Exo-selective Diels-Alder reactions of vinylazepines. Origin of divergent stereoselectivity in Diels-Alder reactions of vinylazepines, vinylpiperideines, and vinylcycloalkenes
Exo-selective Diels-Alder reactions of vinylazepines. Origin of divergent stereoselectivity in Diels-Alder reactions of vinylazepines, vinylpiperideines, and vinylcycloalkenes
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DOI：
10.1021/jo034462h
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发表时间：
2003-11-14
影响因子：
3.6
通讯作者：
Sulikowski, GA
中科院分区：
文献类型：
--
作者：
Boren, B;Hirschi, JS;Sulikowski, GA
乙烯基氮杂卓与N-苯基马来酰亚胺的Diels-Alder反应仅提供外环加成物，而如先前所报道的，在乙烯基哌啶的类似反应中观察到高的内立体选择性。这种奇怪的对比证实了不容易差向异构化的环加合物的X-射线分析。乙烯基氮杂卓、乙烯基哌啶和乙烯基环烯烃的Diels-Alder反应的立体选择性根据详细的二烯结构表现出令人惊讶的发散，并且进行DFT计算（Becke 3LYP）以阐明这些观察结果。模型计算正确地预测了这些反应中的主要立体异构体，尽管它们往往显着低估了立体选择性。结果表明，在预测或控制这类Diels-Alder反应的立体化学的一些一般考虑。
Diels-Alder reactions of vinylazepines with N-phenylmaleimide afforded exclusively the exo cycloadduct, while high endo stereoselectivity was observed, as previously reported, in analogous reactions of vinylpiperideines. This curious contrast was confirmed by X-ray analysis of cycloadducts not susceptible to epimerization. The stereoselectivity of Diels-Alder reactions of vinylazepines, vinylpiperideines, and vinylcycloalkenes exhibits surprising divergence depending on the detailed diene structure, and DFT calculations (Becke3LYP) were undertaken to shed light on these observations. The model calculations correctly predict the major stereoisomers in these reactions, though they tend to significantly underestimate the stereoselectivity. The results suggest some general considerations in predicting or controlling the stereochemistry of this class of Diels-Alder reactions.