Construction of quaternary alkyl motifs through palladium-catalyzed oxidative coupling of 1,3-dicarbonyl compounds with alkenes followed by C-C bond cleavage

A palladium-catalyzed coupling reaction has been developed for the generation of tertiary alkylation products by reacting olefins with diversely functionalized 1,3-dicarbonyls. The reaction involves the tertiary C-H alkylation of 1,3-dicarbonyls with olefins to produce a tertiary alcohol, followed by C-C bond cleavage.

Synthesis of Vicinal Carbocycles by Intramolecular Nickel-Catalyzed Conjunctive Cross-Electrophile Coupling Reaction

A nickel-catalyzed intramolecular conjunctive cross-electrophile coupling reaction has been established. This method enables the synthesis of 3,5-vicinal carbocyclic rings found in numerous biologically active compounds and natural products. We provide mechanistic experiments that indicate this reaction proceeds through alkyl iodides formed in situ, initiates at the secondary electrophilic center, and proceeds through radical intermediates.

Photo-Promoted Decarboxylative Alkylation of α,β-Unsaturated Carboxylic Acids with ICH2CN for the Synthesis of β,γ-Unsaturated Nitriles

An efficient, catalyst/photocatalyst-free, and cost-effective methodology for the decarboxylative alkylation of α,β-unsaturated carboxylic acids to synthesize β,γ-unsaturated nitriles has been developed. The reaction proceeded in an environmentally benign atmosphere of blue light-emitting diode irradiation with K₂CO₃ and water at room temperature. The methodology worked for a wide range of substrates (22 examples) with up to 83% yield. The protocol is also compatible for gram-scale synthesis.

Overcoming Selectivity Issues in Reversible Catalysis: A Transfer Hydrocyanation Exhibiting High Kinetic Control

Reversible catalytic reactions operate under thermodynamic control, and thus, establishing a selective catalytic system poses a considerable challenge. Herein, we report a reversible transfer hydrocyanation protocol that exhibits high selectivity for the thermodynamically less favorable branched isomer. Selectivity is achieved by exploiting the lower barrier for C-CN oxidative addition and reductive elimination at benzylic positions in the absence of a cocatalytic Lewis acid. Through the design of a novel type of HCN donor, a practical, branched-selective, HCN-free transfer hydrocyanation was realized. The synthetically useful resolution of a mixture of branched and linear nitrile isomers was also demonstrated to underline the value of reversible and selective transfer reactions. In a broader context, this work demonstrates that high kinetic selectivity can be achieved in reversible transfer reactions, thus opening new horizons for their synthetic applications.

Cu/Ni-Catalyzed Cyanomethylation of Alkenes with Acetonitrile for the Synthesis of β,γ-Unsaturated Nitriles

We have developed a protocol for the Cu/Ni-catalyzed cyanomethylation of alkenes with acetonitrile for the synthesis of β,γ-unsaturated nitriles. This is the first example of a direct coupling of the alkene sp² C-H bond and the acetonitrile sp³ C-H bond for the preparation of β,γ-unsaturated nitriles. Acetonitrile, an inexpensive and stable solvent, is demonstrated to be a useful cyanomethyl source. The combination of copper and nickel catalysts resulted in a high reaction efficiency.

Iron-catalyzed regioselective alkylation of 1,4-quinones and coumarins with functionalized alkyl bromides

A simple and efficient Fe-catalyzed regioselective alkylation of 1,4-quinones and coumarins, using functionalized alkyl bromides as alkylating reagents, has been developed.

Transition-Metal (Pd, Ni, Mn)-Catalyzed C-C Bond Constructions Involving Unactivated Alkyl Halides and Fundamental Synthetic Building Blocks

The catalytic construction of C-C bonds between organohalide or pseudohalide electrophiles and fundamental building blocks such as alkenes, arenes, or CO are widely utilized metal-catalyzed processes. The use of simple, widely available unactivated alkyl halides in these catalytic transformations has significantly lagged behind the use of aryl or vinyl electrophiles. This difference is primarily due to the relative difficulty of activating alkyl halides with transition metals under mild conditions. This Account details our group's work toward developing a general catalytic manifold for the construction of C-C bonds using unactivated alkyl halides and a range of simple chemical feedstocks. Critical to the strategy was the implementation of new modes of hybrid organometallic-radical reactivity in catalysis. Generation of carbon-centered radicals from alkyl halides using transition metals offers a solution to challenges associated with the application of alkyl electrophiles in classical two-electron reaction modes. A major focus of this work was the development of general palladium-catalyzed carbocyclizations and intermolecular cross-couplings of unactivated alkyl halides (alkyl-Mizoroki-Heck-type reactions). Initial studies centered on the use of alkyl iodides in these processes, but subsequent studies determined that the use of an electron-rich ferrocenyl bisphosphine (dtbpf) enables the palladium-catalyzed carbocyclizations of unactivated alkyl bromides. Mechanistic studies of these reactions revealed interesting details regarding a difference in mechanism between reactions of alkyl iodides and alkyl bromides in carbocyclizations. These studies were consistent with alkyl bromides reacting via an autotandem catalytic process involving atom-transfer radical cyclization (ATRC) followed by catalytic dehydrohalogenation. Reactions of alkyl iodides, on the other hand, involved metal-initiated radical chain pathways. Recent studies have expanded the scope of alkyl-Mizoroki-Heck-type reactions to the use of a first-row transition metal. Inexpensive nickel precatalysts, in combination with the bisphosphine ligand Xantphos, efficiently activate alkyl bromides for both intra- and intermolecular C-C bond-forming reactions. The reaction scope is similar to the palladium-catalyzed system, but in addition, alkene regioisomeric ratios are dramatically improved over those in reactions with palladium, solving one of the drawbacks of our previous work. Initial mechanistic studies were consistent with a hybrid organometallic-radical mechanism for the nickel-catalyzed reactions. The novel reactivity of the palladium catalysts in the alkyl-Mizoroki-Heck-type reactions have also paved the way for the development of other C-C bond-forming processes of unactivated alkyl halides, including aromatic C-H alkylations as well as low-pressure alkoxycarbonylations. Related hybrid organometallic-radical reactivity of manganese has led to an alkene dicarbofunctionalization using alkyl iodides.

