Easy access to 3,8-diaryldifurano[2,3-a:2',3'-f]naphthalenes. A new extended aromatic system

Article abstract of DOI:10.1021/jo005646o

3,8-Diaryldifurano[2,3-a:2',3'-f]naphthalenes were prepared in two simple steps. First, 1,5-dihydroxynaphthalene and 1-aryl-2-bromodecan-1-ones were condensed to the corresponding naphthalene 1,5-diethers. Second, these intermediates were cyclized using methanesulfonic acid in methylene chloride. Seven examples are given, three of which are doubly substituted with octyl chains to enhance the solubility. This increased solubility allowed further modification of the 3,8-aryl groups to attach electron-withdrawing groups (formyl, nitrile, dicyanovinyl, and benzoyl).

Full text of DOI:10.1021/jo005646o

J . Org. Chem. 2000, 65, 8783-8785
8783
Ea sy Access to 3,8-Dia r yld ifu r a n o[2,3-a :2′,3′-f]n a p h th a len es. A New
Exten d ed Ar om a tic System
Mikkel J ørgensen,* Frederik C. Krebs, and Klaus Bechgaard
Condensed Matter Physics and Chemistry Department, Risø National Laboratory,
DK-4000 Roskilde, Denmark
mikkel.joergensen@risoe.dk
Received September 14, 2000
3,8-Diaryldifurano[2,3-a:2′,3′-f]naphthalenes were prepared in two simple steps. First, 1,5-di-
hydroxynaphthalene and 1-aryl-2-bromodecan-1-ones were condensed to the corresponding naph-
thalene 1,5-diethers. Second, these intermediates were cyclized using methanesulfonic acid in
methylene chloride. Seven examples are given, three of which are doubly substituted with octyl
chains to enhance the solubility. This increased solubility allowed further modification of the 3,8-
aryl groups to attach electron-withdrawing groups (formyl, nitrile, dicyanovinyl, and benzoyl).
Sch em e 1
In tr od u ction
Extended aromatic systems have gained interest in
diverse fields such as organic light-emitting diodes,1 two-
photon absorption materials,2 second and higher order
nonlinear optics and large (supramolecular) structures.
New easily prepared building blocks with potential for
further elaboration could add stimulus to these research
areas.
In a search for new extended π-systems with possible
applications in both two-photon absorption and electro-
active polymers we have developed a synthesis of the
hitherto unknown 3,8-diaryldifurano[2,3-a:2′,3′-f]naph-
thalene system (see Scheme 1). The parent compound
difurano[2,3-a:2′,3′-f]naphthalene itself has been de-
scribed only once in the literature.3 Also the 3,8-dimethyl
derivative of this compound has been prepared previously
from 1,5-dipropynyloxynaphthalene by irradiation.4 Fur-
ther removed, but related, are the benzofuranes for which
a somewhat similar synthetic strategy has been devised.5
most general and satisfactorily method, however, was
found to be anhydrous methanesulfonic acid in hot
methylene chloride.
Resu lts a n d Discu ssion
When R2 is hydrogen or methyl these compounds are
only sparingly soluble in organic solvents. To improve the
solubility a variant with octyl chains in the R2 positions
were obtained from 1-aryl-2-bromodecan-1-ones. The
products 2a -c substituted with two octyl chains in the
2 and 7 positions are very soluble at ambient temperature
in common solvents facilitating further reactions shown
in Scheme 2.
An Ullman-type reaction between 2b and copper(I)
cyanide in hot collidine gave the dinitrile 2h . Exchange
of the bromine atoms in compound 2b with lithium atoms
using n-butyllithium in THF and subsequent quenching
of this intermediate with DMF produced the difurano-
naphthalene dialdehyde 2i. This compound was further
modified by condensation with malodinitrile producing
the bis(dicyanovinyl)difuranonaphthalene 2j. A Friedel-
Crafts reaction between the simple diphenyldifuranon-
aphthalene 2a and benzoyl chloride with aluminum
chloride in methylene chloride gave a mixture of mono-
and dibenzoylated product. The latter was purified by
column chromatography and proved to be the meta-
substituted derivative 2k by 1H NMR. A singlet resulting
A two-step synthetic procedure to the 3,8-diaryldifurano-
[2,3-a:2′,3′-f]naphthalenes 2a -g was developed as out-
lined in Scheme 1. One equivalent of 1,5-dihydroxynaph-
thalene was reacted with 2 equiv of an R-bromoaryl
ketone to produce the intermediary naphthalene 1,5-
diethers 1a -g in fair to good yields. Several methods for
the dehydration step to form the difuranonaphthalenes
2a -g were explored such as treatment with either
concentrated sulfuric acid or polyphosphoric acid. The
(1) Sheats, J . R.; Anthoniadis, H.; Hueschen, M.; Leonard, W.;
Miller, J .; Moon, R.; Roitman, D.; Stocking, A. Science 1996, 273, 884.
