Synthesis and self-assembly of 1-deoxyglucose derivatives as low molecular weight organogelators

• Guijun Wang,
• Hao Yang,
• Sherwin Cheuk and
• Sherman Coleman

Beilstein J. Org. Chem. 2011, 7, 234–242, doi:10.3762/bjoc.7.31

• are an important class of molecules. The supramolecular gels formed by carbohydrate derived low molecular weight gelators are interesting soft materials that show great potential for many applications. Previously, we have synthesized a series of methyl 4,6-O-benzylidene-α-D-glucopyranoside derivatives

• series of methyl 4,6-O-benzylidene-α-D-glucopyranoside (1) derivatives (Figure 1), including esters and carbamates with different functional groups. Several of these compounds proved to be effective gelators for organic solvents and aqueous solutions [34][35][36][37]. We found that the structures of the

Synthesis of Ru alkylidene complexes

• Renat Kadyrov and
• Anna Rosiak

Beilstein J. Org. Chem. 2011, 7, 104–110, doi:10.3762/bjoc.7.14

• variety of other alkylidene complexes. Results and Discussion Van der Schaaf and co-workers published in 2000 a simple one-pot procedure for the synthesis of the ruthenium benzylidene complex (iPr3P)2Cl2Ru=CHPh [8]. It was mentioned that also (PCy3)2Cl2Ru=CHPh could be similarly prepared. To our surprise

• , by following exactly the given protocol using DBU as base, a mixture of the desired benzylidene complex (PCy3)2Cl2Ru=CHPh together with the vinylidene complex (PCy3)2Cl2Ru=C=CHPh was obtained. Obviously, the last complex originated from reaction of an intermediate hydride species with phenyl

• NMR: δ = 296.40 (d, J = 113.4), 157.46, 140.27, 32.08 (t, J = 9.1); 30.28, 29.99, 29.70; 27.93 (t, J = 5.0), 27.93, 26.67, 22.97, 21.45. Toluene 137.82, 129.05, 128.24, 125.31, 21.41. Dichlorobis(tricyclohexylphosphine)(benzylidene)ruthenium(II) (1d): The product (violet solid) was prepared according

Olefin metathesis in nano-sized systems

• Didier Astruc,
• Abdou K. Diallo,
• Sylvain Gatard,
• Liyuan Liang,
• Cátia Ornelas,
• Victor Martinez,
• Denise Méry and
• Jaime Ruiz

Beilstein J. Org. Chem. 2011, 7, 94–103, doi:10.3762/bjoc.7.13

• still remained a challenge. The difficulty resided in the need to sustain both metathesis activity and stability of the metallodendrimer. Thus, we selected the ruthenium family of catalysts and designed metallodendrimers containing ruthenium-benzylidene fragments located at the dendrimer periphery and

• ][20] and Leitner [20] had demonstrated the metathesis activity of cis-bis-phosphine ruthenium benzylidene catalysts. We therefore used Reetz’s bis-phosphines derived from the commercial polyamine DSM dendrimers [21]. These dendritic bis-phosphines are useful and versatile in metallodendritic catalysis

• ] catalyzed by [FeICp(η6-C6Me6)] leading to the substitution of a carbonyl of the [Ru3(CO)12] by a dendritic phosphine on each tether [22]. Related dendritic bis-phosphines with two cyclohexyl groups on each phosphorus were decorated with ruthenium benzylidene metathesis functions using Hoveyda’s ruthenium

The cross-metathesis of methyl oleate with cis-2-butene-1,4-diyl diacetate and the influence of protecting groups

• Arno Behr and
• Jessica Pérez Gomes

Beilstein J. Org. Chem. 2011, 7, 1–8, doi:10.3762/bjoc.7.1

• observed between the benzylidene catalyst [Ru]-1 and its indenylidene counterpart [Ru]-3. The self-metathesis of methyl oleate (1) mentioned above could not be suppressed. Other side-reactions were not observed. No double-bound isomerisation took place. Promising results were obtained with catalysts

• content (91.4% oleic acid) was obtained from Emery Oleochemicals. cis-2-Butene-1,4-diol (8) (97%), solvents and reagents were purchased from Sigma-Aldrich. Benzylidene ruthenium catalysts [Ru]-1 and [Ru]-2 were obtained from Sigma-Aldrich and the remaining indenylidene ruthenium catalysts [Ru]-3–[Ru]-8

