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• Nanoceria catalyzes the cyanosilylation of different ketones at rt in high yields. • Nanoceria acts as a bifunctional acid-base solid catalyst. • The solid catalyst can be reused ten times with a simple calcination. • The catalytic activity of nanoceria is independent of the crystalline phase. • Au-nanoceria catalyzes the aerobic oxidation of alcohols/cyanosilylation reaction. The cyanosilylation of carbonyl compounds is a fundamental reaction in organic synthesis, to give cyanohydrins. Ketones are particularly reluctant to cyanosilane addition and require the action of a catalyst, and despite many soluble Brönsted and Lewis acids have been employed for this task, it is difficult to find in the open literature catalytic solids able to carry out the reaction. Here, we show that commercially available nanoceria catalyzes the cyanosilylation of different ketones (21 examples) at temperatures between 0 and 50 °C, in high yields, under solventless conditions if required. The nanoceria network atoms act in a cooperative way to provide a bifunctional acid-base solid catalyst for the cyanosilylation reaction. The amorphization of nanoceria during reaction, due to acid release, does not hamper the catalytic activity and, indeed, different types of nanoceria, even with supported metal nanoparticles on surface, are active for the reaction, enabling extensive reuses after air calcination and the use of the catalytic material for the aerobic oxidation of alcohols / cyanosilylation reaction. [ABSTRACT FROM AUTHOR]

• Bm HNL has the longest half-life among all currently known α/β hydrolase fold HNLs at its optimal pH and temperature. • Polyol addition increases Bm HNL's stability and activity. • Glycerol addition to Bm HNL biocatalysis increases % ee of the synthesized cyanohydrins. HNL catalysis is usually carried out in a biphasic solvent and at low pH to suppress the non-enzymatic synthesis of racemic cyanohydrins. However, enzyme stability under these conditions remain a challenge. We have investigated the effect of different biocatalytic parameters, i.e., pH, temperature, buffer concentrations, presence of stabilizers, organic solvents, and chemical additives on the stability of Baliospermum montanum hydroxynitrile lyase (Bm HNL). Unexpectedly, glycerol (50 mg/mL) added Bm HNL biocatalysis had produced >99% of (S)-mandelonitrile from benzaldehyde, while without glycerol it is 54% ee. Similarly, Bm HNL had converted 3-phenoxy benzaldehyde and 3,5-dimethoxy benzaldehyde, to their corresponding cyanohydrins in the presence of glycerol. Among the different stabilizers added to Bm HNL at low pH, 400 mg/mL of sucrose had increased enzyme's half-life more than fivefold. Bm HNL's stability study showed half-lives of 554, 686, and 690 h at its optimum pH 5.5, temperature 20 °C, buffer concentration, i.e., 100 mM citrate-phosphate pH 5.5. Addition of benzaldehyde as inhibitor, chemical additives, and the presence of organic solvents have decreased both the stability and activity of Bm HNL, compared to their absence. Secondary structural study by CD-spectrophotometer showed that Bm HNL's structure is least affected in the presence of different organic solvents and temperatures. [ABSTRACT FROM AUTHOR]

Abstract This study presents asymmetric synthesis of cyanohydrins in aqueous–organic biphasic system using crude Baliospermum montanum hydroxynitrile lyase (Bm HNL). The effect of various biocatalytic parameters e.g. different organic solvents, ratio of organic solvents, substrate concentration (benzaldehyde and HCN), pH, and temperature were studied to achieve highest % conversion and enantiomeric excess of (S)-mandelonitrile. Among the organic solvents i.e. hexane, toluene, acetonitrile, tert -butyl methyl ether (TBME), di -isopropyl ether (DIPE) and n -butyl acetate studied, 10% n -butyl acetate showed best results. Optimal results were also found with 0.8 mM benzaldehyde, 10 min reaction time, pH 4.2 and substrate to KCN ratio of 1:125. Under optimal biocatalytic conditions more than a dozen of different aromatic aldehydes were converted into corresponding chiral (S)-cyanohydrins. This method also reports the synthesis of eight chiral (S)-cyanohydrins for the first time, not synthesized by any (S)-selective HNL earlier. Graphical abstract fx1 Highlights • Bm HNL catalyzed synthesis of (S)-cyanohydrins was studied for the first time in biphasic media. • Use of crude Bm HNL in biocatalysis have resulted in comparable % ee and conversion of products with that of the use of purified enzymes in case of a few substrates. • Sixteen (S)-cyanohydrins were synthesized using Bm HNL in biphasic media. • Thirteen (S)-cyanohydrins were synthesized by Bm HNL for the first time and eight among them have not been synthesized by any other (S)-selective HNL except this report. [ABSTRACT FROM AUTHOR]

