typically of the form Ru[(R)-BINAP]X2, where X is a halogen, leads to one of the enantiomers reacting preferentially faster. The relative free energy for a representative reaction is shown below. As can be seen, the epimerization intermediate is lower in free energy than the transition states for hydrogenation, resulting in rapid racemization and high yields of a single enantiomer of the product. The enantiomers interconvert through their common enol, which is the energetic minimum located between the enantiomers. The shown reaction yields a 93% ee sample of the anti product shown above. Solvent choice appears to have a major influence on the diastereoselectivity, as dichloromethane and methanol both show effectiveness for certain substrates. Noyori and others have also developed newer catalysts which have improved on both ee and diastereomeric ratio (dr). Genêt and coworkers developed SYNPHOS, a BINAP analogue which forms ruthenium complexes, which perform highly selective asymmetric hydrogenations. Enantiopure Ru[SYNPHOS]Br2 was shown to selectively hydrogenate racemic α-amino-β-ketoesters to enantiopure aminoalcohols, as shown below utilizing (R)-SYNPHOS. 1,2-syn amino alcohols were prepared from benzoyl protected amino compounds, whereas anti products were prepared from hydrochloride salts of the amine. Fu acylation modification Recently, Gregory Fu and colleagues reported a modification of their earlier kinetic resolution work to produce an effective dynamic kinetic resolution. Using the ruthenium racemization catalyst shown to the right, and his planar chiral DMAP catalyst, Fu has demonstrated the dynamic kinetic resolution of secondary alcohols yielding up to 99% and 93% ee, as shown below. Work is ongoing to further develop the applications of the widely used DMAP catalyst to dynamic kinetic resolution. Enzymatic dynamic kinetic resolutions A number of enzymatic dynamic kinetic resolutions have been reported. A prime example using PSL effectively resolves racemic acyloins in the presence of triethylamine and vinyl acetate as the acylating agent. As shown below, the product was isolated in 75% yield and 97% ee. Without the presence of the base, regular kinetic resolution occurred, resulting in 45% yield of >99% ee acylated product and 53% of the starting material in 92% ee. Another excellent, though not high-yielding, example is the kinetic resolution of (±)-8-amino-5,6,7,8-tetrahydroquinoline. When exposed to Candida antarctica lipase B (CALB) in toluene and ethyl acetate for 3–24 hours, normal kinetic resolution occurs, resulting in 45% yield of 97% ee of starting material and 45% yield of >97% ee acylated amine product. However, when the reaction is allowed to stir for