SYNTHESIS OF LICOFLAVONE-A AND 6',6'-DIMETHYLPYRANO(2',3'.7,8)FLAVONE

Licoflavone-A assigned structure of 6-C-prenyl-7,4'-dihydroxyflavone 5 has been synthesized by condensing 5-C-prenyl-2-hydroxy-4-prenyloxyacetophenone 2 with p-prenyloxybenzaldehyde in the presence of alkali. The resulting chalcone 3 on cyclodehydrogenation with DDQ gave 6-C-prenyl-7,4'-diprenyloxyflavone 4 which on boiling with aqueous morpholine afforded the natural product. This synthesis uses, for the first time, protection of phenolic hydroxyls by O-prenylation and DDQ for conversion of chalcone to flavone. 6',6'-Dimethylpyrano (2',3':7,8)navone 8 has been synthesized by the Hlubucek reaction of 7-hydroxyflavone 6 with 2-chloro-2-methyl-3-butyne. © 1979.