Total Synthesis of (+)‐Melonine and (+)‐ <i> N ₄ </i> ‐Oxy Melonine Enabled by an Intramolecular Alkene Diamination Reaction

Abstract

Abstract Among more than four thousand monoterpene indole alkaloids (MIAs) isolated to date, only a few feature a 2,2,3‐trisubstituted indoline moiety. (+)‐Melonine and (+)‐ N 4 ‐oxy melonine possess a highly rearranged carbon framework, presumably arising from cyclization of a rearranged iminium ion of quebrachamine precursor. We report herein the first enantioselective total synthesis of (+)‐melonine and (+)‐ N 4 ‐oxy melonine featuring: a) a highly enantioselective CBS reduction followed by a stereospecific Johnson‐Claisen rearrangement for the synthesis of enantioenriched β ‐substituted γ , δ ‐unsaturated ester; b) Bower's bis‐cyclizative diamination of alkene, enabling the conversion of a functionalized cycloheptene to the tetracyclic core of the natural products; and c) an AlMe 3 ‐mediated lactamization that concurrently achieves desymmetrization at the C20 prochiral center.