Direct Borylation Research Articles

ChemInform Abstract: Functional Group Directed C—H Borylation

AbstractReview: 51 refs.

Direct Borylation of Arenes Catalyzed by Ir(I)-bpy-PMO

Correction to: Direct Borylation of Arenes Catalyzed by Ir(I)-bpy-PMO Synfacts 2014; 10(06): 0651-0651DOI: 10.1055/s-0033-1339092

Direct Borylation of Arenes Catalyzed by Ir(I)-bpy-PMO

Direct Borylation of Arenes Catalyzed by Ir(I)-bpy-PMO

Facile Synthesis of Nitrogen-containing Polycyclic Aromatic Hydrocarbons from Perylene Bisimides

Abstract We have developed a facile procedure for the synthesis of π-extended fluorubins from perylene bisimides. Iridium-catalyzed direct borylation, the Suzuki–Miyaura cross-coupling, and an acid-condensation sequence afforded π-extended fluorubins 1 in moderate yields. X-ray diffraction analysis revealed a planar structure of 1. In addition, optical analysis and DFT calculations indicated the presence of intramolecular charge-transfer interactions in 1c.

Direct Borylation of Primary CH Bonds in Functionalized Molecules by Palladium Catalysis

Organoborane compounds are among the most commonly employed intermediates in organic synthesis and serve as crucial precursors to alcohols, amines, and various functionalized molecules. A simple palladium-based system catalyzes the conversion of primary C(sp(3) )H bonds in functionalized complex organic molecules into alkyl boronate esters. Amino acids, amino alcohols, alkyl amines, and a series of bioactive molecules can be functionalized with the use of readily available and removable directing groups in the presence of commercially available additives, simple ligands, and oxygen (O2 ) as the terminal oxidant. This approach represents an economic and environmentally friendly method that could find broad applications.

Direct Borylation of Primary CH Bonds in Functionalized Molecules by Palladium Catalysis

AbstractOrganoborane compounds are among the most commonly employed intermediates in organic synthesis and serve as crucial precursors to alcohols, amines, and various functionalized molecules. A simple palladium‐based system catalyzes the conversion of primary C(sp3)H bonds in functionalized complex organic molecules into alkyl boronate esters. Amino acids, amino alcohols, alkyl amines, and a series of bioactive molecules can be functionalized with the use of readily available and removable directing groups in the presence of commercially available additives, simple ligands, and oxygen (O2) as the terminal oxidant. This approach represents an economic and environmentally friendly method that could find broad applications.

Catalytic Generation of Borenium Ions by Cooperative B–H Bond Activation: The Elusive Direct Electrophilic Borylation of Nitrogen Heterocycles with Pinacolborane

The B-H bond of typical boranes is heterolytically split by the polar Ru-S bond of a tethered ruthenium(II) thiolate complex, affording a ruthenium(II) hydride and borenium ions with a dative interaction with the sulfur atom. These stable adducts were spectroscopically characterized, and in one case, the B-H bond activation step was crystallographically verified, a snapshot of the σ-bond metathesis. The borenium ions derived from 9-borabicyclo[3.3.1]nonane dimer [(9-BBN)2], pinacolborane (pinBH), and catecholborane (catBH) allowed for electrophilic aromatic substitution of indoles. The unprecedented electrophilic borylation with the pinB cation was further elaborated for various nitrogen heterocycles.

Haloboration of internal alkynes with boronium and borenium cations as a route to tetrasubstituted alkenes.

Hail boration! 2-Dimethylaminopyridine-ligated dihaloborocations [X2B(2-DMAP)](+) with a strained four-membered boracycle were used for the haloboration of terminal and dialkyl internal alkynes (see scheme). Esterification then provided vinyl boronate esters as useful precursors to tetrasubstituted alkenes. Following mechanistic studies, the scope of the haloboration was expanded simply by variation of the amine. Pin = 2,3-dimethyl-2,3-butanedioxy.

