Coupling Of Bromides Research Articles

Iron-Catalyzed Cross-Electrophile Coupling for the Formation of All-Carbon Quaternary Centers.

Quaternary carbon centers are desirable targets for drug discovery and complex molecule synthesis, yet the synthesis of these motifs within traditional cross-coupling paradigms remains a significant challenge due to competing β-hydride elimination pathways. In contrast, the bimolecular homolytic substitution (SH2) mechanism offers a unique and attractive alternative pathway. Metal porphyrin complexes have emerged as privileged catalysts owing to their ability to selectively form primary metal-alkyl complexes, thereby eliminating the challenges associated with tertiary alkyl complexation with a metal center. Herein, we report an iron-catalyzed cross-electrophile coupling of tertiary bromides and primary alkyl electrophiles for the formation of all-carbon quaternary centers through a biomimetic SH2 mechanism.

Cooperative Catalytic Coupling of Benzyl Chlorides and Bromides with Electron-Deficient Alkenes.

Benzyl radicals are an important class of intermediate. The use of visible light to generate them directly from their respective halides is an ideal synthetic strategy. The central impediment associated with their direct single-electron reduction (photo- or electro-) lies in their highly variable and structurally dependent reduction potential, which combine to make the identification of a general set of conditions difficult. Herein, we have employed a strategy of nucleophilic cooperative catalysis in which catalytic lutidine undergoes halide substitution, which decreases and levels the reduction potential. This allows a general set of photocatalytic conditions to transform a broad range of benzyl halides into radicals that can be used in the synthesis of more complex molecules, exemplified here by Giese coupling with electron-deficient alkenes.

Harnessing redox-inactive rare-earth metals for photocatalytic reductive coupling of benzyl bromides

Compared with rare and expensive late-transition metals, rare-earth photocatalysts are much less investigated in synthetic chemistry, particularly concerning redox-inactive rare-earth metals. Herein, we describe a general strategy to realize the redox-inactive rare-earth photocatalysis by grafting a light-absorbing scaffold onto common ligands in rare-earth organometallics. Three guanidinate rare-earth complexes with photocatalytic functions were synthesized and found to exhibit higher catalytic efficiency than phenothiazine in the reductive homocoupling of benzyl bromides. These preliminary results illustrated that our “grafting” strategy could serve as a facile methodology for the construction of redox-inactive rare-earth photocatalysis systems.

Nickel metallaphotoredox-catalyzed C–O bond activation/Csp2–Csp3 coupling enabled by phosphine

A novel and general nickel/photoredox dual catalysis platform for benzyl alcohol C–O bond activation/Csp2–Csp3 cross coupling of benzothiazolyl bromide and free alcohol, enabled by the catalytic generation of an alkyl radical, is reported.

Decarboxylative Cross-Electrophile Coupling of (Hetero)Aromatic Bromides and NHP Esters.

Aryl bromides are known to be challenging substrates in the decarboxylative cross-electrophile coupling with redox-active NHP esters-the majority of such processes utilize aryl iodides. Herein, we describe the development of conditions that are suitable for the decarboxylative cross-electrophile coupling of NHP esters and a wide range of (hetero)aryl bromides. The key advances that allowed for the use of aryl bromides in this reaction are (1) the identification of ligand L3 as an optimal ligand for the use of electron-neutral and deficient aryl bromides and (2) the significant improvement in yield that iodide salts and excess heterogenous zinc impart to this reaction. A wide variety of NHP esters perform well under the optimized conditions, including methyl, primary, secondary, and several strained tertiary systems. Likewise, a variety of aromatic and heteroaromatic bromides relevant to medicinal chemistry perform well in this transformation, including an aryl bromide precursor to the known drug dapagliflozin.

Electrochemical Nickel-Catalyzed C(sp3)-C(sp3) Cross-Coupling of Alkyl Halides with Alkyl Tosylates.

Formation of new C(sp3)-C(sp3) bonds is a powerful synthetic tool to increase molecular diversity, which is highly sought after in medicinal chemistry. Traditional generation of carbon nucleophiles and more modern cross-electrophile-coupling methods typically lack sufficient selectivity when cross-coupling of analogous C(sp3)-containing reactants is attempted. Herein, we present a nickel-catalyzed, electrochemically driven method for the coupling of alkyl bromides with alkyl tosylates. Selective cross-coupling transformations were achieved even between C(sp3)-secondary bromides and tosylates. Key to achieve high selectivity was the combination of the tosylates with sodium bromide as the supporting electrolyte, gradually generating small amounts of the more reactive bromide by substitution and ensuring that one of the reaction partners in the nickel-catalyzed electroreductive process is maintained in excess during a large part of the process. The method has been demonstrated for a wide range of substrates (>30 compounds) in moderate to good yields. Further expanding the scope of electroorganic synthesis to C(sp3)-C(sp3) cross-coupling reactions is anticipated to facilitate the switch to green organic synthesis and encourage future innovative electrochemical transformations.

