Synthesis and molecular structure of symmetrical 1,8-diarylnaphthalenes

Article abstract of DOI:10.1002/ejoc.201000685

The synthesis of substituted 1,8-diarylnaphthalenes is reported. A bis-Suzuki coupling strategy starting from 1,8-dibromonaphthalene provides a useful and general route to the 1,8-diarylnaphthalene scaffold. In this context, N-heterocyclic benzhydrylamine ligands, in combination with PdCl₂, were found to form especially efficient catalytic systems. The syn/anti ratios were determined in solution from their ¹H NMR spectra. Analysis of the molecular structure in the solid state for six new targets focused on deformation of the naphthalene core. The observed lack of planarity occurs as a result of several parameters, such as the nature and number of substituents, the substitution pattern as well as steric congestion and π-stacking between cofacial rings. The synthesis of substituted 1,8-diarylnaphthalenes using bis-Suzuki coupling of 1,8-dibromonaphathalene is described. Molecular structures in the solid state for six new compounds were analyzed. The influence of several parameters on naphthalene core deformation are described.

Full text of DOI:10.1002/ejoc.201000685

FULL PAPER
DOI: 10.1002/ejoc.201000685
Synthesis and Molecular Structure of Symmetrical 1,8-Diarylnaphthalenes
Grégory Pieters,[a] Vincent Terrasson,[a] Anne Gaucher,*[a] Damien Prim,*[a] and
Jerôme Marrot[a]
Keywords: Conformation analysis / N ligands / Palladium / Stacking interactions / Structure elucidation
The synthesis of substituted 1,8-diarylnaphthalenes is re-
ported. A bis-Suzuki coupling strategy starting from 1,8-di-
bromonaphthalene provides a useful and general route to the
1,8-diarylnaphthalene scaffold. In this context, N-heterocy-
clic benzhydrylamine ligands, in combination with PdCl2,
were found to form especially efficient catalytic systems. The
syn/anti ratios were determined in solution from their 1H
NMR spectra. Analysis of the molecular structure in the solid
state for six new targets focused on deformation of the naph-
thalene core. The observed lack of planarity occurs as a re-
sult of several parameters, such as the nature and number of
substituents, the substitution pattern as well as steric conges-
tion and π-stacking between cofacial rings.
π interactions have been characterized in cyclic oligophenyl-
enes containing two 1,8-diarylnaphthalene subunits.[8] Co-
facially arranged mono- or polymeric metal sandwich com-
plexes have also attracted interest for their electrical, op-
tical, and magnetic properties.[9] Moreover, the pillared 1,8-
diarylnaphthalene motif has been used to elaborate cofacial
salen-type ligands and their corresponding Mn com-
plexes.[10] More recently, we described a short route to 6,11-
diamino[6]carbohelicenes starting from 1,8-diarylnaphtha-
lene.[11]
Thus, steric and electronic interactions between two cofa-
cial aromatics as well as the substitution pattern are not
only essential to the aforementioned applications, but also
deeply impact the preparation of 1,8-diarylnaphthalenes.
Most of these molecules are obtained through metal-as-
sisted carbon–carbon bond formation. Ni- and Cu- fol-
lowed by Pd-based catalytic systems have successively been
used to transform 1,8-dihalonaphthalenes into the expected
1,8-diarylnaphthalenes (Figure 1).[1–11,12]
Introduction
The 1,8-diarylnaphthalene scaffold is a fascinating exam-
ple of unusual geometry in organic molecules. Introduction
of two aromatic groups into both peri-positions of the
naphthalene core causes severe repulsion between the
stacked rings. This unique topology is not only due to the
nature of the aromatics but also to the presence of ad-
ditional substituents and their substitution pattern.[1] Gen-
eration of steric compression at the rings, which are con-
strained to face each other, may generate structural defor-
mations such as non-planarity of the almost perpendicular
naphthalene skeleton.[2] Since the first synthesis of 1,8-
bis(2,2Ј-dimethyl-1,1Ј-diphenyl)naphthalene by Clough and
Roberts,[3] several groups have described its syntheses and
analyses, for example, the anti/syn isomerization of such
motifs.[1a,4] Recently, some appealing applications have
taken advantage of the difficult or impossible rotations of
the aryl rings along the naphthalene axis. Indeed, 1,8-diac-
ridyl-, 1,8-diquinolyl-, or 1,8-dipyridyl-naphthalenes have
been developed as promising candidates for new photolumi-
nescent or chiral sensors and stereodynamic switches.[1a,5]
In addition, π-stacking between cofacial aromatics were
found to be essential in 1,8-diarylnaphthalene-based non-
linear optic chromophores or abiotic hydrid oligoamides.[6]
Blue-transparent frequency-doubling devices incorporating
thienyl, oligothienyl, or mixed pyridyl–thienyl branched
naphthalenes have also been recently reported.[7] Strong π–
Figure 1. Metal-assisted preparation of 1,8-diarylnaphthalenes.
