Yuichi Kaneko

The catalytic asymmetric aldol reaction of silyl ketene acetals with aldehydes in the presence of a chiral borane complex. Nitroethane as a highly effective solvent for catalytic conditions

Abstract Catalytic asymmetric aldol reactions of silyl ketene acetals with aldehydes in the presence of 20 mol % of the chiral borane reagent, prepared in situ from the p-nitrobenzenesulfonamide of (S)-valine and BH 3 ·THF complex, gave β-hydroxy carboxylic acid esters in good chemical yields along with excellent enantioselectivity under conditions that employ nitroethane as an effective solvent.

First general synthesis of monosilyl acetals. Trimethylsilyl trapping of the intermediate in DIBALH reduction of carboxylic acid esters using trimethylsilyl trifluoromethanesulfonate

Abstract The intermediate generated by the DIBALH reduction of carboxylic acid esters reacts with trimethylsilyl trifluoromethanesulfonate (TMSOTf) in the presence of pyridine to afford the corresponding monosilyl acetals in good yields.

Direct enantioselective synthesis of syn-1,3-diols by the reaction of aldehydes with enol silyl ethers in the presence of a chiral borane complex. Successive asymmetric aldol reaction and asymmetric reduction with one promoter ☆

Abstract A stoichiometric amount of the chiral borane 1 turned out to successively promote the asymmetric aldol reaction of aldehydes with enol silyl ethers and the following asymmetric reduction in one pot to afford syn -1,3-diols with high enantioselectivity.

Lewis acid-mediated reaction with silyl ketene acetals and allylstannane of the aluminum acetals generated by DIBALH reduction of α-amino acid esters

Abstract The intermediates generated by DIBALH reduction of α-amino acid esters undergo condensation without racemization with silyl ketene acetals and allylstannane in the presence of Lewis acid to afford the corresponding β-hydroxy esters and homoallylic alcohols in good yields while achieving high syn selectivity via an aluminum-assisted chelation control.

Polymer-supported chiral borane promoters for the asymmetric aldol reaction of benzaldehyde with silyl ketene acetal

Abstract Chiral polymers ( A and B ) having pendant α-amino acid moiety were prepared by suspension copolymerization. A polymer-supported chiral borane, formed from chiral polymer A and BH 3 ·THF, effectively promoted the aldol reaction in THF of benzaldehyde with silyl ketene acetal in a similar enantioselectivity to that using the corresponding soluble counterpart. Some interesting polymer effects were also found on solvent and reaction temperature.

Isolation and characterization of [(RhCp*)2{η1:η4:η2-μ-CHC(Ph)CHC(Ph)CHCH2}]+ (Cp*=η5-C5Me5). Reinvestigation of the carbon–carbon bond formation between μ-CH2 group and alkynes in [(RhCp*)2(μ-CH2)2(CH3CN)2]2+

Abstract On reinvestigation of the reaction of [(RhCp*) 2 ( μ -CH 2 ) 2 (CH 3 CN) 2 ] 2+ ( 1 ) with alkynes we have found a much cleaner reaction system than the previous ones which has allowed us to elucidate the reaction mechanism of the intriguing carbon–carbon bond formation of the μ -CH 2 groups and alkynes and to isolate the pure reaction product of [(RhCp*) 2 { η 1 : η 4 : η 2 - μ -CHC(Ph)CHC(Ph)CHCH 2 }] + ( 2 ). The structure of 2 as the BPh 4 − salt has been determined by an X-ray diffraction study. Similar dirhodium complexes [(RhCp*) 2 { η 1 : η 4 : η 2 - μ -CHC(COOMe)CHC(COOMe)CHCH 2 }] + ( 3 ) and [(RhCp*) 2 { η 1 : η 4 : η 2 - μ -CHC(COOMe)CHC(Ph)CHCH 2 }] + ( 4 ) have been prepared and characterized spectroscopically.

Very short asymmetric synthesis of (1S, 3S, 5R)-1,3-dimethyl-2,9-dioxabicyclo[3.3.1]nonane via tandem enantioselective reactions promoted by one chiral borane

Abstract A very short asymmetric synthesis of the title compound has been realized with a chiral borane-mediated aldol reaction strategy with high enantio- and diastereoselectivities.