Decarboxylative Aminomethylation of Aryl‐ and Vinylsulfonates through Combined Nickel‐ and Photoredox‐Catalyzed Cross‐Coupling

A mild approach for the decarboxylative aminomethylation of aryl sulfonates by the combination of photoredox and nickel catalysis through C?O bond cleavage is described for the first time. A wide range of aryl triflates as well as aryl mesylates, tosylates and alkenyl triflates afford the corresponding products in good to excellent yields.     

Visible‐Light‐Catalyzed Direct Benzylic C(sp3)–H Amination Reaction by Cross‐Dehydrogenative Coupling

A conceptually new and synthetically valuable cross‐dehydrogenative benzylic C(sp³)–H amination reaction is reported by visible‐light photoredox catalysis. This protocol employs DCA (9,10‐dicyanoanthracene) as a visible‐light‐absorbing photoredox catalyst and an amide as the nitrogen source without the need of either a transition metal or an external oxidant.     

Nitrimines as Reagents for Metal‐Free Formal C(sp2)–C(sp2) Cross‐Coupling Reactions

Nitrimines are employed as powerful reagents for metal‐free formal C(sp²)–C(sp²) cross‐coupling reactions. The new chemical process is tolerant of a wide array of nitrimine and heterocyclic coupling partners giving rise to the corresponding di‐ or trisubstituted alkenes, typically in high yield and with high stereoselectivity. This method is ideal for the metal‐free construction of heterocycle‐containing drug targets, such as phenprocoumon.     

Nickel Catalysis Enables Oxidative C(sp2)–H/C(sp2)–H Cross‐Coupling Reactions between Two Heteroarenes

Nickel can be used to promote oxidative C(sp²)?H/C(sp²)?H cross‐coupling between two heteroarenes. The reaction scope can be extended to aromatic carboxamides as the coupling partner. The reaction exhibits high functional‐group compatibility and broad substrate scope. The silver oxidant can be recycled to reduce costs and waste, which is very useful for practical applications.     

Gold‐Catalyzed Homogeneous Oxidative Cross‐Coupling Reactions

Oxidizing gold? A gold(I)/gold(III) catalytic cycle is essential for the first oxidative cross‐coupling reaction in gold catalysis. By using Selectfluor for gold(I) oxidation, this chemistry reveals the synthetic potential of incorporating gold(I)/gold(III) catalytic cycles into contemporary gold chemistry and promises a new area of gold research by merging powerful gold catalysis and oxidative metal‐catalyzed cross‐coupling reactions.

     

α‐Arylation/Heteroarylation of Chiral α‐Aminomethyltrifluoroborates by Synergistic Iridium Photoredox/Nickel Cross‐Coupling Catalysis

Direct access to complex, enantiopure benzylamine architectures using a synergistic iridium photoredox/nickel cross‐coupling dual catalysis strategy has been developed. New C(sp³)? C(sp²) bonds are forged starting from abundant and inexpensive natural amino acids.     

Microwave‐Assisted Heterogeneous Cross‐Coupling Reactions Catalyzed by Nickel‐in‐Charcoal (Ni/C)

A study involving the relatively rare combination of heterogeneous catalysis conducted under microwave conditions is presented. Carbon–carbon bond formation, including Negishi and Suzuki couplings, can be quickly effected with aryl chloride partners by using a base metal (nickel) adsorbed in the pores of activated charcoal. Aminations were also studied, along with cross‐couplings of vinyl alanes with benzylic chlorides as a means to stereodefined allylated aromatics. Reaction times for all these processes are typically reduced from several hours to minutes in a microwave reactor.     

Expedient Synthesis of Chiral α‐Amino Acids through Nickel‐Catalyzed Reductive Cross‐Coupling

A novel method for the synthesis of non‐natural L ‐ and D ‐amino acids by a Ni‐catalyzed reductive cross‐coupling reaction is described. This strategy enables the racemization‐free cross‐coupling of serine/homoserine‐ derived iodides with aryl/acyl/alkyl halides. It provides convenient access to varieties of enantiopure and functionalized amino acids, which are important building blocks in bioactive compounds and pharmaceuticals.     

Iron‐Catalyzed Oxidative Heterocoupling Between Aliphatic and Aromatic Organozinc Reagents: A Novel Pathway for Functionalized Aryl–Alkyl Cross‐Coupling Reactions

Aryl–alkyl cross‐coupling products are obtained by the iron‐catalyzed oxidative heterocoupling of organozinc reagents under mild conditions. This novel reaction pathway is versatile, allowing for the use of primary and secondary aliphatic diorganozinc reagents as coupling partners as well as tolerating functionalized aryl‐ and alkylzinc reagents.

     

Visible Light Activation of Boronic Esters Enables Efficient Photoredox C(sp2)–C(sp3) Cross‐Couplings in Flow

We report herein a new method for the photoredox activation of boronic esters. Using these reagents, an efficient and high‐throughput continuous flow process was developed to perform a dual iridium‐ and nickel‐catalyzed C(sp²)–C(sp³) coupling by circumventing solubility issues associated with potassium trifluoroborate salts. Formation of an adduct with a pyridine‐derived Lewis base was found to be essential for the photoredox activation of the boronic esters. Based on these results we were able to develop a further simplified visible light mediated C(sp²)–C(sp³) coupling method using boronic esters and cyano heteroarenes under flow conditions.     

