Orthogonal protection of saccharide polyols through solvent-free one-pot sequences based on regioselective silylations

• Serena Traboni,
• Emiliano Bedini and
• Alfonso Iadonisi

Beilstein J. Org. Chem. 2016, 12, 2748–2756, doi:10.3762/bjoc.12.271

• conducted in short times with the requisite silyl chloride and a very limited excess of pyridine (2–3 equivalents). Under these conditions, that can be regarded as solvent-free conditions in view of the insolubility of the polyol substrates, the reactions are faster than in most examples reported in the

• of the silylation approach was significantly extended with the development of unprecedented “one-pot” and “solvent-free” sequences allowing the regioselective silylation/alkylation (or the reverse sequence) of saccharide polyols in short times. The developed methodologies represent a very useful and

• experimentally simple tool for the straightforward access to saccharide building-blocks useful in organic synthesis. Keywords: carbohydrates; one-pot synthesis; regioselective protection; silyl protecting group; solvent-free reaction; Introduction The application of an orthogonal set of protecting groups

Selective synthesis of thioethers in the presence of a transition-metal-free solid Lewis acid

• Federica Santoro,
• Matteo Mariani,
• Federica Zaccheria,
• Rinaldo Psaro and
• Nicoletta Ravasio

Beilstein J. Org. Chem. 2016, 12, 2627–2635, doi:10.3762/bjoc.12.259

• alumina catalyst with a very low content in alumina gave excellent results in terms of both activity and selectivity also under solvent-free conditions. The reaction rate follows the electron density of the carbinol atom in the substrate alcohol and yields up to 99% and can be obtained for a wide range of

• thiols and benzylic alcohols under solvent-free conditions in excellent yields [21]. We already reported on the use of amorphous solid acid catalysts in organic synthesis. These solids are formed by dispersing a small amount of an inorganic oxide with Lewis acid nature onto the surface of silica [22]. In

• report that excellent yields can be obtained in the presence of an amorphous solid catalyst under solvent-free conditions. Results and Discussion In order to test our hypothesis we carried out the reaction of 1-(4-methoxyphenyl)ethanol (1a) and benzyl mercaptan (2a) in the presence of different solid

A new protocol for the synthesis of 4,7,12,15-tetrachloro[2.2]paracyclophane

• Donghui Pan,
• Yanbin Wang and
• Guomin Xiao

Beilstein J. Org. Chem. 2016, 12, 2443–2449, doi:10.3762/bjoc.12.237

• precursor of parylene D, from 2,5-dichloro-p-xylene. In the first bromination step, with H2O2–HBr as a bromide source, this procedure becomes organic-waste-free and organic-solvent-free and can appropriately replace the existing bromination methods. The Winberg elimination–dimerization step, using aqueous

• step, 1-(bromomethyl)-2,5-dichloro-4-methylbenzene was synthesized with high yield and selectivity from 2,5-dichloro-p-xylene by using a H2O2–HBr couple in water. The use of H2O2–HBr as a bromide source made this procedure organic-waste-free, organic-solvent-free and an appropriate replacement of the

Efficient mechanochemical synthesis of regioselective persubstituted cyclodextrins

• Laszlo Jicsinszky,
• Marina Caporaso,
• Katia Martina,
• Emanuela Calcio Gaudino and
• Giancarlo Cravotto

Beilstein J. Org. Chem. 2016, 12, 2364–2371, doi:10.3762/bjoc.12.230

• -6-substituted cyclodextrin derivative syntheses have been effectively carried out in a planetary ball mill under solvent-free conditions. The preparation of Bridion® and important per-6-amino/thiocyclodextrin intermediates without polar aprotic solvents, a source of byproducts and persistent

• very strong complexes with not only the native but with the substituted CDs, too. Although a solvent-free synthetic method does not solve the problem of complexation but the reduced amount of reagents can simplify the purification. Heptakis(6-azido-6-deoxy)-β-CD is the precursor to per-6-amino-β-CD

