Synthetic Strategy for Unsymmetrical α-Fluoro-α'-aryl Ketones

α-Fluoro-α'-aryl ketones are crucial in pharmaceuticals and agrochemicals. However, synthesizing unsymmetrical α-fluoro-α'-aryl ketones poses regioselective challenges. This study presents a one-pot aryl-oxy-fluorination method for synthesizing such unsymmetrical fluoro-aryl ketones. Using ynamide, aryl boronic acid, and F-source under Pd-catalysis, this method efficiently produces a wide range of valuable α-fluoro-α'-aryl ketones with potential applications. Through a combination of control experiments and DFT studies, we proposed a reaction mechanism involving in situ acetic acid formation.

Palladium-catalyzed hydroarylation of 1,3-diynes with arylboronic acids

Transition-metal-catalyzed selective hydroarylation of alkynes represents a state-of-the-art approach in organic chemistry. Herein, we report the reaction of symmetrical 1,3-diynes and arylboronic acids, with Pd(OAc)2 as the catalyst and PCy3 as the ligand, affording functionalized enynes in good to excellent yields. Its efficiency is demonstrated by its good functional group tolerance and broad substrate scope. This method offers a general, convenient, and practical strategy for the modular synthesis of multisubstituted enynes. To comprehensively elucidate the mechanism of the Pd-based catalytic system in the hydroarylation of 1,3-diynes, we performed detailed DFT computations for the Pd-catalyzed hydroarylation reaction.

Copper-Catalyzed Regio- and Stereoselective Hydroarylation of Ynamide

Presented herein is a copper-catalyzed trans-hydroarylation of ynamides. The reaction showcases the assembly of boronic acids across the carbon-carbon triple bond of ynamides. The reaction proceeds under mild conditions offering a complementary approach for the versatile synthesis of multifunctional (E)-α,β-disubstituted enamides. Moreover, the hydroarylation process is highly regio- and stereoselective. The transformation shows a broad scope (30 examples) and tolerates a wide range of labile functional groups. Control experiments provide substantive evidence supporting the mechanistic cycle and the observed selectivity.

Pd-Catalyzed Regioselective (Markovnikov) Addition of Aryl Boronic Acids to Terminal Alkynes of 1,3-Dicarbonyl Compounds and Cyclization/Debenzoylation of Olefinic Dicarbonyl: Access to Arylated Pyran and (E)-4-Methylene-1,6-diphenylhex-5-en-1-one

This Letter outlines palladium-catalyzed regioselective (Markovnikov's) addition of aryl boronic acids to propargyl 1,3-dicarbonyl alkyne to accomplish olefinic/diene 1,3-dicarbonyl compounds without the need for water workup. This methodology showcases remarkable performance with wide-ranging substrate diversity, achieving high yields while employing merely 3 mol % [Pd] alongside a mild KOAc base. Moreover, the utility of dicarbonyl olefins is exemplified through their application in intramolecular cyclization and debenzoylation reactions to access valuable trisubstituted pyran building blocks and (E)-4-methylene-1,6-diphenylhex-5-en-1-one synthesis.

Palladium-catalyzed regioselective decarboxylative hydroarylation of alkynyl carboxylic acids with arylboronic acids

The synthesis of (deuterated) 1,1-disubstituted alkenes via Pd-catalyzed decarboxylative hydroarylation of alkynyl carboxylic acids with arylboronic acids has been developed. The reaction features excellent regioselectivity, a broad substrate scope and gram-scale synthetic ability and offers a general synthetic method to synthesize 1,1-dideuterio olefins. Preliminary mechanism investigations indicate that 1,1-disubstituted alkenes are formed by hydroarylation of terminal alkynes generated by in situ decarboxylation of alkynyl carboxylic acids.

Three Component syn-1,2-Arylmethylation of Internal Alkynes

A Pd-catalyzed three-component syn-1,2-arylmethylation of internal alkynes (ynamides/yne-acetates/alkynes) is described. The readily available and bench stable coupling partners iodo-arenes, and methyl boronic acid are successfully used in this coupling strategy to access the methyl-containing tetra-substituted olefins; the scope is broad showing excellent functional-group tolerance. Notably, the transformation is regio- as well as stereoselective. The biologically relevant motifs (BRM) bearing iodo-arenes and ynamides are also used for the late-stage syn-1,2-arylmethylation of alkynes. Aryl-alkylation, aryl-trideuteriomethylation, alkynyl-methylation, and alkenyl-methylation of ynamides are also presented. The Me-substituted alkenes are further transformed into synthetically important β-amino-indenones and α-fluoro-α'-methyl ketones.

