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Alkene-directed, nickel-catalyzed alkyne coupling reactions.
Karen M Miller1, Torsak Luanphaisarnnont, Carmela Molinaro
1Massachusetts Institute of Technology, Department of Chemistry, Cambridge, Massachusetts, USA.
Journal of the American Chemical Society
|April 1, 2004
Summary
Nickel-catalyzed coupling reactions of 1,3-enynes with aldehydes and epoxides show enhanced reactivity and regioselectivity due to the conjugated alkene. This enables the synthesis of valuable diene products and allylic alcohols.
Area of Science:
- Organic Chemistry
- Organometallic Chemistry
- Catalysis
Background:
- Nickel-catalyzed coupling reactions are crucial in organic synthesis.
- 1,3-enynes are versatile building blocks but their reactivity and regioselectivity in coupling reactions can be challenging.
- Controlling regioselectivity in metal-catalyzed transformations is a key area of research.
Purpose of the Study:
- To investigate the role of the conjugated alkene in nickel-catalyzed coupling reactions of 1,3-enynes with aldehydes and epoxides.
- To understand the mechanism governing reactivity and regioselectivity.
- To develop a method for synthesizing highly substituted 1,3-dienes and subsequently allylic/homoallylic alcohols.
Main Methods:
- Nickel-catalyzed coupling of 1,3-enynes with aldehydes and epoxides.
- Systematic variation of alkyne substituents and alkene substitution degrees.
- Mechanistic studies to probe the role of the alkene in regioselectivity determination.
- Subsequent rhodium-catalyzed hydrogenation of the diene products.
Main Results:
- The conjugated alkene in 1,3-enynes uniformly directs regioselectivity in nickel-catalyzed coupling reactions.
- Reactivity is significantly enhanced, irrespective of alkyne substituent or alkene substitution.
- Highly substituted 1,3-diene products are efficiently synthesized.
- A subsequent rhodium-catalyzed hydrogenation provides access to previously inaccessible allylic and homoallylic alcohols with high regioselectivity.
Conclusions:
- The conjugated alkene plays a critical role in directing regioselectivity through temporary interaction with the nickel catalyst.
- This alkene-directed nickel catalysis offers a powerful and general method for synthesizing complex dienes.
- The developed methodology provides a novel route to regioselectively synthesized allylic and homoallylic alcohols.
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