Reductions of aldehydes and ketones with a readily available N-heterocyclic carbene borane and acetic acid

• Vladimir Lamm,
• Xiangcheng Pan,
• Tsuyoshi Taniguchi and
• Dennis P. Curran

Beilstein J. Org. Chem. 2013, 9, 675–680, doi:10.3762/bjoc.9.76

• ethyl acetate (EtOAc) was complete in 30 min and gave 3-phenylpropanol (3) in 86% yield after evaporation and flash chromatography (Scheme 2). Other acids including pyridinium p-toluenesulfonate, benzohydroxamic acid, and 2,2-dimethyl-1,3-dioxane-4,6-dione (Meldrum’s acid) also promoted this reduction

Asymmetric Diels–Alder reaction with >C=P– functionality of the 2-phosphaindolizine-η¹-P-aluminium(O-menthoxy) dichloride complex: experimental and theoretical results

• Rajendra K. Jangid,
• Nidhi Sogani,
• Neelima Gupta,
• Raj K. Bansal,
• Moritz von Hopffgarten and
• Gernot Frenking

Beilstein J. Org. Chem. 2013, 9, 392–400, doi:10.3762/bjoc.9.40

• theoretically as well as experimentally [16]. In this context, we found that 1,3-bis(alkoxycarbonyl)-2-phosphaindolizines (1a, Z = CO2R1) prepared through 1,5-electrocyclization of in situ generated bis(pyridinium ylidyl)phosphenium chlorides [17] lead to successful DA reaction [18][19], but 3-alkoxycarbonyl-2

Glycosylation efficiencies on different solid supports using a hydrogenolysis-labile linker

• Mayeul Collot,
• Steffen Eller,
• Markus Weishaupt and
• Peter H. Seeberger

Beilstein J. Org. Chem. 2013, 9, 97–105, doi:10.3762/bjoc.9.13

• resins, an additional Zemplén cleavage site for fast LC–MS analysis is introduced. Synthesis of linker 1. Reactions and conditions: (a) NEt3, DCM, rt, 84%; (b) DHP, pyridinium p-toluenesulfonate, DCM, rt, quant.; (c) 2 M aq NaOH, THF, rt, 91%; (d) DSC, NEt3, CH3CN, 0 °C to rt; (e) NEt3, DCM, rt, 80% over

Supramolecular hydrogels formed from poly(viologen) cross-linked with cyclodextrin dimers and their physical properties

• Yoshinori Takashima,
• Yang Yuting,
• Miyuki Otsubo,
• Hiroyasu Yamaguchi and
• Akira Harada

Beilstein J. Org. Chem. 2012, 8, 1594–1600, doi:10.3762/bjoc.8.182

• range of the 1H NMR time scale due to the slow equilibrium [19][20]. Cationic groups, such as pyridinium and pyridylpyridinium terminal groups, inhibit the decomposition of polyrotaxane and stabilize the complexes between α-CD and cationic alkanediyl compounds [21][22][23]. Herein, to study the

Cation affinity numbers of Lewis bases

• Christoph Lindner,
• Raman Tandon,
• Boris Maryasin,
• Evgeny Larionov and
• Hendrik Zipse

Beilstein J. Org. Chem. 2012, 8, 1406–1442, doi:10.3762/bjoc.8.163

• -position are significantly more effective than aryl substituents in stabilizing the pyridinium ions formed through acetyl cation addition. Photo-switchable 3,4-diaminopyridines including a diazo moiety are potentially useful as special-purpose catalysts. The azobenzene substituent itself is electron

Stereoselective synthesis of trans-fused iridoid lactones and their identification in the parasitoid wasp Alloxysta victrix, Part I: Dihydronepetalactones

• Nicole Zimmermann,
• Robert Hilgraf,
• Lutz Lehmann,
• Daniel Ibarra and
• Wittko Francke

Beilstein J. Org. Chem. 2012, 8, 1246–1255, doi:10.3762/bjoc.8.140

• intermediate 16 was transformed to the aldehyde 23. In the course of this short sequence, the free hydroxy group of 16 was protected as the TBDMS ether to yield 21 which afforded the mono-protected diol 22 after treatment with KOH in methanol. Subsequently, 22 was oxidized with pyridinium dichromate to give

Control over molecular motion using the cis–trans photoisomerization of the azo group

• Estíbaliz Merino and
• María Ribagorda

Beilstein J. Org. Chem. 2012, 8, 1071–1090, doi:10.3762/bjoc.8.119

• fluorescence emitted by the pyridinium salt free cyclophane. The azobenzene trans-10 is conveniently replaced with electron donor units, so that when it is associated, as azo-10∙11, the fluorescence is completely inhibited by charge-transfer interactions. The photoexcitation carried out by irradiation with

