Direct coupling of haloquinolines and sulfonyl chlorides leading to sulfonylated quinolines in water

Unconventional approaches for the introduction of sulfur-based functional groups

Organosulfur compounds have a pivotal role in the functionalities of many natural products, pharmaceuticals and organic materials. For these reasons, the search for new methodologies for the formation of carbon-sulfur bonds has been the object of intensive work for organic chemists. However, the proposed strategies suffer from various drawbacks, such as volatility, toxicity, and instability of the sulfur sources or the use of VOC solvents. In this review, we summarise the recent protocols which have the goal of obtaining sulfones, thioethers, thiazines, thiazepines and sulfonamides in an unconventional and/or sustainable way. The use of starting materials less invasive and toxic with respect to the traditional reagents, alternative solvents such as water, ionic liquids or deep eutectic solvents, the exploitation of ultrasound and electrochemistry, increasing the efficiency of the process, are reported. Moreover, representative reaction mechanisms are also discussed.

An efficient imidation of thioethers with nitrene in water

The first imidation of thioethers with free nitrene in water was realized. N-Cbz sulfilimines are formed via imidation of thioethers with free nitrene generated from α elimination of nosyloxycarbamates. In this work, water is successfully applied as solvent for free nitrene, and transition metal catalyst is not needed.

Recent advances in the synthesis of biologically and pharmaceutically active quinoline and its analogues: a review

Recently, quinoline has become an essential heterocyclic compound due to its versatile applications in the fields of industrial and synthetic organic chemistry. It is a vital scaffold for leads in drug discovery and plays a major role in the field of medicinal chemistry. Nowadays there are plenty of articles reporting syntheses of the main scaffold and its functionalization for biological and pharmaceutical activities. So far, a wide range of synthesis protocols have been reported in the literature for the construction of this scaffold. For example, Gould-Jacob, Friedländer, Pfitzinger, Skraup, Doebner-von Miller and Conrad-Limpach are well-known classical synthesis protocols used up to now for the construction of the principal quinoline scaffold. Transition metal catalysed reactions, metal-free ionic liquid mediated reactions, ultrasound irradiation reactions and green reaction protocols are also useful for the construction and functionalization of this compound. The main part of this review focuses on and highlights the above-mentioned synthesis procedures and findings to tackle the drawbacks of the syntheses and side effects on the environment. Furthermore, various selected quinolines and derivatives with potential biological and pharmaceutical activities will be presented.

Recent Advances of Sulfonylation Reactions in Water

BACKGROUND

The sulfonyl groups are general structural moieties present in agrochemicals, pharmaceuticals, and natural products. Recently, many efforts have been focused on developing efficient procedures for preparation of organic sulfones.

MATERIALS AND METHODS

Water, a proton source, is considered one of the most ideal and promising solvents in organic synthesis for its easy availability, low cost, nontoxic and nonflammable characteristics. From the green and sustainable point of view, more and more reactions are designed proceeding in water.

OBJECTIVE

The review focuses on recent advances of sulfonylation reactions proceeding in water. Sulfonylation reactions using sodium sulfinates, sulfonyl hydrazides, sulfinic acids, and sulfonyl chlorides as sulfonating agents were introduced in detail.

RESULTS AND DISCUSSION

In this review, sulfonylation reactions proceeding in water developed in recent four yields were presented. Sulfonylation reactions using water as solvent have attracted more and more attention because water is one of the most ideal and promising solvents in organic synthesis for its facile availability, low cost, nontoxic and nonflammable properties.

CONCLUSION

Numerous sulfonating agents such as sodium sulfinates, sulfonyl hydrazides, sulfinic acid, sulfonyl chlorides and disulfides are efficient for sulfonylation reactions which proceed in water.

Visible-Light-Induced Metal-Free Synthesis of 2-Phosphorylated Thioflavones in Water

The introduction of phosphorus functional groups into the skeleton of thioflavones is an attractive task and of great significance. Herein, a metal-free visible-light-induced radical cascade cyclization was developed for the preparation of 2-phosphorylated thioflavones from methylthiolated alkynones and phosphine oxides. In water as a green reaction medium, a large number of such 2-phosphorylated thioflavones were prepared, catalyzed by 4CzIPN [1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene] under visible-light irradiation. These reactions could be performed at ambient temperature and feature simple operation, wide reaction scope, and recyclability of aqueous media.

