Efficient copper-catalyzed coupling of aryl iodides and thiobenzoic acid

Nickel-Catalyzed Acid Chlorides with Tetrasulfides for the Synthesis of Thioesters and Acyl Disulfides

Herein, we report a novel method for the synthesis of thioesters and acyl disulfides via nickel-catalyzed reductive cross-electrophile coupling of acid chlorides with tetrasulfides. This approach for the synthesis of thioesters and acyl disulfides is convenient and practical under mild reaction conditions, relying on easy availability. In addition, a wide range of thioesters and acyl disulfides were obtained in medium to good yields with good functional group tolerance. Moreover, thioesters and acyl disulfides can also be prepared at the gram scale, indicating that they have certain potential for industrial application.

Facile synthesis of sulfinate esters from aryl iodides via direct oxidation of thioesters

A practical method to synthesize sulfinate esters from aryl iodides is disclosed. Direct oxidation of thioesters prepared by copper-catalyzed C-S formation of aryl iodides realized the efficient synthesis of sulfinate esters. Due to the good accessibility of aryl iodides, a wide variety of sulfinate esters were prepared from easily available starting materials such as carboxylic acids and anilines.

Deaminative carbonylative thioesterification of activated alkylamines with thiophenols under transition-metal-free conditions

A transition-metal-free radical carbonylation of activated alkylamines with thiophenols has been successfully developed. Various thioesters were selectively produced with moderate to good yields.

Autocatalytic Synthesis of Thioesters via Thiocarbonylation of gem-Difluoroalkenes

Herein, we report a new method for the synthesis of acyethanethioates via thiocarbonylation of gem-difluoroalkenes with thiols. This reaction provides a new pathway to prepare thioesters under mild conditions without the use of any additives. Mechanistic studies revealed that in situ generated HF facilitated the C-F bond cleavage in an autocatalytic manner.

Synthesis of Tetrasubstituted Thiophenes via Direct Metalation

Thiophene moiety can be derivatized by various synthetic procedures. The most convenient method seems to be derivatization via direct metalation, but synthesis of polysubstituted thiophenes bearing reactive groups is difficult because of high reactivity of organometallic reagents. This work reports the preparation of complex heterocyclic compounds using direct metalation of thiophenes with various reagents (Knochel-Hauser bases, LDA) as an efficient synthetic tool.

Palladium-catalyzed carbonylation of thioacetates and aryl iodides for the synthesis of S-aryl thioesters

Palladium-catalyzed carbonylation of thioacetates and aryl iodides provided thioesters in good yields.

Transition-metal-catalyzed synthesis of phenols and aryl thiols

Phenols and aryl thiols are fundamental building blocks in organic synthesis and final products with interesting biological activities. Over the past decades, substantial progress has been made in transition-metal-catalyzed coupling reactions, which resulted in the emergence of new methods for the synthesis of phenols and aryl thiols. Aryl halides have been extensively studied as substrates for the synthesis of phenols and aryl thiols. In very recent years, C-H activation represents a powerful strategy for the construction of functionalized phenols directly from various arenes. However, the synthesis of aryl thiols through C-H activation has not been reported. In this review, a brief overview is given of the recent advances in synthetic strategies for both phenols and aryl thiols.

Insights into Thiol-Aromatic Interactions: A Stereoelectronic Basis for S-H/π Interactions

