5- Substituted 2-amino-l,3,4-thiadiazoles

Finally the aminothiadiazoles have been used to prepare bright red dyes. In particular the dyes derived from 5-substituted 2-amino-l,3,4-thiadiazoles (52) (70GEP2028396) and the 3-substituted 5-amino-l,2,4-thiadiazoles (53) (70GEP2006131) by coupling with dialkyl-anilines are neutral to bluish-reds of outstanding brightness and colour strength. 

A large variety of a-halocarbonyl compounds undergo cyclo-condensation with 5-substituted 2-amino[l,3,4]thiadiazoles to give 2,5,6-trisubstituted imidazo[2,l-ft][l,3,4]thiadiazoles (56) (Equation (118)) (Table 23a). 

The standard synthesis of 5-substituted 2-amino-l,3,4-thiadiazoles from thiosemicarbazides and carboxylic acids has been improved by the use of a mixture (3 1) of polyphosphoric acid and concentrated sulphuric acid as the condensing agent the use of either acid alone produces lower yields. ... 

Substituted (ethyl, -propyl, benzyl), cyclohexyl, 2-furyl, and 2-thienyl) 2-amino-l,3,4-thiadiazoles 451 react with a-bromoarylketones to give imidazo[2,l- ][l,3,4]thiadiazoles 161 in good yields (Equation 103) (Table 59) <2006BMC3069, 2006TL2811>. 

Various 2-substituted l,3,4-thiadiazoline-5-thiones can be prepared in good yield by the reaction of amidrazones with CS2 in ethanol at room temperature (Scheme 21a) (70CPB1696). 4-Aryl-2-benzoyl-5-imino-A2-l,3,4-thiadiazolines are prepared from activated thiocyanates and benzenediazonium chloride, presumably via a hydrazone (Scheme 21b) (75TL163). 2-Thio- and 2-amino-l,3,4-thiadiazoles carrying a carbamate in the 5-position are obtained in one step by the reaction of a dithioimidate with a hydrazide. The yields are quite high (Scheme 22a) (80ZC413). 

Azole approach. 2-Amino-l,3,4-thiadiazoles react with appropriately substituted a,/3-unsaturated carbonyl compounds to form fused pyrimidines (729). The orientation of the substituents in the fusion products suggests that the reaction is initiated by Michael addition of the amino group. 1,3-Dicarbonyl compounds will condense in the same manner to yield the salt (729) from a /3-keto ester the 5-oxo derivative (730) is formed (73ABC1197). 

As a rule, oxadiazoles and thiadiazoles are not nitrated. Reports on the production of 2-nitro-5-amino-l,3,4-thiadiazole during the nitration of 2-amino-l,3,4-thiadiaz-ole [274] proved erroneous [275], The compound obtained in this case was 2-nit-ramino-l,3,4-thiadiazole [275], There is only a single paper on the nitration of derivatives of 1,3,4-oxa- and 1,3,4-thiadiazoles [276], 2-Dimethylamino-l,3,4-oxa-and 2-dimethylamino-l,3,4-thiadiazoles react with the nitrating mixture with the formation of 2-dimethylamino-5-nitro derivatives. Aryl-substituted oxadiazoles and thiadiazoles are nitrated in the phenyl ring [277, 278],... 

The synthesis of 2-substituted 6-arylimidazo[2,l-6][l,3,4]thiadiazoles (56) can be achieved also by treatment of 5-substituted 2-amino[l,2,4]thiadiazoles with acetophenones in the presence of an oxidant (Equation (120)) <89IJC(B)500,93MI805-04,94JCR(S)38>. 

Addition of two equivalents of 1 to l,6-disubstituted-2,5-dithiobiureas 32a-c in tetrahydrofuran (THF) at room temperature led to thiadiazole derivatives 33 and 34 as side products as well as l,2-bis[5-(substituted-amino)-l,3,4-thiadiazole-2-yl]-hydrazines 35 as the major product (Scheme 8). CT complexation was proved as an initial state (04ZN(B)910). 

