Oxaziridines. and

The introduction of a second heteroatom (other than sulfur) does not change drastically the absorption characteristics of small heterocycles. Oxaziridine and diaziridine are still transparent to light of wavelengths above 220 nm (Section 5.08.2.3.2). 

Whereas oxaziridine and diaziridine were partial subjects of comprehensive theoretical studies on cyclic compounds (73MI50800), diazirine and some of its simple derivatives were the special target of quantum chemical investigations. Since diazirine, the lowest molecular weight heterocycle, has only five atoms and is of high symmetry, there was a chance for ab initio calculations, which followed some semiempirical studies. 

S.08.2.3.1 NMR investigations on oxaziridines and diaziridines, configurational stability at nitrogen... 

Simple oxaziridines and diaziridines do not absorb in the near UV. Lack of absorption was one argument to distinguish between true three-membered ring structures and unsaturated open chain isomers like nitrones or hydrazones. 

Experiments with cyclic thioethers (80JCS(P1)1693), thiourea, thiocyanate and ethyl xan-thate always led to destruction of oxaziridines (73AJC2159). Products of complicated consecutive reactions could be isolated but only with some difficulty, e.g. (92) from a reaction with carbon disulfide (74JOC957), and (93), obtained by trapping with butadiene a product of a reaction between an oxaziridine and a thiirane (80JOC1691). 

Most ground state syntheses of oxaziridines and diaziridines follow the general scheme outlined for (242). Syntheses from starting materials containing a hetero-hetero bond, reported in the older literature, have not been confirmed. 

The earliest attempts to obtain optically active sulfoxides by the oxidation of sulfides using oxidants such as chiral peracids did not fare well. The enantiomeric purities obtained were very low. Biological oxidants offered great improvement in a few cases, but not in others. Lately, some very encouraging progress has been made using chiral oxaziridines and peroxometal complexes as oxidants. Newer developments in the use of both chemical oxidants and biological oxidants are described below. 

Bonaccorsi, R., E. Scrocco, and J. Tomasi. 1971. Molecular SCF Calculations for the Ground State of Some Three-Membered Ring Molecules Cis and Trans Diaziridine, Oxaziridine and the Corresponding Imminium Ions. Theor. Chim. Acta 21,17. 

Photochemical Rearrangement Isomerization of nitrones to oxaziri-dines is a general reaction of various cyclic and acyclic nitrones (447-449). When this reaction is reversible, many transformations of nitrone to oxaziridine and back to nitrone can be carried out without decomposition. This reaction is of special interest in view of light energy accumulation (450, 451). 

Photolysis of , 4,5-triphenyl-1,2,3-triazole 1-oxide gives the 1,3,4,5-oxatriazine (13) (80AJC2447). This is the only reported example of this monocyclic ring system, and the mechanism of its formation (Scheme 35) probably involves the intermediacy of an oxaziridine and an oxygen walk process not uncommon in the photochemistry of heterocyclic iV-oxides. 

Figure 6B.2. Transition-state models for epoxidation with optically active oxaziridines and dioxiranes.

Tables 8 and 9 and Figure 5 show that the rate data for hydrolysis of nitrone are almost identical to that for the hydrolysis of oxaziridine under all conditions of acidity at 24.2 °C. This evidence confirms that the salt of both oxaziridine and nitrone has the same kinetics on addition to water and forms products at a rate greater than that of unprotonated oxaziridine or nitrone. The decreasing rate at higher acidities is due to decreasing water activity in the acid media and is well explained by the Bunnett and Bunnett-Olsen criteria of the mechanism. The presented evidence57 is consistent with the mechanism outlined in Scheme 3, for example, a rapid protonation pre-equilibrium of nitrone (II) and oxaziridine (I) to form a common intermediate (HI) followed by slow nucleophilic attack by water and rapid decomposition to benzaldehyde and t-butylhydroxylamine.

They have further pointed out that the lower regioselectivity observed in the thermal rearrangement of oxaziridines does not rule out the above stereoelectronic requirement. In this case, the energy required for the reaction in sufficient to induce both nitrogen inversion in the starting oxaziridine and migration of the C-substituents. 

In the N-sulfonyl imine-catalyzed sulfoxidation, aqueous hydrogen peroxide serves as the final oxidizing agent, which is clearly of practical advantage. In principle it can be assumed that either an oxaziridine (F, Scheme 10.17) or a hydroper-oxy hemiaminal (H, Scheme 10.17) can result as the active species from the reaction of the N-sulfonyl imine E with hydrogen peroxide (Scheme 10.17). For imine 79 the idea of an intermediate oxaziridine is supported by the experimental finding that oxidation by the isolated oxaziridine and in the catalytic reaction (using 79 and... 

We based the possible oxidizing power of the oxaziridine on the observation that photolysis of pyridine N-oxides apparently generates oxaziridines, and that the photolysis of pyridine N-oxide itself gener-... 

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