Triazoles and ring-fused derivatives

A microreview on the copper(I)-catalyzed alkyne-azide click cycloadditions from a mechanistic and synthetic perspective has been written 06EJO51 . 

A three-component coupling was used to prepare a series of 1,4-disubstituted-l,2,3-triazoles 129 from the corresponding acetylated Baylis-Hillman adducts 127, sodium azide and terminal alkynes 128 06TL3059 . This same reaction was also carried out in either water or in 

R1 = Ph, Ar, 3-furyl, n-CsHn R2 = Ph, n-CsHn, CH2CH2OH EWG = C02Me, C02Et, CN 

Tandem azidination- and hydroazidination-Hiiisgen [3 +2] cycloadditions of ynamides are regioselective and chemoselective, leading to the synthesis of chiral amide-substituted 1,2,3-triazoles 06OBC2679 . A series of diversely l-substituted-4-amino-l,2,3-triazoles 132 were synthesized by the copper-catalyzed [3+2] cycloaddition between azides 130 and ynamides 131 06T3837 . 

Other non-traditional preparations of 1,2,3-triazoles have been reported. The rearrangement in dioxane/water of (Z)-arylhydrazones of 5-amino-3-benzoyl-l,2,4-oxadiazole into (2-aryl-5-phenyl-27/-l,2,3-triazol-4-yl)ureas was investigated mechanistically in terms of substituents on different pathways 06JOC5616 . A general and efficient method for the preparation of 2,4-diary 1-1,2,3-triazoles 140 from a-hydroxyacetophenones 139 and arylhydrazines is reported 06SC2461 . 5-Alkylamino-] //-], 2,3-triazoles were obtained by base-mediated cleavage of cycloadducts of azides to cyclic ketene acetals 06S1943 . Oxidation of N- 

Ruthenium catalysts were used as alternatives to the usual copper catalysts. Ynamides 102 reacted with various azides 103 in the ruthenium-catalyzed Huisgen [3+2] cycloaddition reaction to yield l-protected-5-amido 1,2,3-triazoles 104 07T8094 . The formation of 1,5- 

Click chemistry also found applications in peptides and peptidomimetics. Alkyne-azide cycloaddition between two peptide strands provided an efficient convergent synthesis of triazole ring-based P-tum mimics 07CC3069 . The synthesis of a-substituted prolines has been accomplished by microwave-assisted Huisgen 1,3-dipolar cycloaddition between azides and orthogonally protected a-propynyl proline in the presence of Cu(I) sulfate 07SL2882 . The synthesis of new trifluoromethyl peptidomimetics with a triazole moiety has been reported 07TL8360 . 

Benzotriazole was found to be an efficient ligand for the Cu(I) iodide-catalyzed N-arylation of imidazoles with aryl and heteroaryl halides 07TL4207 . The first enantioselective conjugate addition reaction of I //-benzotriazole with a variety of enones catalyzed by a cinchona alkaloid thiourea affords Michael adducts in good yields with moderate to good enantioselectivities has been reported 07S2576 . 

A new synthetic route for the access to [1,2,3]triazolo[l, 5- [l, 4Jbcnzodiazcpincs and other derivatives has been described 07TL3495 . 

3-Dipolar cycloadditions have been the most common methods for the syntheses of various 

Other metal-mediated reactions of azide reagents to terminal alkynes have also been reported. Indium(ll) triflate catalyzed tandem azidation/l,3-dipolar cycloaddition of various (o,(o-dialkoxyalkynes 134 with trimethylsilyl azide yielded fused 1,2,3-triazoles 135 05TL8639 . A new ruthenium-catalyzed process for the regioselective synthesis of 1,5-disubstituted-1,2,3-triazoles has been developed 05JA15998 . 

3-Triazoles can also be prepared from in situ formation of azides from halo compormds. For example, 1,4-disubstituted-1,2,3-triazoles 138 were obtained in excellent yields by a convenient one-pot procedure from a variety of aryl and alkyl iodides 136 and terminal alkynes 137 without isolation of potentially unstable organic azide intermediates 05SL2941 . Efficient one-pot synthesis of 1,2,3-triazoles from in situ formation of azides from benzyl and alkyl halides with alkynes has also been reported 05SL943 . 

Cycloaddition of aryl imines 155 with diazomethane followed by oxidation of the intermediate triazoline with potassium permanganate afforded l-(4-methylsulfonylphenyl)-5-ary 1-1,2,3-triazoles 156 05JHC33 . l,2,3-Triazolo-3 -deoxycarbanucleosides and their analogs were prepared efficiently by palladium(0)-catalyzed reactions 05T11744 . Base-induced generation of aryl(l,2,3-triazol-lyl)carbenes from l-[(7V-phenylsulfonyl)benzohydrazonoyl)- 

3-triazoles and their ring enlargement to 3-ary 1-1,2,4-triazenes has been published 05H(65)279 . 

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This chapter covers literature published since 1982 early materials are included here only where needed as a basis for describing further developments or where not previously mentioned in CHEC-1 <84CHEC-l(5)669>. The structural types surveyed here include 1,2,3-triazoles, benzotriazoles, their dihydro derivatives and carbocyclic fused compounds. Compounds with heterocyclic fused rings are not included. The nomenclature system was discussed in CHEC-T <84CHEC-I(5)670>. 

Several unique heterocyclic fused-1,2,4-triazole structures have been published. Pyridine amination of 216 with O-mesitylenesulfonylhydroxylamine followed by condensation with various aryl and heterocyclic aldehydes and subsequent cyclization and oxidation gave triazolopyridines 217 <03TL1675>. Triazolopyridines 217 were utilized in the direct conversion to the triazolopyridine amides 218 with methylaluminoxane premixed with amines in a combinatorial library synthesis. A convenient synthesis of novel 4-(l,2,4-triazol-l-yl)-2-pyrazolines and their derivatives has been reported <03SC1449>. A novel triheterocyclic ring system, thieno[2,3-y][l,2,4]triazolo[l,5-a]azepines, has been published <03S1231>. 

New fused tetrazoloazines that have been reported include tetrazolo[5,l-a]isoquinolines,665 tetrazolo[5, l-6]benzothiazoles,666 and tetrazolopyridines.667 Reactions of fused tetrazoloazines, or the azido isomers, that have been reported include hydrolytic cleavage of the pyrimidine ring of tetrazolopyrimidines,66 pyrolysis of 3-azido-pyridazine 2-oxides,66 and photolysis of azido-l,3,5-triazine.670 Dipole moments of 3-azido-1,2,4-triazole derivatives have also been reported.671... 

Ring closure reactions of a 4-hydrazino[l]benzofuro[2,3- /]pyridazine, derived from naturally occurring rotenone, yielded [l]benzofuro[2,3-d]pyridazines fused with 1,2,4-triazole, 1,2,4-triazine, and 1,2,4-triazepine derivatives <01JHC1097>. 

Mercapto-4-amino[l,2,4]triazole can also be transformed to derivatives of the title ring system by 1,3-dioxo reagents. These transformations are summarized in Table 6. In most of these cases, 5,5-dimethylcyclohexane-l,3-dione was used, and, accordingly, this procedure can lead to some cyclohexenyl-fused derivatives. 

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