Catalytic Hydrogenolysis of 7, 7-Dihalo- and 7-Halobicyclo[4.1.O]heptanes

Abstract

7, 7-Difluro-, 7-chloro-7-fuluoro- and 7-bromo-7-fluorobicyclo[4.1.O]heptanes were hydrogenated over Pd-C in methanol solution at room temperature under the atmospheric pressure or at 80°C under 50 kg/cm' in order to investigate the effect of halogens in the regioselective cleavage of the cyclopropane ring and the effect of amines as additives. The hydrogenolysis of the cyclopropane rings occurred at the C₁-C₅ bond selectively to give ring-enlarged products. The endo-fluoro isomers gave cycloheptane solely while the exo-fluoro isomers gave cycloheptane and fluorocycloheptane. The addition of amines retarded the cleavage of the ring but accelerated the hydrogenolysis of the C-Br bond. The hydrogenation of 7fluoro-, 7-chloro- and 7-bromobicyclo[4.1.O]heptane was investigated under the same conditions. The endo-isomers of 7-fluoro and 7-chloro derivatives were hydrogenolyzed at the C₁-C₆ bond to give cycloheptane but the exo-isomers resisted to the hydrogenolysis. On the other hand, the endo-7-bromo derivative was cleaved at the C₁-C₆ bond accompanied by the cleavage of the C-Br bond and the exo-7-bromo derivative was cleaved at the C-Br bond preferentially accompanied by the cleavage of the C₁-C₇ bond.