RuII -Catalyzed Annulative Coupling of Benzoic Acids with Vinyl Sulfone via Weak Carboxylate-Assisted C−H Bond Activation

Facile Synthesis of Alkylidene Phthalides by Rhodium-Catalyzed Domino C-H Acylation/Annulation of Benzamides with Aliphatic Carboxylic Acids

The Rh-catalyzed ortho-C(sp² )-H functionalization of 8-aminoquinoline-derived benzamides with aliphatic acyl fluorides generated in situ from the corresponding acids has been developed. This reaction initiated with 8-aminoquinoline-directed ortho-C(sp² )-H acylation, which was accompanied by subsequent intramolecular nucleophilic acyl substitution of amide group to produce alkylidene phthalides This approach exhibits high stereo-selectivity for Z-isomer products, and tolerates a variety of functional groups as well as aliphatic carboxylic acids with diverse structural scaffolds.

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.

Enhancing Ru(II)-Catalysis with Visible-Light-Mediated Dye-Sensitized TiO2 Photocatalysis for Oxidative C-H Olefination of Arene Carboxylic Acids at Room Temperature

Erythrosine B sensitized TiO₂ photocatalysis has been combined with Ru(II)-catalysis to accomplish an oxidative olefination/annulation of benzoic acids with activated olefins under mild conditions that tolerates useful functionalities, such as halides, free hydroxy, acetamido, etc. The morphology of the photocatalyst is unaffected during the reaction and it can be reused. Mechanistic studies favor the involvement of a photo-induced single electron transfer process.

Synthesis of Phthalides and α,β-butenolides by Transition Metal-Catalyzed Activation of C-H Bonds

Phthalides and α,β-butenolides are two related classes of oxygenated heterocycles with a wide range of biological activities. An innovative strategy to prepare these compounds is based on C-H bond functionalization reactions, in which two simple, unfunctionalized molecules are coupled together with cleavage of a C-H bond and formation of a C-X bond (X=C or heteroatom). This paper reviews the methods for the synthesis of phthalides and α,β-butenolides by C-H bond functionalization from non-halogenated starting materials. Over 30 methods are reported, mostly developed during the past ten years.