Ruthenium‐Catalyzed C7‐Formylmethylation or Sequential Acetalization of Indolines with Vinylene Carbonate in Different Solvents

Synthesis of 1H-isothiochromenes by regioselective C-C and C-S bond formation of enaminothiones with alkynes under rhodium catalysis

The rhodium-catalyzed sulfur-directed C-H bond activation and tandem cyclization of enaminothiones with alkynes proceed efficiently. Most products of 1H-isothiochromenes with various substituents are achieved in good yields by regioselective C-C and C-S bond formation. This protocol has some advantages over the traditional methods in synthesizing 1H-isothiochromenes in terms of stable and easily available coupling substrates, simple and one-pot operation, step and atom economy, and highly unique sulfur-containing heterocyclic products.

Transition Metal-Catalyzed Direct Functionalization of Carbazoles

Carbazoles are an important class of nitrogen-containing heterocycles found in diverse natural products, bioactive molecules, and functional materials. Their broader applications have driven extensive research into their synthesis and functionalization. Among various approaches, transition metal-catalyzed C-H activation has emerged as a powerful tool for direct functionalization, offering regioselectivity, efficiency, and sustainability. This review comprehensively summarizes advancements in transition metal-catalyzed C-H functionalization of carbazoles. Various catalytic systems employing palladium, ruthenium, rhodium, nickel, cobalt, copper, and iron have enabled alkylation, alkenylation, acylation, arylation, alkynylation, and heteroatom incorporation in carbazoles. These methodologies enabled late-stage diversification and have opened avenues for accessing structurally complex carbazole derivatives with tailored properties. The review aims to provide a comprehensive guide for researchers exploring carbazole functionalization via C-H activation, highlighting key mechanistic insights, scope, and emerging trends in this field.

Rhodium-catalyzed C-H activation and three-component tandem annulation leading to isoquinolones

A rhodium-catalyzed C-H activation and three-component coupling of oxazolines, vinylene carbonate and carboxylic acids has been developed. Various isoquinolone products were constructed under redox-neutral conditions with satisfactory yields. It is worth noting that diverse bioactive carboxylic acids have been proven to be effective substrates, and their application in this protocol has expanded the range of isoquinolones with biologically relevant motifs. Multi-dimensional mechanism exploration experiments and derivatization reactions were studied in sequence to explore the details and application prospects of this transformation. It offers an alternative approach for the synthesis of useful isoquinolone derivatives.

Ruthenium-catalyzed monodeuterium-methylenation of two indole units with vinylene carbonate as a novel methylene precursor

A new example of deuteration, involving ruthenium-catalyzed monodeuterium-methylenation of indole units with vinylene carbonate, is described. This reaction was used to build an array of promising highly deuterated bisindolylmethanes (d-BIMs). This methodology featured excellent functional group compatibility with diverse substrate categories such as indoles, N,N-dialkylanilines, and 1,3-dicarbonyls as well as having showcased the distinct chemical function of VC as an innovative methylene precursor.

Ruthenium(II)-Catalyzed C-H/C-H (4+2) Annulation of 2-Aryl-N-heterocycles with Vinylene Carbonate

A ruthenium(II)-catalyzed direct C-H/C-H (4+2) annulation of 2-aryl-N-heterocycles such as 2-aryl-4H-pyrido[1,2-a]pyrimidin-4-ones, 2-arylimidazo[1,2-a]pyridines, 2-aryl-2H-indazoles and 2-arylquinolin-4(1H)-ones with vinylene carbonate has been described. This one-pot cascade strategy provided the diversely substituted fused-polyheterocycles such as 7H-benzo[h]pyrido[2,1-b]quinazolin-7-ones, naphtho[1',2':4,5]imidazo[1,2-a]pyridines, indazolo[2,3-a]quinolines and benzo[c]acridin-7(12H)-ones in moderate to excellent yields. The developed protocol exhibited a broad substrate scope with good functional group tolerance and acid/base-free conditions. Based on a preliminary mechanistic investigation, a tentative mechanism of Ru(II)-catalyzed (4+2) annulation reaction has been proposed.

