Continuous proline catalysis via leaching of solid proline

• Suzanne M. Opalka,
• Ashley R. Longstreet and
• D. Tyler McQuade

Beilstein J. Org. Chem. 2011, 7, 1671–1679, doi:10.3762/bjoc.7.197

• homogeneous catalyst can be prepared continuously via reaction with a packed-bed of a catalyst precursor. Specifically, we perform continuous proline catalyzed α-aminoxylations using a packed-bed of L-proline. The system relies on a multistep sequence in which an aldehyde and thiourea additive are passed

• . Keywords: aminoxylation; flow chemistry; heterogeneous catalysis; packed-bed microreactor; proline/thiourea catalysis; Introduction Continuous flow chemistry [1][2][3], performed in small dimension tubing or channels, differs from batch chemistry in that mixing and heat transfer are significantly faster

• combined with nitrosobenzene in the coil, the desired product was not detected by crude 1H NMR analysis (Table 1, entry 1). This indicates that, with this reactor setup, the reaction is too slow without a urea additive to be a viable method. Additionally, flowing thiourea 3b (0.047 M in EtOAc) through the

Synthesis of diverse dihydropyrimidine-related scaffolds by fluorous benzaldehyde-based Biginelli reaction and post-condensation modifications

• Bruno Piqani and
• Wei Zhang

Beilstein J. Org. Chem. 2011, 7, 1294–1298, doi:10.3762/bjoc.7.150

• by the reaction of phenols with perfluorooctanesulfonyl fluoride, by following the reported procedure [13]. Compounds 1 were used as a limiting agent to react with urea/thiourea 2 and acetylacetone 3 for the Biginelli reactions. The reactions were promoted by Yb(OTf)3 as a catalyst [14][15

NMR studies of anion-induced conformational changes in diindolylureas and diindolylthioureas

• Damjan Makuc,
• Jennifer R. Hiscock,
• Mark E. Light,
• Philip A. Gale and
• Janez Plavec

Beilstein J. Org. Chem. 2011, 7, 1205–1214, doi:10.3762/bjoc.7.140

• hydrogen bonds stabilize the PO43− anion. In solution, the thiourea analogues such as compound 2 show significantly lower affinities for oxo-anions than do the urea analogues. We had previously proposed that this may be due to the larger size of the sulfur atom resulting in a lower propensity of these

• anion binding relative to thiourea 2 (the data were supported by the stability constant determinations performed previously and shown in Table 1). The larger sulfur atom can prevent the receptor 2 from adopting a planar conformation, which may reduce the affinity of this receptor for anionic guests

Recent advances in the gold-catalyzed additions to C–C multiple bonds

• He Huang,
• Yu Zhou and
• Hong Liu

Beilstein J. Org. Chem. 2011, 7, 897–936, doi:10.3762/bjoc.7.103

• ee values have been obtained with thiourea-cinchonine [176], chiral carbene [177], BINAP [178][179][180], and BIPHEP [181][182][183][184][185][186][187][188][189][190] analogs. Monge et al. reported a direct asymmetric one-pot synthesis of optically active 2,3-dihydropyrroles from propargyl

• malononitriles 375 and N-Boc-protected imines 374 (Scheme 60) [176]. In the alkyne hydroamination (which is based on a bifunctional organocatalytic Mannich-type reaction, subsequent gold-catalyzed alkyne hydroamination and isomerization) thiourea-based hydrogen bonding organocatalyst 373 and PPh3AuNTf2 proved to

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

• of the enantiomers of hindered enone 46 by addition, oxidation and elimination of a sulfenic acid under basic conditions (Scheme 18) [45]. Xiao and co-workers developed an organocatalytic process for the addition of thiols to nitroalkenes [46]. Using thiourea organocatalyst 48, conjugate addition of

An overview of the key routes to the best selling 5-membered ring heterocyclic pharmaceuticals

• Marcus Baumann,
• Ian R. Baxendale,
• Steven V. Ley and
• Nikzad Nikbin

Beilstein J. Org. Chem. 2011, 7, 442–495, doi:10.3762/bjoc.7.57

Air-stable, recyclable, and time-efficient diphenylphosphinite cellulose-supported palladium nanoparticles as a catalyst for Suzuki–Miyaura reactions

• Qingwei Du and
• Yiqun Li

Beilstein J. Org. Chem. 2011, 7, 378–385, doi:10.3762/bjoc.7.48

• ], N-heterocyclic carbenes [13][14][15], P,O-based ligands [16], bis(thiourea) ligands [17], and thiosemicarbazone [18], etc. However, the separation of the catalyst and ligands from the final product is problematic. In this regard, studies on heterogeneous catalysts have drawn much attention because

