Bridged ring systems stereochemistry

Using stereobonds to imply perspective One exception to the rule above occurs when the stereocentre is part of a bridged ring system. In this case the reentrant bonds are drawn using stereobonds since they are naturally pointing out of the plane of the paper, and the alternative results in ambiguous stereochemistry. 

These examples illustrate both the utility and the limitations of the rearrangement as part of a synthetic strategy. These may be summarized in the following terms. Firstly, there are many powerful methods with well-established regiospecificity that lead to the bridged ring system of defined stereochemistry, for example the Diels-Alder strategy (Scheme 4). 

Roseophilin (273), a deeply red-colored pentacyclic compound isolated from the culture broth of Streptomyces griseoviridis, is a novel antitumor antibiotic. Compound 273 possesses a topologically unique pentacyclic skeleton, consisting of a 13-membered macrocycle incorporated in an ansa-bridged azafulvene, which in turn is linked to a conjugated heterocyclic ring system. The absolute stereochemistry of roseophilin, as depicted in Fig. 9, was unknown until the first total synthesis published by Tius and Harrington in 2001 [125]. All syn-... 

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