1 -Phenyl-4,5-dihydro-1 //-1,2,3-triazoles

Azides can use enamines as dipolarophiles for ],3 cycloadditions to form triazolines. These azides can be formate ester azides (186), phenyl azides (187-195), arylsulfony] azides (191-193,196), or benzoylazides (197,198). For example, the reaction between phenyl azide (138) and the piperidine enamine of propionaldehyde (139) gives 1 -phenyl-4-methy l-5-( 1 -piperidino)-4,5-dihydro-l,2,3-triazole (140), exclusively, in a 53% yield (190). None of the isomeric l-phenyl-5-methyl product was formed. This indicates that the... 

The only triazole salt of type 83 that has been reported was obtained by the reaction of 2,3-dihydro-2,5-dimethyl-l-phenyl-l,2,4-triazole-3-thione (84) with methyl iodide to give 83 (R = R = Me, R " = Ph, R" = MeS). 

Friesner and coworkers investigated the 1,3-dipolar addition of phenyl azide 60 to carbon-carbon double bonds forming l-phenyl-4,5-dihydro-l//-l,2,3-triazoles (61 and 62) (Scheme 39) [99JPC(A)1276]. 

Ethyl l//-azepine-l-carboxylate (1) undergoes slow cycloaddition with diethyl diazenedicar-boxylate to give the [4 + 2] 7t-adduct 14 and not, as was first thought, the [6 + 2] 7t-adduct.257 4-Phenyl-l,2-dihydro-l,2,4-triazole-3,5-dione257 258 and phthalazine-1,4-dione257 react likewise. 

Reduction of the 1//-1,2-benzodiazepines 6 with lithium aluminum hydride results in the dihydro compounds 8, which are dehydrogenated to the 3H-1,2-benzodiazepines 9 by 4-phenyl-4//-l,2,4-triazole-3,5-dione.123 The products readily revert to the 1//-tautomers in the presence of sodium methoxide. 3//-1,2-Benzodiazepines react with 3-chloroperoxybenzoic acid to give mixtures of 1- and 2-oxides, 10 and 11, in which the latter predominate. Treatment of the 2-oxides 11 with nucleophiles provides 3-substituted H- 1.2-benzodiazepines 12. Selected examples are given.124... 

Nitron (4.5-Dihvdro-l, 4-diphenyl-3,5-phenyl-imine-1,2,4-triazole, or l,4-Diphenyl-3,5-endo-anilino-4,5-dihydro-l, 2,4-triazole). N C(NFh>2.CH.N.Ph, C20H16N4, mw 312.36 ... 

CN 4-[4-[4-[4-[[2-(2,4-dichlorophenyl)-2-( 1H-1,2,4-triazol-1 -ylmethyl)-1,3-dioxolan-4-yl]methoxy]phenyl]-l-piperazinyl]phenyl]-2,4-dihydro-2-(l-methylpropyl)-3//-l,2,4-triazol-3-one... 

Dihydro-3-methoxy-4-methyl-5-oxo-A/-[[2-(tri-fluoromethoxy)phenyl]sulfonyl]-1H-1,2,4-triazole-1-carboxamide, sodium salt... 

A/-[2,4-dichloro-5-[4-(difluoromethyl)-4,5-dihydro-3-methyl-5-0X0-1H-1,2,4-triazol-1-yl]phenyl]methane-sulfonamide... 

Morpholino-3-[4-phenyl(thiosemicarbazido)carbonyl]quinoxaline (129) gave 2-morpholino-3-(4-phenyl-5-thioxo-5,6-dihydro-4//-l,2,4-triazol-3-yl)quin-oxaline (130) (2M NaOH, reflux, 3 h 35%), 2-(5-anilino-l,3,4-thiadiazol-2-yl)-3-morpholinoquinoxaline (131, X = S) (98% H2S04, 0°C, 1 h, then 20°C, 12 h 89%), or 2-(5-anilino-l,3,4-oxadiazol-2-yl)-3-morpholinoquinoxaline (131, X = O) (NaOH, H20, EtOH, 1/Ki J, dropwise, 5°C — 95°C, 4 h 81%) 688 analogs of all three products were made similarly.688... 

Some interesting fused 1,2,3-triazole ring systems have been reported. A series of 5-piperidyl-substituted 7-hydroxy-3f/-l,2,3-triazolo[4,5-d]pyrimidines 143 has been synthesized from pipecolinate esters, benzylazides, and cyanoacetamide <06CHE246>. 4-Alkylidene-5,6-dihydro-4//-pyrrolo-[l,2-c][l,2,3]triazoles 144 were prepared from alkylidenecyclopropanes via diiodogenation/Cu(I)-catalyzed 1,3-dipolar cycloaddition/intra-molecular Heck reaction sequence <06SL1446>. 6,6-Dimethyl-2-phenyl-4,5,6,7-tetrahydro-27/-benzotriazol-4-one 145 were prepared from A-(5,5-dimethyl-3-oxocyclohexenyl)-S,S-diphenylsulfilimine and... 

