Nickel-catalyzed migratory alkyl–alkyl cross-coupling reaction

The selective cross-coupling of activated electrophiles with unactivated ones has been regarded as a challenging task in cross-electrophile couplings. Herein we describe a migratory cross-coupling strategy, which can overcome this obstacle to access the desired cross-coupling products. Accordingly, a selective migratory cross-coupling of two alkyl electrophiles has been accomplished by nickel catalysis. Remarkably, this alkyl–alkyl cross-coupling reaction provides a platform to prepare 2°–2° carbon–carbon bonds from 1° and 2° carbon coupling partners. Preliminary mechanistic studies suggest that chain-walking occurs at both alkyl halides in this reaction, thus a catalytic cycle with the key step involving two alkylnickel(ii) species is proposed for this transformation.

The selective cross-coupling of activated electrophiles with unactivated ones has been regarded as a challenging task in cross-electrophile couplings.     

Direct aminoalkylation of arenes, heteroarenes, and alkenes via Ni-catalyzed Negishi cross-coupling reactions

A room-temperature Ni-catalyzed cross-coupling of aryl, heteroaryl, and alkenyl electrophiles with aminoalkylzinc bromides, readily available from the corresponding aminoalkyl chlorides via Grignard reagents, was developed. The reaction allows a convenient one-step preparation of various aminoalkyl products, including piperidine and tropane derivatives. Such functionalized amine moieties are widely present in various biologically active molecules. Aryl, heteroaryl, and alkenyl iodides, bromides, chlorides and triflates are suitable electrophiles. A short total synthesis of two natural products, (±)-galipinine and (±)-cusparine, is also reported.     

Cross-coupling of mesylated phenol derivatives with potassium ammonio- and amidomethyltrifluoroborates

A large array of aryl and heteroaryl mesylates have been successfully employed as electrophiles in a Csp(2)-Csp(3) Suzuki-Miyaura cross-coupling with potassium ammonio- and amidomethyltrifluoroborates to afford the corresponding products in high yields.     

Nickel catalyzed cross-coupling of aryl C-O based electrophiles with aryl neopentylglycolboronates

The efficiency of mesylates, sulfamates, esters, carbonates, carbamates, and methyl ethers as C-O-based electrophiles attached to the 1- or 2-position of naphthalene and to activated and nonactivated phenyl substrates was compared for the first time in Ni-catalyzed cross-coupling with phenyl neopentylglycolboronates containing electron-rich and electron-deficient substituents in their para-position. These experiments were performed in the presence of four different Ni(II)- and Ni(0)-based catalysts. Ni(II)-based catalysts mediate the cross-coupling of most 2-naphthyl C-O electrophiles with both arylboronic acids and with neopentylglycolboronates when K(3)PO(4) is used as base. The same catalysts are not efficient when CsF is used as base. However, Ni(0)-based catalysts exhibit selective efficiency, and when reactive, their efficiency is higher than that of Ni(II)-based catalysts in the presence of both K(3)PO(4) and CsF. These results provide both reaction conditions for the cross-coupling, and for the elaboration of orthogonal cross-coupling methodologies of various C-O based electrophiles with aryl neopentylglycolboronates. With the exception of mesylates and sulfamates the efficiency of all other 2-naphthyl C-O electrophiles was lower in cross-coupling with aryl neopentylglycolboronates than with arylboronic acids.     

2-Pyridyl and 3-pyridylzinc bromides: direct preparation and coupling reaction

A facile synthetic approach to the direct preparation of 2-pyridyl and 3-pyridylzinc bromides has been demonstrated using Rieke zinc with 2-bromopyridine and 3-bromopyridine, respectively. A variety of different electrophiles have been coupled with the resulting organozinc reagents to give the corresponding cross-coupling products in moderate to good yields.     

Preparation of highly functionalized arylmagnesium reagents by the addition of magnesium phenylselenide to arynes

The described polyfunctional arylmagnesium reagents, resulting from the highly regioselective addition of magnesium phenylselenide to functionalized arynes, can be trapped by a range of electrophiles, yielding polyfunctional selenoethers in 45-85% yields. Furthermore, these Grignard reagents can be used in Negishi cross-coupling reactions with iodoarenes after transmetalation to the corresponding arylzinc compounds, furnishing functionalized biaryl products in 55-73% yields.     

Csp3−PIII Bond Formation via Cross-Coupling of Umpolung Carbonyls with Phosphine Halides Catalyzed by Nickel

A novel method for the formation of Csp³−P^III bonds via the nickel-catalyzed cross-coupling of Umpolung carbonyls and phosphine chlorides is reported herein. This process leads to a series of alkylphosphines, which are characterized as sulfides or borane-phosphine complexes after undergoing further transformation with moderate to good yields. Invaluable free alkylphosphines can be easily obtained by desulfurization or deboration of the products. A possible mechanistic pathway is also discussed. This report represents the first example of using renewable carbonyls as latent organometallic reagent surrogates for cross-coupling with heteroatom electrophiles.     