Boron Lewis Acid Catalyzed Intermolecular trans-Hydroarylation of Ynamides with Hydroxyarenes

An atom-economic protocol for the efficient and highly chemo- and stereoselective trans-hydroarylation of ynamides with hydroxyarenes catalyzed by B(C₆F₅)₃ has been developed. Use of readily available starting materials, low catalyst loading, mild reaction conditions, a broad substrate scope, ease of scale-up, and versatile functionalizations of the enamide products make this approach very practical and attractive.

Noncovalent Interaction- and Steric Effect-Controlled Regiodivergent Selectivity in Dimeric Manganese-Catalyzed Hydroarylation of Internal Alkynes: A Computational Study

Selective hydroarylation of internal alkynes catalyzed by a dimeric manganese complex provides a powerful strategy for the construction of multisubstituted alkenes. In this work, density functional theory (DFT) calculations and experimental studies were carried out to explore the mechanism and origin of regiodivergent hydroarylation of internal alkynes reported by our group. The results demonstrate that this reaction first proceeds via a bimetallic mechanism to generate the active catalyst that subsequently undergoes a monometallic mechanism to run the three-stage catalytic cycle: alkyne migratory insertion, protonation, and active catalyst regeneration. Alkyne migratory insertion is considered as the regioselectivity-determining step. Energy decomposition analyses on insertion transition states suggest that the interaction between the substrate and catalyst is mainly responsible for the observed exclusive γ-selectivity of 1a, while the deformation of these two sections induced by the sterically hindered phenyl group and aryl group accounts for the complete β-position arylation of 1e. The decrease of γ-selectivity with the regulation of a tertiary alcohol motif in 1a originates from the reduced noncovalent interaction. The computational results provide important insights into the origin of regiodivergent selectivities and useful information for further designing and adjusting the strategy in Mn-catalyzed alkyne hydroarylation.

Palladium-Catalyzed Regioselective Arylalkenylation of Ynamides

A cationic palladium-catalyzed arylalkenylation of ynamides is presented. The putative keteniminium arylpalladium intermediate likely dictates the regioselective carbopalladation of the ynamide to form a vinylpalladium species. The capture of this complex by the olefin yields linear conjugated β-alkenyl aminodienes (especially with trans selectivity). The transformation features a broad scope with labile functional group tolerance and makes 42 unusual molecular scaffolds with structural diversity. DFT studies provide valuable insights into the reaction mechanism.

Brønsted acid-mediated reactions of ynamides

Over the past two decades, the development and application of ynamide chemistry have received more and more attention. Ynamides have proven to be versatile reagents for organic synthesis, and have been widely applied to the rapid assembly of a diverse range of structurally complex N-containing molecules, especially the valuable N-heterocycles. In comparison with the well-established transition metal-catalyzed reactions of ynamides, metal-free ynamide transformations have relatively seldom been exploited. Recently, Brønsted acid-mediated reactions of ynamides represent significant advances in ynamide chemistry. This review summarizes the latest trends and developments of Brønsted acid-mediated reactions of ynamides, including cycloaddition, cyclization, intramolecular alkoxylation-initiated rearrangement, oxygen atom transfer reactions and hydro-heteroatom addition reactions.

anti-Hydroarylation of Activated Internal Alkynes: Merging Pd and Energy Transfer Catalysis

A general catalytic anti-hydroarylation of electron-deficient internal alkynes compatible with both electron-poor and electron-rich aryl reagents is reported. This selectivity is achieved through a sequential syn-carbopalladation of the alkyne by an Ar-Pd species, followed by a tandem, Ir-photocatalyzed, counter-thermodynamic E → Z isomerization. The use of ortho-substituted boronic acids enables direct access to pharmaceutically relevant heterocyclic cores via a cascade process. Mechanistic insight into the involvement of Ar-Pd versus Pd-H as an active species is provided.

Copper-catalyzed tandem cis-carbometallation/cyclization of imine-ynamides with arylboronic acids

An efficient copper-catalyzed tandem regioselective cis-carbometallation/cyclization of imine-ynamides with arylboronic acids has been developed. This method leads to a facile and practical synthesis of valuable 2,3-disubstituted indolines in moderate to excellent yields and features a broad substrate scope and wide functional group tolerance. Other significant features of this protocol include the use of readily available starting materials, high flexibility, simple procedure and mild reaction conditions.

