Futoshi Kurashima

Enantioselective electrocatalytic oxidation of racemic sec-alcohols using a chiral 1-azaspiro[5.5]undecane-N-oxyl radical

Nitroxyl radical (6S,7R,10R)-4-acetylamino-2,2,7-trimethyl-10-isopropyl-1-azaspiro[5.5]-undecane-N-oxyl reveals a reversible redox peak in cyclic voltammetry at + 0.62 V vs. Ag/AgCl. A preparative electrocatalytic oxidation of racemic sec-alcohols on the nitroxyl radical yielded mixtures of 51.4 – 63.9 % ketones and 36.1 – 48.6 % alcohols by 10 h of electrolysis. The current efficiency and turnover number of the reactions were 85.6 – 87.9 % and 20.6 – 25.6, respectively. The enantiopurity of the remaining (R)-isomers was 50 – 70 % and the S values as a selective factor was 4.1 – 4.6.

Preparative, electroenzymatic reduction of ketones on an all components-immobilized graphite felt electrode

Abstract A thin cation-exchange polymer (Nafion)- and poly(acrylic acid) layers-coated graphite felt electrode immobilizing all mediation components of methyl viologen, NAD + , diaphorase and alcohol dehydrogenase to construct a complete bioelectrochemical reactor was prepared and applied to electroenzymatic reduction of ketones in a phosphate buffer at constant potential of −0.80 V vs sce . S -Isomers of 2- and 3-methylcyclohexanone were enantioselectively reduced to the corresponding (1 S , 2 S )-(+)-2- and (1 S , 3 S )-(−)-3-methylcyclohexanol, respectively, in high current efficiency (98.6 and 96.5%), high reduction yield (almost quantitatively) and high enantiomeric excess (ee) (100 and 93.1%), respectively. The unreacted ketones, ( R )-(−)-2- and ( R )-(+)-3-methylcyclohexanone, were recovered in high recovery yield (100 and 96%) and high ee (99.6 and 95.8%), respectively.

Enantioselective electrocatalytic oxidation of racemic alcohols on a TEMPO-modified graphite felt electrode by use of chiral base (TEMPO = 2,2,6,6-tetramethylpiperidin-1-yloxyl)

The S-isomers of four racemic sec-alcohols, which possess a chiral centre at the α-position to the hydroxy group, were oxidized to the corresponding ketones whereas the R-isomers remained unreacted on a TEMPO-modified graphite felt electrode in the presence of (–)-sparteine, where the enantiopurity of the remaining R-isomers was > 99% and the current efficiency for the produced ketones was > 90%.

Electrocatalytic reduction of aldehydes and ketones on nickel(II) tetraazamacrocyclic complex-modified graphite felt electrode

Abstract Electrocatalytic reduction of aldehydes and ketones was studied using a nickel(II) tetraazamacrocyclic complex-modified graphite felt (GF) electrode. The nickel(II) tetraazamacrocyclic complex-modified GF electrode was prepared by attaching nickel(II) (6-(2′-hydroxyethyl)-1,4,8,11-tetraazacyclotetradecane)perchlorate chemically to the carboxyl groups of a thin poly(acrylic acid) (PAA) layer coated on the GF. The modified electrode gave a reversible electron transfer for the nickel(II)–nickel(I) redox couple in cyclic voltammetry at −0.95 V versus Ag/AgCl. A preparative electrocatalytic reduction of aldehydes and ketones to the corresponding alcohol and pinacol compounds was successfully achieved on the modified electrode with an adequate current efficiency (46.9–75.9%), conversion (48.1–84.6%) and turnover number of the nickel catalyst (1053–2267).

Enantioselective electrocatalytic oxidation of racemic amines using a chiral 1-azaspiro[5.5]undecane N -oxyl radical

A preparative electrocatalytic oxidation of racemic amines, which contain a chiral centre α to the amino group, on (6S, 7R, 10R)-4-acetylamino-2,2,7-trimethyl-10-isopropyl-1-azaspiro[5.5]undecane N-oxyl yielded mixtures of carbonyl compounds (54.3–66.1%) and amines (33.9–45.7%) after 5 h of electrolysis, in which the current efficiency, turnover number, enantiopurity of the remaining (R)-isomers and S values were 90.7–94.8%, 21.7–26.5, 62–78% and 4.7–5.8, respectively.

Asymmetric electrochemical lactonization of diols on a chiral 1-azaspiro[5.5]undecane N-oxyl radical mediator-modified graphite felt electrode.

A graphite felt electrode modified with (6S,7R,10R)-4-amino-2,2,7-trimethyl-10-isopropyl-1-azaspiro[5.5]undecane N-oxyl was prepared for electrocatalytic oxidation of diols; electrolysis of diols on the modified electrode yielded optically active lactones (92.0-96.4%), with an enantiopurity of 82-99% ee.

Voltammetric behavior of poly(amidoamine) dendrimers containing nitroxyl radical end groups

Abstract A series of fully functionalized poly(amidoamine) dendrimers with 4-carboxy-2,2,6,6-tetramethylpiperidin-1-yloxyl end groups were prepared. Cyclic voltammetric studies indicated that the pendant nitroxyl radical end groups are non-interacting electrochemically equivalent redox centers, which are oxidizable at the same potential. The results of controlled-potential electrolysis of the dendrimers showed that all the nitroxyl radical groups at the periphery of the dendrimers are accessible to the electrode surface for electron transfer.

Electrocatalyric Oxidation on an (S)-Enantioselective Chiral Tempo-Modified Electrode

(6S, 7R, 10R)-1-aza-4-amino-2, 2, 7-trimethyl-10-isopropylspiro[5.5]undecane-1-yloxyl (Chiral TEMPO)-modified electrode was prepared by attaching this mediator chemically to the carboxyl groups of thin poly(acrylic acid) (PAA) layer coated on graphite felt (GF). Preparative electrolysis of racemic sec-alcohols and diols on Chiral TEMPO-modified GF electrode proceeded electrocatalytically in the presence of achiral base such as 2,6-lutidine, and yielded the corresponding products with high current efficiency and (S)-enantioselectivity.