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

Cascade Oxidative Trifluoromethylthiolation and Cyclization of 3-Alkyl-1-(2-(alkynyl)phenyl)indoles

Persulfate-promoted radical cascade trifluoromethylthiolation and cyclization of 3-alkyl-1-(2-(alkynyl)phenyl)indoles with AgSCF₃ were investigated. This protocol provides a novel route to CF₃S-substituted indolo[1,2-a]quinoline-7-carbaldehydes and CF₃S-substituted indolo[1,2-a]quinoline-7-methanone derivatives via the formation of the C-SCF₃ bond and C-C bond and benzylic carbon oxidation in a single step. This reaction can accommodate a broad range of functional groups. The single-crystal X-ray diffraction data confirm the chemical structure of the product. A scale-up experiment and radical inhibition experiments were operated in the reaction system. Photophysical properties of some selected 5-((trifluoromethyl)thio)indolo[1,2-a]quinoline-7-carbaldehydes were studied by UV-visible and fluorescence spectroscopy.

Menge W, Martens G, op het Veld SJ, Th.H. van Eupen J, Demon M, van Achterberg TA, Arisse-Thijssen MJ, Santegoeds-Lenssen EW, van der Lee MM, Ubink R, Arends RJ, Sesink A, Blomenröhr M, Marco Timmers C. Discovery of SYD5115, a novel orally active small molecule TSH-R antagonist

The thyrotropin receptor (TSH-R) regulates the thyroid gland and is normally activated by thyrotropin. In patients with Graves' disease, TSH-R is also stimulated by stimulatory TSH-R autoantibodies leading to hyperthyroidism. In this paper, we describe the discovery of SYD5115 (67), a novel small molecule TSH-R antagonist with nanomolar potency. SYD5115 also blocks stimulating antibody induced synthesis of the thyroid hormone thyroxine (T₄) in vivo, after a single oral dose. During optimization, several issues had to be addressed such as the low metabolic stability and the potential mutagenicity of our first series of compounds.

Unbiased C3‐Electrophilic Indoles: Triflic Acid Mediated C3‐Regioselective Hydroarylation of N−H Indoles**

The direct dearomative addition of arenes to the C3 position of unprotected indoles is reported under operationally simple conditions, using triflic acid at room temperature. The present regioselective hydroarylation is a straightforward manner to generate an electrophilic indole at the C3 position from unbiased indoles in sharp contrast to previous strategies. This atom‐economical method delivers biologically relevant 3‐arylindolines and 3,3‐spiroindolines in high yields and regioselectivities from both intra‐ and intermolecular processes. DFT computations suggest the stabilization of cationic or dicationic intermediates with H‐bonded (TfOH)_n clusters.

Synthesis of Aza-Eight-Membered Ring-Fused Indolines Initiated by Zn-Catalyzed C2 Alkylation of Indoles and Subsequent Base-Promoted Ring Expansion

A novel and efficient synthesis of aza-eight-membered ring-fused indolines has been developed. This process is realized by zinc-catalyzed C2 alkylation of indoles and subsequent base-promoted ring expansion of the newly formed six-membered ring with alkynes. Easily accessible starting materials, good functional group tolerance, and high atom economy make this procedure attractive.

Pd/Xiang-Phos-catalyzed enantioselective intermolecular carboheterofunctionalization under mild conditions

A mild and practical Pd/Xiang-Phos-catalyzed enantioselective intermolecular carboheterofunctionalization reaction of 2,3-dihydrofurans is developed, leading to various optically active fused furoindolines and tetrahydrofurobenzofurans. The key to this transformation is employing two newly modified N-Me-Xiang-Phos ligands ((S, R S)- N-Me-X4/X5) as chiral ligands under mild conditions. Moreover, this synthetic methodology can be efficiently applied to a variety of complex polysubstituted heterocycles with high chemo-, regio-, and enantio-selectivities via introducing diverse substituents on furan rings, which were hard to access by other routes.

Dearomatization Reactions of Indoles to Access 3D Indoline Structures

This Account summarizes our involvement in the development of dearomatization reactions of indoles that has for origin a total synthesis problematic. We present the effort from our group to obtain 3D-indolines scaffold from the umpolung of N-acyl indoles via activation with FeCl3 to the oxidative spirocyclizations of N-EWG indoles and via the use of electrochemistry.