Phenyl-1,2-dihydro-3//-l,2,4-triazole-3-selenones 130a-d were delivered as minor products from the reaction of a range of acyl chlorides with potassium isoselenocyanate (Equation 40 and Table 23) <2006H(68)1191>. 

Heating of a solution of 5-ethyl-3-phenyl-l,3,4-thiadiazol-2(377)-imine 85 in aq. NaOH to 80°C for 5h gave the 5-ethyl-2,3-dihydro-2-phenyl-l/7-l,2,4-triazole-3-thione 86 via Dimroth rearrangement (Scheme 7) <2002HCA1883>. Nucleophilic attack of the hydroxide on the electrophilic C-5 resulted in ring opening and, after rotation around the C(2)-N(3) bond and subsequent recyclization, triazole thione 86 formed. 

The reaction of 2-anilino-l,4-naphthoquinone 374 with benzoylacetic acid hydrazide gives 3-hydrazino-pyrazolyl derivative 375, that is acetylated to produce 5-[[l,4-dihydro-l,4-dioxo-3-(phenylamino)-2-naphthalenyl]sulfonyl]-3-methyl-6-phenyl-5/7-pyrazolo[5,l-c][l,2,4]triazole 51. This latter derivative is also obtained in 51% yield from reaction of 374 with benzoylacetic acid hydrazide in the presence of a mixture of acetic acid-sodium acetate <2004PS(179)1907> (Scheme 39). 

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>. 

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>. 

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>. 

Alkenylidene cyclopropanes react readily with 246 to yield 1,4-diazo-bicyclo[3,3,0]oxtanes, whereas methylidene cyclopropane reacts only very slowly with 246 to yield a 2 + 2 cycloadduct (73AJ1553). Compound 246 also reacts with 5-methylfuran-2(3//)-one in an acyl-ene reaction to yield 7-acetyl-6,7-dihydro-2-phenyl-2.ff-pyrazolo[I,2-a]-l,2,4,-triazol-l,3, 5-trione [80JCS(P1)843]. 

Treatment of 6-(l,2-diacetoxyethyl)-2-phenyl-2,6-dihydro-4//-furo[3,4-with hydrazine hydrate in methanol resulted in opening of the lactone ring accompanied by deacetylation to produce compound 63 (Equation 8) <2000JIG168>. 

Unter zusatzlicher Gerustumlagerung reagieren l-(2-Nitro-phenyl)-4,5-dihydro-l,2,3-triazole... 

Die Beliehtung von Sydnonen licfert 1,2,3-Triazole und/oder 5-Oxo-4,5-dihydro-l, 3,4-oxadiazole. Bei der Beliehtung von 3-Phenyl-sydnon erhalt man als Hauptprodukt 5-Oxo-4-phenyl-4,5-dihydro-1.3 A-oxadiazot -. 

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. 

Another interesting synthesis of spiro[2.3]hexan-4-one (16) comprised of dipolar attack of 4-phenyl-l,2-dihydro-4//-l,2,4-triazole-3,5-dione on bicyclopropylidcnc to give a zwitterion 17, which underwent ring enlargement to 18 before ring closure to diaziridine 19 took place. Accordingly, in the presence of water, 18 was trapped with formation of spiro[2.3]hexan-4-one (16) which was also obtained from 19 by saponification.118... 

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). 

Treatment of verdazyls (48) with mineral acids resulted in disproportionation to 1,2,3,4-tetrahydro-1,2,4,5-tetrazines (75) and l,6-dihydro-l,2,4,5-tetrazinium salts (76). Here one molecule of the verdazyl is reduced to (75) and the other is oxidized to (76). The mechanism of this reaction has been studied by Polumbrik and his group (72ZOR1925). Heating 3-phenyl-1,2-dihydro-1,2,4,5-tetrazine-6(5/f)-thione (77) in 2N hydrochloric acid led to the isolation of 3-phenyl-l,2,4-triazole-5-thione (78) (77KGS1564). 

In the first step the formation of 5-phenyl-2-TMS-l, 2,3,4,-tetrazole (374) occurs which can either be hydrolyzed to 5-phenyl-l,2,3,4-tetrazole (375) or pyrolysed to give a N-TMS-benzaldehydehydrazonium compound (376). 376 can furthermore either dimerize to form 3,6-diphenyl-l,2,5-bis(TMS)-2,5-dihydro-l,2,4,5-tetrazine (377) and after subsequent hydrolysis and oxidation 3,6-diphenyl-l,2,4,5-tetrazine (3 79) or on the other hand react with a further equivalent 373 yielding in the last step 3,5-diphenyl-l, 2,4-triazole (381)214 (Scheme 55). 

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