Use of activated enol ethers in the synthesis of pyrazoles: reactions with hydrazine and a study of pyrazole tautomerism

• Denisa Tarabová,
• Stanislava Šoralová,
• Martin Breza,
• Marek Fronc,
• Wolfgang Holzer and
• Viktor Milata

Beilstein J. Org. Chem. 2014, 10, 752–760, doi:10.3762/bjoc.10.70

• ethers react surprisingly easily with various nucleophiles such as amines, thiols, alcohols or C-anions [2] under the conditions of nucleophilic vinylic substitution [3]. When using bi- or trifunctional nucleophiles, cyclic or bicyclic products are formed. Activated enol ethers thus represent

End-group-functionalized poly(N,N-diethylacrylamide) via free-radical chain transfer polymerization: Influence of sulfur oxidation and cyclodextrin on self-organization and cloud points in water

• Sebastian Reinelt,
• Daniel Steinke and
• Helmut Ritter

Beilstein J. Org. Chem. 2014, 10, 680–691, doi:10.3762/bjoc.10.61

• the thiols 3-(4-(1,1-dimethylethan-1-yl)phenoxy)propane-1-thiol (6a) and 3-(4-(2,4,4-trimethylpentan-2-yl)phenoxy)propane-1-thiol (6b) in good yields after purification. The successful synthesis was furthermore confirmed by 1H NMR, 13C NMR and FTIR spectroscopy as well as mass spectrometry (see

Synthesis of five- and six-membered cyclic organic peroxides: Key transformations into peroxide ring-retaining products

• Alexander O. Terent'ev,
• Dmitry A. Borisov,
• Vera A. Vil’ and
• Valery M. Dembitsky

Beilstein J. Org. Chem. 2014, 10, 34–114, doi:10.3762/bjoc.10.6

• -dioxanes Modern approaches to the synthesis of 1,2-dioxanes are based on reactions with singlet oxygen, the oxidative coupling of carbonyl compounds and alkenes in the presence of manganese and cerium salts, the co-oxidation of alkenes and thiols with oxygen, the Isayama–Mukaiyama peroxidation, the

• proceeds through a formation of an enol-containing complex with a metal ion (Scheme 57, Table 14). 3.3. Oxidation of 1,5-dienes in the presence of thiols The co-oxidation of 1,4-dienes and thiols (thiol–olefin co-oxygenation, TOCO reaction) was described for the first time by Beckwith and Wagner as a

Silica: An efficient catalyst for one-pot regioselective synthesis of dithioethers

• Samir Kundu,
• Babli Roy and
• Basudeb Basu

Beilstein J. Org. Chem. 2014, 10, 26–33, doi:10.3762/bjoc.10.5

• employed in asymmetric hydrogenation [18]. Vicinal dithioethers are generally synthesised either by the metal-catalyzed addition of disulfides to alkenes [19][20] or by the traditional nucleophilic substitution of 1,2-dihalides with suitable thiols/thiolates [21][22]. They are also prepared by consecutive

• attractive features in terms of the concepts of Green chemistry. Previously, we have developed silica-promoted facile and highly selective methods for N and S-alkylations/acylation from amines or thiols, respectively [37][38]. An equimolar mixture of a benzenethiol and allyl bromide on treatment with silica

• afforded allyl(phenyl)sulfane in excellent yield. Since alkenes are also known to undergo ‘click’ addition with thiols [39][40], excess use of thiols could effectively produce dithioethers, and based on a regioselective addition one could achieve either vicinal or 1,3-dithioethers in one-pot consecutive

Polymeric redox-responsive delivery systems bearing ammonium salts cross-linked via disulfides

• Christian Dollendorf,
• Martin Hetzer and
• Helmut Ritter

Beilstein J. Org. Chem. 2013, 9, 1652–1662, doi:10.3762/bjoc.9.189

• cannot only reduce disulfide bonds to thiols but it can also reduce the functional groups of dyes or substances. For example, methylene blue showed an initial loss of color during the release investigations due to the reduction by DTT, but regained it after exposure to oxygen as the leuco form of

Use of 3-[¹⁸F]fluoropropanesulfonyl chloride as a prosthetic agent for the radiolabelling of amines: Investigation of precursor molecules, labelling conditions and enzymatic stability of the corresponding sulfonamides

• Reik Löser,
• Steffen Fischer,
• Achim Hiller,
• Martin Köckerling,
• Uta Funke,
• Aurélie Maisonial,
• Peter Brust and
• Jörg Steinbach