The allylic chalcogen effect in olefin metathesis

• Yuya A. Lin and
• Benjamin G. Davis

Beilstein J. Org. Chem. 2010, 6, 1219–1228, doi:10.3762/bjoc.6.140

• generation catalyst (3), where the catalytically active species is stabilized by a hemilabile benzylidene ligand. The activating effect of the allylic hydroxy group in RCM is further supported by the dramatic decrease in conversion when the free OH group was protected (i.e., R ≠ H, R′ = Me) in pathway B

The catalytic performance of Ru–NHC alkylidene complexes: PCy₃ versus pyridine as the dissociating ligand

• Stefan Krehl,
• Diana Geißler,
• Sylvia Hauke,
• Oliver Kunz,
• Lucia Staude and
• Bernd Schmidt

Beilstein J. Org. Chem. 2010, 6, 1188–1198, doi:10.3762/bjoc.6.136

• benzylidene complexes bearing a tricyclohexylphosphine or a pyridine ligand in ring closing metathesis (RCM), cross metathesis, and ring closing enyne metathesis (RCEYM) reactions is compared. While the PCy3 complexes perform significantly better in RCM and RCEYM reactions than the pyridine complex, all

• alkylidene moiety originates from 2,2-diphenylcyclopropene, was soon replaced by the second version B [9], since the benzylidene ligand is more conveniently available from phenyldiazomethane. The obvious disadvantages of handling non-stabilized diazo compounds stimulated investigations into the use of

• robustness and tolerance towards several functional groups [19]. A third major topic in catalyst development has been the variation of the dissociating “placeholder”-ligand. In this respect, the introduction and further improvement of hemilabile benzylidene ligands by Hoveyda [20], Grela[21] and Blechert [22

Tandem catalysis of ring-closing metathesis/atom transfer radical reactions with homobimetallic ruthenium–arene complexes

• Yannick Borguet,
• Xavier Sauvage,
• Guillermo Zaragoza,
• Albert Demonceau and
• Lionel Delaude

Beilstein J. Org. Chem. 2010, 6, 1167–1173, doi:10.3762/bjoc.6.133

• synthesis [7][8][9][10]. The monometallic ruthenium–benzylidene complex [RuCl2(=CHPh)(PCy3)2] (3) and its second- or even third-generation analogues developed by Grubbs and co-workers are prominent examples of catalyst precursors that were applied to olefin metathesis in tandem with ATRA [11], ATRC [11][12

• mixture revealed the presence of at least five different ruthenium–phosphine species in solution. Unless all these species are able to promote the ATRC reaction, the catalytic switch required to complete the tandem process should therefore be far less efficient with monometallic benzylidene complex 3 than

• (Table 1, entry 1). This experiment confirmed the necessity of mediating the transformation of 5 into 6 with a transition metal complex. Unlike the Grubbs benzylidene catalyst 3, bimetallic compound 1 was an efficient catalyst precursor for this reaction (Table 1, entries 2 and 4). Opstal and Verpoort

New library of aminosulfonyl-tagged Hoveyda–Grubbs type complexes: Synthesis, kinetic studies and activity in olefin metathesis transformations

• Etienne Borré,
• Frederic Caijo,
• Christophe Crévisy and
• Marc Mauduit

Beilstein J. Org. Chem. 2010, 6, 1159–1166, doi:10.3762/bjoc.6.132

• of the active species (due to NHC), these catalysts still required a high catalytic loading (up to 20 mol % in some cases [7]). Later, Hoveyda synthesized a recyclable phosphine-free precatalyst (2a) [8] based on a release/return concept of the benzylidene ether fragment. Electronic or steric

• between the SIPr unit and the electronic activation of the benzylidene fragment. Conclusion A new library of Hoveyda type catalysts bearing aminosulfonyl functions has been synthesized. Their activity profiles have been investigated through kinetic studies and through evaluation of a group of substrates

• -dimesitylimidazolidin-2-ylidene)(2-isopropoxy-5-(trifluoromethylsulfonamido)benzylidene)ruthenium(II) chloride (4a): Following the general procedure using the ligand 6a, complex 4a was isolated as a green powder (62 mg, 73%). 1H (400 MHz, CDCl3, δ): 1.13 (d, J = 6.1 Hz, 6H, 2 CH3), 2.34 (s, 18H, 6 CH), 4.08 (s, 4H, 2

