Strecker degradation of amino acids promoted by a camphor-derived sulfonamide

• M. Fernanda N. N. Carvalho,
• M. João Ferreira,
• Ana S. O. Knittel,
• Maria da Conceição Oliveira,
• João Costa Pessoa,
• Rudolf Herrmann and
• Gabriele Wagner

Beilstein J. Org. Chem. 2016, 12, 732–744, doi:10.3762/bjoc.12.73

• between H10A and H3A observed in the experimental NOESY spectrum (Figure 6) allows the assignment of the configuration (S)-3A (with H3A in exo position) to compound 2. The attribution was further confirmed by comparing the calculated chemical shifts for all carbon and hydrogen atoms with the experimental

(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

• enantioselective synthesis of 3,4-dihydrocoumarins 150 bearing an all-carbon spiro-quaternary stereocenter utilizing Takemoto’s organocatalyst 77 (Scheme 48) [69]. The domino process is initiated by a Michael addition followed by acetalization, and subsequent PCC oxidation in an one-pot transformation. In 2012

Cupreines and cupreidines: an established class of bifunctional cinchona organocatalysts

• Laura A. Bryant,
• Rossana Fanelli and
• Alexander J. A. Cobb

Beilstein J. Org. Chem. 2016, 12, 429–443, doi:10.3762/bjoc.12.46

• processes Asymmetric oxidative coupling All carbon quaternary centers are prevalent in both natural and pharmaceutical compounds, but rank amongst the hardest to synthesize in a stereoselective manner. Dixon and co-workers have addressed this through the development of an asymmetric organocatalytic

Enantioselective [3 + 2] annulation of α-substituted allenoates with β,γ-unsaturated N-sulfonylimines catalyzed by a bifunctional dipeptide phosphine

• Huanzhen Ni,
• Weijun Yao and
• Yixin Lu

Beilstein J. Org. Chem. 2016, 12, 343–348, doi:10.3762/bjoc.12.37

• of a dipeptide phosphine catalyst, a wide range of highly functionalized cyclopentenes bearing an all-carbon quaternary center were obtained in moderate to good yields and with good to excellent enantioselectivities. Keywords: [3 + 2] annulation; α-substituted allenoate; dipeptide phosphine

• -sulfonylimines proceeded in an unexpected [3 + 2] annulation mode to afford a cyclopentene ring with an all-carbon quaternary center (Scheme 1) [48]. In recent years our group has developed a family of amino acid-derived bifunctional phosphines and has intensively investigated related asymmetric transformations

• reactions yielded highly functionalized cyclopentenes with an all-carbon quaternary center in moderate to good yields and good to excellent enantioselectivities. Further extension of the reaction reported herein and mechanistic studies are ongoing in our laboratory. Experimental General procedure for the [3

Polydisperse methyl β-cyclodextrin–epichlorohydrin polymers: variable contact time ¹³C CP-MAS solid-state NMR characterization

• Isabelle Mallard,
• Davy Baudelet,
• Franca Castiglione,
• Monica Ferro,
• Walter Panzeri,
• Enzio Ragg and
• Andrea Mele

Beilstein J. Org. Chem. 2015, 11, 2785–2794, doi:10.3762/bjoc.11.299

• of D3 is shown in Figure 5), and native CRYSMEB to test the applicability of this measurement to the samples. The CP build-up curves for all carbon atoms of CRYSMEB are reported in Figure 6 and the results observed for the polymers D1 and D3 are shown in Figure 7 as an example. In all cases the

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

• (Scheme 16). In 2014, Cai et al. [46] applied the desymmetrization strategy to construct chiral cyano-bearing all-carbon quaternary stereocenters, affording 1,2,3,4-tetrahydroquinoline analogues in good yields and excellent enantioselectivities (Scheme 17). The same group also observed that achiral

• desymmetrization strategy. Construction of cyano-bearing all-carbon quaternary stereocenters. An unexpected inversion of the enantioselectivity in the asymmetric C–N coupling reactions using chiral octahydro-1H-indole-2-carboxylic acid as the ligand. Differentiation of two nucleophilic amide groups. Synthesis of

Copper-catalysed asymmetric allylic alkylation of alkylzirconocenes to racemic 3,6-dihydro-2H-pyrans

• Emeline Rideau and
• Stephen P. Fletcher

Beilstein J. Org. Chem. 2015, 11, 2435–2443, doi:10.3762/bjoc.11.264

• obtained by ring-closing methods [29][30]. To extend our previously reported DYKATs beyond all-carbon electrophiles we decided to examine 3-chloro-3,6-dihydro-2H-pyran (2a, Scheme 1b). This was envisaged to be a challenging substrate. The presence of oxygen in the ring would modify the electronics, and

