Potassium Alkyltrifluoroborates Research Articles

Photoinduced Alkylsulfonylation and Cyanoalkylsulfonylation of Morita-Baylis-Hillman Adducts via Multicomponent Insertion of Sulfur Dioxide.

General and convenient visible-light-promoted alkylsulfonylation and cyanoalkylsulfonylation of MBH adducts have been developed through the multicomponent insertion of sulfur dioxide, enabling the assembly of two C-S bonds to generate structurally diverse allylic alkylsulfones (43 examples in total). The reaction of MBH adducts with potassium alkyltrifluoroborates and 1,4-diazabicyclo[2.2.2]octane bis(sulfur dioxide) adduct afforded sulfones with generally good yields. Notably, the addition of N,N,N',N'-tetramethylethylenediamine as a base into the photocatalytic system led to yielding an alkyl sulfonyl unit and cyano group-anchored trisubstituted alkenes by utilizing cycloketone oxime esters as C-radical precursors. Both of these reactions have constructed two C-S bonds, and all desired products were obtained in moderate to excellent yields with complete stereospecificity.

Enantioenriched Allylesters via a Copper-Catalyzed Diene Carboesterification with Alkyltrifluoroborates and Carboxylic Acids.

The rapid synthesis of a range of enantioenriched allylic esters is enabled by a new 3-component catalytic enantioselective 1,2-carboesterification of readily available dienes with carboxylic acids and potassium alkyltrifluoroborates. The chiral copper catalyst, formed in situ from Cu(OTf)2 and (4S,4'S)-2,2'-(cyclopentane-1,1-diyl)bis(4-phenyl-4,5-dihydrooxazole), is implicated in both the generation of alkyl radicals from the alkyltrifluoroborates as well as the enantioselective formation of C-O bonds. Potassium salts of primary and secondary alkyltrifluoroborates as well as several benzylic trifluoroborates, tert-butyltrifluoroborate, and phenyltrifluoroborate participate in the reaction. The regioselectivity and enantioselectivity are strongly impacted by variations in all of the reaction components, which in turn are thought to impact the C-O bond-forming reductive elimination from a [Cu(III)] intermediate.

Photoinduced radical alkylation of aldehydes with potassium alkyltrifluoroborates

A method for radical addition at aldehydes is described. The reaction is based on the interplay of radical attack and cleavage processes occurring at a boron complexed carbonyl group.

Isocyanides as Catalytic Electron Acceptors in the Visible Light Promoted Oxidative Formation of Benzyl and Acyl Radicals.

The recent disclosure of the ability of aromatic isocyanides to harvest visible light and act as single electron acceptors when reacting with tertiary aromatic amines has triggered a renewed interest in their application to the development of green photoredox catalytic methodologies. Accordingly, the present work explores their ability to promote the generation of both alkyl and acyl radicals starting from radical precursors such as Hantzsch esters, potassium alkyltrifluoroborates, and α-oxoacids. Mechanistic studies involving UV-visible absorption and fluorescence experiments, electrochemical measurements of the ground-state redox potentials along with computational calculations of both the ground- and the excited-state redox potentials of a set of nine different aromatic isocyanides provided key insights to promote a rationale design of a new generation of isocyanide-based organic photoredox catalysts. Importantly, the green potential of the investigated chemistry has been herein demonstrated by a direct and easy access to deuterium labeled compounds.

Access to axially chiral styrenes via a photoinduced asymmetric radical reaction involving a sulfur dioxide insertion

The wide applicability in various fields enables development of novel methods to access axially chiral styrenes to be of significance. Among the developed and potential synthetic strategies for this type of framework, the route based on an asymmetric radical process is more challenging and has not been achieved so far. Here we report a photo-promoted, three-component, asymmetric free radical reaction of potassium alkyltrifluoroborates, potassium metabisulfite, and 1-alkynylnaphthalen-2-ols, delivering axially chiral ( S , E )-1-(1-(alkylsulfonyl)-2-vinyl)naphthalen-2-ols with excellent enantioselectivity (93%–99% enantiomeric excess) and good yield (up to 97%). The transformation involves in situ generation of alkylsulfonyl radicals, tandem enantioselective radical addition, and a reduction process of radical species. • Photoinduced asymmetric catalytic radical approach to access axially chiral styrenes • A rare success in the field of asymmetric sulfur dioxide insertion • Broad substrate scope with excellent enantioselectivity and regioselectivity Development of new pathways for generation of axially chiral styrenes has gained great attention in recent years because of the wide applicability of axially chiral styrenes in chiral ligands, catalysts, and functional materials. Among the developed and potential synthetic strategies for synthesis of axially chiral styrenes, the synthetic route through an asymmetric radical process is more challenging and has not been achieved so far. Here we developed a photoinduced asymmetric catalytic radical approach to access sulfonyl-containing axially chiral styrenes with excellent enantioselectivity, regioselectivity, good yield, and broad substrate scope. Control experiments and DFT calculations were carried to understand the mechanism and the origin of the high enantioselectivity and Z/E selectivity of the reaction. Photoinduced three-component asymmetric free radical reaction of potassium alkyltrifluoroborates, potassium metabisulfite and 1-alkynylnaphthalen-2-ols, delivering axially chiral ( S , E )-1-(1-(alkylsulfonyl)-2-vinyl)naphthalen-2-ols with excellent enantioselectivity (93%–99% ee) and good yield (up to 97%). The transformation involves in situ generation of alkylsulfonyl radicals and a tandem enantioselective radical addition process.