Effects of anion complexation on the photoreactivity of bisureido- and bisthioureido-substituted dibenzobarrelene derivatives

• Heiko Ihmels and
• Jia Luo

Beilstein J. Org. Chem. 2011, 7, 278–289, doi:10.3762/bjoc.7.37

• , however, are efficiently transformed to the dibenzosemibullvalene product upon irradiation, presumably by suppressing the self-quenching of the thiourea units in the complex. The association of the ureido-substituted dibenzobarrelene derivative with (S)-mandelate and irradiation of this complex led to the

• latter in solution. For that purpose the dibenzobarrelene chromophore was functionalized with ureido or thioureido substituents, since these functionalities are strong hydrogen bonding donors, which may associate with (chiral) anions [38][39]. Moreover, the versatile use of urea and thiourea derivatives

• -substituted derivatives 1h and 1i have significantly improved solubility in organic solvents; i.e., compound 1h has good solubility in acetone, acetonitrile and alcohols, while thiourea 1i dissolves in most polar organic solvents. Because of their favorable solubility in organic solvents, the dibenzobarrelene

Palladium-catalyzed formation of oxazolidinones from biscarbamates: a mechanistic study

• Benan Kilbas and
• Metin Balci

Beilstein J. Org. Chem. 2011, 7, 246–253, doi:10.3762/bjoc.7.33

• of 6 [18]. Selective reduction of the peroxide linkage in 6 was carried out with thiourea under very mild conditions to give the diol 7 [19]. Since only the oxygen–oxygen bond is broken in this reaction, the configuration at all carbon atoms is preserved. Oxazolidinone 9 was synthesized by two

• than the trans-coupling [23][24], we assigned the exo-configuration to the cyano group in 12. Selective reduction of the peroxide linkages in 12 and 13 with thiourea under very mild conditions afforded the diols 14 and 18a, respectively. For further characterization, the diols were converted to the

• , 56.08; H, 4.67; N, 3.85; S, 8.63. rel-(1R,2S,5R,6S)-2,5-Dihydroxybicyclo[4.1.0]hept-3-ene-7-exo-carbonitrile (14): To a magnetically stirred solution of endoperoxide 12 (1.00 g, 6.71 mmol) in MeOH/CHCl3 solution (30 mL), was added thiourea (513 mg, 6.75 mmol) over a 10 min period at room temperature and

An easy assembled fluorescent sensor for dicarboxylates and acidic amino acids

• Xiao-bo Zhou,
• Yuk-Wang Yip,
• Wing-Hong Chan and
• Albert W. M. Lee

Beilstein J. Org. Chem. 2011, 7, 75–81, doi:10.3762/bjoc.7.11

• Xiao-bo Zhou Yuk-Wang Yip Wing-Hong Chan Albert W. M. Lee Department of Chemistry, Hong Kong Baptist University, Kowloon Tong, Hong Kong SAR, China 10.3762/bjoc.7.11 Abstract Two mesitylene based neutral receptors 1 and 2 bearing two thiourea binding sites were constructed as fluorescent probes

• molecular platform via thiourea formation to give the key intermediate 4 in 70% yield. As a result of steric hindrance, an attempt to make the corresponding bis-thiourea adduct from 3 and 9-aminomethylanthracene was unsuccessful. However, 4 underwent a smooth addition reaction with the structurally less

• charge neutral thiourea-based fluorescent PET sensor motif, which is immune from cross pH interference, was adopted in our approach [28]. The congested mesitylene derivative type of structure built in 1 may confer the molecule with sufficient rigidity favoring its selective binding with guest molecules

A new fluorescent chemosensor for fluoride anion based on a pyrrole–isoxazole derivative

• Zhipei Yang,
• Kai Zhang,
• Fangbin Gong,
• Shayu Li,
• Jun Chen,
• Jin Shi Ma,
• Lyubov N. Sobenina,
• Albina I. Mikhaleva,
• Guoqiang Yang and
• Boris A. Trofimov

Beilstein J. Org. Chem. 2011, 7, 46–52, doi:10.3762/bjoc.7.8

• reported in recent years, those employing polarized NH groups as anion-binding motifs have attracted considerable attention. Typical examples are charge neutral receptors containing pyrrole, amide, indolocarbazole, guanidium, imidazolium and urea/thiourea moieties. Usually, the anions are recognized via H

• -bonding, which is not easy to differentiate from deprotonation of protons on the receptor-NH [4][5]. Some urea/thiourea-containing receptors could particularly recognize Y-shaped oxoanions by H-bonding and more basic anions such as fluoride by deprotonation. Fluoride is primarily used for prevention of

