Showing papers on "Benzaldehyde published in 1988"

Enantioselective alkylation of carbonyl compounds. From stoichiometric to catalytic asymmetric induction

Abstract: Multinuclear organometallic species play a significant role in alkylation of carbonyl compounds. Enantioselective alkylation of aldehydes using a 1: 1 reagent/substrate stoichiometry is achievable by chirally modified lithium/magnesium binary organometallic reagents. For example, diethylmagnesium treated with di-O-lithio-(S)-2.2'- dihydroxy- 1, 1'-binaphthyl reacts with benzaldehyde in a THF- dimethoxyethane mixture at -100 OC to give (S)- 1-phenyl- 1- propanol in 92% ee. In the presence of a catalytic quantity of (4-3- exo-(dimethy1amino)isoborneol (DAIB), reaction of dialkylzincs and aldehydes in nonpolar media is accelerated greatly to lead to the corresponding S alcohols in very high enantiomeric excesses (up to 99% ee). The enantioselective catalysis involves fluxional organozinc species and the product-forming dinuclear intermediate possesses DAIB auxiliary, an aldehyde ligand, and three alkyl groups, where it is the bridging alkyl group, rather than the terminal alkyls, that migrates from zinc to the carbonyl carbon.

Asymmetric Hydrocyanation of Aldehydes Using Chiral Titanium Reagents

Abstract: Two highly enantioselective methods for hydrocyanation of aldehydes were developed by using chiral alkoxytitanium reagents. Treatment of benzaldehyde with cyanotrimethylsilane in the presence of a ...

General method for the asymmetric synthesis of α-amino acids via alkylation of the chiral nickel(II) Schiff base complexes of glycine and alanine

Abstract: Nickel(II) complexes of Schiff bases derived from (S)-o-[(N-benzylprolyl)amino] benzaldehyde and alanine (3), or (S)-O-[(N-benzylpropyl)amino]benzophenone and alanine (4), or glycine (5) have been used for the asymmetric synthesis of α-amino acids under a variety of conditions. The method of choice consists of the reaction of the corresponding complex with the appropriate alkyl halide in DMF at 25 °C using solid NaOH as a catalyst. Low diastereoselective excess (d.e.) is observed for the alkylation of complex (3) with benzyl bromide and allyl bromide. Large selectivity (80%) is observed for the alkylation of complex (4). Optically pure (R)- and (S)-α-methyl-α-amino acids [(S)-α-methylphenylalanine, (S)-α-allylalanine and (S)-O-benzyl-α-methyltyrosine] were obtained (70–90%) after the alkylated diastereoisomeric complexes had been separated on SiO2 and hydrolysed with aqueous HCl. The initial chiral reagents were recovered (80–92%). The alkylation of complex (5) gave (S)-alanine, (S)-valine, (S)-phenylalanine, (S)-tryptophan, (S)-isoleucine, (S)-2-aminohexanoic acid, and 3,4dimethoxyphenylalanine with optical yields of 70–92%. The optically pure α-amino acids were obtained after the separation of the alkylated diastereoisomeric complexes on SiO2. The stereochemical mechanism of the alkylation reaction is discussed.

Ultrasound in organic synthesis. 13. Some fundamental aspects of the sonochemical Barbier reaction

Abstract: Addition chimique du benzaldehyde avec le bromo-1 heptane sur support de lithium. Formation du phenyl-1 octanol-1

N,N'-dibenzyl-N,N'-ethylenetartramide: a rationally designed chiral auxiliary for the allylboration reaction

Abstract: Reaction du compose du titre avec des propanals, cyclohexanals et benzaldehyde: obtention d'alcools homoallyliques

Activity measurements and spectroscopic studies of the catalytic oxidation of toluene over silica-supported vanadium oxides

Abstract: Vanadium oxides on silica gel (Davison 952) with varying vanadium concentrations have been investigated for the activities and selectivities in the oxidation of toluene. These results were correlated with the features shown by X.r.d., ESCA, u.v.–visible and i.r. studies of adsorbed CO. The catalysts show a low activity in comparison with V/alumina. The support alone shows 60% selectivity for benzaldehyde formation. From i.r. data it is suggested that this benzaldehyde is formed on sites in association with sodium impurities. Introduction of vanadium increases the rate of reaction but the selectivity is shifted towards carbon oxides. The increased activity at low vanadium content is due to isolated four-coordinated vanadium species. U.v.–visible data show that the isolated species agglomerate at further loading to polyvanadium chains. These polymers possess an increased activity as a further route of reduction of VV to VIV is present. Five-coordinated vanadium of the same activity as the chains and producing selective oxidation products other than benzaldehyde is found with a loading of 2% V. Larger agglomerates and V2O5 crystallites are present on the 10% V catalyst. These species only give a somewhat increased activity, but with a product pattern different from crystalline V2O5 and 10% V/alumina.