• reaction of 6I-monotosyl-β-CD has been demonstrated in a previous article [22]. Most interestingly, the side reactions that appear to be unavoidable in the classical solution syntheses can be eliminated in the solvent-free method described for the preparation of various CD derivatives. HEBM was found to be

Solvent-free, visible-light photocatalytic alcohol oxidations applying an organic photocatalyst

• Martin Obst and
• Burkhard König

Beilstein J. Org. Chem. 2016, 12, 2358–2363, doi:10.3762/bjoc.12.229

• Martin Obst Burkhard Konig Institute of Organic Chemistry, University of Regensburg, Universitätsstraße 31, 93040 Regensburg, Germany 10.3762/bjoc.12.229 Abstract A method for the solvent-free photocatalytic conversion of solid and liquid substrates was developed, using a novel rod mill apparatus

• reaction mixture. The corresponding carbonyl compounds were obtained in moderate to good yields. Keywords: benzylic alcohol; oxidation; photocatalysis; solvent free; visible light; Introduction According to a classification made by Wilhelm Ostwald, one of the pioneers in the field of physical chemistry

• solvent-free conversion of solid reactants. The reaction is driven by mechanical energy, which is for instance realized by grinding in ball mills or pestle and mortar. Obviously, this method possesses several advantages compared to reactions, which are performed in solution: toxic solvents and wastes are

Tunable microwave-assisted method for the solvent-free and catalyst-free peracetylation of natural products

• Manuela Oliverio,
• Paola Costanzo,
• Monica Nardi,
• Carla Calandruccio,
• Raffaele Salerno and
• Antonio Procopio

Beilstein J. Org. Chem. 2016, 12, 2222–2233, doi:10.3762/bjoc.12.214

• of hydrophilic products and to obtain safe and stable pro-drugs. Results: A totally green, solvent-free and catalyst-free microwave (MW)-assisted method for peracetylation of natural products such as oleuropein, alpha-hederin, quercetin and rutin is presented. By simply tuning the MW heating program

• green acetylation of hydrophilic biological molecules, potentially easily scalable for industrial applications, including pharmaceutical, cosmetic and food industry. Keywords: catalyst-free; microwaves; peracetylation; polyhydroxylated compounds; solvent-free; Introduction Peracetylation of alcohols

• preferably acetic anhydride in solvent free conditions, in presence of non-toxic homogeneous catalysts such as environmental safe Lewis acids [13][14]. Moreover, the need to easily recover and reuse the catalyst, thus reducing the work-up procedure to a simple filtration, resulted in the growing use of

Silica-supported sulfonic acids as recyclable catalyst for esterification of levulinic acid with stoichiometric amounts of alcohols

• Raimondo Maggi,
• N. Raveendran Shiju,
• Veronica Santacroce,
• Giovanni Maestri,
• Franca Bigi and
• Gadi Rothenberg

Beilstein J. Org. Chem. 2016, 12, 2173–2180, doi:10.3762/bjoc.12.207

• sulfonated catalyst (1%), an equimolecular amount of reagents under solvent free conditions, and varying the temperature between 50–100 °C. Results are reported in Table 3. In all cases, the selectivity towards the esterification product 3a remained complete. A comparable yield of 3a was recovered reducing

• h) and provides good to excellent yields with various primary and secondary alcohols. The selectivity towards desired products remained complete in all cases. The coproduct of the reaction, namely water, did not hamper the efficiency of this solvent-free process. The selected catalyst is cheap, can

• chromatography on silica gel (eluent = hexane/ethyl acetate) and characterised by multinuclear NMR. Anchoring methodologies: a) impregnation; b) covalent binding. Activity of the supported sulfonic acid catalyst within the first six cycles. Reaction conditions: 1 mol % cat., acid:alcohol ratio = 1:1, solvent

