Synthesis of Pyranoisoflavones from Pyronochalcones: Synthesis of Elongatin and Its Angular Isomer

Article abstract of DOI:10.1246/bcsj.62.826

Elongatin (4',5-dihydroxy-2',5'-dimethoxy-2'',2''-dimethylpyrano<5'',6''-g>isoflavone) was synthesized by an oxidative rearrangement of the corresponding pyronochalcone <6-(1-oxo-3-phenyl-2-propenyl)-4-chromanone> with thallium(III) nitrate and a regioselective reduction of 7-(4-benzoyloxy-2,5-dimethoxyphenyl)-2,3-dihydro-2,2-dimethyl-5-tosyloxy-4H,6H-benzo<1,2-b:5,4-b'>dipyran-4,6-dione with sodium borohydride-palladium chloride, followed by dehydration of the resultant alcohol and hydrolysis.Its angular isomer (4',5-dihydroxy-2',5'-dimethoxy-2'',2''-dimethylpyrano<6'',5''-h>isoflavone) was also synthesized from the corresponding pyronochalcone in a similar manner.