1,2-Aryl and 1,2-Hydride Migration in Transition Metal Complex Catalyzed Diazo Decomposition:  A Novel Approach to α-Aryl-β-enamino Esters

N-Tosyl diazoketamines were prepared by addition of the ethyl α-diazoacetate anion to N-sulfonylimines. The diazo decomposition of the diazoketamines with Rh2(OAc)4 complex resulted in aryl migration to give α-aryl-β-enamino esters in good yields and high stereoselectivity. The effect of the catalysts on the migratory aptitude of 1,2-aryl over 1,2-hydride migration was studied. A reaction mechanism involving a “bridged” phenonium ion is proposed.