A novel route to 1-substituted 3-(dialkylamino)-9-oxo-9H-indeno[2,1-c]- pyridine-4-carbonitriles

Article abstract of DOI:10.1002/hlca.200890033

Heptalenecarbaldehydes 1/1′ as well as aromatic aldehydes react with 3-(dicyanomethylidene)-indan-1-one in boiling EtOH and in the presence of secondary amines to yield 3-(dialkylamino)-1,2-dihydro-9-oxo-9H-indeno[2,1-c] pyridine-4-carbonitriles (Schemes 2 and 4, and Fig. 1). The 1,2-dihydro forms can be dehydrogenated easily with KMnO₄ in acetone at 0° (Scheme 3) or chloranil (=2,3,5,6-tetrachlorocyclohexa-2,5-diene-1,4-dione) in a 'one-pot' reaction in dioxane at ambient temperature (Table 1). The structures of the indeno[2,1-c]pyridine-4-carbonitriles 5′ and 6a have been verified by X-ray crystal-structure analyses (Fig. 2 and 4). The inherent merocyanine system of the dihydro forms results in a broad absorption band in the range of 515-530 nm in their UV/VIS spectra (Table 2 and Fig. 3). The dehydrogenated compounds 5, 5′, and 7a-7f exhibit their longest-wavelength absorption maximum at ca. 380 nm (Table 2). In contrast to 5 and 5′, 7a-7f in solution exhibit a blue-green fluorescence with emission bands at around 460 and 480 nm (Table 4 and Fig. 5).

Full text of DOI:10.1002/hlca.200890033

Helvetica Chimica Acta – Vol. 91 (2008)
265
A Novel Route to 1-Substituted 3-(Dialkylamino)-9-oxo-9H-indeno[2,1-c]-
pyridine-4-carbonitriles
by Thomas Landmesser1), Anthony Linden, and Hans-Jürgen Hansen*
Organisch-chemisches Institut der Universität, Winterthurerstrasse 190, CH-8057Zürich
Heptalenecarbaldehydes 1/1’ as well as aromatic aldehydes react with 3-(dicyanomethylidene)-
indan-1-one in boiling EtOH and in the presence of secondary amines to yield 3-(dialkylamino)-1,2-
dihydro-9-oxo-9H-indeno[2,1-c]pyridine-4-carbonitriles (Schemes 2 and 4, and Fig. 1). The 1,2-dihydro
forms can be dehydrogenated easily with KMnO4 in acetone at 08 (Scheme 3) or chloranil (¼2,3,5,6-
tetrachlorocyclohexa-2,5-diene-1,4-dione) in a ꢀone-potꢁ reaction in dioxane at ambient temperature
(Table 1). The structures of the indeno[2,1-c]pyridine-4-carbonitriles 5’ and 6a have been verified by X-
ray crystal-structure analyses (Fig. 2 and 4). The inherent merocyanine system of the dihydro forms
results in a broad absorption band in the range of 515 – 530 nm in their UV/VIS spectra (Table 2 and
Fig. 3). The dehydrogenated compounds 5, 5’, and 7a – 7f exhibit their longest-wavelength absorption
maximum at ca. 380 nm (Table 2). In contrast to 5 and 5’, 7a – 7f in solution exhibit a blue-green
fluorescence with emission bands at around 460 and 480 nm (Table 4 and Fig. 5).
1. Introduction. – In the course of our investigations of thermally and photochemi-
cally switchable p-donor,p-acceptor-substituted heptalenes [1 – 3], we became inter-
ested in Knoevenagel-type condensation reactions of heptalene-carbaldehydes with p-
acceptor-carrying methylidene compounds such as malononitrile or 3-(dicyanomethyl-
idene)indan-1-one, a method to prepare the corresponding ethenylheptalenes. Where-
as we encountered no problems to synthesize b,b-dicyanoethenyl-substituted hepta-
lenes (Scheme 1) [4] by this route, the reaction with the indan-1-one did not work very
well during our first attempts. We isolated in this case, in low yield, violet crystals of a
compound, the spectra of which were not at all in accordance with the expected product
3 or its double-bond-shifted (DBS) isomer 3’ (Scheme 2). Moreover, the spectra
indicated that the Knoevenagel catalyst, piperidine, had become an integral part of the
unknown structure. A crystallographic analysis of the violet crystals revealed finally the
structure of an 1-heptalenyl-substituted 1,2-dihydro-9-oxo-3-(piperidin-1-yl)-9H-in-
deno[2,1-c]pyridine-4-carbonitrile 4’ (Fig. 1). On standing in solution, 4’ slowly
underwent dehydrogenation, a process, which could be performed cleanly with KMnO4
in acetone at 08 (Scheme 3). The two yellow-to-orange-colored DBS isomers 5 and 5’
were obtained as a 1:3 mixture, which we could not separate chromatographically.
However, both compounds crystallized in morphologically different forms, so that the
conglomerate of crystals could be separated manually. The structure of 5’ was again
secured by an X-ray crystal-diffraction analysis (Fig. 2).
1
)
Part of the Ph.D. thesis of T. L., University of Zurich, 2001; current address: Siegfried AG, Untere
Brühlstrasse 4, CH-4800 Zofingen.
ꢂ 2008 Verlag Helvetica Chimica Acta AG, Zürich

