Potassium Alkynyltrifluoroborates Research Articles

Cobalt-Catalyzed Enantioselective Alkynylation of Oxabicyclic Alkenes

AbstractEfficient access to enantioenriched cyclic homopropargylic alcohols through an unprecedented cobalt-catalyzed asymmetric alkynylation of oxabicyclic alkenes has been developed. By using inexpensive cobalt salt/chiral bisphosphine ligand as the catalyst and easy-to-handle potassium alkynyltrifluoroborates as the nucleophile, synthetically valuable homopropargylic alcohols are obtained in moderate to good yields and high enantioselectivities.

Ligand-Controlled Nickel-Catalyzed Reactions of Benzocyclobutenones with Alkynyltrifluoroborates: Diverse Construction of Polysubstituted Naphthols.

Ligand-controlled nickel-catalyzed selective cleavage of the C1-C2 or C1-C8 bond of benzocyclobutenones (BCBs) is reported. The delicate selection of dpppe or PMe3 as the ligand led to predictably divergent synthesis of a wide range of 1-naphthols and 2-naphthols without C2 and C3 substituents, respectively, from BCBs and potassium alkynyltrifluoroborate, and the increase in the amount of PMe3 resulted in tandem reaction of 2 equiv of BCB with the borate to afford 3,4,5-trisubstituted 2-naphthols. The fabulous ligand effect resulted in the facile and unique construction of multisubstituted naphthols with well-controlled regioselectivity and a high degree of structural diversity.

Iridium-catalyzed enantioselective alkynylation and kinetic resolution of alkyl allylic alcohols.

Herein, we report an efficient kinetic resolution of alkyl allylic alcohols enabled by an iridium-catalyzed enantioselective alkynylation of alkyl allylic alcohols with potassium alkynyltrifluoroborates. A wide range of chiral 1,4-enynes bearing various functional groups and unreacted enantioenriched allylic alcohols were obtained with excellent enantioselectivities and high kinetic resolution performance (s-factor up to 922). Additionally, this method is particularly effective for preparing some useful optically pure alkyl allylic alcohols, such as the key components towards the synthesis of prostaglandins and naturally occurring matsutakeols, which are difficult to access via other asymmetric reactions. Mechanistic studies revealed that the efficient kinetic resolution might be due to the significant distinction of the η 2-coordination between the (R)- and (S)-allylic alcohols with the iridium/(phosphoramidite, olefin) complex.

Reaction of Alkynyl- and Alkenyltrifluoroborates with Propargyldicobalt Cations: Alkynylation, Alkenylation, and Cyclopropanation Product Pathways.

The Lewis acid-mediated Nicholas reactions of propargyl acetate-Co2(CO)6 complexes with a series of potassium alkynyltrifluoroborates and potassium alkenyltrifluoroborates are described. Alkynyltrifluoroborates directly alkynylate the intermediate propargyldicobalt cations. In contrast, alkenyltrifluoroborates proceed through one of the three modes of dominant reactivity: C-2-substituted alkenyltrifluorobrates directly alkenylate, predominantly with the retention of stereochemistry. C-1-substituted alkenyltrifluoroborates alkenylate at C-2. Potassium vinyltrifluoroborate incorporates a cyclopropane at the site propargyl to alkynedicobalt. Computational analysis of these systems explains the differential modes of reactivity of alkenyltrifluoroborates and outlines the probable mechanisms for the formation of each product.

Organocatalytic Enantioselective Conjugate Alkynylation of β-Aminoenones: Access to Chiral β-Alkynyl-β-Amino Carbonyl Derivatives.

Readily available potassium alkynyltrifluoroborates were used for organocatalytic asymmetric conjugate alkynylation of β-enaminones. The interception of a modified binaphthol catalyst and in situ generated organodifluoroboranes proved important to access functionalized β-alkynyl-β-amino carbonyls and derivatives with improved chemo-reactivity and enantio-induction. Mechanistic studies revealed the impact of molecular sieves on efficiency and stereocontrol. The products undergo additional functionalization to yield a diverse set of valuable β-alkynyl-β-amino carbonyl scaffolds.

