N-Vinylation of Imidazole and Benzimidazole with a Paramagnetic Vinyl Bromide

Györgyi Úr,Tamás Kálai,Gergely Gulyás Fekete,Kálmán Hideg

doi:10.3390/m980

Abstract

An N-vinylation of imidazole and benzimidazole with a paramagnetic vinyl bromide was investigated. Among the tested procedures, Pd-catalyzed reaction was the most powerful one. The N-vinylation of 2-aminobenzimidazole with a β-bromo-α,β-unsaturated pyrroline nitroxide aldehyde offered 1,1,3,3-tetramethyl-1H-benzimidazo[1,2-a]pyrrolo[3,4-e]pyrimidin-2(3H)-yloxyl radical and the corresponding non-cyclized Schiff base. The reaction of a β-bromo-α,β-unsaturated pyrroline nitroxide aldehyde with imidazole gave β-imidazo-α,β-unsaturated pyrroline nitroxide aldehyde, which was reduced to the alcohol and converted to an unstable allyl chloride.

Highlights

Nitroxides belong to a group of stable organic radicals, containing the nitroxyl group as a part of aliphatic, aromatic, bicyclic, or heterocyclic scaffolds
The most commonly used nitroxides are piperidine, pyrrolidine, pyrroline, isoindoline, oxazolidine, imidazoline, and imidazolidine nitroxides with a broad range of applications
We have reported Buchwald-Hartwig amidation procedures for nitroxide-condensed lactam and pyrimidine ring constructions [15] starting from β-bromo-α,β-unsaturated pyrroline nitroxide aldehyde

Summary

Introduction

Nitroxides belong to a group of stable organic radicals, containing the nitroxyl group as a part of aliphatic, aromatic, bicyclic, or heterocyclic scaffolds. The most commonly used nitroxides are piperidine, pyrrolidine, pyrroline, isoindoline, oxazolidine, imidazoline, and imidazolidine nitroxides with a broad range of applications They are used as co-oxidants in organic chemistry [1], spin labels on biomolecules [2], as antioxidants and antiproliferative drugs [3,4], mediators of polymerization [5], redox active materials in batteries [6], sensor molecules [7], and as magnetic imaging (MRI) [8] and electron paramagnetic imaging (EPRI) [9] contrast agents, just to name a few examples. We report the extension of the Buchwald-Hartwig cross-coupling for the N-vinylation of imidazoles and benzimidazoles with paramagnetic vinyl bromides

Discussion

Materials and Methods

Conclusions