Regioselective Intramolecular Reactions of 2-Indolylacyl Radicals with Pyridines:A Direct Synthetic Entry to Ellipticine Quinones

摘要

2-Indolylacyl radicals generated from the corresponding selenoesters under hexabutylditin-hv conditions undergo regioselective intramolecular reaction with unprotonated pyridines to give polycyclic indolylpyridyl ketones.For substrates bearing a(3-pyridyl)methyl moiety connected to the 3-position of the indole ring,the cyclization provides easy access to ellipticine quinones.Intramolecular reactions of nucleophilic carbon-centered radicals with aromatic systems are often of synthetic value for the construction of polycyclic compounds incorporating aromatic rings.Fully aromatic products are generally obtained after the oxidation of the initially formed cyclohexadienyl radical,which takes place even under the most commonly used tributyltin hydride- AIBN reductive conditions.