Enantioselective Synthesis of Cryptopleurine and Boehmeriasin A via ­Organocatalytic Intramolecular Aza-Michael Addition

The enantioselective synthesis of phenanthroquinolizidine alkaloids cryptopleurine and boehmeriasin A was achieved in eight steps from commercial available Cbz-protected 2-piperidinone in 22% and 20% overall yield, respectively. The key steps of this route are intramolecular enantioselective aza-Michael addition, intramolecular aldol addition, and oxidative coupling.