A peri-cyclised naphthalene dimer: Synthesis and properties of an unusual Vilsmeier-Haack product of 1,3,6,8-tetramethoxynaphthalene

Article abstract of DOI:10.1002/ejoc.201200512

An unusual peri-dimerised product was obtained when subjecting 1,3,6,8-tetramethoxynaphthalene to Vilsmeier-Haack reaction conditions (POCl₃/DMF). The formation of this peri-dimerised naphthalene product suggests that 1,3,6,8-tetramethoxynaphthalene has comparable reactivity to that of Proton Sponge [1,8-bis(dimethylamino)naphthalene]. The octamethoxy peri-dimer was characterised using NMR spectroscopy, mass spectrometry, UV/Vis spectroscopy, Raman spectroscopy, electrochemistry, X-ray crystallography and DFT calculations. The one-electron oxidation of the peri-dimerised naphthalene compound yielded a radical cation that was studied by EPR spectroscopy and UV/Vis spectroscopy at low temperatures. The experimental observations were confirmed by DFT calculations. The Vilsmeier-Haack reaction (POCl ₃/DMF) of 1,3,6,8-tetramethoxynaphthalene gave an unusual peri-cyclised dimer as well as the 1-naphthaldehyde. The dimer is a potent donor molecule. Copyright

Full text of DOI:10.1002/ejoc.201200512

Job/Unit: O20512
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Date: 03-07-12 15:50:59
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FULL PAPER
DOI: 10.1002/ejoc.201200512
A peri-Cyclised Naphthalene Dimer: Synthesis and Properties of an Unusual
Vilsmeier–Haack Product of 1,3,6,8-Tetramethoxynaphthalene
Michael Pittelkow,*[a] Christian B. Nielsen,[a] Theis Brock-Nannestad,[a]
Magnus Schau-Magnussen,[a] and Jørn B. Christensen*[a]
Keywords: Naphthalenes / Density functional calculations / peri-Effect / Dimerization / Arenes / Radical ions
An unusual peri-dimerised product was obtained when sub-
jecting 1,3,6,8-tetramethoxynaphthalene to Vilsmeier–Haack
reaction conditions (POCl3/DMF). The formation of this peri-
dimerised naphthalene product suggests that 1,3,6,8-tetra-
methoxynaphthalene has comparable reactivity to that of
Proton Sponge [1,8-bis(dimethylamino)naphthalene]. The
octamethoxy peri-dimer was characterised using NMR spec-
troscopy, mass spectrometry, UV/Vis spectroscopy, Raman
spectroscopy, electrochemistry, X-ray crystallography and
DFT calculations. The one-electron oxidation of the peri-di-
merised naphthalene compound yielded a radical cation that
was studied by EPR spectroscopy and UV/Vis spectroscopy
at low temperatures. The experimental observations were
confirmed by DFT calculations.
alene cores are particularly effective in the stabilisation of
naphthylmethyl carbocations (especially in the α-position).
An example of such substituents would be the 1,8-bis(di-
methylamino) groups in Proton Sponge. The formation of
stable benzyl-like carbocations in the vicinity of very elec-
tron-rich aromatic cores may give rise to electrophilic aro-
matic substitution reactions. Some of the unusual peri-
cyclised structures isolated by Pozharskii and co-workers
are shown in Figure 1.
Introduction
The 1- and 8-positions in naphthalenes are peri (literally
meaning “near”) to each other.[1,2] Two substituents in peri
positions are (for most functional groups) located in closer
proximity to each other than are substituents in ortho posi-
tions. The peri positions in naphthalenes are the simplest
example of a peri region in polycyclic aromatic hydro-
carbons (PAHs), making it the most obvious system to
study to understand the reactivity of larger PAHs. Balasub-
ramaniyan recognised that steric strain due to bulky substi-
tution at interfering positions can be relieved in a number
of ways, including stretching of bonds, in-plane deflection
of the substituents, out-of-plane deflection of the substitu-
ents, and distortion or buckling of the naphthalene nu-
cleus.[1] When designing materials based on naphthalenes
(or larger PAHs), the peri-effect must be taken into con-
sideration to account for factors that seem straightforward
when designing materials based on benzene.[3] Overcrowd-
ing has a profound influence on the properties of materials
based on PAHs, and issues such as planarity of the aromatic
core, reactivity, and substituent effects are less trivial than
for benzene-based materials.[4]
Figure 1. Proton Sponge [1,8-bis(dimethylamino)naphthalene] and
peri-cyclised structures.
