Allylic Boranes Research Articles

Synthesis of Five-Membered Organoborate Heterocycles via a Metal-Free Carboboration and Their Use in Cross-Coupling Reactions

AbstractTreatment of various vinylbenzopyridines with allyl(dichloro)borane affords five-membered organoborate heterocycles via a metal-free carboboration. The reaction between these organoborates and Grignard reagents increases the number of derivatives belonging to this novel family of four-coordinate organoboron compounds. Some of them were used as reagents in phenylations and methylations in moderate to high yields under standard palladium-catalyzed cross-coupling reaction conditions.

Copper-Catalyzed Ring-Opening/Borylation of Cyclopropenes

Copper-Catalyzed Ring-Opening/Borylation of Cyclopropenes

Mechanism in palladium-catalyzed dearomative allylic reactions of benzyl phosphates with allyl borates: Insights from DFT calculations

Dearomatic reactions are very important to build alicyclic moieties and expand the structural diversity. Muto and Yamaguchi recently investigated the Pd-catalyzed dearomative allylic reactions of allyl borates with benzyl phosphates to give final compounds. Herein, the calculations were conducted to explore the reaction mechanism and selectivity, and the results clarified that the dearomatic product through carbon–carbon bond formation between η3-exo-(naphthyl)methyl para-carbon atom and allyl terminal carbon atom (TS3 = 7.3 kcal/mol) is energetically more favorable than the other carbon–carbon bond formation paths to afford aromatic and dearomatic compounds.

Dearomative Allylation of Naphthyl Cyanohydrins by Palladium Catalysis: Catalyst-Enhanced Site Selectivity.

A dearomative allylation of naphthyl cyanohydrins with allyl borates and allyl stannanes under palladium catalysis was developed. At the initial stage of this study, the dearomative reaction (C4 substitution of the aromatics) was competing with benzyl substitution. To circumvent this issue, the use of palladium and meta-disubstituted triarylphosphine as the catalyst in a 1:1 ratio was found to enhance the site selectivity, furnishing the desired dearomatized products. Further derivatizations of products were also successful.

Photoredox radical borylation of electron-deficient alkenes with NHC-boranes.

An efficient photoredox radical borylation of electron-deficient Morita-Baylis-Hillman type alkenes is achieved to afford multi-functionalized allylic boranes. The reaction demonstrates a wide substrate scope and showcases excellent functional group tolerance. It has advantages over the traditional ionic hydroboration methods in the construction of allylic boranes in terms of simple operation, mild conditions, and step-economy.

Electrophilic Amination of Allylic Boranes with Azodicarboxylates: Synthesis of α,α-Disubstituted Allylic Amine Derivatives

The electrophilic amination of allylic boranes, which are prepared from allenes and 9-borabicyclo[3.3.1]nonane (9-BBN), with azodicarboxylates as an aminating reagent is reported. 9-BBN-based allyl...

Pd-Catalyzed Dearomative Three-Component Reaction of Bromoarenes with Diazo Compounds and Allylborates

A catalytic dearomative three-component reaction of bromoarenes with TMS-diazomethane and allyl borate was developed. The key of this assembling reaction is the use of a diazo compound to generate a Pd-π-benzyl intermediate through a Pd-carbene species. This method allowed for a dearomative functionalization, using arenes as limiting reagents. Heteroaryl bromides were also applicable to give dearomatized structures under the reaction conditions.

Electrophilic cyanation of allylic boranes: synthesis of β,γ-unsaturated nitriles containing allylic quaternary carbon centers.

The electrophilic cyanation of allylic boranes, a process that is applicable to the construction of allylic quaternary carbon centers, is reported. The reaction has a broad substrate scope with a high functional group tolerance. The results represent an unprecedented and powerful tool for preparing synthetically useful β,γ-unsaturated nitriles, including derivatives that have been difficult to access using existing methods. The synthetic utility of the method was further demonstrated by functional group interconversions of the cyano group of the products.

Allyl borates: a novel class of polyhomologation initiators.

Allyl borates, a new class of monofunctional polyhomologation initiators, are reported. These monofunctional initiators are less sensitive and more effective towards polymethylene-based architectures. As an example, the synthesis of α-vinyl-ω-hydroxypolymethylenes is given. By designing/synthesizing different allylic borate initiators, and using 1H and 11B NMR spectroscopy, the initiation mechanism was elucidated.

Chelation-assisted substrate-controlled asymmetric lithiation-allylboration of chiral carbamate 1,2,4-butanetriol acetonide.

The lithiation of 2-(2,2-dimethyl-1,3-dioxolan-4-yl)ethyl diisopropylcarbamate (1) is achieved freely by sec-butyllithium in diethylether with high lk-diastereoselectivity: the bicyclic chelate complexes 3a and 3b are reacted with electrophiles to form optically active precursors 4a and 4b with >95% diastereoselectivity. In addition, tertiary diamines can undergo an external complexation in contest with the internal oxygen ligand, leading to improved stereoselectivities. The further reactions of lithiated carbamates with trans alkenyl-9-BBN derivatives after 1,2 metallate rearrangements, gave the key intermediate α-substituted allylic boranes 7. Subsequent allylboration of aldehydes gave (Z)-anti-homoallylic alcohols 8 in good yield and excellent d.r.

ChemInform Abstract: Synthesis of Highly‐Substituted Enantiomerically Pure Allylboronic Esters and Investigation of Their Stereoselective Addition to Aldehydes.

