3-Bromo-4-methylbicyclo[6.3.0]undecane-2,6-dione, (I), 5-bromo-4-methylbicyclo[6.3.0]undecane-2,6-dione, (II), 3,5-dibromo-4-methylbicyclo[6.3.0]undecane-2,6-dione, (III), and 1,7-dibromo-4-methylbicyclo[6.3.0]undecane-2,6-dione, (IV)

The structures of the four title compounds, C₁₂H₁₇BrO₂, (I), C₁₂H₁₇BrO₂, (II), C₁₂H₁₆Br₂O₂, (III), and C₁₂H₁₆Br₂O₂, (IV), which were obtained from the bromination of trans-4-methylbicyclo[6.3.0]undecane-2,6-dione, have been determined. The eight-membered rings in compounds (I)-(IV) take the boat-chair form.

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