A joint theoretical and experimental insight into the electronic structure of chromophores derived from 6H,12H-5,11-methano-dibenzo[b,f][1,5]diazocine

Article abstract of DOI:10.1002/hlca.200790216

We report on the synthesis and electronic spectra of the chiral, donor-acceptor (push-pull) chromophores (±)-4 and (±)-5 with a 6H,12H-5,11-methanodibenzo[b,f][1,5]diazocine scaffold (Scheme 1 and Fig. 2). The electronic structures of these compounds were investigated at a quantum-chemical level (Figs. 2 and 3). The chemical reactivity of 6H,12H-5,11-methanodibenzo[b,f][1,5]diazocine ((±)-11) towards aromatic electrophilic substitution (Scheme 2 and Table) provided additional information about its electronic structure and confirmed nonnegligible derealization of the lone pair of the bridge-head N-atoms in this heterocyclic system.

Full text of DOI:10.1002/hlca.200790216

Helvetica Chimica Acta – Vol. 90 (2007)
2087
A Joint Theoretical and Experimental Insight into the Electronic Structure of
Chromophores Derived from 6H,12H-5,11-Methano-
dibenzo[b,f][1,5]diazocine
by Vincent Lemaur and J e´ r oˆ me Cornil
Laboratory for Chemistry of Novel Materials, University of Mons-Hainaut, B-7000 Mons
and
Delphine Didier, Aline Mujawase, and Sergey Sergeyev*
Laboratory of Polymer Chemistry, Universit e´ Libre de Bruxelles (U.L.B.), CP 206/01,
Boulevard du Triomphe, B-1050 Bruxelles
(
phone: þ 3226505392; fax: þ 3226505410; e-mail: sserguee@ulb.ac.be)
We report on the synthesis and electronic spectra of the chiral, donor-acceptor (push-pull)
chromophores (Æ)-4 and (Æ)-5 with 6H,12H-5,11-methanodibenzo[b,f][1,5]diazocine scaffold
Scheme 1 and Fig. 2). The electronic structures of these compounds were investigated at a quantum-
a
(
chemical level (Figs. 2 and 3). The chemical reactivity of 6H,12H-5,11-methanodibenzo[b,f][1,5]diazo-
cine ((Æ)-11) towards aromatic electrophilic substitution (Scheme 2 and Table) provided additional
information about its electronic structure and confirmed nonnegligible delocalization of the lone pair of
the bridge-head N-atoms in this heterocyclic system.
Introduction. – Trçgerꢀs base (¼(Æ)-2,8-dimethyl-6H,12H-5,11-methanodiben-
zo[b,f][1,5]diazocine, (Æ)-1; Fig. 1) is a chiral diamine with two stereogenic bridge-
head N-atoms. The unusual rigid, V-shaped geometry with the two aromatic rings
nearly perpendicular to each other has encouraged many elegant applications of
Trçgerꢀs base analogs in supramolecular chemistry and molecular recognition. To this
end, the 6H,12H-5,11-methanodibenzo[b,f][1,5]diazocine scaffold has been trans-
formed to increasingly sophisticated derivatives via metal-mediated reactions [1].
Among others, molecular-torsion balances for quantification of weak forces [2], the
regio- and stereoselective synthesis of fullerenes with inherently chiral addition
patterns [3][4], and chirality transfer in scissor-like heterotopic [Zn(porphyrinato)]
assemblies [5] should be mentioned (for recent comprehensive reviews, see [6]).
Fig. 1. Trçgerꢀs base: Structure and AM1-optimized geometry of the (S,S)-enantiomer
ꢁ
2007 Verlag Helvetica Chimica Acta AG, Zürich

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Helvetica Chimica Acta – Vol. 90 (2007)
Most of the applications reported up to date exploited the folded geometry and the
chirality of Trçgerꢀs base. However, another interesting structural feature, namely the
two tertiary-amine functions, was hardly used until now. Due to the presence of two N-
atoms, Trçgerꢀs base can be viewed as a structural analog of N,N-dialkylanilines
(
¼ N,N-dialkylbenzenamines), which have found extensive application in the design of
chromophores with nonlinear optical (NLO) properties [7].
