Reactions of trans-5-palladatricyclo[4.1.0.0(2,4)] heptanes: Stereoselective formation of highly substituted 1,1 '-bi(cyclopropyl) compounds and (3Z)-1,3,5-hexatrienes

The reaction of the racemic trans-5-palladatricyclo[4.1.0.0(2,4)]heptanes w ith hydrogen or NaBH4 led to (1R*,2R*,1'R*,2'R*)-bi(cyclopropyl) compounds in a highly stereoselective reaction. Reactions with halogens, di-benzoyl p eroxide, or cerium(rv) ammonium nitrate (CAN) afforded (3Z)-1,3,5-hexatrien es. The stereoselectivity was also high; the only exception was the reactio n with bromine in dichloro-methane, where small amounts of the correspondin g (3E)-1,3,5-hexatrienes were observed as byproducts. The X-ray structure i nvestigation of one bi(cyclopropyl) compound and one (3Z)-1,3,5-hexatriene proved the stereo-chemical assignments. On the other hand, extensive NMR in vestigations of two asymmetrical derivatives of the (3Z)-1,3,5-hexatrienes did not allow such an assignment of the double-bond geometry because of the spherical molecular shape of the (3Z)-1,3,5-hexatrienes. Both the reaction with hydrogen and the reaction with oxidants probably proceed through Pd-I V intermediates.