Copper(I)-catalyzed regioselective monoborylation of 1,3-enynes with an internal triple bond: selective synthesis of 1,3-dienylboronates and 3-alkynylboronates

Electrochemically Enabled Hydroxyphosphorylation of 1,3-Enynes to Access Phosphinyl-Substituted Propargyl Alcohols

Catalytic difunctionalization with the direct activation of (O)P-H bonds has been recently established as a potentially robust platform to generate valuable organophosphorus compounds. In terms of 1,3-enynes, despite of the various catalytic methods developed for hydrophosphorylation, the radical-mediated hetero-functionalization of two different atoms has been less explored. In this study, we disclosed an electrochemically induced hydroxyphosphorylation of 1,3-enynes for the construction of phosphinyl-substituted propargyl alcohols. The system involves the direct activation of both arylphosphine oxides and oxygen in ambient air with no external metal or additive needed. The use of electrochemistry ensures the regioselective, atom-economic and eco-friendly for the difunctionalization process. This strategy highlights the advantages of mild reaction conditions, readily available starting materials and broad substrate scope, showing its practical synthetic value in organic synthesis.

Regioselective Condensation Polymerization of Propargylic Electrophiles Enabled by Catalytic Element-Cupration

Here, we report a set of new polymerization reactions enabled by the 1,2-regioselective hydro- and silylcupration of enyne-type propargylic electrophiles. Highly regioregular head-to-tail poly(2-butyne-1,4-diyl)s (HT-PBD), bearing either methyl or silylmethyl side chains, are synthesized for the first time. A rapid entry into carbon-rich copolymers with adjustable silicon content is developed via in situ monomer bifurcation. Furthermore, a one-pot polymerization/semireduction sequence is developed to access a cis-poly(butadiene)-derived backbone by a ligand swap on copper hydride species. Interestingly, borocupration, typically exhibiting identical regioselectivity with its hydro- and silyl analogues, seems to proceed in a 3,4-selective manner. Computational studies suggest the possible role of the propargylic leaving group in this selectivity switch. This work presents a new class of regioregular sp-carbon-rich polymers and meanwhile a novel approach to organosilicon materials.

Efficient and selective external activator-free cobalt catalyst for hydroboration of terminal alkynes enabled by BiPyPhos

Herein, a robust catalyst system, composed of a bipyridine-based diphosphine ligand (BiPyPhos) and a cobalt precursor Co(acac)2, is successfully developed and applied in the hydroboration of terminal alkynes, exclusively affording various versatile β-E-vinylboronates in high yields at room temperature.

Cobalt-Catalyzed Selective Hydroboration of 1,3-Enynes with HBpin toward 1,3-Dienylboronate Esters

An efficient cobalt-catalyzed selective hydroboration of 1,3-enynes with HBpin toward 1,3-dienylboronate esters is disclosed. With a commercially available catalytic system of Co(acac)2 and dppf, the hydroboration reactions proceeded well to afford a wide range of 1,3-dienylborates in moderate to high yields. This protocol features a cheap base-metal catalytic system, broad substrate scope, excellent selectivity, easy gram-scale preparation, and good functional group tolerance and provides access to synthetically valuable 1,3-dienylborates.

Unlocking Diverse π-Bond Enrichment Frameworks by the Synthesis and Conversion of Boronated Phenyldiethynylethylenes

