4,5,6,7-Tetrachlorobenzo[<i>d</i>][1,3,2]dioxaborol- 2-ol as an Effective Catalyst for the Amide Condensation of Sterically Demanding Carboxylic Acids
作者:Toshikatsu Maki、Kazuaki Ishihara、Hisashi Yamamoto
DOI:10.1021/ol060216r
日期:2006.3.1
4,5,6,7-Tetrachlorobenzo[d][1,3,2]dioxaborole (4a) and 4,5,6,7-tetrachlorobenzo[d][1,3,2]dioxaborol-2-ol (4b) are effective catalysts for the dehydrative amide condensation between an equimolar mixture of carboxylic acids and amines. In particular, these catalysts are greatly superior to 3,5-bis(trifluoromethyl)phenylboronic acid (1) for the amide condensation of sterically demanding carboxylic acids. In contrast, 4c, which is prepared from a 1:2 molar mixture of B(OH)3 and tetrachlorocatechol, is effective as a Lewis acid-assisted Bronsted acid (LBA) catalyst for Ritter reaction.