Reaction Of Organoboranes Research Articles

Post‐Functionalization of Organoboranes by Cu‐Catalyzed Azide Alkyne [3+2]‐Cycloaddition Reaction

AbstractThe copper‐catalyzed azide alkyne [3+2]‐cycloaddition (CuAAC) reaction of organoboranes represents an attractive area of research within the field of click chemistry, with diverse applications in organic synthesis, medicinal chemistry, or materials science. Despite the potential issues caused by the copper insertion into the carbon‐boron bond, significant progress has been made to harness the reactivity of organoboron compounds in CuAAC. This review provides an overview of the catalytic methods reported for CuAAC with various organoboranes, discussing the stability of the boron group and highlighting recent advancements in this area.

Interrupted Homolytic Substitution Enables Organoboron Compounds to Inhibit Radical Chain Reactions Rather than Initiate Them.

The reactions of organoboranes with peroxyl radicals are key to their use as radical initiators for a vast array of radical chain reactions, particularly at low temperatures where high stereoselectivity or regioselectivity is desired. Whereas these reactions generally proceed via concerted homolytic substitution (SH2) mechanisms, organoboranes that bear groups that can stabilize tetracoordinate boron radical "ate" complexes (e.g., catecholboranes) undergo this reaction via a stepwise addition/fragmentation sequence and serve as useful stoichiometric alkyl radical precursors. Here we show that arylboronic esters and amides derived from catecholborane and diaminonaphthaleneborane, respectively, are potent radical-trapping antioxidants (RTAs). Mechanistic studies reveal that this is because the radical "ate" complexes derived from peroxyl radical addition to boron are sufficiently persistent to trap another radical in an interrupted SH2 reaction. Remarkably, the reactivity of these organoboranes as inhibitors of autoxidation was shown to translate from simple hydrocarbons to the phospholipids of biological membranes such that they can inhibit ferroptosis, the cell death modality driven by lipid autoxidation and relevant in neurodegeneration and other major pathologies. The unique mechanism of these organoboranes is one of only a handful of RTA mechanisms that are not based on H-atom transfer processes and provide a new dimension to boron chemistry and its applications.

Nickel and Copper‐Catalyzed Carbonylation Reaction of Organoboranes

AbstractCarbonylation of arylboronic acid derivatives employing Cr(CO)6 as the carbonyl source and NiCl2(dmg)/4,4′‐bipy as the catalyst under air without applying external oxidant has been reported for the amide and ester synthesis (dmg=dimethylgloxime; bipy=bipyridine). Moreover, CHCl3 was also used as another carbonyl source for the amide synthesis with CuI/1,10‐phenanthroline catalytic system.

Reactions of organoboranes with carbanions bearing three potential leaving groups: unusual processes, products and mechanisms

Known reagents that transfer three alkyl groups of a trialkylborane intramolecularly to a single carbon atom lack features to influence stereochemistry. We have investigated four reagents of type LiCCl2X, where X might be amenable to variation. All behaved differently. With X=OR (R=cyclohexyl, menthyl), the reagent decomposed, leading to only low yields of triple migration products. With X=S(O)Ph, a single migration occurred, followed by isomerisation to boron enolate-like species that hydrolysed to α-chloroalkyl phenyl sulfoxides or reacted with aldehydes to aldol-like products. With X=SO2Ph, the major product was the corresponding α,α-dichloroalkyl phenyl sulfone, apparently formed through a redox reaction. With X=S(O)(NMe)Ph, products of three intramolecular alkyl migrations were obtained with unhindered trialkylboranes. Attempts have been made to gain understanding of the sulfoxide process by investigating proportions of aldol-like products, using X-ray crystallography and ab initio calculations.

Hydroboration of unsaturated fatty acid methyl esters and conversion of the boron adducts*

Unsaturated FAMEs can be modified to higher value compounds by hydroboration of the double bond. The added boron atom can be replaced in a subsequent oxidation by a hydroxy group. This way methyl 10‐undecenoate (1b), methyl oleate (3a), methyl ricinoleate ((9Z,12R)‐6a), and methyl linoleate (9) were converted into methyl 11‐hydroxyundecanoate and methyl hydroxyoctadecanoates in 82–92% yield. Organoboranes isomerize at higher temperatures. Hydroboration of oleic acid and subsequent heating to 220°C led after oxidative work‐up to 70% of 1,4‐octadecanediol. Presumably a 1,4‐oxaborinane intermediate is involved. Alkyl groups of organoboranes can be attached to the carbonyl‐equivalent: dichloromethyl methyl ether (DCME). With this reaction the boranes of the esters 1b and 3a were converted in 55–80% yield to dimers with an inserted ketocarbonyl group. Ester 9 afforded in the same reaction methyl nonadecanoates with an integrated cyclopentene ring.Practical applications: Hydroboration–oxidation allows the partially regioselective conversion of unsaturated FAMEs into hydroxy‐ and dihydroxyesters. Thermal isomerization of the boranes from methyl oleate, oleic acid, and oleyl alcohol leads after oxidative work‐up to the 1,4‐diol: 1,4‐octadecanediol as main product. These products are useful as components for polyesters, polyurethanes, and precursors for heterocycles. Reaction of organoboranes from unsaturated FAMEs with the carbonyl equivalent: DCME provides a one‐step access to 1,ω‐diesters with an internal keto group, which can be applied for coupling, cross‐linking, and further conversion. The borane · THF complex is commercially available in amounts of 0.8 mol and more to do exploratory research toward such applications.

