Transition-metal-free coupling reactions

Metal-free arylation of pyrimidines through a photochemical process

Pyrimidinyl and pyrazinyl radicals were generated under moderate energetic irradiation conditions (UVA), and proved to be prompt to undergo C-C bond formation processes. Hetero-biaryl derivatives were obtained in good to high yields with highly interesting functional group selectivities. Bis hetero-biaryls were also easily accessible leading to original compounds, ready for further transformations. Experiments supporting radical processes have been reported.

Aryl Nitriles from Alkynes Using tert-Butyl Nitrite: Metal-Free Approach to C≡C Bond Cleavage

Alkyne C≡C bond breaking, outside of alkyne metathesis, remains an underdeveloped area in reaction discovery. Recently, nitrogenation has been reported to allow nitrile formation from alkynes. A new protocol for the metal-free C≡C bond cleavage of terminal alkynes to produce nitriles is reported. This method provides an opportunity to synthesize a vast range of nitriles containing aryl, heteroaryl, and natural product derivatives (38 examples). In addition, the potential of (t)BuONO to act as a powerful nitrogenating agent for terminal aryl alkynes is demonstrated.

β-Arylation of oxime ethers using diaryliodonium salts through activation of inert C(sp)-H bonds using a palladium catalyst

An efficient method of selective β-arylation of oxime ethers was realized by using a palladium catalyst with diaryliodonium salts as the key arylation reagents. The reaction proceeded smoothly through the activation of inert C(sp3)-H bonds to give corresponding ketones and aldehydes. This convenient procedure can be successfully applied to construct new C(sp3)-C(sp2) bonds on a number of complex molecules derived from natural products and thus serves as a practical synthetic tool for direct late-stage C(sp3)-H functionalization.

Base-Promoted Formal [4 + 3] Annulation between 2-Fluorophenylacetylenes and Ketones: A Route to Benzoxepines

The first base-promoted formal [4 + 3] annulation between 2-fluorophenylacetylenes and ketones has been disclosed. The reaction proceeds through a tandem α-vinylation of ketones followed by an intramolecular nucleophilic aromatic substitution (SNAr) reaction of the in situ generated β,γ-unsaturated ketone intermediates, providing a straightforward access to a wide range of functionalized benzoxepines in moderate to high yields. The transition-metal-free methodology featured a wide substrate scope, the use of easily available starting materials, and a high functional group tolerance.

Iodine-catalyzed oxidative C–C bond cleavage for benzoic acids and benzamides from alkyl aryl ketones

Iodine-catalyzed, aerial oxygen supported C–C bond cleavage reaction of aryl alkyl ketones for the synthesis of benzoic acids and benzamides. Also benzylidene acetones and phenylacetylenes were converted to their aromatic acids at this conditions.

Hypoiodite-catalysed oxidative cyclisation of Michael adducts of chalcones with 1,3-dicarbonyl compounds: a facile and versatile approach to substituted furans and cyclopropanes

Hypoiodite catalysis for selective oxidative cyclization has been developed, yielding either furans or cyclopropanes with excellent diastereoselectivity.

Potassium carbonate-mediated tandem C–S and C–N coupling reaction for the synthesis of phenothiazines under transition-metal-free and ligand-free conditions

A potassium carbonate-mediated tandem coupling reaction for the synthesis of phenothiazines is described. This protocol affords an efficient approach for the construction of phenothiazine derivatives without the need for addition of transition-metal catalyst or ligand.

Metal free TBHP-promoted intramolecular carbonylation of arenes via radical cross-dehydrogenative coupling: synthesis of indenoquinolinones, 4-azafluorenones and fluorenones

Analogues of indenoquinolinones, 4-azafluorenones and fluorenones were accessed in good to excellent yields. One of the synthesized derivative is known for antibacterial activity.

Predicting the reducing power of organic super electron donors

This work describes an improved, more accurate model for the calculation of electron transfer energetics of organic super electron donors.

Transition-metal-free C–C bond cleavage and formation: efficient synthesis of 2,3-diarylimidazo[1,2-α]pyridines from 2-aminopyridines and alkynoates

A highly efficient transition-metal-free cyclization reaction for the synthesis of 2,3-diarylimidazo[1,2-α]pyridines is described.

NHPI and ferric nitrate: a mild and selective system for aerobic oxidation of benzylic methylenes

An NHPI and ferric nitrate system was developed for efficient oxidation of benzylic methylenes with 1 atm of oxygen at 25 °C, providing up to 97% yield.

Microwave assisted synthesis of phenanthridinones and dihydrophenanthridines by vasicine/KOtBu promoted intramolecular C–H arylation

Vasicine and KOtBu promoted intramolecular C–H arylation has been demonstrated for synthesis of phenanthridinones and dihydrophenanthridines with various aryl halides under microwave conditions.

Iodine(iii)-mediated oxidative intramolecular arene–alkene coupling exemplified in the synthesis of phenanthrenes

A novel iodine(iii)-mediated synthesis of substituted phenanthrenes from ortho-vinylated biaryl derivatives through 6-endo-trig selective oxidative intramolecular arene–alkene coupling is reported.

Metal-free regioselective construction of indolin-3-ones via hypervalent iodine oxidation of N-substituted indoles

A metal-free method for regioselective construction of 2-acetoxy indolin-3-ones from N-substituted indoles using PhI(OAc)₂ was developed under mild reaction conditions.

CuI assisted desulfurative Sonogashira reaction of mercapto N-heterocyclic derivatives with alkynes

A palladium catalyzed Sonogashira reaction of mercapto N-heterocyclic derivatives with terminal alkynes by using CuI as the desulfurative reagent was described in this report.

