Department of Chemistry, The University of Texas at San Antonio, One UTSA Circle, San Antonio, TX, 78249, USA.
Angew Chem Int Ed Engl. 2020 Aug 3;59(32):13613-13617. doi: 10.1002/anie.202004328. Epub 2020 Jun 5.
The direct Friedel-Crafts-type coupling and dedinitrogenation reactions of vinyldiazo compounds with aromatic compounds using a metal-free strategy are described. This Brønsted acid catalyzed method is efficient for the formation of α-diazo β-carbocations (vinyldiazonium ions), vinyl carbocations, and allylic or homoallylic carbocation species via vinyldiazo compounds. By choosing suitable nucleophilic reagents to selectively capture these intermediates, both trisubstituted α,β-unsaturated esters, β-indole-substituted diazo esters, and dienes are obtained with good to high yields and selectivity. Experimental insights implicate a reaction mechanism involving the selective protonation of vinyldiazo compounds and the subsequent release of dinitrogen to form vinyl cations that undergo intramolecular 1,3- and 1,4- hydride transfer processes as well as fragmentation.
本文描述了一种无需金属的策略，通过自由基型偶联和脱氮反应，将乙烯基重氮化合物与芳族化合物直接偶联。该 Brønsted 酸催化方法对于通过乙烯基重氮化合物形成α-重氮β-碳阳离子（乙烯基重氮离子）、乙烯基碳阳离子以及烯丙基或同烯丙基碳阳离子物种非常有效。通过选择合适的亲核试剂来选择性捕获这些中间体，可以以良好到高产率和选择性得到均三取代的α，β-不饱和酯、β-吲哚取代的重氮酯和二烯。实验洞察表明，反应机理涉及乙烯基重氮化合物的选择性质子化以及随后释放氮气以形成乙烯基阳离子，该阳离子经历分子内 1,3-和 1,4-氢转移过程以及碎裂。
