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When irradiated by UVA, a Ni(II) precatalyst integrating a benzophenone chromophore in its structure catalyzes the regioselective cycloaddition of alkynes and azides to produce 1,5‐disubsituted 1,2,3‐triazoles with 1,5:1,4 regioisomer ratios ranging from 1.7:1 to >20:1. Speciation and reactivity studies revealed that the reaction most likely proceeds through a Ni(I)/Ni(III) catalytic cycle. [ABSTRACT FROM AUTHOR]

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 a directing group constituted the key parameter enabling both efficient regioselective protonation of the carbon–carbon triple bond and chiral induction. The key cationic intermediate could be depicted either as a cationic vinylidene ortho‐quinone methide or a stabilized vinyl cation. Atropoisomeric phenanthrenes derivatives were produced in high yields and good enantioselectivities under mild, metal‐free reaction conditions in the presence of chiral N‐triflylphosphoramide catalysts. The carbenic nature of the cationic intermediate was also exploited to describe an example of alkyne/alkane cycloisomerization. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]