Aldehydes aliphatic/aromatic

Aldehydes and the corresponding 2-aminopyridine, pyrazine, or pyrimidine are admixed in presence of a catalytic amount of clay (50 mg) to generate iminium intermediate. Isocyanides are subsequently added to the same container and the reactants are further exposed to MW to afford the corresponding imidazo[l,2-a]pyridines, imi-dazo[l,2-a]pyrazines and imidazo[l,2-a]pyrimidines (Scheme 6.48). The process is general for all the three components, e. g. aldehydes (aliphatic, aromatic and vinylic), isocyanides (aliphatic, aromatic and cyclic) and amines (2-aminopyridine, 2-amino-pyrazine and 2-aminopyrimidine). A library of imidazo[l,2-a]pyridines, imidazo[l,2-ajpyrazines and imidazo[l,2-a]pyrimidines can be readily obtained by varying the three components [151]. 

Lysine, 4-amino Aldehydes (aliphatic, aromatic, Reductive alkylation... 

Nickel-catalyzed transformations of SCBs have been studied by Oshima and co-workers <20060L483>. Nickel-catalyzed ring opening of SCBs with aldehydes affords the corresponding alkoxyallylsilanes (Scheme 55). This transformation represents a hydrosilane-free reductive silylation of aldehydes. A wide range of aldehydes (aliphatic, aromatic, electron-rich, and electron-deficient) can be converted to akoxyallylsilanes. 

Wittig-Horner reaction. The reagent reacts with a wide range of aldehydes, aliphatic, aromatic, and a,P-unsaturated, in the presence of a base to form (E)-a-methyl-a, -unsaturated esters stereoselectively. The reaction can be carried out either with potassium t-butoxide in DMF or with K,COj in QH /HjO and Aliquat 336 as phase-transfer agent. 

A variety of aldehydes—aliphatic, aromatic, and heterocyclic—have been condensed with hydantoin. Sodium acetate in a mixture of acetic acid and acetic anhydride as well as pyridine containing traces of piperidine serves as condensing agent. Reduction of the double bond is accomplished with phosphorus and hydriodic acid, ammonium sulfide, or stannous chloride, In a more recent modification, the hydantoins are synthesized from aldehyde or ketone cyanohydrins and ammonium... 

Perfect chemoselectivity (100% of dithioacetals) was also achieved with kaolinitic clays as catalysts for protection of various aldehydes (aliphatic, aromatic, heteroaromatic, a,(I-unsaturated) with 1,2-ethanedithiol <1996TL4605>. 

In the preparation of a combinatorial library of a,[3-unsaturated carboxylic acids, a group from Rhone Poulenc Rorer utilized the H WE-olefination reaction. Starting from 1-substituted phosphonoacetic acid anchored to polystyrene, a 48-membered library containing a diverse set of aldehydes (aliphatic, aromatic and basic) was produced, with an (E/Z)-ratio that was highly dependant on the a-substituent of the phosphonate, where hydrogen gave a 9 1 ratio in favor of the (Ej-product... 

In nonaqueous solutions, however, reduction of hydrazones may take place in a different way. As shown by Kitaev and Skrebkova [144], phenylhydrazones, nitrophenylhydrazones, semi- and thio-semicarbazones, nicotinyl- and isonicotinylhydrazones, benzoyl-hydrazines, and also the products from the coupling of diazonium salts with diphenyldiketopyrazolidine and barbituric acid, which are derivatives of aromatic aldehydes, aliphatic aromatic ketones, or... 

Torlon-type polymers are unaffected by aliphatic, aromatic, chlorinated and fluorinated hydrocarbons, dilute acids, aldehydes, ketones, ethers and esters. Resistance to alkalis is poor. They have excellent resistance to radiation. If a total of 10 Mrad is absorbed at a radiation dosage of 1 Mrad/h the tensile strength decreases by only 5%. 

Cinnamic Acid.—The reaction, which takes place when an aldehyde (aliphatic or aromatic) acts on the sodium salt of an aliphatic acid in presence of the anhychide, is known as Perkin s reaction, and has a ery wide application. Accoid-ing to the result of Fittig s researches on the properties of the unsaturated acids described below, the reaction occurs in two steps. The aldeh) de forms first an additive compound with the acid, the aldehyde caibon attaching itself to the n-carbon ii.e.i nevt the carbovyl) of the acid. A saturated hydiOKy-acid is formed, which is stable, if the a-carbon is attached to only one atom of hydrogen, as in the case of isobutync acid,... 

The wide range of applicability of the reaction can be seen from Table I. Formaldehyde, aliphatic aldehydes, and aromatic and hetero-... 

Aliphatic, aromatic and vinylic aldehydes can be employed in this reaction with similar yields and enantioselectivities. When chiral aldehydes are utilized, excellent diastereoselectivity is obtained for matched cases, whereas mismatched cases yield products with moderate to good diastereoselectivity (Scheme 9.13a) [67]. The limitation of the methodology is that only terminal vinylepoxides can be obtained. 

The tartrate ester modified allylboronates, the diisopropyl 2-allyl-l,3,2-dioxaborolane-4,5-di-carboxylates, are attractive reagents for organic synthesis owing to their ease of preparation and stability to storage71. In the best cases these reagents are about as enantioselective as the allyl(diisopinocampheyl)boranes (82-88% ee with unhindered aliphatic aldehydes), but with hindered aliphatic, aromatic, a,/l-unsaturated and many a- and /5-alkoxy-substituted aldehydes the enantioselectivity falls to 55-75% ee71a-b... 