Two known lanthanide complexes, [KLa(HL 1 ) 2 {(CH 3 ) 2 NCHO} 2 (H 2 O) 3 ] ( 1 ) and [Sm(H 2 O) 9 ]( E -H 2 L 2 ) 3 ·2H 2 O ( 2 ) were prepared by reaction of lanthanum(III) and samarium(III) nitrates with potassium 3-(2-(2,4-dioxopentan-3-ylidene)hydrazinyl)-2-hydroxy-5-nitrobenzenesulfonate (KH 2 L 1 ) and potassium ( E,Z )-5-chloro-3-(2-(1,3-dioxo-1-phenylbutan-2-ylidene)hydrazinyl)-2-hydroxybenzenesulfonate (KH 2 L 2 ), respectively. Catalytic activities of 1 and 2 were evaluated in the cyanosilylation of aldehydes with trimethylsilyl cyanide in different solvents such as tetrahydrofuran, dichloromethane or methanol. Complex 1 was found to be efficient catalyst for the cyanosilylation reaction in methanol medium at room temperature, producing cyanohydrin trimethylsilyl ethers with good yields (76–99%). [ABSTRACT FROM AUTHOR]

The first example of the diastereoselective construction of polysubstituted 2,3-dihydrofurans incorporating contiguous quaternary and tertiary carbon centers via a Lewis base-catalyzed one-pot cascade sequence is described. The diversity and complexity of the final products can be efficiently constructed with high diastereoselectivities via this catalytic multistep process under mild reaction conditions. [ABSTRACT FROM AUTHOR]

Hydroxynitrile lyases (HNLs) are increasingly finding application in the synthesis of enantiomerically pure cyanohydrins which are important intermediates in the production of pharmaceuticals and agrochemicals. Synthesis of enantiopure mandelonitrile was carried out using HNL of wild apricot ( Prunus armeniaca L.) [ ParsHNL] in aqueous/organic biphasic system. The optimum pH and temperature of the reaction were 4.0 and 15 °C respectively, which are important parameters to suppress the non-enzymatic catalysis. ParsHNL catalyses synthesis of ( R)-mandelonitrile in methyl- tbutyl ether (MTBE)/citrate buffer biphasic system with >99% ee. Synthesis of mandelonitrile was carried out in batch reaction at 40 ml scale and finally 2.7 mmoles of ( R)-mandelonitrile was recovered which corresponded to 90% molar conversion in 46 h reaction. In fed batch reaction 6.37 mmoles of ( R)-mandelonitrile could be produced which corresponds to 91% molar conversion in 46 h. In both reactions, enzyme produces ( R)-mandelonitrile with > 99% ee which showed enhanced selectivity as compared to aqueous reaction (96% ee) by ParsHNL. The results showed potential of ParsHNL to synthesize ( R)-mandelonitrile in both, batch reaction and fed-batch reaction and can be effectively used in the synthesis of ( R)-mandelonitrile. Graphical Abstract: [ABSTRACT FROM AUTHOR]

The article presents a study to describe an efficient protocol for the conjugate addition of cyanide to alpha, beta-unsaturated ketones 1a-j using trimethylsilyl cyanide (TMSCN) as cyanide source and Amb-F as solid catalyst under solvent-free conditions (SolFC). It discusses the addition of TMSCN to (E)-hept-3-en-2-one (1a). The study suggests that an initial 1,2-addition of cyanide to the a,b-unsaturated ketone 1 occurs giving the cyanohydrin trimethylsilyl ether 2.

