1.2.4- Triazol-3-ones, 4-amino-2,4-dihydro

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>. 

Schiff bases (112) derived from 4-chlorobenzaldehyde and 1-substituted-5-amino-3-methylthio-l,2,4-triazoles (111) underwent cyclization with phe-noxyacetyl chloride or dichloroacetic acid in the presence of phosphoryl chloride and dimethylformamide to give the 7-(4-chlorophenyl)-fram-6,7-dihydro-3-methylthio-6-phenoxy-l-substituted-l,2,4-triazolo[4,3-a]pyrimidin-5-one 113 and l-substituted-6-chloro-7-(4-chlorophenyl)-3-methylthio 1,2,4-triazolo[4,3-a]pyrimidin-5-one 114, respectively (88JHC173) (Scheme 47). 

The amination of 5-phenyl-l,5-dihydro[l,2,3]triazolo[4,5- /]-l,2,3-triazole (31) with o-(mesityl-sulfonyl)hydroxylamine afforded two V-aminated products distinguishable on the basis of their l3C NMR spectra (Equation (1)). The major product (46%), showed one carbon signal other than those from the phenyl ring and was therefore assigned as the symmetrical 2-amino derivative (32). The minor product showed two l3C signals in addition to those from the phenyl ring and was believed to be represented by structure (33) or (34) (33) is the preferred isomer on the basis of the similarity of its NMR spectrum to that of known l-acetyl-5-phenyltriazolotriazole. 

The 1,3,4-oxadiazolium salts (288) react with hydrazines to give the dihydro-1,2,4,5-tetrazines (290) and 4-amino-l,2,4-triazoles (76KGS629, 74ZOR377, 71DOK(200)134, 71MIP22100). This reaction probably proceeds via the intermediates (289). Similarly, 2-methylmercapto-l,3,4-oxadiazolium salts (291) and hydrazines afford the 1,4-dihydro-l,2,4,5-tetrazin-6(5//)-ones (292) (76CZ496). 

Reaction of 1,2,4-triazol-4-ylamidines (473) with diethyl carbonate in the presence of sodium ethoxyethoxide led (70JPR669) to intermediate 474 which, upon cyclization, gave the l,2,4-triazolo[3,4-/]l,2,4-triazino-8-ones (475). Kurasawa and his group (85JHC1715) reported that the reaction of 3-(a-hydroxyimino-4-amino-5-methyl-4//-l,2,4-triazol-3-ylmethyl)2-oxo-l,2-dihydroquinoxaline (476) with orthoesters and iron powder in acetic acid gave l,2,4-triazolo[3,4-/]l,2,4-triazines 480 and its 7,8-dihydro isomers 479. 

To obtain 2-amino-l,6-dihydro-8-azapurine, 96 (and its 2-methyl and 3-benzyl analogs) were refluxed with cyanogen bromide in methanol (4 h), giving 40-75% yields of the correspondingly alkylated products. 4-Amino-5-ethoxycarbonylaminomethyl-l,2,3-triazole (99) (from 96 and ethyl chloroformate), when refluxed in butanolic sodium butoxide (1 h), produced 7-methyl-l,6-dihydro-8-azapurin-2-one the 8-methyl and 9-ben-zyl analogs were made similarly (76-92% yield). ... 

A derivative of a hitherto unknown nucleus was produced when 4-amino-5-aminomethyl-3-methyltriazole was refluxed with carbon disulfide and triethylamine in pyridine, which yielded 3-methyl-3,7-dihydro-l,2,3-triazolo-[4,5-d][l,3]thiazine-5-thione (98) (3 hr, 53%) the 3-benzyl analog was made similarly (63%) [80JCS(P1)2009]. Cyclization of 4-anilino-5-ethoxycarbonyltriazole with polyphosphoric acid produced 1 f/-triazolo-[4,5-h]quinol-4-one (99) [80EUP(A)2562]. Similarly, ring closure of 4-(2-pyridylamino)triazole-5-carboxylic acid (or its esters) gave l//-pyrido-[l,2-a]-l,2,3-triazolo[4,5-d]pyrimidin-4-one (100) (77GEP2757929). 4-Amino-5-formyl-3-methyltriazole and pentane-2,4-dione, set aside in 20% sulfuric acid, yielded 3,5-dimethyl-3//-l,2,3-triazolo [4,5-6] pyridin-6-yl... 