Beilstein J. Org. Chem. 2013, 9, 1002–1011, doi:10.3762/bjoc.9.115

• chlorides can be generated by oxidation with aqueous chlorine from a variety of organosulfur species such as thiols, sulfides, disulfides, thioesters, isothiouronium salts, xanthates and thiocyanates [22]. The latter class of organic sulfur compounds seems to be most advantageous, as organic thiocyanates

Appel-reagent-mediated transformation of glycosyl hemiacetal derivatives into thioglycosides and glycosyl thiols

• Tamashree Ghosh,
• Abhishek Santra and
• Anup Kumar Misra

Beilstein J. Org. Chem. 2013, 9, 974–982, doi:10.3762/bjoc.9.112

• thiols in a one-pot two-step reaction sequence mediated by Appel reagent (carbon tetrabromide and triphenylphosphine). 1,2-trans-Thioglycosides and β-glycosyl thiol derivatives were stereoselectively formed by the reaction of the in situ generated glycosyl bromides with thiols and sodium

• enzymatic hydrolysis, several thioglycosides have been evaluated as enzyme inhibitors [13][14]. As a consequence a large number of reports have appeared in the past for the preparation of thioglycosides. Conventionally, thioglycosides are prepared by the reaction of glycosyl acetates with thiols or

• agents (triphenylphosphine or combination of triethylsilane and BF3·OEt2) followed by the reaction of the in situ generated thiolate ions with glycosyl bromides under phase-transfer conditions [23] or in ionic liquids [24]; (b) reaction of glycosyl bromides with thiols under phase-transfer conditions [25

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

• Silvia M. Soria-Castro and
• Alicia B. Peñéñory

Beilstein J. Org. Chem. 2013, 9, 467–475, doi:10.3762/bjoc.9.50

• diverse heterocycles containing sulfur atoms by intra- [42][43][44] and intermolecular [45][46][47] reactions. Aryl thioesters are versatile intermediates for the synthesis of a variety of sulfur compounds including aryl thiols, aryl alkyl sulfides, aryl sulfenyl chlorides, aryl sulfonyl chlorides [48

Thioester derivatives of the natural product psammaplin A as potent histone deacetylase inhibitors

• Matthias G. J. Baud,
• Thomas Leiser,
• Vanessa Petrucci,
• Mekala Gunaratnam,
• Stephen Neidle,
• Franz-Josef Meyer-Almes and
• Matthew J. Fuchter

Beilstein J. Org. Chem. 2013, 9, 81–88, doi:10.3762/bjoc.9.11

• cell-based assays (Table 1, columns 1–3). Compound 8, which contains an oxime moiety, was the most potent compound in each case, followed by methyloxime 7, and finally ketone 9. These findings parallel our previous SAR data for the corresponding thiols [20], and reflect the previously established

• potencies of our acetate-protected analogues approached those of their corresponding thiols (Table 1, see notea), while being approximately 10-fold more potent than the parental disulfide series (Table 1, see notea). For example, 8 was found to be highly potent against rHDAC1, displaying an IC50 of 5 nM

• could potentially be responsible for thioester hydrolysis. We prepared and used synthetic probe 10 [30] (Scheme 3) in order to test this hypothesis. Coumarin-based probe 10 is known to react extremely fast with thiols through a Michael addition reaction. While the fluorescence of 10 is efficiently

Peptoids and polyamines going sweet: Modular synthesis of glycosylated peptoids and polyamines using click chemistry

• Daniel Fürniss,
• Timo Mack,
• Frank Hahn,
• Sidonie B. L. Vollrath,
• Katarzyna Koroniak,
• Ute Schepers and
• Stefan Bräse

Beilstein J. Org. Chem. 2013, 9, 56–63, doi:10.3762/bjoc.9.7

• attachment to other molecules through a variety of functional groups, such as amines (–NH2) and carboxylic acids (–COOH) resulting in peptide bonds, thiols (–SH) resulting in disulfides, thioethers or thioesters, aldehydes (–CHO) and hydroxy (–OH) groups. Nonetheless, coupling to these groups often requires

Reactions of salicylaldehyde and enolates or their equivalents: versatile synthetic routes to chromane derivatives

• Ishmael B. Masesane and
• Zelalem Yibralign Desta

Beilstein J. Org. Chem. 2012, 8, 2166–2175, doi:10.3762/bjoc.8.244

• [28], as catalytic reagents for silylation of alcohols, phenols, and thiols using hexamethyldisilazane [29], in conversion of urazoles to triazolinediones [30], and in oxidation of 1,3,5-trisubstituted pyrazolines [31]. Molecular sieves have been used as solid-phase catalysts in the preparation of 2

