Hydroarylation Of Alkynes Research Articles

Synthesis of Benzo[a]carbazoles and Dibenzo[c,g]carbazoles via Sequential Gold Catalysis and Photomediated Cyclization.

Herein, we report a reaction protocol for the construction of benzo[a]carbazole and dibenzo[c,g]carbazole frameworks. The detailed gold catalytic reaction conditions developed for the challenging intermolecular carbon nucleophilic addition to internal alkynes are realized, giving the desired alkyne hydroarylation products in good yields. The resulting trisubstituted alkenes are able to undergo photomediated cyclization, furnishing the desired carbazole molecules with excellent yields and high efficiency.

A novel Fe(III) and 2-amino-perimidinium based hybrid material catalyzed friedel–Crafts type hydroarylation of alkynes: Scope and mechanism

A new inorganic-organic hybrid material with the structural formula (C51H66N9)3[FeCl4]·2Cl consisting of iron(III) center, 2-amino-perimidinium ligand and free chloride ions was synthesized. In addition, the compound was characterized by single-crystal X-ray diffraction and Fourier-transform infrared spectroscopy techniques. The structural arrangements and hydrogen bonding interactions in the compound were studied and successfully employed in the catalytic hydroarylation of alkynes and arenes to produce the corresponding 1,1-diaryl alkene derivatives. Gratifyingly, when nitromethane was employed as a solvent, the title compound displayed excellent catalytic activity with moderate to high conversions. Stoichiometric reactions and experimental data both provided key evidence in support of the reaction mechanism.

Synthesis and Photophysical Properties of β-Alkenyl-Substituted BODIPY Dyes by Indium(III)-Catalyzed Intermolecular Alkyne Hydroarylation.

A new atom-economical synthesis of β-alkenyl-substituted BODIPYs via indium(III)-catalyzed intermolecular alkyne hydroarylation with meso-substituted BODIPYs is described. While catalysis with InI3 allows the double β-functionalization of BODIPY, resulting in regioselectively branched β,β'-disubstituted alkenyl BODIPYs, catalytic InCl3 enables the formation of linear β-substituted alkenyl BODIPYs. Subsequent In(III)-catalyzed intermolecular alkyne hydroarylation allows the synthesis of unsymmetrical push-pull BODIPY derivatives. Therefore, indium catalysis offers complementary regioselectivity in good chemical yields and functional group tolerance. The resulting BODIPY dyes displayed bathochromically shifted absorption and emission according to the electron-nature of the substituents in the alkenyl moiety with high molar extinction coefficients (ε up to 88,200 M-1 cm-1) and quantum yields (0.14-0.96).

Catalytic asymmetric construction of helicenes via transformation of biaryls.

This review showcases a systematic overview of the available tools for the catalytic asymmetric transformation of biaryl substrates toward the construction of challenging enantioenriched helicenes and the conceptual aspects associated with each type of transformation. Depending on the properties of the biaryl and the nature of the process, several methodologies have been developed, including olefin metathesis, hydroarylation of alkynes, C-X (X = C, O, N) coupling, and C-H functionalization. Pioneering studies and an array of representative reactions are discussed to underscore the potential of these synthetic protocols.

Gold-catalyzed benzannulations of 2-alkenylindoles with alkynes: a protecting-group-free regioselective approach to carbazoles.

A gold(I)-catalyzed protecting-group-free benzannulation approach to functionalized NH-carbazoles was accomplished via the hydroarylation of alkynes with 2-alkenylindoles. A broad spectrum of terminal and internal alkynes and 2-alkenylindoles successfully participated in this annulation reaction. The protocol efficiently enabled the formation of substituted NH-carbazoles with moderate to specific regioselectivities. The synthetic utility of this protocol was demonstrated by a variety of post-functionalizations.

Stereo-selective synthesis of complex dienes and eneynes by sequential hydroarylation and olefinic C–H functionalization

We present a preparation of complex dienes and eneynes by Rh-catalyzed hydroarylation of internal alkynes and Pd-catalyzed olefinic C–H alkenylation, alkynylation and allylation, enabled by the chelation assistance of pyrazinamide or picolinamide.

Pd(II)-catalyzed hydroarylations/hydroalkenylations of terminal alkynes: regioselective synthesis of allylic, homoallylic, and 1,3-diene systems.

A Pd-catalyzed regioselective hydroarylation of terminal alkynes containing a heteroatom has been developed via carbopalladation for the synthesis of allylic ethers, amines, and homoallylic alcohols. Moreover, hydroalkenylation of alkynes produces a variety of stereodefined 1,4-dienes with high regioselectivity. The important features of the present protocol are that it is highly regioselective, operationally rapid, and scalable with a huge substrate scope using only 3 mol% of PdCl2(PPh3)2 catalyst in the presence of a mild base KOAc.

