Rhodium-catalyzed carbometalation of ynamides with organoboron reagents

Trifluoromethyl Group (CF3) Induced Regioselective Larock Indole Synthesis from Unsymmetric β-CF3-1,3-enynes

The indole skeleton exists widely in natural products, pharmaceuticals, and materials. We disclose here a trifluoromethyl group induced regioselective Larock indole synthetic method from unsymmetric 2-CF3-1,3-enynes. The presence of a trifluoromethyl group is determinable for the regioselectivity. Once the CF3 group was replaced with the methyl or phenyl group, a ratio of 1:1 to 1:1.4 isomers were obtained. This strategy features good regioselectivity, broad substrate scope, and high functional group tolerance. The protocol reported here offers an alternative solution to the rare 3,4-functionalization of 2-CF3-1,3-enynes. The products were further transformed to show distinctive reactivity in hydroboration-oxidation and hydro-bromination.

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.

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.

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.

Cationic-palladium catalyzed regio- and stereoselective syn-1,2-dicarbofunctionalization of unsymmetrical internal alkynes

π-Extended tetrasubstituted olefins are widely found motifs in natural products, leading drugs, and agrochemicals. Thus, development of modular strategies for the synthesis of complex all-carbon-substituted olefins always draws attention. The difunctionalization of unsymmetrical alkynes is an attractive approach but it has remained faced with regioselectivity issues. Here we report the discovery of a regio- and stereoselective syn-1,2-dicarbofunctionalization of unsymmetrical internal alkynes. A cationic Pd-catalyzed three-component coupling of aryl diazonium salts, aryl boronic acids (or olefins) and yne-acetates enables access to all-carbon substituted unsymmetrical olefins. The transformation features broad scope with labile functional group tolerance, building broad chemical space of structural diversity (94 molecules). The value of this synthetic method is demonstrated by the direct transformation of natural products and drug candidates containing yne-acetates, to enable highly substituted structurally complex allyl acetate analogues of biologically important compounds. Synthetic versatility of the carboxylate bearing highly substituted olefins is also presented. The reaction outcome is attributed to the in situ formation of stabilized cationic aryl-Pd species, which regulates regioselective aryl-palladation of unsymmetrical yne-acetates. Control experiments reveal the synergy between the carboxylate protecting group and the cationic Pd-intermediate in the regioselectivity and reaction productivity; density functional theory (DFT) studies rationalize the selectivity of the reaction.

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.

Nickel-Catalyzed β-Regioselective Amination/Cyclization of Ynamide-Nitriles with Amines: Synthesis of Functionalized 3-Aminoindoles and 4-Aminoisoquinolines

A highly regioselective nickel/Lewis acid catalyzed amination/cyclization of ynamide-nitriles with amines involving β-addition has been developed. The reaction offers an attractive and efficient route for the synthesis of 3-aminoindoles and 4-aminoisoquinoline derivatives. The Ts-group on the ynamide acts as a directing group to produce the alkenyl nickel species with high regioselectivity.

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.

Hydroxy group-enabled highly regio- and stereo-selective hydrocarboxylation of alkynes

Hydrogen bonding-enabled highly regio- and stereo-selective hydrocarboxylation of alkynes has been successfully developed to afford 3-hydroxy-2(E)-alkenoates with up to 97% yield.

Here we present an example of utilizing hydroxy groups for regioselectivity control in the addition reaction of alkynes—a highly efficient Pd-catalyzed syn-hydrocarboxylation of readily available 2-alkynylic alcohols with CO in the presence of alcohols with an unprecedented regioselectivity affording 3-hydroxy-2(E)-alkenoates. The role of the hydroxy group has been carefully studied. The synthetic potential of the products has also been demonstrated.

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.

PIFA-BF3·OEt2 mediated intramolecular regioselective domino cyclization of ynamides: A novel method for the synthesis of tetrahydroisoquinoline-oxazol-2(3H)-ones

The transition metal-free intramolecular regioselective domino cyclization of N-Boc protected ynamides has been developed to provide the corresponding tetrahydroisoquinoline-oxazo-2(3H)-ones in moderate to good yields.

Cu-Catalyzed Alkylative Carboxylation of Ynamides with Dialkylzinc Reagents and Carbon Dioxide

Alkylative carboxylation of ynamides with CO2 and dialkylzinc reagents using a N-heterocyclic carbene (NHC)-copper catalyst has been developed. A variety of ynamides, both cyclic and acyclic, undergo this transformation under mild conditions to afford the corresponding α,β-unsaturated carboxylic acids, which contain the α,β-dehydroamino acid skeleton. The present alkylative carboxylation formally consists of Cu-catalyzed carbozincation of ynamides with dialkylzinc reagents with the subsequent nucleophilic carboxylation of the resulting alkenylzinc species with CO2 . Dialkylzinc reagents bearing a β-hydrogen atom such as Et2 Zn and Bu2 Zn still afford the alkylated products despite the potential for β-hydride elimination. This protocol would be a desirable method for the synthesis of highly substituted α,β- dehydroamino acid derivatives due to its high regio- and stereoselectivity, simple one-pot procedure, and its use of CO2 as a starting material.

