Nonconventional Electrophilic Heteroaromatic Substitutions: Ring vs. Side-Chain Reactivity of 2,5-Dimethyl Five-Membered Ring Heterocycles toward Electron-Deficient Aromatics

Article abstract of DOI:10.1021/jo00197a007

4,6-Dinitrobenzofuroxan (DNBF) and 4,6-dinitrobenzofurazan (DNBZ) behave as conventional electrophiles toward 2,5-dimethylpyrrole, 2,5-dimethylthiophene, and 2-methylbenzofuran, adding to the unsubstituted β-carbon to form the corresponding ? adducts in Me2SO.In contrast reactions with 2,5-dimethylfuran result in electrophilic substitution of a methyl group as the only observed process.The mechanism of the latter reaction is discussed with reference to previously reported results.This leads to some reconsideration of current notions regarding the mechanism of electrophilic side-chain reactions of 2,5-dimethyl five-membered ring heterocycles.It is also concluded that DNBF and DNBZ have an electrophilic character of the same order as that of 2,4-dinitrobenzenediazonium cation.