Benzenoid versus Annulenoid Aromaticity: Synthesis and Properties of Kekulene

Abstract

same conditions neither 1,3-cyclooctadiene nor 1,3,5-cyclooctatriene can be converted in significant amounts into ( 6 ) , 1,3,6-cyclooctatriene on the other hand reacts smoothly to give this product; addition of the BuLi-reagent to (2) and (4) does occur and in the case of (2) bicyclo[3.3.0]oct-2-ene (8) is formed. This suggests that (1) and BuLi.TMEDA initially form ( 3 ) . which is transformed into ( 5 ) bv loss of LiH and TMEDA. Double metalation of ( 5 ) yields the intermediate (6). ProcedureCompound (1) (12m1, 10.6g, 98mmol) is added to C6H5Nars1 (0.31 mol) in olefin-free pentane (1 50 ml) and TMEDA (95ml), and the mixture is stirred under reflux for 20 h. A slow current of dry O2 is then passed over the well stirred mixture at -5°C for ca. 24h. After filtrationr7] the solution is vacuum distilled, freed from TMEDA with S N HC1, neutralized, anddried. G C analysis reveals 1.5 % (163 mg, 1.5mmol) of (8) and 78.5 % (8 g, 76.9mmol) of (7), based on quantitatively consumed (1). The remainder of (1) is present as oligomerization product in the distillation residue.

Extraordinary Transformations to Achieve the Synthesis of Remarkable Aromatic Compounds

“…Ring-closing metathesis (RCM) was used by Ben King in his synthesis of "septulene" (76), [61] a higher homologue of Staab's famous molecule kekulene (73). [62] Septulene (76) was synthesized by a very short metathesis-based synthetic sequence (Scheme 18) that contrasts the much longer cyclophane-based synthesis of kekulene. Suzuki-Miyaura polymerization of boronate 74 was observed to afford a small amount of cyclic oligomers 75 along with the linear polymers.…”

Theoretical Study of Hole-Containing Macromolecular Diamond Lattices and Corona-Diamondoid Molecules or their Heteroatomic Derivatives

“…Then the "kink" of the chiral [123]triamantane appears as an angle of 90°. With four such "kinks" at the corners of a square corresponding to four [12]triamantane units, one obtains the coronamantane represented in Figure 16. It has the molecular formula C 80 H 80 , and partition formula C 20 (CH) 40 (CH 2 ) 20 .…”

“…In this series the steric strain decreases gradually, but kekulene (4) prepared by Staab and Diederich is the first non-strained coronoid, with six inner hydrogens which are sufficiently remote from each other for minimizing any strain. 12,13 For arriving at the kekulene structure, one has to excise the six carbon atoms of the central benzenoid ring from the kekuléan circumcoronene with 19 benzenoid rings.…”

Electronic properties of kekulene

“…2. EXPERIMENTAL Purified kekulene [1,2] was dissolved in zone-refined liquid 1,2,4,5-tetrachlorobenzene or 1,2,4,5-tetrabromobenzene. Polycrystalline samples were prepared by rapidly cooling the liquid samples and by tempering them at room temperature for several weeks.…”

“…INTRODUCTION Kekulene [1,2] is the first example of a new class of aromatic compounds in which the annelation of six-membered rings leads to a cyclic system enclosing a cavity lined with hydrogen atoms (figure 1). On the basis of the X-ray structure analysis [2] the sextet notation for kekulene shown in figure 1 is undoubtedly the best representation of the actual bonding situation out of the 200 possible structures with different arrangements of double and single bonds which can be formulated [3].…”