A new approach to the synthesis of benzofuro[3,2-b]quinolines, benzothieno[3,2-b]quinolines and indolo[3,2-b]quinolines

Treatment of 2-hydroxy-, 2-mercapto-, and 2-ethoxycarbonylamino-benzonitriles 12 with 2-fluoro- or 2-nitrophenacylbromides 13 under alkaline conditions provided the corresponding benzofuran, benzothiophene, and indole intermediates 10, respectivelly. Nucleophilic cyclization of these compounds led to the corresponding tetracyclic quinolinones 7a, 7b, and 3. Denitrocyclization reaction of compounds 10 (R = NO2) was found especially useful. Compounds 7a, 7b, and 3 were converted to their chloro derivatives 14a-c, which were reduced with hydrogen and a catalyst to the corresponding compounds 8a, 8b, and 2. The presented pathway represents a new method of preparation of quindoline 2 and its O and S analogs 8. Chloro derivatives 14 are reactive enough to provide the corresponding methoxy derivatives 15 and dimethylamino derivatives 16. Methylation of compounds 7a and 7b with iodomethane providing mixtures of major N-methyl derivatives 17 and minor O-methyl derivatives 15 were also studied.