Copper-Catalyzed Cross-Coupling of Boronic Esters with Aryl Iodides and Application to the Carboboration of Alkynes and Allenes

Copper-catalyzed cross-coupling of aryl-, primary alkyl-, and secondary alkylboranes with heteroaryl bromides

A method for the Cu-catalyzed cross-coupling of both aryl and alkylboranes with aryl bromides is described. The method employs an inexpensive Cu-catalyst and functions for a variety of heterocyclic as well as electron deficient aryl bromides. In addition, aryl iodides of varying substitution patterns and electronic properties work well.

Stereo- and Regiocontrolled Methylboration of Terminal Alkynes

A scalable and operationally simple synthesis of trisubstituted alkenyl boronic esters has been achieved using a Zr-catalyzed carboalumination of terminal alkynes followed by in situ transmetalation with i-PrOBpin. The products are formed in good yields and with excellent regioselectivity and perfect stereoselectivity. The new procedure provides a significant improvement over the previously reported syntheses.

Copper-Catalyzed Synthesis of Tetrasubstituted Enynylboronates via Chemo-, Regio-, and Stereoselective Borylalkynylation

An efficient, catalytic method for accessing tetrasubstituted enynylboronates has been established via copper-catalyzed chemo-, regio-, and stereoselective borylalkynylation of internal alkynes. In this protocol, a range of symmetrical and unsymmetrical internal alkynes with aryl, heteroaryl, and alkyl substituents afforded fully substituted enynylboron compounds in good yields and with high levels of regio- and stereoselectivity, up to a ratio of >20:1. The enynylboron products could be further utilized in transforming the C-B bond into C-C bonds by coupling reactions.

The Hydrophobic Effect Applied to Organic Synthesis: Recent Synthetic Chemistry "in Water"

Recent developments over the past few years in aqueous micellar catalysis are discussed. Applications to problems in synthesis are highlighted, enabled by the use of surfactants that self-aggregate in water into micelles as nanoreactors. These include amphiphiles that have been available for some time, as well as those that have been newly designed. Reactions catalyzed by transition metals, including Pd, Cu, Rh, and Au, are of particular focus.

Iron-Catalyzed Hydroborylative Cyclization of 1,6-Enynes

We report first Fe-catalyzed hydroborylative cyclization reaction. The process provides one C-C and one C-B bond in a single operation and shows a wide scope, allowing the formation of carbo- and heterocycles containing a homoallylic boryl unit that can be further functionalized. The reaction takes place in smooth conditions, with inexpensive catalytic system and full atom economy since HBpin is the borylation agent, in contrast to our previously reported Pd-catalyzed reaction. Both aryl and alkyl substituted alkynes are reactive, revealing a wide reaction scope. Mechanistic studies suggest the intermediacy of Fe^II -hydride active catalyst capable to react with the alkyne group prior to alkene insertion, and computational studies suggest the occurrence of barrierless σ-bond metathesis involving HBpin and Fe-C bonds along the catalytic cycle.

Cu/Pd cooperatively catalyzed tandem intramolecular anti-Markovnikov hydroarylation of unsaturated amides: facile construction of 3,4-dihydroquinolinones via borylation/intramolecular C(sp3)–C(sp2) cross coupling

An anti-Markovnikov hydroarylation of unsaturated amides via a Cu/Pd synergistically catalyzed cascade borylation/intramolecular sp²–sp³ cross coupling has been disclosed.

A tetranuclear CuII2DyIII2 coordination cluster as a Suzuki (C–C) coupling reaction promoter

The air stable and high yielding tetranuclear coordination cluster [CuII2DyIII2L₄(NO₃)₂(CH₃CN)₂]·2(CH₃CN) promotes the Suzuki coupling reaction of phenylboronic acid with substituted aryl halides under environmentally benign conditions.

