N-Silyl Protecting Groups for Labile Aziridines:  Application toward the Synthesis of N-H Aziridinomitosenes

Hindered N-silylamines were examined for their utility to serve as protecting groups for the labile aziridine nitrogen found within the highly sensitive aziridinomitosene framework. tert-Butyldiphenylsilyl and modified tert-butyldiphenylsilyl groups were the most resistant to nitrogen−silicon bond cleavage under various reaction conditions and were thus employed in transformations relevant to aziridinomitosene synthesis. The N-silylaziridines 7a, 21a, and 21b underwent azomethine ylide cycloaddition and afforded, upon deprotection, the N-H aziridine 24 in 18−32% overall yield for the three steps.