[a] Institut Lavoisier de Versailles,
These cross-coupling reactions, which have been reported
to be sensitive to the nature and steric bulk of both part-
ners, often afford mixtures of bis- or monocoupling prod-
ucts. Suzuki- and Stille-type couplings are most commonly
employed, with the latter being recently found to be supe-
rior for highly congested partners. High yields in the cou-
Université de Versailles-Saint-Quentin-en-Yvelines,
45, Avenue des Etats-Unis, 78035 Versailles, France
Fax: +33-1-39254452
E-mail: prim@chimie.uvsq.fr
anne.gaucher@chimie.uvsq.fr
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201000685.
View this journal online at
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Synthesis and Structure of 1,8-Diarylnaphthalenes
pling may be obtained by using: (i) diiodonaphthalene de- performed with a very bulky boronic acid, such as naph-
rivatives; in this case the practicality of the overall process thylboronic acid, the the bis-coupling product 14 could be
is somewhat hampered by their tedious preparation; (ii) di- obtained in 65% yield. Employing heterocyclic boronic acid
bromonaphthalenes, which require 5 to 30% catalyst load- derivatives in the reaction appeared to be less versatile. In-
ings to ensure completion of coupling reactions. In ad- deed, the 1,8-di(3-thienyl)naphthalene was isolated in 73%
dition, both these procedures suffer from lack of generality. yield, whereas no coupling reaction occurred with pyridinyl
Further developments and new potential applications of boronic acids. This result may be due to a possible decom-
1,8-diarylnaphthalenes require reliable and convenient pre- plexation process that operates with the benzhydrylamine
parative methods that (i) allow access to variously substi- ligand during the catalytic coupling reaction.
tuted targets regardless of the nature and position of the
substituents; (ii) take into account the availability of the
starting materials; (iii) use easy-to-handle catalyst; (iv) re-
quire low catalyst loadings. We first report in this paper the
preparation of new 1,8-diarylnaphthalenes from dibro-
monaphthalene (1) through Suzuki type coupling reactions
using a phosphane-free catalytic system. The ease of access
to the starting material and the wide range of commercially
available boronic acids appears to favor this alternative ap-
proach. In addition, we recently described the preparation
of new nitrogen-based palladium(II) complexes that were
found to be stable and highly efficient in the syntheses of
biphenyls.[13] In the second part of this paper, we report the
results of our investigations into the molecular structure of
1,8-diarylnaphthalenes by means of 1H NMR and X-ray
analysis, with particular emphasis on the deformation of
the naphthalene core.
Scheme 1. Synthesis of 1,8-diarylnaphthalenes 3–16.
Results and Discussion
Table 1. Suzuki coupling products.
Synthesis
Most of the Pd-catalyzed reactions described in the lit-
erature for the synthesis of 1,8-diarylnaphthalene deriva-
tives involve the use of phosphane ligands. However, as de-
scribed above, those experimental conditions did not give
satisfactory results. This prompted us to use a phosphane-
free catalytic system (Scheme 1, Table 1).[14] Indeed, 1,8-di-
bromonaphthalene was coupled to a series of commercially
available boronic acids under Suzuki conditions in the pres-
ence of cesium carbonate and 1% palladium(II) complex
2
[13] in N,N-dimethylformamide (DMF)/water (95:5), which
led to the corresponding diarylnaphthalenes in good iso-
lated yields. Table 1 summarizes the results obtained under
the aforementioned conditions. The coupling reaction pro-
ceeded smoothly with most of the tested phenyl boronic
acids, even with ortho-substituted derivatives. Better yields
were observed with boronic acids bearing electron-donating
groups (Table 1, entries 2, 3, 5, 7, 9, and 10). Indeed, the
presence of the corresponding monocoupling product was
only detected when the phenyl boronic acid was substituted
with an electron-withdrawing group (Table 1, entries 4, 6,
8, and 13). Nevertheless, the electronic effects alone do not
completely explain the observed difference in yields. The
steric bulk of the boronic partners may also be responsible
for lower yields. However, even with 4-trifluoromethylphen-
ylboronic acid or 3-nitrophenylboronic acid, the bis-cou-
pling products 6 and 8 were isolated with acceptable 60 and
65% yields. Furthermore, when the Suzuki reaction was [a] Isolated yield.
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G. Pieters, V. Terrasson, A. Gaucher, D. Prim, J. Marrot
FULL PAPER
Molecular Structures
significantly increased the anti/syn ratio. The 86:14 ratio ob-
served in the latter case, may be attributed to an increased
steric repulsion between the electronically “hard” meta-flu-
orine substituents on each of the cofacial aromatics. Switch-
ing from ortho-methyl to ortho-methoxy groups led to a
similar increase in the anti/syn ratio from 74:26 (9) to 90:10
(11 and 12). Within this mixture, the anti conformer should
be favored, in agreement with the ratio determined above.
Since applications in various fields of current research
require the positioning of the cofacial rings to be almost
perpendicular to the naphthalene axis, deformation of the
naphthalene core may hamper further uses. The causes of
such deformation ate thus of considerable interest. The de-
formation of naphthalene planarity may arise from: (i) the
distance between the cofacial rings as a result of either π–π
or steric repulsive interactions; (ii) the number, nature, and
substitution position of additional substituents; (iii) the
presence of syn and/or anti conformers. The influence of
these parameters on the deformation of the naphthalene
core, which can be determined X-ray and, to a lesser extent,
Table 2. The anti/syn ratios in solution for compounds 4, 9–12, and
14–15.
