Synthesis of substituted diazoniapentaphene salts by an unexpected rearrangement-cyclodehydration sequence

Article abstract of DOI:10.1002/ejoc.200500463

The cyclodehydration of bis(pyridiniummethyl)methylbenzenes 3a-b in polyphosphoric acid leads to methyl-substituted diazoniapentaphene salts 4a-b instead of linear diazoniapentacene derivatives, while the 1,3-bis(pyridinium- methyl)bromobenzene 3d forms a

Full text of DOI:10.1002/ejoc.200500463

FULL PAPER
Synthesis of Substituted Diazoniapentaphene Salts by an Unexpected
Rearrangement-Cyclodehydration Sequence
Anton Granzhan,[a] Heiko Ihmels,[a]* Katya Mikhlina,[a] Hans-Jörg Deiseroth,[b] and
Holger Mikus[b]
Dedicated to Professor Werner Mormann on the occasion of his 60th birthday
Keywords: Aromatic ipso-substitution / Nitrogen heterocycles / Rearrangements
The cyclodehydration of bis(pyridiniummethyl)methylben-
zenes 3a–b in polyphosphoric acid leads to methyl-substi-
tuted diazoniapentaphene salts 4a–b instead of linear di-
azoniapentacene derivatives, while the 1,3-bis(pyridinium-
methyl)bromobenzene 3d forms a semi-betaine 4a,12a-di-
lization of 3a in refluxing HBr and conversion of 10b to the
final product 4a by dehydration in polyphosphoric acid. Elec-
tronic absorption and fluorescence properties of the pre-
viously unknown diazoniapentaphene salts have been
studied. Photophysical properties of 4a–b resemble the ones
azoniapentaphen-14-olate 4d under these conditions. The of the parent diazoniapentaphene salts, while semi-betaine
mechanistic details of this rearrangement–cyclodehydration 4d possesses a red-shifted absorption and fluorescence max-
sequence may be explained by an intramolecular ipso-ad- ima, along with significant solvatochromism with respect to
dition to the substituted benzene moiety, followed by an
[1,2]-methyl shift in case of 4a–b or HBr elimination in case
of 4d. The proposed mechanism was confirmed by the isola-
tion of the intermediate hydroxy derivative 10b from the cyc-
the absorption properties.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2005)
DNA-photodamaging properties and compare them with
the ones of annelated quinolizinium derivatives.[5] Recently,
we have shown that dicationic 12a,14a-diazoniapentaphene
2 binds to the double-stranded DNA with a binding con-
stant almost an order of magnitude higher than singly
charged benzoquinolizinium salts and exhibits DNA-pho-
todamaging activity.[8]
Introduction
The synthesis of heterocyclic polyaromatic compounds
is still an important goal in organic chemistry, since such
aromatic heterocycles represent useful lead structures in
bioorganic chemistry and materials science.[1] Along with
azinium and azolium salts, quinolizinium ions and their an-
nelated derivatives represent an interesting, but relatively
unexplored class of heteroaromatic compounds with a qua-
ternary bridgehead nitrogen atom.[2] The quinolizinium
moiety represents a key structural feature in natural pro-
ducts,[3] antitumor compounds,[4] and also constitutes a
promising lead structure for DNA intercalators.[5] Recently,
these heterocycles have been proposed for use in optical in-
formation storage materials and photochromic switches.[6]
Although many standard protocols are known for the syn-
thesis of azoniaaromatics such as quinolizinium deriva-
tives,[7] even simple variations in the structure of the start-
ing material may lead to the formation of unexpected main
products.
According to the well-established cyclodehydration
method of Bradsher,[7] we proposed that the bis(pyridinium)
derivatives 3a–b may be appropriate precursors for the syn-
thesis of 1a and 1b (Scheme 1). It has been observed already
in 1964[9] and confirmed recently[10] that the cyclization of
the salt 3c with an unsubstituted benzene moiety leads to
formation of the angular 4a,12a-diazoniapentaphene 4c in-
stead of the desired diazoniapentacene. Therefore, we have
introduced methyl substituents as protecting groups in the
benzene moiety to avoid the formation of angular deriva-
tives. In a similar approach, these positions have been
blocked by methoxy or acetoxy substituents; however, in
these cases, due to hydrolytic cleavage of the ether or ester
bonds, followed by subsequent aerobic oxidation, the corre-
sponding diazoniapentacene-6,13-diones have been ob-
tained, which could not be reduced to the target diazonia-
pentacenes.[11] Surprisingly, we have found that the substi-
tuted diazoniapentaphene derivatives 4a–b are formed by
a twofold acid-catalyzed cyclodehydration of 3a–b via an
Our initial intention was to synthesize diazoniapentacene
derivatives 1a–b in order to study their DNA-binding and
[a] Universität Siegen, Organische Chemie II,
Adolf-Reichwein-Str., 57068 Siegen, Germany
E-mail: ihmels@chemie.uni-siegen.de
[b] Universität Siegen, Anorganische Chemie I,
Adolf-Reichwein-Str., 57068 Siegen, Germany
4098
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DOI: 10.1002/ejoc.200500463
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Synthesis of Substituted Diazoniapentaphene Salts
FULL PAPER
intramolecular aromatic ipso-substitution followed by a atoms the methyl substituent in position 13 points towards
Wagner–Meerwein migration of a methyl group. In this pa- one of the enantiotopic faces of the aromatic plane with a
per we describe our investigations, which include some deviation angle of about 13°. Thus, 4a is a chiral compound
mechanistic details on this rearrangement-mediated cyclo- and is formed as a racemate that crystallizes in the space
¯
dehydration as well as UV/Vis and fluorescence spectro- group P1, with one single crystal containing both enantio-
scopic data of the new diazoniapentaphenes.
mers in a 1:1 ratio (see part A in Figure 1). It is noteworthy
that the distance between the ring planes of the neighboring
enantiomeric cations is close to 3.7 Å, presumably due to π
stacking (Figure 1, B). The cations overlap with more than
half of the area of their aromatic core. Since the methyl
groups at C13 point into opposite directions within such
a pair, the distances between the C8 and C13Ј atoms are
somewhat larger (3.9 Å).
Similarly to the reaction of 3a, the cyclodehydration of
–
3b (2BF4 ) under the same conditions (PPA, 150 °C, 24 h)
gave the 14-methyl-4a,12a-diazoniapentaphene 4b in 51%
yield (Scheme 2). Its structure was elucidated on the basis
of NOE effects between the methyl group and 13-H, the
1H NMR signal of which is strongly downfield-shifted (δ =
10.52 ppm), since C13 is directly bound to the positively
charged nitrogen (N12a) atom (Figure 2). NOE interactions
between 6-H and 7-H, the signals of which are shifted to
relatively high field (δ = 8.25 and 8.19 ppm), and the
neighboring 5-H and 8-H atoms, respectively, also con-
firmed the assignment of the structure of 4b.
