Alkyl Boron Research Articles

Theoretical Study on the Mechanism of Ni‐Catalyzed Alkyl–Alkyl Suzuki Cross‐Coupling

Ni-catalyzed cross-coupling of unactivated secondary alkyl halides with alkylboranes provides an efficient way to construct alkyl-alkyl bonds. The mechanism of this reaction with the Ni/L1 (L1=trans-N,N'-dimethyl-1,2-cyclohexanediamine) system was examined for the first time by using theoretical calculations. The feasible mechanism was found to involve a Ni(I)-Ni(III) catalytic cycle with three main steps: transmetalation of [Ni(I)(L1)X] (X=Cl, Br) with 9-borabicyclo[3.3.1]nonane (9-BBN)R(1) to produce [Ni(I)(L1)(R(1))], oxidative addition of R(2) X with [Ni(I)(L1)(R(1))] to produce [Ni(III)(L1)(R(1))(R(2))X] through a radical pathway, and C-C reductive elimination to generate the product and [Ni(I)(L1)X]. The transmetalation step is rate-determining for both primary and secondary alkyl bromides. KOiBu decreases the activation barrier of the transmetalation step by forming a potassium alkyl boronate salt with alkyl borane. Tertiary alkyl halides are not reactive because the activation barrier of reductive elimination is too high (+34.7 kcal mol(-1)). On the other hand, the cross-coupling of alkyl chlorides can be catalyzed by Ni/L2 (L2=trans-N,N'-dimethyl-1,2-diphenylethane-1,2-diamine) because the activation barrier of transmetalation with L2 is lower than that with L1. Importantly, the Ni(0)-Ni(II) catalytic cycle is not favored in the present systems because reductive elimination from both singlet and triplet [Ni(II)(L1)(R(1))(R(2))] is very difficult.

Reaction of Grignard Reagents with Diisopropylaminoborane. Synthesis of Alkyl, Aryl, Heteroaryl and Allyl Boronic Acids from Organoc(diisopropyl)aminoborane by a Simple Hydrolysis

Reaction of Grignard Reagents with Diisopropylaminoborane. Synthesis of Alkyl, Aryl, Heteroaryl and Allyl Boronic Acids from Organoc(diisopropyl)aminoborane by a Simple Hydrolysis

Structure-Guided Design of Cell Wall Biosynthesis Inhibitors That Overcome β-Lactam Resistance in Staphylococcus aureus (MRSA)

β-Lactam antibiotics have long been a treatment of choice for bacterial infections since they bind irreversibly to Penicillin-Binding Proteins (PBPs), enzymes that are vital for cell wall biosynthesis. Many pathogens express drug-insensitive PBPs rendering β-lactams ineffective, revealing a need for new types of PBP inhibitors active against resistant strains. We have identified alkyl boronic acids that are active against pathogens including methicillin-resistant S. aureus (MRSA). The crystal structures of PBP1b complexed to 11 different alkyl boronates demonstrate that in vivo efficacy correlates with the mode of inhibitor side chain binding. Staphylococcal membrane analyses reveal that the most potent alkyl boronate targets PBP1, an autolysis system regulator, and PBP2a, a low β-lactam affinity enzyme. This work demonstrates the potential of boronate-based PBP inhibitors for circumventing β-lactam resistance and opens avenues for the development of novel antibiotics that target Gram-positive pathogens.

Asymmetric Conjugate Addition to Borylalkenes

Utilizing chiral rhodium catalysts, arylboron nucleophiles can added asymmetrically to numerous types of activated alkenes, such as α,β-unsaturated ketones, esters, aldehydes, and amides. The authors reveal that protected alkenylboronic acids can be used as electrophiles in this transformation, producing alkyl boron products. This unique Michael acceptor differs from those more commonly used, significantly expanding the scope of asymmetric conjugate additions.

ChemInform Abstract: Selective Copper‐Promoted Cross‐Coupling of Aromatic Amines with Alkyl Boronic Acids.

AbstractThe process allows a simple and mild N‐monoalkylation of various structurally diverse anilines.

Stereospecific Cross-Coupling of Secondary Alkyl β-Trifluoroboratoamides

The stereospecific cross-coupling of enantioenriched nonbenzylic secondary alkyl boron compounds has been achieved. The high selectivity toward product formation over an undesired β-H elimination pathway is achieved via an intramolecular coordination of an ancillary carbonyl to the metal center in the diorganopalladium intermediate.

Selective Copper-Promoted Cross-Coupling of Aromatic Amines with Alkyl Boronic Acids

A simple copper-promoted N-monoalkylation of anilines that utilizes alkyl boronic acids as the alkylating partner is presented. The reaction is carried out in refluxing dioxane, and it allows a number of structurally and electronically diverse anilines to be functionalized in a single step. A broad study was carried out to demonstrate the utility of this new methodology for the preparation of phenethylanilines.

Observations on the Deprotection of Pinanediol and Pinacol Boronate Esters via Fluorinated Intermediates

Methods for the deprotection of pinanediol and pinacol esters of various boronic acids via fluoroborane intermediates were evaluated. Treatment of the boronate esters with potassium hydrogen difluoride normally gives trifluoroborate salts; in the case of alpha-amido alkyl or o-amido phenyl boronate esters, aqueous workup gives difluoroboranes. Procedures for transformation of both trifluoroborates and difluoroboranes to free boronic acids are described.

