Lactam (I) was protected as the tert-butyl carbamate (II) by treatment with Boc2O in the presence of Et3N and DMAP. After reduction of (II) with NaBH4 in EtOH at -25 C, reaction with ethanolic HCl produced the ethoxy derivative (III). Treatment with TiCl4 in CH2Cl2 at -30 C generated the intermediate iminium salt (IV), that was converted into the target benzoquinolizinone system (VI) by the tandem Mannich-Michael condensation with 2-(trimethylsilyloxy)-1,3-butadiene (V). Finally, oxidation of (V) with mercuric acetate produced the desired unsaturated compound.