In the course of our own study on chromophores with potential NLO activities, we
decided to explore the C -symmetrical V-shaped scaffold of 6H,12H-5,11-methanodi-
2
benzo[b,f][1,5]diazocine that provides a possibility to create two chromophore units
within one molecule, their dipole moments being nonantiparallel to each other. The
introduction of chirality elements within the conjugated system might prove beneficial
for obtaining noncentrosymmetrical crystals. The latter feature constitutes an
important prerequisite for the observation of second-order NLO phenomena. An
example of V-shaped design of push-pull chromophores is known and is based on
axially chiral C -symmetrical binaphtalenol derivatives, which have exhibited high first-
2
order hyperpolarizabilities [8].
In the early stage of our research, we are interested in simple model systems with
two diarylethene chromophore units integrated into the scaffold of 6H,12H-5,11-
methanodibenzo[b,f][1,5]diazocine. In this context, the nature of the electronic
structure and optical properties of these systems are worth being investigated, since
the analogy between an open-chain molecule and a bicyclic system is not straightfor-
ward. We thus undertook theoretical and experimental studies on simple model
systems with the aim to estimate delocalization of the lone pair on the N-atoms and its
impact on the optical properties.
Results and Discussion. – A structural concept that has been extensively used in the
design of second-order NLO chromophores involves an aromatic conjugated p-system
end-capped with electron donating (D) and accepting (A) groups (D- p-A or push-pull
design). A prototypical and extensively studied molecule is 4-(N,N-dimethylamino)-4’-
nitrostilbene (¼ N,N-dimethyl-4-[2-(4-nitrophenyl)ethenyl]benzenamine ¼ DANS; 2).
Another system that attracted our attention is the cationic styryl dye 3 which is soluble
in polar protic solvents. It is, therefore, interesting for biological applications such as
fluorescence imaging since cationic dye molecules are well known to intercalate with
DNA [9]. By analogy with 2 and 3, we designed the bis-chromophore systems (Æ)-4 and
(
(
Æ)-5 based on the scaffold of 6H,12H-5,11-methanodibenzo[b,f][1,5]diazocine
Scheme 1).
DANS (2) was prepared from 4-(dimethylamino)benzaldehyde (6) according to the
published procedure [10]. Its analog (Æ)-4 bearing two chromophore units was
synthesized from dialdehyde (Æ)-7 (prepared according to known procedures starting
from 4-iodoaniline [3][11]) by the same method. Base-catalyzed Knoevenagel –
Doebner condensation of (Æ)-7 with an excess of 4-nitrobenzeneacetic acid (8) gave
dinitroolefine (Æ)-4 in a modest yield (25%) after column chromatography.
Styryl dye 3 was synthesized by the Knoevenagel condensation of quaternary
benzothiazolium salt 9 with aldehyde 6 in the presence of pyridine. For the synthesis of
bis-chromophore (Æ)-5, the same synthetic procedure was amended: condensation of
dialdehyde (Æ)-7 with 2 equiv. of quaternary salt 9 afforded bis-benzothiazolium

Helvetica Chimica Acta – Vol. 90 (2007)
2089
Scheme 1. Synthesis of 2, 3, (Æ)-4, and (Æ)-5. Py ¼ pyridine.
derivative (Æ)-5, which was purified by crystallization from EtOH. Both bis-
chromophores (Æ)-4 and (Æ)-5 were isolated as pure (E,E) isomers, as evidenced by
3
the value of the coupling constants J(H,H) for the olefinic protons (16.5 Hz for (Æ)-4
and 15.9 Hz for (Æ)-5; cf. 16.2 Hz for 2 and 15.3 Hz for 3).