To investigate the versatility of this rearrangement, we
have prepared compound 3d in which the methyl group was
replaced by a bromine substituent (Scheme 3). After the
cyclization step at the conditions previously employed, a
purple product was isolated in 56% yield which, at first
glance, was different from the weakly yellow salts 4a–b.
However, NMR spectra of the product showed 13 non-
Scheme 1.
1
equivalent low-field H signals and 20 distinct 13C signals,
Results and Discussion
which were consistent with an unsymmetric monosubsti-
tuted diazoniapentaphene structure. While NMR spec-
troscopy did not give unambiguous information about the
Synthesis
The bis(pyridiniummethyl)benzene derivatives 3a–b were nature of the substituent, in ESI mass spectra only a single
obtained according to Scheme 2. The bis(bromomethyl)ar- peak with an m/z value of 297 was observed.[13] This ion
enes 5 and 7c were treated with excess of 2-(1Ј,3Ј-dioxolan- mass as well as the isotopic pattern was not consistent with
2Ј-yl)pyridine (6). N-Methyl-2-pyrrolidone (NMP) is a su- a bromo-substituted derivative. On the basis of mass spec-
perior solvent for this twofold quaternization, giving nearly tra and elemental analysis, we have assigned the structure
quantitative yields in all cases. The bromide ion in 3a–b of semi-betaine 4d to the product. This structure is further
was exchanged with tetrafluoroborate to avoid a competing supported by a 13C NMR signal at δ = 164.3 ppm at C14,
nucleophilic substitution reaction during the second cyclo- which is characteristic for pyridinium-3-olates[14] and by an
dehydration step.[10,12] Nevertheless, cyclodehydration of IR band at ν
= 1552 cm–1, which is typical of a phenol-
˜
max
–
3a (2BF4 ) in polyphosphoric acid (PPA) at 150 °C gave a ate C–O– bond. This structure assignment is in accordance
single product in 30% yield whose NMR spectra were not with the observations that under neutral or alkaline condi-
consistent with the structure of the diazoniapentacene 1a. tions 11-hydroxybenzo[b]quinolizinium forms a betaine, the
Thus, 12 non-equivalent low-field shifted aromatic 1H electronic spectra of which resemble those of compound
NMR signals and 20 non-equivalent 13C NMR signals, as 4d.[15]
well as two independent signals for the methyl groups, were
In contrast, an attempt to cyclize the bis-pyridinium salt
detected. In addition, ESI mass spectrometry and elemental 3e derived from 2,6-bis(bromomethyl)trifluoromethylben-
analysis revealed that the product is a constitutional isomer zene 9 under the similar conditions (PPA, 160 °C, 48 h) gave
of 1a. The lack of symmetry already indicated a pentaphene only an non-separable mixture of unidentified products.
structure rather than a pentacene skeleton. In fact, X-ray- The cyclization of 3e in methanesulfonic acid under slightly
diffraction analysis showed that the 6,13-dimethyl-4a,8a-di- milder conditions (120 °C, 3 h) gave presumably a product
azoniapentaphene 4a was formed as reaction product. No- of mono-cyclization which, however, could not be obtained
tably, due to steric repulsion with the neighboring hydrogen in pure form. Apparently, the strong electron-acceptor
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Scheme 2. Reagents and conditions: (i) NMP, room temp., 7 days (95 %); (ii) aq. NaBF4 (92 %); (iii) PPA, 150 °C, 24 h (30 %);
(iv) BF3·THF, THF, 0 °C Ǟ room temp., 18 h (92%); (v) aq. HBr (48%), 50 °C, 1 h (85%); (vi) 6, NMP, room temp., 2 days (96%);
(vii) aq. NaBF4 (93%); (viii) PPA, 150 °C, 24 h (51%).
Figure 1. (A) The molecular structure (ORTEP view) of an enantiomeric pair of 4a in the solid state. The thermal ellipsoids for non-H
–
atoms are shown with 50% probability. (B) Crystal packing of 4a extending along the b axis. The hydrogen atoms and selected BF4
anions have been omitted for clarity. Enantiomers are shown in different colors.
property of the trifluoromethyl group deactivates the ben-
zene ring and suppresses the ipso- and ortho-substitution,
so that electrophilic substitution to give the angular penta-
phene derivative and the linear pentacene derivative does
not take place.
Mechanism of the Cyclodehydration of 3a, 3b, and 3d
The formation of the diazoniapentaphene derivatives 4a–
b may be rationalized by a cyclodehydration which involves
an ipso-addition of the protonated aldehyde group followed
by a methyl migration. Thus, after aldehyde deprotection
and the first cyclodehydration sequence, the benzo[b]quino-
lizinium derivative 10a is the proposed intermediate
(Scheme 4). Apparently, the methyl groups do not protect
1
Figure 2. H NMR shifts and characteristic NOE effects in 4b.
4100
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Synthesis of Substituted Diazoniapentaphene Salts
FULL PAPER
Scheme 3. Reagents and conditions: (i) 6, NMP, room temp., 7 days (91%); (ii) aq. NaBF4 (80%); (iii) PPA, 150 °C, 72 h (56%); (iv) 6,
NMP, room temp., 7 days (72%); (v) aq. NaBF4 (75%); (vi) PPA, 160 °C, 48 h.
these positions from electrophilic ipso addition, so that an getically favorable aromatization is probably the driving
angular annelation takes place along with subsequent de- force for this methyl shift. The proposed mechanism is sup-
–
protonation to give the intermediate 10b. Although there ported by the isolation of intermediate 10b (2BF4 ), which
are only few examples for an ipso substitution of an ortho- was formed when the dibromide salt 3a was cyclized under
alkyl group in the presence of a second hydrogen-substi- slightly milder reaction conditions, i.e. in refluxing aq. HBr
tuted orthoЈ position,[16] this addition is in agreement with (48%). Although compound 10b was isolated in rather low
1
theoretical and experimental studies which show that yield (35%), the H NMR spectrum of the crude product,
benzo[b]quinolizinium derivatives exhibit a significantly obtained by precipitation of the reaction mixture with ace-
higher reactivity towards electrophiles at positions 7 and 10 tone, did not reveal the presence of any side products. This
as compared to positions 8 and 9.[7c] Thus, sulfonation and indicates that the competing nucleophilic substitution of the
bromination of the benzo[b]quinolizinium cation are re- pyridinium residue with bromide does not take place under
ported to occur at position 10,[17] whereas chlorination re- these conditions.