Entry
anti/syn ratio Probe Characteristic 1H NMR shift
(T = 20 °C)
δ (anti)
δ (syn)
1
2
3
4
5
6
7
4
9
78:22
74:26
CH3
CH3
CH3
OCH3 3.47
OCH3 3.45
Ar(H) 6.95
1.89
1.79
1.80
1.92
1.86
1.85
3.79, 3.56
3.53
6.75
1.83
1
by H NMR analysis, has thus been determined and is dis-
10 79:21
11 90:10
12 90:10
14 82:18
15 86:14
cussed herein. To this end, the molecular structures of six
1,8-diarylnaphthalenes have been determined by X-ray
structure analysis and the degree of naphthalene core defor-
mation is compared.
CH3
1.86
Finally, we succeeded in the determination of the anti/syn
ratio for compound 14, bearing two cofacial 1-naphthyl
units (entry 6). As previously described,[15] in comparison
with compound 4 the presence of bulky naphthyl rings did
not significantly affect the anti/syn ratio (entry 6). The 82:18
anti/syn ratio calculated from the 1H NMR spectra may re-
sult from a compromise between an overall increase in the
bulk of the cofacial rings and a decrease in the hybridiza-
tion order from an sp3-C (methyl in 4) to an sp2-C (aro-
matic in 14).
Structures in Solution
1H NMR analysis may be useful to determine the
anti/syn ratio. However, the ease with which such infor-
mation can be obtained is strongly dependent on the nature
and position of additional probes, such as methyl groups.
As shown below, we were able to gain such information for
1,8-naphthalenes 4, 9–12, and 14–15. In contrast, careful
1
analyses of the H NMR spectra for compounds 8 and 13,
did not allow the anti/syn ratios to be determined even un-
der a range of temperature conditions. The H NMR spec-
1
troscopic data for 1,8-diarylnaphthalene 4 showed charac-
teristic features, and the observed privileged conformers is
noteworthy. As expected, both syn (minor, δ = 1.87 ppm for
CH3) and anti (major, δ = 1.84 ppm for CH3) conformers
were observed in a 22:78 ratio. The latter combined both
“in” and “out” forms as shown in Figure 2.[3]
Structures in the Solid State
Slow evaporation of solutions of 4, 6, 7, 11, 13, and 14
afforded suitable crystals that were subjected to X-ray
analysis. Selected data (crystallization space group, the con-
former present in the cell unit, bond lengths, and π–π inter-
actions) are gathered in Tables 3 and 4.
Table 3. Space group and conformer observed in the solid state.
Entry
Space group
Conformer
1
2
3
4
5
6
4
7
14
11
13
6
P21/c
P1
Ibca
P21/c
P21/c
P21/n
syn
–
anti
anti
syn
–
¯
Figure 2. Compound 4, syn and anti conformers.
Table 2 summarizes the anti/syn ratios determined from
1
the H NMR spectra, which are in agreement with a ther-
modynamically favored anti conformer in all cases. The
anti/syn ratios were determined by integration of the methyl
and methoxy group signals and, when possible, characteris-
tic naphthyl protons. Comparison of the anti/syn ratios for
compounds 4 and 9–10 revealed little influence of the para-
substituent; in these compounds the ratios ranged from
74:26 to 79:21 regardless of the nature of the substituent,
indicating that only the ortho-methyl group affected the
anti/syn distribution. Interestingly, moving from a para- to a
meta-fluoro-substitution pattern in 10 and 15, respectively,
Table 4. Bond lengths and π–π interactions.
Entry
Bond lengths [Å]
C(a)–C(b) C(b)–C(c) C(c)–C(d) C(d)–C(e)
π–π interaction
[Å]
1
2
3
4
5
6
7
4
7
1.507
1.492
1.497
1.500
1.490
1.490
1.489
1.439
1.441
1.439
1.435
1.440
1.441
1.439
1.467
1.441
1.439
1.438
1.444
1.441
1.439
1.511
1.492
1.497
1.500
1.485
1.488
1.490
3.66
3.52
3.49
3.51
3.46
3.46
3.60
14
11
13
13
6
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Eur. J. Org. Chem. 2010, 5800–5806

Synthesis and Structure of 1,8-Diarylnaphthalenes
Careful examination of the X-ray data revealed a number distances were observed for 1- and 2-naphthalenyl substitu-
of features that deserves some comment: (i) compounds 4, ents in 13 and 14, in which the planarity of the aromatic
6, 7, 11, 13, and 14 do not crystallize in the same space cofacial rings, and thus weaker steric congestion, is com-
group; compounds 4, 11, and 13 crystallize in monoclinic bined with stronger π–π interactions. A significant increase
P21/c space group, whereas compounds 7 and 14 crystallize in the distance between face-to-face rings was observed for
¯
in P1 and Ibca space groups, respectively. (ii) An examina- compounds 6 and syn-4. The increase (to 3.60 Å) may be
tion of the cell units and packing revealed the presence of attributed to steric repulsions between the electronically
one or more conformers. Unexpectedly, in the case of com- hard fluorine substituents bound to carbon atoms in the
pound 4, initial analysis of the X-ray data showed the sole CF3 moieties.[16] Both the syn conformation in 4 and the
presence of the minor syn-4 conformer, indicating a selec- steric crowding imposed by the presence of methyl groups
tive crystallization process (Figure 3). Unfortunately, exten- at the same naphthalene side may explain the further in-
sive attempts to obtain suitable crystals of the anti con- crease to 3.66 Å. Based on a recent paper dealing with acen-
former failed. In contrast, only the anti-in conformer was aphtene analogues,[17] a series of selected additional data
observed for diarylnaphthalenes 14 and 11. The crystal (interatomic distances, angles, and torsional angles) are
structure of 13, in which the naphthalene bears two cofacial gathered in Table 5, for compounds 4, 6, 7, 11, 13, and 14.
