Photocatalyzed Giese‐type alkylations of C(sp3)−H bonds are very attractive reactions in the context of atom‐economy in C−C bond formation. The main limitation of such reactions is that when using highly polymerizable olefin acceptors, such as unsubstituted acrylates, acrylonitrile, or methyl vinyl ketone, radical polymerization often becomes the dominant or exclusive reaction pathway. Herein, we report that the polymerization of such olefins is strongly limited or suppressed when combining the photocatalytic activity of benzophenone (BP) with a catalytic amount of Cu(OAc)2. Under mild and operationally simple conditions, the Giese adducts resulting from the C(sp3)−H functionalization of amines, alcohols, ethers, and cycloalkanes could be synthesized. Preliminary mechanistic studies have revealed that the reaction does not proceed through a radical chain, but through a dual BP/Cu photocatalytic process, in which both CuII and low‐valent CuI/0 species, generated in situ by reduction by the BP ketyl radical, may react with α‐keto or α‐cyano intermediate radicals, thus preventing polymerization.
Cross dehydrogenative couplings on ethers occur very effectively using N-fluorobis(phenyl)sulfonimide (NFSI) as oxidizing agent under UVA irradiation in the presence of 2 mol% benzophenone. The reaction was shown to proceed first by fast radical fluorination of the α-C-H bond of ethers, followed by HF elimination to yield the highly electrophilic oxocarbenium ion as a key intermediate.
The first example of an enantioselective carbocyclization of an alkyne-containing substrate catalyzed by chiral Brønsted acids was achieved. The use of the 2-hydroxynaphthyl substituent on the alkyne as ad irecting group constituted the key parameter enabling both efficient regioselective protonation of the carbon-carbon triple bond and chiral induction. The keyc ationici ntermediate could be depicted either as ac ationic vinylidene ortho-quinonem ethide or as tabilized vinyl cation. Atropoisomeric phenanthrenes derivatives were produced in high yields and good enantioselectivities under mild, metal-free reactionc onditions in the presence of chiral Ntriflylphosphoramide catalysts. The carbenic nature of the cationic intermediate was also exploitedt odescribe an example of alkyne/alkane cycloisomerization.
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