Absolute configuration of flavanone–benzofuranone-type biflavonoids and 2-benzyl-2-hydroxybenzofuranones

The O-1–C-2 and C-3–C-4 bonds in the flavanone–benzofuranone-type biflavonoids 1 and 3 are subject to cleavage with sodium cyanoboranuide in trifluoroacetic acid at 0 °C. Conformational information available from computational data in conjunction with 1H NMR and CD spectroscopic observations of the biflavonoids and their degradation products have permitted assignment of absolute configuration to three biflavonoids and the 2-benzyl-2-hydroxy-1-benzofuran-3(2H)-one group of natural products.