Thiols can engage favorably with aromatic rings in S-H/π interactions, within abiological systems and within proteins. However, the underlying bases for S-H/π interactions are not well understood. The crystal structure of Boc-l-4-thiolphenylalanine tert-butyl ester revealed crystal organization centered on the interaction of the thiol S-H with the aromatic ring of an adjacent molecule, with a through-space Hthiol···Caromatic distance of 2.71 Å, below the 2.90 Å sum of the van der Waals radii of H and C. The nature of this interaction was further examined by DFT calculations, IR spectroscopy, solid-state NMR spectroscopy, and analysis of the Cambridge Structural Database. The S-H/π interaction was found to be driven significantly by favorable molecular orbital interactions, between an aromatic π donor orbital and the S-H σ* acceptor orbital (a π → σ* interaction). For comparison, a structural analysis of O-H/π interactions and of cation/π interactions of alkali metal cations with aromatic rings was conducted. Na+ and K+ exhibit a significant preference for the centroid of the aromatic ring and distances near the sum of the van der Waals and ionic radii, as expected for predominantly electrostatic interactions. Li+ deviates substantially from Na+ and K+. The S-H/π interaction differs from classical cation/π interactions by the preferential alignment of the S-H σ* toward the ring carbons and an aromatic π orbital rather than toward the aromatic centroid. These results describe a potentially broadly applicable approach to understanding the interactions of weakly polar bonds with π systems.

4R- and 4S-iodophenyl hydroxyproline, 4R-pentynoyl hydroxyproline, and S-propargyl-4-thiolphenylalanine: conformationally biased and tunable amino acids for bioorthogonal reactions

Bioorthogonal reactions allow the introduction of new functionalities into peptides, proteins, and other biological molecules. The most readily accessible amino acids for bioorthogonal reactions have modest conformational preferences or bases for molecular interactions. Herein we describe the synthesis of 4 novel amino acids containing functional groups for bioorthogonal reactions. (2S,4R)- and (2S,4S)-iodophenyl ethers of hydroxyproline are capable of modification via rapid, specific Suzuki and Sonogashira reactions in water. The synthesis of these amino acids, as Boc-, Fmoc- and free amino acids, was achieved through succinct sequences. These amino acids exhibit well-defined conformational preferences, with the 4S-iodophenyl hydroxyproline crystallographically exhibiting β-turn (ϕ, ψ∼-80°, 0°) or relatively extended (ϕ, ψ∼-80°, +170°) conformations, while the 4R-diastereomer prefers a more compact conformation (ϕ∼-60°). The aryloxyproline diastereomers present the aryl groups in a highly divergent manner, suggesting their stereospecific use in molecular design, medicinal chemistry, and catalysis. Thus, the 4R- and 4S-iodophenyl hydroxyprolines can be differentially applied in distinct structural contexts. The pentynoate ester of 4R-hydroxyproline introduces an alkyne functional group within an amino acid that prefers compact conformations. The propargyl thioether of 4-thiolphenylalanine was synthesized via copper-mediated cross-coupling reaction of thioacetic acid with protected 4-iodophenylalanine, followed by thiolysis and alkylation. This amino acid combines an alkyne functional group with an aromatic amino acid and the ability to tune aromatic and side chain properties via sulfur oxidation. These amino acids provide novel loci for peptide functionalization, with greater control of conformation possible than with other amino acids containing these functional groups.

Catalyst-free direct decarboxylative coupling of α-keto acids with thiols: a facile access to thioesters

A catalyst-free protocol has been demonstrated for the synthesis of thioesters via the direct decarboxylation of α-keto acids with thiols.

Syntheses of thiol and selenol esters by oxidative coupling reaction of aldehydes with RYYR (Y = S, Se) under metal-free conditions

Thiol (selenol) esters were synthesized by a direct oxidative coupling reaction of aldehydes with disulfides (diselenides) under metal-free conditions.

Efficient Cu-catalyzed base-free C-S coupling under conventional and microwave heating. A simple access to S-heterocycles and sulfides

S-aryl thioacetates can be prepared by reaction of inexpensive potassium thioacetate with both electron-rich and electron-poor aryl iodides under a base-free copper/ligand catalytic system. CuI as copper source affords S-aryl thioacetates in good to excellent yields, by using 1,10-phenanthroline as a ligand in toluene at 100 °C after 24 h. Under microwave irradiation the time was drastically reduced to 2 h. Both procedures are simple and involve a low-cost catalytic system. This methodology was also applied to the “one-pot” synthesis of target heterocycles, such as 3H-benzo[c][1,2]dithiol-3-one and 2-methylbenzothiazole, alkyl aryl sulfides, diaryl disulfides and asymmetric diaryl sulfides in good yields.

