Bicyclo octadiene ring

The reaction can be carried out intramolecularly to produce, in one step, three new rings in moderate yield (Equation (36)).149 It is noteworthy that up to six stereogenic centers could be formed. Additionally, cobalt-catalyzed [4 + 2 + 2]-cycloadditions of bicyclo[2.2.2]octadienes have been reported (Equations (37) and (38)).150... 

V.P. Conticello, D.L. Gin, and R.H. Grubbs, Ring-opening metathesis polymerization of substituted bicyclo[2.2.2]octadienes a new precursor route to poly(p-phenylene vinylene), J. Am. Chem. Soc., 114 9708-9710, 1992. 

The increase in ring size from the norbomadiene-type to bicyclo[2.2.2]octadiene systems appears not to affect the overall reaction outcome. Again the interaction involves... 

Natural products containing six-membered rings are ubiquitous, therefore the following set of target molecules are limited to those containing eight-membered rings that would be accessible via [4+4] cycloadditions. Notably, 1,5-cyclo-octadienes 88 can be converted to bicyclo[3.3.0]octanes 201 transannular electrophilic [124] and radical cyclization (Sch. 44) [125]. 

Dowbenko (1964) has shown that carbon tetrachloride, chloroform and several other compounds react with a s-cis-l,5-cyclo-octadiene by a free-radical transannular 1,5-cyclo-addition to give derivatives of bicyclo-[3,3,0]octane. He suggested that the cyclo-addition may occur by a concerted reaction in which the configuration of the diene is such that the two double bonds lie in close proximity, or alternatively by a step-wise reaction which involves a free-radical addition across the ring. 

Intramolecular coupling between non-conjugated double bonds suitably disposed for transannular reaction has been carried out anodically Both norbornadiene (31) and bicyclo[2.2.2]-2,5-octadiene (32) reacted to yield 35-40% of products containing a cyclopropyl ring ... 

Davidiol D (754) isolated from the roots of Sophora davidii was the first natural instance of a resveratrol pentamer [339]. The pentamers amurensins E (751) and F (752) were isolated from the roots of Vitis amurensis Rupr. with an unsaturated benzofuran ring [216]. Upunoside A (753) isolated from the stem of Upuna borneensis (Dipterocarpaceae) is the first instance of a resveratrol pentamer glucoside, and the aglycon has dibenzo-fused bicyclo[5.3.0]octadiene and two dihydrobenzofuran moieties [223], Fig. (45). 

The cyclopropane ring in dibenzannulated tricyclo[3.3.0.0 ]octa-3,6-diene was opened to give the symmetric bicyclo[3.3.0]octadiene skeleton 18. ... 

Similar stereoselectivities arc observed with nonconjugaled dienes which give bicyclic cyclobu-tanes with trans fusion of the annulated ring. Thus, 1,7-octadiene, treated with the same photochemically activated nickel complexes, gives trans-bicyclo[4.2.0]octane (6) in 21 % yield, after the resulting metallacycle is exposed to air24. 

Pyrolysis of trans-l-ethynyl-2-vinylcyclobutane at 460°C gave a mixture of butadiene and vinylacetylene (36 %X isomeric bicyclo[3,3,0]octadienes (30.5%), 4-ethynylcyclohexene (29%), l-vinyl-l,3-hexadiene (3.5%), and a small amount of styrene.At higher temperatures, styrene was the main product. These products could be accommodated with a mechanism involving initial homolysis of the 1,2-bond of the cyclobutane ring, and fragmentation or recyclization of the resultant biradical. 

Gold(I) catalysis has been reported to convert cyclopentenes to cyclohexadienes and involves ring expansion and a [l,2]-alkynyl shift. It is thought to be initiated by the cleavage of the bridging C-C bond and the proposed allyl-gold cation intermediate is trapped with alcohol to give bicyclo[3.2.1]octadiene and tricyclo[3.2.1.0 ]octane derivatives (Scheme 110). ° ... 

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