Mechanistic studies of an L-proline-catalyzed pyridazine formation involving a Diels–Alder reaction with inverse electron demand

• Anne Schnell,
• J. Alexander Willms,
• S. Nozinovic and
• Marianne Engeser

Beilstein J. Org. Chem. 2019, 15, 30–43, doi:10.3762/bjoc.15.3

• with liquid or gas chromatography. Further, ESI signal intensities do not directly correlate to concentrations in solution, but to the ESI response of the pertaining molecules [3][22]. The ESI response is influenced by a variety of factors like chargeability and surface activity of a given analyte and

Volatiles from the hypoxylaceous fungi Hypoxylon griseobrunneum and Hypoxylon macrocarpum

• Jan Rinkel,
• Alexander Babczyk,
• Tao Wang,
• Marc Stadler and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2018, 14, 2974–2990, doi:10.3762/bjoc.14.277

• that was supported by a feeding experiment with (methyl-2H3)methionine. Keywords: constitutional isomerism; gas chromatography; mass spectrometry; natural products; volatiles; Introduction Fungi release a large number of different volatiles that belong to all kinds of natural product classes [1

• of Scheme 2. Note that because of an isotope effect the isotopomers of 24 can be separated by gas chromatography depending on their deuterium content [34][35], which makes the usage of (methyl-2H3)methionine superior to the usage of 13C-labelled methionine that would not have led to chromatographic

• to all six commercially available isomers (Table 6) showed the identity of the natural product and 3,4-dimethoxybenzaldehyde (42). Finally, two trace compounds with almost identical mass spectra (Figure 8B and Figure 8C), but clear separation by gas chromatography, were suggested to be

Efficient catalytic alkyne metathesis with a fluoroalkoxy-supported ditungsten(III) complex

• Henrike Ehrhorn,
• Janin Schlösser,
• Dirk Bockfeld and
• Matthias Tamm

Beilstein J. Org. Chem. 2018, 14, 2425–2434, doi:10.3762/bjoc.14.220

• initially monitored over time through gas chromatography, affording the conversion versus time diagram depicted in Figure 4. Figure 4 clearly shows that both tungsten complexes are active in the metathesis of 1-phenyl-1-propyne, with the bimetallic compound W2F3 (grey) showing a slower initiation rate

Bioinspired cobalt cubanes with tunable redox potentials for photocatalytic water oxidation and CO₂ reduction

• Zhishan Luo,
• Yidong Hou,
• Jinshui Zhang,
• Sibo Wang and
• Xinchen Wang

Beilstein J. Org. Chem. 2018, 14, 2331–2339, doi:10.3762/bjoc.14.208

• the reaction solution was maintained at room temperature by a flow of cooling water during the reaction. The evolved gases were analyzed in-situ by gas chromatography equipped with a thermal conductive detector (TCD) and a 5 Å molecular sieves column, using Argon as the carrier gas. Photocatalytic

Volatiles from the xylarialean fungus Hypoxylon invadens

• Jeroen S. Dickschat,
• Tao Wang and
• Marc Stadler

Beilstein J. Org. Chem. 2018, 14, 734–746, doi:10.3762/bjoc.14.62

• with different ring substitution patterns. For the set of identified compounds a plausible biosynthetic scheme was suggested that gives further support for the assigned structures. Keywords: constitutional isomerism; gas chromatography; mass spectrometry; natural products; volatiles; Introduction The

Stepwise radical cation Diels–Alder reaction via multiple pathways

• Ryo Shimizu,
• Yohei Okada and
• Kazuhiro Chiba

Beilstein J. Org. Chem. 2018, 14, 704–708, doi:10.3762/bjoc.14.59

• the reaction was indeed stepwise. When the reaction was carefully monitored by gas chromatography–mass spectrometry (GC–MS), we found that an adduct was generated in the early stage that was not the Diels–Alder product 3. Therefore, we intentionally stopped the reaction after 0.1 F/mol of electricity

Investigating radical cation chain processes in the electrocatalytic Diels–Alder reaction

• Yasushi Imada,
• Yohei Okada and
• Kazuhiro Chiba

Beilstein J. Org. Chem. 2018, 14, 642–647, doi:10.3762/bjoc.14.51

• to suppress it (Table 1, entry 4). As a result, the current efficiency reached up to 8000%, meaning that one electron was able to produce 80 molecules of the Diels–Alder adduct 3. With the optimized conditions (Table 1, entry 4) in hand, we monitored the reaction by gas chromatography mass