–
sults in the 7,10-disubstituted product.[18] Under the em-
The structure of 10b (2BF4 ) is confirmed by 1H- and 13
C
ployed acidic conditions, the hydroxy functionality is pro- NMR, mass-spectrometric and elemental analyses. Espe-
tonated and water acts as a leaving group to give the cation cially characteristic is the coupling of the hydroxyl proton
10c. Finally, a Wagner–Meerwein [1,2]-methyl migration with 13-H [3J(H,H) = 4.7 Hz] and the NOE effect between
followed by deprotonation leads to a fully aromatic diazoni- the latter and the methyl group at C13a.
apentaphene. Although alkyl migrations are observed ex-
Compound 10b has two stereogenic centers, and there-
tremely rarely upon aromatic ipso substitution,[19] the ener- fore the formation of four stereoisomers is possible. How-
Scheme 4. Mechanism of formation of 10b and 4a.
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A. Granzhan, H. Ihmels, K. Mikhlina, H.-J. Deiseroth, H. Mikus
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ever, NMR spectra give evidence that only one dia- Electronic Spectra of Diazoniapentaphene Derivatives
stereomer (as a racemate) has formed. Indeed, the integra-
tion of NOE spectra showed that the distance between
Diazoniapentaphene salts are known to have strong ab-
13-H and the methyl group at C13a is consistent with the sorption in the UV region of the electromagnetic spectrum
structure of the anti-isomer shown on Scheme 4. This struc- and significant fluorescence properties.[9] To study the effect
ture was further confirmed by the X-ray diffraction analysis of the substituents on their electronic spectra, we have com-
(Figure 3, A). Thus, the racemate of anti-10b crystallizes in pared the spectral properties of the compounds 4a–b with
the chiral space group P21/n as a crystalline hydrate con- those of the unsubstituted diazoniapentaphenes. Absorp-
taining one water molecule per cation and forming ordered tion spectra of 4a and 4b (Figure 4) resemble the ones of
layers of enantiomers (Figure 3, B).
the parent compounds and confirm the assignment of di-
azoniapentaphene structure to these compounds. Absorp-
tion spectra consist of several strong p- and β-absorption
bands in the UV region (εmax Ͼ 4×104 cm–1 –1) and much
weaker α-bands in the visible region (400–500 nm). How-
ever, derivative 4a shows much less pronounced fine struc-
ture in the UV region than the parent compound (Figure 4,
A). This confirms the deviation from the planar structure,
as it had been shown for methyl-substituted phenan-
threnes.[21] In case of derivative 4b, this effect is less pro-
nounced (Figure 4, B).
Compounds 4a–b are strongly fluorescent in most sol-
vents, such as water, alcohols and acetonitrile (Table 1). The
fluorescence emission spectra resemble the ones of the par-
ent diazoniapentaphenes, while introduction of two methyl
groups in 4a leads to a bathochromic shift of the emission
maximum of about 25 nm and reduction of the vibrational
structure as compared to the unsubstituted analogue. At
the same time, the introduction of one methyl group in 4b
results in a bathochromic shift of only 7 nm, and the shape
of the emission spectrum is identical with that of 4c. The
largest fluorescence quantum yields are observed in water
solution (ΦF = 0.32 and 0.41 for 4a and 4b, respectively).
They are about 20% smaller than the values for the unsub-
stituted diazoniapentaphene salts (ΦF = 0.38 for 4a,8a-di-
azoniapentaphene and 0.50 for 4a,12a-diazoniapentaphene
in aqueous solutions, the latter being determined with au-
Figure 3. (A) The molecular structure (ORTEP view) of the enan-
tiomeric pair of 10b in the solid state. The thermal ellipsoids for
non-H atoms are shown with 50% probability. (B) Crystal packing
of 10b extending along the c axis. Selected BF4 anions and water
molecules have been omitted for clarity. Enantiomers are shown in
different colors.
–
The proposed mechanism in Scheme 4 is further sup- thentic samples). In contrast, in dimethyl sulfoxide
ported by the fact that dehydration of 10b in PPA at 150 °C (DMSO) the fluorescence is strongly quenched (ΦF = 0.01–
gives the product 4a in high yield (91%), without formation 0.03 for unsubstituted and methyl-substituted diazoniapen-
of any side products.
taphenes), and the emission spectra are structureless. A sim-
At the moment, no explanation for the medium effect of ilar decrease of fluorescence in DMSO was observed for
acid employed can be provided. It is noteworthy that a re- the related 3a,9a-diazaperylenium dication[23] as well as for
lated effect was observed in the acid-mediated rearrange- benzo[b]quinolizinium salts,[24] and it was correlated with
ments of dienones, such as 10-methyl-2-keto-∆1:9,8:4-hexa- the high electronic donor strength of this solvent in combi-
hydronaphthalene.[20] However, in that case, aqueous HBr nation with the low reduction potential of the chromo-
induced a single [1,2]-methyl shift, while the use of the vig- phore.[24]
orously hygroscopic medium (H2SO4 in acetic anhydride)
Notably, compound 10b, where the fused aromatic sys-
resulted in several consecutive electrophilic rearrangements. tem is disrupted by two methylene groups, also shows rea-
In contrast, upon treatment of 3a with aq. HBr the methyl sonably strong UV absorption and fluorescence properties.
shift does not take place, and the reaction provides the in- Thus, its structureless, broad long-wavelength absorption
termediate 10b.
band is located at 386 nm and has log ε = 4.29 (Figure 5).
In the case of the formation of 4b, a similar mechanism The fluorescence emission spectrum is also very broad with
is likely to take place (Scheme 5, path a); however, with a a maximum centered at around 480–500 nm. As in the case
bromo substituent the aromatization takes place from inter- of the diazoniapentaphenes, the fluorescence intensity is
mediate 11 by HBr elimination (Scheme 5, path b). Obvi- strongest in aqueous solution (ΦF = 0.21), whereas in
ously, the hydroxy group bound to a doubly charged aro- DMSO it is essentially quenched (ΦF Ͻ 0.01). The absorp-
matic system is acidic enough to be deprotonated, giving tion and emission maxima are comparable to the ones of
the semi-betaine 4d as a final product.
the protonated 1-pyridyl-4-phenylbutadienes.[25] Thus, with
4102
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Synthesis of Substituted Diazoniapentaphene Salts
FULL PAPER
Scheme 5. Mechanism of formation of 4b and 4d.
Table 1. Fluorescence properties of diazoniapentaphenes 4a–b.
Solvent[a]
4a
4b
[b]
[c]
[b]
[c]
λmax
ΦF
λmax
ΦF
DMSO
Acetonitrile
523
485
0.02
0.24
469
442
468
443
470
442
469
440
466
0.03
0.21
[d]
[d]
Ethanol
Methanol
Water
–
–
0.15
0.26
0.41
487
483
0.26
0.32
[a] In order of their increasing ETN values.[22] [b] Fluorescence emis-
sion maximum, nm, c(4) = 5 µ; excitation wavelength λex
=
380 nm for all compounds. [c] Fluorescence quantum yield relative
to Coumarin 1, estimated error 10%. [d] Not determined.
respect to the electronic transitions, 10b may be regarded as
a bridged diarylbutadiene derivative, whereas the conforma-
tional restrictions exclude the photoisomerisation, conse-
quently enhancing the quantum yield of fluorescence.