Catalyst and solvent-free alkylation of quinoline N-oxides with olefins: A direct access to quinoline-substituted α-hydroxy carboxylic derivatives

A catalyst/solvent-free, one-pot and operationally simple method for the synthesis of quinoline-substituted α-hydroxy carboxylic derivatives by the hydroxyheteroarylation of olefins with quinoline N-oxides is reported.

Transition-metal-free oxidative C5 C–H-halogenation of 8-aminoquinoline amides using sodium halides

A simple and efficient transition-metal-free oxidative halogenation (Cl, Br) of the C5 C–H bond of 8-aminoquinoline amides, with low-cost and innoxious sodium halides, has been developed.

A metal-free cyclic iminium induced one-pot double annulation cascade: access to dihydroisoquinolinium (DHIQ) salts

A reactive cyclic iminium induced one-pot Groebke–Blackburn–Bienayme (GBB) double annulation cascade (DAC) for the synthesis of skeletally diverse DHIQ salts has been described. The key features of this protocol are solvent-free, robust method, clean reaction profile and operational simplicity.

Transition metal-free decarboxylative alkylation reactions

This review summarizes recent advances in the transition metal-free decarboxylative alkylation of carboxylic acids and their derivatives.

Sterically-controlled intermolecular Friedel–Crafts acylation with twisted amides via selective N–C cleavage under mild conditions

Highly chemoselective Friedel–Crafts acylation of arenes with twisted amides by N–C bond cleavage is reported for the first time.

Regioselective α-arylation of coumarins and 2-pyridones with phenylhydrazines under transition-metal-free conditions

A transition-metal-free regioselective α-arylation of coumarins and 2-pyridones has been accomplished by the reaction of phenylhydrazines with coumarins or 2-pyridones.

N-Hydroxyphthalimide: a new photoredox catalyst for [4+1] radical cyclization of N-methylanilines with isocyanides

A highly regioselective synthesis of 3-iminodihydroindoles using N-methylanilines and isocyanides at room temperature is described. The protocol utilizes N-hydroxyphthalimide as a new single electron transfer photoredox catalyst.

Synthesis of esters via sp3 C–H functionalisation

This review describes various methods for the synthesis of eleven classes of esters involving sp³ C–H functionalisation.

Transition-metal free alkylarylation of acrylamides initiated by radical C–C bond cleavage of the tertiary cycloalkanols

An efficient Na₂S₂O₈-promoted radical cyclization reaction of acrylamides with the tertiary cycloalkanols has been developed. This one pot procedure involves a tandem C–C bond cleavage and two C–C bonds formation process.

Transition-metal-free controlled polymerization of 2-polyfluorophenyl-5-trimethylsilylthiophenes: the substituent impact of fluorine

A transition-metal-free polymerization of a series of 2-polyfluorophenyl-5-trimethylsilylthiophenes promoted by fluoride anions is reported.

Transition metal-free oxidative ortho-acylation of phenols with N-heteroarylmethanes via double C–H activation

The direct oxidative acylation of phenols with N-heteroarylmethanes via sp³C–H and sp²C–H double activation was achieved under metal-free conditions. The reaction proceeds in a facile I₂/DMSO/O₂ system regio-selectively to produce valuable (2-hydroxyphenyl)arylmethanones. A plausible mechanism was proposed.

Hypervalent iodine(iii)-promoted N-incorporation into N-aryl vinylogous carbamates to quinoxaline diesters: access to 1,4,5,8-tetraazaphenanthrene

An oxidative N-incorporation strategy for synthesis of quinoxaline diesters under metal-free and mild reaction conditions is described via the formation of two C(sp²)–N bonds utilizing NaN₃ as the cheap N-atom source.

Transition-metal-free cascade reaction of α-halo-N-tosylhydrazones, indoles and arylboronic acids

A new transition-metal free three-component coupling of α-halo-N-tosylhydrazones, indoles and arylboronic acids, leading to the synthesis of substituted indole derivatives, has been developed.

Metal-free iodine-catalyzed direct cross-dehydrogenative coupling (CDC) between pyrazoles and thiols

A green and efficient iodine-catalyzed cross-dehydrogenative C–S coupling method for the synthesis of C-4 sulfenylated pyrazoles has been initially developed under metal-free conditions.

Benzylation of heterocyclic N-oxides via direct oxidative cross-dehydrogenative coupling with toluene derivatives

A novel cross-dehydrogenative coupling (CDC) of heterocyclic N-oxides with toluene derivatives has been disclosed.

A series of new lanthanide fumarates displaying three types of 3-D frameworks

A series of 3-D new lanthanide fumarates obtained by hydrothermal reaction can be classified into three types, according to the crystal structures, which are related to lanthanide contraction.

Micro-Cu4I4-MOF: reversible iodine adsorption and catalytic properties for tandem reaction of Friedel–Crafts alkylation of indoles with acetals

I₂@Cu₄I₄-MOF can be a highly heterogeneous catalyst to promote the tandem reaction of Friedel–Crafts alkylation of indoles with acetals under solvent-free conditions at room temperature.

DMSO/iodine-catalyzed oxidative C–Se/C–S bond formation: a regioselective synthesis of unsymmetrical chalcogenides with nitrogen- or oxygen-containing arenes

A convenient metal-free and solvent-free iodine-catalyzed regioselective greener protocol to access different types of unsymmetrical chalcogenides with nitrogen- or oxygen-containing arenes through oxidative C–Se/C–S formation via direct C(sp²)–H bond activation was developed.

Arylation with Diaryliodonium Salts

This chapter focuses on recent developments in metal-free and metal-catalyzed arylations with diaryliodonium salts (diaryl-λ3-iodanes). Synthetic routes to diaryliodonium salts are briefly described, and chemoselectivity trends with unsymmetric iodonium salts are discussed.