摘要:
A concise tropolone annulation applicable to rubrolone C ring introduction is detailed based on the room-temperature [4 + 2] cycloaddition reaction of the cyclopropenone ketal 10 with the oxygenated diene 9. Conversion of the sensitive [4 + 2] cycloadduct 11 to the norcaradiene 18, low temperature electrocyclic rearrangement to a cycloheptatrienone ketal, and tautomerization to 12 provided a fully oxygenated tropolone analogous to that found in rubrolone.