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.
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.
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.
作者:SHUNJI NARUTO、OSAMU YONEMITSU
DOI:10.1248/cpb.28.900
日期:——
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.