Cofacial cyclopentadienes. Synthesis and reactions of 1,8-bis(cyclopentadienyl)naphthalene

ansa-metallocene derivatives XXXIX biphenyl-bridged metallocene complexes of titanium, zirconium, and vanadium: Syntheses, crystal structures and enantioseparation

“…These substituents are crucial, however, in that they facilitate the retro-Diels-Alder reaction. While the unsubstituted cycloadduct (R = H) fails to crack at 190°C [17], the substituted derivatives 8a-c re-open at this temperature and are trapped by deprotonation with potassium hydride [33].…”

ansa-Metallocene derivatives. 26. Biphenyl-bridged metallocenes that are chiral, configurationally stable, and free of diastereomers

“…Possibly steric hindrance in the aryllithium is to blame. Also surprising was that the addition of 5b to 6a proceeded predominantly by 1,4-addition even in the presence of CeCl3, for such combinations are known to lead to carbonyl adducts.9 Maybe 2,2'-bis-(dichlorocerio)biphenyl (23) disproportionates to 2,2'-biphenyldiylcerium chloride (24) and cerium trichloride, and the chemistry observed is that of 24 (eq 3). This suggests that if excess CeCl3 were added to the reaction mixture, the ratio of 1,4-to 1,2-adduct would decrease, but experiments failed to confirm the idea.…”

1,8‐Diarylnaphthalenes: Synthesis, Properties, and Applications

“…Synthesis of ansa-ferrocene 43 [46,47] and paramagnetic stacked bisnickelocene 44 [48] complexes has been also described (Scheme 10). Interestingly, the coupling of 1,8-diiodonaphthalene 7 with cyclopentadienylcopper-dimethyl sulfide [46,47] or cyclopentadienylzinc chloride [48] gives 1,8-bis(cyclopentadienyl)naphthalene 40, which rapidly undergoes a sigmatropic shift followed by an intramolecular Diels-Alder reaction yielding adduct 41. A subsequent retro-Diels-Alder reaction in the presence of sodium hydride provides disodium salt 42.…”