Nucleophilic Addition of Grignard Reagents to 3–Acylindoles: Stereoselective Synthesis of Highly Substituted Indoline Scaffolds

Mechanochemical C-H Arylation and Alkylation of Indoles Using 3 d Transition Metal and Zero-Valent Magnesium

Although the 3 d transition-metal catalyzed C-H functionalization have been extensively employed to promote the formation of valuable carbon-carbon bonds, the persistent problems, including the use of sensitive Grignard reagents and the rigorous operations (solvent-drying, inert gas protection, metal pre-activation and RMgX addition rate control), still leave great room for further development of sustainable methodologies. Herein, we report a mechanochemical technology toward in-situ preparation of highly sensitive organomagnesium reagents, and thus building two general 3 d transition-metal catalytic platforms that enables regioselective arylation and alkylation of indoles with a wide variety of halides (including those containing post transformable functionalities and heteroaromatic rings). This mechanochemical strategy also brings unique reactivity and high step-economy in producing functionalized N-free indole products.

Development and Application of Indolines in Pharmaceuticals

In recent years, the incidence of cancer is high around the world, and the resistance of bacteria is increasing. To cope with the potentially adverse side effects of cancer chemotherapy and surgery, researchers are turning to the construction of new drug scaffolds. The indoline structure exists in a huge number of natural products, but drugs with indoline have only been formally studied in recent years. With the deepening of research, drugs containing indoline have played important roles in more disease treatment aspects, such as anti-tumor, anti-bacterial, anti-inflammatory and have been used as analgesics, to treat cardiovascular diseases and so on. The synthesis and pharmacological activity of indoline derivatives is summarized in this review in order to support the addition of the indoline component to the toolbox of medicinal chemists. This review focuses on the advantages of indoline compounds in development and synthesis of and for the use as anticancer drugs, antibacterial drugs, to treat cardiovascular diseases and as anti-inflammatory and analgesic drugs. Indoline structures are commonly found in natural and synthetic compounds with medicinal value and are now beginning to be exploited as the basic backbone of various drugs. As research continues, dihydroindoles and their derivatives will play a greater role in the medical field.

Dearomatization of 3-Nitroindoles Enabled Using Palladium-Catalyzed Decarboxylative [4 + 2] Cycloaddition of 2-Alkylidenetrimethylene Carbonates

A dearomatization process of 3-nitroindoles enabled using palladium-catalyzed decarboxylative [4 + 2] cycloaddition of either 2-alkylidenetrimethylene carbonates or 2-(hydroxymethyl)-3-arylallyl carbonates has been developed, affording a wide range of indoline-fused tetrahydropyrans in good yields with excellent diastereoselectivities. This reaction features a wide substrate scope and mild conditions and represents the first example of the application of π-allyl palladium 1,4-[O,C]-dipole species for the dearomative cycloaddition of electron-deficient heteroarenes.

Iron-Catalyzed Reductive Cyclization by Hydromagnesiation: A Modular Strategy Towards N-Heterocycles

A reductive cyclization to prepare a variety of N-heterocycles, through the use of ortho-vinylanilides, is reported. The reaction is catalyzed by an inexpensive and bench-stable iron complex and generally occurs at ambient temperature. The transformation likely proceeds through hydromagnesiation of the vinyl group, and trapping of the in situ generated benzylic anion by an intramolecular electrophile to form the heterocycle. This iron-catalyzed strategy was shown to be broadly applicable and was utilized in the synthesis of substituted indoles, oxindoles and tetrahydrobenzoazepinoindolone derivatives. Mechanistic studies indicated that the reversibility of the hydride transfer step depends on the reactivity of the tethered electrophile. The synthetic utility of our approach was further demonstrated by the formal synthesis of a reported bioactive compound and a family of natural products.

Organophotocatalytic dearomatization of indoles, pyrroles and benzo(thio)furans via a Giese-type transformation

Accessing fascinating organic and biological significant indolines via dearomatization of indoles represents one of the most efficient approaches. However, it has been difficult for the dearomatization of the electron deficient indoles. Here we report the studies leading to developing a photoredox mediated Giese-type transformation strategy for the dearomatization of the indoles. The reaction has been implemented for chemoselectively breaking indolyl C=C bonds embedded in the aromatic system. The synthetic power of this strategy has been demonstrated by using structurally diverse indoles bearing common electron-withdrawing groups including (thio)ester, amide, ketone, nitrile and even aromatics at either C₂ or C₃ positions and ubiquitous carboxylic acids as radical coupling partner with high trans-stereoselectivity (>20:1 dr). This manifold can also be applied to other aromatic heterocycles including pyrroles, benzofurans and benzothiophenes. Furthermore, enantioselective dearomatization of indoles has been achieved by a chiral camphorsultam auxiliary with high diastereoselectivity.

Synthesis of carbonylated heteroaromatic compounds via visible-light-driven intramolecular decarboxylative cyclization of o-alkynylated carboxylic acids

An efficient strategy for the easy access to carbonylated heteroaromatic compounds has been developed via a visible-light-promoted intramolecular decarboxylative cyclization reaction of o-alkynylated carboxylic acids.

Intermolecular dearomative C2-arylation of N-Ac indoles activated by FeCl3

We report the FeCl₃-mediated direct addition of electron-rich arenes to the C2-position of electrophilic N-Ac indoles under mild conditions (room temperature, air).

Gold-Catalyzed Ring Expansion of Alkynyl Heterocycles through 1,2-Migration of an Endocyclic Carbon-Heteroatom Bond

A mild and efficient gold-catalyzed oxidative ring-expansion of a series of alkynyl heterocycles using pyridine-N-oxide as the oxidant has been developed, which affords highly valuable six- or seven-membered heterocycles with wide functional group toleration. The reaction consists of a regioselective oxidation and a chemoselective migration of an endocyclic carbon-heteroatom bond (favored over C-H migration) with the order of migratory aptitude for carbon-heteroatom bonds being C-S>C-N>C-O. In the absence of an oxidant, polycyclic products are readily constructed through a ring-expansion/Nazarov cyclization reaction sequence.

Regioselective hydroarylation reactions of C3 electrophilic N-acetylindoles activated by FeCl3: an entry to 3-(hetero)arylindolines

A method for the direct and rare umpolung of the 3 position of indoles is reported. The activation of N-acetylindole with iron(III) chloride allows the C-H addition of aromatic and heteroaromatic substrates to the C2=C3 double bond of the indole nucleus to generate a quaternary center at C3 and leads regioselectively to 3-arylindolines. Optimization, scope (50 examples), practicability (gram scale, air atmosphere, room temperature), and mechanistic insights of this process are presented. Synthetic transformations of the indoline products into drug-like compounds are also described.

Palladium-catalyzed formal arylacylation of allenes employing acid chlorides and arylboronic acids

Palladium-catalyzed formal arylacylation of allenes using acid chlorides and arylboronic acids proceeded regio- and stereoselectively.

Synthetic route to chiral indolines via ring-opening/C-N cyclization of activated 2-haloarylaziridines

A practical approach for the synthesis of 3-substituted indolines via regio- and stereoselective SN2-type ring-opening of 2-(2-halophenyl)-N-tosylaziridines with heteroatomic nucleophiles (O, N, and S) followed by palladium-catalyzed intramolecular C-N cyclization is reported in excellent yields (up to >99%) and enantiomeric excess (ee 99%).