Direct dehydrogenative alkyl Heck-couplings of vinylarenes with umpolung aldehydes catalyzed by nickel

Alkenes are fundamental functionalities in nature and highly useful intermediates in organic synthesis, medicinal chemistry and material sciences. Transition-metal-catalyzed Heck couplings with organic halides as electrophiles have been established as a powerful protocol for the synthesis of this valuable building block. However, the requirement of organic halides and the generation of stoichiometric hazardous halide wastes may cause significant sustainable concerns. The halide-free oxidative Heck alkenylations involving organometallics or arenes as the coupling partners provide a facile and alternative pathway. Nonetheless, stoichiometric amounts of extra oxidant are essential in most cases. Herein, we present a direct dehydrogenative alkyl Heck-coupling reaction under oxidant-free conditions, liberating hydrogen, nitrogen and water as the side products. Excellent regioselectivity is achieved via neighboring oxygen atom coordination. Broad substrate scope, great functional group (ketone, ester, phenol, free amine, amide etc) tolerance and modification of pharmaceutical candidates and biological molecules exemplified its generality and practicability.

Electrophilic cyanation of allylic boranes: synthesis of β,γ-unsaturated nitriles containing allylic quaternary carbon centers

The electrophilic cyanation of allylic boranes, a process that enables the construction of allylic quaternary carbon centers, is reported.

Nickel-Catalyzed Mizoroki-Heck-Type Reactions of Unactivated Alkyl Bromides

The development of a general, nickel-catalyzed alkyl-Mizoroki-Heck reaction of unactivated alkyl bromides is described. The mild reaction proceeds efficiently using a wide range of primary and secondary alkyl bromides, and examples of intermolecular cross-couplings are provided. Reaction alkene regioselectivity is significantly enhanced over prior carbocyclizations using palladium catalysis. Mechanistic investigations are consistent with a direct carbocyclization in contrast to the auto-tandem atom-transfer cyclization and halide elimination previously observed with palladium catalysis.

Regioselective Copper-Catalyzed Oxidative Coupling of α-Alkylated Styrenes with Tertiary Alkyl Radicals

A radical-mediated oxidative cross-coupling of readily accessible α-alkylated styrenes with 1,3-dicarbonyl compounds utilizing a combination of Cu(OAc)₂ and air as a catalytic system is described. Rather than requiring α-halocarbonyl compounds, this efficient approach enables direct installation of tertiary functionalized alkyl motifs to olefins with simple carbonyl derivatives. The novel protocol is characterized with high allylic selectivities via a competing β-H elimination. Both radical-clock and -trapping experiments provided clear-cut evidence for the intermediacy of an α-keto carbon-centered radical.

Copper-catalyzed radical Heck type cyclization: a three-component reaction of DABCO·(SO2)2, aryldiazonium tetrafluoroborates and dienes toward sulfonated benzo- seven-membered nitrogen heterocycles

A three-component reaction of the sulfur dioxide surrogate of DABCO·(SO₂)₂, aryldiazonium tetrafluoroborates and dienes has been developed, affording a series of sulfonated nitrogen heterocycles.

Copper-Catalyzed Alkylation of Nitroalkanes with α-Bromonitriles: Synthesis of β-Cyanonitroalkanes

Copper catalysis now enables the efficient C-alkylation of nitroalkanes with α-bromonitriles. Using a simple and inexpensive catalyst, this process provides access to β-cyanonitroalkanes. The method is highly tolerant of various functional groups and substitution patterns. These functionally dense products serve as orthogonally masked 1,3-diamines, which can be revealed selectively for access to differentially substituted diamines. These products can also be exploited for the formation of complex cyanoalkenes and 5-aminoisoxazoles.

Copper-catalyzed decarboxylative cross-coupling of cinnamic acids and ACCN via single electron transfer

A novel and convenient method for the synthesis of β,γ-unsaturated nitriles using ACCN (1,1′-azobis(cyclohexane-1-carbonitrile)) as a cyano source was described.

Iodine-catalyzed radical oxidative annulation for the construction of dihydrofurans and indolizines

Through iodine catalysis, the direct oxidative coupling/annulation of β-keto esters or 2-pyridinyl-β-esters with alkenes was achieved. This reaction procedure provides a simple and selective way for the synthesis of dihydrofurans and indolizines in one step.

Olefinic C–H functionalization through radical alkenylation

This tutorial review provides a comprehensive overview of olefinic C–H functionalization through radical addition and following SET oxidation/elimination.

Nickel N-heterocyclic carbene-catalyzed cross-coupling reaction of aryl aldehydes with organozinc reagents to produce aryl ketones

The transformation of aromatic aldehydes into aryl ketones by nickel-catalyzed cross-coupling has been developed. This transformation represents an efficient and attractive synthetic utilization of organozinc reagents.

Revealing the metal-like behavior of iodine: an iodide-catalysed radical oxidative alkenylation

Catalytic HI elimination similar to the β-hydride elimination of transition metals was realized for the radical alkenylation of sulfonyl hydrazides.