Magnetically Separable CuFe2O4 Nanoparticle Catalyzed C–Se Cross Coupling in Reusable PEG Medium

Abstract A simple and efficient procedure for the synthesis of unsymmetrical diaryl selenides has been developed by magnetically separable CuFe2O4 nanoparticle catalyzed reactions of organoboranes with PhSeBr in recyclable PEG-400 medium at 80 °C and Cs2CO3 as base. Using this protocol, a variety of unsymmetrical selenides were obtained in good to excellent yields. The copper ferrite nanoparticles were magnetically separated, recycled, and reused up to four cycles.

Cross-coupling Reactions of Organoboranes: An Easy Method for C–C Bonding

Abstract The palladium-catalyzed cross-coupling reaction between different types of organoboron compounds and various organic halides or triflates in the presence of base provides a powerful and general methodology for the formation of carbon–carbon bonds. The Csp2–B compounds (such as aryl- and 1-alkenylboron derivatives) and Csp3–B compounds (alkylboron compounds) readily cross-couple with organic electrophiles to give coupled products selectively in high yields. Recently, the Csp–B compounds (1-alkynylboron derivatives) have been also observed to react with organic electrophiles to produce expected cross-coupled products. The overview of some of such coupling reactions is discussed here in this article.

ChemInform Abstract: A Novel Cyclization in the Hydroboration of Divinylstannanes.

Abstract The clean formation of the 3-boryl-1-stannacyclopentane ( 2 ) is observed from the monohydroboration of divinyldimethyltin with 9-BBN-H, a previously unknown process. This heterocyclic system undergoes expected organoborane reactions with the notable exception of the Suzuki-Miyaura coupling where, with bromobenzene, 3-butenyl(dimethyl)phenyltin ( 16 ) is the exclusive coupling product, evidently forming through an unprecedented “stanna-Heck” process.

Polymer-Supported Carboxylate as a New Polymeric Reagent for Synthesis of Alkyl Esters

Polymer supported reagents especially anion exchange resins have been widely applied in organic synthesis. These polymeric reagents are generally used in single step reactions. Their main advantage over monomeric reagents is their insolubility in the reaction medium and consequently the easier workup by a simple filtration. The reactions can often be driven to completion by using excess of these reagents without the fear of separating the unspent reagent from the desired products. The spent polymeric reagents can usually be removed quantitatively and regenerated. In addition, anions bound to the macroporous resin have the advantage that they often react successfully in non-polar solvents. The ester group is an important functional group that can be synthesized in a number of different ways such as acylation of alcohols, oxidation of aldehydes, addition of carboxylic acids to alkenes, reaction of carboxylic acids with diazomethane, Bayer-Villiger oxidation of ketones, reaction of organoboranes with α-halo esters, rearrangement of α-haloketones (Favorskii reaction) and especially for large scale operation by reaction of carboxylate salts or Amberlite IRA-904 supported carboxylate ion with alkyl halides or tosylates. Sodium carboxylate, however, has been the reagent most widely used. Unfortunately, each of these methods suffer from at least one of the following disadvantages: (1) the yields of the reactions are low, (2) the reaction has to be carried out in the presence of phase transfer catalyst, (3) the reaction mixture has to be acidified or the reaction has to be catalyzed by a base such as pyridine, and (4) tedious work-up procedure. Polymer-supported carboxylate ion overcomes most of the above mentioned disadvantages. In this study we wish to report an important, efficient, and easy method for preparation of alkyl acetate or alkyl formate esters from crosslinked poly(4-vinylpyridinium) acetate (I) or crosslinked poly(4-vinylpyridinium) formate (II) with alkyl halides (Scheme 1). While there are numerous applications of solid-supported reagents and scavengers only a few examples for the formation of esters were described. Solid-supported acids were used as catalysts in the esterification of carboxylic acids with alcohols. Carboxylates, generated with solidsupported organic bases, were alkylated with alkyl halides. Solid-supported organic bases were also used as scavenger resins in the esterification of benzyl alcohol with benzyl chlorides, giving clean benzyl esters in high yields. A modification of the Mitsunobu reaction with resin-bound triphenylphosphine and soluble di-t-butylazodicarboxylate was described, that allowed for the isolation of pure products without chromatography. A very recent report described the alkylation of carboxylic acids with carbenium ions, generated from polymer-supported triazines, for the ester formation. We report here a convenient and general procedure for the synthesis of esters from alkyl halides and polymer-supported carboxylate ion that readily prepared from employing the commercially available poly(4-vinylpyridine) (2% crosslinked with DVB) resin as the solid-supported condensation reagent. Crosslinked poly(N-methyl-4-vinylpyridinium) acetate (I) and crosslinked poly(N-methyl-4-vinylpyridinium) formate (II) were prepared by an exchange reaction between crosslinked poly(N-methyl-4-vinylpyridinium) iodide with a slight excess of sodium acetate or sodium formate solution in water. Using these heterogeneous reagents converted benzyl halides to benzyl acetate or benzyl formate esters in acetone under reflux condition. The advantages of this method are: 1) the reaction can be performed in non-aqueous medium; 2) an excess of the reagent can be used; 3) the product can be obtained by simple filtration and evaporation of the solvent; and 4) the polymeric reagent is easily regenerable with a sodium acetate or sodium formate solution. Crosslinked polymers (I) and (II) can be easily prepared and used as mild and efficient polymeric reagents for conversion of benzyl halides to the corresponding benzyl acetate and benzyl formates. It was proved that acetone is the best solvent for these reactions. In these conversions, the best molar ratio of reagent/substrate proved was 1.5, but

