Enantioselective synthesis of cyclopenta[b]benzofurans via an organocatalytic intramolecular double cyclization† †Electronic supplementary information (ESI) available. CCDC 1545253. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c7sc03006a
نویسندگان
چکیده
An enantioselective organocatalytic strategy, combining Brønsted base and N-heterocyclic carbene catalysis in a unique manner, is demonstrated for a concise construction of the privileged cyclopenta[b] benzofuran scaffold, present in many bioactive compounds having both academic and commercial interests. The reaction concept relies on an intramolecular one-pot double cyclization involving a cyclespecific enantioselective Michael addition followed by a benzoin condensation of ortho-substituted cinnamaldehydes. Cyclopenta[b]benzofurans were achieved in moderate to good yields, with excellent stereoselectivities. A proof of principle for a diastereodivergent variation is demonstrated through the synthesis of cyclopenta[b]benzofurans containing two contiguous aromatic substituents in a substitution pattern present in commercial and natural compounds. Furthermore, several transformations have been performed, demonstrating the synthetic utility of the products. Finally, insights into the activation mode and stereoindution models are presented for this new synthetic strategy.
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