Browse
Submit Data
Databases
API
Help

Dataset Information

15 Views

0 Connections

0 Citations

0 Reanalyses

0 Downloads

Omics score: 0

C(spⁿ )-X (n=1-3) Bond Activation by Palladium.

ABSTRACT: We have studied the palladium-mediated activation of C(spⁿ )-X bonds (n = 1-3 and X = H, CH₃ , Cl) in archetypal model substrates H₃ C-CH₂ -X, H₂ C=CH-X and HC≡C-X by catalysts PdL_n with L_n = no ligand, Cl^- , and (PH₃ )₂ , using relativistic density functional theory at ZORA-BLYP/TZ2P. The oxidative addition barrier decreases along this series, even though the strength of the bonds increases going from C(sp³ )-X, to C(sp² )-X, to C(sp)-X. Activation strain and matching energy decomposition analyses reveal that the decreased oxidative addition barrier going from sp³ , to sp² , to sp, originates from a reduction in the destabilizing steric (Pauli) repulsion between catalyst and substrate. This is the direct consequence of the decreasing coordination number of the carbon atom in C(spⁿ )-X, which goes from four, to three, to two along this series. The associated net stabilization of the catalyst-substrate interaction dominates the trend in strain energy which indeed becomes more destabilizing along this same series as the bond becomes stronger from C(sp³ )-X to C(sp)-X.

SUBMITTER: Hansen T

PROVIDER: S-EPMC9306469 | biostudies-literature |

REPOSITORIES: biostudies-literature

ACCESS DATA

Json Xml

Similar Datasets

Enantioselective palladium-catalyzed C(sp2)-C(sp2) σ bond activation of cyclopropenones by merging desymmetrization and (3 + 2) spiroannulation with cyclic 1,3-diketones.

Project description:Catalytic asymmetric variants for functional group transformations based on carbon-carbon bond activation still remain elusive. Herein we present an unprecedented palladium-catalyzed (3 + 2) spiro-annulation merging C(sp2)-C(sp2) σ bond activation and click desymmetrization to form synthetically versatile and value-added oxaspiro products. The operationally straightforward and enantioselective palladium-catalyzed atom-economic annulation process exploits a TADDOL-derived bulky P-ligand bearing a large cavity to control enantioselective spiro-annulation that converts cyclopropenones and cyclic 1,3-diketones into chiral oxaspiro cyclopentenone-lactone scaffolds with good diastereo- and enantio-selectivity. The click-like reaction is a successful methodology with a facile construction of two vicinal carbon quaternary stereocenters and can be used to deliver additional stereocenters during late-state functionalization for the synthesis of highly functionalized or more complex molecules.

| S-EPMC8549799 | biostudies-literature

Reversing conventional site-selectivity in C(sp3)-H bond activation.

Project description:One of the core barriers to developing C-H activation reactions is the ability to distinguish between multiple C-H bonds that are nearly identical in terms of electronic properties and bond strengths. Through recognition of distance and molecular geometry, remote C(sp2)-H bonds have been selectively activated in the presence of proximate ones. Yet achieving such unconventional site selectivity with C(sp3)-H bonds remains a paramount challenge. Here we report a combination of a simple pyruvic acid-derived directing group and a 2-pyridone ligand that enables the preferential activation of the distal γ-C(sp3)-H bond over the proximate β-C(sp3)-H bonds for a wide range of alcohol-derived substrates. A competition experiment between the five- and six-membered cyclopalladation step, as well as kinetic experiments, demonstrate the feasibility of using geometric strain to reverse the conventional site selectivity in C(sp3)-H activation.

| S-EPMC6628918 | biostudies-literature

Palladium-Catalyzed [3 + 2] Cycloaddition via Twofold 1,3-C(sp3)-H Activation.

