Asymmetric Synthesis of Tetracyclic Benzo[<i>a</i>]quinolizidine Targets

We report a novel, facile, and asymmetric approach for the synthesis of polycyclic benzo[a]quinolizidine targets. In the formation of more functionalized derivatives, we have observed the generation of an iminium ether salt intermediate, formed during an unprecedented retro-Diels−Alder/N-acyliminium cyclization cascade. The iminium ether intermediate was isolated in good yield, characterized by X-ray crystallography, and subsequently applied as a synthetic building block.