Construction of the cyclopenta[1,3]cyclopropa[1,2-b]naphthalene system in a one-pot domino reactions

Base treatment of the angucycline oligoketide precursor 6 unexpectedly affo rded the spirocyclization product 7. An additional step in the domino cycli zation process was observed starting from the quinoid bromo diketone 3b to yield stereospecifically the condensed tetracycle 8 with the benzo-annelate d skeleton of the cubebol-type sesquiterpenes. The structure of 8 was confi rmed by X-ray structure analysis. Further extension of the domino sequence by reaction of the dibromide 10 with acetonedicarboxylic eater II gave the cyclization/condensation products 12, 13, or 14, depending on the reaction conditions.