The invention relates to methods for the preparation of an optically inactive and
optically active compounds which are selected from the group consisting of C-3 coupled
biflavonoids and C-3 coupled biflavonoid analogues from a starting material or intermediate which are respectively selected from the group consisting of optically inactive or
optically active flavan-3-ols and
optically active flavan-3-ones, the method comprising the steps of (a) providing an optically inactive or
active compound having a fIavan-3-ol structure or a compound which is a
flavan-3-one, (b) if a compound having a flavan-3-ol structure with a
hydroxy group on the C-3 carbon is selected as starting material, converting the
hydroxy group on the C-3 carbon of the compound having the flavan-3-ol structure to an oxo group to form a flavan-3-one of that compound, (c); providing a compound having a nucleophilic
aromatic moiety, which compound is selected from the group of compounds having a nucleophilic
aromatic moiety and which have
flavonoid base structures and compounds having a nucleophilic
aromatic moiety and which do not have a
flavonoid base structure, (d) contacting the flavan-3-one provided by step (a) or obtained by step (b) with the compound containing the nucleophilic aromatic
moiety in the presence of a Lewis acid; (e) forming a first intermediate compound wherein the oxo group on the C-3 carbon is converted to a
hydroxy group by virtue of
nucleophilic addition when the compound containing the nucleophilic aromatic
moiety is contacted to the C-3 carbon of the flavan-3-one, (f) subjecting the first intermediate compound to
dehydration so as to introduce a
double bond between the C-3 carbon and C-4 carbon of the intermediate compound with the concomitant removal of the hydroxy group from the C-3 carbon to form an optically active flavene compound which is substituted by the nucleophilic aromatic
moiety on the C-3 carbon, (g).