The transition metal-catalyzed hydration of nitriles is an efficient route to amides, which are important synthetic building blocks. Many heterogeneous and homogeneous catalysts have been explored for this reaction, but there are drawbacks to each type of catalyst. Nanoparticle (NP) catalysis is a potential bridge between heterogeneous and homogeneous catalysis, frequently combining the easy separation of heterogeneous catalysts with the tunability of homogeneous catalysts. Although the field of NP catalysts is relatively new, NP catalysts have been explored for a variety of reactions, including a number of nitrile hydration reactions. This review makes a thorough assessment of these nitrile hydration reactions. [ABSTRACT FROM AUTHOR]

Hydroxynitrile lyases ( HNLs), which catalyse the decomposition of cyanohydrins, are found mainly in plants. In vitro, they are able to catalyse the synthesis of enantiopure cyanohydrins, which are versatile building blocks in the chemical industry. Recently, HNLs have also been discovered in bacteria. Here, we report on the detailed biochemical and structural characterization of a hydroxynitrile lyase from Granulicella tundricola ( Gt HNL), which was successfully heterologously expressed in Escherichia coli. The crystal structure was solved at a crystallographic resolution of 2.5 Å and exhibits a cupin fold. As Gt HNL does not show any sequence or structural similarity to any other HNL and does not contain conserved motifs typical of HNLs, cupins represent a new class of HNLs. Gt HNL is metal-dependent, as confirmed by inductively coupled plasma/optical emission spectroscopy, and in the crystal structure, manganese is bound to three histidine and one glutamine residue. Gt HNL displayed a specific activity of 1.74 U·mg−1 at p H 6 with ( R)-mandelonitrile, and synthesized ( R)-mandelonitrile with 90% enantiomeric excess at 80% conversion using 0.5 m benzaldehyde in a biphasic reaction system with methyl tertiary butyl ether. [ABSTRACT FROM AUTHOR]

Abstract: Cyanation-O-protection reaction of ketones with different cyanide sources catalyzed by N-heterocyclic carbenes is reported. Under the catalysis of 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene, various ketones coupled with diethyl cyanophosphonate to produce cyanohydrin-O-phosphates with a quaternary carbon center in moderate to excellent yield. Furthermore, the reaction can be scaled-up easily and high yield maintained. [Copyright &y& Elsevier]

Abstract: The synthesis of two per-O-methylated cyclodextrins with one or two α-hydroxypropionitrile groups attached to the secondary rim is described. The two new cyanohydrins are found to catalyse the hydrolysis of 4-nitrophenyl β-D-glucopyranoside in a buffer solution at pH 8.0 with a rate acceleration of up to 1770. [Copyright &y& Elsevier]

A series of β-hydroxynitriles were efficiently synthesized from the regioselective ring opening of oxiranes by cyanide anion in the presence of silica-bound 3-{2-[poly(ethylene glycol)]ethyl}-substituted 1-methyl-1 H-imidazol-3-ium bromide (SiO2PEGImBr) as a novel recoverable phase-transfer catalyst in H2O ( Scheme 1 and Table 2). The workup procedure was straightforward, and the catalyst could be reused over four times with almost no loss of catalytic activity and selectivity. [ABSTRACT FROM AUTHOR]

Abstract: Both enantiomers of β-nitro alcohols are versatile chiral building blocks. However, their synthesis using enzymes as catalysts has received little attention, with the exception of (S)-β-nitro alcohols produced in a reaction catalyzed by an S-selective hydroxynitrile lyase (HNL) from Hevea brasiliensis (HbHNL). An R-selective HNL containing an α/β-hydrolase fold from the noncyanogenic plant Arabidopsis thaliana (AtHNL) accepts nitromethane (MeNO2) as a donor in a reaction with aromatic aldehydes to yield (R)-β-nitro alcohols (Henry reaction; nitro aldol reaction). This reaction proceeded in an aqueous–organic biphasic system. The organic solvent giving the highest enantioselectivity was n-butyl acetate (AcOBu) with an optimum aqueous phase content of 50% (v/v). This is the first example of the R-HNL-catalyzed synthesis of (R)-β-nitro alcohols. [Copyright &y& Elsevier]

Abstract: Acrylic monomers are a significant part of the global economy, contributing to the manufacture of over a billion tons of diverse polymeric consumer products every year. The development of more efficient, greener methods to manufacture this highly demanded class of compounds is an important goal in the realization of a sustainable chemical industry. The pursuit of environmentally benign production processes has inspired a rich body of industrial and academic research on methods for the catalytic hydration of nitriles, and this review surveys both established and newer methods of generating acrylic amides, acids, and esters from nitrile and cyanohydrin substrates. The review also examines synthetic and mechanistic studies of homogeneously catalyzed nitrile hydration reactions with an emphasis on explicating the parameters that impact catalyst performance. The final section is a discussion of catalyst properties, gleaned from the mechanistic studies, that will be useful in designing the next generation of nitrile hydration catalysts. [Copyright &y& Elsevier]