• advantageous to develop high-effective sensors that can detect fluoride anion in food and animal feed. In this work, we report a new fluoride receptor 1 (Figure 1), 3-amino-5-(4,5,6,7-tetrahydro-1H-indol-2-yl)isoxazole-4-carboxamide [9], which contains receptive groups toward anions and no urea/thiourea

Chain stopper engineering for hydrogen bonded supramolecular polymers

• Thomas Pinault,
• Bruno Andrioletti and
• Laurent Bouteiller

Beilstein J. Org. Chem. 2010, 6, 869–875, doi:10.3762/bjoc.6.102

• viscosity of these solutions can be controlled by adding monofunctional compounds, which interact with the chain extremities: chain stoppers. We have synthesized new substituted ureas and thioureas and tested them as chain stoppers for a bis-urea based supramolecular polymer. In particular, the bis-thiourea

• assemblies as a hydrogen bond donor. For this purpose, we synthesized the bis-thiourea S4, from the corresponding bis-thioisocyanate, because thioureas are known to be strong hydrogen bond donors and weak hydrogen bond acceptors [34][35]. Before evaluating the chain stopper efficiency of these compounds, i.e

• ., their interaction with EHUT, their self-association was probed. Self-association of bis-thiourea Chain stoppers S2 and S3 cannot self-associate because they contain only hydrogen bond acceptors, however this is not the case for S4, and it is of interest to determine the conditions under which S4 can be

Molecular recognition of organic ammonium ions in solution using synthetic receptors

• Andreas Späth and
• Burkhard König

Beilstein J. Org. Chem. 2010, 6, No. 32, doi:10.3762/bjoc.6.32

(Pseudo)amide-linked oligosaccharide mimetics: molecular recognition and supramolecular properties

• José L. Jiménez Blanco,
• Fernando Ortega-Caballero,
• Carmen Ortiz Mellet and
• José M. García Fernández

Beilstein J. Org. Chem. 2010, 6, No. 20, doi:10.3762/bjoc.6.20

• thiourea, urea and guanidine. In this review we summarise the advances over the last decade in the synthesis of oligosaccharide mimetics that possess amide and pseudoamide linkages, as well as studies focussing on their supramolecular and recognition properties. Keywords: carbopeptoids; glycoclusters

• , carbamate and thiourea-linked sugars The replacement of amide groups by pseudoamide (NH–C = X)–Y; X, Y = O, N, S) has been widely used in peptide chemistry to induce well-defined secondary structures. In carbohydrate chemistry, the incorporation of pseudoamide-type intersaccharide linkages has an additional

• pseudooligosaccharides having cyanamide, urea and thiourea-linkages via the Staudinger reaction have been reported [69][70]. In our group, the carbodiimide approach was used to prepare calystegine B2 analogues with the urea-linked disaccharide structure (Figure 15). These compounds, however, did not show inhibitory

Convergent syntheses of Le^X analogues

• An Wang,
• Jenifer Hendel and
• France-Isabelle Auzanneau

Beilstein J. Org. Chem. 2010, 6, No. 17, doi:10.3762/bjoc.6.17

• glucosamine acceptors. The disaccharide 24 was further used in the preparation of the Lex analogues 1–3. Preparation of protected Lex analogues. The chloroacetate in disaccharide 24 was removed with thiourea (C5H5N/EtOH, 70 °C) to give the acceptor disaccharide 28 (61%), which was then fucosylated with the

• (OCH2CH2); 26.44, 25.14 (OCH2CH2CH2CH2); 23.25, 20.64, 20.58, 20.48, 20.48 (CH3CO). HRESIMS Calcd for C37H52Cl2NO16 [M+H]+ 836.2663, found 836.2634. 6-Chlorohexyl 2-acetamido-4-O-(2,3,4,6-tetra-O-acetyl-β-D-galactopyranosyl)-6-O-benzyl-2-deoxy-β-D-glucopyranoside (28). Thiourea (162 mg, 2.13 mmol, 6.0

Synthesis of a new class of aminocyclitol analogues with the conduramine D-2 configuration

• Latif Kelebekli,
• Yunus Kara and
• Murat Celik

Beilstein J. Org. Chem. 2010, 6, No. 15, doi:10.3762/bjoc.6.15

• . Photooxygenation of trans-7,8-diacetoxy- and cis-7,8-dichlorobicyclo[4.2.0]octa-2,4-diene afforded the bicyclic endoperoxides. Reduction of the latter with thiourea followed by a Pd(0) catalyzed ionization/cyclization reaction gave the corresponding oxazolidinone derivatives. Oxidation of the double bond with

