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.
在 50% 的乙醇水溶液中照射时,七种吲哚乙胺异构体的 N-氯乙酰基衍生物通过正位和周位的光环化反应生成相应的偶氮吲哚衍生物。在 2537 Å 光下生成产物的量子产率显示,吲哚环各位置的相对反应性依次为 3>6、4>7、2>5>1。为了确定反应的中间产物并确定光环化的机理,利用 CNDO/2 和 INDO 计算了几种吲哚的前沿电子密度。1 取代吲哚衍生物生成产物的量子产率与 1 甲基吲哚自由基阳离子的单占分子轨道(SOMO)电子密度(ED)有相当好的相关性(相关系数 r=0.82),但 1 未取代化合物生成产物的量子产率与吲哚-1-自由基的 SOMO-ED 有更好的相关性(r=0.90)。这些结果表明,N-氯乙酰吲哚乙胺的光环化机理涉及吲哚自由基阳离子和作为反应中间体的吲哚-1-自由基。