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.

A selective photoinduced radical O-alkenylation of phenols and naphthols with terminal alkynes.

The visible light-promoted O-alkenylation of phenols and naphthols with terminal alkynes is achieved using 2,4,6-tris(4-fluorophenyl)pyrylium tetrafluoroborate (T(p-F)PPT) as a photocatalyst at room temperature without the need of any external ligand or additive. Apart from its excellent functional group tolerance, the protocol described herein represents an appealing alternative strategy to classical transition-metal catalysed hydroarylation reactions. Mechanistic investigations revealed that the reaction involves a radical pathway. The utility of the hydroarylated products for the synthesis of fused benzofurans via a one-pot annulation was also demonstrated. Herein, we report the first intermolecular radical hydroarylation of alkynes.

Synthesis of Nanographenes via Gold-Catalyzed Double Hydroarylation of Alkynes

Synthesis of Nanographenes via Gold-Catalyzed Double Hydroarylation of Alkynes

Gold‐Catalyzed 1,2‐Aryl Shift and Double Alkyne Benzannulation

AbstractThe tandem intramolecular hydroarylation of alkynes accompanied by a 1,2‐aryl shift is described. Harnessing the unique electron‐rich character of 1,4‐dihydropyrrolo[3,2‐b]pyrrole scaffold, we demonstrate that the hydroarylation of alkynes proceeds at the already occupied positions 2 and 5 leading to a 1,2‐aryl shift. Remarkably, the reaction proceeds only in the presence of cationic gold catalyst, and it leads to heretofore unknown π‐expanded, centrosymmetric pyrrolo[3,2‐b]pyrroles. The utility is verified in the preparation of 13 products that bear six conjugated rings. The observed compatibility with various functional groups allows for increased tunability with regard to the photophysical properties as well as providing sites for further functionalization. Computational studies of the reaction mechanism revealed that the formation of the six‐membered rings accompanied with a 1,2‐aryl shift is both kinetically and thermodynamically favourable over plausible formation of products containing 7‐membered rings. Steady‐state UV/Visible spectroscopy reveals that upon photoexcitation, the prepared S‐shaped N‐doped nanographenes undergo mostly radiative relaxation leading to large fluorescence quantum yields. Their optical properties are rationalized through time‐dependent density functional theory calculations. We anticipate that this chemistry will empower the creation of new materials with various functionalities.

Gold-Catalyzed 1,2-Aryl Shift and Double Alkyne Benzannulation.

The tandem intramolecular hydroarylation of alkynes accompanied by a 1,2-aryl shift is described. Harnessing the unique electron-rich character of 1,4-dihydropyrrolo[3,2-b]pyrrole scaffold, we demonstrate that the hydroarylation of alkynes proceeds at the already occupied positions 2 and 5 leading to a 1,2-aryl shift. Remarkably, the reaction proceeds only in the presence of cationic gold catalyst, and it leads to heretofore unknown π-expanded, centrosymmetric pyrrolo[3,2-b]pyrroles. The utility is verified in the preparation of 13 products that bear six conjugated rings. The observed compatibility with various functional groups allows for increased tunability with regard to the photophysical properties as well as providing sites for further functionalization. Computational studies of the reaction mechanism revealed that the formation of the six-membered rings accompanied with a 1,2-aryl shift is both kinetically and thermodynamically favourable over plausible formation of products containing 7-membered rings. Steady-state UV/Visible spectroscopy reveals that upon photoexcitation, the prepared S-shaped N-doped nanographenes undergo mostly radiative relaxation leading to large fluorescence quantum yields. Their optical properties are rationalized through time-dependent density functional theory calculations. We anticipate that this chemistry will empower the creation of new materials with various functionalities.

Atroposelective Synthesis of C-N Vinylindole Atropisomers by Palladium-Catalyzed Asymmetric Hydroarylation of 1-Alkynylindoles.

Transition-metal-catalyzed hydroarylation of unsymmetrical internal alkynes remains challenging because of the difficulty in controlling regioselectivity and stereoselectivity. Moreover, the enantioselective hydroarylation of alkynes using organoboron reagents has not been reported. Herein, we report for the first time that palladium compounds can catalyze the hydroarylation of 1-alkynylindoles with organoborons for the synthesis of chiral C-N atropisomers. A series of rarely reported vinylindole atropisomers was synthesized with excellent regio-, stereo- (Z-selectivity), and enantioselectivity under mild reaction conditions. The ready availability of organoborons and alkynes and the simplicity, high stereoselectivity, and good functional group tolerance of this catalytic system make it highly attractive.

