Oxaziranes preparation

Preparation of Oxaziranes jrom SchiiJ s Bases and Peracids 

Oxaziranes which carry an aryl group on nitrogen occupy a special position. Sometimes, they rearrange even at room temperature, so they cannot easily be isolated. For preparative purposes, rearrangement in hot xylene is suitable. For the rearrangements of iV-alkyl-oxa- 

Oxaziranes are active oxygen compounds and react with a wick variety of reducing agents- The meet important of these is the reaction with potassium iodide since this reaction is the basis of the iodimetric procedure for assay of oxazirane purity. The reaction has also been examined preparatively and forms a basis for reduction of oxaziranrs 

Preparation of Oxaziranes from Schiff s Bases and Peracids 

Some oxaziranes can be prepared very simply from ketones and N-chloroamines. Thus 2-methyl-3,3-pentamethyleneoxazirane is easily obtained from cyclohexanone and iV-methylchloramine its reduction by ferrous salts gives an alkyl radical, which has been used to alkylate, in high yield, protonated heteroaromatic bases in aqueous solution (Scheme 5). 

Caution The preparation and distillation of the oxazirane, like that of any active oxygen compound, should he carried out behind a safety screen. 

The preparation of oxaziranes is almost always carried out by reacting a solution of peracetic acid in a volatile inert solvent at temperatures near 0 0 with the Schiff s base. Without any significant variation in the reaction conditions, a large number of oxaziranes has thus been prepared. Table I gives a selection of the fifty or so known oxaziranes. 

The Preparation of Oxaziranes from Carbonyl Compounds and Derivatives of Hydroxylamine and Chloramine 

For laboratory purposes oxaziranes are conveniently prepared by addition at 10-20 of an anhydrous sohitiou of peracetic acid in methylene chloride to the imine dissolved In the same solvent. The peracetic acid can be readily prepared at ice-bath temperatures by reaction of acetic anhydride with 90% hydrogen peroxide in tbe presenoe of a catalytic amount of sulfuric acid. However, the presence of water in the reaction medium does not appear to have a deleterious effect in many cases, and good yields of oxaziranes are frequently obtained from such Laboratoiy yields of the oxaziranes 

In a study of the chemistry of oxaziranes [75], it was discovered that this class of novel heterocyclic compounds is readily oxidized with peracetic acid to give dimeric nitroso compounds. Since the oxaziranes are, in turn, prepared by a peracetic acid oxidation of imines, the crude imines can, by proper adjust- 

The most useful preparation of oxaziranes is the very ready oxidation of imines with organic peraoids. This is a remarkably general reaction, and, since imines of widely varying structure can easily be 

Horner, L., Jurgens, E. Preparation and properties of some isonitrones (oxaziranes). Chem. Ber. 1957, 90, 2184-2189. 

Particularly for the preparation of aliphatic nitroso compounds, the oxidation of oxaziranes and imines with peracetic acid (Eqs. 6) probably represents the most original and most widely applicable method of preparation. 

Oxygen may be added by means of peracids to the double bond of enamines prepared from 20-oxosteroids. The 17,20-epoxides obtained may be readily hydrolyzed to 17a-hydroxy-20-oxosteroids.88 Schiff bases afford oxaziranes on treatment with peracids.285 By means 

Since many oxaziranes have limited stability in alkaline aohitiona lbi synthesis is not characterized by high yields in moat oases Tt dops. however, extend the apectrutn of available oxaziranes considembly. and a dramatic example of this ia the preparation of the hsumcrir 

Both aromatic and aliphatic nitroso compounds have been prepared by oxidative procedures. While few of the methods can be considered generally applicable, a sufficient variety of reagents have been proposed that it would appear reasonable to state that virtually any nitroso compound may be prepared by one of these procedures. The organic substrates which have been used are oxaziranes and imines, amines, hydroxylamines, and oximes. A byproduct of the oxidation of 4-methylcinnoline (an azo compound) has also been identified as a dimeric nitroso compound. 

Oxaziranes are in a real sense active oxygen compounds and exhibit many reactions grossly analogous to those of organic peroxides. Thus they undergo one electron transfer reaction with ferrous salts and on pyrolysis they are converted to amides. Oxaziranes are also useful synthetic intermediates since in appropriate cases they may be isomerized to aromatic nitrones which are a convenient source of N-alkylhydroxylamines. The reaction of oxaziranes with peracids also provides a source of nitrosoal-kanes and is in many instances the method of choice for preparation of these compounds.  

Two pieces of chemical evidence support the three-membered ring formulation. The bifunctional oxazirane prepared from glyoxal, tert-butylamine, and peracetic acid (6) can be obtained in two crystalline isomeric forms. According to the three-membered ring formula there should be two asymmetric carbon atoms which should allow the existence of meso and racemic forms. A partial optical resolution was carried out with 2-7i-propyl-3-methyl-3-isobutyloxazirane. Brucine was oxidized to the N-oxide with excess of the oxazirane. It was found that the unused oxazirane was optically active. 

The charge of N-<-butylbenzaldimine is adjusted according to the amount of perbenzoic acid available. The perbenzoic acid in benzene is prepared by the procedure of Silbert, Siegel, and Swern, and a 5% excess of this reagent is employed in the oxidation. In one attempt with commercial w-chloroperbenzoic acid instead, the checkers obtained only a 34% yield of oxazirane. 

Under these conditions the peracetic acid reagent apparently depoly-menace the triazine to the inline which is then converted to the oxazirane. Thus 2-w -butyloxazirane was prepared by Application of this synthesis.4 

From a preparative point of view the pbotoohemioaj oxazirane eynthesis has a number of obvious limitatione, but in some easee it may be possible to obtain osaairancs which are not sufficiently stable to obtain by othw methods thus (XV) oould not be synthesized by oxidaticH) of the parent imine at least under ordinary eonditiona. 

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