Unusually Facile Ring-Opening Reaction in the Pyridine System

Article abstract of DOI:10.1021/jo01310a021

Reaction of 2-acetylpyridine with methyl 1-methylhydrazinecarbodithioate (2) resulted in formation of methyl (E,Z,E)-<4-(3,4-dihydro-2,6-dimethyl-3-thioxo-1,2,4-triazin-5(2H)-ylidene)-2-butenylidene>methylhydrazinecarbodithioate (4b) rather than the expected hydrazone, 3b.Reaction of pyridine-2-carboxaldehyde with 2, however, gave mostly the corresponding hydrazone 3a and some triazine 4a.Alkylation of 4a and 4b with iodomethane afforded the 3-methylthio derivatives 8a and 8b, respectively.The structure of 8a was determined by 1H NMR spectrometry and confirmed by a single-crystal X-ray analysis.Reaction of hydrazone 3b with 2 gave 4b, while treatment of 3b with dimethylamine afforded 6-(dimethylamino)-3,6-dihydro-1,3-dimethyl-4H-pyrido<1,2-d>-<1,2,4>triazine-4-thione (14a).Alkylation of 14a with iodomethane in aqueous base resulted in the formation of (Z,E)-4-<2,6-dimethyl-3-(methylthio)-1,2,4-triazin-5(2H)-ylidene>-2-butenal (15).Reaction of aldehyde 15 with 2 gave 4b.