Synthesis of the Azaoxoaporphine Alkaloid Sampangine and Ascididemin‐Type Pyridoacridines through TMPMgCl·LiCl‐Mediated Ring Closure

We report the synthesis of the azaoxoaporphine alkaloid sampangine ( 4 ) and a series of ring A analogues and isomers of the marine pyridoacridine alkaloid ascididemin ( 2 ). This approach starts from readily available 1‐bromo[2,7]naphthyridine ( 12 ) or 4‐bromobenzo[ c ][2,7]naphthyridine ( 5 ), and the ring A scaffold bearing an ester moiety is introduced by a Suzuki or Negishi cross‐coupling reaction. The final cyclization step was achieved through a directed remote ring metallation with the Knochel–Hauser base (TMPMgCl · LiCl; TMP = 2,2,6,6‐tetramethylpiperidinyl), followed by intramolecular trapping of the ester group.