1 Introduction

2 Activation of N-Acyl Indoles with FeCl3

2.1 Hydroarylation of N-Acyl Indoles

2.2 Difunctionalization of N-Acyl Indoles

3 Radical-Mediated Dearomatization of Indoles for the Synthesis of Spirocyclic Indolines

4 Electrochemical Dearomatization of Indoles

4.1 Direct Electrochemical Oxidation of Indoles

4.2 Indirect Electrochemical Oxidation of Indoles

5 Conclusion

Ring-Opening of Indoles: An Unconventional Route for the Transformation of Indoles to 1 H-Pyrazoles Using Lewis Acid

An unusual transformation of indoles to pyrazoles via an aromatic ring-opening strategy has been developed. The salient feature of this strategy involves the C2-N1 bond opening and concomitant cyclization reaction of the C2═C3 bond of the indole moiety with the tosylhydrazone, which proceeds under transition-metal and ligand free conditions. This ring-opening functionalization of indoles provides a wide scope of differently substituted pyrazoles.

Revealing the electrophilicity of N-Ac indoles with FeCl3: a mechanistic study

The puzzling hydroarylation of N-Ac indoles promoted by iron trichloride involves a doubly activated intermediate: as supported by the electron density topology of a crystal, IR monitoring, and DFT calculations.

Lewis Acid Catalyzed Regioselective Hydroheteroarylation of Pentafulvenes

A diverse approach toward the catalytic regioselective nucleophilic addition of nitrogen heterocycles to Lewis acid activated pentafulvenes has been established. The developed protocol introduces pentafulvenes as nonsymmetrical alkenes for the hydroheteroarylation reaction, providing alkylidenecyclopentenylation at the C-3 position of indoles and the C-2 position of pyrrole.

Concise Total Synthesis of (+)-Asperazine, (+)-Pestalazine A, and (+)-iso-Pestalazine A. Structure Revision of (+)-Pestalazine A

The concise, enantioselective total syntheses of (+)-asperazine (1), (+)-iso-pestalazine A (2), and (+)-pestalazine A (3) have been achieved by the development of a late-stage C3-C8' Friedel-Crafts union of polycyclic diketopiperazines. Our modular strategy enables the union of complex polycyclic diketopiperazines in virtually their final forms, thus providing rapid and highly convergent assembly at the challenging quaternary stereocenter of these dimeric alkaloids. The significance of this carbon-carbon bond formation can be gauged by the manifold constraints that were efficiently overcome, namely the substantial steric crowding at both reactive sites, the nucleophilic addition of C8' over N1' to the C3 carbocation, and the multitude of reactivity posed by the use of complex diketopiperazine fragments in the coupling event. The success of the indoline π-nucleophile that evolved through our studies is notable given the paucity of competing reaction pathways observed in the presence of the highly reactive C3 carbocation generated. This first total synthesis of (+)-pestalazine A also allowed us to revise the molecular structure for this natural alkaloid.

Synthesis of benzofuro[3,2-b]indoline amines via deamination-interrupted Fischer indolization and their unexpected reactivity towards nucleophiles

We report the access to the benzofuro[3,2-b]indoline framework via an interrupted Fischer indolization and its unexpected reactivity towards allyl nucleophiles.

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).

Direct oxidative coupling of N-acetyl indoles and phenols for the synthesis of benzofuroindolines related to phalarine

Inspired by the biogenetic synthesis of benzofuroindoline-containing natural products, we designed an oxidative coupling between phenol and N-acetyl indoles. This straightforward and direct radical process, mediated by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone and FeCl3 allowed the regioselective synthesis of benzofuro[3,2-b]indolines, whose structure is found in the natural product phalarine.

Fe-catalyzed cycloaddition of indoles and o-phthalaldehyde for the synthesis of benzo[b]carbazoles with TMSCl- or acid-responsive properties

The indolyl benzo[b]carbazoles achieved by iron catalysis via sequential carbon–carbon bond-forming reaction could be used as fluorescent sensors for TMSCl and acids.