Dehydrogenative Borylation Research Articles

Photocatalyzed H2-Acceptorless Dehydrogenative Borylation by Using Amine Borane

Photocatalyzed H₂-Acceptorless Dehydrogenative Borylation by Using Amine Borane

Co-MOF-Catalyzed Dehydrogenative Borylation of Alkenes

Co-MOF-Catalyzed Dehydrogenative Borylation of Alkenes

Correction to “Facile Synthesis of Vinyl Boronate Esters via Dehydrogenative Borylation of Alkenes Enabled by Co-MOF Catalyst: An Additive Free Approach”

Correction to “Facile Synthesis of Vinyl Boronate Esters via Dehydrogenative Borylation of Alkenes Enabled by Co-MOF Catalyst: An Additive Free Approach”

Facile Synthesis of Vinyl Boronate Esters via Dehydrogenative Borylation of Alkenes Enabled by a Co-MOF Catalyst: An Additive-Free Approach

Facile Synthesis of Vinyl Boronate Esters via Dehydrogenative Borylation of Alkenes Enabled by a Co-MOF Catalyst: An Additive-Free Approach

Carborane–arene fused boracyclic analogues of polycyclic aromatic hydrocarbons accessed by intramolecular borylation

Carborane fused boron doped polycyclic aromatic hydrocarbons were accessed by dehydrobrominative and dehydrogenative borylation.

Catalytic acceptorless dehydrogenative borylation of styrenes enabled by a molecularly defined manganese complex.

In this study, we employed a 3d metal complex as a catalyst to synthesize alkenyl boronate esters through the dehydrogenative coupling of styrenes and pinacolborane. The process generates hydrogen gas as the sole byproduct without requiring an acceptor, rendering it environmentally friendly and atom-efficient. This methodology demonstrated exceptional selectivity for dehydrogenative borylation over direct hydroboration. Additionally, it exhibited a preference for borylating aromatic alkenes over aliphatic ones. Notably, derivatives of natural products and bioactive molecules successfully underwent diversification using this approach. The alkenyl boronate esters served as precursors for the synthesis of various pharmaceuticals and potential anticancer agents. Our research involved comprehensive experimental and computational studies to elucidate the reaction pathway, highlighting the B-H bond cleavage as the rate-determining step. The catalyst's success was attributed to the hemilability and metal-ligand bifunctionality of the ligand backbone.

Cyclododecene isomeric separation by (supported) rhodium(i)-catalysed selective dehydrogenative borylation reaction

A commercially available mixture of cis and trans cyclododecene can be separated after the selective dehydrogenative borylation reaction of the cis isomer, catalyzed by Rh(i) either in soluble complex or solid supported form.

Dehydroborylation of Terminal Alkynes Using Lithium Aminoborohydrides.

Dehydrogenative borylation of terminal alkynes has recently emerged as an atom-economical one-step alternative to traditional alkyne borylation methodologies. Using lithium aminoborohydrides, formed in situ from the corresponding amine-boranes and n-butyllithium, a variety of aromatic and aliphatic terminal alkyne substrates were successfully borylated in high yield. The potential to form mono-, di-, and tri-B-alkynylated products has been shown, though the mono-product is primarily generated using the presented condition. The reaction has been demonstrated at large (up to 50 mmol) scale, and the products are stable to column chromatography as well as acidic and basic aqueous conditions. Alternately, the dehydroborylation can be achieved by treating alkynyllithiums with amine-boranes. In that respect, aldehydes can act as starting materials by conversion to the 1,1-dibromoolefin and in situ rearrangement to the lithium acetylide.

Comparison of Two Zinc Hydride Precatalysts for Selective Dehydrogenative Borylation of Terminal Alkynes: A Detailed Mechanistic Study.

The conjugated bis-guanidinate-stabilized zinc hydride complex (I)-precatalyzed chemoselective dehydroborylation of a wide array of terminal alkynes with excellent yields is reported. Further, precatalyst I is compared with a newly synthesized DiethylNacNac zinc hydride precatalyst (III) for selective dehydroborylation of terminal alkynes, and it is discovered that precatalyst I is more active than III. We have studied intra- and intermolecular chemoselective dehydroborylation of terminal alkynes over other reducible functionalities such as alkene, ester, isocyanide, nitro, and heterocycles. The highly efficient precatalyst I shows a turnover number of 48.5 and turnover frequency of up to 60.5 h-1 in the dehydroborylation of 1-ethynyl-4-fluorobenzene (1i). A plausible mechanism for selective dehydrogenative borylation of alkynes has been proposed based on active catalyst isolation and a series of stoichiometric reactions.

Photoinduced Dehydrogenative Borylation via Dihydrogen Bond Bridged Electron Donor and Acceptor Complexes.

