Asymmetric organocatalysts continued

This gives chapter an overview of natural cinchona alkaloids and synthetic derivatives together with examples of their use in asymmetric organocatalysis. In recent years, the emphasis has been on the development of cinchona-based bifunctional catalysts, in particular species with a thiourea moiety. The search for new cinchona-based organocatalysts continues and new derivatives are relentlessly being prepared and applied for specific enantioselective reactions. The design of these new... 

This chapter presented the current state of the art on the applications of cinchona alkaloids and their derivatives as chiral catalysts in the asymmetric nucleophilic addition of prochiral C=0 and C=N bonds. As shown in many of the examples discussed above, the vast synthetic potential of cinchona alkaloids and their derivatives in these reactions has been well demonstrated over the past few years. Cinchona-based organocatalysts possess diverse chiral skeletons and are easily tunable for diverse catalytic reactions through different mechanisms. Therefore, there is no doubt that the further development of cinchona-based organocatalysts for this major reaction type will continue to provide exciting results in the near future. 

As continuation of this work, a planar chiral [2.2]paracyclophane monophosphine has been applied successfully as an organocatalyst in asymmetric allylic amination of MBH adducts. Up to 71 % ee was achieved using (i )-298 as a catalyst (Scheme 3.127). ... 

Asymmetric organocatalysis is one of the most important focal areas in organic synthesis. Extensive efforts have been made for the development of new advantageous chiral organocatalysts applicable in a broad variety of reaction types and their preparation continues to be an important area of synthetic organic research. The impressive number of reports dealing with the use of chiral organocatalysts for asymmetric synthesis is well representative of the success of such catalysts to promote numerous catalytic transformations. 

Organocatalysis Continuing efforts to harness the cooperative activity of bifunctional organocatalysts have led to the examinations of chiral calix[4]arenes containing amino phenol stractures and chiral per-6-amino-P-cyclodextrin in the asymmetric sulfa-Michael reactions to cyclic and acylic enones.The preliminary results indicated that further structural modification would be required to allow more efficient asymmetric catalyst systems. 

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