Synthesis of (Z)-β-(Carbonylamino)alkenylindium through Regioselective anti-Carboindation of Ynamides and Its Transformation to Multisubstituted Enamides

The regioselective anti-carboindation of ynamides by using InBr₃ and silylated nucleophiles was developed to synthesize (Z)-β-(carbonylamino)alkenylindiums. The X-ray crystallographic analysis of an alkenylindium suggested that the reaction proceeded in an anti-addition fashion. In contrast to reported syn-carbometalations of ynamides by using organometallics, a cooperation of InBr₃ and silylated nucleophiles to ynamides achieved an anti-addition, which was supported by DFT calculations. The scope of substrates included various ynamides and silylated nucleophiles, such as silyl ketene acetals and silyl ketene imines. The transformation of synthesized alkenylindiums by iodination, radical coupling, and Pd-catalyzed cross-coupling successfully afforded trisubstituted enamines with high regio- and stereoselectivities.

Selective Hydroarylation of 1,3-Diynes Using a Dimeric Manganese Catalyst: Modular Synthesis of Z-Enynes

The transition-metal-catalyzed selective hydroarylation of unsymmetrical alkynes represents the state-of-art in organic chemistry, and still mainly relies on the use of precious late-transition-metal catalysts. Reported herein is an unprecedented Mn^I -catalyzed hydroarylation of unsymmetrical 1,3-diyne alcohols with commercially available arylboronic acids with predictive selectivity. This method addresses the challenges in regio-, stereo-, and chemoselectivity. It offers a general, convenient and practical strategy for the modular synthesis of multisubstituted Z-configurated conjugated enynes. This protocol is distinguished by its operational simplicity, complete selectivity, excellent functional-group compatibility, and gram-scale potential. A dimeric Mn^I species, Mn₂ (CO)₈ Br₂ , was proven to be a much more efficient catalyst precursor than Mn(CO)₅ Br.

Palladium-catalyzed dimerization of N-aryl propargylamines for the synthesis of 3-vinylquinolines

A straightforward method for the synthesis of polyfunctionalized quinolines from readily available N-aryl propargylamines under aerobic conditions was developed. It provides convenient access to a variety of synthetically and pharmaceutically important quinolines in moderate to good yields. Control experiments suggest that the cascade reaction might proceed via the Pd-catalyzed electrophilic cyclization of N-aryl propargylamines followed by a hydroarylation process through trapping of the σ-quinolinylpalladium intermediate with a second molecule of the substrate.

Ynamide Preactivation Allows a Regio- and Stereoselective Synthesis of α,β-Disubstituted Enamides

A novel ynamide preactivation strategy enables the use of otherwise incompatible reagents and allows preparation of α,β-disubstituted enamides with high regio- and stereoselectivity. Mechanistic analysis reveals the intermediacy of a triflate-bound intermediate as a solution-stable, effective keteniminium reservoir, whilst still allowing subsequent addition of organometallic reagents.

Enantioselective Nickel-Catalyzed anti-Carbometallative Cyclizations of Alkynyl Electrophiles Enabled by Reversible Alkenylnickel E/Z Isomerization

Nickel-catalyzed additions of arylboronic acids to alkynes, followed by enantioselective cyclizations of the alkenylnickel species onto tethered ketones or enones, are reported. These reactions are reliant upon the formal anti-carbonickelation of the alkyne, which is postulated to occur by the reversible E/Z isomerization of an alkenylnickel species.

Formation of α-chalcogenyl acrylamides through unprecedented chalcogen-mediated metal-free oxyfunctionalization of ynamides with DMSO as an oxidant

A novel chalcogen-mediated metal-free oxyfunctionalization mode of ynamides for the synthesis of α-chalcogenyl acrylamides has been developed.

TfOH-mediated [2 + 2 + 2] cycloadditions of ynamides with two discrete nitriles: synthesis of 4-aminopyrimidine derivatives

In this study, a concise and atom-economical TfOH-mediated [2 + 2 + 2] cycloaddition of ynamides with two discrete nitriles is developed to synthesize multi-substituted 4-aminopyrimidine.

Recent progress towards gold-catalyzed synthesis of N-containing tricyclic compounds based on ynamides

The recent advances in the gold-catalyzed construction of N-containing tricycles based on ynamides are reviewed by highlighting their specificity and applicability, and the mechanistic rationale.

Construction of 1-Naphthols via Benzannulation Based on the Reaction of Aryl tert-Butyl Ynol Ethers with Ynamides or Ynol Ethers

A new version of benzannulation featuring the use of aromatic tert-butyl ynol ethers as the convenient precursors for arylketenes has been developed. Both ynamides and ynol ethers undergo this reaction smoothly, giving 3-amino and 3-alkoxy 1-naphthols in good to excellent yields under the heated reaction conditions. The high efficiency, excellent regioselectivity, good functional group compatibility, and broad substrate scope render this reaction particularly valuable for organic synthesis.