Issue 9, 2018

Design and synthesis of imidazoles linearly connected to carbocyclic and heterocyclic rings via a 1,2,3-triazole linker. Reactivity of β-azolyl enamines towards heteroaromatic azides

Abstract

Herein we report an investigation on the 1,3-dipolar cycloaddition of 5-azido-4-nitroimidazoles to β-azolylenamines and the subsequent transformations of the intermediate 1,2,3-triazolines. 5-Azido-1-methyl-4-nitroimidazoles were combined with β-azolylenamines to form novel imidazoles linearly connected via a 1,2,3-triazole to 1,2,3-thiadiazole and isoxazole rings. On the other hand, in the reaction of β-(imidazol-4-yl)enamine with 1-methyl-4-nitro-5-azidoimidazole, the N,N-dimethyl-N′-(1-methyl-4-nitro-1H-imidazol-5-yl)formimidamide was isolated as a single product. A third type of product, active methylenes containing N-imidazol-5-yl-amidines were obtained in a similar reaction of β-phenylenamine. The factors which govern the outcome of the reactions of these heterocyclic enamines with highly electrophilic imidazolylazides were carefully studied on the basis of DFT calculations with a mPW1K density functional. The formation of various products in the reaction of imidazolyl azides with enamines was rationalized by different transformation pathways of a common 1,2,3-triazoline intermediate. According to the calculations, the two transformation paths, that are different from the path leading to aromatic 1,2,3-triazoles, occur by a stepwise mechanism involving a diazo compound formed by ring-opening of the intermediate 1,2,3-triazolines. Based on literature analysis and theoretical investigations, it is proposed that elimination of an amine from the intermediate 1,2,3-triazolines leading to 1,2,3-triazoles is a base-catalyzed process which takes place via an E1cb mechanism.

Graphical abstract: Design and synthesis of imidazoles linearly connected to carbocyclic and heterocyclic rings via a 1,2,3-triazole linker. Reactivity of β-azolyl enamines towards heteroaromatic azides

Supplementary files

Article information

Article type
Paper
Submitted
02 Nov 2017
Accepted
15 Mar 2018
First published
16 Mar 2018

New J. Chem., 2018,42, 7049-7059

Design and synthesis of imidazoles linearly connected to carbocyclic and heterocyclic rings via a 1,2,3-triazole linker. Reactivity of β-azolyl enamines towards heteroaromatic azides

N. A. Beliaev, M. Z. Shafikov, I. V. Efimov, T. V. Beryozkina, G. Lubec, W. Dehaen and V. A. Bakulev, New J. Chem., 2018, 42, 7049 DOI: 10.1039/C7NJ04243D

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