Bridged fused systems

The trivalent bridge HC is (still) named metheno- although systematically it would be called methanetriyl. For unsaturated bridges, lo- 

Other multivalent bridges are treated in the same way as the corresponding substituent groups. 

To name ring systems of Table 1 as bridges their name-ending. ..ene is converted into. ..eno. 

Simple monocyclic hydrocarbon bridges are named by attaching the morpheme. ..epi... in front of the corresponding fusion term. 

16H-4a, 12a- [ 1,2] Epicyclopentaazuleno [5,6-b] anthracene Chem. Abstr. uses here ... [ T,2 ] -endo-cyclo... 

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Intermediate heterocyclic ylides may be stabilized by [1,2]- or [2,3]- rearrangements (Scheme 5). The [l,2]-shift may result in expelling an ylide heteroatom from the initially formed ylide (Scheme 6). The 1,3-dipolar cycloaddition of ylides generated by carbene cyclization onto the heteroatom of the C=Z double-bond allows an additional ring to be formed and provides a route to bridged and bridged-fused systems (Scheme 7). 

Intramolecular reactions between donor and acceptor centres in fused ring systems provide a general route to bridged polycyclic systems. The cts-decalone mesylate given below contains two d -centres adjacent to the carbonyl function and one a -centre. Treatment of this compound with base leads to reversible enolate formation, and the C-3 carbanion substitutes the mesylate on C-7 (J. Gauthier, 1967 A. Belanger, 1968). 

Buckminster Fuller was the inventor of self-supporting polygon frameworks, e.g., of pavilions. Synonyms (root)ballene, buckminsterfullerenc( BF ), carbosoccer, soo r(ball)ene, spherene. The proposed bridged-fused ring system and von-Baeyer names and numberings vary. 

Table 6 Examples of Bridge Names tor Fused Systems...

Cis-Trans Isomerism of Fused and Bridged Ring Systems... 

Although most of the fundamental studies of cycl[3.2.2]azines were reported in CHEC(1984) (see Section 12.16.6.3 for leading references), there is continuing interest - synthetic, spectroscopic, and theoretical - in these and their benzo- and dibenzo-fused analogues, all of which may be considered as bridged analogues of [10]-, [14]-, and [18]-annulenes, respectively. The same level of theoretical interest continues to apply to those />m -fused systems with a hypervalent sulfur or selenium at the 5 5 ring junction (Section 12.16.6.6). 

The products of these [4 + 2 + 2]-reactions have a high level of molecular complexity, which has been used to advantage in exploring the conversion of the [4 + 2 + 2]-cycloadducts into commonly encountered ring systems. Zeise s dimer, for example, has been employed to carry out a skeletal rearrangement, as illustrated in Scheme 61, producing fused and bridged bicyclic systems found in several natural product families. 

Intramolecular arylation of alkenes. The intramolecular palladium-catalyzed condensation of aryl halides with an alkene group (Heck arylation5) can actually proceed more readily than the original bimolecular version. These intramolecular cyclizations typically proceed in acetonitrile at room temperature, particularly when catalyzed by Ag2C03, which also inhibits isomerization of the double bond of the product. They can be used to obtain spiro, bridged, and fused systems. Even tetrasubstituted alkenes can participate, with formation of quaternary centers.6... 

Curran s retrosynthetic analysis of fused and bridged polycyclic systems through homolytic disconnections... 

We have already referred to the retrosynthetic analysis of dissonant open chain molecules (see Heading 5.5). In this chapter we will deal with Curran s ideas in connection with fused and bridged polycyclic systems present in many natural products. Emphasis on cyclisations leading to 5-membered rings is maintained because ... 

Cyclization reactions in systems with restricted mobility (most notably ring systems) to form either fused or bridged ring systems, in order to determine the relative disposition of substituents, has played an important role in the structural elucidation of many natural products 109. The method is based on the precondition that only one relative configuration will allow ring closure for steric reasons. Two recent examples may serve to illustrate the procedure. 

W2S+W2S] Electrocylizations have been effected for all the fully unsaturated isomers as shown overleaf and for some dihydro derivatives, diazepinones and fused systems (76H(4)1509, 80JCS(P1)1230, 80JCS(Pl)17l8, 76JCS(Pl)362). In some cases such reactions are followed by spontaneous extrusion of the two-atom bridge thus 5H- 1,2-benzodiazepines (88) are... 

Bridging Nomenclature for Use with Fused Systems (IUPAC Rules... 

Chemical Abstracts prefers the sugar terms, especially in the trivial forms however, in some instances, the bicyclo nomenclature is also applied. Surveying the whole original literature, preference is doubtless given to carbohydrate names with frequent use of the trivial isohexide terms, followed by the bridged-systems labeling. The fused systems names are not in vogue. 

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