Iridium-Catalyzed Regio- and Enantioselective Hydroarylation of Alkenyl Ethers by Olefin Isomerization

Iridium-catalyzed hydroarylation of alkenyl ethers, such as allylic and homoallylic ethers, by C−H bond activation gave high yields of the corresponding addition products, where the aryl groups were selectively installed at the α-carbon atom to the alkoxy group. The reaction involves an isomerization of the alkenyl ethers into the corresponding 1-alkenyl ethers, which then undergo the regio- and enantioselective hydroarylation.     

Iridium‐Catalyzed Regio‐ and Enantioselective Hydroarylation of Alkenyl Ethers by Olefin Isomerization

Iridium‐catalyzed hydroarylation of alkenyl ethers, such as allylic and homoallylic ethers, by C−H bond activation gave high yields of the corresponding addition products, where the aryl groups were selectively installed at the α‐carbon atom to the alkoxy group. The reaction involves an isomerization of the alkenyl ethers into the corresponding 1‐alkenyl ethers, which then undergo the regio‐ and enantioselective hydroarylation.     

Palladium-catalyzed asymmetric hydrovinylation under mild conditions using monodentate chiral spiro phosphoramidite and phosphite ligands

Palladium complexes of chiral spiro phosphoramidite and phosphite ligands are effective catalysts in the asymmetric hydrovinylation of vinylarenes with ethylene. The hydrovinylation products were obtained in modest selectivity with enantioselectivities up to 92% ee. The structures of the palladium catalysts have been analyzed by X-ray diffraction. The active catalyst contained one monodentate ligand. A kinetic resolution accompanied the isomerization of the hydrovinylation product in the reaction.     

Synthesis of the phenanthrene and cyclohepta[a]naphthalene skeletons via gold(I)-catalyzed intramolecular cyclization of unactivated cyclic 5-(2-arylethyl)-1,3-dienes

The gold(I)-catalyzed hydroarylation of cyclohexa-1,3-dienes bearing an aryl group and a gem-diester in the tether proceeds in a 1,4-addition manner and in a diastereoselective fashion to afford perhydrophenanthrene rings. The reaction proceeded via attack of the aryl group onto the gold-activated cyclic dienes followed by rearomatization and protodeauration to generate perhydrophenanthrenes in good yields. This hydroarylation can be applied to the synthesis of perhydrocyclohepta[a]naphthalenes from aryl-tethered cycloheptadienes and the gold(I) catalyst.     

Syntheses and applications of 2-phosphino-2'-alkoxy-1,1'-binaphthyl ligands. Development of a working model for asymmetric induction in hydrovinylation reactions

Among the handful of monophosphine ligands that effect asymmetric hydrovinylation of vinylarenes, 2-diphenylphosphino-2'-methoxy-1,1'-binaphthyl (MOP) is among the most accessible. Addition of a methyl group at the 3'-position of this ligand significantly improves the enantioselectivity of hydrovinylation of prototypical alkenes. Introduction of a chiral phospholane at the C2 position of this scaffolding has no effect on the enantioselectivity. These results are consistent with a model proposed for the asymmetric induction for this exacting reaction.     

Trifluoroacetic acid-mediated hydroarylation: synthesis of dihydrocoumarins and dihydroquinolones

[reaction: see text] Trifluoroacetic acid mediates the hydroarylation of alkenes to afford dihydrocoumarins and dihydroquinolones in good yield. Intermolecular hydroarylation of cinnamic acids by phenols is particularly facile, which leads to the conclusion that previous reports of palladium-catalyzed hydroarylation of cinnamic acids in trifluoroacetic acid are erroneous.     

Ruthenium-catalyzed hydrovinylation of N-acetylenamines leading to amines with a quaternary carbon center

A catalytic hydrovinylation of N-acetylenamines with ethylene is reported. This new hydrovinylation reaction is catalyzed by a ruthenium hydride complex, RuHCl(CO)(PCy(3))(2), providing a series of N-acetylamines with a quaternary carbon center with up to 99% yield.     

Nickel(0)‐Catalyzed Hydroarylation of Styrenes and 1,3‐Dienes with Organoboron Compounds

A Ni‐catalyzed hydroarylation of styrenes and 1,3‐dienes with organoboron compounds has been developed. The reaction offers a highly selective approach to diarylalkanes and allylarenes under redox‐neutral conditions. In this hydroarylation reaction, a new strategy that uses the proton of methanol to generate the active catalyst species Ni?H was developed. The Ni‐catalyzed hydroarylation, combined with a Ir‐catalyzed C?H borylation, affords a very efficient and straightforward access to a retinoic acid receptor agonist.     

Chemical libraries via sequential C-H functionalization of phenols

Phenols provide a useful template for diversification via sequential hydroarylation reactions. Specifically, a protocol has been developed that begins with the hydroarylation of cinnamic acids by 3,5-dimethoxyphenol to produce dihydrocoumarins. This activated ester undergoes facile ring-opening with amines to form a C-N bond and regenerate a phenol. The resulting phenol can be further functionalized via a second hydroarylation reaction. Thus, in 3-4 steps, a phenol is coupled with a cinnamic acid, an amine, and a cinnamic or propiolic acid.     

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.     

Proton-catalyzed hydroamination and hydroarylation reactions of anilines and alkenes: a dramatic effect of counteranions on reaction efficiency

The anilinium salt, [PhNH3][B(C6F5)4], has been identified as a catalyst for the hydroamination and hydroarylation of several different types of alkenes with anilines. The weakly coordinating counterion of this acid plays a key role in this transformation. The reaction is facile for styrenes and tolerates norbornene, cyclic alkenes, and cyclohexadiene. Selectivity between hydroamination and hydroarylation products can be tuned using reaction time, temperature, and substrate substitution. Details regarding the substrate scope and selectivity of this hydroamination/hydroarylation reaction are discussed.     

