Reaction of tropone with 2-mercaptoethanol: 1,2-difunctionalization of cycloheptatrienes with oxygen and sulphur in a fused ring

Abstract

Tropone reacts with excess of 2-mercaptoethanol in refluxing benzene in the presence of toluene-p-sulphonic acid to give a 95 : 5 mixture of 2,3-dihydro-9H-cyclohept[1,2-b]-1,4-oxathiin (8) and 2,3-dihydro-5H-cyclohept-[1,2-b]-1,4-oxathiin (9), respectively, in 30% yield overall. Structures (8) and (9) are supported by (i) hydride abstraction by trityl cation to give 2,3-dihydrocyclohept[1,2-b]-1,4-oxathiinylium tetrafluoroborate (10); (ii) oxidation to 2-(2-hydroxyethylthio)tropone (11) by selenium dioxide; and (iii) by a detailed ¹H n.m.r. study with Eu(fod)₃ as a shift reagent.