226. Ringerweiterung bei der Raction eines 1,3-Cyclohexadions mit Diphenylcyclopropenon

Article abstract of DOI:10.1002/hlca.19850680808

The reaction of 5,5-dimethyl-1,3-cyclohexadione (1) in form of its Na-salt with diphenylcyclopropenone (2) in DMF yielded the bicyclic triketone 3 (58percent), the structure of which was deduced as an enolizable bicyclo<5.2.0>nonane-β-diketone from spectral data and from the following reactions: hydrolysis or methanolysis of 3 cleaved the β-dicarbonyl moiety, thereby opening the 4-membered ring to yield the keto acid 9 or its methyl ester 10.Methylation of 3 afforded the two enol ethers 4 and 5.The ether 5 readily underwent a thermal electrocyclic ring opening to the monocyclic enol ether 8, whereas the ether 4 was thermally stable.The same electrocyclic ring opening (in boiling benzene) converted 3 (probably via 3b) to the monocyclic triketone 7, which was also the hydrolysis product of the ring-opened enol ether 8.By heating 3 in DMF/H2O, a partial (56percent) convertion to the lactone 6 took place.The tricyclic intermediate 11 was found useful to rationalize the ring expansion during the formation of 3 from 1 and 2 as well as the corresponding ring concentration during the convertion of 3 into 6.