Oxidation oxaziridines

All attempts to supply physical evidence for the formation of oxaziridines as intermediates in the photolysis of aromatic A -oxides have met with scanty success, so investigators have relied on indirect evidence. Theoretical calculations seem to agree that, in aromatic A -oxides, oxaziridines do not arise from the ground state but very likely from the first excited singlet state. A comprehensive critical review of this subject has appeared. ... 

Oxiranes, Arene Oxides, Oxaziridines, Dioxetanes, Thietanes, Thietes, Thiazetes, and Others... 

A. Hassner, M. Bartok, H. L. Lang, D. R. Boyd, D. M. Jering, M. J. Haddadin, J. R Freeman, W. Adam, F. Yany, D. C. Dittmer, and T. C. Sedergran, Small Ring Heterocycles. Part Three. Oxiranes, Arene Oxides, Oxaziridines, Dioxetanes, Thietanes, Thietes, Thiazetes, and Others, Ch. 1 Oxiranes Ch. 2 Arene Oxides Ch. 3 Oxaziridines... 

The mechanism of this reaction involves an activation of the ammonia and hydrogen peroxide because these compounds do not themselves react (118—121). It appears that acetamide functions as an oxygen transfer agent, possibly as the iminoperacetic acid (41) which then oxidizes the transient Schiff base formed between MEK and ammonia (40) to give the oxaziridine (42), with regeneration of acetamide ... 

There is a scattered body of data in the literature on ordinary photochemical reactions in the pyrimidine and quinazoline series in most cases the mechanisms are unclear. For example, UV irradiation of 4-aminopyrimidine-5-carbonitrile (109 R=H) in methanolic hydrogen chloride gives the 2,6-dimethyl derivative (109 R = Me) in good yield the 5-aminomethyl analogue is made similarly (68T5861). Another random example is the irradiation of 4,6-diphenylpyrimidine 1-oxide in methanol to give 2-methoxy-4,6-diphenyl-pyrimidine, probably by addition of methanol to an intermediate oxaziridine (110) followed by dehydration (76JCS(P1)1202). 

In the oxaziridines (1) ring positions 1, 2 and 3 are attributed to oxygen, nitrogen and carbon respectively. The latter almost always is in the oxidation state of a carbonyl compound and only in rare cases that of a carboxylic acid. Oxaziridinones are not known. The nitrogen can be substituted by aryl, alkyl, H or acyl the substituent causes large differences in chemical behavior. Fused derivatives (4), accessible from cyclic starting materials (Section 5.08.4.1), do not differ from monocyclic oxaziridines. 

Direct proof of an oxaziridine intermediate was achieved in photolysis experiments in an organic glass at 77 K (80JA5643). Oxaziridine (75), formed by photolysis of A/-oxide (74) and evidenced by UV spectroscopy under the above conditions, decomposed at higher temperature to form the imino ether (76) by N—O bond cleavage and C -> O migration of an aryl group. 

With a peroxyacid, the reagent used in their preparation, oxaziridines further react to yield aliphatic nitroso compounds. An electrophilic attack to ring nitrogen is plausible, leading to an intermediate oxaziridine N-oxide (81), which immediately decomposes to a nitroso compound and an aldehyde (57JA6522). 

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. 

Sulfonyloxaziridines were recently proposed as O-transferring reagents. Oxaziridine (89) converted thioethers to sulfoxides (90) and diaryl disulfides into their 5-oxides (91) (78TL5171). Epoxidations are also possible (81TL917). 

Diaziridines, discovered in 1958, six years after the oxaziridines, were almost immediately realized to be structural analogs of oxaziridines. Like these they showed oxidizing properties unexpected for other classes of organic nitrogen compound. Properties in common with oxaziridines include the rearrangement to open chain isomers on heating above 100 °C (for several diaziridines), and their hydrolytic behavior in acidic media, which leads to carbonyl compounds with conservation of the hetero-hetero bond. 

