METAL-CATALYZED REACTIONS OF IMINES WITH ETHYL DIAZOACETATE LEADING TO AZIRIDINES

The metal-catalysed aziridination of imines with ethyl diazoacetate as the carbene fragment donor using various Lewis acids as the catalyst has been investigated. The catalytic properties of different Lewis aci d complexes have been tested and it has been found that both main-grou p complexes, such as BF3 . OEt2, early- and late-transition metal comp lexes, such as TiCl(O-Pr-i)(2) Cu(OTf)(2) and Zn(OTf)(2) and rare-eart h metal complexes, such as Yb(OTf)(3), can catalyse the formation of a ziridines, The aziridination gives mainly the cis-aziridines as the ma jor diastereoisomer, but the selectivity is dependent on the substrate , catalyst and solvent, Zn(OTf)(2) and Yb(OTf)(3) have been-shown to b e general catalysts for the formation of various aziridines using diff erent imines and a variety of reaction conditions. Both Zn(OTf)(2) and Yb(OTf)(3), as well as some of the other Lewis acids, in combination with various chiral ligands, have been tested as catalysts for the for mation of optically active aziridines, but only low ees are obtained. The Zn(OTf)(2)- and Yb(OTf)(3)-catalysed reactions have been investiga ted for imines having both electron-donating and -withdrawing substitu ents, and in reactions containing diethyl fumarate as a trapping reage nt, in attempts to obtain insight into the mechanism of the aziridinat ion.