Cyclization of ortho-hydroxycinnamates to coumarins under mild conditions: A nucleophilic organocatalysis approach

• Florian Boeck,
• Max Blazejak,
• Markus R. Anneser and
• Lukas Hintermann

Beilstein J. Org. Chem. 2012, 8, 1630–1636, doi:10.3762/bjoc.8.186

• initially thought that hydro-heteroatomic nucleophiles such as thiols, which are known to easily undergo hetero-Michael additions [38], could be suitable candidates for the screen. However, coumarin was not formed in the presence of thiols (Table 1, entry 1). We turned our attention to nucleophiles that are

• considered a strategy to perform a fast catalytic conjugate addition of a heteronucleophile to the starting material in order to speed up the overall cyclization reaction. Initial experiments with neutral thiols as nucleophiles were not successful. On the other hand, addition of a nucleophilic

Combined bead polymerization and Cinchona organocatalyst immobilization by thiol–ene addition

• Kim A. Fredriksen,
• Tor E. Kristensen and
• Tore Hansen

Beilstein J. Org. Chem. 2012, 8, 1126–1133, doi:10.3762/bjoc.8.125

• described by Theodor Posner already in 1905 [10], and it has been in more or less continuous use since then. The thiol–ene addition can readily be adapted for polymerization, by using polyfunctional alkenes in combination with polyfunctional thiols [11][12][13]. We envisaged that polymerization into a cross

• reactivity of unsaturated compounds 6–9 towards the thiols is generally so: vinyl ether 6 > allyl ether 9 > acrylate 8 > methacrylate 7 [11]. Thiol–ene additions according to the anionic (Michael-type) mechanism have not been investigated in this work. As a minimum for obtaining cross-linked polymeric

• initiator, such as AIBN, could be utilized, because peroxide initiators, such as dibenzoyl peroxide, oxidise thiols. The thiol-ene polymer beads 10–12 had a distinctively soft and gel-like appearance, but were easily handled like conventional microporous beads. They had favourable swelling characteristics

Multistep organic synthesis of modular photosystems

• Naomi Sakai and
• Stefan Matile

Beilstein J. Org. Chem. 2012, 8, 897–904, doi:10.3762/bjoc.8.102

• surface of monolayer 48 were removed with DTT to afford free thiols on the surface of monolayer 49. For SOSIP [18][19], the concentration of propagators had to be optimized to a critical SOSIP concentration, cSOSIP. Below cSOSIP, ring-opening disulfide-exchange polymerization [27] does not occur, whereas

• thiols on the surface. Recognition of propagators 3 on the surface of 49 places the strained disulfides of asparagusic acid right on top of the activated thiolates on the surface. Covalent capture by ring-opening disulfide exchange generates new thiolates on the surface of the growing photosystem 55 for

Building photoswitchable 3,4'-AMPB peptides: Probing chemical ligation methods with reducible azobenzene thioesters

• Gehad Zeyat and
• Karola Rück-Braun

Beilstein J. Org. Chem. 2012, 8, 890–896, doi:10.3762/bjoc.8.101

• 4,5,6-trimethoxy-2-mercaptobenzyl auxiliary as well as the Nα-2-mercaptoethyl auxiliary. Thus, 3,4'-AMPB derivatives/peptides proved to be significantly less prone to reduction by aliphatic and aromatic thiols than were the 4,4'-AMPB compounds. Keywords: acyl transfer auxiliary; azobenzenes; ligation

• , with a rather labile N–S bond (Scheme 3, reaction 1). Aliphatic thiols readily undergo adduct formation towards the N-sulfenohydrazodiarene intermediates B because of their higher nucleophilicity. Accordingly, we observe a higher tendency toward reduction when applying the aliphatic Nα-2-mercaptoethyl

• thiol molecule at the N-sulfenohydrazodiarene B, yielding the symmetric disulfide and the respective hydrazine thioester or hydrazine peptide (Scheme 3, reaction 2). The reduction of diazene units by thiols has been intensively studied in the past for electron-poor azobenzenes or azodicarboxylates, en

Intramolecular bridges formed by photoswitchable click amino acids

• Christian Hoppmann,
• Ronald Kühne and
• Michael Beyermann

Beilstein J. Org. Chem. 2012, 8, 884–889, doi:10.3762/bjoc.8.100

• thiol–ene click reaction takes place in the presence of endogenous thiols. In most cells the cysteine containing tripeptide glutathione (GSH) is present at millimolar concentrations (0.1 mM–10 mM). Therefore, we investigated the thiol–ene click reaction of PCSaa and cysteine within peptide 1 and 2 in

