PdCl₂-catalyzed efficient transformation of propargylic amines to (E)-α-chloroalkylidene-β-lactams

(Chemical Equation Presented) The PdCl₂-catalyzed cyclocarbonylation reaction of propargylic amines with CuCl₂ and benzoquinone afforded (E)-α-chloroalkylidene-β-lactams in moderate to good yields. The formation of the corresponding Z-isomers or five-membered products was not observed. The reaction of the readily available optically active propargylic amines provides a convenient synthesis of the corresponding (E)-α-chloroalkylidene-β-lactams with high ee values. The structure and the stereochemistry of the products were established by the X-ray single-crystal diffraction study of (E)-6d and (E)-6e, which indicates that the stereoselectivity in this reaction is different from what was observed with propargylic alcohols. A rationale for this reaction was proposed.