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

Abstract—Silver acetate-promoted nitrilimines cycloaddition onto 3(R*)-phenyl-4(R*)-cinnamoyl-2-azetidinone 1 were highly
stereoselective giving 4-(4,5-dihydropyrazol-5-yl) carbonyl-2-azetidinones 5 as the major products and regioisomeric 4-(4,5-
dihydropyrazol-4-yl) carbonyl-2-azetidinones 6 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 2 it resulted in site- and regioselective but not stereoselective cycloaddition, involving the
formation of the four cycloadducts 10–13.