Synthesis of indoles and quinazolines via additive-controlled selective C–H activation/annulation of N-arylamidines and sulfoxonium ylides

Recent approaches for the synthesis of heterocycles from amidines via a metal catalyzed C-H functionalization reaction

Transition metal catalyzed C-H bond activation has become one of the most important tools for constructing new chemical bonds. Introducing directing groups to the substrates is the key to a successful reaction, these directing groups can also be further transformed in the reaction. Amidines with their unique structure and reactivity are ideal substrates for transition metal-catalyzed C-H transformations. This review describes the major advances and mechanistic investigations of the C-H activation/annulation tandem reactions of amidines until early 2024, focusing on metal-catalyzed C-H activation of amidines with unsaturated compounds, such as alkynes, ketone, vinylene carbonate, cyclopropanols and their derivatives. Meanwhile this manuscript also explores the reaction of amidines with different carbene precursors, for example diazo compounds, azide, triazoles, pyriodotriazoles, and sulfoxonium ylides as well as their own C-H bond activation/cyclization reactions. A bright outlook is provided at the end of the manuscript.

Recent Advances in Metal-Catalyzed Approaches for the Synthesis of Quinazoline Derivatives

Quinazolines are an important class of heterocyclic compounds that have proven their significance, especially in the field of organic synthesis and medicinal chemistry because of their wide range of biological and pharmacological properties. Thus, numerous synthetic methods have been developed for the synthesis of quinazolines and their derivatives. This review article briefly outlines the new synthetic methods for compounds containing the quinazoline scaffold employing transition metal-catalyzed reactions.

Copper-Mediated Cyclization of Terminal Alkynes with CF3-Imidoyl Sulfoxonium Ylides To Construct 5-Trifluoromethylpyrroles

A copper-mediated [3 + 2] cyclization of CF3-imidoyl sulfoxonium ylides and terminal alkynes has been demonstrated. This work provides a practical approach for assembling 5-trifluoromethylpyrroles with the merits of a broad substrate scope, good functional tolerance, and mild reaction conditions. Control experiments and DFT studies indicate that this reaction may involve the addition of π-bonds of terminal alkynes by copper-carbene radicals and hydrogen migration.

Transition-Metal-Catalyzed Directed C-H Functionalization in/on Water

Directing group assisted C-H bond functionalization using transition-metal-catalysis has emerged as a reliable synthetic tool for the construction of regioselective carbon-carbon/heteroatom bonds. Off late, "in/on water directed transition-metal-catalysis", though still underdeveloped, has appeared as one of the prominent themes in sustainable organic chemistry. This article covers the advancements, mechanistic insights and application of the sustainable directed C-H bond functionalization of (hetero)arenes in/on water in the presence of transition-metal-catalysis.

Copper(II)/DBU Relay Catalyzed Annulation of α-Carbonyl-γ-alkynyl Sulfoxonium Ylides for Accessing N-Sulfonamido 2H-Isoindoles

A copper(II)/DBU relay catalyzed annulation of α-carbonyl-γ-alkynyl sulfoxonium ylides as a new class of sulfoxonium ylide reagents with sulfonyl hydrazides is reported, enabling intramolecular oxygen migration to produce a series of N-sulfonamido 2H-isoindoles with good yields. The present annulation proceeded readily by combining the Cu(II)-catalyzed 6-endo-dig oxo-cyclization with the DBU-catalyzed isochromene skeletal rearrangement, resulting in the formation of multiple new chemical bonds.

Transition metal-free regioselective direct acylation of quinazolines for the synthesis of acylquinazoline derivatives

An efficient, mild method for direct regioselective acylation of quinazolines under metal-free conditions was developed with bis(trifluoroacetoxy)iodobenzene and trimethylsilyl azide at ambient temperature. The acylation reaction of quinazolines with aldehydes gave the corresponding acyl quinazolines in ethyl acetate with good to excellent yields and excellent functional group tolerance and site selectivity. In addition, the mechanism of the direct acylation of quinazolinone was investigated through HPLC-HRMS (high pressure liquid chromatography-high resolution mass spectrometry) and EPR (electron paramagnetic resonance) strategies.

[Cp*IrCl2]2-Catalyzed Amidocarbonation of Olefins with Sulfoxonium Ylides toward Functionalized Isoindolin-1-ones

A [Cp*IrCl2]2-catalyzed amidocarbonation of olefins with sulfoxonium ylides has been developed to generate diverse biologically important isoindolin-1-ones in high efficiency under mild reaction conditions. Mechanism studies indicated that this cascade reaction was triggered by amino-iridation of the olefin unit to generate iridacycle, followed by formal migratory insertion with sulfoxonium ylides. This newly developed method features broad substrate scopes and operational simplicity.

