Enantioselective Total Synthesis of (+)‐Alstilobanine C, (+)‐Undulifoline, and (−)‐Alpneumine H

Abstract

We report herein the enantioselective total synthesis of three monoterpene indole alkaloids, namely, (+)‐alstilobanine C, (+)‐undulifoline, and (−)‐alpneumine H. The key features of our synthesis include: a) introduction of chirality via enantioselective deprotonation of a prochiral 4‐substituted cyclohexanone; b) use of methoxymethyl (MOM) ether as both a hydroxyl protective group and a latent oxonium species for the formation of bridged oxepane and c) domino double reductive cyclization to build both the indole and the piperidine ring at the end of the synthesis. The synthesis confirmed the absolute configuration of these natural products assigned based on the biogenetic hypothesis.

Enantioselective Total Synthesis of (+)‐Nordasycarpidone, (+)‐Dasycarpidone, and (+)‐Uleine

“…Our group has recently accomplished an enantioselective total synthesis of condyfoline ( 11 ) [20] through a key TiCl 3 ‐mediated reductive cyclization of tetrasubstituted alkene bearing a 2‐nitrophenyl substituent [21] as well as alstilobanine C ( 8 ) and undulifoline ( 9 ) featuring a late stage construction of both the indole and the piperidine rings by way of a double reductive cyclization cascade ( Scheme 1 ,b ) [22] . As a continuation of our interest in the synthesis of indole alkaloids containing a bridged bicyclic ring system, [23–26] we envisaged to develop an alternative strategy to reach the tetracyclic compound 1 .…”