Platinum-Catalyzed Multisubstituted Benzo[b]selenophene Synthesis

Synthesis of Benzoselenophenes via TMSCN-Enabled Radical-Mediated Tandem Reaction Involving Enamides and Elemental Selenium

This study presents a TMSCN-enabled tandem reaction involving enamides and elemental selenium to access a diverse array of benzoselenophenes. Notably, this methodology involves the direct 2-fold C(sp2)-H bond activation without the need for preinstalled halides or boronic acids as reaction handles. The protocol offers several noteworthy features, including the absence of transition metals and strong oxidants, high reaction efficiency, broad substrate scopes, and the use of stable elemental selenium as a selenium source.

Recent Advances in the Synthesis of Selenophenes and Their Derivatives

The selenophene derivatives are an important class of selenium-based heterocyclics. These compounds play an important role in prospecting new drugs, as well as in the development of new light-emitting materials. During the last years, several methods have been emerging to access the selenophene scaffold, employing a diversity of cyclization-based synthetic strategies, involving specific reaction partners and particularities. This review presents a comprehensive discussion on the recent advances in the synthesis of selenophene-based compounds, starting from different precursors, highlighting the main differences, the advantages, and limitations among them.

Gold(I)-NHC-catalysed synthesis of benzofurans via migratory cyclization of 2-alkynylaryl ethers

Homogeneous cationic gold(i) catalysis emerged as a preferred avenue for the activation of alkenes and alkynes towards reactions with weak nucleophiles, especially in cyclization reactions. Here we report an intramolecular carboalkoxylation reaction of electron-rich benzyl ethers of 2-ethynylaryl phenols catalysed by a digold(i)-NHC complex. The reaction proceeds efficiently with low catalyst loading and the resulting 2,3-disubstituted benzofurans form in moderate to good yields. Based on the results of a cross-over experiment, spectroscopic data, and DFT calculations, we propose a mechanism that accounts for the observed chemo- and regioselectivity.

Copper-Catalyzed Sequential Cyclization/Migration of Alkynyl Hydrazides for Construction of Ring-Expanded N-N Fused Pyrazolones

A copper-catalyzed sequential cyclization/migration reaction of alkynyl hydrazides for the synthesis of ring-expanded N-N fused pyrazolones was developed. Control experiments indicate that the copper-ligand complex plays an essential role in the reaction. This approach features a broad scope including some functional group tolerance as well as a nucleophilic addition/1,3-migration/formal 1,2-migration sequence. This protocol provides simple manipulation and less waste due to high yield and atom economy. The synthetic utility of N-N fused pyrazolones was also demonstrated by further transformations.

A Three-Component Strategy for Benzoselenophene Synthesis under Metal-Free Conditions Using Selenium Powder

An efficient three-component benzoselenophenes formation has been developed from substituted indoles, acetophenones, and selenium powder under metal-free conditions. 2-Aryl indoles played an important role to promote benzoselenophene formation from acetophenone derivatives and selenium powder. One C-C and two C-Se bonds were selectively formed to provide 40 new benzoselenophenes in good yields.

Synthesis of 2,3-bis-organochalcogenyl-benzo[b]chalcogenophenes promoted by Oxone®

We report here an alternative and tunable metal-free synthesis of benzo[b]chalcogenophenes via the electrophilic cyclization of 2-functionalized chalcogenoalkynes promoted by Oxone®.

Dissecting the Gold(I)-Catalyzed Carboaminations of N-Allyl Tetrahydro-β-carbolines to Allenes

N-Allyl tetrahydro-β-carbolines undergo gold-catalyzed cyclizations that lead to tetracyclic compounds, resulting from both ring closure and the transfer of the allylic group from the nitrogen to the carbon backbone. The final skeleton obtained depends on the nature of both the R² group of the allene and the R³ group of the allylic residue. Mechanistic studies and DFT calculations allowed the determination of all the mechanistic pathways involved in these processes, stemming from a common intermediate that evolves differently according to the substituents nature.

