Borane-Mediated Highly Secondary Selective Deoxyfluorination of Alcohols.

Organofluorine compounds are vital across multiple sectors, hence highly selective methods to install fluorine are of considerable importance. The deoxyfluorination of alcohols is a key approach to prepare organofluorine compounds, however, a highly secondary (2°)-selective deoxyfluorination of alcohols has not been realized to date. Herein, we report that borane-mediated deoxyfluorination results in high 2°-selectivity in inter- and intra-molecular competition reactions versus primary (1°), tertiary (3°) and even benzylic (Bn) alcohols.

-Directed Two-Fold Bromoboration of Diynes Enables Access to Brominated BN-Embedded PAHs.

-directed 2-fold bromoboration reactions of diynes with BBr have been developed, allowing the access to novel internally BN-doped polycyclic aromatic hydrocarbons from readily available precursors under mild conditions. Computational investigations identified three potential reaction mechanisms, each involving either BBr or [BBr], with low activation barriers ( < 16 kcal/mol) for all pathways. The resulting brominated products can be further functionalized through various cross-coupling protocols, enabling the synthesis of highly luminescent emitters with quantum yield exceeding 90.

A Base-Free Two-Coordinate Oxoborane.

Oxoboranes (R-BO) are transient species that rapidly trimerise to form boroxines. To date, the only method used to stabilise oxoboranes is to add a Lewis base, but this forms a three-coordinate at boron oxoborane that has a different bonding/reactivity profile. Herein we report a base-free, two-coordinate oxoborane that is isolated as a Lewis adduct with AlCl.

Transition Metal-Free Catalytic C-H Zincation and Alumination.

C-H metalation is the most efficient method to prepare aryl-zinc and -aluminium complexes that are ubiquitous nucleophiles. Virtually all C-H metalation routes to form Al/Zn organometallics require stoichiometric, strong Brønsted bases with no base-catalyzed reactions reported. Herein we present a catalytic in amine/ammonium salt (EtN/[(EtN)H]) C-H metalation process to form aryl-zinc and aryl-aluminium complexes.

Borylation-Reduction-Borylation for the Formation of 1,4-Azaborines.

Given the current interest in materials containing 1,4-azaborine units, the development of new routes to these structures is important. Carbonyl directed electrophilic borylation using BBr is a facile method for the -borylation of ,-diaryl-amide derivatives. Subsequent addition of EtSiH results in carbonyl reduction and then formation of 1,4-azaborines that can be protected using a Grignard reagent.

NacNac-zinc-pyridonate mediated ε-caprolactone ROP.

Herein we report the synthesis, isolation and polymerisation activity of two new zinc compounds based on a 2,6-diisopropylphenyl (Dipp) β-diiminate (NacNac) ligand framework with zinc also ligated by an amidate (2-pyridonate or 6-methyl-2-pyridonate) unit. The compounds crystallised as either monomeric (6-Me-2-pyridonate derivative) or dimeric (2-pyridonate) species, although both were found to be monomeric in solution H DOSY NMR spectroscopy, which was supported by DFT calculations. These observations suggest that both complexes initiate ring-opening polymerisation (ROP) through a single-site monometallic mechanism.

Brominated B-Polycyclic Aromatic Hydrocarbons for the Synthesis of Deep-Red to Near-Infrared Delayed Fluorescence Emitters.

Bromo-functionalized B-polycyclic aromatic hydrocarbons (PAHs) with LUMOs of less than -3.0 eV were synthesized and used in cross-couplings to form donor-acceptor materials. These materials spanned a range of S energies, with a number showing thermally activated delayed fluorescence and significant emission in the near-infrared region of the spectrum.

Amides as modifiable directing groups in electrophilic borylation.

Amide directed C-H borylation using ≥two equiv. of BBr forms borenium cations containing a RN(R')C[double bond, length as m-dash]O→B(Ar)Br unit which has significant Lewis acidity at the carbonyl carbon. This enables reduction of the amide unit to an amine using hydrosilanes.

Haloboration of o-Alkynyl Phenols Generates Halogenated Bicyclic-Boronates.

Benzoxaborinines are intermediates en-route to bicyclic boronates that are important active pharmaceutical ingredients (APIs). Herein, the haloboration of o-alkynyl-phenols using BX (X=Cl or Br) is disclosed as a route to form C4-X-benzoxaborinines with good functional group tolerance. Computational studies indicated that there are two similar in barrier mechanisms: (i) double alkyne haloboration followed by retro-haloboration; (ii) concerted trans-haloboration involving an exogenous chloride source.

Understanding and Expanding Zinc Cation/Amine Frustrated Lewis Pair Catalyzed C-H Borylation.

[(NacNac)Zn(DMT)][B(CF)], , (NacNac = {(2,6- PrHC)N(CH)C}CH), DMT = -dimethyl-4-toluidine), was synthesized via two routes starting from either (NacNac)ZnEt or (NacNac)ZnH. Complex is an effective (pre)catalyst for the C-H borylation of (hetero)arenes using catecholborane (CatBH) with H the only byproduct. The scope included weakly activated substrates such as 2-bromothiophene and benzothiophene.

Two Directing Groups Used for Metal Catalysed -C-H Functionalisation Only Effect Electrophilic C-H Borylation.

Two templates used in -directed C-H functionalisation under metal catalysis do not direct -C-H borylation under electrophilic borylation conditions. Using BCl only Lewis adduct formation with Lewis basic sites in the template is observed. While combining BBr and the template containing an amide linker only led to amide directed C-H borylation, with no pyridyl directed borylation.

Synthesis of Electrophiles Derived from Dimeric Aminoboranes and Assessing Their Utility in the Borylation of π Nucleophiles.

