Alcohols as Efficient Intermolecular Initiators for a Highly Stereoselective Polyene Cyclisation Cascade

Area of Science:

• Organic Chemistry
• Synthetic Chemistry
• Catalysis

Background:

• Polyene cyclization is crucial for synthesizing complex natural products and pharmaceuticals.
• Developing highly stereoselective and efficient cyclization methods remains a key challenge in organic synthesis.

Purpose of the Study:

• To develop a novel, highly stereoselective polyene cyclization cascade reaction.
• To explore the use of benzylic and allylic alcohols in a titanium-catalyzed process.
• To demonstrate the utility of the reaction in synthesizing steroid analogues.

Main Methods:

• Utilized benzylic and allylic alcohols as substrates in hexafluoro-2-isopropanol (HFIP) solvent.
• Employed titanium(IV) isopropoxide [Ti(Oⁱ Pr)₄] as a catalyst.
• Investigated mechanistic pathways through subsequent studies.

Main Results:

• Achieved a highly stereoselective polyene cyclization cascade, forming three new carbon-carbon bonds.
• Observed complete stereocontrol over up to five newly formed stereogenic centers.
• Demonstrated high functional group tolerance and atom economy, producing water as the sole byproduct.
• Identified a stereoconvergent mechanism for the reaction.

Conclusions:

• The developed method offers an efficient and stereoselective route to complex polycyclic structures.
• The reaction provides a streamlined pathway for the synthesis of steroid analogues in a single step.
• This work expands the scope of substrates for titanium-catalyzed polyene cyclizations.