Oxidative rearrangements of 2'-hydroxychalcones with lh-l-hydroxy-5-methyl- l,2,3-benziodoxathiole 3,3-dioxide

1H-l-hydroxy-5-methyl-l,2,3-benziodoxathiole 3,3-dioxide (HMBI) has been found to effect the direct conversion of 2'-hydroxychalcones with various B-ring substituents to isoflavones in moderate to good yield (34-83%) in methanol under reflux. The reduced byproduct of HMBI is easily recovered by aqueous extraction and can be recycled and reused with high efficiency. Previous reports of conversions of this type required the use of toxic thallium(III) salts or initial protection of the 2'-hydroxyl group.