General Information. All commercial materials were used as received unless otherwise noted. DCM were dried by distillation over CaH2. Other solvents were purchased from J&K Chemical and used without further purification. To rule out the influence of trace metal ion completely, the base, HFIP and HOSA were purified by standard procedure. General procedure for aziridination of alkenes：To an 8 mL glass vial equipped with magnetic bar was added alkene (1.0 mmol, 1.0 equiv), piperidine (condition [A]: 2.0 mmol, 2.0 equiv) or pyridine (condition : 1.2 mmol, 1.2 equiv; condition [C]: 2.4 mmol, 2.4 equiv) at room temperature. HFIP (2.0 mL) was added for dissolving the reaction mixture to make the concentration 0.5 M. Hydroxylamine-O-sulfonic acid (HOSA) (condition [A]: 2.0 mmol, 2.0 equiv; condition : 1.2 mmol, 1.2 equiv; condition [C]: 2.4 mmol, 2.4 equiv) was added subsequently and then sealed with PTFE cap. The reaction mixture was stirred at rt for 12 h. After that, the reaction mixture was neutralized with saturated NaHCO3 (aq) and extracted with CH2Cl2 for four times. Finally, the concentrated resulting residue was purified by flash column chromatography to afford the desired product with CH2Cl2/MeOH as eluent.