One-pot synthesis of <i>trans</i>-β-lactams from ferrocenylketene generated by thermal Wolff rearrangement

A series of β-lactams containing the ferrocene moiety were synthesized through the Staudinger reaction between ferrocenylketene generated by the thermal Wolff rearrangement of the corresponding diazo ketone and various imines. The stereochemical outcome has been investigated and the <i>trans</i>-products were isolated as the main products, opposite to the reported results by Bonini and coworkers. The absolute configuration of (±)-<i>trans</i>-1,4-diphenyl-3-ferrocenylazetidin-2-one (<b>3c</b>) was determined by X-ray analysis. The stereoselectivity is discussed from the viewpoint of the reaction mechanism.