Temperature-modulated diastereoselective transformations of 2-vinylindoles to tetrahydrocarbazoles and tetrahydrocycloheptadiindoles?

Organic & Biomolecular Chemistry Pub Date: 2018-03-22 DOI: 10.1039/C8OB00228B

Abstract

Direct and expedient access to densely substituted tetrahydrocarbazoles and tetrahydrocycloheptadiindoles bearing multiple contiguous stereocentres has been achieved via a two-fold divergent diastereoselective (dr up to >99?:?1) transformation of 2-vinylindoles. The high-yielding conversions (yield up to 87%) that are amenable for a wide range of substituted 2-vinylindoles proceed through Lewis acid-catalyzed [4 + 2] and [4 + 3] cyclization–aromatization cascade reactions, respectively, involving a heretofore-unprecedented reversal of the polarity (umpolung) of 2-vinylindoles. The two synthetic routes are effortlessly transposable into each other by merely modulating the temperature to furnish the corresponding products in a selective and exclusive fashion. In addition, another novel synthetic route to tetrahydroindolocarbazoles has been developed that advances via a formal [4 + 2] cyclization of 4-vinylindoles involving sequential C3 Michael addition–dearomatization–aromatization cascade reactions.

Graphical abstract: Temperature-modulated diastereoselective transformations of 2-vinylindoles to tetrahydrocarbazoles and tetrahydrocycloheptadiindoles
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