Electronic absorption spectra of the semi-betaine 4d in
most solvents consist of a broad band of moderate intensity
(log ε Ϸ 4.0) at 460–490 nm and a stronger (log ε Ϸ 4.4–
4.6), somewhat structured band in the UV region of the
spectrum.[26] In contrast to the diazoniapentaphenes 4a–c,
Figure 4. (A) Absorption (left part) and normalized fluorescence which exhibit only negligible solvatochromism, the posi-
emission (right part, λex = 380 nm in all cases) spectra of 4a,8a-
tions and intensities of absorption bands of 4d are strongly
diazoniapentaphene bis(tetrafluoroborate) (solid line) and of com-
solvent-dependent (see part A of Figure 6 and Table 2).
pound 4a (dashed line) in water. (B) Absorption (left part) and nor-
Moreover, the energy of the long-wavelength transition
malized fluorescence emission (right part) spectra of 4a,12a-di-
shows an almost linear correlation with the Gutmann’s ac-
azoniapentaphene bis(tetrafluoroborate) 4c (solid line) and its 14-
methyl derivative 4b (dashed line) in water.
ceptor number (AN)[22] of the solvent (r = 0.993, Figure 6,
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Figure 5. Absorption (solid line) and normalized fluorescence
emission (dashed line) spectra of 10b in water. Excitation wave-
length λex = 380 nm.
B) as well as with the Swain’s “acity” parameter A (r =
0.996, data not shown), thus illustrating the ability of the
solvent to interact with the negative charge localized at the
oxygen atom. Thus, the long-wavelength band undergoes a
hypsochromic shift by 30 nm when changing form acetone
(AN = 12.5) to water (AN = 54.8). Unfortunately, the lim-
ited solubility of 4d in solvents with lower AN values ex-
cluded investigations therein. As an extreme case, in tri-
fluoroacetic acid (TFA; AN = 105.3) the spectrum loses the
aforementioned structure completely and attains a typical
aromatic character, similar to that of unsubstituted diazoni-
apentaphenes, with a structured β-band (λmax = 266 nm)
and α-band (430 nm; S0–S1 transition). To a certain extent
Figure 6. (A) Absorption (left part) and normalized fluorescence
emission (right part) spectra of 4a,12a-diazoniapentaphene-14-ol-
ate tetrafluoroborate 4d in water (solid lines), acetone (dashed line)
and trifluoroacetic acid (dotted lines). Experimental conditions see
footnotes to Table 2. (B) Correlation of the position of the lowest-
energy absorption band of 4d with the donor number of the sol-
vent: (1) acetone, (2) pyridine, (3) acetonitrile, (4) DMSO, (5) 2-
propanol, (6) ethanol, (7) methanol, (8) acetic acid, (9) water,
(10) TFA.
the latter overlaps with the strongest p-band (λmax
=
357 nm). We assume that this spectrum represents the fully
protonated dicationic form of 4d. This drastic change, how-
ever, is not observed either in acetic acid or in water, indi-
cating that the acidity is less important for the stabilization
of the semi-betaine 4d than the overall electrophilic proper-
ties characterized by the value of AN. Thus, acetic acid is
more acidic than water, however, the spectrum is more blue-
shifted in water as compared to acetic acid. Addition of e.g.
perchloric acid to aqueous solutions of 4d does not result
in such a severe effect as neat TFA, either.
Salt 4d exhibits weak orange-red fluorescence in most
solvents, with a broad emission band centered at 620–
660 nm (Table 2) and quantum yields in the range of 0.03
to 0.07. Similar to the absorption maxima, the emission
maxima are solvent-dependent, but do not show any evi-
dent correlation with the empiric solvent parameters (sol-
vent polarity function ETN, donor- or acceptor numbers).
In trifluoroacetic acid, dual fluorescence is observed, with
a structured part located at 420–480 nm (blue emission) and
a broader band at 580–600 nm (red emission). We attribute
the blue emission, similar to that of diazoniapentaphenes,
to the fully protonated dicationic form of 4d. The red emis-
sion, observed in all solvents investigated including TFA, is
attributed to the electronic charge-transfer (CT) from the
phenolate oxygen to the diazoniapentaphene core. The CT
the fluorescence band (∆λ1/2 Ϸ 140 nm) and large Stokes
shift values (140–180 nm).
In summary, we have shown that diazoniapentacene de-
rivatives are not available by the established cyclodehy-
dration route. Instead, the corresponding diazoniapenta-
phene derivatives are formed, even when the positions for
electrophilic addition are blocked by methyl or bromo sub-
stituents. Moreover, we elucidated the reaction mechanisms
by the isolation of a reaction intermediate. We showed that
one of the reaction products, namely the betaine-like deriv-
ative 4d exhibits solvatochromic absorption properties and
a relatively large Stokes shift, which represents a useful fea-
ture for optical sensors. Further studies along these lines
are presently under investigation.
Experimental Section
All commercially available chemicals were reagent grade and used
without further purification. Solvents were purified and dried ac-
cording to standard procedures. The melting points were measured
character of this emission is supported by the broadness of with a melting point apparatus (Büchi 510K) and are uncorrected.
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Synthesis of Substituted Diazoniapentaphene Salts
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Although compound 7b was previously prepared by esterifiction of
the 2-methylisophthalic acid followed by reduction of the diester
with lithium aluminium hydride,[29,31] or by two-step reduction of
2,6-dicyanotoluene,[36] we have chosen to reduce the acid 7a directly
by the action of borane–THF complex.[37] Indeed, this reduction
procedure has proved to be less laborious and gave the desired pro-
duct in 92% yield, thus improved with respect to the 87% obtained
by the two-step sequence.
Table 2. Solvatochromic properties of compound 4d.
[b]
[d]
[e]
Solvent[a]
λabs (log ε[c])
λem
ΦF
Acetone
338 (sh[f])
365 (4.27)
381 (4.42)
489 (4.03)
343 (4.00)
369 (4.11)
387 (4.25)
496 (3.97)
335 (4.13)
363 (sh)
650
634
641
667
3.9×10–2
7.1×10–2
2.8×10–2
3.3×10–2
Pyridine
Acetonitrile
DMSO
4a,12a-Diazoniapentaphene 4c and 4a,8a-diazoniapentaphene bis-
(tetrafluoroborates)[9,10] were prepared from 1,4- and 1,3-bis-
(bromomethyl)benzenes, respectively, following the general pro-
cedures (vide infra). The overall yields over 3 synthetic steps were
47 and 48%, correspondingly; spectroscopic data were in agree-
380 (4.41)
485 (4.03)
337 (sh)
ment with those given in ref.[10]
.
