Synthesis of the Tetracyclic Core (ABCE Rings) of Daphenylline

A concise synthesis of the tetracyclic core (ABCE rings) of daphenylline has been accomplished involving a benzobicyclo[3.3.1] lactam as the key intermediate. This bridged bicyclic intermediate was efficiently constructed via a Bronsted acid promoted intramolecular Friedel-Crafts type Michael addition of a delta-benzyl alpha,beta-unsaturated delta-lactam.