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1,2,3-Triazoles produced from 5-Substituted N-Methoxytriazolium Salts

Five reactions, two of which are new, have been observed when 5-substituted 1-methoxy-2-phenyltriazolium salts react with nucleophiles: (i) addition to C-4 with elimination of methanol to give unsymmetrically 4,5-disubstituted triazoles; (ii) displacement of the 5-substituent followed by secondary reactions to give a symmetrically 4,5-disubstituted triazole, a 5-substituted triazole N-oxide, a 4-substituted triazole, or a disubstituted benzeneazoacetonitrile; (iii) deprotonation of the N-methoxy-group with elimination of formaldehyde; (iv) demethylation; (v) abstraction of an α-proton from a 5-alkyl group followed by nucleophilic addition and elimination of methanol to give an α-substituted 5-alkyltriazole.The reactions are of synthetic potential as a means of introducing one or two substituents in the 1,2,3-triazole system.

Electrophilic and Nucleophilic Substitution in the Triazole N-Oxides and N-Methoxytriazolium Salts: Preparation of Substituted 1,2,3-Triazoles

2-Phenyltriazole 1-oxides are activated at C-5 towards both electrophilic and nucleophilic attack.The N-oxides can be selectively halogenated and, in turn, the halogen replaced by strong nucleophiles.On subsequent deoxygenation, the N-oxides yield halogeno-, methylthio-, and methoxy-triazoles.Methylation produces N-methoxytriazolium salts in which H-5 can be replaced by weak nucleophiles, e.g. fluoride ions.Thus fluoro-, chloro-, hydroxy-, alkoxy-, acyloxy-, amino-, substituted amino-, azido-, nitro-, mercapto-, alkylthio-, acylthio-, and cyano-substituents can be introduced in the triazole nucleus.Alternatively deprotonated N-methoxytriazolium salts react with electrophiles producing substituted triazole N-oxides.The reactions of triazole N-oxides with hydrogen chloride to give chlorotriazoles, and with acetyl chloride to give acetoxytriazoles, are explained.