Cu(I)/N,N-Imine Ligand Catalyzed C(sp3)-C(sp) Coupling of Alkyl Bromides with Alkynes: Scope and Mechanistic Investigation.

We have developed an efficient Cu/N,N-bidentate imine ligand catalytic system for C(sp3)-C(sp) coupling to obtain internal alkynes, di/trisubstituted allenes and strained bridged cyclic lactams in moderate to excellent yields from readily available alkyl(benzyl) bromides in one-pot transformation. Density Functional Theory (DFT) assisted mechanistic study along with control experiments support the involvement of bialkynylated copper species which undergo single electron transfer (SET) with alkyl halides to generate radical intermediate in the reaction. The N,N-bidentate imine ligand plays a vital role in stabilization of intermediate copper complex and facilitates the product formation.

Synthesis of linear and branched poly(phenylacetylene)s through Mizoroki-Heck coupling reaction of vinyl bromides

Polyacetylene and its derivatives are a class of traditional conjugated polymers that started the era of conducting plastics. In this paper, we develop a new approach of synthesizing substituted poly(phenylacetylene)s through Mizoroki-Heck coupling of vinyl bromides. A series of α-bromostyrene derivatives are synthesized and used as the monomers for the polycoupling reaction. It is found that K2CO3 is the effective base while Et3N shows almost no catalytic reactivity. Gel permeation chromatography (GPC) results indicate that the molecular weight distribution is broad, which is typical for step growth polymerization. A kinetic study shows that electron withdrawing group on the phenyl ring increase the polymerization rate of the corresponding monomer. Furthermore, incorporating both aryl and vinyl halides into a single vinyl monomer allows the synthesis of branched polyacetylene possessing oligo(phenylene vinylene) at the branch points. The current approach may serve as a new tool for the molecular engineering of substituted polyacetylene materials.

Nickel-Catalyzed Regiodivergent Cross-Electrophile Coupling of Alkyl Bromides Steered by the Ligand

Key words alkyl–alkyl coupling - cross-electrophile coupling - nickel catalysis - regiodivergent coupling

Cooperative NHC and nickel-catalyzed asymmetric reductive coupling of nitrobenzyl bromides and cyclic ketiminesviaSET process

A synergistic NHC/Ni catalyzed asymmetric reductive coupling of nitrobenzyl bromides with cyclic ketiminesviaSET process was realized.

Ni-Catalyzed Reductive Coupling of Heteroaryl Bromides with Tertiary Alkyl Halides.

We disclose here a nickel-catalyzed reductive coupling of bromopyridines with tertiary alkyl bromides for the synthesis of alkylated pyridines bearing an all-carbon quaternary center. This strategy features mild conditions, broad substrate scope, and high functional group tolerance. The method reported here offers an alternative solution to the challenging task of forging sterically congested alkylpyridines, which we believe will significantly benefit the synthetic community and pharmaceutical industry.

Photoredox Csp3−Csp2 Reductive Cross‐Couplings of Cereblon Ligands for PROTAC Linker Exploration in Batch and Flow

AbstractProteolysis‐targeting chimeras (PROTACs) have recently emerged as powerful molecules for targeted protein degradation. As such, synthetic methods for their modular synthesis are of prime importance in medicinal chemistry. We report the development of both batch and flow photoredox methodologies for Csp3−Csp2 cross‐electrophile couplings of alkyl bromides with E3 ligase‐binding aryl bromides (thalidomide and lenalidomide derivatives). Despite the challenging reaction system, containing several insoluble species, conditions were discovered to facilitate stable processing in an oscillatory flow photochemical reactor. The flow approach can enable processing of larger material quantities in a shorter time period. A range of saturated linker molecules, with various functional handles, were successfully combined with four ligand variants using the developed conditions. Finally, scalability in batch and use of an organic photocatalyst were explored.

Three-Component Coupling of Aldimine Esters, 1,3-Butadiene and Alkyl Bromides under Dual Catalysis

Three-Component Coupling of Aldimine Esters, 1,3-Butadiene and Alkyl Bromides under Dual Catalysis

Differential Dihydrofunctionalization: A Dual Catalytic Three-Component Coupling of Alkynes, Alkenyl Bromides, and Pinacolborane.

A new method for differential dihydrofunctionalization of terminal alkynes enables the synthesis of allylic boronate esters through reductive three-component coupling of terminal alkynes, alkenyl bromides, and pinacolborane. The transformation is promoted by cooperative action of a copper/palladium catalyst system and results in hydrofunctionalization of both π-bonds of an alkyne. The synthesis of allylic boronate esters can be accomplished in the presence of a wide range of functional groups, including, esters, nitriles, alkyl halides, sulfonyl esters, acetals, protected terminal alkynes, aryl halides, and silyl ethers. Mechanistic experiments reveal the importance of subtle ligand effects on the performance of the palladium co-catalyst.

