Elusive Alkynylation Achieved | Chemical & Engineering News
Volume 91 Issue 9 | pp. 44-45 | Concentrates
Issue Date: March 4, 2013

Elusive Alkynylation Achieved

Palladium-catalyzed reaction appends alkynes to C–H bonds at sp3 carbon centers for the first time
Department: Science & Technology
News Channels: JACS In C&EN, Organic SCENE
Keywords: alkyne, alkynylation, C–H activation, palladium

Adding an alkyne handle to an already decorated organic molecule gives synthetic chemists the opportunity to create even more elaborate structures. Although there are several options for adding alkynes to organic compounds, examples of tacking carbon-carbon triple bonds onto molecules in place of C–H bonds when the carbon is an sp3-hybridized center are rare. Aiming to expand this area of chemistry, Jin-Quan Yu and colleagues at Scripps Research Institute, in California, developed a palladium-catalyzed alkynylation of the β-carbon in aliphatic amides, shown (J. Am. Chem. Soc., DOI: 10.1021/ja400648w). The reaction makes use of a Pd(0) catalyst bearing an N-heterocyclic carbene or a phosphine ligand and tolerates a wide range of functional groups. Yu’s team used the system to alkynylate more than a dozen different amides, including some containing ethers and trifluoromethyl groups. Mechanistic studies indicate the reaction involves a Pd(0)-catalyzed C−H activation step and does not need external oxidant to close the catalytic cycle. This last feature could improve the sustainability and practicality of C−H activation reactions. The group plans to do an enantioselective version of the alkynylation reaction using chiral ligands.

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Robert Wall  (March 5, 2013 9:42 AM)
I wonder whether the same transformation can be achieved simply by conjugate addition of alkyne anion to acrylic acid derivatives?
Not From the Chatani Group  (March 6, 2013 6:10 PM)
It's interesting that this is the first time an alkyne was appended to an sp3 carbon, given that a similar transformation was accomplished two years ago. See: http://pubs.acs.org/doi/pdf/10.1021/ja206002m
Pigi  (March 7, 2013 10:09 AM)
Why is the alkynylation elusive given that Chatani has achieved this transformation using Pd(II)/Pd(IV)?
Bethany Halford  (March 11, 2013 3:01 PM)
My apologies to the Chatani goup. Perhaps I could have written a better headline that emphasized the fact that this reaction does not need an external oxidant to close the catalytic cycle.
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