DTBB-catalysed lithiation of 1,2-bis(phenylsulfanyl)ethene: does 1-lithio-2-phenylsulfanylethene really exist?

The reaction of (Z)- or (E)-1,2-bis(phenylsulfanyl)ethene () with an excess of lithium and a catalytic amount of 4,4′-di-tert-butylbiphenyl (DTBB, 2.5 mol%) in the presence of a carbonyl compound as electrophile (Barbier conditions) in THF at −78 °C leads, after hydrolysis with water at temperatures ranging between −78 °C and rt, to a mixture of the corresponding (Z/E)-unsaturated 1,4-diols , the diastereomers ratio being independent of the stereochemistry of the starting materials. Allylic alcohols are the main by-products, resulting from a lithium–hydrogen exchange on some of the lithiated intermediates along the whole process. A mechanistic explanation for the observed behaviour is given.