• cyclooctatetraene (8) by the addition of mercury(II) acetate [31]. Tetraphenylporphyrin sensitized photooxygenation of diacetoxydiene 9 with singlet oxygen gave the expected endoperoxide 10. Reduction of the peroxide bond in 10 was performed with thiourea under very mild conditions to give the cis-diol 11 in 99

• the peroxide bond in 20 with thiourea under very mild conditions gave the cis-diol 21 in 95% yield. Diol 21 in THF was treated with 2 equiv of p-toluenesulfonyl isocyanate to give the intermediate bis-carbamate 22 which was then treated as described above for 12 with the same Pd(0) catalyst to afford

Synthesis of indolo[3,2-b]carbazole-based new colorimetric receptor for anions: A unique color change for fluoride ions

• Ajit Kumar Mahapatra,
• Giridhari Hazra and
• Prithidipa Sahoo

Beilstein J. Org. Chem. 2010, 6, No. 12, doi:10.3762/bjoc.6.12

• supramolecular chemistry [1][2]. Most of the synthetic chemosensors generally involve covalent linking of an optical-signaling chromophoric fragment to a neutral anion receptor containing urea [3], thiourea [4], amide [5], phenol [6][7], or pyrrole [8] subunits, which can provide one or more H-bond donor sites

Self-association of an indole based guanidinium-carboxylate-zwitterion: formation of stable dimers in solution and the solid state

• Carolin Rether,
• Wilhelm Sicking,
• Roland Boese and
• Carsten Schmuck

Beilstein J. Org. Chem. 2010, 6, No. 3, doi:10.3762/bjoc.6.3

• -indole-2-carboxylate 3 was reduced by reaction with hydrogen in the presence of Pd/C to provide the amine 4 in a yield of 98%. For the next stept, first, thiourea was N-Boc-protected at both amino-functions following a literature procedure [20]. Thiourea was deprotonated with sodium hydride and

• afterwards reacted with di-tert-butyl dicarbonate to give the di-Boc-protected thiourea 5 in 79% yield. The di-Boc-protected thiourea 5 was then reacted with the amine 4 in the presence of Mukaiyama’s reagent [21] and triethylamine as a base, which provided 6 in a yield of 71% [22]. Deprotection of the two

• (w), 2939 (w), 1668 (s), 1250 (s), 1215(s) cm−1; HR-MS (ESI) calcd for [M+H]+: 205.0972; found 205.0979. N,N’-Di-(tert-butoxycarbonyl)thiourea (5): To a stirred solution of thiourea (570 mg, 7.50 mmol) in dry tetrahydrofuran (150 mL) sodium hydride (1.35 g, 33.80 mmol, 60% in mineral oil) was added

Synthesis and enzymatic evaluation of 2- and 4-aminothiazole- based inhibitors of neuronal nitric oxide synthase

• Graham R. Lawton,
• Haitao Ji,
• Pavel Martásek,
• Linda J. Roman and
• Richard B. Silverman

Beilstein J. Org. Chem. 2009, 5, No. 28, doi:10.3762/bjoc.5.28

• diastereomers was formed, but both were oxidized to α-bromoketone 12. Condensation with thiourea gave the 2-aminothiazole (13). Diprotection of the amine with Boc groups and deprotection of the TBS ether gave trans-alcohol 15. A Mitsunobu reaction was used to install a nitrogen atom in the form of a phthalimide

• in the 5-position could have contributed to binding to restore some of the lost potency. Conclusion 2-Aminothiazole-based nNOS inhibitor 3 was synthesized via a condensation reaction between thiourea and the appropriate α-bromoketone. However, the inhibitor was less potent than the aminopyridine lead

• equiv, THF, −78 °C; ii) 5, THF, −78 °C to rt. Assembly of 2-aminothiazole fragment. i) AllylMgBr, ether, 0 °C, 15 min.; ii) TBSCl, imidazole, DMF, 35 °C, 16 h; iii) m-CPBA, rt, 48 h; iv) LiBr, AcOH, THF, rt, 16h; v) (COCl)2, DMSO, TEA, CH2Cl2, −78 °C, 1 h; vi) thiourea, EtOH, reflux, 5 h; vii) Boc2O

Zeolite catalyzed solvent- free one-pot synthesis of dihydropyrimidin- 2(1H)-ones – A practical synthesis of monastrol

