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Polyring forming processes Polycyclic natural products such as marine toxin gambierol and brevetoxin B (Fig. 1) are intriguing targets in organic synthesis. Polyring forming processes are applied to the total synthesis of these polycyclic molecules.[1] Short sequences of reactions are used in an iterative fashion to build the successive ring structures. Brevetoxin B synthesis Brevetoxin B was first synthesized by K. C. Nicolaou and co-workers in 1995.[2] Along the campaign towards completion of the total synthesis of brevetoxin B, polyring forming processes that consists of iterative epoxide ring-opening reactions was used to construct the ether linkages in one fragment of brevetoxin B (Fig. 2). Polypyran synthesis Mori and co-workers have developed a short iterative strategy for the synthesis of polypyran domains in natural products (Fig. 3).[3] This strategy is also based on epoxide ring-opening reactions and consists totally 6 steps in each iterative cycle. The epoxide is installed using oxiranyl anions generated from reacting epoxide B with strong base such as n-butyllithium. Treating the product C with acid afforded the desired ring product which can be further converted to the next precursor D in four steps. References
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