Isocyanide-based multicomponent reactions towards cyclic constrained peptidomimetics

• Gijs Koopmanschap,
• Eelco Ruijter and
• Romano V.A. Orru

Beilstein J. Org. Chem. 2014, 10, 544–598, doi:10.3762/bjoc.10.50

• temperature and the final tetrazoles 158a–c were obtained in moderate to good yields. Six-membered ring constraints Pipecolic acid In the previous section we discussed some important conformational properties of proline derivatives playing an important role in controlling peptide and protein secondary

Synthesis of 3,4-dihydro-1,8-naphthyridin-2(1H)-ones via microwave-activated inverse electron-demand Diels–Alder reactions

• Salah Fadel,
• Youssef Hajbi,
• Mostafa Khouili,
• Said Lazar,
• Franck Suzenet and
• Gérald Guillaumet

Beilstein J. Org. Chem. 2014, 10, 282–286, doi:10.3762/bjoc.10.24

• optimal experimental conditions already reported with triazines [22][23][24]. In chlorobenzene at 220 °C (optimal reaction temperature for six-membered-ring formation), the corresponding cycloadducts 10–13 were obtained in high yields (Scheme 4, Table 3). We therefore developed an efficient method for the

Advancements in the mechanistic understanding of the copper-catalyzed azide–alkyne cycloaddition

• Regina Berg and
• Bernd F. Straub

Beilstein J. Org. Chem. 2013, 9, 2715–2750, doi:10.3762/bjoc.9.308

An overview of the synthetic routes to the best selling drugs containing 6-membered heterocycles

• Marcus Baumann and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2013, 9, 2265–2319, doi:10.3762/bjoc.9.265

Structure of 1,5-benzodiazepinones in the solid state and in solution: Effect of the fluorination in the six-membered ring

• Marta Pérez-Torralba,
• Rosa M. Claramunt,
• M. Ángeles García,
• Concepción López,
• M. Carmen Torralba,
• M. Rosario Torres,
• Ibon Alkorta and
• José Elguero

Beilstein J. Org. Chem. 2013, 9, 2156–2167, doi:10.3762/bjoc.9.253

Organocatalyzed enantioselective desymmetrization of aziridines and epoxides

• Ping-An Wang

Beilstein J. Org. Chem. 2013, 9, 1677–1695, doi:10.3762/bjoc.9.192

• ). Interestingly, the aziridines with a six-membered ring were desymmetrized to give the corresponding thioethers in excellent yields and enantioselectivities when the molar ratio of aziridine/nucleophile/catalyst is 1.0:1.5:0.1. For the unreactive acyclic and seven-membered ring aziridines, the good

Anodic coupling of carboxylic acids to electron-rich double bonds: A surprising non-Kolbe pathway to lactones

• Robert J. Perkins,
• Hai-Chao Xu,
• John M. Campbell and
• Kevin D. Moeller

Beilstein J. Org. Chem. 2013, 9, 1630–1636, doi:10.3762/bjoc.9.186

• trapping of a ketene dithioacetal derived radical cation by an amine was shown to lower the oxidation potential measured for the ketene dithioacetal by 460 mV [21], a value consistent with the potential measured here for 14a. The oxidation of 14b to afford the six-membered ring product also proceeded well

Structures of the reaction products of the AZADO radical with TCNQF₄ or thiourea

• Hideto Suzuki,
• Yuta Kawahara,
• Hiroki Akutsu,
• Jun-ichi Yamada and
• Shin’ichi Nakatsuji

Beilstein J. Org. Chem. 2013, 9, 1487–1491, doi:10.3762/bjoc.9.169

• AZADO molecule in the next step to give an addition product (a salt) resulting from the addition to one of the double bonds in the six-membered ring. Finally, the oxoammonium cation in the adduct will react with the counter anion from the less hindered site to afford the final product 5 with trans

• -membered ring in a trans-manner, as seen from its molecular structure (Scheme 1) (Figure 2). Therefore, a plausible mechanism of the reaction could be considered as shown in Scheme 2. First, a transient CT complex would be formed between 2 and 3 but it would be unstable enough to be attacked by another

