Potassium Trifluoroborate Research Articles

Synthesis of 3-Methyleneisoindolin-1-ones via Rhodium(III)-Catalyzed C-H/N-H Activation and Annulation of N-Methoxybenzamides with Potassium Vinyltrifluoroborate.

Isoindolinones are vital heterocyclic compounds in medicinal chemistry, notable for their diverse bioactivities. Significant attention has been devoted to their preparation; however, existing methods are unsuitable for constructing unsubstituted 3-methyleneisoindolin-1-ones. Herein, we present a rhodium(III)-catalyzed method for synthesizing unsubstituted 3-methyleneisoindolin-1-ones via C-H/N-H activation and annulation of N-methoxybenzamides with potassium (ethenyl)trifluoroborate. This approach offers mild reaction conditions, high regioselectivity, and efficient yields. Interestingly, sterically demanding or heterocyclic N-methoxyaromaticamides resulted in the formation of 2-vinyl(hetero)aromatic amides instead of 3-methyleneisoindolin-1-ones. Mechanistic insights suggest a rhodacycle intermediate pathway, highlighting the method's potential for developing new bioactive isoindolinone derivatives.

Electrochemical Generation of Aryl Radicals from Organoboron Reagents Enabled by Pulsed Electrosynthesis

AbstractAryl radicals play a pivotal role as reactive intermediates in chemical synthesis, commonly arising from aryl halides and aryl diazo compounds. Expanding the repertoire of sources for aryl radical generation to include abundant and stable organoboron reagents would significantly advance radical chemistry and broaden their reactivity profile. While traditional approaches utilize stoichiometric oxidants or photocatalysis to generate aryl radicals from these reagents, electrochemical conditions have been largely underexplored. Through rigorous mechanistic investigations, we identified fundamental challenges hindering aryl radical generation. In addition to the high oxidation potentials of aromatic organoboron compounds, electrode passivation through radical grafting, homocoupling of aryl radicals, and decomposition issues were identified. We demonstrate that pulsed electrosynthesis enables selective and efficient aryl radical generation by mitigating the fundamental challenges. Our discoveries facilitated the development of the first electrochemical conversion of aryl potassium trifluoroborate salts into aryl C−P bonds. This sustainable and straightforward oxidative electrochemical approach exhibited a broad substrate scope, accommodating various heterocycles and aryl chlorides, typical substrates in transition‐metal catalyzed cross‐coupling reactions. Furthermore, we extended this methodology to form aryl C−Se, C−Te, and C−S bonds, showcasing its versatility and potential in bond formation processes.

Electrochemical Generation of Aryl Radicals from Organoboron Reagents Enabled by Pulsed Electrosynthesis.

Aryl radicals play a pivotal role as reactive intermediates in chemical synthesis, commonly arising from aryl halides and aryl diazo compounds. Expanding the repertoire of sources for aryl radical generation to include abundant and stable organoboron reagents would significantly advance radical chemistry and broaden their reactivity profile. While traditional approaches utilize stoichiometric oxidants or photocatalysis to generate aryl radicals from these reagents, electrochemical conditions have been largely underexplored. Through rigorous mechanistic investigations, we identified fundamental challenges hindering aryl radical generation. In addition to the high oxidation potentials of aromatic organoboron compounds, electrode passivation through radical grafting, homocoupling of aryl radicals, and decomposition issues were identified. We demonstrate that pulsed electrosynthesis enables selective and efficient aryl radical generation by mitigating the fundamental challenges. Our discoveries facilitated the development of the first electrochemical conversion of aryl potassium trifluoroborate salts into aryl C-P bonds. This sustainable and straightforward oxidative electrochemical approach exhibited a broad substrate scope, accommodating various heterocycles and aryl chlorides, typical substrates in transition-metal catalyzed cross-coupling reactions. Furthermore, we extended this methodology to form aryl C-Se, C-Te, and C-S bonds, showcasing its versatility and potential in bond formation processes.

