A novel synthetic route to 3-sulfenyl- and 3-selenylindoles by n-Bu4NI-induced electrophilic cyclization

Synthesis of N-alkyl-3-sulfonylindoles and N-alkyl-3-sulfanylindoles by cascade annulation of 2-alkynyl-N,N-dialkylanilines

Divergent synthesis of N-alkyl-3-sulfonylindoles and N-alkyl-3-sulfanylindoles from 2-alkynyl-N,N-dialkylanilines and sulfonyl hydrazides has been described.

Synthesis of thiophosphates through a three-component reaction by using sulfur dioxide as the sulfur source

Generation of thiophosphates through a three-component reaction of diaryliodonium tetrafluoroborates, 1,4-diazabicyclo[2.2.2]octane-sulfur dioxide (DABCO·(SO₂)₂), and diarylphosphine oxides under visible light irradiation is described.

Cu-Catalyzed first direct access towards 3-sulfenylindoles from aryl halides

The copper-catalyzed cross-coupling of indole derivatives with aryl halides in the presence of thiourea proceeds to give 3-sulfenylindoles in DMSO at 120 °C.

Palladium-Catalyzed Oxidative Sulfenylation of Indoles and Related Electron-Rich Heteroarenes with Aryl Boronic Acids and Elemental Sulfur

An efficient and convenient palladium-catalyzed C-H bond oxidative sulfenylation of indoles and related electron-rich heteroarenes with aryl boronic acids and elemental sulfur has been described. This procedure provides a useful and direct approach for the assembly of a wide range of structurally diverse 3-sulfenylheteroarenes with moderate to excellent yields from simple and readily available starting materials. Moreover, this synthetic protocol is suitable for N-protected and unprotected indoles. Notably, the construction of two C-S bonds in one step was also achieved in this transformation.

Catalytic Synthesis of 3-Thioindoles Using Bunte Salts as Sulfur Sources under Metal-Free Conditions

An efficient catalytic method for the synthesis of 3-thioindoles has been successfully developed, which uses odorless, stable, readily available crystalline Bunte salts as the sulfenylating agents, iodine as nonmetallic catalyst, and DMSO as both the oxidant and solvent. This method is practical and environmentally benign in terms of sulfur sources, catalyst, and solvent. The catalytic reaction is selective at the C3 position of indoles and compatible with a wide range of substrates, giving the desired products in good to excellent yields.

Sonochemistry: An efficient alternative to the synthesis of 3-selanylindoles using CuI as catalyst

Ultrasonic (US) irradiation was successfully used as an alternative energy source to prepare 3-selanylindoles through the direct selanylation of indoles with diorganyl diselenides using CuI (20 mol%) as catalyst and DMSO as the solvent. By using this US-promoted reaction, eleven 3-organylselanylindoles were prepared selectively and in good yields. A comparative study between the reactions under conventional heating, microwave and ultrasound irradiations was performed, and it was observed advantage in using US over the other heating systems.

Expedient Access to Unsymmetrical Diarylindolylmethanes through Palladium-Catalyzed Domino Electrophilic Cyclization-Extended Conjugate Addition Approach

A palladium-catalyzed domino process to access unsymmetrical diarylindolylmethanes has been developed through the annulation of o-alkynylanilines followed by 1,6-conjugate addition with p-quinone methides (p-QMs) under relatively mild conditions. The broad substrate scope of this methodology was demonstrated through the use of a wide range of substituted o-alkynylanilines and p-quinone methides, and in most cases, the unsymmetrical diarylindolylmethanes could be prepared in moderate to excellent yields. Notably, this method does not require any amino group protection. Moreover, 100% atom economy makes this transformation attractive from a green chemistry perspective.

DMSO as oxidant and sulfenylating agent for metal-free oxidation and methylthiolation of alcohol-containing indoles

A new methylthiolation protocol was successfully established for the synthesis of substituted indoles bearing 3-methylthioether moiety, in which new C–S bond and C=O bond were formed using dimethyl sulfoxide as the sulfur source under mild conditions.

Iodine–triphenylphosphine mediated sulfenylation of imidazoheterocycles with sodium sulfinates

An efficient approach to sulfenyl imidazoheterocycles has been developed via iodine–triphenylphosphine mediated direct sulfenylation of imidazoheterocycles with sodium sulfinates under transition-metal-free conditions.