• Mukund G. Kulkarni,
• Sanjay W. Chavhan,
• Mahadev P. Shinde,
• Dnyaneshwar D. Gaikwad,
• Ajit S. Borhade,
• Attrimuni P. Dhondge,
• Yunnus B. Shaikh,
• Vijay B. Ningdale,
• Mayur P. Desai and
• Deekshaputra R. Birhade

Beilstein J. Org. Chem. 2009, 5, No. 4, doi:10.3762/bjoc.5.4

• monastrol, a potent inhibitor of kinesin Eg5. Keywords: Biginelli reaction; DHPMs; neat; MCR; zeolite; Introduction The Biginelli reaction is a well-known multicomponent reaction involving a one-pot cyclocondensation of an aldehyde, β-ketoester and urea/thiourea [1][2][3]. Multicomponent reactions (MCRs

• ethyl acetoacetate, an aromatic aldehyde and urea under strongly acidic conditions furnished the corresponding DHPMs [1]. Unfortunately this method led to low to moderate yields of the desired DHPMs, particularly when substituted aromatic or aliphatic aldehydes and thiourea were employed [14][15][16][17

• aliphatic aldehydes and thiourea were used low yields of DHPMs were realized. Results and Discussion We herein report a one-pot synthesis of DHPMs using a catalytic amount of zeolite under solvent-free conditions. In our quest to bring about the Biginelli reaction, we attempted the reaction using zeolite

Synthesis of 2-substituted 9-oxa-guanines {5-aminooxazolo[5,4-d]pyrimidin- 7(6H)-ones} and 9-oxa-2-thio- xanthines {5-mercaptooxazolo[5,4-d]pyrimidin- 7(6H)-ones}

• Subrata Mandal,
• Wen Tai Li,
• Yan Bai,
• Jon D. Robertus and
• Sean M. Kerwin

Beilstein J. Org. Chem. 2008, 4, No. 26, doi:10.3762/bjoc.4.26

• below) with ammonia in methanol fails to afford 2a. The thiourea 6b and its analog 6a, which was prepared from aminooxazole 3a in 51% yield, were also subjected to cyclization in the presence of ethanolic KOH to afford the 5-mercaptooxazolo[5,4-d]pyrimidin-7(6H)-ones 7a,b (Figure 4). Further elaboration

Perhalogenated pyrimidine scaffolds. Reactions of 5-chloro- 2,4,6-trifluoropyrimidine with nitrogen centred nucleophiles

• Emma L. Parks,
• Graham Sandford,
• John A. Christopher and
• David D. Miller

Beilstein J. Org. Chem. 2008, 4, No. 22, doi:10.3762/bjoc.4.22

• , many pyrimidine derivatives have been used for various medicinal applications (Figure 1) [1][2][3]. Synthesis of pyrimidine rings most commonly involves cyclocondensation reactions of amidine, guanidine or thiourea derivatives with either 1,3-diketone or 1,3-diester systems [4][5]. However, many of

The first organocatalytic carbonyl- ene reaction: isomerisation- free C-C bond formations catalysed by H-bonding thio- ureas

• Matthew L. Clarke,
• Charlotte E. S. Jones and
• Marcia B. France

Beilstein J. Org. Chem. 2007, 3, No. 24, doi:10.1186/1860-5397-3-24

• of highly activated enophiles can be catalysed by H-bonding thio-ureas to give tertiary alcohols in high yields without extensive isomerisation side products. An asymmetric variant of this reaction was realised using a chiral thiourea but was limited by low enantioselectivity (up to 33% e.e.) and low

• was carried out (Scheme 2 and Table 1). N,N'-di [3,5-bis(trifluoromethyl)phenyl]thiourea 5,[18], emerged as by far the most active promoter for this reaction. The catalyst was used at 20 mol % loading and compared against a control reaction with no catalyst. Products were isolated by chromatography

• , but reactions run at both -20 and 0°C using 10 and 25 mol % catalyst respectively gave good yields and only ~30% e.e (Scheme 3 and Table 2). A reaction carried out with stoichiometric amounts of chiral thiourea also gave ~30% e.e. suggesting this is the true selectivity for this reaction with this

Efficient synthesis of 5-substituted 2-aryl- 6-cyanoindolizines via nucleophilic substitution reactions

• Eugene V. Babaev,
• Natalya I. Vasilevich and
• Anna S. Ivushkina

Beilstein J. Org. Chem. 2005, 1, No. 9, doi:10.1186/1860-5397-1-9

• achieved with ethyl mercaptoacetate in ethanolic sodium hydroxide. Interestingly, 2a reacted also with thiourea in refluxing butanol giving indolizinethione 6. The product 6 seems to be the result of decomposition of unstable isothiouronium salt, and the process resembles the known conversion of 2-chloro-3