Department of Chemistry, University of Cyprus, P.O. Box 20537, 1678 Nicosia, Cyprus.
J Org Chem. 2013 Sep 6;78(17):8655-68. doi: 10.1021/jo4013699. Epub 2013 Aug 12.
Eight 2-phenyl-3H-imidazo[4,5-b]quinoline-9-carbonitriles 15 are prepared in four steps from N'-arylbenzamidines 11 and tetracyanoethylene (TCNE) in ~70-90% yields. The transformation involves the initial formation of N-aryl-N'-(1,2,2-tricyanovinyl)benzamidines 12 in 87-99% yields, which in MeCN undergo a 5-exodig cyclization to give the 2-[1-aryl-5-imino-2-phenyl-1H-imidazol-4(5H)-ylidene]malononitriles 13 in 84-92% yields, while in MeOH the (Z)-2-[2-phenyl-4-(arylimino)-1H-imidazol-5(4H)-ylidene]malononitriles 14 are formed in 85-94% yields. The imidazoles 14 can also be prepared directly from imidazoles 13 via a Dimroth rearrangement in either neat MeOH or in DCM with DBU. Subsequent thermolysis of imidazoles 14 in diphenyl ether affords 2-phenyl-3H-imidazo[4,5-b]quinoline-9-carbonitriles 15 in near quantitative yields. Mechanistic rationale is provided for all transformations.
从 N'-芳基苯脒 11 和四氰基乙烯（TCNE）出发，通过四步反应以约 70-90%的收率制备了 15 种 2-苯基-3H-咪唑并[4,5-b]喹啉-9-甲腈。该转化涉及初始形成 N-芳基-N'-(1,2,2-三氰基乙烯基)苯脒 12，收率为 87-99%，在 MeCN 中，它们经历 5-endo 外消旋环化，以 84-92%的收率得到 2-[1-芳基-5-亚氨基-2-苯基-1H-咪唑并[4,5-b]吡啶-4(5H)-亚基]丙二腈 13，而在 MeOH 中，以 85-94%的收率形成(Z)-2-[2-苯基-4-(芳基亚氨基)-1H-咪唑并[4,5-b]吡啶-5(4H)-亚基]丙二腈 14。咪唑 14 也可以直接从咪唑 13 通过在 neat MeOH 或 DCM 中用 DBU 进行 Dimroth 重排来制备。随后，咪唑 14 在二苯醚中的热解以近乎定量的收率得到 2-苯基-3H-咪唑并[4,5-b]喹啉-9-甲腈 15。为所有转化提供了机理依据。
