Total Synthesis of Astellatol.

Area of Science:

• Organic Chemistry
• Natural Product Synthesis
• Total Synthesis

Background:

• Astellatol is a rare sesterterpenoid with a highly congested pentacyclic structure.
• Its complex architecture, including a bicyclo[4.1.1]octane motif and ten stereocenters, presents a significant synthetic challenge.
• The synthesis of astellatol remained an unsolved problem for nearly 30 years.

Purpose of the Study:

• To achieve the first enantiospecific total synthesis of astellatol.
• To develop a scalable and efficient strategy for accessing complex isopropyl trans-hydrindane sesterpenoids.
• To address the challenges associated with synthesizing the trans-hydrindane motif.

Main Methods:

• Utilized an intramolecular Pauson-Khand reaction to construct the core scaffold.
• Employed an unprecedented samarium(II) iodide-mediated reductive radical 1,6-addition to form the cyclobutane ring.
• Implemented a strategic oxidation/reduction sequence for late-stage transformations.

Main Results:

• Successfully completed the enantiospecific total synthesis of astellatol.
• Developed a novel method for constructing the cyclobutane moiety with two quaternary centers.
• Overcame significant challenges in late-stage functionalization and trans-hydrindane synthesis.
• Demonstrated a rapid and scalable approach to diverse sesterterpenoids.

Conclusions:

• The developed synthetic strategy provides a powerful platform for accessing complex sesterterpenoids.
• This work resolves a long-standing synthetic puzzle and offers new insights into trans-hydrindane synthesis.
• The methodology is scalable and applicable to the synthesis of related natural products.