A solvent- and metal-free synthesis of 3-chacogenyl-indoles employing DMSO/I2 as an eco-friendly catalytic oxidation system

Herein, we describe a solvent- and metal-free method for the synthesis of 3-chalcogenyl-indoles from indoles and diorganyl dichalcogenides using an equivalent amount of DMSO as an oxidant, under catalysis by molecular iodine. This mild and eco-friendly approach allowed the preparation of a wide range of 3-selenyl- and 3-sulfenyl-indoles in good to excellent yields.

Visible light-induced 3-sulfenylation of N-methylindoles with arylsulfonyl chlorides

The synthesis of 1-methyl-3-(arylthio)-1H-indoles has been achieved by the photoredox reaction of N-methylindoles with readily available arylsulfonyl chlorides in moderate yields.

A selenium-based ionic liquid as a recyclable solvent for the catalyst-free synthesis of 3-selenylindoles

The ionic liquid 1-butyl-3-methylimidazolium methylselenite, [bmim][SeO2(OCH3)], was successfully used as solvent in the catalyst-free preparation of 3-arylselenylindoles by the reaction of indole with ArSeCl at room temperature. The products were obtained selectively in good yields without the need of any additive and the solvent was easily reused for several cycles with good results.

Tandem aldehyde-alkyne-amine coupling/cycloisomerization: A new synthesis of coumarins

Cu-catalyzed A(3) coupling of ethoxyacetylene, pyrrolidine and salicylaldehydes led to a concomitant cycloisomerization followed by hydrolysis of the resultant vinyl ether to afford coumarins in a cascade process. The reaction proceeded through exclusive 6-endo-dig cyclization and is compatible with halo and keto groups giving coumarins in good to moderate yields.

An efficient synthesis of 2-bromo(chloro)-3-selenyl(sulfenyl)indoles via tandem reactions of 2-(gem-dibromo(chloro)vinyl)anilines with diselenides(disulfides)

A novel and efficient synthesis of 2-bromo(chloro)-3-selenyl(sulfenyl)indoles through tandem reactions of 2-(gem-dibromo(chloro)vinyl)-N-methylsulfonylanilines with diselenides and disulfides in the presence of t-BuOLi and I(2) (10 mol%) in DMSO was developed. The reactions generated the desired products in good yields with high regio-selectivity under transition-metal-free conditions in one-pot.

Metal-Free Synthesis of 3-Sulfenylindoles via an Iodine-Mediated Electrophilic Cyclisation of 2-Alkynylanilines with Disulfides

An efficient and metal-free method was developed to synthesise 3-sulfenylindoles via the iodine-mediated electrophilic cyclisation of 2-alkynylanilines with disulfides. In the presence of I2, various 3-sulfenylindoles were obtained in moderate to high yields.

Venting-while-heating microwave-assisted synthesis of 3-arylthioindoles

We report the first example of venting-while-heating microwave-assisted synthesis of a small library of 3-arylthioindoles. Compounds were prepared in excellent isolated yields (90-98%) within 4 min in a closed vessel by treating indoles with disulfides in the presence of sodium hydride in anhydrous N,N-dimethylformamide. The method was not affected by electron-donating and -withdrawing substituents both on 3-arylthio moiety and at 2- and 5-positions of the indole nucleus.

Intramolecular ipso-halocyclization of 4-(p-unsubstituted-aryl)-1-alkynes leading to spiro[4,5]trienones: scope, application, and mechanistic investigations

A new, general method for the synthesis of spiro[4,5]trienones is described by the intramolecular ipso-halocyclization of 4-(p-unsubstituted-aryl)-1-alkynes. In the presence of halide electrophiles, a variety of 4-(p-unsubstituted-aryl)-1-alkynes underwent the intramolecular ipso-halocyclization with water smoothly, affording the corresponding halo-substituted spiro[4,5]trienones in moderate to good yields. The obtained spiro[4,5]trienones can be applied in constructing the azaquaternary tricyclic skeleton via Pd-catalyzed Heck reaction. Notably, the prepared spiro[4,5]trienones and azaquaternary tricycles are of importance in the areas of pharmaceuticals and agrochemicals. The mechanism of the intramolecular ipso-halocyclization reaction is also discussed according to the (18)O-labeling experiments and DFT calculations.