Both enantiomers of C10b methyl analogs of crispine A and a tetracyclic core of Erythrinaalkaloids were synthesized starting from l-aspartic acid via a common chiral N-arylethyl succinimide intermediate. The pivotal C10a-C10b bond formation and construction of the C10b stereogenic center were achieved via diastereoselective N-acyliminium ion cyclization. The dibenzylamino group gave stereochemical