Air-stable amine- and phosphine-boranes are discovered as donors to integrate with pyridinium acceptor for generating photoactive electron-donor-acceptor (EDA) complexes. Experimental results and DFT calculations suggest a dihydrogen bond bridging the donor and acceptor. Irradiating the EDA complex enables an intra-complex single electron transfer to give a boron-centered radical for dehydrogenative borylation with no need of external photosensitizer and radical initiator. The deprotonation of Wheland-like radical intermediate rather than its generation is believed to determine the good ortho-selectivity based on DFT calculations. A variety of α-borylated pyridine derivatives have been readily synthesized with good functional group tolerance.

Transition-Metal-Free Heterocyclic Carbon-Boron Bond Formation.

Heteroaryl boronic acids and esters are extremely important and valuable intermediates because of their wide application in the synthesis of marketed drugs and bioactive compounds. Over the last couple of decades, the construction of highly important heteroaryl carbon-boron bonds has created huge attention. The transition-metal-free protocols are more green, less sensitive to air and moisture, and also economically advantageous over the transition-metal-based protocols. The transition-metal-free C-H borylation of heteroarenes and C-X (X=halogen) borylation of heteroaryl halides represents an excellent approach for their synthesis. Also, various cyclization and alkyne activation protocols have been recently established for their synthesis. The goal of this review article is to summarize the existing literature and the current state of the art for transition-metal-free synthesis of heteroaryl boronic acid and esters.

An “On‐Demand”, Selective Dehydrogenative Borylation or Hydroboration of Terminal Alkynes Using Zn2+‐based Catalyst

AbstractAn air‐stable dicationic Zn2+ complex (1) in a tripod‐type ligand with non‐bound phosphorus base and three pyridinyl “arms” (TPPh) was synthesized. Remarkably, while 2 mol% of 1 at room temperature selectively catalyzed dehydrogenative borylation of terminal alkynes with HBPin, a lower loading of 1 (0.5 mol%) at 90 °C selectively promoted hydroboration reaction of the same alkynes skipping the dehydrogenative borylation step. The mode of action of 1 was proposed based on experimental observations as well as the mechanism of dehydrogenative borylation was studied by DFT computations.

ZnBr2-Catalyzed Dehydrogenative Borylation of Terminal Alkynes.

The simple, commercially available ZnBr2 has been successfully employed as a highly efficient and chemoselective catalyst for the dehydrogenative borylation of terminal alkynes with HBpin under mild conditions. It shows a good tolerance toward various functional groups such as aryl, alkyl, heteroaryl, etc. The plausible reaction mechanism has been investigated based on the corresponding stoichiometric experiments and DFT calculations.

Stepwise Suzuki−Miyaura Cross‐Coupling of Triborylalkenes Derived from Alkynyl−B(dan)s: Regioselective and Flexible Synthesis of Tetrasubstituted Alkenes

AbstractAlkenes with three boryl groups of differing reactivities were synthesized and subsequently cross‐coupled regioselectively with aryl halides in a stepwise manner to afford tetrasubstituted alkenes. The key triborylalkene is derived from the platinum‐catalyzed diboration of alkynyl−B(dan)s with B2(pin)2. Due to excellent regioselectivity and reaction efficiency of each step starting with alkynyl−B(dan)s, tetrasubstituted alkenes with desired carbon frameworks at desired positions can be prepared in high yields. For example, an alkene with four distinct aryl groups, p‐MeOC6H4, p‐CF3C6H4, p‐MeC6H4, and p‐NCC6H4, was obtained in 71% overall yield via six steps, starting with the dehydrogenative borylation of p‐MeC6H4C≡CH with HB(dan). Moreover, a variety of tetrasubstituted alkenes, including regio‐ and stereoisomers of the above tetraarylalkene, AIE‐active TPTPE and derivatives thereof, and (Z)‐tamoxifen, a well‐known breast cancer drug, were accessed via the developed strategy.magnified image

Rhodium-Catalyzed Deoxygenation and Borylation of Ketones: A Combined Experimental and Theoretical Investigation.

The rhodium-catalyzed deoxygenation and borylation of ketones with B2pin2 have been developed, leading to efficient formation of alkenes, vinylboronates, and vinyldiboronates. These reactions feature mild reaction conditions, a broad substrate scope, and excellent functional-group compatibility. Mechanistic studies support that the ketones initially undergo a Rh-catalyzed deoxygenation to give alkenes via boron enolate intermediates, and the subsequent Rh-catalyzed dehydrogenative borylation of alkenes leads to the formation of vinylboronates and diboration products, which is also supported by density functional theory calculations.

