Bicyclo octanes, disubstituted

In order to obtain good yields from a Weiss reaction sequence, the H+-concentration has to be adjusted properly in the reaction mixture. The reaction is usually carried out in a buffered, weakly acidic or weakly basic solution. By the Weiss reaction simple starting materials are converted into a complex product of defined stereochemistry. There is no simpler procedure for the synthesis of the l,5-c -disubstituted bicyclo[3.3.0]octane skeleton it has for example found application in the synthesis of polyquinanes. ... 

Mehta et al. also studied the facial selectivities of 5,6-exo,eji o-disubstituted bicyclo[2.2.2]octan-2-ones 18 [75, 78]. These systems are related to the 2,3-exo,ex( -disubstituted 7-norbomanones 14, but differ in the direction of the carbonyl n face. Hydride reduction of 5,6-exo,ex( -disubstituted bicyclo[2.2.2] octan-2-ones (18) with NaBH and DIBAL-H and methylation with MeLi were smdied [75, 78],... 

In Charton s work pKa data for 4-X-substituted-bicyclo[2.2.2.]octane-l-carboxylic acids in 50% w/w EtOH-H20 are the basis for primary molecular skeleton, the substituent is somewhat remote from the acidic centre and the geometry for 4-X and 1-COOH closely resembles that for groups in a 1,4-disubstituted benzene)81. However, the pKa value for the vinyl-substituted acid in this solvent was not available, so the 07 value for the vinyl group was calculated by substituting the pKa value for vinylacetic acid in water at 25 °C (4.352) in the regression equation 10 ... 

In the preparative application of [2 + 2]-photocycloadditions of cyclic enones to (substituted) alkenes, two factors concerning product formation are of decisive relevance, namely the regioselectivity and the (overall) rate of conversion. Regarding the regioselectivity in the addition to mono- and 1,1-disubstituted alkenes, Corey had shown that the preferred addition mode of cyclohex-2-enone to isobutene or 1,1-dimethoxyethylene was the one leading to—both cis- and trans-fused—bicyclo[4.2.0]octan-2-ones with the substituents on C(7) [8]. In contrast, in the reaction with acrylonitrile, the alternate orientation was observed to occur preferentially. Similar results were also reported by Cantrell for the photocycloaddition of 3-methyl-cyclohex-2-enone to differently substituted alkenes [14]. No significant differences in the overall rates of product formation for the different alkenes were observed in these studies. In order to explain these observed... 

The external bonds in bicyclo[4.2.0]octan-2-ones can be cleaved both by reductive and oxidative processes, both reactions affording disubstituted cyclohexanones. This is illustrated (Sch. 18) by the SmI2-promoted formation of 3-alkyl-3-ethylcyclohexanones 69 from 6-alkylbicyclo[4.2.0]-octan-2-ones 70 [73], and by the formation of 2-alkyl-3-acylcyclohexanones 71 from 7-trimethylsilyloxybicyclo[4.2.0]octan-2-ones 72 via single electron oxidation [74]. 

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