Visible Light‐Enabled sp(3)‐C−H Functionalization with Chloro‐ and Bromoalkynes: Chemoselective Route to Vinylchlorides or Alkynes

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.