Palladium-Catalyzed Cross-Coupling of Alkenyl Carboxylates

Carboxylate esters have many desirable features as electrophiles for catalytic cross-coupling: they are easy to access, robust during multistep synthesis, and mass-efficient in coupling reactions. Alkenyl carboxylates, a class of readily prepared non-aromatic electrophiles, remain difficult to functionalize through cross-coupling. We demonstrate that Pd catalysis is effective for coupling electron-deficient alkenyl carboxylates with arylboronic acids in the absence of base or oxidants. Furthermore, these reactions can proceed by two distinct mechanisms for C−O bond activation. A Pd^0/II catalytic cycle is viable when using a Pd⁰ precatalyst, with turnover-limiting C−O oxidative addition; however, an alternative pathway that involves alkene carbopalladation and β-carboxyl elimination is proposed for Pd^II precatalysts. This work provides a clear path toward engaging myriad oxygen-based electrophiles in Pd-catalyzed cross-coupling.     

Copper-Catalyzed Enantioconvergent Radical C(sp3)−N Cross-Coupling: Access to α,α-Disubstituted Amino Acids

Transition-metal catalyzed enantioconvergent cross-coupling of tertiary alkyl halides with ammonia offers a rapid avenue to chiral unnatural α,α-disubstituted amino acids. However, the construction of chiral C−N bonds between tertiary-carbon electrophiles and nitrogen nucleophiles presented a great challenge owing to steric congestion. We report a copper-catalyzed enantioconvergent radical C−N cross-coupling of alkyl halides with sulfoximines (as ammonia surrogates) under mild conditions by employing a chiral anionic N,N,N-ligand with a long spreading side arm. An array of α,α-disubstituted amino acid derivatives were obtained with good efficiency and enantioselectivity. The synthetic utility of the strategy has been showcased by the elaboration of the coupling products into different chiral α-fully substituted amine building blocks.     

Approaches to oximidines, lobatamides and related natural products: the coupling reactions of 3-iodoacrolein O-methyl oximes

Both 2E- and 2Z-3-iodoacrolein O-methyl oximes are prepared in two steps from ethyl propiolate. Lithium–iodine exchange is effected and the resulting organolithium reagents added to several electrophiles, including styryl isocyanate which gives a conjugated O-methyl oxime enamide of the type found in the side chains of the oximidine, lobatamide and CJ-12950 natural products. The Pd(0) catalysed cross-coupling of these iodoalkenes is also explored.     

Sonogashira coupling of functionalized trifloyl oxazoles and thiazoles with terminal alkynes: synthesis of disubstituted heterocycles

[reaction: see text] This paper describes Sonogashira cross-coupling of functionalized 2-, 4-, and 5-trifloyl oxazoles and thiazoles with terminal alkynes. This methodology has been extended to 2,4-ditrifloylthiazoles, which results in regioselective cross-coupling at the C2-position of the thiazole. The resulting 2-alkynyl-4-trifloylthiazoles are effective electrophiles in a second palladium(0)-mediated cross-coupling reaction.     

钯催化下有机锡化合物的偶联反应在碳-碳键形成过程中的应用

本文述评了最近几年来钯催化的有机锡化合物与有机亲电试剂的交叉偶联反应在有机合成中用于碳-碳键形成的主要研究成果。主要讨论了直接交叉偶联反应,CO或烯键插入的交叉偶联反应和机理。     

Atom-efficient metal-catalyzed cross-coupling reaction of indium organometallics with organic electrophiles.

The novel metal-catalyzed cross-coupling reaction of indium organometallics with organic electrophiles is described. Triorganoindium compounds (R(3)In) containing alkyl, vinyl, aryl, and alkynyl groups are efficiently prepared from the corresponding lithium or magnesium organometallics by reaction with indium trichloride. The cross-coupling reaction of R(3)In with aryl halides and pseudohalides (iodide 2, bromide 5, and triflate 4), vinyl triflates, benzyl bromides, and acid chlorides proceeds under palladium catalysis in excellent yields and with high chemoselectivity. Indium organometallics also react with aryl chlorides as under nickel catalysis. In the cross-coupling reaction the triorganoindium compounds transfer, in a clear example of atom economy, all three of the organic groups attached to the metal, as shown by the necessity of using only 34 mol % of indium. The feasibility of using R(3)In in reactions with different electrophiles, along with the high yields and chemoselectivities obtained, reveals indium organometallics to be useful alternatives to other organometallics in cross-coupling reactions.     

