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.