The catalytic potential of carbon nucleophiles has seldom been disclosed due to their reactivity toward carbon electrophiles to form stable carbon-carbon bonds, which are too strong to be cleaved for the expected catalytic cycles. We have developed an efficient catalytic cyanosilylation of carbonyl compounds with an in situ generated alkene/phosphine adduct, which is tuned not to couple with a carbonyl compound or an electron-deficient alkene under the reaction conditions when its nucleophilicity is translated into catalytic activity. In the presence of 3 mol% of methyl acrylate and 3 mol% of triphenylphosphine, a broad range of alkyl, alkenyl, and aryl ketones and aldehydes undergo cyanosilylation reaction with trimethylsilyl cyanide at room temperature to yield structurally diversified cyanohydrin silyl ethers in excellent yields. By using methyl acrylate/triphenylphosphine as a highly effective nucleophilic catalyst system for the cyanosilylation of carbonyl compounds, this study demonstrates a new concept for the development of useful organocatalysis utilizing the nucleophilicity of alkene/phosphine adducts generated in situ. [ABSTRACT FROM AUTHOR]

Summary: The α/β hydrolase superfamily contains mainly esterases, which catalyze hydrolysis, but also includes hydroxynitrile lyases, which catalyze addition of cyanide to aldehydes, a carbon-carbon bond formation. Here, we convert a plant esterase, SABP2, into a hydroxynitrile lyase using just two amino acid substitutions. Variant SABP2-G12T-M239K lost the ability to catalyze ester hydrolysis (<0.9 mU/mg) and gained the ability to catalyze the release of cyanide from mandelonitrile (20 mU/mg, kcat/KM = 70 min-1M-1). This variant also catalyzed the reverse reaction, formation of mandelonitrile with low enantioselectivity: 20% ee (S), E = 1.5. The specificity constant for the lysis of mandelontrile is 13,000-fold faster than the uncatalyzed reaction and only 1300-fold less efficient (kcat/KM) than hydroxynitrile lyase from rubber tree. [ABSTRACT FROM AUTHOR]

A molecular recognition mechanism based on dimeric model for cyclic dipeptide Cyclo[(S)-His-(S)-Phe] (abridged CHP) catalyzed autoinduction is proposed according to the inference of previous experimental findings, which is supported by theoretical calculation with Oniom(B3LYP/3-21G*:AM1) method. The most unstable CHP dimer whose intermolecular hydrogen bonds are immensely lessened by two intramolecular hydrogen bonds is defined as the highest active component (IIa) existing in solid among the three possible dimers (Ia, IIa, and IIb). The carbonyl group of benzaldehyde coordinates to CHP dimer (IIa) by a hydrogen bond with Phe–NαH rather than His–NαH and HCN interacted with the imidazole moiety of His residue to form cyanide ion. In view of the theoretical calculation and experimental results, the structures of the nine-ring complexes derived from interaction between catalytic active dimer CHP(IIa) and cyanohydrins were postulated to explain the enantioselective autoinduction: The structure of no nitrile involved six-ring complex derived from interaction between catalytic active dimer CHP(IIa) and cyanohydrins were postulated to explain the elimination of enantioselective autoinduction. [ABSTRACT FROM AUTHOR]

The nitroaldol (Henry) reaction is a valuable C−C bond-forming reaction resulting in β-nitro alcohols, which are important building blocks for the synthesis of bioactive compounds. Metal-dependent bacterial hydroxynitrile lyases with a cupin fold couple nitromethane or nitroethane and various aldehydes to yield ( R)-β-nitro alcohols with up to 90 % conversion and up to ≥99 % enantiomeric excess. [ABSTRACT FROM AUTHOR]

Abstract: One-pot three components synthesis of O-acetylcyanohydrins has been developed in the presence of B(C6F5)3 as the catalyst. Variety of aldehydes or ketones reacts with TMSCN and acetic anhydride (Ac2O) under the influence of 1mol% of B(C6F5)3 to give good to excellent yield of the products without solvent at rt. [Copyright &y& Elsevier]

