3-Phenyl triazolo thiadiazole

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. 

The 2-[4-aryl(thiocarbamoylhydrazino)]-5-phenyl[l,3,4]thiadiazoles 51 can react in two ways. Upon heating, reaction leads to cyclized 6-phenyl[l,2,4]triazolo[3,4-A][l,3,4]thiadiazole-3(27f)thiones 52 and, on the other hand, the thiosemicarbazides 51 undergo cyclodesulfurization affording [l,2,4]triazolo[3,4-A][l,3,4]thiadiazoles 53 when treated with dicyclohexylcarbodiimide (Scheme 5) <1986JHC1339>. 

The Schiff base derivatives 73 of the 3-hetaryl-substituted 4-amino-3-thiol-l,2,4-triazoles, on treatment with acetic anhydride, undergo cyclization to give the corresponding 3-substituted-5-acetyl-5,6-dihydro-6-phenyl[l,2,4]triazolo[3,4-7][l,3,4]thiadiazoles 76 (Equation 16) <1990IJB135>. Similar treatment of 4-(A-bcnzoylamino)-4,5-dihydro-l-methyl-3-mcthylthio-1 //-[ 1,2,4 triazolc-5-thione 77 leads to the [l,2,4]triazolo[3,4-4][l,3,4]thiadiazolium trifluoromethanesulfonate 78 (Equation 17) <1986LA1540>. 

Refluxing the 4-amino-3-ethoxycarbonylthio-5-phenyM//-[l,2,4]triazole 79 in pyridine induces cyclization to 3-phenyl[l,2,4]triazolo[3,4- ][l,3,4]thiadiazol-6(5//)-one 80 (Equation 18) <1991RRC619>. 

Heating to reflux a pyridine solution of 3-substituted-5-(l-aroyl-l-bromo)methylthio-4-phenylamino-4//-[l,2,4]tria-zoles 81 (available from the corresponding 1,2,4-triazoles with phenacyl bromides and subsequent ultraviolet (UV) light-induced bromination) affords 3-substituted-6-aroyl-5,6-dihydro-5-phenyl[l,2,4]triazolo[3,4-6][l,3,4]thiadiazoles 82 (Equation 19) <1993IJH135>. 

For 2-methyl-5-phenyl-s-triazolo[3,4-61-1,3,4-thiadiazole (350) and 4-methyl-s-triazolo[3,4-6]benzothiazole (182, R = Me), dipole moments were found to be 4.96 and 5.98, respectively.435 For compounds containing only nitrogen as a heteroatom, dipole moment measurements have been used to study annular tautomerism (Section IV,A,1) using Eq. (36).356... 

Amino-5-phenyl-l,3,4-thiadiazole (112 R = NH2) on diazotization gives the 2-chloro derivative (112 R = Cl), which on treatment with hydrazine followed by benzoylation gives (112 R = NHNHCOPh). Cyclization with phosphorus oxychloride yields the triazolo derivative (113) in moderate yield (66JOC3528). 

Diamino-2-pheny)triazole and sulfur monochloride, when refluxed in benzene, produced 5-phenyl-5//-[l,2,3]triazolo[4,5-c][l,2,5]thiadiazole (96) (18 hr, 38%), which belongs to the larger family of heteropentalenes... 

The structure of 3-(2-aminophenyl)-6-phenyl[l,2,4]triazolo[3,4-Z)][l,3,4]thiadiazole (3) is based on its determination by x-ray crystallography it indicates that in the course of its formation (cf. 8.07.8.3.1) a thioaroyl group has migrated and has been incorporated into the thiadiazole ring of the product <89LA1055>. 

Similarly, 2-hydrazino-5-phenyl[l,3,4]thiadiazole (118) and carbon disulfide in the presence of potassium hydroxide give 6-phenyl[l,2,4]triazolo[3,4-6][l,3,4]thiadiazole-3(2//)-thione (119) <86JHC1339). The same product (119) is obtained from the reaction with arylisothiocyanates on reflux in ethanol (Scheme 11) <66JOC3528>. 

When the reaction of (118) with arylisothiocyanates is carried out in the presence of dicyclo-carbodiimide 3-arylamino-6-phenyl[l,2,4]triazolo[3,4-i][l,3,4]thiadiazoles (120) are formed instead (Scheme 11) <86JHC1339>. 

Hydrazino-3-phenyl[l,2,4]oxadiazole (123) and -thiadiazole (124) react with formic acid to give 3-phenyl[l,2,4]triazolo[4,3-rf][l,2,4]oxadiazole (125) and -thiadiazole (126), respectively (Equation (32)) <91MI 807-05>. 

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