Aryl Thiocyanates Research Articles

Microwave‐Assisted Metal‐Free C(sp2)−H Thiocyanation of Aromatic Amines

AbstractIn this work, we present a rapid, metal‐free and efficient method for thiocyanation of aromatic amines under microwave irradiation for the synthesis of aryl thiocyanates using inexpensive and nontoxic NH4SCN as thiocyanato source and K2S2O8 as an oxidant. This protocol tolerates a wide range of substituted anilines to provide the corresponding thiocyanated products in good to excellent yields. The features of this strategy include a broad substrate scope, high functional group tolerance, mild reaction conditions, and short reaction time.

Regioselective C-H Thiocyanation of Arenes by Iron(III) Chloride Catalysis.

Aryl thiocyanates are flexible synthetic intermediates that can be used in the preparation of a diverse range of arene building blocks for medicinal chemistry. Here, we report a fast and efficient Lewis acid-catalyzed method for the regioselective thiocyanation of arenes. Iron(III) chloride was found to be an effective Lewis acid for the activation of N-thiocyanatosaccharin and the subsequent thiocyanation of a wide range of activated arenes. The procedure was applicable for the thiocyanation of biologically active compounds such as metaxalone and an estradiol derivative and was used as part of a one-pot tandem iron-catalytic process for the regioselective, dual functionalization of an arene building block.

Synthesis of Aryl Thiocyanates and Aryl Selenocyanates via Visible‐Light Activation of Arylazo Sulfones

AbstractTwo visible‐light mediated protocols (based on a copper photoredox catalyzed and on a photochemical reaction, respectively) for the preparation of aryl thiocyanates and aryl selenocyanates from arylazo sulfones are presented herein, by exploiting the peculiar photoreactivity and redox activity of such substrates. The developed reactions take place in good to satisfactory yields and with a large scope.magnified image

Direct Access to Thiocyano-Thioesters from Cyclic Thioacetals via Photoredox Catalysis: An Introduction of Two Functional Groups in One Pot.

The cyanation of organic compounds is an important synthetic transformation and mainly relies on a toxic CN source. Undeniably, thiocyanate salt has emerged as a very mild and environmentally benign CN source, yet its synthetic utility for cyanation is highly limited to very few types of organic compounds. Herein, we report the direct cyanation of cyclic thioacetals for accessing compounds with two different functional groups (thiocyano-thioesters) in one pot using sodium thiocyanate via photoredox catalysis. The protocol has been further extended for the direct cyanation of disulfides and diselenide to access aryl thiocyanates and aryl selenocyanate. A plausible mechanism has been proposed based on a series of control experiments, cyclic voltammetry and Stern-Volmer studies.

Mechanochemical Thiocyanation of Aryl Compounds via C-H Functionalization.

Aryl thiocyanate compounds are important building blocks for the synthesis of bioactive compounds and intermediates for several functional groups. Reported thiocyanation reactions via C–H functionalization have limited substrate scope and low RME. The ball-milling method reported here uses ammonium persulfate and ammonium thiocyanate as reagents and silica as a grinding auxiliary. It afforded aryl thiocyanates with moderate to excellent yields for a wide variety of aryl compounds (36 examples, 8–96% yield), such as anilines, phenols, anisoles, thioanisole, and indole, thus tolerating substrates with sensitive functional groups. New products such as benzo[d][1,3]oxathiol-2-ones were obtained with C-4 substituted phenols. Thus, to our knowledge, we report, for the first time, aryl thiocyanation reaction by ball-milling at room temperature and solvent-free conditions, with short reaction times and no workup. Analysis of several mass-based green metrics indicates that it is an efficient greener method.

Chemoselective RuII‐Catalyzed Synthesis of Aryl Thiocyanates and Step‐wise Double [2+2+2] Cycloadditions to 2‐Aryl Thiopyridines

RuII‐catalyzed intermolecular double [2+2+2] cycloadditions of 1,6‐diynes and alkynylthiocyanates have been developed for the synthesis of 2‐aryl thiopyridines. Aryl thiocyanates were isolated chemoselectively as a result of initial intermolecular [2+2+2] cycloaddition product. The method offers operational simplicity and is atom economical in nature.

