Tetraepoxy[22]annulene(2.2.2.0): a tetraepoxy-bridged neutral aromatic [22]annulene of a new type

We describe the synthesis of tetraepoxy[22]annulene(2.2.2.0) 4, the first aromatic annulene of type B by a cyclizing twofold Wittig reaction of 2,2'-bifuran-5,5'-dicarbaldehyde (5) and the bis[phosphonium] salt 8. The configuration of 4, mainly determined by NMR spectroscopy is (Z,E,Z). Ac...

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Bibliographic Details
Published inHelvetica chimica acta Vol. 81; no. 6; pp. 1077 - 1087
Main Authors Markl, G, Sauer, H, Stiegler, J, Kreitmeier, P, Burgemeister, T
Format Journal Article
LanguageGerman
Published BERLIN Wiley 01.01.1998
Subjects
Chemistry
Chemistry, Multidisciplinary
Physical Sciences
Science & Technology
DICATION
PORPHYRIN
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Summary:We describe the synthesis of tetraepoxy[22]annulene(2.2.2.0) 4, the first aromatic annulene of type B by a cyclizing twofold Wittig reaction of 2,2'-bifuran-5,5'-dicarbaldehyde (5) and the bis[phosphonium] salt 8. The configuration of 4, mainly determined by NMR spectroscopy is (Z,E,Z). According to the UV/VIS spectrum and the H-1-NMR data, the electronic situation in 4 is quite different from that of tetraepoxy[22]annulene(3.0.3.0) 2 and tetraepoxy[22]annulene(2.1.2.1) 3. According to variable-temperature H-1-NMR spectroscopy, 4 is a highly dynamic system, where the (E)-double bond rotates around the adjacent sigma-bonds. At ca. -130 degrees, this dynamic process is frozen, and 4 appears as a diatropic aromatic system; the free activation energy of the rotation Delta G double dagger is ca. 5.75 kcal/mol.
ISSN:0018-019X
DOI:10.1002/hlca.19980810521