The π-bond enrichment frameworks not only serve as a crucial building block in organic synthesis but also assume a pivotal role in the fields of materials science, biomedicine, photochemistry, and other related disciplines owing to their distinctive structural characteristics. The incorporation of various substituents into the C═C double bonds of tetrasubstituted alkenes is currently a highly significant research area. However, the synthesis of tetrasubstituted alkenes with diverse substituents on double bonds poses a significant challenge in achieving stereoselectivity. Here, we reported an efficient and convergent route of Cu-catalyzed borylalkynylation of both symmetrical and unsymmetrical 1,3-diynes, B2pin2, and acetylene bromide to the construction of boronated phenyldiethynylethylene (BPDEE) derivatives with excellent chemo-, stereo-, and regioselectivities. BPDEE derivatives could transform into novel tetrasubstituted organic π-conjugated gem-diphenyldiethynylethylene (DPDEE), vinylphenyldiethynylethylene (VPDEE), and phenyltriethynylethylene (PTEE) derivatives by a stepwise process, which provides a flexible platform for the synthesis of complex π-bond enrichment frameworks that were difficult to synthesize by previous methods. The initial optical characterization revealed that the synthesized molecules exhibited aggregation-induced emission (AIE) properties, which further establishes the groundwork for future applications and enriches and advances the field of functional π-conjugated frameworks research.

Transition Metal-Free Regio- and Stereo-Selective trans Hydroboration of 1,3-Diynes: A Phosphine-Catalyzed Access to (E)-1-Boryl-1,3-Enynes

We report a transition metal-free, regio- and stereo-selective, phosphine-catalyzed method for the trans hydroboration of 1,3-diynes with pinacolborane that affords (E)-1-boryl-1,3-enynes. The reaction proceeds with excellent selectivity for boron addition to the external carbon of the 1,3-diyne framework as unambiguously established by NMR and X-ray crystallographic studies. The reaction displays a broad substrate scope including unsymmetrical diynes to generate products in high yield (up to 95 %). Experimental and theoretical studies suggest that phosphine attack on the alkyne is a key process in the catalytic cycle.

Preparation of Dienyl Boronates by Tandem Ene-Yne Metathesis/Dienyl Isomerization: Ready Access to Diene Building Blocks for the Synthesis of Polyenes

The ene-yne metathesis of alkenyl boronates with terminal alkynes is reported. These challenging metatheses were accomplished using a Grubbs catalyst bearing the cyclic alkyl amino carbene (CAAC) ligand, whereas N-heterocyclic carbene (NHC) derived catalysts gave lower yields. Subsequent dienyl isomerization via a cobalt-catalyzed hydrogen atom transfer (HAT) furnished the more substituted dienyl boronate with high EE/EZ ratios. Finally, the resulting dienyl boronate products were successfully used in Suzuki-Miyaura cross-coupling reactions and in a Diels-Alder cycloaddition.

Regioselective catalytic carbonylation and borylation of alkynes with aryldiazonium salts toward α-unsubstituted β-boryl ketones

A new Pd/Cu-catalyzed carbonylation and borylation of alkynes with aryldiazonium salts toward α-unsubstituted β-boryl ketones with complete regioselectivity has been developed. This transformation shows broad substrate scope and excellent functional-group tolerance. Moreover, the obtained 1,2-carbonylboration products provide substantial opportunities for further transformations which cannot be obtained by known carbonylation procedures. Preliminary mechanistic studies indicate that the three hydrogen atoms of the products originated from ethyl acetate.

The Rise of 1,4-BN-Heteroarenes: Synthesis, Properties, and Applications

BN-heteroarenes, which employ both boron and nitrogen in aromatic hydrocarbons, have gained great attention in the fields of organic chemistry and materials science. Nevertheless, the extensive studies on BN-heteroarenes are largely limited to 1,2-azaborine-based compounds with B-N covalent bonds, whereas 1,3- and 1,4-BN-heteroarenes are relatively rare due to their greater challenge in the synthesis. Recently, significant progresses have been achieved in the synthesis and applications of BN-heteroarenes featuring 1,4-azaborines, especially driven by their significant potential as multiresonant thermally activated delayed fluorescence (MR-TADF) materials. Therefore, it is timely to review these advances from the chemistry perspective. This review summarizes the synthetic methods and recent achievements of 1,4-azaborine-based BN-heteroarenes and discusses their unique properties and potential applications of this emerging class of materials, highlighting the value of 1,4-BN-heteroarenes beyond MR-TADF materials. It is hoped that this review would stimulate the conversation and cooperation between chemists who are interested in azaborine chemistry and materials scientists working in the fields of organic optoelectronics, metal catalysis, and carbon-based nanoscience etc.

