Boron Reagents Research Articles

Synthesis of diaryl selenides using electrophilic selenium species and nucleophilic boron reagents in ionic liquids

We described herein the use of imidazolium ionic liquids [bmim]PF6 and [bmim]BF4 in the selective, metal and catalyst-free synthesis of unsymmetrical diaryl selenides by electrophilic substitution in arylboron reagents with arylselenium halides (Cl and Br) at room temperature. This is a general substitution reaction and it was performed with arylboronic acids or potassium aryltrifluoroborates bearing electron-withdrawing or electron-donating groups, affording the corresponding diaryl selenides in good to excellent yields. The ionic liquid [bmim][PF6] was easily recovered and utilized for further substitution reactions.

Palladium-catalyzed, direct boronic acid synthesis from aryl chlorides: a simplified route to diverse boronate ester derivatives.

Although much current research focuses on developing new boron reagents and identifying robust catalytic systems for the cross-coupling of these reagents, the fundamental preparations of the nucleophilic partners (i.e., boronic acids and derivatives) has been studied to a lesser extent. Most current methods to access boronic acids are indirect and require harsh conditions or expensive reagents. A simple and efficient palladium-catalyzed, direct synthesis of arylboronic acids from the corresponding aryl chlorides using an underutilized reagent, tetrahydroxydiboron B(2)(OH)(4), is reported. To ensure preservation of the carbon-boron bond, the boronic acids were efficiently converted to the trifluoroborate derivatives in good to excellent yields without the use of a workup or isolation. Further, the intermediate boronic acids can be easily converted to a wide range of useful boronates. Finally, a two-step, one-pot method was developed to couple two aryl chlorides efficiently in a Suzuki-Miyaura-type reaction.

ChemInform Abstract: Stereocontrol in Allylboration Reactions

Abstraat: Crotyl-boronates add to aldehydes with high simple diastereoselection, such that E-crotyl-boronates give d-homoallyl alcohols, and Z-crotyl-boronates their =-counterparts. This reaction has been extended to stereoselective ring closure reactions by intramolecular allylboration. Moreover, by using suitably substituted crotyl boronates homoallyl alcohols having quarternary stereogenic carbon centers have been obtained with good diastereoselection. The development of chiral crotyl boronate reagents, having an additional stereogenic center a to the boron atom, allowed reactions with aldehydes to be accomplished with full transfer of chirality; i.e. control of the absolute configuration of the products.

ChemInform Abstract: Chiral Lewis Acids in Catalytic Asymmetric Reactions

This review examines the recent advances in the use of chiral Lewis acids, usually generated in situ from a Lewis acid and a chiral auxiliary, in the Diels-Alder reaction, the ene reaction, the hydrocyanation of aldehydes, the ring-opening of epoxides and various miscellaneous reactions. Structural studies of the complex formed between carbonyl compounds and Lewis acids are also reported. The Sharpless epoxidation is not covered by this review. 1. Introduction 2. Asymmetric Diels-Alder Reactions 2.1. Chiral Titanium Reagents 2.2. Chiral Aluminum Reagents 2.3. Chiral Boron Reagents 2.4. Chiral Ruthenium Reagents 3. Asymmetric [2+2] Cycloaddition Reactions 4. Asymmetric Ene Reaction 5. Asymmetric Hydrocyanation of Aldehydes 6. Asymmetric Ring Opening of Epoxides 7. Miscellaneous Asymmetric Reactions 8. Structural Studies on the Complexes of Carbonyl Compounds and Lewis Acids

ChemInform Abstract: The Asymmetric Diels-Alder Reaction of α,β-Unsaturated Aldehydes with Dienes Using a Chiral Boron Reagent as a Catalyst.

The asymmetric Diels–Alder reaction of α,β-unsaturated aldehydes with cyclopentadiene is catalyzed by a novel chiral boron reagent generated in situ from boron tribromide and a chiral prolinol derivative, to afford the corresponding adducts in good yields with fairly good to excellent ees.

ChemInform Abstract: Asymmetric Aza-Diels-Alder Reaction Mediated by Chiral Boron Reagent.

