Medium-ring 3-cycloalkenones with electron-withdrawing substituents at the 3-position have been synthesized and subjected to base-catalyzed isomerizations. In a given ring size in the seven-and eight-membered carbocycles, the substituents studied caused similar shifts in the equilibria toward the 3-cycloalkenones relative to the unsubstituted cases. Steric effects of the substituents are therefore not significant. As the ring size is increased, the preference for the 3-cycloalkenone becomes more pronounced. In the nine-and ten-membered systems, an additional equilibrium involving formation of 4-cycloalkenones appears. Decreased effectiveness of conjugative interactions in endocyclic dienolates and in 2-cycloalkenones with increasing ring size is suggested.
ASJC Scopus subject areas
- Organic Chemistry