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

Abstract

Abstract 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 boronydride–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.