In elegant work by Pozharskii and co-workers on the
substitution of 1,8-bis(dimethylamino)naphthalene (Proton
Sponge) by various electrophilic reagents, some unusual
products have been described (Figure 1).[5] Electron-donat-
ing substituents placed in strategic positions on naphth-
In a recent study, we have used DFT calculations to pre-
dict the energy requirements for the formation of various
methoxy-substituted naphthylmethyl carbocations.[6] These
calculations showed that the energy requirements for the
formation of the carbocation are sensitive to a number of
factors, such as substitution pattern, planarity of the aro-
matic core, and the peri-effect. The most pronounced desta-
bilising effect proved to be overcrowding of the periphery
of the aromatic core, which forced the substituents out of
the aromatic plane, thus interrupting the conjugation.
[a] Department of Chemistry, University of Copenhagen,
Universitetsparken 5, 2100 Copenhagen Ø, Denmark
E-mail: pittel@kiku.dk
jbc@kiku.dk
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201200512.
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M. Pittelkow, J. B. Christensen et al.
FULL PAPER
These computational considerations indicated that
a
performing NMR spectroscopy, the compound was sensi-
2,4,5,7-tetramethoxy-1-naphthylmethyl carbocation would tive to trace amounts of acid in the CDCl3. The proton
be the most stable methoxy-substituted naphthylmethyl NMR spectrum of 5 showed only a few signals, indicating
carbocation.
a high degree of symmetry. Mass spectrometry (FAB+) and
In this paper, we show that the introduction of four elemental analysis indicated a dimeric condensation prod-
methoxy substituents in such a way as to avoid over-crowd- uct. We speculate that the mechanism for the formation of
ing of the periphery of the naphthalene core results in an 5 is a double electrophilic aromatic substitution reaction at
effect on the reactivity of the aromatic core comparable to the peri positions on opposite molecules. Dehydration and
that arising from the introduction of the peri-bis(dimethyl- cyclisation would give the locked polycyclic molecule.
amino) substituents in Proton Sponge. Furthermore, we
show that the dimeric naphthalene compound formed is a
potent donor molecule in which the two naphthalene moie-
ties interact with each other through space.
X-ray Crystallographic Analysis
Upon crystallisation by slow concentration of a solution
of 5 in a 1:1 mixture of CH3CN/heptane, two distinct crys-
tal morphologies of the same compound appeared: one
consisting of white plates (5a, with heptane, Figure 2) and
one consisting of white octahedral crystals (5b, with MeCN,
Figure 3). The structure of 5 was confirmed to be a product
Synthesis
Tetrahydroxynaphthalene (2) was prepared in 56% yield
by modifying the procedure of Tanaka et al.[7] Thus, chro-
motropic acid sodium salt (1) was heated with a mixture of
Ba(OH)2(s), KOH(s), and NaOH(s) to 250 °C under a flow
of N2 overnight. Tetramethylation proceeded to completion
upon heating an acetone suspension of the tetrahydroxy
compound with excess dimethyl sulfate and K2CO3 for 48 h
(85%). It was found to be more convenient to methylate
the crude 1,3,6,8-tetrahydroxynaphthalene to yield 1,3,6,8-
tetramethoxynaphthalene (3).[8]
The transformation of 1,3,6,8-tetramethoxynaphthalene
(3) into aldehyde 4 using a Vilsmeier–Haack formylation
(POCl3 in DMF) proved to be highly dependent on concen-
tration, temperature and reaction time (Scheme 1).[8,9] At
temperatures below –10 °C, no reaction occurred, and only
when allowing the reaction mixture to heat up slowly to
–5 °C did the formylation reaction take place. When per-
forming this reaction under relatively dilute conditions
(0.03 m) at –5 °C, aldehyde 4 was isolated as a single isomer
in moderate yield (52%) after 2 h. When scaling this reac-
tion up to gram scale, we carried out the reaction in a more
concentrated solution (0.16 m), and the reaction mixture
was stirred at room temperature overnight. This resulted in
a disappointing 2% yield of the aldehyde and the formation
of another compound as the major product (5, 65%). When
Figure 2. X-ray crystal structure of MeCN-solvated compound 5b.
