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 imidazo4,5-e1,3thiazino2,3-c1,2,4triazines of angular structure while the cyclocondensation of 4a,7a-diarylsubstituted compounds led to imidazo4,5-e1,3thiazino3,2-b1,2,4triazines of linear structure. The scope of the method was extended to benzimidazolethione that reacted with 3-aryl-2(3)-halogenacrylates or acrylonitriles to give benzo4,5imidazo2,1-b1,3thiazines.