Recent developments in synthetic methods for benzo[b]heteroles

Benzo[b]heteroles containing heteroatoms other than nitrogen and oxygen have received considerable attention for their potential applications in materials science. This poses an increasing demand for efficient, selective, and broad-scope methods for their synthesis. This review article summarizes the recent developments in synthetic methods and approaches to access representative members of the benzoheterole family.

Selenium analogues of raloxifene as promising antiproliferative agents in treatment of breast cancer

Synthetic protocols for the preparation of selenium analogues of raloxifene were elaborated. General aim of the current research is to improve the positive impact of selenium atom introduction in drug design. Antiproliferative activity on CCL-8 (mouse sarcoma), MDA-MB-435s (human melanoma), MES-SA (human uterus sarcoma), MCF-7 (human breast adenocarcinoma), HT-1080 (human fibrosarcoma), MG-22A (mouse hepatoma) tumor cell lines, and normal cell line NIH 3T3 (mouse fibroblasts) was studied. Influence of aminoethoxy "tail" and benzoyl group position on SAR was discussed. Results of in vivo studies on BALB/c female mice with 4T1 cell induced breast cancer model showed that selenium analogue of raloxifene is able to suppress estrogen-depending tumor growth.

Versatile synthesis of benzothiophenes and benzoselenophenes by rapid assembly of arylzinc reagents, alkynes, and elemental chalcogens

Rapidly aSSembled: The combination of cobalt-catalyzed migratory arylzincation and copper-mediated/catalyzed chalcogenative cyclization allows the construction of benzothiophenes and benzoselenophenes from arylzinc reagents, alkynes, and elemental chalcogens. Benzothiophenes and benzoselenophenes diversely functionalized at the benzene ring moiety can be prepared, which are not readily accessible by conventional methods.

[3,3]-Sigmatropic rearrangement step in the gold-catalyzed cyclization of allyl-(ortho-alkinylphenyl)methyl ethers

The gold-catalyzed conversion of allyl-(ortho-alkynylphenyl)methyl ethers was investigated, and allylated isochromenes were obtained. An optimization of the catalysis conditions with respect to different phosphane and carbene ligands on gold, different counterions, and different solvents was conducted. Subsequently, the scope and limitations of this reaction were investigated with 21 substrates. The mechanistic studies show an allylic inversion, as supported by NMR data and an X-ray crystal structure analysis, as well as an intermolecular reaction, as determined by crossover experiments. There is no competition of protodeauration even in the presence of water. All these observations differ from other related conversions and clearly indicate product formation by a [3,3]sigmatropic rearrangement in the step forming the new C-C bond.

Selective base-promoted synthesis of substituted selenophenes by carbocyclization of (Z)-benzylselenoenynes

We herein described the synthesis of several 3-benzyl-2,5-diarylselenophene derivatives in moderate to good yields using (Z)-benzylselenoenynes as starting material in carbocyclization reactions. The reactions were carried out under mild conditions using only t-BuOK as base, in the complete absence of transition metals or additives. The cyclized 3-benzyl-2,5-diarylselenophenes obtained in the current protocol appear highly promising and attractive intermediates for the synthesis of polysubstituted selenophenes. For instance, 3-benzyl-2,5-diphenylselenophene was treated with Br(2) provided the corresponding 3-benzyl-4-bromo-2,5-diphenylselenophene in high yield. 4-Bromoselenophene derivative was applied as substrate in the palladium catalyzed cross-coupling reactions with boronic acids to give the Suzuki type products in excellent yields.

New development of synthesis and reactivity of seleno- and tellurophenes

Due to the many new and remarkable findings and applications that have been published in recent years in seleno- and tellurophene chemistry, this review revisits the different aspects of this chemistry, including synthesis, reactivity and applications in the field of heterocycles.