REARRANGEMENT REACTIONS OF N-PHOSPHINOYL-O-SULPHONYLHYDROXYLAMINES WITH AMINES UNDER COMPETITIVE CONDITIONS - POSSIBLE INVOLVEMENT OF MONOMERIC METAPHOSPHONIMIDATES AND PHOSPHONAMIDIC SULFONIC MIXED ANHYDRIDES

The O-methylsulphonyl-N-phosphinoylhydroxylamines, RPhP(O)NHOMs (R = Ph, Me, Et, Pri), react with an excess of an equimolar mixture of isopropylamine and t-butylamine to give the rearrangement products RP(O)(NHPh)(NHPri) and RP(O)(NHPh)(NHBut). In the absence of solvent, there is little discrimination between the competing amines (NHPri/NHBut product ratio 1.45-1.65), as would be expected if rearrangement gave initially a reactive monomeric metaphosphonimidate. However, use of a diluent (CH2Cl2) greatly increases the selectivity, implying that much of the initial metaphosphonimidate does not go directly to product. Instead, it seems to recombine with the sulphonate anion to form a phosphonamidic sulphonic mixed anhydride. The observed rearrangement products could then result from reaction of the mixed anhydride with the amines. This may proceed with high selectivity by an SN2(P) mechanism, or with low selectivity by a preassociative elimination-addition mechanism.