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Simple, Mild, and Practical Esterification, Thioesterification, and Amide Formation Utilizing p ‐Toluenesulfonyl Chloride and N ‐Methylimidazole
Author(s) -
Wakasugi Kazunori,
Iida Akira,
Misaki Tomonori,
Nishii Yoshinori,
Tanabe Yoo
Publication year - 2003
Publication title -
advanced synthesis and catalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.541
H-Index - 155
eISSN - 1615-4169
pISSN - 1615-4150
DOI - 10.1002/adsc.200303093
Subject(s) - chemistry , reagent , racemization , amide , amine gas treating , organic chemistry , acyl chloride , primary (astronomy) , chloride , nucleophilic acyl substitution , carboxylic acid , amino acid , acylation , catalysis , biochemistry , physics , astronomy
We have developed an efficient method for the esterification or thioesterification of equimolar amounts of carboxylic acids and alcohols or thiols using a novel reagent, p ‐toluenesulfonyl chloride (TsCl) together with N ‐methylimidazole. The present method is simple, mild, and reactive, uses readily available and economical reagents. The choice of amine is critical for the present method. The amine, N ‐methylimidazole, has two roles: (i) as an HCl scavenger for the initial smooth generation of mixed anhydrides between carboxylic acids and TsCl and (ii) successive formation of highly reactive ammonium intermediates from mixed anhydrides. This method could be applied to various types of carboxylic acids, alcohols, and thiols: a) several functionalities were tolerated; b) two N ‐Cbz amino acids were smoothly esterified without racemization; and c) the labile 1β‐methylcarbapenem key intermediate and a pyrethroid insecticide, prallethrin, were successfully prepared. The related amide formation between carboxylic acids and primary or secondary amines was also performed. The proposed reaction mechanism involves a novel method for producing the reactive acylammonium intermediates. The production of these intermediates was rationally supported by a careful 1 H NMR monitoring study.