Studies toward a synthesis of trilobatin B, a lignan from the liverwort Bazzania trilobata: asymmetric construction of the tetrahydrofuran segment

A novel and stereocontrolled process is described for the asymmetric synthesis of the tetrahydrofuran segment of a 2,3-dicarboxy-6,7-dihydroxy-1-(3′,4′-dihydroxyphenyl)-1,2- dihydronaphthalene mono-ester, trilobatin B, a lignan from the liverwort Bazzania trilobata. The key cis-substituted lactone ring was constructed in a stereoselective manner by Horner-Emmons reaction followed by the subsequent tandem Michael addition and cyclization of two types of lactol intermediates elaborated from natural sources.