“…275 Furan building blocks were used in the syntheses of the diatropic compounds 237 and 238. [276][277][278] The chemical shifts of the indicated hydrogens show that the diamagnetic ring current decreases in the order 237 > 238 (Scheme 83). The porphyrin ring system remains a fascinating one because of its high biological significance as a carrier for oxygen and carbon dioxide when chelating iron.…”
Section: Bicyclic and Polycyclic Hetarenesmentioning
confidence: 99%
“…A bispyridine derivative of dibenzo-hexaaza[18]annulene 236 was prepared by Bell and Guzzo − The chemical shifts of the indicated hydrogens show that the diamagnetic ring current decreases in the order 237 > 238 (Scheme ). 83 Annulenes with Pyridines and Furan Building Blocks …”
Section: 9 Bicyclic and Polycyclic Hetarenesmentioning
“…275 Furan building blocks were used in the syntheses of the diatropic compounds 237 and 238. [276][277][278] The chemical shifts of the indicated hydrogens show that the diamagnetic ring current decreases in the order 237 > 238 (Scheme 83). The porphyrin ring system remains a fascinating one because of its high biological significance as a carrier for oxygen and carbon dioxide when chelating iron.…”
Section: Bicyclic and Polycyclic Hetarenesmentioning
confidence: 99%
“…A bispyridine derivative of dibenzo-hexaaza[18]annulene 236 was prepared by Bell and Guzzo − The chemical shifts of the indicated hydrogens show that the diamagnetic ring current decreases in the order 237 > 238 (Scheme ). 83 Annulenes with Pyridines and Furan Building Blocks …”
Section: 9 Bicyclic and Polycyclic Hetarenesmentioning
“…1848) [4]. Auch durch Wittig-Reaktion von 3-[5-(Dimethoxymethyl)furan-2-yl)prop-2-enal mit { furan-2-yl]methyl}triphenylphosphonium-bromid [13] und anschliessende Hydrolyse des erhaltenen Bis-acetals ist 6 zugänglich (Ausbeute 75%, Schmp. 176 ± 1778).…”
Neutral Aromatic Tetraepoxyannulenes: Tetraepoxy[26]annulenes(4.2.2.2) and Tetraepoxy[30]annulenes(4.4.4
.2) ± Systems with High Molecular DynamicsThe twofold cyclizing Wittig reaction of the bis-aldehyde 6 with the ylide of the bis-phosphonium salt 7 yields tetraepoxy[26]annulene(4.2.2.2) 4, which exists in the two isomeric forms 4a (EE,Z,E,Z) and 4b (EE,Z,E,E). Annulene 4a is a highly dynamic system down to À 808. Temperature-dependent 1 H-NMR spectra of 4a establish that the (E,E)-buta-1,3-dien-1,4-diyl as well as the (E)-ethen-1,2-diyl bridges rotate around the adjacent s-bonds in a synchronous manner. Isomer 4b, for steric reasons, is rigid. By Wittig reaction of the bisaldehyde 8 with the ylide of the bis-phosphonium salt 9, the tetraepoxy[30]annulene(4.4.4.2) 5 is obtained, which exists also in two isomeric forms, 5a and 5b. Only 5a (EE,ZE,EE,Z) can be isolated in pure form. Like 4a, 5a is highly dynamic, the (E,E)-buta-1,3-dien-1,4-diyl as well as the opposite (E)-ethen-1,2-diyl bridge being able to rotate down to À 808. The 1 H-NMR spectrum at À 808 indicates that 5a exists in the stable conformation 5a'. The 26-and 30-membered annulenes belong to the most expanded neutral annulenes known hitherto; their 1 H-NMR spectra confirm that they still have diatropic, aromatic character. 1. Einleitung. ± Während zahlreiche antiaromatische Tetraepoxy[m 2]annulene (m 22, 26, 30, 34, 38) bekannt sind, die zu den aromatischen Tetraoxa[m]porphyrindikationen oxidiert werden können, wurden bislang nur wenige neutrale, aromatische Tetraepoxyannulene beschrieben. Wir unterscheiden zwei Klassen neutraler aromatischer Annulene. Im Tetraepoxy[22]annulen(2.1.2.1) 1 [1] und im Tetraepoxy[22]annulen(3.0.3.0) 2 [2] setzt die Konjugation des Makrocyclus formal eine partielle Entaromatisierung der Furan-Ringe voraus, während im Tetraepoxy[22]annulen(2.2.2.0) (3) [3] eine makrocyclische Konjugation formal unter Beibehaltung der Furan-Konjugation möglich ist. Entsprechend diesen unterschiedlichen Bindungsverhältnissen sind die spektroskopischen Eigenschaften der Annulene 1 und 2 deutlich verschieden von denen von 3 (Tab. 1). Wir berichten hier über das Tetraepoxy[26]annulen(4.2.2.2) 4 und das Tetraepoxy-[30]annulen(4.4.4.2) 5, deren Bindungsverhältnisse denen von 3 entsprechen sollten.
“…Alle berechneten Strukturen wurden mit der AM1-Methode [8] als closedshell-Systeme mit der RHF-Näherung ohne Symmetrie-Restriktionen optimiert, die gefundenen Minimumstrukturen und Übergangszustände wurden durch Schwingungsanalysen charakterisiert. 3,5,7,9,11,13,15,17-nonaen; 6 bzw. 7).…”
Section: Einleitung ± Die Synthese Des [18]annulens (1) Durch Sondheunclassified
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
