Boraei, Ahmed T. A. and El Ashry, El Sayed H. and Duerkop, Axel (2016) Regioselectivity of the alkylation of S-substituted 1,2,4-triazoles with dihaloalkanes. CHEMISTRY CENTRAL JOURNAL, 10: 22. ISSN 1752-153X,
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Background: 1,2,4-Triazole3-thiones are good scaffolds for preparation of new lead compounds. Their derivatives attracted the attention of chemists due to their wide spectrum of biological activities. Alkylsulfanyl-1,2,4-triazoles have three nucleophilic sites (nitrogens) ready for reaction with electrophiles. Herein, new regioselective isomers were synthesized by the reaction of benzylsulfanyl-1,2,4-triazole with various dihaloalkanes. Regioselectivity was determined by X-ray crystallography and NMR. Results: Coupling of 3-benzylsufanyl-5-(1H-indolyl)-1,2,4-triazole with dibromomethane, 1,2-dichloroethane, 1,3-dibromopropane and di(bromomethyl)quinoxaline was investigated in the presence of potassium carbonate in acetone. In the case of dibromomethane three different bis(triazolyl)methane isomers (-N-1-CH2-N-1-4, -N-1-CH2-N-2-5, -N-2-CH2-N-2-6) were formed in which the two bromide atoms were replaced by two triazole moieties. Among these isomers the reaction was regioselective towards the -N-1-CH2-N-2-5 isomer due to the steric effect. In the case of 1,3-dibromopropane two compounds were obtained due to the alkylation at N(2) to give 2-(3-bromopropyl)-triazole 8 and alkylation at N(1) was followed by cyclization at the indole nitrogen to form a condensed indolo-triazolo-diazepine 10. Upon alkylation of 3-benzylsufanyl-5-(1H-indolyl)-1,2,4-triazole with di(bromomethyl)quinoxaline, two bis(triazolyl-methyl)quinoxaline isomers were separated and characterized as (-N-1-CH2-N-1-) 11 and (-N-2-CH2-N-2-) 12. Single-crystal X-ray diffraction assisted the elucidation and confirmation of the structures of the isomers. An AM1 theoretical study explained the regioselectivity of the alkylation. Conclusions: On reacting S-protected 1,2,4-triazoles with various alkylating agents, only N(1) and N(2) attack the electrophilic carbons. N(2) alkylated isomers are preferentially formed.
| Item Type: | Article |
|---|---|
| Uncontrolled Keywords: | DERIVATIVES; TRANSFORMATIONS; 1,2,4-Triazoles; Alkylation; Regioselectivity; Single-crystal X-ray diffraction |
| Subjects: | 500 Science > 540 Chemistry & allied sciences |
| Divisions: | Chemistry and Pharmacy > Institut für Analytische Chemie, Chemo- und Biosensorik |
| Depositing User: | Dr. Gernot Deinzer |
| Date Deposited: | 05 Apr 2019 07:17 |
| Last Modified: | 05 Apr 2019 07:17 |
| URI: | https://pred.uni-regensburg.de/id/eprint/3057 |
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