Yoshiaki Ohgo

Asymmetric alkylation of aromatic aldehydes with diethylzinc catalyzed by a fluorous BINOL–Ti complex in an organic and fluorous biphase system

Fluorous chiral BINOL ((R)-FBINOL) was prepared by short reaction steps in good overall yield and was applied to the catalytic asymmetric alkylation in a toluene and FC-72 biphase system. The (R)-FBINOL–Ti complex in the FC-72 phase was consecutively reused in the biphase system and the enantioselectivity was still higher than 80% ee at the 5th reaction.

Recyclable fluorous chiral ligands and catalysts: Asymmetric addition of diethylzinc to aromatic aldehydes catalyzed by fluorous BINOL-Ti complexes

Fluorous chiral BINOLs were prepared and used as the ligands for the titanium catalyzed asymmetric addition of Et2Zn to aromatic aldehydes. Consecutive reactions were examined by utilizing fluorous–organic biphase and fluorous solid phase extraction techniques. Enantioselectivities were similar in consecutive reactions and were close to that attained in the non-fluorous system. The solid phase extraction method also enabled us to perform a simultaneous screening procedure.

Preparation of a Fluorous Chiral BINOL Derivative and Application to an Asymmetric Protonation Reaction

Fluorous Chiral Proton Source (R,S)-FDHPEB resulted in a higher enantioselectivity (95% ee) than that of the original nonfluorous (R,S)-DHPEB (87% ee) in an enantioselective protonation of a samarium enolate. (R,S)-FDHPEB was easily recovered by a simple filtration through a fluorous reverse phase silica gel and was recyclable.

Catalytic enantioselective protonation of a samarium enolate with fluorous chiral and achiral proton sources in fluorous biphasic systems

Abstract Enantioselectivities near maximum values were obtained in the catalytic reaction by a ropid addition of a fluorous achiral alcohol (Rfh 3 COH) to the reaction mixture: for DHPEX in Rfh 3 COH/THF solid-liquid biphase system and for a fluorous chiral alcohol in THF/FC-72 liquid-liquid biphase system.

Preparation of a fluorous chiral BINAP and application to an asymmetric Heck reaction

Abstract Fluorous chiral BINAP (( R )-F 13 BINAP) was prepared and was applied to an asymmetric Heck reaction. The enantioselectivity was similar in BTF homogeneous system (90% ee) to that of the original non-fluorous reaction and marginally higher in benzene and FC-72 biphasic system (93% ee) than that of the original non-fluorous one.

Enantioselective protonation of samarium enolates derived from α-heterosubstituted ketones and lactone by SmI2-mediated reduction

Abstract SmI2-mediated reductive cleavage of α-hetero substituents of α-alkyl or α-aryl ketones and lactone gave the corresponding “thermodynamic samarium enolates”. Enantioselective protonation of the samarium enolates with C2-symmetric chiral diols afforded the corresponding ketones and lactone in moderate to high enantioselectivities.

Enantioselective addition of diethylzinc to aldehydes catalyzed by fluorous β-aminoalcohols

Abstract A fluorous aminoalcohol prepared from ephedrine has been used as a catalyst for the enantioselective addition of diethylzinc to aldehydes to afford the corresponding alcohols in up to 84% ee. The fluorous amino alcohol was easily recovered by a simple filtration through a fluorous reverse phase silica gel and was reusable without purification.

SmI2-mediated reductive enolization of α-hetero-substituted ketones and enantioselective protonation

Abstract High enantioselectivity (up to 94% ee) has been achieved in the protonation of samarium enolates which were generated by SmI 2 -mediated reduction of 2-aryl-2-methoxycyclohexanones using a C 2 -symmetric chiral diol as a proton source.

Catalytic enantioselective protonation of samarium enolates by a C2-symmetric chiral diol

Abstract Relatively high enantioselectivity (up to 93% ee) has been achieved in the catalytic protonation of samarium enolates by the use of a C 2 -symmetric homochiral diol as the catalyst and trityl alcohol as an achiral proton source for regeneration of the catalyst.

Enantioselective protonation of samarium enolates by a C2-symmetric chiral diol

Abstract High enantioselectivity (up to 97%ee) have been achieved in the protonation of samarium enolates which were generated by SmI 2 -mediated cross-coupling reaction between unsymmtrical dialkylketene and allyl iodide, using a C 2 -symmetric chiral diol as a proton source. The stereochemistry of enolate formation and of the enantioselective protonation is discussed.