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Helvetica Chimica Acta – Vol. 91 (2008)
Scheme 1
a) CH2(CN)2, cat. Piperidine, EtOH, reflux; 31% [4]b).
a) A mixture of 57% of 1 and 43% of 1’ was used. b) Yields up to 86% of a 1:3 mixture of 2/2’ are
obtained with TiCl4/pyridine at 08 to r.t.
Scheme 2
c
a) See Footnote a of Scheme 1. b) Neither 3’ nor its DBS isomer 3 were found. ) The crystallized form
represented pure 4’.
Since the formation of 4’, followed by dehydrogenation to 5/5’ seemed to represent
a new path for the synthesis of 1-substituted 3-(dialkylamino)-9-oxo-9H-indeno[2,1-
c]pyridine-4-carbonitriles, we reacted 3-(dicyanomethylidene)indan-1-one, which is
easily available from indane-1,3-dione and malononitrile [5], with other aldehydes and
secondary amines, and here we report on these investigations.

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267
Fig. 1. Stereoscopic view of the X-ray crystal structure of 4’. The (P,1S)-configuration is shown (atoms
with 50% probability ellipsoids).
Scheme 3
2. Results. – 2.1. Product Formation. The formation of 4’ from heptalene-
carbaldehydes 1/1’, 3-(dicyanomethylidene)indan-1-one, and piperidine in boiling
EtOH is indeed a general reaction of the indanone, aromatic aldehydes, and secondary
amines. In these cases, however, the primary compounds 6 were accompanied by their
dehydrogenated forms 7, or the latter represented the solely found form (Scheme 4).
Attempts to realize the formation of 6 or just 7 with other aldehydes such as methanal,
propanal, 2,2-dimethylpropanal (pivalaldehyde), and 3,3-dimethylpropenal (sene-
cioaldehyde) were less successful, since complex inseparable mixtures, which may have
contained small amounts of compounds of type 6 and 7, were formed in low yields.
In further experiments, we tried to develop a more convenient one-pot procedure
for the formation of the stable aromatized forms 7. Benzoquinones such as 2,3-dichloro-
5,6-dicyano-1,4-benzoquinone (DDQ) or o- and p-chloranil are generally excellent
dehydrogenating reagents for 1,2- or 1,4-dihydroaromatic compounds [6], which can be
applied in solvents such as 1,4-dioxane, wherein the [5 þ 1] cyclocondensation reaction

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Helvetica Chimica Acta – Vol. 91 (2008)
Fig. 2. Stereoscopic view of the X-ray crystal structure of 5’. The (P)-configuration is shown (atoms with
50% probability ellipsoids).
Scheme 4
to 6 also took place. We found that the indeno[2,1-c]pyridine-4-carbonitriles 7 were
indeed the sole products, when the reaction of the indanone, aldehyde, and secondary
amine was performed in 1,4-dioxane at room temperature, followed by the addition of
chloranil (¼2,3,5,6-tetrachlorocyclohexa-2,5-diene-1,4-dione; Table 1). The yields of 7
were grosso modo the same as the total yields of 6 and 7 in EtOH. The yield of the DBS
isomers 5 and 5’ was distinctly higher than in EtOH, but still lower than for the aromatic
aldehydes with the exception of pyridine-4-carbaldehyde and cinnamaldehyde. The
slightly different basicity of the tested secondary amines, Et2NH (pKa 10.5), piperidine