A three-component condensation of 3-amino-l, 2,4-triazole (or its 5-Me and 5-methylthio derivatives), 1 and DMF-dimethylacetal afforded 8,9-dihydro[l,2,4]triazolo[l,5-fl]quinazolin-6(7H)-ones (06RCB1224). Condensation of 3,4,5-triamino-l,2,4-triazole with aromatic aldehydes and dimedone afforded partially hydrogenated 9-aryl-[l,2,4]triazolo[5,l-frJquinazolin-8-ones. The structure of 2-amino-6,6-dimethyl-3-(4-nitro-benzylidene)amino-9-(4-nitrophenyl)-5,6,7,9-tetrahydro[l,2,4]triazolo[5,l-fr]-quinazolin-8-one was confirmed by X-ray analysis (05RCB2903). 

Heated without solvent, the 5-amino-l-(l-carboxyalkyl)-3-methylthio-l//[l,2,4]triazoles (259) undergo cyclization to yield 5,6-dihydro-2-methylsulfonyl-4//-imidazo[l,2-Z>][l,2,4]triazol-5-ones (260) (Equation (71)) <85JHC385>. 

Hydrazidoyl halides react with 2-amino[l,2,4]triazole to give 5-substituted 6-arylhydrazono-6//-imidazo[l,2-i][l,2,4]triazoles (350) and 6-arylhydrazono-5,6-dihydro-4//-imidazo[l,2-/>][ 1,2,4]-triazol-5-ones (351), respectively the latter products are not determined with respect to the tautomeric structures of the H-, 3H-, or 4/7-form (Scheme 32) <83JHC639>. 

Other fused 1,3,4-thiadiazoles have been prepared and include 4H-1,3,4-thiadiazolo[2,3-c]-l,2,4-triazin-4-ones (108) which were obtained by the reaction of 4-amino-4,5-dihydro-3-(methylthio)-l,2,4-triazin-5-ones (107) with benzoyl isothiocyanates and with methoxycarbonyl isothiocyanates. The corresponding five membered fused system (110) was prepared by reaction of the triazole (109) with benzoyl isothiocyanate <97JHC1351>. ... 

Thirupaiah and Vedula devised a one-pot synthesis of substituted 2,3-dihydro-2-(6-(4-hydroxy-6-methyl-2-oxo-2f/-pyran-3-yl)-7f/- [ 1,2,4] tr iazolo [3,4-i ] [ 1,3 >4] -thiadiazin-3-yl)phthalazine-l, 4-diones 13 (Scheme 9) (14SC513). Treatment of 3-(2-bromoacetyl)-4-hydroxy-6-methyl-2f/-pyran-2-one (14) with 4-amino-5-hydrazino-4f/-[l,2,4]triazole-... 

Multicomponent approaches toward the formation of more complex phthalazine-containing compounds were reported in 2014. A four-component one-pot condensation reaction was employed by Dabiri and coworkers to generate (1,2,3-triazol-4-yl)methyl-3-amino-5,10-dihydro-5,10-dioxo-lH-pyrazolo[l,2-f)]phthalazine-2-carboxylates 26 (Scheme 18) (14SC2037). Catalyzed by Cu(OAc)2 (10mol%) and sodium ascorbate (20mol%), the reaction of benzaldehyde derivatives (1 equivalent), azides (1 equivalent), prop-2-ynyl-2-cyanoacetate (27) (1 equivalent), and phthalhydrazide (28) (1... 

A series of novel 5-amino-7-aryl-7,8-dihydro-[l,2,4]triazolo[4,3-a]-pyrimidine-6-carbonitriles (138) were synthesized by a concise, mild, one-pot three-component reaction of 3-amino-l,2,4-triazole, malononitrile, and aryl aldehydes in the presence of NaOH (20 mol%) in ethanol under heating or ultrasonic irradiation as shown in Scheme 8.46 (Ablajan et al. 2012). 

Keten 55-acetals are obtained from thioamides that have at least one hydrogen atom a- to the thiocarbonyl group by 5-methylation and treatment of the imidium ester with propane-1,3-dithiol. Treatment of the imidium esters from NN-disubstituted thioamides with 4-amino-4-methylpentan-2-ol gives 2-substituted 4,6,6-trimethyl-5,6-dihydro-l,3-oxazines, and with sodium azide they give alkylidenetriazenes (1,2,3-triazabutadienes) (77), not dihydrothia(5 )triazoles (78), as previously claimed (see Vol. 3, p. 399). Structure (77) was demonstrated by Z-ray studies. 

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