Birch reduction of a dibenzazonine base (1) with sodium produced the desired diene (2) in a good yield. The diene (2) was heated with 10% sulfuric acid and cyclized readily to provide the erythrina base (3) as a sole product, which was subsequently converted by treatment with excess diazomethane to the known base, cis-15, 16-dimethoxyerythrinan-3-one (4).
