Synthetic and Quantum Mechanical Studies into the N-Heterocyclic Carbene Catalyzed (4 + 2) Cycloaddition

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• 作者：Sarah J. Ryan ; Andreas Stasch ; Michael N. Paddon-Row ; David W. Lupton
• 刊名：The Journal of Organic Chemistry
• 出版年：2012
• 出版时间：January 20, 2012
• 年：2012
• 卷：77
• 期：2
• 页码：1113-1124
• 全文大小：678K
• 年卷期：v.77,no.2(January 20, 2012)
• ISSN：1520-6904

文摘

The N-heterocyclic carbene catalyzed (4 + 2) cycloaddition between 伪,尾-unsaturated acid fluorides and TMS dienol ethers provides cyclohexene fused 尾-lactone intermediates stable below 鈭?0 掳C. These can be intercepted reductively or with organolithium reagents to produce diastereomerically pure cyclohexenes (>20:1 dr) with up to four contiguous stereocenters. The mechanism has been investigated using theoretical calculations and by examining secondary kinetic isotope effects. Together these studies implicate the formation of a diastereomerically pure 尾-lactone intermediate by a stepwise (4 + 2) cycloaddition involving Michael addition, aldol cyclization, and lactonization.