Chemical consequences of the intramolecular interaction between a sulphur atom and a methoxycarbonyl group in fluorene systems

Abstract

The intramolecular interaction between a sulphur atom and a methoxycarbonyl group was found to affect their chemical reactivity. The rates of C–S bond cleavage in methyl 9,9-bis(ethylthio) fluorene-x-carboxylate, where x is 1, 2, or 3, with sodium ethanethiolate show that the rate is minimal, though comparable with the others, when x= 1, because of steric effects. In contrast, methyl 9-(ethylthio)fluorene-x-carboxylates, where x is 1, 2, or 3, exhibit the maximum rate when x= 1. The rates of ester exchange in the presence of toluene-p-sulphonic acid indicate that the reaction is accelerated by the presence of two ethylthio groups at the 9-position of methyl fluorene-1-carboxylate but no significant effect is detected if there is only one ethylthio group. The hydrolysis of the thioketal group in 9,9-bis(ethylthio)fluorene is also accelerated by the presence of a 1-methoxycarbonyl group. The implications of these results are discussed with the use of a model compound.