Activation of carboxylic acids by pyrocarbonates. Synthesis of arylamides of N -protected amino acids and small peptides using dialkyl pyrocarbonates as condensing reagents

Activation of carboxylic acids was achieved via dialkyl pyrocarbonates (ROCO)₂O, (R = ethyl, isopropyl, sec-butyl, tert-butyl) in aprotic solvents in the presence of tertiary amines. A convenient one-pot procedure for the preparation of arylamides from N-protected amino acids including arginine and from di-tert-butyl pyrocarbonate in the presence of pyridine (Boc₂O-pyridine system) was reported. Analogously, diisopropyl, di-sec-butyl or diethyl pyrocarbonate could be used in the presence of N-methylmorpholine or triethylamine. A wide variety of N-protected amino acid arylamides were prepared in good yields.