Monoaza[5]helicenes. Part 2: Synthesis, characterisation and theoretical calculations

Article abstract of DOI:10.1016/j.tet.2005.09.132

The synthesis of four different monoaza[5]helicenes is reported, to complete the whole series of these compounds, so that systematic studies on their properties can be carried out. They were fully characterised via NMR. A theoretical approach to explain w

Full text of DOI:10.1016/j.tet.2005.09.132

Tetrahedron 62 (2006) 139–148
Monoaza[5]helicenes. Part 2: Synthesis, characterisation and
theoretical calculations
b
c
Sergio Abbate,a Cristina Bazzini,b Tullio Caronna,b, Francesca Fontana, Cristian Gambarotti,
*
Fabrizio Gangemi,a Giovanna Longhi,a Andrea Mele,c Isabella Natali Sorab and Walter Panzerid
aDipartimento di Scienze Biomediche e Biotecnologie, Universita‘ di Brescia, Viale Europa 11, I-25123 Brescia
b
`
Dipartimento di Ingegneria Industriale dell’Universita di Bergamo, Viale Marconi 5, I-24044 Dalmine (Bg), Italy
cDipartimento di Chimica, Materiali ed Ingegneria Chimica ‘Giulio Natta’ del Politecnico, Via Mancinelli 7, I-20131 Milano, Italy
dCNR-Istituto di Chimica del Riconascimento Molecolare, Via Mancinelli 7, I-Milano, Italy
Received 24 June 2005; revised 13 September 2005; accepted 29 September 2005
Available online 27 October 2005
Abstract—The synthesis of four different monoaza[5]helicenes is reported, to complete the whole series of these compounds, so that
systematic studies on their properties can be carried out. They were fully characterised via NMR. A theoretical approach to explain why ring
closure occurs to give the most crowded compound is reported, in comparison with earlier calculation methods.
q 2005 Elsevier Ltd. All rights reserved.
1. Introduction
possible isomers because few aza[5]helicenes are known in
the literature,4–13 and there is no systematic study of their
properties. This is despite the potential applications of
helicenes that can be found, for example, in the fields of
non-linear optics (NLO)14 and circularly polarised
luminescence.15
Photochemical cyclisation of stilbene derivatives is a well
known method to obtain polycyclic molecules. In a previous
paper,1 which is part 1 of this work, we described the
cyclisation of some ethylenic derivatives that allowed us to
obtain a number of monoaza and diaza[5]helicenes. These
molecules showed interesting properties depending on the
position of the nitrogen in the helicene framework, like, for
example, varying characteristic triplet lifetime or rate of
racemisation.1,2 Unfortunately, for different reasons, this
synthetic approach appeared not to be of general appli-
cation. In addition, among all possible products from ring
closure reactions, helicene, the most crowded system, was
obtained in all the cases we studied. Consequently, we were
interested both in finding a way to obtain those aza[5]-
helicenes that could not be synthesized with the route
reported previously,1 and also in applying theoretical
considerations for the starting materials we used, to justify
the photochemical cyclisation to give the helicene. In an
earlier paper, we reported several different reasons why a
single approach appeared not to be of general application,3
and did not allow the formation of all the desired monoaza
and diazahelicenes. We were interested in obtaining all the
Indeed, the study we carried out on the already synthesized
helicenes, showed a very long lifetime of the triplet state and
a tendency to p–p stacking both in the solid state and for the
azahelicenes by themselves or even for some metal
complexes, allowing the build up of columnar system
arranged in the space with a particular geometry, and with a
control over chirality that may be valuable in designing new
materials for optoelectronic applications.16–20
2. Results and discussion
2.1. Synthetic studies
The synthetic route we followed to obtain the azahelicenes
was very simple and started from the synthesis of 1,2-
disubstituted ethylenes (obtained through Wittig reaction
from the appropriate aldehyde with the suitable
phosphonium salt) that were afterwards cyclised photo-
chemically to the desired helicenes as first described by
Martin for the carbohelicene21 and described in Scheme 1
for the synthesis of 4-aza[5]helicene.
Keywords: Helical structures; Helicenes; Molecular orbital calculations;
Photochemistry.
Corresponding author. Address: Dipartimento di Ingegneria Industriale
`
Universita degli Studi, di Bergamo, Viale G. Marconi, 5, 24044 Dalmine,
Italy. Tel.: C39 035 2052322; fax: C39 035 562 779;
e-mail: tullio.caronna@unibg.it
*
0040–4020/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2005.09.132

140
S. Abbate et al. / Tetrahedron 62 (2006) 139–148
is 6-bromomethylisoquinoline, and we could not develop a
synthetic strategy to obtain them. Also the preparation of
7-aza[5]helicene showed some difficulties, and attempts to
repeat a published synthesis were unsuccessful.12
For these reasons, we decided to find a different approach to
their synthesis, looking also to the possibility that it may
open the route to obtain other diazahelicenes.
Scheme 1.
