Schiff-type condensation product

Oxaziridines are generally formed by the action of a peracid on a combination of a carbonyl compound and an amine, either as a Schiff base (243) or a simple mixture. Yields are between 65 and 90%. Although oxygenation of Schiff bases is formally analogous to epoxidation of alkenes, the true mechanism is still under discussion. More favored than an epoxidation-type mechanism is formation of a condensation product (244), from which an acyloxy group is displaced with formation of an O—N bond. 

The acid-catalyzed conversion of the l,2,3,4-tetrahydro-j8-carboline derivative 337 (R = CHg) into the strychnine-type ring system 338 has been attributed to an equilibrium involving the protonated Schiff s base 339 of tryptamine (i.e., the intermediate in the Pictet-Spengler type synthesis of tetrahydro-j8-carbolines, cf. Section III, A, 1, a), and the a- (337) and the j8-condensation products (340). 

The mechanistic pathway of the ordinary Friedlander synthesis is not rigorously known. Two steps are formulated. In a first step a condensation reaction, catalyzed by acid or base, takes place, that can lead to formation of two different types of products (a) an imine (Schiff base) 4, or (b) an o ,/3-unsaturated carbonyl compound 5 ... 

A method for the preparation of cyclonite from sulphamic acid, formaldehyde and nitric acid was developed in 1934 by Wolfram [38], It is known as the W-meth-od and the cyclonite so obtained is known as W-Salz . The W-method is based on the condensation of the potassium salt of sulphamic acid with formaldehyde and the nitration of the condensation product ( white salt , a Schiff s base of the type XVIII) with nitric acid. 

Formaldehyde dehydrogenase catalyzes the oxidation of a number of aldehydes, including formaldehyde, to the corresponding acid. The enzyme is important as it catalyzes the detoxification of formaldehyde, a chemical present in small concentrations in most or all biological tissues. Formaldehyde, as well as other aldehydes, spontaneously condense with amino groups — via a Schiff base linkage — to form a condensation product. This type of condensation product is not desirable, and contributes to a small extent to the various types of damage inflicted upon the proteins of the body. 

Prepare a solution of 3-hydroxybenzaldehyde (10.0 g, 82 mmol) in methanol (30 mL) in a 100 mL round-bottomed flask equipped with a stirrer bar. The mixture may require a little gentle warming with a heat gun to aid dissolution. Add a solution of tris(2-aminoethyl)amine (4.0 g, 7 mmol) in methanol (50 mL) and stir at room temperature for 10 min. The reaction is slightly exothermic upon completion the reaction mixture cools to room temperature. Unusually for a Schiff base condensation of this type there is very little change in colour. Place an ice bath under the reaction vessel and stir until the product precipitates as a cream solid. Filter the product and wash with a small amount of cold ethanol to give A1,A1,A1-tris(3-(2-aminoethylimino)methylphenol) (7) as a cream microcrystalline powder. 

The versatility of 5-nitrosopyrimidines in pteridine syntheses was noticed by Pachter (64MI21603) during modification of the Timmis condensation between (262) and benzyl methyl ketone simple condensation leads to 4-amino-7-methyl-2,6-diphenylpteridine (264) but in the presence of cyanide ion 4,7-diamino-2,6-diphenylpteridine (265) is formed (equation 90). The mechanism of this reaction is still uncertain (63JOC1187) it may involve an oxidation of an intermediate hydroxylamine derivative, nitrone formation similar to the Krohnke reaction, or nucleophilic addition of the cyanide ion to the Schiff s base function (266) followed by cyclization to a 7-amino-5,6-dihydropteridine derivative (267), oxidation to a quinonoid-type product (268) and loss of the acyl group (equation 91). Extension of these principles to a-aryl- and a-alkyl-acetoacetonitriles omits the oxidation step and gives higher yields, and forms 6-alkyl-7-aminopteridines, which cannot be obtained directly from simple aliphatic ketones. 

From the reaction between 2,3,4,5-tetra-O-acetyl-aWe/ii/do-D-ribose and aniline in ethanol it was possible to isolate a crystalline compound which, on elemental analysis, appeared to be of the Schiff-base type (IV) with one molecule of ethanol of crystallization. Similarly, when the condensation was performed in methanolic solution the product corresponded to a compound of the same type with methanol of crystallization. 

The reactions of Cp2TiCl2 with a class of organometallic thiosemicarbazones (LH), derived by condensing acetylferrocene with substituted thiosemicarbazides or with Schiff bases (L), derived by the condensation of acetylferrocene with ethylenediamine, 0-phenylenediamine, 4-methyl-o-phenylenediamine, 1,8-diaminonaphtha-lene, and 2,6-diaminopyridine, have been studied to give a type of bimetallic products Cp2TiClFe(L). Attempts... 

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