XY–ZH systems as potential 1,3-dipoles. Part 11. Stereochemistry of 1,3-dipoles generated by the decarboxylative route to azomethine ylides

Abstract: The decarboxylative reaction of aryl aldehydes with cyclic secondary α-amino acids or primary α-amino acids in the presence of N-methyl- or N-phenyl-maleimide leads, via an intermediate azomethine ylide, to mixtures of bicyclic pyrrolidine cycloadducts in good yield. Cyclic secondary α-amino acids, where the carboxylic group is non-benzylic, give cycloadducts arising from a stereospecifically generated anti-dipole. Acyclic α-amino acids, and cyclic secondary α-amino acids with the carboxylic group located at a benzylic site, give rise to cycloadducts derived from both anti- and syn-configurations of the intermediate azomethine glides. The reactions show little discrimination between endo- and exo-transition states for the cycloadditions.

Benzyl alcohol dehydrogenase and benzaldehyde dehydrogenase II from Acinetobacter calcoaceticus. Substrate specificities and inhibition studies.

Abstract: The apparent Km and maximum velocity values of benzyl alcohol dehydrogenase and benzaldehyde dehydrogenase II from Acinetobacter calcoaceticus were determined for a range of alcohols and aldehydes and the corresponding turnover numbers and specificity constants were calculated. Benzyl alcohol was the most effective alcohol substrate for benzyl alcohol dehydrogenase. Perillyl alcohol was the second most effective substrate, and was the only non-aromatic alcohol oxidized. The other substrates of benzyl alcohol dehydrogenase were all aromatic in nature, with para-substituted derivatives of benzyl alcohol being better substrates than other derivatives. Coniferyl alcohol and cinnamyl alcohol were also substrates. Benzaldehyde was much the most effective substrate for benzaldehyde dehydrogenase II. Benzaldehydes with a single small substituent group in the meta or para position were better substrates than any other benzaldehyde derivatives. Benzaldehyde dehydrogenase II could also oxidize the aliphatic aldehydes hexan-1-al and octan-1-al, although poorly. Benzaldehyde dehydrogenase II was substrate-inhibited by benzaldehyde when the assay concentration exceeded approx. 10 microM. Benzaldehyde dehydrogenase II, but not benzyl alcohol dehydrogenase, exhibited esterase activity with 4-nitrophenyl acetate as substrate. Both benzyl alcohol dehydrogenase and benzaldehyde dehydrogenase II were inhibited by the thiol-blocking reagents iodoacetate, iodoacetamide, 4-chloromercuribenzoate and N-ethylmaleimide. Benzyl alcohol or benzaldehyde respectively protected against these inhibitions. NAD+ also gave some protection. Neither benzyl alcohol dehydrogenase nor benzaldehyde dehydrogenase II was inhibited by the metal-ion-chelating agents EDTA, 2,2'-bipyridyl, pyrazole or 2-phenanthroline. Neither enzyme was inhibited by a range of plausible metabolic inhibitors such as mandelate, phenylglyoxylate, benzoate, succinate, acetyl-CoA, ATP or ADP. Benzaldehyde dehydrogenase II was sensitive to inhibition by several aromatic aldehydes; in particular, ortho-substituted benzaldehydes such as 2-bromo-, 2-chloro- and 2-fluoro-benzaldehydes were potent inhibitors of the enzyme.

Remarkable effects of a pentafluorophenyl group on the stereoselective reactions of a chiral iron acyl complex

Abstract: Un nouveau complexe acyl chiral du fer [(C 6 F 5 )Ph 2 P](CO)CpFeCOMe (I), est synthetise par photolyse UV de Cp(CO) 2 FeMe en presence de PPh 2 (C 6 F 5 ) suivie d'une carbonylation Etude des reactions d'aldolisation du benzaldehyde et de sa phenylimine avec les enolates de lithium, d'etain, d'aluminium, et de cuivre du complexe (I)

Benzyl alcohol dehydrogenase and benzaldehyde dehydrogenase II from Acinetobacter calcoaceticus. Purification and preliminary characterization.

