Electrophilic and nucleophilic substitution in the triazole N-oxides and N-methoxytriazolium salts: preparation of substituted 1,2,3-triazoles

Abstract

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.