New efficient synthesis of 1H-imidazo-[4,5-c]quinolines by a sequential Van Leusen/Staudinger/aza-Wittig/ carbodiimide-mediated cyclization

A new efficient synthesis of multisubstituted 1H-imidazo-[4,5-c]quinoline derivatives via sequential van Leusen/Staudinger/aza-Wittig/carbodiimide-mediated cyclization was developed. Azides 4, obtained from Van Leusen reaction of 2-azidobenzaldehyde 1, amine 2 and TosMIC (tosylmethyl isocyanide) 3, reacted with triphenyl phosphine to produce iminophosphorane 5. A tandem aza-Wittig reaction of iminophosphorane 5 with isocyanate generated 1H-imidazo-[4,5-c]quinoline 7 through carbodiimide intermediate 6 in moderate to good yield.