Synthesis and structural characterization of an oxaziridine derived from 6-azadiosgenin

•The first spirostanic oxaziridine 18 was synthesized from diosgenin.•Derivatives 12 and 16 are valuable for subsequent modifications on the steroid core.•Cyclization of the isocyanate 15 precursor can be tuned to give mainly 16 or 17.•The stereochemistry of the oxaziridine 18 was established as β-configuration.•X-ray of compound 11a confirmed the preferred α-epoxy orientation at C-5 and C-6.