Reactions of oxaziridines involving no partner

Retardation by a factor of 1000 by use of benzene in place of ethanol in the rearrangement of (58) points to appreciable charge separation in the transition state. 

Rearrangement involving cleavage of the C—O bond is also observed with the phenyl isocyanate adduct (59). In place of an O-acylated nitrone its product (60) of acyl migration is isolated (67JPR(36)86). 

The isomerization of oxaziridines (1) to acid amides with migration of a substituent from C to N is a general reaction and is always observed when no other reactions predominate under the relatively harsh conditions (heating to above 150 °C or photolysis). Even then one can make acid amide formation the main reaction by working at 300 °C (57JA5739) and by dilution techniques. For example, caprolactam (63) is formed in 88% yield by flash pyrolysis of oxaziridine (52) at about 300 °C, whereas decomposition of (52) at lower temperatures gives almost no (63) (77JPR274). 

In the 2-aryloxaziridines, acid amide formation proceeds under mild conditions and is the most often observed stabilization reaction of these very unstable compounds. Heating at 75 °C for 30-45 min is sufficient to convert N-arylspirooxaziridines (64 R = Ar) to the isomeric lactams (65) in 75-90% yield. 

3-Diaryloxaziridines are even less stable. With oxaziridines (66 Ar = Ph or 4-Me2NC6H4) acid amide formation at 25 °C proceeded in the course of 66 and 10 h respectively in the latter case there were equal amounts of H and aryl migration. Ethanol as solvent again accelerated the reaction, in the latter case by a factor of lO.  

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