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269
Table 1. One-Pot Formation of 1-Substituted 3-(Dialkylamino)-9-oxo-9H-indeno[1,2-c]pyridine-4-car-
bonitriles with Chloranil as Dehydrogenating Reagenta)
R
R’
Product
Yield [%]b)
1,5,6,8,10-Pentamethylheptalen-2- and -4-yl
Ph
Ph
Ph
Thien-2-yl
Pyridin-4-yl
(E)-Styryl
À(CH2)5À
À(CH2)5À
Et
À(CH2)4À
À(CH2)5À
À(CH2)5À
À(CH2)5À
5, 5’
7a
7b
7e
7c
7d
7f
44c)
66
63
68
60
26
12d)
a) 1 mol-equiv. of the indanone was reacted with 1.2 mol-equiv. of aldehyde and sec-amine; after 14 h,
1.1 mol-equiv. of chloranil were added. b) Yield of chromatographically purified material. c) 1 : 1 Mixture
of the two DBS isomers 5 and 5’. d) Reaction time 18 h without subsequent addition of chloranil.
(pKa 11.1), and pyrrolidine (pKa 11.3), does not play an important role, since all three
amines gave with benzaldehyde and the indanone similar yields of 7b, 7a, and 7e,
respectively, with a weak trend following the increasing basicity of the amines.
The formation of 7f represented a special case, since 7f, on heating in solution, was
easily transformed into the 1-phenyl-substituted indeno[2,1-c]pyridine-4-carbonitrile
7a under formal loss of acetylene. The temperature had, therefore, to be the room
temperature, also during the procedure of workup and isolation of 7f. The yield did not
exceed 12%, and the addition of chloranil was not necessary. Obviously, the primary
product 6f was already dehydrogenated under the reaction conditions in 1,4-dioxane2).
2.2. Spectroscopic and Structural Characteristics of the New Indeno[2,1-c]pyridine-
4-carbonitriles and Their 1,2-Dihydro Forms. Most noticeable is the change of color
from red to yellow in going from the 1,2-dihydro-9H-indeno[2,1-c]pyridine-4-carbo-
nitriles to their dehydrogenated forms, which indicates a fundamental difference of the
two chromophoric systems. Indeed, whereas the 9H-indeno[2,1-c]pyridines exhibit
absorption bands grosso modo comparable with those of fluorenones (cf., e.g., [7 ]),
however, with larger molar extinction coefficients due to the presence of auxochromic
2
)
We undertook no further experiments to uncover the reason for the ease of dehydrogenation in this
case. Air was not excluded in the experiments. Therefore, O2 could be responsible for the
dehydrogenation. But this would not explain the low yield of 7f. Another hydrogen acceptor could
be the reactant 3-(dicyanomethylidene)indan-1-one, an assumption in agreement with the low yield
of 7f. A further driving force for the ready dehydrogenation of 6f may be found in the perfect planar
s-cis-conformation of the ethenyl group of the (E)-configured styryl (¼2-phenylethenyl) moiety
with respect to the C(1)¼N(2) bond of 7f according to AM1 calculations, which guarantees an
optimal p-stabilization (see also Sect. 2.2).

