Studies on the reaction of aziridines with nitriles and carbonyls: synthesis of imidazolines and oxazolidines

Reaction of N-tosylaziridines with nitriles and carbonyls to produce imidazolines and oxazolidines has been studied in the presence of a variety of Lewis acids. The reaction is efficient with 1 equiv of BF3.Et2O or Et3OBF4 in CH2Cl2. However, it is catalytic with metal triflates that give the best results for cycloaddition of N-tosylaziridine with nitriles under solvent free conditions. The same reaction with carbonyls proceeds best in CH2Cl2 in the presence of molecular sieves. Among various triflates, Zn(OTf)2 has been found to be the best. The cleavage of the N-Ts bond of the cyclized products has been studied in order to make it more versatile in synthesis. The mechanistic aspect of the reaction has been studied by using chiral aziridines as substrates. These formal [3+2] cycloaddition reactions of aziridines with nitriles and carbonyls proceed in a Ritter fashion.