IMDA-radical cyclization approach to (+)-himbacine.

Area of Science:

• Organic Chemistry
• Medicinal Chemistry
• Synthetic Chemistry

Background:

• Muscarinic receptors play crucial roles in various physiological processes.
• Selective antagonists for muscarinic receptors are valuable therapeutic agents.
• Himbacine is a known selective muscarinic receptor antagonist with potential pharmacological applications.

Purpose of the Study:

• To achieve the first formal total synthesis of the selective muscarinic receptor antagonist himbacine.
• To explore and establish efficient synthetic routes for complex alkaloid structures.
• To investigate novel carbon-carbon bond-forming reactions in the context of natural product synthesis.

Main Methods:

• The synthesis employed a strategic combination of key C-C bond-forming reactions.
• Intramolecular Diels-Alder reaction was utilized for core structure construction.
• Stille coupling reactions and a 6-exo-trig acyl radical cyclization to a conjugated enyne were critical steps.

Main Results:

• A successful formal total synthesis of himbacine was accomplished.
• The study demonstrated the utility of the chosen synthetic methodologies for constructing the himbacine scaffold.
• An unexpected conversion of a secondary alcohol to a chloride was observed during thionocarbonate formation, offering insights into reaction mechanisms.

Conclusions:

• The presented synthetic route provides a viable pathway for accessing himbacine and related analogs.
• The findings contribute to the field of synthetic organic chemistry by showcasing advanced C-C bond-forming strategies.
• Further investigation into the observed unexpected transformation may lead to new synthetic methodologies.