Asymmetric Total Synthesis of (−)-Spirochensilide A, Part 1: Diastereoselective Synthesis of the ABCD Ring and Stereoselective Total Synthesis of 13(R)‑Demethyl Spirochensilide A

A concise and diastereoselective construction of the ABCD ring system of spirochensilide A is described. The key steps of this synthesis are a semipinacol rearrangement reaction to stereoselectively construct the AB ring system bearing two vicinal quaternary chiral centers and a Co-mediated Pauson–Khand reaction to form the spiro-based bicyclic CD ring system. This chemistry leads to the stereoselective synthesis of 13­(R)-demethyl spirochensilide A, paving the way for the first asymmetric total synthesis of (−)-spirochensilide A.