Dibenzo[a,o]phenanthro[3,4-s]pycene, a Configurationally Stable Double Helicene:  Synthesis and Determination of Its Conformation by NMR and GIAO Calculations

Abstract

[reaction: see text] A double helicene formed by a pentahelicene and a heptahelicene with two rings in common was obtained by palladium-catalyzed cyclotrimerization of 3,4-didehydrophenanthrene and was characterized conformationally by NMR and GIAO calculations.

Synthesis and Characterization of Novel Chiral Conjugated Materials

“…Recently, double helicene 48, in which two benzene rings are shared by [5]-and [7]helicene, was prepared via nonphotochemical Pd-catalyzed cyclotrimerization of 3,4-didehydrophenanthrene derived from 47 ( Figure 15.17) [88]. The 1 H NMR spectrum for racemic 48 showed better agreement with the calculated spectrum for the diastereomer with homochiral versus heterochiral helicenes.…”

“…The 1 H NMR spectrum for racemic 48 showed better agreement with the calculated spectrum for the diastereomer with homochiral versus heterochiral helicenes. The characterization of double helicenes did not include X-ray crystallography [21,88].…”

Bottom‐up Approaches to Nanographenes through Organic Synthesis

“…This allowed us to isolate the thermodynamically unstable C 2 -symmetric conformer of hexabenzotriphenylene (15), which was structurally characterized by X-ray diffraction analysis by Bennett, Wenger, and coworkers [24]. Similarly, palladium-catalyzed [2+2+2]cycloaddition of 4,5-didehydrophenanthrene (26, Scheme 11.4) afforded double helicene 16 [25], while the regioisomeric aryne 1,2-didehydrophenanthrene (27) led to a mixture of compounds 14 and 17 [26]. Palladium-catalyzed cocyclotrimerization of two molecules of 2,3-didehydrotriphenylene (28) and benzyne (29) afforded polyarene 18 among other PAHs [27].…”

Pd(0)‐ and Pd(II)‐Catalyzed Reactions of Alkynes and Benzynes

“…Hexabenzo[a,c,g,I,m,o]triphenylene (260) was obtained as a single product in 39 % yield from 9,10-didehydrophenanthrene generated from 259 [80]. Cyclization of 3,4-didehydrophenanthrene 261 gave rise to the polycyclic compound 262, which has a double helicene structure, in 26 % yield [81]. Pd-catalyzed cocyclization of arynes with alkynes also proceeds smoothly.…”