• amount of TCNQF4 (3) did not give dark blue crystals but gave an orange solid. After purification, the orange crystals obtained were proved to be the addition product 5 and not a CT complex as seen from the X-ray analysis. Furthermore, the addition was found to take place to a double bond of the six

Anionic cascade reactions. One-pot assembly of (Z)-chloro-exo-methylenetetrahydrofurans from β-hydroxyketones

• István E. Markó and
• Florian T. Schevenels

Beilstein J. Org. Chem. 2013, 9, 1319–1325, doi:10.3762/bjoc.9.148

• -methyleneketals [1][2][3]. This unique transformation is particularly efficient in the case of six-membered ring ketones (Scheme 1). In an attempt to extend the scope of this cascade process to acyclic ketones, acetone was submitted to the usual reaction conditions. To our surprise, the expected adduct 5 was

Host–guest complexes of mixed glycol-bipyridine cryptands: prediction of ion selectivity by quantum chemical calculations, part V

• Svetlana Begel,
• Ralph Puchta and
• Rudi van Eldik

Beilstein J. Org. Chem. 2013, 9, 1252–1268, doi:10.3762/bjoc.9.142

• ) building block causes a stronger contraction of the cryptand hole, since the two pyridine rings are stiffened by a third, weaker aromatic six-membered ring (according to Clar’s rule [72][73][74]) as was explained above. Hence, the subsequent substitution by (bpy) and (phen) moieties reduces the size of the

Conformational analysis and intramolecular interactions in monosubstituted phenylboranes and phenylboronic acids

• Josué M. Silla,
• Rodrigo A. Cormanich,
• Roberto Rittner and
• Matheus P. Freitas

Beilstein J. Org. Chem. 2013, 9, 1127–1134, doi:10.3762/bjoc.9.125

• constant. Better electron donors than fluorine (N, P and S) perform such an interaction. An intramolecular hydrogen bond F∙∙∙HO appears in 2-fluorophenylboronic acid and it contributes for the conformational stability, since a six-membered ring is formed from this interaction, which is more efficient than

Diastereoselective synthesis of nitroso acetals from (S,E)-γ-aminated nitroalkenes via multicomponent [4 + 2]/[3 + 2] cycloadditions promoted by LiCl or LiClO₄

• Leandro Lara de Carvalho,
• Robert Alan Burrow and
• Vera Lúcia Patrocinio Pereira

Beilstein J. Org. Chem. 2013, 9, 838–845, doi:10.3762/bjoc.9.96

• resulting from the endo approach of the smaller dipolarophile MVK by the Re face of the nitronate. It is worthwhile to mention that, depending of the nitroso acetal structure, an opening of the six-membered ring is caused due to a greater sensitivity to the reaction medium, leading to generation of the

• could be corroborated by X-ray analysis of 11b, since the diastereoselection of the [4 + 2]-step was the same for all cycloadditions investigated (Figure 1 and Figure 2). The determination of the vicinal H,H constant coupling of the protons located in the six-membered ring was not so simple due to the

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

• unstable with respect to dimerisation or oligomerisation. In 1,2-dihydro-1,2-azaborine, such a dimerisation is not observed, probably due to the aromatic character of the six-membered ring. In 3, however, this aromatic stabilisation is no longer available. For the sake of simplicity, we only considered

A new intermediate in the Prins reaction

• Shinichi Yamabe,
• Takeshi Fukuda and
• Shoko Yamazaki

Beilstein J. Org. Chem. 2013, 9, 476–485, doi:10.3762/bjoc.9.51

• was used, and water or glacial acetic acid was the solvent. A general Prins reaction is shown in Scheme 1. A typical Prins reaction is exhibited in Scheme 2 [4]. Here, the six-membered ring compound, 4,4-dimethyl-1,3-dioxane, is the major product along with 3-methyl-1,3-butane-diol. The 1,3-dioxane is

• the carbonyl group. In this case, 1,3-diol(Me) is the alcohol, and the second formaldehyde is of the C=O group. Closure of the six-membered ring from the ether(Me) [TS4(Me)] gives the product 4-methyl-1,3-dioxane, dioxane(Me). Thus, the obtained route (ii), precursor (Me) → diol(Me) → ether(Me

