The asymmetric aziridination of cyclicenones with N-tosyloxycarbamates, using N-neopentyl 1,2-diphenylethylenediamine as a catalyst, and its application to the formal total synthesis of (−)-agelastatin A, using a one-pot silylation-selenylation procedure and the regioselective aziridine-opening by an azide anion as key steps, are described.