Progress in Transition Metal Catalyzed C-H Functionalization Directed by Carboxyl Group

Practical synthesis of isocoumarins via Rh(III)-catalyzed C-H activation/annulation cascade

Herein, we report an unprecedented Rh(III)-catalyzed C-H activation/annulation cascade of readily available enaminones with iodonium ylides towards the convenient synthesis of isocoumarins. This coupling system proceeds in useful chemical yields (up to 93%) via a cascade C-H activation, Rh-carbenoid migratory insertion and acid-promoted intramolecular annulation. The success of gram-scale reaction and diverse functionalization of isocoumarins demonstrated the synthetic utility of this protocol.

Iridium(I)-Catalyzed Isoindolinone-Directed Branched-Selective Aromatic C-H Alkylation with Simple Alkenes

We report an iridium(I)-catalyzed branched-selective C–H alkylation of N-arylisoindolinones with simple alkenes as the alkylating agents. The amide carbonyl group of the isoindolinone motif acts as the directing group to assist the ortho C–H activation of the N-aryl ring. With this atom-economic and highly branched-selective protocol, an array of biologically relevant N-arylisoindolinones were obtained in good yields. Asymmetric control was achieved with up to 87:13 er when a BiPhePhos-like chiral ligand was employed.

Weakly Coordinating, Hydroxyl Directed Ruthenium Catalyzed C-H Alkylation of Ubiquitous Benzyl Alcohols with Maleimides

Benzyl alcohols have been employed as effective coupling partners in Ru-catalyzed C-H functionalization reactions, and their annulation with maleimides then offers efficient synthesis of useful ortho substituted succinimide aromatic aldehydes and ketones. Detailed mechanistic studies have been demonstrated by performing preliminary reactions, deuterium studies, and competitive experiments.

Ru-catalysed C(sp2)-H vinylation/annulation of benzoic acids and alkynes: rapid access to medium-sized lactones

An unprecedented ruthenium catalysed [4+4] annulation of readily available benzoic acids and alkynes is reported for the first time. The carboxylate group acts as both a directing group and an internal nucleophilic reagent to facilitate a C(sp²)-H vinylation/annulation cascade. This reaction avoids the classically oxidative [4+2] annulation, allowing the efficient synthesis of a wide array of eight-membered lactones under oxidant-free conditions. Moreover, this catalytic system can be successfully extended to [4+3] and [4+5] annulations for the assembly of seven- and nine-membered lactones.

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.

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.