2-naphthalenyl groups, exhibits two syn conformers. (iii) In accordance with Cross et al.,[17] θ and φ values indicate
Table 4 summarizes selected bond lengths C(a)–C(b), C(b)– the degree of distortion of the naphthalene unit, whereas τ
C(c), C(c)–C(d), and C(d)–C(e) (see Figure 2 for atom lab- defines the relative conformation of the peri-phenyl ring
els), which may be affected by the steric compression at the and the interatomic distances (χ).
cofacial rings. It is worth noting that bond lengths C(a)–
C(b) and C(d)–C(e) are almost identical in the same mole-
cule, regardless of the conformation and the nature of the
substituents. Symmetrical diarylnaphthalenes 7 and 6 as
well as anti conformers 14 and 11 exhibit identical C(b)–
C(c) and C(c)–C(d) bond lengths, which may be explained
by mean of symmetry and homogeneous spreading of both
repulsion and steric compression over the naphthalene core.
In contrast, a marked difference in bond lengths [C(b)–C(c)
(1.439 Å) compared to C(c)–C(d) (1.467 Å)] is observed in
syn-4. In this case, an increase in the steric congestion, com-
bined with the syn conformation, may explain the observed
slight deformation and dissymmetry of the naphthalene
core. The through-space distance between the cofacial rings
(π–π interactions) may also reflect steric compression.
Table 5. Selected geometrical parameters.
Entry
1
θ [°]
φ [°]
τ [°]
χ [Å]
syn-4
6
17.58
2.53
2.24
3.06
3.97
6.26
5.35
3.08
3.62
3.66
3.66
1.68
2.26
84.50
75.81
3.019
2
3
4
5
6
18.09
20.28
16.12
16.60
16.43
115.37
117.74
122.76
122.34
107.64
106.86
106.90
106.90
67.97
3.000
3.024
2.940
2.956
2.986
7
anti-11
anti-14
syn-13
65.14
The observed θ (16.12 to 20.28°) and φ (1.68 to 6.26°)
values are consistent with an overall increase in the steric
bulk and strain in the molecule. Interestingly, these values
are somewhat different to those observed in the acenapht-
ene series, indicating the small influence of the additional
ethylene moiety compared with the naphthalene core. Inter-
estingly, the peri-aryl rings face each other at angles varying
from 56 to 74°. These values, which are larger than the cor-
responding angles in acenaphtenes, may be attributed to the
higher degree of flexibility of the naphthalene core.
Further examination of the X-ray structure revealed a
clear deformation of the naphthalene unit, depending on
the cofacial substituents (Figure 4). Because the naphtha-
lene plane deviation may be induced by face-to-face aro-
matics, it can be estimated from the dihedral angles abcd
and bcde.
The sums of dihedral angles, which range from 0.4 to
13.4°, are gathered in Table 6. Surprisingly, the presence of
two ortho methyl groups in syn-4 only slightly influenced
the alignment of the naphthalene unit. Almost perfect
Figure 3. Side view crystal structures of 4 (top left), 7 (top center),
6 (top right), 14 (bottom left), 13 (bottom center), and 11 (bottom
right).
Distances ranged from 3.46 to 3.52 Å in diarylnaphtha- stacking between both o-tolyl substituents is evidenced in
lenes 6, 7, anti-11, 13, and anti-14, regardless of the substit- the view along the naphthalene axis. An increase in the esti-
uent size. Interestingly, no difference was observed between mated deviation to 7.3–8.4° was observed for compounds
the two syn forms isolated for 13. In addition, the shortest 6, 11, and 13–14. Interestingly, the torsion angle does not
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G. Pieters, V. Terrasson, A. Gaucher, D. Prim, J. Marrot
FULL PAPER
mation, whereas the presence of four methyl substituents in
7 generated the highest steric compression and the largest
naphthalene torsion.
Experimental Section
General: Reactions were carried out in round-bottomed flasks
equipped with a magnetic stirring bar and capped with a septum.