Solvent-free synthesis of novel para-menthane-3,8-diol ester derivatives from citronellal using a polymer-supported scandium triflate catalyst

• Lubabalo Mafu,
• Ben Zeelie and
• Paul Watts

Beilstein J. Org. Chem. 2016, 12, 2046–2054, doi:10.3762/bjoc.12.193

• environmentally friendly method for the synthesis of para-menthane-3,8-diol from natural citronellal oil in 96% yield, under solvent free aqueous conditions. The acylation of para-menthane-3,8-diol with various acid anhydrides over polymer-supported scandium triflate (PS-Sc(OTf)3) catalyst was subsequently

• developed, where both hydroxy groups of para-menthane-3,8-diol could be simultaneous acylated under mild reaction conditions to form the corresponding diesters in good yields. The advantages of this method include a simple procedure from natural resources, using solvent-free reaction conditions. Keywords

• was used. Moreover, all the reactions were carried-out under solvent-free conditions. Reaction parameters such as temperature, reaction time and reagent molar ratio were studied towards the substrate conversion and product selectivity. Effect of reaction temperature and reaction time In order to

Microwave-assisted cyclizations promoted by polyphosphoric acid esters: a general method for 1-aryl-2-iminoazacycloalkanes

• Jimena E. Díaz,
• María C. Mollo and
• Liliana R. Orelli

Beilstein J. Org. Chem. 2016, 12, 2026–2031, doi:10.3762/bjoc.12.190

• trimethylsilyl polyphosphate (PPSE) in solvent-free conditions allowed for the synthesis of 1-aryl-2-iminopiperidines and hitherto unreported 1-aryl-2-iminoazepanes. The cyclization reaction involves good to high yields and short reaction times, and represents a novel application of PPA esters in heterocyclic

• under certain conditions [45][46]. Using a dichloromethane solution of PPSE, compound 4a was obtained exclusively (Table 2, entries 4–6), while working under solvent-free conditions further improved the yield (Table 2, entry 7). Employing the optimized reaction conditions (neat PPSE, 30 min at 150 °C

• reaction under solvent-free conditions at 150 °C, compound 7a was obtained in modest yield (Table 4, entry 5). Significantly better results were achieved by increasing the temperature to 200 °C (Table 4, entry 6). Employing the optimized reaction conditions, we synthesized some novel 1-aryl-2-iminoazepanes

Ionic liquids as transesterification catalysts: applications for the synthesis of linear and cyclic organic carbonates

• Maurizio Selva,
• Alvise Perosa,
• Sandro Guidi and
• Lisa Cattelan

Beilstein J. Org. Chem. 2016, 12, 1911–1924, doi:10.3762/bjoc.12.181

• -value chemicals. This holds true also for enzyme-catalyzed transesterification reactions. To cite a few examples, the literature claims the use of lipase as a biocatalyst for i) the reaction of glycerol with DMC for the synthesis of glycerol carbonate (GlyC) under solvent-free conditions. A 60% yield

TMSBr-mediated solvent- and work-up-free synthesis of α-2-deoxyglycosides from glycals

• Mei-Yuan Hsu,
• Yi-Pei Liu,
• Sarah Lam,
• Su-Ching Lin and
• Cheng-Chung Wang

Beilstein J. Org. Chem. 2016, 12, 1758–1764, doi:10.3762/bjoc.12.164

• University, Taipei 106, Taiwan Department of Chemistry, National Central University, Jhongli 320, Taiwan 10.3762/bjoc.12.164 Abstract The thio-additions of glycals were efficiently promoted by a stoichiometric amount of trimethylsilyl bromide (TMSBr) to produce S-2-deoxyglycosides under solvent-free

• was manipulated by the neighbouring group effect on C2 [67][69][70][71], which is absent in 2-deoxyglycosides. Mild, work-up- and solvent-free reaction conditions for highly stereoselective 2-deoxyglycosylation is therefore desirable. Here, we present a solvent- and work-up-free approach to prepare S

