Iodoarene-catalyzed cyclizations of N-propargylamides and β-amidoketones: synthesis of 2-oxazolines

• Somaia Kamouka and
• Wesley J. Moran

Beilstein J. Org. Chem. 2017, 13, 1823–1827, doi:10.3762/bjoc.13.177

• tolerated. Alkylketone substrates were also successfully converted to 2-oxazolines. Installation of substituents on the tether led to facile formation of product 6m containing a quaternary carbon and compounds 6n and 6o but without any observed diastereoselectivity. Interestingly, the selectivity for 6o

A speedy route to sterically encumbered, benzene-fused derivatives of privileged, naturally occurring hexahydropyrrolo[1,2-b]isoquinoline

• Olga Bakulina,
• Alexander Ivanov,
• Vitalii Suslonov,
• Dmitry Dar’in and
• Mikhail Krasavin

Beilstein J. Org. Chem. 2017, 13, 1413–1424, doi:10.3762/bjoc.13.138

• hexahydropyrrolo[1,2-b]isoquinolone derivatives fused with benzene 10 that have pronounced three-dimensional features and potentially contain several quaternary carbon centers (Figure 2). The first aspect has been recently recognized [29] as a central principle in drug design ensuring effective interaction of

Switchable highly regioselective synthesis of 3,4-dihydroquinoxalin-2(1H)ones from o-phenylenediamines and aroylpyruvates

• Juraj Dobiaš,
• Marek Ondruš,
• Gabriela Addová and
• Andrej Boháč

Beilstein J. Org. Chem. 2017, 13, 1350–1360, doi:10.3762/bjoc.13.132

• , which showed an important four-bonded interaction between the hydrogen of the methylene C(3)=CH- group and the quaternary carbon C(4a) (Figure 2). The carbon C(4a) was interconnected in the HMBC with 2 other three-bonded interactions with hydrogen H-C(8) and H-C(6), whereas for the 16d (SYN) isomer the

Nucleophilic and electrophilic cyclization of N-alkyne-substituted pyrrole derivatives: Synthesis of pyrrolopyrazinone, pyrrolotriazinone, and pyrrolooxazinone moieties

• Işıl Yenice,
• Sinan Basceken and
• Metin Balci

Beilstein J. Org. Chem. 2017, 13, 825–834, doi:10.3762/bjoc.13.83

• broad singlet. The double bond proton in 12c resonating at 6.94 ppm as a singlet shows strong correlation in the HMBC spectrum with the quaternary carbon atoms resonating at 132.3, 130.8, and 123.1 as well as with the tertiary carbon atoms (=CH) at 118.6 ppm (Figure 4). This information clearly shows

• that the double bond (CH=C) is located between the pyrrole nitrogen atom and the benzene ring (Figure 4). On the other hand, the methylene protons in 13c resonating at 4.26 ppm as a singlet shows strong correlation with the quaternary carbon atoms resonating at 137.2 and 135.2 as well as with the

Synthesis of ribavirin 2’-Me-C-nucleoside analogues

• Fanny Cosson,
• Aline Faroux,
• Jean-Pierre Baltaze,
• Jonathan Farjon,
• Régis Guillot,
• Jacques Uziel and
• Nadège Lubin-Germain

Beilstein J. Org. Chem. 2017, 13, 755–761, doi:10.3762/bjoc.13.74

• , France Laboratoire CEISAM, UMR 6230, University of Nantes, 2 rue de la Houssinière, Nantes, France 10.3762/bjoc.13.74 Abstract An efficient synthetic pathway leading to two carbonated analogues of ribavirin is described. The key-steps in the synthesis of these ribosyltriazoles bearing a quaternary

• carbon atom in the 2’-position are an indium-mediated alkynylation and a 1,3-dipolar cyclization. Keywords: alkynylation; antiviral; cancer; C-nucleosides; ribavirin; Introduction The triazole nucleoside ribavirin (RBV, Figure 1) is used for the treatment of a number of viral infections and may be

Secondary metabolome and its defensive role in the aeolidoidean Phyllodesmium longicirrum, (Gastropoda, Heterobranchia, Nudibranchia)

