Facile and Metal-Free Synthesis of Isoflavones Using α-Aryl-β,β-Ditosyloxy Ketones

Abstract

Considering the drawbacks associated with available synthetic methodologies of isoflavones, herein we have reported a metal-free and eco-friendly approach to these natural products. In the present study, we have carried out the synthesis of eight isoflavone derivatives 7a–7h using α-aryl-β,β-ditosyloxy ketone protocol. Initially, we have protected the 2’-hydroxy group of respective chalcone moiety in order to remove its interference under reaction conditions. The protected chalcones were then subjected to 1,2-aryl migration by being treated with hydroxy(tosyloxy)iodobenzene (HTIB) reagent in a non-nucleophilic solvent (CH₂Cl₂). This migration furnished the formation of α-aryl-β,β-ditosyloxy ketones via C−C bond formation from their corresponding chalcones in moderate to good yields (55–82 %). The ambiguity regarding the exact molecular structure of the α-aryl-β,β-ditosyloxy ketones was examined through the single crystal X-ray diffraction data. At last, the synthesis of isoflavones was carried out in moderate to good yields (50–80 %) by performing the reaction of α-aryl-β,β-ditosyloxy ketones with sodium hydroxide in aqueous methanol.