5,10-Diborylated naphtho[1,2-c:5,6-c′]bis[1,2,5]thiadiazole: a ready-to-use precursor for the synthesis of high-performance semiconducting polymers

5,10-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)naphtho[1,2-c:5,6-c′]bis[1,2,5]thiadiazole was successfully developed by the direct borylation reaction on the parent heterocycle and was utilized for the synthesis of naphtho[1,2-c:5,6-c′]bis[1,2,5]thiadiazole-based donor–acceptor copolymers.

Mechanistic Studies into Amine-Mediated Electrophilic Arene Borylation and Its Application in MIDA Boronate Synthesis

Direct electrophilic borylation using Y(2)BCl (Y(2) = Cl(2) or o-catecholato) with equimolar AlCl(3) and a tertiary amine has been applied to a wide range of arenes and heteroarenes. In situ functionalization of the ArBCl(2) products is possible with TMS(2)MIDA, to afford bench-stable and easily isolable MIDA-boronates in moderate to good yields. According to a combined experimental and computational study, the borylation of activated arenes at 20 °C proceeds through an S(E)Ar mechanism with borenium cations, [Y(2)B(amine)](+), the key electrophiles. For catecholato-borocations, two amine dependent reaction pathways were identified: (i) With [CatB(NEt(3))](+), an additional base is necessary to accomplish rapid borylation by deprotonation of the borylated arenium cation (σ complex), which otherwise would rather decompose to the starting materials than liberate the free amine to effect deprotonation. Apart from amines, the additional base may also be the arene itself when it is sufficiently basic (e.g., N-Me-indole). (ii) When the amine component of the borocation is less nucleophilic (e.g., 2,6-lutidine), no additional base is required due to more facile amine dissociation from the boron center in the borylated arenium cation intermediate. Borenium cations do not borylate poorly activated arenes (e.g., toluene) even at high temperatures; instead, the key electrophile in this case involves the product from interaction of AlCl(3) with Y(2)BCl. When an extremely bulky amine is used, borylation again does not proceed via a borenium cation; instead, a number of mechanisms are feasible including via a boron electrophile generated by coordination of AlCl(3) to Y(2)BCl, or by initial (heteroarene)AlCl(3) adduct formation followed by deprotonation and transmetalation.

Functionalization of Hexa‐peri‐hexabenzocoronenes: Investigation of the Substituent Effects on a Superbenzene

We have demonstrated that the iridium-catalyzed direct borylation of hexa-peri-hexabenzocoronene (HBC) enables regioselective introduction of boryl groups to the para-, ortho-, and meta-substituted HBCs in high yields. The boryl groups have been transformed into various functionalities such as hydroxy, cyano, ethynyl, and amino groups. We have elucidated that the substituents significantly influence the photophysical properties of HBCs to enhance fluorescence quantum yields. DFT calculations revealed that the origin of the substituent effect is the lift in degeneracy in the frontier orbitals by an interaction with electron-donating and electron-withdrawing substituents at the para- and ortho-positions. The change in molecular orbitals results in an increase of the transition probability from the S(0)→S(1) states. In addition, the two-photon absorption cross-section values of para-substituted HBCs are significantly larger than those of ortho- and meta-substituted HBCs.

Borylation on Benzo[1,2-b:4,5-b′]- and Naphtho[1,2-b:5,6-b′]dichalcogenophenes: Different Chalcogene Atom Effects on Borylation Reaction Depending on Fused Ring Structure

The direct borylation reactions of two types of α-silyl-protected acenedichalcogenophenes, i.e., benzo[1,2-b:4,5-b']- and naphtho[1,2-b:5,6-b']dichalcogenophenes, were examined, and it was observed that the reaction efficiency largely depends on the fused ring structure and chalcogenophene ring.

Orthogonally Functionalized Naphthodithiophenes: Selective Protection and Borylation

Selective functionalization protocols of naphtho[1,2-b;5,6-b']dithiophene (NDT3) by combining protection of the thiophene α-positions and direct borylation on the naphthalene core are described, which allows synthesizing a number of new NDT3-based building blocks with various substituents and isomeric NDT3-based polymers with different main chain structures. The same protocol is applicable to other isomeric naphthodithiophenes (NDTs), which affords a set of key building blocks for the development of elaborated functional π-materials.

