Tris(pentafluorophenyl)borane [B(C6F5)3]-catalyzed Friedel–Crafts reactions of activated arenes and heteroarenes with α-amidosulfones: the synthesis of unsymmetrical triarylmethanes

Catalyst- and Additive-free, Regioselective 1,6-Hydroarylation of para-Quinone Methides with Anilines in HFIP

A simple and efficient method for the synthesis of diarylmethyl-functionalized anilines through the hexafluoroisopropanol (HFIP)-mediated regioselective 1,6-hydroarylation reaction of para-quinone methides (p-QMs) with anilines under catalyst- and additive-free conditions is reported. Various kinds of p-QMs and amines (e. g. primary, secondary and tertiary amines) are well tolerated in this transformation without the pre-protection of amino group, and the corresponding products could be generated with good to excellent yields and satisfactory regioselectivity under the optimized reaction conditions. In addition to adaptable amine compounds, indoles and their derivatives are also compatible with this reaction system. This transformation can be easily extended to a gram scale-synthesis level to synthesize the target product. Furthermore, it is worth noting that some complex small aniline molecules with biological activity can be selectively modified using this method. The possible reaction mechanism is proposed through the step-by-step control experiments and DFT calculations, showing that the key process for achieving the regioselective 1,6-hydroarylation of p-QMs is the hydrogen bonding effect of HFIP to substrates.

Lewis-Acid-Catalyzed Selective Friedel-Crafts Reaction or Annulation between Anilines and Glyoxylates

A Lewis-acid-catalyzed selective reaction between anilines and glyoxylates was developed for synthesis of diarylmethanes or oxoimidazolidines. Under the catalysis of AgOTf, a series of anilines-based diarylmethanes, including primary, secondary, and tertiary anilines, were obtained in moderate to good yields. Moreover, stereoselective oxoimidazolidines were performed with the catalysis of Cu(OAc)₂·H₂O.

Transition-Metal-Free Synthesis of Polyfunctional Triarylmethanes and 1,1-Diarylalkanes by Sequential Cross-Coupling of Benzal Diacetates with Organozinc Reagents

A variety of functionalized triarylmethane and 1,1-diarylalkane derivatives were prepared via a transition-metal-free, one-pot and two-step procedure, involving the reaction of various benzal diacetates with organozinc reagents. A sequential cross-coupling is enabled by changing the solvent from THF to toluene, and a two-step SN 1-type mechanism was proposed and evidenced by experimental studies. The synthetic utility of the method is further demonstrated by the synthesis of several biologically relevant molecules, such as an anti-tuberculosis agent, an anti-breast cancer agent, a precursor of a sphingosine-1-phosphate (S1P) receptor modulator, and a FLAP inhibitor.

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.

Metal-free iodine-promoted direct synthesis of unsymmetrical triarylmethanes

Completely unsymmetrical triarylmethanes were prepared in a one-pot reaction via o-QM intermediates generated in situ.

Pd-Catalyzed Desulfonative Cross-Coupling of Benzylic Sulfone Derivatives with 1,3-Oxazoles

The Pd-catalyzed desulfonative cross-coupling reaction of benzylic sulfone derivatives with 1,3-oxazoles via a deprotonative pathway has been developed. Broad substrate scope for both sulfone and 1,3-oxazole partners is observed, affording a variety of 1,3-oxazole-containing triarylmethanes. Sulfone partners that are primary benzylic, secondary benzylic, and benzhydryl are all effective. Using this method, the straightforward synthesis of multiply arylated structures has been demonstrated.

Sulfonyl Azoles in the Synthesis of 3-Functionalized Azole Derivatives

Sulfonyl indoles, as well as related azolyl derivatives, have been recently introduced in synthesis as stable precursors of reactive indolenine intermediates. This personal account reports on the discovery of sulfonyl azoles and their practical utilization in many synthetic processes for the preparation of functionalized 3-substituted indoles, indazoles, and pyrroles. The indolenine intermediates obtained by treatment of sulfonyl azoles with Brønsted bases or Lewis acids can be considered as vinylogous imino derivatives that can be made to react with different nucleophilic reagents. These include organometallic reagents, reducing agents, stabilized carbanions, and heteronucleophiles. The controlled and mild conditions for the generation of indolenines from sulfonyl azoles make these substrates particularly useful in asymmetric synthesis, exploiting organo- or metal-catalyzed processes. Although less exploited, sulfonyl indoles can also be involved in photochemical processes for the preparation of polycyclic derivatives.

B(C6F5)3 catalysed 1,6-conjugate allylation of para-quinone methides: expedient access to allyl diarylmethanes

An efficient protocol for the synthesis of unsymmetrical allyl diarylmethanes through a Lewis acid catalysed 1,6-conjugate addition of allylsilanes to para-quinone methides is described.