(b) Hide, F.; D´ıaz-Garz´ıa, M. A.; Schwartz, B. J .; Heeger, A. J . Acc.
Chem. Res. 1997, 30, 430.
(2) Albota, M.; Beljonne, D.; Bre´das, J .-L.; Ehrlich, J . E.; Fu, J .-Y.;
Heikal, A.; Hess, S. E.; Kogej, T.; Levin, M. D.; Marder, S. R.; McCord-
Maughon, D.; Perry, J . W.; Ro¨ckel, H.; Rumi, M.; Subramaniam, G.;
Webb, W. W.; Wu, X.-L.; Xu, C. Science 1998, 281, 1653.
(3) Dingankar, P. R.; Gore, T. S.; Gogte, V. N. Indian J . Chem. 1971,
9, 24.
(4) Moghaddam, F. M.; Sharifi A.; Saidi, M. R. J . Chem. Res. Synop.
1996, 7, 338.
(5) Habermann, J .; Ley, S. V.; Smits, R. J . Chem. Soc., Perkin Trans.
1 1999, 2421.
10.1021/jo005646o CCC: $19.00 © 2000 American Chemical Society
Published on Web 11/15/2000

8784 J . Org. Chem., Vol. 65, No. 25, 2000
J ørgensen et al.
Sch em e 2. F u r th er Mod ifica tion s of th e 3,8-Dia r yld ifu r a n on a p h th a len e System a
a
i: Cu(I)CN, ii: n-BuLi in THF at -78 °C, then DMF, iii: malodinitrile, iv: PhCOCl, AlCl3.
F igu r e 1. Stereoview of compound 2f (solid) and 2g (dotted) overlaid. It is noticeable that the substituent phenyl rings in compound
2g are more in plane with the central part of the molecule than compound 2f. This observation also hosts the explanation for the
yellow color of compound 2g as opposed to the colorless compound 2f.
from the isolated protons on the phenyl rings is observed
rather than a pattern due to, for example, a para
substitution. This outcome of the reaction is somewhat
surprising. The most reactive positions in the molecule
for electrophilic substitution would be expected to be in
the electron rich naphthalene nucleus rather than in the
phenyl groups. And even if the phenyl groups are the
preferred place of attack then para-substitution should
be favored. When the aluminum chloride was added to
the solution of 2a in methylene chloride, a dark red color
was observed indicating that a complex between the two
had formed presumably via oxygen-aluminum contacts.
This may explain the outcome of the reaction since it
would lead to a deactivation of the central difuranon-
aphthalene moiety and at the same time favoring meta-
substitution due to electron withdrawal from the phenyl
groups.
X-r a y Cr ysta llogr a p h y. The molecular conformation
of compounds 2f and 2g was found to be very similar and
in agreement with the proposed when considering the
aromatic core. It was, however, puzzling that crystals of
compound 2f are colorless whereas crystals of compound
2g had a pronounced yellow color. At first it was believed
that this was due to a crystal packing effect. When
considering the crystal structures this could, however,
not be the case due to the more extensive overlap between
neighboring molecules in compound 2f as compared to
compound 2g. It was found that the ethylene bridge in
compound 2g forces the plane of the substituent phenyl
ring to become more coplanar with the central aromatic
part than observed in compound 2f. The torsion angles
defining the tilt of the substituent phenyl ring with
respect to the plane of the central aromatic part was
found to be, respectively, 44.633° for compound 2f and
18.547° and 16.035° for compound 2g (there is one
molecule in the asymmetric of compound 2g and thus two
different torsion angles). This has been illustrated in
Figure 1 where the molecular structures have been
overlaid to emphasize the similarity in the central part
of the molecule and the dissimilarity in the conformation
of the substituent phenyl rings.
Exp er im en ta l Section
Gen er a l Section . Melting points are uncorrected. All
commercially available chemicals were used without further
purification. All solvent were reagent grade or better except
for THF which was freshly distilled from sodium-benzophe-
none ketyl.
1,5-Bis(p h en a cyl-2-yloxy)n a p h th a len es (1a -g). Gen -
er a l P r oced u r e. 1,5-Dihydroxynaphthalene (3.20 g, 20.0
mmol), the appropriate 2-bromo-1-phenyl ketone (45 mmol),
and dry K2CO3 (ca. 8 g) was mixed in HPLC grade acetone or
acetonitrile (100 mL) and heated to reflux under argon 4 h.