The absorption spectra of 2, 3, (Æ)-4, and (Æ)-5 are shown in Fig. 2. The lowest-
frequency absorption is shifted hypsochromically by 58 nm (0.43eV) for (Æ)-4
compared to DANS (2) and by 95 nm (0.51 eV) for (Æ)-5 compared to the styryl dye
3
. The molar absorption coefficients of (Æ)-4 and (Æ)-5 are close to twice the
corresponding values of 2 and 3, respectively.
The spectral characteristics, i.e., the hypsochromic shift of the absorption maxima
and increase of the absorption coefficients on going from 2 to (Æ)-4 or from 3 to (Æ)-5
were rationalized at a quantum-chemical level. To do so, we first optimized the
geometry of the compounds at the semi-empirical Hartree – Fock Austin model 1
(AM1) level using the AMPAC package [12]. Semi-empirical Hartree – Fock inter-
mediate neglect of differential overlap (INDO) calculations coupled to a single
configuration interaction (SCI) scheme were then carried out on the basis of the
optimized geometries to simulate the electronic and optical properties [13]; the

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Helvetica Chimica Acta – Vol. 90 (2007)
Fig. 2. a) UV/VIS Spectra (CH Cl ) of 2 (—) and ( Æ )-4 (– – –). b) UV/VIS Spectra (EtOH) of 3 (—) and
2
2
(Æ)-5 ( – – –). c)INDO-Simulated absorption spectra of 2 (—) and (S,S)-4 (– – –).
configurations in the SCI expansion were generated by promoting a single electron
from one of the highest N occupied molecular orbitals to one of the lowest N
unoccupied levels (N is, in our case, half the number of p-electrons of the molecule).
Although INDO is not the most up-to-date quantum-chemical approach, it remains in
our experience the best compromise to describe the optical properties of conjugated
systems in general. We have not privileged the time-dependent density-functional-
theory (TD-DFT) method which tends to strongly underestimate optical-transition
energies when the size of the conjugated backbone becomes too large (see the recent
review [14] for a detailed discussion). Here, we focus exclusively on compounds 2 and
(Æ)-4 whose optical properties are not expected to be significantly affected by solvent
effects that are neglected here, in contrast to the charged compounds 3 and (Æ)-5 [15].
The AM1-optimized geometries of 2 and (S,S)-4 (the (S,S)-enantiomer was
arbitrarily chosen for calculations) exhibit a twist angle of ca. 408 between the benzene
rings. This deviation from planarity results from the fact that the torsion-potential
profile of phenylenevinylene segments is flat for moderate torsion angles [16]. The
INDO/SCI results show that the molar absorption coefficient of the lowest-optically
allowed transition is increased by ca. 70% in (S,S)-4 compared to 2 (see Fig. 2,c). The
lowest-frequency absorption of (S,S)-4 located at ca. 344 nm is composed of two
distinct excited states lying very close in energy (338 and 347 nm). The electronic
transitions describing these two excited states involve the HOMO ꢀ 1, HOMO, LUMO,
and LUMO þ 1 levels that correspond to the bonding and antibonding combination of
the HOMO and LUMO orbitals of compound 2, respectively.
