3-Aryl-2(3)-halogenacrylates as Key Synthons in the Regioselective Synthesis of Two Types of Imidazothiazinotriazines

A method for the synthesis of two series of regioisomeric imidazothiazinotriazines was developed by cyclocondensation of imidazotriazinethiones with 3-aryl-2(3)-halogenacrylates or corresponding acrylonitriles. Regioselectivity of the process depended on the substituents at positions 4a and 7a of imidazotriazinethione. The reaction of 4a,7a-unsubstituted derivatives resulted in imidazo[4,5-<i>e</i>][1,3]thiazino[2,3-<i>c</i>][1,2,4]triazines of angular structure while the cyclocondensation of 4a,7a-diarylsubstituted compounds led to imidazo[4,5-<i>e</i>][1,3]thiazino[3,2-<i>b</i>][1,2,4]triazines of linear structure. The scope of the method was extended to benzimidazolethione that reacted with 3-aryl-2(3)-halogenacrylates or acrylonitriles to give benzo[4,5]imidazo[2,1-<i>b</i>][1,3]thiazines.