Photodehydrocyclizations in stilbene-like compounds. X. Rearrangements in the photocyclization of 4,5-diphenyltriphenylene and 4,5-diphenylphenanthrene

Activated Phenacenes from Phenylenes by Nickel‐Catalyzed Alkyne Cycloadditions

“…As a consequence, the molecule is chiral and configurationally rigid, as evidenced by the NMR spectra, which reveal dissymmetry of both aryl groups at À60 8C. [7] Those at C5/8 exhibited coalescence by rotation on warming to room temperature, DG 6 ¼ 287 = (13.0AE0.1) kcal mol À1 . The ortho and meta CH signals of the bay phenyls remained anisochronous up to 70 8C, when slight line broadening occurred, suggesting a barrier to rotation and/or enantiomerization [15] of > 20 kcal mol À1 .…”

“…[7] Inspection of the product structures reveals remarkable selectivity toward the formation of phenacene (sub)units derived from multiple insertions, even though only one equivalent of alkyne reagent is present. Consequently, varying amounts of starting phenylenes are recovered, but the mass balances are good to excellent.…”

“…Each one of the ensuing topologies (six of which were detailed by X-ray analysis; Table 1) [7] exhibits unique features as a result of p-activation through benzocyclobutadienofusion and/or extreme s-distortion from planarity caused by the crowded 4,5-diphenylphenanthrene [8] substructures. Thus, yellow 4 presents the unknown benzo [3,4]cyclobuta[1,2-a]-phenanthrene connectivity.…”

“…This phenomenon is also observed for 6, 7, and 9. [7,10] The activation of the phenanthrene nucleus is structurally evident in the change in the sequence of bond alternation in the annelated terminal ring [7] and in the electronic spectrum [e.g., highest l max = 420 nm; cf. phenanthrene: 345 nm, or the "hexagonal squeeze" [11] [4]phenacene (chrysene): 360 nm].…”

“…benzo[g]chrysene: 371 nm). [7,14] Turning to the [5]phenacene structures, colorless derivative 5 (l max = 405 nm) suffers the consequences of severe twisting caused by the 5,6,7,8-tetraphenyl substitution, most dramatically illustrated by the bay region twist C6-C6a-C6b-C7 = 31.18, the associated deplanarization of the internal phenanthrene unit (dihedral angles in the individual benzene rings up to 238), the extreme dihedral angle of the bonds to the attached 6,7-phenyls of 76.28, and bond elongation (relative to [5]phenacene] along the path C4a-C8a. As a consequence, the molecule is chiral and configurationally rigid, as evidenced by the NMR spectra, which reveal dissymmetry of both aryl groups at À60 8C.…”