Synthesis of [1]Benzothieno[3,2-b][1]benzothiophenes through Iodine-Mediated Sulfur Insertion Reaction

[1]Benzothieno[3,2-b][1]benzothiophenes (BTBTs) are important molecules that have been extensively studied as high-performance organic field-effect transistors (OFETs). Therefore, it is important to develop a simple synthetic method for these molecules. In this paper, a synthetic method to obtain the BTBTs from 2-arylbenzo[b]thiophenes and elemental sulfur, in which two C-S bonds are formed at once, is described. In this method, molecular iodine plays a very important role as an additive. The role of iodine is discussed in the presumed reaction pathways.

Tunable Regioselective Allylic Alkylation/Iodination of Imidazoheterocycles in Water

The switchable roles of allylic alcohol and molecular iodine as reagents and catalysts have been demonstrated in the regioselective allylic alkylation and iodination of imidazoheterocycles employing the mixture of allylic alcohol-I2. First, we have explored the catalytic activity of iodine for the allylation of imidazoheterocycles using allylic alcohol in an aqueous medium. The allylation of a library of imidazoheterocycles and other electron-rich heterocycles like indole, pyrazole, 4-hydroxy coumarin, and 6-amino uracil has been achieved by employing this methodology. The efficiency of the I2 catalyst for N-allylation of azoles has also been demonstrated. Next, we have shown that this mixture of allylic alcohol and I2 could be beneficial for the iodination of imidazoheterocycles under room temperature. Mechanistic studies indicate that the activation of allylic alcohol by molecular iodine took place probably through halogen bonding, and NMR studies show that the reaction did not proceed through allylic ether formation.

Construction of diverse spirooxindoles via a domino reaction of arylamines, but-2-ynedioates and 3-hydroxy-3-(indol-3-yl)indolin-2-ones

An iodine-promoted domino reaction of arylamines/benzylamines, dialkyl but-2-ynedioates and 3-hydroxy-3-(indol-3-yl)indolin-2-ones showed very interesting molecular diversity. The reaction in acetonitrile at 65 °C in the presence of 30% mmol I2 resulted in spiro[indoline-3,1'-pyrido[4,3-b]indoles] in satisfactory yields. When anilines without para-substituents were used in the reaction, a direct substitution of the hydroxyl group to 2-(phenylamino)maleate at the para-position of aniline gave chain products in good yields. Additionally, similar reactions with benzylamines not only gave spiro[indoline-3,1'-pyrido[4,3-b]indoles], but also afforded spiro[indoline-3,1'-pyrano[4,3-b]indol]-2-ones in lower yields. A plausible domino annulation mechanism was rationally proposed for the formation of different kinds of polycyclic compounds.

Molecular-iodine catalyzed selective construction of cyclopenta[b]indoles from indoles and acetone: a green gateway to indole-fused cycles

Molecular-iodine catalyzed access to an important class of bio-relevant indole derivatives, cyclopenta[b]indoles, has been achieved via a cascade addition/intramolecular cyclization reaction of indoles and acetone. Explorations of diverse substitution patterns revealed an essential substrate-control in the reaction. The high-density electronic core of indole is pivotal in favouring the formation of indolyl-cyclopenta[b]indole derivatives; in contrast, the electron deficiency of the core hindered the cyclization process, directing the formation of bis(indolyl)propanes. Investigations on the mechanistic pathway revealed that bis(indolyl)alkanes were the intermediates for the addition-cyclization process. This simple experimental method provides sustainable synthetic access to cyclopentannulated indoles.

Synthesis of [1]Benzothieno[2,3-b][1]benzothiophenes from 3-Arylbenzo[b]thiophenes through Iodine-Mediated Sulfur Insertion Reaction

The reaction of 3-arylbenzo[b]thiophenes and elemental sulfur to obtain [1]benzothieno[2,3-b][1]benzothiophenes (BTBTs) is reported. The addition of molecular iodine is essential for the reaction. In previous reactions that used 1,1-diarylethylenes as the starting material, side products that were difficult to separate were generated. The present reaction does not produce such side products and is therefore advantageous for obtaining BTBTs in high yield and purity.

