This Review summarizes the advances in fluorination via C(sp 2)-H and C(sp 3)-H activation. Transition metal catalyzed approaches championed by palladium have allowed the installation of a fluorine substituent at C(sp 2) and C(sp 3) sites exploiting the reactivity of high oxidation transition metal fluoride complexes combined with the use of directing group (some transient) to control regio-and stereoselectivity. The large majority of known methods employ electrophilic fluorination reagents, but methods combining a nucleophilic fluoride source with an oxidant have appeared. A number of ligands have proven to be effective for C(sp 3)-H fluorination directed by weakly coordinating auxiliaries, thereby enabling control over reactivity and selectivity. Methods relying on the formation of radical intermediates are complementary to transition metal catalyzed processes as they allow for undirected C(sp 3)-H fluorination. To date, radical C-H fluorinations mainly employ electrophilic N-F fluorination reagents but a unique bio-inspired Mn(III)-catalyzed oxidative C-H fluorination has been developed. Overall, the field of late stage nucleophilic C-H fluorination has progressed much more slowly, a state of play explaining why C-H 18 F-fluorination is still in its infancy. C-F reductive elimination C(sp 2)-H C(sp 3)-H C(sp 3)-H

Cyclo[18]carbon (C 18 , a molecular carbon allotrope) can be synthesized by dehalogenation of a bromocyclocarbon precursor, C 18 Br 6 , in 64% yield, by atomic manipulation on a sodium chloride bilayer on Cu(111) at 5 K, and imaged by high-resolution atomic force microscopy. This method of generating C 18 gives a higher yield than that reported previously from the cyclocarbon oxide C 24 O 6 . The experimental images of C 18 were compared with simulated images for four theoretical model geometries, including possible bond-angle alternation: D 18 h cumulene, D 9 h polyyne, D 9 h cumulene, and C 9 h polyyne. Cumulenic structures, with ( D 9 h ) and without ( D 18 h ) bond-angle alternation, can be excluded. Polyynic structures, with ( C 9 h ) and without ( D 9 h ) bond-angle alternation, both show a good agreement with the experiment and are challenging to differentiate.

Photoredox catalysis has transformed the landscape of radical-based synthetic chemistry. Additions of radicals generated through photoredox catalysis to carbon−carbon πbonds are well-established; however, this approach has yet to be applied to the functionalization of carbon−carbon σ-bonds. Here, we report the first such use of photoredox catalysis to promote the addition of organic halides to the carbocycle [1.1.1]propellane; the product bicyclo[1.1.1]pentanes (BCPs) are motifs of high importance in the pharmaceutical industry and in materials chemistry. Showing broad substrate scope and functional group tolerance, this methodology results in the first examples of bicyclopentylation of sp 2 carbon−halogen bonds to access (hetero)arylated BCPs, as well as the functionalization of nonstabilized sp 3 radicals. Substrates containing alkene acceptors allow the single-step construction of polycyclic bicyclopentane products through unprecedented atom transfer radical cyclization cascades, while the potential to accelerate drug discovery is demonstrated through late-stage bicyclopentylations of natural productlike and druglike molecules. Mechanistic investigations demonstrate the importance of the photocatalyst in this chemistry and provide insight into the balance of radical stability and strain relief in the reaction cycle.

Calculating reaction energy profiles to aid in mechanistic elucidation has long been the domain of the expert computational chemist. Here, we introduce autodE (https://github.com/duartegroup/autodE), an open‐source Python package capable of locating transition states (TSs) and minima and delivering a full reaction energy profile from 1D or 2D chemical representations. autodE is broadly applicable to study organic and organometallic reaction classes, including addition, substitution, elimination, migratory insertion, oxidative addition, and reductive elimination; it accounts for conformational sampling of both minima and TSs and is compatible with many electronic structure packages. The general applicability of autodE is demonstrated in complex multi‐step reactions, including cobalt‐ and rhodium‐catalyzed hydroformylation and an Ireland–Claisen rearrangement.

Synthetic anion transporters show much promise as potential anti‐cancer agents and therapeutics for diseases associated with mis‐regulation of protein anion channels. In such applications high activity and anion selectivity are crucial to overcome competing proton or hydroxide transport which dissipates cellular pH gradients. Here, highly active bidentate halogen bonding and chalcogen bonding anion carriers based on electron deficient iodo‐ and telluromethyl−triazole derivatives are reported. Anion transport experiments in lipid bilayer vesicles reveal record nanomolar chloride transport activity for the bidentate halogen bonding anion carrier, and remarkably high chloride over proton/hydroxide selectivity for the chalcogen bonding anionophore. Computational studies provide further insight into the role of sigma‐hole mediated anion recognition and desolvation at the membrane interface. Comparison with hydrogen bonding analogues demonstrates the importance of employing sigma‐hole donor motifs in synthetic anionophores for achieving both high transport activity and selectivity.

Small-ring cage hydrocarbons are common bioisosteres for para-substituted benzene rings in drug design 1 . The popularity of these structures derives from the superior pharmacokinetic properties they exhibit compared to the parent aromatics, including improved solubility and reduced susceptibility to metabolism 2,3 . A prime example is the bicyclo[1.1.1]pentane motif, which is mainly synthesised by ring-opening of the inter-bridgehead bond of the strained hydrocarbon [1.1.1]propellane with radicals or anions 4 . In contrast, scaffolds mimicking metasubstituted arenes are lacking due to the challenge of synthesising saturated isosteres that accurately reproduce substituent vectors 5 . Here we show that bicyclo[3.1.1]heptanes (BCHeps), hydrocarbons whose bridgehead substituents map precisely onto the geometry of meta-substituted benzenes, can be conveniently accessed from [3.1.1]propellane. We found that [3.1.1]propellane can be synthesized on multigram scale, and readily undergoes a range of radical-based transformations to generate medicinally-relevant carbon-and heteroatom-substituted BCHeps, including pharmaceutical

Transmembrane ion transport by synthetic anionophores is typically achieved using polar hydrogen bonding anion receptors. Here we show that readily accessible halogen and hydrogen bonding 1,2,3triazole derivatives can efficiently mediate anion transport across lipid bilayer membranes with unusual anti-Hofmeister selectivity. Importantly, the results demonstrate that the iodo-triazole systems exhibit the highest reported activity to date for halogen bonding anionophores, and enhanced transport efficiency relative to the hydrogen bonding analogues. In contrast, the analogous fluoro-triazole systems, which are unable to form intermolecular interactions with anions, are inactive. The halogen bonding anionophores also exhibit a remarkable intrinsic chloride over hydroxide selectivity, which is usually observed only in more complex anionophore designs, in contrast to the readily accessible acyclic systems reported here. This highlights the potential of iodo-triazoles as synthetically accessible and versatile motifs for developing more efficient anion transport systems. Computational studies provide further insight into the nature of the anion-triazole intermolecular interactions, examining the origins of the observed transport activity and selectivity of the systems, and revealing the role of enhanced charge delocalisation in the halogen bonding anion complexes.a Effective concentration to reach 50% of maximal activity in the HPTS assay, determined from Hill analysis of the relative uorescence intensity at t ¼ 288 s, immediately prior to vesicle lysis. Experiments conducted in LUVs of POPC (mean diameter 200 nm) loaded with 1 mM HPTS, NaCl (100 mM) and buffered at pH 7.0 with 10 mM HEPES. For compounds of low activity, estimated lower bounds for the EC 50 value are given. b Hill coefficient. c Calculated log P. d Insufficient activity for Hill analysis.

A unified framework that explains the reactivity of [1.1.1]propellane through electron delocalization.