Biomimetic Synthesis of Biflavanoids

The presence of subsituents in positions orto or peri to the interflavanoid bond increases the activation energy (AGrot.) required for fast rotation, and recording of n.m.r. spectra at considerably elevated temperatures (90 —110° C) is accordingly required in order to simplify those spectra in which duplication and/or broadening of resonances due to dynamic rotational isomerism is evident under ambient conditions (70, 13, 14). 

from coupling constants of heterocyclic protons, from circular dichroism, and from knowledge of the absolute configuration of the 

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