Concerted and stepwise mechanisms in the Diels–Alder and Michael reactions of furans with methyl 3-nitroacrylate — Experimental and theoretical studies

Author:

Itoh Kuniaki,Kitoh Kazue,Kishimoto Shigehisa

Abstract

The Diels–Alder reactions of the furans (1a–1c) and methyl 3-nitroacrylate (2) produce the cycloadducts via a concerted mechanism. Then, the products subsequently undergo retro-Diels–Alder reactions to give the Michael adducts via a stepwise mechanism. We have used both experimental and theoretical methods to investigate the mechanism for, and the regio- and stereo-selectivity in, the Diels–Alder and Michael reactions. To account for the selectivity observed in these additions, we examined the frontier molecular orbitals involved, and to locate the transition states (TS), we employed a B3LYP/6-31G* level density functional calculation. We were able to explain the regio- and stereo-selectivity of the four possible Diels–Alder adducts observed in the experiments by a comparison of their calculated activation energies, which ranged from 11 to 18 kcal/mol (1 cal = 4.184 J). The s-cis forms of the dienophile (2) were found to be more stable than the s-trans forms, both in the ground state and in the transition state. In addition, the endo transition structures for the ester group exhibited a lower energy barrier by 0.3 kcal/mol than their exo counterparts, a value that is in disagreement with the experimental results. The presence of the nitro group in 2 may play an important role in determining the selectivity. Our attempts to find a stepwise mechanism leading to the Diels–Alder adduct via a zwitterion were unsuccessful. We did find that two stepwise processes lead to the formation of Michael adducts generated via an electrophilic attack by 2 at the α position of 1b and 1c, and an intramolecular proton-transfer mediated by the formation of a four-membered structure. The potential energies for these reactions showed values in the following ranges: 17 kcal/mol for 5a and 5b, and 11 to 12 kcal/mol for 7a and 7b for the first step, and, for the proton-transfer step, 48–51 kcal/mol for 5a and 5b, and 41–45 kcal/mol for 7a and 7b. Solvent effects in chloroform on the Michael addition did not appear in the electrophilic attack step (less than 4 kcal/mol), but the transition state of the later process was stabilized by 6–13 kcal/mol.Key words: Diels–Alder reactions, Michael reactions, density functional method, furan, retro-Diels–Alder reactions, solvent effect.

Publisher

Canadian Science Publishing

Subject

Organic Chemistry,General Chemistry,Catalysis

Cited by 18 articles. 订阅此论文施引文献 订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献

同舟云学术

1.学者识别学者识别

2.学术分析学术分析

3.人才评估人才评估

"同舟云学术"是以全球学者为主线,采集、加工和组织学术论文而形成的新型学术文献查询和分析系统,可以对全球学者进行文献检索和人才价值评估。用户可以通过关注某些学科领域的顶尖人物而持续追踪该领域的学科进展和研究前沿。经过近期的数据扩容,当前同舟云学术共收录了国内外主流学术期刊6万余种,收集的期刊论文及会议论文总量共计约1.5亿篇,并以每天添加12000余篇中外论文的速度递增。我们也可以为用户提供个性化、定制化的学者数据。欢迎来电咨询!咨询电话:010-8811{复制后删除}0370

www.globalauthorid.com

TOP

Copyright © 2019-2024 北京同舟云网络信息技术有限公司
京公网安备11010802033243号  京ICP备18003416号-3