Polymerization of novel methacrylated anthraquinone dyes

• Christian Dollendorf,
• Susanne Katharina Kreth,
• Soo Whan Choi and
• Helmut Ritter

Beilstein J. Org. Chem. 2013, 9, 453–459, doi:10.3762/bjoc.9.48

• be assumed that the driving force for the ring closure is the formation of a six-membered ring; however, the mechanism has not been investigated in detail so far. Since the ring closure does not affect the spectral properties, 14 can still be used as a polymerizable red dye. In this work, side

Design and synthesis of quasi-diastereomeric molecules with unchanging central, regenerating axial and switchable helical chirality via cleavage and formation of Ni(II)–O and Ni(II)–N coordination bonds

• Vadim A. Soloshonok,
• José Luis Aceña,
• Hisanori Ueki and
• Jianlin Han

Beilstein J. Org. Chem. 2012, 8, 1920–1928, doi:10.3762/bjoc.8.223

• diastereomeric complexes (Ra*,Ph*,Sc*)-2 and (Ra*,Mh*,Rc*)-3, which contain at least three elements of chirality, namely stereogenic center, axis and helix (Scheme 1). The structure of these complexes incorporated two five- and one six-membered ring displaying a square-planar geometry. It is worth mentioning

Determination of the relative configuration of tropinone and granatanone aldols by using TBDMS ethers

• Ryszard Lazny,
• Aneta Nodzewska,
• Katarzyna Sidorowicz and
• Przemyslaw Kalicki

Beilstein J. Org. Chem. 2012, 8, 1877–1883, doi:10.3762/bjoc.8.216

• (Figure 3) by X-ray diffraction. Atoms H1 and H8 were found in syn relation to each other, while the 1′-hydroxybenzyl group at C1 is on the exo side of the bicyclic tropane scaffold pointing towards the C4–N1–C7 bridge (pseudoaxial on the tropinone six-membered ring). The crystal structure is also

Evaluation of a chiral cubane-based Schiff base ligand in asymmetric catalysis reactions

• Kyle F. Biegasiewicz,
• Michelle L. Ingalsbe,
• Jeffrey D. St. Denis,
• James L. Gleason,
• Junming Ho,
• Michelle L. Coote,
• G. Paul Savage and
• Ronny Priefer

Beilstein J. Org. Chem. 2012, 8, 1814–1818, doi:10.3762/bjoc.8.207

• cyclopropanation and Michael addition reactions. Although there was no increase in stereocontrol, upon computational evaluation using both M06L and B3LYP calculations, it was revealed that a pseudo six-membered ring exists, through H-bonding of a cubyl hydrogen to the copper core. This decreases the steric bulk

• complex. In addition, H-bonding with cubyl hydrogens and the copper core yielded a pseudo six-membered ring, which decreased the N–C–C–N dihedral angle. Structure of (1R,2R)-N,N’-bis[(4-iodocuban-1-yl)methylene]-trans-1,2-diamino cyclohexane (1). M06L DFT global minima for (a) (1R,2R)-N,N’-bis[(4

Imidazolinium and amidinium salts as Lewis acid organocatalysts

• Oksana Sereda,
• Nicole Clemens,
• Tatjana Heckel and
• René Wilhelm

Beilstein J. Org. Chem. 2012, 8, 1798–1803, doi:10.3762/bjoc.8.205

• geometry of 7-membered 1,3-diazepinium cations such as 19 does not allow the planar conformation to be kept, thus the positive charge is less delocalized over the NCN atoms (Scheme 4) [26][27][28][29]. Salt 16, incorporating a six-membered ring as the smallest ring, displayed a catalytic activity between

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

• -membered ring to bicyclic 3,4-diaminopyridines leads to tricyclic diaminopyridines 407, 408, and 410 and is accompanied by an increase in acetyl cation affinities above 240 kJ/mol. Annelation of a carbocyclic ring thus has a comparabel effect as already observed for DMAP (54) and its ring-extended forms

• respective ACA values (Table 14). Most of the 3,4-diaminopyridines (58, 59, 63, 399–408) show ACA values which are roughly between 235 and 243 kJ/mol. However, the introduction of a (thio)urea moiety as in 383–387, 389–394, and 397 lowers the ACA value by 10 to 25 kJ/mol. Annelation of an additional six

