Masaji Ohno

A catalytic enantioselective reaction using a C2-symmetric disulfonamide as a chiral ligand: Alkylation of aldehydes catalyzed by disulfonamide-Ti(O-i-Pr)4-Dialkyl zinc system

Abstract Excellent enantioselective alkylation of aldehydes with dialkylzinc has been developed. This methodology is based on the concept of modifying the Lewis acid with a C 2 -symmetric, electron-withdrawing disulfonamide. The chiral Lewis acid catalysts used in the present study are the titanium complex, prepared in-situ from disulfonamide and Ti(O-i-Pr) 4 .

Asymmetric induction catalyzed by conjugate bases of chiral proton acids as ligands: enantioselective addition of dialkylzinc-orthotitanate complex to benzaldehyde with catalytic ability of a remarkable high order

Abstract The addition of diethylzinc-orthotitanate complex to benzaldehyde catalyzed by 0.0001∼0.04 equiv of chiral sulfonamide-titanate complex in toluene at 0∼ −30° gives optically active 1-phenylpropanol in both high ee and chemical yields. NMR study suggests alkyltitanium is generated from diethylzinc and the titanate in situ.

Enantioselective alkylation of aldehyde catalyzed by disulfonamide-Ti(O-i-Pr)4-dialkyl zinc system

Abstract The reaction of Et 2 Zn-Ti(O- i -Pr) 4 -disulfonamide 1 with various aldehydes is examined. High enantioselectivity (> 90% e.e.) is achieved using less than 0.04 equivalent of chiral disulfonamide 1 .

A catalytic enantioselective reaction using a C2-symmetric disulfonamide as a chiral ligand: cyclopropanation of allylic alcohols by the Et2Zn-CH2I2-disulfonamide system

Abstract The first catalytic, enantioselective Simmons-Smith cyclopropanation of an allylic alochol has been achieved by the reaction of an allylic alcohol with Et 2 Zn and CH 2 I 2 in the presence of a catalytic amount of chiral disulfonamide 1 .

Creation of novel chiral synthons with enzymes and applications to natural product synthesis. 15. Efficient introduction of chiral centers into cyclohexane ring

Abstract The chiral half-ester 2 obtained by asymmetric hydrolysis of the symmetric diester 1 with pig liver esterase has been shown to be a versatile synthon for various chiral cyclohexane derivatives.

A catalytic enantioselective reaction using a C2-symmetric disulfonamide as a chiral ligand: Simmons-Smith cyclopropanation of allylic alcohols by the Et2Zn-CH2I2-disulfonamide system

Abstract The first catalytic, enantioselective Simmons-Smith cyclopropanation of an allylic alochol has been achieved by the reaction of an allylic alcohol with Et 2 Zn and CH 2 I 2 in the presence of a catalytic amount of chiral disulfonamide 1 .

A stereocontrolled synthesis of (−)-bestatin from an acyclic allylamine by iodocyclocarbamation

Abstract 1,2-Asymmetric induction of iodocyclocarbamation is described by using allylamines 2 and 6 and the method has been successfully applied to a stereocontrolled synthesis of bestatin.

A general approach to trans-carbapenem antibiotics. Enantioselective synthesis of key intermediates for (+)-PS-5, (+)-PS-6, and (+)-thienamycin

Abstract (S)-4-[(Methoxycarbonyl)methyl]-2-azetidinone prepared by chemico-enzymatic approach has been efficiently converted to key intermediates for the synthesis of natural trans -carbapenem antibiotics, (+)-PS-5, (+)-PS-6, and (+)-thienamycin.

Synthetic studies on biologically active natural products by a chemicoenzymatic approach: Enantioselective synthesis of C- and N-nucleosides, showdomycin, 6-azapseudouridine and cordycepin

Abstract An efficient synthesis of C- and N-nucleosides has been developed in an enantioselective and stereocontrolled manner starting from Diels-Alder adduct of furan and dimethyl acetylenedicarboxylate by chemicoenzymatic strategy. The symmetric unsaturated dimethyl esters 2 and 3 were almost quantitatively hydrolysed with pig liver esterase to yield half-esters 4 and 5 with reasonably high optical yields. Decarboxylative ozonolysis of the chiral half-esters 4 followed by chemical transformation afforded methyl L -riboside 12, but after the enantiomer conversion (4 to 13 and 5 to 28) the methyl D -riboside (17), ( + )-showdomycin (22), and ( − )-6-azapseudouridine (27), were obtained from 13, and ( − )-cordycepin (32) was obtained from 28.

Gallium reagents in organic synthesis: Dimethylgallium chloride and triflate as activators in glycosidation using glycopyranosyl fluorides

Abstract Gallium compounds were utilized in organic synthesis for the first time. Dimethylgallium chloride and dimethylgallium triflate was found to efficiently promote the glycosidation using several glycopyranosyl fluorides.