An asymmetric aza-Diels-Alder reaction of an imines mediated by an in situ generated chiral boron complex is described. The method is successful with several aldimines and affords products of up to 9O% ee

ChemInform Abstract: Novel Asymmetric Synthesis of β-Lactams with 3-(1′-Hydroxyethyl) Substituents: Boron Reagent Mediated Aldol Reaction of Chiral Imines and Silyl Ketene Acetals Derived from 3-Hydroxybutyrate.

Abstract An asymmetric reaction of chiral imines with silyl ketene acetals, prepared from (3R)-hydroxybutyrate, mediated by a boron reagent is described. The method successfully affords β-amino esters with high diastereoselectivity, which can be converted to optically pure β-lactams. This result indicated that a formal total synthesis of (+)-thienamycin is achieved by a simple and practical procedure.

Benzylic Boron Reagents Behaving as Allylic Boron Reagents towards Aldehydes: A New Asymmetric Reaction Leading to Homoallylic Alcohols with Concomitant Dearomatisation

Benzylic Boron Reagents Behaving as Allylic Boron Reagents towards Aldehydes: A New Asymmetric Reaction Leading to Homoallylic Alcohols with Concomitant Dearomatisation

Solution Reactions of a Bis(pyrrolylaldiminate)copper(II) Complex with Peralkyl Zinc, Aluminum, and Boron Reagents: Investigation of the Pathways Responsible for Copper Metal Deposition

The solution reactions of bis(N-isopropylpyrrolylaldiminate)copper(II) (CuL2) with AlMe3, BEt3, and ZnEt2 have been studied. In all cases, reduction occurs in two stages via a stable copper(I) pyrrolylaldiminate complex (Cu2L2), with each stage initiated by copper alkyl complex formation. Reduction from “LCuR” (R = Me or Et) occurs with release of R2 or L−R, consistent with bimolecular C−C or C−N bond-forming reductive elimination. At room temperature or below, copper deposition from “CuMe” occurs exclusively via reductive elimination of ethane, whereas decomposition of “CuEt” yields ethylene, ethane, and hydrogen, indicative of both β-hydride elimination and reductive elimination. The reaction byproducts [Cu2L2], [LAlMe2], [L2AlMe], [AlL3], [LBEt2], [LZnEt], [ZnL2], L−Me, and L−Et were synthesized independently and isolated as pure compounds. All compounds are thermally stable, with the exception of LZnEt, which undergoes ligand redistribution to form ZnL2 and ZnEt2 in solution and as a solid at elevated temperatures. With the exception of [LZnEt] and [Cu2L2], these complexes are also volatile; monoligated [LAlMe2] and [LBEt2] are particularly volatile, and therefore more desirable as byproducts in ALD or pulsed-CVD.

ChemInform Abstract: Application of the Lithiation—Borylation Reaction to the Preparation of Enantioenriched Allylic Boron Reagents and Subsequent in situ Conversion into 1,2,4‐Trisubstituted Homoallylic Alcohols with Complete Control over All Elements of Stereochemistry.

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ChemInform Abstract: Preparation and Use of Sterically Hindered Organobis(2,4,6-triisopropylphenyl)hydroborates and Their Polystyrene Derivatives for the Diastereoselective Reduction of Ketones.

Preparations of benzyl and phenylbis(2,4,6-triisopropylphenyl)hydroborates [organoditripylhydroborates] are outlined. The lithium and potassium benzylditripylhydroborates reduce substituted cyclohexanones with diastereoselectivities comparable to those obtained with the most selective reagents known (e.g. 99% cis-4-methylcyclohexanol from 4-methylcyclohexanone). Lithium phenylditripylhydroborate also reduces ketones with significant selectivity. For example, 4-methylcyclohexanone is reduced to cis-4-methylcyclohexanol in 88% isomeric purity. Unlike with most other highly selective reagents the reactions take place at room temperature and have the additional advantage that the boron reagent can be recovered quantitatively. Coupling of Merrifield’s resin with ditripylfluoroborane in the presence of lithium naphthalenide affords (ditripylborylmethyl)polystyrene. Similarly, coupling of bromopolystyrene with ditripylfluoroborane in the presence of n-BuLi affords (ditripylboryl)polystyrene. Reactions of these polymeric organoboranes with t-BuLi give the corresponding polymer-supported lithium hydroborates. Lithium ditripylhydroboratylmethylpolystyrene reduces cyclic ketones in identical fashion to its non-polymeric counterpart, giving the corresponding thermodynamically less stable alcohols in 99% or better isomeric purity. Similarly, lithium ditripylhydroboratylpolystyrene behaves like its non-polymeric counterpart and reduces 4-methylcyclohexanone to cis-4-methylcyclohexanol in 89% isomeric purity. Recovery and reuse of the organoboranes are even easier for the polymeric reagents.

