An Oxy‐Anion Accelerated [1,5]‐ o ‐Quinone Methide Shift During the Nucleophilic Epoxidation of Salicylfulvene

A new facet of nucleophilic fulvene epoxidations has been uncovered. 6‐Arylfulvenes containing an ortho or para hydroxyl group react with basic hydrogen peroxide in an unusual manner; the epoxidation of the fulvene exocyclic double bond is followed by a phenoxide ion‐initiated epoxide ring opening to form an o ‐quinone methide ( o ‐QM) intermediate. The resulting cyclopentadienolate undergoes an unusual oxy‐anion accelerated [1,5]‐sigmatropic o‐QM shift . Computational studies reveal that the activation energy for the [1,5]‐QM‐shift in the cyclopentadienolate intermediate is quite low, signifying the acceleration caused by the oxy‐anion group. Placement of a second hydroxyl group in the 6‐aryl ring at C5 epoxidation via electron donation to the o ‐QM carbon; instead, an intramolecular oxa‐6‐π‐electrocyclization of the o ‐QM intermediate onto the cyclopentadiene is observed.