Ruthenium-catalyzed alkene-alkyne coupling of disubstituted olefins: application to the stereoselective synthesis of trisubstituted enecarbamates

The Ru-catalyzed alkene-alkyne coupling reaction has been demonstrated to be an enabling methodology for the synthesis of complex molecules. However, to date, it has been limited to monosubstituted olefins. Herein we report the first general utilization of disubstituted olefins in the Ru-catalyzed alkene-alkyne coupling reaction by employing carbamate directing groups. The products are stereodefined trisusbstituted enecarbamates. The elaboration of these structures toward the asymmetric synthesis of complex aminocyclopentitols and 1,2-amino alcohols is discussed.

Preparation of (Z)-α,β-disubstituted enamides via palladium-catalyzed addition of boronic acids to ynamides

A Pd-catalyzed, highly regio- and stereoselective addition of boronic acids to ynamides has been realized. This protocol generates (Z)-α,β-disubstituted enamides in high yields with excellent regio- and stereoselectivity under the mild reaction conditions, thereby providing a good complementary method for the diverse synthesis of multifunctional enamides. A wide collection of functional groups are found to be tolerated. It represents a straightforward and useful means to assemble stereodefined enamides from readily available starting materials.

An unprecedented Pd-catalyzed trans-addition of boronic acids to ynamides

An unusual Pd-catalyzed trans-addition of boronic acids to ynamides has been realized in this paper, providing α,β-disubstituted enamides in good yields with excellent regio- and stereoselectivity.

Regio- and stereoselective carbometallation reactions of N-alkynylamides and sulfonamides

The carbocupration reactions of heterosubstituted alkynes allow the regio- and stereoselective formation of vinyl organometallic species. N-Alkynylamides (ynamides) are particularly useful substrates for the highly regioselective carbocupration reaction, as they lead to the stereodefined formation of vinylcopper species geminated to the amide moiety. The latter species are involved in numerous synthetically useful transformations leading to valuable building blocks in organic synthesis. Here we describe in full the results of our studies related to the carbometallation reactions of N-alkynylamides.

Rhodium-catalyzed [2 + 2] cycloaddition of ynamides with nitroalkenes

In the presence of a diene-ligated rhodium complex, ynamides and nitroalkenes undergo catalytic [2 + 2] cycloadditions to provide cyclobutenamides. The presence of sodium tetraphenylborate was found to be crucial for the reactions to proceed efficiently.

Palladium-catalyzed hydroacyloxylation of ynamides

In the presence of substoichiometric Pd(OAc)(2), carboxylic acids undergo highly regio- and stereoselective additions to ynamides to provide α-acyloxyenamides.

N-allyl-N-sulfonyl ynamides as synthetic precursors to amidines and vinylogous amidines. An unexpected N-to-C 1,3-sulfonyl shift in nitrile synthesis

A detailed study of amidine synthesis from N-allyl-N-sulfonyl ynamides is described here. Mechanistically, this is a fascinating reaction consisting of diverging pathways that could lead to deallylation or allyl transfer depending upon the oxidation state of palladium catalysts, the nucleophilicity of amines, and the nature of the ligands. It essentially constitutes a Pd(0)-catalyzed aza-Claisen rearrangement of N-allyl ynamides, which can also be accomplished thermally. An observation of N-to-C 1,3-sulfonyl shift was made when examining these aza-Claisen rearrangements thermally. This represents a useful approach to nitrile synthesis. While attempts to render this 1,3-sulfonyl shift stereoselective failed, we uncovered another set of tandem sigmatropic rearrangements, leading to vinyl imidate formation. Collectively, this work showcases the rich array of chemistry one can discover using these ynamides.

Regio- and stereoselective synthesis of 2-amino-1,3-diene derivatives by ruthenium-catalyzed coupling of ynamides and ethylene

A ruthenium-catalyzed hydrovinylation-type cross-coupling of ynamides and ethylene proceeds via ruthenacyclopentene to give 2-aminobuta-1,3-diene derivatives in a highly regioselective manner. It was also demonstrated that 2-aminobuta-1,3-diene derivatives reacted with various dienophiles or singlet oxygen to give a cyclic enamide derivative.