Condition-Controlled Chemoselectivity Switching of Spiro-Epoxy Oxindoles: Access to Spiro-Oxetane Oxindoles

Abstract A condition-controlled switch in chemoselectivity has been achieved in the reaction of spiro-epoxy oxindoles with sulfur ylides. In contrast to the previously observed cyclopropanation pathway, Lewis acid catalysis with tert-BuOK in tert-BuOH at elevated temperature redirects the reaction toward a Corey–Chaykovsky-type ring expansion, affording spiro-2′-oxetane oxindoles in good yields. This transformation provides direct access to oxindoles bearing a strained four-membered oxetane ring at the C3 position, a spirocyclic motif of growing interest in medicinal chemistry.