Nucleophilic Lewis Base Dependent Addition Reactions of Allenoates with Trifluoromethylated Cyclic Ketimines

A detailed investigation on the different reactivity patterns shown by phosphorus- and nitrogen-containing Lewis base catalysts in the reactions of allenoates with cyclic trifluoromethyl ketimines was accomplished. With PPh₃, [3 + 2] annulations proceeded smoothly to afford dihydropyrrole derivatives in excellent yields. Under the catalysis of DABCO, [2 + 2] annulations occurred, producing azetidine derivatives in good to high yields. However, in the presence of pyridine, α,α′-disubstituted allenoates were obtained in very high yields via aza-Morita–Baylis–Hillman reactions. These studies provide an opportunity for diverse synthesis of a variety of <i>N</i>-heterocyclic compounds from the same starting materials