Scheme 1. Reagents and conditions: (a) Ba(OH)2·8H2O, KOH,
NaOH, 260 °C, 12 h, 56%; (b) (i) Ba(OH)2·8H2O, KOH, NaOH,
260 °C, 12 h, (ii) Me2SO4, acetone, K2CO3, 48 h, 60% (two steps);
Figure 3. Views of the X-ray crystal structure of the heptane-sol-
(c) POCl3, DMF, c = 0.03 m, –5 °C, 2 h, 52% (4); (d) POCl3, DMF, vated crystals of 5a showing the chains of alkane surrounded by
c = 0.16 m, –5 °C, 24 h, 65% (5).
molecules of 5.
2
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A peri-Cyclised Naphthalene Dimer
of dimerisation of 4 with the loss of one water molecule.
The molecule is highly symmetrical with only two different
types of methoxy substituent and only one type of aromatic
protons. The two naphthalene moieties are connected
through the peri positions forming an eight-membered ring.
This eight-membered ring is further bridged by an oxygen
atom to complete the rigid polycyclic structure of 5.
When viewing only one molecule of 5, the angle between
the two naphthalene moieties (mean planes) is 111.7°, and
all the methoxy groups have their methyl moieties in the
plane of the aromatic ring. The coplanarity of the methoxy
substituents is a feature that is supported by our computa-
tional predictions.[6]
The two different crystal morphologies were a result of
co-crystallisation with each of the two crystallisation sol-
vents. In the MeCN-solvated crystal structure, the density
of 5 is higher than in the heptane-solvated crystals of 5.
The heptane-solvated crystals are particularly interesting as
the disordered chains of heptane are part of an inclusion
complex with 5, as seen in the packing of the crystal struc-
ture (Figure 2).
where ω is the frequency, ωo is electronic origin frequency,
ωp is the phonon frequency, Si is the Huang–Rhys factor, i
is a normal mode in the final state with frequency ωp, σ is
the width of the broadened line at half height for the elec-
tronic transition at ωo, and ni is the progression of the ith
normal mode in the Poisson distribution. The “+” sign is
used for analysing absorption spectra and the “–” sign for
emission spectra (see Supporting Information).
Two vibrational modes were used to model the fine struc-
ture in the absorption band centered around 3.6 eV ob-
served in the spectrum of 5, whereas only one vibrational
mode was used to model the band observed at ca. 5.4 eV.
One of the two modes contributing to the low-energy band
is actually an overtone of the other. For the phonon energy,
we found values of 0.18 eV (1450 cm–1) and 0.39 eV
(2981 cm–1), the latter being assigned as an overtone. The
corresponding S values are 1.15 and 0.27, respectively. A
strong band at 1392 cm–1 and a weaker band at 1450 cm–1
were found in the Raman spectrum of 5 (see Supporting
Information). From the analysis, a value for the energy of
the electronic transition S0ǞS1 of 3.43 eV was found.