Asymmetric Rh(I)-Catalyzed Addition of MIDA Boronates to N-tert-Butanesulfinyl Aldimines: Development and Comparison to Trifluoroborates

The Rh(I)-catalyzed addition of alkenyl and aryl MIDA boronates to N-tert-butanesulfinyl aromatic and aliphatic imines proceeds in good yields (up to 99%) and with very high selectivity (98:2 to >99:1). In comparison to trifluoroborates, higher yields and selectivities are observed for the addition to N-tert-butanesulfinyl aromatic imines. This new method expands upon the versatility of the Rh(I)-catalyzed addition of boron reagents to imines, thereby further enabling the synthesis of chiral alpha-branched amines.

Application of the Lithiation−Borylation Reaction to the Preparation of Enantioenriched Allylic Boron Reagents and Subsequent in Situ Conversion into 1,2,4-Trisubstituted Homoallylic Alcohols with Complete Control over All Elements of Stereochemistry

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionORIGINAL ARTICLEThis notice is a correctionApplication of the Lithiation−Borylation Reaction to the Preparation of Enantioenriched Allylic Boron Reagents and Subsequent in Situ Conversion into 1,2,4-Trisubstituted Homoallylic Alcohols with Complete Control over All Elements of StereochemistryMartin Althaus, Adeem Mahmood, José Ramón Suárez, Stephen P. Thomas, and Varinder K. Aggarwal*Cite this: J. Am. Chem. Soc. 2010, 132, 16, 5922Publication Date (Web):April 5, 2010Publication History Received23 March 2010Published online5 April 2010Published inissue 28 April 2010https://doi.org/10.1021/ja102041sCopyright © 2010 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views1831Altmetric-Citations2LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (52 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information SUBJECTS:Alcohols,Chemical reactions,Chemical structure,Molecular structure,Organic compounds Get e-Alerts

Application of the Lithiation−Borylation Reaction to the Preparation of Enantioenriched Allylic Boron Reagents and Subsequent In Situ Conversion into 1,2,4-Trisubstituted Homoallylic Alcohols with Complete Control over All Elements of Stereochemistry

The reactions of Hoppe's lithiated carbamates with vinylboranes and boronic esters give allylic boranes/boronic esters, and subsequent addition of aldehydes provides a new route to enantioenriched homoallylic alcohols with high enantiomeric ratios and diastereomeric ratios. Specifically, reactions of sparteine-complexed lithiated carbamates with trans-alkenyl-9-BBN derivatives followed by addition of aldehydes gave (Z)-anti-homoallylic alcohols in greater than 95:5 er and 99:1 dr. However, in the special case of the methyl-substituted lithiated carbamate, diamine-free conditions were required to achieve high selectivity. Reactions of sparteine-complexed lithiated carbamates with (Z)-alkenyl pinacol boronic esters and (E)-alkenyl neopentyl boronic esters gave (E)-syn- and (E)-anti-homoallylic alcohols, respectively, in greater than 96:4 er and 98:2 dr. In these reactions, a Lewis acid (MgBr(2) or BF(3) x OEt(2)) was required to promote both the 1,2-metalate rearrangement and the addition of the intermediate allylic boronic ester to the aldehyde. This methodology provides a general route to each of the three classes of homoallylic alcohols with high selectivity.

Reactivity of an oxoboryl complex toward fluorinated aryl boron reagents

X-Ray and IR data of unprecedented oxoboryl species indicate a significant alteration in the B[triple bond]O bond strength underlining the novel oxoboryl complexes' close relationship with the well investigated and important class of carbonyl complexes.

