The Control of the Nitrogen Inversion in Alkyl-Substituted Diaziridines

For the first time the nitrogen inversion barriers in 3,3‐unsubstituted trans‐diaziridines, such as 1,2‐di‐tert‐butyldiaziridine (1) and 1,2‐di‐n‐butyldiaziridine (2) were determined. Enantioselective stopped‐flow multidimensional gas chromatography was used to investigate the enantiomerization barrier of 1 between 126.2 and 171.0 °C (ΔG${{{\ne}\hfill \atop {\rm gas}\hfill}}$(150.7 °C) = 135.8±0.2 kJ mol−1, ΔH${{{\ne}\hfill \atop {\rm gas}\hfill}}$ = 116.1±2.5 kJ mol−1, ΔS${{{\ne}\hfill \atop {\rm gas}\hfill}}$ = −46±2 J K−1 mol−1). The separation of the enantiomers has been achieved in presence of the chiral stationary phase (CSP) Chirasil‐β‐Dex with a high separation factor (α = 1.44 at 80 °C). In a complementary approach, the enantiomerization barriers of 1,2‐di‐tert‐butyldiaziridine (1), 1,2‐di‐n‐butyldiaziridine (2), 1‐n‐butyl‐3,3‐dimethyldiaziridine (3), and 1,2,3,3‐tetramethyldiaziridine (4) were determined for comparison by enantioselective dynamic chromatography (DGC) and computer simulation of the dynamic elution profiles. The enantiomerization barrier of 2 was shown to be the highest among the nonsterically hindered diaziridines studied so far, whereas 1 exhibited the highest value found for strained nitrogen‐containing rings, that is, aziridines, diaziridines and oxaziridines. The nitrogen inversion barriers of 1,2‐di‐tert‐butyldiaziridine, 1,2‐di‐n‐butyldiaziridine‐n‐butyl‐3,3‐dimethyldiaziridine, and 1,2,3,3‐tetramethyldiaziridine (see scheme) were determined by enantioselective gas chromatographic techniques. 1,2‐Di‐tert‐butyldiaziridine exhibited the highest enantiomerization barrier for strained nitrogen‐containing rings.