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Oxidative Coupling of αω,‐Di(cyclopentadienyl)alkane‐diides
Author(s) -
You Shaochun,
Gubler Matthias,
Neuenschwander Markus
Publication year - 1994
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.19940770515
Subject(s) - intramolecular force , chemistry , cyclopentadienyl complex , intermolecular force , yield (engineering) , oxidative coupling of methane , stereochemistry , alkane , crystallography , catalysis , molecule , organic chemistry , materials science , metallurgy
The Cu II ‐induced oxidative coupling of αω,‐di(cyclopentadienyl)alkane‐diides 6 ( n = 2–5) has been shown to proceed mainly by an intermolecular pathway to give polymers 8 , while the yield of intramolecular coupling 6 → 7 strongly decreases with increasing number n of C‐atoms of the alkyl chain ( Scheme 3 ). For n = 2, intramolecular coupling may be considerably enhanced by replacing the H‐atoms of the CH 2 CH 2 bridge of 6a ( n = 2) by Me groups. In this case, intramolecular couplings 11 → 20 ( Scheme 7 ) and 22 → 23 + 24 ( Scheme 8 ) are accomplished with a total yield of 59% and 54%, respectively. All the intramolecular couplings investigated so far proceed stereoselectively to give the C 2 ‐symmetrical cyclohexanes 7a, 20 and 23 with a fixed chair conformation. These results are easily explained, if a conformational equilibrium E ⇄ F is operative in which large substituents R are assumed to enhance the gauche ‐conformation F which is the favored conformation for intramolecular couplings. Bridged dihydropentafulvalenes 20 and 23 are quantitatively rearranged to the thermodynamically favored bridged pentafulvenes 27 and 28 under base or acid catalysis, respectively ( Scheme 9 ).