Dihydroquinolinone (I) was protected as the tert-butyl carbamate (II) by condensation with di-tert-butyl dicarbonate. Reduction of (II) with NaBH4 in EtOH at -25 C, followed by reaction with ethanolic HCl provided ethoxy compound (III). Subsequent treatment of (III) with 2-silyloxy-1,3-butadiene (V) and trimethylsilyl triflate afforded benzoquinolizinone (VI), through the sequence of Mannich condensation of intermediate N-tert-Boc iminium salt (IV) with silyl enol ether (V), followed by Michael cyclization of the unsaturated ketone. Then, oxidation with mercuric acetate provided the target 4-4a unsaturated compound together with a minor amount of 1,2-unsaturated product.