Biomimetic Approach toward the Total Synthesis of rac-2-(Acylmethylene)pyrrolidine Alkaloids.

2-(Acylmethylene)pyrrolidine derivatives were synthesized via intermolecular decarbonylative Mannich reaction from various methyl ketones and 1-alkyl-1-pyrroliniums, generated in situ from 1-alkylprolines. This approach mimics the biosynthetic pathway and provides a direct access to a series of 2-(acylmethylene)pyrrolidine alkaloids, including hygrine, N-methylruspolinone, dehydrodarlinine, and ruspolinone.