Metal-Free Oxidative Functionalization of a C(sp3)–H Bond Adjacent to Nitrogen and Intramolecular Aromatic Cyclization for the Preparation of 6-Amidophenanthridines

Electro-oxidative Methylation of 2-Isocyanobiaryls Using N,N-dimethylformamide (DMF) as Carbon Source: Synthesis of 6-Methylphenanthridines

A benign electrochemical method to access 6-methylphenanthridines from 2-isocyanobiaryls using N,N-dimethylformamide (DMF) as a methyl source is reported. The protocol operates at ambient temperature without the need for harmful methylating reagents. Mechanistic studies suggested that DMF delivered a methylene synthon, followed by reduction at the cathode and tautomerization. The method offers environmental benefits by avoiding metal-based reagents and harsh conditions.

Metal-free 2-isocyanobiaryl-based cyclization reactions: phenanthridine framework synthesis

The development of transition metal-free 2-isocyanobiaryl-based reactions has received much attention due to the widespread presence of phenanthidine frameworks as products in pharmacological chemistry and materials science. This review article focuses on the achievements from 2013 until now in various metal-free catalyzed reactions and discusses challenging mechanisms and features of the transformations.

Factors Governing Reactivity and Selectivity in Hydrogen Atom Transfer from C(sp3)-H Bonds of Nitrogen-Containing Heterocycles to the Cumyloxyl Radical

A kinetic study of the hydrogen atom transfer (HAT) reactions from nitrogen-containing heterocycles (secondary and tertiary lactams, 2-imidazolidinones, 2-oxazolidinones, and succinimides) to the cumyloxyl radical has been carried out employing laser flash photolysis with ns time resolution. HAT occurs from the C–H bonds that are α to nitrogen, activated by hyperconjugative overlap with the N–C=O π system. In the lactam series, the second-order HAT rate constant (k_H) was observed to decrease by a factor of ∼4 going from the five- and six-membered ring derivatives to the eight-membered ones, a behavior that was rationalized on the basis of a reduced extent of hyperconjugative activation associated to the greater flexibility of the larger rings compared to the smaller ones. In the five-membered-ring substrate series, the k_H values were observed to increase by >3 orders of magnitude on going from succinimide to 2-imidazolidinones, a behavior that was explained in terms of the divergent contribution of hyperconjugative activation and deactivating electronic effects determined by ring functionalities. The results are discussed in the framework of the development of HAT-based C–H bond functionalization procedures.

C-centered radical-initiated cyclization by directed C(sp3)–H oxidative functionalization

C(sp3)–H functionalization is attracting constant attention. This review emphasizes C-centered radicals initiated cyclization strategies by directed C(sp3)–H oxidative functionalization since 2012.

C(sp3)–H functionalization with isocyanides

This review highlights the state-of-the-art advances in C(sp³)–H functionalization involving isocyanides through the synergistic combination of isocyanide insertion and C(sp³)–H bond activation.

Photocatalyzed syntheses of phenanthrenes and their aza-analogues. A review

Phenanthrenes and their aza-analogues have important applications in materials science and in medicine. Aim of this review is to collect recent reports describing their synthesis, which make use of radical cyclizations promoted by a visible light-triggered photocatalytic process.

Black TiO2 nanoparticles with efficient photocatalytic activity under visible light at low temperature: regioselective C–N bond cleavage toward the synthesis of thioureas, sulfonamides, and propargylamines

Several different colored forms of TiO₂ were prepared through the easy treatment of white TiO₂ and NaBH₄ as a safe hydrogen source. Then, tertiary amines were harnessed toward the regioselective synthesis of three prominent scaffolds.

Radical Cyanotrifluoromethylation of Isocyanides: Step-Economical Access to CF3-Containing Nitriles, Amines, and Imines

A novel copper-catalyzed radical cyanotrifluoromethylation has been achieved through a multicomponent reaction of isocyanides, Togni's reagent, and trimethylsilyl cyanides, affording trifluoroacetimidoyl nitriles in good yields. This reaction demonstrates a unique feature of merging two valuable functional groups-trifluoromethyl (CF₃) and cyan (CN)-onto the same C atom. The transformation proceeds by the initial addition of the CF₃ radical to isocyanide and the subsequent intermolecular C-CN formation. The products can be successfully transformed to a series of CF₃-containing amines and imines that may serve in the synthesis of valuable pharmaceuticals and agrochemicals.

A Synthetic Route to Sodium α-Aminoalkanesulfinates and Their Application in the Generation of α-Aminoalkyl Radicals for Radical Addition Reactions

The synthesis of sodium α-aminoalkanesulfinates and their synthetic utility as α-aminoalkyl radical precursors are reported. A variety of α-aminoalkanesulfinates were readily obtained from the reaction between the anions of N-Boc-protected alkylamines and 1,4-diazabicyclo[2.2.2]octanebis(sulfur dioxide). Treatment of sodium α-aminoalkanesulfinates with (diacetoxyiodo)benzene easily generated the corresponding α-aminoalkyl radicals under mild conditions, which were then applied in radical 1,2-addition to imines, radical 1,4-addition to electron-deficient olefins, and radical addition/cyclization to 2-isocyanobiphenyls.

