Chiral alcohols hydrogen bonding ability

A major advantage that nonenzymic chiral catalysts might have over enzymes, then, is their potential ability to accept substrates of different structures by contrast, an enzyme will select only its substrate from a mixture. Striking examples are the chiral phosphine-rhodium catalysts, which catalyze die hydrogenation of double bonds to produce chiral amino acids (10-12), and the titanium isopropoxide-tartrate complex of Sharpless (11,13,14), which catalyzes the epoxidation of numerous allylic alcohols. Since the enantiomeric purities of the products from these reactions are exceedingly high (>90%), we might conclude... 

A suspension of sodium borohydride is essentially inert to chiral amino alcohols and is unable to reduce ketoxime O-alkyl ethers. On the other hand, when combined with a Lewis acid (e.g., ZrCb), sodium borohydride reacts with chiral amino alcohols with evolution of hydrogen to form a chiral borohydride reagent. This chirally modified borohydride has the ability to reduce the C —N double bond of ketone O-alkyl ethers to give chiral primary amines in 78-95% yield with 43-90% ee34. 

The inversion in alcohol has been attributed to the formation of hemiketals. Considering only the non-reacting solvents, the best correlation was established between the ee and the solvent basicity represented by the H-bond acceptor ability (P). Solvent acidity (a) did not play any significant role. The experimental results are validated by theoretical calculations. Palladium(ll) trifluoroacaetate-catalysed AH of 2-substituted 0 3-toluenesulfonamidoalkyl)indoles in the presence of (7 )-H8-BINAP as the chiral ligand and TsOH as the Brpnsted acid yielded chiral 2,3-disubstituted indolines with up to 91% Nitrobenzene is hydrogenated to aniline almost quantitatively with Pd-MCM-41 (g) catalyst in supercritical carbon dioxide. Experimental and DFT studies showed that a stepwise mechanism is operative. ... 

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