CATALYTIC FORMATION OF AZIRIDINES FROM IMINES - CHARACTERIZATION OF AN INTERMEDIATE IN SNCL4-CATALYZED AZIRIDINATION AND MECHANISTIC CONSIDERATIONS

The tin(IV) catalysed aziridination of imines using ethyl diazoacetate as the carbene fragment donor has been investigated from a synthetic and mechanistic point of view. For imines substituted with aromatic su bstituents, an intermediate in the aziridination reaction has been iso lated and characterised by X-ray diffraction, This intermediate is an octahedral complex with a trans coordination of two imines and in whic h the imines have isomerised from trans to cis by the reaction with/co ordination to tin(IV). Tin(IV) is a very effective catalyst for the az iridination of various imines giving cis-aziridines as the major produ ct, The aziridination can proceed with a very low catalyst load as 0.0 5 mol% of SnCl4 is sufficient to achieve a high conversion, For the fo rmation of aziridines a linear plot of the experimental data is obtain ed by means of the Hammett equation for a series of competition experi ments. Based on the results the mechanism for the aziridination is dis cussed in terms of a Lewis acid activation of the imine for a nucleoph ilic attack of ethyl diazoacetate.