Copper-catalysed asymmetric reductive cross-coupling of prochiral alkenes

Asymmetric construction of C(sp3)-C(sp3) bond with good stereocontrol of the two connecting carbon centres retaining all carbon or hydrogen substituents is a challenging target in transition metal catalysis. Transition metal-catalysed reductive coupling of unsaturated π-substrates is considered as a potent tool to expediently develop the molecular complexity with high atom efficiency. However, such an asymmetric and intermolecular process has yet to be developed fully. Herein, we report an efficient strategy to reductively couple two prochiral conjugate alkenes using a copper-catalysed tandem protocol in the presence of diboron. Notably, this transformation incorporates a wide range of terminal and internal enynes as coupling partners and facilitates highly diastereo- and enantioselective synthesis of organoboron derivatives with multiple adjacent stereocentres in a single operation.

Palladium-catalyzed hydroboration reaction of unactivated alkynes with bis (pinacolato) diboron in water

A highly efficient and mild palladium-catalyzed hydroboration of unactivated internal alkynes in water is described. Both aryl- and alkyl-substituted alkynes proceeded smoothly within the reaction time to afford the desired vinylboronates in moderate to high yields. Bis (pinacolato) diboron was used to afford α- and β-hydroborated products in the presence of HOAc. These reactions showed high reactivities and tolerance, thus providing a promising method for the synthesis of alkenyl boron compounds.

Recent advances in Cu-catalyzed transformations of internal alkynes to alkenes and heterocycles

Numerous metal-catalyzed reactions involving internal alkynes and aimed towards synthetically and pharmacologically important alkenes and heterocycles have appeared in the literature. Among these, Cu-catalyzed reactions have a special place, which has prompted the investigation and development of carbon-carbon and carbon-heteroatom bond-forming reactions. These reactions possess wide scope, and during the paths of these reactions, either stable or in situ intermediates are formed via the addition of Cu as a core catalyst or synergistic catalyst. In this review, we aim to report different contributions relating to Cu-catalyzed reactions of internal alkynes for the synthesis of different valuable alkenes and heterocycles which have appeared in the literature in the last decade. We anticipate that this appraisal will deliver basic insights for the further advancement of Cu-catalyzed reactions in organic chemistry.

Design, Synthesis, and Antifungal Activity of 16,17-Dihydroheronamide C and ent-Heronamide C

16,17-Dihydroheronamide C (8) and ent-heronamide C (ent-1) were designed as probes for the mode-of-action analysis of heronamide C (1). These molecules were synthesized by utilizing a highly modular strategy developed in the preceding paper. The evaluation of the antifungal activity of these compounds revealed the exceptional importance of the C16-C17 double bond for the antifungal activity of heronamide C and the existence of chiral recognition between heronamide C (1) and cell membrane components.

Toward the Creation of Induced Pluripotent Small (iPS) Molecules: Establishment of a Modular Synthetic Strategy for the Heronamide C-type Polyene Macrolactams and Their Conformational and Reactivity Analysis

A highly modular synthetic strategy for the heronamide C-type polyene macrolactams was established by synthesizing 8-deoxyheronamide C (2). The developed strategy enabled not only the total synthesis of 8-deoxyheronamide C (2) but also the unified synthesis of four heronamide-like molecules named "heronamidoids" (5-8). Conformational and reactivity analysis of the heronamidoids clarified that (1) the C19 stereochemistry mainly affected the conformation of the amide linkage, resulting in the change of alignment of two polyene units and reactivity toward photochemical [6π + 6π] cycloaddition, and (2) the C8,C9-diol moiety is important for the conversion to the heronamide A-type skeleton from the heronamide C skeleton.

