Rearrangement of o-nitrobenzaldehyde in the Hantzsch reaction

The reaction of 5-hydroxy-2-nitrobenzaldehyde with ethyl acetoacetate in am monia gave the two expected isomeric 1,4- and 1,2-dihydropyridines resultin g from the normal Hantzsch reaction. However, the combination of 2-nitroben zaldehyde with ethyl acetoacetate under the same conditions yielded four pr oducts: the two normal isomeric dihydropyridines and two tricyclic compound s. When we attempted to independently synthesize the two tricyclic compound s by reductive cyclization of 4-(2-nitrophenyl)-2,6-dimethyl-3,5-dicarbetox y-1,4-dihydropyridine and 2-(2-nitrophenyl)4,6-dimethyl-3,5-dicarbetoxy-1,2 -dihydropyridine with tin (II) chloride in hydrochloric acid media, we obta ined instead an indole and a quinoline derivative, respectively.