Regioselective C−H Alkylation via Carboxylate‐Directed Hydroarylation in Water

Boron-Catalyzed Michael Reaction of Donor-Acceptor Carboxylic Acid Pairs Enabling Direct Synthesis of 1,5-Dicarboxylic Acids

A boron-catalyzed Michael reaction using pairs of carboxylic acids was developed. The reaction occurs through dual activation of the two substrates by a boron catalyst, which facilitates boron enolate formation from the donor carboxylic acid with simultaneous activation of the α,β-unsaturated carboxylic acid as the acceptor. α-Aryl and α-alkenyl carboxylic acids were applicable as donors. The versatility and utility of this reaction were demonstrated by the direct use of pharmaceuticals as donor carboxylic acids.

Promoting Catalytic C-Selective Sulfonylation of Cyclopropanols against Conventional O-Sulfonylation Using Readily Available Sulfonyl Chlorides

Against the backdrop of the well-known O-sulfonylation of cyclopropyl alcohols with sulfonyl chlorides, we examined the feasibility of conducting regioselective C-sulfonylation. By emulating an umpolung strategy-guided design, we report for the first time the Cu(II)-catalyzed β-sulfonylation of cyclopropanols by a mechanism that potentially involves an oxidative addition of a sulfonyl radical to a metal homoenolate. Unlike reported methods, this protocol allows a practical synthetic route to γ-keto sulfone building blocks from cyclopropanols by leveraging commercially available aryl- and alkyl-sulfonyl chlorides, common reagents in organic chemistry laboratories. Using operationally simple open-flask conditions, the preparative scope of starting materials was demonstrated using an array of aryl- and alkyl-substituted sulfonyl chlorides and cyclopropanols (43 examples, up to 96% yield).

Cp*Rh(III)/boron hybrid catalysis for directed C-H addition to β-substituted α,β-unsaturated carboxylic acids

The C-H bond addition reaction of 2-phenylpyridine derivatives with α,β-unsaturated carboxylic acids catalyzed by Cp*Rh(III)/BH₃·SMe₂ is reported. Activation of C-H bonds with the rhodium catalyst and activation of α,β-unsaturated carboxylic acids with the boron catalyst cooperatively work, and a BINOL-urea hybrid ligand significantly improved the reactivity. With the optimized hybrid catalytic system, various β-disubstituted carboxylic acids were obtained under mild reaction conditions.

Ruthenium(II)-Catalyzed Redox-Neutral C-H Alkylation of Arylamides with Unactivated Olefins

A Ru(II)-catalyzed weak chelating group-aided ortho-C-H alkylation of arylamides with unactivated olefins in a redox-neutral fashion has been demonstrated. The present alkylation reaction was well-suited for various substituted arylamides and unactivated aliphatic alkenes. In this alkylation reaction, pivalic acid plays dual role in which it delivers the proton source in a protonation step and the corresponding acetate moiety deprotonates the ortho-C-H bond of the arylamides.

Ru-Catalyzed (E)-Specific ortho-C-H Alkenylation of Arenecarboxylic Acids by Coupling with Alkenyl Bromides

In the presence of [p-cymene)RuCl₂]₂, (E)-configured alkenyl bromides couple with aromatic carboxylates to form ortho-vinylbenzoic acids. This C-H vinylation proceeds in high yields without any activating phosphine ligands and has an excellent functional group tolerance. Starting from commonly available (E/Z )-mixtures of alkenyl bromides, (E)-configured vinyl arenes or dienes are formed exclusively. Mechanistic studies show that this selectivity is achieved because the (E)-configured alkenyl bromides undergo a smooth coupling, whereas the (Z)-isomers are rapidly eliminated with the formation of alkynes.

A facile method for Rh-catalyzed decarbonylative ortho-C–H alkylation of (hetero)arenes with alkyl carboxylic acids

A facile and effective method for Rh-catalyzed direct ortho-alkylation of C–H bonds in (hetero)arenes with commercially available carboxylic acids has been developed. This strategy was initiated by in situ conversion of carboxylic acids to anhydrides which, without isolation, underwent Rh-catalyzed direct decarbonylative cross-coupling of aryl carboxamides containing 8-aminoquinoline. The reaction proceeds with high regioselectivity and exhibits a broad substrate scope as well as functional group tolerance.

A facile and effective method for Rh-catalyzed direct ortho-alkylation of C–H bonds in (hetero)arenes with commercially available carboxylic acids has been developed.

Regioselective C-H Alkenylation and Unsymmetrical Bis-olefination of Heteroarene Carboxylic Acids with Ruthenium Catalysis in Water

An efficient weak carboxylate-assisted oxidative cross-dehydrogenative C-H/C-H coupling (CDC) of heteroarenes with readily available olefins has been devised employing water as green solvent under ruthenium(II) catalysis. The reaction is operationally simple, accommodates a large variety of heteroaromatic carboxylic acids as well as olefins, and facilitates a diverse array of high-value olefin-tethered heteroarenes in high yields (up to 87%). The potential of this ortho-C-H bond activation strategy has also been exploited toward tunable synthesis of densely functionalized heteroarenes through challenging unsymmetrical bis-olefination process in a one-pot sequential fashion. Mechanistic investigation demonstrates a reversible ruthenation process and C-H metalation step might not be involved in the rate-determining step.

Palladium-Catalyzed Site-Selective Benzocyclization of Naphthoic Acids with Diaryliodonium Salts: Efficient Access to Benzanthrones

Dual activation of both C-I and vicinal C-H bonds of diaryliodonium salts allowing for diarylation is a subject of rapid construction of π-extended frameworks. Here, we report palladium-catalyzed cascade of C₈-arylation/intramolecular Friedel-Crafts acylation of α-naphthoic acids in the synthesis of benzanthrone derivatives. The step-economical protocol tolerates various substrates, which resulted in a potential molecular library for developing functional polycyclic scaffolds. The approach relies on the synergistic action of strong acid with palladium catalysts to form two bonds in a one-pot procedure.

Cross-Dehydrogenative Coupling/Annulation of Arene Carboxylic Acids and Alkenes in Water with Ruthenium(II) Catalyst and Air

A cross-dehydrogenative coupling of arene carboxylic acids with olefins is reported with ruthenium(II) catalyst employing air and water as green oxidant and solvent, respectively. It offers a robust synthesis of valuable phthalide molecules. A one-pot sequential strategy is also disclosed to access Heck-type products that are apparently difficult to make directly from arene carboxylic acids.

Rh-Catalyzed Annulation of Benzoic Acids, Formaldehyde, and Malonates via ortho-Hydroarylation to Indanones

A three-component reaction from readily available low-cost materials of benzoic acids, formaldehyde, and malonates for the preparation of indanones by rhodium catalysis is reported. The annulation is initiated by an ortho-hydroarylation of benzoic acids, and a Lewis acid is not required. The solvent has a significant influence to the reaction, and 2-substituted or nonsubstituted indanones are obtained by the change of solvent.

Carboxylate-directed C-H allylation with allyl alcohols or ethers

A [Ru(p-cymene)Cl2]2 catalyst activates allyl alcohols and ethers for the regioselective ortho-C-H allylation of aromatic and heteroaromatic carboxylates. The reaction is orthogonal to most C-H functionalisations with allyl alcohols in that allyl arenes rather than carbonyl compounds are obtained. A wide range of substrates are thus smoothly transformed to allylarenes at 50 °C in phosphate-buffered 2,2,2-trichloroethanol. The reaction concept combines the use of abundant reagents and directing groups in a sustainable, waste-minimised method for C-C bond formation.