Ring-Expansion Protocol: Preparation of Synthetically Versatile Dihydrotropones

A ring-expansion protocol that consisted of the 1,2-addition of various enolate nucleophiles to 6-trimethylsiloxy-2-cyclohexene-1-one (1) and the NaIO(4)-promoted oxidative ring opening of the resulting diols 2, followed by an intramolecular Knoevenagel condensation, furnished versatile dihydrotropones 6. Maintaining Z-configuration in the oxidative ring-opening products 3 is crucial for the success of the ring-expansion strategy. Dihydrotropones 6 are ripe for further elaborations such as oxidation to tropones 8 and Diels-Alder reaction with the Danishefsky's diene 10 to afford polycyclic compounds 12.