Engaging vinylene carbonate in ruthenium-catalyzed regioselective C-4 methylenation and C-8 formylmethylation of isoquinolinones

Herein, we disclose the first reports on the utilization of vinylene carbonate as a C1 methylene source in ruthenium-catalyzed additive controlled regioselective C4-methylenation and weak chelation-assisted C8-formylmethylation of isoquinolinones. Adopting vinylene carbonate as both a C2 and C1 synthon is an important highlight of this work. Amide carbonyl acts as the traceless directing group in C8-formylmethylation. Remarkably, in this reaction, two C-C bonds form in one-pot producing dimeric isoquinolinones by employing vinylene carbonate as a methylene surrogate in the presence of copper acetate as an additive. Importantly, unsymmetrical dimers were achievable, albeit in low yield. Extensive control experiments are conducted to decipher the reaction mechanism. It is evident from the mechanistic studies, that the formation of a formylmethyl group in situ at the C4-carbon undergoes dimerization, oxidation and subsequent decarboxylation to produce methylene-bridged isoquinolinone dimers. This protocol is scalable and compatible with a repertoire of substrates and shows high functional group tolerance. Harnessing vinylene carbonate as both a C2 and C1 synthon is an important highlight of this work.

Synthesis of Fluoren-9-ones via Pd-Catalyzed Annulation of 2-Iodobiphenyls with Vinylene Carbonate

A palladium-catalyzed reaction for intermolecular selective C-H cyclocarbonylation of 2-iodobiphenyls is described. Intriguingly, the vinylene carbonate acts as a carbon monoxide transfer agent to enable the annulation reaction. Moreover, as a versatile synthon, fluoren-9-one can be transformed into a variety of functionalized organic molecules, such as [1,1'-biphenyl]-2-carboxylic acid, 1'H,3'H-spiro[fluorene-9,2'-perimidine] and N-tosylhydrazones.

Rhodium-catalyzed divergent dehydroxylation/alkenylation of hydroxyisoindolinones with vinylene carbonate

Herein, a novel organic transformation involving rhodium-catalyzed divergent dehydroxylation/alkenylation of hydroxyisoindolinone with vinylene carbonate is reported, and a series of architecturally rigid and widely used spirolactams are obtained with excellent functional group tolerance and high selectivity. Remarkably, the promising vinylene carbonate reagent presents a distinct chemical reactivity as a vinyl-oxygen cyclic synthon and first transfers the C-H bond to spiroheterocycle scaffolds. Moreover, another chemoselectivity, direct dehydrogenative coupling with vinylene carbonate, is also presented. This protocol is compatible with green chemistry and only releases H2O and CO2 as byproducts.

Experimental and Computational Studies on RuII -Catalyzed C7-Allylation of Indolines with Allyl Bromide

The selective C7-allylation of indolines with allyl bromide under ruthenium catalysis has been revealed here. Under established reaction conditions, C7-allylation of various indolines, including drug compounds, was accomplished with good selectivity and yields. Based on combined experimental and density functional theory (DFT) studies, the olefin insertion route was energetically favorable among four possible pathways. Experimental and DFT studies further revealed that the C-H activation is a reversible rate-limiting step.

Cobalt(III)-Catalyzed Directed C-7 Selective C-H Alkynylation of Indolines with Bromoalkynes

A cobalt(III)-catalyzed directed C-7 alkynylation of indolines with easily accessible bromoalkynes has been developed. The reaction has a broad substrate scope with excellent yields and represents a powerful route to the synthesis of 7-alkynyl-substituted indolines. In addition, the reaction can be extended to the coupling of N-aryl 7-azaindoles, highlighting the synthetic practicability of the strategy.