Since the photochemical ring closure had proven to be one
of the simplest ways to obtain these compounds, we decided
to study the photochemical ring closure of different
ethylenic compounds, namely the compound carrying
three ortho-condensed rings on one side of the ethene and
one ring on the other side. The synthesis of these derivatives
easily gave the desired helicenes, and eventually opened the
route for the formation of some diaza[5]helicenes or of
larger azahelicenes. We can anticipate that ring closure on
the other side of the phenanthrene (or phenanthridine),
giving a completely flat molecule with less strain, does not
occur, at least in the case we studied.
The synthesis of the 2-methyl-benzo[f]isoquinoline27
allowed to obtain the 7-aza[5]helicene (6) with a fair
overall yield in few steps (Scheme 3).
Scheme 2.
Despite the fact that generally the methyl group a to the
heteroaromatic nitrogen is easily functionalised, in this
phenanthridine it appeared to be rather unreactive.
Transformation into the N-oxide allowed instead facile
functionalisation through a rearrangement reaction. The
other steps were rather obvious.
Following this synthetic approach, it was possible to
synthesize nine different azahelicenes, namely 4-, 5-,
6-aza and 4,11-, 5,10-, 6,9-, 4,9-, 4,10- and 5,9-diaza[5]-
helicenes. Other synthetic approaches were envisioned for
the synthesis of carbo- and heterohelicenes,22–26 but, in our
opinion, when it is possible to apply the above route, this is
the shortest, simplest and highest yielding. This approach,
for different reasons, was not useful for obtaining the 2- and
7-aza derivatives (see Scheme 2), as well as for the
preparation of the other monoazahelicenes. For
example, we were not able to prepare 1-(2-naphthyl),2-(6-
isoquinolyl) ethylene, the precursor for the 3-aza[5]-
helicene, because 6-carboxaldehydeisoquinoline, to the
best of our knowledge, is not reported in the literature, nor
For the synthesis of 1- and 3-aza[5]helicenes two
approaches are possible. The first starts by building an
ethene derivative with a phenanthrene on one side and a
3-pyridine on the other. Its photochemical ring closure
yielded two desired azahelicenes (10) and (11) in 9:1 ratio
(Scheme 4).
The second synthetic approach may appear longer, because
it was necessary to synthesize a starting phenanthridine
Scheme 3.

S. Abbate et al. / Tetrahedron 62 (2006) 139–148
141
Scheme 4.
derivative. This was achieved through a Wittig reaction
between terephthalaldehyde and the phosphonium salt of
3-bromomethylpyridine. With the use of an excess of
terephthalaldehyde, it was possible to obtain the substitution
of one aldehydic group only. Interestingly, the direct
photolysis of this derivative did not give any ring closure,
possibly because the n/p* transition is lower in energy
respect to the p/p* transition. Confirmation of this
hypothesis came from the transformation of the aldehyde
to the corresponding dimethylketal. Irradiation of this
derivative gave the two phenanthridines in very high overall
yield (95%). Hydrolysis to their corresponding aldehydes
was quantitative, and their separation was easily achieved
(with an isomeric ratio of (14):(15) 1:8). The subsequent
synthetic sequences to give (10) or (11) are illustrated in
Scheme 5.
Since the yields were high in both cases, but the final
amount of the two helicenes were different, one can choose
the method depending on the helicene desired.
The synthesis of 2-aza[5]helicene was different, because, as
we already stated, the photochemical ring closure of 7-(2-
naphthalen-2-yl-vinyl)-isoquinoline yielded to the corre-
sponding perylene, and the photochemical approach starting
from either 4-(2-phenathrene-3-yl-vinyl)-pyridine or
9-styryl-benzo[h]isoquinoline gave the same result.
Since the last step cannot be a photochemical one, we
designed another way to obtain the ring closure. This was
obtained starting from benzo[h]isoquinoline-9-carbalde-
hyde (synthesised as illustrated in Scheme 6) and the
2-methylphosphonium salt of 1-bromobenzene. The
Scheme 5.

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S. Abbate et al. / Tetrahedron 62 (2006) 139–148
Scheme 6.
treatment of this derivative with (tert-butyl)3SnH yielded
the desired 2-aza[5]helicene (21). (Scheme 6).
2.2. Calculations
As pointed out in the first part of the paper, the
photochemical cyclisation of these derivatives gave rise to
the most crowded azahelicene rather that to the correspond-
ing less strained dibenzo[a,h]anthracene (only the positions
involved in the ring closure are highlighted in the scheme
below for the sake of clarity).
Theoretical considerations and calculations on these
mechanisms are already present in the literature. Some
authors,28,29 working in the context of the Hu¨ckel model,
proposed a ‘free valence’ atomic index to characterize the
reactivity of atoms in molecules, but generally they did not
work together with experimental photochemists providing
them with fresh experimental data. For these reasons, we
decided to perform some calculations regarding the
formation of the azahelicenes reported in this paper.
Compounds (16), 9-styryl-benzo[h]isoquinoline (22) and
(17) have been analysed by means of ab initio calculations
using the package GAUSSIAN03.30
Scheme 7.
of the Natural Bond Orbital program included in the
package GAUSSIAN03.31
The ground-state geometry was determined by means of a
DFT calculation with B3LYP functional and 6-31G basis
set. Excited states have then been computed using the CIS
method with the same basis set and geometry optimization
has been carried out for the first excited state.