Regioselective cycloaddition of potassium alkynyltrifluoroborates with 3-azetidinones and 3-oxetanone by nickel-catalysed C-C bond activation.

In the presence of a nickel catalyst, the intermolecular (4+2) cycloaddition of potassium alkynyltrifluoroborates with 3-azetidinones and 3-oxetanone leads to the formation of borylated dihydropyridinones and dihydropyranones without unwanted carbon-boron bond cleavage. The regioselectivity is influenced only by the trifluoroborate group, and only one regioisomer is obtained, whether the other alkyne substituent is an alkyl, vinyl, or (hetero)aryl group.

Nicholas Reactions of Alkynyl- and Alkenyltrifluoroborates

The Lewis acid mediated Nicholas reaction of potassium alkynyltrifluoroborates and propargyl acetate-hexacarbonyldicobalt complexes affords 1,4-diyne dicobalt hexacarbonyl complexes in good yields. The analogous Nicholas reactions of potassium alkenyltrifluoro­borates give 1,3-enyne dicobalt hexacarbonyl complexes in most cases, although the initial site of reaction can vary. Potassium vinyltrifluoroborate itself affords alkynylcyclopropane complexes.

Interrupting Nazarov Reaction with Different Trapping Modality: Utilizing Potassium Alkynyltrifluoroborate as a σ-Nucleophile.

The putative oxyallyl cation intermediate generated following Nazarov cyclization of dienone has been successfully intercepted with potassium alkynyltrifluoroborates which act as σ-nucleophiles in the presence of BF3·Et2O. This new trapping modality allowed unprecedented introduction of an alkynyl moiety to the cyclopentanone framework by means of an interrupted Nazarov reaction. The α-alkynyl cyclopentanone product can be further transformed into an array of densely functionalized cyclic compounds.

Metal-free methodology for the preparation of sterically hindered alkynoylphenols and its application to the synthesis of flavones and aurones

A metal-free synthesis for the preparation of sterically demanding ortho-demethylated ynones from mixed anhydrides and potassium alkynyltrifluoroborate salts has been developed. The one-pot reaction proceeds rapidly in the presence of a Lewis acid without the exclusion of air and moisture. This method is advantageous in that it is operationally simple, proceeds under mild conditions, and has a broad substrate scope. 2,6-Dimethoxy substituted anhydrides afford the corresponding mono-demethylated ynone products in good yields. In particular, 2-hydroxy substituted ynone products are valuable synthetic intermediates because their conversion to biologically active natural product scaffolds is straightforward. Flavones were obtained via 6-endo cyclization of the o-alkynyoylphenol intermediates under acidic conditions. Cesium carbonate was found to promote rapid 5-exo cyclization to furnish aurone products.

Metal-free Synthesis of Ynones from Acyl Chlorides and Potassium Alkynyltrifluoroborate Salts

Ynones are a valuable functional group and building block in organic synthesis. Ynones serve as a precursor to many important organic functional groups and scaffolds. Traditional methods for the preparation of ynones are associated with drawbacks including harsh conditions, multiple purification steps, and the presence of unwanted byproducts. An alternative method for the straightforward preparation of ynones from acyl chlorides and potassium alkynyltrifluoroborate salts is described herein. The adoption of organotrifluoroborate salts as an alternative to organometallic reagents for the formation of new carbon-carbon bonds has a number of advantages. Potassium organotrifluoroborate salts are shelf stable, have good functional group tolerance, low toxicity, and a wide variety are straightforward to prepare. The title reaction proceeds rapidly at ambient temperature in the presence of a Lewis acid without the exclusion of air and moisture. Fair to excellent yields may be obtained via reaction of various aryl and alkyl acid chlorides with alkynyltrifluoroborate salts in the presence of boron trichloride.

Metal-free synthesis of ynones from acyl chlorides and potassium alkynyltrifluoroborate salts.