Electro-organic synthesis of isatins and hydrazones through C-N cross-coupling and C(sp2)-H/C(sp3)-H functionalization

An efficient and unique approach to synthesize isatin (indole-2,3-dione) from 2-aminoacetophenone under electrochemical conditions supported by I2-DMSO through C-N cross-coupling and C(sp2)-H/C(sp3)-H functionalization is presented. This synthetic method spans a wide range of substituted 2-aminoacetophenone substrates. The use of iodine as a promoter and shorter reaction times produced good to very good yields of isatin derivatives, which is a significant improvement over the reaction in a batch process. Further, hydrazones of isatin were synthesized by using hydrazine hydrate which produces electrochemically active molecules, namely isatin-hydrazones. The hydrazones of acetophenone were also obtained using the same reaction protocol. Additionally, the effect of increasing scan rate studied using cyclic voltammetry shows that the process followed a diffusion-controlled mechanism.

Electro-organic green synthesis of dicyano-2-(2-oxoindolin-3-ylidene) malononitriles using molecular iodine as catalyst

The first electrochemical molecular iodine promoted, domino reactions for the green synthesis of biologically relevant dicyano 2-(2-oxoindolin-3-ylidene) malononitriles (11 examples, up to 94% yield) from readily available isatin derivatives, malononitrile, and iodine at room temperature have been presented. This synthesis method showed tolerance towards various EDG and EWG and was completed in a short reaction time at the constant low current density of 5 mA cm^-2 in the low redox potential range of -0.14 to 0.07 V. The present study exhibited by-product-free formation, easy operation, and product isolation. In particular the formation of a C[double bond, length as m-dash]C bond was observed at room temperature with a high atom economy. Furthermore, in the present study, the electrochemical behavior of dicyano 2-(2-oxoindolin-3-ylidene) malononitrile derivatives using a cyclic voltammetry (CV) technique in 0.1 M NaClO₄ in acetonitrile solution was studied. All the chosen substituted isatin exhibited well-defined diffusion-controlled quasi-reversible redox peaks except 5-substituted derivatives. This synthesis could serve as an alternative strategy to synthesize other biologically important oxoindolin-3-ylidene malononitrile derivatives.

Recent Advancements on Metal-Free Vicinal Diamination of Alkenes: Synthetic Strategies and Mechanistic Insights

The oxidative aminative vicinal difunctionalization of alkenes or related chemical feedstocks has emerged as sustainable and multipurpose strategies that can efficiently construct two -N bonds, and simultaneously prepare the synthetically fascinating molecules and catalysis in organic synthesis that typically required multi-step reactions. This review summarized the impressive breakthroughs on synthetic methodologies (2015-2022) documented especially over inter/intra-molecular vicinal diamination of alkenes with electron-rich or deficient diverse nitrogen sources. These unprecedented strategies predominantly involved iodine-based reagents/catalysts, which resent the interest of organic chemists due to their impressive role as flexible, non-toxic, and environmentally friendly reagents, resulting in a wide variety of synthetically useful organic molecules. Moreover, the information collected also describes the significant role of catalyst, terminal oxidant, substrate scope, synthetic applications, and their unsuccessful results to highlight the limitations. Special emphasis has been given to proposed mechanistic pathways to determine the key factors governing the issues of regioselectivity, enantioselectivity, and diastereoselectivity ratios.

Molecular Iodine-Catalyzed N-Benzylic Sulfonamides C-N Bond Cleavage for the Decarboxylative Substitution of β-Keto Acids

Abstract:

A molecular iodine-catalyzed system for the decarboxylative substitution reactions of β-keto acids with N-benzylic sulfonamides via sp3 C-N bond cleavage has been disclosed. This procedure provides a series of α-functionalized ketones in good to excellent yields. Furthermore, the practicability of this method could be manifested efficiently in a gram-scale synthesis.

One-Pot Synthesis of Benzoazole-Substituted Thioenamines via a Cross Dehydrogenation Coupling (CDC) Reaction

An iodine-catalyzed synthesis of benzoazole-substituted thioenamines in a one-pot manner was reported. Using 2-aminothiophenols (or 2-aminophenols or 1,2-phenylenediamines), tetramethylthiuram disulfide (TMTD), and enamines (mainly indoles) as starting materials, the target C(sp²)-S formation products (benzoazole-substituted thioenamines) could be furnished smoothly in good yields. The reaction might proceed through an electrophilic substitution pathway in a cross dehydrogenation coupling (CDC) manner. The protocol is metal-free and features easy performance, a one-pot manner, a good functional group tolerance, and good yields.