Electrophilic Substitutions of 2, 8-Dimethoxy- and 2, 8-Diethyldibenzofurans

Abstract

A few electrophilic substitutions of 2, 8-dimethoxydibenzofuran (DMD) and 2, 8-diethyldibenzofuran (DED) have been carried out. The isomer distributions obtained here have been compared with the electrophilic reactivity order estimated by HMO calculations, 3->1->4positions. Reactions of DMD with 99% HNO₃/Ac₂0 or AcOH, with n-BuONO₂/AlCl₃, and with AcCl or PhCOCl in the presence of Aida gave a mixture of the 1- and 3-substituted isomers in agreement with the estimated order, though the isomer ratios depended on the reaction. Nitrations and benzoylation of DED also gave a mixture, of the 1- and 3-isomers. In contrast, acetylation, propionylation, and isobutyrylation of DED in dichloromethane solution gave only the 3-substituted products. These acylations in nitrobenzene gave the 4acylated products as the major product along with the 3-isomer. A steric hyndrance of the 9-hydrogen and the ethyl group against to the attack of acylinium ion at the 1-position of DED has been considered.