DFT Investigation of a Nonclassical Oxidative Addition-Reductive Elimination Pathway in the Pd(0)/Pd(II)/Pd(0) Cycle for Dual Hydroamination of Cycloheptatriene to Tropene.

Density functional theory calculations were conducted to investigate the Pd-catalyzed dual hydroamination of cycloheptatriene leading to tropene formation. The results reveal a nonclassical oxidative addition-reductive elimination mechanism operating within the Pd(0)/Pd(II)/Pd(0) catalytic cycle. In this mechanism, the Pd(0) to Pd(II) transformation occurs via an outer-sphere protonation-oxidation process, while the reverse Pd(II) to Pd(0) transformation proceeds through nucleophilic attack-induced reductive coupling.

Chemodivergent, enantio- and regioselective couplings of alkynes, aldehydes and silanes enabled by nickel/N-heterocyclic carbene catalysis.

Divergent synthesis of valuable molecules through common starting materials and metal catalysis represents a longstanding challenge and a significant research goal. We here describe chemodivergent, highly enantio- and regioselective nickel-catalyzed reductive and dehydrogenative coupling reactions of alkynes, aldehydes, and silanes. A single chiral Ni-based catalyst is leveraged to directly prepare three distinct enantioenriched products (silyl-protected trisubstituted chiral allylic alcohols, oxasilacyclopentenes, and silicon-stereogenic oxasilacyclopentenes) in a single chemical operation.

Mechanistic Insights from Density Functional Theory into Rh/Acid-Catalyzed Synthesis of 1,2-Dihydroquinolines via Skeleton-Reorganizing Coupling of Cycloheptatriene and Amines.

Density functional theory calculations were conducted to refine our understanding at the molecular level of the synthesis of fused 1,2-dihydroquinolines through Rh- and acid-catalyzed skeleton-reorganizing coupling reactions of cycloheptatriene with amines. The results reveal that the reaction progresses via cascade catalysis, consisting of consecutive steps of Rh-catalyzed intermolecular coupling involving two Rh-Rh-Rh transformations with a maximum energy barrier of 27.1 kcal/mol, followed by acid-catalyzed intramolecular skeleton reorganization with a peak energy barrier of 23.

Middle and Late Pleistocene Denisovan subsistence at Baishiya Karst Cave.

Genetic and fragmented palaeoanthropological data suggest that Denisovans were once widely distributed across eastern Eurasia. Despite limited archaeological evidence, this indicates that Denisovans were capable of adapting to a highly diverse range of environments. Here we integrate zooarchaeological and proteomic analyses of the late Middle to Late Pleistocene faunal assemblage from Baishiya Karst Cave on the Tibetan Plateau, where a Denisovan mandible and Denisovan sedimentary mitochondrial DNA were found.

DFT Calculations Rationalize Unconventional Regioselectivity in Pd-Catalyzed Defluorinative Alkylation of -Difluorocyclopropanes with Hydrazones.

Density functional theory (DFT) calculations have been conducted to gain insight into the unique formation of the branched alkylation product in the Pd-catalyzed defluorinative alkylation of -difluorocyclopropanes with hydrazones. The reaction is established to occur in sequence through oxidative addition, β-F elimination, η-η isomerization, transmetalation, η-η isomerization, 3,3'-reductive elimination, deprotonation/N extrusion, and proton abstraction. The rate-determining step of the reaction is identified as the β-F elimination, featuring an energy barrier of 28.

DFT Insight into a Strain-Release Mechanism in Bicyclo[1.1.0]butanes via Concerted Activation of Central and Lateral C-C Bonds with Rh(III) Catalysis.

Transition-metal-catalyzed, strain-release-driven transformations of "spring-loaded" bicyclo[1.1.0]butanes (BCBs) are considered potent tools in synthetic organic chemistry.

Mechanism and Enantioselectivity in QUINOX-Catalyzed Asymmetric Allylations of Aromatic Aldehydes: Solvent and Substituent Effects.

