Oxaziridine reactions thermal

The unstable dibenz[c,/][l,2]oxazepines (312 R = CN, Cl) have been isolated as the major products of the UV irradiation of 9-cyano- and 9-chloro-acridine 10-oxides (310) in benzene (c/. the analogous Af-imide to 1,2-diazepine conversion on p. 598). Although none of the oxaziridine tautomer (311) was detectable by UV spectroscopy, the subsequent deoxygenation of (312) to acridine suggests the existence of a thermal equilibrium between (311) and (312) (79T1273). These dibenzo compounds (312) are the only fully unsaturated oxazepines yet isolated but the 2,3-benzoxazepin-l-one system (314) has recently been prepared by the reaction of benzonitrile oxide with the benzopyranone (313) (80JCS(Pl)846). 

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. 

A potentially important industrial application of this reaction involves the thermal rearrangement of 3,3-pentamethylene-oxaziridine 67 to e-caprolactam, a reaction that is strongly catalyzed by transition-metal ions. ... 

There are a number of thermal and photochemical reactions for which oxaziridine intermediates have been proposed but never isolated. These include, among others, the photochemical Beckmann rearrangement of oximes, many photochemical reactions of aromatic A -oxides, and the thermal rearrangement of nitrones to amides. A brief discussion of the first two seems warranted in this review because they have been studied extensively and some strong inferential evidence for oxaziridine intermediates has been obtained. 

Thermal isomerization of oxaziridines into amides and lactams, one of the most widespread reactions of oxaziridines, fails with the compounds unsubstituted at nitrogen. Obviously NH-transfer reactions predominate. Lactam formation from 34 could be brought about only by a kind of flash pyrolysis slowly adding 34 to preheated paraffin at 300°C gave caprolactam 44 (85%). 

Reactions.—Desulphurization of thiirans to alkenes remains an important strategy for the preparation of hindered alkenes, e.g. (14), and is the most typical thiiran reaction. Phosphines and phosphites are the reagents that are most often used. Lithium reagents desulphurize rra s-2,3-diphenylthiiran to ( )-stilbene, while the ds-isomer is converted into a 1 1 mixture of (Z)-stilbene and the two isomers of tr-mercaptostilbene. 2-Phenylthiiran is desulphurized by cf-metallated isocyanides. Thermal extrusions of sulphur include the conversion of (15) into (16), amongst others. Desulphurizations using zinc and acetic acid, molybdenum or palladium complexes, and the oxaziridine (17) have been reported. 

Nitrones are isomerized to oxaziridines photochemically. This reaction is reversed thermally ... 

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