Optimisation of BACE1 inhibition of tripartite structures by modification of membrane anchors, spacers and pharmacophores - development of potential agents for the treatment of Alzheimer's disease

Systematic variation of membrane anchor, spacer and pharmacophore building blocks leads to an optimisation of the inhibitory effect of tripartite structures towards BACE1-induced cleavage of the amyloid precursor protein (APP).

A new single-photon emission computed tomography (SPECT) imaging agent for serotonin transporters: [(125)I]Flip-IDAM, (2-((2-((dimethylamino)methyl)-4-iodophenyl)thio)phenyl)methanol

New ligands for in vivo brain imaging of serotonin transporter (SERT) with single photon emission tomography (SPECT) were prepared and evaluated. An efficient synthesis and radiolabeling of a biphenylthiol, FLIP-IDAM, 4, was accomplished. The affinity of FLIP-IDAM was evaluated by an in vitro inhibitory binding assay using [(125)I]-IDAM as radioligand in rat brain tissue homogenates (K(i) = 0.03 nM). New [(125)I]Flip-IDAM exhibited excellent binding affinity to SERT binding sites with a high hypothalamus to cerebellum ratio of 4 at 30 min post iv injection. The faster in vivo kinetics for brain uptake and a rapid washout from non-specific regions provide excellent signal to noise ratio. This new agent, when labeled with (123)I, may be a useful imaging agent for mapping SERT binding sites in the human brain.

Synthesis of thiophenylalanine-containing peptides via Cu(I)-mediated cross-coupling

Aryl thiolates have unique reactive, redox, electronic, and spectroscopic properties. A practical approach to synthesize peptides containing thiophenylalanine has been developed via a novel Cu(I)-mediated cross-coupling reaction between thiolacetic acid and iodophenylalanine-containing peptides in the solid phase. This approach is compatible with all canonical proteinogenic functional groups, providing general access to aryl thiolates in peptides. Peptides containing thiophenylalanine (pK(a) 6.4) were readily elaborated to contain methyl, allyl, and nitrobenzyl thioethers, disulfides, sulfoxides, sulfones, or sulfonates.

Optimization of 3-(phenylthio)quinolinium compounds against opportunistic fungal pathogens

Ring-opened benzothieno[3,2-b]quinolinium salts (3) were designed and synthesized with substitution on the thiophene moiety. In vitro screenings were carried out against fungal pathogens including Cryptococcus neoformans, Candida albicans, Candida glabrata, Candida krusei and Aspergillus fumigatus. In all, by replacing the N-methyl group (2) with N-ω-phenylpentyl or ω-cyclohexylpentyl group to form substituted 3-(phenylthio)quinolinium compounds produced remarkable potencies, as high as 300-fold (cf, cryptolepine (1)=250 μg/mL vs 11p=0.8 μg/mL for C. albicans) over the starting tetracyclic parent. In addition, all the N-ω-cyclohexylpentyl analogs produced superior activity against all the microorganisms tested than the N-ω-phenylpentyl substituted compounds. The potential of these compounds to induce toxicity in Vero cells was also investigated and the majority of them showed lower or no cytotoxicity at 10 μg/mL than amphotericin B, the gold standard in antifungal drug development. For instance, the trifluoromethyl substituted analogs (11n-p) have selectivity indices over 2-fold better than those of amphotericin B in C. neoformans. Overall, this ring-opened scafford of benzothienoquinolines, with substitution on the thiophenyl moiety, serves as a new lead for further development.

