Construction of the 3-prenyl-4-oxa-tricyclo[4.3.1.03,7]dec-8-en-2-one core of caged xanthonoid natural products via tandem Wessely oxidation–intramolecular [4+2] cycloaddition

A two-step protocol based on tandem Wessely oxidation/intramolecular Diels–Alder reaction to provide general access to the 3-prenyl-4-oxa-tricyclo[4.3.1.03,7]dec-8-en-2-one core present in the caged Garcinia xanthonoids is demonstrated. These readily accessible tricyclic scaffolds also provide ready entry into a variety of substituted γ-lactones through a photochemical 1,3-acyl shift and decarbonylation.