Tertiary N-acyl phosphoramidates : a mechanistic study of their formation and collapse in reactions with nucleophiles
Different synthetic approaches to tertiary mixed phosphoric-carboxylic imides(III) are discussed. The preparation of (III) via the N-acylation of phosphoramidates was investigated. The reaction of PhC(O)X (X = Br, Cl, F) with the conjugate base of (EtO)₂P(O)NHMe (IX) yields three products: PhCO₂Et (4), PhC(O)NHMe (5) and (PhCO)₂NMe (6). (5) and (6) are formed via the initial rapid formation of (EtO)₂P(O)-NMe-C(O)Ph (IIIe), while (4) results from the E1cB related reaction of (EtO)₂P(O)NMe involving electrophilic assistance by PhC(O)X. The attack of various nucleophilic species at the mixed-imide (IIIe) was studied, and the possible mechanisms of the P-N bond cleavage, followed by the N-methyl transfer from the phosphoryl to the carbonyl centre are discussed.
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