Preparation of Cyclic N-tert-Butylsulfonyl Enamines by Rh(II)-Mediated Ring Expansion of α-Diazoesters

The anion derived from ethyl diazoacetate adds to N-tert- butylsulfonyl ketimines to give b-tert-butylsulfonylamino a-diazo- esters, which are further transformed into cyclic enamines by treat- ment with Rh2(OAc)4, through 1,2-C-C bond migration of a Rh(II) carbene intermediate.