σ-Complex formation and aromatic substitution with thiolates and nitroaryl thioethers

Abstract

U.v. and ¹H n.m.r. evidence for the first gem-bisalkylthio-analogue of a Meisenheimer complex is reported. This substance was obtained, in equilibrium with the 1,3-bisalkylthio-analogue (which preponderates), on mixing ethyl thiopicrate with sodium ethanethiolate in dimethyl sulphoxide. These complexes are ephemeral species, however, because of a remarkable specific substitution of the p-nitro-group by ethanethiolate to give 1,4-bisethylthio-2,6-dinitrobenzene in high yield. In the corresponding reaction of p-tolyl thiopicrate with sodium toluene-p-thiolate. decay of Meisenheimer-type intermediates was too fast to be studied by n.m.r.; besides the product of para-substitution, products of ortho- and of ortho-plus para-substitution were detected.