Binaphthyl-anchored antibacterial tripeptide derivatives with hydrophobic C-terminal amino acid variations

• John B. Bremner,
• Paul A. Keller,
• Stephen G. Pyne,
• Mark J. Robertson,
• K. Sakthivel,
• Kittiya Somphol,
• Dean Baylis,
• Jonathan A. Coates,
• John Deadman,
• Dharshini Jeevarajah and
• David I. Rhodes

Beilstein J. Org. Chem. 2012, 8, 1265–1270, doi:10.3762/bjoc.8.142

• hydrophobicity while increasing the hydrophilicity of the six-membered ring in 2c through inclusion of a ring oxygen atom, as in 2d, had a significant detrimental effect on the activity against the vancomycin-resistant strains VRE449 and VRE820. Interestingly, the placement of an extra methylene group in the

Conformational analysis, stereoelectronic interactions and NMR properties of 2-fluorobicyclo[2.2.1]heptan-7-ols

• Fátima M. P. de Rezende,
• Marilua A. Moreira,
• Rodrigo A. Cormanich and
• Matheus P. Freitas

Beilstein J. Org. Chem. 2012, 8, 1227–1232, doi:10.3762/bjoc.8.137

• perform well in estimating 19F-based couplings [23]), and a high correlation was found (R2 = 0.97), indicating that such an interaction, and thus the F∙∙∙HO intramolecular HB forming a six-membered ring, modulates the 1hJF,H(O) SSCC (Figure 4), which is governed by the Fermi contact term. The SSCC

Synthesis of 2,6-disubstituted tetrahydroazulene derivatives

• Zakir Hussain,
• Henning Hopf,
• Khurshid Ayub and
• S. Holger Eichhorn

Beilstein J. Org. Chem. 2012, 8, 693–698, doi:10.3762/bjoc.8.77

• , which was recrystallized from hexane and dichloromethane to afford single crystals suitable for X-ray analysis. The X-ray data [20] showed that the central, six-membered ring is almost planar but is slightly folded about the axis C(2)···C(6); the five-membered ring is essentially planar. The two larger

Photochemical and thermal intramolecular 1,3-dipolar cycloaddition reactions of new o-stilbene-methylene-3-sydnones and their synthesis

• Kristina Butković,
• Željko Marinić,
• Krešimir Molčanov,
• Biserka Kojić-Prodić and
• Marija Šindler-Kulyk

Beilstein J. Org. Chem. 2011, 7, 1663–1670, doi:10.3762/bjoc.7.196

• protons A and B with an aromatic proton (H-2) at 7.00 ppm is seen, as well as the interaction of proton C with protons E and D. Since the NOE interaction is seen between protons A and E we concluded that protons A and E must lie on the same side of the six-membered ring. In addition, the interaction of

Intramolecular hydroamination of alkynic sulfonamides catalyzed by a gold–triethynylphosphine complex: Construction of azepine frameworks by 7-exo-dig cyclization

• Hideto Ito,
• Tomoya Harada,
• Hirohisa Ohmiya and
• Masaya Sawamura

Beilstein J. Org. Chem. 2011, 7, 951–959, doi:10.3762/bjoc.7.106

• participated in the cyclization to form azabicylo[5.4.0]decene 5o in 76% yield along with a small amount of exomethylene isomer 6o (5o/6o 98:2, Table 4, entry 4). Effect of ring sizes We also evaluated the triethynylphosphine L1, X-Phos, and IPr for an acceleration effect in the six-membered, ring forming

• , gold-catalyzed hydroamination of N-(5-hexyn-1-yl)-p-toluenesulfonamide 7. As expected from entropy considerations, the six-membered ring formations of 7 with these ligands were generally much faster than the seven-membered ring formations of 4: The reaction with 0.5 mol % catalyst loading at room

• temperature completed within 1 h irrespective of the ligand used. When the catalyst loading was reduced to 0.1 mol %, however, the superiority of L1 to X-Phos and IPr became significant, as shown in Table 5. The reaction with L1 at room temperature afforded the six-membered ring product 8 in 91% isolated