Chemistry of bis-spiroacetal systems: Natural products, synthesis and stereochemistry

In recent years a number of compounds containing bis-spiroacetal systems have been isolated from nature. Predominantly of dinoflagellate origin, they have stimulated much synthetic interest due to their potent biological activity and synthetically challenging structural features. Although the chemistry of bicyclic spiroacetals is well understood, that of the tricyclic bis-spiroacetals has been less fully explored. This review describes the strategies employed to construct bis-spiroacetals with particular reference to stereochemical issues associated with the quaternary spirocentres.