Base-Catalyzed Asymmetric α-Functionalization of 2-(Cyanomethyl)azaarene N-Oxides Leading to Quaternary Stereocenters

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• 作者：Joseba Izquierdo ; Aitor Landa ; Iñaki Bastida ; Rosa López ; Mikel Oiarbide ; Claudio Palomo
• 刊名：Journal of the American Chemical Society
• 出版年：2016
• 出版时间：March 16, 2016
• 年：2016
• 卷：138
• 期：10
• 页码：3282-3285
• 全文大小：441K
• ISSN：1520-5126

文摘

A simple, new strategy for the direct asymmetric α-functionalization of 2-alkyl azaarenes is described. Specifically, a Brønsted base catalyzed conjugate addition of substituted 2-cyanomethylpyridine (and pyrazine) N-oxides to acrylate equivalents to afford hitherto elusive 2-tert-alkyl azaaryl adducts with high enantioselectivity (up to 94% ee) is realized. Extension of the method to the α-amination reaction by using azodicarboxylate esters as electrophiles is also demonstrated. Key for success is the N-oxide functionality of substrates that acts as a removable activating and stereodirecting group. A bifunctional Brønsted base catalyst bearing a squaramide with an attached bulky silyl group is also disclosed.