Efficient Synthesis of 4‐Hydroxycyclopentenones: Dysprosium(III) Triflate Catalyzed Piancatelli Rearrangement.

4-Hydroxycyclopentenones represent a privileged scaffold in chemical synthesis. A dysprosium(III) trifluoromethanesulfonate catalyzed rearrangement of furylcarbinols to 4-hydroxycyclopentenones via a 4π electrocyclization has been developed. The catalytic Piancatelli rearrangement affords a single trans-diastereomer from both aryl and alkyl substituted furylcarbinols.