A facile and practical preparation of 5,7‐dihydroxy‐3‐(4‐nitrophenyl)‐4H‐1‐benzopyran‐4‐one

In spite of the fact that several preparative methods for the synthesis of hydroxylated isoflavones were reported during the past fifty years, none is suitable for the preparation of isoflavones containing 5,7‐dihydroxyl functions. This paper reports a simple, large scale preparation of 5,7‐dihydroxy‐3‐(4‐nitrophenyl)‐4H‐1‐benzopyran‐4‐one (2a) by the condensation of the readily available 4‐nitrobenzyl 2,4,6‐trihydroxyphenyl ketone (1a) and acetic‐formic anhydride in high yields. Similar isoflavones, such as 7‐hydroxy‐3‐(4‐nitrophenyl)‐4H‐1‐benzopyran‐4‐one (2b) can also be obtained in good yields in analogous manner.