Electrochemically Induced Hetero-[4+2]-Cycloaddition Reactions Between 2-Vinylpyrroles andβ-Acceptor-Substituted Enamines
作者:Thomas Peglow、Siegfried Blechert、Eberhard Steckhan
DOI:10.1002/(sici)1521-3765(199801)4:1<107::aid-chem107>3.0.co;2-e
日期:1998.1
Recently, we reported on radical cation cycloaddition reactions between 2-vinylindoles and beta-acceptor-substituted enamines, which provide a new pathway to pyrido[1,2-a] indoles.([1]) In order to broaden the synthetic scope of this reaction, we have developed hetero-[4+2]-cycloaddition reactions between a number of readily accessible 2-vinylpyrroles, acting as heterodienes, and beta-acceptor-substituted enamines. This reaction is induced by electrochemically generated radical cations of either the 2-vinylpyrrole diene or the enamine dienophile. These electron-transfer-induced reactions open up a novel route to highly substituted indolizines in moderate yields. We propose a mechanism that explains both the complete regio-control of this cycloaddition as well as the product formation, irrespective of the inducing radical cation species.