The Franck–Condon analysis of the bands observed in
the spectrum of 3 revealed phonon energies of 0.16 and
0.32 eV, with corresponding S values of 1.44 and 0.97, thus
an overtone is likely to be contributing to the phonon cou-
pling.[11] Attempts to describe the spectrum with only one
vibrational mode were not successful, and including more
than two modes did not result in a better fit. Previous work
on the photophysics of conjugated polymers has shown that
the Huang–Rhys factor for a specific transition decreases
when the chain-length is increased. Along with the observa-
tion that there is a redshift in the absorption spectra for the
lowest-lying states when going from 3 to 5, this indicates
that there is an electronic communication between the two
naphthalene rings in 5.
Optical and Vibrational Spectroscopy
In Figure 4, the UV/Vis spectra of 1,3,6,8-tetrameth-
oxynaphthalene (3) and dimer 5 in acetonitrile are shown.
For 3, two bands were observed, with vibrational fine struc-
ture only being observed for the low-energy band. Fine
structure was observed for both of the bands observed in
the spectrum of 5, and a Franck–Condon analysis using the
Huang–Rhys approach was carried out for both bands.[10]
The purpose of this analysis was to quantify the S1 energy
in order to scrutinise the ability of subsequent DFT calcula-
tions to predict the electronic structure of the molecule.
DFT Calculations
Calculations were performed on 5 using the well-estab-
lished B3LYP/6-31G(d) level of theory. Initially, a geometry
optimisation was carried out, and using this geometry the
excitation energies and oscillator strengths for the 30 lowest
states were calculated. The results of these calculations are
shown in the Supporting Information. In Figure 5, the
HOMO and LUMO of 5 are shown, indicating some elec-
tronic through-bond communication between the two naph-
thalene moieties. In particular, in the HOMO–1 and
LUMO orbitals, part of the orbitals extends from one
naphthalene unit to the other across the eight-membered
ring. A single electronic transition governing the low energy
of the spectrum was observed with an excitation energy of
Figure 4. UV/Vis spectra of dimer 5 and 1,3,6,8-tetramethoxynaph-
thalene (3) in MeCN. The red curves are the calculated bands based
on the Franck–Condon analysis.
The Franck–Condon/Huang–Rhys analysis was carried 3.47 eV, in good agreement with the experimentally ob-
according to the following expression,[11]
served value.
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M. Pittelkow, J. B. Christensen et al.
FULL PAPER
Figure 5. Orbital picture for the HOMO–1, HOMO, LUMO and
LUMO+1 of the naphthalene dimer 5.
Figure 6. Top: EPR spectrum of oxidised dimer 5 at 170 K (g =
2.002). Middle and bottom: CV and SW voltammograms of dimer
5 in CH2Cl2 with 0.1 m Bu4NPF6 as the supporting electrolyte
against the Fc/Fc+ couple. The scan rate was 0.3 V/s.
Electrochemistry and EPR Spectroscopy
Electrochemical measurements of dimer 5 showed two
independent oxidations at approximately 0.75 V and 0.86 V
against the Fc/Fc+ couple. In Figure 6, the cyclic voltam-
mogram and the square wave (SW) voltammogram are
shown. In the SW voltammogram it is especially clear that
the oxidation proceeds in two steps. This indicates that the
oxidation of the first naphthalene moiety influences the oxi-
dation of the second naphthalene moiety.
in liquid N2, and then a solution of the oxidant in MeCN
was added and frozen. This mixture was then allowed to
warm up and mix in the cooled EPR apparatus, and EPR
spectra were recorded at different temperatures. At 70 K,
the EPR signal was very weak, but gradual heating of the
sample to 170 K gave a convincing EPR signal (Figure 6).
The EPR signal corresponds to the mono-oxidised species.
Even with an excess of the oxidising agent, the doubly oxi-
dised species was not observed by EPR. A UV/Vis spectrum
of the oxidised species was recorded at ca. 195 K, and it
showed a band at 642 nm. This band is presumably due to
the radical cation.