Synthesis of α-Carbonyl-α'-amide Sulfoxonium Ylides from Isocyanates with Complete Atom Economy

An efficient catalyst- and additive-free facile synthesis of α-carbonyl-α'-amide sulfoxonium ylides from isocyanates and β-ketosulfoxonium ylides with complete atom economy has been described. The β-ketosulfoxonium ylides and isocyanates adorned with various functional groups were well-tolerated and afforded moderate to high yields of the α-carbonyl-α'-amide sulfoxonium ylide derivatives. Finally, using large-scale reactions and converting the synthesized ylides into other valuable compounds, we demonstrated the practicality of this synthetic method.

Synthesis of Tetrahydro-2H-thiopyran 1,1-Dioxides via [1+1+1+1+1+1] Annulation: An Unconventional Usage of a Tethered C-S Synthon

An unprecedented [1+1+1+1+1+1] annulation process has been developed for the construction of tetrahydro-2H-thiopyran 1,1-dioxides. Notably, rongalite acted as a tethered C-S synthon in this reaction and can be chemoselectively used as triple C1 units and as a source of sulfone. Mechanistic investigation indicated that two different carbon-increasing models are involved in this reaction in which rongalite serves as C1 units.

Condition-Dependent Selective Synthesis of Indolo[1,2-c]quinazolines and Indolo[3,2-c]quinolines from 2-(1H-Indol-2-yl)anilines and Sulfoxonium Ylides

In this paper, a selective synthesis of indolo[1,2-c]quinazolines and indolo[3,2-c]quinolines through the cascade reactions of 2-(1H-indol-2-yl)anilines with sulfoxonium ylides is presented. The formation of products involves the generation of a carbene species from sulfoxonium ylide and its N-H bond insertion reaction with 2-(1H-indol-2-yl)aniline followed by deoxygenative imine formation, intramolecular N- or C- nucleophilic addition and deoxygenative aromatization. This switchable synthesis was condition-dependent. In the presence of K₂CO₃ in CH₃CN, the reaction mainly furnished indolo[1,2-c]quinazolines. In the presence of HOAc in dioxane, it selectively afforded indolo[3,2-c]quinolines. In addition, direct C-H/N-H functionalization of the products obtained provides a convenient and direct access to polycyclic heteroaromatic compounds. These novel protocols have advantages such as readily accessible substrates, easily tunable selectivity, good compatibility with diverse functional groups, and the use of air as a cost-free and sustainable oxidant.

Catalyst-Controlled C-H Transformation of Pyrazolidinones with 1,3-Diynes for Highly Selective Synthesis of Functionalized Bisindoles and Indoles

An efficacious synthetic solution to offer functionalized bisindoles and indoles has been developed based on catalyst-controlled C-H functionalization of pyrazolidinones and 1,3-diynes with highly selective control of both chemoselectivity and regioselectivity. This straightforward pathway conquers chemo- and regioselectivity challenges concerning the use of 1,3-diynes.

Cobalt(III)-Catalyzed C–H Activation/Annulation Cascade Reaction of N-Chlorobenzamides with 2-Acetylenic Ketones at Room Temperature

A mild cascade annulation of Co(III)-catalyzed N-chlorobenz­amides with 2-acetylenic ketones at room temperature is reported. This reaction sets N–Cl bond of N-chlorobenzamide as an internal oxidant, displaying broad functional group tolerance and excellent reverse selectivity of alkyne insertion under mild and safe conditions. The cascade reaction offers a straightforward and mild protocol to construct isoquinolones in high yields at room temperature.

Hydrazine-Directed Rh(III) Catalyzed (4+2) Annulation with Sulfoxonium Ylides: Synthesis and Photophysical Properties of Dihydrocinnolines

We herein report hydrazine-directed, Rh(III) catalyzed (4+2) annulation of N-alkyl aryl hydrazines with sulfoxonium ylides as a safe carbene precursor. The reaction shows excellent functional group tolerance with broad substrate...

One-pot synthesis of 3-trifluoromethylbenzo[b][1,4]oxazines from CF3-imidoyl sulfoxonium ylides with 2-bromophenols

A one-pot two-step fashion for the synthesis of 3-trifluoromethyl-1,4-benzoxazines from CF3-imidoyl sulfoxonium ylides and 2-bromophenols via lithium-bromide-promoted O–H insertion of sulfoxonium ylides and annulation has been demonstrated.

