Kinetic resolution of racemic α-tert-alkyl-α-hydroxy esters by enantiomer-selective carbamoylation.

Kinetic resolution of sterically hindered racemic α-tert-alkyl-α-hydroxy esters is performed by enantiomer-selective carbamoylation with the t-Bu-Box-Cu(II) catalyst (Box = bis(oxazoline)). The reaction with 0.5 equiv of n-C(3)H(7)NCO is carried out with a substrate-to-catalyst molar ratio of 500-5000 at -20 to 25 °C. The high enantiomer-discrimination ability of the catalyst achieves an excellent stereoselectivity factor (s = k(fast)/k(slow)) of 261 in the best case. A catalytic cycle for this reaction is proposed.

Asymmetric hydrogenation of bicyclic ketones catalyzed by BINAP/IPHAN-Ru(II) complex.

Hydrogenation of 3-quinuclidinone and bicyclo[2.2.2]octan-2-one with a combined catalyst system of RuCl(2)[(S)-binap][(R)-iphan] and t-C(4)H(9)OK in 2-propanol afforded the chiral alcohols in 97-98% ee. 2-Diphenylmethyl-3-quinuclidinone was hydrogenated with the same catalyst to the cis alcohol with perfect diastereo- and enantioselectivity. The reaction of unsymmetrical ketones with a bicyclo[2.2.1] or -[2.2.2] skeleton gave the corresponding alcohols with high stereoselectivity.

Asymmetric hydrogenation of aromatic ketones catalyzed by the TolBINAP/DMAPEN-ruthenium(II) complex: a significant effect of N-substituents of chiral 1,2-diamine ligands on enantioselectivity.

Asymmetric hydrogenation of acetophenone in the presence of Ru(II) catalysts coordinated by TolBINAP and a series of chiral 1,2-diamines was studied. The sense and degree of enantioselectivity were highly dependent on the N-substituents of the diamine ligands. The N-substituent effect was discussed in detail. Among these catalysts, the (S)-TolBINAP/(R)-DMAPEN-Ru(II) complex showed the highest enantioselectivity. The 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 the anti-alcohol (syn:anti = 3:97) in 98% ee, while the reaction of alpha-amidopropiophenones resulted in the syn-alcohols (syn:anti = 96:4 to >99:1) in >98% ee.

Enantiomer-selective carbamoylation of racemic alpha-hydroxy gamma-lactones with chiral Cu(II) Catalysts: an example of a highly active Lewis acid catalyzed reaction.

Enantiomer-selective carbamoylation of racemic alpha-hydroxy gamma-lactones with half equivalents of isocyanates in the presence of chiral Cu(II) catalysts was studied. Among a series of catalyst bearing chiral bis(oxazoline) (box) and pyridine(bisoxazoline) ligands, [Cu(tBu-box)]X(2) [X=OSO(2)CF(3) (3 a), SbF(6) (3 b)] showed the highest enantioselectivity in the reaction of pantolactone (1 a). Use of n-C(3)H(7)NCO, a small alkyl isocyanate, in CH(2)Cl(2) solution was important to achieve a high level of enantiomer selection. The tBu-box-Cu(II) catalyst efficiently differentiated two enantiomers of beta-substituted alpha-hydroxy gamma-lactones under the optimized reaction conditions, resulting in a stereoselectivity factor (s=k(fast)/k(slow)) of up to 209. Furthermore, this catalyst is highly active, so that the carbamoylation can be conducted with a substrate-to-catalyst molar ratio of 2000-3000. A catalytic cycle of this reaction is also proposed.

General asymmetric hydrogenation of alpha-branched aromatic ketones catalyzed by TolBINAP/DMAPEN-ruthenium(II) complex.

[reaction: see text] 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.

Highly active and selective palladium catalyst for hydroesterification of styrene and vinyl acetate promoted by polymeric sulfonic acids.

Highly efficient, selective and recyclable palladium catalyst systems for hydroesterification of styrene and vinyl acetate were realized by using 1,2-bis(di-tert-butylphosphinomethyl)benzene as ligand and polymeric sulfonic acids of limited SO(3)H loadings as promoter.

BINAP/1,4-diamine-ruthenium(II) complexes for efficient asymmetric hydrogenation of 1-tetralones and analogues.

A combined system of a RuCl(2)(binap)(1,4-diamine) complex and t-C(4)H(9)OK in i-C(3)H(7)OH catalyzes enantioselective hydrogenation of various 1-tetralone derivatives and some methylated 2-cyclohexenones. Hydrogenation of 2-methyl-1-tetralone under dynamic kinetic resolution gives the cis alcohol with high ee. [reaction: see text]