Electrocrystallisation of dimer 5 with Bu4NPF6 in
CH2Cl2 was attempted with approximately 10 μA using a
standard setup. The solution turned green, and a dark pre-
cipitate was observed. However, no X-ray quality crystals
were obtained. Upon chemical oxidation of 5 by addition
–
of NO+BF4 in MeCN to a solution of 5 in CH2Cl2, the
mixture immediately turned green, but the colour quickly
turned yellow/orange. This solution was characterised by
UV/Vis spectroscopy and EPR spectroscopy. The UV/Vis
spectrum showed a band at 510 nm. The solution was yel-
low-fluorescent, and MALDI-TOF analysis and TLC
Conclusions
The formation of a peri-cyclised dimeric species of
analysis of the oxidised solution did not show the presence 1,3,6,8-tetramethoxynaphthaldehyde under Vilsmeier–
of the starting material. The yellow/orange species was Haack conditions has been observed. The dimer has been
EPR-silent. During the oxidation, a green colour was ob- characterised by NMR spectroscopy, mass spectrometry, el-
served, and if the oxidation was performed at –78 °C, the emental analysis, UV/Vis spectroscopy, fluorescence spec-
green colour persisted for several minutes. This green spe- troscopy, Raman spectroscopy, electrochemistry, ESR spec-
cies was EPR-active, and the EPR spectroscopy was per- troscopy, and single-crystal X-ray crystallography. The
formed in the cold. A solution of 5 in CH2Cl2 was frozen spectroscopic properties have been confirmed by DFT cal-
4
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A peri-Cyclised Naphthalene Dimer
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
culations. This dimeric species is formed as a consequence
of the electron-rich nature of the aromatic core induced by
the four methoxy substituents. These four methoxy substit-
uents affect the reactivity of the aromatic core similarly to
how the two peri-(dimethylamino) substituents affect the re-
activity of Proton Sponge. The two naphthalene moieties
communicate, as observed by UV/Vis spectroscopy, and a
radical cation is observed by EPR spectroscopy. Donor ma-
terials based on electron-rich naphthalene compounds
could compliment the properties of other electron-rich aro-
matic compounds such as TTF, thiophene and alkoxybenz-
enes. Further studies into the reactivity of these types of
compounds are necessary to allow their implementation in
materials science.
Table 1. X-ray structure and refinement data for 5a and 5b.
5a
5a
Empirical formula
Formula mass
C30H30O9·C3H7
577.63
C30H30O9·0.5C2H3N
555.07
Crystal system
a [Å]
b [Å]
c [Å]
tetragonal
12.6748(10)
12.6748(10)
36.6642(19)
90
monoclinic
30.9946(7)
7.8373(10)
21.5701(25)
90
α [°]
β [°]
90
90
5890.3(7)
122(1)
I4, 2d
99.328(9)
90
5170.2(9)
122(1)
C2/c
8
γ [°]
V [Å3]
Temperature [K]
Space group
Z
8
Experimental Section
Radiation type
Mo-Kα
0.094
Mo-Kα
0.105
μ [mm–1]
General Experimental Procedures: Thin-layer chromatography
(TLC) was carried out using aluminium sheets pre-coated with sil-
ica gel 60F (Merck 5554). Dry column vacuum chromatography
was carried out using silica gel 60 (Merck 9385, 0.015–
0.040 mm).[12] Melting points were determined with a Büchi melt-
ing point apparatus. 1H NMR (300 MHz) and 13C NMR (75 MHz)
spectra were recorded using a Varian instrument. Samples were
prepared using deuterated solvents (CDCl3, [D6]DMSO, CD2Cl2)
purchased from Cambridge Isotope Labs. Fast atom bombardment
(FAB) spectra were obtained with a Jeol JMS-HX 110 tandem mass
spectrometer in the positive-ion mode using 3-nitrobenzyl alcohol
(NBA) as matrix. EI mass spectra were recorded with a ZAB-EQ
(VG-Analytical) instrument. Microanalyses were performed by
Mrs. Birgitta Kegel at the Microanalytical Laboratory of the De-
partment of Chemistry, University of Copenhagen. UV/Vis spectra
were recorded with a Cary 5E spectrometer (Varian Inc.) with pure
solvent as baseline. The Raman spectra were recorded with a
Bruker IFS66 NIR-FT instrument equipped with an FRA106 Ra-
man module. An Nd:YAG laser operating at 1064 nm with an out-
put of 300 mW was used as the excitation source. The detector was
