Synthesis of imidazo[4,5- e ][1,3]thiazino[2,3- c ][1,2,4]triazines via a base-induced rearrangement of functionalized imidazo[4,5- e ]thiazolo[2,3- c ][1,2,4]triazines.

A series of imidazo[4,5- e ][1,3]thiazino[2,3- c ][1,2,4]triazines was synthesized via a cascade sequence of hydrolysis and skeletal rearrangement of imidazo[4,5- e ]thiazolo[2,3- c ][1,2,4]triazin-7(8 H )-ylidene)acetic acid esters in methanol upon treatment with excess KOH. Imidazo[4,5- e ]thiazolo[3,2- b ][1,2,4]triazin-6(7 H )-ylidene)acetic acid esters are also suitable substrates for the reaction. In this case hydrolysis and thiazole ring expansion were accompanied with the change of the thiazolotriazine junction type from thiazolo[3,2- b ][1,2,4]triazine to thiazino[2,3- c ][1,2,4]triazine.