370 (4.23)
385 (4.31)
406 (sh)
489 (3.90)
380 (4.31)
403 (sh)
478 (3.87)
334 (sh)
379 (4.37)
402 (sh)
475 (3.94)
378 (4.35)
400 (sh)
472 (3.90)
376 (4.51)
464 (3.95)
373 (4.52)
400 (sh)
2,6-Bis(hydroxymethyl)toluene (7b): A solution of 2-methylisoph-
thalic acid 7a (7.21 g, 40.0 mmol) in dry THF (100 mL) was cooled
to 0 °C and deoxygenated by passing a stream of argon. To a stirred
solution, borane (100 mL of 1  THF complex, 100 mmol) was
added dropwise under argon atmosphere within 4 h, whereas the
reaction mixture has turned into a jelly-like bulk. After 18 h at
room temperature, water (100 mL) was added carefully. After hy-
drogen evolution has ceased, the solution was saturated with solid
potassium carbonate. The organic layer was separated; the aqueous
layer was extracted with diethyl ether (3×30 mL) and the combined
organic layers were washed with water and dried over anhydrous
magnesium sulfate. After removal of the solvents in vacuo, 7b
(5.60 g, 92%) was obtained as a white solid, m.p. 116–118 °C
(ref.[29,36] 122–124 °C), which was used without further purification.
1H NMR (200 MHz, [D6]DMSO): δ = 2.15 (s, 3 H, CH3), 4.49 (d,
2-Propanol
Ethanol
635
642
4.4×10–2
5.4×10–2
Methanol
644
6.5×10–2
Acetic acid
Water
629
626
3.8×10–2
3.0×10–2
3
3J = 5.3 Hz, 4 H, CH2), 5.05 (t, J = 5.3 Hz, 2 H, OH), 7.11 (m, 1
H, 4-H), 7.25 (m, 2 H, 3-H, 5-H). 13C NMR (50 MHz, [D6]
DMSO): δ = 13.8 (CH3), 62.1 (CH2OH), 125.9 (C4), 127.0 (C3,
C5), 134.0 (C1), 140.3 (C2, C6).
459 (4.00)
[h]
Trifluoroacetic acid 266 (4.52)
357 (4.61)
437[g]
463
573
406 (3.92)
430 (3.81)
2,6-Bis(bromomethyl)toluene (7c) was prepared from 2,6-bis(hyd-
roxymethyl)toluene 7b as described in the literature; m.p. 85–87 °C
(ref.[29,31] 94–95 °C), and used in the next step without purification.
[a] In order of their increasing AN value.[27] [b] Absorption maxi-
mum, nm, c(4d) = 50 µ. [c] Molar decadic extinction coefficient
(cm–1

–1). [d] Fluorescence emission maximum, nm, c(4d) =
General Procedure for Quaternizations of Bis(bromomethyl)arenes
with 2-(1,3-Dioxolan-2-yl)pyridine: To a solution of bis(bromome-
thyl) derivative (20 mmol) in a minimal amount of N-methyl-2-pyr-
rolidone (usually 15–20 mL), 2-(1,3-dioxolan-2-yl)pyridine (6)
(7.2 g, 48 mmol) was added. The reaction mixture was stirred for
5-7 days under moisture protection, whereas a white precipitate
has formed. The reaction mixture was poured into ethyl acetate
(300 mL), the solid was separated, washed several times with ethyl
acetate and dry diethyl ether, and dried in vacuo/P2O5, to give the
white amorphous dibromide salt 3 (2Br–).
10 µ; excitation wavelength λex = 480 nm. [e] Fluorescence quan-
tum yield relative to Cresyl Violet, estimated error 10%. [f] Shoul-
der. [g] Excitation wavelength λex = 405 nm. [h] Not determined.
Mass spectra (ESI in the positive-ion mode) were recorded with a
Finnigan LCQ Deca instrument (source voltage 6 kV). NMR spec-
tra were measured on
a
Bruker AC200 (1H: 200 MHz,
13C: 50 MHz) and Bruker Avance 400 (1H: 400 MHz,
13C: 100 MHz) spectrometer at 20 °C; chemical shifts are given in
ppm (δ) values (internal standards TMS for 1H- and 13C NMR
spectroscopy and hexafluorobenzene, δF = –162.8 ppm, for 19F
NMR spectroscopy). Infrared spectra were obtained with a Perkin–
Elmer 1750 Fourier-transform spectrometer in KBr pellets; only
significant frequencies are given. Elemental microanalyses of all
new compounds were performed by Mr. H. Bodenstedt (Institut für
Organische Chemie, University of Siegen).
A part of it (10 mmol) was dissolved in minimal amount of water
(ca. 10 mL) and treated with concentrated aqueous solution of
NaBF4 (4.4 g, 40 mmol). The milky reaction mixture was heated
gently until a clear solution was obtained. Upon slow cooling to
–
+5 °C, a crystalline bis(tetrafluoroborate) 3 (2BF4 ) separated al-
most quantitatively. It was separated, washed with a plenty of cold
water, and dried in vacuo/P2O5.
The following compounds were obtained according to the pub-
lished procedures: 2-(1,3-dioxolan-2-yl)pyridine (6),[28] 2-methyl-
isophthalic acid (7a),[29–31] 1-bromo-2,6-bis(bromomethyl)benzene
(8),[32] 2,6-bis(bromomethyl)trifluoromethylbenzene (9).[33] Re-
peated attempt to prepare 1,4-bis(bromomethyl)-2,5-dimethylben-
zene (5) by bromomethylation of p-xylene in 48% aq. HBr[34] gave
maximum 40% yield in contrast to 97% yield claimed by the au-
thors. We have found that reaction with 33% HBr in glacial acetic
acid gives better yield of this product.[35]
1,4-Bis{[1-(1,3-dioxolan-2-yl)pyridinium]methyl}-2,5-dimethylben-
zene Dibromide [3a (2Br–)]: Yield 11.3 g (95%); m.p. (decomp.) 186–
–
188 °C (EtOH). 3a (2BF4 ): M.p. 240–242 °C (EtOH/MeCN). 1H
NMR (400 MHz, [D6]DMSO): δ = 2.20 (s, 6 H, CH3), 4.11 [s, 8
H, CH(OCH2)2], 5.95 (s, 4 H, CH2N+), 6.46 [s, 2 H, CH(OCH2)2],
6.73 (s, 2 H, 3-H, 6-H), 8.20 (dd, 3J1 = 7, 3J2 = 6.3 Hz, 2 H, 5Ј-H),
8.37 (d, 3J = 7 Hz, 2 H, 3Ј-H), 8.74–8.90 (m, 4 H, 4Ј-H, 6Ј-H) ppm.
