Zinc(II)-catalysed transformation of epoxides to aziridines

Abstract

The Lewis acid-catalysed transformation of epoxides to aziridines with iminophosphoranes as the nitrogen-fragment donor has been investigated. Of the Lewis acids tested, zinc(II) complexes had the best catalytic properties. The method works best for terminal and cyclic epoxides, internal epoxides being less reactive. Of the various iminophosphoranes employed N-(triphenylphosphoranylidene)-aniline and -isopropylamine were the most successful. The zinc(II)-catalysed reaction has been studied for chiral styrene oxides for which the enantiomeric excess of the aziridine produced is dependent on the reaction time. The reaction of achiral and chiral styrene oxides and N-(triphenylphosphoranylidene)aniline in the presence of a zinc(II) complex having a chiral ligand has been investigated as has the reaction for cis-deuteriostyrene oxide in order to obtain information about the stereochemical outcome of the reaction. A mechanism for the title reaction is discussed on the basis of the experimental results.