Synthesis of Symmetrical and Nonsymmetrical Polyenes by Iterative and Bidirectional Palladium-Catalyzed Cross-Coupling Reactions

Bifunctional unsaturated reagents designed to undergo palladium-catalyzed cross-coupling reactions with complementary polyenyl connective fragments are highly useful for the undoubtedly challenging synthesis of polyenes. The current toolkit of building blocks for the bidirectional formation of Csp²−Csp² single bonds of polyenes includes homo-bisfunctionalized reagents with equal or unequal reactivity (due to steric and/or electronic factors), and hetero-bisfunctionalized counterparts containing either two different nucleophiles, two electrophiles or one of these functionalities and a latent nucleophile that can be unmasked when desired. The combination of these bifunctional linchpin reagents using tactics that modulate the reactivity of each terminus in order to achieve the required connection have streamlined the synthesis of polyenes of great complexity using (iterative) cross-coupling methods for Csp²−Csp² bond formation. Reaction conditions for the Pd-catalyzed cross-coupling reactions are mild and functional-group-tolerant, and therefore these protocols allow to construct the polyene structures using shorter unsaturated reactants with the desired geometries, since in general the products preserve the stereochemical information of the connected cross-coupling partners.     

A novel method for the construction of (z,e)- or (z,z)-conjugated alkadienyl carboxylates

[reaction: see text] The stereocontrolled dehydrobromination of 1,2-dibromoethyl carboxylates giving (Z)-2-bromovinyl carboxylates could readily be approached by using DBU and a catalytic amount of hydroquinone as a base at -78 degrees C. The first investigation on the Suzuki-type cross-coupling of (Z)-2-bromovinyl carboxylates as electrophiles with stereodefined alkenylboronic acids provides a novel method for the construction of (Z,E)- or (Z,Z)-conjugated alkadienyl carboxylate moieties, which are often present in a range of natural products.     

Rh(Ⅰ)-catalyzed borylation of primary alkyl chlorides

Rhodium-catalyzed cross-coupling reactions of unactivated primary alkyl chlorides with diboron reagents have been developed as practical methods for the synthesis of alkylboronic esters. These reactions expand the concept and utility of Rh(I)-catalyzed cross-coupling of aliphatic electrophiles.     

Nickel-catalyzed reductive cross-coupling of polyfluoroarenes with alkyl electrophiles by site-selective C–F bond activation

A nickel-catalyzed reductive cross-coupling reactions between polyfluoroarenes and alkyl electrophiles is reported to access substituted fluoroarenes through chelation-assisted C–F activation. Diverse primary and secondary alkyl (pseudo)halides can be employed to couple with polyfluoroarenes, showing excellent regioselectivity. Furthermore, the nickel-catalyzed asymmetric cross-coupling of polyfluoroarenes with racemic alkyl halides is preliminarily explored. In addition, the practicability of the title transformation is also demonstrated by total synthesis of losmapimod and an analog as key steps. The developed method exhibits many advantages, including economic catalytic systems, commercially available alkyl electrophiles, and lack of sensitive organometallic reagents.     

Pd-catalyzed carbonylative cross-coupling reactions by triorganoindiums: highly efficient transfer of organic groups attached to indium under atmospheric pressure

[reaction: see text] A highly atom-efficient synthetic method of unsymmetrical ketones was developed by using trialkyl- and triarylindiums, which could be employed as effective cross-coupling partners in Pd-catalyzed carbonylative cross-coupling reactions with a variety of organic electrophiles. The present method produced unsymmetrical ketones and 1,4-diacylbenzenes in good yields with highly efficient transfer of almost all the organic groups attached to the indium under atmospheric pressure of CO gas in THF at 66 degrees C.     

Silicon-based cross-coupling reaction: an environmentally benign version

Much attention has been paid to the cross-coupling reaction of organosilicon compounds due to their stability, non-toxicity, and natural abundance of silicon. In addition, the silicon-based cross-coupling has many advantages over other cross-coupling protocols. Successful examples of the silicon-based cross-coupling reaction are reviewed, focusing especially on the advances made in the last decade. Having had a number of highly effective palladium catalysts developed mainly for other cross-coupling reactions, the development of the silicon-based protocol owes heavily to the design of organosilicon reagents which effectively undergo transmetalation, a key elemental step of the silicon-based cross-coupling reaction. This tutorial review thus classifies various organosilicon reagents depending on substituents on silicon and surveys their cross-coupling reactions with various electrophiles.     

Impact of N-Aryl- and NHC Core-Substituents on the Coupling of Alkylzinc Nucleophiles: Is Bigger always Better?

Bulky Pd−N-heterocyclic carbene (NHC) catalysts (e. g., N-(di-2,6-(3-pentyl)phenyl), IPent) have been shown to have significantly higher reactivity in a wide variety of cross-coupling applications (i. e., C−C, C−S, C−N) than less hindered variants (e. g., N-(di-2,6-(isopropyl)phenyl), IPr). Further, chlorinating the backbone of the NHC ring sees an even greater increase in reactivity. In the cross-coupling of (hetero)aryl electrophiles to secondary alkyl nucleophiles, making the N-aryl groups larger reduces the amount of β-hydride elimination leading to alkene byproducts and chlorinating the NHC core had an even greater effect, all but eliminating alkene formation. In the present study involving the cross-coupling of primary alkyl electrophiles and nucleophiles, a sharp and surprising reversal of all of the above trends was observed. Bulkier catalysts had generally slower rate of reaction and β-hydride elimination worsened leading to extensive amounts of alkene byproducts.