In the present study, we have to take into account that the
computational approach is different from a mere Hu¨ckel
method and we need to define an atomic quantity FA that
mimics the ‘free valence’ atomic index. We introduce:
For each molecule two equilibrium configurations have
been considered, the first one with a cis-geometry, close to
the helicene structure (upper part in Scheme 7), while the
second one with a trans-geometry close to the corresponding
dibenzo[a,h]anthracene (lower part in Scheme 7).
X
ðwÞ
FA Z VA K
b
(1)
AB
BsA
where VA is the atomic valence returned by the NBO
program as the sum of occupation numbers of the valence
orbitals (as opposed to core orbitals) of atom A, b is the
In order to find an explanation for the different behaviour of
the experiments for the production of helicenes with respect
to other possible products, such as perilenes, (See Scheme 2)
the value of an atomic index has been calculated by means
(w)
AB
Wiberg bond index32 of atoms A and B, and the sum is made
over all the atoms B other than A.

S. Abbate et al. / Tetrahedron 62 (2006) 139–148
143
Table 1. Differences of the ‘F’ atomic indices in the excited state over the
atoms of the scheme for the three structures (16), (22) and (17) (see Eq. 1
and discussion in the text)
In Table 2, we report the sum F*xCF*y for the reacting
atoms x and y, as suggested in Ref. 29.
F*21KF*1
F*22KF*14
F*22KF*12
For compounds (16) and (17) the closure that yields the
helicene is favoured with respect to the formation of the
anthracene, and in accord to Table 1, this corresponds to the
highest (positive) values for F*xKF*y. In the case of (22)
however, the highest value for F*xKF*y regards the closure
between positions 21 and 1 suggesting that the perylene is
formed first with this closure; the second highest value is
calculated for positions 14 and 22. As matter of fact, even
working at very low conversion, we were not able to detect
any trace of the 2-aza[5]helicene that may close later to the
perilene.
(16)
(22)
(17)
—
0.30355
K0.03046
0.02078
0.01551
0.03432
0.01026
K0.00775
0.00445
Table 2. Sums of the ‘F’ atomic indices in the excited state over the atoms
of the Scheme 7 for the three structures (16), (22) and (17) (see Eq. 1 and
text)
(F*21CF*1)
(F*22CF*14
)
(F*22CF*12)
(16)
(22)
(17)
—
0.27981
0.61301
0.46762
0.48835
0.47542
0.50340
0.51153
0.50255
The calculations reported are for the cis conformers; we notice
that the trans conformers have lower values for F*xKF*y,
despite the fact that their ground state energies are slightly
lower with the choice of the 6-31G basis set. Similar trends are
found in Table 2, but the correlation with the observed
reactivities of the studied molecules is not so immediate. Our
obvious conclusion is that the first method seems to give better
results for these indices.
The above index has been calculated both in the ground
state (FA) and in the first excited state (FA*).
In Table 1, we report the values of the differences F*xKF*y
for the positions considered in the above scheme; x and y
indicate the reacting atoms, which have somewhat
arbitrarily been chosen in the following order: x is on the
benzene ring, y is on the phenanthridine system.
Of course, more theoretical work should probably be done
and further examples need to be considered to reach a
definite conclusion; we also expect further support will
Figure 1. Isovalue surfaces of LUMO of the two conformers of (16) in the first excited state optimised geometries. The two colours refer to the two phases of
the wavefunction.

144
S. Abbate et al. / Tetrahedron 62 (2006) 139–148
come from future synthetic work. Also, due comparison
with previous theoretical approaches in the literature28,29
will be made in forthcoming work.
this class of molecules. The combined use of spin–spin
coupling constants in aromatic and heteroaromatic systems
and H–H NOE proved to be a general strategy for the
elucidation of these structures. The Wiberg bond indexes
seem to explain why the photochemical reactions bring to
the most crowded of the two possible final molecules.
Further insight into this problem may be achieved by
looking at the isovalue surface of LUMO orbital constructed
with the aid of Gaussview package.30 In Figure 1, we
present the case of (16). A considerable superposition of the
wavefunction for atoms 22 and 14 is observed, preparing
compound (16) to react to helicene. In the single
configuration interaction approach, the lower energy
transition of both conformers has a fairly dominant
contribution from HOMO–UMO, as expected, and its
calculated dipole strength is higher than the dipole strength
calculated for the two following transitions.
4. Experimental
All the solvents were distilled and dried before use.
Benzaldehyde, terephthalaldeyde, bromomethylbenzene,
3-picoline, 3-pyridine aldehyde, 1-bromo,2-bromomethyl-
benzene, 2,2-dimethoxypropane, triphenylphosphine, azo-
bisisobutyronitrile (AIBN),(tert-butyl)3 tin hydride, acetic
anhydride, SeO2 and 1-bromo-pyrrolidine-2,5-dione
(N-bromosuccinimide) are commercial products and were
used without further purification. SeO2 and Se (as product of
the reactions) are poisonous and particular care must be
used (well aerated hood and heavy gloves) when handled.
