Asymmetric rhodium-catalyzed addition of thiols to allenes: synthesis of branched allylic thioethers and sulfones.

A highly regio- and enantioselective hydrothiolation of terminal allenes, a reaction which fulfills the criteria of atom economy, is reported. Applying two chiral rhodium catalyst systems, a wide variety of thiols and allenes could be coupled. Oxidation gave access to the corresponding allylic sulfones in essentially enantiomerically pure form. The reaction tolerates a variety of functional groups and labeling experiments gave first insights into the reaction mechanism of this new methodology.