The photoisomerization of the BF 3 , BCl 3 and BBr 3 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•BF 3 and 1•BCl 3 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•BX 3 . It was not possible to establish the primary product distribution, obtained from 1•BBr 3 as further photoisomerization of 2•BBr 3 occurred even at very low degrees of conversion. The mechanisms and synthetic utility of these reactions is discussed.