Tele- versus normal substitution in the reaction of 1,4-dialkyl-2,3-dinitronaphthalenes with sodium arenethiolates in dmso

Abstract

1,4-Dimethyl-2,3-dinitronaphthalene ( 1) reacts with sodium arenethiolates in DMSO to give 2-arylthio-1, 4-dimethyl-3-nitronaphthalene ( 3) [normal substitution product (NSP)] and 1-arylthiomethyl-4-methyl-3-nitronaphthalene ( 5) [ tele-substitution product (TSP)]. The percentage of TSP is found to increase with the enhancement of the reaction temperature, the presence of electron-withdrawing substituents in the arenethiolate; the increase of steric hindrance in the nucleophile, and the substitution of two Et for two Me groups in 1. A mechanism, involving a partial tautomerization of 1 into 2,3-dinitro-4-methyl-1-methylene-1,2-dihydronaphthalene ( 7) followed by attack of the nucleophile on this tautomeric form, is suggested to account for the formation of TSP. The analogous reactions on 1,4-dimethyl-2,3-dinitrobenzene and 5,8-dimethyl- and 5,8-diethyl-6,7-dinitro-1,2,3,4-tetrahydronaphthalene yield only NSPs. Some double bonds localization together with steric compression in the congested naphthalene derivative are suggested to play an important role in driving the reaction along the tele-substitution pathway.