Tricyclo undecane group

Under the same conditions, tricyclo[5.3.1.0]undecanes are accessible from 5-sub-stituted 2-cyclohexen-l-one as 2-370 with a shorter tether by one CH2-group. Recently, another Michael/Michael/aldol transformation was employed by Paulsen and coworkers to obtain access to the central aromatic core of compounds as 2-376 (Scheme 2.89) [206]. It is of value that such products are thought to act as cholesterol ester transfer protein (CETP) inhibitors, and the application of these drugs should prevent reduction of the HDL-cholesterol level and therefore reduce the risk of coronary heart diseases [207]. 

The first naturally occurring tricyclo[6.3.0.0 ]undecane to be synthesized was isocomene (757), a colorless oily sesquiterpene hydrocarbon isolated from several plant sources. In 1979, Paquette and Han reported an efficient, stereospecific approach starting with a preformed bicyclic enone, to which the third five-membered ring was appended with proper attention to stereochemistry and position of unsaturation (Scheme LXXX) The pivotal steps are seen to be the stannic chloride-induced cyclization of aldehyde 732 and the conjugate addition of lithium dimethylcuprate to 733 which sets the stereochemistry of the last methyl group. 

Enchaining radical cyclizations steps to provide polycyclic compounds is the simplest approach. Because the 5-exo cychzation is the most straightforward mode of cychzation, polyquinanes have been the object of many studies [20]. Roimd-trip strategies as defined by Haney and Curran [21], from a vinyl radical such as 8 have been developed by Takasu et al. [22] and revisited by Tripp et al. (Scheme 3) [23]. Mixtures of diastereomers 9 are obtained from hnear precursor 7. The same group has examined the intramolecular addition of a vinyl radical onto a dienoate to produce [4 -l-1]- or [4 + 2]-annulated compounds [24]. Tandem 5-exo-trig cyclizations have also been shown to yield tricyclo[6.2.1.0 ]undecan-4-one and related polycyclic compounds, using a nickel-catalyzed electroreduction [25]. 

Deprotonation of the dication cij-1,6-dimethyl-l,6-diazoniabicyclo[4.4.0]decane (66) results in products derived from deprotonation at a methyl group, including 1-methyl-l-azonia-6-bicyclo[4.4.1]undecane (67) <84JCS(P2)4ll, 86J0C3169>, and deprotonation of the dication of 6-methyl-l,6-diazoniatricyclo[6.2.2.0 ]dodecane (68) affords the monoion of 1-methyl-l-azonia-6-aza-tricyclo[7.2.1.0 "]dodecane (69) <86JOC3i69>. 

Fused Five-membered Rings.—The c/s,flnri,c/s-tricyclo[6.3.0.0 ]undecane system found in the hirsutane group of sesquiterpenes poses a formidable... 

---