Catalytic preparation of aziridines with an iron Lewis acid

The iron Lewis acid, [(eta(5)-C5H5)Fe(CO)(2)(THF)](+)[BF4](-), was found to be an effective catalyst for the preparation of aziridines. This new method provides a facile, one-step route to predominantly cis-aziridines, with yields up to 95%, from compounds with a diazo functionality and a variety of substituted N-benzylidene imines with N-aryl or N-alkyl groups. The reaction mechanism is believed to proceed through an electrophilic iminium ion intermediate. To support this idea, the iron Lewis acid-imine complex [(eta(5)-C5H5)Fe(CO)(2)(PhCH=NPh)](+)[BF4](-) was prepared, characterized, and reacted with different diazo compounds to provide the resultant cis-aziridines. Alternatively, it may be possible that the aziridines were derived from an electrophilic carbenoid intermediate, as is often proposed. Thus, the iron carbene [(eta(5)-C5H5)Fe(CO)(2)(CHPh)](+)[SO3CF3](-) was prepared and treated with N-benzylideneaniline; however, the resultant aziridine was not formed.