The photoisomerization of the BF3, BCl3 and BBr3 complexes of eucarvone (2,6,6-trimethylcyclohepta-2,4-dienone), 1, have been examined. Irradiation of these zwitterions at low temperature gave, after subsequent recovery of decomplexed materials, 3,7,7-trimethylbicyclo-[4.1.0]hept-2-en-4-one, 2, 2-methyl-5-isopropylphenol, 3, 2-methyl-6-isopropylphenol, 4, dehydrocamphor, 5, and carvone, 6. In the case of 1•BF3 and 1•BCl3 the initial photoproducts were shown to be the complexes of 2, 3, 4, and 5. The complexes of 6 were shown to arise from a secondary photoisomerization of 2•BX3. It was not possible to establish the primary product distribution, obtained from 1•BBr3 as further photoisomerization of 2•BBr3 occurred even at very low degrees of conversion. The mechanisms and synthetic utility of these reactions is discussed.

The protonation and formation of the boron trifluoride, trichloride, and tribromide adducts of eucarvone, 1, are described. Examination of the nmr and uv spectra of these systems showed that in each case the proton or Lewis acid was bonded to the carbonyl oxygen of 1. From the various 13C chemical shifts of the Lewis acid adducts of 1, it is concluded that there is significantly less positive charge induced on the dienylic part of these molecules than is found with protonated 1. All of these cationic systems undergo a ring inversion process, the barriers of which are about 1 kcal/mol greater than that reported for the comparable inversion of 1.