DMF was distilled from CaH2. TLC analyses were performed on
Merck silica gel 60 F254 TLC plates (0.5 mm thickness); PE = pe-
troleum ether. 1H and 13C NMR spectra were recorded with Bruker
200 and Advance-300 spectrometers and referenced to CDCl3.
High-resolution mass spectroscopy (HRMS) data were recorded
with an Autospec Ultima (Waters/Micromass) device with a resolu-
tion of 5000 RP at 5%. Melting points were measured with a Büchi
B-545 apparatus.
Figure 4. View along the naphthalene axis of 4 (top left), 6 (top
center), 11 (top right), 13 (bottom left), 7 (bottom center), and 14
(bottom right).
General Procedure for the Suzuki Coupling: To a stirred suspension
of 1,8-dibromonaphthalene (1; 50 mg; 0.17 mmol), boronic acid
(0.42 mmol; 2.4 equiv.), and Cs2CO3 (285 mg, 0.87 mmol; 5 equiv.)
in DMF/H2O (95:5, 1 mL), was added the palladium complex 2
(0.8 mg; 1 mol-%). The mixture was stirred at 100 °C overnight.
Diethyl ether (20 mL) and H2O (20 mL) were then added and the
aqueous phase was extracted with diethyl ether (2ϫ10 mL). The
combined organic layers were dried (MgSO4), filtered, and concen-
trated under vacuum. The crude product was purified by flash
chromatography on silica gel to give the substituted 1,8-diarylnaph-
thalene as a solid. The atom numbering system used in the follow-
ing data is shown below.
seem to be dependent on the nature of the conformer, be-
cause syn-13, anti-11, and 14 display similar deformations.
Similarly, para-CF3 (Table 5, entry 2), ortho-methoxy
(Table 5, entry 4) as well as 1- or 2-naphthyl groups
(Table 5, entries 5 and 6) induce a slight deformation of
the naphthalene unit. In contrast, a large deformation is
observed for compound 7 (Table 5, entry 3). The presence
of four methyl groups, all located in meta positions of cofa-
cial aromatics, likely generates higher steric compression
and maximizes naphthalene torsion.
Table 6. Dihedral angles in naphthalenes.
Entry
Sum of dihedral angles [°]
abcd – edcb
1
2
3
4
5
6
syn-4
6
0.4
8.3
13.4
7.3
8.4
7.7
1,8-Diphenylnaphthalene (3): Purified by flash chromatography on
silica gel (PE) as a white solid (39 mg, 80%). H NMR (300 MHz,
7
1
anti-11
anti-14
syn-13
CDCl3): δ = 7.98 (dd, J = 8.1, 1.2 Hz, 2 H, H-n4), 7.58 (t, J = 7.0,
1.2 Hz, 2 H, H-n3), 7.44 (dd, J = 7.1, 1.3 Hz, 2 H, H-n2), 7.10–6.9
(m, 10 H, H-2 to H-6) ppm. 13C NMR (75 MHz, CDCl3): δ =
143.0, 140.4, 135.4, 131.0, 129.8, 129.2, 128.5, 127.1, 125.6,
125.1 ppm. Data are in accordance with the literature.[12]
1,8-Di(o-tolyl)naphthalene (4): Purified by flash chromatography on
silica gel (PE) as a yellow solid (43 mg, 80%). 1H NMR (300 MHz,
CDCl3): δ = 7.98 (dd, J = 8.3, 1.0 Hz, 2 H, H-n4), 7.53 (t, J =
7.6 Hz, 2 H, H-n3), 7.21 (dd, J = 7.0, 1.2 Hz, 2 H, H-n2), 7.03 (d,
J = 7.6 Hz, 2 H, H-6), 6.95–6.71 (m, J = 21.1, 6.7 Hz, 6 H), 1.92 [s,
2 H, CH3(syn)], 1.89 [s, 4 H, CH3(anti)] ppm. 13C NMR (75 MHz,
CDCl3): δ = 142.4, 142.00, 139.8, 139.7, 135.5, 135.1, 134.7, 131.4,
130.2, 130.1, 129.9, 128.9, 128.5, 128.4, 128.3, 126.7, 126.1, 125.0,
124.8, 124.4, 124.3, 20.6 ppm. HRMS (EI): calcd. for C24H20 [M]+
308.1565; found 308.1566. Data are in accordance with the litera-
ture.[11]
Conclusions
Fourteen 1,8-diarylnaphthalenes bearing various substit-
uents have been synthesized using a reliable and general bis-
Suzuki methodology. N-heterocyclic benzhydrylamine-
based PdII complexes were used as highly efficient catalytic
systems to afford the target compounds in high yields re-
gardless of the steric bulk of the substituents. The anti/syn
1
ratios were determined in solution from H NMR spectra
and ranged from 74:26 to 90:10, depending on the substitu-
tion pattern. Crystal structures have been determined and
compared to each other in the context of the naphthalene
core deformation. We have found that the steric crowding
imposed by the presence of substituents at cofacial rings
may significantly affect the alignment of the naphthalene
skeleton. The syn-4 conformer displayed an almost perfect
1,8-Bis(4-methoxyphenyl)naphthalene (5): Purified by flash
chromatography on silica gel (PE/AcOEt, 95:5) as a white solid
1
(50 mg, 85%); m.p. 147 °C. H NMR (300 MHz, CDCl3): δ = 7.93
(dd, J = 8.2, 1.3 Hz, 2 H, H-n4), 7.53 (t, J = 7.1 Hz, 2 H, H-n3),
7.41 (dd, J = 7.1, 1.4 Hz, 2 H, H-n2), 6.94–6.76 (m, 4 H, H-2 and
H-6), 6.56–6.41 (m, 4 H, H-3 and H-5), 3.73 (s, 6 H, OCH3) ppm.