The hypsochromic shift of the lowest frequency absorption observed in the
experimental spectra on going from 2 to (S,S)-4 is also reproduced by our simulations
(
Fig. 2) though being underestimated (25 nm vs. 58 nm, resp.). Note that similar shifts
are obtained when the two chromophores are constrained to be planar. This shift
originates from a large stabilization of the HOMO orbital in (S,S)-4 (ꢀ 7.90 eV)
compared to 2 (ꢀ 7.32 eV) (see Fig. 3). In contrast, the LUMO level is slightly

Helvetica Chimica Acta – Vol. 90 (2007)
2091
stabilized when going from 2 (ꢀ1.39 eV) to (S,S)-4 (ꢀ1.53 eV). To shed light into the
large stabilization of the HOMO orbital, we first compared the electronic structure of
compound 2 to that of the model compound (S,S)-10 with only one styryl chromophore
unit (see Fig. 3). The stabilization of the HOMO orbital by ca. 0.4 eV on going from 2
to (S,S)-10 results from the fact that the methano bridge of 6H,12H-5,11-methano-
dibenzo[b,f][1,5]diazocine implies a change in the orientation of the p orbital of the N-
z
atom of the amino group with respect to the benzene ring. In molecule 2, the p orbital
z
of the N-atom of the amino group is fully conjugated with the p orbitals of the adjacent
z
ring, whereas the conjugation is reduced in (S,S)-10 due to the geometric constraints
induced by the bridge. Since the p orbital of the N-atom of the amino group
z
significantly contributes to the HOMO level, this reduction of conjugation is at the
origin of the large stabilization of the HOMO level. The fact that the LUMO level is
not significantly modified on going from 2 to (S,S)-10 is explained by the localization of
this orbital at the terminal NO groups (see Fig. 3 for the graphical representation of
2
the HOMO/LUMO levels of 2, (S,S)-4, and (S,S)-10). The HOMO level is further
stabilized by ca. 0.15 eV on going from (S,S)-10 to (S,S)-4. This weaker contribution to
the HOMO shift is attributed to changes in the amplitude of the electrostatic
interactions when the second polar chromophore moiety is introduced into the
6
H,12H-5,11-methanodibenzo[b,f][1,5]diazocine scaffold. The very small splitting
calculated between the highest two occupied and lowest two unoccupied levels
0.06 eV and 0.003 eV, resp.) in (S,S)-4 points to a weak electronic coupling between
(
the two chromophore units within the molecule. Thus, such systems do not allow for a
Fig. 3. Energy diagram and shape of the HOMO and LUMO orbitals in 2, (S,S)- 10, and (S,S)- 4. The size
and color of the circles describe the amplitude and sign of the LCAO (linear combination of atomic
orbitals) coefficients associated with the p-atomic orbitals.

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092
Helvetica Chimica Acta – Vol. 90 (2007)
delocalization of molecular orbitals along the conjugated backbone via ꢂp – s – p
through-bond couplingꢀ, as it has been shown for bis-chromophore systems with 1,3-
bis(methylene)cyclobutane or cyclodiborazane cores [17].
Additional experimental information on the electronic structure of 6H,12H-5,11-
methanodibenzo[b,f][1,5]diazocine can be obtained from its reactivity in electrophilic
substitution reactions. Indeed, N,N-dialkylanilines are highly reactive towards various
electrophiles and often give exclusively the products of substitution in the para-position
with respect to the dialkylamino group. We applied to (Æ)-6H,12H-5,11-methanodi-
benzo[b,f][1,5]diazocine ((Æ)-11) some electrophilic substitutions that are well known
for N,N-dialkylanilines (Scheme 2). The results of these experiments with PhNMe to
2
give substituted anilines 12 and with (Æ)-11 to give products of single or two-fold
substitution (Æ)-13 and (Æ)-14, respectively, are summarized in the Table. They clearly
show a much lower reactivity of (Æ)-11 vs. PhNMe . For instance, a Vilsmeier – Haack
2
formylation of PhNMe gave 70% of aldehyde 12a. On the contrary, with (Æ)-11, no
2
formylation took place under identical conditions. A recently described mild iodination
a
Scheme 2. Reactions of PhNMe and (Æ)-11 with Selected Electrophiles )
2
a) For conditions and yields, see Table.
Table. Reactions of PhNMe and (Æ)-11 with Selected Electrophiles. See also Scheme 2.
2
Method Conditionsa)
X
12 ([%]) ) from (Æ)-13 ([%]) ) (Æ)-14 ([%]) )
b
b
b
PhNMe2
from (Æ)-11
from (Æ)-11
A
B1
B2
DMF, POCl , 2 h, 1008
I2, dioxane/pyridine, 1 h, r.t.
ICl (1.1 equiv.), In(OTf) 3
CHO 12a (70) [18]
(Æ)-13a (0)
(Æ)-13b (0)
–
(Æ)-14a (0)
(Æ)-14b (0)
–
3
I
I
12b (98) [19]
12b (98) [20]
(
0.5 equiv.), MeCN, 1 h, r.t.
