Azirines and Aziridines

The main rontes to aziridine inclnde alkali-catalysed cyclisation of 2-halo-amines or of a 2-hydroxyamine snlfonate ester, as illnstrated, or by additions to alkenes or imines. 

Varions homochiral aziridines can be easily obtained from serinef ° such substances can be transformed into a range of polyfnnctional homochiral intermediates and products. 

Reversing the sense of cyclisation, A-chloro-amines, with a suitable C-H-acidifying substitutent, can be ring closed efficiently producing A-alkyl-aziridines.  

Aziridines can be obtained from alkenes using iodine isocyanate or iodine azide. The product from the latter reaction can be converted into the aziridine via reduction, or into an azirine via elimination of hydrogen iodide and pyrolysis.  

Aziridines can also be prepared by addition of nitrenes to alkenes, or by the use of nitrogen-transfer agents analogons to epoxidising agents.  

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The intermolecular cycloaddition of an electron-deficient species such as a nitrene, a nitrenium ion or a carbene (or their formal equivalents) to the ir-bond of an alkene, alkyne, imine, or nitrile is a significant approach to aziridines and azirines (Scheme 2). 

Ring opening of aziridines and azirines by hydrofluorination 91T5329. Synthesis of JV-arylaziridines based on l-chloroalkyl(aryl)sulfoxides 91YZ205. 

The ring expansion of aziridines and azirines corresponds to this type of ring closure leading to A2-thiazolines. iV-Thioacylaziridines (366) rearrange under acid conditions to 2-aryl-A2-thiazolines (368) either by an S l or S 2 mechanism, depending on the nature of the acid catalyst and the solvent used (69JA5835,69JA5841). 

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