From N-oxides of aromatic bases oxaziridines were obtained only at very low temperatures, but oxaziridines were often postulated as intermediates in the photoconversion of such N-oxides (Section 5.08.3.1.2). Isolation of the more stable photoisomers of nitrones also causes some problems due to their thermal and photochemical instability leading to acid amides, e.g. (69TL2281), or, by fragmentation, to carbonyl compounds and products of stabilization of nitrenes, e.g. from (260) (69ZN(B)477). 

Even the trivial decomposition of oxaziridines may have some importance. In the oxidation of s-alkylamines to ketones conversion to the Schiff base of 2-pyridinealdehyde was proposed, followed by peracid oxidation to the oxaziridine (295). Decomposition by alkali yields the ketone added excess acetone suppresses condensation of pyridinealdehyde with dialkyl ketone (75AJC2547). 

Aliphatic nitroso compounds are obtained either by hypobromite oxidation of alkylhy-droxylamines made by oxaziridine hydrolysis, or directly from oxaziridines by action of a second mole of peracid (Section 5.08.3.1.3). 

Three preparations of 1-azetine iV-oxides have been reported. Oxidation of the 2-aryl-l-azetine (222) with MCPBA gives the nitrone (223) (79CB3914>. However, similar treatment of 2-alkoxy-l-azetines fails to give the corresponding iV-oxides but yields products derived from oxaziridines (cf. Section 5.09.4.2.3). 

Electronic spectral considerations were invoked by Boyer et in favor of the i/i-o-dinitroso- structure and by Mallory and Wood against an oxaziridine formulation for the jV-oxide structure. The spectra of some nitrobenzofuroxans have been reported. 

David-Thieffiry oxidation 542 Davis s (camphorsulfonyl)-oxa-ziridine 725,728 Davis s oxaziridine 459 DCBI 697 f. 

The first reported derivative of 1,2-oxazepine was dibenz[f,/][l,2]oxazepine-ll-carbonitrile (3 a). This, together with small amounts of compounds 4 and 5, is formed when acridine-9-carbonitrile 10-oxide (la) is irradiated with UV light,6,7 It is likely that the reaction proceeds by way of the oxaziridine valence tautomer 2a, which, however, was not detected.7 Photo-isomcrization of 9-chloroacridine 10-oxide (lb) yields the 11-chlorodibenzoxazepine 3b.6,7... 

Irradiation of the unsymmetrically substituted 2,3,4,6-tetraphenylpyridine 1-oxide (5) under these conditions gives 2,4,6,7-tetraphenyl-l, 3-oxazepine (7) in 30 % yield, together with 2,4,5,6-tetraphenylpyridin-3-ol (10) in 37% yield and 2,3,4,6-tetraphenylpyridine (30%).11 It has been suggested that the reaction proceeds by way of the oxaziridines 6 (which yields 7) and 8 (which yields the isomeric oxazepine 9) the latter rearranges to the pyridinol 10. 

Oxidation of benzodiazepinone 1 with 3-chloroperoxybenzoic acid gives a mixture of the oxaziridine 2 (10%) and the benzodiazepinone 4-oxidc 3 (40%).165... 

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. 

Davis and coworkers40 have developed use of diastereomerically pure 2-sulfonyl and 2-sulfamyloxaziridines for asymmetric oxidation of sulfides into sulfoxides (equation 7). The best results (using the sulfamyloxaziridines) range from 38 to 68% enantiomeric purity of the resultant sulfoxides. The structural diversity of such substituted oxaziridines, their... 

Oxathiane dioxides lithiated 641 synthesis of 638, 647 Oxathiane oxides, synthesis of 352 Oxathiolane oxides, synthesis of 241 Oxaziridines 72, 254, 826 as optically active oxidizing agents 291 Oxazolidinones 826 Oxazolines 619, 788... 

The unusual oxaziridine analog 91 has also been synthesized by oxidizing the glycolate imine 90 of diphenyl aminomethylphosphonate 89 with wi-chloroperbenzoic acid (MCPBA). The resulting adduct was thermally quite labile but could be isolated after removing all of the volatile side components in vacuo (2). 

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