Project description:Cycloaddition reactions provide an expeditious route to construct ring systems in a highly convergent and stereoselective manner. For a typical cycloaddition reaction to occur, however, the installation of multiple reactive functional groups (π-bonds, leaving group, etc.) is required within the substrates, compromising the overall efficiency or scope of the cycloaddition reaction. Here, we report a palladium-catalyzed [3 + 2] reaction that utilizes twofold C(sp3)-H activation to generate the three-carbon unit for formal cycloaddition. The initial β-C(sp3)-H activation of aliphatic amide, followed by maleimide insertion, triggers a relayed, second C(sp3)-H activation to complete a formal [3 + 2] cycloaddition. The key to success was the use of weakly coordinating amide as the directing group, as previous studies have shown that Heck or alkylation pathways are preferred when stronger-coordinating directing groups are used with maleimide coupling partners. To promote the amide-directed C(sp3)-H activation step, the use of pyridine-3-sulfonic acid ligands is crucial. This method is compatible with a wide range of amide substrates, including lactams, which lead to spiro-bicyclic products. The [3 + 2] product is also shown to undergo a reductive desymmetrization process to access chiral cyclopentane bearing multiple stereocenters with excellent enantioselectivity.

| S-EPMC7654568 | biostudies-literature

Hydrodealkenylative C(sp3)-C(sp2) bond fragmentation.

Project description:Chemical synthesis typically relies on reactions that generate complexity through elaboration of simple starting materials. Less common are deconstructive strategies toward complexity-particularly those involving carbon-carbon bond scission. Here, we introduce one such transformation: the hydrodealkenylative cleavage of C(sp3)-C(sp2) bonds, conducted below room temperature, using ozone, an iron salt, and a hydrogen atom donor. These reactions are performed in nonanhydrous solvents and open to the air; reach completion within 30 minutes; and deliver their products in high yields, even on decagram scales. We have used this broadly functionality tolerant transformation to produce desirable synthetic intermediates, many of which are optically active, from abundantly available terpenes and terpenoid-derived precursors. We have also applied it in the formal total syntheses of complex molecules.

| S-EPMC6625654 | biostudies-literature

C-H bond activation at palladium(IV) centers.

Project description:This communication describes the first observation and study of C-H activation at a Pd(IV) center. This transformation was achieved by designing model complexes in which the rate of reductive elimination is slowed relative to that of the desired C-H activation process. Remarkably, the C-H activation reaction can proceed under mild conditions and with complementary site selectivity to analogous transformations at Pd(II). These results provide a platform for incorporating this new reaction as a step in catalytic processes.

| S-EPMC3233235 | biostudies-literature

Silacyclization through palladium-catalyzed intermolecular silicon-based C(sp2)-C(sp3) cross-coupling.

Project description:Silicon-based cross-coupling has been recognized as one of the most reliable alternatives for constructing carbon-carbon bonds. However, the employment of such reaction as an efficient ring expansion strategy for silacycle synthesis is comparatively little known. Herein, we develop the first intermolecular silacyclization strategy involving Pd-catalyzed silicon-based C(sp2)-C(sp3) cross-coupling. This method allows the modular assembly of a vast array of structurally novel and interesting sila-benzo[b]oxepines with good functional group tolerance. The key to success for this reaction is that silicon atoms have a stronger affinity for oxygen nucleophiles than carbon nucleophiles, and silacyclobutanes (SCBs) have inherent ring-strain-release Lewis acidity.

| S-EPMC8565370 | biostudies-literature

Temperature-modulated selective C(sp3)-H or C(sp2)-H arylation through palladium catalysis.