Formal [4+2] Reaction between 1,3‐Diynes and Pyrroles: Gold(I)‐Catalyzed Indole Synthesis by Double Hydroarylation

Indole synthesis by a gold(I)‐catalyzed intermolecular formal [4+2] reaction between 1,3‐diynes and pyrroles has been developed. This reaction involves the hydroarylation of 1,3‐diynes with pyrroles followed by an intramolecular hydroarylation to give the 4,7‐disubstituted indoles. This reaction can also be applied to the synthesis of carbazoles when indoles are used as the nucleophiles instead of pyrroles.     

Palladium-catalyzed hydroarylation of alkynes with arenediazonium salts

The palladium-catalyzed hydroarylation of arenediazonium tetrafluoroborates with alkynes in the presence of triphenylsilane affords stereoselectively hydroarylation products in moderate to high yields. The reaction tolerates a variety of substituents including keto, ester, cyano, and nitro groups and can be performed as a one-pot procedure generating the arenediazonium salt in situ. With ethyl phenylpropynoate as the starting alkyne, the hydroarylation affords ethyl (Z)-2-arylcinnamates stereo- and regioselectively.     

Regioselective C−H Hydroarylation of Internal Alkynes with Arenecarboxylates: Carboxylates as Deciduous Directing Groups

In the presence of catalytic [Ru(p‐cym)I₂]₂ and the base guanidine carbonate, benzoic acids react with internal alkynes to give the corresponding 2‐vinylbenzoic acids. This alkyne hydroarylation is generally applicable to diversely substituted electron‐rich and electron‐poor benzoic and acrylic acids. Aryl(alkyl)acetylenes react regioselectively with formation of the alkyl‐branched hydroarylation products, and propargylic alcohols are converted into γ‐alkylidene‐δ‐lactones. The hydroarylation can also be conducted decarboxylatively with a different choice of catalyst and reaction conditions. This reaction variant, which does not proceed via intermediate formation of 2‐vinylbenzoic acids, opens up a regioselective, waste‐minimized synthetic entry to vinylarenes.     

Gold(I)-catalyzed polycyclizations of polyenyne-type anilines based on hydroamination and consecutive hydroarylation cascade

A hydroamination-double hydroarylation cascade using aniline derivatives bearing a trienyne moiety as the substrate was efficiently promoted by a gold(I) catalyst to produce benzo[a]naphtho[2,1-c]carbazole derivatives in good yields. This reaction is applicable to various substituted trienyne-type anilines, including 2,3-diethynylthiophene derivatives. The reaction of anilines bearing a tetraenyne and pentaenyne moiety allows direct construction of highly fused carbazoles by tetra- and pentacyclization, respectively, through hydroamination and consecutive hydroarylation without producing any theoretical waste products from the substrates.     

Gold-catalyzed hydroarylation of allenes: a highly regioselective carbon-carbon bond formation producing six-membered rings

Gold-catalyzed intramolecular hydroarylation of allenic anilines and phenols offers an efficient route to dihydroquinoline and chromene derivatives under mild reaction conditions. The hydroarylation takes place at the terminal or central allenic carbon depending on the substrate structure, leading to a highly selective formation of six-membered rings.     

Redox-triggered hydroarylation of o-(hydroxyalkyl)arylalkynes with arylsulfonyl chlorides using visible light catalysis

A new radical-mediated method for the synthesis of 1-(2-(1,2-diarylvinyl)phenyl)ethan-1-ones by the redox hydroarylation of o-(hydroxyalkyl)arylalkynes with arylsulfonyl chlorides is described. This visible light catalysis method proceeds via a sequence of the radical addition of aryl group across the C-C triple bond, protonation and redox reaction, and represents a new redox transformation reaction directed by a neighboring hydroxyl group.     

Gold catalysis: five new bonds by a domino hydroarylation/cycloisomerization

The gold-catalyzed reaction of furans possessing one unsubstituted 2-position with ethynyl vinyl ketones bearing alkyl groups on the alkene led to interesting phenols of the indan-1-one-type by a domino hydroarylation/cycloisomerization. The yields were moderate but higher than in longer routes described before. With ethynyl vinyl ketones that have an aryl substituent, the chemoselectivity of the reaction was different. Then products from an initial reaction at the ethynyl group were observed.     

Highly efficient iodine-catalyzed hydroarylation of arenes with styrenes

Iodine mediates the hydroarylation of styrenes with arenes and heteroarenes to afford 1,1-diarylalkanes in good to high yields. Details regarding the substrate scope and selectivity of this hydroarylation reaction are discussed.     

Rhodium-Catalyzed Alkylation of C−H Bonds in Aromatic Amides with Non-activated 1-Alkenes: The Possible Generation of Carbene Intermediates from Alkenes

The alkylation of C−H bonds (hydroarylation) in aromatic amides with non-activated 1-alkenes using a rhodium catalyst and assisted by an 8-aminoquinoline directing group is reported. The addition of a carboxylic acid is crucial for the success of this reaction. The results of deuterium-labeling experiments indicate that one of deuterium atoms in the alkene is missing, suggesting that the reaction does not proceed through the commonly accepted mechanism for C−H alkylation reactions. Instead the reaction is proposed to proceed through a carbene mechanism. The carbene mechanism is also supported by preliminary DFT calculations.