A Zinc Catalyzed C(sp3 )-C(sp2 ) Suzuki-Miyaura Cross-Coupling Reaction Mediated by Aryl-Zincates

The Suzuki-Miyaura (SM) reaction is one of the most important methods for C-C bond formation in chemical synthesis. In this communication, we show for the first time that the low toxicity, inexpensive element zinc is able to catalyze SM reactions. The cross-coupling of benzyl bromides with aryl borates is catalyzed by ZnBr2 , in a process that is free from added ligand, and is compatible with a range of functionalized benzyl bromides and arylboronic acid pinacol esters. Initial mechanistic investigations indicate that the selective in situ formation of triaryl zincates is crucial to promote selective cross-coupling reactivity, which is facilitated by employing an arylborate of optimal nucleophilicity.

Cu/Mn bimetallic catalysis enables carbonylative Suzuki-Miyaura coupling with unactivated alkyl electrophiles

A bimetallic system consisting of Cu-carbene and Mn-carbonyl co-catalysts was employed for carbonylative C-C coupling of arylboronic esters with alkyl halides, allowing for the convergent synthesis of ketones. The system operates under mild conditions and exhibits complementary reactivity to Pd catalysis. The method is compatible with a wide range of arylboronic ester nucleophiles and proceeds smoothly for both primary and secondary alkyl iodide electrophiles. Preliminary mechanistic experiments corroborate a hypothetical catalytic mechanism consisting of co-dependent cycles wherein the Cu-carbene co-catalyst engages in transmetallation to generate an organocopper nucleophile, while the Mn-carbonyl co-catalyst activates the alkyl halide electrophile by single-electron transfer and then undergoes reversible carbonylation to generate an acylmanganese electrophile. The two cycles then intersect with a heterobimetallic, product-releasing C-C coupling step.

Copper-Catalyzed Borylative Cyclization of in Situ Generated o-Allenylaryl Nitriles with Bis(pinacolato)diboron

A Cu-catalyzed cascade borylcupration/cyclization of in situ generated allene-nitriles with B₂pin₂ has been developed, which provides highly substituted 3-boryl-1-naphthylamines with excellent regioselectivity and wide functional group compatibility. It has been shown that, for the first time, the catalytically generated allylcopper species can be captured by a cyano group from a normal nitrile to furnish a carbocycle.

Enantioselective copper catalysed, direct functionalisation of allenes via allyl copper intermediates

We explore the breadth of the copper catalysed functionalisation of allenes, which enables efficient access to enantioenriched, densely functionalised molecules.

The direct functionalisation of allenes under copper catalysis enables efficient access to enantioenriched, densely functionalised molecules. In this review we explore the breadth and depth of a versatile reaction manifold, which involves the element-cupration of allenes to generate allyl copper intermediates that are subsequently coupled with diverse arrays of electrophiles.

Copper(i)-catalyzed sulfonylative Suzuki-Miyaura cross-coupling

Using a simple copper(i) catalyst has allowed a high yielding sulfonylative-Suzuki-Miyaura cross-coupling reaction to be developed. The process provides a single step route to diaryl sulfones from the direct combination of aryl boronic acids, sulfur dioxide and aryl iodides, and represents the first sulfonylative variant of a classic cross-coupling reaction. Sulfur dioxide is delivered from the surrogate reagent, DABSO. Variation of the reaction conditions allowed interruption of the sulfonylative-Suzuki coupling, resulting in the formation of a presumed Cu-sulfinate intermediate. These sulfinates could be trapped as their sodium salts and treated with electrophiles to allow access to arylalkyl sulfones, β-hydroxyl sulfones, sulfonamides and sulfonyl fluorides.

Divergent Synthetic Access to E- and Z-Stereodefined All-Carbon-Substituted Olefin Scaffolds: Application to Parallel Synthesis of (E)- and (Z)-Tamoxifens

A highly substrate-general synthesis of all-carbon-substituted E- and Z-stereodefined olefins is performed. The method comprises two sets of parallel and stereocomplementary preparations of (E)- and (Z)-α,β-unsaturated esters involving two robust and distinctive reactions: 1) stereocomplementary enol tosylations using readily available TsCl/diamine/(LiCl) base reagents, and 2) stereoretentive Negishi cross-coupling using the catalysts [Pd(dppe)Cl2] (for E) and [Pd(dppb)Cl2] (for Z). The present parallel approach is categorized as both type I (convergent approach: 16 examples, 56-87 % yield) and type II (divergent approach: 18 examples, 70-95 % yield). The obtained (E)- and (Z)-α,β-unsaturated ester scaffolds are successfully transformed into various E- and Z-stereodefined known and novel olefins (8×2 derivatization arrays). As a demonstration, application to the parallel synthesis of both (E)- and (Z)-tamoxifens, a representative motif of all-carbon-substituted olefins, is accomplished in a total of eight steps with an overall yield of 58 % (average 93 %) and 57 % (average 93 %), respectively.