About the activity and selectivity of less well-known metathesis catalysts during ADMET polymerizations

• Hatice Mutlu,
• Lucas Montero de Espinosa,
• Oĝuz Türünç and
• Michael A. R. Meier

Beilstein J. Org. Chem. 2010, 6, 1149–1158, doi:10.3762/bjoc.6.131

• attractive alternative to the Ru–benzylidene compounds. It was shown that all indenylidene Ru-catalysts were more robust under the demanding reaction conditions (temperature and functional group tolerance) compared to their Ru–benzylidene counterparts [32][33][34][35][36][37][38][39][40]. In addition, good

• ]. Research performed by Monsaert et al. illustrated that C2 enables high conversions in ROMP of 1,5-cyclooctadiene, and conversions of up to 80% in the RCM of diethyl diallylmalonate in short reaction times (5–10 min), thus being superior to the benzylidene analogue [35]. Recently, a useful and practical

• structural regularity can be obtained by with BQ. Conclusion The indenylidene Ru-complexes provided an attractive alternative to the benzylidene compounds and allowed polyesters of up to 17000 Da via ADMET polymerization to be prepared, even at elevated temperatures with enhanced activity. Unfortunately, the

Backbone tuning in indenylidene–ruthenium complexes bearing an unsaturated N-heterocyclic carbene

• César A. Urbina-Blanco,
• Xavier Bantreil,
• Hervé Clavier,
• Alexandra M. Z. Slawin and
• Steven P. Nolan

Beilstein J. Org. Chem. 2010, 6, 1120–1126, doi:10.3762/bjoc.6.128

• precursors [22] and their straightforward synthesis. The higher steric hindrance and improved electronic donor ability of the indenylidene moiety also contribute to the observed increased stability compared to benzylidene congeners. This family of complexes displayed interesting stability even when forcing

Light-induced olefin metathesis

• Yuval Vidavsky and
• N. Gabriel Lemcoff

Beilstein J. Org. Chem. 2010, 6, 1106–1119, doi:10.3762/bjoc.6.127

• respective yields and the required reaction times. In line with the development of ruthenium benzylidene initiators [66][67], the phosphane ligand was replaced by an N-heterocyclic carbene (NHCs) in the photoactivated precatalysts. Accordingly, Noels et al. [68][69] synthesised a range of NHC substituted

• , photoactivation of sulfur-chelated ruthenium benzylidene complexes was found to depend on the generation of the active trans-dichloro isomer via 14-electron intermediates. The design of a photoswitchable system was based on the fact that the latent isomer (cis-dichloro) was thermodynamically more stable than its

• . Ruthenium complexes with p-cymene and NHC ligands. Photoactivated cationic ROMP precatalysts. Different monomers for PROMP. Light-induced cationic catalysts for ROMP. Sulfur chelated ruthenium benzylidene pre-catalysts for olefin metathesis. Photoacid generators for photoinduced metathesis. Encapsulated 39

Halide exchanged Hoveyda-type complexes in olefin metathesis

• Julia Wappel,
• César A. Urbina-Blanco,
• Mudassar Abbas,
• Jörg H. Albering,
• Robert Saf,
• Steven P. Nolan and
• Christian Slugovc

Beilstein J. Org. Chem. 2010, 6, 1091–1098, doi:10.3762/bjoc.6.125

• (Scheme 1). M2 is a relatively more economic alternative to G2, bearing an indenylidene instead of a benzylidene ligand [22][23][24]. Adopting Hoveyda’s protocol for obtaining 1 from G2 [25] and using 1-isopropoxy-2-(prop-1-en-1-yl)benzene as the carbene precursor, 1 can be obtained in 78% yield

Synthesis of 6-PEtN-α-D-GalpNAc-(1–>6)-β-D-Galp-(1–>4)-β-D-GlcpNAc-(1–>3)-β-D-Galp-(1–>4)-β-D-Glcp, a Haemophilus influenzae lipopolysacharide structure, and biotin and protein conjugates thereof

