By direct coupling 7-azaindole and cyclic imines, such as 3,4-dihydroisoquinoline, 6,7-dihydrothieno[3,2-c]pyridine, 3,4-dihydro-β-carboline, and 4,5-dihydro-3H-benz[c]azepine, new 3-substituted 7-azaindole derivatives have been synthesized. The reaction was extended to 4-azaindoles and 6-azaindoles, as electron-rich aromatic compounds. The lowest reactivity was observed in the case of C-3 substitution of 5-azaindole. In this case, the aza-Friedel-Crafts reaction took place by using 10 mol % of p-toluenesulfonic acid (p-TSA) as the catalyst. The role of the acid catalyst can be explained by the different pKa values of the azaindoles. All reactions were performed in solvent-free conditions by using both classical heating and microwave irradiation. In all cases, microwave heating proved to be more convenient to synthesize new C-3-substituted azaindole derivatives.
Keywords: 4-azaindole; 5-azaindole; 6-azaindole; 7-azaindole; aza-Friedel-Crafts reaction; cyclic imines; microwave reaction.