Recent advances in the asymmetric phosphoric acid-catalyzed synthesis of axially chiral compounds

• Alemayehu Gashaw Woldegiorgis and
• Xufeng Lin

Beilstein J. Org. Chem. 2021, 17, 2729–2764, doi:10.3762/bjoc.17.185

• axial chirality. In the presence of CPA 15, the axially chiral 3,3′-bisindoles 53 were synthesized via a dynamic kinetic resolution (DKR) process in overall moderate yields (up to 79%) and good enantioselectivities (up to 94:6 er, Scheme 18) [68]. The authors investigated the high rotation barrier and

Polarity effects in 4-fluoro- and 4-(trifluoromethyl)prolines

• Vladimir Kubyshkin

Beilstein J. Org. Chem. 2020, 16, 1837–1852, doi:10.3762/bjoc.16.151

• the stability of the ground-state amide bond, thereby elevating the rotation barrier [84][95]. Interestingly, the increase of the barrier when going from benzene to water (Δwater/benzene = E≠in water − E≠in benzene) was found larger in 1 compared to 2, whereas in the diastereomeric couple 3 and 4 only

• , and the amide-bond rotation barrier was higher compared to the other diastereomer, 5. The lack of rotational averaging in 5 and 6 leads to the interesting fact that the lipophilicity was different for these two diastereomers (ΔlogP = 0.15). This suggests that the solvation by water slightly differs

• between the diastereomeric species. Indeed, this conclusion was further corroborated by the rotation barrier data, which showed higher Δwater/benzene for the less lipophilic diastereomer, 6 (Table 4). Overall, the effects from fluorination in both diastereomeric compounds, 5 and 6, were found to be weak

Arylisoquinoline-derived organoboron dyes with a triaryl skeleton show dual fluorescence

• Vânia F. Pais,
• Tristan Neumann,
• Ignacio Vayá,
• M. Consuelo Jiménez,
• Abel Ros and
• Uwe Pischel

Beilstein J. Org. Chem. 2019, 15, 2612–2622, doi:10.3762/bjoc.15.254

• separation times higher than 2 minutes are in accordance with a high rotation barrier. All compounds were identified by their 1H and 13C NMR spectra. The sp2 character of the boron was confirmed by 11B NMR spectroscopy, revealing a typical resonance signal at 31–32 ppm [43]. Hence, the isoquinoline nitrogen

The phenyl vinyl ether–methanol complex: a model system for quantum chemistry benchmarking

• Dominic Bernhard,
• Fabian Dietrich,
• Mariyam Fatima,
• Cristóbal Pérez,
• Hannes C. Gottschalk,
• Axel Wuttke,
• Ricardo A. Mata,
• Martin A. Suhm,
• Melanie Schnell and
• Markus Gerhards

Beilstein J. Org. Chem. 2018, 14, 1642–1654, doi:10.3762/bjoc.14.140

• methanol (373 cm−1) and also lower than the calculated barrier height of 341 cm−1 (cf. Table S9, Supporting Information File 1). This somewhat lower methyl group internal rotation barrier for the OH–O’ isomer could point to a softening of the C–O bond of methanol due to the hydrogen bond. The DID plots in

Synthesis and NMR studies of malonyl-linked glycoconjugates of N-(2-aminoethyl)glycine. Building blocks for the construction of combinatorial glycopeptide libraries

• Markus Nörrlinger,
• Sven Hafner and
• Thomas Ziegler

Beilstein J. Org. Chem. 2016, 12, 1939–1948, doi:10.3762/bjoc.12.183

• at 3.36 and 3.93 ppm. Therefore, the signal of the protons at 3.20 ppm and the doublet at 8.18 ppm belong to the trans rotamer whereas the doublet at 8.01 ppm should belong to the cis rotameric structure. Calculation of ΔG‡r-values In order to evaluate the rotation barrier around the tertiary peptide

• . It is obvious that the different saccharide moieties do not significantly influence the rotation barrier around the tertiary peptide bond. Furthermore, the calculated ΔG‡r values are in good accordance with those of other PNA derivates (17.9–19 kcal/mol) [27][28]. Conclusion We have described the

