Aldehyde-condensing agent

This reaction involves the condensation of an aldehyde or ketone with an a-halo ester in the presence of a basic condensing agent (sodium ethoxlde, sodamide, finely divided sodium or potassium iert.-butoxide) to give a glycldio (or ap-epoxy) ester. Thus acetophenone and ethyl chloroacetate yield phenyl-methylglycidic ester (I) ... 

The condensation of aldehydes and ketones with succinic esters in the presence of sodium ethoxide is known as the Stobbe condensation. The reaction with sodium ethoxide is comparatively slow and a httlo reduction of the ketonic compound to the carbinol usually occurs a shorter reaction time and a better yield is generally obtained with the more powerful condensing agent potassium ieri.-butoxide or with sodium hydride. Thus benzophenone condenses with diethyl succinate in the presence of potassium [Pg.919]

L cysteine (118) giving dihydroaemginoic acid (119), reduction of the carboxyl group to the aldehyde 121 and condensation of the latter with L-iV-methyl-cysteine. Details will be given for the procedure worked out by Zamri and Abdallah 397). The first condensation step was effected in a phosphate buffer (pH 6.4) to minimize epimerization at C-4. Then the carboxyl group was reacted with iV,(9-dimethyl-hydroxylamine (120) using diethylcyanophosphonate as condensation agent. Reduction with LiAlHa yielded the aldehyde 121, which then was treated with L-A-methyl-cysteine. A mixture of the four stereoisomers of (66), (4 R,2"5,4"R), (4 5,2"5,4"R), A R,2 R,A R), A S,2 R,A R) in a ratio of 2 1 2 5 was obtained. 

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]. 

By using condensing agents which are not at the same time dehydrating agents, the intermediate aldol compound can be isolated (see p. 101). A mixture of acetaldehyde and benzaldehyde yields cinnamic aldehyde by the action of hydrogen chloride, sodium hydrate, or sodium ethylate. (B., 17, 2117 20, 657.)... 

It will be seen that only an aldehyde with at least one a-hydrogen can condense with itself or with another aldehyde. This latter, however, need have no particular structure. Condensing agents stronger than those mentioned above eliminate water if possible, after condensation. Two a-hydrogen atoms in an aldehyde are necessary for this change (see Reaction XXIV.). 

The ketone undergoing condensation must have at least one H attached to the a-C. If it has two, then, on heating, these ketols eliminate water to give olefinic ketones. It is to be noted that no condensation takes place at the oxy-carbon of the ketone. An excess of the ketone must always be used to minimise the condensation of two molecules of the aldehyde to an aldol compound. If the reaction is carried out at a high temperature, and with more powerful condensing agents, the unsaturated ketone is directly obtained (see Reaction XXIV.). (B., 25, 3165 C., 1905, II., 752.)... 

Esters, such as those of malonic, acetoacetic or cyanoacetic acids, in which the methylene group is doubly activated, will condense even with ketones. By varying the proportion of aldehyde or ketone to ester, 2 mols. of the former can be made to condense with 1 of the latter, using the basic condensing agents only (4, below). The following will illustrate these points — ... 

Reaction LXXXI. Action of Hydrogen Chloride on a Mixture of an Aldehyde and an Alcohol. (B., 30, 3053 31, 545.)—The reaction is of the same type as the preceding. Under the influence of condensing agents, calcium chloride, hydrogen chloride, etc., aldehydes combine with alcohols to yield the ethers of the hypothetical dihydroxy compounds from which the aldehydes are derived. Ketones form these compounds only with difficulty. 

Three monoacetals, o-,70 wi-97 and p-nitrobenzylidene-dulcitol,97 have been described, the first being formulated, without proof, as the 3,4-derivative. The only triacetal of dulcitol of which we are aware is a tri-(o-nitrobenzylidene)-dulcitol prepared from the aldehyde and the hexitol using as the condensing agent phosphorus pentoxide,70 instead of 75% sulfuric acid which gives the diacetal already mentioned.48 6 Photochemical transformations of o-nitrobenzylidene acetals are discussed on page 148. 

Emerson and Waters alkylated primary aromatic amines with C2-C7 aliphatic aldehydes and benzaldehyde over Raney Ni in the presence of sodium acetate as a condensing agent and obtained /V-alkylanilincs in 47-65% yields.33 With C2-C5 aldehydes, up to 10% of the tertiary amines were produced, but no tertiary amines were found in the case of heptanal and benzaldehyde. With acetaldehyde in the absence of sodium acetate, aniline was recovered unchanged over platinum oxide and a mixture of amines resulted over Raney Ni, compared to 41 and 58% yields of N-ethylaniline over platinum oxide and Raney Ni (eq. 6.12), respectively, in the presence of sodium acetate. 

The use of carbodiimides in organic synthesis includes the Moffat oxidation of primary alcohols to aldehydes using a dicyclohexylcarbodiimide/DMSO adduct as reagent. Also, conversion of alcohols or phenols into hydrocarbons via hydrogenation of acylisoureas derived from the corresponding carbodiimide adducts is a useful reaction. Furthermore, aldoximes, on treatment with carbodiimides, are converted into nitriles, and numerous uses of carbodiimides as condensation agents or catalysts are known (see Chapter 13). 

The reaction is usually carried out be heating equimolar quantities of the aldehyde and salt with excess of the anhydride for 8 hours at 170-180°. Lower temperatures are often employed when potassium acetate or trialkylamines are used as condensing agents. Continuous removal of acetic acid during the reaction was found to have no effect on the yield of cinnamic acid. Substitution of diacetimide for acetic anhydride gives cinnamide (77%). ... 

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... 

A number of carbinols has been prepared by the reaction of tetramethylpyrazine with aldehydes and ketones using phenyllithium as the condensing agent (648). 

A further example is the synthesis of 3H-pyrrolizine from the reagent and pyrrole-2-aldehyde (Eastman) in ether with sodium hydride as condensing agent. 

For bringing about the first reaction the following-named substances may be used as condensation agents hydrochloric acid, acetic anhydride, as well as primary and secondary amines (ethyl amine, diethyl amine, piperidine, and others). For the second reaction the bases mentioned may be used. A small quantity of one of these may produce la rge quantities of the condensation product this is a case of a so-called continuous reaction. It is probable that the amine reacts first with the aldehyde, water being eliminated 1... 

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