Regioselective synthesis of imidazo[1,2-a][1,3,5]triazines and 3,4-dihydroimidazo[1,2-a][1,3,5]triazines from [1,3,5]triazin-2,4-diamines

An efficient and practical procedure was developed to prepare novel imidazo[1,2-a][1,3,5]triazines and 3,4-dihydroimidazo[1,2-a][1,3,5]triazines with a good regioselectivity and high yields, starting from dicyandiamide and the corresponding arylamines. Mechanistic studies for the subsequent cyclocondensation with chloroacetaldehyde support a pathway, which begins with the displacement of the chloro atom activated by an adjacent CO group, followed by cyclization and dehydration.