Aminoimidazo[1,2-a]pyridines: regioselective synthesis of substituted imidazonaphthyridines, azacarbolines and cyclazines

In order to study the regioselectivity of thermal cyclocondensation, aminoimidazo[1,2-a]pyridines (AIP) were prepared, further converted into iminophosphoranes , and ultimately converted regioselectively in angular annulated imidazonaphthyridines (IN) , , , or linear annulated dipyridoimidazole (DPI) . From 2-substituted derivative , the peri annulated product was obtained. The starting amines reacted with aldehydes to yield regioselectively IN , , , , DPI , and TIBO like structures and , as proved by X-ray analysis. The 1,2- or 1,4-addition between amines and α,β-unsaturated aldehydes concerning the pyridine and imidazole moieties is discussed in the light of these results.