13C NMR (100 MHz, [D6]DMSO): δ = 18.1 (CH3), 57.8 (CH2N+),
Eur. J. Org. Chem. 2005, 4098–4108
www.eurjoc.org
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4105

A. Granzhan, H. Ihmels, K. Mikhlina, H.-J. Deiseroth, H. Mikus
65.6 [CH(OCH2)2], 97.1 [CH(OCH2)2], 126.2 (CH), 128.7 (CH), H), 8.54 (dd, 3J1 = 9, 3J2 = 7 Hz, 1 H, 11-H), 8.56 (dd, 3J1 = 9, 3J2
FULL PAPER
129.9 (CH), 132.4 (Cq), 134.7 (Cq), 146.7 (CH), 147.4 (CH), 152.2
(Cq) ppm. C26H30B2F8N2O4 (608.1): calcd. C 51.35, H 4.97, N 4.61;
found: C 51.14, H 4.90, N 4.64.
= 7 Hz, 1 H, 2-H), 9.05 (d, 3J = 9 Hz, 1 H, 1-H), 9.13 (d, 3J =
9 Hz, 1 H, 12-H), 9.54 (d, 3J = 7 Hz, 1 H, 9-H), 9.66 (d, 3J = 7 Hz,
1 H, 4-H), 9.78 (s, 1 H, 14-H), 9.90 (s, 1 H, 8-H), 10.19 (s, 1 H, 5-
H) ppm. 13C NMR (100 MHz, [D6]DMSO): δ = 18.8 (CH3), 19.8
(CH3), 124.7, 125.2, 125.8, 126.5, 126.9, 128.3, 128.4, 130.7, 133.1,
133.5, 134.3, 135.2, 135.9, 136.2, 136.3, 136.3, 137.0, 139.4, 140.6
ppm. MS (ESI): m/z (%) = 155 (100) [M2+], 309 (48) [M – H]+, 320
(25) [M + F]+, 397 (26) [M + BF4]+, 881 (38) [2M + 3BF4]+, 1364
2,6-Bis{[1-(1,3-dioxolan-2-yl)pyridinium]methyl}toluene Dibromide
[3b (2Br–)]: Yield 11.1 g (96%); m.p. (decomp.) 130–133 °C (EtOH).
–
3b (2BF4 ): M.p. 174–176 °C (water). 1H NMR (400 MHz, [D6]-
DMSO): δ = 2.23 (s, 3 H, CH3), 4.11 [s, 8 H, CH(OCH2)2], 6.07 (s,
4 H, CH2N+), 6.50 [s, 2 H, CH(OCH2)2], 6.86 (d, 3J = 7.8 Hz, 2
(6) [3M + 5BF ]+. IR (KBr): νmax = 524 (BF4 ), 792s, 1062s (BF4 ),
–
–
˜
3
H, 3-H, 5-H), 7.29 (t, 3J = 7.8 Hz, 1 H, 4-H), 8.20 (dd, J1 = 8, 3J2
4
1389s, 1502, 1646s cm–1. C22H18B2F8N2 (484.0): calcd. C 54.59,
3
= 6 Hz, 2 H, 5Ј-H), 8.38 (d, J = 8 Hz, 2 H, 3Ј-H), 8.74–8.78 (m,
H 3.75, N 5.79; found: C 54.46, H 3.61, N 5.85.
4 H, 4Ј-H, 6Ј-H) ppm. 13C NMR (100 MHz, [D6]DMSO): δ = 14.2
(CH3), 58.4 (CH2N+), 65.6 [CH(OCH2)2], 97.1 [CH(OCH2)2], 126.2
(CH), 127.3 (CH), 128.7 (CH), 128.8 (CH), 132.7 (Cq), 135.3 (Cq),
146.5 (CH), 147.4 (CH), 152.3 (Cq) ppm. C25H28B2F8N2O4 (594.1):
calcd. C 50.54, H 4.75, N 4.72; found: C 50.57, H 4.52, N 4.72.
14-Methyl-4a,12a-diazoniapentaphene Bis(tetrafluoroborate) (4b):
Yield 0.81 g (51 %), recrystallization from MeCN/water, dark-
brown fine crystalline solid; m.p. Ͼ 300 °C. 1H NMR (400 MHz,
3
[D6]DMSO): δ = 3.58 (s, 3 H, CH3), 8.19 (d, J = 9.2 Hz, 1 H, 7-
3
3
H), 8.25 (d, J = 9.2 Hz, 1 H, 6-H), 8.26 (dd, J = 7 Hz, 1 H, 11-
2,6-Bis{[1-(1,3-dioxolan-2-yl)pyridinium]methyl}bromobenzene Di-
3
3
3
bromide [3d (2Br–)]: Yield 11.7 g (91%); m.p. 175–178 °C (EtOH).
H), 8.32 (dd, J = 7 Hz, 1 H, 3-H), 8.50 (dd, J1 = 9, J2 = 7 Hz,
1 H, 10-H), 8.57 (dd, J1 = 9, J2 = 7 Hz, 1 H, 2-H), 8.74 (d, J =
9 Hz, 1 H, 9-H), 9.15 (d, J = 9 Hz, 1 H, 1-H), 9.16 (s, 1 H, 8-H),
3
3
3
–
3d (2BF4 ): M.p. 196–200 °C (water). 1H NMR (400 MHz, [D6]-
3
DMSO): δ = 4.07 [s, 8 H, CH(OCH2)2], 6.11 (s, 4 H, CH2N+), 6.49
9.53 (d, 3J = 7 Hz, 1 H, 4-H), 9.81 (d, 3J = 7 Hz, 1 H, 12-H), 10.08
(s, 1 H, 5-H), 10.52 (s, 1 H, 13-H) ppm. 13C NMR (100 MHz, [D6]-
DMSO): δ = 18.3 (CH3), 121.0, 122.3, 123.3, 123.4, 124.4, 125.0,
125.5, 127.9, 129.8, 130.0, 133.1, 134.0, 135.6, 135.9, 136.0, 136.4,
137.1, 138.8, 139.7, 139.8 ppm. MS (ESI): m/z (%) = 148 (59)
[M]2+, 295 (100) [M – H]+, 315 (21) [M + F]+, 383 (13) [M + BF4]
3
[s, 2 H, CH(OCH2)2], 6.91 (d, J = 7.8 Hz, 2 H, 3-H, 5-H), 7.44 (t,
3
3J = 7.8 Hz, 1 H, 4-H), 8.26 (dd, J1 = 8, 3J2 = 6.1 Hz, 2 H, 5Ј-H),
8.39 (d, 3J = 8 Hz, 2 H, 3Ј-H), 8.80 (dd, 3J = 8 Hz, 2 H, 4Ј-H),
3
8.96 (d, J = 6.1 Hz, 2 H, 6Ј-H) ppm. 13C NMR (100 MHz, [D6]-
DMSO): δ = 60.6 (CH2N+), 65.6 [CH(OCH2)2], 97.2 [CH(OCH2)2],
123.2 (Cq), 126.4 (CH), 128.8 (CH), 129.1 (CH), 129.8 (CH), 134.4
(Cq), 147.3 (CH), 147.8 (CH), 152.3 (Cq) ppm. C24H25B2BrF8N2O4
(659.0): calcd. C 43.74, H 3.82, N 4.25; found: C 4.34, H 3.80,
N 4.21.