stacking between the o-tolyl substituents and little defor- 13C NMR (75 MHz, CDCl3): δ = 157.6, 140.1, 135.7, 135.4, 130.8,
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Synthesis and Structure of 1,8-Diarylnaphthalenes
130.7, 129.6, 128.3, 125.0, 112.7, 55.2 ppm. Data are in accordance
with the literature.[10a]
H, H-6), 7.00–6.85 (dt, J = 7.4, 1.0 Hz, 2 H, H-5), 6.73 (dt, J =
7.4, 1.0 Hz, 2 H, H-4), 6.23 (d, J = 8.2 Hz, 2 H, H-3), 3.79 [s, 0.2
H, OCH3 (syn)], 3.56 [s, 0.2 H, OCH3 (syn)], 3.47 [s, 5.6 H, OCH3
(anti)] ppm. 13C NMR (75 MHz, CDCl3): δ = 155.5, 137.5, 134.1,
132.4, 131.9, 131.4, 130.9, 130.7, 130.1, 129.9, 128.8, 128.7, 128.2,
127.5, 124.9, 124.6, 119.0, 118.5, 108.9, 108.3, 54.7, 54.1 ppm.
HRMS (ESI): calcd. for C24H20O2Na 393.0851; found 393.0851.
1,8-Bis(4-trifluoromethylphenyl)naphthalene (6): Purified by flash
chromatography on silica gel (PE/CH2Cl2, 99:1) as a white solid
1
(43 mg, 60%); m.p. 202 °C. H NMR (300 MHz, CDCl3): δ = 8.02
(d, J = 8.3 Hz, 2 H, H-n4), 7.60 (t, J = 7.6 Hz, 2 H, H-n3), 7.41
(d, J = 7.0 Hz, 2 H, H-n2), 7.23 (d, J = 8.1 Hz, H-3 and H-5), 7.06
(d, J = 8.1 Hz, 4 H, H-2 and H-6) ppm. 13C NMR (75 MHz,
CDCl3): δ = 146.4, 138.5, 135.3, 131.1, 130.1, 129.4, 128.9, 128.5,
128.1, 125.7, 125.3, 124.1, 122.1 ppm. HRMS (EI): calcd. for
(C24H14F6) [M]+ 416.0999; found 416.1000.
1,8-Bis(2,4-dimethoxyphenyl)naphthalene (12): Purified by flash
chromatography on silica gel (PE/AcOEt, 95:5) as a white solid
1
(58 mg, 85%); m.p. 163 °C. H NMR (300 MHz, CDCl3): δ = 7.90
(dd, J = 8.3, 1.3 Hz, 2 H, H-n4), 7.54–7.42 (t, J = 7.1 Hz, 2 H, H-
n3), 7.31 [dd, J = 7.0, 1.4 Hz, 0.2 H, H-n2 (syn)], 7.21 [dd, J = 7.0,
1.4 Hz, 1.8 H, H-n2 (anti)], 6.96 [d, J = 8.2 Hz, 1.8 H, H-6 (anti)],
6.71 [d, J = 8.1 Hz, 0.2 H, H-6 (syn)], 6.32 [dd, J = 8.2, 2.3 Hz, 1.8
H, H-5 (anti)], 6.14 [m, 0.4 H, H-3 and H-5 (syn)], 5.84 [s, 0.9 H,
H-3 (anti)], 5.83 [s, 0.9 H, H-3 (anti)], 3.77 [s, 5.3 H, OCH3 (para,
anti)], 3.76 [s, 0.7 H, OCH3 (para, syn)], 3.53 [s, 0.7 H, OCH3 (ortho,
syn)], 3.45 [s, 5.3 H, OCH3 (ortho, anti)] ppm. 13C NMR (75 MHz,
CDCl3): δ = 159.9, 159.3, 156.7, 156.4, 137.2, 136.3, 134.2, 132.6,
131.6, 130.8, 130.1, 129.9, 128.7, 128.6, 125.1, 124.9, 124.6, 124.5,
103.3, 102.8, 97.1, 95.9, 55.3, 55.2, 54.8, 54.3, 54.2 ppm. HRMS
(ESI): calcd. for C26H22O4Na 423.1572; found 423.1567.
