Conrotatory ring closure of 1-halo-3-aza-4-alkyl-1,3-dienes in refluxing to
luene gives rise to 3-halo-4-aryl-2-azetidinones in satisfactory yields. De
halogenation of the resulting beta-lactams by tris(trimethylsilyl)silane fu
rnished 3-unsubstituted azetidinones, valuable intermediates in the synthes
is of biologically active compounds.