ASYMMETRIC-SYNTHESIS OF DIBENZYLBUTYROLACTONES AND ARYLTETRALIN LIGNAN LACTONES BY TANDEM CONJUGATE ADDITION TO A CHIRAL BUTENOLIDE

Addition of sulfur-stabilised carbanions to (-)-5-(1-menthyloxy)furan- 2(5H)-one followed by reaction with an aromatic aldehyde affords a sho rt synthesis of enantiomerically pure dibenzylbutyrolactone derivative s. Desulfurisation with NaBH4/NiCl2 proceeds in almost quantitative yi eld, and reduction with NaBH4/KOH gives the parent dibenzylbutyrolacto nes including (-)-6-epipodorhizol. These undergo cyclisation with acid to give homochiral aryltetralins including (-)-deoxyisopodophyllotoxi n in high yield.