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) 5a-e were prepared, further converted into iminophosphoranes 7a-e, and ultimately converted regioselectively in angular annulated imidazonaphthyridines (IN) 8a, 10a, 11a, 12a or linear annulated dipyridoimidazole (DPI) 17a. From 2-substituted derivative 23, the peri annulated product 24a was obtained. The starting amines 5a-f reacted with aldehydes to yield regioselectively IN 8a-c, 10a-c, 11a-c, 12a,b, DPI 16a-e, 17a-d and TIBO like structures (+/-)-13 and 24a-c, as proved by X-ray analysis. The 1,2- or 1,4-addition between amines and alpha,beta-unsaturated aldehydes concerning the pyridine and imidazole moieties is discussed in the light of these results. (C) 2002 Published by Elsevier Science Ltd.