Various applications of the domino cycloaddition/N-acyliminium ion cyc
lization cascade are reported. The key step in the process involves th
e generation of a reactive N-acyliminium ion by fragmentation of an am
ino substituted [4 + 2]-cycloadduct. The successful synthesis of a num
ber of alkaloids by this sequence of reactions reveals the usefulness
and importance of this unique domino cascade.