Recent advances towards azobenzene-based light-driven real-time information-transmitting materials

• Jaume García-Amorós and
• Dolores Velasco

Beilstein J. Org. Chem. 2012, 8, 1003–1017, doi:10.3762/bjoc.8.113

• -azobenzene derivatives. This notable red-shift of the absorption wavelength arises from the strong charge transfer from the alkoxy group to the positively-charged nitrogen atom of the pyridinium salt. Figure 8 shows the transient absorption generated upon pulsed laser irradiation of ethanol solutions of azo

• electron transfer from the alkoxy group to the pyridinium salt produces a partial breaking of the double N–N bond of the azo moiety, thereby facilitating the rotation around this bond to recover the more stable initial trans configuration in a quick fashion [56]. Type-II azoderivatives: photochromic

• azoderivatives [63]. This section collects different families of azoderivatives that combine the two strategies aforementioned: the presence of powerful electron-withdrawing groups, like nitro or pyridinium salts, and the existence of a phenol function in the convenient positions (2’ and 4’) of the azobenzene

Hybrid super electron donors – preparation and reactivity

• Jean Garnier,
• Douglas W. Thomson,
• Shengze Zhou,
• Phillip I. Jolly,
• Leonard E. A. Berlouis and
• John A. Murphy

Beilstein J. Org. Chem. 2012, 8, 994–1002, doi:10.3762/bjoc.8.112

• studies on deprotonation of pyridinium salts [21]. However, 38 is a dication, and, to attain neutrality, could lose two protons. Compound 3 could be a strong base (in support of this, we have witnessed complete conversion of the analogous donor 2 to form 40 by rapid exchange in CD3CN as solvent; see

• protonation, then it should undergo easy fragmentation to 45, featuring a pyridinium salt and an imidazolylidene, and in these circumstances, it would be difficult to understand why this electron-donor system works well. However, if isomeric compound 44 is the product of protonation, then its fragmentation to

Volatile organic compounds produced by the phytopathogenic bacterium Xanthomonas campestris pv. vesicatoria 85-10

• Teresa Weise,
• Marco Kai,
• Anja Gummesson,
• Armin Troeger,
• Stephan von Reuß,
• Silvia Piepenborn,
• Francine Kosterka,
• Martin Sklorz,
• Ralf Zimmermann,
• Wittko Francke and
• Birgit Piechulla

Beilstein J. Org. Chem. 2012, 8, 579–596, doi:10.3762/bjoc.8.65

• available (Aldrich) 1-bromo-5-methylhexane (B) according to the standard procedure [72]. The resulting 2-benzyloxy-10-methylundec-4-yne (C) was hydrogenated over 10% Pd/C-catalyst at 1 atm. The crude secondary alcohol was oxidized with pyridinium dichromate [73][74] to yield the corresponding ketone

• the solvent was removed in vacuo. To a solution of 950 mg (5.1 mmol) of the crude 9-methylundecane-2-ol in 50 mL dichloromethane was added 2.3 g (1.2 equiv) pyridinium dichromate, and the mixture was vigorously stirred for 12 h at RT. As a gas-chromatographic control revealed the reaction to be

• incomplete, another 1.2 equiv of pyridinium dichromate was added, and the mixture was heated under reflux for 6 h. After filtration over silica and concentration in vacuo, the crude ketone was purified by column chromatography on silica with cyclohexane/diethyl ether 20:1. A final Kugelrohr distillation of

Syntheses and applications of furanyl-functionalised 2,2’:6’,2’’-terpyridines

• Jérôme Husson and
• Michael Knorr

Beilstein J. Org. Chem. 2012, 8, 379–389, doi:10.3762/bjoc.8.41

• these with pyridinium salt 8 afforded 1,5-diketo-derivatives 9–11 through Michael addition. These derivatives are generally not isolated, but undergo in situ ring closure performed in the presence of an ammonia source, such as ammonium acetate, leading to terpyridines 12–14 (Scheme 1) [4][15]. In the

• sodium hydroxide without solvent, thus yielding 1,5-diketo-derivatives. Ring closure was then carried out in methanol in the presence of ammonium acetate, according to Scheme 2. In addition to reducing the amount of solvent , this one-pot two-steps procedure avoids preparation of pyridinium salt 8

• synthesis starts with 6-carboxy-2-acetylpyridine (20), which is reacted with furfural (1), thus providing chalcone 21. This is then reacted with di-pyridinium salt 22 in the presence of ammonium acetate to afford quinquepyridine 23 (Scheme 4). Another possibility to access the key intermediate “1,5-diketone

Organic synthesis using (diacetoxyiodo)benzene (DIB): Unexpected and novel oxidation of 3-oxo-butanamides to 2,2-dihalo-N-phenylacetamides

