Cyanhydrin synthesis

Induction of Asymmetry by Amino Acids. No fewer than sis types of reactions can be carried out with yields of 75—100% usiag amino acid catalysts, ie, catalytic hydrogenation, iatramolecular aldol cyclizations, cyanhydrin synthesis, alkylation of carbonyl compounds, hydrosdylation, and epoxidations (91). 

The presence of oe-hydroxycarboxylic acids together with a-aminoacids could lead to an estimate of the local concentration of ammonia when these molecules were synthesised. Such an estimation method implies the assumption that the syntheses of the two classes of molecules were simultaneous and started from the same organic substrate, i.e. aldehydes25 . From aldehydes, aminoacids can be obtained by the Strecker synthesis (aldehyde, HCN, NH3 in aqueous solution), while hydroxyacids can be synthesised from the cyanhydrin synthesis (aldehyde + HCN) followed by a hydrolysis. Nevertheless, it must be emphasised that all aminoacids detected in carbonaceous chondrites cannot be obtained by the Strecker synthesis. This remark limits the interest of the previous arguments concerning the concentration of NH3 during the accretion phase. 

A similar mixture in whieh the ( )-isoretronecanol predominated resulted from the Dieckmann ring closure of methyl 3-(2 -carbomethoxy-A-p5T rolidyl)propionate (XLII) to XLIII followed by the cyanhydrin synthesis. 

Peptide-catalysed Cyanations Cyanhydrin Synthesis and Strecker Reactions... 

In the context of asymmetric cyanhydrin synthesis applying q cZo-peptide 50 as catalyst Danda and coworkers studied the positive influence of lowered viscosity of the reaction mixture on enantioselectivity and the asymmetric autocatalytic properties of the reaction system.During the following years other groups carried out further computational and mechanistic... 

The isotopically labeled a-hydroxy carboxylic group indicates the use of the cyanide ion in cyanhydrin synthesis and consequently 1,2-CO disconnection in the first retrosynthetic step (Scheme 5.5). 

Aldonic acids may also be prepared from an aldose with one carbon atom less by the Kiliani cyanhydrin synthesis (see Chapter I, p. 37). A new asymmetric centre is produced and two epimeric acids in varying amounts . 

Initial preparative work with oxynitrilases in neutral aqueous solution [517, 518] was hampered by the fact that under these reaction conditions the enzymatic addition has to compete with a spontaneous chemical reaction which limits enantioselectivity. Major improvements in optical purity of cyanohydrins were achieved by conducting the addition under acidic conditions to suppress the uncatalyzed side reaction [519], or by switching to a water immiscible organic solvent as the reaction medium [520], preferably diisopropyl ether. For the latter case, the enzymes are readily immobilized by physical adsorption onto cellulose. A continuous process has been developed for chiral cyanohydrin synthesis using an enzyme membrane reactor [61]. Acetone cyanhydrin can replace the highly toxic hydrocyanic acid as the cyanide source [521], Inexpensive defatted almond meal has been found to be a convenient substitute for the purified (R)-oxynitrilase without sacrificing enantioselectivity [522-524], Similarly, lyophilized and powered Sorghum bicolor shoots have been successfully tested as an alternative source for the purified (S)-oxynitrilase [525],... 

Brussee, J., Van der Gen, A. Biocatalysis in the Enantioselective Formation of Chiral Cyanhydrins, Valuable Building Blocks in Organic Synthesis. In Stereoselective Biocatalysis, Patel, R. N. Ed., Dekker New York, 2000, p. 289. 

A new synthesis of reserpine (Scheme 19)60 makes use of a very neat synthesis of cw-hydroisoquinoline derivatives, e.g. (Ill), by means of a Diels- Alder /Cope rearrangement sequence. Manipulation of (111) by unexceptional methods then gives (112), which possesses the required stereochemistry in ring E. Oxidative cyclization of (112) affords 3-isoreserpinediol (113) but, unfortunately, some inside isomer, originating from the cyclization of C-2 with C-21, is also obtained. The synthesis also loses some elegance in the multi-stage conversion of 3-isoreserpinediol into 3-isoreserpine (114), since, in the Swem oxidation of the C-16 aldehyde cyanhydrin by means of DMSO with oxalyl chloride as activator, the over-oxidized products (115) and (116) were obtained. However, reduction of (115) gave 3-isoreserpine (114), which has previously been converted into reserpine by four different methods. 

The total synthesis of the seneciphyllic acids has been effected by Edwards et al. (176). The cyanhydrin of 3-rnethylbut-3-en-2-one (CXXXIII) was converted by way of the orthomethyl ester to methyl... 

The most common procedure for the technical synthesis of the monomer methyl methacrylate (MMA) is the reaction of acetone cyanhydrine with water and methanol in the presence of concentrated sulfuric acid [11] ... 

Acrylonitrile (AN) was first synthesized in 1893 by Moureu [593], who was also the first (one year later) to report on an acrylonitrile polymer (PAN). The first synthesis of AN was based on the dehydration of ethylene cyanhydrine (1-cyanoethanol) or acrylamide. Early industrial processes for AN production also used ethylene cyanhydrine as starting material, but since 1960 practically the entire AN production has been based on catalytic ammonoxidation of propene. More detailed information on the industrial production processes for AN is given in Ref. [594]. A number of recently published review papers from Japan deals with the ammonoxidation of propane rather than propene to produce acrylonitrile [595 599]. Information on toxicity, mutagenicity, teratogenicity and carcinogenicity of acrylonitrile can be found in Refs. [600-604]. 

Cyanotrimethylsilane has found extensive use as a reagent for a variety of synthetic transformations, and an improved synthesis has been described. The preparation of silylated cyanhydrins has also been improved in a two-stage one-pot synthesis which utilises cyanotrimethylsilane, prepared without isolation and prior to the addition of the carbonyl component (Scheme 24). ... 

Rubranitrose has been characterized as 2,3,6-trideoxy-3-C-methyl-4-0-methyl-3-nitro-L-xylo-hexose (23) by X-ray crystal analysis of its B-acetate ° and confirmed as an L-series sugar derivative by a synthesis from 2-deoxy-D-ribo-hexose using the cyanhydrin aziridine chacin-branching procedure outlined in Scheme 7. ... 

Some methods for the synthesis of thiophene-substituted 1,4-diketones begin with the transformation of acetylthiophene. 2-Acetylthiophene 61 is reacted in a Mannich reaction with formaldehyde and dimethylamine to yield the corresponding Maimich base 62 in 70% yield. The Mannich base 62 is then subjected to a Stetter reaction [109] which results in l,4-di-(2 -thienyl)-l,4-butanedione 63 in 70% yield via the cyanhydrine of 2-thiophenecarbaldehyde [110]. Reaction of Mannich base 62 with the isomeric 3-thiophenecarbaldehyde under the same conditions results in l-(2 -thienyl)-4-(3 -thienyl)-l,4-butanedione 64 in lower (35%) yield [Eq. (27)] [110]. 

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