A Unified Approach to Polycyclic Alkaloids of the Ingenamine Estate: Total Syntheses of Keramaphidin B, Ingenamine, and Nominal Njaoamine I

Many polycyclic marine alkaloids are thought to derive from partly reduced macrocyclic alkylpyridine derivatives via a transannular Diels-Alder reaction that forms their common etheno-bridged diaza-decaline core ("Baldwin-Whitehead hypothesis"). Rather than trying to emulate this biosynthesis pathway, a route to these natural products following purely chemical logic was pursued. Specifically, a Michael/Michael addition cascade provided rapid...