Photoredox-Catalyzed Radical-Radical Coupling of Potassium Trifluoroborates with Acyl Azoliums.

Potassium trifluoroborates have gained significant utility as coupling partners in organic synthesis, particularly in the Suzuki-Miyaura coupling reaction. Recently, they have also been used as radical precursors under oxidative conditions to generate carbon-centered radicals. These versatile reagents have found new applications in photoredox catalysis, including radical substitution, conjugate addition reactions, and transition metal dual catalysis. In addition, this photomediated redox neutral process has enabled radical-radical coupling with persistent radicals in the absence of a metal, and this process remains to be fully explored. In this study, we report the radical-radical coupling of benzylic potassium trifluoroborate salts with isolated acyl azolium triflates, which are persistent radical precursors. The reaction is catalyzed by an organic photocatalyst and forms isolable tertiary alcohol species. These compounds can be transformed into a range of substituted ketone products by simple treatment with a mild base.

Convergent Deboronative and Decarboxylative Phosphonylation Enabled by the Phosphite Radical Trap "BecaP".

Carbon-phosphorus bond formation is significant in synthetic chemistry because phosphorus-containing compounds offer numerous indispensable biochemical roles. While there is a plethora of methods to access organophosphorus compounds, phosphonylations of readily accessible alkyl radicals to form aliphatic phosphonates are rare and not commonly used in synthesis. Herein, we introduce a novel phosphorus radical trap "BecaP" that enables facile and efficient phosphonylation of alkyl radicals under visible light photocatalytic conditions. Importantly, the ambiphilic nature of BecaP allows redox neutral reactions with both nucleophilic (activated by single-electron oxidation) and electrophilic (activated by single-electron reduction) alkyl radical precursors. Thus, a broad scope of feedstock alkyl potassium trifluoroborate salts and redox active carboxylate esters could be employed, with each class of substrate proceeding through a distinct mechanistic pathway. The mild conditions are applicable to the late-stage installation of phosphonate motifs into medicinal agents and natural products, which is showcased by the straightforward conversion of baclofen (muscle relaxant) to phaclofen (GABAB antagonist).

Regioselective Iridium-Catalyzed C8-H Borylation of 4-Quinolones via Transient O-Borylated Quinolines.

The quinolone-quinoline tautomerization is harnessed to effect the regioselective C8-borylation of biologically important 4-quinolones by using [Ir(OMe)(cod)]2 as the catalyst precursor, the silica-supported monodentate phosphine Si-SMAP as the ligand, and B2 pin2 as the boron source. Initially, O-borylation of the quinoline tautomer takes place. Critically, the newly formed 4-(pinBO)-quinolines then undergo N-directed selective Ir-catalyzed borylation at C8. Hydrolysis of the OBpin moiety on workup returns the system to the quinolone tautomer. The C8-borylated quinolines were converted to their corresponding potassium trifluoroborate (BF3 K) salts and to their C8-chlorinated quinolone derivatives. The two-step C-H borylation-chlorination reaction sequence resulted in various C8-Cl quinolones in good yields. Conversion to C8-OH-, C8-NH2 -, and C8-Ar-substituted quinolones was also feasible by using this methodology.

Ferrocenium Boronic Acid Catalyzed Deoxygenative Coupling of Alcohols with Carbon- and Nitrogen-Based Borate and Silane Nucleophiles.

A boronic acid catalyzed carbon-carbon and carbon-nitrogen bond-forming reaction for the functionalization of various π-activated alcohols has been developed. Ferrocenium boronic acid hexafluoroantimonate salt was identified as an effective catalyst in the direct deoxygenative coupling of alcohols with a variety of potassium trifluoroborate and organosilane nucleophiles. In a comparison between these two classes of nucleophiles, the use of organosilanes leads to higher reaction yields, increased diversity of the alcohol substrate scope, and high E/Z selectivity. Furthermore, the reaction proceeds under mild conditions and yields up to 98%. Computational studies provide a rationalization for a mechanistic pathway for the retention of E/Z stereochemistry when E or Z alkenyl silanes are used as nucleophiles. This methodology is complementary to existing methodologies for deoxygenative coupling reactions involving organosilanes, and it is effective with a variety of organosilane nucleophile sub-types, including allylic, vinylic, and propargylic trimethylsilanes.

