Biomimetic building-up of the carbamic moiety: the intermediacy of carboxyphosphate analogues in the synthesis of N-aryl carbamate esters from arylamines and organic carbonates promoted by phosphorus acids

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The reaction of aromatic amines with dimethyl carbonate (DMC) or diphenyl carbonate (DPC) in the presence of organo-phosphorus acids [Ph 2P(O)OH ( 1); (PhO) 2P(O)OH ( 2); (BuO) 2P(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 2P(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