Copper-catalyzed asymmetric conjugate addition of organometallic reagents to extended Michael acceptors

• Thibault E. Schmid,
• Sammy Drissi-Amraoui,
• Christophe Crévisy,
• Olivier Baslé and
• Marc Mauduit

Beilstein J. Org. Chem. 2015, 11, 2418–2434, doi:10.3762/bjoc.11.263

• /L13) resulted in a surprising inversion of the regioselectivity. Indeed, the addition of ethylmagnesium bromide onto cyclic dienones occurred at the 1,4-position, affording compounds featuring an all-carbon quaternary center. The authors suggested that the chelating hydroxyalkyl chain was at the

Interactions between tetrathiafulvalene units in dimeric structures – the influence of cyclic cores

• Huixin Jiang,
• Virginia Mazzanti,
• Christian R. Parker,
• Søren Lindbæk Broman,
• Jens Heide Wallberg,
• Karol Lušpai,
• Adam Brincko,
• Henrik G. Kjaergaard,
• Anders Kadziola,
• Peter Rapta,
• Ole Hammerich and
• Mogens Brøndsted Nielsen

Beilstein J. Org. Chem. 2015, 11, 930–948, doi:10.3762/bjoc.11.104

• , but the interaction can here also be increased by “doubly-bridging” them [13]. Those redox groups that have shown the best interaction along the all-carbon bridges are the organometallic metal centres Re(NO)(PPh3)Cp* [24], Ru(dppe)Cp* [25], and Fe(dppe)Cp* [26] (Cp* = 1,2,3,4,5

Attempts to prepare an all-carbon indigoid system

• Şeref Yildizhan,
• Henning Hopf and
• Peter G. Jones

Beilstein J. Org. Chem. 2015, 11, 363–372, doi:10.3762/bjoc.11.42

• Braunschweig, Germany, Fax: (+49)531-391-5387 10.3762/bjoc.11.42 Abstract First attempts are described to prepare a precursor for an all-carbon analog of indigo, the tetracyclic triene 4. Starting from indan-2-one (9) the α-methylene ketone 13 was prepared. Upon subjecting this compound to a McMurry coupling

• only been described more recently [14]. As far as we are aware, however, no attempt to prepare an all-carbon equivalent of indigo has ever been described. A system that could qualify as such an all-carbon analog of 1 is the bis-anion 5, which itself should be obtainable by anionization of the linearly

• mirror symmetry (rmsd 0.04 Å). Our final attempt for the present to prepare a precursor hydrocarbon for an all-carbon indigoid system rests on the observation that the Thiele condensation of indene (6) with acetone in pyrrolidine/methanol yields the benzofulvene 29 (Scheme 6). A suitable methylene

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

• dust mite deterrent; thus, in addition to its ornamental value, the hiba tree also provides and environmentally benign means of pest control [23][24]. (−)-Thujopsene (10) has attractive features to the synthetic chemist. Its tricyclo[5.4.0.01,3]undecane skeleton contains three contiguous all-carbon

• bromolactonization of 22 to build in the requisite syn relationship between the carboxylate group and the 3-hydroxy group, ultimately leading to quinic acid. Unlike the allylic alkylations in Scheme 1, which form all-carbon stereocenters, we envisioned a unique modification of the silyl enol ether version to access

• [71]. It features a tetracyclic scaffold with a nine-membered ring and an all-carbon quaternary stereocenter. This alkaloid is a microtubule-disrupting agent that displays similar cellular effects to paclitaxel [72][73]. Because of its biological activities and potential pharmaceutical use, many

Derivatives of the triaminoguanidinium ion, 3. Multiple N-functionalization of the triaminoguanidinium ion with isocyanates and isothiocyanates

• Jan Szabo,
• Kerstin Karger,
• Nicolas Bucher and
• Gerhard Maas

Beilstein J. Org. Chem. 2014, 10, 2255–2262, doi:10.3762/bjoc.10.234

• CH2 group are found to be diastereotopic, that is, the cation permanently exists in a chiral conformation; severe steric hindrance obviously excludes a conformation with all carbon and nitrogen atoms in a common plane. In contrast to the spectra of 7a–c, those of 7d–f are characterized by strong line

C–H-Functionalization logic guides the synthesis of a carbacyclopamine analog

• Sebastian Rabe,
• Johann Moschner,
• Marina Bantzi,
• Philipp Heretsch and
• Athanassios Giannis