NMR spectra were run either on Bruker ARX 400 or Bruker
Avance 500 spectrometers operating at proton resonance
frequencies of 400 and 500 MHz, respectively. The
products were dissolved in CDCl3 and tetramethylsilane
2.3. NMR
The assignment of the NMR spectra of the final helicenes
was achieved by the combined use of spin–spin coupling
constants in aromatic and heteroaromatic systems and H–H
NOE, according to a general strategy already outlined in
previous papers.1,3
In particular, we took advantage of the J coupling patterns
within heteroaromatic bases to assign the signals in the
N-containing part of the helicene. This approach can be
conveniently used for the structural assessment of
compounds (10), (11) and (21). Nevertheless, the assign-
ment of the NMR spectrum of (6) deserves mention. Indeed,
the position of the nitrogen atom in the molecular
framework is such that the two naphthalene residues
(C1–1 and C9–94) are in very similar chemical environ-
1
(TMS) was added as reference. H{1H} NOE difference
spectra and two-dimensional NOESY were carried out by
using standard literature pulse sequences. Electron ioniza-
tion mass spectra were recorded on a Finnigan MAT TSQ
70 instrument (70 ev, EI); the samples were introduced in
the spectrometer source by direct probe insertion.
Irradiations were carried out on a Rayonet RPR-100
photochemical reactor equipped with 16 interchangeable
lamps irradiating either at 254, 300, or 350 nm as well in the
visible range, dissolving the substance in the appropriate
solvent. The ATR FT-IR spectra were recorded on a Avatar
370-Thermo.
1
ments, making the discrimination of their H NMR signals
difficult. In this case, the assignment of H8 was the starting
point, due to its diagnostic chemical shift. Selective
irradiation of H8 gave 9.1% steady state NOE on H9. The
3
large J(H9–90) value (8.8 Hz) provided the assignment of
the coupling partner H10. The signal assigned to H10
showed, by suitable resolution enhancement, a doublet of
doublets multiplicity, with very small splitting (0.8 Hz) due
to long range coupling with H14. The latter coupling is
reported as ‘zig zag’ coupling in naphthalene derivatives.33
This interpretation was confirmed by selective decoupling
experiments. The unambiguous assignment of H14
(8.67 ppm) allowed us to assign the structurally related H1
(8.59 ppm). Steady state NOE difference spectra obtained
after selective saturation of H1 and H14 allowed the
assignment of the partially overlapped signals of H2 and
H13. NOESY experiments allowed the assignment of H3
and H12, due to their dipolar contacts with already
attributed H2 and H13. In turn, H3 and H12 gave cross
peaks with the strongly overlapped H4 and H11 (8.01 and
8.02 ppm, respectively). The assignment of H5 was
achieved via NOE with H4 and 5J(H5–5)Z0.8 Hz. The
remaining doublet at 8.16 ppm was eventually assigned to
H6.
4.1. Wittig reactions
General procedure. In a typical procedure in a flask
containing a mixture of the aldehyde (1 mmol) and
triphenyl-phosphonium bromide derivative (1 mmol) in
methanol (15 mL), MeONa (0.065 g, 1.2 mmol) was
added under stirring. The mixture was gently boiled for
3 h. After cooling, water was added, and the solution
extracted many times with a large volume of CH2Cl2. After
drying and solvent evacuation, the residue was chromato-
graphed on silica gel. (Solvents), yield%, mp and physical
properties are reported for each case.
4.2. Photochemical reactions
General procedure. The appropriate ethene derivative
(1.0 mmol) was dissolved in benzene (150 mL) in a Pyrex
vessel open to the air. The vessel was irradiated at 350 nm
for a time ranging between 24 and 36 h. The irradiation was
stopped when, and if, some tar begun to form. The solvent
was removed under vacuum, and the residue was
chromatographed on silica gel. Rf,(Solvents), yield%, mp,
MS and NMR are reported for each case.
3. Conclusions
The synthesis of four aza[5]helicenes is presented in order to
complete the preparation of all the monoaza derivative of

S. Abbate et al. / Tetrahedron 62 (2006) 139–148
145
4.2.1. 2-Methylbenzo[f]isoquinoline. This compound was
obtained as reported in the literature in 15% overall yield,
mp 91–93 8C (lit. 93–95).9
acetate 2:3) in 70% yield as a yellow solid, mp 106–108 8C,
MS m/z 209 (MC, 55%), 181 (100%), 152 (MC, 53%), IR
(cmK1): 3031, 2938, 1740, 1457, 1375, 1228, 1098, 1054,
1
900, 823, 755, H NMR 5.03 (s, 2H, CH2), 7.71 (m, 2H,
2CH), 7.80 (d, 1H, JZ9.2 Hz, 1CH), 7.83 (d, 1H, JZ
9.2 Hz, 1CH), 7.94 (dd, 1H, JZ9.1, 1.9 Hz, 1CH), 8.43 (s,
1H, CH), 8.70 (dd, 1H, JZ9.1, 1.9 Hz, 1CH), 9.22 (s, 1H,
1CH), elemental analysis calcd(%) for C14H11NO (209.2):
C 80.36, H 5.30, N 6.69, found C 80.09, H 5.32, N 6.67.