Transition metal catalyzed synthesis of aryl sulfides

The presence of aryl sulfides in biologically active compounds has resulted in the development of new methods to form carbon-sulfur bonds. The synthesis of aryl sulfides via metal catalysis has significantly increased in recent years. Historically, thiolates and sulfides have been thought to plague catalyst activity in the presence of transition metals. Indeed, strong coordination of thiolates and thioethers to transition metals can often hinder catalytic activity; however, various catalysts are able to withstand catalyst deactivation and form aryl carbon-sulfur bonds in high-yielding transformations. This review discusses the metal-catalyzed arylation of thiols and the use of disulfides as metal-thiolate precursors for the formation of C-S bonds.

Ultrasound promoted synthesis of thioesters from 2-mercaptobenzoxa(thia)zoles

An ultrasound-enhanced method has been developed for the synthesis of a variety of thioesters from benzoyl chlorides and 2-mercaptobenzoxa(thia)zoles. Applying this methodology, 14 compounds were synthesized in excellent yields.

A general and efficient approach to aryl thiols: CuI-catalyzed coupling of aryl iodides with sulfur and subsequent reduction

A CuI-catalyzed coupling reaction of aryl iodides and sulfur powder takes place in the presence of K(2)CO(3) at 90 degrees C. The coupling mixture is directly treated with NaBH(4) or triphenylphosphine to afford aryl thiols in good to excellent yields. A wide range of substituted aryl thiols that bear methoxy, hydroxyl, carboxylate, amido, keto, bromo, and fluoro groups can be assembled through this procedure.

Resting state and elementary steps of the coupling of aryl halides with thiols catalyzed by alkylbisphosphine complexes of palladium

Detailed mechanistic studies on the coupling of aryl halides with thiols catalyzed by palladium complexes of the alkylbisphosphine ligand CyPF-(t)Bu (1-dicyclohexylphosphino-2-di-tert-butylphosphinoethylferrocene) are reported. The elementary steps that constitute the catalytic cycle, i.e. oxidative addition, transmetalation and reductive elimination, have been studied, and their relative rates are reported. Each of the steps of the catalytic process occurs at temperatures that are much lower than those required for the reactions catalyzed by a combination of palladium precursors and CyPF-(t)Bu. To explain these differences in rates between the catalytic and stoichiometric reactions, studies were conducted to identify the resting state of the catalyst of the reactions catalyzed by a combination of Pd(OAc)(2) and CyPF-(t)Bu, a combination of Pd(dba)(2) and CyPF-(t)Bu, or the likely intermediate Pd(CyPF-(t)Bu)(Ar)(Br). These data show that the major palladium complex in each case lies off of the catalytic cycle. The resting state of the reactions catalyzed by Pd(OAc)(2) and CyPF-(t)Bu was the palladium bis-thiolate complex [Pd(CyPF-(t)Bu)(SR)(2)] (R = alkyl or aryl). The resting state in reactions catalyzed by Pd(2)(dba)(3) and CyPF-(t)Bu was the binuclear complex [Pd(CyPF-(t)Bu)](2)(mu(2),eta(2)-dba) (9). The resting states of reactions of both aromatic and aliphatic thiols catalyzed by [Pd(CyPF-(t)Bu)(p-tolyl)(Br)] (3a) were the hydridopalladium thiolate complexes [Pd(CyPF-(t)Bu)(H)(SR)] (R= alkyl and aryl). All these palladium species have been prepared independently, and the mechanisms by which they enter the catalytic cycle have been examined in detail. These features of the reaction catalyzed by palladium and CyPF-(t)Bu have been compared with those of reactions catalyzed by the alkylbisphosphine DiPPF and Pd(OAc)(2) or Pd(dba)(2). Our data indicate that the resting states of these reactions are similar to each other and that our mechanistic conclusions about reactions catalyzed by palladium and CyPF-(t)Bu can be extrapolated to reactions catalyzed by complexes of other electron-rich bisphosphines.

General and practical synthesis of benzothiazoles

The carbon-sulfur bond formation of aryl bromides and triflates catalyzed by a new catalyst system, Pd2(dba)3/xantphos, has been demonstrated. Based on this finding, a novel and practical synthesis of benzothiazoles has been developed. This new methodology allows for the assembly of a wide range of benzothiazoles.