1.2.4- Triazolo thiadiazoles

Treatment of 5,7-diamino-l,3,4-thiadiazolo[3,2-n]pyrimidinium ehloride (25) with Vilsmeier reagent gave the 7-formamido-l,2,4-triazolo[l,5-c]pyrimidin-5-one (27) (90JHC851) (Seheme 42). Compound 27 has presumably been formed via rupture of the 1,3,4-thiadiazole ring of 25 and... 

Heating the 5-isocyano-l,3,4-thiadiazolo[3,2- ]pyrimidin-5-one 115 with 10% hydrochloric acid gave a mixture of the 5-imino-l,3,4-thiadiazolo[3,2- ]pyrimidin-7-one 116 (10%) and the l,2,4-triazolo[l,5-c]pyrimidine-5,7-dione 117 (35%) (91JHC489). Formation of 117 probably occurred through thiadiazole ring rupture of 116 and recyclizatioii with its imino function together with desulfurization (Scheme 43). 

Two Nitrogen Atoms and One Sulfur Atom. s -Triazolo[3,4-d]-l,3,4-thiadiazole derivatives 98Ft(48)561. 

Bakulev et al. reported the synthesis of 5//-[l,2,3]triazolo[5,l-i>] [l,3,4]thiadiazines starting from 5-N-nitrosylamino-l,2,3-thiadiazole 68. Reduction of 68 with SnCh and 1A/HC1 and then subsequent reaction with a ketone gave the imine 69. Treatment of 69 with thionyl chloride at -80 °C led to the formation of the isolable triazolothiazine 70 which on further reaction with thionyl chloride at room temperature gave the corresponding chloro derivative 71 <00MC19>. 

The reaction of 3-methyl-6-(4-chlorophenyl)[l,2,4]triazolo[3,4-7]-l,3,4-thiadiazole 319 with thioglycolic acid gives thiazolo[2,3-3]-.r-triazolo[3,4-7][l,2,3]thiadiazol-6(7//)-one 320 (Equation 56) <2002IJH167>. 

A series of substituted triazolo[3,4- ][l,3,4]thiadiazoles 455 have been submitted to reaction with different two-carbon activated reagents such as chloranil or 2,3-dichloroquinoxaline, to give the complex linear heterocycles 456... 

The first single-crystal structure was reported for 6-methyl-3-phenyl-.r-triazolo[3,4-3]-l,3,4-thiadiazole in which the nucleus of the triazolothiadiazole system was planar confirming the aromatic character of the lOn-electron system <1974CSC7>. This is generally the case for the entire series of 5,5-fused heterocycles. 

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