• efficient chemical synthesis of a series of novel PNA-based glycopeptoids. We also studied the cis/trans rotamers of these glycopeptoids via temperature-dependent 1H NMR spectroscopy by determining the corresponding coalescence temperatures (Tc = 90–95 °C) and by calculating the specific rotation barrier

Further exploration of the heterocyclic diversity accessible from the allylation chemistry of indigo

• Alireza Shakoori,
• John B. Bremner,
• Mohammed K. Abdel-Hamid,
• Anthony C. Willis,
• Rachada Haritakun and
• Paul A. Keller

Beilstein J. Org. Chem. 2015, 11, 481–492, doi:10.3762/bjoc.11.54

• -membered ring [8]. However, analysis of the 13C NMR spectra of these products indicated only a single set of peaks in each case and no evidence for a diastereomeric mixture. Presumably, the atropisomeric rotation barrier is sufficiently low at room temperature to allow for interconversion. While

Reaction of 2,2,4,4-tetrakis(trifluoromethyl)-1,3-dithiethane with N-vinyl compounds

• Viacheslav A. Petrov and
• Will Marshall

Beilstein J. Org. Chem. 2013, 9, 2615–2619, doi:10.3762/bjoc.9.295

• a significantly lower rotation barrier around the C–N bond in these two materials. The structures of both 3c and 3d were established by single crystal X-ray diffraction. Compounds 3b and 3e were also prepared in 56–60% yield by using a one-step process in which dimer 1 was generated by the reaction

Fifty years of oxacalix[3]arenes: A review

• Kevin Cottet,
• Paula M. Marcos and
• Peter J. Cragg

Beilstein J. Org. Chem. 2012, 8, 201–226, doi:10.3762/bjoc.8.22

• , the presence of a hydrogen-bond motif in the cone conformer makes it the more stable form. In 1985, Gutsche investigated the conformational flexibility of parent calix[n]arenes (n = 4–8) and oxacalixarenes by temperature-dependent 1H NMR [5]. The through-the-annulus rotation barrier for oxacalix[3

When cyclopropenes meet gold catalysts

• Frédéric Miege,
• Christophe Meyer and
• Janine Cossy

Beilstein J. Org. Chem. 2011, 7, 717–734, doi:10.3762/bjoc.7.82

• more restricted rotation around the C2–C3 bond at −80 °C, but the rotation barrier estimated to be 46 ± 1 kJ·mol–1 was still comparable in magnitude to rotation around a sterically hindered σ bond (such as in hexachloroethane) (Scheme 2) [16]. These experiments appeared to be useful for the

• -substituted organogold species, were calculated. Unlike in the case of the allylic cation bearing an acetal moiety at C3, incorporation of the gold center at C1 in the 3,3-dimethyl substituted allylic cation raised the rotation barrier considerably to 94 kJ·mol−1, and hence the latter species should be

Synthesis of Ru alkylidene complexes

• Renat Kadyrov and
• Anna Rosiak

Beilstein J. Org. Chem. 2011, 7, 104–110, doi:10.3762/bjoc.7.14

• (thienyl) bond was estimated (ΔG≠303K = 12.6 kcal/mol). Keywords: alkylidene complexes; metathesis; rotation barrier; ruthenium; Introduction The key to active ruthenium metathesis initiators is the accessibility of the ruthenium precursor containing the alkylidene moiety. The most commonly used

• ) [13] internal rotation barriers of styrene, 2-vinylthiophene (Ea = 4.8 kcal/mol) [14] and is comparable with rotation barrier of the aryl ring in chromium carbene complexes (ΔG≠298K = 13.0–16.2 kcal/mol) [15]. Experimental Routine, 2D-correlation spectra (1H,1H-COSY) and SELNOE experiments were

Ring strain and total syntheses of modified macrocycles of the isoplagiochin type

• Andreas Speicher,
• Timo Backes,
• Kerstin Hesidens and
• Jürgen Kolz

Beilstein J. Org. Chem. 2009, 5, No. 71, doi:10.3762/bjoc.5.71

• NMR investigations from −20 up to 55 °C resulted in coalescence of the methoxy signals. By an approximation method [16] as well as by exact line form analysis [17] the rotation barrier could be calculated to ~66 kJ/mol indicating that the conformers are stable within the NMR time scale but cannot be