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groups, their 1,2-dihydro forms show a broad symmetric absorption band at 516 –
531 nm (see Fig. 3 and Table 2), which is best explained as charge-transfer (CT)
transition of the inherent merocyanine-type partial structure, composed of the two
amino N-atoms on one end and the C¼O group on the other.
Fig. 3. UV/VIS Spectrum (MeCN) of 6a
Table 2. Characteristic UV/VIS and IR Data of the New 1,2-Dihydro-indeno[2,1-c]pyridine-4-carbo-
nitriles and Indeno[2,1-c]pyridine-4-carbonitriles
Fluorenone UV/VISa)
IRb) [cmÀ1
]
Fluorenone UV/VISc)
IRb) [cmÀ1
]
[nm (log e)]
[nm (log e)]
n˜(C¼O) n˜(CꢀN)
n˜(C¼O) n˜(CꢀN)
4’
531 (3.80)
1673s
2184s
5’
5
367(4.11)
371 (4.13)
375 (4.11)
373 (4.10)
390 (4.22)
380 (4.10)
373 (4.13)
392 (4.27)
1707 s
1706s
1705s
1700s
1691s
1706s
1701s
1691s
2213m
2209m
2207m
2210m
2208m
2208w
2215m
2217m
4d)
6a
516 (3.85)
516 (3.86)
510 (3.87)
1667s
1665s
1668s
2184s
2171s
2185s
7a
7b
7c
7d
7e
7f
6b
6c
6dd)
6ee)
6fd)
a) Longest-wavelength CT band in MeCN. b) IR Spectra in KBr. c) Longest-wavelength band in
cyclohexane. d) Not found; see text. e) Not prepared.
Further structural factors that contribute to the long-wavelength absorption of the
1,2-dihydro structures are the cross-conjugated benzo ring and the CN group at C(4).

Helvetica Chimica Acta – Vol. 91 (2008)
271
Additional spectroscopic information on the strong conjugative interaction of the
merocyanine system of the 1,2-dihydro forms is derived from a comparison of the bond
stretching frequencies of the C¼O and the CꢀN group with those of the corresponding
dehydrogenated forms (Table 2). Whereas n˜ (C¼O) of the latter lies ca. 20 cmÀ1 below
that of indeno[2,1-c]pyridine itself (1720 – 1725 cmÀ1 (CHCl3) [8][9]), mainly due to
the dialkylamino group at C(3), one finds, for the 1,2-dihydro forms, wavenumbers of
1665 – 1673 cmÀ1, which indicate a strong conjugative interaction within the merocya-
nine partial structure in the ground state. That the CN group at C(4) participates in the
merocyanine system can again be seen by a comparison of its wavenumbers, which
change from ca. 2180 to 2210 cmÀ1 on dehydrogenation, again in good agreement with
˜n(CꢀN) of 2226 cmÀ1 of benzonitrile (film [10]), taking into account the ortho-
neighborhood of the dialkylamino substituent. The strong conjugation within the
merocyanine part of the 1,2-dihydro forms can also be recognized by comparison of the
chemical shift of HÀC(5) and HÀC(8), which lie in both structures fully within the
deshielding area of the CꢀN and the C¼O group, respectively, thus exposed to a
downshift of ca. 0.5 ppm on dehydrogenation of the 1,2-dihydro forms (Table 3).
Table 3. Chemical Shifts d [ppm] of HÀC(5) and HÀC(8) of the 1,2-Dihydroindeno-pyridines and
Indeno-pyridinesa)
1,2-Dihydro-indeno-pyridines
HÀC(5)
HÀC(8)b)
Indeno-pyridines
HÀC(5)
HÀC(8)
4’
7.85
7.83
7.93
7.85
ca. 7.3
ca. 7.3
ca. 7.3
ca. 7.3
5’
8.39
8.42
8.49
8.39
7.71
7.71
7.71
7.74
6a
6b
6c
7a
7b
7c
a) In CDCl3. b) The signals of HÀC(6,7,8) are superimposed in the narrow range of 7.4 – 7.2 ppm.
A closer inspection of the X-ray crystal structure of 4’ (Fig. 1) provides a deeper
insight into the structural characteristics of the 1-substituted 3-(dialkylamino)-1,2-
dihydroindeno[2,1-c]pyridine-4-carbonitriles. The crystal structure of 4’ shows a single
diastereoisomer with a relative (P)-configuration of the heptalene part and (1S)-
configuration at the dihydro-indeno-pyridine part. The benzene ring is planar as
expected. The connected 1,2-dihydropyridine ring, however, forms a shallow boat
conformation with the heptalenyl substituent at C(1) in flagpole position. The bottom
plane contains the atoms N(2), C(3), C(4a), and C(8a), with C(1) and C(4) as bow and
stern atoms. The dihedral angles between the bottom plane and those of the planes
formed by C(9a), C(1), and N(2), and C(3), C(4), and C(4a) amount to 15.8(2)8 and
6.7(2)8, respectively. Moreover, N(2) shows almost no pyramidalization, since its
deviation from the plane of C(1), HÀN(2), and C(3) is 0.023(2) Š. In other words, it is
sp2-hybridized and thus fully integrated in the conjugation of the merocyanine system.
The situation of the N-atom of the piperidine ring linked to C(3) is somewhat different.
It deviates by 0.178(2) Š from the plane formed by C(3) and the two adjacent C-atoms
of the piperidine ring, and, in addition, the interplane angle with N(2), C(3), and C(4)
amounts to 37.7(3)8, i.e., the N-atom of the piperidine ring is almost sp3-hybridized, and
its conjugative contribution to the merocyanine system must therefore be distinctly
smaller than that of the other endocyclic N-atom. The distance between the closest H-

