Formation of vinyl sulphides via successive sigmatropic rearrangements of an allylic sulphonium ylide

Abstract

It is shown that the sulphonium ylide (VIII) derived from the bisallylic sulphonium salt bis-(2,3-dimethoxycarbonylprop-2-enyl)methylsulphonium tetrafluoroborate (VII) undergoes a [2,3] sigmatropic rearrangement to produce the diastereoisomers (IX) and (X) of tetramethyl 3-(methylthio)hexa-1,5-diene-1,2,4,5-tetracarboxylate. The stereochemical outcome of the Cope rearrangements of the sulphides (IX) and (X) to (E,E)- and (Z,E)-tetramethyl 6-(methylthio)hexa-1,5-diene-1,2,4,5-tetracarboxylate (XI) and (XII), respectively, is invoked to determine the relative configurations at the chiral centres of (IX) and (X).