Annulated heterocycles from methyl 6-chloro-5-formyl-2-methyl-4-(2-nitrophenyl)-1,4-dihydropyridine-3-carboxylate

The pyridone 1a reacts with POCl3/DMF to yield the title compound 2a. After irradiation of 2a the enolether 3 is isolated, as shown by an X-ray structure determination. The pyridine 4 obtained by dehydrogenation of 2a leads under reductive conditions to the benzo[c][2,7]naphthyridines 5-7. The reaction of 4 with o-phenylenediamine gives the benzimidazole 8, while using 2-aminophenol or 2-aminothiophene respectively the pyrido[2,3-b[1,5]benzoxazepine 11 and the corresponding benzothiazepine 12 are obtained.