Chemical Properties of Bi- and Tricyclic Aziridines

The chemical properties of bi- and tricyclic aziridines are determined, first of all, by the presence of the sterically strained three-membered cycle as well as the two nitrogen atoms, which are basic centers. The most interesting reactions are the processes involving the carbon-carbon single bond cleavage of the aziridine cycle which will be considered later. 

The possibility of bicyclic aziridine hydrochloride salt formation was first mentioned in [88]. The hydrochlorides of some azirenoimidazoles were obtained by passing dry hydrogen chloride through ether solutions. However, the protonation direction was not established in that work. 

The behavior of dihydroazirenoimidazoles and tetrahydroazirenopyrazines in the presence of acids was studied in [112] in detail. The authors note that protonation not accompanied by further transformations takes place under mild conditions (dilute HC1 in ethanol at room temperature). l-(4-Nitrophe-nyl)-6-phenyl-3,5a-dihydro-1 //-azireno[ 1,2-c]imidazole and 1 -(4-nitrophenyl-6-phenyl-1,3,4,6a-tetrahydroazireno[l, 2- f]pyrazine hydrochlorides were obtained according to the procedure described in [88]. 

The basic character of the ketimine nitrogen atom in azirenoimidazoles is also shown by its propensity to react with trimethyloxonium tetrafluoroborate, leading to the appropriate salt [113]. 

As already mentioned, most interesting are the properties of the aziridines connected with cleavage of the C-C bond of the sterically strained three-membered cycle, namely, thermo- and photoinduced cycloaddition reactions. Photo- and thermochromism inherent to these compounds are also linked with the breaking of this bond in the literature. 

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Fused aziridines are interesting compounds owing to the fact that the strained three-membered ring can easily open and cause dipolar cycloaddition reactions as well as their photochromic properties. Therefore, most of this chapter covers the chemical and photochemical properties of bi- and tricyclic aziridines. Some properties of aziridinyl ketones are also reviewed, in particular, reactions leading to aziridinyl anils. 

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