BF2‐Chelates of N‐Acylhydrazones as Versatile Coupling Partners in Photoredox Promoted Reactions

AbstractFive‐membered difluoroboryl chelate complexes are competent substrates for radical reactions with various radical precursors including potassium trifluoroborates, bis(catecholato)siliconates, 4‐alkyl‐substituted Hantzsch esters, dihydroquinazolinones, esters of N‐hydroxyphthalimide, Katritzky salts, alkyl iodides and thiols. Using these reagents, primary, secondary, and tertiary radicals can be generated under oxidative or reductive conditions and add at the C=N bond of the difluoroboryl chelates leading to hydrazide products.

Defect passivation with potassium trifluoroborate for efficient spray-coated perovskite solar cells in air

Defects as non-radiative recombination centers hinder the further efficiency improvements of perovskite solar cells (PSCs). Additive engineering has been demonstrated to be an effective method for defect passivation in perovskite films. Here, we employed (4-methoxyphenyl) potassium trifluoroborate (C7H7BF3KO) with and K+ functional groups to passivate spray-coated (FAPbI3) x (MAPbBr3)1–x perovskite and eliminate hysteresis. It is shown that the F of can form hydrogen bonds with the H atom in the amino group of MA+/FA+ ions of perovskite, thus reducing the generation of MA+/FA+ vacancies and improving device efficiency. Meanwhile, K+ and reduced MA+/FA+ vacancies can inhibit ion migration, thereby eliminating hysteresis. With the aid of C7H7BF3KO, we obtained hysteresis-free PSCs with the maximum efficiency of 19.5% by spray-coating in air. Our work demonstrates that additive engineering is promising to improve the performance of spray-coated PSCs.

Expedient Synthesis of Oxaboracyclic Compounds Based on Naphthalene and Biphenyl Backbone and Phase-Dependent Luminescence of their Chelate Complexes.

The approach to a series of six- and seven-membered oxaboraheterocycles based on naphthalene or biphenyl backbones was developed. The key synthetic step involved Br/Li exchange in respective potassium (bromoaryl)trifluoroborates followed by quenching with selected electrophiles (CO2 , DMF, Me2 Si(H)Cl) and hydrolytic workup. Two ring-expanded benzoxaborole congeners were obtained by an additional reduction step with LiAlH4 or NaBH4 . The obtained boracyclic compounds were characterized in detail by NMR spectroscopy and single-crystal X-ray diffraction. Specifically, biphenyl-based systems show dynamic behaviour interpreted in terms of inversion of non-planar seven-membered boraheterocycles. The acidity of the obtained compounds varies very strongly (pKa ranges from 3.1-9.6) depending on their structure. Due to the enhanced boron Lewis acidity, selected compounds were used as a basis for luminescent complexes with 8-hydroxyquinoline. A strong phase-dependent variation of emission-band maximum (480-527 nm) and photoluminescence quantum yield (10-95 %) was observed, which was rationalized in terms of specific aggregation effects.

Ethyl-, vinyl- and ethynylcyanoborates: room temperature borate ionic liquids with saturated and unsaturated hydrocarbon chains.

Ethyl-, vinyl- and ethynyltricyano and dicyanofluoroborates were prepared on a gram scale from commercially available potassium trifluoroborates and trimethylsilylcyanide. Salt metathesis resulted in the corresponding EMIm-salts that are hydrophobic room-temperature ionic liquids (RTILs). The new RTILs exhibit unprecedented large electrochemical windows in combination with high thermal stabilities, low dynamic viscosities and high specific conductivities. These properties make them promising materials, especially for electrochemical applications.