ICl (2.2 equiv.), In(OTf) 3
1 equiv.), MeCN, 24 h, r.t.
NBS (1 equiv.), DMF, 12 h, r.t.
NBS (2 equiv.), DMF, 18 h, r.t.
B2
I
–
(Æ)-13b (23)
(Æ)-14b(traces)
(
C
C
C
Br
Br
12c (91) c)
–
–
–
–
(Æ)-13c (30)
(Æ)-14c (30)
NBS (2.5 equiv.), DMF, 18 h, 808 Br
(Æ)-13c (25)
(Æ)-14c (56)
a) DMF ¼ N,N-Dimethylformamide, TfO ¼ trifluoromethanesulfonate, and NBS ¼ N-bromosuccini-
b
c
mide. ) Isolated yield of analytically pure products. ) Prepared according to the published general
procedure for the bromination of N,N-dialkylanilines [21].

Helvetica Chimica Acta – Vol. 90 (2007)
2093
of PhNMe with molecular I in dioxane/pyridine gave a nearly quantitative yield of the
2
2
para-iodo derivative 12b, while the starting material was quantitatively recovered in the
case of (Æ)-11. Thus, the aromatic rings of the 6H,12H-5,11-methanodibenzo[b,f][1,5]-
diazocine system appear to be inert towards less reactive electrophiles.
However, some other transformations demonstrated the feasibility of electrophilic
substitution of (Æ)-11. For example, bromination of PhNMe with N-bromosuccinimide
2
(
NBS) gave nearly quantitative yields of 4-bromoaniline (12c). When (Æ)-11 was
treated with 2 equiv. of NBS in DMF, 30% of bromide (Æ)-13c together with 30% of
dibromide (Æ)-14c and ca. 10% of the starting material were isolated after 18 h at room
temperature. When this reaction was performed at elevated temperature and with
excess of NBS, the yield of the product of two-fold substitution (Æ)-14c was increased
to 57%, while the yield of bromide (Æ)-13c was decreased to 25%, and no starting
material was isolated. In addition, iodination of (Æ)-11 with ICl in the presence of
In(OTf) as an activating Lewis acid proceeded much slower and with lower yield
3
compared to PhNMe2.
The results of the reactions between (Æ)-11 and different electrophiles establish the
much lower reactivity of 6H,12H-5,11-methanodibenzo[b,f][1,5]diazocine compared to
that of N,N-dialkylanilines. At the same time, these results suggest that the impact of a
resonance structure such as A (Scheme 2) in (Æ)-11 is small but not negligible. Indeed,
aromatic electrophilic substitution, if any, occurs exclusively at C(2) and C(8) of
6
H,12H-5,11-methanodibenzo[b,f][1,5]diazocine, i.e., in the para-position to the N-
atom, and no isomeric products were isolated. In addition, (Æ)-11 demonstrates a
higher reactivity towards electrophiles compared to benzene, which does not give
products of substitution with NBS and requires catalysis with Lewis acids and higher
temperatures to obtain products of electrophilic bromination [22]. Thus, the data on
the chemical reactivity of (Æ)-11 in reactions with various electrophiles are consistent
with the results of the calculations that predict, on the HOMO level, smaller LCAO
coefficients on the N-atoms of 6H,12H-5,11-methanodibenzo[b,f][1,5]diazocine de-
rivatives than on those of PhNMe -derived analogs, but which are by no means
2
negligible.
Conclusions. – In summary, we have reported the synthesis of chiral, donor-acceptor
(push-pull) chromophores with a 6H,12H-5,11-methanodibenzo[b,f][1,5]diazocine
scaffold. Theoretical calculations demonstrate a significant stabilization of the HOMO
level resulting in a pronounced hypsochromic shift of the lowest-frequency absorption,
compared to similar chromophores derived from PhNMe . The theoretical results and
2
the spectral studies in combination with the data on the chemical reactivity of 6H,12H-
5,11-methanodibenzo[b,f][1,5]diazocine towards aromatic electrophilic substitution
confirms the nonnegligible delocalization of the lone pair of the bridge-head N-atoms
in this heterocyclic system. We are currently working on the synthesis of novel
chromophores with a 6H,12H-5,11-methanodibenzo[b,f][1,5]diazocine scaffold as well
as on the studies of their nonlinear optical properties.
