Routes to chiral N-acyliminium ion precursors for the synthesis of optically active pure ring-fused pyrroloisoquinoline alkaloids.

Pyrrolisoquinoline (B) is found as a major structural motif of the erythrina alkaloid group of natural products. We recognised that a suitably substituted bicyclic lactam (A) could act as a precursor in an intramolecular N-acyliminium mediated cyclisation reaction in a stereoselective approach to the core of the erythrinane target ring system....cont'd