Aziridinations three-membered cycles

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. 

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. 

Stereoselective Synthesis of 2,3-Disubstituted Aziridines Three-membered aza-cycle, aziridine shows significant biological activities and is found in many natural as well as synthetic analogs (Figure 40.5). The stereoselective synthesis of this subunit is very important, and in this regard, a carboamination reaction can be considered a useful tool. 

Indeed, this MCR worked extremely well by simply stirring the three components in trifluoroethanol (TFE) at room temperature. Interestingly, no high-dilution conditions were required for the above transformation. Authors prepared 12-, 15-and 18-membered macrocycles and even nine-membered medium-sized cycles in excellent yields with diastereoselectivities. Two examples were depicted in Scheme 11. Thus, stirring a TFE solution of aziridine aldehyde 29, dipeptide 30 and ferf-butyl isocyanide at room temperature for 4 h afforded a nine-membered cycle 31 in 83% yield. Similarly, a 18-membered cyclopeptide 33 was obtained in 77% yield by the reaction of 29, pentapeptide 32 and ferf-butyl isocyanide. In both examples, the cyclic compounds 31 and 33 were formed with high diastereoselectivities (dr > 20/1). This is intriguing, as Ugi reaction provided generally low to moderate stereoselection when chiral substrates was used as inputs ([66-72] for enantioselective isocyanide-based MCRs, see [73-80]). 

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