S. S. is indebted to Prof. Y. Geerts, Universit e´ Libre de Bruxelles, for the opportunity to conduct an
independent research program in his laboratory and for generous financial support. We thank Prof. R.
Flammang and co-workers, Universit e´ Mons-Hainaut, for the measurement of mass spectra. The work in
Mons was supported by the Belgian Federal Government ꢁInteruniversity Attraction Pole in Supra-

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094
Helvetica Chimica Acta – Vol. 90 (2007)
molecular Chemistry and Catalysis, PAI 5/3ꢀ, and the Belgian National Fund for Scientific Research
FNRS/FRFC). J. C. is an FNRS Research Associate.
(
Experimental Part
General. All chemicals were purchased from Aldrich, Acros, or TCI and used without further
purification unless stated otherwise. THF was refluxed over Na and benzophenone until a blue-violet
color persisted and distilled directly into the reaction flask. The following compounds were prepared
according to previously published procedures: 2 [10], (Æ)-7 [3], and (Æ)-11 [23] (we found our recently
published procedure for the synthesis of (Æ)-11 more convenient than the method of Kaupp et al. [24]).
Column chromatography (CC): silica gel 60 (Macherey-Nagel, particle size 0.04 – 0.063 mm). TLC:
precoated silica gel 60 F254 plates (Merck). UV/VIS Spectra: Agilent 8453-UV/VIS-NIR spectropho-
ꢀ
1
ꢀ1
1
13
tometer; 1 cm cell at r.t.; lmax (emax [m cm ]) in nm. H- (300 MHz) and C-NMR (75 MHz) Spectra:
Bruker Avance-300 spectrometer; CDCl solns.; chemical shifts d in ppm rel. to Me Si, coupling constants
3
4
J in Hz. MS: Waters AutoSpec-6F instrument for EI and Waters QToF-2 instrument for ESI; in m/z with
the lowest isotope mass. The analytical data of 12c were identical to those of the authentic material
purchased from Aldrich; the data of 13b,c [23] and 14b,c [11] were identical to those previously
published.
2
-[(1E)-2-[4-(Dimethylamino)phenyl]ethenyl]-3-ethylbenzothiazol-3-ium Iodide (3). A stirred
mixture of (4-dimethylamino)benzaldehyde (6; 0.447 g, 3.00 mmol), 3-ethyl-2-methylbenzothiazol-3-
ium iodide (9; 0.806 g, 2.64 mmol), pyridine (0.35 ml), and EtOH (35 ml) was heated to reflux for 18 h.
The mixture was then allowed to reach r.t., and the resulting solid was filtered, washed with cold EtOH,
and dried. Crystallization from EtOH (40 ml) afforded pure 3 · EtOH (1.09 g, 86%). Crystalline maroon
1
solid. UV/VIS (EtOH): 528 (34000). H-NMR (300 MHz, (CD ) SO, 258): 1.44 (t, J ¼ 7.1, 3 H); 3.12 (s,
3
2
6
H); 4.84 (q, J ¼ 6.9, 2 H); 6.84 (d, J ¼ 9.3, 2 H); 7.62 (d, J ¼ 15.3, 1 H); 7.64 – 7.82 (m, 2 H); 7.94 (d, J ¼
13
8
.7, 2 H); 8.09 (d, J ¼ 15.3, 1 H); 8.14 (d, J ¼ 8.4, 1 H); 8.31 (d, J ¼ 7.8, 1 H). C-NMR (75 MHz,
(
1
CD ) SO, 258): 13.7; 40.3; 43.4; 105.4; 111.8; 115.6; 121.3; 123.9; 127.1; 127.3; 128.8; 132.9; 140.7; 150.6;
3
2
þ
þ
53.4; 170.7. ESI-MS: 309.2 (M , C H N S ; calc. 309.1).
