Radical-nucleophilic substitution (SRN1) reactions. Part 5. Anions of nitroimidazoles in SRN1 and oxidative addition reactions

Abstract

The anions of 2- and 4(5)-nitroimidazole, and 2-methyl-4(5)-nitroimidazole, have been shown to undergo S_RN1 reactions with a range of halogeno-nitroalkanes (which include p-nitrobenzyl chloride, 2-bromo- and 2-chloro-2-nitropropane, 2,2-dinitropropane, 5-bromo-5-nitro-1,3-dioxane, and 2-(bromo- and chloromethyl)-1-methyl-5-nitroimidazole to yield the corresponding N(1)-(nitroalkyl) derivatives. The anions of 2-methyl-4(5)-nitro- and 4(5)-nitro-imidazole, but not the anion of 2-nitroimidazole, underwent oxidative addition to the anion of 2-nitropropane (using potassium ferricyanide and sodium persulphate as oxidants) to yield the corresponding N(1)-(1-methyl-1-nitroethyl) derivatives. The anions of 2-methyl-4-nitro- and 4-nitro-imidazole have also been shown to act as nucleofuges in the S_RN1 reactions between their 1-(1-methyl-1-nitroethyl)-derivatives [Me₂C(NO₂)-X] and anions (which include Me₂CNO₂^– and PhSO₂^–). Steric constraints, kinetic control, and the nature of the intermediate radical anions in the above reactions are discussed.