Beilstein J. Org. Chem. 2014, 10, 1564–1569, doi:10.3762/bjoc.10.161

• States 10.3762/bjoc.10.161 Abstract The chemical synthesis of carbacyclopamine analog 2, a cyclopamine analog with an all-carbon E-ring, is reported. The use of C–H-functionalization logic and further metal-catalyzed transformations allows for a concise entry to this new class of acid-stable cyclopamine

• intermediate in the synthesis of 2 (see Scheme 1). We envisioned a rhodium-catalyzed C–H-insertion into the C17–H bond to occur with a high degree of selectivity (both regio- and stereoselectivity) to form the all-carbon E-ring (for its structure see 11, Scheme 2). Furthermore, a Wagner–Meerwein rearrangement

• -functionalization logic [11]. In addition, the rational design and chemical synthesis of several analogs and derivatives by this [12][13] and other groups [14][15][16][17] have been disclosed. Here, we report the synthesis of a carbacyclopamine analog (2, Figure 1), an analog of the natural product with an all

Synthesis of the B-seco limonoid core scaffold

• Hanna Bruss,
• Hannah Schuster,
• Rémi Martinez,
• Markus Kaiser,
• Andrey P. Antonchick and
• Herbert Waldmann

Beilstein J. Org. Chem. 2014, 10, 194–208, doi:10.3762/bjoc.10.15

• quaternary centers at the ring junction. We decided to start the sequence with known enone 15 [39] and intended to construct the all-carbon quaternary center at C13 by substrate controlled α-functionalization. The second quaternary center at C14 might be established by 1,2-addition and finally, ring-closing

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

• complex, encompasses internally monosubstituted allenes, as well as disubstituted counterparts, offering a direct entry to 5,7 bicyclic systems including those with all-carbon quaternary stereocenters at the ring fusion. In contrast to the intramolecular counterpart, gold-catalyzed intermolecular

Linkage of α-cyclodextrin-terminated poly(dimethylsiloxanes) by inclusion of quasi bifunctional ferrocene

• Helmut Ritter,
• Berit Knudsen and
• Valerij Durnev

Beilstein J. Org. Chem. 2013, 9, 1278–1284, doi:10.3762/bjoc.9.144

• structure of the α-CD:ferrocene complex has been analyzed by X-ray-diffraction [6]. These studies showed that the ferrocene molecule is encapsulated by two α-CD rings in a tail-to-tail orientation, where all carbon atoms of the cyclopentadienyl rings are in close contact with the cavity of the cyclodextrin

Ring opening of 2-aza-3-borabicyclo[2.2.0]hex-5-ene, the Dewar form of 1,2-dihydro-1,2-azaborine: stepwise versus concerted mechanisms

• Holger F. Bettinger and
• Otto Hauler

Beilstein J. Org. Chem. 2013, 9, 761–766, doi:10.3762/bjoc.9.86

• connect the Dewar form 3 to 1,2-dihydro-1,2-azaborine. These transition states are similar in geometry to those described earlier for the all-carbon system (see Figure 1 and Figure 2) [14]. The C1–C4 distance is shorter in TS1 (2.247 Å) than it is in TS2 (2.313 Å). The BN unit is a bystander in these two

• mechanisms as it is not involved in the ring-opening process. The energies of these transition states were refined with multireference perturbation theory (MRMP2). In agreement with the results obtained for the all-carbon system [14], the barrier for the orbital-symmetry-allowed conrotatory ring opening is

• lower (26.5 kcal mol−1) than it is for the forbidden disrotatory reaction (30.1 kcal mol−1) (Table 1). The energy difference of about 4 kcal mol–1 is slightly smaller than that reported for the all-carbon system (7 kcal mol−1) [14]. Due to the use of different levels of theory (MRMP2 in the present work

Intramolecular carbonickelation of alkenes

• Rudy Lhermet,
• Muriel Durandetti and
• Jacques Maddaluno

Beilstein J. Org. Chem. 2013, 9, 710–716, doi:10.3762/bjoc.9.81

• % GC yield, 28% isolated yield) is obtained together with the indoline 11c, in an indol/indoline 10c/11c ratio of 80/20. Creation of an all-carbon quaternary center at a ring junction The success of the above experiments prompted us to conduct this reaction with trisubstituted olefins, in an effort to

• construct tricyclic skeletons with an all-carbon quaternary center at a ring junction. This pattern is found in important natural products such as morphine whose ACE ring system exhibits a tetrahydrodibenzofuran motif with an angular ethylamino chain on C13. We thought that the nickel-catalyzed

