Highly efficient synthesis and NMR features of novel fused pyrimidothiazinium trihalogenides

Condensed pyrimidines are a popular class of heterocyclic compounds because they have a wide range of biological activity. This article aims to evaluate the simple, catalyst-free procedure of synthesis of novel fused pyrimidothiazines. An efficient access to a series of pyrazolo[4′,3′:5,6]pyrimido[2,1-b][1,3]thiazinium, pyrazolo[3′,4′:5,6]pyrimido[2,1-b][1,3]-thiazinium, and benzo[b]thieno[4′,3′:5,6]pyrimido[2,1-b][1,3]thiazinium trihalogenides was developed via electrophilic heterocyclization of corresponding pyrimidine cinnamyl thioethers under the action of halogens. The XDR and complex NMR investigations were used for solving of final products structure; the anisochronism was observed in the NMR spectra of synthesized compounds for the pairs of ortho- and meta-protons, as well as the N-phenyl substituents associated with them.