1,8-Bis(3,5-dimethylphenyl)naphthalene (7): Purified by flash
chromatography on silica gel (PE) as a white solid (50 mg, 86%);
1
m.p. 139 °C. H NMR (300 MHz, CDCl3): δ = 7.95 (dd, J = 8.2,
1.4 Hz, 2 H, H-n4), 7.56 (t, J = 7.5 Hz, 2 H, H-n3), 7.46 (dd, J =
7.0, 1.5 Hz, 2 H, H-n2), 6.66 (s, 4 H, H-2 and H-6), 6.60 (s, 2 H,
H-4), 2.17 (s, 12 H, CH3) ppm. 13C NMR (75 MHz, CDCl3): δ =
142.91, 140.74, 136.19, 135.39, 130.50, 129.37, 128.33, 127.50,
127.13, 124.96, 21.09 ppm. HRMS (EI): calcd. for (C26H24) [M]+
336.1878; found 336.1875.
1,8-Bis(3-nitrophenyl)naphthalene (8): Purified by flash chromatog-
raphy on silica gel (PE/AcOEt, 90:10) as a pale-yellow solid (42 mg,
1
65%); m.p. 189 °C. H NMR (300 MHz, CDCl3): δ = 8.07 (dd, J
1,8-Di(2-naphthyl)naphthalene (13): Purified by flash chromatog-
raphy on silica gel (PE) as a white solid (46 mg, 70%); m.p. 144 °C.
1H NMR (300 MHz, CDCl3): δ = 7.90 (d, J = 8.0 Hz, 2 H, H-n4),
7.72–6.76 (m, 18 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 140.4,
140.1, 135.3, 132.3, 132.1, 131.3, 131.1, 130.9, 130.7, 128.7, 128.3,
128.1, 127.6, 127.2, 126.9, 126.5, 126.2, 125.8, 125.3, 125.1,
124.9 ppm. Data are in accordance with the literature.[14]
= 8.3, 1.1 Hz, 2 H, H-n4), 7.91–7.54 (m, 7 H), 7.46 (dd, J = 7.1,
1.2 Hz, 2 H, H-n2), 7.35–7.13 (m, 3 H) ppm. 13C NMR (75 MHz,
CDCl3): δ = 146.9, 144.3, 136.8, 135.4, 135.1, 135.0, 131.5, 130.1,
128.5, 128.4, 125.6, 125.1, 124.7, 121.1 ppm. HRMS (ESI): calcd.
for C22H14N2O4Na 393.0851; found 393.0851.
1,8-Bis(2-methyl-4-methoxyphenyl)naphthalene (9): Purified by flash
chromatography on silica gel (PE/AcOEt, 95:5) as a white solid
(53 mg, 85%); m.p. 124 °C. 1H NMR (300 MHz, CDCl3, 300 K): δ
= 7.91 (dd, J = 8.3, 1.3 Hz, 2 H, H-n4), 7.49 (dt, J = 8.3, 1.3 Hz,
2 H, H-n3), 7.19 (dd, J = 7.0, 1.3 Hz, 2 H, H-n2), 6.90 [d, J =
8.3 Hz, 1.6 H, H-6 (anti)], 6.69 [d, J = 8.1 Hz, 0.4 H, H-6 (syn)],
6.39 (dd, J = 8.3, 2.7 Hz, 2 H, H-5), 6.34 [2ϫs, 0.4 H, H-3 (syn)],
6.29 [2ϫs, 1.6 H, H-3 (anti)], 3.74 [s, 1.2 H, OCH3 (para, syn)],
3.73 [s, 4.8 H, OCH3 (para, anti)], 1.86 [s, 1.2 H, CH3 (syn)], 1.79
[s, 4.8 H, CH3 (anti)] ppm. 13C NMR (75 MHz, CDCl3, 300 K): δ
= 158.0, 157.5, 139.4, 139.3, 136.8, 136.4, 135.3, 134.8, 134.7, 132.2,
130.9, 130.3, 130.1, 128.9, 128.5, 128.4, 124.9, 124.7, 114.3, 114.2,
110.2, 109.8, 56.1, 20.9, 20.8 ppm. Data are in accordance with the
literature.[11]
1,8-Di(1-naphthyl)naphthalene (14): Purified by flash chromatog-
raphy on silica gel (PE) as a white solid (43 mg, 65%); m.p. 174 °C.