In the heterocyclic field, sulphur substitutions include the sulphonation of quinoline to produce mainly the 8-acid, plus the 5-, 6-, and 7-acids, the chlorosulphonation of 2-(3,4-dicholorophenyl)- and 2-(3-pyridyl)-imidazole (on the imidazole ring) and of 2-(4-chlorophenyl)imidazole on both aromatic rings, the tosylation at N-3 of some 2-(monosubstituted amino)-l,3,4-thiadiazoles (which isomerise to products that are sulphonylated on the exocyclic nitrogen), and the thiolation of 2-methylindolizine with diaryl disulphides to form (53). ... 

Substituted-1,3,4-thiadiazol-2-yl)-4-quinazolones 2-Amino-5-(l-iftethyl-2-nitro-5-imidazolyl)-1,3,4-thiadiazole 2-Anilino-5-(amino-oxy)methyl-l,3,4-thiadiazole Substituted 2-acylamino-1,3>4-thiadiazoles l,3,4-Thiadiazol-2-yl- -mercaptocinnamamides N-(2-Anilino-l,3,4-thiadiazol-S-ylmethoxy)phthalimide N -(l,3,4-Thiadiazol-2-yl)-N -benzylidenesulphanUainides 2-p -AminobenzenesuIphonamido-S-ethyl 1,3,4-... 

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>. 

The most widely used method for the preparation of [l,2,4]triazolo[3,4-A][l,3,4]thiadiazoles 85 employs 4-amino-5-thio-4/7-[l,2,4]triazoles 83 or 4-amino[l,2,4]-triazole-5(47T)-thiones 84 as starting materials. The reaction of the triazoles 83 or 84 with carbonic acid derivatives furnishes [l,2,4]triazolo[3,4-4][l,3,4]thiadiazoles with a heteroatom substituent (N, O, S) at position 6 the O- and S-functions are formulated as 6-hydroxy and 6-thio derivatives 85a or as thiadiazol-(5/7)6-ones and -thiadiazole-(577)6-thiones 85b, respectively reaction with carboxylic acid derivatives provides the 6-substituted-[l,2,4]triazolo[3,4-4][l,3,4]-thiadiazoles 85c (Equation 20 Table 3). 

Contrasting with the reported formation of fused [l,3,4]thiadiazole rings in the course of the reaction of 3-substituted-4-amino-5-thio-47/-[l,2,4]triazoles 83 with various isothiocyanates (cf. Section 11.07.8.3, Table 3), the reactions with methyl isothiocyanate and with phenylisocyanate afford 3,7-disubstituted-6,7-dihydro-57/-[l,2,4]triazolo[4,3-f] [l,2,4]triazole-6-thiones 110 and -triazole-6-ones 111, respectively (Equation 29) <1986MI607, 1992IJB167>.The same reaction of 4-amino-l-methyl-3,5-bis(methylthio)[l,2,4]triazolium iodide 112 with aryl isothiocyanates yields the mesoionic compounds 113 (Equation 30) <1984TL5427, 1986T2121>. 

Two other results should be reviewed here, too. The substituted thiadiazolo[3,2-trifluoromethyl groups) was described by Sokolov and Aksinenko <2003IZV2053> 2-amino-5-methyl[l,3,4]thiadiazole 165 was heated with iV-ethoxycarbonyl-bis-trifluoroacetone imine in DMF in the presence of />-toluenesulfonic acid to yield the cyclized product 166 in good yield (77%). 

The reaction of 2-amino-2//-azirines (58) with 5-substituted l,3,4-thiadiazol-2(3H)-ones (59) yields dipolar 1 1 adducts as shown in Scheme 8. The reactions were carried out at room temperature in 2-propanol and the percentage yields (in parentheses) were somewhat dependent on the nature of the substituent at C(5) as follows CFj (76), CN (83), MeSO (95), CCI3 (54), MeO (84) and CF3... 

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