Asymmetric Intermolecular Pauson−Khand Reactions of Unstrained Olefins:  The (o-Dimethylamino)phenylsulfinyl Group as an Efficient Chiral Auxiliary

The first asymmetric version of intermolecular Pauson-Khand reactions of unstrained alkenes is described. Generally simple acyclic alkenes exhibit low reactivity and regioselectivity in intermolecular Pauson-Khand reactions; however, o-(dimethylamino)phenyl vinyl sulfoxide reacts under very mild conditions with a wide variety of terminal alkynes in a completely regioselective and highly stereoselective manner. The utility of the resulting 5-sulfinyl-2-cyclopentenones in asymmetric synthesis is illustrated by a very short enantioselective synthesis of the antibiotic (-)-pentenomycin I.