1.2.3- Triazolium salts, 1,2-disubstituted

Thiadiazole with MeaO BF gives the diquaternary salt (95) diquaternary salts are also known in the 1,2,4-triazole series. 1,3-Disubstituted 1,2,4-triazolium salts can be further alkylated to diquaternary derivatives. 

Disubstituted triazolium salts are prepared from alkyl or aryl hydrazines via an oxadiazolium salt 28 (Scheme 16). Addition of a chiral amine on this salt resulted in a ring opening - ring closure reaction affording the triazolium salts 29. 

Rovis and co-workers further extended the scope of the reaction to the enantio-and diastereoselective cyclisation of a,P-disubstituted Michael acceptors 137. The high diastereoselectivity of the process relies on selective protonation of the resnltant enolate after conjugate addition. It was found that HMDS (formed dnring deprotonation of the triazolium salt pre-catalyst) was detrimental to the... 

Oxidation of a-diketone hydrazone imines with cuprammonium salts gives 2/f-triazoles. With substituted imines (using W-bromosuccin-imide as oxidant) 1,2-disubstituted triazolium salts are obtained (Scheme 33). ... 

With N-1-substituted -triazoles, 1,3-disubstituted triazolium salts... 

Af, A -Disubstituted hydrazones rearrange smoothly to furnish 1,2,3-triazolium salts, hydrazides give triazolones (35), and amidrazones (36) afford (37) (Scheme 12) <91KGS822,92KGS969). 

The meso-ionic l,2,4-triazol-3-ones (200) are stable to acid, but alkaline hydrolysis gives 1,4-disubstituted semicarbazides. They do not normally participate in 1,3-dipolar cycloadditions, but the meso-ionic 1,4-diphenyl-l,2,4-triazol-3-one (200, R = R = Ph, R = H) and benzyne yielded 2-phenylindazole. 1,2,4-Triazolium salts (211) are formed with triethyloxonium tetrafluoroborate. Reduction of the meso-ionic compound 200, R = Me, R = R = Ph, with lithium aluminum hydride gives the triazolidinone 212. ... 

Scheme 61, yielded thiazole 200 as the major product, along with minor amounts of carbinol 201 [152]. On the other hand, treatment of the imine formed from 199 and p-methoxyphenylamine with catalytic tetrabutylammonium cyanide, produced suc-cinimide derivative 202. In both cases, the process is initiated by nucleophilic attack to the carbaldehyde C=0 (or azomethine s C=N) group, which is followed up by an anionic rearrangement. A variation of the above process using as catalysts /V-heterocyclic carbenes (NHC) derived from base treatment of azolium, imidazo-lium, or triazolium salts, has also been developed to access gem-disubstituted succinimides [153, 154]. Unfortunately, an attempt of kinetic resolution of racemic 4-formyl (3-lactams by using chiral NHC resulted in moderate selectivities only [154]. 

The difference in activation of halogen at the 4- and 5-position is much larger than in 1,3-disubstituted 1,2,3-triazolium salts (1988BSB573) and is useful for the regioselective introduction of nucleophiles in 1,2,3-triazoles. 

This section deals with the chemistry of 5-substituted 1,2,3,4-thiatriazoles (1), A2- (2) and A3-l,2,3,4-thiatriazolines (3) (4,5- and 2,5-dihydro-l,2,3,4-thiatriazoles, respectively), 3,5-disubstituted 1,2,3,4-oxa- (4) and -thia-triazolium salts (5) and the novel 1,2,3,4-selenatriazoles (6). This last group has a close chemical resemblance to 1,2,3,4-thiatriazoles. 5-Substituted 1,2,3,4-oxatriazoles have not been isolated. In contrast to the 5-substituted... 

Urazoles 202 were easily converted to their corresponding triazolinediones 203 with silica sulfuric acid and sodium nitrite <03SC833>. 3-Phenylthio-1,2,4-triazoles 204 were alkylated to their triazolium salts 205, which under aqueous basic conditions provided 2,4-disubstituted-l,2,4-triazol-3-ones 206 <03H(60)351>. 

Substituted thiazolo[3,2-c][l,2,3]triazoles (50) react with alkyl halides at 2-N affording the corresponding quaternary 2,3-disubstituted thiazolo[3,2-c][l,2,3]triazolium salts (52) (Equation (4)) <91X2851, <94H2017>. 

Shortly thereafter, the Bode group reported the remarkable finding that a similar cyclopentene formation catalyzed by a chiral triazolium salt led to the formation of cis-disubstituted cyclopentenes in good yield and with... 

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