Aldehydes, aromatic, reaction with

Claisen-Schmidt reaction. Aromatic aldehydes condense with aliphatic or mixed alkyl-aryl ketones in the presence of aqueous alkali to form ap-unsaturated ketones ... 

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. 

Claisen-Schmidt reaction (Section 18.10) A mixed aldol condensation in which an aromatic aldehyde reacts with an enolizable aldehyde or ketone. 

Aliphatic and aromatic aldehydes condensed with 2-amino-(62BRP898414), 5-amino- (80AJC1147), or 8-amino-l,2,4-triazolo[l,5-cjpyrimidines (68JOC530) to give the related Schiff bases. Treatment of the 2-amino-5-methyl-l,2,4-triazolo[l,5-c]quinazoline 11 with formaldehyde and piperidine in the presence of acetic acid gave the 2-hydroxymethyl-amino-5-(2-piperidinoethyl) derivative 172. Utilization of aromatic aldehydes and piperidine in this reaction gave the 2-arylideneamino-5-styryl derivatives 173 (68CB2106) (Scheme 67). 

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). 

The aldol-like reaction of an aromatic aldehyde 1 with a carboxylic anhydride 2 is referred to as the Perkin reaction. As with the related Knoevenagel reaction, an o ,/3-unsaturated carboxylic acid is obtained as product the /3-aryl derivatives 3 are also known as cinnamic acids. 

A variant of the Perkin reaction is the Erlenmeyer-Plochl-azlactone synthesis By condensation of an aromatic aldehyde 1 with an N-acyl glycine 5 in the presence of sodium acetate and acetic anhydride, an azlactone 6 is obtained via the following mechanism ... 

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... 

Crossed aldol condensations, where both aldehydes (or other suitable carbonyl compounds) have a-H atoms, are not normally of any preparative value as a mixture of four different products can result. Crossed aldol reactions can be of synthetic utility, where one aldehyde has no a-H, however, and can thus act only as a carbanion acceptor. An example is the Claisen-Schmidt condensation of aromatic aldehydes (98) with simple aliphatic aldehydes or (usually methyl) ketones in the presence of 10% aqueous KOH (dehydration always takes place subsequent to the initial carbanion addition under these conditions) ... 

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. 

Aliphatic and aromatic aldehydes condense with aliphatic and aromatic primary amines to form JV-substituted imines. The reaction is catalyzed by acids and is generally carried out by refluxing the amine and the carbonyl compound with an azeotroping agent in order to separate the water formed. The aliphatic imines (C5-C10) are obtained in good yield but are unstable and must be used directly after their distillation [2b], Tertiary aliphatic and aromatic aldehydes at room temperature react readily and nearly quantitatively with amines to give the imines without the aid of catalysts [la]. Primary aliphatic aldehydes tend to give polymeric materials with amines as a result of the ease of their aldol condensation [3]. The use of low temperatures and potassium hydroxide favors the formation of the imine product [4a, b]. Secondary aliphatic aldehydes readily form imines with amines with little or no side reactions [5]. 

The aldol-type reaction of a cyclic enol ester, 5-methyl-2(3//)-furanone (4b), was carried out with three kinds of catalytic systems PdCl2 (PhCN)2-SnCl2, Ni(Cod)2/Ph3P-Zn, and Pd(OAc)2/PPh3-Zn. In the presence of the first catalyst, aromatic aldehydes condense with 4b to give ds-)3-acetyl-y-aryl-y-butyrolactones (47), but alkanals are mainly con-... 

Diperoxyketals and Diperoxyacetals. Aromatic aldehydes react with alkyl hydroperoxides in the presence of strong acid catalysts such as sulfuric acid to form diperoxyacetals (1, X = OOR5 R1 = H, R2 = Ar. R3 = R3 = alkyl). Diperoxyketals (1, X = OCR5 R1, R2, R3. R3 = alkyl) are generally prepared by acid-catalyzed reaction of a ketone with two equivalents of an alkyl hydroperoxide. 

Two moles of aromatic aldehyde react with ethyl diazoacetate to form diastereomeric 1,3-dioxolanes.124 The reaction is catalysed by dirhodium(II) species, and proceeds via a carbonyl ylid. Stereo-control can be achieved using a bulky diazo substrate, and electronic effects of aromatic substituents are important. Different reactions show evidence of either a metal-stabilized ylid, a free ylid, or competition between the two. 

Sano et al. have reported the synthesis of the 2-benzazepines 266. The steps involved reaction of the aromatic aldehydes 260 with the amine 261 to give the imines 262, followed by reduction to the amines 263, N-formylation to 264, and oxidation to the corresponding sulfoxides 265 (Scheme 34). The seven-membered ring was then formed by a modified Pummerer reaction on 265, which was then used to complete the seven-membered ring in yields ranging from 45% to 78% (e.g., 266 R1 = R2 = H, R3 = OMe, R4 = H 78%) <2001H(54)967>. 

A retrosynthetic analysis of a,/J-unsaturated ketones leading to various methods of synthesis is outlined in Section 5.18.2, p. 798. These methods are equally applicable to aromatic aldehydes. Aromatic aldehydes condense with aliphatic or mixed alkyl aryl ketones in the presence of aqueous alkali to form a,[i-unsaturated ketones (the Claisen-Schmidt reaction). 

Aromatic aldehydes react with triphenylphosphine and trichloroacetic acid derivatives (Cl3C-C02Et, CI3C-CN) to give benzylidene dichlorides or o -chlorocinnam-ates.351 Substituent and reaction condition effects on chemo- and regio-selectivity are described. 

However, the key disadvantage of the reaction described in [199] is observed in the first step—synthesis of unsaturated ketoacids 236 with very low yields (20-30%) [200]. The same authors [201] proposed a multicomponent approach to azolopyr-imidinecarboxylic acids. The reactions of pyruvic acid 239 and aromatic aldehydes 240 with 2-aminobenzimidazole, 5-aminotetrazole 156 and 3-amino-1,2,4-triazole 147 in alcohols, DMF and acetic acid were studied (Scheme 3.67). 

Organoboranes do not normally react with carbonyl compounds in Grignard-like fashion with the exception of allylboranes. Aromatic aldehydes reacted with dialkylboron chloride derivatives in the presence of base to generate arylalkylmethanols in good yields (Equation (132)). On the other hand, reactions of aromatic aldehydes with dialkylboron chlorides in the presence of oxygen resulted in chlorination (Equation (133)).595... 

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