Oxaziridines configurational stability

S.08.2.3.1 NMR investigations on oxaziridines and diaziridines, configurational stability at nitrogen... 

Oxaziridines For oxaziridines the N-inversion barrier is considerably higher than that for similar aziridines. A-Alkyloxaziridines show a high degree of configurational stability of the pyramidal nitrogen with inversion barriers... 

The photochemical synthesis of optically active oxaziridines from prochiral nitrones was driven by an interest in examining the configurational stability of the oxaziridin nitrogen atom. Nitrone 7 was irradiated at — 78°C in a 1 1 mixture of ( + )- or (— )-2,2,2-trifluorophenylethanol (8) and fhiorotrichloromethane yielding nitrone 9lent-9 in 30% ee (absolute stereochemistry unknown) [17,18]. At room temperature this selectivity decreased to 5% ee. Less bulky residues also reduced the selectivity. An exchange of f-butyl by /-propyl led to 20% ee at — 78°C (Scheme 5). 

The addition of oxygen across the C—N double bond is a common and synthetically useful process. The product oxaziridines are of interest for theoretical reasons (largely due to the high configurational stability of the chiral nitrogen), as reagents (such as oxygen transfer moieties), and as synthetic intermediates. The stereochemical aspects of oxaziridine synthesis and reactivity have been reviewed. ... 

Configurational stability became evident from the preparative results, when both diastereomeric oxaziridines with E-Z isomerism and optically active oxaziridines were prepared. 

A high inversion barrier at nitrogen was found for diaziridines, which parallels the configurational stability at oxaziridine nitrogen. It was first discovered from NMR data and was proved by separation into E and Z isomers and finally by obtaining optically active diaziridines. 

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