Enantioselective Synthesis of Triarylmethanes via Organocatalytic 1,6‐Addition of Arylboronic Acids to para ‐Quinone Methides

Asymmetric Synthesis of Triphenylmethanes via Organocatalytic Regio- and Enantioselective Friedel-Crafts Alkylation of Aniline Derivatives

Herein, we described a highly regio- and enantioselective Friedel-Crafts alkylation of aniline derivatives with in situ generated ortho-quinone methides enabled by chiral phosphoric acid, furnishing a wide range of enantioenriched triarylmethanes bearing three similar benzene rings in high yields (up to 98%) with excellent stereoselectivities (up to 98% ee). Furthermore, the large-scale reactions and diversified transformations of product demonstrate the practicality of the protocol. Density functional theory calculations elucidate the origin of the enantioselectivity.

Solvent-Mediated Tunable Regiodivergent C6- and N1-Alkylations of 2,3-Disubstituted Indoles with p-Quinone Methides

Indium-catalyzed, solvent-enabled regioselective C6- or N1-alkylations of 2,3-disubstituted indoles with para-quinone methides are developed under mild conditions. Notably, highly selective and switchable alkylations were selectively achieved by adjusting the reaction conditions. Moreover, scalability and further transformations of the alkylation products are demonstrated, and this operationally simple methodology is amenable to the late-stage C6-functionalization of the indomethacin drug. The reaction pathways were explained with the support of experimental and density functional theory studies.

Room-Temperature ZnBr2 -Catalyzed Regioselective 1,6-Hydroarylation of Electron-Rich Arenes to para-Quinone Methides: Synthesis of Unsymmetrical Triarylmethanes

A mild and efficient Zn(II)-catalyzed regioselective 1,6-hydroarylation of para-quinone methides (p-QMs) with electron-rich arenes protocol is reported. A variety of electron-rich arenes and para-quinone methides are well tolerated under mild conditions, delivering a broad range of triarylmethanes in good to excellent yields. The present method also works well for the hydroarylation of p-QMs with other nucleophiles, such as aniline, indole and phenol derivatives, offering the corresponding triarylmethanes with good yields under the standard conditions. The possible mechanism for the formation of C(sp³ )-C(sp² ) bonds in hydroarylation reactions has been explored by step-by-step control experiments, and the reaction may follow a second-order manner in a chemical kinetic study.

Enantioselective synthesis of triarylmethanes via organocatalytic transfer hydrogenation of para-quinone methides

A new organocatalytic asymmetric method for the synthesis of enantioenriched triarylmethanes is developed. Different from the conventional approaches featuring asymmetric arylation, the present study employs asymmetric reduction via C-H bond formation as the key step. This approach does not require the presence of a heteroaryl ring or the presynthesis of unstable para-quinone methides. Instead, the stable racemic triarylmethanols were used as substrates for the in situ generation of the intermediates with a suitable chiral phosphoric acid catalyst.

Silver(i)-catalyzed novel ipso-cycloaddition and retro-Friedel–Crafts reaction of ortho-hydroxyphenyl-substituted para-quinone methides

The Lewis acid AgPF6 was found to catalyze novel [2 + 2] ipso-cycloaddition and retro-Friedel–Crafts reaction of o-hydroxyphenyl-substituted p-quinone methides in the presence of H2O, affording the polysubstituted triarylmethanes in up to 97% yields.

Non-hydrogen bond catalyst-mediated diastereoselective conjugate additions of 5H-oxazol-4-ones to o-hydroxyphenyl-substituted p-quinone methides

An efficient DBU-catalyzed conjugate addition of 5H-oxazol-4-ones to o-hydroxyphenyl-substituted p-quinone methides has been developed, affording the valuable diarylmethanes in high yields with excellent diastereoselectivity. This strategy demonstrates a robust access to a wide range of diarylmethane derivatives possessing biologically significant o-hydroxyphenol and p-hydroxyphenol moieties under mild reaction conditions.

CF3-Containing para-Quinone Methides for Organic Synthesis

A new family of CF3-containing para-quinone methides (CF3-QMs) was systematically investigated for its suitability in organic synthesis. Addition of different nucleophiles gives access to target molecules with a benzylic CF3-containing stereogenic center straightforwardly. The electrophilicity parameter E of the prototypical CF3-QM 2,6-di-tert-butyl-4-(2,2,2-trifluoroethylidene)cyclohexa-2,5-dien-1-one was determined to be -11.68 according to the Mayr scale, making it one of the most reactive quinone methides known so far.

Enantio- and diastereoselective diarylmethylation of 1,3-dicarbonyl compounds

A Cu-catalyzed enantio- and diastereoselective diarylmethylation of 1,3-dicarbonyl compounds is described. It is a successful example of constructing all-carbon quaternary stereocenters from 3 °C–H nucleophiles, a challenging topic in synthetic chemistry. In the present work, two contiguous stereocenters are constructed with high levels of stereoselectivity and atom economy. The broad scope of 1,3-dicarbonyl nucleophiles and the tolerance of a wide range of functional groups make this protocol of great importance in the synthesis of chiral diarylmethane compounds.

A Cu-catalyzed enantio- and diastereoselective diarylmethylation of 1,3-dicarbonyl compounds is described. Two contiguous stereocenters including one all-carbon quaternary stereocenter are constructed with good stereoselectivity and atom economy.