+, 853 (18) [2M + 3BF ]+. IR (KBr): ν
= 523 (BF4–), 1056s
˜
4
max
(BF4–), 1343, 1449, 1641 w cm–1. C21H16B2F8N2 (470.0): calcd.
C 53.67, H 3.43, N 5.96; found: C 53.73, H 3.43, N 6.31.
2,6-Bis{[1-(1,3-dioxolan-2-yl)pyridinium]methyl}trifluoromethyl-
4a,12a-Diazoniapentaphen-14-olate Tetrafluoroborate (4d): Yield
0.65 g (56%), recrystallization from nitromethane, purple needles,
m.p. Ͼ 300 °C. 1H NMR (400 MHz, [D6]DMSO): δ = 7.53 (d, 3J
benzene Dibromide [3e (2Br–)]: Yield 9.2 g (72%); m.p. 149–151 °C
–
(EtOH). 3e (2BF4 ): M.p. 196–198 °C (water). 1H NMR (400 MHz,
[D6]DMSO): δ = 4.05 [m, 8 H, CH(OCH2)2], 6.27 (s, 4 H, CH2N+),
6.43 [s, 2 H, CH(OCH2)2], 6.85 (d, 3J = 8.0 Hz, 2 H, 3-H, 5-H),
3
= 9.0 Hz, 1 H, 7-H), 7.58 (d, J = 9.0 Hz, 1 H, 6-H), 7.77–7.82 (m,
3
3
3 H, 2-H, 3-H, 11-H), 7.97 (dd, J1 = 8.5, J1 = 7.8 Hz, 1 H, 10-
3
3
3
3
7.62 (t, J = 8.0 Hz, 1 H, 4-H), 8.29 (dd, J1 = 8.0, J2 = 6.0 Hz, 2
H), 8.15 (d, J = 8.5 Hz, 1 H, 9-H), 8.23 (s, 1 H, 5-H), 8.37–8.39
(m, 2 H, 1-H, 8-H), 8.80–8.84 (m, 1 H, 4-H), 9.28 (d, J = 6.5 Hz,
3
3
3
H, 5Ј-H), 8.40 (d, J = 8.0 Hz, 2 H, 3Ј-H), 8.82 (dd, J = 8.0 Hz,
2 H, 4Ј-H), 9.01 (d, 3J = 6.0 Hz, 2 H, 6Ј-H) ppm. 13C NMR
1 H, 12-H), 11.46 (s, 1 H, 13-H) ppm. 13C NMR (100 MHz, [D6]-
DMSO): δ = 110.2 (Cq), 113.6 (CH, C5), 122.5 (CH), 122.6 (CH),
123.9 (CH), 124.1 (CH), 125.3 (Cq), 126.1 (CH, C9), 127.4 (CH,
C7), 128.6 (Cq), 129.8 (CH), 132.9 (CH, C6), 133.0 (CH), 133.3
(CH), 133.9 (CH, C4), 135.6 (CH, C12), 137.0 (Cq), 138.1 (Cq),
164.2 (Cq, C14) ppm. MS (ESI): m/z (%) = 297 (100) [M]+, 329 (24)
(100 MHz, [D6]DMSO): δ = 58.3 (q, JC,F = 6 Hz, CH2N+), 65.5
4
2
[CH(OCH2)2], 97.1 [CH(OCH2)2], 124.4 (q, JC,F = 30 Hz, Cq),
124.5 (q, 1JC,F = 277 Hz, CF3) 126.5 (CH), 128.9 (CH), 129.4 (CH),
133.5 (Cq), 133.8 (CH), 147.8 (CH), 148.0 (CH), 152.3 (Cq) ppm.
–
19F NMR (376 MHz, [D6]DMSO): δ = –144.0 (BF4 ), –48.1 (CF3)
[M + O ]+. IR (KBr): ν
= 480, 522 (BF4 ), 1061s (BF4 ), 1185,
–
–
ppm. C25H25B2BrF11N2O4 (648.1): calcd. C 46.33, H 3.89, N 4.32;
found: C 46.57, H 3.69, N 4.35.
˜
2
max
1459s, 1510, 1552s (C–O phenolate), 1640w cm–1. C20H13BF4N2O
(384.1): calcd. C 62.53, H 3.41, N 7.29; found: C 62.66, H 3.34,
N 7.49.
General Procedure for Ring Closure Reactions in PPA: The corre-
–
sponding bis(tetrafluoroborate) 3a–d (2BF4 ) (2.00 g) in PPA (20 g)
was slowly heated under argon atmosphere to 150 °C, and the reac-
tion mixture was stirred at this temperature for 24–36 h. After cool-
ing to about 100 °C, water (40 mL) was carefully added and the
mixture was stirred at this temperature for 30 min for hydrolysis of
the PPA. The mixture was cooled to room temperature and treated
with excess of NaBF4 (15–30 mmol, concentrated aqueous solu-
tion). The dark solution (sometimes containing small amounts of
dark precipitate) was extracted with nitromethane (4×40 mL). The
organic phases were combined, washed with water (20 mL) and the
solvents evaporated in vacuo; the residue was recrystallized from a
suitable solvent.
6,13a-Dimethyl-13,13a-dihydro-4a,8a-diazoniapentaphen-13-ol Bis-
(tetrafluoroborate) (10b): A solution of the dibromide 3a (2Br–)
(3.57 g, 6.00 mmol) in 48% aq. HBr (35 mL) was stirred under re-
flux for 2 h, and 20 mL of liquid were distilled off. The residue was
poured into acetone (200 mL); the yellow precipitate was collected
and washed with acetone. It was dissolved in 5% aq. HBr (5 mL)
and diluted with 96% ethanol (500 mL); the turbid solution was
filtered and the filtrate concentrated in vacuo. The residue was di-
luted with water (15 mL) and treated with 50% aq. HBF4 (3 mL),
to afford 9b (1.05 g, 35%) as yellow crystalline solid. An analytical
sample was recrystallized from acetonitrile/water. Brown prisms,
1
6,13-Dimethyl-4a,8a-diazoniapentaphene Bis(tetrafluoroborate) (4a):
Yield 0.44 g (30 %), recrystallization from MeCN/water, brown
crystalline solid; m.p. Ͼ 300 °C. 1H NMR (400 MHz, [D6]DMSO):
δ = 2.83 (s, 3 H, C6–CH3), 3.53 (s, 3 H, C13–CH3), 7.94 (s, 1 H,
decomp. at Ͼ 200 °C. H NMR (400 MHz, [D6]DMSO): δ = 1.36
3
(s, 3 H, C13a–CH3), 2.43 (s, 3 H, C6–CH3), 5.86 (d, J = 4.7 Hz,
1 H, 13-H), 6.83 (d, 3J = 4.7 Hz, 1 H, OH), 6.95 (s, 1 H, 7-H), 7.81
3
(s, 1 H, 8-H), 8.10–8.14 (m, 1 H, 3-H), 8.19 (d, J = 7.7 Hz, 1 H,
3
3
3
7-H), 8.31 (dd, 3J = 7 Hz, 1 H, 10-H), 8.35 (dd, J = 7 Hz, 1 H, 3-
12-H), 8.24 (dd, J1 = 6, J1 = 9 Hz, 1 H, 10-H), 8.37-8.40 (m, 2
4106
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
Eur. J. Org. Chem. 2005, 4098–4108

Synthesis of Substituted Diazoniapentaphene Salts
FULL PAPER
Table 3. Crystal data and structure refinement details of the compounds 4a and 10b.
