Effective Preparation of Valuable Biologically Active Compounds Employing Catalytic Construction of Polycyclic Ring System

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When various functional groups exist on a polycyclic skeleton, the three-dimensional relationships of the functional groups are restricted and a specific biological activity would be expected due to the rigid conformation. Therefore, the development of an efficient method for the construction of polycyclic ring systems is highly desired, particularly in the field of medicinal chemistry.Cascade reactions are useful methods for the construction of polycyclic skeletons, which are important cores for biological activities. A variety of cascade reactions, carried out under multiple reaction conditions, such as pericyclic, polar, radical, and transition metal-catalyzed reaction conditions, have been investigated.Culmorin, pentalenene, pentalenic acid, deoxypentalenic acid, longiborneol, cedrandiol, 8, 14-cedranoxide, atisirene, atisine, and estrane-type steroids were synthesized via the intramolecular double Michael reaction. Aza double Michael reaction was applied to the syntheses of tylophorine, epilupinine, tacamonine, and paroxetine. Furthermore, sequential Michael and aldol reactions were performed in both intramolecular and intermolecular manners, leading to the formation of polycyclic compounds fused to a four-membered ring. Synthesis of paesslerin A utilizing a multicomponent cascade reaction revealed an error in the proposed structure.Unique cascade reactions, performed under radical and transition metal-catalyzed reaction conditions, were also investigated. With the combination of several cascade reactions, serofendic acids and methyl 7β-hydroxykaurenoate, both of which have neuroprotective activity, were synthesized in a selective manner.