ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The CuII-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 CH2CH2 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 C2-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).
Additional Material:
2 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19940770515