Transition‐Metal‐Free Selective Synthesis of (Z)‐1,2‐Diarylthio‐1‐arylalkenes, (2‐Arylethene‐1,1,2‐triyl)tris(arylsulfane)s and Alkynyl Sulfides from Thiocyanates and Terminal Arylalkynes

AbstractA transition‐metal‐free strategy using organic thiocyanate as a source of ArS or RS moiety allowed a facile and efficient synthesis of bis(tris)‐vinyl sulfides and alkynyl thioethers under mild conditions. The types of thiocyanates and the choice of bases and solvents had significant effects on the outcomes of the reactions. Aryl thiocyanates reacted with terminal arylalkynes in DMF in the presence of t‐BuOK or MOH (M=Cs, K, Na) at room temperature to form (Z)‐1,2‐diarylthio‐1‐arylalkenes in 24–93% yields, while the same reactions with alkyl thiocyanates provided alkyl alkynyl sulfides in 40–96% yields. Using NaH instead of t‐BuOK or MOH as a base in the similar reactions of aryl thiocyanates and terminal arylalkynes led to the formation of (2‐arylethene‐1,1,2‐triyl)tris(arylsulfane)s in 33–85% yields. Varying the solvent from DMF to THF, the reactions of aryl thiocyanates with terminal arylalkynes at −78 °C to room temperature in the presence of t‐BuOK supplied aryl alkynyl sulfides in 34–96% yields. Aryl and alkyl selenocyanates were also suitable substrates in these reactions. This work is the first time transition‐metal‐free selective construction of (Z)‐1,2‐diarylthio‐1‐arylalkenes, (2‐arylethene‐1,1,2‐triyl)tris(arylsulfane), and alkynyl sulfides from organic thiocyanates and terminal arylalkynes in the presence of a certain base.

A mild copper-catalyzed aerobic oxidative thiocyanation of arylboronic acids with TMSNCS.

A facile and efficient transformation of arylboronic acids to their corresponding aryl thiocyanates has been successfully developed. Based on the CuCl-catalyzed oxidative cross-coupling reaction between arylboronic acids and trimethylsilylisothiocyanate (TMSNCS) under oxygen atmosphere, the transformation can be readily conducted at ambient temperature. The newly-developed protocol provided a competitive synthetic approach to aryl thiocyanates that can tolerate a broad range of reactive functional groups and/or strong electron-withdrawing groups.

An efficient and regioselective thiocyanation of aromatic and heteroaromatic compounds using cross-linked poly (4-vinylpyridine)-supported thiocyanate as a versatile reagent and potassium peroxydisulfate as a strong oxidizing agent

A green and regioselective thiocyanation of aromatic and heteroaromatic compounds has been achieved via a simple protocol using cross-linked poly (4-vinylpyridine)-supported thiocyanate ion, [P4-VP]SCN, as a versatile polymeric reagent and potassium persulfate as a strong oxidizing agent, under heterogeneous conditions.Various indoles, phenol and aniline derivatives, and pyrroles were transformed into their corresponding aryl thiocyanates in high to excellent yields. This procedure offers advantages such as short reaction time, simple reaction work-up, and the polymeric reagents can be regenerated and reused for several times without significant loss of their activity.

Synthesis of Aryl Thiocyanates via Copper-Catalyzed Aerobic Oxidative Cross-Coupling between Arylboronic Acids and KSCN

A new protocol for the preparation of aryl thiocyanates by the cross-coupling reaction of arylboronic acids with KSCN salt is described. The coupling reaction was catalyzed by 20 mol% of copper acetate in the presence of 2.0 equivalents 4-methylpyridine serving both as ligand and base under 0.2 MPa of molecular oxygen. A variety of arylboronic acids, including those with substituents at <i>ortho</i> position, were suitable under the reaction conditions.

An Efficient and Simple Method for Diazotization-Thiocyanation of Aryl Amine using Cross-Linked Poly (4-Vinylpyridine) Supported Thiocyanate Ion

An efficient and simple method for the facile synthesis of arylthiocyanates via diazotization-thiocyanation of aryl amines using cross-linked poly (4-vinylpyridine) supported thiocyanate ion is described. Various primary aromatic amines, with electron-withdrawing and electron-donating groups, were transformed into aryl thiocyanates in high to excellent yields in a short reaction time. The present procedure offers advantages such as short reaction time, simple reaction work-up, and the polymeric reagents can also be regenerated and reused for several times without significant loss of their activity. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.

