New Routes for the Synthesis Novel Heterocyclic via Formation of C-N Bond and via Cleavage a Thiazine Ring of 1,4-Benzothiazine

The reactions of 2-aminothiophenol with acetylacetone in refluxing DMSO or ethanol wasinvestigated. Treatment of 1 with enaminone 5 gave 1,4-benzothiazine derivative 6. A reasonable mechanism represented the formation of pyridone derivative 11 by treatment of 2 with malononitrile. Reactions of 2 with cyanoacetohydrazide, thiosemicarbazide,hydrazine hydrate and phenyl hydrazine afforded the compounds 13, 15 and, 17a-b respectively. Condensation of 13 with 4-methoxy benzaldehyde gave 18. The latter compound reacted with malononitrile gave pyridone derivative 19. A reasonable mechanism interpreted the formation of pyrazolo[3,4-b]pyridine derivative 20 from the reaction of 13 with DMF-DMA via cleavage of a thiazine ring of 1,4-benzothiazine. The structures of all newly synthesized compounds elucidated by elemental analysis 1H-NMR and 13C-NMR spectra, Ms and X-ray crystallographic investigations. The reported crystal structures of these novel 1,4-benzothiazine derivatives are expected to be a remarkable contribution to the crystallographic database of heterocyclic compounds.