Bridged bicyclo ring system

Bridged Hydrocarbon Ring Systems. These compounds are named by prefixing the parent ring with bicyclo, tncyclo, etc.,orin some complex... 

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... 

Another common ring system is the norbornane, or bicyclo[2.2.1.)heptane, structure. Like decalin, norbornane is a bicycloalkane, so called because two rings would have to be broken open to generate an acyclic structure. Its systematic name, bicyclo[2.2.1 heptane, reflects the fact that the molecule has seven carbons, is bicyclic, and has three "bridges" of 2, 2, and 1 carbon atoms connecting the two bridgehead carbons. 

Intramolecular cycloadditions are among the most efficient methods for the synthesis of fused bicyclic ring systems [30]. From this perspective, the hetisine skeleton encompasses two key retro-cycloaddition key elements. (1) a bridging pyrrolidine ring accessible via a [3+2] azomethine dipolar cycloaddition and (2) a [2.2.2] bicyclo-octane accessible via a [4+2] Diels-Alder carbocyclic cycloaddition (Chart 1.4). While intramolecular [4+2] Diels—Alder cycloadditions to form [2.2.2] bicycle-octane systems have extensive precedence [3+2], azomethine dipolar cycloadditions to form highly fused aza systems are rare [31-33]. The staging of these two operations in sequence is critical to a unified synthetic plan. As the proposed [3+2] dipolar cycloaddition is expected to be the more challenging of the two transformations, it should be conducted in an early phase in the forward synthetic direction. As a result, a retrosynthetic analysis would entail initial consideration of the [4+2] cycloaddition to arrive at the optimal retrosynthetic C-C bond disconnections for this transformation. 

Two possible intramolecular disconnections are available for the [2.2.2] bicyclo-octane ring system (path A and path B, Scheme 1.4). The choice between the initial [4+2] disconnections A and B at first appears inconsequential leading to idealized intermediates of comparable complexity (54 and 57). However, when the [4+2] and [3+2] disconnections are considered in sequence, the difference becomes clear. For path A, retrosynthetic [3+2] disconnection of intermediate 54 leads to the conceptual precursor 56, which embodies a considerable simplification. In contrast, path B reveals a retrosynthetic [3+2] disconnection of intermediate 57 to provide the precursor 59, a considerably less simplified medium-ring bridged macrocycle. Thus, unification of the [3+2]/[4+2] dual cycloaddition strategy, using the staging... 

The chemistry of the bicyclo[2.2.1]heptane ring system, with and without double bonds in the two-carbon bridges, includes many well-known and interesting features which illustrate important stereochemical aspects of some organic reaction mechanisms. Among derivatives of... 

SAMPLE SOLUTION (a) The bicyclo[2.2.1]heptane ring system is one of the most frequently encountered bicyclic structural types. It contains seven carbon atoms, as indicated by the suffix -heptane. The bridging groups contain two, two, and one carbon, respectively. 

Sections VILA and VII.B cover cyclic derivatives which contain the cyclopropane or cyclo-propene unit in a fused ring system according to scheme 9 or 10. Structures of many simple molecules of this class were determined long ago. Some of them will be mentioned here further structural data and references are given in previous reviews. Bridged derivatives of bicyclo[ 1.1.0]butane are discussed in Sections VII. C. 1 and VII. C.2. 

The sesquiterpene (+)-asteriscanolide 1 was first isolated from Asteriscus aquaticus L and characterized by San Feliciano in 1985.1 It has captured the attention of organic chemists mainly because of its uncommon bicyclo[6.3.0]undecane ring system bridged by a butyrolactone fragment. The only prior enantioselective synthesis of 1 has been described by Wender in 1988 featuring an Ni(0)-promoted [4 + 4]-cycloaddition.2 Booker-Milburn and co-workers described the sequential application of intramolecular [2 + 2]-photocycloaddition, Curtius rearrangement, and oxidative fragmentation to produce the 7-desmethyl derivative in 1997.3... 

Many bridged ring systems are named by the von Baeyer system. Von Baeyer names are used mostly for bridged ring systems and occasionally for nonbridged ring systems. Examples of von Baeyer names are bicyclo[3.2.1]octane and tricyclo[7.4.1.0 ]tetradecane. 

Bicyclo denotes two rings and octane denotes a total of eight skeletal atoms in the ring system. [3.2.1] gives the sizes of the three bridges connecting two bridgehead atoms. 

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