Elongatin, 4', 5-dihydroxy-2', 5'-dimethoxy-2", 2"-dimethylpyrano[5", 6"-g]isoflavone (1), was prepared by the oxidative rearrangement of 6'-acetoxy-2', 4-bis(benzyloxy)-2, 5-dimethoxy-2", 2"-dimethyldihydropyrano[5", 6"-c]chalcone (15) with thallium(III) nitrate and by dehy-drogenation of the resultant linear 4', 5-dihydroxy-2', 5'-dimethoxy-2", 2"-dimethyldihydropyrano-[5", 6"-g]isoflavone (19) with 2, 3-dichloro-5, 6-dicyano-1, 4-benzoquinone. Its angular isomer, 4', 5-dihydroxy-2', 5'-dimethoxy-2", 2"-dimethylpyrano[6", 5"-h]isoflavone (2), was also synthesized from the corresponding chalcone (28) in a similar manner and then converted into toxicarol isoflavone (3).