Junko Umezawa

Stereocontrol of a tertiary hydroxyl group via microbial epoxidation. A facile synthesis of prostaglandin ω-chains

Abstract Optically active 1,2-epoxy-2-methylalkanes(1), useful precursors of tertiary alcohols, were prepared by microbial oxidation and converted to prostaglandin ω-chains.

Stereo- and regiocontrolled synthesis of fluorohydrins from optically active epoxides

Abstract The hydrofluorination of optically active terminal epoxides, which were produced by a microbial reaction, with HF-amine reagents were studied. 1,2-Epoxyoctane and glycidyl hexyl ether gave the corresponding 2-fluoro-1-alkanol derivatives with inversion of the asymmetric center with high stereospecificity, while in the hydrofluorination of pentafluorostyrene oxide and 2-methyl-1,2-epoxyhexane, partial racemization occurred. The basicity of the amine used, the HF/amine ratio in the HF-amine reagent, and the substituent on the epoxide affected the stereospecificity and regioselectivity of the hydrofluorination of the epoxides.

Asymmetric synthesis of α-methyl carboxylic acid derivatives. Stereochemistry in acidic ring opening of epoxides

Abstract Optically active α-methyl carboxylic acid derivatives were prepared via reaction of microbially produced epoxides with trimethylaluminum. Stereochemistry of the ring opening reaction was discussed through an MO calculation.

Synthesis of optically active oxazolines from optically active epoxides

Abstract The reaction of optically active terminal epoxides, which were produced by a microbial reaction, with acetonitrile in the presence of a protic acid or Lewis acid was studied. 1,2-Epoxyoctane, 2-methyl-1,2-epoxyhexane, and pentafluorostyrene oxide gave the corresponding 4-substituted 2-methyl-2-oxazoline derivatives with moderate to excellent regioselectivity. The reactions proceeded with an inversion of the asymmetric center with high stereospecificity under AlCl 3 - or SnCl 4 -catalyzed conditions, while partial racemization occurred under HF- or CF 3 SO 3 H-catalyzed conditions. The acid used and the substituent on the epoxide affected the stereospecificity and regioselectivity of the oxazoline formation. 4-Hexyl-2-methyl-2-oxazoline obtained with high stereospecificity was converted into 2-aminooctanoic acid via 2-aminooctanol.

New Chiral Dopants Based on the 2-Fluoro-2-Methylalkoxy Tail for Use in Ferroelectric Liquid Crystal Mixtures

Abstract A new class of FLC materials based on the 2-fluoro-2-methylalkoxy tail is reported. This new class of materials consistently shows an N* helical pitch opposite in sign to that of the polarization. These materials are compared to their 2-fluoroalkoxy analogs to explore the methyl groups effect on the N* pitch and polarization.