β-Lactam Synthesis via Skeletal Rearrange-ment of O-Propargyl Arylaldoximes

Significance

O-Propargyl arylaldoximes were found to undergo an astonishing skeletal rearrangement to β-lactams, when they were subjected to catalytic amounts of CuBr at high temperatures. In this process, five covalent bonds (C=N, N-O, C-O, C-C and CºC) are cleaved. The regio-selectivity of the rearrangement can be rather ­attributed to the structure of the starting material than to the electronic character of the substituents, as it was shown by an exchange of the R^³ and R^² group.