4.2.2. 2-Methylbenzoisoquinoline N-oxide (1). The pro-
cedure used was adapted from the literature for the
N-oxidation of the heterocyclic bases.34 2-Methylbenzoiso-
quinoline (1.00 g, 5.2 mmol) was dissolved in acetic acid
(3 mL) and hydrogen peroxide 30% (5 mL) was added. The
solution was warmed at 70 8C for 72 h. The solvent was
evaporated and the residue was basified with a solution of
NaHCO3 and extracted with CHCl3. After drying of the
organic phase, the solvent was evacuated and the residue
was triturated with diethyl ether to give (1) as a white solid
in 85% yield, mp 145–147 8C, MS m/z 209 (MC, 100%),
208 (78%), IR (cmK1): 3384, 3038, 2918, 1600, 1454, 1317,
1237, 1180, 1162, 1000, 877, 803, 745, 618, 1H NMR 2.75
(s, 3H, 1CH3), 7.52 (d, 1H, JZ9.0 Hz, 1CH), 7.68 (m, 2H,
2CH), 7.78 (d, 1H, JZ9.0 Hz, 1CH), 7.88 (dd, 1H, JZ7.0,
2.0 Hz, 1CH), 8.36 (s, 1H, CH), 8.48 (dd, 1H, JZ7.0,
2.0 Hz, 1CH), 8.84 (s, 1H, CH), Elemental analysis
calcd(%) for C14H11NO (209.2): C 80.36, H 5.30, N 6.69,
found C 80.50, H 5.30, N 6.67.
4.2.5. 2-Benzo[f]isoquinolinecarbaldehyde (4). The pro-
cedure used was adapted from the literature36 for the
oxidation of the heterocyclic alcohols. Compound (3)
(0.50 g, 2.4 mmol) was dissolved in dioxane (15 mL) and
SeO2 (0.27 g, 2.4 mmol) was added. The resulting mixture
was boiled for 3 h. After cooling, Se was filtered off, the
solvent evacuated and the residue chromatographed on
silica gel (hexane/ethyl acetate 2:3)to give (4) in 26% yield,
and recovering unreacted (3) quantitatively. (4) is a yellow
solid, mp 127–129 8C, MS m/z 207 (MC, 52%), 179
(100%), 152 (46%), IR (cmK1): 2843, 1691, 1402, 1116,
897, 821, 798, 734, 703, 600, elemental analysis calcd(%)
for C14H9NO (207.2): C 81.14, H 4.38, N 6.76, found C
81.35, H 4.37, N 6.79.
4.2.3. Acetic acid benzo[f]isoquinolin-2-ylmethyl ester
(2). Compound (1) (0.50 g, 2.4 mmol) was dissolved in
acetic anhydride (8 mL) and refluxed for 24 h.35 After
cooling off the solution, the excess of acetic anhydride was
eliminated under vacuum leaving an almost pure product.
Compound (2) was obtained as brown oil in 96% yield, MS
m/z 251 (MC, 100%), IR (cmK1): 2922, 1716, 1229, 1031,
4.2.6. 2-Styrylbenzo[f]isoquinoline (5). For the prepa-
ration see the general procedure. Compound (5)(ethyl
acetate) was obtained as a yellow solid in 80% yield, mp
147–149, MS m/z 281 (MC, 39%), 280 (100%), IR (cmK1):
2926, 1736, 1594, 1453, 1295, 974, 878, 825, 761, 600, 1H
NMR 7.30 (m, 2H, 2CH), 7.40 (m, 3H, 3CH), 7.43 (d, 1H,
JZ16.1 Hz, 1H), 7.66 (d, 2H, JZ7.0 Hz, 2CH), 7.72 (m,
2H, 2CH), 7.88 (d, 1H, JZ16.1 Hz, 1H),7.93 (m, 1H, 1CH),
8.42 (s, 1H, CH), 8.72 (m, 1H, CH), 9.23 (s, 1H, CH),
elemental analysis calcd(%) for C21H15N (281.4): C 89.65,
H 5.37, N 4.98, found C 89.38, H 5.37, N 4.96.
1
877, 814, 743, H NMR 2.22 (s, 3H, CH3), 5.43 (s, 2H,
CH2), 7.72 (m, 2H, 2CH), 7.78 (d, 1H, JZ8.8 Hz, 1CH),
7.82 (d, 1H, JZ8.8 Hz, 1CH), 7.93 (m, 1H, 1CH), 8.43 (s,
1H, CH), 8.65 (m, 1H, 1CH), 9.22 (s, 1H, 1CH), elemental
analysis calcd(%) for C16H13NO2 (251.3): C 76.48, H 5.22,
N 5.57, found C 76.66, H 5.23, N 5.56.
4.2.7. 7-Aza[5]helicene (6). For the preparation see the
general procedure.(6) was obtained as a yellow solid in yield
75%, mp 142–145 8C, MS m/z 279 (MC, 54%), 278 (100%),
IR (cmK1): 2920, 818, 745, 715, 660, 614, 607, elemental
analysis calcd(%) for C21H13N (279.3): C 90.30, H 4.69, N
5.01, found C 90.08, H 4.70, N 5.02. NMR is reported in
Table 3.
4.2.4. 2-Methylolbenzo[f]isoquinoline (3). Compound (2)
(0.50 g, 1.99 mmol) was dissolved in concentrated hydro-
chloric acid, and the solution boiled for 18 h.35 The solution
was then cooled in an ice bath and basified with a solution of
NaOH 2 M. The solution was extracted with diethyl ether.