Site-Fixed Hydroboration of Terminal and Internal Alkenes using BX3 /i Pr2 NEt*

An unprecedented and general hydroboration of alkenes with BX₃ (X=Br, Cl) as the boration reagent in the presence of ⁱ Pr₂ NEt is reported. The addition of ⁱ Pr₂ NEt not only suppresses alkene polymerization and haloboration side reactions but also provides an "H" source for hydroboration. More importantly, the site-fixed installation of a boryl group at the original position of the internal double bond is readily achieved in contrast to conventional transition-metal-catalyzed hydroboration processes. Further application to the synthesis of 1,n-diborylalkanes (n=3-10) is also demonstrated. Preliminary mechanistic studies reveal a major reaction pathway that involves radical species and operates through a frustrated Lewis pair type single-electron-transfer mechanism.

Rare-Earth-Catalyzed Selective 1,4-Hydrosilylation of Branched 1,3-Enynes Giving Tetrasubstituted Silylallenes

Allenes are versatile synthons in organic synthesis and medicinal chemistry because of their diverse reactivities. Catalytic 1,4-hydrosilylation of 1,3-enynes may present the straightforward strategy for synthesis of silylallenes. However, the transition-metal-catalyzed reaction has not been successful due to poor selectivity and very limited substrate scopes. We report here the efficient and selective 1,4-hydrosilylation of branched 1,3-enynes enabled by the ene-diamido rare-earth ate catalysts using both alkyl and aryl hydrosilanes, leading to the exclusive formation of tetrasubstituted silylallenes. Deuteration reaction, kinetic study, and DFT calculations were conducted to investigate the possible mechanism, revealing crucial roles of high Lewis acidity, large ionic radius, and ate structure of the rare-earth catalysts.

Late 3d Metal-Catalyzed (Cross-) Dimerization of Terminal and Internal Alkynes

This review will outline the recent advances in chemo-, regio-, and stereoselective (cross-) dimerization of terminal alkynes to generate 1,3-enynes using different types of iron and cobalt catalysts with altering oxidation states of the active species. In general, the used ligands have a crucial effect on the stereoselectivity of the reaction; e.g., bidentate phosphine ligands in cobalt catalysts can generate the E-configured head-to-head dimerization product, while tridentate phosphine ligands can generate either the Z-configured head-to-head dimerization product or the branched head-to-tail isomer. Furthermore, the hydroalkynylation of silyl-substituted acetylenes as donors to internal alkynes as acceptors will be discussed using cobalt and nickel catalysts.

The Formosalides: Structure Determination by Total Synthesis

Total synthesis allowed the constitution of the cytotoxic marine macrolides of the formosalide family to be confirmed and their previously unknown stereostructure to be assigned with confidence. The underlying blueprint was inherently modular to ensure that each conceivable isomer could be reached. This flexibility derived from the use of strictly catalyst controlled transformations to set the stereocenters, except for the anomeric position, which is under thermodynamic control; as an extra safety measure, all stereogenic centers were set prior to ring closure to preclude any interference of the conformation adopted by the macrolactone rings of the different diastereomers. Late-stage macrocyclization by ring-closing alkyne metathesis was followed by a platinum-catalyzed transannular 6-exo-dig hydroalkoxylation/ketalization to craft the polycyclic frame. The side chain featuring a very labile unsaturation pattern was finally attached to the core by Stille coupling.

Copper-catalyzed functionalization of enynes

The copper-catalyzed functionalization of enyne derivatives has recently emerged as a powerful approach in contemporary synthesis. Enynes are versatile and readily accessible substrates that can undergo a variety of reactions to yield densely functionalized, enantioenriched products. In this perspective, we review copper-catalyzed transformations of enynes, such as boro- and hydrofunctionalizations, copper-mediated radical difunctionalizations, and cyclizations. Particular attention is given to the regiodivergent functionalization of 1,3-enynes, and the current mechanistic understanding of such processes.

Silylboranes as Powerful Tools in Organic Synthesis: Stereo- and Regioselective Reactions with 1,n-Enynes

Bismetalated alkenes, accessible by element–element addition to alkynes, are valuable building blocks in organic synthesis, providing wide opportunities for divergent synthesis. Silaboration of alkynes with a pendant olefinic group, catalyzed by group 10 metal complexes, and subsequent transformation of the silicon and boron functional groups give access to densely functionalized 1,3-dienes and 1,3,5-trienes with defined stereo- and regiochemistry, 1,2-dienes, and carbocyclic and heterocyclic products.

