A study of nuclear prenylation of [beta]-resacetophenone-II: synthesis of bavachalcone, 4'-O-methylbavachalcone and bavachin

Abstract

Reaction of β-resacetophenone with 2-methyl-but-3-en-2-ol in the presence of boron trifluoride-etherate at room temperature is found to yield a mixture of three separable 5-C-prenyl-(40%), 3-C-ptenyl-(25%) and 3,5-di-C-prenyl-(15%) resacetophenones. 5-C-Prenylresacetophenone and its 4-methyl ether have been condensed separately with p-hydroxybenzaldehyde obtaining bavachalcone and 4'-O-methylbavachalcone respectively. The former on cyclization gives the natural flavanone, bavachin. The names given by discoverers to this group of compounds require a change in order to make the relationships easily understandable. The names of the flavanones bavachin and isobavachin are taken as the basis; bavachinin is then 7-O-methylbavachin. Just as isobavalson is related to isobavachin, so the name bavachalcone should appropriately be assigned to the chalcone corresponding to bavachin; it may be expected to occur in this plant and elsewhere. So the chalcone named earlier as "bavachalcone'rd will now be 4-O-methylbavachalcone and it rightly corresponds to 7-O-methylbavachin. We have adopted this change in this paper.