A Catalytic Asymmetric Chlorocyclization of Unsaturated Amides

摘要

Stereodefined carbon-halogen bonds are ubiquitous in nature with several natural products exhibiting this motif.While the biogenetic origins of this unique chiral functionality has been a subject of several investigations in the past, attempts by organic chemists to forge the carbon-halogen bond stereoselectively have largely been unsuccessful. This problem has come into focus only recently. Several elegant reports of asymmetric halogenations of alkenes and alkynes followed by an intramolecular attack of a pendant nucleophile have appeared in the literature in the last decade. Kang et al. reported a cobalt-salen catalyzed iodoetherification reaction. An asymmetric fluorocyclization of allyl silanes mediated by a cinchona alkaloid dimer was reported by Gouverneur and co-workers. Tang and co-workers disclosed an asymmetric bromolactonization of enynes catalyzed by a cinchona alkaloid derived urea; other bromolactonizations have also appeared following the disclosure of their report.