The organic layer was dried and the residue was
chromatographed on silica gel, to give (3) (hexane/ethyl
Table 3. NMR data for the aza[5]helicenes (10), (21), (11) and (6)
(10)
(21)
(11)
(6)
H1
H2
H3
H4
H5
H6
H7
H8
—
9.89s
—
8.56d, JZ5.6 Hz
7.70d, JZ5.6 Hz
8.28br d, JZ6.0 Hz
8.38br d, JZ6.0 Hz
—
9.35br s
8.02m
8.59ddd, JZ0.8, 1.2, 8.5 Hz
7.35ddd, JZ1.4, 6.9, 8.5 Hz
7.59ddd, JZ1.2, 6.9, 8.0 Hz
8.01dd, JZ1.4, 8.0 Hz
8.10dd, JZ0.8, 8.8 Hz
8.10d, JZ8.8 Hz
—
9.33s
7.99d, JZ8.8 Hz
8.04dd, JZ0.8, 8.8 Hz
8.02dd, JZ1.4, 8.0 Hz
7.66ddd, JZ1.2, 6.9, 8.0 Hz
7.39ddd, JZ1.6, 6.9, 8.5 Hz
8.67ddd, JZ0.8, 1.2, 8.5 Hz
8.70dd, JZ1.8, 4.2 Hz
7.50dd, JZ4.2, 8.1 Hz
8.26dd, JZ1.8, 8.1 Hz
7.88d, JZ8.5 Hz
8.08d, JZ8.6 Hz
a
7.98d, JZ8.5 Hz
8.02m
7.99d, JZ8.3 Hzb
7.91d, JZ8.3 Hzb
7.96d, JZ8.5 Hzc
7.86d, JZ8.5 Hzc
7.93dd, JZ1.6, 8.0 Hz
7.54ddd, JZ1.5, 6.8, 8.0 Hz
7.27ddd, JZ1.6, 6.8, 8.3 Hz
8.05d, JZ8.3 Hz
7.99d, JZ8.3 Hzd
7.92d, JZ8.3 Hzd
7.90d, JZ8.6 Hz
7.90dd, JZ0.8, 8.6 Hz
7.99d, JZ8.1 Hz
7.58ddd, JZ1.2, 6.9, 8.1 Hz
7.35ddd, JZ1.4, 6.9, 8.4 Hz
8.46ddd, JZ0.8, 1.2, 8.4 Hz
a
a
a
a
H9
H10
H11
H12
H13
H14
7.97d, JZ8.2 Hz
7.54t, JZ7.3 Hz
7.36t, JZ7.3 Hz
8.58d, JZ8.2 Hz
a 7.97–7.84 ppm, m, H6CH7CH8CH9CH10.
The assignment can be reversed.
b,c,d

146
S. Abbate et al. / Tetrahedron 62 (2006) 139–148
4.2.8. 3-Bromomethylphenanthrene (7). The compound
was prepared similarly to the procedure reported to obtain
9-bromomethylphenanthrene37 by boiling 3-methylphenan-
threne (1.0 g, 5.2 mmol) with N-bromosuccinimide (0.93 g,
5.2 mmol) and a few crystals of benzoylperoxide in CCl4 for
4 h. (7) Was obtained as a white solid in 96% yield, mp 95–
96 8C, MS m/z 271 (MC, 8%), 270 (9%), 191 (100%),
Elemental analysis calcd(%) for C15H11Br (271.3): C 66.44,
H 4.09, Br 29.47, found C 66.49, H 4.09, Br 29.51
MeOH (10 mL) and a few crystals of p-toluenesulfonic acid
were added. The solution was boiled, distilling off the
azeotrope of MeOH–acetone.40 At the end of the reaction
MeONa was added and the solvent evaporated. The residue
was dissolved in CH2Cl2, washed with water and dried on
Na2SO4. Compound (13) was obtained as a yellow oil in 98%
yield and MS m/z 255 (MC, 8%), 224 (100%); the product was
used without further characterisation.
4.2.14. Benzo[h]quinoline-9-carbaldehyde (14) and ben-
zo[f]isoquinoline-9-carbaldehyde (15). The irradiation
was carried out in acetonitrile (200 mL) for 48 h at
254 nm. At the end of the irradiation, the solution was
stirred with HCl 1 M for 2 h to hydrolyse the ketals. The
organic layer was washed with water, dried and the solvent
removed. The residue was chromatographed on silica gel
obtaining (14) and (15). Compound (14) (hexane/ethyl
acetate 1:1) was obtained as yellow solid in 11% yield, mp
110–112 8C, MS m/z: 207 (MC, 100%), 206 (62%), 178
(91%), 150 (18%), IR (cmK1): 2880, 2792, 1689, 1579,
1278, 1233, 1180, 1165, 880, 776, 702, 595, 1H NMR 7.61
(dd, 1H, JZ8.0, 4.6 Hz, 1CH), 7.87 (d not resolved, 2H,
2CH), 8.01 (d, 1H, JZ8.3 Hz, 1CH), 8.21 (dd, 1H, JZ8.3,
1.7 Hz, 1CH), 8.24 (dd, 1H, JZ8.0, 1.7 Hz, 1CH), 9.08 (dd,
1H, JZ4.6, 1.7 Hz, 1CH), 9.80 (s, 1H, 1CH), 10.34 (s, 1H,
CHO), elemental analysis calcd(%) for C14H9NO (207.2): C
81.14, H 4.38, N 6.76, found C 80.86, H 4.39, N 6.74.
