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 N-heterocyclic compounds from the
same starting materials.