Homolytic reactions of oxaziridines

Oxaziridines substituted in the 2-position with primary or secondary alkyl groups undergo decomposition at room temperature. In the course of some weeks, slow decomposition of undiluted compounds occurs, the pattern of which is analogous to that of acidic or alkaline N—O cleavage (Sections 5.08.3.1.3 and 4), Radical attack on a C—H bond in (109) effects N—O cleavage, probably synchronously (57JA5739). In the example presented here, methyl isobutyl ketone and ammonia were isolated after two hour s heating at 150 °C. 

Homolytic oxaziridine decomposition can be easily initiated by iron(II) ion in acidic media. Catalytic amounts are sufficient because chain reactions proceed. The reaction proceeds obviously in the case of 2-r-alkyloxaziridines like (56), where it yields the isomeric acid amide (111) (57JA5739). 

When )3-scission can occur in the radical, further reactions compete with acid amide formation. Thus oxaziridine (112) with iron(II) ion and acid yields stabilization products of the isopropyl radical. If a-hydrogen is present in the Af-alkyl group, radical attack on this position in (113) occurs additionally according to the pattern of liquid phase decomposition. 

In spirooxaziridines like (114), /3-scission proceeds with ring opening. Stoichiometric amounts of iron(II) salt in acidic solution lead to the dicarboxylic acid derivative (115). The radical undergoes some interesting reactions with added unsaturated compounds. For example, pyridine yields a mixture of 2- and 4-alkylation products in 80% yield. Catalytic amounts of iron(II) ion are sufficient here since the adduct of the radical with pyridine is oxidized by iron(III) ion to the final product (116), thus regenerating iron(II) ion (68TL5609). 

Action of catalytic amounts of vanadium compounds on oxaziridine (52) yields caprolactam almost quantitatively. Reductive opening of the oxaziridine ring and /3-scission yield radical (118), which recyclizes with elimination of the metal ion to form the lactam (63) (77JPR274). 

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There are differences in the high temperature behavior. While oxaziridines almost always isomerize to acid amides, a similar reaction of diaziridines, which should lead to amidines, has not been observed. Sensitivity towards bases, often encountered in oxaziridines, is observed only in some special substituted diaziridines. The tendency of some classes of oxaziridines to transfer the nitrogen function also lacks in the diaziridine field. On homolytic reactions of diaziridines there are only a few observations. 

Homolytic cleavage of oxaziridines by ferrous salts, already described by Emmons, is a useful source of alkyl radicals. From oxaziridine 28, easily accessible from cyclohexanone and Af-chloromethylamine, on the action of ferrous salt, reaction products of radical 29 are obtained In the presence of FeCl2 oj-chlorohexanoic acid methylamide (30) is formed quantitatively in the absence of reaction partners, dimerization occurs to 31. As shown in a very careful investigation by Hawkins in the case of the N-cyclohexyl compound, the dicarboxylic acid derivative is accompanied by appreciable quantities of branched-acid derivatives, formed by a radical rearrangement 29 -> 32. The radical 29 adds to pyridine and gives rise, after rearomatization, to the formation of 70-80% of 2- and 4-substituted pyridine (33). ... 

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