Imine oxidation with peroxy acids

Imines are oxidized by peroxy acids to oxaziridines, with the formation of nitrones as a competing process (Scheme 25).Oxaziridines are probably formed by a two-step process involving nucleophilic addition of the peroxy acid to the CWN bond, followed by elimination, as illustrated nitrones are formed by competing N-oxidation. The oxidation of chiral imines to oxaziridines by MCTBA proceeds with good, but not complete, diastereoselectivity. ... 

Oxidative deamination of a secondary amine to the ketone can be effected by formation of the imine with 2-pyridinecarboxaldehyde, reaction of the imine with peroxy-acid to form the oxaziridine, and alkaline hydrolysis (KOH-H2O-DMF-MeaCO). The steps are illustrated for 3a-amino-5a-cholestane (235), leading to (239) a IVa-aminoandrostane also gave the corresponding ketone. ... 

Oxaziridines are versatile epoxidizing agents in synthetic chemistry [58]. They are prepared by oxidation of imines or imminium compounds with peroxy acids or KMPS in the alkaline pH... 

The influ nee of reaction conditions on the stereochemistry of the oxidation of optically act ve or racemic Af-diphenylmethylene a-methylbenzylamines 40 with chiral or achiral peroxy acids to oxaziridines was investigated. It was found that asymmetric induction at the ring nitrogen in the resulting oxaziridine from optically active imine 40 does not depend on the nature of the peroxy acid or the solvent. However, the diastereoselectivity seems to be dependent only on the reaction temperature. The ratio of the resulting oxaziridine diastereomers changed by 10% when the reaction temperature was raised from — 30°C to -t-40°C. On the other hand, the enantioselectivity was found to depend on the chirality of the peroxy acid, the temperature, and the solvent. For example, the optical yield of the major oxaziridine diastereomer decreased from 3.4 to 1.3 when the solvent was changed from chloroform to methanol in the oxidation of racemic 40. 

A chiral substituent on nitrogen can direct the predominant attack of an oxidizing agent to one dia-stereotopic face of an imine. Ratios as high as 97 3 were observed in a series of imines derived from a-methylbenzylamine (equation 43). The oxidation of achiral imines with optically active peroxy acids, most notably monoperoxycamphoric acid [(+)-MPCA], do afford optically active oxaziridines, but not generally in synthetically useful optical ratios, but ratios as high as 80 20 have been reported. ... 

Rings containing Two Heteroatoms.—Direct Insertion. Peroxy-acid oxidation of the cyclic imine (262) yielded the corresponding oxaziridine (263), which rearranged when irradiated with u.v. light (2537 A) to iV-acetylpyrroIidine (264). A study of the proportion of cis- and /rawf-oxaziridines (266) and... 

It is noteworthy that quick and effective formation of diaryl nitrones can be achieved through oxidation of diaryl imines with Oxone (potassium peroxy-monosulfate) in such media as aqueous solution of NaHCC>3 in acetonitrile or acetone. When oxidized under such conditions, dialkyl or monoaryl imines give oxaziridines (17). Oxidation of 3,4-dihydroisoquinoline (9) with Oxone initially leads to the formation of oxaziridine (10) which is easily transformed into the corresponding 3,4-dihydroisoquinoline A-oxide (11) upon treatment with catalytic amounts of p-toluenesulfonic acid (Scheme 2.4) (18). 

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