The copper-catalysed aziridination of styrene with copper-exchanged zeolite Y (CuHY) and copper(II) triflate (Cu(OTf)(2)) as catalysts is described and discussed. In particular, the effects of reaction conditions on the yield and enantiomeric excess of the aziridine product are described using [N-(p-nitrophenyisulfonyl)imino]phenyliodinane (PhI=NNs) as nitrene donor. By careful control of the styrene:nitrene donor molar ratio and the solvent, an ee of 95% can be obtained for the heterogeneously catalysed bis(oxazoline)-modified zeolite CuHY The ee achieved with the zeolite immobilised catalyst is significantly higher than that achieved for the non-immobilised homogeneous catalyst under comparable reaction conditions. (C) 2002 Elsevier Science B.V. All rights reserved.