Synthetic strategy toward ineleganolide: A cautionary tale

Convenient Access to a Strained Bicyclic Enone: A Concise and Improved Formal Synthesis of Ineleganolide

The norcembranoid and cembranoid diterpenoids represent an intriguing class of natural products isolated from marine sources. Their chemical synthesis has been a challenging and exciting field of research over the past two decades, owing largely to their structural complexity. We recently disclosed a total synthesis of a member of this class, ineleganolide, in a 23 step longest linear sequence. In search of a shorter, more efficient route, we have devised a new strategy for the synthesis of a key bicyclic enone. Disclosed herein is our improved synthesis of this strained intermediate, completing the formal synthesis of ineleganolide in only 14 steps, thereby shortening our previous synthesis by 9 steps. Dedicated to Prof. Thomas Maimone on his receipt of the Tetrahedron Young Investigator Award 2024.

A Convergent Total Synthesis of (+)-Ineleganolide

We report the total synthesis of the furanobutenolide-derived diterpenoid (+)-ineleganolide. The synthetic approach relies on a convergent strategy based on the coupling of two enantioenriched fragments, which are derived from (-)-linalool and (+)-norcarvone, respectively. A high-yielding, one-step Michael addition and aldol cascade furnishes a pentacyclic framework as a single diastereomer, thereby overcoming previous challenges in controlling stereochemistry. The endgame features an O2-facilitated C-H oxidation and a samarium diiodide-induced semipinacol rearrangement to furnish the highly rigid central seven-membered ring.

Total Syntheses of (+)-Ineleganolide and (-)-Sinulochmodin C

Described herein are the first total syntheses of the nor-furanocembranoid natural products (+)-ineleganolide (1) and (-)-sinulochmodin C (2). The synthetic strategy is predicated on a transannular Michael reaction that provides both natural products from a common macrocyclic intermediate and leverages a diastereoselective radical cyclization to furnish a key bicyclic lactone. The latter is further advanced to a macrocyclic precursor via a Nozaki-Hiyama-Kishi cyclization and a one-pot furan oxidation/oxa-Michael cascade. Unexpected stereochemical nuances that guided the evolution and eventual completion of the total synthesis are discussed.