The cooled reaction mixture was then poured into water and
filtered, washed with water, and then recrystallized from a
suitable solvent.
3,8-Dia r yld ifu r a n o[2,3-a :2′,3′-f]n a p h th a len es (2a -g).
Gen er a l P r oced u r e. 1,5-Bis(phenacyloxy)-naphthalene (1a -
g) in methylene chloride was added 10 equiv of CH3SO3H to
give a deep red or violet solution/suspension. The reaction
mixture was stirred 1 h at reflux and then poured onto ice
and the solvent evaporated to precipitate the product. After
filtering and washing with water, ethanol, and diethyl ether,
the product was recrystallized.
3,8-Bis(4-cya n op h en yl)d ifu r a n o[2,3-a :2′,3′-f]n a p h th a -
len e 2h . Compound 2b (1.5 g, 2 mmol) and Cu(I)CN (3 g, 33
mmol) was mixed in collidine (25 mL) and heated to reflux
overnight. The solvent was distilled in a vacuum and the
residue extracted with methylene chloride. The organic phase
was washed several times with dilute ammonia to remove
copper salts. Evaporation in a vacuum gave a semisolid that
could be crystallized from acetonitrile. Yield: 52%. mp 142-3
°C. 1H NMR (250.1 MHz, CDCl3) δ: 0.90 (t, 6H, J ) 7 Hz),
1.2-1.4 (m, 20H), 1.90 (p, 4H, J ) 7 Hz), 2.99 (t, 4H, J ) 8
Hz), 7.69 (d, 4H, J ) 8 Hz), 7.73 (d, 2H, J ) 9 Hz), 7.85 (d,

3,8-Diaryldifurano[2,3-a:2′,3′-f]naphthalenes
J . Org. Chem., Vol. 65, No. 25, 2000 8785
4H, J ) 8 Hz), 8.20 (d, 2H, J ) 9 Hz). 13C NMR (62.9 MHz,
CDCl3) δ: 14.5, 23.0, 27.4, 29.0, 29.6, 29.7, 29.8, 32.2, 111.1,
116.2, 117.3, 118.7, 119.0, 119.3, 123.2, 130.1, 133.1, 138.5,
150.4, 156.0 ppm. Anal. Calcd for C44H46N2O2: C, 83.24; H,
7.30; N, 4.41. Found: C, 82.94; H, 7.36; N, 4.38.
ane-ethyl acetate (3:1) as eluent gave the pure dibenzoylated
1
product 2k . Yield: 0.43 g 54%. mp 171-2 °C. H NMR (250.1
MHz, CDCl3) δ:0.89 (t, 6H, J ) 7 Hz), 1.2-1.5 (m, 24H), 2.62
(t, 4H, J ) 7 Hz), 7.2-7.4 (m, 16H, 7.78 (s, 2H), 7.91 (d, 4H,
J ) 8 Hz). 13C NMR (62.9 MHz, CDCl3) δ: 14.5, 23.1, 27.0,
28.2, 29.5, 29.6, 29.8, 32.3, 115.7, 118.1, 119.8, 124.5, 127.7,
128.8, 129.2, 129.5, 130.4, 130.5, 132.4, 138.5, 149.3, 156.4,
198.6 ppm. Anal. Calcd for C56H56O4: C, 84.81; H, 7.12.
Found: C, 84.68; H, 7.02.
3,8-Bis(4-for m ylp h en yl)d ifu r a n o[2,3-a :2′,3′-f]n a p h th a -
len e 2i. Dibromodifuranonaphthalene 2b 5.0 g, 6.7 mmol was
dissolved in dry THF (100 mL) in a three-necked flask with
an argon bubbler and a septum and then cooled on a dry ice-
acetone bath to -78 °C. n-Butyllithium in hexanes (15 mmol)
was added and allowed to react at low temperature for 10 min.
DMF (5 mL, excess) was added, and the cooling bath was
removed. When the temperature had reached ambient after
30 min, dilute hydrochloric acid was added and the mixture
evaporated to dryness in a vacuum. The solid was triturated
with water and filtered to remove the salts. The dried product
was recrystallized from acetonitrile. Yield 83% mp 124-5 °C.
