Vol. 30. pp. 1323 to 1326.
Pergamon Press 1914.
Printed in Great Britain
STUDIES ON REACTIONS OF THE N-PHOSPHONIUM
SALTS OF PYRIDINES-VII
IN THE PRESENCE
N. YAMAZAKI* and F. HIGASHI
Department of Polymer Science, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo,
(Received in Japan 7 October 1973; Received in fhe UKforpublication
3 1 December 1973)
Ah&act-Peptides and active esters of amino acids were produced in high yields from carboxyl and amino or hydroxyl components in pyridine with an equivalent amount of diphenyl phosphite or half an equivalent amount of triphenyl phosphite and tertiary amines. Condensation reactions competed with the reaction with a phenoxy group of the phosphite to produce the phenyl ester and were governed by the tertiary amine employed in the reaction. The reactions are assumed to proceed via the Nphosphonium salts of pyridines, similar to those obtained by the oxidation of phosphorus compounds with mercuric salts in pyridine.
Triphenyl phosphite has been shown to react with carboxylic acids in the presence of pyridine to afford the corresponding phenyl esters,’ and the reaction has been proposed to proceed via an acyloxy phosphonium salt (Eq 1): Mitin et al suggest that the phosphite promotes a coupling reaction between carboxylic acids and amines in the presence of imidazole (Eq 2), and have successfully used the reaction for peptide synthesis.’
given by the oxidation of phosphorous acid and its esters with mercuric salts and halogeds in pyridines.’ In the course of our studies on the application of an electrolytic process instead of chemical oxidation for the oxidation of the phosphorous compounds, we have found that the coupling reactions between carboxyl and amino or hydroxyl components are accomplished without oxidation,