• Andreas Sundgren,
• Martina Lahmann and
• Stefan Oscarson

Beilstein J. Org. Chem. 2010, 6, 704–708, doi:10.3762/bjoc.6.80

• designed and synthesised (Scheme 1). Reductive ring opening, with BH3/Bu2BOTf [12], of the benzylidene acetal in the known ethyl thioglycoside 1 [13] gave the 6-hydroxy derivative 2 (85%), which was then silylated to afford donor 3 (90%). Regioselective silylation of the 2-azido-galactose ethyl

• are often used as acceptors for regioselective glycosidations in the 3-position. However, the selectivity is dependent on the donor, promoter and conditions employed [15], e.g., it has been shown that donors containing a 4,6-O-benzylidene acetal can give a mixture of products [16]. Hence, the diol 7

• [17] was transformed using benzaldehyde dimethyl acetal and camphorsulfonic acid stereo-selectively into the corresponding 3,4-endo-benzylidene derivative 8 which was in turn converted to the 3-hydroxy derivative 9 by NaBH3CN/HCl-mediated reductive opening of the acetal ring [18] (80% overall yield

Synthesis and crossover reaction of TEMPO containing block copolymer via ROMP

• Olubummo Adekunle,
• Susanne Tanner and
• Wolfgang H. Binder

Beilstein J. Org. Chem. 2010, 6, No. 59, doi:10.3762/bjoc.6.59

• (benzylidene)] G1 (PCy3 = tricyclohexylphosphine), [(H2IMes)(PCy3)Cl2Ru(benzylidene)] G2 (H2IMes = 1,3-bis(mesityl)-2-imidazolidinylidene), [(H2IMes)(py)2Cl2Ru(benzylidene)] G3 (py = pyridine or 3-bromopyridine) and Umicore type initiators [(PCy3)2Cl2Ru(3-phenylinden-1-ylidene)] U1 (PCy3

• polymer synthesis. Alternatively, Grubbs’ third generation catalyst G3 introduced by Grubbs et al. [10] has an ultrafast initiating ruthenium benzylidene. The rate of reaction of G3 with ethyl vinyl ether thus is six orders of magnitude higher than for G2 [10], leading to a faster initiation and often

• lower polydispersities of the resulting polymers. Recently, structural variations of G1–G3 catalysts generated a new series of catalysts U1–U3 bearing indenyl-carbenes instead of benzylidene-carbenes. These new catalysts are now commercially available and are well known as the Umicore catalysts (NEOLYST

Bis(oxazolines) based on glycopyranosides – steric, configurational and conformational influences on stereoselectivity

• Tobias Minuth and
• Mike M. K. Boysen

Beilstein J. Org. Chem. 2010, 6, No. 23, doi:10.3762/bjoc.6.23

• have introduced new glucosamine-derived bis(oxazolines) 2a–c with uniform protective groups on all oxygen functions [19][20][21] and derivatives 3a–f with cyclic 4,6-O-benzylidene protection as well as various other 3-O-substituents that differ in steric demand and electronic nature [20][21]. These

• conformation of the pyranose scaffold – a twist conformation for ligands 2a–c without 4,6-O-benzylidene protection (Scheme 1, conformer A) and a partially chair-like conformation for ligands 3a–f (Scheme 1, conformer B) fixed by the annulated 4,6-O-benzylidene group – has a direct impact on the

• presence of 15-crown-5 [27][28] to afford 10 in similar yields as the oxidation-reduction sequence (Scheme 2). After deprotection of the phthalimide (phthN) [29], the free amine 11 was transformed into the 4,6-O-benzylidene protected ligand by our standard protocol for the preparation of carbohydrate bis

Chemical synthesis using enzymatically generated building units for construction of the human milk pentasaccharides sialyllacto-N-tetraose and sialyllacto-N-neotetraose epimer

• Dirk Schmidt and
• Joachim Thiem

Beilstein J. Org. Chem. 2010, 6, No. 18, doi:10.3762/bjoc.6.18

• ′-benzylidene-protected derivative 11 in almost quantitative yield by transacetalization with benzaldehyde dimethylacetal in acetonitrile under p-toluenesulfonic acid catalysis. Subsequent peracetylation with acetic anhydride/pyridine, selective cleavage of the benzylidene group with 80% acetic acid at 90 °C

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

• , peracetate 10 was deacetylated (NaOMe/MeOH) and converted to the benzylidene acetal 11 by reaction with benzaldehyde dimethyl acetal under camphorsulfonic acid (CSA) catalysis. Chloroacetylation of alcohol 11 gave the intermediate 12 which was converted to acceptor 4 via the reductive opening of the