• Alexander Bogdanov,
• Cora Hertzer,
• Stefan Kehraus,
• Samuel Nietzer,
• Sven Rohde,
• Peter J. Schupp,
• Heike Wägele and
• Gabriele M. König

Beilstein J. Org. Chem. 2017, 13, 502–519, doi:10.3762/bjoc.13.50

• 1H,1H spin system required heteronuclear long range correlations for the elucidation of the remaining structural features and the closure of the cembrane ring. Methylene group CH2-3 exhibited HMBC correlations with resonances of the keto at C-2, sp2 quaternary carbon C-4 and tertiary carbon C-5 and

Methylenelactide: vinyl polymerization and spatial reactivity effects

• Judita Britner and
• Helmut Ritter

Beilstein J. Org. Chem. 2016, 12, 2378–2389, doi:10.3762/bjoc.12.232

• ); Introduction Methylenelactide (MLA) with the IUPAC name (6S)-3-methylene-6-methyl-1,4-dioxane-2,5-dione is a radically polymerizable vinyl-lactide derivative. The molecule’s quaternary carbon atom located at the double bond is substituted with an electron withdrawing (“pulling”) carbonyl group and an electron

• density of the vinyl protons than the electron-pushing substituent (Table S1, Figures S2 and S3, Supporting Information File 1). We further employed 13C NMR spectroscopy to provide a better view on the electron density of the double bond. It turned out that the quaternary carbon atoms of the double bond

New furoisocoumarins and isocoumarins from the mangrove endophytic fungus Aspergillus sp. 085242

• Ze’en Xiao,
• Senhua Chen,
• Runlin Cai,
• Shao’e Lin,
• Kui Hong and
• Zhigang She

Beilstein J. Org. Chem. 2016, 12, 2077–2085, doi:10.3762/bjoc.12.196

• , suggesting a molecular formula of C15H16O3. A careful comparison of its 1H and 13C NMR spectra (Table 1) with those of 2 indicated that compound 3 also shared the same isocoumarin skeleton as compound 2. The main differences were that an additional olefinic methine carbon at δC 99.6 and a quaternary carbon

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

• 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

Enantioconvergent catalysis

• Justin T. Mohr,
• Jared T. Moore and
• Brian M. Stoltz

Beilstein J. Org. Chem. 2016, 12, 2038–2045, doi:10.3762/bjoc.12.192

• reaction was reported by Stoltz for the generation of enantioenriched all-carbon quaternary stereocenters from racemic allyl β-ketoesters (e.g., (±)-20 → (+)-23, Scheme 5) [29]. This particular reaction is especially unusual since the stereoablative step requires scission of a C–C bond at a quaternary

• carbon stereocenter to form achiral enolate intermediate 22. Since no kinetic resolution of the racemic starting material was observed, yields in excess of 90% with up to 92% ee could be obtained. In further studies, it was found that the putative enolate intermediate could also be trapped by a proton

Modular synthesis of the pyrimidine core of the manzacidins by divergent Tsuji–Trost coupling

• Sebastian Bretzke,
• Stephan Scheeff,
• Felicitas Vollmeyer,
• Friederike Eberhagen,
• Frank Rominger and
• Dirk Menche

Beilstein J. Org. Chem. 2016, 12, 1111–1121, doi:10.3762/bjoc.12.107

• ), their unique architecture is characterized by an ester-linked bromopyrrole carboxylic acid and a tetrahydropyrimidine ring in which one of the amino groups is attached to a quaternary carbon center. Due to their intriguing structures in combination with the promising biological properties this class of

Towards the total synthesis of keramaphidin B

• Pavol Jakubec,
• Alistair J. M. Farley and
• Darren J. Dixon

Beilstein J. Org. Chem. 2016, 12, 1096–1100, doi:10.3762/bjoc.12.104

• stereochemical configuration of the quaternary carbon was established by a diastereoselective Michael addition between a chiral, single enantiomer, cyclic β-amido ester and a nitroolefin, and, in the case of nakadomarin A the reaction could be rendered catalytic using a bifunctional cinchonine-derived urea

• hydroxypropyl chain attached to the quaternary stereocentre, poised for further functionalisation. Having established that the cinchonine-derived bifunctional Brønsted base/thiourea organocatalyst 12 was effective for installing two stereocentres including the quaternary carbon in a model system, we next

