Derivatives of 3H-1,2,3-triazolo[4,5-d][1,3]thiazine, a new heterocyclic nucleus. Some shifts of a methylene group from a nitrogen to a sulphur atom

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Contrary to expectations, 3-alkyl derivatives of 4-amino-5-aminomethyl-3H-1,2,3-triazole (2b and c), when heated with carbon disulphide and a base, did not give a 1,3,6,9-tetrahydro-8-azapurine-2-thione (3b) but a 3-alkyl-3,7-dihydro-1,2,3-triazolo[4,5-d][1,3]thiazine-5(4H)-thione, e.g. (5). This thione (5), the nucleus of which was hitherto unknown, could be methylated on the exocyclic sulphur atom to give the methylthio-derivative (6a), which was readily converted into the amino- and hydrazine-analogues (6b and c). The reaction mechanism that produced the thione (5) depends on the transfer of a 5-methylene group from a nitrogen to a sulphur atom, apparently involving triazol-5-lmethyldithiocarbamate intermediates [(4)→(8)]. Two sulphide by-products (9) and (11) were isolated which had also undergone this very unusual N → S shift. 1H N.m.r., i.r., and mass spectrometric data are presented and discussed.