Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 26, Issue 67, Pages 15573-15580Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.202001259
Keywords
C-H functionalization; hydroalkylation; photoorganocatalysis
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Funding
- DAAD (German Academic Exchange Service)
- Landesgraduiertenfcrderung of the state of Baden-Wurttemberg
- Projekt DEAL
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An unprecedented direct atom-economic chemo- and regioselective hydroalkylation of chloroalkynes and an sp(3)-C-H alkynylation of bromoalkynes was achieved. The reaction partners are unfunctionalized ethers, alcohols, amides, and even non-activated hydrocarbons. We found that a household fluorescent bulb was able to excite a diaryl ketone, which then selectively abstracts a H-atom from an sp(3)-C-H bond. The product of a formal alkyne insertion into the sp(3)-C-H bond was obtained with chloroalkynes, providing valuable vinyl chlorides. The photo-organocatalytic hydrogen atom transfer strategy gives rise to a broad range of diversely functionalized olefins. When bromoalkynes are applied in the presence of a base, a chemoselectivity switch to an alkynylation is observed. This reaction can even be performed for the alkynylation of unactivated sp(3)-C-H bonds, in this case with a preference of the more substituted carbon. Accompanying quantum chemical calculations indicate a vinyl radical intermediate with pronounced linear coordination of the carbon radical center, thus enabling the formation of both diastereoisomers after H-atom abstraction, suggesting that the (Z)-diastereoisomer is preferred, which supports the experimentally observed (E/Z)-distribution.
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