The synthesis of functionalized bridged polycycles via C–H bond insertion

• Jiun-Le Shih,
• Po-An Chen and
• Jeremy A. May

Beilstein J. Org. Chem. 2016, 12, 985–999, doi:10.3762/bjoc.12.97

• conformation of the cyclooctyl ring may also play a role in the selectivity as discussed below. The White group used rhodium dimers as catalysts to form the central quaternary carbon of (+)-codeine (Scheme 9) [62]. This insertion into the benzylic methine of 43 was quite selective, with only a single reported

Three new trixane glycosides obtained from the leaves of Jungia sellowii Less. using centrifugal partition chromatography

• Luíse Azevedo,
• Larissa Faqueti,
• Marina Kritsanida,
• Antonia Efstathiou,
• Despina Smirlis,
• Gilberto C. Franchi Jr,
• Grégory Genta-Jouve,
• Sylvie Michel,
• Louis P. Sandjo,
• Raphaël Grougnet and
• Maique W. Biavatti

Beilstein J. Org. Chem. 2016, 12, 674–683, doi:10.3762/bjoc.12.68

• aglycone to be a sesquiterpene [33]. Based on previous reports, the signals of a CH group at δ 2.12/65.2 (C-10) and a quaternary carbon at δ 53.8 (C-6) observed in the NMR spectra of compound 1 suggested a trixane scaffold for this secondary metabolite [34]. C-10 and C-6 are respectively shared by two and

(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

• proceeded in good to excellent yield and excellent enantioselectivity for almost all of the substrates that were tested. This methodology was further extended in the total synthesis of (−)-mesembrine. This natural product contains a sterically hindered and arylated quaternary carbon center, which was

Application of 7-azaisatins in enantioselective Morita–Baylis–Hillman reaction

• Qing He,
• Gu Zhan,
• Wei Du and
• Ying-Chun Chen

Beilstein J. Org. Chem. 2016, 12, 309–313, doi:10.3762/bjoc.12.33

• formation of stereogenic quaternary carbon centers by enantioselective MBH reactions has been a fascinating and challenging area, because the compatible electrophiles are always limited to aldehydes or derivatives thereof. Since the first elegant work on the enantioselective MBH reaction between isatins and

Genicunolide A, B and C: three new triterpenoids from Euphorbia geniculata

• Alia Farozi,
• Javid A. Banday and
• Shakeel A. Shah

Beilstein J. Org. Chem. 2015, 11, 2707–2712, doi:10.3762/bjoc.11.291

• -oriented. The proton at δ 2.82 was correlated to the olefinic carbon at δC 157 ppm (C-14), three bonds away and allowed joining of spin systems separated by a methyl-bearing quaternary carbon on one side. The chemical shifts, multiplicity and coupling constants of the A-ring carbinylic protons and an

Recent advances in copper-catalyzed asymmetric coupling reactions

• Fengtao Zhou and
• Qian Cai

Beilstein J. Org. Chem. 2015, 11, 2600–2615, doi:10.3762/bjoc.11.280

• the copper/NHC-catalyzed asymmetric allylic substitution of allyl phosphates with arylboronates. Furthermore, they applied the method to the construction of quaternary carbon stereocenters with good enantioselectivity (up to 90% ee) with disubstituted allyl phosphates. The enantioselectivity was later

• improved to 92% ee with a new chiral catalyst (Scheme 25) [65]. In 2012, Hoveyda and Jung reported a copper/NHC-catalyzed asymmetric allylic substitution of allyl phosphates with allenylboronates [66], leading to chiral allenes bearing a tertiary or quaternary carbon stereogenic center in high yields and

• with excellent enantioselectivity (Scheme 26). The copper/NHC catalyst system was also applied to the allylic substitution of allyl phosphates with commercially available or easily accessible vinylboron reagents, leading to chiral alkenes bearing a quaternary carbon stereocenter. The utility of this

The marine sponge Agelas citrina as a source of the new pyrrole–imidazole alkaloids citrinamines A–D and N-methylagelongine

