Bridged Polycyclic Structures

All bicyclo compounds require three numbers in brackets, tricyclo require four, and so on, and these numbers indicate the number of carbons in the bridges and are used to locate substituents, heteroatoms, and unsaturation. The name of the parent alkane includes the total number of atoms in the bridges and bridgeheads (excluding substituents) and is given after the brackets. The use of prefixes exo, endo, syn, and anti to indicate stereochemical choices is demonstrated generally as shown below. 

If they are traus, there will be two as aud two ps as illustrated. If there is a zero bridge, the positiou of the bridgehead hydrogens is indicated with Greek letters. 

Sometimes a bridgehead substituent will have a higher priority than the smallest bridge thereon. The designation for that bridgehead will indicate the position, a or p, of that higher-priority substituent rather than the bridge as illustrated in the next example. 

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Balaban, A.T. 1973. Chemical graphs. XVIII. Graphs of degrees four or less, isomers of annulenes, and nomenclature of bridged polycyclic structures. Rev. Roum. Chim. 18 635-653. 

A.T. Balaban, "Chemical Graphs. XVIIL Graphs of Degree Four or Less, Isomers of Animlenes, and Nomenclature of Bridged Polycyclic Structures, Rev. Roum. Chim. 18 (1973), 635-53. 

The discussion in this text has presented rules by which it becomes possible to plan syntheses in a reasonable manner. This textbook approach to retrosynthesis stands in contrast to many surprising artistic solutions to synthesis problems. Such solutions may arise by imaginative incorporation of skeletal rearrangements into the plaiming of syntheses [167]. This holds particularly for the synthesis of bridged polycyclic structures. Scheme 6.48 illustrates some examples relating to the synthesis of the quadrone skeleton. 

One of the most interesting aspects of the synthetic problem in the case of longifolene, as also with other bridged polycyclic structures, is the extraordinary variety and diversity of pathways by which the carbon network may be assembled. The importance of exhaustive analysis of the topological properties of the carbon network to define the range of possible precursors from which the desired skeleton can be produced by establishing one or two connecting bonds has been discussed in detail by Corey (Ref. 1). 

As it is a bridged polycyclic system, twistane has "strategic bonds" (bonds 11 and 12 in the conventional numbering adopted in structure l), the disconnection of which leads to rather simple intermediate precursors. 

This review covers nonannelated and annelated eight-membered heterocycles containing one nitrogen. However, it does not include polycyclic structures where nitrogen is the bridgehead atom (1), nor where nonadjacent ring carbons are linked by a bridge (2). 

The isomeric products of the xanthone synthases are the precursors of the majority of plant xanthones (77). This class of secondary metabolites also includes prenylated compounds with high pharmaceutical potential. Gambogic acid is a bridged polycyclic derivative that induces apoptosis independent of the cell cycle through a novel mechanism of caspase activation (22). Rubraxanthone inhibits methicillin-resistant strains of Staphylococcus aureus 23). Its activity compares to that of the antibiotic vancomycin. Bioactive complex benzophenone derivatives may serve as potential lead compounds for designing drugs. Synthetic approaches to these fascinating structures have recently been developed 24,25). 

The organic chemical structural types believed to be characteristic of coals include complex polycyclic aromatic ring systems with connecting bridges and varied oxygen-, sulfur-, and nitrogen-containing functionalities. 

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