Access to chiral β-sulfonyl carbonyl compounds via photoinduced organocatalytic asymmetric radical sulfonylation with sulfur dioxide.

An organocatalytic enantioselective radical reaction of potassium alkyltrifluoroborates, DABCO·(SO2)2 and α,β-unsaturated carbonyl compounds under photoinduced conditions is developed, which provides an efficient pathway for the synthesis of chiral β-sulfonyl carbonyl compounds in good yields with excellent enantioselectivity (up to 96% ee). Aside from α,β-unsaturated carbonyl compounds with auxiliary groups, common chalcone substrates are also well compatible with this organocatalytic system. This method proceeds through an organocatalytic enantioselective radical sulfonylation under photoinduced conditions, and represents a rare example of asymmetric transformation involving sulfur dioxide insertion.

Manganese(III)‐Promoted Double Carbonylation of Anilines Toward α‐Ketoamides Synthesis

AbstractEmploying anilines as nucleophiles in double carbonylation is a longstanding challenge. In this communication, a Mn(III)‐promoted double carbonylation of alkylborates or Hantzsch esters with anilines toward the synthesis of α‐ketoamides has been developed. By using easily available potassium alkyltrifluoroborates or Hantzsch esters as the starting material, and cheap and non‐toxic Mn(OAc)3 ⋅ 2H2O as the promotor, a broad range of alkyl α‐ketoamide derivatives were synthesized in moderate to good yields with excellent selectivity.magnified image

Photoinduced reaction of potassium alkyltrifluoroborates, sulfur dioxide and para-quinone methides via radical 1,6-addition

A photoinduced reaction of potassium alkyltrifluoroborates, sulfur dioxide, and para-quinone methides under visible light irradiation at room temperature is developed, giving rise to diarylmethyl alkylsulfones in moderate to good yields. This reaction works well under photocatalysis with a broad substrate scope by using DABCO·(SO2)2 as the source of sulfur dioxide. Mechanistic study shows that this transformation is initiated by alkyl radicals generated in situ from potassium alkyltrifluoroborates in the presence of photocatalyst. The subsequent insertion of sulfur dioxide and radical 1,6-addition of para-quinone methides with alkylsulfonyl radical intermediates afford the corresponding diarylmethyl alkylsulfones.

Synergistic photoredox and tertiary amine catalysis: generation of allylic sulfones from Morita–Baylis–Hillman acetates and sulfur dioxide

The first example of the synthesis of allylic sulfones through synergistic photoredox and tertiary amine catalysis, starting from MBH acetates, DABCO·(SO2)2 and 4-substituted Hantzsch esters or potassium alkyltrifluoroborates via a radical pathway, is reported.

Synthesis of Benzylureas and Related Amine Derivatives via Copper-Catalyzed Three-Component Carboamination of Styrenes.

A direct assembly of secondary benzylureas and related amine derivatives via copper-catalyzed carboamination of styrenes with potassium alkyltrifluoroborates and ureas, anilines, or an amide is reported. Terminal and 1,2-disubstituted alkenes, as well as dienes, participate in this three-component coupling reaction. The reaction mechanism likely involves the addition of an alkyl radical to the styrene, followed by metal-mediated oxidative coupling of the resulting benzylic radical with the amine derivative. Factors that impact substrate reactivity and regioselectivity are discussed.

Photoinduced synthesis of alkylalkynyl sulfones through a reaction of potassium alkyltrifluoroborates, sulfur dioxide, and alkynyl bromides

A photoinduced reaction of potassium alkyltrifluoroborates, sodium metabisulfite, and alkynyl bromides under visible light irradiation at room temperature is developed.

Fluoroalkylselenolation of Alkyl Silanes/Trifluoroborates under Metal‐Free Visible‐Light Photoredox Catalysis

Herein a metal‐free fluoroalkylselenolation of alkylsilanes as well as potassium alkyltrifluoroborates under visible light photocatalysis is disclosed. The developed methodologies are performed under mild conditions, room temperature in the presence of an organic photocatalyst and blue LED irradiation. Mechanistic investigations including luminescence and EPR spectroscopy allow us to shed light on both mechanisms.

