在合成 vibsanin E 的过程中，紫外线辅助 [4 + 2] 环加成反应的机理研究。

Mechanistic studies of UV assisted [4 + 2] cycloadditions in synthetic efforts toward vibsanin E.

作者信息

Nikolai Joachim, Loe Øystein, Dominiak Paulina M, Gerlitz Oksana O, Autschbach Jochen, Davies Huw M L

机构信息

Department of Chemistry, University at Buffalo, The State University of New York, Buffalo, New York 14260-3000, USA.

出版信息

J Am Chem Soc. 2007 Sep 5;129(35):10763-72. doi: 10.1021/ja072090e. Epub 2007 Aug 11.

DOI:10.1021/ja072090e

PMID:17691775

Abstract

Quantum chemical DFT calculations at the B3LYP/6-31G(d) level have been used to study the stereochemical course of the photochemical cycloaddition of enone 9 with dienes. The observed products of this photochemically induced cycloaddition showed a stereoselectivity, which is opposite to what would be expected by FMO considerations. The quantum chemical calculations revealed that the unusual stereoselectivity of the reaction can be rationalized by assuming a stereospecific photochemical cis-trans isomerization of enone 9 to trans isomer 9a followed by a thermal Diels-Alder reaction of the diene onto the highly reactive trans enone. The photochemical reaction step involves the selective formation of a twisted triplet intermediate, which accounts for the selectivity of the reaction.

摘要

采用B3LYP/6 - 31G(d)水平的量子化学密度泛函理论（DFT）计算方法，研究了烯酮9与二烯的光化学环加成反应的立体化学过程。该光化学诱导环加成反应的观测产物表现出立体选择性，这与前线分子轨道（FMO）理论预期的结果相反。量子化学计算表明，该反应异常的立体选择性可通过假定烯酮9发生立体专一性的光化学顺 - 反异构化生成反式异构体9a，随后二烯与高活性的反式烯酮发生热狄尔斯 - 阿尔德反应来解释。光化学反应步骤涉及选择性形成扭曲的三线态中间体，这说明了反应的选择性。