Total Syntheses of Angular [7]-, [8]-, and [9]Phenylene by Triple Cobalt-Catalyzed Cycloisomerization: Remarkably Flexible Heliphenes

Heliphenes and Related Structures

“…Syntheses of [6]-, [7]-, [8]-, and [9] heliphenes have been reported by Vollhardt and coworkers [55,58], and theoretical considerations by Mezey and coworkers [24]. The present paper discusses structures that could be derived from heliphenes and may constitute the object of future synthetic efforts.…”

“…Stereo-views of the dimer of the intramolecular straightdehydrogenation product of [12]heliphene. like all benzenoids, are fairly rigid so that helicenes afford stable enantiomers, heliphenes are very floppy and cannot be resolved into enantiomers [55,58]. In Fig.…”

“…Stereo-views of a zigzag phenylene-nanotube (analog of a single-wall zigzag graphitic nanotube). Vollhardt and his coworkers have developed the rich and interesting chemistry of higher stable biphenylene homologues ("[n]phenylenes"), in which condensed 4-membered rings alternate with benzenoid rings: reviews [46][47][48] and synthetic strategies [49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64]. Flash vacuum pyrolysis was an early method, which reached its limit at [4]phenylenes.…”

Synthesis and Characterization of Novel Chiral Conjugated Materials

“…However, signifi cant electron delocalization was found [59,60]. Based on the linear plot of λ max vs 1/(n + 0.5), the optical band gaps E g = 2.2 eV (n = 2-9) or E g = 2.1 eV (n = 4-9) may be es timated for the corresponding polyheliphene.…”

“…Vollhardt's group adopted the cobalt-catalyzed photochemical cyclotrimerization of alkynes for the rapid construction of a novel class of helicenes, helical [59,60]. This class of helicenes have a signifi cantly in creased helical radius compared with benzene-based helicenes.…”