A novel synthesis of furocoumarins was developed by a reaction between oxime esters and 4-hydroxycoumarins. The reaction was proposed to undergo radical mechanism mediated by iodine, a cheap and common laboratory reagent. Mechanistic studies showed the key for the successful transformation was the presence of α-iodoimine intermediate which facilitated the ring-closing step. The developed conditions produced good functional group tolerance with a wide range of high-profile furocoumarin product. The potential for this strategy to be applied in other syntheses of heterocyclic compounds is highly achievable.
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