1H NMR (300 MHz, CDCl3): δ = 8.10 (d, J = 8.1 Hz, 2 H), 7.60
(m, 4 H), 7.43–7.19 (m, 8 H), 7.10 (d, J = 8.2 Hz, 2 H), 7.00 (t, J
= 7.5 Hz, 1 H), 6.96–6.88 (m, 1.6 H), 6.71 [t, J = 7.5 Hz, 0.4 H
(syn)], 6.50 (d, J = 7.0 Hz, 2 H), 6.2 (t, J = 8.1 Hz, 2 H) ppm. 13C
NMR (75 MHz, CDCl3): δ = 140.0, 139.2, 138.6, 134.7, 132.5,
132.4, 132.2, 132.1, 131.6, 130.9, 130.8, 128.9, 128.8, 128.3, 127.6,
126.9, 126.8, 126.5, 126.4, 126.2, 125.2, 125.1, 124.9, 124.8, 124.6,
124.5, 123.9, 123.2 ppm. Data are in accordance with the litera-
ture.[14]
1,8-Bis(5-fluoro-2-methylphenyl)naphthalene (15): Purified by flash
chromatography on silica gel (PE) as a yellow solid (37 mg, 62%);
m.p. 98 °C. 1H NMR (300 MHz, CDCl3): δ = 7.97 (dd, J = 8.1,
1.1 Hz, 2 H, H-n4), 7.53 (t, J = 7.5 Hz, 2 H, H-n3), 7.22 (m, 2 H,
H-n2), 6.85 (d, J = 6.0 Hz, 0.85 H), 6.83 (d, J = 6.0 Hz, 0.85 H),
6.80 [d, J = 6.0 Hz, 0.15 H (syn)], 6.78 [d, J = 6.0 Hz, 0.15 H (syn)],
6.67–6.37 (m, 4 H), 1.86 [s, 5.1 H, CH3 (anti)], 1.83 [s, 0.9 H, CH3
(syn)] ppm. 13C NMR (75 MHz, CDCl3): δ = 160.0 (d, J = 242 Hz),
143.7, 143.6, 143.4, 143.3, 138.2, 138.1, 135.1, 134.8, 131.4, 131.3,
130.2, 130.1, 130.3, 130.3, 130.1, 130.0, 129.8, 129.6, 129.0, 125.1,
125.0, 118.0 (d, J = 21 Hz), 115.2 (d, J = 21 Hz), 113.6 (d, J =
21 Hz), 113.2 (d, J = 21 Hz), 19.6 ppm. HRMS (EI): calcd. for
(C24H18F2) [M]+ 344.1377; found 344.1379.
1,8-Bis(2-methyl-4-fluorophenyl)naphthalene (10): Purified by flash
chromatography on silica gel (PE) as a yellow solid (41 mg, 68%);
1
m.p. 158 °C. H NMR (300 MHz, CDCl3): δ = 7.95 (dd, J = 8.1,
0.8 Hz, 2 H, H-n4), 7.58–7.42 (m, 2 H, H-n3), 7.17 (m, 2 H, H-
n2), 6.94 (d, J = 6.0 Hz, 1.6 H), 6.91 (d, J = 6.0 Hz, 0.8 H), 6.74
[d, J = 6.0 Hz, 0.2 H (syn)], 6.72 [d, J = 6.0 Hz, 0.2 H (syn)], 6.68–
6.52 [m, 2 H (anti)], 1.85 [s, 1.5 H, CH3 (syn)], 1.80 [s, 4.5 H, CH3
(anti)] ppm. 13C NMR (75 MHz, CDCl3): δ = 162.0 (d, J =
245 Hz), 160.0 (d, J = 244 Hz), 138.5, 138.4, 138.3, 138.2, 138.0,
137.9, 137.8, 137.6, 137.4, 135.1, 134.8, 132.7, 132.5, 130.5, 130.4,
130.3, 130.2, 129.5, 129.3, 128.9, 128.8, 125.1, 124.9, 115.3 (d, J =
21 Hz), 115.2 (d, J = 21 Hz), 111.2 (d, J = 21 Hz), 111.1 (d, J =
21 Hz), 20.74, 20.71 ppm. HRMS (EI): calcd. for (C24H18F2) [M]+
344.1377; found 344.1376.
1,8-Di(3-thienyl)naphthalene (16): Purified by flash chromatography
1
on silica gel (PE) as a white solid (37 mg, 73%); m.p. 156 °C. H
1,8-Bis(2-methoxyphenyl)naphthalene (11): Purified by flash
NMR (200 MHz, CDCl3): δ = 7.93 (dd, J = 7.2, 2.4 Hz, 2 H, H-
n4), 7.63–7.41 (m, 4 H, H-n3 and H-n2), 6.90 (m, 4 H), 6.63 (dd,
chromatography on silica gel (PE/AcOEt, 97.5:2.5) as a white solid
1
(38 mg, 64%); m.p. 208 °C. H NMR (200 MHz, CDCl3): δ = 7.92 J = 4.7, 0.8 Hz, 2 H) ppm. 13C NMR (50 MHz, CDCl3): δ = 143.6,
(dd, J = 8.3, 1.3 Hz, 2 H, H-n4), 7.50 (t, J = 8.1 Hz, 2 H, H-n3),
7.21 (dd, J = 7.0, 1.4 Hz, 2 H, H-n2), 7.08 (dd, J = 7.3, 1.8 Hz, 2
135.2, 134.9, 130.7, 129.7, 129.4, 128.7, 125.1, 123.4, 121.9 ppm.
HRMS (EI): calcd. for (C18H12S2) [M]+ 292.0380; found 292.3767.
Eur. J. Org. Chem. 2010, 5800–5806
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
5805

G. Pieters, V. Terrasson, A. Gaucher, D. Prim, J. Marrot
FULL PAPER
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Received: May 12, 2010
Published Online: September 1, 2010
5806
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© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2010, 5800–5806