Enantioselective, Brønsted acid-catalyzed cycloadditions of alkylidene-2H- and alkylidene-3H-pyrroles towards the rapid and stereoselective assembly of bicyclic nitrogen heterocycles

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We intend to establish the first Brønsted acid-catalyzed cycloadditions of transient alkylidene-2H-pyrroles und alkylidene-3H-pyrroles towards the enantioselective synthesis of complex, pyrrole-fused nitrogen heterocycles. The structurally related, but significantly more stable alkylidene-3H-indoles have found widespread use in heterocyclic synthesis whereas the corresponding alkylidene pyrroles are virtually unknown. We are convinced that they bear an enormous synthetic potential for the stereoselective synthesis of a multitude of heterocyclic compounds in particular via cycloadditions, which we want to exploit in this project in the broadest sense. Specifically, we intend to study [6p+2p]- und [6p+4p]-cycloadditions of both alkylidene-2H-pyrroles and alkylidene-3H-pyrroles with various electronrich alkenes, dienes, and 1,3-dipoles in order to furnish bicyclic, pyrrole-fused heterocycles in a single step with high enantioselectivity which have not been accessible previously. As substrates for the cycloadditions the corresponding pyrrole-2- and pyrrole-3-carbinols will be employed which under BINOL-phosphoric acid catalysis are expected to be dehydrated to the Brønsted acid-bound, transient, and highly reactive alkylidene-2- and alkylidene-3-pyrroles, respectively. These in turn will then react in situ with the electronrich 2p- and 4p-components. The projected syntheses are based upon solid and successful preliminary work. In addition, we intend to study the mechanism of the cycloadditions through theoretical calculations.