Abstract: 1, 6-Dimethylbicyclo [4. I. 0]-4-hepten-3-one-exo-7-dl (941) was stereospecifically synthesized in seven steps from o-xylene. The reaction of LiCu (CH,)> with 941 gave a 48: 52 mixture of the normal conjugate addition product exo-1, 5, 6-trimethylbicyclo [4.1. 0] heptan-3-one-exo-7-d1 (1941) and of the cyclopropane ring opened product 5-(ethyl-/-dl)-4, S-dimethyl-3-cyclohexenone (12-dl). The stereochemistry of the ring-opened product 12- ...