1H NMR (250.1 MHz, CDCl3) δ: 0.88 (t, 6H, J ) 7 Hz), 1.2-
1.4 (m, 20H), 1.89 (p, 4H, J ) 7 Hz), 7.74 (d, 4H, J ) 8 Hz),
7.75 (d, 2H, J ) 9 Hz), 8.04 (d, 4H, J ) 8 Hz), 8.18 (d, 2H, J
) 9 Hz). 13C NMR (62.9 MHz, CDCl3) δ: 14.5, 23.0, 27.5, 29.1,
29.6, 29.7, 29.8, 32.2, 116.0, 117.8, 118.9, 119.0, 123.4, 130.0,
130.7, 135.4, 140.1, 150.4, 156.0, 192.2 ppm. Anal. Calcd for
Cr ysta llogr a p h y Meth od s. Crystals of 2f and 2g were
drawn directly from the mother liquor, coated with a thin layer
of oil, mounted on glass needles using grease (Apiezon), and
transferred quickly into the cold nitrogen stream on the
diffractometer. Data were collected on a Siemens SMART
Platform diffractometer with a CCD area sensitive detector.
Absorption corrections were made using SADABS.6 Direct
methods for the structure solution and full-matrix least-
squares refinements were used. Hydrogen atoms were included
in calculated positions. Programs used were SMART, SAINT,
and SHELXTL from Siemens.7,8 The structures were checked
for overlooked symmetry using MISSYM and for voids in
PLATON.9 The crystals scattered X-rays weakly and this posed
particular problems for compound 2g in terms of the data
quality. What could be observed safely from the crystal-
lographic data were molecular geometry and packing arrange-
ments. Atomic coordinates and further crystallographic details
have been deposited with the Cambridge Crystallographic
Data Centre, University Chemical Laboratory, Lensfield Road,
Cambridge CB2 1EW, England.
C
44H48O4: C, 82.46; H, 7.55. Found: C, 82.45; H, 7.51.
3,8-Bis(4-d icya n ovin ylp h en yl)d ifu r a n o[2,3-a :2′,3′-f]-
n a p h th a len e 2j. Diformyldifuranonaphthalene 2i (1.0 g, 1.6
mmol) and malodinitrile (0.5 g, 7.6 mmol) was dissolved in
methylene chloride (25 mL), and one drop of concentrated
hydrochloric acid was added. The reaction mixture was heated
to reflux for a few minutes and then evaporated to dryness
and recrystallized from ethanol. Yield: 32%. mp 182-3 °C
(color change from yellow to orange at ca. 140 °C). 1H NMR
(250.1 MHz, CDCl3) δ: 0.87 (t, 6H, J ) 7 Hz), 1.2-1.4 (m,
20H), 1.90 (p, 4H, J ) 7 Hz), 3.01 (t, 4H, J ) 8 Hz), 7.75 (d,
2H, J ) 8 Hz), 7.77 (d, 4H, J ) 8 Hz), 7.82 (s, 2H), 8.08 (d,
4H, J ) 8 Hz), 8.19 (d, 2H, J ) 8 Hz).). 13C NMR (62.9 MHz,
CDCl3) δ: 14.5, 23.0, 27.6, 29.1, 29.6, 29.7, 29.8, 32.2, 82.5,
113.2, 114.3, 116.3, 117.5, 118.9, 119.0, 123.1, 129.9, 130.3,
131.8, 140.6, 150.5, 156.7, 159.5 ppm. Anal. Calcd for
Ackn owledgm en t. This work was carried out within
the framework of the Danish Polymer Centre.
Su p p or tin g In for m a tion Ava ila ble: Product character-
ization data for the compounds 1a -g and 2a -g. Tables of
fractional coordinates, equivalent isotropic and anisotropic
thermal parameters, bond lengths and bond angles, powder
diffractograms. This material is available free of charge via
the Internet at http://pubs.acs.org..
C
50H48N4O2*CH2Cl2: C, 74.90; H, 6.04; N, 6.72. Found: C,
75.29; H, 5.92; N, 6.77.
J O005646O
3,8-Bis(3-b en zoylp h en yl)d ifu r a n o[2,3-a :2′,3′-f]n a p h -
th a len e 2k . Compound 2a (0.58 g, 1.00 mmol) and benzoyl
chloride (0.35 g, 2.5 mmol) was dissolved in methylene chloride
(25 mL). Aluminum chloride (0.45 g, 3.4 mmol) was added,
and the dark red mixture was stirred at ambient temperature
for 15 min and then quenched by addition of water. The
solvents were removed in a vacuum, and the reddish residue
was washed with ethanol and then crystallized from heptane.
Further purification by chromatography on silica using hex-
(6) Emperical absorption program (SADABS) written by George
Sheldrick for the Siemens SMART platform.
(7) Sheldrick, G. M. SHELXTL95. Siemens Analytical X-ray Instru-
ments Inc.: Madison, WI, 1995.
(8) Siemens. SMART and SAINT. Area-Detector Control and Inte-
gration Software. Siemens Analytical X-ray Instruments Inc.: Madison
WI, 1995.
(9) Spek, A. L. Acta Crystallogr. 1990, A46, C-31.