Dimeric aminoboranes, [HBNR] (R = Me or CHCH) containing BN cores, can be activated by I, HNTf (NTf = [N(SOCF)]), or [PhC][B(CF)] to form isolable HB(μ-NR)BHX (for X = I or NTf). For X = [B(CF)] further reactivity, presumably between [HB(μ-NMe)BH][B(CF)] and aminoborane, forms a BN-based monocation containing a three-center two electron B-(μ-H)-B moiety. The structures of HB(μ-NMe)BH(I) and [(μ-NMe)BH(NTf)] indicated a sterically crowded environment around boron, and this leads to the less common O-bound mode of NTf binding.

Borylation Directed Borylation of Indoles Using Pyrazabole Electrophiles: A One-Pot Route to C7-Borylated-Indolines.

Pyrazabole (1) is a readily accessible diboron compound that can be transformed into ditopic electrophiles. In 1 (and derivatives), the B⋅⋅⋅B separation is ca. 3 Å, appropriate for one boron centre bonding to N and one to the C7 of indoles and indolines.

Developing organoboranes as phase transfer catalysts for nucleophilic fluorination using CsF.

Despite the general high fluorophilicity of boron, organoboranes such as BEt and 3,5-(CF)CH-BPin are shown herein for the first time, to our knowledge, to be effective (solid to solution) phase-transfer catalysts for the fluorination of certain organohalides with CsF. Significant (up to 30% e.e.

Enhanced N-directed electrophilic C-H borylation generates BN-[5]- and [6]helicenes with improved photophysical properties.

Helicenes are chiral polycyclic aromatic hydrocarbons (PAHs) of significant interest, in supramolecular chemistry, materials science and asymmetric catalysis. Herein an enhanced N-directed electrophilic C-H borylation methodology has been developed that provides access to azaborine containing helicenes (BN-helicenes). This borylation process proceeds protonation of an aminoborane with bistriflimidic acid.

Formation of a hydride containing amido-zincate using pinacolborane.

Amido-zincates containing hydrides are underexplored yet potentially useful complexes. Attempts to access this type of zincate through combining amido-organo zincates and pinacolborane (HBPin) Zn-C/H-BPin exchange led instead to preferential formation of amide-BPin and/or [amide-BPin(Y)] (Y = Ph, amide, H), when the amide is hexamethyldisilazide or 2,2,6,6-tetramethylpiperidide and the hydrocarbyl group was phenyl or ethyl. In contrast, the use of a dipyridylamide (dpa) based arylzinc complex led to Zn-C/H-BPin metathesis being the major outcome.

Zinc catalysed electrophilic C-H borylation of heteroarenes.

Cationic zinc Lewis acids catalyse the C-H borylation of heteroarenes using pinacol borane (HBPin) or catechol borane (HBCat). An electrophile derived from [IDippZnEt][B(CF)] (IDipp = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) combined with ,-dimethyl--toluidine (DMT) proved the most active in terms of C-H borylation scope and yield. Using this combination weakly activated heteroarenes, such as thiophene, were amenable to catalytic C-H borylation using HBCat.

Haloboration: scope, mechanism and utility.

Haloboration, the addition of B-X (X = Cl, Br, I) across an unsaturated moiety , C[double bond, length as m-dash]Y or C[triple bond, length as m-dash]Y (Y = C, N, ), is dramatically less utilised than the ubiquitous hydroboration reaction. However, haloboration of alkynes in particular is a useful tool to access ambiphilic 1,2-disubstituted alkenes. The stereochemical outcome of the reaction is easily controlled and the resulting products have proven to be valuable building blocks in organic synthesis and materials chemistry.

Acyl-Directed ortho-Borylation of Anilines and C7 Borylation of Indoles using just BBr.

Indoles are privileged heterocycles found in many biologically active pharmaceuticals and natural products. However, the selective functionalization of the benzenoid moiety in indoles in preference to the more reactive pyrrolic unit is a significant challenge. Herein we report that N-acyl directing groups enable the C7-selective C-H borylation of indoles using just BBr .

Borylative cyclisation of diynes using BCl and borocations.

The borylative cyclisation of 1,2-dialkynyl benzenes with BCl3 leads to dibenzopentalenes (via intramolecular SEAr) or benzofulvenes (via chloride addition) depending on substituents, with stabilised vinyl cation intermediates (e.g. with a p-MeO-C6H4-group) favouring the latter.

Reductive α-borylation of α,β-unsaturated esters using NHC-BH activated by I as a metal-free route to α-boryl esters.

Useful α-boryl esters can be synthesized in one step from α,β-unsaturated esters using just a simple to access NHC-BH (NHC = N-heterocyclic carbene) and catalytic I. The scope of this reductive α-borylation methodology is excellent and includes a range of alkyl, aryl substituted and cyclic and acyclic α,β-unsaturated esters. Mechanistic studies involving reductive borylation of a cyclic α,β-unsaturated ester with NHC-BD/I indicated that concerted hydroboration of the alkene moiety in the α,β-unsaturated ester proceeds instead of a stepwise process involving initial 1,4-hydroboration; this is in contrast to the recently reported reductive α-silylation.

Selective Boryl-Anion Migration in a Vinyl sp -sp Diborane Induced by Soft Borane Lewis Acids.

An intramolecular 1,2-boryl-anion migration from boron to carbon has been achieved by selective activation of the π system in [(vinyl)B Pin )] using "soft" BR electrophiles (BR =BPh or 9-aryl-BBN). The soft character is key to ensure 1,2-migration proceeds instead of oxygen coordination/B-O activation. The BR -induced 1,2-boryl-anion migration represents a triple borylation of a vinyl Grignard reagent using only B Pin and BR and forms differentially protected 1,1,2-triborylated alkanes.