Aldehydes reacting with

Aromatic aldehydes react with the dimedone reagent (Section 111,70,2). All aromatic aldehydes (i) reduce ammoniacal silver nitrate solution and (ii) restore the colour of SchifiF s reagent many react with sodium bisulphite solution. They do not, in general, reduce Fehling s solution or Benedict s solution. Unlike aliphatic aldehydes, they usually undergo the Cannizzaro reaction (see Section IV,123) under the influence of sodium hydroxide solution. For full experimental details of the above tests, see under Ali-phalic Aldehydes, Section 111,70. They are easily oxidised by dilute alkaline permanganate solution at the ordinary temperature after removal of the manganese dioxide by sulphur dioxide or by sodium bisulphite, the acid can be obtained by acidification of the solution. 

Azines, Aldehydes react with hydrazine to yield azines the reaction cannot usually be arrested at the hydrazone stage. This reaction may be illustrated by the preparation of bevzalazine from benzaldehyde ... 

Indeed formaldehyde is so reactive toward nucleophilic addition that it suppresses the self condensation of the other component by reacting rapidly with any enolate present Aromatic aldehydes cannot form enolates and a large number of mixed aldol con densations have been carried out m which an aromatic aldehyde reacts with an enolate... 

Analogously, aldehydes react with ammonia [7664-41-7] or primary amines to form Schiff bases. Subsequent reduction produces a new amine. The addition of hydrogen cyanide [74-90-8] sodium bisulfite [7631-90-5] amines, alcohols, or thiols to the carbonyl group usually requires the presence of a catalyst to assist in reaching the desired equilibrium product. 

Ketones and aldehydes react with ethylene glycol under acidic conditions to form 1,3-dioxolanes (cychc ketals and acetals) (eq. 7). 

Aldehydes react with alkenylborates to give 1,3-diols upon oxidation of the intermediate (300). Alkynylborates ate transformed by epoxides into homoallyhc alcohols and alkenylborates into 1,4-diols (300,301). Carbon dioxide reacts with alkenylborates to yield catboxyhc acids (302). The scope of these transformations is further extended by the use of functionalized electrophiles and borates, often reacting with high stereoselectivity. For example, in the... 

In the presence of strong acid catalysts such as sulfuric acid, aUphatic (R CHO) aldehydes react with alkyl hydroperoxides, eg, tert-55ky hydroperoxides, to form hydroxyalkyl alkyl peroxides (1), where X = OH R, = hydrogen, alkyl and = tert — alkyl. 

Other Aldehydes. The higher aldehydes react with phenol in much the same manner as formaldehyde, although at much lower rates. 

Aldehydes react with monohydric alkanolamines to give monocychc oxazohdines... 

A new, versatile and selective synthesis of 6- and 7-substituted pteridines was reported by Rosowsky (73JOC2073). /3-Keto sulfoxides, which can be viewed as latent a keto aldehydes, react with (251) to give 6-substituted pterins, and the use of a-keto aldehyde hemithioacetals leads in a regiospecific synthesis to the isomeric 7-substituted pterins (equation 85). 

Aldehydes react with a-nitroacetophenone in refluxing toluene to generate a 3-acetyl-2-isoxazoline (78USP4092327), while a-nitroacetophenone oxides react with alkenes to provide 2-isoxazolines (Scheme 121) (79ZOR735, 79ZOR2408, 80CPB479>. 

Heating the sugars with strong add yields furfural derivatives. Under these conditions aldohexoses can eliminate formaldehyde and water to yield furfural. This aldehyde reacts with amines to yield colored Schiff s bases. 

Most of the straight-chain aliphatic aldehydes react with sulfur tetrafluoride in the usual manner to give the expected 1,1-difluoroalkanes as the only isolable products, reasonable yields are obtained in a narrow temperature range, from -20 to 40 C. An exception is butyraldehyde, which, when treated with sulfur tetrafluoride below 0 C, gives, in addition to 1,1-difluorobutane, considerable amounts of bis(l -fluorobutyl) ether [169] (equation 81)... 

Because aldehydes react with aminofluorosulfuranes more readily than ketones, keto aldehydes can be selectively fluorinated at the formyl group [94, 183] Haloacetaldehydes react with DAST to give bis(l-fluorohaloethyl) ethers as the only or main products [170] (equation 96)... 