Dipeptide cyclo[(S)-His-(S)-PheI 1, first applied by Inoue et al. in 1981, catalyzes the hydrocyanation of aromatic aldehydes very efficiently. Enantioselective autoinduction has also been reported for the process. We have employed QM (density functional theory and MP2), molecular mechanics (MM), and molecular dynamics (MD) methods to (i) derive a mechanistic picture for catalysis and (ii) reveal the origin of stereochemistry and autoinduction. A dimer is proposed to be the catalytic species, in which one imidazole group is essential for the delivery of the nucleophile and the second imidazole group acts as an acid, accompanied with n-interaction for most favorable substrate binding. Hydrogen-bonding via hydroxy groups is crucial for catalysis also. MD studies indicate stability of the dimer only in non-polar media, which is consistent with the need of the experimental (heterogeneous) reaction conditions to achieve high enantioselectivities. DFT and MP2 results suggest the incorporation of the product cyanohydrin via extended edge-to-face π-interaction over three aromatic units. Transition states derived from this model are in good agreement with experimental findings and enantioselectivities. [ABSTRACT FROM AUTHOR]

High-yielding cyanosilylation of ketones with NaCN and various chlorotrialkylsilanes in DMSO proceeds smoothly without catalysis to give silyl-protected ketone cyanohydrins. The unique role of DMSO consists in rendering naked cyanide anions that reversibly add to the C=O bond at the rate-determining step followed by fast trapping of the transient tertiary sodium cyanoalcoholates with chlorotrialkylsilanes or in situ generated cyanotrialkylsilanes. Preparatively, the reaction matches the best known catalytic cyanosilylation systems applying expensive Me3SiCN and demonstrates unprecedented efficiency in the synthesis of sterically congested trialkylsilyl-protected cyanohydrins. [ABSTRACT FROM AUTHOR]

Abstract: A variety of cyanohydrin THP ethers were readily prepared from carbonyl compounds with trimethylsilyl cyanide and tetrahydropyran-2-yl acetate under the influence of a catalytic amount of iron(III) triflate in a convenient one-pot procedure. This method was also effective to prepare O-protected cyanohydrins by various acetal-type protective groups. [Copyright &y& Elsevier]

Benzil (1,2-diphenylethane-1,2-dione) undergoes cyanide catalyzed condensation with benzaldehyde to yield O-benzoylated benzoin (2-benzoyl-1,2-diphenylethanone). In this study, the experimentally suggested mechanism has been modeled with PM3 and verified with B3LYP. The effect of the substituent on the reaction yield has been rationalized by considering two benzil derivatives; 1,2-bis(2-chlorophenyl)ethane-1,2-dione and 1,2-bis(2-fluorophenyl)ethane-1,2-dione and three benzaldehyde derivatives; o-fluorobenzaldehyde, o-methylbenzaldehyde and 2-pyridinecarboxaldehyde. The effect of the solvent has been modeled by using the isodensity-surface polarizable continuum (IPCM) model. Reactivity descriptors have been used to justify the reactivity differences of the various substituents. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [ABSTRACT FROM AUTHOR]

Abstract: Cyanohydrins 2 of O-protected 4-hydroxycyclohexanones 1 are excellent starting compounds for the synthesis of Isorengyol ( I ) and Rengyol ( II ). The cyano group of the O-benzyl derivative 2d is first converted into the corresponding aldehyde 4 , which via Wittig olefination led to the vinyl compound 6 . Hydroboration of the trans-derivative ( trans-6 ) leads, after debenzylation, to Isorengyol, whereas hydroboration and debenzylation of the cis-isomer ( cis-6 ) gives Rengyol. With hydroxynitrile lyases (HNLs) as catalysts the stereoselective preparation of cis- as well as trans-cyanohydrin 2d is possible, which enables the selective preparation of Isorengyol or Rengyol, respectively. The trans-configuration of Isorengyol and the cis-configuration of Rengyol were secured by X-ray crystal structure analysis. [Copyright &y& Elsevier]

Various aldehydes undergo enantioselective silylcyanation with (CH3)3SiCN trimethylsilylcyanation (TMSCN) employing chiral Mn(salen) and achiral POPh3 as the catalysts. This is the double activation where Mn(salen) plays the role of Lewis acid and POPh3 Lewis base. Numerous aldehydes are subject to the enantioselective addition of TMSCN at 0°C. Hydrolysis of the adduct gave cyanohydrin with up to 96% yield and 62% ee. [ABSTRACT FROM AUTHOR]