• Wei-Bing Liu,
• Cui Chen,
• Qing Zhang and
• Zhi-Bo Zhu

Beilstein J. Org. Chem. 2012, 8, 344–348, doi:10.3762/bjoc.8.38

• (Scheme 2). To the best of our knowledge, there are several reports on chlorination and bromination reactions with PhI(OAc)2 and a halogen source such as TMSBr, lithium halide or pyridinium halide [32][33][34]. Also, there are several reports on the synthesis of difunctionalized acetamide derivatives [35

Fifty years of oxacalix[3]arenes: A review

• Kevin Cottet,
• Paula M. Marcos and
• Peter J. Cragg

Beilstein J. Org. Chem. 2012, 8, 201–226, doi:10.3762/bjoc.8.22

• M−1, but when Ga3+ was present this dropped to 2833 M−1, suggesting that the macrocyclic cavity, while preorganized for the smaller cations, was too rigid for the extended ammonium cation. One of the more unusual derivatives to have been prepared, 50, incorporates an N-pyridinium dye on one of the

Imidazole as a parent π-conjugated backbone in charge-transfer chromophores

• Jiří Kulhánek and
• Filip Bureš

Beilstein J. Org. Chem. 2012, 8, 25–49, doi:10.3762/bjoc.8.4

• theoretically. Abe et al. studied pyridinium betaines of general formula 72 consisting of negatively charged benzimidazolate and a positively charged pyridinium ion (Figure 13; [79]). Moreover, the π-conjugated system was systematically enlarged and either donor- or acceptor-substituted in order to generate D-π

• systems 35–43 [25][62][63][64][65][66]. Structure of benzimidazoles (44–47), imidazophenanthrolines (48–57), imidazophenanthrenes (58–60), fluorophores 61, 62, and TCAQ-imidazo-TTF (63) chromophores [23][24][67][68][69][70][71]. General structures of bis(benzimidazole) chromophores 67–71 and pyridinium

Highly efficient cyclosarin degradation mediated by a β-cyclodextrin derivative containing an oxime-derived substituent

• Michael Zengerle,
• Florian Brandhuber,
• Christian Schneider,
• Franz Worek,
• Georg Reiter and
• Stefan Kubik

Beilstein J. Org. Chem. 2011, 7, 1543–1554, doi:10.3762/bjoc.7.182

• corresponding pyridine aldoximes or ketoximes (Scheme 4) all of which are easily accessible from the commercially available aldehydes or ketones by reaction with hydroxylamine [32]. Attempts to also prepare the analogous derivative with the oxime group in the 2-position of the pyridinium ring, by reaction of 3

• of a binary solvent mixture, acetonitrile/0.025% aqueous ammonia. All products were thus obtained in analytically pure form, which is necessary to ensure that the subsequent evaluation of activity yields reliable results. Elemental analyses and NMR spectroscopy indicated that the pyridinium

• , indicates that the activity of these cyclodextrin derivatives depends sensitively on the structural parameters of the substituents in combination with the electronic properties. The generally larger activity of the pyridinium derivatives such as 1b–e and 2a with respect to compounds containing a neutral

A new phenylethyl alkyl amide from the Ambrostoma quadriimpressum Motschulsky

• Guolei Zhao,
• Chao Yang,
• Bing Li and
• Wujiong Xia

Beilstein J. Org. Chem. 2011, 7, 1342–1346, doi:10.3762/bjoc.7.158

• -heptylidenetriphenylphosphonium bromide in the presence of n-BuLi gave adduct 11 as an (E/Z)-mixture (E/Z = 1:5) in 75% yield. Selective removal of the TBS group with pyridinium tosylate gave 12 in 98% yield [21]. With the alcohol 12 in hand, our next step was to synthesize the phosphonium salt 15 [22][23] (Scheme 4). Therefore

Functionalization of anthracene: A selective route to brominated 1,4-anthraquinones

• Kiymet Berkil Akar,
• Osman Cakmak,
• Orhan Büyükgüngör and
• Ertan Sahin

Beilstein J. Org. Chem. 2011, 7, 1036–1045, doi:10.3762/bjoc.7.118

• -tribromoanthracene-1,4-dione (28) To a solution of pyridinium chlorochromate (300 mg, 1.08 mmol) in methylene chloride (30 mL) was added a solution of 2,9,10-tribromo-1,4-dihydroanthracene-1,4-diol (27) (222 mg, 0.504 mmol) in methylene chloride (25 mL). The mixture was stirred at ambient temperature for 3 d

Oxidative allylic rearrangement of cycloalkenols: Formal total synthesis of enantiomerically pure trisporic acid B