Atroposelective Synthesis of C−N Vinylindole Atropisomers by Palladium‐Catalyzed Asymmetric Hydroarylation of 1‐Alkynylindoles

AbstractTransition‐metal‐catalyzed hydroarylation of unsymmetrical internal alkynes remains challenging because of the difficulty in controlling regioselectivity and stereoselectivity. Moreover, the enantioselective hydroarylation of alkynes using organoboron reagents has not been reported. Herein, we report for the first time that palladium compounds can catalyze the hydroarylation of 1‐alkynylindoles with organoborons for the synthesis of chiral C−N atropisomers. A series of rarely reported vinylindole atropisomers was synthesized with excellent regio‐, stereo‐ (Z‐selectivity), and enantioselectivity under mild reaction conditions. The ready availability of organoborons and alkynes and the simplicity, high stereoselectivity, and good functional group tolerance of this catalytic system make it highly attractive.

Synthesis of (±)-Angustatin A: Assembly of the Phenanthrene Moiety Despite Increasing Ring Strain.

The synthesis of (±)-angustatin A, a phenanthrene-containing cyclophane that possesses conformational chirality, is reported. Key steps include a Pd-catalyzed Negishi coupling to assemble the necessary terphenyl intermediate, its closure into a 14-membered macrocycle via a catalytic-in-phosphine Wittig olefination, and finally a Pt-catalyzed alkyne hydroarylation, which is able to assemble the phenanthrene unit despite the thermodynamic cost of significantly bending arene A from the ideal plane.

N-heterocyclic iminium ions catalyzed Friedel–Crafts type alkenylation of arenes with alkynes: A metal free and solvent free approach

The current manuscript elucidates a pioneering approach for achieving regioselective Markovnikov-type hydroarylation of alkynes, without the use of any metal catalysts. The aforementioned process is expedited through the implementation of 2-amino-perimidinium bromide and TFA as catalyst systems and is executed in the absence of solvents, thereby expanding the range of substrates (including arenes and alkynes). The correlation between the stoichiometric reactions and experimental data substantiates the postulated reaction mechanism.

Synthesis of 4‐Furan‐ and 4‐Pyrrol‐3‐yl‐2H‐chromenes from Naturally‐occurring Compounds by Gold(I)‐Catalyed Domino Reactions

AbstractA gold‐catalyzed cascade double cyclization reaction has been designed to synthesize heterobiaryl compounds such as furanyl and pyrrolyl 2H‐chromenes from bis(alkynyl)‐1,2‐diols and 1,2‐amino alcohols. The starting materials are readily available from biomass platform molecules such as α‐hydroxy acids and α‐amino acids. The process involves an initial heterocyclodehydration step enabling the formation of the furan or pyrrole ring, followed by an alkyne hydroarylation to form the chromene core.

Atroposelective Synthesis of Axially Chiral Styrenes by Nickel Hydride-Catalyzed Hydroarylation of Alkynes

Key words alkynes - atroposelectivity - axial chirality - hydroarylation - nickel catalysis

Chromium-catalyzed arylation and hydroarylation of terminal alkynes

A facile and direct approach for chromium-catalyzed terminal alkynes arylation and hydroarylation was developed. This method provides a useful route for preparation of diaryl unsaturated compounds from readily available terminal alkynes and arylmagnesium bromide in moderate yields under mild conditions.

Enantioselective Au-Catalyzed Synthesis of Thia[5]- and Thia[6]helicenes and Their Transformation into Bowl-shaped Pleiadenes.

A series of helically shaped benzo[b]chryseno[4,3-d]thiophenes, naphtho[1,2-b]phenanthro[4,3-d]thiophenes, and chryseno[3,4-b]naphtho[1,2-d]thiophenes is synthesized via a highly enantioselective Au-catalyzed intramolecular alkyne hydroarylation reaction. The inversion barriers of the structures obtained are determined both theoretically and experimentally, and their chiroptical properties are reported. Preliminary studies on the post-synthetic functionalization of these thiahelicenes and their transformation into azahelicenes are also presented. In addition, a straightforward one-step protocol is developed, which wraps the initially obtained chryseno[3,4-b]naphtho[1,2-d]thiophenes into bowl-shaped pleiadene derivatives without erosion of the enantiopurity. The number of structurally related products that are obtained with high enantioselectivity enables the establishment of comprehensive correlations between the structure and conformational stability or (chir)optical properties.