Asymmetric synthesis of dibenzylbutyrolactones and aryltetralin lignan lactones by tandem conjugate addition to a chiral butenolide

Abstract

Addition of sulfur-stabilised carbanions to (–)-5-(1-menthyloxy)furan-2(5H)-one followed by reaction with an aromatic aldehyde affords a short synthesis of enantiomerically pure dibenzylbutyrolactone derivatives. Desulfurisation with NaBH₄/NiCl₂ proceeds in almost quantitative yield, and reduction with NaBH₄/KOH gives the parent dibenzylbutyroactones including (–)-6-epi-podorhizol. These undergo cyclisation with acid to give homochiral aryltetralins including (–)-deoxyisopodophyllotoxin in high yield.