Nitrilimine cycloaddition onto 2-azetidinones bearing alkenyl dipolarophile(s)

Silver acetate-promoted nitrilimines cycloaddition onto 3(R*)-phenyl-4(R*)-cinnamoyl-2-azetidinone were highly stereoselective giving 4-(4,5-dihydropyrazol-5-yl) carbonyl-2-azetidinones as the major products and regioisomeric 4-(4,5-dihydropyrazol-4-yl) carbonyl-2-azetidinones as the minor one. When the same protocol was applied to the novel 3(R*)-phenyl-4(S*)-(4-benzoyl-E,E-1,3-butadienyl)-2-azetidinone it resulted in site- and regioselective but not stereoselective cycloaddition, involving the formation of the four cycloadducts .