Assymetric synthesis

Cationic ring-opening polymerization of optically active 4-methylOXL and subsequent hydrolysis resulted in optically active polypropyleneimine36). The optically active polyethyleneimine was effective in the assymetric synthesis of cyanohydrins37). 

The selective catalytic hydrogenation of exocyclic a,/3-unsaturated ketones was successfully utilized in the assymetric synthesis process of the chiral building blocks, a-hydroxy acids. The influence of the catalyst support, solvent and additives in the selective 1,4-reduction was studied in a series of exocyclic enone systems (Scheme The best conditions for the selective reduction of the exocyclic double bond were obtained in an apolar solvent like toluene over a range of Pd-supported catalysts (Pd black, Pd/Ti02, Pd/Al203, Pd/SiOa, Pd/C). The usage of polar solvents like methanol and DMF decreased the selectivity dramatically but addition of triethyl amine, pyridine or potassium acetate to the reaction mixtures revert this result successfully. 

Scheme 16 An example of synthesis and application of chiral metal clusters in assymetric PKRs...

In August 1911 I visited Werner for the first time. On the spot he suggested that I study the synthesis and resolution of diaminediethylene-diamine cobaltic salts (Co(NH3)2en2)X3. Such assymetric molecular complexes had not yet been studied. I solved this problem after one year, and it was published jointly with Werner in Berichte der Deutschen... 

The assymetric Strecker reaction of diverse imines, including aldimines as well as ketoimines, with HCN or TMSCN provides a direct access to various unnatural and natural amino acids in high enantiomeric excesses, using soluble or resin-linked non-metal Schiff bases the corresponding chiral catalysts are obtained and optimized by parallel combinatorial library synthesis [93]. A rather general asymmetric Strecker-type synthesis of various imines and a, 9-unsaturated derivatives is catalyzed by chiral bifunctional Lewis acid-Lewis base aluminum-containing complexes [94]. When chiral (salen)Al(III) complexes are employed for the hydrocyanation of aromatic substituted imines, excellent yields and enatio-selectivities are obtained [94]. 

Gao C, Yan D, (2011) Synthesis of hyperbranched polymers via polymerization of assymetric monomer Pairs. In Yan D, Gao C, Frey H (eds) Hyperbranched polymers, chapter 4. John Wiley and Sons, Hoboken... 

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