Asymmetric cyanohydrination

Catalytic Asymmetric Cyanohydrin Synthesis," North. M. Synlett, 1993, 807... 

The best results for the asymmetric cyanohydrination reactions are obtained through biocatalysis, using the readily available enzyme oxynitrilase. This provides cyanohydrins from a number of substances with over 98% ee.146... 

Chemists in Japan have studied an asymmetric cyanohydrin synthesis addition of hydrogen cyanide to benzaldehyde using synthetic peptides as catalysts 75). 

Some insoluble organic macromolecules catalyze polar organic reactions (7). Asymmetric cyanohydrin formation is catalyzed by ami-nated cellulose with 22% optical yield and is an early example of this type of catalysis (8). Polypeptides that create a unique microenvironment through hydrogen bonding catalyze many organic reactions. Poly-[(S)-amino acids] accelerate the epoxidation of chalcone with alkaline... 

M. North, Catalytic asymmetric cyanohydrin synthesis, Synlett 1993, 807-820. 

Asymmetric cyanohydrin synthesis from aldehydes using trimethylsilyl cyanide (TMSCN) has been carried out using a chiral Al(salen) complex-triphenylphosphine Lewis acid-base combination.263... 

The reinvestigation of Breding s asymmetric cyanohydrin synthesis by Prelog during the mid-1950s [33] undoubtedly promoted the concept of asymmetric synthesis, and led the way to more efficient reactions. The advent of synthetically useful levels of enantioselectivity can be dated to the late 1950s, when Pracejus reported that methyl phenyl lcetene could be converted to (—)-a-phenyl methylpro-pionate in 74% ee by using O-acetylquinine as catalyst [34]. 

North M, Usanov DL, Young C (2008) Lewis acid catalyzed asymmetric cyanohydrin synthesis. Chem Rev 108 5146-5226... 

Chemically Catalyzed Asymmetric Cyanohydrin Syntheses Brunei, J.-M. Holmes, I.P. Angew. Chem. Int. Ed. 2004, 43,2752. 

Asymmetric cyanohydrin synthesis remains an important reaction for organocatalysis and many of the catalyst classes discussed in subsequent chapters give highly effective catalysts for this reaction. These include Cinchona alkaloid derivatives, thioureas, guanidines, amine-oxides, diols and diamines. 

In this chapter, remarkable advances in the research devoted to peptide catalysed alcohol esterifications, 1,4-conjugate additions, aldol reactions, Strecker synthesis, asymmetric cyanohydrin synthesis and alkene epoxida-tion are discussed. 

Since the introduction of the first peptide organocatalyst in the 1980s, a considerable number of new peptide frameworks have been developed that are able to effectively catalyse several important transformations including alcohol esterifications, 1,4-conjugate additions, aldol reactions, Strecker synthesis, asymmetric cyanohydrin synthesis and alkene epoxidation are discussed. A few successful examples of solid-supported peptides and reactions in ball milling under solvent-free conditions have been demonstrated. These methods combine the advantages of being economically and environmentally friendly processes. 

Chiral aluminium complexes are widely used as hard chiral Lewis acids due to their cheapness, easy preparation, and high reactivity. Impressive achievements have been obtained in asymmetric cyanohydrin synthesis,... 

Historically, enzyme catalysis has played a highly prominent role, with the first enzyme-catalyzed asymmetric addition of HCN to aldehydes dating back to 1908 [167]. A wide range of both aromatic and aliphatic ketones are suitable substrates and produce cyanohydrins of high optical purity. The most readily available and hence most commonly employed enzyme for asymmetric cyanohydrin formation is (R)-hydroxynitrile lyase isolated from almonds. Recent cloning and over-expression techniques have also made a number of (S)-hydroxynitrile lyases available for organic synthesis [164, 165]. This was utilized in Griengl s synthesis of coriolic acid (255), a natural product that displays calcium ionophoric activity and acts as a prostacyclin mimic (Scheme 2.32) [168]. Thus, an (S)-hydroxynitrile lyase was cloned from rubber trees (Hevea brasiliensis), overexpressed in Pichia pastoris, and used to provide cyanohydrin 254 in 99 % ee. 

---