Oxidative Coupling of αω,‐Di(cyclopentadienyl)alkane‐diides

Abstract

The Cu"-induced oxidative coupling of a,w -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 11 = 2, intramolecular coupling may be considerably enhanced by replacing the H-atoms of the CH,CH, 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-symrnetrical cyclohexanes 7a, 20 and 23 with a fixed chair conformation. These results are easily explained, if a conformational equilibrium E F?. 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).

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“…98 (2015)7 47 Scheme 16. Examples of Intramolecular Oxidative Couplings of Cyclopentadienides [59] 26 ) Singly occupied molecular orbital. 27 )T he sequence 54a !…”

Role of torsional strain in the ring-opening polymerisation of low strain [n]nickelocenophanes

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