Rearrangements of organic peroxides and related processes

• Ivan A. Yaremenko,
• Vera A. Vil’,
• Dmitry V. Demchuk and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2016, 12, 1647–1748, doi:10.3762/bjoc.12.162

• -dioxolanes 151 are rearranged similarly to the Criegee mechanism into diketone derivatives 152 (Scheme 44) [298]. Unlike the Baeyer–Villiger rearrangement, in which only mono-O-insertion can take place, the Criegee rearrangement of peroxide 153 in an acidic medium and under solvent-free conditions does not

Microwave-assisted synthesis of (aminomethylene)bisphosphine oxides and (aminomethylene)bisphosphonates by a three-component condensation

• Erika Bálint,
• Ádám Tajti,
• Anna Dzielak,
• Gerhard Hägele and
• György Keglevich

Beilstein J. Org. Chem. 2016, 12, 1493–1502, doi:10.3762/bjoc.12.146

• Chemistry, Heinrich-Heine-University Düsseldorf, 40225 Düsseldorf, Germany 10.3762/bjoc.12.146 Abstract A practical method was elaborated for the synthesis of (aminomethylene)bisphosphine oxides comprising the catalyst- and solvent-free microwave-assisted three-component condensation of primary amines

• [15][16][17][18][19][20][21]. The use of crown ethers with an NH unit, or thienopyrimidine amines as starting materials was also reported [22][23]. The catalyst- and solvent-free methods required long reaction times and/or a high temperature [6][7][8][9][10][11][12][13][14][21][22][23]. Ionic liquids

Multicomponent reactions: A simple and efficient route to heterocyclic phosphonates

• Mohammad Haji

Beilstein J. Org. Chem. 2016, 12, 1269–1301, doi:10.3762/bjoc.12.121

• substituted isatins 30 with aniline (32) and dimethyl- or diethyl phosphite under solvent-free conditions in the presence of magnetic Fe3O4 nanoparticle-supported phosphotungstic acid as a recyclable catalyst at 80 °C furnished α-aminophosphonates 33 in yields from 80% to 98% depending on the reaction time

• -methyl-3-formylchromone (75) with some 1,2-, 1,3- and 1,4-bi-nucleophiles and diethyl phosphonate under solvent-free conditions have been developed by E. Ali et al. [46]. The resulting α-aminophosphonate intermediates 77 and 80 were non-isolable and interconverted to the corresponding heterocyclic

• 1,2-dihydropyridine-3-phosphonate 259. Yavari et al. have described the phosphorylation of benzothiazole (263) and isoquinoline (246) through a one-pot three-component reaction with activated acetylenes 260 and diphenyl phosphonate (261) under solvent-free conditions at room temperature (Scheme 54

Supported bifunctional thioureas as recoverable and reusable catalysts for enantioselective nitro-Michael reactions

• José M. Andrés,
• Miriam Ceballos,
• Alicia Maestro,
• Isabel Sanz and
• Rafael Pedrosa

Beilstein J. Org. Chem. 2016, 12, 628–635, doi:10.3762/bjoc.12.61

• with chiral bifunctional thioureas looking for a greener process [28], easier recovering and recyclability of the catalyst, and solvent-free reaction conditions. Along these lines, we have recently reported the bottom-up synthesis of polymeric thioureas [29], and the anchorage of (L)-valine-derived

• (1a) under solvent-free conditions in a ball mill providing the addition product 7aa in excellent yield, total diastereoselectivity, and very good enantioselectitvity. Experimental General remarks 13C NMR (126 MHz) and 1H NMR (500 MHz) spectra were recorded in CDCl3 as the solvent. Chemical shifts for

(Thio)urea-mediated synthesis of functionalized six-membered rings with multiple chiral centers

