Dimerization of Allylbenzenes into Cyclolignans by a Metathesis-Oxidation Sequence

Allylbenzenes form dimeric cyclolignans in a two-step, one-pot sequence involving Ru-catalyzed olefin metathesis followed by iron- or acid-catalyzed oxidation with DDQ. Alternatively, performing the oxidation step under wet conditions leads to benzyl styryl ketones as the major products. The mechanistic investigation suggests that the oxidation process relies on the combination of single electron transfer, hydrogen atom transfer, and proton transfer steps. The developed metathesis-oxidation sequence enables a straightforward and scalable preparation of arylnaphthalene and aryltetralin types of cyclolignans, such as oleralignan B and its derivatives.