Akira Nishinaga

Asymmetric induction in oxygenation of styrene catalyzed by cobalt schiff base complex

Abstract The oxygenation of styrene catalyzed by optically active cobalt Schiff base complexes in 2-propanol gives an enantiomer excess of 1-phenyl-ethanol. The asymmetric induction may be accomplished in two steps: addition of CoH species to styrene and decomposition of 1-phenylethyl hydroperoxide.

Conversion of 2′-hydroxychalcones to flavanones catalyzed by cobalt Schiff base complex

Abstract Co(salpr) catalyzes the conversion of 2′-hydroxychalcones to flavanones in methanol under oxygen. Base catalysis by Co(salpr) (OH) produced in situ is responsible for the reaction, which is found to proceed reversibly.

Substrate anion cobalt(III) complex intermediate in model quercetinase reaction using cobalt schiff base complex

Abstract 4′-Methoxyflavonolatocobalt(III) (salen), a key intermediate for model quercetinase reaction is synthesized. The complex undergoes dioxygenolysis of the heterocyclic ring in DMF by apparently a nonradical process.

Highly selective aldol reaction of dibenzoylmethanes with formaldehyde catalyzed by cobalt schiff base complex under neutral conditions

Abstract Coordinatively saturated hydroxocobalt(III) Schiff base complexes catalyze highly selective aldol reaction of dibenzoylmethanes with formaldehyde in methanol to give 1,3-dibenzoylpropanes, resulting from retro-Claisen reaction of 1,1,3,3-tetrabenzoylpropanes, which are obtained quantitatively in dichloromethane. Coordinatively saturated cobalt(III) Schiff base complexes ligating a substrate anion as a monodentate ligand is found to be the reactive species.

Structural effect of cobalt Schiff base complex catalyst on its catalytic activity in dioxygenolysis of 3-methylindole

Abstract Dioxygenolysis of 3-methylindole catalyzed by a series of cobalt(II) Schiff base complexes electronically and sterically designed gives 2-( N -formylamino)acetophenone as the sole product, but the reaction rate depended largely on the structure of the complex: the more positive E ° (Co II / Co III ) brings about the more catalytic activity. Steric hindrance of coordination of the substrate to the catalyst retards the reaction.

Catalysis by cobalt Schiff's base complexes in highly selective conversion of arylglyoxals to α-aryl-α-hydroxyacetic esters

Cobalt Schiffs base complexes catalyse highly selective conversion of arylglyoxals to α-aryl-α-hydroxyacetic esters in alcohols; Lewis acidity of CoIII species may be responsible for the catalysis.

Base-catalysed oxygenolysis of 3-hydroxyflavones

3-Hydroxyflavones, except those containing a 7-hydroxy-group, undergo base-catalysed oxygenolysis under mild conditions leading to oxidative cleavage of the heterocyclic ring to give the corresponding depsides and carbon monoxide in excellent yields. The same result is obtained in the reaction of quercetinase, a dioxygenase. The oxygenation of 3,4′,7-trihydroxyflavone in aqueous solution gave p-hydroxyphenylglyoxylic acid and 2,4-dihydroxybenzoic acid; in absolute methanol containing sodium methoxide methyl 4-hydroxyphenylglyoxylate and methyl 2,4-dihydroxybenzoate as well as 4-hydroxyphenylglyoxylic acid were obtained. The formation of these products is rationalized by assuming that 2-hydroperoxy-4′,7-dihydroxyflavan-3,4-dione is formed first and is reduced with the intervention of the 7-hydroxy-group to give 2,4′,7-trihydroxyflavan-3,4-dione, which is solvated and oxidized under the reaction conditions. 2′-Substituted-3-hydroxyflavones were not susceptible to oxygenolysis.

Base-catalysed autoxidation of 3,4′-dihydroxyflavone

Autoxidation of 3,4′-dihydroxyflavone in dimethylformamide in the presence of potassium t-butoxide results in oxidative cleavage of the hetrocyclic ring to give 2-(4-hydroxybenzoyloxy) benzoic acid and carbon monoxide in excellent yields; this provides a nonenzymic model for the reaction of quercetinas.

Co(salen) catalyzed oxidation of 2,4,6-trisubstituted anilines with tert-butylhydroperoxide

Abstract Co(salen) catalyzed oxidation of 2,4,6-trisubstituted (preferentially 2,6-di-tert-butylated) anilines withtert-butylhydroperoxide gives 4-tert-butylperoxy-2,5-cyclohexadien-1-imine and nitrobenzene derivatives. The relative ratio of the products depends on the nature of the substituents in the substrate.

Cobalt schiff base complex promoted retro-claisen reaction of 1-(2-hydroxyphenyl)-3-phenyl-1,3-propanediones and flavone formation

Abstract Co(salpr) promotes the conversion of 1-(2-hydroxyphenyl)-3-phenyl-1,3-propanediones to retro-Claisen reaction products and flavones in methanol under oxygen. Base catalysis by Co(salpr)(OH) produced in situ is responsible for the reaction.