• Giorgos Koutoulogenis,
• Nikolaos Kaplaneris and
• Christoforos G. Kokotos

Beilstein J. Org. Chem. 2016, 12, 462–495, doi:10.3762/bjoc.12.48

• screening of various catalysts, organocatalyst 43 and 4-methoxybenzoic acid as a cocatalyst, was identified as the optimum for the reaction of (E)-2-nitroallyl acetate 40 with cyclohexanone 41 to provide nitrobicyclo[3.3.1]nonan-9-one 42, in solvent-free conditions. This reaction provides products with

Enabling technologies and green processes in cyclodextrin chemistry

• Giancarlo Cravotto,
• Marina Caporaso,
• Laszlo Jicsinszky and
• Katia Martina

Beilstein J. Org. Chem. 2016, 12, 278–294, doi:10.3762/bjoc.12.30

• CD derivatives, CD grafted materials and polymers. Mechanochemical methods have successfully furnished greener, solvent-free syntheses and efficient complexation, while flow microreactors may well improve the repeatability and optimization of critical synthetic protocols. Keywords: ball milling

• structure-dependent behaviour, which can be either favourable or unfavourable, because of the solid-state structure. Although BM reactions are often said to be solvent-free, some inert solvents can also be used particularly when the reagent mass ratio is very high. A lack of solvent(s) may suggest that ball

Simple activation by acid of latent Ru-NHC-based metathesis initiators bearing 8-quinolinolate co-ligands

• Julia Wappel,
• Roland C. Fischer,
• Luigi Cavallo,
• Christian Slugovc and
• Albert Poater

Beilstein J. Org. Chem. 2016, 12, 154–165, doi:10.3762/bjoc.12.17

• outstanding solubility in nonpolar solvents such as n-pentane as well as in nonpolar substrates such as dicylopentadiene (DCPD). Both properties are desired properties for employing the compounds as initiators in solvent free polymerizations. In case of the reaction of M31 with 5,7-dichloro-8-hydroxyquinoline

• latency towards cyclic olefins. The new pre-catalysts can be triggered using HCl. Due to their extremely good solubility in apolar solvents and substrates they are useful candidates for solvent-free polymerizations. Their latency also makes them very suitable for the polymerization of strained monomers

Enantioselective additions of copper acetylides to cyclic iminium and oxocarbenium ions

• Jixin Liu,
• Srimoyee Dasgupta and
• Mary P. Watson

Beilstein J. Org. Chem. 2015, 11, 2696–2706, doi:10.3762/bjoc.11.290

• report is the first and only example to date of alkynylation of an imine or iminium ion to form a chiral tetrasubstituted center with high ee. Enantioselective, copper-catalyzed alkynylations have also been accomplished under solvent-free conditions. In 2013, Su and co-workers established that the CDC

• reaction of N-aryltetrahydroisoquinolines and alkynes can be accomplished under high-speed ball-milling conditions with copper balls (Scheme 9) [31]. Under these solvent-free reaction conditions, isoquinolines 28 were formed more quickly than the in-solvent reactions previously reported, but the ee’s are

Efficient synthetic protocols for the preparation of common N-heterocyclic carbene precursors

• Morgan Hans,
• Jan Lorkowski,
• Albert Demonceau and
• Lionel Delaude

Beilstein J. Org. Chem. 2015, 11, 2318–2325, doi:10.3762/bjoc.11.252

• and ZnCl2. This Friedel–Crafts alkylation was carried out under solvent-free conditions and afforded high yields of the bulky aniline needed to follow the Arduengo formylative cyclization path. It was originally performed in a sealed tube under autogeneous pressure at 160 °C. We checked that the

Convenient preparation of high molecular weight poly(dimethylsiloxane) using thermally latent NHC-catalysis: a structure-activity correlation

• Stefan Naumann,
• Johannes Klein,
• Dongren Wang and
• Michael R. Buchmeiser

Beilstein J. Org. Chem. 2015, 11, 2261–2266, doi:10.3762/bjoc.11.246

• stable at room temperature over long periods of time (observed for up to 2 years) without decomposition, exclusion of humidity provided. Polymerization experiments with D4 were conducted solvent-free at elevated temperature (80 °C, 16 h), both in presence and absence of an initiator (benzyl alcohol, BnOH

