Photocatalytic Alkylation of Pyrroles and Indoles with α-Diazo Esters

Catalyst-controlled site-selective N-H and C3-arylation of carbazole via carbene transfer reactions

A site-selective direct arylation reaction of carbazole and other N-heterocycles with diazo-naphthalen-2(1H)-ones has been developed. While Au(i)-NHC catalysts lead to selective C3-arylation, palladium acetate allows for selective N-H arylation, displaying complete site-selectivity each. To show the applicability of these arylation reactions, one-pot, two-fold diarylation reactions of carbazole were demonstrated.

Catalyst-free, visible-light-promoted S-H insertion reaction between thiols and α-diazoesters

A visible-light-promoted S-H insertion reaction between thiols and α-diazoesters was developed. The reaction proceeded smoothly at room temperature with a broad substrate scope, affording various thioethers in moderate to excellent yields. The catalyst- and additive-free nature, sustainable energy source and mild reaction conditions make this strategy more eco-friendly.

Recent Advances in Rapid Synthesis of Non-proteinogenic Amino Acids from Proteinogenic Amino Acids Derivatives via Direct Photo-Mediated C-H Functionalization

Non-proteinogenic amino acids have attracted tremendous interest for their essential applications in the realm of biology and chemistry. Recently, rising C-H functionalization has been considered an alternative powerful method for the direct synthesis of non-proteinogenic amino acids. Meanwhile, photochemistry has become popular for its predominant advantages of mild conditions and conservation of energy. Therefore, C-H functionalization and photochemistry have been merged to synthesize diverse non-proteinogenic amino acids in a mild and environmentally friendly way. In this review, the recent developments in the photo-mediated C-H functionalization of proteinogenic amino acids derivatives for the rapid synthesis of versatile non-proteinogenic amino acids are presented. Moreover, postulated mechanisms are also described wherever needed.

Ruthenium-Catalyzed C–H Activations for the Synthesis of Indole Derivatives

The synthesis of substituted indoles has received great attention in the field of organic synthesis methodology. C–H activation makes it possible to obtain a variety of designed indole derivatives in mild conditions. Ruthenium catalyst, as one of the most significant transition-metal catalysts, has been contributing in the synthesis of indole scaffolds through C–H activation and C–H activation on indoles. Herein, we attempt to present an overview about the construction strategies of indole scaffold and site-specific modifications for indole scaffold via ruthenium-catalyzed C–H activations in recent years.

Tridentate Nickel(II)-Catalyzed Chemodivergent C-H Functionalization and Cyclopropanation: Regioselective and Diastereoselective Access to Substituted Aromatic Heterocycles

A Schiff-base nickel(II)-phosphene-catalyzed chemodivergent C-H functionalization and cyclopropanation of aromatic heterocycles is reported in moderate to excellent yields and very good regioselectivity and diastereoselectivity. The weak, noncovalent interaction between the phosphene ligand and Ni center facilitates the ligand dissociation, generating the electronically and coordinatively unsaturated active catalyst. The proposed mechanisms for the reported reactions are in good accord with the experimental results and theoretical calculations, providing a suitable model of stereocontrol for the cyclopropanation reaction.

Blue LED Mediated Intramolecular C-H Functionalization and Cyclopropanation of Tryptamines: Synthesis of Azepino[4, 5-b]indoles and Natural Product Inspired Polycyclic Indoles

We report a novel blue LED mediated intramolecular C-H functionalization of tryptamine derivatives to generate azepino[4, 5-b]indoles (4) in moderate to good yields. By altering the substitution at the tryptamine nitrogen, intramolecular cyclopropanation is achieved in high yields under the same reactions condition to provide natural product inspired polycyclic indoles (6), which are further transformed to spiropiperidino (5 and 8) indoles in decent yields. The mechanism of formation of the compounds was investigated through DFT studies.

Regioselective Arene C-H Alkylation Enabled by Organic Photoredox Catalysis

Expanding the toolbox of C-H functionalization reactions applicable to the late-stage modification of complex molecules is of interest in medicinal chemistry, wherein the preparation of structural variants of known pharmacophores is a key strategy for drug development. One manifold for the functionalization of aromatic molecules utilizes diazo compounds and a transition-metal catalyst to generate a metallocarbene species, which is capable of direct insertion into an aromatic C-H bond. However, these high-energy intermediates can often require directing groups or a large excess of substrate to achieve efficient and selective reactivity. Herein, we report that arene cation radicals generated by organic photoredox catalysis engage in formal C-H functionalization reactions with diazoacetate derivatives, furnishing sp2 -sp3 coupled products with moderate-to-good regioselectivity. In contrast to previous methods utilizing metallocarbene intermediates, this transformation does not proceed via a carbene intermediate, nor does it require the presence of a transition-metal catalyst.

B(C6F5)3-Catalyzed Direct C3 Alkylation of Indoles and Oxindoles

The direct C3 alkylation of indoles and oxindoles is a challenging transformation, and only a few direct methods exist. Utilizing the underexplored ability of triaryl boranes to mediate the heterolytic cleavage of α-nitrogen C–H bonds in amines, we have developed a catalytic approach for the direct C3 alkylation of a wide range of indoles and oxindoles using amine-based alkylating agents. We also employed this borane-catalyzed strategy in an alkylation-ring opening cascade.

Synthesis of Antitricyclic Morpholine Derivatives through Iodine(III)-Mediated Intramolecular Umpolung Cycloaddition of Olefins

A (diacetoxyiodo)benzene-mediated intramolecular cycloaddition of olefins to construct tricyclic morpholines is presented. A series of substituted tricyclic morpholines were obtained in one-step simple operation under mild conditions, and the NMR studies were employed to see the interaction of reactants. The studies on stereochemistry showed that transformation of Z-alkene was inhibited, which is interpreted by density functional theory calculations on Z- and E-transition state models, and only E-alkene resulted in an anticycloaddition product, which is testified by a single-crystal X-ray diffraction analysis.

Tandem Carbenoid C-H Functionalization/Conia-ene Cyclization of N-Propargyl Indoles Generates Pyrroloindoles under Cooperative Rh(II)/Zn(II) Catalysis

The decomposition of diazodicarbonyl compounds in the presence of various metal catalysts has become a reliable method for the functionalization of indoles via carbenoid intermediates. Exploiting the nucleophilic reactivity of the in situ generated malonic ester product formed, we herein report a tandem C-H functionalization/Conia-ene cyclization of N-alkyne tethered indoles. This double functionalization of diazodicarbonyls generates a range of pyrrolo[1,2-a]-, pyrido[1,2-a]-, and azepino[1,2-a]indole products with good synthetic efficiency.

Visible light-induced photocatalytic C–H ethoxycarbonylmethylation of imidazoheterocycles with ethyl diazoacetate

A visible-light-promoted regioselective ethoxycarbonylmethylation of imidazoheterocycles has been developed using an α-diazoester via a radical pathway.

Photochemical α-carboxyalkylation of tryptophols and tryptamines via C–H functionalization

A process for the α-carboxyalkylation of tryptophols and tryptamines by the functionalization of C–H bonds under visible light irradiation has been developed.

Palladium-catalyzed regioselective C–H alkynylation of indoles with haloalkynes: access to functionalized 7-alkynylindoles

A palladium-catalyzed exclusively selective alkynylation of indoles has been reported, affording concise access to 7-alkynylindoles from readily available starting materials.