Discovery of practical production processes for arylsulfur pentafluorides and their higher homologues, bis- and tris(sulfur pentafluorides): Beginning of a new era of “super-trifluoromethyl” arene chemistry and its industry

• Teruo Umemoto,
• Lloyd M. Garrick and
• Norimichi Saito

Beilstein J. Org. Chem. 2012, 8, 461–471, doi:10.3762/bjoc.8.53

• the production of various arylsulfur pentafluorides and their higher homologues, bis- and tris(sulfur pentafluorides), from the corresponding diaryl disulfides or aryl thiols. The method consists of two steps: (Step 1) treatment of a diaryl disulfide or an aryl thiol with chlorine in the presence of

• due to the steric hindrance of the relatively large bromo substituent at the ortho position. Arylsulfur chlorotetrafluorides were also prepared from the corresponding aryl thiols in high yields, as shown in runs 2 and 4, Table 1. The method using aryl thiols as starting materials was successfully

• ). Conclusion We have developed the first practical and economical method for the production of various arylsulfur pentafluorides and their higher homologues, which consists of the treatment of diaryl disulfides or aryl thiols with chlorine in the presence of potassium or cesium fluoride, followed by treatment

Liquid-crystalline nanoparticles: Hybrid design and mesophase structures

• Gareth L. Nealon,
• Romain Greget,
• Cristina Dominguez,
• Zsuzsanna T. Nagy,
• Daniel Guillon,
• Jean-Louis Gallani and
• Bertrand Donnio

Beilstein J. Org. Chem. 2012, 8, 349–370, doi:10.3762/bjoc.8.39

• hexagonal lattices has been observed for simple monolayer-protected NPs on surfaces [52]. Whilst theoretical treatments predict that Au NPs coated with simple linear thiols should exhibit spontaneous asymmetry at low temperatures or in solution [53][54][55], simple NP-hybrids of this type are yet to exhibit

• observed mesophase behaviour of hybrid pseudospherical NPs. Another detailed investigation into the disposition of the ligands about mesogenic Au NPs was reported based on hybrid particles prepared in a two-step process by using a wider suite of mesogenic cyanobiphenyl based thiols [62]. Gold NPs of ~2.4

• nm diameter were first synthesised and isolated with a triphenylphosphine protective layer, followed by the addition of thiols 68–12 (Figure 3). The authors estimated the number of ligands attached to the NPs after the exchange process to be ~150–215, which indicated a very dense packing on the

Natural product biosyntheses in cyanobacteria: A treasure trove of unique enzymes

• Jan-Christoph Kehr,
• Douglas Gatte Picchi and
• Elke Dittmann

Beilstein J. Org. Chem. 2011, 7, 1622–1635, doi:10.3762/bjoc.7.191

• of bacteria. The characteristic feature of the group is lanthionine bridges, which are formed by dehydration of serine or threonine followed by intramolecular addition of cysteine thiols to the resulting dehydro amino acids. Lantipeptides exhibit a variety of bioactivities, in particular

Ratiometric fluorescent probe for enantioselective detection of D-cysteine in aqueous solution

• Xiao-bo Zhou,
• Wing-Hong Chan,
• Albert W. M. Lee and
• Chi-Chung Yeung

Beilstein J. Org. Chem. 2011, 7, 1508–1515, doi:10.3762/bjoc.7.176

• ; fluorescence; ratiometric; Introduction The rapid, sensitive, and selective sensing of biologically relevant thiols including cysteine (Cys), homocysteine (Hcy) and glutathione (GSH) has attracted significant interest in the sensor community (Figure 1) [1]. All three of these thiols are present in living

• cells at different concentration levels and play vital roles in controlling redox-related biological processes [2]. Abnormal levels of Cys and Hcy are associated with a variety of human diseases [3][4][5]. Hence, the development of efficient and selective methods capable of quantifying biological thiols

• under physiological conditions is of interest in a wide variety of disciplines including chemistry and medicine. Owing to the intrinsic sensitivity of fluorescence, the development of fluorescent probes for thiols has been extensively invesigated. The subject has been recently reviewed by Yoon and

Nano copper oxide catalyzed synthesis of symmetrical diaryl sulfides under ligand free conditions

• K. Harsha Vardhan Reddy,
• V. Prakash Reddy,
• A. Ashwan Kumar,
• G. Kranthi and
• Y.V.D. Nageswar

