Temperature-modulated diastereoselective transformations of 2-vinylindoles to tetrahydrocarbazoles and tetrahydrocycloheptadiindoles
Organic & Biomolecular Chemistry(2018)
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 heretoforeunprecedented 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.
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Key words
tetrahydrocycloheptadiindoles,tetrahydrocarbazoles,diastereoselective transformations,temperature-modulated
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