Olefin metathesis in air

• Lorenzo Piola,
• Fady Nahra and
• Steven P. Nolan

Beilstein J. Org. Chem. 2015, 11, 2038–2056, doi:10.3762/bjoc.11.221

• % of Ru at 150 °C in air, under solvent-free conditions for several days, to afford 1,2-bis(silyl)ethenes in moderate to good yields [33]. Reactions without oxygen showed no conversion, highlighting the important role that the latter plays in the activation of the catalyst. In 1992, Grubbs and co

• 2nd generation catalyst (33) and a variation of the latter (66, Figure 8) in the RCM of diethyl diallylmalonate (29) [66]. Reactions were performed with very low catalyst loading (from 2.5 to 0.04 mol %), at 30 °C, under air in nondegassed DCM, nondegassed methyl decanoate and under solvent-free

Investigation on the reactivity of α-azidochalcones with carboxylic acids: Formation of α-amido-1,3-diketones and highly substituted 2-(trifluoromethyl)oxazoles

• Kandasamy Rajaguru,
• Arumugam Mariappan,
• Rajendran Suresh,
• Periasamy Manivannan and
• Shanmugam Muthusubramanian

Beilstein J. Org. Chem. 2015, 11, 2021–2028, doi:10.3762/bjoc.11.219

• temperature, it affords highly substituted 2-(trifluoromethyl)oxazoles. These flexible transformations proceed under solvent free conditions in good to excellent yields without any catalyst. Keywords: α-amido-1,3-diketones; α-azidochalcones; carboxylic acids; 2H-azirines; oxazoles; Introduction α

Aerobic addition of secondary phosphine oxides to vinyl sulfides: a shortcut to 1-hydroxy-2-(organosulfanyl)ethyl(diorganyl)phosphine oxides

• Svetlana F. Malysheva,
• Alexander V. Artem’ev,
• Nina K. Gusarova,
• Nataliya A. Belogorlova,
• Alexander I. Albanov,
• C. W. Liu and
• Boris A. Trofimov

Beilstein J. Org. Chem. 2015, 11, 1985–1990, doi:10.3762/bjoc.11.214

• Chemistry, National Dong Hwa University, Hualien 97401, Taiwan 10.3762/bjoc.11.214 Abstract Secondary phosphine oxides react with vinyl sulfides (both alkyl- and aryl-substituted sulfides) under aerobic and solvent-free conditions (80 °C, air, 7–30 h) to afford 1-hydroxy-2-(organosulfanyl)ethyl(diorganyl

• addition of P–H species to the C=C bonds readily proceeds in the absence of any catalyst or initiator (Scheme 1). The reactions occur under mild solvent-free conditions (70–80 °C, inert atmosphere, 3–15 h) to chemo- and regioselectively furnish the anti-Markovnikov adducts in excellent yields (up to 99

Robust bifunctional aluminium–salen catalysts for the preparation of cyclic carbonates from carbon dioxide and epoxides

• Yuri A. Rulev,
• Zalina Gugkaeva,
• Victor I. Maleev,
• Michael North and
• Yuri N. Belokon

Beilstein J. Org. Chem. 2015, 11, 1614–1623, doi:10.3762/bjoc.11.176

• salts and increasing the steric hindrance around the ammonium salts. Herein, we report the synthesis of two aluminium–salen complexes incorporating quaternary ammonium salts directly attached to the salen ligand and their catalytic activities for the coupling of epoxides and carbon dioxide under solvent

• free conditions. Catalyst recycling experiments are also reported and show the robustness of this system. Results and Discussion The preparation of salen ligands 8a and 8b was conducted according to Scheme 2, starting from tert-butylphenol, which was formylated and then nitrated to produce 5-nitro-3