Ring-opening reaction of unactivated 3-arylaziridine-2-carboxylates with nitrile reagents

Ring-opening reactions of unactivated 3-arylaziridine-2-carboxylates with nitrile reagents, using trans-1-benzyl-3-(3,4-methylenedioxyphenyl)aziridine-2-carboxylate as a typical aziridine substrate, were examined. Formation of azomethine ylide by C2–C3 bond cleavage was observed when the aziridine was treated with trimethylsilyl cyanide under thermal conditions. On the other hand the use of bromine cyanide (BrCN) and diethylaluminum cyanide (Et2AlCN) led to N–C3 bond cleavage and the stereospecificity was found to be dependent on the reagent used. Additional aluminum-catalyzed ring-opening reactions disclosed that the potential cationic character of the C3 benzylic position and stereochemical requirements of substituents in the arylaziridine system control the reactivity. Furthermore, the synthetic utility of the ring-opening reaction was demonstrated not only by application to the cyclization of a ring-opened cyanopropanoate to an isoquinoline skeleton but also by the extension of other carbon nucleophile from nitrile (C1) to a ketene acetal (C2).