Imines and derivatives. Part 24. Nitrone synthesis by imine oxidation using either a peroxyacid or dimethyldioxirane

Abstract

The oxidation of N-alkyl imines by m-chloroperoxybenzoic acid to yield nitrones was facilitated by (i) the presence of C-aryl substituents, (ii) steric inhibition of attack at the imino C-atom, (iii) electron donating para-substituents on the C-aryl substituent, (iv) non-hydroxylic solvents, (v) optimal conjugation between C-aryl substituents and the imino group, and (vi) less bulky N-alkyl groups.The oxidation of N-alkyl imines by dimethyldioxirane (DIM D) in dichloromethane-acetone solution yielded nitrones without evidence of oxaziridine formation. The yields of isolated nitrones were higher for C,C-diary1 imines and for imines bearing less bulky N-alkyl substituents. N-H substituted ketimines were found to yield oximes after reaction with dimethyldioxirane.

Synthesis of oxaziridines by oxidation of imines with the trichloroacetonitrile–hydrogen peroxide system

“…Accordingly, the separation of (E) and (Z) oxaziridines often requires repeated column chromatography. Furthermore, N-oxides were also formed with oxaziridines when N-arylidenealkylamines with electron-donating aromatic substituents were oxidised by peracids in aprotic solvents [27].…”

Kinetic study of oxidation of N‐(α‐methylbenzylidene) anilines by dimethyldioxirane

“…In the reaction with m ‐Cl‐peroxybenzoic acid, oxaziridines are the main products and nitrones are formed only in a few cases. Nitrones are preferably formed when a carbon atom of an imine group is stericly hindered 2,3. The formation of nitrones in reactions with peroxyacids was characterized as an abnormal pathway for the reaction and the formation of oxaziridine as normal 4.…”

“…The formation of nitrones in the reactions of C ‐aryl‐ N ‐alkyl imines with dimethyldioxirane was ascribed to the electrophilic nature of this oxidizing agent 3. Overoxidation of C ‐aryl N ‐alkyl imines by dimethyldioxirane results in aldehydes and nitroalkanes 8.…”

Dimethyldioxirane

“…Secondary benzylamines give nitrones (eq 22 A related transformation is the oxidation of imines to nitrones by DDO (eq 23). 32 It is interesting that the isomeric oxaziridines are not produced here, given that peracids favor these heterocycles. Oxidation of Sulfur Functional Groups.…”