• benzylidene acetal using NaCNBH3 and HCl·Et2O in anhydrous THF at 0 °C. Both 6-azidohexyl acceptors 6 and 5 were prepared from the anomeric mixture of the known tetraacetate 13 [44]. Thus, tetraacetate 13 was reacted with 6-chlorohexanol (4 equiv) in the presence of BF3·OEt2 (5 equiv). To promote coupling

• (NaN3, DMF, 80 °C) gave the known [46] 6-azidohexyl glycoside 15 quantitatively. Zemplén deacetylation of triacetate 15 followed by conversion of the triol to the 4,6-benzylidene acetal (16) and then chloroacetylation at O-3 gave intermediate 17 that was submitted to reductive opening of the benzylidene

Acid- mediated reactions under microfluidic conditions: A new strategy for practical synthesis of biofunctional natural products

• Katsunori Tanaka and
• Koichi Fukase

Beilstein J. Org. Chem. 2009, 5, No. 40, doi:10.3762/bjoc.5.40

• benzylidene acetal groups, and dehydration, which are the keys to the practical synthesis of N-glycans and the immunostimulating natural product, pristane. A distinctly different reactivity from that in conventional batch stirring was found; the vigorous micromixing of the reactants with the concentrated

• preparing bioactive natural products [27][28][29][30][31][32][33]. Our successful examples are cation-mediated reactions, such as α-sialylation [28][32], β-mannosylation [31], and reductive opening of the benzylidene acetal groups in sugars [30], for which improved procedure under the microfluidic

• of benzylidene acetal group, for the large-scale preparation of the fragment b [30] could also be circumvented under the microfluidic conditions, as will be discussed in the following sections. Microfluidic α-sialylation We have previously developed an efficient α-sialylation by utilizing the highly

Recent progress on the total synthesis of acetogenins from Annonaceae

• Nianguang Li,
• Zhihao Shi,
• Yuping Tang,
• Jianwei Chen and
• Xiang Li

Beilstein J. Org. Chem. 2008, 4, No. 48, doi:10.3762/bjoc.4.48

• of 67 to 1,3-dimesitylimidazol-2-ylidene ruthenium benzylidene catalyst (RuCl2(=C(H)-Ph)(PCy3)(IMes)) after protection of the free hydroxyl group afforded the RCM product 68. Hydrogenation of the double bond of dihydrofuran 68 and iodination of the primary alcohol gave 69, which was then utilized to

Solvent- controlled regioselective protection of allyl- 4,6-benzylidene glucopyranosides

• Kerry Ann Ness and
• Marie E. Migaud

Beilstein J. Org. Chem. 2007, 3, No. 26, doi:10.1186/1860-5397-3-26

• silylation at the 2-position of allyl 4,6-O-benzylidene α-D-glucopyranoside in high yields and which does not require the use of catalysts. Background Numerous syntheses of oligosaccharides incorporating glucose moieties have been reported. In most cases, a limiting synthetic factor is the number of

• benzylation of methyl 4,6-O-benzylidene glucopyranoside claim isolated yields ranging from the 37% and below [9] to 75% and above [10]. Others reported multi-step procedures to achieve introduction of a suitable protecting group at the 2-position of the 4,6-O-benzylidene 1-O-alkyl protected glucose [11] or

• used enzymes to achieve selectivity [12]. Results and discussion While preparing the partially protected glucose 1 from α-allyl-4,6-benzylidene glucoside 2 (Scheme 1), we observed that mono-benzylation could be achieved, if instead of DMF and the usual reagents' combination (i.e. NaH, BnBr, Bu4NI), THF

An efficient synthesis of novel pyrano[2,3-d]- and furopyrano[2,3-d]pyrimidines via indium- catalyzed multi- component domino reaction

• Dipak Prajapati and
• Mukut Gohain

Beilstein J. Org. Chem. 2006, 2, No. 11, doi:10.1186/1860-5397-2-11

• summarized in the Table 1. Remarkably, this Diels-Alder reaction was also proceeded similarly when 5-benzylidene barbituric acid was employed directly with 2,3-dihydrofuran in presence of 1 mol% of indium(III) chloride. The corresponding furopyrano [2,3-d]pyrimidine derivatives 7 were obtained in almost