Computational investigations were conducted on the QUINOX-catalyzed asymmetric allylation of aromatic aldehydes with allyltrichlorosilanes. Our calculations provide evidence that the catalytic allylation can follow distinct mechanisms, depending on the solvent employed. In toluene and CHCl, the QUINOX-catalyzed allylation predominantly follows an associative pathway, while in CHCN, a dissociative pathway becomes more favorable.

Theoretical Insight into the Palladium-Catalyzed Prenylation and Geranylation of Oxindoles with Isoprene.

This work presents a comprehensive mechanistic study of the ligand-controlled palladium-catalyzed prenylation (with C added) and geranylation (with C added) reactions of oxindole with isoprene. The calculated results indicate that the prenylation with the bis-phosphine ligand and geranylation with the monophosphine ligand fundamentally share a common mechanism. This mechanism involves the formation of two crucial species: a η-allyl-Pd(II) cation and an oxindole carbon anion.

Origin of Enantio- and Chemoselectivity in the Synthesis of Spirocycles via Palladium/Xu-Phos-Catalyzed Cascade Heck/Remote C(sp)-H Alkylation: A Computational Mechanistic Study.

Density functional theory (DFT) calculations were performed to study the mechanism and factors affecting the enantio-, regio-, and chemoselectivities in the palladium/Xu-Phos-catalyzed cascade Heck/remote C(sp)-H alkylation reaction. The active catalyst is found to be able to sustain coordination with P and S atoms and can adapt its coordination mode to accommodate the significant steric hindrance between the ligand and substrate, unlike previous findings that showed coordination with P and O atoms. The reaction is established to occur in sequence through the oxidative addition of the aryl iodide to Pd(0), intramolecular alkene insertion, C(sp)-H bond activation, and C(sp)-C(sp) bond reductive elimination.

New insights into the mechanism of synergetic photoredox/copper(i)-catalyzed carbocyanation of 1,3-dienes: a DFT study.

This work presents a DFT-based computational study to understand the mechanism, and regio- and enantioselectivities in the synergetic photoredox/copper(i)-catalyzed carbocyanation of 1,3-dienes with alkyl redox-active esters. The calculated results show an unprecedented copper catalytic mechanism, where the reaction follows a catalytic cycle involving Cu-only catalysis, instead of a Cu(i)/Cu(ii)/Cu(iii)/Cu(i) cycle as proposed in the experimental study. Moreover, it is found that the critical step involves the reaction of the cyanocopper(i) species with an allyl cation rather than the cyanocopper(ii) species reacting with an allyl radical as proposed in the experiment, and that the photocatalyst is regenerated single electron transfer from the allyl radical to the oxidized photocatalyst.

L-Shaped Heterobidentate Imidazo[1,5-a]pyridin-3-ylidene (N,C)-Ligands for Oxidant-Free Au /Au Catalysis.

In the last decade, major advances have been made in homogeneous gold catalysis. However, Au /Au catalytic cycle remains much less explored due to the reluctance of Au to undergo oxidative addition and the stability of the Au intermediate. Herein, we report activation of aryl halides at gold(I) enabled by NHC (NHC=N-heterocyclic carbene) ligands through the development of a new class of L-shaped heterobidentate ImPy (ImPy=imidazo[1,5-a]pyridin-3-ylidene) N,C ligands that feature hemilabile character of the amino group in combination with strong σ-donation of the carbene center in a rigid conformation, imposed by the ligand architecture.

Enantio- and Regioselective Ni-Catalyzed -C-H Alkylation of Pyridines with Styrenes via Intermolecular Hydroarylation.

Direct asymmetric functionalization of the pyridyl C-H bond represents a longstanding challenge in organic chemistry. We herein describe the first enantioselective -C-H activation of pyridines through the use of a Ni-Al bimetallic catalyst system and N-heterocyclic carbene (NHC) ligand for intermolecular hydroarylation of styrenes. The reaction procceds in high to excellent enantioselectivities (up to 98.

