A catalyst system consisting of RuCl2[(S)-tolbinap][(R)-dmapen] and t-C4H9OK in 2-propanol effects asymmetric hydrogenation of arylglyoxal dialkylacetals to give the alpha-hydroxy acetals in up to 98% ee. Hydrogenation of racemic alpha-amidopropiophenones under dynamic kinetic resolution predominantly gives the syn alcohols in up to 99% ee and > 98% de, while the reaction of racemic bezoin methyl ether gives the anti alcohols in excellent stereoselectivity.
Asymmetric reduction of α-keto acetals with potassium 9-O-(1,2-isopropylidene-5-deoxy-D-xylofuranosyl)-9-boratabicyclo[3.3.1]nonane. Enantioselective synthesis of α-hydroxy acetals with high optical purities
作者:Byung Tae Cho、Yu Sung Chun
DOI:10.1016/0957-4166(94)80142-8
日期:1994.7
Asymmetric reduction of alpha-keto acetals with a chiral borohydride, potassiun 9-O-(1,2-isopropylidene-5-deoxy-alpha-D-xylofuranosyl)-9-boratabicyclo[3.3.1]nonane in THF at -78 degrees C provided the corresponding alpha-hydroxy acetals with 87-99% ee.
Asymmetric Hydrogenation of Aromatic Ketones Catalyzed by the TolBINAP/DMAPEN−Ruthenium(II) Complex: A Significant Effect of <i>N</i>-Substituents of Chiral 1,2-Diamine Ligands on Enantioselectivity
mode of enantioface selection was interpreted by using transition state models based on the X-ray structure of the catalyst precursor. The chiral catalyst effected the hydrogenation of alkyl aryl ketones and arylglyoxal dialkyl acetals to afford the chiral alcohol in >99% ee in the best cases. Hydrogenation of racemic benzoin methyl ether with the chiral catalyst through dynamic kinetic resolution gave
Catalytic enantioselective reactions. Part 16. Oxazaborolidine-catalyzed asymmetric borane reduction of α-keto acetals
作者:Byung Tae Cho、Yu Sung Chun
DOI:10.1039/a903335a
日期:——
Asymmetricreductions of α-keto acetals using various oxazaborolidines and borane reagents as catalyst and the hydride source, respectively, were compared. The reduction catalyzed by Corey’s CBS reagents with N-phenylamine–borane reagents provided α-hydroxy acetals with very high enantioselectivities for most aromatic analogues.