Aromatic aldehydes, condensation

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

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). 

A. The Basic Series.—In general, aromatic aldehydes condense with aromatic amines in the presence of zinc chloride to form triphenylmethane derivatives (0. Fischer) phenols and phenyl ethers behave similarly in the presence of concentrated sulphuric acid (Baeyer). The products formed are the leuco-compounds of well-known dyes. 

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-... 

Keywords malonic acid, aromatic aldehyde, condensation, microwave irradiation, benzylidenemalonic acid... 

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 condense with phenols, e. g. benzaldehyde and naphthol give hydroxy-dinaphthyl-phenyl methane ... 

Aromatic aldehydes condense well with aliphatic ketones such as acetone to give either the mono- 31 or di-adducts 29 depending on conditions.4 In an excess of acetone, 31 is the main... 

Both aliphatic and aromatic aldehydes condense with primary amines, aliphatic and aromatic, to form N substituted imines. The purely aliphatic imines (C, to C,) can be obtained in 50 80% yield however, these compounds are unstable and should be used immediately after distillation. ... 

Reactions of piperazine-2,5-diones with phosphorus pentachloride and phosphorus pentabromide have been described in Sections V.ID and V.IF, respectively. Aromatic aldehydes condense with 3-methylpiperazine-2,5-dione in the presence of acetic anhydride to form mainly mono-A -acetyl derivatives of trans-3-arylidene-6-methylpiperazine-2,5-diones (e.g., 96, R = Ac) (1066). In these products the acetyl group was shown to be attached to position 1 and the 4,5-amide group was found to be sterically hindered. Photolysis formed the cis isomers. Both isomers were deacetylated with methanolic potassium hydroxide (1066). Condensation of 1,4-diacetylpiperazine-2,5-diones with aldehydes has been applied to the synthesis of unsymmetrical 3,6-diarylidenepiperazine-2,5-diones and the reaction has been extended to l,4-diacetyl-3,6-dimethylpiperazine-2,5-diones (1624). Treatment of (96, R = H) with triethyloxonium tetrafluoroborate in dichloromethane gave the monoimino ether, 5-benzylidene-6-ethoxy-3-hydroxy-2-methyl-2,5-dihydropyrazine (97) (1066). l-Methylpiperazine-2,5-dione similarly treated gave 5-ethoxy-l-methyl-2-oxo-l,2,3,6-tetrahydropyrazine (which was condensed with anthranilic acid at 150° to 2-methyl-l,2-dihydropyrazino[2,l-fi]quinazoline-3(4/0.6-dione (98) (1625), and l,4-dimethylpiperazine-2,5-dione gave 5-ethoxy-l,4-dimethyl-2-oxo-1,2,3,4-tetrahydropyrazine and 5,5-diethoxy-l,4-dimethylpiperazin-2-one (1626). 

The Erlenmeyer azalactone synthesis generally affords predominantly, and often exclusively, (Z) isomers (32). However, a simple method for the synthesis of ( ) isomers (33), obtained previously by separation of isomeric mixtures or isomerization procedures, has been reported. Aromatic aldehydes condense with hippuric acid when heated in polyphosphoric acid (PPA) to afford (33) in 80-90% yields (equation 17 Table 4). Alternatively, the (Z) isomers may be heated in PPA to afford the corresponding ( ) isomers in excellent yield. The authors note that hippuric acid is not converted to (26) in PPA, the generally accepted intermediate in the Erlenmeyer synthesis. Furthermore, both isomers of 2-(benzamid-oyl)cinnamic acid, (34) and (35), obtained by the alkaline hydrolysis of (32 R = H, Ar = Ph) and (33 R = H, Ar = Ph), respectively are converted to (33 R = H, Ar = Ph) in PPA (Scheme 9). The authors therefore suggest a mechanism involving condensation, first of the aldehyde and hippuric acid followed by... 

Rao3 recently reported that aromatic aldehydes condense with hip-puric acid in polyphosphoric acid (PPA) to give the generally inaccessible lower-melting geometric isomers of 4-aryl-methylene-2-phenyl-2-oxazolin-5-ones, e.g., 1, Eq. (1). The Erlenmeyer method and its minor variations, such as use of 4-chloromethylene or 4-ethoxy-methylene azlactones, always afford the geometric isomer,1,2 e.g., 2. Compound 2 is quantitatively isomerized to 1 in PPA [Eq. (2)]. The... 

Aromatic aldehydes condense with azidoacetates to produce species which by treatment with trivalent phophorus compounds give aza-ylids which undergo intramolecular aza-Wittig condensations giving aromatic isoquinolines. ... 

Aromatic aldehydes Condensation with barbituric acid OxlO - 10- mol - ... 

Benzaldehyde and other aromatic aldehydes condense with hydrazine or its salts to form water-insoluble colorless aldazines. Owing to its greater solubility in water, salicylaldehyde (I) is especially useful as specific reagent. It reacts with hydrazine ... 

---