Tf₂O-TMDS combination for the direct reductive transformation of secondary amides to aldimines, aldehydes, and/or amines

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• 作者：Qi-Wei Lang ; Xiu-Ning Hu ; Pei-Qiang Huang
• 关键词：secondary amides ; amide activation ; partial reduction ; aldimines ; N ; deacylation
• 刊名：Science China Chemistry
• 出版年：2016
• 出版时间：December 2016
• 年：2016
• 卷：59
• 期：12
• 页码：1638-1644
• 全文大小：
• 刊物类别：Chemistry and Materials Science
• 刊物主题：Chemistry/Food Science, general;
• 出版者：Science China Press
• ISSN：1869-1870
• 卷排序：59

文摘

The direct partial reduction of highly stable secondary amides to more reactive aldimines and aldehydes is a challenging yet highly demanding transformation. In this context, only three methods have been reported. We report herein an improved version of the Charette’s method. Our protocol consists of activation of secondary amides with triflic anhydride/2-fluoropyridine, and partial reduction of the resulting intermediates with 1,1,3,3-tetramethyldisiloxane (TMDS), which delivered aldimines or aldehydes upon acidic hydrolysis. Aromatic amides were reduced to the corresponding aldimines in 85%–100% NMR yields, and yields (NMR) from aliphatic amides were 72%–86%. Acidic hydrolysis of the aldimine intermediates afforded, in one-pot, the corresponding aldehydes in 80%–96% yields. A simple protocol was established to isolate labile aldimines in pure form in 92%–96% yields. The improved method gave generally higher yields as compared to the known ones, and features the use of cheaper and more atom-economical TMDS as a chemoselective reducing agent. In addition, a convenient extraction protocol has been established to allow the isolation of amines, which constitutes a mild method for the N-deacylation of amides, another highly desirable transformation. The extended method retains the advantages of the original method of Charette in terms of mild conditions, good functional group tolerance, and excellent chemoselectivity.