4b
10a
Molecular formula
Temperature [K]
Wavelength [Å]
Space group
C22H18B2F8N2
173(2)
C22H22B2F8N2O2
123(2)
0.71073
P 21/n (No. 14, cell choice 2)
a = 11.921(1) Å
b = 15.150(1) Å
c = 13.503(1) Å
α = 90°
β = 112.15(1)°
γ = 90°
0.71073
¯
P1 (No. 2)
Unit cell dimensions
a = 10.538(1) Å
b = 7.4098(7) Å
c = 13.373(1) Å
α = 93.29(1)°
β = 102.77(1)°
γ = 86.60(1)°
1015.5(2)
Volume [Å3]
2258.7(3)
Z
2
4
Calculated density [gcm–3]
Absorption coefficient [mm–1]
F(000)
1.583
0.144
492
1.529
0.141
1064
Crystal size
Measured θ range
Limiting indices
0.3 mm×0.3 mm×0.2 mm
2.76 Ն θ Ն 30.44
–14 Ն h Ն 14
–10 Ն k Ն 10
–18 Ն l Ն 18
15232/5598
0.3 mm×0.3 mm×0.2 mm
2.11 Ն θ Ն 27.16
–15 Ն h Ն 15
–19 Ն k Ն 19
–17 Ն l Ն 17
19635/4803
Reflections collected/unique
Rint
0.0475
0.0731
Data/restraints/parameters
Goodness of fit on F2
R values [I2 Ն 2σ(I)]
R values (all data)
5598/0/309
0.943
R1 = 0.0440, wR2 = 0.0746
R1 = 0.0746, wR2 = 0.1209
0.686 and –0.305 e/Å3
4803/0/349
0.918
R1 = 0.0628, wR2 = 0.1549
R1 = 0.1212, wR2 = 0.1759
0.690 and –0.519 e/Å3
Final Fourier residuals
H, 1-H, 2-H), 8.69 (dd, J1 = 7.8, J1 = 9 Hz, 1 H, 11-H), 8.76 (s, determined by the standard method[38] with Coumarin 1 (Aldrich,
3
3
1 H, 14-H), 9.08 (d, 3J = 6 Hz, 1 H, 9-H), 9.35 (d, 3J = 6.7 Hz, 1 H,
4-H), 9.46 (s, 1 H, 5-H) ppm. 13C NMR (100 MHz, [D6]DMSO): δ
ΦF = 0.73 in ethanol)[39] or Cresyl Violet (Radiant Dyes, ΦF = 0.54
in methanol)[40] as references; refractive indices of the solvents were
= 18.8 (C6–CH3), 26.1 (C13a–CH3), 41.7 (Cq, C13a), 69.4 (CH, taken into account.
C13), 123.0 (CH), 124.0 (CH), 125.0 (CH), 126.3 (CH), 126.5 (CH),
X-ray Structure Analysis: Single crystals of 4a and 10b were ob-
128.2 (CH), 128.8 (Cq), 128.9 (CH), 132.8 (CH), 134.1 (Cq), 135.5
(Cq), 137.0 (CH), 137.6 (CH), 141.7 (Cq), 143.4 (CH), 146.2 (Cq),
147.1 (CH), 147.2 (Cq) ppm. MS (ESI): m/z (%) = 148 (16) [M –
OH – CH3]2+, 327 (100) [M – H]+, 415 (14) [M + BF4]+, 917 (14)
tained by crystallization from acetontrile/water. The single crystal
measurements were performed with a STOE IPDS. The program
SHELXS-97[41] was used to perform the structure solutions, apply-
ing direct methods. The structures were refined with the program
SHELXL-97.[42] The hydrogen atoms were placed with a constant
C–H distance of 0.98 Å in geometrically idealized positions, using
a riding model. For 10b, the hydrogen atoms belonging to crystalli-
zation water molecules could not be refined. Crystal data and
structure refinement details of the compounds 4a and 10b are given
in Table 3. CCDC-275724 (for 4a) and -275725 (for 10b) contain
the supplementary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
[2M + 3BF ]+. IR (KBr): ν
= 485, 522 (BF4 ), 1054s (BF4 ),
–
–
˜
4
max
1374, 1413, 1502 s, 1637s cm–1. C22H20B2F8N2O (502.0): calcd.
C 52.63, H 4.02, N 5.58; found: C 52.73, H 3.92, N 5.67.
Dehydration of 10b in PPA: Compound 10b (0.251 g, 0.50 mmol)
in PPA (2.50 g) was stirred under argon atmosphere for 18 h at
150 °C. After cooling to 100 °C, a solution of NaBF4 (0.11 g,
1.0 mmol) in water (6 mL) was added, and the reaction mixture
was stirred at 80–100 °C for 15 min. After cooling to room tem-
perature, the solution was extracted with nitromethane (4×5 mL).
The combined organic layers were washed with water (2×5 mL),
and the solvent was removed in vacuo, to give pure 4a (0.220 g,
91 %) as a yellow solid; spectroscopic data being identical with
those given above.
Acknowledgments
This work was generously financed by the Deutsche Forschungsge-
meinschaft.
Spectrophotometric Measurements: UV/Visible spectra were re-
corded on a Varian Cary 100 double-beam spectrophotometer; cor-
rected steady-state emission spectra were recorded on a Varian
Cary Eclipse fluorescence spectrometer. All spectrophotometric
measurements were performed in thermostatted quartz sample cells
at 20 °C, using spectral grade solvents (Fluka, Riedel-de Haën).
Working solutions were freshly prepared by dilution of stock solu-
tions (1×10–3  in acetonitrile). If not stated otherwise, the solu-
tion concentrations were 20 µ for absorption spectroscopy and
5.0 µ for fluorescence spectroscopy. Spectrophotometer slit widths
were kept 2 nm for absorption spectroscopy and 5/5 nm for emis-
sion spectroscopy. The relative fluorescence quantum yields were
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4107

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Published Online: August 15, 2005
4108
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
Eur. J. Org. Chem. 2005, 4098–4108