17676-32-3Relevant articles and documents
Cyclooctatetraene dianion from 1,5-cyclooctadiene. A synthesis in the presence of naphthalene radical anion
Simons, Leslie H.,Lagowski
, p. 1771 - 1773 (2002)
A novel synthesis of cyclooctatetraene dianion from 1,5-cyclooctadiene (1,5-COD) is described. The reaction of the potassium-naphthalene adduct with 1,5-COD proceeds at room temperature over 3 days in heptane/tetrahydrofuran to produce the target compound.
Heats of Generation of Substituted Annulene Dianions
Stevenson, Gerald R.,Nebgen, Mark A.
, p. 5509 - 5513 (1986)
Calorimetric studies have shown that either a phenyl or tert-butoxy substituent on annulene () increases the heat of generation (ΔHgen0) of the respective dianion 0 for R-(HMPA) + 2Na(s) --> R-2- + 2Na+(HMPA)> in hexamethylphosphoramide relative to that of .The values for ΔHgen0 are -51, -38, and -42 kcal/mol respectively for R=H, C4H9, and C6H5.The destabilization of the dianion relative to the neutral molecule due to the presence of a phenyl group is accounted for by the fact that the phenyl group is nearly orthogonal to the charged eight-member ring system.This is supported by the NMR spectrum of Ph-2-. 1H NMR studies carried out upon the solvent (HMPA) in the presence of *- show that the Knight shift is very close to that predicted from changes in bulk paramagnetic susceptibility.This confirms the facts that *-(HMPA) is free of ion association and that ion association must be present to provide a mechanism of spin transfer from the anion radical to the solvent.The previously reported dissociation enthalpy of 2-,K+ in HMPA has been combined with several calorimetrically determined values and an extra thermodynamic parameter to obtain a value of -195 kcal/mol for a single ion heat of solvatation of the dianion of annulene in HMPA.
Isotopic Exchange Involving the Annulene Anion Radical and Its Dimerization to the Annulene Anion Radical
Stevenson, Cheryl D.,Burton, Richard D.,Peters, Steve J.,Reiter, Richard C.
, p. 5838 - 5842 (2007/10/02)
The addition of D2O to hexamethylphosphoramide solutions of the potassium salt of the annulene anion radical results in the slow (days) formation of the monodeuteriated anion radical (C8H7D1.1-).However, several days after a similar addition to the sodium salt solution, no C8H7D1.1- is present.Instead, the anion radical of annulene is found.These observations led to EPR and NMR studies, which have revealed the mechanism of each process.The mechanisms are based upon the facts that ion association is necessary for the isotope exchange reaction and the absence of ion association is required for the dimerization.Solutions of deuteriated annulene anion radical, annulene dianion, annulene anion radical, and annulene dianion can be readily generated from reduced solutions of annulene for EPR, NMR, etc. studies by making use of the isotopic exchange and dimerization mentioned above.
Is pseudorotation the operational pathway for bond shifting within [8]annulenes? Probe of planarization requirements by 1,3-annulation of the cyclooctatetraene ring. Kinetic analysis of racemization and 2-D NMR quantitation of π-Bond alternation and ring inversion as a function of polymethylene chain length
Paquette,Wang,Luo,Cottrell,Clough,Anderson
, p. 239 - 253 (2007/10/02)
The chiral 1,3-bridged cyclooctatetraenes 9a-c have been prepared in nine steps from the appropriate 2-cycloalkenone precursors. Following annulation with ethyl acetoacetate to give 15, trans-1,2-dichloroethylene was cycloadded photochemically in a [2 + 2] reaction and a cyclobutene ring was ultimately formed. Once reduction to alcohol 19 was accomplished, dehydration was effected and the bicyclo[4.2.0]octatrienes so generated underwent disrotatory ring opening to deliver the [8]annulenes. The rates of this electrocyclic ring opening were determined in two examples. Polarimetric studies provided quantitative measure of the readiness with which planar dianion formation occurs as a function of loop size. Unexpectedly, attempts to resolve these molecules failed to deliver them in optically active condition because of too rapid enantiomerization via ring inversion and/or bond shifting. The rates of these processes were determined by 2-D dynamic NMR methods, the data revealing that both processes are accelerated relative to nonbridged models. These and related findings are interpreted in terms of a pseudorotation scheme leading to flattened saddle and not planar-alternate transition states. The unique features associated with this mechanistic phenomenon are discussed.