Compound (15) (hexane/ethyl acetate 1:1) was obtained as
yellow solid in 85% yield, mp 154–157 8C, MS m/z: 207
(MC, 100%), 206 (72%), 178 (23%), 151 (57%), IR (cmK1):
3005, 1739, 1695, 1515, 1373, 1289, 1223, 1207, 1193, 844,
4.2.9. 3-Phenanthrylmethyl-triphenyl-phosphonium-
bromide (8). The compound was prepared from (7)
(1.35 g, 5.0 mmol) and triphenylphosphine (1.31 g,
5.0 mmol) in boiling toluene (35 mL). The phosphonium
salt precipitated and was filtered off at the end of the
reaction. Compound (8) was obtained as a white solid in
78% yield, mp 270–272 8C dec, and was used directly
without further characterisation.
4.2.10. 3-(2-Phenanthren-3-yl-vinyl)-pyridine (9). For the
preparation see the general procedure. Compound (9) was
obtained as orange solid in 60% yield, mp 110–112, MS m/z
1
281 (MC, 71%), 280 (100%), H NMR 7.15 (d, 2H, JZ
8.8 Hz, 2CH), 7.22 (d, 2H, JZ8.6 Hz, 2CH), 7.40 (m, 4H,
4CH), 7.45 (m, 2H, 2CH), 7.65 (d, 1H, JZ8.8 Hz, 1CH),
7.71 (d, 1H, JZ8.8 Hz, 1CH), 8.42 (dd, 1H, JZ7.8, 1.6 Hz,
1CH), 8.44 (s, 1H, 1CH), 8.48 (s, 1H, 1CH), elemental
analysis calcd(%) for C21H15N (281.4): C 89.65, H 5.37, N
4.98, found C 89.76, H 5.37, N 4.99.
4.2.11. 1-Aza[5]helicene (10) and 3-aza[5]helicene (11).
For the preparation see the general procedure. Compound
(10) (hexane/ethyl acetate 5:1) was obtained as a yellow
solid in 87% yield, mp 164–165 8C, MS m/z: 279 (MC,
30%), 278 (100%), IR (cmK1): 2900, 2839, 1619, 1563,
1256, 842, 723, 686, 643, 615, elemental analysis calcd(%)
for C21H13N (279.3): C 90.30, H 4.69, N 5.01, found C
90.47, H 4.68, N 5.02 (11) (hexane/ethyl acetate 1:2) was
obtained as yellow solid in 11% yield, mp 178–179 8C, MS
m/z 279 (MC, 52%), 278 (100%), IR (cmK1): 3069, 2970,
2931, 2861, 1730, 1632, 1592, 1261, 1284, 846, 746, 654,
615, elemental analysis calcd(%) for C21H13N (279.3): C
90.30, H 4.69, N 5.01, found C 89.97, H 4.69, N 5.00. NMR
are reported in Table 3.
1
775, 745, 707, 615, 601, H NMR 7.92 (d, 1H, JZ8.9 Hz,
1CH), 7.99 (d, 1H, JZ8.9 Hz, 1CH), 8.08 (d, 1H, JZ
8.3 Hz, 1CH), 8.21 (d, 1H, JZ8.3 Hz, 1CH), 8.52 (d, 1H,
JZ5.8 Hz, 1CH), 8.86 (d, 1H, JZ5.8 Hz, 1CH), 9.18 (s, 1H,
1CH), 9.32 (s, 1H, 1CH), 10.31 (s, 1H, CHO), elemental
analysis calcd(%) for C14H9NO (207.2) C 81.14, H 4.38, N
6.76, found C 81.43, H 4.38, N 6.70.
4.2.15. 9-Styryl-benzo[h]quinoline (16) and 9-styryl-
benzo[f]isoquinoline (17). For the preparation see the
general procedure. Compound (16) (hexane/ethyl acetate
2:3) was obtained as yellow solid in 69% yield, mp 92–
95 8C, MS m/z 281 (MC, 80%), 280 (100%), IR (cmK1):
2992, 2900, 2725, 1485, 1427, 1377, 980, 962, 831, 761,
693, 615, 1H NMR 7.29 (m, 1H, 1CH), 7.40 (m, 4H, 4CH),
7.53 (dd, 2H, JZ8.0, 4.4 Hz, 2CH), 7.59 (dd, 2H, JZ8.0,
1.8 Hz, 2CH), 7.66 (dd, 1H, JZ8.8, 6.2 Hz, 1CH), 7.79 (d,
1H, JZ8.8 Hz, 1CH), 7.90 (m, 2H, 2CH), 8.18 (dd, 1CH,
JZ8.0, 1.8 Hz, 1CH), 9.02 (dd, 1H, JZ4.4, 1.8 Hz, 1CH),
9.38 (s, 1H, 1CH), elemental analysis calcd(%) for C21H15N
(281.4): C 89.65, H 5.37, N 4.98, found C 89.64, H 5.38,
N 5.00. For the preparation see the general procedure.