Rhodium-Catalysed Regioselective [4+2]-type Annulation of 1-H-Indazoles with Propargyl Alcohols: A direct entry to 6-alkenylindazolo[3,2-a]isoquinolines

An efficient method for the synthesis of 6-vinylindazolo[3,2-a]isoquinolines via rhodium(III)-catalysed C-H bond activation/subsequent [4+2] cyclization starting from easily available 3-aryl-1-H-indazoles and propargyl alcohols has been developed. A series of vinyl-annulated...

Open-Air Dual-Diamination of Aromatic Aldehydes: Direct Synthesis of Azolo-Fused 1,3,5-Triazines Facilitated by Ammonium Iodide

A new and practical protocol for the synthesis of medicinally privileged azolo[1,3,5]triazines by simply heating under air has been presented. The in situ generated N-azolo amidines from commercially available aromatic aldehydes and 3-aminoazoles with ammonium iodide undergo the second diamination to accomplish the [3 + 1 + 1 + 1] heteroannulation reaction. This convenient process is appreciated by high efficiency, broad substrate scope, gram-scale synthesis, and operational simplicity under reagent-free conditions.

Direct and Regioselective Palladium(II)-Catalyzed B(4)-H Monoacyloxylation and B(4,5)-H Diacetoxylation of o-Carborane Acids with Phenyliodonium Dicarboxylates

A direct B(4)-H monoacyloxylation via a Pd-catalyzed regioselective B(4)-H activation of o-carborane acids with phenyliodonium dicarboxylates was developed, and a series of B(4)-H monoacyloxylated o-carboranes decorated with active groups were synthesized with moderate to good yields as well as excellent selectivity. In addition, a direct B(4,5)-H diacetoxylation from o-carborane acids with phenyliodonium diacetate was demonstrated.

Pd-Catalyzed Sequential Formation of C-C Bonds: A New Strategy for the Synthesis of (E)-α,β-Unsaturated Carbonyl Compounds from Sulfoxonium Ylides and 1-Iodo-2-((2-methylallyl)oxy)benzene Compounds

α,β-Unsaturated carbonyl compounds are significant moieties in many biological molecules and have attracted considerable attention in organic synthetic chemistry. A Pd-catalyzed cascade cyclization for the synthesis of (E)-α,β-unsaturated carbonyl compounds with the sequential formation of C-C bonds was developed. This method offers high efficiency, good functional group tolerance, and moderate to excellent yields and generally displays high stereoselectivity.

Rhodium(III)-Catalyzed [4 + 2] Annulation of N-Arylbenzamidines with Propargyl Alcohols: Highly Regioselective Synthesis of 1-Aminoisoquinolines Controlled by Noncovalent Interaction

A highly regioselective synthesis of 1-aminoisoquinolines has been explored via rhodium(III)-catalyzed C-H bond activation/annulation reactions of propargyl alcohols with N-arylbenzamidines. The imidamide was used as the directing group and the nitrogen source of the heterocycle and for regulating the regioselective migratory insertion of propargyl alcohol through a hydrogen bond. In this transformation, a specific isomer was obtained that would provide a new strategy for the synthesis of 1-aminoisoquinolines with biological activity.

Hydroxyl-Directed Ruthenium-Catalyzed peri-Selective C-H Acylmethylation and Annulation of Naphthols with Sulfoxonium Ylides

Herein, we report a highly efficient ruthenium-catalyzed peri-selective C(sp²)-H acylmethylation of 1-naphthols with α-carbonyl sulfoxonium ylides by utilizing hydroxyl as a weakly coordinating directing group. This new method imparts good reactivity, excellent chemo- and regioselectivity, and broad functional group tolerance and involves mild reaction conditions. The C-H acylmethylated products can be readily cyclized into fluorescent annulated pyrans by a one-pot process.

Annulation of Conjugated Azine-Imine with a Sulfoxonium Ylide in a Noncarbenoid Route to Synthesize Multisubstituted Imidazole-Fused Heterocycles

A new [4+1]-annulation of in situ generated heterocyclic azine-aldimines with β-keto sulfoxonium ylides has been developed. The reaction constructs N-fused imidazole rings. In the reaction, the ylides play a dual-functional role of a nucleophilic 1,1-dipolar one-carbon synthon and a source of an internal oxidant, dimethyl sulfoxide, that promotes in situ dehydrogenation to product scaffolds. The method enables access to imidazo-pyridine, pyrazine, and pyrimidine heteroaromatics.

Recent advances in Rh(iii)/Ir(iii)-catalyzed C–H functionalization/annulation via carbene migratory insertion

The review highlighted diverse annulations, including nitrogen, oxygen, sulfur heterocycles and carbocylizations via Rh(iii)/Ir(iii)-catalyzed C–H functionalization/annulation with various arene and carbene precursors.