Aromatic aldehydes cannot fonn enolates, and a large number of mixed aldol condensations have been cariied out in which an aromatic aldehyde reacts with an enolate. 

We have previously discussed that keto-aldehydes react with anilines first at the aldehyde carbon to form the aldimine. Subsequent condensation with another aniline formed a bis-imine or enamino-imine. The aniline of the ketimine normally cyclizes on the aldimine (24 —> 26). Conversely, cyclization of the aldimine could be forced with minimal aniline migration to the ketimine using PPA (30 —> 31). The use of unsymmetrical ketones has not been thoroughly explored a few examples are cited below. One-pot enamine formation and cyclization occurred when aniline 48 was reacted with dione 49 in the presence of catalytic p-TsOH and heat. Imine formation occurred at the less-hindered ketone, and cyclization with attack on the reactive carbonyl was preferred. ... 

The isolation of several pairs of geometric isomers of 4-unsaturated-5-oxazolones has been described. Generally, only one isomer is obtained when an aldehyde reacts with hippuric acid in the presence of acetic anhydride. Occasionally, mixtures have been separated in base-catalyzed reactions. In acetic anhydride-sulfuric acid or in 100% sulfuric acid, a mixture is obtained, and it has been suggested that sulfuric acid inhibits mutarotation of the intermediate addition product 53, which is a mixture of diastereomers (see, e.g., compound... 

This catalyst was successfully applied to the Diels-Alder reaction of propargyl aldehydes as dienophUes [12] (Scheme 1.21, Table 1.8). Though 2-hutyn-l-al and 2-oc-tyn-l-al are unreactive dienophUes, silyl- and stannyl-suhstituted a,/ -acetylenic aldehydes react with cydopentadiene readily in the presence of 20 mol% of the catalyst at low temperature to give hicyclo[2.2.1]heptadiene derivatives in high optical purity these derivatives are synthetically useful chiral building blocks. 

In all the reactions described so far a chiral Lewis acid has been employed to promote the Diels-Alder reaction, but recently a completely different methodology for the asymmetric Diels-Alder reaction has been published. MacMillan and coworkers reported that the chiral secondary amine 40 catalyzes the Diels-Alder reaction between a,/ -unsaturated aldehydes and a variety of dienes [59]. The reaction mechanism is shown in Scheme 1.73. An a,/ -unsaturated aldehyde reacts with the chiral amine 40 to give an iminium ion that is sufficiently activated to engage a diene reaction partner. Diels-Alder reaction leads to a new iminium ion, which upon hydrolysis af-... 

Semi-carbazones.—Most aldehydes react with semi-carbazide, forming... 

Chlorovinyl aldehydes react with benzene-1,2-diamine in the presence of hydogen chloride to yield 1,5-benzodiazepinium salts 15. Selected examples are given.266... 

The second important group of configuralionally stable bis-protected a-amino aldehydes are the V-dibenzvl derivatives 5, easily prepared from amino acids in a three-step procedure65. These aldehydes react with various nucleophiles to normally provide the nonchelation-con-trolled adducts in high diastereoselectivity. This anti selectivity is observed when diethyl ether or telrahydrofuran is used as reaction solvent. Certain Lewis acidic nucleophiles or additives, such as tin(IV) chloride, in dichloromethane as solvent force chelation and therefore provide the. syn-adducts, once again with a high diastereoselectivity. 

Historically the Strecker synthesis of a-amino acids constitutes the first chemical access to this important class of compounds1, In this process, an aldehyde reacts with ammonia and hydrogen cyanide to form an a-amino nitrile2 which subsequently is hydrolyzed to give the corresponding amino acid3... 

The reaction has also been applied to compounds with other leaving groups. Diazo ketones, diazo esters, diazo nitriles, and diazo aldehydes react with trialkylboranes in a similar manner, for example. 

P-Keto esters have been prepared in moderate to high yields by treatment of aldehydes with diethyl diazoacetate in the presence of a catalytic amount of a Lewis acid such as SnCL, BF3, or GeCL. The reaction was successful for both aliphatic and aromatic aldehydes, but the former react more rapidly than the latter, and the difference is great enough to allow selective reactivity. In a similar process, aldehydes react with certain carbanions stabilized by boron, in the presence of (F3CC0)20 or NCS, to give ketones. 