Volatiles from the tropical ascomycete Daldinia clavata (Hypoxylaceae, Xylariales)

• Tao Wang,
• Kathrin I. Mohr,
• Marc Stadler and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2018, 14, 135–147, doi:10.3762/bjoc.14.9

• natural product is 6-nonyl-2H-pyran-2-one. The antimicrobial and cytotoxic effects of the synthetic volatiles are also reported. Keywords: enantioselective synthesis; gas chromatography; mass spectrometry; natural products; volatiles; Introduction A large variety of volatile organic compounds from

Comparative profiling of well-defined copper reagents and precursors for the trifluoromethylation of aryl iodides

• Peter T. Kaplan,
• Jessica A. Lloyd,
• Mason T. Chin and
• David A. Vicic

Beilstein J. Org. Chem. 2017, 13, 2297–2303, doi:10.3762/bjoc.13.225

• published procedure were used to ensure homogeneity for all the different complexes described in Scheme 1. Conversions to 4-(trifluoromethyl)-1,1’-biphenyl were then monitored by gas chromatography relative to a calibrated internal standard. Experiments were performed in triplicate, and the average yields

• . First, in order to explore reactivities with more electron rich aryl iodides, we investigated the use of 4-iodotoluene as a substrate for trifluoromethylation reactions. Because the product 1-methyl-4-(trifluoromethyl)benzene had similar retention times as the solvents in the gas chromatography analyses

• for the systems described in Scheme 1. These runs represent “standard” conditions described in Scheme 3 and the Experimental section. Yields were monitored by gas chromatography relative to a calibrated internal standard. Yields of 4-(trifluoromethyl)-1,1’-biphenyl over time for the systems described

The effect of milling frequency on a mechanochemical organic reaction monitored by in situ Raman spectroscopy

• Patrick A. Julien,
• Ivani Malvestiti and
• Tomislav Friščić

Beilstein J. Org. Chem. 2017, 13, 2160–2168, doi:10.3762/bjoc.13.216

• of reactive encounters between the particles. In contrast, ex situ gas chromatography studies of the Knoevenagel condensation between vanillin and barbituric acid in a planetary mill revealed a sigmoidal dependence of reaction yield with time [22]. Similarly, sigmoidal dynamics were detected by in

New bio-nanocomposites based on iron oxides and polysaccharides applied to oxidation and alkylation reactions

• Daily Rodríguez-Padrón,
• Alina M. Balu,
• Antonio A. Romero and
• Rafael Luque

Beilstein J. Org. Chem. 2017, 13, 1982–1993, doi:10.3762/bjoc.13.194

• nanomaterials for 1 and 2 min, respectively (Table 6). The alkylation reaction with conventional heating (Scheme 3) was followed by gas chromatography. After 30 min, the conversion was greater than 99% for all of the three materials and the selectivity values were slightly higher compared with the microwave

• injected into a gas chromatograph through a microreactor in which the catalyst was previously sited. The injected base was analyzed by gas chromatography with a flame ionization detector and using an analytical column of 0.5 m length, containing 5 wt % of polyphenylether in the Chromosorb AW-DMCS in 80/100

• were calculated from the chromatograms by: where cinitial and cfinal are the concentrations of the reagents before and after the reaction, respectively, and cproduct is the concentration of the product, as determined by gas chromatography (GC). The samples were analyzed with a HP5890 Series II gas

An efficient Pd–NHC catalyst system in situ generated from Na₂PdCl₄ and PEG-functionalized imidazolium salts for Mizoroki–Heck reactions in water

• Nan Sun,
• Meng Chen,
• Liqun Jin,
• Wei Zhao,
• Baoxiang Hu,
• Zhenlu Shen and
• Xinquan Hu

Beilstein J. Org. Chem. 2017, 13, 1735–1744, doi:10.3762/bjoc.13.168

• mode. High-resolution mass spectra were recorded in the EI mode on a Waters GCT Premier TOF mass spectrometer with an Agilent 6890 gas chromatography using a DB-XLB column (30 m × 0.25 mm (i.d.), 0.25 μm). Melting points (uncorrected) were determined on a Büchi M-565 apparatus. Gas chromatography (GC

