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We report Pd(II)-catalyzed cyclative C(sp3)–H arylation of ketones with a transient directing group (TDG). Based on calculations, the oxidative addition step implicates a highly strained trigonal b...

Summary Functionalization of arenes represents the most efficient approach for constructing a core backbone of important aryl compounds. Compared with the well-developed electrophilic aromatic substitution and transition-metal-catalyzed C–H activation, nucleophilic aromatic substitution remains challenging because of the lack of a convenient route for rapid conversion of the σH adduct to other stable and versatile intermediates in situ. Guided by computational design, we were able to realize asymmetric nucleophilic aromatic substitution by introducing a nitroso group on naphthalene via chiral phosphoric acid catalysis. This strategy enables efficient construction of atropisomeric indole-naphthalenes and indole-anilines with excellent stereocontrol. Density functional theory (DFT) calculations provide further insights into the origins of enantioselectivity and the reaction mechanisms. The successful application in the synthesis of NOBINs (2-amino-2′-hydroxy-1,1′-binaphthyl) extends the utility of this strategy.

Expanded helicenes are large, structurally flexible π-frameworks that can be viewed as building blocks for more complex chiral nanocarbons. Here we report a gram-scale synthesis of an alkyne-functionalized expanded [11]helicene and its single-step transformation into two structurally and functionally distinct types of macrocyclic derivatives: (1) a figure-eight dimer via alkyne metathesis (also gram scale) and (2) two arylene-bridged expanded helicenes via Zr-mediated, formal [2+2+n] cycloadditions. The phenylene-bridged helicene displays a substantially higher enantiomerization barrier (22.1 kcal/mol) than its helicene precursor (

Many Pd-catalyzed C–H functionalization reactions utilize stoichiometric Ag(I)-salts as additives. Ag additives are typically used either as a terminal oxidant or as a halide scavenger for Pd catalyst regeneration. However, recent experimental and computational studies have shown that Ag(I)-salts may play additional roles in C–H activation processes. Notably, cooperative Pd–Ag bimetallic C–H activations and Ag(I)-mediated Pd-catalyzed C–H arylations can occur. The non-oxidative roles of Ag(I) salts in Pd-catalyzed C-H activation are highlighted in this mini-review.

A new tool for probing enantioselective reaction mechanisms is introduced. Monitoring the temporal change in product enantiomeric excess after addition of the opposite enantiomer of the ligand during the reaction provides a means of probing dynamic ligand exchange in enantioselective C-H iodination catalyzed by Pd with monoprotected amino acid ligands (MPAAs). This work has general potential to provide insights about the dynamics of catalyst and ligand molecularity and exchange.

A simple and efficient nitrile-directed meta-C-H olefination, acetoxylation, and iodination of biaryl compounds is reported. Compared to the previous approach of installing a complex U-shaped template to achieve a molecular U-turn and assemble the large-sized cyclophane transition state for the remote C-H activation, a synthetically useful phenyl nitrile functional group could also direct remote meta-C-H activation. This reaction provides a useful method for the modification of biaryl compounds because the nitrile group can be readily converted to amines, acids, amides, or other heterocycles. Notably, the remote meta-selectivity of biphenylnitriles could not be expected from previous results with a macrocyclophane nitrile template. DFT computational studies show that a ligand-containing Pd-Ag heterodimeric transition state (TS) favors the desired remote meta-selectivity. Control experiments demonstrate the directing effect of the nitrile group and exclude the possibility of non-directed meta-C-H activation. Substituted 2-pyridone ligands were found to be key in assisting the cleavage of the meta-C-H bond in the concerted metalation-deprotonation (CMD) process.

Site-selective functionalization of C–H bonds will ultimately afford chemists transformative tools for editing and constructing complex molecular architectures. Towards this goal, developing strategies to activate C–H bonds that are distal from a functional group is essential. In this context, distinguishing remote C–H bonds on adjacent carbon atoms is an extraordinary challenge due to the lack of electronic or steric bias between the two positions. Herein, we report the design of a catalytic system leveraging a remote directing template and a transient norbornene mediator to selectively activate a previously inaccessible remote C–H bond that is one bond further away. The generality of this approach has been demonstrated with a range of heterocycles, including a complex anti-leukemia agent, and hydrocinnamic acid substrates., Graphical Abstract

Site-selective functionalizations of C–H bonds will ultimately afford chemists transformative tools for editing and constructing complex molecular architectures1-4. Towards this goal, developing strategies to activate C–H bonds that are distal from a functional group is essential4-6. In this context, distinguishing remote C–H bonds on adjacent carbon atoms is an extraordinary challenge due to the lack of electronic or steric bias between the two positions. Herein, we report the design of a catalytic system leveraging a remote directing template and a transient norbornene mediator to selectively activate a previously inaccessible remote C–H bond that is one bond further away. The generality of this approach has been demonstrated with a range of heterocycles, including a complex anti-leukemia agent, and hydrocinnamic acid substrates.

Summary A cornerstone of modern synthetic chemistry rests on the ability to manipulate the reactivity of a carbon center by rendering it either electrophilic or nucleophilic. However, accessing a similar reactivity spectrum with boron-based reagents has been significantly more challenging. While classical nucleophilic carbon-based reagents normally do not require steric protection, readily accessible, unprotected boron-based nucleophiles have not yet been realized. Herein, we demonstrate that the bench-stable closo-hexaborate cluster anion can engage in a nucleophilic substitution reaction with a wide array of organic and main-group electrophiles. The resulting molecules containing B‒C bonds can be further converted to tricoordinate boron species widely used in organic synthesis.

The enantioselective Pd(II)-catalyzed γ-C-H arylation of picolinamides with a chiral BINOL phosphate ligand was explored using density functional theory (DFT). Enantioselectivity arises from attractive aryl-aryl interactions between the pseudoequatorial phenyl substituent of the substrate and the chiral BINOL phosphate ligand.