Carbon–Carbon Cross‐Coupling Reactions Catalyzed by a Two‐Coordinate Nickel(II)–Bis(amido) Complex via Observable NiI,NiII, and NiIII Intermediates

Recently, the development of more sustainable catalytic systems based on abundant first‐row metals, especially nickel, for cross‐coupling reactions has attracted significant interest. One of the key intermediates invoked in these reactions is a Ni^III–alkyl species, but no such species that is part of a competent catalytic cycle has yet been isolated. Herein, we report a carbon–carbon cross‐coupling system based on a two‐coordinate Ni^II–bis(amido) complex in which a Ni^III–alkyl species can be isolated and fully characterized. This study details compelling experimental evidence of the role played by this Ni^III–alkyl species as well as those of other key Ni^I and Ni^II intermediates. The catalytic cycle described herein is also one of the first examples of a two‐coordinate complex that competently catalyzes an organic transformation, potentially leading to a new class of catalysts based on the unique ability of first‐row transition metals to accommodate two‐coordinate complexes.     

Stereospecific Pd‐Catalyzed Intermolecular C(sp3)–C(sp) Cross‐Coupling of Diarylmethyl Carbonates and Terminal Alkynes Under Base‐Free Conditions

A palladium‐catalyzed intermolecular decarboxylative C(sp³)–C(sp) coupling of diarylmethyl carbonates and terminal alkynes has been developed. The reaction proceeds smoothly under external base‐free conditions to deliver the corresponding alkynylated diarylmethanes with the liberation of CO₂ and MeOH as the sole byproducts. Moreover, enantioenriched diarylmethyl carbonates are stereospecifically converted to optically active cross‐coupling products with inversion of configuration. Thus, the stereospecific palladium catalysis can provide new and unique access to the alkynylated chiral tertiary stereocenters, which are relatively difficult to construct by conventional methods.     

Asymmetric Organocatalytic Direct C(sp2)H/C(sp3)H Oxidative Cross‐Coupling by Chiral Iodine Reagents

An asymmetric organocatalytic direct C? H/C? H oxidative coupling reaction of N¹,N³‐diphenylmalonamides has been well established by using chiral organoiodine compounds as catalysts, wherein four C? H bonds were stereoselectively functionalized to give structurally diverse spirooxindoles with high levels of enantioselectivity. More importantly, the findings indicated that chiral hypervalent organoiodine reagents can serve as alternative catalysts for the creation of enantioselective functionalization of inactive C? H bonds.     

Double Heck Cross‐Coupling Reactions of Dibrominated Pyridines

Double Heck cross‐coupling reactions of 2,3‐ and 3,5‐dibromopyridine with various alkenes afforded the corresponding novel di(alkenyl)pyridines. The Heck reaction of 2,5‐dibromopyridine unexpectedly afforded 5,5′‐di(alkenyl)‐2,2′‐bipyridines by palladium‐catalyzed dimerization to give 5,5′‐dibromo‐2,2′‐bipyridine and subsequent twofold Heck reaction.     

Copper‐catalyzed C(sp2)–C(sp) Sonogashira‐type cross‐coupling reactions accelerated by polycyclic aromatic hydrocarbons

Copper‐catalyzed Sonogashira‐type reactions were dramatically accelerated by introducing a catalytic amount of polycyclic aromatic hydrocarbon additive. This novel catalytic system features low copper loading (0.5 mol% < Cu < 5 mol%), broad reaction scope and remarkable substrate tolerance. Both aromatic and aliphatic terminal alkynes as well as diverse aryl iodides were employed in this transformation, affording respectable yields of the desired products. The novel Cu(OTf)₂/pyrene system was subsequently employed to synthesize phenylacetylene‐based fluorescent compounds. Copyright © 2015 John Wiley & Sons, Ltd.     

Enantioselective Construction of α‐Chiral Silanes by Nickel‐Catalyzed C(sp3)−C(sp3) Cross‐Coupling

An enantioselective C(sp³)?C(sp³) cross‐coupling of racemic α‐silylated alkyl iodides and alkylzinc reagents is reported. The reaction is catalyzed by NiCl₂/(S,S)‐Bn‐Pybox and yields α‐chiral silanes with high enantiocontrol. The catalyst system does not promote the cross‐coupling of the corresponding carbon analogue, corroborating the stabilizing effect of the silyl group on the alkyl radical intermediate (α‐silicon effect). Both coupling partners can be, but do not need to be, functionalized, and hence, even α‐chiral silanes with no functional group in direct proximity of the asymmetrically substituted carbon atom become accessible. This distinguishes the new method from established approaches for the synthesis of α‐chiral silanes.     

Tandem Catalytic C(sp3)H Amination/Sila‐Sonogashira–Hagihara Coupling Reactions with Iodine Reagents

A new tandem C? N and C? C bond‐forming reaction has been achieved through Rh^II/Pd⁰ catalysis. The sequence first involves an iodine(III) oxidant, then the in situ generated iodine(I) by‐product is used as a coupling partner. The overall process demonstrates the synthetic value of iodoarenes produced in trivalent iodine reagent mediated oxidations.