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At least 163 records · Page 9Linked to original sources
PubMed2001

The development of new monometallic bifunctional catalysts with Lewis acid and Lewis base properties, and their application in asymmetric cyanation reactions.

Bifunctional catalysts can drastically improve the efficiency of asymmetric processes with respect to enantioselectivity and/or conversion rate. A new type of chiral bifunctional catalyst has been developed recently in the Shibasaki group that contains both Lewis acid and Lewis base moieties. These monometallic and bifunctional phosphinoyl-containing catalysts are able to coordinate both nucleophilic and electrophilic substrates in the transition state. Several successful applications of this new catalytic concept in the field of asymmetric cyanation reactions have already been reported, for example, the asymmetric hydrocyanation of aldehydes and imines as well as the asymmetric Reissert reaction. The development and principle of this catalytic concept as well as main applications thereof are reviewed in this article.

Journal Article↗
PubMed2003

Aerobic ruthenium-catalyzed oxidative cyanation of tertiary amines with sodium cyanide.

RuCl3-catalyzed oxidative cyanation of tertiary amines with sodium cyanide under molecular oxygen (1 atm) at 60 degrees C gives the corresponding alpha-aminonitriles, which are versatile synthetic intermediates of various compounds such as amino acids and unsymmetrical 1,2-diamines, in excellent yields. This reaction is clean and should be an environmentally benign and useful process.

Amines↗
PubMed2005

Dual Lewis acid-Lewis base activation in enantioselective cyanation of aldehydes using acetyl cyanide and cyanoformate as cyanide sources.

Dual activation by a chiral Lewis acid and an achiral or chiral Lewis base enabled cyanation of both aromatic and aliphatic aldehydes with acetyl cyanide and ethyl cyanoformate to provide direct access to O-acetylated and O-alkoxycarbonylated cyanohydrins, respectively, under mild conditions. With a combination of a Ti-salen catalyst and Et3N, benzaldehyde was converted to the O-acetylated cyanohydrin with 94% ee within 10 h at -40 degrees C in 89% isolated yield.

Aldehydes↗
PubMed2005

Ligand-free palladium-catalyzed cyanation of aryl halides.

[reaction: see text] A practical, ligand-free cyanation of aryl bromides that utilizes as little as 0.1 mol % Pd(OAc)(2) in combination with a nontoxic cyanide source, M(4)[Fe(CN)(6)] (M = K, Na), is described. The reactions are performed in DMAC at 120 degrees C and provide the corresponding aryl nitrile in 83-96% yield, typically in less than 5 h. TON values of up to 7100 were attained.

Journal Article↗
PubMed2005

Highly diastereoselective cyanation of methyl ketimines obtained from (R)-glyceraldehyde.

[reaction: see text] Addition of trimethylsilyl cyanide to ketimines derived from (R)-2,2-dimethyl-1,3-dioxolan-4-yl methyl ketone to generate a quaternary stereocenter has been achieved with high yields and excellent diastereoselectivity. The stereoselectivity was found to be temperature and solvent dependent. The beta-hydroxy-alpha-amino nitrile of syn configuration was the major compound in kinetically controlled reactions, whereas the anti stereoisomer was obtained in excess in thermodynamically controlled reactions. Double stereodifferentiation under kinetic control conditions was successful, and the cyanation reaction occurred with complete syn diastereoselectivity using the matched pair. The versatility of the resulting amino nitrile as a synthetic intermediate was tested by performing the synthesis of orthogonally protected (R)-(2-aminomethyl)alanine.

Cyanides↗
PubMed2006

Palladium-catalyzed, copper(I)-mediated coupling of boronic acids and benzylthiocyanate. A cyanide-free cyanation of boronic acids.

A new method for the synthesis of nitriles is described. As a complement to the classic cyanation of aryl halides using cyanide sources and a transition metal catalyst, the palladium-catalyzed cross-coupling of thiocyanates with boronic acids in the presence of copper(I) thiophene-2-carboxylate (CuTC) affords nitriles in good to excellent yields.

Boronic Acids↗
PubMed2006

Stereocontrolled route to vicinal diamines by [3.3] sigmatropic rearrangement of allyl cyanate: asymmetric synthesis of anti-(2R,3R)- and syn-(2R,3S)-2,3-diaminobutanoic acids.

A stereocontrolled route via allyl 1,2-diols to vicinal diamines based on the [3.3] sigmatropic rearrangement of allyl cyanate has been developed. Our approach consists of two consecutive steps: stereoselective construction of allyl anti- and syn-1,2-diols followed by [1,3]-chirality transfer by sigmatropic rearrangement, which allow an access to anti-(2R,3R)- and syn-(2R,3S)-2,3-diaminobutanoic acids. [reaction: see text]

Acetaldehyde↗
PubMed1997

A study of cognitive functions in methyl-iso-cyanate victims one year after bhopal accident.

There is a paucity of information regarding the late effects of methyl-iso-cyanate (MIC) poisoning. In this study, the clinical and cognitive functions of 52 MIC victims were evaluated one year after the Bhopal gas accident. There were 15 severely, 14 moderately, and 23 mildly affected patients. Their mean age was 38.2 (range 15-65) years and 30 patients were males. Their clinical picture was dominated by respiratory symptoms in 36 patients, of which 17 had abnormal chest radiographs. Neurological examination of these patients was normal. Psychometry in 33 patients revealed significant impairment of standard progressive matrices (SPM), associate learning and motor speed and precision tests (p < 0.01) in severely exposed MIC patients. In the moderately affected group associate learning and motor speed and precision were significantly impaired. Motor speed and precision tests had significant positive correlation with eye signs (r = 0.42) and disability score (r = 0.68). Our results suggest significant cognitive impairment in severely exposed MIC victims.

Accidents, Occupational↗