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atom in the equatorial position of the piperidine chair conformation and the C-atom of
the CN group is 2.36 Š. Therefore, it is this steric interaction that hinders the coplanar
arrangement of the N-atom of the piperidine ring with C(3)¼C(4) of the dihydropyr-
idine moiety.
The latter situation is not very much changed by dehydrogenation (cf. Fig. 2). The
pyridine ring of 5’ is almost planar, however, slightly tilted against the benzene ring (V
(C(4)ÀC(4a)ÀC(4b)ÀC(5)) amounts to 7.2(3)8). The N-atom of the CN group is
0.475(2) Š out of the pyridine plane, since HÀC(5) is pointing toward the C-atom of
the CN group (d ¼ 2.64 Š), and the distance to the closest equatorial H-atom of the
piperidine chair is 2.36 Š. The N-atom of the piperidine ring is 0.197(2) Š out of the
plane of its three surrounding atoms, and the pyridine plane and the plane of the
piperidine N-atom with its two adjacent C-atoms form a tilt angle of 38.1(2)8.
Since all new 3-(dialkylamino)indeno[2,1-c]pyridine-4-carbonitriles, except for 5
and 5’ with the heptalenyl substituent at C(1), showed a distinct blue-green
fluorescence under normal light, which was most intense for 7f with the (E)-styryl
substituent at C(1) (see below), we performed a further X-ray crystal-structure analysis
of 7a (Fig. 4). The structural characteristics of 7a are similar to those of 5’ with the
exception that, for 7a, the piperidine N-atom is 0.068(2) Š out of the plane of its three
surrounding atoms, so it is close to being planar. In other words, its conjugative
interaction with the p-system of the 9-oxo-9H-indeno[2,1-c]pyridine-4-carbonitrile
backbone is much stronger as in the case of 5’. This structure also has an interplane
angle of 19.4(2)8 between the pyridine and the piperidine part, which is just half as
large as in the case of 5’. As a further result, the distance between the closest equatorial
H-atom of the piperidine chair and the C-atom of the CN group has shrunk to 2.24 Š
compared with the distance in 5’. The distance between HÀC(5) and the C-atom of the
CN group (d ¼ 2.59 Š) is within the estimated standard deviations the same as in 5’,
however, with the tendency of being a bit shorter. The same is true for the torsion angle
V (C(4)ÀC(4a)ÀC(4b)ÀC(5)), which amounts in this case to 4.8(3)8. Furthermore,
Fig. 4. Stereoscopic view of the X-ray crystal structure of 7a (atoms with 50% probability ellipsoids)

