Bicyclo[6.3.0]undecapentaenyl Anion: The Next Higher Homolog of the Indenyl Anion with Exceptionally Large Ion‐Pairing Effects on its Tropicity. Issue 3 (2nd December 2013)

• Record Type: Journal Article
• Authors: Ozoe, Hiroaki; Uno, Yasutaka; Kitamura, Chitoshi; Kurata, Hiroyuki; Oda, Masaji; Jones, John W.; Scott, Lawrence T.; Kawase, Takeshi
• Is Part Of: Chemistry, an Asian journal. Volume 9:Issue 3(2014:Mar.)
• Page Start: 893
• Page End: 900
• Publication Date: 2013-12-02
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1002/asia.201301307
• Languages: English
• ISSNs: 1861-4728

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>The title anion <bold>1</bold> 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 <sup>1</sup>H NMR spectra of <bold>1⋅</bold>Li<sup>+</sup> in [D<sub>8</sub>]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 <bold>1</bold>, in a contact ion pair (Li<sup>+</sup> 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 <bold>1</bold> in a separated ion pair (Li<sup>+</sup> at low temperatures in THF or at ambient temperature in DMSO) behaves as an overall paratropic species with a 12 π‐electron periphery. <sup>13</sup>C NMR spectroscopy indicates no major skeletal rearrangement and only small variations of the electron density. The variable tropicity of <bold>1</bold> can be ascribed to small conformational changes of the molecule. In addition to its unusual, tunable tropicity, anion <bold>1</bold> 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 <bold>1</bold> should have the highest electron density. In agreement with this prediction, the reactions of <bold>1</bold> 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 <bold>1</bold> with appropriate electrophiles.</p> </abstract>