Condensed Ring Systems incorporating 1,2,5-Thiadiazole

In a preliminary report, Tsuji has described the Vilsmeier-Haack reaction of 3-amino-6-methyl-4(3jff)-oxo-2(l/f)-pyrimidinethione (153). The action of dimethylformamidine and phosphorus oxychloride affords the two formamidines 

Further examples of meso-ionic l,3,4-thiadiazolo[3,2-a]pyrimidine-5,7-diones (156) have been prepared by previously described methods (see Vol. 3, p. 702). Certain of these compounds possess in vitro antibacterial activity.  

spectra of 5-oxothiadiazolopyrimidines (159) have Amax at ca. 300 nm, while those of the 7-oxo-isomerides (161) have Amai at 260—270 nm, suggesting that TT-electrons are more delocalized in the former ring system. I.r., n.m.r., and mass spectral data are in accord with this view.  

Selected members of the l,3,4-thiadiazolo[3,2-a]pyrimidine ring system possess larvicidal activity (housefly), protective activity against bacterial leaf-blight disease of the rice plant, and herbicidal activity.  

Taniguchi, and K. Maekawa, J. Fac. Agric., Kyushu Unit ., 1975, 20, 7 Chem. 

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Condensed ring systems incorporating 1,2,4-thiadiazole are formed when a heterocyclic compound (178) functioning as the amidine is condensed with chlorothioformyl chloride (179) or ethyldithiocarbonyl chloride (180) the scope of this synthesis is very wide indeed. 

The condensation of sulphamide and diethyl oxalate produces 3,4-dihydroxy-1,2,5-thiadiazole 1,1-dioxide as the dipotassium salt in high yield. The free acid (177) is an excellent precursor for the preparation of other functional derivatives, and for building up fused ring systems incorporating the 1,2,5-thiadiazole 1,1-dioxide structure (see below). The two isomeric benzothiadiazole acetoximes (178) and (179) undergo the Beckmann reaction, resulting in the fission of their carbocyclic ring. This provides an effective synthesis of novel ajS-unsaturated 1,2,5-thiadiazoles (180 X = COaH, Y = CR=CHCN X =... 

Benzo[l,2-c 3,4-c 5,6-c ]tris[l,2,5]thiadiazole.—Four related condensed tetracyclic ring systems incorporating 1,2,5-thiadiazole (202 X = S, Se, CH, or CH=CH) are accessible from a common starting material, benzo[l,2-c 3,4-c ]-bis[l,2,5]thiadiazole (200), which is converted into the diamine (201) and variously cyclized to (202). The condensation of (201) and 9,10-phenanthrene-quinone in boiling acetic acid similarly yields the heptacyclic ring system dibenzo-[a,c]bis[l,2,5]thiadiazolo[3,4-/r.3, 4V]phenazine. 2... 

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