64147-73-5Relevant academic research and scientific papers
Bicyclo[6.3.0]undecapentaenyl anion: The next higher homolog of the indenyl anion with exceptionally large ion-pairing effects on its tropicity
Ozoe, Hiroaki,Uno, Yasutaka,Kitamura, Chitoshi,Kurata, Hiroyuki,Oda, Masaji,Jones Jr., John W.,Scott, Lawrence T.,Kawase, Takeshi
, p. 893 - 900 (2014)
The title anion 1 was generated as a fairly thermally stable species in tetrahydrofuran (THF) and dimethylsulfoxide (DMSO) by the action of several bases (sodium hydride, potassium hydride, lithium diisopropylamide, and lithium hexamethyldisilazide) with appropriate bicyclo[6.3.0]undecapentaenes. Variable-temperature 1H NMR spectra of 1×Li+ in [D8]THF reveal that the anion exhibits exceptionally large ion-pairing effects; proton chemical shifts vary by more than 1 ppm as a function of ion-pairing conditions. Thus, anion 1, in a contact ion pair (Li+ at ambient temperature in THF), behaves as an aromatic cyclopentadienyl anion that is perturbed only slightly by the electronic effects of a paramagnetic cyclooctatetraene (COT), whereas 1 in a separated ion pair (Li+ at low temperatures in THF or at ambient temperature in DMSO) behaves as an overall paratropic species with a 12 π-electron periphery. 13C NMR spectroscopy indicates no major skeletal rearrangement and only small variations of the electron density. The variable tropicity of 1 can be ascribed to small conformational changes of the molecule. In addition to its unusual, tunable tropicity, anion 1 can also serve as a versatile building block for the synthesis of cyclopentanoid conjugated systems fused to a fully unsaturated eight-membered ring. A theoretical calculation predicts that the 10-position of 1 should have the highest electron density. In agreement with this prediction, the reactions of 1 with electrophiles occur predominantly at the 10-position. The corresponding ferrocene, two fulvenes, two diazo derivatives, and a COT-fused azulene were obtained by the reactions of 1 with appropriate electrophiles. Split personality: The bicyclo[6.3.0]undecapentaenyl anion, which is the next higher homolog of the indenyl anion, behaves as an aromatic cyclopentadienide ion slightly perturbed by the effects of a paramagnetic cyclooctatetraene in a contact ion pair, whereas in a solvent-separated ion pair it is an overall paratropic species owing to a 12 π-electron periphery (see picture). Copyright
