Straightforward Construction of Fused 6,7,5-Tricarbocyclic Systems by Tandem [5 + 2]/[4 + 2] Cycloadditions

One-pot coupling of an intramolecular thermal [5C + 2C] pyrone-alkene cycloaddition to a [4C + 2C] Diels-Alder reaction provides immediate access to 6,7,5-tricarbocyclic systems bearing a 1,4-oxa-bridge in the seven-membered carbocycle. The transformation entails the net formation of four carbon-carbon bonds and creates three new cycles and a minimum of five new stereocenters. Preliminary attempts to open the oxa-bridge by reaction of the adducts with samarium diiodide and trimethylsilyl triflate led to relatively unexpected deoxygenated and aromatized products.