Ynones are a valuable functional group and building block in organic synthesis. Ynones serve as a precursor to many important organic functional groups and scaffolds. Traditional methods for the preparation of ynones are associated with drawbacks including harsh conditions, multiple purification steps, and the presence of unwanted byproducts. An alternative method for the straightforward preparation of ynones from acyl chlorides and potassium alkynyltrifluoroborate salts is described herein. The adoption of organotrifluoroborate salts as an alternative to organometallic reagents for the formation of new carbon-carbon bonds has a number of advantages. Potassium organotrifluoroborate salts are shelf stable, have good functional group tolerance, low toxicity, and a wide variety are straightforward to prepare. The title reaction proceeds rapidly at ambient temperature in the presence of a Lewis acid without the exclusion of air and moisture. Fair to excellent yields may be obtained via reaction of various aryl and alkyl acid chlorides with alkynyltrifluoroborate salts in the presence of boron trichloride.

ChemInform Abstract: Copper‐Mediated Trifluoromethylation of Potassium Alkynyltrifluoroborates with Langlois′ Reagent.

Synthesis of trifluoromethylated acetylenes by copper-mediated trifluoromethylation of potassium alkynyltrifluoroborates with CF3 radicals generated from NaSO2CF3 and tert-butyl hydroperoxide (TBHP) is communicated. The trifluoromethylated acetylenes were obtained in good to moderate yields. The presented method tolerates a wide range of aromatic, heteroaromatic, and aliphatic potassium alkynyltrifluoroborates.

ChemInform Abstract: Metal‐Free Synthesis of Ynones from Acyl Chlorides and Potassium Alkynyltrifluoroborate Salts.

AbstractThis simple method tolerates air and moisture.

ChemInform Abstract: Pd‐Catalyzed Alkynylation of 2‐Chloroacetates and 2‐Chloroacetamides with Potassium Alkynyltrifluoroborates.

AbstractA protocol is developed to allow the coupling of N‐substituted chloroacetamides and analogous esters with alkynyltrifluoroborates to give β,γ‐alkynyl amides and esters in good yields.

Copper-mediated trifluoromethylation of potassium alkynyltrifluoroborates with Langlois' reagent

Synthesis of trifluoromethylated acetylenes by copper-mediated trifluoromethylation of potassium alkynyltrifluoroborates with CF3 radicals generated from NaSO2CF3 and tert-butyl hydroperoxide (TBHP) is communicated. The trifluoromethylated acetylenes were obtained in good to moderate yields. The presented method tolerates a wide range of aromatic, heteroaromatic, and aliphatic potassium alkynyltrifluoroborates.

Metal-Free Synthesis of Ynones from Acyl Chlorides and Potassium Alkynyltrifluoroborate Salts

A straightforward method for the preparation of ynones from acyl chlorides and potassium alkynyltrifluoroborate salts has been developed. The one-pot reaction proceeds rapidly in the presence of a Lewis acid without exclusion of air and moisture.

Ytterbium(III)‐Catalyzed Addition Reaction of Alkynyltrifluoroborate Salts to α‐Imino Esters: Efficient Synthesis of β‐Unsaturated α‐Amino Esters

AbstractWe describe the development of a mild and efficient method for the preparation of β‐unsaturated α‐amino esters through the ytterbium triflate catalyzed addition of potassium alkynyltrifluoroborate salts to imino esters. The synthetic viability of this protocol was supported by its high yields, short reaction times, and efficiency with regard to the scope of the substrates.

Pd-Catalyzed Alkynylation with Potassium Alkynyltrifluoroborates

Pd-Catalyzed Alkynylation with Potassium Alkynyltrifluoroborates

ChemInform Abstract: Iridium‐Catalyzed Enantioselective Allylic Alkynylation.

AbstractThis method allows the highly enantioselective substitution of racemic allylic alcohols with potassium alkynyltrifluoroborates with excellent branched‐to‐linear selectivity.

Pd-catalyzed alkynylation of 2-chloroacetates and 2-chloroacetamides with potassium alkynyltrifluoroborates.

The synthesis of β,γ-alkynyl esters and amides using air-stable potassium alkynyltrifluoroborates as nucleophilic partners in a mild Suzuki-Miyaura cross-coupling reaction has been achieved. Propargyl esters and amides were obtained in high yields using a low catalyst loading, and the substrate scope of the reaction has been significantly improved over previous methods.