a Ge diode cooled to liquid-nitrogen temperature. 1,3,6,8-Tetra-
methoxynaphthalene was synthesised according to ref.[8]
No. of reflections measured
No. of independent reflections 6489
Rint
95824
74180
8970
0.1162
0.0538
0.1261
0.0866
0.1511
1.090
0.0721
0.0605
Final R1 value [IϾ2σ(I)]
Final wR(F2) value [IϾ2σ(I)] 0.1590
Final R1 value (all data)
Final wR(F2) value (all data)
Goodness of fit on F2
0.0855
0.1817
1.125
Calculations: The Gaussian 03 suite of programs was used for the
DFT calculations.[15] Initially, geometry optimisations were carried
out at the B3LYP/6-31G(d) level of theory, where all the structures
were constrained to C2v symmetry. Frequency calculations were
then carried out to assure that the structures were indeed minima
on the potential energy surface (no imaginary frequencies). TD-
DFT calculations and single-point calculations on the anion radi-
cals were then carried out at the B3LYP/6-31G(d) level of theory on
these optimised structures. The Gaussian archive entries for these
calculations are included in the Supporting Information.
GaussView 3.0 was used for generating the orbital plots.
Cyclic Voltammetry: Tetrabutylammonium tetrafluoroborate,
Bu4NBF4 (Aldrich, 98%) and acetonitrile, MeCN (Lab-Scan,
HPLC grade) were used as received. The cell was a cylindrical vial
equipped with a Teflon top with holes to accommodate the Pt
working electrode, the Pt counter electrode and the Fc/Fc+ elec-
trode. The electrochemical equipment was from CHI instruments
(CH630), with iR compensation. The solutions for voltammetry
were 1 mm in substrate, and were made by dissolving an accurately
weighed amount of the substrate in the required volume of an
MeCN/Bu4NBF4 (0.1 m) solution. The volume of the resulting
solutions was typically between 5 and 10 mL. The solutions were
purged with nitrogen saturated with MeCN for at least 10 min prior
to the measurements.
Electron Paramagnetic Resonance Spectroscopy: EPR spectra were
recorded using a Bruker Elexsys E-500 instrument equipped with
an EIP 538B frequency counter and an ER035M NMR Gauss me-
ter. The EPR spectroscopy was performed in the cold.
X-ray Crystallography: All single-crystal X-ray diffraction data
were collected at 122(1) K with a Nonius KappaCCD area-detector
diffractometer equipped with an Oxford Cryostreams low-tempera-
ture device using graphite-monochromated Mo-Kα radiation (λ =
0.71073 Å). The structures were solved by direct methods
(SHELXS97), and refined using the SHELXL97 software pack-
age.[13] All non-hydrogen atoms were refined anisotropically, hydro-
gen atoms were located in the difference Fourier map and refined
isotropically as constraint riding their parent atom in a fixed geom-
etry. The structure of 5a contains disordered solvent. The packing
of 5a facilitates solvent-accessible channels in which the alkanes of
crystallisation are distributed disorderedly. The disorder was mod-
elled by a hexane molecule which by symmetry results in solvent
chains running through the structure. Crystal structure and refine-
ment data for 5a and 5b are summarised in Table 1. The molecular
structure diagrams were made with the ORTEP-3 and Mercury
Dimer 5: 1,3,6,8-Tetramethoxynaphthalene (3) (1.55 g, 6.24 mmol)
was dissolved in anhydrous DMF (40 mL), and the mixture was
cooled to –5 °C. POCl3 (1.72 mL, 2.87 g, 18.7 mmol) was added
dropwise over 5 min. The reaction mixture was stirred for 30 min
at –5 °C, and then water (20 mL) was added, and the reaction mix-
ture was stirred at room temperature for 16 h. The yellow mixture
was extracted with CH2Cl2 (6ϫ40 mL), dried (MgSO4), and fil-
tered through paper, and the solvents were evaporated to dryness
3.0.1 programs[14] (Figures 2 and 3). CCDC-870028 (for 5a) and in vacuo. Dry column vacuum chromatography (heptane to EtOAc
-870029 (for 5b) contain the supplementary crystallographic data with 10% increments) yielded aldehyde 4 as a colourless solid (yield
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M. Pittelkow, J. B. Christensen et al.