Combined Photoredox and Carbene Catalysis for the Synthesis of γ-Aryloxy Ketones.

N-heterocyclic carbenes (NHCs) have emerged as catalysts for the construction of C-C bonds in the synthesis of substituted ketones under single-electron processes. Despite these recent reports, there still remains a need to increase the utility and practicality of these reactions by exploring new radical coupling partners. Herein, we report the synthesis of γ-aryloxyketones via combined NHC/photoredox catalysis. In this reaction, an α-aryloxymethyl radical is generated via oxidation of an aryloxymethyl potassium trifluoroborate salt, which is then added into styrene derivatives to provide a stabilized benzylic radical. Subsequent radical-radical coupling reaction with an azolium radical affords the γ-aryloxy ketone products.

Generation of Functionalized Alkyl Radicals via the Direct Photoexcitation of 2,2'-(Pyridine-2,6-diyl)diphenol-Based Borates.

A new type of alkylborate was developed for the purpose of generating radicals via direct photoexcitation. These borates were prepared using 2,2'-(pyridine-2,6-diyl)diphenol as a tridentate ligand together with organoboronic acids or potassium trifluoroborates. The ready availability of organoboron compounds is a significant advantage of this direct photoexcitation protocol. The excited states of these borates can also serve as strong reductants, enabling various transformations.

Gem‐Difluorocyclopropanation of Alkenyl Trifluoroborates with the CF3SiMe3–NaI System

Difluorocyclopropanation of alkenyl trifluoroborates using TMSCF3–NaI system was reported for the first time. The developed method allowed preparation of monocyclic, spiro‐ and fused‐bicyclic gem‐difluorocyclopropanes bearing additional functional groups. The preparation of potassium (2,2‐difluorocyclopropyl)trifluoroborates was achieved in up to 90 % yield on a multigram scale.

Regio‐ and Stereoselective Synthesis of Enynyl Boronates via Ruthenium‐Catalyzed Hydroboration of 1,4‐Diaryl‐Substituted 1,3‐Diynes

AbstractA facile ruthenium‐catalyzed regio‐ and stereoselective hydroboration of symmetrical, aromatic 1,3‐diynes with pinacolborane towards 2‐boryl‐1,4‐diaryl‐buta‐1‐en‐3‐ynes and their further transformation into potassium trifluoroborate salts is presented. The reaction proceeded efficiently for 1,4‐diphenylbutadiynes with various substituents on the phenyl rings and heterocyclic 1,4‐di(thiophen‐3‐yl)buta‐1,3‐diyne. The resulting products were isolated and fully characterized (1H, 13C, 11B and 1D NOESY NMR, IR, GC‐MS, HRMS or elemental analysis). Moreover, the crystal structure of an enynyl boronate was determined, proving the addition of boryl moiety at the internal carbon in the diyne, according to the anti‐Markovnikov rule. The results presented here are the first examples of selective catalytic monohydroboration of conjugated diynes. The products obtained due to the presence of the boryl group and the unsaturated bonds are potential synthons in the synthesis of natural compounds or active pharmaceutical ingredients (API). The model Suzuki coupling of 2‐boryl‐1,4‐diphenyl‐buta‐1‐en‐3‐ynes with iodobenzene was carried out to illustrate the utility of the resulting compounds.magnified image

Enantioselective synthesis of α-amino esters through Petasis borono-Mannich multicomponent reaction of potassium trifluoroborate salts

Enantioselective synthesis of α-amino esters have been achieved through the Petasis borono-Mannich multicomponent reaction using ( R)-BINOL-derived catalysts with stable heteroaryl and alkenyl trifluoroborate salts under mild conditions. The reaction provides direct access to optically active α-amino esters with moderate to good yields and enantioselectivities.

