Enantioselective Synthesis of Four Natural Homoisoflavonoids

Four naturally occurring sappanin-type homoisoflavonoids were synthesized in optically active form with the stereogenic centers of predefined absolute configuration constructed by using Evans' asymmetric aldol reaction. Analysis of the synthesized compounds not only confirmed the previously assigned planar structures but also was used to determine the absolute configurations of the natural products. Errors in previously reported NMR signals/solvents are also revealed.