Additive-Controlled Divergent Synthesis of Fluorenone-4-carboxylic Acids and Diphenic Anhydrides via Rhodium-Catalyzed Oxidative Dimeric Cyclization of Aromatic Acids

A rhodium-catalyzed one-pot access to valuable polycyclic frameworks of fluorenone-4-carboxylic acids and diphenic anhydrides via the oxidative dimeric cyclization of aromatic acids has been developed. This transformation proceeded via carboxyl-assisted 2-fold C-H activation followed by intramolecular Friedel-Crafts or dehydration reactions. The silver salt additive plays a vital role in the chemoselectivity of the products. Diphenic anhydride 3l exhibits a maximum fluorescence quantum yield of up to 59%.

One-Step Syntheses of 3,4-Disubstituted Isochroman-1-ones by the Annulation of Benzoic Acids with Nitroalkenes

The Rh(III)-catalyzed annulation of benzoic acids with nitroalkenes was disclosed to afford a wide range of 3,4-disubstituted isochroman-1-ones with excellent regioselectivity and high catalytic efficiency. Both aromatic and aliphatic nitroalkenes participated in this cyclization reaction successfully. The synthetic value of 3,4-disubstituted isochroman-1-ones was proven by a series of derivatizations. Furthermore, a reliable mechanism is outlined on the basis of experimental investigations and related precedents.

Rh-Catalyzed Coupling of Acrylic/Benzoic Acids with α-Diazocarbonyl Compounds: An Alternative Route for α-Pyrones and Isocoumarins

A coupling of acrylic acids/benzoic acids with α-diazocarbonyl compounds has been realized by a combined catalytic system of rhodium catalyst and Zn(OAc)₂ additive. The presence of Zn(OAc)₂ obviously accelerates the C(sp²)-H activation and destructed the formation of carboxylic ester that is formed via a nucleophilic O-H insertion to metal carbenoid. The procedure featured mild reaction conditions and broad substrate scope, providing a straightforward approach to the synthesis of α-pyrones and isocoumarins without the transformation of carboxylic acids to the corresponding amides.

Modular construction of functionalized anilines via switchable C–H and N-alkylations of traceless N-nitroso anilines with olefins

Switchable C–H or N-alkylations of N-nitroso anilines with olefins.

Synthesis of Cyclopentenones through Rhodium-Catalyzed C-H Annulation of Acrylic Acids with Formaldehyde and Malonates

An efficient rhodium-catalyzed protocol for the synthesis of cyclopentenones based on a three-component reaction of acrylic acids, formaldehyde, and malonates via vinylic C-H activation is reported. Exploratory studies showed that 5-alkylation of as-prepared cyclopentenones could be realized smoothly by the treatment of a variety of alkyl halides with a Na₂CO₃/MeOH solution. Excess formaldehyde and malonate led to a multicomponent reaction that afforded the multisubstituted cyclopentenones through a Michael addition.

Transition-metal-free decarboxylative ipso amination of aryl carboxylic acids

An unprecedented DMAP-catalysed decarboxylative amination of carboxylic acids has been achieved under metal free conditions, enabling the convenient synthesis of structurally diverse aryl and alkyl amines.

Recent Advances on Synthetic Methodology Merging C-H Functionalization and C-C Cleavage

The functionalization of C-H bonds has become a major thread of research in organic synthesis that can be assessed from different angles, for instance depending on the type of catalyst employed or the overall transformation that is carried out. This review compiles recent progress in synthetic methodology that merges the functionalization of C-H bonds along with the cleavage of C-C bonds, either in intra- or intermolecular fashion. The manuscript is organized in two main sections according to the type of substrate in which the cleavage of the C-C bond takes place, basically attending to the scission of strained or unstrained C-C bonds. Furthermore, the related research works have been grouped on the basis of the mechanistic aspects of the different transformations that are carried out, i.e.,: (a) classic transition metal catalysis where organometallic intermediates are involved; (b) processes occurring via radical intermediates generated through the use of radical initiators or photochemically; and (c) reactions that are catalyzed or mediated by suitable Lewis or Brønsted acid or bases, where molecular rearrangements take place. Thus, throughout the review a wide range of synthetic approaches show that the combination of C-H and C-C cleavage in single synthetic operations can serve as a platform to achieve complex molecular skeletons in a straightforward manner, among them interesting carbo- and heterocyclic scaffolds.

Palladium/Copper Cocatalyzed C-H Activation and C-C Bond Regioselective Cleavage Reaction for the Synthesis of Fused Chromeno Quinolines

A method for the synthesis of fused chromeno quinolines by the palladium/copper cocatalyzed C-H bond activation and C-C bond cleavage reaction has been developed. A variety of fused chromeno quinoline derivatives could be synthesized by coumarin derivatives and anilines through the C-C bond cleavage/C-H functionalization/C-C bond formation process. The MTT assay was used to evaluate the chromeno quinolines against the human cervix tumor cells (HeLa), 3c and 9c without coordination metals showed good inhibition effect.

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.

A family of structural and functional models for the active site of a unique dioxygenase: Acireductone dioxygenase (ARD)

We report the synthesis and biomimetic activity of a family of model complexes with relevance to acireductone dioxygenase (ARD), an enzyme that displays dual function based on metal identity found in the methionine salvage pathway (MSP). Three complexes with related structural motifs were synthesized and characterized derived from phenolate, and pyridine N₄O Schiff-base ligands. They display pseudo-octahedral Ni(II)-N₄O ligand coordination with water at the sixth site, in close alignment to the structure in the resting state of ARD. The three featured complexes exhibit carbon‑carbon bond cleavage activation of lithium acetylacetonate, which was used as a model enzyme substrate. Computationally derived mechanistic routes for the observed reactivity consistent with experimental conditions are herein proposed. The mechanism suggests the possibility of Ni(II)-substrate interactions, followed by oxygen insertion. These results constitute only the third functional model system of ARD, in an attempt to further advance biomimetic contributions to the ongoing debate of ARD's unique metal mediated, regioselective oxidative cleavage.

A removable directing group-assisted Rh(iii)-catalyzed direct C–H bond activation/annulation cascade to synthesize highly fused isoquinolines

A removable directing group-assisted Rh(iii)-catalyzed direct C–H bond activation/annulation cascade was developed to synthesize highly fused isoquinolines with good to excellent yields and a good functional group tolerance.

Rhodium(iii)-catalyzed synthesis of 3-trifluoromethylindanones from N-methoxybenzamides via C–H activation and Claisen/retro-Claisen reaction

An efficient synthesis of 3-trifluoromethylindanones via C–H annulation of N-methoxybenzamides with β-trifluoromethyl-α,β-unsaturated ketones under Rh(iii)-catalysis is described.