The mechanism of the aziridination reaction of imines and ethyl diazoacetate catalyzed by the chiral Br�nsted acid (S)-VANOL-B3 is studied using a combination of experimental 13C kinetic isotope effects (KIEs) and theoretical calculations. The reaction is found to proceed via a stepwise mechanism with reversible formation of a diazonium ion intermediate followed by rate-limiting SN2-like ring closure to form the aziridine ring. This result is in conflict with the recently reported mechanism of the achiral Br�nsted acid (triflic acid) catalyzed aziridination reaction of a more electrophilic imine and ethyldiazoacetate (Troyer, T. L.; Muchalski, H.; Hong, K. B.; Johnston, J. N. Org. Lett. 2011  , 13, 1790-1792). Is the reaction mechanism dependent on the imine substrate or does the counter-ion change the rate-limiting step? We report here the results from an extensive investigation into origin of this mechanistic discrepancy.

Isotope effects and mechanism of BrØnsted acid catalyzed aziridination reactions

244th National Meeting (2012)

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