Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India.
Org Lett. 2012 Jun 1;14(11):2810-3. doi: 10.1021/ol301036u. Epub 2012 May 8.
The mechanism and stereoselectivity in a chiral N-heterocyclic carbene-catalyzed desymmetrization of a 1,3-diketone is established by using density functional theory computations. The Breslow intermediate formation is identified to involve Hunig's base-assisted proton transfer. The relative energies of stereoselectivity-determining intramolecular aldol cyclization transition states reveal that in the most preferred mode the re-face of enolate adds to the si-face of carbonyl leading to a tricyclic lactone with a configuration (2aS,4aS,8'S) in excellent agreement with previous experimental reports.
通过使用密度泛函理论计算，建立了手性 N-杂环卡宾催化 1,3-二酮去对称化反应的机理和立体选择性。确定 Breslow 中间体的形成涉及 Hunig 碱辅助质子转移。立体选择性决定的分子内Aldol 环化过渡态的相对能量表明，在最优选的模式下，烯醇盐的 re-面加成到羰基的 si-面，导致具有(2aS,4aS,8'S)构型的三环内酯，与先前的实验报道非常一致。
