The isopavinan alkaloids thalidine and 0-methylthalisopavine and the pavinan alkaloids bisnorargemonine and argemonine were synthesized as the racemates and natural isomers from the appropriate form of N-norreticuline. The sequence utilizing (S)-(-)-N-norreticuline afforded the natural alkaloids and confirmed the absolute stereochemistry previously assigned to these compounds by several methods. The tetracyclic skeleton of both ...