作者:Tory N. Cayzer、Natalie A. Miller、Michael N. Paddon-Row、Michael S. Sherburn
DOI:10.1039/b602618d
日期:——
This combined experimentalâcomputational investigation demonstrates that the presence of a removable bromine substituent on a diene leads to complete Ï-diastereofacial and endo/exo stereoselection in both intermolecular and intramolecular DielsâAlder reactions. The influence of the bromine upon stereoselectivity is dramatic: the cycloaddition of nonbrominated precursor 18EEEEEE, for example, gives four diastereomeric products in a 55â¶13â¶16â¶16 ratio; the bromine-containing analogue gives one stereoisomer within the limits of detection. The examination of B3LYP/6-31+G(d) transition structures allows an interpretation of these experimental findings. A method for the completely stereoselective synthesis of complimentary diastereomeric products (30ZZZZZZ and 31ZZZZ) from the same simple starting materials (28 and 2) is reported. Discrepancies between calculation and experiment in an earlier investigation into the DielsâAlder reaction are explained.
这项实验与计算相结合的研究表明,二烯上可移动溴取代基的存在会导致分子间和分子内 DielsâAlder 反应中完全的Ï-非对映面和内/外立体选择。溴对立体选择性的影响非常明显:例如,非溴化前体 18EEEEEE 的环加成反应产生了四种非对映异构产物,比例为 55¶13¶16¶16;而含溴的类似物只产生了一种立体异构体,且在检测范围内。对 B3LYP/6-31+G(d) 转换结构的研究可以解释这些实验结果。报告还介绍了一种从相同的简单起始材料(28 和 2)完全立体选择性合成互补非对映异构产物(30ZZZZZZZZZ 和 31ZZZZZ)的方法。解释了早先研究 DielsâAlder 反应时计算与实验之间的差异。