Sterically crowded cyclohexanes—10 Synthesis, conformation and dynamics of 8,8,13,13-tetramethyltetraspiro[2.0.3.1.3.1.3.0]heptadecane

Synthese und konformative Eigenschaften des sterisch überladenen,D3d-symmetrischen all-trans-Hexa(spirotetrahydrofuranyl)cyclohexans

“…[3] Angesichts der vielen Umsetzungen, die mit [Cp * 2 Sm] dungsklasse, die für ihre anomalen topologischen Eigenschaften und ungewöhnlich hohen Barrieren bezüglich einer konformativen Isomerisierung bekannt ist. [9] Im Hinblick auf 2 schienen die Barrieren der Sessel 3Sessel-Umwandlung bei 11 ± 13 [9,10] Eine Vielzahl von Messungen ergab in der Tat, daû äq-2 selbst unter drastischen Bedingungen (LiBF 4 in Benzol/ Acetonitril (1:1) bei 175 8C, geschlossenes Reaktionsgefäû) keine meûbare Fähigkeit zur Komplexierung von Lithiumionen aufweist. Daher wurden dynamische NMR-Untersuchungen durchgeführt, um die Möglichkeit einer ¾quilibrierung mit ax-2 bei hoher Temperatur zu prüfen.…”

“…1974, 35, 165) gefunden. [9] Bifaciale Ionophore sind nahezu unbekannt, siehe a) W. Y. Lee, C. H. Park, J. Org.…”

Percycloalkylated cyclohexanes: attempted synthesis of a trispropellane

“…These, in turn, depend on the topology, i.e., on the ring size and on the way the rings are tied up. Of a number of examples known, [2][3][4][5][6][7][8] [6.4]rotane 1 7 and [6.5]coronane 2 5 mark two extremes: the spiroannelated 1 exists at room temperature in a fixed chair conformation and its barrier of inversion (DG s 487 ¼156.8 kJ/mol) exceeds those of other percycloalkylated cyclohexanes by far. 9 In contrast, the edge-annelated 2 adopts at room temperature a flexible chair conformation and its barrier of inversion (DG s 173 35.9 kJ/mol) falls even below that of cyclohexane (DG s 298 ¼42.3 kJ/mol).…”

Synthesis and Conformational Properties of the Sterically CrowdedD3d-Symmetric all-trans Hexa(spirotetrahydrofuranyl)cyclohexane System

“…[9] With respect to 2, the barriers for the chair-to-chair interconversions for 11 ± 13 [9,10] seemed most meaningful. These data suggest that the 2-ax > 2-eq equilibrium should be characterized by a barrier significantly higher than that exhibited by 13 because of the constancy of the spiro substitution and the five-membered nature of its spirocyclic rings.…”

“…Since glycosylations can cause restrictions of the conformational flexibility of peptides, they play a significant role in peptide folding processes. [9] In many cases, the glycosylation of naturally occurring and non-natural peptides leads to a change in their activity profile. For instance, the analgesic activity of enkephalines [10] could be increased by glycosylation which is attributed, among others, to an improved passage of the glycosylated form across the blood/brain barrier.…”