The reaction of spiroepoxycyclohexadienones 1 with TMSCN in the presence of catalytic amounts of Bu4NCN results in the formation of two diastereomeric cyanohydrins. Alternatively, the reaction of 1 with equimolecular amounts of Bu4NCN gave rise to products arising from two other different reaction paths. [Copyright &y& Elsevier]

The room temperature addition of trimethylsilylcyanide to aromatic and aliphatic aldehydes to give the corresponding cyanohydrins is efficiently catalysed by 1 mol% of ((2,6-bis(N-cyclohexyl)imino)phenyl)aquoplatinum(II) trifluoromethanesulfonate 1a. This methodology is also applicable to the addition of trimethylsilylcyanide to Schiff bases resulting in the formation of α-amino nitriles. [Copyright &y& Elsevier]

Two vanadyl salen complexes having peripheral styryl substituents have been reacted with 1-methyl-3-(3-mercaptopropyl)-imidazolium chloride using azoisobutyronitrile as radical initiator. The resulting compounds contain at the same time a vanadyl salen complex and one imidazolium cation. In agreement with the expectations in view of their structure, these compounds were insoluble in conventional organic solvents, but completely miscible in imidazolium ionic liquids. These vanadyl salen complexes bonded to an imidazolium cation are highly active and reusable catalysts for the cyanosilylation of aldehydes. Moderate enantiomeric excesses were obtained using the chiral version of this complex. [Copyright &y& Elsevier]

The addition of HCN to 4-alkylcyclohexanones 1 to give cyanohydrins 2 is strongly catalyzed by hydroxy-ni trile lyases (HNLs). With PaHNL, from bitter almond, trans-addition occurs almost exclusively, yielding trans-2. With MeHNL, from cassava, cis-addition is preferred to give cis-2. cis-Selectivity is nearly quantitative, especially for cyclohexanones with larger 4-substituents. Comparable results with respect to the stereoselectivity were observed in the HNL-catalyzed addition of HCN to 4-alkoxycyclohexanones 3a–g. In contrast, the stereoselectivity in the HNL-catalyzed addition to 4-alkanoyloxycyclohexanones 3h–k is very poor. The transformation of cis-4-propylcyclohexanone cyanohydrin (2c) into the corresponding cis-spirotetronic acid 7 occurs without any isomerization.Key words: enzyme, hydroxynitrile lyase, cyclohexanones, cyanohydrins, cis/trans-stereoselectivity.L'addition du HCN sur les 4-alkylcyclohexanones (1) conduisant à la formation de cyanohydrines (2) est fortement catalysée par les lyases d'hydroxynitriles (« HNL »). Sous l'influence d'une PaHNL obtenue à partir de l'amande amère, l'addition se fait pratiquement exclusivement de façon trans, conduisant aux trans-2. Avec une MeHNL tirée de cassava, l'addition se fait préférentiellement de façon cis pour conduire aux cis-2. Dans les cas de cyclohexanones portant des substituants encombrants en position 4, la sélectivité cis est pratiquement quantitative. Des résultats de stéréosélectivités comparables sont aussi obtenus lors de l'addition de HCN, catalysée par une lyase d'hydroxynitrile, aux 4-alcoxycyclohexanones (3a-g). Par opposition, la stéréosélectivité de l'addition de HCN, catalysée par une lyase d'hydroxynitrile, sur les 4-alcanoyloxycyclohexanones (3h-k) est très faible. La transformation de la cyanohydrine de la cis-4-propylcyclohexanone (2c) en acide cis-spirotétronique correspondant (7) se réalise sans épimérisation.Mots clés : enzyme, lyase d'hydroxynitrile, cyclohexanones, cyanohydrines, stéréosélectivité cis/trans.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

This paper reviews our work with enantioselective lanthanide reagents and catalysts for organic synthesis. Heterometallic reagents M3[Ln(binol)3] (M=Li; Ln=lanthanide; H2binol=binaphthol) mediate the addition of RLi to aldehydes with ee''s of up to 84%. Structural studies have been carried out where M=Li or Na, Ln=Eu, Y or Yb and with enantiomerically pure or racemic binol. There are important differences in coordination chemistry dependent on the ionic radius of M and Ln. [LnCl3(pybox)2] are effective catalysts for the silylcyanation of aldehydes, giving ee''s of up to 89% under convenient reaction conditions. Structural studies have been undertaken on [Ln(OTf)3(Pri&z.sbnd;pybox)2] for Ln=La, Eu or Yb. [Copyright &y& Elsevier]

