D,/-Benzoin

D. Benzoin-a-oxime (cupron) (VII). This compound yields a green predpitate, CuC14Hu02N, with copper in dilute ammoniacal solution, which may be dried to constant weight at 100 °C. Ions which are predpitated by aqueous ammonia are kept in solution by the addition of tartrate the reagent is then spedfic for copper. Copper may thus be separated from cadmium, lead, nickel, cobalt, zinc, aluminium, and small amounts of iron. 

Die aus Alkoholen mit Thionylchlorid erhaltlichen Chlorsulfite werden durch Na-triumboranat in Athanolzu Kohlenwasserstoffen reduziert5,6 z.B. 4-Methyl-benzoin zum 1 -Oxo-2-phenyl-I-(4-methyl-phenyl)-athan (74% d.Th.)6 ... 

Endprodukt der Reduktion von Hydroxy- und 1,3-Dihydroxy-accton in Ammo-niak/Ammoniumchlorid (pH 9,3) an Quecksilbcr (—1,7 V) ist Aceton5. In waGrigcm 1,4-Dioxan (Leitsalz Natriumacetat) erhalt man bei 75-80° aus 4,4 -Dimethoxy-benzoin 70°/(1 d.Th. /-Oxo-1,2-bis- 4-methoxy-phenyl]-athan6. 

Immobilization of (3-D-glucosidase from almonds on photo-crosslinkable resin prepolymer (ENTP-4000) was carried out by the following procedure. One gram of ENTP-4000 was mixed with 10 mg of a photosensitizer, benzoin ethyl ether, and 110 mg of (3-D-glucosidase from almonds (3.4 units mg ). The mixture was layered on a sheet of transparent polyester film (thickness, ca. 0.5 mm). The layer was covered with transparent thin film and then illuminated with chemical lamps (wavelength range 300 00 nm) for 3 min. The gel film thus obtained was cut into small pieces (0.5 x 5 x 5 mm) and used for bioconversion reaction. 

Homoenolate Reactivity The ability to generate homoenolates from enals and its application to the preparation of y-butyrolactones 30, through reaction with an aldehyde or aryl trifluoromethyl ketone, was reported independently by Glorius [8], and Bode and Burstein [9] (Scheme 12.4). A sterically demanding NHC catalyst is required to promote reactivity at the d terminus and to prevent competitive benzoin dimerisation. Nair and co-workers have reported a similar spiro-y-lactone formation reaction using cyclic 1,2-diones, including cyclohexane-1,2-dione and substituted isatin derivatives [10]. 

This method has an analogy in the well known acyloin condensation, a reaction which takes place between two molecules of an aromatic aldehyde in a solution containing an alkali cyanide. Thus for example, benzaldehyde gives rise to benzoin, a compound in which the enediolic system, —C(OH)=C(OH)—, exists mainly in the ketonic form —CO—CHOH—. If a hydroxy aldehyde like D-glucose (X) is allowed to... 

As shown for 47 in Scheme 9, different methods were applied for the syntheses of these compounds (48 synthesized according to methods a-c). All reactions were carried out in acetonitrile at room temperature and compounds 47-jCH3CN and 48 were isolated as crystalline solids. The benzoin-mediated Si-C cleavage reactions (methods b-d in Scheme 9) are especially remarkable. 

Chemists were using cyanide ion for the synthesis of 1,2-D systems even before the concept of "reactivity inversion" was formally established. Thus, in the classical benzoin condensation, the cyanide-induced coupling of two aromatic aldehydes takes place according to the following mechanism [7] (Scheme 5.6) ... 

However, cyanide ion is not suitable for inducing a benzoin-type condensation between two aliphatic aldehydes, since the basic character of this ion induces an aldol condensation between them. In Nature, nevertheless, condensations of this type take place easily. As Breslow proposed in 1958 [8], such condensations are catalysed by thiamine pyrophosphate 6 (or cocarboxylase), the active part of which is the conjugate base of the "thiazolium cation present in it. According to Breslow [8a], the mechanism is, in fact, identical to that described for the cyanide ion (see Scheme 5.7) that is to say, the conjugate base of thiamine (TPP ) reacts with an "aldehyde equivalent -such as an a-ketoacid 2- to generate the corresponding "active aldehyde" 8 with umpoled reactivity, which then reacts with the electrophile to give finally, after elimination of "thiamine anion", a 1,2-D system (9). 

D. A. Nelson, Separation ofbenzoic acid, ethyl p-aminobenzoate and benzoin using ion exchange chromatography , http //www. dartmouth.edu/academia/chem/chemexp/organic man.html. 

P. Dtinkelmann, D. Kolter-Jung, A. Nitsche, A. S. Demir, P. Siegert, B. Lingen, M. Baumann, M. Pohl, M. Muller, Development of a donor-acceptor concept for enzymatic cross-coupling reactions of aldehydes, the first asymmetric cross-benzoin condensation. f Am. Chem. Soc. 2002, 124, 12084-12085. 

Using only benzaldehyde as substrate (see Fig. 3.1.8a), (R)-benzoin can be obtained on a 200 mg scale from a 40 mb two-phase system. This corresponds to a volumetric productivity of 53 g L d for the organic phase, or 20 g d with respect to the overall reaction volume. When using 2-chlorobenzaldehyde and 3-methoxybenzaldehyde as substrate in equimolar amounts, (R)-2-chloro-3 -methoxybenzoin is formed as the main product with approximately 80% selectivity (see Fig. 3.1.8b). The symmetric benzoins (2,2 -dichlorobenzoin, 3,3 -dimethoxybenzoin) are formed as side-products. The main product is obtained on a 150 mg scale, which corresponds to a volumetric productivity of 40 g L d with regard to the organic phase. 

Compound Extracts or Bouquets.—Extrait de bouquet.—Extraits de jasmin et violette, each two pints extraits d acaeia, rose, ceillet, et des flenrs d oranger, each one pint flowers of benzoin, two drachms tincture of amber, four ounces. Mix and filter. 

Both benzil and benzoin are reduced by TiCl3 in an acidic medium to hydrobenzoin (95% yield) but in this case the meso-isomer is strongly favored over the d/-isomer (—80 20). 

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