ChemInform Abstract: Metal‐Free Electrophilic Fluorination of Alkyl Trifluoroborates and Boronic Acids.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Complete Stereoretention in the Rhodium‐Catalyzed 1,2‐Addition of Chiral Secondary and Tertiary Alkyl Potassium Trifluoroborate Salts to Aldehydes

Nevertheless, we recognized the significant potential thatwould ensue if we could induce alkyl boron derivatives tocouple to electrophiles. Herein we describe our success inachieving this goal and furthermore demonstrate completestereoretention in reactions involving not only secondary butalso tertiary chiral alkyl derivatives.We elected to study the reactions of secondary benzylicboron derivatives because they were expected to undergomore rapid transmetalation. They were easily prepared inhigh enantioregioselectivity by the reaction of Hoppeslithiated carbamates with aryl/alkyl boronic esters by usingmethodology that we recently reported (Scheme 1).

Boron‐Based Diastereomerism and Enantiomerism in Imine Complexes – Determination of the Absolute Configuration at Boron by CD Spectroscopy

AbstractBoron turns out to be a stable stereogenic center in imine complexes of aryl and alkyl boronates. Diastereomerically pure complexes 7a–c are obtained from chiral imine ligands 5a,b that are derived from the amino alcohol (R)‐4. The configuration at the boron atom is determined by crystal structure analyses. Racemic boronates 10a–c, available from a condensation of aryl boronic acids 6 with the achiral imine ligand 9, can be separated into stable enantiomers by HPLC on a chiral column. The racemization barrier ΔG≠ has been determined to amount to 105–115 kJ mol–1. The comparison of calculated and measured CD spectra permits to assign unambiguously the absolute configuration to boron in the enantiomeric boronate‐imine complex 10a.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

A Highly Selective Tandem Cross-Coupling ofgem-Dihaloolefins for a Modular, Efficient Synthesis of Highly Functionalized Indoles

A highly efficient method of indole synthesis using gem-dihalovinylaniline substrates and an organoboron reagent was developed via a Pd-catalyzed tandem intramolecular amination and an intermolecular Suzuki coupling. Aryl, alkenyl, and alkyl boron reagents are all successfully employed, making for a versatile modular approach. The reaction tolerates a variety of substitution patterns on the aniline leading to indoles with group at C2-C7. The orthogonal approach of the sequential copper- and palladium-mediated synthesis of 1,2-diarylindoles exploited the wide availability of diverse organoboron reagents.

Cesium Alkyltrifluoroborates from Asymmetric Boronic Esters

Cesium alkyltrifluoroborates are precipitated in high yields by the reaction of pinanediol (alkyl)boronates in diethyl ether with equivalent amounts of a mixture of aqueous hydrofluoric acid and cesium fluoride.

Tandem Carbocupration/Oxygenation of Terminal Alkynes.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Palladium-Catalyzed Coupling of Thiol Esters with Aryl and Primary and Secondary Alkyl Organoindium Reagents

Thiol esters and organoindium reagents undergo palladium-catalyzed cross-coupling under mild conditions to give ketones in moderate to excellent yields. Aryl and primary/secondary alkyl organoindium reagents can be used as coupling partners. This method has two advantages over the cross-coupling of thiol esters with boron and tin reagents: (1) no added copper reagent is required to mediate the reaction and (2) for the case of alkyl transfer, no added base is required to activate organoindium reagents for cross-coupling as is required for the coupling of alkyl boron reagents with thiol esters.

Synthesis of Non‐Proteinogenic Phenylalanine Analogues by Suzuki Cross‐Coupling of a Serine‐Derived Alkyl Boronic Acid.

Protected serine-derived boronic acids have been prepared as β-anionic alanine equivalents, and undergo efficient Suzuki cross-coupling with a variety of aryl halides to give, after elaboration, non-proteinogenic phenylalanine analogues.

Di(isopropylprenyl)borane: A New Hydroboration Reagent for the Synthesis of Alkyl and Alkenyl Boronic Acids.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Di(isopropylprenyl)borane: A new hydroboration reagent for the synthesis of alkyl and alkenyl boronic acids.

Di(isopropylprenyl)borane: A new hydroboration reagent for the synthesis of alkyl and alkenyl boronic acids.

Di(isopropylprenyl)borane: A New Hydroboration Reagent for the Synthesis of Alkyl and Alkenyl Boronic Acids

Vom Guten das Beste: Das Hydroborierungs-Reagens 1 verbindet die Selektivität von Disiamylboran (2) mit der Reaktivität der Allylborane 3 gegenüber Carbonylverbindungen. Da die Boronsäuren durch einfache Hydrolyse in protischem Medium mit bis zu 99 % Anti-Markownikow-Selektivität entstehen, können auch die sonst üblichen oxidativen Aufarbeitungsbedingungen vermieden werden. Eine Eintopfreaktion aus Hydroborierung und Suzuki-Miyaura-Reaktion erweitert den Nutzen von 1 für Synthesen.

Retarded Anionic Polymerization of Styrene, 6. Influence of Zinc and Boron Derivatives on the Reactivity of Polystyryllithium

Zinc and boron derivatives were used as additives for the retardation of styrene polymerization initiated by sec-butyllithium. The formation of mixed complexes between polystyryllithium (PSLi) and alkyl zinc or boron derivatives as well as a transmetallation reaction between PSLi and alkoxyborane was studied by UV-vis spectroscopy. Kinetic studies performed in the presence of the additives show that the rate of polymerization is divided only by two with diethylzinc at [Zn]/[Li] = 8 suggesting the contribution of remaining non-complexed PSLi. On the contrary, the rate was found to decrease noticeably with triethylborane upon increasing the [B]/[PSLi] ratio, in agreement with the formation, at 20°C, of ate complexes more stable than than with diethylzinc. However, the dissociation constant of the complexation equilibrium between R 3 B and PSLi is higlhy dependent on the temperature, and the retardation is not so effective at T>100°C. The same retardation effect was observed with borane alkoxides. Transmetallation reaction involving PSLi and B-OR bonds is first observed yielding B(PS) x derivatives. Retardation is governed by the concentration of the remaining PSLi species.