Three‐Component Reaction of Potassium Alkyltrifluoroborates, Sulfur Dioxide and Allylic Bromides under Visible‐Light Irradiation

AbstractDiverse allylic sulfones are generated through a three‐component reaction of potassium alkyltrifluoroborates, sulfur dioxide and allylic bromides in the presence of 9‐mesityl‐10‐methyl acridinium perchlorate under visible light irradiation at room temperature. This transformation proceeds efficiently, and a broad reaction scope is demonstrated with good functional groups tolerance. This reaction is initiated by the treatment of potassium alkyltrifluoroborate under visible‐light irradiation in the presence of a photocatalyst, leading to alkyl radical. This alkyl radical intermediate is trapped by sulfur dioxide to provide alkylsulfonyl radical, which then undergoes further transformation to afford the corresponding allylic sulfone.

Merging photoredox catalysis with allylboration. The photochemical perfluoroalkylation of unsaturated potassium alkyltrifluoroborates and synthesis of fluorinated alcohols

The development of a visible light-mediated atom transfer radical addition (ATRA) of perfluoroalkyl iodides to potassium 1-penten-5-yl-, vinyl- and allyltrifluoroborates using the reductive quenching of [Ru(bpy)3]Cl2 or [Ru(bpy)3](PF6)2 is described. Using an operationally simple and mild protocol, the corresponding potassium trifluoroborates containing perfluoroalkyl groups were obtained in moderate to high yields. In the case of potassium allyltrifluoroborate, the use of acetone as the solvent resulted in allylboration followed by ATRA of perfluoroalkyl iodides to the formed homoallyl alcohol. A one-pot protocol was developed for the synthesis of a series of fluorinated alcohols using potassium allyltrifluoroborate, perfluoroalkyl iodides and selected aliphatic ketones.

Photocatalytic Reaction of Potassium Alkyltrifluoroborates and Sulfur Dioxide with Alkenes.

A three-component reaction of potassium alkyltrifluoroborates, the sulfur dioxide surrogate of DABCO·(SO2)2, and alkenes under photocatalysis in the presence of visible light is developed. This reaction works efficiently at room temperature with the insertion of sulfur dioxide under mild conditions, affording diverse sulfones in good to excellent yields. The alkyl radical and alkylsulfonyl radical are generated as key intermediates, and a reductive single-electron transfer is involved in the reaction process.

Visible light-promoted alkylation of imines using potassium organotrifluoroborates.

A mild, redox-neutral, alkylation of imines with potassium alkyltrifluoroborates is described. The reaction proceeds under photoredox conditions at ∼30 °C with primary, secondary, and tertiary alkyltrifluoroborates, leading to alkylation products in moderate to good yield in most cases. Aryl-, vinyl-, and cyclopropyltrifluoroborates failed to react under the reported conditions.

Silver(I)-mediated Reaction of 2-Isocyanobiaryl with Alkyl Trifluoroborates: Efficient Synthesis of 6-Alkylated Phenanthridines

A silver-mediated free-radical cascade cyclization of isocyanides with potassium alkyl trifluoroborates was developed. The procedure tolerates a series of functional groups, including chloro, bromo, ester, ketone, and amide. Additionally, it is not sensitive to steric hindrance. Thus, this reaction represents a very useful strategy for the production of 6-alkylated phenanthridine derivatives. The addition of alkyl radical to the isonitrile, followed by a radical aromatic cyclization, is involved in this transformation.

Generation of Diversity Sets with High sp3 Fraction Using the Photoredox Coupling of Organotrifluoroborates and Organosilicates with Heteroaryl/Aryl Bromides in Continuous Flow.

The photoredox cross-coupling of aryl halides and potassium alkyl trifluoroborates is a very effective means to form Csp3-Csp2 bonds. However, this transformation is inefficient for the coupling of unactivated primary trifluoroborates. We have developed a generally useful, continuous flow Csp3-Csp2 coupling procedure for the synthesis of diverse product sets that is compatible with both trifluoroborates and silicate reagents. This universal protocol provides diversity sets from both primary and secondary coupling partners. This easily scalable procedure widens the substrate scope of the coupling reaction and is efficient for producing a greater range of analogues bearing a high sp3 fraction.

Photoinduced synthesis of (E)-vinyl sulfones through the insertion of sulfur dioxide

Under visible light irradiation, a three-component reaction of potassium alkyltrifluoroborates, sulfur dioxide and alkynes with the assistance of photocatalysis and in the presence of copper(ii) triflate is described. This transformation affords (E)-vinyl sulfones efficiently with excellent regioselectivity and stereoselectivity under mild conditions.

Rh(III)-catalyzed oxidative ortho-C–H alkylation of 2,4-diarylquinazoline with potassium alkyltrifluoroborates

Alkyltrifluoroborates were used for Rh(III)-catalyzed ortho-alkylation of 2,4-disubstituted quinazoline via C–H bond activation. The reaction proceeded well with a broad substrate scope, providing a direct way to access high functional quinazoline core structure derivatives in yields up to 95%.