Boraformylation and Silaformylation of Allenes

The boraformylation of allenes with B₂ (pin)₂ and a formate ester as boron and formyl source, respectively, proceeds in the presence of a copper catalyst. The reaction selectively affords the corresponding β-boryl β,γ-unsaturated aldehydes in good to high yields. Furthermore, the silaformylation of allenes was achieved with a formate ester and PhMe₂ Si-B(pin) as the silicon source.

Copper(i)-catalyzed 5-exo-trig radical cyclization/borylation of alkyl halides: access to functionalized pyrrolidine derivatives

This work reports the copper(i)-catalyzed 5-exo-trigradical cyclization/borylation of alkyl halides bearing an alkene moiety, during which a C–C bond and a C–B bond were formed in one step.

Theoretical study on homolytic B–B cleavages of diboron(4) compounds

The B–B BDEs of diboron(4) compounds and the Pt–B and Cu–B BDEs of their corresponding complexes were investigated by SOGGA11-X method.

Insight into Transmetalation Enables Cobalt-Catalyzed Suzuki-Miyaura Cross Coupling

Among the fundamental transformations that comprise a catalytic cycle for cross coupling, transmetalation from the nucleophile to the metal catalyst is perhaps the least understood. Optimizing this elementary step has enabled the first example of a cobalt-catalyzed Suzuki-Miyaura cross coupling between aryl triflate electrophiles and heteroaryl boron nucleophiles. Key to this discovery was the preparation and characterization of a new class of tetrahedral, high-spin bis(phosphino)pyridine cobalt(I) alkoxide and aryloxide complexes, (^iPrPNP)CoOR, and optimizing their reactivity with 2-benzofuranylBPin (Pin = pinacolate). Cobalt compounds with small alkoxide substituents such as R = methyl and ethyl underwent swift transmetalation at 23 °C but also proved kinetically unstable toward β-H elimination. Secondary alkoxides such as R = ⁱPr or CH(Ph)Me balanced stability and reactivity. Isolation and structural characterization of the product following transmetalation, (^iPrPNP)Co(2-benzofuranyl), established a planar, diamagnetic cobalt(I) complex, demonstrating the high- and low-spin states of cobalt(I) rapidly interconvert during this reaction. The insights from the studies in this elementary step guided selection of appropriate reaction conditions to enable the first examples of cobalt-catalyzed C-C bond formation between neutral boron nucleophiles and aryl triflate electrophiles, and a model for the successful transmetalation reactivity is proposed.

Enantioselective Generation of Adjacent Stereocenters in a Copper-Catalyzed Three-Component Coupling of Imines, Allenes, and Diboranes

A highly enantio- and diastereoselective copper-catalyzed three-component coupling affords the first general synthesis of homoallylic amines bearing adjacent stereocenters from achiral starting materials. The method utilizes a commercially available NHC ligand and copper source, operates at ambient temperature, couples readily available simple imines, allenes, and diboranes, and yields high-value homoallylic amines that exhibit versatile amino, alkenyl, and boryl units.

Catalytic Enantioselective Conjugate Additions of (pin)B-Substituted Allylcopper Compounds Generated in situ from Butadiene or Isoprene

Multicomponent catalytic enantioselective transformations that entail the combination of butadiene or isoprene (common feedstock), an enoate (prepared in one step) and B2 (pin)2 (commercially available) are presented. These processes constitute an uncommon instance of conjugate addition of an allyl moiety and afford the desired products in up to 83 % yield and 98:2 enantiomeric ratio. Based on DFT calculations stereochemical models and rationale for the observed profiles in selectivity are provided.