Mechanochemical borylation of aryldiazonium salts; merging light and ball milling

• José G. Hernández

Beilstein J. Org. Chem. 2017, 13, 1463–1469, doi:10.3762/bjoc.13.144

• the presence of 1,1-diphenylethene (4) as a radical inhibitor was conducted. After the standard 1 h of milling, the formation of 3a was slowed down and the analysis of the reaction mixture by gas chromatography–mass spectrometry showed the presence of the phenyl radical trapping adduct 5 (Scheme 1

Polyketide stereocontrol: a study in chemical biology

• Kira J. Weissman

Beilstein J. Org. Chem. 2017, 13, 348–371, doi:10.3762/bjoc.13.39

• product structures by gas-chromatography/mass spectrometry (GC–MS) and liquid chromatography (LC)–MS. Review Biosynthesis of complex polyketides by modular PKSs and stereochemical considerations The reduced or complex class of polyketides is assembled in bacteria by gigantic multienzymes called polyketide

NMR reaction monitoring in flow synthesis

• M. Victoria Gomez and
• Antonio de la Hoz

Beilstein J. Org. Chem. 2017, 13, 285–300, doi:10.3762/bjoc.13.31

• in which the WET sequence is incorporated into the end of the mix delay. NMR spectroscopy can be coupled to most separation techniques, including gas chromatography (GC), supercritical fluid chromatography (SFC), gel-permeation chromatography (GPC), high-performance liquid chromatography (HPLC

• a closed circuit, at a flow rate of 1 mL min−1. The kinetic rate could be studied as a function of the catalyst concentration and good agreement was found with the results obtained by gas chromatography. As expected for a first-order reaction, a linear dependence of the kinetic constant on the

Synthesis and evaluation of anti-oxidant and cytotoxic activities of novel 10-undecenoic acid methyl ester based lipoconjugates of phenolic acids

• Naganna Narra,
• Shiva Shanker Kaki,
• Rachapudi Badari Narayana Prasad,
• Sunil Misra,
• Koude Dhevendar,
• Venkateshwarlu Kontham and
• Padmaja V. Korlipara

Beilstein J. Org. Chem. 2017, 13, 26–32, doi:10.3762/bjoc.13.4

• molecules were determined with a capillary tube melting point apparatus. Gas chromatography (GC) was performed on an Agilent 6890N gas chromatograph (Delaware, USA) equipped with a flame ionization detector using a HP-1 capillary column (30 m × 0.25 mm × 0.25 μm). The injector and detector temperatures were

Identification, synthesis and mass spectrometry of a macrolide from the African reed frog Hyperolius cinnamomeoventris

• Markus Menke,
• Pardha Saradhi Peram,
• Iris Starnberger,
• Walter Hödl,
• Gregory F.M. Jongsma,
• David C. Blackburn,
• Mark-Oliver Rödel,
• Miguel Vences and
• Stefan Schulz

Beilstein J. Org. Chem. 2016, 12, 2731–2738, doi:10.3762/bjoc.12.269

• , is usually not possible from an EI mass spectrum. In the article, we present the synthesis and for the first time elucidate the structure of macrolides from the frog family Hyperoliidae. Keywords: chemical communication; chiral gas chromatography; macrocyclic lactones; ring-closing metathesis

• natural compound, the other enantiomer (S)-1 was needed as well. It was synthesized according to the synthesis shown in Scheme 2, starting from (S)-propylene oxide instead of the (R)-enantiomer 13. The stereochemistry was determined by chiral gas chromatography as shown in Figure 4. The coinjection of

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

• temperatures ranging from 50 to 80 °C, while other parameters such as stoichiometric ratio, reaction time, catalyst loading and stirring rate were kept constant. The reactions were followed by taking samples at hourly time intervals and quantified by gas chromatography. Figure 1 shows the graphical

• C0 = quaternary carbon. Gas chromatography (GC–MS) spectrometry was performed on a HP F5890 series LL plus gas chromatograph coupled to an HP 5972 series mass selective detector. The GC was equipped with a HP-5 MS capillary column (30 mm × 0.25 mm i.d.) and ultra-high purity helium (99.999%) carrier

The EIMS fragmentation mechanisms of the sesquiterpenes corvol ethers A and B, epi-cubebol and isodauc-8-en-11-ol

