6π Photocyclization to cis-Hexahydrocarbazol-4-ones:SubstrateModification,Mechanism and Scope

摘要

Photochemical organic transformations provide easy access to molecular structuresthat are difficult,if not impossible,to obtain via conventional reactions.Numerousapproaches toward natural product synthesis have been reported where a photochemicaltransformation represents a key step.1 Indoline derivatives are a very important class ofheterocyclic compounds due to their presence as core structures in many naturally occurringalkaloids and pharmaceutical compounds.In pioneering work,Chapman and co-workers2demonstrated that N-alkyl-N-aryl-enamines produce upon irradiation mainly trans-fusedhexahydrocarbazoles,while Schultz et al.3 reported the formation of cis-fuseddihydrobenzofurans from β-aryloxyenones via photochemical conrotatory ring closurefollowed by epimerization.These and other reports proved the efficiency of a [6π]photocyclization reaction in the generation of complex carbo-and heterocycles from simplestarting materials.