Synthesis of (±)-eschscholtzine. The absolute configuration of (–)-argemonine, (–)-eschscholtzine, and related alkaloids

The structure of (–)-eschscholtzine (IV) is confirmed by synthesis of the racemic form. Degradation of (–)-argemonine (I) to a derivative of L-aspartic acid provides rigorous proof of the absolute configuration of the alkaloid. This knowledge allows assignment of absolute configuration to be made for (–)-norargemonine (II), (–)-bisnorargemonine (III), (–)-eschscholtzine (IV), (–)-caryachine (V), and (–)-eschscholtzidine (VI).