Compound (17) (hexane/ethyl acetate 1:3) was obtained as
yellow solid in 92% yield, mp 180–182 8C, MS m/z 281
(MC, 100%), 280 (64%), IR (cmK1): 3077, 3054, 2954,
1562, 1430, 969, 835, 737, 696, 629, 1H NMR 7.36 (d, 1H,
JZ7.3 Hz, 1CH), 7.42 (m, 2H, 2CH), 7.44 (d, 2H, JZ
7.3 Hz, 2CH), 7.61 (d, 2H, JZ7.3 Hz, 2CH), 7.95 (d, 1H,
JZ8.8 Hz, 1CH), 8.06 (d, 1H, JZ8.2 Hz, 1CH), 8.11 (d,
1H, JZ8.8 Hz, 1CH), 8.15 (d, 1H, JZ8.2 Hz, 1CH), 8.78 (s
and d, JZ6.4 Hz, 2H, 2CH), 8.94 (d, 1H, JZ6.4 Hz, 1CH),
9.41 (s, 1H, CH), elemental analysis calcd(%) for C21H15N
4.2.12. 4-(2-Pyridin-3-yl-vinyl)-benzaldehyde (12). For
the preparation see the general procedure, the only
difference was that the molar ratio terephthaldehyde/
3-pyridinylphosphonium bromide was 5:1.38,39 (12)
(hexane/ethyl acetate 1:2) was obtained as orange oil in
70% yield, MS m/z 209 (MC, 100%), 208 (51%), 180
(92%), 152 (43%), IR (cmK1): 1759, 1577, 1398, 1238,
1
1200, 1064, 977, 829, H NMR 6.69 (d, 1H, JZ12.0 Hz,
CH), 6.79 (d, 1H, JZ12.0 Hz, CH), 7.16 (dd, 1H, JZ7.8,
5.1 Hz, 1CH), 7.35 (d, 2H, JZ8.2 Hz, 2CH), 7.49 (d, 1H,
JZ7.8 Hz, 1CH), 7.75 (d, 2H, JZ8.2 Hz, 2CH), 8.43 (s and
d, 2H, JZ5.1 Hz, 2CH), 9.95 (s, 1H, 1CHO), elemental
analysis calcd(%) for C14H11NO (209.2): C 80.36, H 5.30, N
6.69, found C 80.64, H 5.31, N 6.72.
4.2.13. 4-(2-Pyridin-3-yl-vinyl)-benzaldehyde dimethoxy-
acetal (13). Compound (12) (1.0 g, 4.8 mmol) and 2,2-
dimethoxyacetone (10 mL, 80 mmol) were dissolved in

S. Abbate et al. / Tetrahedron 62 (2006) 139–148
147
(281.4): C 89.65, H 5.37, N 4.98, found C 89.45, H 5.36, N
4.96.
additional 8 h. The organic phase was separated, dried and
evaporated. Compound (19) (hexane/ethyl acetate 2:3) was
obtained as yellow solid in 5% yield, mp 152–154 8C, MS
m/z 279 (MC, 35%), 278 (100%), IR (cmK1): 3197, 1633,
1600, 1454, 1085, 1039, 880, 802, 745, 639, elemental
analysis calcd(%) for C21H13N (279.3): C 90.30, H 4.69, N
5.01, found C 90.11, H 4.70, N 5.01. NMR is reported in
Table 3.
4.2.16. 1-Aza[5]helicene (10) and 3-aza[5]helicene (11).
For the preparation see the general procedure. Compound
(10) yield 80%, (11) yield 95%.
4.2.17. 1-(2-Pyridin-4-yl-vinyl)benzaldehyde (18). This
compound may be synthesised in two equivalent ways: the
first started from the phosphonium salt of 4-bromomethyl-
pyridine with terephthalaldehyde under the same experi-
mental conditions as (12) yield 90%, or by direct
condensation of 4-methylpyridine (1.9 mL, 20 mmol) with
terephthalaldeyde (5.4 g, 40 mmol) in acetic anhydride
(20 mL) and boiling for 5 h (Yield 85%).41 (18)(CH2Cl2/
ethyl acetate 4:1) was obtained as yellow solid, mp 110–
112 8C (lit. 113.5–115 8C), MS m/z 209 (MC, 80%), 180
(100%), 152 (61%), IR (cmK1): 1749, 1694, 1497, 1232,
Acknowledgements
The authors kindly acknowledge MIUR for financial
support.
1
References and notes
1200, 965, 824, H NMR 7.04 (d, 1H, JZ16.5 Hz, 1CH),
7.29 (d, 1H, JZ16, 5 Hz, 1CH), 7.37 (dd, 2H, JZ4.4,
1.5 Hz, 2CH), 7.55 (m, 4H, 4CH), 8.58 (dd, 2H, JZ4.4,
1.5 Hz, 2CH), 10.10 (s, 1H, CHO), elemental analysis
calcd(%) for C14H11NO (209.2): C 80.36, H 5.30, N 6.69,
found C 80.17, H 5.31, N 6.72.
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