Density Functional Theory Study of Gold-Catalyzed 1,2-Diarylation of Alkenes: π-Activation Migratory Insertion Mechanisms.

Density functional theory calculations are carried out to better understand the first gold-catalyzed 1,2-diarylation reactions of alkenes reported in the recent literature. The calculations on two representative reactions, aryl alkene/aryl iodide coupling pair (the aryl-I bond is located outside the aryl alkene) versus iodoaryl alkene/indole coupling pair (the aryl-I bond is located in the aryl alkene), confirm that the reaction involves a π-activation mechanism rather than the general migratory insertion mechanism in previously known metal catalysis by Pd, Ni, and Cu complexes. Theoretical results rationalize the regioselectivity of the reactions controlled by the aryl-I bond position (intermolecular or intramolecular) and also the ligand and substituent effects on the reactivity.

Earliest parietal art: hominin hand and foot traces from the middle Pleistocene of Tibet.

At Quesang on the Tibetan Plateau we report a series of hand and foot impressions that appear to have been intentionally placed on the surface of a unit of soft travertine. The travertine was deposited by water from a hot spring which is now inactive and as the travertine lithified it preserved the traces. On the basis of the sizes of the hand and foot traces, we suggest that two track-makers were involved and were likely children.

Human population history at the crossroads of East and Southeast Asia since 11,000 years ago.

Past human genetic diversity and migration between southern China and Southeast Asia have not been well characterized, in part due to poor preservation of ancient DNA in hot and humid regions. We sequenced 31 ancient genomes from southern China (Guangxi and Fujian), including two ∼12,000- to 10,000-year-old individuals representing the oldest humans sequenced from southern China. We discovered a deeply diverged East Asian ancestry in the Guangxi region that persisted until at least 6,000 years ago.

Mechanistic insights into Ni-catalyzed hydrogen atom transfer (HAT)-triggered hydrodefluorination of CF-substituted alkenes.

We report the first computational study on a nickel hydride HAT-initiated catalytic reaction, a novel hydrodefluorination of CF3-substituted aryl alkenes to afford gem-difluoroalkenes. This study provides detailed mechanistic insights into the reaction, including HAT from NiH to C[double bond, length as m-dash]C, a carbon radical rebound to nickel to facilitate chemoselective defluorination, and a two-state reactivity of Ni(ii) enabling σ-bond metathesis with PhSiH3 to regenerate the catalyst. The findings can have implications for developing new metal hydride HAT-initiated reactions.

DFT Mechanistic Study of Ir/Ni-Metallaphotoredox-Catalyzed Difluoromethylation of Aryl Bromides.

The work by MacMillan et al. ( 2018, 57, 12543-12548) developed an Ir/Ni-metallaphotoredox-catalyzed difluoromethylation strategy of aryl bromides using CHFBr as the CHF reagent in the presence of tris(trimethylsilyl)silane. Here, we present a density functional theory (DFT)-based computational study to understand special dual catalysis promoting the C(sp)-C(sp) coupling.

Mechanistic Insights into Formation of All-Carbon Quaternary Centers via Scandium-Catalyzed C-H Alkylation of Imidazoles with 1,1-Disubstituted Alkenes.

This density functional theory (DFT) study reveals a detailed plausible mechanism for the Sc-catalyzed C-H cycloaddition of imidazoles to 1,1-disubstituted alkenes to form all-carbon quaternary stereocenters. The Sc complex binds the imidazole substrate to enable deprotonative C2-H bond activation by the Sc-bound α-carbon to afford the active species. This complex undergoes intramolecular cyclization (C═C into Sc-imidazolyl insertion) with exo-selectivity, generating a β-all-carbon-substituted quaternary center in the polycyclic imidazole derivative.

Mechanistic Insight into Palladium-Catalyzed γ-C(sp)-H Arylation of Alkylamines with 2-Iodobenzoic Acid: Role of the -Carboxylate Group.

