Metal‐Free Rearrangement of Spirofurooxindoles into Spiropentenoneoxindoles and Indoles: Implications for the Mechanism and Stereochemistry of the Piancatelli Rearrangement

Spirofurooxindoles derived from α-furylcarbinols were rearranged into spirocyclopentenoneoxindoles exclusively or as a mixture of spirocyclopentenoneoxindoles and indoles under different reaction conditions. Along with our previous studies, the stepwise C-Piancatelli rearrangement has been presented for the first time.