Useful Reactions in Modern Pheromone Synthesis

AbstractFor Abstract see ChemInform Abstract in Full Text.

Useful Reactions in Modern Pheromone Synthesis

Various aspects of pheromone synthesis are reviewed by analyzing examples published between 1990 and early 2003. Syntheses executed with new methodologies such as organoborane reactions, organotransition metal chemistry including olefin metathesis, asymmetric epoxidation, asymmetric dihydroxylation, other asymmetric chemical processes, and stereoselective biocatalysis are selected to illustrate the usefulness of new reactions in pheromone synthesis.

A novel cyclization in the hydroboration of divinylstannanes

Abstract The clean formation of the 3-boryl-1-stannacyclopentane ( 2 ) is observed from the monohydroboration of divinyldimethyltin with 9-BBN-H, a previously unknown process. This heterocyclic system undergoes expected organoborane reactions with the notable exception of the Suzuki-Miyaura coupling where, with bromobenzene, 3-butenyl(dimethyl)phenyltin ( 16 ) is the exclusive coupling product, evidently forming through an unprecedented “stanna-Heck” process.

Highly selective coupling of organoboron compounds via oxovanadium(V)-induced oxidation

Reaction of organoboranes or organoborane ate complexes (obtained by treatment with BunLi or CsF) with oxovanadium(V) compounds results in the intramolecular oxidative coupling of organic groups on the boranes or borates.

ChemInform Abstract: The Reactions of Organoboranes with Carbonyl Compounds and Their Derivatives

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 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.

Synthesis of Alkylarylcarbinols via the Reaction of Organoboranes with Arylmethyl Chlorides

(α-Chloroaryl)methyl anions, generated in situ by the deprotonation of arylmethyl chlorides with dicyclohexylamide, readily react with either trialkylboranes or alkylboronic esters to produce alkylarylcarbinols in good yields after oxidation. This reaction provides a very facile procedure for the synthesis of alkylarylcarbinols.

Evidence for the Formation of Acylboronate Intermediates in the Carbonylation Reactions of Organoboranes

Trialkylboranes react with acyllithium reagents to yield ketones after oxidation with hydrogen peroxide. The ketones contain one alkyl group supplied by the alkyllithium reagent and one alkyl group supplied by the organoborane. The experimental results support the hypothesis that an acylboronate is an intermediate in the reactions of organoboranes with carbon monoxide. The yields are modest due to an apparent competition between carbon monoxide and organoborane for the alkyllithium needed to generate the acyl anion. 13 refs., 2 tabs.

New synthetic transformations via organoboron compounds

Abstract

A convenient synthesis of N-boc protected primary amines via the reaction of organoboranes with Li or K t-butyl-N-tosyloxycarbamate

Primary and secondary alkylboranes reacted rapidly at low temperature with Li or K t-butyl-N-tosyloxycarbamate (LiBTOC or KBTOC) to give the corresponding N-Boc protected primary amines in modest to good yields (16–81%).

The reactions of organoboranes with N-chloro-N-sodiocarbamates: A novel synthesis of N-alkylcarbamates.

Trialkylboranes react with N-chloro-N-sodiocarbamates to form N-alkylcarbamates in yields ranging from 50–88%. The reaction is best carried out without intermediate isolation of the N-chlorocarbamate salt. Only one of the alkyl groups of the trialkylborane is utilized.

ChemInform Abstract: The Reaction of Organoboranes with Trimethylsilyl Azide in a Neutral Medium: Synthesis of Primary Amines.

AbstractThe terminal olefins (Ia) ‐ (Id) are hydroborated and then directly treated with trimethylsilyl azide (II), yielding the primary amines (IIIa) ‐ (IIId).