Oxaziridine reactions with nucleophiles

One Nitrogen and One Oxygen Atom Oxaziridines, reaction with nucleophiles 81YGK952. 

S.08.3.1.4 Reactions of oxaziridines with nucleophiles and reducing agents... 

The most important and well-defined reactions involving attack at nitrogen are those discovered by Schmitz and co-workers. A -Unsubstituted oxaziridines react with a variety of nucleophiles to effect transfer of the NH group from the oxa-ziridine to the nucleophile. Many of these reactions resemble nitrene or nitrenoid reactions although little mechanistic work has been reported, it seems better to classify them as involving nucleophilic substitution followed by elimination ... 

Although A -acyloxaziridines are known, a systematic examination of their reactions with basic reagents has not been made. In the case of Af-(A -phenylcarbamyl)-oxaziridines, nucleophiles appear to attack at nitrogen either intermolecularly or intramolecularly by way of diaziridinone formation. This work has recently been summarized. ... 

The mechanisms of these reactions are highly speculative because several steps must be involved, but it can generally be said that the Japanese workers propose a scheme similar to that of Hata and Watanabe for reactions of oxaziridines with nucleophiles, in which the transition state for the initial reaction has a nitrenoid character and leads to an ylide intermediate. On the other hand, Abou-Gharbia and Joullie propose cycloaddition of a zwitterionic ring-opened oxaziridine leading to a heterocycle that subsequently decomposes. 

The reactions of oxaziridines with nucleophilic reagents have been... 

An anomalous reaction of 2-benzenesulfonyl-3-aryloxaziridines (Davis reagents) with indoles has been reported.48 hi this it appears that a re-bond in the indole acts nucleophilically to attack the O of the oxaziridine ring and thereby cleave the O—N bond. 

Secondary amines reacted to form hydrazines in yields of 90% and better. Aniline can be converted to phenylhydrazine. Sometimes the addition was followed by the elimination of water rather than the aminated nucleophile. For example, treatment of 3,3-pentamethyleneoxaziridine with methoxide ion produced cyclohexanone oxime (9-methyl ether. Formanilide reacted with 3-phenyloxaziridine in the presence of sodium ethoxide to produce benzaldehyde phenyUiydrazone. " Of considerable interest is the reaction of Schiff bases with these oxaziridines to produce diaziridines. Other examples are given in Schmitz recent review. One intramolecular version of this kind of amination is known oxaziridine 57 was converted to benzophenone and 5,6-dihydro-4H-l, 2-thiazine 58 upon heating. ... 

The mechanism of oxygen transfer from oxaziridines to nucleophiles is believed to involve an Sn2 type reaction and this assumption is supported by theoretical and experimental studies. When sulfides are oxidized to the corresponding sulfoxides and sulfones, the molecular recognition is steric in origin, and it is determined by the substituents on both the substrate and the oxaziridine. For the oxidation of enolates, the molecular recognition is explained with an Sn2 mechanism as well as by an open (non-chelated) transition state where the nonbonded interactions are minimized. The mechanism of oxygen transfer to an enolate to form the corresponding acyloin is shown below. ... 

The treatment of simple and fused oxaziridines with sulfur-containing nucleophiles such as thiourea, potassium thiocyanate, potassium ethyl-xanthate, potassium selenocyanate, and triphenyl-phosphine sulfide resulted in the formation of the related imines, most probably—in analogy to the results of the treatment of oxiranes with the same reagents—via the corresponding thiaziridine intermediate. The proposed reaction mechanism is given in Scheme 8 <73AJC2159>. 

In the presence of CsF, carbonyl difluoride combines with the oxaziridine (13.16) to form a high yield of CF3N(0Cp3)C(0)F [1834]. The result indicates that the [CF3O] nucleophile, generated from the reaction of CsF with COF, attacks the nitrogen atom, and this is confirmed, in a separate experiment, in which the salt Cs[OCF3] was employed in the reaction. 

---