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Electrochemical Hydroboration of Alkynes
Maude Aelterman1, Morgane Sayes2, Philippe Jubault1
1Normandie Université, INSA Rouen, UNIROUEN, CNRS, COBRA (UMR 6014), 76000, Rouen, France.
Researchers developed a new electrochemical hydroboration method for alkynes using bis(pinacolato)diboron. This metal-free process efficiently yields hydroboration products from various alkynes without needing a hydride source.
Area of Science:
- Organic Chemistry
- Electrochemistry
- Catalysis
Background:
- Hydroboration is a key organic transformation.
- Traditional methods often require metal catalysts or stoichiometric reductants.
- Developing metal-free and efficient hydroboration techniques is desirable.
Purpose of the Study:
- To report a novel electrochemical hydroboration of alkynes.
- To utilize bis(pinacolato)diboron (B2Pin2) as a boron source.
- To achieve hydroboration without metal catalysts or hydride sources.
Main Methods:
- Electrochemical oxidation of B2Pin2 in the presence of alkynes.
- Utilizing an undivided electrochemical cell.
- In situ generation of a borate intermediate followed by oxidation.
Main Results:
- Successful hydroboration of a wide range of alkynes.
- Good to excellent yields of hydroboration products were obtained.
- The reaction proceeded efficiently without metal catalysts or hydride sources.
Conclusions:
- The developed electrochemical method offers a sustainable and efficient route to alkyne hydroboration.
- The reaction mechanism likely involves the electrochemical oxidation of an in situ formed borate to a boryl radical.
- This work presents an unprecedented metal-free hydroboration manifold.
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02:47Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
02:40Alkynes to Aldehydes and Ketones: Acid-Catalyzed Hydration
Analogous to alkenes, alkynes also undergo acid-catalyzed hydration. While the addition of water to an alkene gives an alcohol, hydration of alkynes produces different products such as aldehydes and ketones.
02:35Electrophilic Addition to Alkynes: Hydrohalogenation
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Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
02:24Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation
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