Differential Dihydrofunctionalization: A Dual Catalytic Three‐Component Coupling of Alkynes, Alkenyl Bromides, and Pinacolborane

AbstractA new method for differential dihydrofunctionalization of terminal alkynes enables the synthesis of allylic boronate esters through reductive three‐component coupling of terminal alkynes, alkenyl bromides, and pinacolborane. The transformation is promoted by cooperative action of a copper/palladium catalyst system and results in hydrofunctionalization of both π‐bonds of an alkyne. The synthesis of allylic boronate esters can be accomplished in the presence of a wide range of functional groups, including, esters, nitriles, alkyl halides, sulfonyl esters, acetals, protected terminal alkynes, aryl halides, and silyl ethers. Mechanistic experiments reveal the importance of subtle ligand effects on the performance of the palladium co‐catalyst.

Nickel-Catalysed Cross-Electrophile Coupling of Benzyl Bromides and Sulfonium Salts towards the Synthesis of Dihydrostilbenes.

A nickel-catalysed reductive cross-coupling reaction between benzyl sulfonium salts and benzyl bromides is reported. Simple, stable and readily available sulfonium salts have shown their ability as leaving groups in cross-electrophile coupling, allowing the formation of challenging sp3 -sp3 carbon-carbon bonds, towards the synthesis of interesting dihydrostilbene derivatives. In addition, benzyl tosyl derivatives have been demonstrated to be suitable substrates for reductive cross-coupling by in-situ formation of the corresponding sulfonium salt.

α-Amino Radical Halogen Atom Transfer Agents for Metallaphotoredox-Catalyzed Cross-Electrophile Couplings of Distinct Organic Halides.

α‐Amino radicals from simple tertiary amines were employed as halogen atom transfer (XAT) agents in metallaphotoredox catalysis for cross‐electrophile couplings of organic bromides with organic iodides. This XAT strategy proved to be efficient for the generation of carbon radicals from a range of partners (alkyl, aryl, alkenyl, and alkynyl iodides). The reactivities of these radical intermediates were captured by nickel catalysis with organobromides including aryl, heteroaryl, alkenyl, and alkyl bromides, enabling six diverse C−C bond formations. Classic named reactions including Negishi, Suzuki, Heck, and Sonogashira reactions were readily achieved in a net‐reductive fashion under mild conditions. More importantly, the cross coupling was viable with either organic bromide or iodide as limiting reactant based on the availability of substrates, which is beneficial to the late‐stage functionalization of complex molecules. The scalability of this method in batch and flow was investigated, further demonstrating its applicability.

Nickel-Catalyzed Reductive Csp3-Ge Coupling of Alkyl Bromides with Chlorogermanes.

Reductive cross-coupling provides facile access to organogermanes, but it remains largely unexplored. Herein we report a nickel-catalyzed reductive Csp3-Ge coupling of alkyl bromides with chlorogermanes. This work has established a new method for producing alkylgermanes. The reaction proceeds under very mild conditions and tolerates various functionalities including ether, alcohol, alkene, nitrile, amine, ester, phosphonates, amides, ketone, and aldehyde. The application of this method to the modification of bioactive molecules is demonstrated.

TBAI-catalyzed C–N bond formation through oxidative coupling of benzyl bromides with amines: a new avenue to the synthesis of amides

A new green approach for the synthesis of amide through TBAI-catalyzed oxidative coupling of benzyl bromides with amine was developed in the presence of tert-butyl hydroperoxide (TBHP) as an oxidant. Various electron-donating and withdrawing groups containing benzyl bromides and various amines, were subjected to the reaction and transformed to the corresponding amide in good to excellent yields.

Investigations into mechanism and origin of regioselectivity in the metallaphotoredox-catalyzed α-arylation of N-alkylbenzamides.

A mechanistic study on the α-arylation of N-alkylbenzamides catalyzed by a dual nickel/photoredox system using aryl bromides is reported herein. This study elucidates the origins of site-selectivity of the transformation, which is controlled by the generation of a hydrogen atom transfer (HAT) agent by a photocatalyst and bromide ions in solution. Tetrabutylammonium bromide was identified as a crucial additive and source of a potent HAT agent, which led to increases in yields and a lowering of the stoichiometries of the aryl bromide coupling partner. NMR titration experiments and Stern–Volmer quenching studies provide evidence for complexation to and oxidation of bromide by the photocatalyst, while elementary steps involving deprotonation of the N-alkylbenzamide or 1,5-HAT were ruled out through mechanistic probes and kinetic isotope effect analysis. This study serves as a valuable tool to better understand the α-arylation of N-alkylbenzamides, and has broader implications in halide-mediated C–H functionalization reactions.