Highly Regio- and Stereoselective Synthesis of Z and E Enol Esters by an Amine-Catalyzed Conjugate Addition–Rearrangement Reaction of Ynals with Carboxylic Acids

详细信息    查看全文

• 作者：He Huang ; Xinshuai Zhang ; Chenguang Yu ; Xiangmin Li ; Yueteng Zhang ; Wei Wang
• 刊名：ACS Catalysis
• 出版年：2016
• 出版时间：December 2, 2016
• 年：2016
• 卷：6
• 期：12
• 页码：8030-8035
• 全文大小：592K
• ISSN：2155-5435

文摘

The broad synthetic utility of labile enol esters demands efficient methods for the stereo- and regioselective synthesis of both Z and E isomers. The available synthetic methods dominated by metal catalysis cannot meet the challenge. We wish to report a metal-free organocatalytic divergent approach to both E and Z isomers of enol esters from the same reactant pools with the same catalytic system. A process involves an amine-catalyzed conjugate addition of carboxylic acids to ynals, which triggers a rearrangement leading to enol esters. The reaction proceeds highly regio- and stereoselectively. Simple manipulation of reaction temperatures enabled us to produce Z isomers at 0 °C (Z:E (15–20):1), whereas E isomers were produced at 30 °C (E:Z (15–20):1). Furthermore, the mild reaction conditions accommodate a broad array of densely functionalized carboxylic acids for the process, including complex biologically relevant structures and ynals. Therefore, synthetically valued, structurally diverse enol esters are efficiently synthesized. Preliminary mechanistic studies suggest an amine-promoted conjugate addition–rearrangement pathway to be responsible for the formation of the enol esters.