Density functional theory calculations were performed to understand the distinctly different reactivities of carboxylate-substituted aryl halides and pristine aryl halides toward the Pd-catalyzed γ-C(sp)-H arylation of secondary alkylamines. It is found that, when 2-iodobenzoic acid (a representative of -carboxylate-substituted aryl halides) is used as an aryl transfer agent, the arylation reaction is energetically favorable, while when the pristine aryl halide iodobenzene is used as the aryl transfer reagent, the reaction is kinetically difficult. Our calculations showed an operative Pd/Pd/Pd redox cycle, which differs in the mechanistic details from the cycle proposed by the experimental authors.

Site- and Enantiodifferentiating C(sp)-H Oxidation Enables Asymmetric Access to Structurally and Stereochemically Diverse Saturated Cyclic Ethers.

A manganese-catalyzed site- and enantiodifferentiating oxidation of C(sp)-H bonds in saturated cyclic ethers has been described. The mild and practical method is applicable to a range of tetrahydrofurans, tetrahydropyrans, and medium-sized cyclic ethers with multiple stereocenters and diverse substituent patterns in high efficiency with extremely efficient site- and enantiodiscrimination. Late-stage application in complex biological active molecules was further demonstrated.

Denisovan DNA in Late Pleistocene sediments from Baishiya Karst Cave on the Tibetan Plateau.

A late Middle Pleistocene mandible from Baishiya Karst Cave (BKC) on the Tibetan Plateau has been inferred to be from a Denisovan, an Asian hominin related to Neanderthals, on the basis of an amino acid substitution in its collagen. Here we describe the stratigraphy, chronology, and mitochondrial DNA extracted from the sediments in BKC. We recover Denisovan mitochondrial DNA from sediments deposited ~100 thousand and ~60 thousand years ago (ka) and possibly as recently as ~45 ka.

Mechanism and Origins of Enantio- and Regioselectivities in Catalytic Asymmetric Minisci-Type Addition to Heteroarenes.

This work presents a density functional theory (DFT) study on the mechanism and origins of enantio- and regioselectivities in dual photoredox/chiral Brønsted acid-catalyzed asymmetric Minisci-type addition of carbon-centered radicals to N-heteroarenes [, , , 419-422]. The previously proposed mechanism has been partially revised. First, photoexcited *[Ir] is reductively quenched by TRIP anion rather than the experimentally proposed neutral radical generated from the chiral Brønsted acid cycle.

Computational Study on Why and How of Nonconventional meta-C-H Arylation of Electron-Rich Arenes via Pd/Quinoxaline-Based Ligand/Norbornene Cooperative Catalysis.

By performing density functional theory (DFT) calculation, this work aims at understanding the nonconventional meta-C-H arylation reaction of electronic-rich arenes with aryl iodide via a Pd/quinoxaline-based ligand/norbornene cooperative catalysis. The reaction is indicated to be initiated either from the ortho-C-H carbopalladation to give the meta-monoarylation product via a sequence of subsequent steps, including norbornene insertion, meta-C-H activation, oxidative addition, and reductive elimination via the Pd(II)/Pd(IV)/Pd(II) redox cycle, norbornene extrusion, and protodepalladation, or from the para-C-H carbopalladation to form the meta-diarylation product via two sequential arylation processes following similar mechanisms. The initial carbopalladation process promoted by the ligand is characterized as the rate-determining step of the reaction.

Theoretical Insight into Palladium(II)-Counterion-Ligand Cooperative Regiodivergent Syntheses of Indolo[3,2-]coumarins and Benzofuro[3,2-]quinolinones from Diphenylethyne Derivatives.

With two distinct active sites, 2-hydroxy-2'-amino-diphenylethyne derivatives can offer benzofuro[3,2-]quinolinones via the O-attack/N-carbonylation cyclization or indolo[3,2-]coumarins via the N-attackO-carbonylation cyclization. This work presents a density functional theory-based computational study to understand the mechanism and origin of the palladium(II)-catalyzed regiodivergent reactivity of diphenylethyne derivatives. It is indicated that the reaction features a palladium(II)-counterion-ligand cooperative catalysis.