Ethoxycarbonyl cyanohydrins and O-acyl cyanohydrins are examples of O-protected cyanohydrins in which the protecting group presents an electrophilic center, contributing to additional reaction pathways. The first section of this review describes recent advances on the synthesis of O-ethoxycarbonyl and O-acyl protected cyanohydrins. Reactions using KCN or alkyl cyanoformates as the cyanide ion source are described, as well as organic and transition metal catalysis used in their preparation, including asymmetric cyanation. In a second part, transformations, and synthetic applications of O-ethoxycarbonyl/acyl cyanohydrins are presented. A variety of structures has been obtained starting from such protected cyanohydrins and, in particular, the synthesis of oxazoles, 1,4-diketones, 1,3-diketones, 2-vinyl-2-cyclopentenones through various methods are discussed. [ABSTRACT FROM AUTHOR]

Abstract: Chemoenzymatic asymmetric synthesis of antidepressant agent venlafaxine and its analogue have been reported in this communication. The main highlight of the reported synthesis is the stereoselective synthesis of cyanohydrins by (S)-hydroxynitrile lyase (Hevea brasiliensis) followed by lipase catalyzed kinetic resolution. [Copyright &y& Elsevier]

Formaldehyde and other simple carbonyl compounds are known to react rapidly with HCN in aqueous solution to produce the corresponding cyanohydrin compounds. We have observed that these cyanohydrins markedly accelerate the rate of HCN oligomeri-zation, both in homogeneous solution as well as in the frozen state. These results, for which a tentative mechanism is suggested, significantly extend the possible range of conditions for HCN oligomerization on the prebiotic Earth. [ABSTRACT FROM AUTHOR]

An abstract of the study "Efficient Nickel-Catalyzed Hydrocyanation of Alkenes Using Acetone Cyanohydrin as a Safer Cyano Source" by A. Khalaj and M. J. Khalaj is presented.

The developed method offers an alternative access to β-cyanohydrins and β-amino nitriles from 1,1-disubstituted propargyl alcohols and amines, respectively. [ABSTRACT FROM AUTHOR]

This article focuses on remarkable supramolecular catalysis of glycoside hydrolysis by a cyclodextrin cyanohydrin. The mildness, selectivity, and rate of enzymatic catalysis greatly exceed ordinary chemical catalysis. Enzymes use binding and proximity effects to achieve astounding rate enhancements for specific reactions and substrates. The authors reports on their remarkable observation that the dicyanohydrin 3 is a significantly better artificial enzyme, achieving kcat/kuncat of 200-2000 for hydrolysis of aryl glycosides. Compound 3 is obtained by reaction of known β-cyclodextrin dialdehyde with KCN in 77% yield, followed by hydrogenolysis of the benzyl protection groups. The cyanohydrin synthesis appears essentially stereoselective, and a single diastereomer is in any case obtained after purification.

A variety of cyanohydrin alkyl ethers were readily prepared from aldehydes with trimethylsilyl cyanide and alkoxy-trimethylsilane under the influence of a catalytic amount of iron(III) chloride in a convenient one-pot procedure. [ABSTRACT FROM AUTHOR]

The synthesis of a novel homochiral metal-organic catalyst for asymmetric cyanation of aldehydes is reported. [ABSTRACT FROM AUTHOR]

The indium triiodide-catalyzed transformation of carboxylic acids to β-hydroxy esters and cyanohydrins of type (XVII) is described. [ABSTRACT FROM AUTHOR]

A nickel(0) complex effectively catalyzes a sequential coupling reaction between allenes, alkynes and hydrogen cyanide generated from acetone cyanohydrin in a highly regio- and stereoselective fashion. [ABSTRACT FROM AUTHOR]

The title Ru(II)-catalyst systems exhibit excellent reactivity and enantioselectivity for asymmetric cyanosilylation of benzaldehyde. [ABSTRACT FROM AUTHOR]

In situ formed Ti(IV) complexes of pyrrolidine-based chiral salen ligands (I) derived from L-tartaric acid are evaluated in the enantioselective trimethylsilylcyanation of aromatic aldehydes. [ABSTRACT FROM AUTHOR]