Synthesis of some mono- and bis-spiro-β-lactams of benzylisatin

Some new mono- and bis-spiro-β-lactams of benzylisatin were prepared by Staudinger’s ketene–imine [2+2] cycloaddition reaction. The cycloadducts were characterized by spectral data including 1H NMR, 13C NMR, IR and mass spectra. The configuration of benzylisatin and one of mono-spiro-β-lactams (5a) was established by X-ray crystal analysis.