Organocatalysis chiral bifunctional catalyst

Finally in Chapters 11-13, some of the more recent discoveries that have led to a renaissance in the field of organocatalysis are described. Included in this section are the development of chiral Brdnsted acids and Lewis acidic metals bearing the conjugate base of the Bronsted acids as the ligands and the chiral bifunctional acid-base catalysts. 

Keywords Asymmetric organocatalysis Bifunctional catalyst Brpnsted base Chiral scaffold Cinchona akaloid Cyclohexane-diamine Guanidine... 

Another important class of covalent catalysis is carried ont by chiral iV-heterocyclic carbenes [15] that react with carbonyl componnds forming chiral acyl anion eqniva-lents whose reaction with the corresponding electrophile complete the catalytic cycle (F, Fig. 2.2). Finally, it is worthy to mention the ability of certain bifnnctional organo-catalysts to perform simultaneous activation of the nncleophile and the electrophile. The nse of bifunctional organocatalysis has been shown to be very snccessfnl in conjngate additions. 

Although boron is a metalloid, one can nonetheless include boron-derived compounds in a book on organocatalysis as not being transition metal containing catalysts Planar chiral boronic acids have been employed as amide couphng catalysts, actually as bifunctional Lewis acid/base activators. Whiting s [51] group reported the preparation [52] of two amino-boronic ferrocenes (see Scheme 8.17). Their use... 

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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