Cayzer Tory N, Miller Natalie A, Paddon-Row Michael N, Sherburn Michael S
Research School of Chemistry, Australian National University, Canberra, ACT 0200, Australia.
Org Biomol Chem. 2006 May 21;4(10):2019-24. doi: 10.1039/b602618d. Epub 2006 Apr 18.
This combined experimental-computational investigation demonstrates that the presence of a removable bromine substituent on a diene leads to complete pi-diastereofacial and endo/exo stereoselection in both intermolecular and intramolecular Diels-Alder reactions. The influence of the bromine upon stereoselectivity is dramatic: the cycloaddition of nonbrominated precursor 18E, for example, gives four diastereomeric products in a 55:13:16:16 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 (30Z and 31Z) from the same simple starting materials (28 and 2) is reported. Discrepancies between calculation and experiment in an earlier investigation into the Diels-Alder reaction are explained.
这项结合实验与计算的研究表明，二烯上存在可移除的溴取代基会在分子间和分子内狄尔斯-阿尔德反应中导致完全的π-非对映面和内型/外型立体选择性。溴对立体选择性的影响非常显著：例如，未溴化的前体18E的环加成反应会以55:13:16:16的比例生成四种非对映体产物；含溴类似物在检测限内只生成一种立体异构体。对B3LYP/6-31+G(d)过渡态结构的研究有助于解释这些实验结果。报道了一种从相同简单起始原料（28和2）完全立体选择性合成互补非对映体产物（30Z和31Z）的方法。解释了早期狄尔斯-阿尔德反应研究中计算与实验之间的差异。