• Patrick Rabe and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2016, 12, 1380–1394, doi:10.3762/bjoc.12.132

• EIMS fragmentation mechanisms of the two sesquiterpene ethers corvol ethers A and B, and the sesquiterpene alcohols epi-cubebol and isodauc-8-en-11-ol. Keywords: bacteria; isotopic labelling; mass spectrometry; reaction mechanisms; terpenes; Introduction Gas chromatography coupled to electron impact

Natural products from microbes associated with insects

• Christine Beemelmanns,
• Huijuan Guo,
• Maja Rischer and
• Michael Poulsen

Beilstein J. Org. Chem. 2016, 12, 314–327, doi:10.3762/bjoc.12.34

• on the outer cocoon surface. Subsequent gas chromatography–mass spectrometry (GC–MS) analyses and expression studies revealed that the production of both antibiotics peaked within the first two weeks after cocoon spinning [45]. Although expression levels decreased shortly afterwards, the antibiotic

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

• stationary phases in high-resolution gas chromatography or as drug carriers [26]. CDs and their persubstituted derivatives have recently received a great deal of attention from the field of chromatographic separations. The development of new CD derivatives as important selectors for analytical chiral

Thermal and oxidative stability of Atlantic salmon oil (Salmo salar L.) and complexation with β-cyclodextrin

• Daniel I. Hădărugă,
• Mustafa Ünlüsayin,
• Alexandra T. Gruia,
• Cristina Birău (Mitroi),
• Gerlinde Rusu and
• Nicoleta G. Hădărugă

Beilstein J. Org. Chem. 2016, 12, 179–191, doi:10.3762/bjoc.12.20

• FAs (and the corresponding glycerides) are easily degraded by oxidation, especially at higher temperatures. An appropriate method for evaluating the overall FA profile is the gas chromatography–mass spectrometry (GC–MS) analysis of the FAs, derivatized to the corresponding methyl esters. The relative

Iron complexes of tetramine ligands catalyse allylic hydroxyamination via a nitroso–ene mechanism

• David Porter,
• Belinda M.-L. Poon and
• Peter J. Rutledge

Beilstein J. Org. Chem. 2015, 11, 2549–2556, doi:10.3762/bjoc.11.275

• ). Infrared spectra were recorded on a Bruker ALPHA FTIR spectrophotometer (ZnSe ATR). Gas chromatography was carried out on a Hewlett Packard 5890A and 5890 Series II Gas chromatographs with ChemStation software using HP1 (Crosslinked Methyl Silicone Gum) and CP-Chirasil-Dex CB columns, respectively. Both

• characterization data, GC conditions, UV–vis and 1H NMR spectra. Acknowledgements We thank the University of Sydney for financial support, Dr. Keith Fisher for assistance with acquisition of mass spectra, and Dr. Kelvin Picker for help with gas chromatography.

Comparison of the catalytic activity for the Suzuki–Miyaura reaction of (η⁵-Cp)Pd(IPr)Cl with (η³-cinnamyl)Pd(IPr)(Cl) and (η³-1-t-Bu-indenyl)Pd(IPr)(Cl)

• Patrick R. Melvin,
• Nilay Hazari,
• Hannah M. C. Lant,
• Ian L. Peczak and
• Hemali P. Shah

Beilstein J. Org. Chem. 2015, 11, 2476–2486, doi:10.3762/bjoc.11.269

• . Deuterated solvents were obtained from Cambridge Isotope Laboratories. MeOH-d4 and THF-d8 were not dried but were degassed prior to use through three freeze-pump-thaw cycles. Agilent-400, -500 and -600 spectrometers were used to record NMR spectra at ambient probe temperatures. Gas chromatography analyses

Synthesis of α,β-unsaturated esters via a chemo-enzymatic chain elongation approach by combining carboxylic acid reduction and Wittig reaction

• Yitao Duan,
• Peiyuan Yao,
• Yuncheng Du,
• Jinhui Feng,
• Qiaqing Wu and
• Dunming Zhu

Beilstein J. Org. Chem. 2015, 11, 2245–2251, doi:10.3762/bjoc.11.243

• extracts were dried over anhydrous sodium sulfate and analysed by gas chromatography (GC) to determine the amount of substrate (a) and products (aldehyde b) in the mixture. All experiments were conducted in triplicate. Substrate specificity The reduction of a series of carboxylic acids was carried out by