AbstractA highly stereoselective addition of preformed enantiomerically pure allyl boranes is applicable to a broad variety of aldehydes bearing different functional groups in good to high yields.

A bidirectional S(E)' strategy for 1,5-syn and 1,5-anti stereocontrol toward the synthesis of complex polyols.

Studies report a bidirectional S(E)' strategy applicable for the stereocontrolled synthesis of nonracemic 1,5-syn and 1,5-anti diols and their derivatives. Nonracemic 1,3,2-diazaborolidine auxiliaries are incorporated by chemoselective tin-boron exchange to provide reactive allylic boranes. The convergent pathway utilizes sequential reactions with two aldehydes producing stereochemical outcomes from cyclic, closed, and open transition state preferences, respectively. Synthesis of fragment 16 of peloruside A is accomplished in four steps from readily available aldehydes 9 and 13.

“Design” of Boron‐Based Compounds as Pro‐Nucleophiles and Co‐Catalysts for Indium(I)‐Catalyzed Allyl Transfer to Various Csp3‐Type Electrophiles

We have recently uncovered a general indium(I)-catalyzed method for allylations and propargylation of acetals and ketals with a water- and air-stable allyl boronate. By using a more reactive allyl borane, we have successfully extended this methodology to the more challenging C-C coupling with ethers. Herein, we report an improved methodology for the indium(I)-catalyzed allylation of acetals and ethers, through combination of the allyl boronate with a commercially available "hard" Lewis acid, B-methoxy-9-BBN (BBN=borabicyclo[3.3.1]nonane), as an effective co-catalyst. Significantly, our work highlights for the first time the correlation between the Lewis acidity of "electrophilic" boron-based compounds and their "nucleophilic" reactivity in Csp(3)-Csp(3) couplings, catalyzed by a "soft" low-oxidation main group metal. In addition, we also report several applications of these methodologies to the selective synthesis of various carbohydrate derivatives.

ChemInform Abstract: Reductive Mono- and Trans-α,α′-diallylation of Aromatic Nitrogen Heterocycles by Allylboranes

Reductive trans-u,d-diallylation of pyridines, 4,4'-dipyridyl, pyrrole and isoquinoline as well as reductive monoallylation of pyrrole, indole, quinolines, isoquinoline and phenanthridine by allylic boranes were discovered. A convenient method for trans- + cis-isomerization of trans-2,6-diallyl-A3- piperideines and trans-2,5-diallylpylidine was found.

ChemInform Abstract: Stereoselective Synthesis of γ‐Substituted (Z)‐Allylic Boranes via Kinetically Controlled Hydroboration of Allenes with 10‐TMS‐9‐Borabicyclo[3.3.2]decane.

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.

Stereoselective Synthesis of γ-Substituted (Z)-Allylic Boranes via Kinetically Controlled Hydroboration of Allenes with 10-TMS-9-borabicyclo[3.3.2]decane

Kinetically controlled hydroboration of allenes 8 and 14a-d with the readily accessible Soderquist borane 7, which is generated in situ from borohydride 6, constitutes a convenient and preparatively useful method for synthesis of (Z)-gamma-(substituted)allylboranes 9 and 15a-d. These allylboranes undergo highly diastereo- (> or = 90: 10) and enantioselective (typically 89-96% e.e.) allylboration reactions with representative aldehydes to give syn-beta-functionalized homoallylic alcohols.

Allylic boranes are chemist’s best friends: Reactivity, applications, new opportunities

Fruitful methods for the preparation of various (poly)unsaturated, (poly)cyclic and cage organic compounds with the use of allylic type organoboranes have been developed. Allylborane reactions proceeding with the rearrangement of allylic moiety or via a direct rupture of the B–C bond (with retention) little known to the boron community are considered. Synthesis of boron containing clathrochelates and some transformations of 1-boraadamantane, a unique cage compound, are also described.

Reactions of boron trifluoride with allylic boranes and 1-boraadamantane

The reactions of boron trifluoride with triallyl- and allyldialkylboranes represent a convenient non-catalytic approach to allyl(difluoro)boranes. The rupture of 1-boraadamantane core with BF3 leads to 3-fluoro-7-difluoroborylmethyl-3-borabicyclo-[3.3.1]nonane derivatives.

A Practical Synthesis of the Ansa Chain of Benzenic Ansamycin Antibiotics: Total Synthesis of an Ansatrienol Derivative

A practical and stereocontrolled synthetic approach towards the ansa chain of the benzenic ansamycins (mycotrienins) is described, which can be scaled up to multigram quantities. Key features of the synthesis are the formation of the Z-configured tri­substituted double bond by a one-pot esterification of allyl(diisopropoxy)borane and ring-closing metathesis, formation of the β-keto ester via ethyl diazoacetate addition to an aldehyde, and use of the Duthaler-Hafner acetate aldol reaction for the introduction of the stereocenter at C3. The practicality of this synthesis is demonstrated by the preparation of an ansatrienol derivative, representing­ a formal total synthesis of the ansatrienins.

Asymmetric Synthesis of α‐Substituted Allyl Boranes and Their Application in the Synthesis of Iso‐agatharesinol

Use your borane: A stereocontrolled synthesis of allyl boranes from chiral sulfur ylides and their subsequent reaction with aldehydes to give homoallylic alcohols is described. The allyl boranes also could undergo a stereospecific 1,3-borotropic rearrangement to give another set of homoallylic alcohols (see scheme). The reaction has been applied to an efficient synthesis of iso-agatharesinol.