Enantioselective Total Synthesis of (+)‐Flavisiamine F via Late‐Stage Visible‐Light‐Induced Photochemical Cyclization

The structural features Kopsia alkaloids, in particular multiple all‐carbon quaternary stereocenters in a caged and strained polycyclic skeleton, poses particular challenges for enantioselective total synthesis. Herein, we reported the first total synthesis of (+)‐flavisiamine F. The synthetic approach involved a room‐temperature Overman rearrangement for introducing the chiral amine at C21, a TMS‐promoted ketal Claisen rearrangement for constructing the all‐carbon quaternary stereocenter at C20, and a late‐stage visible‐light‐induced photochemical cyclization for establishing the all‐carbon quaternary stereocenter at C7.     

A Concise Total Synthesis of (+)‐Waihoensene Guided by Quaternary Center Analysis

The four contiguous all‐carbon quaternary centers of waihoensene, coupled with the absence of any traditional reactive functional groups other than a single alkene, render it a particularly challenging synthetic target among angular triquinane natural products. Here, we show that its polycyclic frame can be assembled concisely by using a strategically chosen quaternary center to guide the formation of the other three through judiciously selected C?C bond formation reactions. Those events, which included a unique Conia‐ene cyclization and a challenging Pauson–Khand reaction, afforded a 17‐step synthesis of the molecule in enantioenriched form.