• Silke Dubberke,
• Muhammad Abbas and
• Bernhard Westermann

Beilstein J. Org. Chem. 2011, 7, 421–425, doi:10.3762/bjoc.7.54

• the synthesis of natural occurring terpenes, i. a., trisporic acid and its derivatives. An advanced building block has been synthesized in a short reaction sequence, which involves an oxidative allylic rearrangement initiated by pyridinium dichromate (PDC) as the key step. Keywords: enzymatic

Molecular rearrangements of superelectrophiles

• Douglas A. Klumpp

Beilstein J. Org. Chem. 2011, 7, 346–363, doi:10.3762/bjoc.7.45

• nitrogen atom. In the case of α-isomer 108, the developing azonium cation may be stabilized by resonance interaction with the phenyl group of 111. However, with the β-isomer 109 the developing azonium cation is located next to the pyridinium ring 116. Evidently, structure 116 is destabilized by the

Anthracene appended pyridinium amide–urea conjugate in selective fluorometric sensing of L-N-acetylvaline salt

• Kumaresh Ghosh,
• Tanmay Sarkar and
• Asoke P. Chattopadhyay

Beilstein J. Org. Chem. 2010, 6, 1211–1218, doi:10.3762/bjoc.6.139

• Kumaresh Ghosh Tanmay Sarkar Asoke P. Chattopadhyay Department of Chemistry, University of Kalyani, Kalyani-741235, India, Fax +91-33-25828282 10.3762/bjoc.6.139 Abstract A new anthracene labeled pyridinium amide–urea conjugate 1 has been designed and synthesized. The receptor shows a different

• ; pyridinium amide–urea conjugate; Introduction The design and synthesis of artificial receptors capable of recognizing α-hydroxy and N-acetyl-α-amino acid carboxylates (i.e., salts of α-amino acids) is an active area of interest in supramolecular chemistry due to the biological significance and practical

• carboxylates [21][22], we reported receptors of various structures with different binding sites. The pyridinium motif, which was first used by Jeong et al. for carboxylate binding [23], was one of the binding sites in our designed receptors [24][25][26]. The pyridinium motif is unique due to its contribution

Pyridinium based amphiphilic hydrogelators as potential antibacterial agents

• Sayanti Brahmachari,
• Sisir Debnath,
• Sounak Dutta and
• Prasanta Kumar Das

Beilstein J. Org. Chem. 2010, 6, 859–868, doi:10.3762/bjoc.6.101

• rapid expansion of this field. In the present work we report the facile synthesis of amphiphilic hydrogelators having a quaternary pyridinium unit coupled to a hydrophobic long alkyl chain through an amide bond. Different amphiphiles with various hydrophobic chain length and polar head groups were

• rationally designed and synthesized to develop a structure-property relation. A judicious combination of hydrophilic and hydrophobic segments led to the development of pyridinium based amphiphilic hydrogelators having a minimum gelation concentration of 1.7%, w/v. Field emission scanning electronic

• originates from the interdigitated bilayer packing of the amphiphile leading to the development of an efficient hydrogel. Interestingly, the presence of the pyridinium scaffold along with the long alkyl chain render these amphiphiles inherently antibacterial. The amphiphilic hydrogelators exhibited high

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

• results only in the formation of a chlorohydroquinone pyridinium species [72], and neutral conditions are required in this case [69]. For the synthesis of poly(SCF3) substituted p-hydroquinones, Scribner oxidized 2,6-bis(SCF3)-4-methoxyphenol to generate 2,6-bis(SCF3)-1,4-benzoquinone. The addition of

Shelf-stable electrophilic trifluoromethylating reagents: A brief historical perspective

• Norio Shibata,
• Andrej Matsnev and
• Dominique Cahard

Beilstein J. Org. Chem. 2010, 6, No. 65, doi:10.3762/bjoc.6.65

• products in high yields. Primary and secondary amines also reacted with 20b to afford N-CF3 products in good yields. Tertiary amines as well as pyridines gave quaternary ammonium and pyridinium salts, respectively. Electrophilic trifluoromethylation could also be achieved by thermal decomposition of 2

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

Fused bicyclic piperidines and dihydropyridines by dearomatising cyclisation of the enolates of nicotinyl-substituted esters and ketones

• Heloise Brice,
• Jonathan Clayden and
• Stuart D. Hamilton

Beilstein J. Org. Chem. 2010, 6, No. 22, doi:10.3762/bjoc.6.22

• it into a silyl enol ether 9. Silyl enol ethers and ketene acetals are known to add effectively to pyridinium species in an intermolecular manner [42][43][44][45][46]. Thus 7 was converted to silyl enol ether 9 in excellent yield under standard conditions. A single geometrical isomer was obtained