Convenient synthesis of 6-alkyl phenanthridines and 1-alkyl isoquinolines via silver-catalyzed oxidative radical decarboxylation

A convenient and efficient protocol for the synthesis of 6-alkyl phenanthridines and 1-alkyl isoquinolines has been developed. The reaction relies on the coupling of 2-isocyanobiphenyls and vinyl isonitriles with alkyl radicals formed by the silver-catalyzed decarboxylation of stoichiometric aliphatic carboxylic acids, and affords diverse phenanthridine and isoquinoline derivatives under mild reaction conditions. The experiment of β-scission of cyclobutylcarbinyl radicals is used to shed light on the reaction mechanism.

Copper-catalyzed synthesis of α-amino nitriles through methyl transfer from DMF to aromatic amines

A copper-catalyzed activation of C(sp³)–H bonds of DMF at room temperature was developed, which results in methyl transfer to aromatic amines for efficient synthesis of exceedingly valuable α-amino nitriles.

Iron-catalyzed cascade addition/cyclization of 2-biphenyl isocyanides with toluenes: a highly efficient approach to 6-benzylated phenanthridines

A highly efficient Fe-catalyzed cascade addition/cyclization of 2-biphenyl isocyanides with toluenes for the synthesis of 6-benzylated phenanthridines has been reported.

Recent Advances in Radical C-H Activation/Radical Cross-Coupling

Research and industrial interest in radical C-H activation/radical cross-coupling chemistry has continuously grown over the past few decades. These reactions offer fascinating and unconventional approaches toward connecting molecular fragments with high atom- and step-economy that are often complementary to traditional methods. Success in this area of research was made possible through the development of photocatalysis and first-row transition metal catalysis along with the use of peroxides as radical initiators. This Review provides a brief and concise overview of the current status and latest methodologies using radicals or radical cations as key intermediates produced via radical C-H activation. This Review includes radical addition, radical cascade cyclization, radical/radical cross-coupling, coupling of radicals with M-R groups, and coupling of radical cations with nucleophiles (Nu).

Introduction of Quinolines and Isoquinolines onto Nonactivated α-C-H Bond of Tertiary Amides through a Radical Pathway

Treatment of quinolines and isoquinolines with benzoyl peroxide in tertiary amides, such as N,N-dimethylacetamide, N,N-dimethylpropionamide, and N-acetylpyrrolidine, etc., under irradiation with a Hg lamp in the temperature range of 35 °C to 40 °C gave C-C-bonded quinolines and isoquinolines bearing amide groups with high regioselectivity in good to moderate yields, respectively, under transition-metal-free conditions.

Visible-light-mediated radical insertion/cyclization cascade reaction: synthesis of phenanthridines and isoquinolines from isocyanides

The development of a visible-light promoted radical insertion/cyclization cascade reaction to generate phenanthridines and isoquinolines from isocyanides under mild reaction conditions is reported.

Kinetic Study of the Reaction of the Phthalimide-N-oxyl Radical with Amides: Structural and Medium Effects on the Hydrogen Atom Transfer Reactivity and Selectivity

A kinetic study of the hydrogen atom transfer (HAT) reactions from a series of secondary N-(4-X-benzyl)acetamides and tertiary amides to the phthalimide-N-oxyl radical (PINO) has been carried out. The results indicate that HAT is strongly influenced by structural and medium effects; in particular, the addition of Brønsted and Lewis acids determines a significant deactivation of C-H bonds α to the amide nitrogen of these substrates. Thus, by changing the reaction medium, it is possible to carefully control the regioselectivity of the aerobic oxidation of amides catalyzed by N-hydroxyphthalimide, widening the synthetic versatility of this process.

Cascade alkylarylation of substituted N-allylbenzamides for the construction of dihydroisoquinolin-1(2H)-ones and isoquinoline-1,3(2H,4H)-diones

An oxidative reaction for the synthesis of 4-alkyl-substituted dihydroisoquinolin-1(2H)-ones with N-allylbenzamide derivatives as starting materials has been developed. The radical alkylarylation reaction proceeds through a sequence of alkylation and intramolecular cyclization. The substituent on the C–C double bond was found to play a key role for the progress of the reaction to give the expected products with good chemical yields. Additionally, N-methacryloylbenzamides were also suitable substrates for the current reaction and provided the alkyl-substituted isoquinoline-1,3(2H,4H)-diones in good yield.

Recent progress in imidoyl radical-involved reactions

This review discusses the recent progress in imidoyl radical-involved reactions including the synthesis of functionalized heterocycles, nitriles, imines, amines,etc.

Visible-light-promoted synthesis of phenanthridines via an intermolecular isocyanide insertion reaction

An isocyanide insertion reaction promoted by the combination of an amide and a photoredox is now presented.

Metal-free domino one-pot protocols for quinoline synthesis

Metal-free domino one-pot protocols for quinoline synthesis have been reviewed.

DBU-promoted cyclization of vinyl isocyanides with ethers via the functionalization of a C(sp3)–H bond for the synthesis of isoquinolines

A DBU-promoted cascade functionalization of a C(sp³)–H bond adjacent to oxygen and a radical cyclization reaction of vinyl isocyanides was developed to easily access multi-functionalized isoquinolines.