Project description:Transition metal-catalysed C-H bond functionalisations have been extensively developed in organic and medicinal chemistry. Among these catalytic approaches, the selective activation of C(sp3)-H and C(sp2)-H bonds is particularly appealing for its remarkable synthetic versatility, yet it remains highly challenging. Herein, we demonstrate the first example of temperature-dependent selective C-H functionalisation of unactivated C(sp3)-H or C(sp2)-H bonds at remote positions through palladium catalysis using 7-pyridyl-pyrazolo[1,5-a]pyrimidine as a new directing group. At 120 °C, C(sp3)-H arylation was triggered by the chelation of a rare [6,5]-fused palladacycle, whereas at 140 °C, C(sp2)-H arylation proceeded instead through the formation of a 16-membered tetramer containing four 7-pyridyl-pyrazolo[1,5-a]pyrimidine-palladium chelation units. The subsequent mechanistic study revealed that both C-H activations shared a common 6-membered palladacycle intermediate, which was then directly transformed to either the [6,5]-fused palladacycle for C(sp3)-H activation at 120 °C or the tetramer for C(sp2)-H arylation at 140 °C with catalytic amounts of Pd(OAc)2 and AcOH. Raising the temperature from 120 °C to 140 °C can also convert the [6,5]-fused palladacycle to the tetramer with the above-mentioned catalysts, hence completing the C(sp2)-H arylation ultimately.

| S-EPMC8162910 | biostudies-literature

Synthesis of Asthma Drug Zafirlukast (Accolate) Using Intramolecular Oxidative Coupling via sp3 C-H Bond Activation.

Project description:The FDA-approved drug for the treatment of asthma, zafirlukast, is synthesized engaging multiple catalytic reactions including a new method for the construction of 3-aroylindoles via oxidative cyclization. The highlights include transition-metal and peroxide free C-H bond activation using the stoichiometric amount of sodium persulfate as an oxidizing agent in the construction of 3-aroylindole, avoiding transition metal, with over 28% overall yield. The complete process has a turnaround time of 28 h to get the target molecule starting from substituted aniline, with practically no protecting groups.

| S-EPMC6641481 | biostudies-literature

Photoactive electron donor-acceptor complex platform for Ni-mediated C(sp3)-C(sp2) bond formation.

Project description:A dual photochemical/nickel-mediated decarboxylative strategy for the assembly of C(sp3)-C(sp2) linkages is disclosed. Under light irradiation at 390 nm, commercially available and inexpensive Hantzsch ester (HE) functions as a potent organic photoreductant to deliver catalytically active Ni(0) species through single-electron transfer (SET) manifolds. As part of its dual role, the Hantzsch ester effects a decarboxylative-based radical generation through electron donor-acceptor (EDA) complex activation. This homogeneous, net-reductive platform bypasses the need for exogenous photocatalysts, stoichiometric metal reductants, and additives. Under this cross-electrophile paradigm, the coupling of diverse C(sp3)-centered radical architectures (including primary, secondary, stabilized benzylic, α-oxy, and α-amino systems) with (hetero)aryl bromides has been accomplished. The protocol proceeds under mild reaction conditions in the presence of sensitive functional groups and pharmaceutically relevant cores.

| S-EPMC8179655 | biostudies-literature

Enantioselective palladium/copper-catalyzed C-C σ-bond activation synergized with Sonogashira-type C(sp3)-C(sp) cross-coupling alkynylation.

Project description:The Sonogashira-type cross-coupling reaction is one of the most significant alkynylation transformations in organic chemistry. However, highly enantioselective alkynylation via the Sonogashira-type cross-coupling reaction is rather limited, mainly due to the difficulties in matching the stereoselective induction of chiral ligands with the combinational behavior of Pd/Cu-based bimetallic catalysts. We herein report novel enantioselective palladium/copper-catalyzed alkyl alkynylation of cyclobutanones with terminal alkynes via tandem C-C bond activation/Sonogashira-type cross coupling reaction, in which a novel chiral TADDOL-derived phosphoramidite ligand bearing fluorine and silicon-based bulky groups simplified as TFSi-Phos is found to be an efficient ligand for both C(sp2)-C(sp3) bond cleavage and new C(sp3)-C(sp) bond formation. A wide range of chiral alkynylated indanones bearing an all-carbon quaternary stereocenter are obtained efficiently with up to 97.5 : 2.5 er.

| S-EPMC6761865 | biostudies-other