Activated Nitrites in Heterocyclic Synthesis: Syntheses of Thiazole, Pyrazole and 4H-l,4-Benzothiazine Derivatives

4-Arylazo-3-phenyl-5-aminopyrazoles (5a, b) and substituted hydroxythiazoles 8a, b were synthesized from the reaction of 4a, b with hydrazine hydrate and mercaptoacetic acid respectively. Compounds 5a, b and 8a, b were also obtained from coupling of 2a, b with 6 and 7, respectively. 4H-1, 4-Benzothiazine 11 was prepared from 1 and 10. The resaction of the diazonium salts 2a-c with diethyl 3-amino-2-cyanopenet-2-en-1, 5-dicarboxylate 12 was also reported.