4-Amino-1,2,3-triazoles, 4,5-dihydro-

Amino-5-hydrazi no- 1,2,4 triazole Dihydro-chloride, HjN-HN-C-NH-N + 2HC1,... 

Regarding the series of hetero aromatic pentacyclic compounds with three heteroatoms, an accelerated synthesis of 3,5-disubstituted 4-amino-1,2,4-triazoles 66 under microwave irradiation has been reported by thermic rearrangement of dihydro-1,2,4,5 tetrazine 65 (Scheme 22). This product was obtained by reaction of aromatic nitriles with hydrazine under microwave irradiation [53]. The main limitation of the method is that exclusively symmetrically 3,5-disubstituted (aromatic) triazoles can be obtained. 

Amino-1,2,4-triazole has been obtained from orthoformic ester and hydrazine hydrate in a sealed tube at 120° 1 by heating formylhydrazine at 150-210° 2-3-4 by heating N,N -diformyl-hydrazine at 160° 5 by decarboxylation of 4-amino-1,2,4-tria-zoldicarboxylic acid 6 by fusion of l,2-dihydro-l,2,4,5-tetrazine 6 and by heating l,2-dihydro-l,2,4,5-tetrazinedicarboxylic add above its melting point.4-6-7... 

Dimethoxy-3-methyl-l-(4-nitrophenyl)-iV-(5, 6 -dihydrothiazolo[3,2-b][l,2,4]triazol-2 -yl)isoquinolinmm bromide 45 is also prepared by reacting 4,5-dimethoxy-2-(4-nitrobenzoyl)phenylacetone 219 with 2-amino-5,6-dihydro-thiazolo[3,2- ][ 1,2,4]triazole 42 <2003JHC821, 2003JHC1041> (Equation 23). 

The reaction of 2-amino-guanidine-1 -acetic acid hydroiodide 331 with carbon disulfide, heating the substrates in DMF at 130-140 °C for 12 h, produces compound 332 in 76% yield. This compound was subjected to cyclization reaction with acetic anhydride to give 6,7-dihydro-5-oxo-imidazo[2,l-f][l,2,4]triazole 102 in 76% yield (Scheme 32) <1998MI1>. 

In the ring closure of 5-amino-2,3-dihydro-17/-l,2,4-triazolo-3-thione 431 (R = NH2) with 1,2-dibromoethane in the presence of sodium methoxide (2equiv), compound 42 was formed as the main product (Scheme 50) <2003JHC821>. Similarly, the same type of functionalized thiazolo[3,2-A][l,2,4]triazoles 440 and 441 were isolated in the reaction of 1,2-dibromoethane with 2,3-dihydro-17/-l,2,4-triazolo-3-thione (431, R = H) or 2,3-dihydro-5-methyl-l/7-l,2,4-triazolo-3-thione (431, R = Me), using DMF as the solvent in the presence of potassium carbonate and benzyltriethylammonium chloride (CBTEA) (Scheme 50) <2004PS(179)1799>. 

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>. 

Treatment of 4-amino-3-phenyl-5-thio-477-[l,2,4]triazole 83 with bromoacylacetylenes gives the corresponding 6-(acyl-methylene)-5,6-dihydro-3-phenyl[l,2,4]triazolo[3,4- ][l,3,4]thiadiazohydrobromides 88 (Equation 23) <1988ZOR2151>. 

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>. 

Erba et al. (102) observed a novel formation of pyrrole imines 181 from the 1,3-dipolar cycloaddition of mtinchnones 179 and 5-amino-l-aryl-4,5-dihydro-4-methylene-1,2,3-triazoles 180 (Table 10.4). Treatment with benzaldehyde yielded 3-formylpyrroles (182). The reaction presumably involves loss of carbon dioxide, nitrogen, and morpholine from the initial cycloadduct. Unsymmetrical mtinchnones behave regioselectively and furnish products derived from bonding between C(2) of... 

Kohlensaure-arylamid-hydrazide cyclisieren mit Bromcyan unter analogen Versuchsbedingun-gen wie Carbonsaure-hydrazideohneIsolierung von Zwischenprodukten zu 2-Amino-5-ary 1-amino-1,3,4-oxadiazolen276. Die Reaktion laBt sich nicht auf Kohlensaure-anilid-(l-phe-nyl-hydrazid) ubertragen, da hier 3-Amino-l,4-diphenyl-5-oxo-4,5-dihydro-1,2,4-triazol ent-... 

Mit Hydrazin erhalt man aus 1,3,4-Oxadiazolium-Salzen fiber isolierbare acyclische Zwischen-produkte sowohl 3-Amino-l,2,4-triazole, als auch 1,2-Dihydro-1,2,4.5-tetrazine746. Der Reaktionsverlauf wird wesentlich durch die Substituenten des 1,3,4-Oxadiazols und die Reaktionsbedingungen bestimmt. Beim Erhitzen mit Phenyl-hydrazin erhalt man als ringoffene Verbindung ein Hydrazin- und Formazan-Derivat746. 