Heterogeneous and Catalytic Thiocyanation of Aromatic Compounds in Aqueous Media

This article describes a highly efficient heterogeneous catalytic thiocyanation of indoles, substituted anilines (electron rich and electron deficient) and N-substituted aromatic amines in water under mild and green conditions. The reaction of substrates with KSCN in the presence of silica sulfuric acid (SSA) and silica boron sulfonic acid (SBSA) as heterogeneous catalysts and H2O2 or UHP (urea hydrogen peroxide) as green oxidants produces aryl thiocyanates in short reaction times and high yields. Moreover, in this article, some novel aryl thiocyanates were synthesized.

Sodium Monobromoisocyanurate: A New Catalyst for Direct Synthesis of Aryl Thiocyanates

An efficient and highly selective methods for the preparation of arylthiocyanates by thiocyanation with ammonium Thiocyanates in the presence of sodium mono bromoisocyanurate as a catalyst in methanol under mild conditions to afford the corresponding aryl and para substituted thiocyanates. The use of sodium mono bromoisocyanurate is simple and more convenient.

IBX: A Novel and Versatile Oxidant for Electrophilic Thiocyanation of Indoles, Pyrrole and Arylamines

The direct thiocyanation of indoles and pyrrole with ammonium thiocyanate has been achieved using o-iodoxybenzoic acid (IBX) under mild and neutral conditions to produce indol-3-yl and pyrrol-2-yl thiocyanates, respectively, in excellent yields and with high selectivity. This method is effective even with N-substituted arylamines for the preparation of aryl thiocyanates.

Synthesis of Aryl Thiocyanates using Al2O3/MeSO3H (AMA) as a Novel Heterogeneous System

Indoles and various aromatic and heteroaromatic compounds undergo smooth thiocyanation with ammonium thiocyanate in the presence of a mixture of Al2O3/MeSO3H (AMA) under mild conditions without use of any organic solvents to afford the corresponding aryl thiocyanates in excellent yields and with high selectivity. The reactions proceed rapidly at room temperature.

A unique autocatalytic process and evidence for a concerted-stepwise mechanism transition in the dissociative electron-transfer reduction of aryl thiocyanates.

Electrochemical reduction of p-methyl-, p-methoxy-, and 3,5-dinitrophenyl thiocyanates as well as p-methyl- and p-methoxyphenyl disulfides was investigated in acetonitrile at an inert electrode. This series of compounds reveals a striking change in the reductive cleavage mechanism of the S-CN bond in thiocyanates as a function of the substituent on the aryl ring of the aryl thiocyanate. With nitro substituents, a stepwise mechanism, with an anion radical as the intermediate, takes place. When electron-donating groups (methyl and methoxy) are present, voltammetric as well as convolution analyses provide clear evidence for a transition between the concerted and stepwise mechanisms based on the magnitude of the transfer coefficient alpha. Moreover, a very interesting autocatalytic process is involved during the electrochemical reduction of these compounds. This process involves a nucleophilic substitution reaction on the initial aryl thiocyanate by the electrochemically generated arenethiolate ion. As a result of this unusual process, the electrochemical characteristics (peak potential and peak width) of the investigated series are concentration dependent.

ChemInform Abstract: An Efficient Synthesis Route to Aryl Thiocyanates from Arenesulfinates.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Preparation of Arylthiocyanates Using N,N′-Dibromo-N,N′-bis(2,5-dimethylbenzenesulphonyl) ethylenediamine and N,NDibromo-2,5-dimethylbenzenesulphonamide in the Presence of KSCN as a Novel Thiocyanating Reagent

N-Bromosulphonamides, synthesized via direct bromination of sulphonamides, react with several types of arene substrates in the presence of KSCN to afford aryl thiocyanates. The method appears to be generally applicable to benzenoid substrates with a wide range of substituents, such as N,N-dimethylaniline, p-xylene, anisole, mesitylene and cumene.

AN EFFICIENT SYNTHETIC ROUTE TO ARYL THIOCYANATES FROM ARENESULFINATES

An efficient procedure for the conversion of the inexpensive and readily available arenesulfinate (sodium) salts in three steps into the corresponding aryl thiocyanates is described. Overall yields are high, and the presence of both electronwith drawing and electron-donating substituents is well tolerated.

A FACILE SYNTHESIS OF ARYL THIOCYANATES USING SODIUM PERBORATE

A simple and convenient synthesis of aryl thiocyanates in high yields using sodium perborate is described.