The Pictet-Spengler reaction has mainly been investigated as a potential source of polycyclic heterocycles for combinatorial apphcations or in natural product synthesis [149]. Tryptophan or differently substituted tryptamines are the preferred substrates in a cyclocondensation that involves also aldehydes or activated ketones in the presence of an acid catalyst. Several versions of microwave-assisted Pictet-Spengler reactions have been reported in the hter-ature. Microwave irradiation allowed the use of mild Lewis acid catalysts such as Sc(OTf)3 in the reaction of tryptophan methyl esters 234 with different substituted aldehydes (aliphatic or aromatic) [150]. Under these conditions the reaction was carried out in a one-pot process without initial formation of the imine (Scheme 86). 

Through extensive screening of compounds, " " " it was revealed that this enzyme accepts a very wide range of substrates. In addition to phosphorylated aldose, which are the native substrate, non-phosphorylated aldose, simple aliphatic, aromatic, heterocyclic and functionalized aldehydes, even with an increased hydropho-bicity, work as substrates. The stereochemical course has been elucidated in Fig. 18. The hydroxyl group on the 2-position of the aldehyde is very important and 2-deoxygenated aldehydes were rather weak substrates. The substrates with d-configuration at the 2-position have a stronger affinity to TKase than L-form. 

The reaction of aliphatic, aromatic, heterocyclic, conjugated, and polyhydroxy aldehydes with NBS and ammonia gave the corresponding nitriles in high yields at 0°C in water (Eq. 9.18).39 Ceric ammonium nitrate (CAN)40 and iodine41 are also effective as the oxidizing reagents. 

A-Acylimidazoles are easily reduced to the corresponding aldehydes with LiAlH4 in THF or ether as solvent.[1] Thus, aliphatic, conjugated aliphatic, aromatic, conjugated aromatic, and heteroaromatic aldehydes can all be obtained in this way in moderate to high yields. 

In the Diels-Alder reaction with inverse electron demand, the overlap of the LUMO of the 1-oxa-l,3-butadiene with the HOMO of the dienophile is dominant. Since the electron-withdrawing group at the oxabutadiene at the 3-position lowers its LUMO dramatically, the cycloaddition as well as the condensation usually take place at room or slightly elevated temperature. There is actually no restriction for the aldehydes. Thus, aromatic, heteroaromatic, saturated aliphatic and unsaturated aliphatic aldehydes may be used. For example, a-oxocarbocylic esters or 1,2-dike-tones for instance have been employed as ketones. Furthermore, 1,3-dicarbonyl compounds cyclic and acyclic substances such as Meldmm s acid, barbituric acid and derivates, coumarins, any type of cycloalkane-1,3-dione, (1-ketoesters, and 1,3-diones as well as their phosphorus, nitrogen and sulfur analogues, can also be ap-... 

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... 

Metalated cyclic aldo-nitrones are characterized by high reactivity toward electrophilic reagents. Reactions with aldehydes and ketones afford satisfactory yields of a-hydroxymethyl substituted derivatives of nitrones (551). The reactions were also carried out with a number of aliphatic, aromatic, and hetero-aromatic aldehydes and ketones (Schemes 2.124 and 2.125). 

Ex situ formation of (33) followed by addition to a mixture of CHCI3 and aldehyde (aliphatic or aromatic) in DMF at low temperature leads to deprotonation of CHCI3 but not of the aldehyde, and formation of the trichlorocarbinol takes place without formation of side products by aldol condensation, Scheme 21 [99]. The reaction could also be carried out (75-86% yield for butanal) using polymeric amides as a PB and with similar conditions [74]. 

On the other hand, the method of Mukaiyama can be succesfully applied to silyl enol ethers of acetic and propionic acid derivatives. For example, perfect stereochemical control is attained in the reaction of silyl enol ether of 5-ethyl propanethioate with several aldehydes including aromatic, aliphatic and a,j5-unsaturated aldehydes, with syir.anti ratios of 100 0 and an ee >98%, provided that a polar solvent, such as propionitrile, and the "slow addition procedure " are used. Thus, a typical experimental procedure is as follows [32e] to a solution of tin(II) triflate (0.08 mmol, 20 mol%) in propionitrile (1 ml) was added (5)-l-methyl-2-[(iV-l-naphthylamino)methyl]pyrrolidine (97b. 0.088 mmol) in propionitrile (1 ml). The mixture was cooled at -78 °C, then a mixture of silyl enol ether of 5-ethyl propanethioate (99, 0.44 mmol) and an aldehyde (0.4 mmol) was slowly added to this solution over a period of 3 h, and the mixture stirred for a further 2 h. After work-up the aldol adduct was isolated as the corresponding trimethylsilyl ether. Most probably the catalytic cycle is that shown in Scheme 9.30. 

Under the above-described conditions, esters are nnaffected and aliphatic ketones are barely rednced. In the presence of zinc iodide, however, aliphatic ketones, as well as aldehydes and aromatic ketones, are converted into methyl ethers in high yields. If alcohols other than methanol are nsed, the corresponding alkyl ethers are obtained. 

C02Et Br KOf-Bu/THF/-20°C aliphatic and aromatic aldehydes aliphatic, cycloaliphatic and aromatic ketone, a,p-unsaturated aldehydes and ketones 52-90... 

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