Characterization of potassium (2-phenylacetyl) trifluoroborate salt by using the UV–Visible, FT-IR and FT-Raman spectra

The potassium 2-phenylacetyl-trifluoroborate (PTFB) salt has been experimentally characterized by using FT-IR, FT-Raman and ultraviolet–visible spectroscopies while its structures were theoretically determined in gas phase and in aqueous solution by using B3LYP/6–311++G** method. The studies in solution were performed at the same level of theory with the integral equation formalism variant polarised continuum method (IEFPCM) and the universal solvation model. The comparisons among the predicted IR, Raman and UV–Visible spectra have evidenced good concordance with the corresponding experimental ones. PTFB presents a solvation energy of −87.64 kJ/mol, a value lower than the observed for 5-hydroxypentanoyl-trifluoroborate (HTFB) (−103.73 kJ/mol) and 2-isonicotinoyl-trifluoroborate (ITFB) (−95.05 kJ/mol) and higher than 3-furoyl-trifluoroborate (FTFB) (−84.72 kJ/mol). Evidently, the phenyl ring in PTFB decreases the solubility of this salt, as compared with hydroxypentanoyl chain in HTFB, furoyl ring in FTFB and pyridine ring in IFTB. The bond orders studies support the ionic characteristics of K⋯B bonds while the NBO studies reveal a lower stability of PTFB in aqueous solution, as compared with the value in gas phase probably due to the low solvation energy of PTFB in this medium. The four interactions observed for PTFB in gas phase by the AIM analyses support the high stability of PTFB in gas phase. The gap values show that PTFB is most reactive in gas phase than in aqueous solution while the comparisons with other salts containing pyridine ring instead phenyl one reveal that reactivity increase when in the 5 position of pyridine ring is incorporates a Br atom in the structure of salt. Hence, the following reactivity order it is observed in gas phase: Br-ITFB > ITFB > PTFB changing in solution to: ITFB > Br-ITFB > PTFB. In solution, probably the salt is most reactive due to the most negative nucleophilicity index and higher electrophilicity index. The harmonic force fields, force constants and complete assignments of all vibration normal modes for PTFB in both media for first time are reported.

Remarkable Reactivity of Boron-Substituted Furans in the Diels-Alder Reactions with Maleic Anhydride.

The reactivity of boron-substituted furans as dienes in the Diels-Alder reaction with maleic anhydride has been investigated. Gratifyingly, the furans with boryl substituents at C-3 gave the exo cycloadduct exclusively with excellent yields. In particular, the potassium trifluoroborate exhibited outstanding reactivity at room temperature. Theoretical calculations suggested that the trifluoroborate group is highly activating and also that the thermodynamics is the main factor that determines whether the products can be obtained efficiently or not.

Iron (III)‐Promoted Synthesis of Substituted 4H‐Chalcogenochromenes and Chemoselective Functionalization

AbstractThe iron(III)‐promoted synthesis of densely‐substituted 4H‐chalcogenchromene from organochalcogen propargylamines in the presence of diaryl dichalcogenides is reported. Subsequent C2‐functionalization with electrophiles and potassium trifluoroborate salts via Suzuki‐Miyaura coupling reaction are also presented. A plausible mechanism based on HRMS experiments is proposed and discussed.magnified image

Oxidative C[sbnd]H alkynylation of 3,6-dihydro-2H-pyrans

Current synthesis of α-substituted 3,6-dihydro-2H-pyrans dominantly relies on functional group transformation. Herein, a direct and practical oxidative CH alkynylation and alkenylation of 3,6-dihydro-2H-pyran skeletons with a range of potassium trifluoroborates is developed. The metal-free process is well tolerated with a wide variety of 3,6-dihydro-2H-pyrans, rapidly providing a library of 2,4-disubstituted 3,6-dihydro-2H-pyrans with diverse patterns of α-functionalities for further diversification and bioactive small molecule identification.