Subject Aromatic aldehydes

Further, isoxazole derivatives were subjected to two related reactions. 3,5-Dimethylisoxazole was found to react in the presence of dry hydrogen chloride with aromatic aldehydes (chlorobenzylation, 72- 71),and with formaldehyde in the presence of sulfuric acid it undergoes hydroxymethylation (72- 73). ... 

Tu found that when aniline was used instead of the secondary amine under otherwise identical conditions 2,4-diphenyl-substituted quinoline was formed in 56% yield. Phenylacetylene and aniline were initially used as model substrates for exploring the aldehyde scope. With aromatic aldehydes the reactions proceeded smoothly to give the corresponding quinolines in moderate to good yields. A heteroaromatic aldehyde is also compatible with this transformation and the expected product was afforded in 83% yield. However, when ahphatic aldehydes were subjected to the reaction, the desired product was obtained in low yield (Scheme 19) [34]. 

Reversed micelles have also shown to be useful not only in bioconversions, but also in organic synthesis. Shield et al. (1986) have reviewed this subject and brought out its advantages in peptide synthesis, oxidation or reduction of steroids, selective oxidation of isomeric mixtures of aromatics, etc. In the oxidation of aromatic aldehydes to carboxylic acids with enzymes hosted in reverse micelles, the ortho substituted substrates react much more slowly than other isomers. 

P-Hydroxyketones are also subject to fragmentation. Lewis acids promote fragmentation of mixed aldol products derived from aromatic aldehydes.100... 

Et2Zn also participates in the reductive coupling as a formal hydride source. Results for the Ni-catalyzed, Et2Zn-promoted homoallylation of carbonyl compounds with isoprene are summarized in Table 7 [30]. Et2Zn is so reactive that for the reaction with reactive aromatic aldehydes it causes direct ethylation of aldehydes, and the yields of homoallylation are diminished (runs 1 and 2). Unsaturated aldehydes seem to be subject to the Michael addition of Et2Zn. Accordingly, for the reaction with cinnamaldehyde, none of the expected homoallylation product is produced instead, the 1,4-addition product of Et2Zn, 3-phenylpentanal is produced exclusively (run 3). 

The research has inspired related investigation into the coupling reaction between aromatic aldehydes and benzyl bromide or chloride in water. The yields are slightly higher than the results for allylation despite the fact that aqueous benzylation is intrinsically more difficult than allylation. It is also found that the coupling reaction is chemoselective for aromatic aldehydes over aliphatic aldehydes, and also for aromatic aldehydes over aromatic ketones.98 Aqueous Grignard chemistry is attractive for its use of an environmentally benign solvent, and has been the subject of several... 

Some 4,5-dihydro[l,2,4]triazolo[3,4-r-]benzo[l,2,4]triazines 57 easily reacted with aromatic aldehydes to result in the formation of synthetically valuable azomethine imines 58 <2005EJO3553>. The transformation took place at room temperature in the presence of tetrafluoroboric acid in 10 min in high yields. The product 58 was conveniently prepared and stored in the form of tetrafluoroborate salt, and was subjected to further reactions (e.g., 1,3-dipolar cycoadditions see Section 11.19.5.4.) by in situ liberation of the free base prior to transformation. 

Toniolo reported the carbonylation of aromatic aldehydes containing electron-donating substituents with a Pd/PPh3 catalyst system in the presence of HC1 to give phenylacetic acid derivatives [64]. No activity was observed in the absence of PPI13 or HC1, and high yields could be achieved with alkanols as solvent (e.g., EtOH). It is believed that the mechanism involves HC1 addition to the aldehyde, with the resultant chlorohydrin being subject to oxidative addition to Pd, CO insertion, and alcoholysis. Upon Cl -o- OR substitution with the formed mandelic acid derivative, a second carbonylation takes place,... 

Ethanal (acetaldehyde), the product of ADH and CYP action on ethanol is the substrate for isoforms of ALDH. Like ADH, ALDH isoenzymes are not entirely substrate specific and will act on aliphatic and aromatic aldehydes to generate the corresponding carboxylic acid. There are nine genes encoding ALDH isoforms and all are subject to polymorphism and the enzyme products of ALDH gene expression are found widely in... 

In the process of developing the Stetter reaction in ionic liquids, Gree and coworkers applied their methodology to the synthesis of haloperidol (Scheme 25) [101], A variety of aromatic aldehydes react with methyl acrylate 160 when butyl-methylimidazolium tetrafluoroborate [bmim][BF ] is used as solvent. In the synthesis of haloperidol, electron-deficient aldehyde 153 was subjected to standard reaction conditions with 160 to provide 161 in good yield. 

