Cyclic hemithioacetals: analogues of thiosugars with sulphur in the ring

Abstract

Tetrahydro-2-hydroxythiophen, tetrahydro-2-hydroxy(thiopyran), and 2-hydroxythiepan, the first examples of simple cyclic hemithioacetals with sulphur in the ring, have been synthesised. Tautomeric change to the open-chain mercapto-aldehyde occurs much more readily with the seven-than with the five- and the six-membered-ring compounds, but 2-hydroxythiepan, unlike the two lower homologues, does not undergo self-condensation to form a dithioacetal. A modified structure, based on the nuclear magnetic resonance spectrum, is proposed for the dimer of 2,3-dihydrothiophen.