Transition-metal-free sulfonylations of methylthiolated alkynones to synthesize 3-sulfonylated thioflavones

A set of transition-metal-free NaI/TBHP-mediated sulfonylation cyclization reactions of methylthiolated alkynones with sulfonyl hydrazides was developed, by which various 3-sulfonylated thioflavones were prepared under mild reaction conditions.

Visible-light-promoted acridine red catalyzed aerobic oxidative decarboxylative acylation of α-oxo-carboxylic acids with quinoxalin-2(1H)-ones

Visible-light-mediated procedure has been developed for the synthesis of 3-acyl quinoxalin-2(1H)-ones through acridine red catalyzed decarboxylative acylation of α-oxo-carboxylic acids with quinoxalin-2(1H)-ones.

Transition-metal- and oxidant-free three-component reaction of quinoline N-oxides, sodium metabisulfite and aryldiazonium tetrafluoroborates via a dual radical coupling process

A convenient and straightforward three-component transformation of quinoline N-oxides, sodium metabisulfite and aryldiazonium tetrafluoroborates has been developed, providing the target products in moderate to good yields. Compared with previous studies, the present methodology avoids the use of transition-metal catalysts and excess oxidants, providing a simple and practical alternative approach for the construction of 2-sulfonylquinolines. Control experiments indicate that a dual radical coupling process is responsible for this reaction.

Covalent Organic Frameworks: A Sustainable Photocatalyst toward Visible-Light-Accelerated C3 Arylation and Alkylation of Quinoxalin-2(1H)-ones

A practical and scalable protocol for visible-light-accelerated arylation and alkylation of quinoxalin-2(1H)-ones with hydrazines is reported. In this protocol, a hydrazone-based two-dimensional covalent organic frameworks (2D-COF-1) was employed as the heterogeneous photocatalyst (PC). Due to its excellent photocatalytic properties, good chemical stability and heterogeneous nature, the present method exhibits high efficiency, good functional group tolerance, easy scalability and remarkable catalyst reusability. More importantly, it provides an alternative way that allows rapid access to various C3 arylated or alkylated quinoxalin-2(1H)-ones in a greener and sustainable manner.

Metal-Free Catalytic Synthesis of Thiocarbamates Using Sodium Sulfinates as the Sulfur Source

A novel molecular iodine-catalyzed protocol for the construction of thiocarbamates from readily available sodium sulfinates, isocyanides, and water has been described. The present methodology offers a facile and practical route to a variety of thiocarbamates in moderate to good yields with favorable functional group tolerance by use odorless sodium sulfinates as the sulfur source. The mechanistic studies suggest the present transformation involves a radical process.

Visible-light-promoted hydroxysulfonylation of alkylidenecyclopropanes: synthesis of cyclopropane-containing β-hydroxysulfones

Cyclopropane-containing β-hydroxysulfones and cyclopropyl styrenes have been synthesised from readily available ACPs and sulfuryl chloride via visible-light photoredox catalysis.

Visible-light-promoted direct C–H/S–H cross-coupling of quinoxalin-2(1H)-ones with thiols leading to 3-sulfenylated quinoxalin-2(1H)-ones in air

A new and efficient visible-light-mediated strategy has been developed for the synthesis of 3-sulfenylated quinoxalin-2(1H)-ones via rhodamine B catalyzed C–H/S–H cross-coupling of quinoxalin-2(1H)-ones with thiols in air at room temperature.

Metal-free sulfonyl radical-initiated cascade cyclization to access sulfonated indolo[1,2-a]quinolines

A metal-free cascade reaction was developed for the synthesis of indolo[1,2-a]quinoline derivatives from arylsulfonyl hydrazides and 1-(2-(arylethynyl)phenyl)indoles in the presence of TBAI/TBHP.

Selective assembly of N1- and N2-alkylated 1,2,3-triazoles via copper-catalyzed decarboxylative cycloaddition of alkynyl carboxylic acids with ethers and azidotrimethylsilane

An efficient and regiocontrolled method for the synthesis of various N1- and N2 alkylated 1,2,3-triazoles via copper-catalyzed decarboxylative cycloaddition of alkynyl carboxylic acids with ethers and azidotrimethylsilane.