Photochemical synthesis of 1,2,3,4-tetrahydroisoquinolin-3-ones and oxindoles from N-chloroacetyl derivatives of benzylamines and anilines. Role of intramolecular exciplex formation and cis conformation of amide bonds.
作者:TATSUO HAMADA、YOHMEI OKUNO、MASAYUKI OHMORI、TAKAO NISHI、OSAMU YONEMITSU
DOI:10.1248/cpb.29.128
日期:——
Although N-chloroacetyl derivatives of benzylamines (2, 8) and anilines (21, 25, 29) disappeared quite rapidly when irradiated with a high pressure mercury lamp, no photocyclization to six- and five-membered lactams occurred. Measurements of fluorescence quenching and disappearance quantum yields of N-chloroacetyl-(3, 4-dimethoxylphenyl)-alkylamines having various lengths of alkyl chain revealed that the shorter the alkyl chain is, the more efficient the exciplex formation is. Therefore, the failure of photocyclization seemed to be due to trans conformation of amide bonds in the benzylamine and aniline derivatives. Introduction of an alkyl group on the amide nitrogen changed the stable conformation of amides from trans to cis, and hence N-alkyl-N-chloroacetylbenzylamines (11, 13, 15, 17, 19) readily gave the corresponding 1, 2, 3, 4-tetrahydroisoquinolin-3-ones (12, 14, 16, 18, 20) on irradiation. Oxindoles (36, 38, 40, 41, 43, 46) were similarly synthesized by photocyclization of N-alkyl-N-chloroacetylanilines (35, 37, 39, 42, 45).
虽然苄胺(2、8)和苯胺(21、25、29)的 N-氯乙酰基衍生物在高压汞灯照射下会迅速消失,但并没有发生六元和五元内酰胺的光环化反应。对不同烷基链长度的 N-氯乙酰基-(3, 4-二甲氧基苯基)-烷基胺的荧光淬灭和消失量子产率的测量表明,烷基链越短,形成复合物的效率越高。因此,光环化失败似乎是由于苄胺和苯胺衍生物中酰胺键的反式构象造成的。因此,N-烷基-N-氯乙酰基苄胺(11、13、15、17、19)在辐照下很容易生成相应的 1、2、3、4-四氢异喹啉-3-酮(12、14、16、18、20)。通过 N-烷基-N-氯乙酰苯胺(35、37、39、42、45)的光环化反应,也同样合成了氧化吲哚(36、38、40、41、43、46)。