A General and Efficient Method for the Selective Synthesis of β-Hydroxy Sulfides and β-Hydroxy Sulfoxides Catalyzed by Gallium(III) Triflate

One-pot synthesis of benzofused 8-oxabicyclo[3.3.1]nonanes via GaCl3-mediated cyclocondensation of o-allylbenzaldehydes and 1,3-dicarbonyl synthons

GaCl3-mediated one-pot cyclocondensation of o-allylbenzaldehydes and 1,3-dicarbonyls generates benzofused 8-oxabicyclo[3.3.1]nonanes in moderate to good yields in refluxing MeNO2 under easy-operational conditions. A plausible mechanism is proposed and discussed here. In the overall reaction process, various metal chloride-promoted conditions were investigated for one-pot cyclocondensation.

A visible-light-induced thiol addition/aerobic oxidation cascade reaction of epoxides and thiols for the synthesis of β-hydroxylsulfoxides

A photochemical thiol addition/aerobic oxidation cascade reaction has been developed. This protocol enables efficient oxidative coupling of epoxides and thiols to access structurally valuable β-hydroxylsulfoxides. A broad range of functional groups are compatible to obtain moderate to good yields of the target products. Mechanistic studies revealed a sequential reaction pathway involving base-promoted thiol addition of thiols to epoxides and visible-light-induced aerobic oxygenation of thioethers.

Boronic acid-catalysed C-3 selective ring opening of 3,4-epoxy alcohols with thiophenols and thiols

In this protocol we described a boronic acid-catalysed C-3 selective ring opening of 3,4-epoxy alcohols with thiophenols and thiols as nucleophiles. This diastereo- and enantiospecific reaction provides an efficient entry to prepare a variety of hydroxyl sulfides. Through the directing effect of the hydroxyl group, nucleophilic attack on the C-3 position of the epoxide moiety is favoured. It can be rationalized in a proposed transition state, in which the boronic acid catalyst tethers both epoxides and S-nucleophiles.

Direct halosulfenylation of benzo[b]furans: a metal-free synthesis of 3-halo-2-thiobenzo[b]furans

The first example of the direct halosulfenylation of benzo[b]furans with commercially available disulfides and N-halosuccinimides has been achieved, providing an efficient metal-free synthetic pathway to access diverse 3-halo-2-thiobenzo[b]furans in moderate to excellent yields. In particular, a halogen (e.g., bromo or iodo) substituent on the benzo[b]furan ring is amenable for further synthetic elaborations thereby broadening the diversity of the products.

Synthesis of 1,4-oxathian-2-ones by triton B-catalyzed one-pot reaction of epoxides with ethyl mercaptoacetate

A rapid one-pot reaction of epoxides with ethyl mercaptoacetate furnishing 1,4-oxathian-2-ones in the presence of a catalytic amount of eco-friendly triton B is reported. High regioselectivity is due to the nucleophilic attack on the less sterically hindered carbon atom of the aliphatic unsymmetrical epoxide.

β-Hydroxy sulfides and their syntheses

Sulfur-containing natural products are ubiquitous in nature, their most abundant source being marine organisms since sulfur, in the form of the sulfate ion, is the second most abundant anion in sea water after chloride. As part of natural products, sulfur can appear in a multitude of combinations and oxidation states: thiol, sulfide (acyclic or heterocyclic), disulfide, sulfoxide, sulfonate, thioaminal, hemithioacetal, various thioesters, thiocarbamate and isothiocyanate. This review article focuses on β-hydroxy sulfides and analogs; their presence in natural products, general protocols for their synthesis, and examples of their application in target oriented synthesis.

Acidic Mesoporous Zeolite ZSM-5 Supported Cu Catalyst with Good Catalytic Performance in the Hydroxysulfurization of Styrenes with Disulfides

Development of highly active heterogeneous catalysts is an effective strategy for modern organic synthesis chemistry. In this work, acidic mesoporous zeolite ZSM-5 (HZSM-5-M), acidic-free mesoporous zeolite TS-1 (TS-1-M), and basic ETS-10 zeolite supported metal Cu catalysts were prepared to investigate their catalytic performances in the hydroxysulfurization of styrenes with diaryl disulfides. The effect of pore size and acidities of the supports, as well as the Cu species electronic properties of the catalysts on reaction activity were investigated. The results show that Cu⁺ and Cu²⁺ binded on HZSM-5-M show the highest activity and product selectivity for the desired β-hydroxysulfides compounds.