Pr)4, " borohydride-exchange resin,and formic acid. When the last is used, the process is called the Wallach reaction. Conjugated aldehydes are converted to alkenyl-amines with the amine/silica gel followed by reduction with zinc borohydride.In the particular case where primary or secondary amines are reductively methylated with formaldehyde and formic acid, the method is called the Esch-weiler-Clarke procedure. It is possible to use ammonium (or amine) salts of formic acid, " or formamides, as a substitute for the Wallach conditions. This method is called the Leuckart reaction,and in this case the products obtained are often the N-formyl derivatives of the amines instead of the free amines. Primary and secondary amines can be iV-ethylated (e.g., ArNHR ArNREt) by treatment with NaBH4 in acetic acid. Aldehydes react with aniline in the presence of Mont-morillonite KIO clay and microwaves to give the amine. Formaldehyde with formic acid converts secondary amines to the N-methyl derivative with microwave irradiation. 

There are a few other methods for converting ketones or aldehydes to alkenes. When a ketone is treated with CH3CHBr2/Sm/Sml2, with a catalytic amount of CrCls, for example, the alkene is formed. In another reaction, an aldehydes reacted with EtCHBr(OAc) in the presence of Zn/CrCl3 to give the alkene. ... 

Color reactions are more or less clearly defined reactions of the substances with suitable reagents. Substance-specific reactions are not usually available, e. g. many compounds with aromatic skeletons give both a positive Vitali-Morin reaction [1 -4] and a positive Marquis reaction [4]. Again, numerous aldehydes react with electron-rich compounds in acidic medium to yield colored substances (cf. Chapters 2 and 3.1). 

Another reagent that has found use in pinacolic coupling is prepared from VC13 and zinc dust.264 This reagent is selective for aldehydes that can form chelated intermediates, such as (3-formylamides, a-amidoaldehydes, a-phosphinoylaldehydes,265 and 8-ketoaldehydes.266 The vanadium reagent can be used for both homodimerization and heterodimerization. In the latter case, the reactive aldehyde is added to an excess of the second aldehyde. Under these conditions, the ketyl intermediate formed from the chelated aldehyde reacts with the second aldehyde. 

The reaction of an a-halo carbonyl compound with zinc, tin, or indium together with an aldehyde in water gave a direct cross-aldol reaction product (Eq. 8.90).226,227 A direct Reformatsky-type reaction occurred when an aromatic aldehyde reacted with an a-bromo ester in water mediated by zinc in low yields. Recently, it was found that such a reaction mediated by indium was successful and was promoted by son-ication (Eq. 8.91).228 The combination of BiCl3-Al,229 CdCl2-Sm,230 and Zn-Et3B-Eb0231 is also an effective mediator. Bismuth metal, upon activation by zinc fluoride, effected the crossed aldol reaction between a-bromo carbonyl compounds and aldehydes in aqueous media. The reaction was found to be regiospecific and syn-diastereoselective (Eq. 8.92).232... 

Another approach to cyclic nitronates has been developed by Rosini et al. in which nitro-aldol and subsequent cyclization is used as a key step. For example, 2,3-epoxy aldehydes react with ethyl nitroacetate on alumina surface in the absence of solvent to give 4-hydroxyisoxazoline 2-oxides in good yields (Eq. 8.80).130... 

In reactions of chiral aldehydes, TiIV compounds work well as both activators and chelation control agents, a- or A-oxygcnated chiral aldehydes react with allylsilanes to afford chiral homoallylic alcohols with high selectivity (Scheme 22).85 These chiral alcohols are useful synthetic units for the synthesis of highly functionalized chiral compounds. Cyclic chiral 0,0- and A/O-acetals react with allylsilanes in the same way.86,87 Allenylsilanes have also been reported as allylation agents. 

Various non-conjugated diene aldehydes react with Et3SiH/Ni(cod)2/PPh3 to give O-triethylsilylated cycloalkanols in low to high yields. Acyclic dienes can lead to the silylated cycloalkanols in moderate yields with the proper catalyst (Eq. 188).348 Bicyclic systems are also generated by this methodology (Eq. 189).349... 

Aldehydes react with hydrazine hydrate and sulfur in a high yielding one-pot synthesis of 2,5-dialkyl- and 2,5-diaryl-1,3,4-thiadiazoles via a diazene intermediate (see Section 5.10.9.2.1) <1980LA1216, 1983JHC1399>. Although this synthetic procedure is rare, examples can be found in CHEC-II(1996) <1996CHEC-II(4)379>. 

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