A vast array of piperidine containing cores, both natural and synthetic, are of biological and medicinal interest. These heterocyclic scaffolds have been the subjects of considerable synthetic efforts, especially for the construction of optically active compounds. In this context, Khan et al. reported a catalytic bromodi-methylsulfonium bromide (BDMS) three-component reaction of 1,3-dicarbonyls with aromatic aldehydes and aromatic amines for a facile access to highly functionalized piperidines (Scheme 24) [104]. This strategy is an interesting illustration of... 

To determine the reasons for this, DHP s were prepared from a mixture of [ring-2-3H] p-coumaryl alcohol and [or-14C] coniferyl alcohol in the presence of carbohydrates by the procedure described above (35). The LCC fraction so obtained was subjected to combustion, and the exact p-hydroxyphenylpropane guaiacylpropane ratio was determined from the activity of 3H20 and 14C02 released (Figure 2). A portion of the same LCC fraction was also oxidized with nitrobenzene and alkali, and the resulting liberated aromatic aldehydes were then analyzed by HPLC. Results are shown in Table V. 

Dialdehydes as substrates for BFD Being aware that meta-substituted aromatic aldehydes provide the highest ee values combined with good to excellent conversion rates, we subjected isophthalaldehyde 37 to the BFD-catalyzed coupling reaction (Scheme 2.2.7.20) [57]. 

Nitroalcohols 3a-j were isolated in good yields when a mixture of aromatic aldehydes 1 (10 mmol) and nitro compound 2 (10 mmol) adsorbed on Si02 (finer than 200 mesh, 5 g) and taken in a open Pyrex test tube was subjected to micro-wave irradiation in a domestic microwave oven (BPL, BMO 700T) at an out-put of about 600 W. After cooling the reaction mass to room temperature, the products were isolated by extracting with dichloromethane and evaporation of the sol-... 

Secondary amines can be prepared from the primary amine and carbonyl compounds by way of the reduction of the derived Schiff bases, with or without the isolation of these intermediates. This procedure represents one aspect of the general method of reductive alkylation discussed in Section 5.16.3, p. 776. With aromatic primary amines and aromatic aldehydes the Schiff bases are usually readily isolable in the crystalline state and can then be subsequently subjected to a suitable reduction procedure, often by hydrogenation over a Raney nickel catalyst at moderate temperatures and pressures. A convenient procedure, which is illustrated in Expt 6.58, uses sodium borohydride in methanol, a reagent which owing to its selective reducing properties (Section 5.4.1, p. 519) does not affect other reducible functional groups (particularly the nitro group) which may be present in the Schiff base contrast the use of sodium borohydride in the presence of palladium-on-carbon, p. 894. 

Enantioselective synthesis ofa-hydroxy acid derivatives. Recently, Aggarwal has reported an enantioselective approach to the synthesis of a-hydroxy acid derivatives using trans- 1,3-dithiane- 1,3-dioxide. For example, reaction of trans-1,3-dithiane-1,3-dioxide with an aromatic aldehyde liberates the alcohol which is protected as the tetrahydropyranyl (THP) ether the resulting product may then be subjected to a Pummerer reaction, using trifluoroacetic anhydride, to give a thiolester. Transthiolesterification of this product using LiSEt gives the... 

Methylpyrrolo[3,4-f]isoxazoles 48, prepared from 3-(l-aminoalkyl)isoxazole-4-carboxylic esters (see Section 4.03.9.1.6), after deprotonation and condensation with aromatic aldehydes afforded compounds 49 that were subjected to N-O bond cleavage the use of Mo(CO)6 gave 3-enoyltetramic acids 50, whereas H2-catalyst allowed further reduction to 3-acyltetramic acids 51 (Scheme 12) <2004SL2815>. 

The nature of donor-acceptor complexes has been the subject of various NMR studies conducted as early as the 1960s. Early calorimetric studies showed that boron trihalides are capable of forming donor-acceptor complexes with a number of Lewis bases and the heats of adduct formation for some of these complexes were determined. Gaseous boron trifluoride, for example, was shown to form a ctxnplex with ethyl acetate in a highly exothermic reaction (-A// = 32.9 0.2 kcal mol ). IR and UV analysis of BF3 complexes of aromatic aldehydes indicated a o-complex with a lengthened CVO bond and a highly delocalized ir-system. More detailed structural information, however, was acquired only after closer inspection by low temperature H, B, C and F NMR studies. ... 

The synthesis of the bisbenzannelated spiroketal core of the y-rubromycins was achieved by the research team of C.B. de Koning." The key step was the Nef reaction of a nitroolefin, which was prepared by the Henry reaction between an aromatic aldehyde and a nitroalkane. The nitroolefin was a mixture of two stereoisomers, and it was subjected to catalytic hydrogenation in the presence of hydrochloric acid. The hydrogenation accomplished two different tasks it first converted the nitroalkene to the corresponding oxime and removed the benzyl protecting groups. The oxime intermediate was hydrolyzed to a ketone that underwent spontaneous spirocyclization to afford the desired spiroketal product. 

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