Metal-Catalyzed Directed Regio- and Enantioselective Ring-Opening of Epoxides

Control of regio- and stereoselectivity of chemical reactions is the central theme in synthetic chemistry. Regioselective and enantiospecific ring opening of readily available enantioenriched epoxides precursors provides a straightforward access to diverse highly functionalized molecules which can serve as chiral building blocks for synthesis of biologically active compounds. However, prior to our research work, the scope of catalytic highly regioselective ring opening of epoxides is limited to structurally or electronically biased epoxides, such as terminal and aromatic epoxides. Regioselective ring-opening of epoxides with substituents on both sides demonstrating similar steric and electronic effects is still a formidable challenge for organic chemists. To address this challenge, our approach is to use the readily available functional moiety incorporated in an epoxide as a directing group to realize the regioselective nucleophilic attack on the oxirane ring. Alternatively, asymmetric ring-opening of epoxides can also provide the ring-opening products in highly enantioenriched form. However, excellent results are usually obtained in the case of the kinetic resolution of terminal epoxides or the desymmetrization of meso-epoxides. In these cases, the issue of regiocontrol of the ring-opening is circumvented or minimized. Based on our successful results of regioselective ring-opening of functionalized epoxides by implementing the directed ring-opening strategy, we also investigated the enantioselective ring-opening of internal epoxides bearing a functional moiety as directing group. This Account summarizes our research on metal-catalyzed directed ring-opening reactions of epoxides, which encompasses the following breakthroughs: (1) highly regioselective ring-opening of various substrates including epoxy allylic alcohols, epoxy homoallylic alcohols and epoxy allylic sulfonamides with a variety of N-, O-, and halide-nucleophiles catalyzed by W-, Mo-, or Ni-salt; (2) first kinetic resolutions of epoxy allylic alcohols, epoxy homoallylic alcohols, and epoxy allylic sulfonamides with various amines as nucleophiles, which were catalyzed by W-bishydroxamic acid (W-BHA), nickel-BINAM, and Gd-N,N'-dioxide catalytic system, respectively; (3) successful implementation of the strategy of combined asymmetric syntheses by the combination of the enantioselective epoxidation and the enantioselective ring-opening of 2,3-epoxy alcohols establishing a new entry to prepare amino alcohols in regio-, diastereo-, and enantiomerically pure form.

One-Pot Parallel Synthesis of Alkyl Sulfides, Sulfoxides, and Sulfones

A simple and cost-effective one-pot parallel synthesis approach to sulfides, sulfoxides, and sulfones from thiourea was elaborated. The method combines two procedures optimized to the parallel synthesis conditions: alkylation of thiourea with alkyl chlorides and mono or full oxidation of in situ generated sulfides with H2O2 or H2O2-(NH4)2MoO4. The experimental set up required commonly used lab equipment: conventional oven and ultrasonic bath; the work up includes filtration or extraction with chloroform. The method was evaluated on an 81 member library of drug-like sulfides, sulfoxides, and sulfones yielding the compounds on a 30-300 mg scale. A small-scale synthesis of 2-(benzhydrylsulfinyl)acetamide (modafinil) utilizing our approach resulted in similar efficiency to the published procedures.

Gallium(III) triflate: an efficient and a sustainable Lewis acid catalyst for organic synthetic transformations

