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

Photovoltaic-driven organic electrosynthesis and efforts toward more sustainable oxidation reactions

• Bichlien H. Nguyen,
• Robert J. Perkins,
• Jake A. Smith and
• Kevin D. Moeller

Beilstein J. Org. Chem. 2015, 11, 280–287, doi:10.3762/bjoc.11.32

• barriers of quaternary carbon and six-membered ring formation. The use of the second nucleophile and a fast initial trapping reaction reduced the cation character of the radical cation intermediate, slowed competitive elimination reactions, and allowed for the desired quaternary carbon formation. In these

Aspergiloid I, an unprecedented spirolactone norditerpenoid from the plant-derived endophytic fungus Aspergillus sp. YXf3

• Zhi Kai Guo,
• Rong Wang,
• Wei Huang,
• Xiao Nian Li,
• Rong Jiang,
• Ren Xiang Tan and
• Hui Ming Ge

Beilstein J. Org. Chem. 2014, 10, 2677–2682, doi:10.3762/bjoc.10.282

• singlet methyl groups’ protons H3-17 and H3-18 to C-3, C-4, and C-5 indicate that C-17 and C-18 were located on the same quaternary carbon C-4, which was connected by C-3 and C-5. HMBC correlations from the hydroxy proton (δH 5.21) to C-5, and C-6 (acquired in DMSO-d6), and from H-5 to C-1, C-6, and C-7

• (acquired in CDCl3) assigned the connectivity of the C-6 to C-1, C-5, and C-7. The other singlet methyl group, C-16, and the terminal vinyl group (C-14–C-15), were also located on the same quaternary carbon, C-10, which was flanked by C-9 and C-11 deduced from the HMBC correlations from H2-9 to C-10, C-11

Formal total syntheses of classic natural product target molecules via palladium-catalyzed enantioselective alkylation

• Yiyang Liu,
• Marc Liniger,
• Ryan M. McFadden,
• Jenny L. Roizen,
• Jacquie Malette,
• Corey M. Reeves,
• Douglas C. Behenna,
• Masaki Seto,
• Jimin Kim,
• Justin T. Mohr,
• Scott C. Virgil and
• Brian M. Stoltz

Beilstein J. Org. Chem. 2014, 10, 2501–2512, doi:10.3762/bjoc.10.261

• construction of building blocks bearing quaternary carbon and fully substituted tertiary centers [1][2]. A recent addition developed by our laboratory is the allylic alkylation of nonstabilized enolate precursors to form α-quaternary carbonyl compounds (Scheme 1) [3]. Once the key stereocenter is set by this

Chiral phosphines in nucleophilic organocatalysis

• Yumei Xiao,
• Zhanhu Sun,
• Hongchao Guo and
• Ohyun Kwon

Beilstein J. Org. Chem. 2014, 10, 2089–2121, doi:10.3762/bjoc.10.218

• (Scheme 48) [91]. The reaction worked efficiently in the presence of 4 Å molecular sieves in toluene at room temperature to furnish a variety of functionalized cyclopentenes bearing quaternary carbon stereocenters in 29–92% yield with 66–98% ee. Unfortunately, the reaction times were long (up to 7 days

Reaction of selected carbohydrate aldehydes with benzylmagnesium halides: benzyl versus o-tolyl rearrangement

• Maroš Bella,
• Bohumil Steiner,
• Vratislav Langer and
• Miroslav Koóš

Beilstein J. Org. Chem. 2014, 10, 1942–1950, doi:10.3762/bjoc.10.202

• spectroscopy (gCOSY, gTOCSY, gHSQCAD, gHMBCAD, and gH2BC) including 1D sequences with selective excitations (1DNOESY, 1DTOCSY, and 1DROESY) were used for the signal assignments. The quaternary carbon atoms were identified on the basis of a semi-selective INEPT experiment and a 1D INADEQUATE pulse sequence

Synthesis and solvodynamic diameter measurements of closely related mannodendrimers for the study of multivalent carbohydrate–protein interactions

• Yoann M. Chabre,
• Alex Papadopoulos,
• Alexandre A. Arnold and
• René Roy

Beilstein J. Org. Chem. 2014, 10, 1524–1535, doi:10.3762/bjoc.10.157

• a branching unit (TRIS) at the G(1) level. Thus, compounds 12, 17, and 21 differ by having nine atoms between the anomeric carbon and the focal quaternary carbon of TRIS followed by two, four, and nine atoms to reach the benzene carbon, respectively (~4, 6, and 12 Å). Finally, the synthesis of a 27