19 21 2
(
Æ)-2,8-Bis[(1E)-2-(4-nitrophenyl)ethenyl]-6H,12H-5,11-methanodibenzo[b,f][1,5]diazocine ((Æ)-
4
). A mixture of aldehyde (Æ)-7 (0.278 g, 0.5 mmol), 4-nitrobenzeneacetic acid (8; 0.543 g, 3 mmol),
and piperidine (0.30 ml, 3 mmol) was heated for 20 h at 1208 (bath temp.). The mixture was allowed to
reach r.t. and then dissolved in CH Cl (20 ml). The resulting soln. was subjected to CC (SiO , CH Cl /
2
2
2
2
2
1
AcOEt 5 :1): pure (Æ)-4 (108 mg, 21%). Orange solid. UV/VIS (EtOH): 382 (51000). H-NMR
(
300 MHz, CDCl , 258): 4.24 (d, J ¼ 16.8, 2 H); 4.34 (s, 2 H); 4.75 (d, J ¼ 16.8, 2 H); 6.98 (d, J ¼ 16.5,
3
2
CH¼CH); 7.09 – 7.19 (m, 6 H); 7.37 (dd, J ¼ 8.4, 1.8, 2 H); 7.54 (d, J ¼ 8.7, 4 H); 8.17 (d, J ¼ 8.7, 4 H).
13
C-NMR (75 MHz, CDCl , 258): 58.7 (2 C); 66.9 (1 C); 124.2 (4 C); 125.4 (2 C); 125.5 (2 C); 125.8 (2 C);
3
1
26.1 (2 C); 126.6 (4 C); 128.2 (2 C); 132.2 (2 C); 132.6 (2 C); 143.9 (2 C); 146.6 (2 C); 148.8 (2 C). HR-
þ
þ
EI-MS: 516.1766 (M , C H N O ; calc. 516.1798).
31
24
4
4
(
Æ)-2,2’-[6H,12H-5,11-methanodibenzo[b,f][1,5]diazocin-2,8-diyldi-(1E)-ethene-2,1-diyl]bis[3-eth-
ylbenzothiazol-3-ium] Diiodide ((Æ)-5). As described for 3, with (Æ)-7 (0.139 g, 0.499 mmol), 9 (0.308 g,
1
.01 mmol), pyridine (0.14 ml), and EtOH (15 ml): pure (Æ)-5 (0.225 g, 53%). Crystalline orange solid.
1
UV/VIS (EtOH): 433 (52000). H-NMR (300 MHz, (CD ) SO, 258): 1.44 (t, J ¼ 7.1, 6 H); 4.32 – 4.41 (m,
3
2
4
H); 4.84 (d, J ¼ 16.5, 2 H); 4.93 (q, J ¼ 7.1, 4 H); 7.39 (d, J ¼ 8.7, 2 H); 7.72 – 7.96 (m, 10 H); 8.13 (d,
13
J ¼ 15.9, 2 CH¼CH); 8.28 (d, J ¼ 8.7, 2 H); 8.42 (d, J ¼ 6.9, 2 H). C-NMR (75 MHz, (CD ) SO, 258):
3
2
1
4.1 (2 C); 44.3 (2 C); 58.1 (2 C); 65.8 (1 C); 111.7 (2 C); 116.5 (2 C); 124.3 (2 C); 125.3 (2 C); 128.0
(
(
2 C); 128.2 (2 C); 128.9 (2 C); 129.0 (4 C); 129.2 (2 C); 129.4 (2 C); 140.8 (2 C); 148.8 (2 C); 152.4
2
þ
2þ
4 2
2 C); 171.4 (2 C). HR-ESI-MS: 299.1111 (M , C H N S ; calc. 299.1107).
37
34
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1] U. Kiehne, T. Weilandt, A. Lützen, Org. Lett. 2007, 9, 1283; D. Didier, S. Sergeyev, Tetrahedron 2007,
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Helvetica Chimica Acta – Vol. 90 (2007)
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Received June 5, 2007