Reactions of tetracyanoethylene with N′-arylbenzamidines: A route to 2-phenyl-3 H -imidazo[4,5- b ]quinoline-9-carbonitriles

Abstract

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. © 2013 American Chemical Society.