• Christine Cychon,
• Ellen Lichte and
• Matthias Köck

Beilstein J. Org. Chem. 2015, 11, 2029–2037, doi:10.3762/bjoc.11.220

• NMR spectrum and a sp2 quaternary carbon (δC 171.7 ppm) in the 1D 13C spectrum verified the oxidation of one aminoimidazole ring at position C-15 like in mauritiamine (7) and nagelamide P (18). Based on 1H,1H-NOESY correlations H-8 (3.90 ppm) to H-10 and H-8´ (4.01 ppm) to H-10´ and the corresponding

Mechanism, kinetics and selectivity of selenocyclization of 5-alkenylhydantoins: an experimental and computational study

• Biljana M. Šmit,
• Radoslav Z. Pavlović,
• Dejan A. Milenković and
• Zoran S. Marković

Beilstein J. Org. Chem. 2015, 11, 1865–1875, doi:10.3762/bjoc.11.200

• reaction which is not stereoselective and thus obtained as racemic mixture. All calculations were done for the enantiomers with S configuration at the quaternary carbon atom of the hydantoin nucleus. The selected 1H chemical shifts of these intermediates, calculated and experimental, are listed in Table 1

Pyridinoacridine alkaloids of marine origin: NMR and MS spectral data, synthesis, biosynthesis and biological activity

• Louis P. Sandjo,
• Victor Kuete and
• Maique W. Biavatti

Beilstein J. Org. Chem. 2015, 11, 1667–1699, doi:10.3762/bjoc.11.183

• , dihydroacridine, and quinolone cores are features regularly found in these alkaloid skeletons. The lack of hydrogen atoms next to quaternary carbon atoms for two or three rings makes the chemical shift assignment a difficult task. In this regard, one of the aims of this review is the compilation of previously

Synthesis of γ-hydroxypropyl P-chirogenic (±)-phosphorus oxide derivatives by regioselective ring-opening of oxaphospholane 2-oxide precursors

• Iris Binyamin,
• Shoval Meidan-Shani and
• Nissan Ashkenazi

Beilstein J. Org. Chem. 2015, 11, 1332–1339, doi:10.3762/bjoc.11.143

• informative are the 13C NMR spectra. In comparison to the phosphinates, the 13C NMR showed an average JP-C of 95 Hz for the phenyl quaternary carbon at +132 ppm. The JP-C of the carbons were smaller than in the phosphinate system: JP-C of 65–73 Hz for the propyl carbon, and JP-C of 70 Hz for the R group

The chemical behavior of terminally tert-butylated polyolefins

• Dagmar Klein,
• Henning Hopf,
• Peter G. Jones,
• Ina Dix and
• Ralf Hänel

Beilstein J. Org. Chem. 2015, 11, 1246–1258, doi:10.3762/bjoc.11.139

• . Since we were not able to obtain X-ray data for these adducts, their exact stereostructures must be left open for the time being. It is quite clear, though, that the terminal, highly substituted quaternary carbon atoms protect their neighboring double bond from further attack. The attack by “positive

New depsidones and isoindolinones from the mangrove endophytic fungus Meyerozyma guilliermondii (HZ-Y₂) isolated from the South China Sea

• Senhua Chen,
• Zhaoming Liu,
• Yayue Liu,
• Yongjun Lu,
• Lei He and
• Zhigang She

Beilstein J. Org. Chem. 2015, 11, 1187–1193, doi:10.3762/bjoc.11.133

• , 2.47). The 13C NMR and DEPT spectra revealed the presence of 15 carbons (Table 1), of which 12 aromatic carbons for two phenyl units, one quaternary carbon belonging to a carbonyl carbon, and the other two sp3 carbons corresponding to two methyls. The HMBC correlations from H-5 to C-8, C-7, C-4, C-3, C

Cathodic hydrodimerization of nitroolefins

• Michael Weßling and
• Hans J. Schäfer

Beilstein J. Org. Chem. 2015, 11, 1163–1174, doi:10.3762/bjoc.11.131

• resonances. Signals of aliphatic quaternary carbon atoms were not detected. The differences between the signals of single diastereomers of a dimer correlate very well with the results of the proton resonance experiments. The measured values agree quite well with increment calculations (Table 7) [31