Ir-Catalyzed Direct Borylation at the 4-Position of Pyrene

The first direct borylation of a C-H bond at the 4-position of pyrene was achieved using [Ir(COD)Cl](2)/dtbpy as the catalyst precursor and B(2)pin(2) as the boron source. The position-related photophysical properties of pyrene derivatives are reported.

A Perspective on Direct Electrophilic Arene Borylation

Direct electrophilic arene borylation is introduced as a new synthetic approach to aryl boronate esters. This perspective covers both the key historic breakthroughs and the more recent developments in this area.

Synthesis of Oxygen-Substituted Hexa-peri-hexabenzocoronenes through Ir-Catalyzed Direct Borylation

Direct C-H borylation of hexa-peri-hexabenzocoronenes (HBCs) has been achieved under iridium catalysis, which allows efficient synthesis of hydroxy-substituted HBCs by oxidation of the boryl groups. Further oxidation of dihydroxy HBC with phenyliodine bis(trifluoroacetate) (PIFA) afforded tetraoxo-substituted HBC without any regioisomers, which can be considered as a π-extended quinone.

ChemInform Abstract: Recent Progress in the Preparation of Organoboron Reagents via Direct Borylations

AbstractReview: ca. 50 refs.

ChemInform Abstract: Simple Inexpensive Boron Electrophiles for Direct Arene Borylation.

AbstractThe regioselective title synthesis can be used for large‐scale production.

Iridium-catalyzed direct borylation of phenacenes

Iridium-catalyzed borylation of phenacenes with bis(pinacolato)diboron proceeds either in an edge-selective manner for diborylation or an edge/side-selective manner for tetraborylation. Multiply borylated [n]phenacenes (n=3–5) were synthesized in reasonable yields.

Synthesis, Structure, and Reactivity of Hydridoiridium Complexes Bearing a Pincer‐Type PSiP Ligand

A series of iridium tetrahydride complexes [Ir(H)(4)(PSiP-R)] bearing a tridentate pincer-type bis(phosphino)silyl ligand ([{2-(R(2)P)C(6)H(4)}(2)MeSi](-), PSiP-R, R=Cy, iPr, or tBu) were synthesized by the reduction of [IrCl(H)(PSiP-R)] with Me(4)N·BH(4) under argon. The same reaction under a nitrogen atmosphere afforded a rare example of thermally stable iridium(III)-dinitrogen complexes, [Ir(H)(2)(N(2))(PSiP-R)]. Two isomeric dinitrogen complexes were produced, in which the PSiP ligand coordinated to the iridium center in meridional and facial orientations, respectively. Attempted substitution of the dinitrogen ligand in [Ir(H)(2)(N(2))(PSiP-Cy)] with PMe(3) required heating at 150 °C to give the expected [Ir(H)(2)(PMe(3))(PSiP-Cy)] and a trigonal bipyramidal iridium(I)-dinitrogen complex, [Ir(N(2))(PMe(3))(PSiP-Cy)]. The reaction of [Ir(H)(4)(PSiP-Cy)] with three equivalents of 2-norbornene (nbe) in benzene afforded [Ir(I)(nbe)(PSiP-Cy)] in a high yield, while a similar reaction of [Ir(H)(4)(PSiP-R)] with an excess of 3,3-dimethylbutene (tbe) in benzene gave the C-H bond activation product, [Ir(III)(H)(Ph)(PSiP-R)], in high yield. The oxidative addition of benzene is reversible; heating [Ir(III)(H)(Ph)(PSiP-Cy)] in the presence of PPh(3) in benzene resulted in reductive elimination of benzene, coordination of PPh(3), and activation of the C-H bond of one aromatic ring in PPh(3). [Ir(III)(H)(Ph)(PSiP-R)] catalyzed a direct borylation reaction of the benzene C-H bond with bis(pinacolato)diboron. Molecular structures of most of the new complexes in this study were determined by a single-crystal X-ray analysis.