BIOMIMETIC BUILDING-UP OF THE CARBAMIC MOIETY - THE INTERMEDIACY OF CARBOXYPHOSPHATE ANALOGS IN THE SYNTHESIS OF N-ARYL CARBAMATE ESTERS FROM ARYLAMINES AND ORGANIC CARBONATES PROMOTED BY PHOSPHORUS-ACIDS

The reaction of aromatic amines with dimethyl carbonate (DMC) or diphenyl carbonate (DPC) in the presence of organo-phosphorus acids [Ph(2)P(O)OH (1); (PhO)(2)P(O)OH (2); (BuO)(2)P(O)OH/(BuO)P(O)(OH)(2) equimolar mixture (3)] affords carbamate esters, ArNHC(O)OR (R = Me, Ph) with high selectivity. The catalytic role played by the P-acid has been investigated and rationalized in terms of a reaction mechanism involving the intermediate formation of a carbonic-phosphinic(phosphoric) anhydride X(2)P(O)OC(O)OR (X = Ph, PhO; R = Me, Ph). The proposed mechanism shows intriguing analogies with the mechanism of formation of carbamate anion in living systems by carbamoyl phosphate synthetase (CPS) enzyme.