Ruthenium-catalyzed coupling of α-carbonyl phosphoniums with sulfoxonium ylides via C–H activation/Wittig reaction sequences

A Ru(ii)-catalyzed coupling of various α-carbonyl phosphoniums with sulfoxonium ylides has been realized for the facile synthesis of 1-naphthols in good to excellent yields.

Synthesis of 3-spirooxindole 3H-indoles through Rh(iii)-catalyzed [4 + 1] redox-neutral spirocyclization of N-aryl amidines with diazo oxindoles

Presented herein is a novel synthesis of 3-spirooxindole 3H-indoles via the coupling and spirocyclization of N-aryl amidines with diazo oxindoles.

Synthesis of 1,3-Benzodiazepines through [5 + 2] Annulation of N-Aryl Amidines with Propargylic Esters

In this paper, an efficient synthesis of functionalized 1,3-benzodiazepines through an unprecedented [5 + 2] annulation of N-aryl amidines with propargylic esters is presented. The reactions proceed through Rh(III)-catalyzed C(sp²)-H alkenylation followed by annulation and deacetoxylation along with cascade C-H/N-H/C-O bond cleavage and C-C/C-N bond formation. Furthermore, the cytotoxicity of selected products against several human cancer cell lines was tested, which demonstrated their good potential for pharmaceutical applications.

Palladium-catalyzed cross-coupling reaction of sulfoxonium ylides and benzyl bromides by carbene migratory insertion

A palladium-catalyzed cross-coupling reaction of sulfoxonium ylides and benzyl bromides has been developed, which has potential safety advantages over previous carbene coupling reactions using either diazo compounds or their in situ precursors. This reaction affords polysubstituted olefins, and features good substrate tolerance and is suitable for late-stage modification of biologically active molecules. Pd-carbene migratory insertion is supposed to be involved in this coupling reaction.

Freire CS, Silvestre AJD, Freire MG. The Role of Ionic Liquids in the Pharmaceutical Field: An Overview of Relevant Applications

Solubility, bioavailability, permeation, polymorphism, and stability concerns associated to solid-state pharmaceuticals demand for effective solutions. To overcome some of these drawbacks, ionic liquids (ILs) have been investigated as solvents, reagents, and anti-solvents in the synthesis and crystallization of active pharmaceutical ingredients (APIs), as solvents, co-solvents and emulsifiers in drug formulations, as pharmaceuticals (API-ILs) aiming liquid therapeutics, and in the development and/or improvement of drug-delivery-based systems. The present review focuses on the use of ILs in the pharmaceutical field, covering their multiple applications from pharmaceutical synthesis to drug delivery. The most relevant research conducted up to date is presented and discussed, together with a critical analysis of the most significant IL-based strategies in order to improve the performance of therapeutics and drug delivery systems.

Rhodium(III)-catalysed decarboxylative C-H functionalization of isoxazoles with alkenes and sulfoxonium ylides

Decarboxylative C-H functionalization of isoxazoles with electron-deficient alkenes and sulfoxonium ylides at the C5 position was achieved in the presence of rhodium(iii) catalysts to give the corresponding alkenylation and acylmethylation products, respectively.

Ruthenium(II)-Catalyzed Homocoupling of α-Carbonyl Sulfoxonium Ylides Under Mild Conditions: Methodology Development and Mechanistic DFT Study

A mild ruthenium(II)-catalyzed homocoupling of α-carbonyl sulfoxonium ylides was developed and the detailed mechanism was understood based on DFT calculations in the current report. The catalytic system utilizes the α-carbonyl sulfoxonium ylide as both the directing group for ortho-sp2 C-H activation and the acylmethylating reagent for C-C coupling. Various substituents are compatible in the transformation and a variety of isocoumarin derivatives were synthesized at room temperature without any protection. The theoretical results disclosed that the full catalytic cycle contains eight elementary steps, and in all the cationic Ru(II) monomer is involved as the catalytic active species. The acid additive is responsible for protonation of the ylide carbon prior to the intramolecular nucleophilic addition and C-C bond cleavage. Interestingly, the intermediacy of free acylmethylation intermediate or its enol isomer is not necessary for the transformation.

Metal-Free Chemoselective Reaction of Sulfoxonium Ylides and Thiosulfonates: Diverse Synthesis of 1,4-Diketones, Aryl Sulfursulfoxonium Ylides, and β-Keto Thiosulfones Derivatives

A diverse chemoselective insertion reaction of sulfoxonium ylides and thiosulfonates under transition-metal-free conditions is developed, which successfully affords 1,4-diketone compounds, arylthiosulfoxide-ylides, and β-keto thiosulfones, respectively. The nucleophilic addition of two molecular sulfoxonium ylides to construct sulfone-substituted 1,4-dione compounds is the highlight of this work.