Bicyclo 3.3.1 nonane systems, reaction

Nucleophilic attack occurs at C(2) of the diene. The 1,3-cyclohexadiene complex 66 is converted to the homoallyl anionic complex 67 by nucleophilic attack, and the 3-alkyl-1-cyclohexene 68 is obtained by protonation. Insertion of CO to 67 generates the acyl complex 69, and its protonation and reductive elimination afford the aldehyde 70 [20]. Reaction of the butadiene complex 56 with an anion derived from ester 71 under CO atmosphere generates the homoallyl complex 72 and then the acyl complex 73 by CO insertion. The cyclopentanone complex 74 is formed by intramolecular insertion of alkene, and the 3-substituted cyclopentanone 75 is obtained by reductive elimination. The intramolecular version, when applied to the 1,3-cyclohexadiene complex 76 bearing an ester chain at C(5), offers a good synthetic route to the bicyclo[3.3.1]nonane system 78 via intermediate 77 [21]. 

Extension of the TMM strategy to intramolecular reactions greatly expands the scope of this BCR methodology. The precursors are readily available, e.g. from the silyl Grignard reagent (123) and w-oxo-a,p-unsaturated substrates (equation 126). Ester- and sulfonyl-substituted bicyclo[3.3.0 octane and bicy-clo[4.3.0]nonane systems are readily constructed in a single step from acyclic material (equations 127, 128). ... 

An interesting example of a reaction involving conformational equilibria in 3,7,9-substituted bicyclo[3.3.1]nonane systems is the base-induced rearrangement of endo-7,7-dimethylbicyclo[3.3.1]nonan-3-ol-9-one (80) into 81. The rearrangement is rationalized by a reversible intramolecular transfer of hydride from the carbinol methine to the carbonyl carbon (60). The reacting centers at C-3 and C-9 are only placed in proximity when the cyclohexanol ring adopts a boat conformation. The resulting ketol 81 is 2.7 kcal mol 1 more stable than its isomer 80 (60). 

Moreover, these conformational regularities are important in the study of reaction mechanisms, including intramolecular migrations, rearrangements, and solvolyses of bicyclo[3.3.1]nonane systems (e.g., see references 60,250, and 251). 

When the target bicycle lacks a suitably placed double bond in a six-membered ring, retrosynthesis starts with FGA (= add double bond) [95, 96, 97, 98]. In bicyclization reactions forming an endoendo bond, the stereochemistry of the reaction has to be monitored (formation of a cis or of a trans fusion of the two rings). With anellated systems of a five- to a six-membered ring the cis juncture is thermodynamically favored. This renders it possible to reach a cis fused bicyclo[4.3.0]nonane system by an epimerization process following the bicyclization reaction [99] (Scheme 6.25). 

The intermediates in the production of (140) were isolated when the formation of ring A was carried out under mild conditions (without boiling with sodium methoxide) which led through the diketone (139) to the epim-eric ketols (141). Rings A and B of these compounds form a bicyclo-[3,3,1]-nonane system [57] originally, these products were assigned the structure of compounds (142) epimeric at C5 with the decalin system of rings A and B [56]. The ratio of the isomers of ketol (141) formed depends on the reaction conditions and, in the first place, on the concentra-... 

Various bicyclic and polycyclic compounds are produced by intramolecular reactions] 127]. In the syntheses of the decalin systems 157 [38] and 158 [128], cis ring Junctions are selectively generated. In the formation of 158, allyhc silyl ether remains intact. A bridged bicyclo[3.3. l]nonane ring 159 was constructed... 

However, in a reaction similar to (26), the bicyclic system shown in reaction (27) is formed and the 1,3,3,5,7-pentamethyl-7-monochloro-l,3,5,7-tetrasila-bicyclo-[3.3.1]-nonane is obtained. 

Transannular hydride shifts, first detected by Cope and coworkers in solvolyses of cyclooctene oxide, have subsequently been found in a number of related systems, e.g. cyclooctadiene monoepoxides, CA o-bicyclo[3.3.1 ]non-2-ene epoxide and l-oxaspiro[2.6]nonane. In general these reactions do not involve skeletal rearrangements, and they will not be discussed in detail. 

Partial desilylation by means of acetic acid gives the corresponding monosilyl products 7 73 and 7 77 and after subsequent intramolecular hydrosilylation 7,7-dimethyl-7-sila-bicyclo[2,2.1]-heptane (174) and 9,9-dimethyl-9-sila-bicyclol4.2.1]-nonane (178), respectively, can be obtained Adamantanone (179) plus system B (using dichlorodimethylsilane instead of 742) gives rise to 2,2-dimethyl-l,3-dioxa-2-sila-4,5-bis(adamanta)dispiro-cyclopentane (750) ° (see also for the alternative compound with two Me2Si moieties. This reaction is affected via UV irradiation). 

A 5-exo reaction can be observed when ,/Tepoxycyclohexenone is treated with tin(lV) chloride. After a regioselective oxirane ring opening, cyclization follows via axial attack of the alkyne group. The terminal vinyl cation is trapped by chloride and the bicyclo[4 3.0]nonan-2-one system 1 is formed stereoselectively in 94% yield5. 

---