• the expected (and sole) tricyclic product 14 in 52% isolated yield, resulting from a nickel-catalyzed intramolecular base-free Heck-type coupling and exhibiting an all-carbon quaternary center at a cis-ring junction (as established by NOESY experiments). This result, added to that obtained above with

The chemistry of bisallenes

• Henning Hopf and
• Georgios Markopoulos

Beilstein J. Org. Chem. 2012, 8, 1936–1998, doi:10.3762/bjoc.8.225

• in 7 (n = 1) is replaced by a heteroatom, the heteroorganic bisallenes 16 result, in their simplest form as ethers (X = O), amines (X = NR), thioethers (X = S), etc. Analogously bisallenic epoxides (17, X = O) or aziridines (17, X = NR) can formally be generated from the corresponding all-carbon

Iridium-catalyzed intramolecular [4 + 2] cycloadditions of alkynyl halides

• Andrew Tigchelaar and
• William Tam

Beilstein J. Org. Chem. 2012, 8, 1765–1770, doi:10.3762/bjoc.8.201

• nitrogen-tethered substrates (Table 3, entries 4 and 5) when changing R1 = H to R1 = Me, as the reaction time increased from 3 to 4 h and the yield decreased slightly. The all-carbon tethered substrates (Table 3, entries 6 and 7) required longer reaction times, but the cycloadditions occurred in good

Valence isomerization of cyclohepta-1,3,5-triene and its heteroelement analogues

• Helen Jansen,
• J. Chris Slootweg and
• Koop Lammertsma

Beilstein J. Org. Chem. 2011, 7, 1713–1721, doi:10.3762/bjoc.7.201

• Helen Jansen J. Chris Slootweg Koop Lammertsma Department of Chemistry and Pharmaceutical Sciences, VU University Amsterdam, De Boelelaan 1083, 1081 HV, Amsterdam, The Netherlands 10.3762/bjoc.7.201 Abstract The valence isomerization of the all-carbon and heteroelement analogues of cyclohepta

• necessitates a brief overview of the parent all-carbon system. This section is followed by one in which experimental data on the oxepine, thiepine, 1H-azepine, and 1H-phosphepine valence isomerizations are compared with those obtained by theoretical calculations. Computational methods have the advantage that

• -oxabicyclo[2.3.0]hepta-3,6-diene (13) [38][51], while under thermal, photochemical or acidic conditions, the three-membered ring of bicyclic 4 opens, generating phenol [67][68], in analogy to the all-carbon norcaradiene (2), which gives toluene. In addition, 4 undergoes highly selective Diels–Alder reactions

Recent developments in gold-catalyzed cycloaddition reactions

• Fernando López and
• José L. Mascareñas

Beilstein J. Org. Chem. 2011, 7, 1075–1094, doi:10.3762/bjoc.7.124

• authors proposed that these intermediates formally behave as an all-carbon 1,4-dipole that intermolecularly reacts with the indole providing the final polycyclic furan adducts 9 in a regioselective fashion (Scheme 4) [46]. In 2009, J. Zhang reported a gold(I)-catalyzed tandem cyclization/(3 + 3

Metathesis access to monocyclic iminocyclitol-based therapeutic agents

• Ileana Dragutan,
• Valerian Dragutan,
• Carmen Mitan,
• Hermanus C.M. Vosloo,
• Lionel Delaude and
• Albert Demonceau

Beilstein J. Org. Chem. 2011, 7, 699–716, doi:10.3762/bjoc.7.81

• iminocyclitols is dictated by the stereochemistry at all carbon atoms of the pyrrolidine ring system which can adopt either a manno or a galacto conformation, therefore inhibiting either α-mannosidases (e.g., 11–13) or α-galactosidases (e.g., 14) (Scheme 2). A characteristic feature in 11–14 is the presence of a

Palladium-catalyzed formation of oxazolidinones from biscarbamates: a mechanistic study

• Benan Kilbas and
• Metin Balci

Beilstein J. Org. Chem. 2011, 7, 246–253, doi:10.3762/bjoc.7.33

• of 6 [18]. Selective reduction of the peroxide linkage in 6 was carried out with thiourea under very mild conditions to give the diol 7 [19]. Since only the oxygen–oxygen bond is broken in this reaction, the configuration at all carbon atoms is preserved. Oxazolidinone 9 was synthesized by two

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

• amino acids with allyl alcohol mediated by catalyst 4 was investigated. Unexpectedly, S-allylcysteine derivative 21a was the only substrate that afforded a synthetically useful amount of CM product, whereas the reaction of the all carbon analogue homoallylglycine (20) and sulfide derivatives, S-butenyl