Green chemical processes play a crucial role in sustainable development, and efficient recyclable catalysts that can be conveniently applied in various chemical reactions are the key elements for the development of sustainable synthetic processes. Many organic transformations rely on Lewis and Brønsted acid catalysts, and such molecules have been widely studied in organic synthesis. Over the years, researchers have looked for Lewis acid catalysts that provide high selectivity and high turnover frequency but are also stable in aqueous media and recoverable. Since the first preparation of trifluoromethanesulfonic acid by Hazeldine (triflic acid, HOTf), researchers have synthesized and used numerous metal triflates in a variety of organic reactions. Even though the rare earth metal triflates have played a major role in these studies, the majority of rare earth triflates lack one or more of the primary properties of sustainable catalysts: low cost and easy availability of the metals, easy preparation of triflates, aqueous/thermal stability, recyclability, and catalytic efficiency. In this Account, we describe the synthetic applications of Ga(OTf)(3) and its advantages over similar catalysts. Ga(OTf)(3) can be conveniently prepared from gallium metal or gallium chloride in excess of trifluoromethanesulfonic acid (triflic acid) under reflux. Among many Lewis acid catalysts recently studied, Ga(OTf)(3) is water tolerant and soluble and requires very low catalyst loading to drive various acid-catalyzed reactions including Friedel-Crafts alkylation, hydroxyalkylation, and acylation selectively and efficiently. In many reactions Ga(OTf)(3) demonstrated high chemo- and regioselectivity, high yields, excellent stability, and recyclability. We successfully synthesized many biologically active heterocycles and their fluoroanalogs under mild conditions. Many challenging reactions such as the ketonic Strecker reactions proceed efficiently via Ga(OTf)(3) catalysis. Because it is stable in water, this catalyst provides the opportunity to study substrates and develop new synthetic protocols in aqueous media, significantly reducing the production of hazardous waste from organic solvents and toxic catalyst systems.

Rongalite Promoted Highly Regioselective Synthesis of β-hydroxytellurides

Ditellurides undergo facile cleavage on treatment with rongalite (sodium hydroxymethanesulfinate) to generate tellurium anions in situ, which undergo ring opening of epoxides in high regioselective manner. A simple, cost-effective method has been developed to prepare β-hydroxytellurides with good yields.

Selective Synthesis of “Paco” or “Alt” Isomers of Acetoxylcalixarenes Catalysed by Bi(OTf)3

The “paco” or “alt” isomers of acetoxylcalixarenes were selectively prepared in the presence of catalytic amount (2 mol%) of Bi(OTf)3,. Calix[4]arenes selectively gave two different isomers under specified conditions with a good selectivity, but, calix[6]arenes and calix[8]arenes only gave the “alt” isomers with a high selectivity.

Solvent-Free Synthesis of 3,5-di(Hetero)Aryl-1,2,4-Thiadiazoles by Grinding of Thioamides under Oxidative Conditions

An efficient and facile synthesis of 3,5-di(hetero)aryl-1,2,4-thiadiazoles by oxidative dimerisation of thioamides by grinding with NBS under solvent-free conditions at room temperature has been developed. The efficiency of this reaction was demonstrated by the compatibility with trifluoromethyl, methyl, methoxy, chloro, pyridyl and thienyl groups. This method has notable advantages in terms of short reaction times, high yields and is a more practical alternative to the existing methods to access these compounds.

Synthesis of quinoxalines catalysed by cetyltrimethyl ammonium bromide (CTAB) in aqueous media

A facile and simple method has been developed for the condensation of 1,2-diaminobenzenes with α-bromoketones to form quinoxalines with good yields using cetyltrimethyl ammonium bromide (CTAB) in aqueous media. The efficiency of this reaction was demonstrated by the compatibility with nitro, methyl, methoxy, fluoro chloro bromo and furanyl groups. The important features of the methodology are broad substrate scope, simple workup, and no requirement for metal catalysts.

Sodium dithionite-promoted synthesis of 2-arylbenzothiazoles by reaction of 2,2'-disulfanediyldianiline with aldehydes in water

Sodium dithionite-promoted synthesis of 2-arylbenzothiazoles by reaction of 2,2'-disulfanediyldianiline with aldehydes in the presence of sodium dodecyl sulfate in water has been developed. Possible reaction pathways are discussed and the effects of different promoter on the reaction are investigated. The important features of this methodology are simple work-up, environmentally benign, high yields, metal-free, and inexpensive reagents.

An Efficient, Catalyst- and Solvent-Free Synthesis of imidazo[1,2-a]pyridines and 2,4-disubstituted thiazoles on Grinding

An efficient synthesis of imidazo[1,2- a]pyridines and 2,4-disubstituted thiazoles in excellent yield under catalyst-and solvent-free conditions at room temperature on grinding has been developed. The important features of this method are that it is reasonably fast, very clean, high yielding, simple workup and environmentally benign.