1 Introduction

2 Background

3 Reactions with 1,3-Enynes

4 Cyclization 1,6-Enynes

5 Cyclization 1,7-Enynes

6 Cyclization of 1,n-Enynes (n > 7)

7 Cyclization of Dienynes and Enediynes

8 Cyclization of 1,6-Diynes

9 Conclusions

Iridium-Catalyzed γ-Selective Hydroboration of γ-Substituted Allylic Amides

Reported here for the first time is the Ir-catalyzed γ-selective hydroboration of γ-substituted allylic amides under mild reaction conditions. A variety of functional groups could be compatible with reaction conditions, affording γ-branched amides in good yields with ≤97% γ-selectivity. We have also demonstrated that the obtained borylated products could be used in a series of C-O, C-F, C-Br, and C-C bond-forming reactions.

Enantio- and Diastereoselective Synthesis of Homopropargyl Amines by Copper-Catalyzed Coupling of Imines, 1,3-Enynes, and Diborons

An efficient, enantio- and diastereoselective, copper-catalyzed coupling of imines, 1,3-enynes, and diborons is reported. The process shows broad substrate scope and delivers complex, chiral homopropargyl amines; useful building blocks on the way to biologically-relevant compounds. In particular, functionalized homopropargyl amines bearing up to three contiguous stereocenters can be prepared in a single step.

Ligand-controlled copper-catalyzed 1,2 or 1,4-protoborylation of 2-trifluoromethyl-1,3-conjugated enynes

A novel ligand-controlled highly regioselective synthesis of CF₃-substituted homopropargylboronates and homoallenylboronates via copper-catalyzed 1,2 or 1,4-protoborylation of 2-trifluoromethyl-1,3-conjugated enynes with B₂pin₂ was developed.

Iridium-Catalyzed Distal Hydroboration of Aliphatic Internal Alkenes

The regioselective hydroboration of aliphatic internal alkenes remains a great challenge. Reported herein is an iridium-catalyzed hydroboration of aliphatic internal alkenes, providing distal-borylated products in good to excellent yields with high regioselectivity (up to 99:1). We also demonstrate that the C-B bond of the distal-borylated product can be readily converted into other functional groups. DFT calculations indicate that the reaction proceeds through an unexpected Ir^III /Ir^V cycle.

Racemic Vinylallenes in Catalytic Enantioselective Multicomponent Processes: Rapid Generation of Complexity through 1,6-Conjugate Additions

Racemic vinylallenes are shown to be effective substrates for catalytic multicomponent diastereo- and enantioselective 1,6-conjugate addition of multifunctional allyl moieties to easily accessible α,β,γ,δ-unsaturated diesters. Reactions may be catalyzed by 5.0 mol % of a readily accessible NHC-Cu complex at ambient temperature, and other than a vinylallene, involve B₂ (pin)₂ and an α,β,γ,δ-unsaturated diester. A variety of vinylallenes were converted to products bearing a Z-trisubstituted alkenyl-B(pin) moiety, a vinyl group, a β,γ-unsaturated diester unit, and vicinal stereogenic centers in up to 67 % yield, 87:13 Z/E ratio, >98:2 d.r., and 98:2 e.r. Chemoselective modifications involving the alkenyl-B(pin), the vinyl, or the 1,2-disubstituted olefin moieties were carried out to demonstrate versatility and utility. Stereochemical models, based on mechanistic and DFT studies, demonstrate the dynamic behavior of intermediated Cu-allyl species and account for various selectivity profiles.

Transition-metal-free borylation of propargylic alcohols: structurally variable synthesis in ionic liquid medium

Transition-metal-free borylation of unactivated propargylic alcohols in basic ionic liquids allowed the construction of various highly functionalized vinylboronates.