Activation of carboxylic acids by pyrocarbonates. Synthesis of symmetric anhydrides and esters of N-protected amino acids using dialkyl pyrocarbonates as condensing reagents.
Activation of carboxylic acids was achieved via dialkyl pyrocarbonates (ROCO)2O, R = C2H5, i-C3H7, sec-C4H9, tert.-C4H9) in aprotic solvents in the presence tertiary amines. A convenient procedure for the preparation of carboxylic acid anhydrides from carboxylic acids and di-tert.-butyl pyrocarbonate in the presence of pyridine is reported. Analogously, di-isopropyl- or diethyl pyrocarbonate may be used in the presence of N-methylmorpholine (triethylamine). With pyridine, di-isopropyl- or diethyl pyrocarbonate carboxylic acids form isopropyl- or ethyl esters, respectively. A wide variety of esters were prepared in good yields in a one-pot procedure from carboxylic acids, including N-protected amino acids, and alcohols or from phenols by means of di-tert.-butyl pyrocarbonate in the presence of pyridine (Boc2O-pyridine system). t-Butyl esters of carboxylic acids were obtained by the same procedure with 4-dimethylaminopyridine. In the absence of carboxylic acid, with 4-dimethylaminopyridine Boc2O and alcohols generate alkyl tert.-butyl carbonates.
Pozdnev
V F
VF
Institute of Biological and Medical Chemistry, Academy of Medical Sciences, Moscow, Russia.
D000596:Amino Acids / Q000737:chemistry*; D000812:Anhydrides / Q000138:chemical synthesis*; D002264:Carboxylic Acids / Q000737:chemistry*; D004047:Diethyl Pyrocarbonate / Q000031:analogs & derivatives* / Q000737:chemistry; D004952:Esters / Q000138:chemical synthesis*
D000596:Amino Acids; D000812:Anhydrides; D002264:Carboxylic Acids; D004952:Esters; C079227:pyrocarbonic acid; D004047:Diethyl Pyrocarbonate