Bronsted Acid Catalyzed Friedel-Crafts-Type Coupling and Dedinitrogenation Reactions of Vinyldiazo Compounds

摘要

The direct Friedel-Crafts-type coupling and dedinitrogenation reactions of vinyldiazo compounds with aromatic compounds using a metal-free strategy are described. This Bronsted acid catalyzed method is efficient for the formation of alpha-diazo beta-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 alpha,beta-unsaturated esters, beta-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.