Synthesis of Bi-and Tricyclic Aziridine Derivatives

Another process worth mentioning is the cis-trans isomerization of aziridi-nyl ketones. The transformation of tnms-aziridines into the cis form was carried out in a methanol-acetone solution in the presence of triethylbenzylammonium hydrochloride [85]. However, the best yields of the cis isomer (up to 90%) were detected by the same authors when water was added to the reaction mixture [86]. The reverse transition from the trans configuration into the cis form is possible using methanolic solution of sodium methylate [87] or potassium hydroxide [35]. 

Aldehydes, symmetric and asymmetric ketones, such as formaldehyde, acetaldehyde, substituted benzaldehydes and cyclic ketones, were introduced into the reaction along with acetone. The reaction is reversible azirenoimidazoles undergo reverse transformation forming tnms-aziridinyl ketones in acetic acid. 

The reaction is diastereoselective and in all cases only exo isomer of 83 is separated. However, target azirenoimidazoles 83 containing different substituents in positions 2 and 8 cannot be obtained by this method. Other multi-component and one-pot synthesis procedures for synthesis of similar polycyclic structures are also described [98, 99, 100, 101, 102, 103, 104]. 

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