ChemInform Abstract: Introduction of Allyl and Prenyl Side-Chains into Aromatic Systems by Suzuki Cross-Coupling Reactions.

Fil: Gerbino, Dario Cesar. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Bahia Blanca. Instituto de Quimica del Sur. Universidad Nacional del Sur. Departamento de Quimica. Instituto de Quimica del Sur; Argentina

Identification and Counting of Carbonyl and Hydroxyl Functionalities in Protonated Bifunctional Analytes by Using Solution Derivatization Prior to Mass Spectrometric Analysis Via Ion-Molecule Reactions

A mass spectrometric method has been developed for the identification of carbonyl and hydroxyl functional groups, as well as for counting the functional groups, in previously unknown protonated bifunctional oxygen-containing analytes. This method utilizes solution reduction before mass spectrometric analysis to convert the carbonyl groups to hydroxyl groups. Gas-phase ion-molecule reactions of the protonated reduced analytes with neutral trimethylborate (TMB) in a FT-ICR mass spectrometer give diagnostic product ions. The reaction sequence likely involves three consecutive steps, proton abstraction from the protonated analyte by TMB, addition of the neutral analyte to the boron reagent, and elimination of a neutral methanol molecule. The number of methanol molecules eliminated upon reactions with TMB reveals the number of hydroxyl groups in the analyte. Comparison of the reactions of the original and reduced analytes reveals the presence and number of carbonyl and hydroxyl groups in the analyte.

Pd-Catalyzed Synthesis of Benzothiophenes from gem-Dihalovinyl Thiophenols

Based on an analogous synthesis of 2-substituted indoles from gem-dihalovinyl anilines (Y.-Q. Fang, M. Lautens J. Org. Chem. 2007, 73, 538), the preparation of 2-substituted benzothiophenes from gem-dihalovinyl thiophenols under Pd catalysis is described. The reaction involves an intramolecular S-vinylation and an intermolecular C-C bond formation. The majority of the examples are given for the Suzuki-Miyaura reaction for which PdCl2/S-Phos as a catalytic system and K3PO4/Et3N as combination of bases were found to be the optimized conditions compatible with a variety of different boron reagents. Four examples of Heck and Sonogashira cross-coupling reactions in tandem with the C-S coupling were also presented as an extension of the reaction.

Versatile synthetic methods for the engineering of thiophene-substituted Bodipy dyes

Novel thienyl-borondiazadipyrromethene ( Bodipy) dyes have been prepared using boronic acids or boronate reagents as cross-coupling mediators. A key dichloro/bromo- Bodipy starting material appears to be a useful starting material for such coupling reactions, enabling the synthesis of various symmetrically and unsymmetrically substituted thienyl-dyes. An alternative means of introducing thienyl substituents is through Knoevenagel substitution in the 3 and 5 positions of Bodipy by reaction with a formyl-functionalized thiophene derivative, resulting in systems of extended delocalization. All these Bodipy derivatives are stable and exhibit pronounced fluorescence on irradiation in the S 0→S 1 transition.

Synthesis of quaternary ammonium ion‐grafted polyolefins via activation of inert CH bonds and nitroxide mediated radical polymerization

AbstractA TEMPO‐functionalized isotactic poly(1‐butene) macroinitiator was synthesized via rhodium‐catalyzed activation of the alkane CH bonds in polyolefin side chain using a boron reagent and subsequent transformations of the boronate ester group in the polymer. These functionalization processes did not induce cross‐linking or degradation of the polymer chains. Nitroxide mediated radical polymerization of dipropyl(4‐vinylphenyl)amine with the macroinitiator produced high‐molecular weight amine‐grafted copolymers of the polyolefin. Adjusting the ratio of polar monomer concentration to macroinitiator concentration controlled the concentrations of amine blocks in the graft copolymers up to 10 mol %. Quaternization of the amine‐grafted copolymers with methyl triflate generated ammonium ion blocks along the side chain of the graft copolymers. A systematic decrease of contact angle in a series of ammonium ion‐grafted copolymers was observed through water contact angle measurements, suggesting that the graft polymerization and the quaternization led to increased hydrophilicity in the polymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4519–4531, 2009