Communication
Scheme 1. Synthesis of 4,9-benzo[c]phenanthrene derivatives.
interactions between the two fjord hydrogens. The shortest
measureable CÀC distance is 3.79 , which may be a result of
ClÀCl interactions, which are also 3.79 . The coupled product
12 also exhibits considerable distortion about the central core,
whereas the introduction of the aryl residues at C-4/C-9 has
little impact on the overall molecular geometry.
Scheme 2. Synthesis of 7-benzo[k]tetraphene derivatives.
In the solid state 12 prefers to adopt a slip-stack arrange-
ment where neighbouring molecules face in alternating direc-
tions, a packing regimen which results in short CÀC contacts.
DFT analysis (B3LYP/6-31+G(d)) of 11 indicates that the lone
pairs on the chlorine substituents contribute significantly to
the HOMO, whereas the dihedral angle of 56.68 about the bi-
aryl axis in 12 allows some communication from the core to
HOMO and LUMO of the peripheral aromatic substituents.
Having established that the BHQ benzannulation reaction
provides rapid access to [4]catafusenes the synthesis of higher
homologues was then pursued. To this end, alkylation of 2-
bromo-a-tetralone 14 (Scheme 2) with 1-naphthol 15, followed
by Wittig olefination afforded the exocyclic alkene 16. The
ortho-Claisen rearrangement of 16 also proceeded under un-
usually mild conditions (pyridine; 1158C; 2 h), and afforded 17
in essentially quantitative yield. Trichloroacetylation of 17 gen-
erated the key intermediate 18, which, upon benzannulation
(diglyme; CuCl, 5 mol%; 1628C; 50%), afforded 19, presumably
the result of an initial 8-endo-trig-cyclisation pathway (TS A).
Dehydrogenation of 19 (DDQ, 2 equiv; o-DCB; 1508C; 30 min)
afforded isomerically pure 20, a colourless, crystalline solid in
65% yield. Palladium-catalysed cross-coupling of 20 with
PhMgBr afforded 21 in 71% yield, demonstrating the synthetic
utility of these chlorinated PAHs.
poor interaction between the respective sets of MOs, which is
also evident in the solution-state electronic properties of this
molecule.
The potential of this new methodology was underscored by
the development of a two-directional BHQ reaction in the syn-
thesis of 7,17-dichlorodinaphtho[1,2,-b:1’,2’-k]chrysene, 27, an
example of a higher cata-PAH for which there is no general
synthetic strategy.[6] Etherification of 14 with 1,5-dihydroxy-
naphthalene afforded diketone 22, which, upon Wittig olefina-
tion to 23 and subsequent double ortho-Claisen rearrange-
ment (pyridine; 1158C; mW reactor), afforded the oxygen sensi-
tive bis-phenol 24. Immediate trichloroacetylation of 24 afford-
ed the stable bis-trichloroacetate 25, a high-melting crystalline
solid in multi-gram quantities. The BHQ reaction of 25 leading
to 26 required some optimisation, and was best effected using
microwave activation in the prescence of the pre-formed
copper-NHC complex 29 as catalyst[9b] (DCE; 29, 5 mol%;
2008C; mW reactor; 2 h; 87%; see Scheme 3).
Dehydrogenation of 26 (DDQ, 3 equiv; o-DCB; 1508C; mW re-
actor; 30 min; 83%) furnished the target PAH 27, a compound
which is insoluble at ambient temperatures. Remarkably, des-
pite this lack of solubility, 27 underwent a Kumada–Corriu
coupling with a simple solubilising group using Organ’s
PEPPSI-IPr catalyst, affording 28 in excellent isolated yield.
Gratifyingly 28 exhibited good solubility and solid-phase stabil-
ity, characteristics which are essential for device fabrication. Re-
crystallisation of 27 from o-DCB at 1818C eventually afforded
material suitable for crystallographic analysis. This analysis re-
vealed that 27 adopts a columnar p–p stacking morphology
(Figure 4) with edge–face interactions between adjacent
stacks, whereas DFT calculations indicated that the non-linear
annulation mode in 27 lessens the degree of conjugation of
the terminal rings with the central core.
The XRD data and DFT MO plots for 20 and 21 are present-
ed in Figure 3. Chloride 20 adopts a dimeric-herringbone pack-
ing arrangement, where pairs of molecules are held together
cofacially at the van der Waals distance, stabilised by the asym-
metric polarisation afforded by the chlorine substituent. Inter-
dimeric interactions are largely CH-p in nature, resulting in
a shortest CÀC interatomic distance of 3.59 . Similarly, 21
packs as a dimeric aggregate in the solid state, and again ex-
hibits an extensive network of CH-p interactions. The phenyl
substituents in 21 are essentially orthogonal to the plane con-
taining the central core, a structural feature which results in
Chem. Eur. J. 2015, 21, 9970 – 9974
9971 ꢀ 2015 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim