Ruthenium-catalyzed ring-opening and ring-closing enyne metathesis

Area of Science:

• Organic Chemistry
• Catalysis
• Metathesis Reactions

Background:

• Olefin metathesis is a powerful tool for carbon-carbon bond formation.
• Ruthenium-carbene complexes are highly active and versatile metathesis catalysts.
• Enyne metathesis offers unique pathways for constructing complex cyclic structures.

Purpose of the Study:

• To investigate the utility of ruthenium-carbene complexes in a novel ring-opening and ring-closing metathesis reaction.
• To explore the synthesis of cyclized trienes from enynes containing cycloalkene moieties.
• To determine the optimal reaction conditions for this transformation.

Main Methods:

• A CH2Cl2 solution of an enyne with a cycloalkene moiety was treated with a ruthenium-carbene complex (10 mol %).
• The reaction was conducted at room temperature under an ethylene gas atmosphere (1 atm).
• Control experiments were performed under argon gas to assess the role of ethylene.

Main Results:

• The reaction successfully afforded cyclized trienes via a tandem ring-opening and ring-closing metathesis.
• The presence of ethylene gas was crucial for the cyclization; no product was obtained under argon.
• Enynes featuring a terminal alkyne moiety yielded good results, indicating substrate scope.

Conclusions:

• Ruthenium-carbene catalyzed tandem ring-opening and ring-closing metathesis is an effective method for synthesizing cyclized trienes.
• Ethylene plays a critical role in this metathesis pathway.
• The reaction shows promise for the synthesis of complex cyclic molecules from readily available enynes.