The total syntheses of dl-aspidospermine (Ia) were reported by Stork et al. in 1963 and by Ban et al. in 1964. The key intermediates of the same plane formulas(II and III) in both syntheses were prepared in independent ways, whose physico-chemical properties were quite different. At first, IIa and IIIa were given by Stork to his compounds, and accordingly IIb and IIIb corresponding to the conformation of IIb were preferred by us to our compounds on taking the above assignment into consideration, although the possibility of IIa to our compound was alternatively deduced based on n.m.r. spectral data. For clarification of this point, trans-decahydroquinolone(VI) was synthesized by the method of Grob and derived to VII, whose n.m.r. spectra were compared with the corresponding compounds including II, XI-A and XI-B. In addition, the fact that the intramolecular hydrogen bonding was observed with XIII-B and not with XIII-A, concludes that our intermediates(II and XI-A) are of A/B trans and the Stork's compound(II) and XI-B are of A/B cis. Subsequently, the fused form of C-ring to A- and B- rings in II and III was carefully investigated, and in conclusion IIc and IIIa were given to our intermediates. From IIIa, there were synthesized dl-aspidospermide and the other diastereoisomer of the natural alkaloid, the structure, of the latter was elucidated by X-ray crystallography to be XXVIII, which is compatible with the above assignment to our intermediates.
