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The Quest for Bridgehead Bridgehead Dications with Bicyclo[2.2.2]octyl Skeletons
Author(s) -
de Meijere Armin,
Schallner Otto,
Mateescu G. D.,
Gölitz Peter,
Bischof Peter
Publication year - 1985
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19850680505
Subject(s) - dication , chemistry , bicyclic molecule , mindo , delocalized electron , nonane , stereochemistry , ion , medicinal chemistry , molecule , organic chemistry
It is predicted by MINDO/3 calculations that the 1,5‐trishomobarrelenediyl dication 4 would be as much stabilized over the bicyclo[2.2.2]octanediyl dication 3 as the monocation 7 ‐H is energetically favored over the hypothetical 1‐bicyclo[2.2.2]octyl 10 ‐H. In spite of this, the bridgehead cations generated from the 1,5‐dihalo‐trishomobarrelenes 6 ‐F, 6 ‐Cl, 6 ‐Br, and 6 ‐I and from the 1,5‐diol 6 ‐OH under long‐lived ion conditions were only the 5‐substituted monocations 7 ‐F, 7 ‐Cl, 7 ‐Br, 7 ‐I, and 7 ‐OH, respectively, unequivocally identified by their 1 H‐ and 13 C‐NMR spectra as well as quenching products. Although there is efficient charge delocalization in 7 ‐X, as revealed by the 13 C‐chemical shifts, the lack of formation of the bridgehead bridgehead dication 4 is not due to an unforeseen destabilization by the three α‐annellated cyclopropyl groups. Even the 1,5‐dichlorotetracyclo[3.3.2.0 2,4 .0 6,8 ]decanes 17 ‐Cl 2 and 19 ‐Cl 2 and 1,5‐dichlorotricyclo[3.2.2.0 2,4 ]nonane 12 ‐Cl 2 with only two and one α‐cyclopropyl groups, respectively, gave the bridgehead monocations 18 ‐Cl, 20 ‐Cl, and 13 ‐Cl, respectively.