Organocatalysts multifunctional

Cinchona alkaloids are readily available natural chiral compounds and have a long history to be utilized as organocatalysts in asymmetric catalysis [3, 4]. They are multifunctional, tunable, and more importantly, they could promote a diversity of reactions through different catalytic mechanisms, which make them privileged catalysts in organocatalysis. In this chapter, the applications of cinchona alkaloids and their derivatives for asymmetric cydoaddition reactions after 2000, especially for the construction of a variety of five- and six-membered cyclic compounds, are discussed. 

As discussed above, the vast synthetic potential of cinchona alkaloids and their derivatives in the asymmetric cycloadditions has been well demonstrated over the past few years. Cinchona-based organocatalysts possess diverse chiral skeletons and are multifunctional. There is no doubt that the further development of cinchona-based organocatalysts and their catalyzed cycloaddition reactions will continue to provide exciting results in the near future. 

Up to now we have grouped organocatalysts according to their reported essential mode of action. In many instances, however, this is an oversimplification and the mechanisms involved are more complex. In many instances, in particular when enantioselective transformations are implicated, organocatalysts behave as multifunctional molecules. This is clearly suggested, for instance, by the significant... 

Yamaguchi s pioneering report on asymmetric Michael addition of nitromethane to cyclic ketones catalyzed by proline rubidium salt [58], Hanessian and Pham [59] developed the first organocatalytic system for such a reaction where proline and trans-2,5 -dimethy Ipiperazine 64 additive were used as the catalyst. Later on, with the same additive, improved selectivities were obtained when using pyrrolidine-tetrazole 61 [60] and tra i-4,5-methano-L-proline 62 [61] as the organocatalyst. In 2008, multifunctional primary amine 63 [62] was also proved to be effective catalyst for such a reaction (Scheme 5.31). 

Recently, Chen, Jorgensen, and coworkers discovered a novel activation mode by the condensation of chiral amines with polyenals 37 to generate reactive trien-amine intermediates J that can participate in asymmetric Diels-Alder reactions with different classes of dienophiles (Scheme 38.12) to afford cycloadducts 38 [20]. With the use of chiral diarylprolinol silyl ether 40 as organocatalysts, various spi-rocyclic oxindoles 41 and multifunctional cyclohexenes 43 can be obtained in high... 

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