A general anti-Baldwin radical 4-exo-dig cyclization from nitrogen-substituted alkynes is reported. Upon reaction with a heteroleptic copper complex in the presence of an amine and under visible light irradiation, a range of ynamides were shown to smoothly cyclize to the corresponding azetidines, useful building blocks in natural product synthesis and medicinal chemistry, with full control of the regioselectivity of the cyclization resulting from a unique and underrated radical 4-exo-dig pathway.

The direct functionalization of CÀ H bonds is among the most fundamental chemical transformations in organic synthesis. However, when the innate reactivity of the substrate cannot be utilized for the functionalization of a given single CÀ H bond, this selective CÀ H bond functionalization mostly relies on the use of directing groups that allow bringing the catalyst in close proximity to the CÀ H bond to be activated and these directing groups need to be installed before and cleaved after the transformation, which involves two additional undesired synthetic operations. These additional steps dramatically reduce the overall impact and the attractiveness of CÀ H bond functionalization techniques since classical approaches based on substrate pre-functionalization are sometimes still more straightforward and appealing. During the past decade, a different approach involving both the in situ installation and removal of the directing group, which can then often be used in a catalytic manner, has emerged: the transient directing group strategy. In addition to its innovative character, this strategy has brought CÀ H bond functionalization to an unprecedented level of usefulness and has enabled the development of remarkably efficient processes for the direct and selective introduction of functional groups onto both aromatic and aliphatic substrates. The processes unlocked by the development of these transient directing groups will be comprehensively overviewed in this review article.

Ammonium salts are usually considered as highly challenging to reduce into the corresponding radicals because of the strength of their carbon–nitrogen bond. Here, we disclose that several ammonium salts can be readily activated using iridium photoredox catalysis to form radicals and illustrate the synthetic utility of this activation of strong C–N bonds with hydrodeamination reactions and radical couplings. Cyclic voltammetry was exploited to rationalize the reactivity observed for the activation of these ammonium salts.

Anilines selectively arylated at their ortho-, meta- or para- positions are useful building blocks in synthesis and have found applications in many areas. The most straightforward method for their synthesis relies on the direct arylation of a C(sp2)-H bond of anilines, an attractive strategy avoiding the prefunctionalization of the starting anilines provided that such arylations proceed with high levels of regioselectivity. Such reactions are presented and discussed, in a comprehensive manner, in this review article, with an emphasis on the regioselectivity of the processes and factors governing both the reactivity and selectivity.

An original and straightforward entry to polysubstituted indenes from readily available ynamides is reported. Upon reaction with a N-heterocyclic carbene−gold complex under mild conditions, activated keteniminium ions are generated whose unique electrophilicity triggers a [1,5]-hydride shift and a subsequent cyclization. The presence of an endocyclic enamide in the densely functionalized resulting indenes was shown to be especially useful and versatile, offering a range of opportunities for their further postfunctionalization.

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