Beyond the corey reaction: one-step diolefination of cyclic ketones

Area of Science:

• Organic Chemistry
• Reaction Mechanisms
• Synthetic Methodology

Background:

• Cyclic ketones are versatile building blocks in organic synthesis.
• The Corey reaction with sulfonium ylides typically yields epoxides.
• Understanding competing reaction pathways is crucial for synthetic control.

Purpose of the Study:

• To investigate the reactivity of cyclic ketones with dimethylsulfoxonium methylide.
• To elucidate the mechanism of the Yurchenko diolefination reaction.
• To determine the influence of reaction conditions on product distribution.

Main Methods:

• Reactions of cycloheptanone, cyclodecanone, and cycloundecanone with dimethylsulfoxonium methylide.
• Varied stoichiometry of ylide and base (NaH) in diglyme at 130°C.
• Mechanistic studies involving computational analysis (MP2/cc-pVDZ).

Main Results:

• Excess dimethylsulfoxonium methylide favors oxirane formation (Corey reaction).
• Excess base promotes 1,3-terminal diene formation (Yurchenko diolefination).
• A [2,3]-sigmatropic rearrangement of the ylide is proposed as the key step in diolefination, with a low activation barrier.
• Cyclododecanone and cycloheptanone are more reactive in the Yurchenko reaction than cyclodecanone.

Conclusions:

• The reaction pathway is controllable by adjusting the base-to-ylide ratio.
• The Yurchenko diolefination proceeds via a novel mechanistic pathway involving sigmatropic rearrangement.
• Ring size influences the reactivity of cyclic ketones in the Yurchenko reaction, with medium-sized rings being less reactive.