FULL PAPER
1999, 48, 1299–1309; b) A. F. Pozharskii, Russ. Chem. Rev.
1998, 67, 1–24; c) A. F. Pozharskii, O. V. Ryabtsova, N. V. Vis-
torobskii, Z. A. Starikova, Russ. Chem. Bull. 2000, 49, 1097–
1102.
M. Pittelkow, J. B. Christensen, T. I. Sølling, Org. Biomol.
Chem. 2005, 3, 2441–2449.
H. Tanaka, Y. Ohne, N. Ogawa, T. Tamura, Agric. Biol. Chem.
1963, 27, 48.
M. Pittelkow, U. Boas, J. B. Christensen, Org. Lett. 2006, 8,
5817–5820.
40 mg, 2%) and the dimer 5 as a colourless solid (yield 1.1 g, 65%).
M.p. 256–258 °C (decomposition). H NMR (CDCl3): δ = 6.83 (s,
1
2 H), 6.43 (s, 4 H), 3.97 (s, 12 H), 3.91 (s, 12 H) ppm. 13C NMR
(CDCl3): δ = 157.5, 153.1, 131.2, 112.5, 108.2, 93.8, 64.5, 56.5,
56.3 ppm. MS (FAB+): m/z = 534.2. HRMS (FAB+): calcd. for
C30H30O9 534.1890; found 534.1904. C15H16O5 (276.29): calcd. C
67.41, H 5.66; found C 67.03, H 5.71.
[6]
[7]
[8]
Supporting Information (see footnote on the first page of this arti-
cle): NMR and Raman spectra, computational data.
[9]
G. Jones, S. P. Stanforth, Org. React. 1997, 49, 1–330.
[10]
K. Kanemoto, T. Sudo, I. Akai, H. Hashimoto, T. Karasawa,
Y. Aso, T. Otsubo, Phys. Rev. B 2006, 73, 235203.
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Professor Jesper Bendix is thanked for valuable discussions and
Associate Professor Jørgen Glerup is thanked for assistance with
the EPR experiments. Flemming Hansen is acknowledged for col-
lecting the crystal structure data and the Center for Crystallo-
graphic Studies for the use of their equipment. The Lundbeck
Foundation (Junior Group Leader Fellowship for M. P.), the
Danish Research Council for Independent Research (a Steno Fel-
lowship for M. P., a Postdoc fellowship for T. B. N. and instrument
grant #09-066663) and the University of Copenhagen are acknowl-
edged for financial support.
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Published Online: ᭿
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© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 0000, 0–0

Job/Unit: O20512
/KAP1
Date: 03-07-12 15:50:59
Pages: 7
A peri-Cyclised Naphthalene Dimer
peri-Cyclised Naphthalene Dimer
The Vilsmeier–Haack reaction (POCl3/
DMF) of 1,3,6,8-tetramethoxynaphthalene
gave an unusual peri-cyclised dimer as well
as the 1-naphthaldehyde. The dimer is a po-
tent donor molecule.
M. Pittelkow,* C. B. Nielsen,
T. Brock-Nannestad,
M. Schau-Magnussen,
J. B. Christensen* ............................. 1–7
A peri-Cyclised Naphthalene Dimer: Syn-
thesis and Properties of an Unusual
Vilsmeier–Haack Product of 1,3,6,8-Tetra-
methoxynaphthalene
Keywords: Naphthalenes / Density func-
tional calculations / peri-Effect / Dimeri-
zation / Arenes / Radical ions
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
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