Thiazolo 4,5-6 and -c pyridines

Thiazolo[4,5-6(and -c)]pyridines [CsNS-CsN].—Oxidative cyclization of the thioamide (96) gives 6-methyl-2-(2-pyridyl)thiazolo[4,5-h]pyridine. The isomeric thiazolo[4,5-c]pyridine and 2-(2-pyridyl)thiazolo[5,4-6]pyridine may be prepared similarly. 

Thiazolo[5,4-6]pyridines [CsNS-CsN].—Condensation of 3-amino-2-chloropyri-dine with carbon disulphide in DMF yields thiazolo[5,4-h]pyridine-2-thione (97), which exists predominantly as this tautomer in neutral media. 2-Chloro-3-isocyanatopyridine reacts with various iV-substituted piperazines to give the 

Thiopyrano-7 T-[2,3-d]tliiazoles [CsNS-CsS].— The 5-arylidene-l,3-thiazoIidine-2,4-dithiones (98 Ar = Ph, o-ClCeH4, or o-, p-MeOC, ,) undergo 1,4-cycloaddition with various alkenes R CH=CHR (e.g. R = CN or C02Et, R = H) and related compounds to give tetrahydrothiopyrano-7 -[2,3-d]thiazole-2-thiones.  

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