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Title: Regiospecific reactions of 1,2,4-triazole
Author: Small, A.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1991
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An in-depth study on the alkylation of the ambident 1,2,4-triazole nucleophile has been made. Typical alkylations of 1,2,4-trizole with alkyl halides or epoxides in the presence of base, yield both the 1-isomer and small quantitities (ca 5-30%) of the 4-isomer. Subsequent research enabled three novel regiospecific 1,2,4-triazole alkylations to be developed. Firstly, it was found that 1-alkyl-1,2,4-triazole derivatives can be obtained regiospecifically upon the reaction of 1,2,4-triazole with alkyl halide at elevated temperatures in the absence of base. The reactions proceed through the intermediacy of a quaternary salt which breaks down in heat to give only the thermodynamically stable 1-isomer. Knowledge of this quaternary salt mechanism enabled a novel isomerisation process to be developed. It was found that on heating with a catalytic quantity of corresponding alkyl or phenacyl halide, 4-alkyl- or 4-phenacyl-1,2,4-triazoles isomerise via quaternary salts to their 1-substituted isomers. The reactions of 1,2,4-triazole with aldehydes offered another regiospecific route to the 1-isomer. The initially obtained hemi-aminal was readily converted to the α-methanesulphonate ester (mesyl) leaving group. Nucleophilic substitution upon this reactive ester then allowed the formation of various α-substituted-1-alkyl-1,2,4-triazole derivatives, many of which are commercially important. The above alkylation via the hemi-aminal was unsuccessful for aromatic aldehydes where hemi-aminal formation does not occur. An alternative process was developed which utilised the reaction of 1-trifluoroacetyl-1,2,4-triazole with aldehyde to form the 1-(1-trifluoroacetoxyalkyl)-1,2,4-triazole derivative. Subsequent nucleophilic substitution of the trifluoroacetoxy group again allowed the formation of various α-substituted-1-alkyl-1,2,4-triazole derivatives.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available