Catalyst Development in the Dehydrogenative Borylation of Alkenes for the Synthesis Vinylboronate Esters

AbstractCatalytic dehydrogenative borylation of alkenes provides an efficient and straightforward method for the preparation of synthetically useful vinylboronate esters. Here, we present a summary of developments and recent advances in this area, classified according to the various reactants and catalyst systems.1 Introduction2 Catalytic Dehydrogenative Borylation of Alkenes by Using Boranes3 Catalytic Dehydrogenative Borylation of Alkenes by Using Diboranes4 Zirconium-Catalyzed H 2 –Acceptorless Dehydrogenative Borylation of Alkenes with Boranes5 Conclusion and Outlook

Combined Experimental and Computational Studies of the Mechanism of Dehydrogenative Borylation of Terminal Alkynes Catalyzed by PNP Complexes of Iridium

Iridium complexes supported by four different diarylamido/bis(phosphine) PNP ligands have been studied as catalysts for the dehydrogenative borylation of terminal alkynes (DHBTA). Experimental mechanistic investigations on a representative ligand system established that the reaction rate is zeroth order in the concentration of the borylating agent HBpin, first order in [alkyne] and in [Ir], and inverse first order in [H2]. These findings are understood as arising from the formation of the saturated, 18-electron resting state (PNP)IrH3Bpin (5a), which is required to dissociate H2 in order to enter the C–H oxidative addition reaction with the alkyne. However, the overall highest transition state corresponds to the B–H rotation following C–H oxidative addition. This realization follows from the density functional theory (DFT) calculations and is consistent with the modest experimentally determined kinetic isotope effect of 1.5(1) for C–H/C–D. DFT-calculated ΔG298⧧ = 17.6 kcal/mol and ΔH⧧ = 13.9 kcal/mol match the experimentally determined values (ΔG298⧧ = 20(2) kcal/mol and ΔH⧧ = 16(2) kcal/mol) reasonably well. DFT calculations were used to demonstrate that the boryl migration from the amido N to Ir is too high in energy to play a part in the DHBTA mechanism in the (PNP)Ir system. This is in surprising contrast to the seemingly closely related (SiNN)Ir system studied previously. DFT calculations further provide insights into the greater kinetic barrier for activating a C–H bond of a terminal alkyne trans to a boryl ligand versus trans to a hydride, explaining why diboryl Ir compounds are not catalytically competent in this system.

Synthesis of Stereodefined 1,1-Diborylalkenes via Copper-Catalyzed Diboration of Terminal Alkynes.

A copper-catalyzed method for the E-selective 1,1-diboration of terminal alkynes is described. The tandem process involves sequential dehydrogenative borylation of the alkyne substrate with HBdan (1,8-diaminonaphthalatoborane), followed by hydroboration with HBpin (pinacolborane). This method proceeds efficiently under mild conditions, furnishing 1,1-diborylalkenes with excellent stereoselectivity and broad functional group tolerance. Taking advantage of the different reactivities of the two boryl moieties, the products can then be employed in stepwise cross-couplings with aryl halides for the stereocontrolled construction of trisubstituted alkenes.

Air- and Water-Tolerant (PNP)Ir Precatalyst for the Dehydrogenative Borylation of Terminal Alkynes

This work discloses the facile synthesis and efficacy of (PNP)IrH(OAc), a precatalyst for the dehydrogenative borylation of terminal alkynes (DHBTA). Unlike the previously reported precatalysts in ...

Synthesis and Rh-catalyzed reductive cyclization of 1,6-enynes and 1,6-diynes containing alkynylboronate termini

Ir-catalyzed dehydrogenative borylation of terminal alkynes (DHBTA) has been used to borylate the C(sp)-H bond in a series of 1,6-enynes and 1,6-diynes. Ir catalysts based on the diarylamido/bis(phosphine) PNP ligands proved to be capable of performing DHBTA on these substrates. The alkynylboronate products were then explored as substrates in reductive cyclization reactions designed to yield five-membered carbocycles and heterocycles with preservation of the carbon-boron bond. The reductive cyclization of enynes with H2 was carried out using cationic Rh catalysts (after the work of Krische et al.) supported by bidentate phosphine ligands, of which BINAP proved to be the generally best performing. Reductive cyclization of borylated enynes typically resulted in mixtures of isomeric products. Attempts to optimize the reductive cyclization of borylated 1,6-enynes to yield a single product were not successful; in addition, the distribution of products in these reactions was poorly reproducible. On the other hand, reductive cyclization of 1,6-diynes with the same Rh catalysts was better behaved, allowing for selectivity and reproducibility. In particular, alkynylboronate derivatives of bis(propargyl)amine underwent smooth reductive cyclization to 3,4-substituted pyrroles. The influence of substituents and conditions on the product distribution was explored and representative reactions utilizing new borylated heterocycles in Suzuki coupling reactions were carried out.