New insight into the mechanism of hypervalent iodine oxidation of flavanones

Flavanone (1) on oxidation with iodobenzene diacetate (PIDA) in the presence of sulfuric acid in trimethyl orthoformate (TMOF) undergoes a stereospecific ring contraction by an aryl shift to result in trans methyl 2-aryl-2,3-dihydrobenzo[b]furan-3-carboxylate (4a) as a major product. The mechanism of this transformation has been discussed on the basis of NMR, CD and chiral HPLC evidence.