Photochemical Synthesis of Azepinoindoles and Azocinoindoles from N-Chloroacetylindolylethylamines, and a Mechanistic Study based on the Correlation between Quantum Yields and Calculated Frontier Electron Densities of Indole Radicals

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On irradiation in 50% aqueous ethanol, the N-chloroacetyl derivatives of seven isomeric indolylethylamines gave the corresponding azocinoindole derivatives through photocyclization at the ortho and peri positions. Quantum yields for product formation with 2537 Å light showed the relative reactivity at each position of the indole ring to be in the order 3>6,4>7,2>5>1. In order to identify the reactive intermediary species and to establish the mechanism of the photocyclizations, frontier electron densities of several species of indole were calculated by CNDO/2 and INDO. The quantum yields for product formation from 1-substituted indole derivatives correlated fairly well (correlation coefficient r=0.82) with the singly occupied molecular orbitals (SOMO) electron densities (ED) of the 1-methylindole radical cation, but there was a better correlation (r=0.90) between the quantum yields for product formation from 1-unsubstituted compounds and the SOMO-ED of the indole-1-radical. These results show that the mechanism of the photocyclization of N-chloroacetylindolylethylamines involves both indole radical cations and indole-1-radicals as reactive intermediary species.
公益社団法人日本薬学会の論文
1980-03-25