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

Article abstract of DOI:10.1016/j.tet.2005.07.056

The reaction of (Z)- or (E)-1,2-bis(phenylsulfanyl)ethene (1) 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 2, the diastereomers ratio being independent of the stereochemistry of the starting materials. Allylic alcohols 3 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.