ready [2,3] sigmatropic rearrangement to N-allyl-N-thiomethylphosphinic amides.