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Bridged Polycyclic Molecules

In the preceding example we did not consider cycloaddition reactions since these would not offer any suitable alternative synthetic pathway. The bicyclic isoquinuclidine derivative given below (G. Biichi, 1963, 1966A) contains only unstrained six-membered rings, and the refro-Diels-Alder transform is obviously the furthest-reaching simplification and the fastest antithetical route to commercial starting materials. Both bridgehead atoms can be introduced in one step. [Pg.212]

The two-bond disconnection (retro-cycloaddition) approach also often works very well if the target molecule contains three-, four-, or five-membered rings (see section 1.13 and 2.5). The following tricyclic aziridine can be transformed by one step into a monocyclic amine (W, Nagata, 1968). In synthesis one would have to convert the amine into a nitrene, which-would add spontaneously to a C—C double bond in the vicinity. [Pg.212]


There are many examples of polycyclic molecules and bridged molecules that have one or more double bonds. There is flattening of the ring containing the C==C... [Pg.187]

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 ... [Pg.204]

There are many examples of polycyclic molecules and bridged molecules that have one or more double bonds. There is flattening of the ring containing the C=C unit, and this can have a significant effect on the molecule. Norbomene (bicyclo[2.2. l]hept-2-ene 134) is a simple example and it has been calculated that it contains a distorted... [Pg.228]

Once the molecule is designed on a symbolic level, then the 3D structures of the conformational surface are directly constructed by using the 3D coordinate representations of the symbolic models, which are also coded in the template library. Cohen s procedure and related ones, however, are limited by the size and the nature of the sets of templates and assembly rules. The latter are not large enough to provide 3D building for complicated molecules such as bridged and polycyclic systems. For example, it is known that Cohen s script system often fails in generating 3D models of polycyclic molecules with more than three cycles. [Pg.51]

Rhodium Catalysts. In the early stage of developing rhodium catalysis for intramolecular cyclopropanation, Rh2(OAc>4 was widely used in the construction of bridged or fused polycyclic molecules. For instance, it was used as a catalyst to obtain a tricyclic ketone used as an intermediate of eucalyptol in good... [Pg.892]

By combining rings in spiro, fused, and bridged fashion, very complex polycyclic molecules can be constructed. [Pg.220]

As in the case of acyclic compounds, the level of difficulty of the synthesis of a cyclic compound depends upon whether the molecule is a consonant or a dissonant system. However, some additional difficulties may be encountered in molecules with medium-sized rings as well as in polycyclic bridged compounds, which are treated in the next Chapter. On the other hand, as we have seen in Heading 4.3, even simple monofunctionalised cyclic molecules may require a FGA operation before bond disconnection of the cyclic network at the ipso-, a- or 13-positions can be effected. [Pg.158]

The conformational kinetic control of the chiral centres present in a molecule may be exemplified by the rran -diaxial opening of an epoxide i rf a polycyclic system [7]. In this case, the less stable conformation is also "frozen" by forming an auxiliary lactone bridge, which reverses temporarily the conformations of the rings and the substituents. [Pg.223]

The program also allows you to see the bridgeheads (for polycyclic bridge systems), core bonds and strategic bonds of the active molecule. You must enter the appropriate menus "See bridgehead sites," "See core bonds," and "See strategic bonds" Process menu). Examples of the application of these options to the porantherine molecule are shown ... [Pg.466]


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Bridged polycycles

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