Synthesis of Triarylmethanes by Decarbonylation of 3,3-Diaryl Benzofuranones

A simple protocol for the synthesis of triarylmethane derivatives with three different (hetero)aryl groups by decarbonylation of 3,3-diaryl benzofuranones, which can easily be prepared via arylation of benzofuranones, was developed. The reaction proceeds on heating in dimethylformamide (DMF) in the presence of CH₃ONa and water to generate the products in good to excellent yields. This reaction can be easily scaled up to give a triarylmethane in a gram scale. Further chemical manipulation of the products enabled useful transformations of the phenol ring, including reduction, arylation, cyclization, etc.

Gold-catalyzed domino reactions of alkynol and p-quinone methides: divergent synthesis of fused- and spiro-ketals

A gold-catalyzed domino reaction of alkynyl alcohols and p-quinone methides to obtain divergent fused- and spiro-ketals has been developed.

Catalytic asymmetric 1,4-type Friedel–Crafts (hetero)arylations of 1-azadienes: the highly enantioselective syntheses of chiral hetero-triarylmethanes

Strategies for achieving the direct catalytic asymmetric syntheses of benzofuran-containing hetero-triarylmethanes using a 1,4-type Friedel–Crafts (hetero)arylation reaction were developed.

Construction of chiral chroman scaffolds via catalytic asymmetric (4 + 2) cyclizations of para-quinone methide derivatives with 3-vinylindoles

The title reaction has been established in the presence of chiral phosphoric acid, affording chiral chroman derivatives bearing an indole moiety in high yields and with moderate to good stereoselectivities.

Regioselective catalytic asymmetric N-alkylation of isoxazol-5-ones with para-quinone methides

A highly regioselective and enantioselective N-alkylation of isoxazol-5-ones with para-quinone methides has been developed to obtain enantioenriched N-diarylmethane substituted isoxazolinones with high yields and enantioselectivities.

δ-Cyano substituted para-quinone methides enable access to unsymmetric tri- and tetraarylmethanes containing all-carbon quaternary stereocenters

Placing an electron-withdrawing cyano group into the δ-position of para-quinone methides enables facile access to unsymmetrical tri- and tetraarylmethanes bearing all-carbon quaternary stereocenters.

Transition metal-free synthesis of α-aryl ketones via oxyallyl cation capture with arylboronic acids

α-Arylated ketones were accessed via oxyallyl cation capture with arylboronic acids in good yields with broad substrate tolerance.

Visible-light-promoted radical cross-coupling of para-quinone methides with N-substituted anilines: an efficient approach to 2,2-diarylethylamines

A series of 2,2-diarylethylamines were accessed via visible-light-promoted radical cross-coupling of p-QMs with N-alkyl anilines.

Organocatalytic Remote Stereocontrolled 1,8-Additions of Thiazolones to Propargylic Aza-p-quinone Methides

A remote stereocontrolled 1,8-conjugate addition of thiazolones to propargylic aza-p-quinone methides formed from propargylic alcohols has been developed with the aid of a chiral phosphoric acid, and this represents the first report on organocatalytic stereocontrolled 1,8-addition of propargylic aza-p-quinone methides. Notably, the remote stereocontrolled activation protocol enables the construction of vicinal sulfur-containing quaternary carbon stereocenters and axially chiral tetrasubstituted allenes and promotes the chemistry of chiral phosphoric acids.

Catalytic Asymmetric Conjugate Addition of Indoles to para-Quinone Methide Derivatives

A catalytic asymmetric conjugate addition of indoles to o-hydroxyphenyl substituted p-quinone methides has been established in the presence of chiral phosphoric acid, which afforded chiral indole-containing triarylmethanes in generally high yields (54-98%) and good enantioselectivities (90:10-96:4 enantiomeric ratio). The control experiments indicated that o-hydroxyphenyl substituted p-quinone methides had a high possibility to transform into o-quinone methides in the presence of chiral phosphoric acid, and the formation of o-quinone methides might be a necessity for the reaction. This reaction will not only contribute to the research field of catalytic asymmetric transformations of p-quinone methides and o-quinone methides but also provide a useful method for the construction of enantioenriched triarylmethane frameworks.

Diastereoselective construction of 3-aryl-substituted indolines via annulation of in situ generated p-quinone methides

A highly diastereoselective [4 + 1] annulation reaction of in situ generated p-quinone methides for the synthesis of 3-aryl-substituted indolines has been developed.

Organocatalytic enantioselective conjugate addition of 2-naphthols to ortho-hydroxyphenyl substituted para-quinone methides: access to unsymmetrical triarylmethanes

The enantioselective conjugate addition of 2-naphthols to ortho-hydroxyphenyl substituted para-quinone methides has been achieved with the aid of a chiral phosphoric acid. Importantly, the reaction took place with excellent chemo- and regioselectivities. In addition, the protocol features a low catalyst loading, mild reaction conditions, and enables the formation of unsymmetrical triarylmethanes in good to high yields with generally high enantioselectivities.

The enantioselective conjugate addition of 2-naphthols to ortho-hydroxyphenyl substituted para-quinone methides has been achieved with the aid of a chiral phosphoric acid.