Silver and gold-catalyzed multicomponent reactions

• Giorgio Abbiati and
• Elisabetta Rossi

Beilstein J. Org. Chem. 2014, 10, 481–513, doi:10.3762/bjoc.10.46

• corresponding propargylamines 7 containing a quaternary carbon center [37] (Scheme 8). Aliphatic alkynes and acyclic amines gave the corresponding products in low yields, whereas the methodology was ineffective for aromatic ketones. Gold-catalyzed A3-MCRs were also applied with the aim to functionalize

Decandrinin, an unprecedented C₉-spiro-fused 7,8-seco-ent-abietane from the Godavari mangrove Ceriops decandra

• Hui Wang,
• Min-Yi Li,
• Félix Zongwe Katele,
• Tirumani Satyanandamurty,
• Jun Wu and
• Gerhard Bringmann

Beilstein J. Org. Chem. 2014, 10, 276–281, doi:10.3762/bjoc.10.23

• carbonyl carbon (δC 170.9) of a δ-lactone suggested its location at C-7, while those from H2-11, H-14, and H3-20 to the quaternary carbon (δC 88.3) placed it at C-9 (Figure 2). The NOE interactions for the two methyl groups at C-4 suggested that one methyl group is located at the same side as H-5, while

Tanzawaic acids I–L: Four new polyketides from Penicillium sp. IBWF104-06

• Louis P. Sandjo,
• Eckhard Thines,
• Till Opatz and
• Anja Schüffler

Beilstein J. Org. Chem. 2014, 10, 251–258, doi:10.3762/bjoc.10.20

• with only one CH3 group appearing as a doublet at δH 0.98 (d, J = 6.2 Hz, H-18)/δC 23.4. The second CH3 group observed as a doublet in compounds 1–3 appeared in the 1H NMR spectrum of 4 as a singlet (δH 1.20, H-17) and showed a HMBC correlation with the quaternary carbon at δC 70.1 (C-10) (Figure 4

Plakilactones G and H from a marine sponge. Stereochemical determination of highly flexible systems by quantitative NMR-derived interproton distances combined with quantum mechanical calculations of ¹³C chemical shifts

• Simone Di Micco,
• Angela Zampella,
• Maria Valeria D’Auria,
• Carmen Festa,
• Simona De Marino,
• Raffaele Riccio,
• Craig P. Butts and
• Giuseppe Bifulco

Beilstein J. Org. Chem. 2013, 9, 2940–2949, doi:10.3762/bjoc.9.331

• oxygenated carbons and one acyl group. The acyl carbon signal at 175.9 ppm (C-1), along with the oxygenated carbon resonance at δC 91.9 (C-4) suggested the presence of a lactone. The olefinic methine carbon at δC 153.5 (C-3) with the quaternary carbon at δC 136.6 (C-2) completed the five-membered α,β

SF002-96-1, a new drimane sesquiterpene lactone from an Aspergillus species, inhibits survivin expression

• Silke Felix,
• Louis P. Sandjo,
• Till Opatz and
• Gerhard Erkel

Beilstein J. Org. Chem. 2013, 9, 2866–2876, doi:10.3762/bjoc.9.323

• contact with methylene protons at δ 1.57 and 1.66 while the latter presented the same correlation with methylene protons at δ 1.34 and 1.37. The protons of two geminal methyl groups (δ 0.97, 1.15) displayed HBMC correlations with the methine carbon at δ 45.7, a quaternary carbon at δ 34.0 and the

The myxocoumarins A and B from Stigmatella aurantiaca strain MYX-030

• Tobias A. M. Gulder,
• Snežana Neff,
• Traugott Schüz,
• Tammo Winkler,
• René Gees and
• Bettina Böhlendorf

Beilstein J. Org. Chem. 2013, 9, 2579–2585, doi:10.3762/bjoc.9.293

• ). These signals were assigned to three methyl groups (14.0, 16.5, and 21.2 ppm), eight methylene units (22.6, 23.4, 29.2, 29.3, 29.4, 29.8, 31.8, and 38.3 ppm), a quaternary carbon at 46.5 ppm, a heteroatom-substituted quaternary carbon – most likely a tertiary alcohol – at 79.1 ppm, an ester-type

• groups to each other, to the putative ester functionality, the quaternary carbon at 46.5 ppm, and the tertiary alcohol carbon at 79.1 ppm led to the assembly of structural fragment II (F-II, Figure 2). Further substitution of the latter was obvious from HMBC cross peaks of the diastereotopic CH2 group

Gold(I)-catalyzed enantioselective cycloaddition reactions

• Fernando López and
• José L. Mascareñas

Beilstein J. Org. Chem. 2013, 9, 2250–2264, doi:10.3762/bjoc.9.264

• allowed the preparation of cyclobutanes 20 containing challenging quaternary carbon centers (Scheme 12). From a mechanistic point of view, these [2 + 2] cycloadditions, either in racemic or asymmetric versions, have been proposed to proceed through a stepwise cationic pathway consisting of an initial