Amines oxaziridines

Nitrogen chirality may also be produced by the action of an achiral peroxyacid on a Schiff base containing a chiral amine (75JOC3878). In this case the oxaziridine contains a configurationally known centre of chirality relative to this, absolute configurations of the centres of chirality at nitrogen and carbon, and thus the complete absolute configuration of the molecule, can be determined (see Section 5.08.2.2). 

Oxaziridines are powerful oxidizing agents. Free halogen is formed from hydrobromic acid (B-67MI50800). Reduction by iodide in acidic media generally yields a carbonyl compound, an amine and two equivalents of iodine from an oxaziridine (1). With 2-alkyl-, 2-acyl and with N-unsubstituted oxaziridines the reaction proceeds practically quantitatively and has been used in characterization. Owing to fast competing reactions, iodide reduction of 2-aryloxaziridines does not proceed quantitatively but may serve as a hint to their presence. 

It was reported only recently that A-methyl transfer from an oxaziridine to an amine occurs with formation of an N—N bond (79JA6671). N—N bond forming reactions with A-unsubstituted oxaziridines had been found immediately after discovery of this class of compound (64CB2521) and have led to simple hydrazine syntheses (79AHC(24)63). Secondary amines like diethylamine or morpholine are A-aminated by (52) in the course of some minutes at room temperature with yields exceeding 90% (77JPR195). Further examples are the amination of aniline to phenylhydrazine, and of the Schiff base (96) to the diaziridine (97). 

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. 

Two substituents on two N atoms increase the number of diaziridine structures as compared with oxaziridines, while some limitations as to the nature of substituents on N and C decrease it. Favored starting materials are formaldehyde, aliphatic aldehydes and ketones, together with ammonia and simple aliphatic amines. Aromatic amines do not react. Suitable aminating agents are chloramine, N-chloroalkylamines, hydroxylamine-O-sulfonic acid and their simple alkyl derivatives, but also oxaziridines unsubstituted at nitrogen. Combination of a carbonyl compound, an amine and an aminating agent leads to the standard procedures of diaziridine synthesis. 

This type of amination by an oxaziridine is assumed to be the key step of a novel process for hydrazine manufacture, in the course of which butanone in solution with ammonia is reacted with hydrogen peroxide and acetonitrile. The smooth formation of oxaziridines from Schiff bases and hydrogen peroxide-nitrile mixtures is as well known as NH transfer from an oxaziridine like (300), suggesting the intermediacy of (300) as the N—N forming agent (72TL633). 

Singlet phenylnitrene, and hence /V,A -diethyl-3//-azcpin-2-amines, e. g. 102, can be generated by the thermolysis of A,-phenyl-Af,<9-bis(trimcthylsi]yl)hydroxylamine (100) in the presence of dialkylamines the reaction fails, however, with arylamines.210 Photofragmentation of the spiro oxaziridine 101 in diethylamine solution also produces the 3//-azepine 102,2,1 and an oxaziridine intermediate is probably involved in the formation, in low yield (1 %), of azepine 102 by the photolysis of A/,A( -diarylbenzoquinonc diimine A/,A/ -dioxides in benzene/die-thylamine solution.212... 

Electrophilic amination reactions by means of oxaziridines have been reviewed105. Cyclohexylidenehydrazines 86 are formed from secondary amines such as diethylamine, dibutylamine and morpholine and the spirooxaziridine 85105. 

Fluoroalcohols 1 have been employed in assigning absolute configuration of amines (30), benzothiophene oxides (45), lactones (33,46), oxaziridines (41), and an amine oxide (47). 

To avoid overoxidation, primary amines (e.g. 128, equation 89) can be converted into Schiff bases with an aromatic aldehyde. Subsequent oxidation of the resultant imines 129 with an excess of peracids produces oxaziridines 130 and/or nitrones 131. Both of them produce hydroxylamines 132 (equation 89) upon hydrolysis in moderate to good overall yields. Yields of hydroxylamines are considerably better if anisaldehyde instead of benzaldehyde is used for the protection . ... 

Oxidation of secondary amines with oxaziridine 144 provides moderate yields of hydroxylamines 145, although overoxidation invariably results in formation of nitrones 146 (equation 96). ... 

N-Acetyl derivatives of 3-phenyloxaziridine can also transfer their nitrogen function to nucleophiles. 2-(4 -Nitrobenzoyl)-3-phenyloxaziridine (69) converts piperidine to the acyl-hydrazine (101) in 92% yield within some minutes at room temperature (67JPR(36)86). Since (69) is stable in the absence of a nucleophile a nitrene is not involved in the reaction, which is assumed to occur by nucleophilic attack of the amine on the oxaziridine nitrogen. 

Aliphatic primary amines are known to be oxidized by dimethyl dioxiranes to various products such as oximes, nitroso dimers, nitroalkanes, nitrones and oxaziridines under various conditions depending upon the oxidation reaction171. In contrast, when secondary amines lacking a-hydrogens are allowed to react with Oxone and PTC in buffered acetone solution at 0 °C, nitroxides are obtained in good yields in a few minutes (equation 61)172. 

Oxaziridines unsubstituted at nitrogen (9, R =H) (in general used as aminating reagents, see Sections 3.5.4 and 3.5.6), are prepared by treatment of carbonyl compounds with chloramine or hydroxylamine-O-sulfonic acid in aqueous media (91S327). This method is, however, limited to certain carbonyl compounds with cyclohexanone, followed by butanone, benzaldehyde, and trichloroacetaldehyde giving the best results. 

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