The synthesis of oxazaborolidines from amides derived from ephedrine and pseudoephedrine by treatment with BH3-THF is reported. The reaction affords chiral oxazaborolidines with nitrogen atom substituents of different steric requirements enlarging the potential of new oxazaborolidines prepared from readily available ephedrines. These may be useful in asymmetric synthesis.
General Asymmetric Hydrogenation of α-Branched Aromatic Ketones Catalyzed by TolBINAP/DMAPEN−Ruthenium(II) Complex
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.
Mueller,H.K. et al., Journal fur praktische Chemie (Leipzig 1954), 1973, vol. 315, p. 1045 - 1056
作者:Mueller,H.K. et al.
DOI:——
日期:——
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