Synthetical experiments in the chromone group

Summary

A synthesis of tectorigenin (5: 7: 4′-trihydroxy-6-methoxyisoflavone), which occurs as the 7-glucoside (tectoridin) in the rhizome of Iris tectorum, is described. 5: 7-Dihydroxy-6-methoxy-4′-nitroisoflavone (V) was prepared by the action of ethyl orthoformate, pyridine and piperidine on 2: 4: 6-trihydroxy-3-methoxyphenyl 4-nitrobenzyl ketone (IV). The fact that cyclization of the ketone (IV) proceeded in the desired direction to give the isoflavone (V), and not the isomeric 5: 7-dihydroxy-8-methoxy-4′-nitroisoflavone (VII), was shown by methylation, which yielded a substance different from 5: 7: 8-trimethoxy-4′-nitroisoflavone (IX); the latter (IX) was prepared by ethyl orthoformate cyclization of 2: 4-dihydroxy-3: 6-dimethoxyphenyl 4-nitrobenzyl ketone (X) to 7-hydroxy-5: 8-dimethoxy-4′-nitroisoflavone (XI), followed by methylation. The nitroisoflavone (V) was reduced to the amine (VI), which was diazotized and treated with boiling sulphuric acid. 5: 7: 4′-Trihydroxy-6-methoxyisoflavone (I) thus obtained agreed in all its properties with natural tectorigenin.