Beilstein J. Org. Chem. 2011, 7, 886–891, doi:10.3762/bjoc.7.101

• reactions mediated by recyclable copper oxide nanoparticles under ligand free conditions. This protocol avoids foul smelling thiols, for the synthesis of a variety of symmetrical diaryl sulfides, via the cross-coupling of different aryl halides with potassium thiocyanate, affording corresponding products in

• cobalt [42] have been used in cross-coupling reactions, developed for the formation of carbon–sulfur bonds. Most of these coupling protocols involve the reaction between thiols and aryl halides, resulting in the formation of C–S bonds. Most of these metal-catalyzed reactions involve volatile and foul

• -smelling thiols as the main drawback, which leads to environmental and safety problems. To overcome these problems, Zhou [43] and coworkers recently reported an efficient C–S bond formation by the reaction of potassium thiocyanate and aryl halides in the presence of a copper catalyst and a ligand in

Gold-catalyzed propargylic substitutions: Scope and synthetic developments

• Olivier Debleds,
• Eric Gayon,
• Emmanuel Vrancken and
• Jean-Marc Campagne

Beilstein J. Org. Chem. 2011, 7, 866–877, doi:10.3762/bjoc.7.99

• , alcohols, thiols, electron rich aromatic compounds), and showed that gold probably acts as a Lewis acid to promote the formation of a stabilized propargylic carbocation intermediate [23][24]. A related reaction was subsequently reported by Dyker [25] in 2006, using azulene and 1,3-dimethoxybenzene in

• effective in these reactions including alcohols, thiols, hydrides (from Et3SiH or PMHS), electron-rich aromatic and hetero-aromatic derivatives such as anisole or furan, and deactivated nitrogen nucleophiles such as phenylsulfonamide (compounds 3–8, Scheme 4). In some instances unexpected selectivities and

Asymmetric synthesis of tertiary thiols and thioethers

• Jonathan Clayden and
• Paul MacLellan

Beilstein J. Org. Chem. 2011, 7, 582–595, doi:10.3762/bjoc.7.68

• Jonathan Clayden Paul MacLellan School of Chemistry, University of Manchester, Oxford Rd, Manchester M13 9PL, UK 10.3762/bjoc.7.68 Abstract Enantiomerically pure tertiary thiols provide a major synthetic challenge, and despite the importance of chiral sulfur-containing compounds in biological and

• medicinal chemistry, surprisingly few effective methods are suitable for the asymmetric synthesis of tertiary thiols. This review details the most practical of the methods available. Keywords: asymmetric synthesis; organolithium; sulfur; substitution; thiol; Introduction Organosulfur compounds play key

• , sulfimines and sulfilimines [9]. Chiral sulfoxides and sulfonium ylids have themselves been extensively used as tools for asymmetric synthesis [3]. With regard to chiral sulfur(II) compounds – namely thiols and thioethers (sulfides) with chirality at carbon – methods available for their asymmetric

Miniemulsion polymerization as a versatile tool for the synthesis of functionalized polymers

• Daniel Crespy and
• Katharina Landfester

Beilstein J. Org. Chem. 2010, 6, 1132–1148, doi:10.3762/bjoc.6.130

• thiols, whereas the nanogels were stable in PBS solution. Radiation-induced polymerization Miniemulsions initiated by 60Co γ-rays are reported in a separate paragraph because of their peculiarities. The γ-ray initiated miniemulsion polymerization was conducted to synthesize polystyrene particles [125

Aromatic and heterocyclic perfluoroalkyl sulfides. Methods of preparation

• Vladimir N. Boiko

Beilstein J. Org. Chem. 2010, 6, 880–921, doi:10.3762/bjoc.6.88

• partly fluorinated aliphatic moieties have been widely used for a number of years. Their methods of preparation, for example, by the reaction of thiols with fluoro-olefins or with chloropolyfluoroalkanes are well known and have been widely used. In contrast, sulfides with fully fluorinated aliphatic

• polarity, and in spite of their tendency to undergo homolytic decomposition under UV irradiation, it is probable that they are also able to react with thiolate anions by a similar mechanism. Indeed, they react readily with aliphatic, aromatic and heterocyclic thiols [143][144][145][146], and with seleno

• % for 4-SH- [146], 64% for 2,4-(SH)2- [143] and 37% for 2,4,6-(SH)3- [163]. 4.1.2. Perfluoroalkylation of heterocyclic thiols Heterocyclic thiol form S-perfluoroalkyl derivatives when irradiated in liquid ammonia in the presence of iodoperfluoroalkanes. The type of heterocyclic ring and the position of