Bridgehead bicyclo nonanes with

The l3C, DEPT-135, and DEPT-90 experiments showed a nonconjugated ketone at 5 209.8, flanked by two quaternary bridgehead carbons (5 59.5 and 68.9), an enolized 1,3-diketone [5 117.9 and 194.5 (2x)], a methylene carbon at 5 42.7, and a methine carbon at 5 47.0 which, together with a quaternary carbon at 5 50.4, established the bicyclo[3.3.1]nonane system in xanthochymol (138). The DEPT-135 showed five sp2 methines and six aliphatic methylenes. The number of methine carbons, five sp2 and two aliphatic, was confirmed by a DEPT-90 experiment. The carbon and DEPT experiments further indirectly confirmed the AMX 3-spin system with l3C quaternary aromatic resonances at 5 128.7, 145.3, and 151.4, and the number of prenyl groups as four (two isopent-2-enyl and two isopent-3-enyl groups). 

A synthesis of tricyclo[3,3,3,0 ]undec-2(6)-ene (252), starting from bicyclo[3,2,2]-nonane-6,8-dione, has been described (252) is reactive and was characterized as its Diels-Alder adduct with diphenylisobenzofuran. In the absence of the diene, the production of (252) leads to the formation of the dimer (253), which is clearly the result of the ene addition of two molecules of the bridgehead olefin. 

Substantial data are available for both the cis- and the trans-fused systems. Exo and endo are used for cis-bicyclo[4.3.0]nonanes, as well as for those having a double bond emanating from a bridgehead (though these are listed with the trans-fused compounds). For the trans-fused comounds, the orientation of the hydrogen on C-1 is defined as alpha (A), while beta (B) refers to the orientation of the C-6 hydrogen. Groups are then defined based on the side of the molecule that they are on. 

Both the cis- and trans-fused compounds represent valuable models for other, cyclohexane-based systems. Stereochemistry in the cis compounds is specified simply as exo and endo, while the orientations of groups in the trans series and those with a bridgehead double bond are specified based on their orientation as axial (A) or equatorial (E) substituents. Note that this system is distinct from that used with the trans-fused bicyclo[4.3.0]nonanes but it was felt that this inconsistency would be more than repaid here by the ease with which the spatial orientation of the groups could be visualized. Corresponding use of axial and equatorial for the [4.3.0]nonanes would have required new definitions of orientations of substituents on the five-membered ring. 

Bridgehead functionalization. C1O3 added in small portions with cooling below 35° during 1 hr. to a soln. of bicyclo[3.3.1]nonane in acetic acid-acetic anhydride, and stirred 6 hrs. at room temp. l-bicyclo[3.3.1]nonanol. Y 40-50%. F. e. s. R. C. Bingham and P. v. R. Schleyer, J. Org. Chem. 36, 1198 (1971). 

---