Abstract: A quick, reliable, purification procedure was developed for purifying both benzyl alcohol dehydrogenase and benzaldehyde dehydrogenase II from a single batch of Acinetobacter calcoaceticus N.C.I.B. 8250. The procedure involved disruption of the bacteria in the French pressure cell and preparation of a high-speed supernatant, followed by chromatography on DEAE-Sephacel, affinity chromatography on Blue Sepharose CL-6B and Matrex Gel Red A, and finally gel filtration through a Superose 12 fast-protein-liquid-chromatography column. The enzymes co-purified as far as the Blue Sepharose CL-6B step were separated on the Matrex Gel Red A column. The final preparations of benzyl alcohol dehydrogenase and benzaldehyde dehydrogenase II gave single bands on electrophoresis under non-denaturing conditions or on SDS/polyacrylamide-gel electrophoresis. The enzymes are tetramers, as judged by comparison of their subunit (benzyl alcohol dehydrogenase, 39,700; benzaldehyde dehydrogenase II, 55,000) and native (benzyl alcohol dehydrogenase, 155,000; benzaldehyde dehydrogenase II, 222,500) Mr values, estimated by SDS/polyacrylamide-gel electrophoresis and gel filtration respectively. The optimum pH values for the oxidation reactions were 9.2 for benzyl alcohol dehydrogenase and 9.5 for benzaldehyde dehydrogenase II. The pH optimum for the reduction reaction for benzyl alcohol dehydrogenase was 8.9. The equilibrium constant for oxidation of benzyl alcohol to benzaldehyde by benzyl alcohol dehydrogenase was determined to be 3.08 x 10(-11) M; the ready reversibility of the reaction catalysed by benzyl alcohol dehydrogenase necessitated the development of an assay procedure in which hydrazine was used to trap the benzaldehyde formed by the NAD+-dependent oxidation of benzyl alcohol. The oxidation reaction catalysed by benzaldehyde dehydrogenase II was essentially irreversible. The maximum velocities for the oxidation reactions catalysed by benzyl alcohol dehydrogenase and benzaldehyde dehydrogenase II were 231 and 76 mumol/min per mg of protein respectively; the maximum velocity of the reduction reaction of benzyl alcohol dehydrogenase was 366 mumol/min per mg of protein. The pI values were 5.0 for benzyl alcohol dehydrogenase and 4.6 for benzaldehyde dehydrogenase II. Neither enzyme activity was affected when assayed in the presence of a range of salts. Absorption spectra of the two enzymes showed no evidence that they contain any cofactors such as cytochrome, flavin, or pyrroloquinoline quinone. The kinetic coefficients of the purified enzymes with benzyl alcohol, benzaldehyde, NAD+ and NADH are also presented.

Barium Ferrate Monohydrate BaFeO4·H2O, a Useful Oxidant for the Oxidation of Organic Compounds under Aprotic Conditions

Abstract: Preparation of barium ferrate monohydrate with a slight modification is described. It is shown that this reagent is capable of oxidizing different organic compounds and could be used as a versatile reagent in organic synthesis. Primary and secondary alcohols are converted to their carbonyl compounds, α-hydroxy ketones to their diketones, and hydroquinones to their quinones. Aromatic amines are converted to their azo compounds, benzylamine to benzaldehyde, phenylhydrazones and oximes to their carbonyl compounds. Thiols are also converted to their disulfides in high yields. This reagent seems to be a non-toxic and a non-pollutant compound.

Decarboxylative incorporation of α-oxobutyrate and α-oxovalerate into (R)-α-hydroxyethyl- and n-propyl ketones on reaction with aromatic and α,β-unsaturated aldehydes in Baker's yeast

Abstract: Decarboxylative incorporation of linear C3, C4, and C5α-oxo acids into (R)α-hydroxy ketones (2), (9) and (10) is observed when benzaldehyde (1) is incubated with baker's yeast; α,β-unsaturated aldehydes (11) and (15) with the C3 and C4 acids yield (R)-α-hydroxy methyl and ethyl ketones (16), (20), (19), and (21).