Besonders wichtige Kuppler sind 4-Amino-pyrazole mit unsubstituierter 5-Stellung. Die aus ihnen resultierenden Azo-Verbindungen sind grungelbe Farbstoffe, die auch zur Syn-these von optischen Aulhellern vom 2,4-Dihydro--Typ die-nen1 ... 

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). 

R1 = R2 = H) gave the triazolo[l,5-a]pyrimidines (125), but with 124 (R1 = R2 = Me) afforded the dioxo derivative 126, and with a-cyano- y-butyrolactones (127) or 2-amino-3-ethoxycarbonyl-5,6-dihydro-4//-thiopyran (129) gave the triazolopyrimidines 128 and 130, respectively (81JHC1287). Treatment of 4-ethoxymethylene-2-phenyl-5(4//)-oxazolone (131) with 5-amino-3-methylthio-l//-1,2,4-triazoles gave the triazolo[l,5-a]pyrimidi-none 132 and the [4,3-a] isomer 133 (93H955) (Scheme 24). 

Dihydro-1,2,4,5-tetrazines, formulated as the 1,2-dihydro tautomers (40), rearrange under the influence of acids to 4-amino-1,2,4-triazoles (70) (78HC(33)1075, p. 1151). Further acidic hydrolysis of (70) resulted in the formation of various products, such as diacylhy-drazines, hydrazine, carboxylic acids and 1,3,4-oxadiazoles (71) (78HC(33)1075, p. 1151). 

The 1,3,4-oxadiazolium salts (288) react with hydrazines to give the dihydro-1,2,4,5-tetrazines (290) and 4-amino-1,2,4-triazoles (76KGS629, 74ZOR377, 7lDOK(200)134,... 

Artemov and Shvaika treated a number of 2-aryl-l,3,4-oxadiazole-5(4//)-thiones (293) with methylhydrazine (R = Me) and obtained a mixture of 1-methyl-1,4-dihydro-1,2,4,5-tetrazine-6(5/f)-thiones (294) and 4-methylamino-l,2,4-triazole-3-thiones (295 R = Me) (71KGS905). A similar reaction was reported by Konig and his coworkers, who treated 5-(4-pyridyl)-l,3,4-oxadiazole-2-thione (293 Ar = py) with hydrazine (R = H) and obtained a compound which was either the l,2,4,5-tetrazine-6-thione (294 R = H) or the 4-amino-l,2,4-triazole-3-thione (295 R = H) (54CB825,56GEP953801). 

Like the oxadiazolium salts (288), 1,3,4-thiadiazolium salts (296) can also react with hydrazines to afford 1,4-disubstituted l,4-dihydro-l,2,4,5-tetrazines (290). By this method, 1,4-dihydro-1,2,4,5-tetrazines with four different substituents can be prepared this seems to be the only method for preparation of such compounds, and proceeds in yields of 70-99%. The 4-amino-l,2,4-triazoles were isolated as side-products (74ZOR377, 71DOK(200)134, 71MIP22100). 

Activated hydrazine derivatives of carboxylic acids (337, 338) can dimerize to afford dihydro-1,2,4,5-tetrazines (89) which can be oxidized to the tetrazines (39) but which can also rearrange to 4-amino-1,2,4-triazoles (339). In many cases where the isolated products have been formulated as dihydro-1,2,4,5-tetrazines (89) it has either been shown, or it can be assumed, that in fact 4-amino-l,2,4-triazoles (339) were obtained. Very often the formation of dihydro-1,2,4,5-tetrazines (89) is a side-reaction in the synthesis of activated hydrazine derivatives of carboxylic acids, such as amidrazones (337 Y = NH2), hydrazidines (337 Y = NHNH2), thiohydrazides (338 X = S) and so on and not the attempted reaction. Therefore the number of effective synthetic processes for dihydrotetrazines (89) or tetrazines (39) by this synthetic principle is not very high. 

Vilsmeier reaction, 4, 1051 Furo[3,2-6]pyrroles MO calculations, 6, 979 synthesis, 4, 1069 6, 1009 Furo[3,4-a]pyrrolo[2,1,5-cd]indolizine nomenclature, 1, 22 Furopyrylium salts, 4, 993-995 Furoquinolines biosynthesis, 4, 992 occurrence, 4, 988 pharmacology, 4, 992 reactions, 4, 988 synthesis, 4, 989 Furo[3,2-c]quinolines, 4, 991 Furo[3,4-fe]quinoxaline, 1,3-diphenyl-synthesis, 4, 993 Furoquinoxalines, 4, 992 Furo[2,3-6]quinoxalines synthesis, 4, 992 Furosemide toxicity, 1, 136 Furospinulosin UV spectra, 4, 587 Furospongin-I mass spectrometry, 4, 583 Furo[3,4-d][l,2,3]triazole, 2,6-dihydro-synthesis, 6, 996 Furo[3,4 -d][ 1,2,3]triazoles synthesis, 6, 996 Furoxan, 4-amino-3-aryl-tautomerism, 6, 404 Furoxan, 4-amino-3-methyl-synthesis, 4, 414 Furoxan, 4-aryl-3-methyl-rearrangement, 6, 408 Furoxan, 3-aryl-4-nitro-synthesis, 6, 414 Furoxan, 4-benzoyl-3-methyl-oxime... 

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