We wished to establish the effect of various aziridine N-substituents on the performance of the cyclization reaction (Scheme 4). With N-H aziridine 1 (Scheme 4, Entry 1), no reaction was observed, either with Ph3C + BF4 -or with BINOL-phosphoric acid. In contrast, with N-phthalimido aziridine 2, cyclization afforded product in a 59% isolated yield (Scheme 4, Entry 2). With more electron withdrawing substituents, such as acetate (Scheme 4, Entry 3) and tosylate (Scheme 4, Entry 5) groups, cyclization markedly improved. Even appending naproxen, a remarkably bulky substituent, did not inhibit cyclization (Scheme 4, Entry 4). Interestingly, even though benzyloxycarbonyl groups (Cbz) activate aziridines for ring-opening (Scheme 4, Entry 6), the yield of our cyclization dropped with N-Cbz aziridine 6. The yield of product was excellent, however, with phosphoramidate 7. Overall, a wide variety of N-substituents are tolerated by our cyclization protocol, but the aziridine must be at least somewhat activated to engage productively.