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Condensation reactions glyoxal

Mechanistically, the reaction of diketosulfides and glyoxal likely proceeds via an initial aldol reaction to provide 22. A second intramolecular aldol reaction and the elimination of two equivalents of water produce the thiophene 23. The timing of the elimination reactions and the ring-closing, carbonyl condensation reaction is not completely understood. However, 2,5-disubstituted thiophenes 23 are available in good yields via this process. [Pg.203]

Aromatic aldehydes 1 can undergo a condensation reaction to form a-hydroxy ketones 2 (also called benzoins) upon treatment with cyanide anions.This reaction, which is called benzoin condensation, works by that particular procedure with certain aromatic aldehydes and with glyoxals (RCOCHO). [Pg.37]

The presence of intense peaks corresponding to the halved molecular weight in the mass spectra of the compounds prepared from a condensation reaction between the trimeric dihydrate of glyoxal and A, A -dialkylsulfamides lent credence to the proposition that the products of reaction were the [l,3]dioxolo[4,5-c][l,2,5]thiadiazoles 49 and not the alternative tetracyclic structures 50 <2001MC138>. [Pg.211]

The reaction is facile, and it is still the most widely used for the synthesis of both quinoxaline itself and many of its substituted derivatives. The condensation of glyoxal with o-phenylenediamine, followed by sodium carbonate addition, yields quinoxaline in almost quantitative yield.10... [Pg.370]

The standard synthesis for cyclam was developed by Barefield and Wagner in 1976.29 They used similar starting materials to the van Alphen procedure but the cyclisation yield is improved through the use of a nickel (II) template. Glyoxal completes the macrocycle by a Schiff base condensation reaction. The resulting imine functionalities are reduced with sodium borohydride to leave the complexed macrocycle. The metal ion is then removed by reaction with cyanide and the free ligand extracted with chloroform (Scheme 3.19). Yields are typically in the region of 60%. [Pg.200]

CL-20 is obtained by the condension of glyoxal with benzylamine in an acid catalyzed reaction to yield hexabenzylhexaaxaisowurtzitane (Fig. 1.8). Afterwards the benzyl groups are replaced under reducing conditions (Pd-C catalyst) by easily removable acetyl substituents. Nitration to form CL-20 takes place in the final reaction step. [Pg.16]

With unsymmetrically substituted 1,2-dicarbonyl compounds the reaction, following routes c or d, might afford isomeric reaction products. This has been in fact established when condensing methyl-glyoxal with cyanoacethydrazide. The isomeric 6-methyl (19) and 5-methyl (20) derivatives were obtained in a 2 1 ratio. [Pg.230]

The reactivity of the hetero ring, with electron deficient 2(3)-positions, has been compared to glyoxal diimine." Quinoxalines are deactivated towards electrophilic substitutions, however, substitution is most likely to occur at the equivalent positions 5 and 8, where electron-localization calculations show the highest electron density to be. Electron-donor substituents in the benzenoid ring facilitate electrophilic substitution and, when activating substituents are present in the hetero ring, the site of reaction depends on the reaction conditions. In deprotonated alkyl-substituted quinoxalines an increased number of resonance possibilities exists and mildly basic conditions arc usually required for condensation reactions. [Pg.193]

Properties Yellow crystals or light-yellow liquid mild odor. Mp 15C, bp 51C, d 1.14 (20/20C), bulkd 10.0 lb/gal (20C), vapor has a green color and burns with a violet flame, refr index 1.3826 (20C). Polymerizes on standing or in presence of a trace of water. An aqueous solution contains monomolecu-lar glyoxal and reacts weakly to acid. Undergoes many addition and condensation reactions with amines, amides, aldehydes and hydroxyl-containing materials. Glyoxal VP resists discoloration. [Pg.616]

Polymer 56, soluble in DMF or DMSO, can be prepared by the condensation of amino-substituted [Ru(bpy)3]2+ with glyoxal [112]. This polymer showed weaker emission than the free Ru chromophore that was attributed to less efficient intersystem crossing to the 3MLCT state. Similar condensation reactions with diacid anhydrides to produce polyimides have been reported [113]. These polymers showed long-wavelength emission associated with charge-transfer states. [Pg.263]

A third basic synthetic approach to L-ascorbic acid involves the combination of C4 and C2 carbon units. An example of this is the benzoin condensation reaction between L-threose and ethyl glyoxalate in the presence of sodium cyanide (Figure 4.6 j. [Pg.57]

Diaminopyridine has been condensed with glyoxal, benzil, - diacetyl,and the pyridils 4. ° Ethyl oxalate yields the 2,3-dioxo compound. The conditions employed for these condensations can be critical. Thus glyoxal in neutral solution yields an unidentified, insoluble, infusible solid, whereas in the presence of acetic acid the reaction readily provides the parent heterocycle.The preferred method makes use of glyoxal sodium bisulfite. Many symmetrical dicarbonyl compounds have been condensed with a variety of 2,3-diaminopyridines substituted in the pyridine ring by bromo, ° chloro, methyl, " or combinations of these substituents. ... [Pg.498]

Another belt-shaped molecule is cucurbituril (53) which was presumably synthesized as early as 1905 by Behrend et al. [42]. The structural formula of 53 was resolved in 1981 by Freeman. Mock, and Shih [43] only when modern spectroscopic methods were available. Cucurbituril (53) is easily obtained from urea, glyoxal, and formaldehyde in an acid-catalyzed condensation reaction with glycoluril (52) as an intermediate. The initially formed polycondensation product, insoluble in all common solvents, is treated with hot concentrated sulfuric acid. After dilution with water and subsequent boiling a solid is obtained in a yield of 40-70%. The H-NMR spectrum shows only three signals of equal intensity and the infrared spectrum suggests retention of the glycoluril moieties. The compound is not suitable for usual mass spectrometry due to its low volatility. However, an X-ray crystal structure of the calcium complex obtained from sulfuric acid solution was undertaken. [Pg.194]

The new condensation reactions of amines with glyoxal to yield hexa-azaisowurtzitane derivatives 51 appear to be limited to benzylamine and certain phenyl-substituted benzylamines. Primary aliphatic amines and anilines usually form dicarbinolamines 52 or diimines 53 (Refs. 108-112). With certain arylamines, such as 2-chloroaniline or aniline itself, one may obtain 52 or l,r,2,2 -tetrakis(arylamino)ethanes (Ref. 109). The condensation of benzylamine with glyoxal was apparently not described in the literature prior to our report (Ref. 107). However, condensations of a-methylbenzylamine and a,o -dimethylbenzyiamine with glyoxal have been reported to produce diimines (53, R = QHjCHCHj and QH5C(CH3)2, respectively) (Refs. 111,112). [Pg.113]

Starting material for the synthesis of varenicline is o-bromofluorobenzene, which reacts (via benzyne) with cyclopentadiene in a Diels-Alder reaction. Oxidative ring-opening and reductive amination provides a N-benzylbenz-azepine derivative. After N-protection with trifluoroacetic anhydride, nitration with a mixture of nitric andtrifluoromethanesulfonic acids, reduction, and condensation with glyoxal, hydrolysis of the trifluoroacetamide as a final step provides the active compound in good overall yield. [568, 569]... [Pg.498]


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See also in sourсe #XX -- [ Pg.18 ]




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