Helvetica Chimica Acta – Vol. 91 (2008)
273
the bond angles at C(3), C(4), and the amino-N atom are all distorted with the larger
angle always such that it appears the piperidine ring is trying to get away from the CN
group, the N-atom of which is as in 5’ 0.456(2) Š out of the plane of the pyridine ring. It
is also of interest to note that the interplane angle between the pyridine ring and its 1-
Ph substituent amounts to 37.6(2)8, which indicates a conjugation between both
aromatic systems.
Comparing the crystal structures of 5’ and 7a, it can be said that both structures
have to compensate for steric interactions between the piperidin-1-yl substituent at
C(3) and the CN group at C(4), the latter being under the influence of a certain
buttressing effect of HÀC(5). Therefore, C(4) slightly deviates from the plane of the
pyridine ring, which is documented by the size of deviation of V (C(4)ÀC(4a)ÀC(4b)À
C(5)) from 08 and more clearly seen by the deviation of the N-atom of the CN group
from the plane of the pyridine ring. On the other hand, the change of the electron-
donating heptalenyl substituent (12p-electron system) to the electron-accepting Ph
substituent as an aromatic 6p-electron system at C(1) leads to a more planar pyridine
ring and also to a more effective conjugative interaction of the N-atom of the piperidine
moiety with the indeno-pyridine part. This latter should also be effective in the case of
the other amino substituents at C(3), as well as of the other aromatic or hetero-
aromatic substituents at C(1).
The new indeno-pyridine-carbonitriles 7a – 7f show, as mentioned above, a blue-
green fluorescence. When we measured their emission spectra in cyclohexane, we were
amazed to find that all compounds exhibited two closely lying emission maxima of
almost equal intensity in the vicinity of 460 and 480 nm (Table 4). As an example, the
absorption and emission spectra of 7f are shown in Fig. 5. The energy gap of the two
emission bands amounts to 2 – 3 kcal molÀ1. Since we conducted no further experi-
ments, we can only speculate on the origin of the two bands. The two bands are mostly
superimposed with a tailing to longer wavelength. It seems that the two emission bands
belong to two S1 states of the 3-amino-indeno-pyridines, which are slightly different in
energy and which show an almost unresolved vibration fine structure. It can be assumed
that one of the states is a p,p* state with charge-transfer contribution of the amino
group (cf. the jump of acidity by DpKa ca. 6 of phenols and aromatic ammonium ions or
amines on excitation [11]). On the other hand, 2-aminopyridine is a stronger base than
pyridine itself (cf. pKa 6.82 and 5.25 (H2O) [12]), so that the second fluorescent state
could be an n,p* state.
2.3. Formation of Indeno[2,1-c]pyridine-4-carbonitriles. Well-established proce-
dures for the formation of indeno[2,1-c]pyridines are the ring closure of 4-aryl nicotinic
acid derivatives with polyphosphoric acid at 2008 and above (see [8][13][14] and earlier
literature cited there)3). 9-Oxo-9H-indeno[2,1-c]pyridine itself has been obtained inter
alia by dichromate oxidation of 9H-indeno[2,1-c]pyridine, which is formed in excellent
yield by flash vacuum pyrolysis at 5008 of (phenyl)(pyridin-4-yl)diazomethane by a
series of carbene – carbene rearrangements [8]. Close to our synthesis is the reaction of
3-(dicyanomethylidene)indan-1-one with diaryl formamidines in boiling CHCl3, which
leads in good yields via 8 and 9 to 3-(arylamino)-9-oxo-9H-indeno[2,1-c]pyridine-4-
carbonitriles 10 (Scheme 5) [17], whereby the step 9 ! 10 corresponds to a Dimroth
3
)
See also [15][16] for the synthesis of more complex indeno-pyridines.

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Helvetica Chimica Acta – Vol. 91 (2008)
Fig. 5. UV/VIS (—) and Fluorescence (----) spectra of 7f (cyclohexane)
Table 4. Fluorescence Data of the New 3-(Dialkylamino)indeno-pyridine-carbonitrilesa)
Fluorenone
lemiss [nm]
Dl [nm]
DE [kcal · molÀ1
]
6a
6b
6c
6d
6e
6f
476, 460
475, 454
487, 463
476, 459
475, 452
487, 462
16
21
24
17
23
25
2.1
2.8
3.0
2.2
3.1
3.2
a) In cyclohexane.
rearrangement. The global transformation can be described as a [4 þ 2] cycloconden-
sation reaction in contrast to our synthesis, which has to be regarded as a [5 þ 1]
cyclocondensation reaction, whereby the N-atom of the involved CN group becomes
the pyridine N-atom4).
In the present case, we assume that the product formation starts with a normal
Knoevenagel reaction between the indanone and the aldehyde, followed by a
nucleophilic attack of the secondary amine at the CN group in the inward position
4
)
Pyridine syntheses with cyano groups as the N-atom donor in the ring-forming process are
numerous (see [18 – 20] and earlier literature cited there).

Helvetica Chimica Acta – Vol. 91 (2008)
275
Scheme 5
with respect to the ensuing ring formation (Scheme 6). It is an open question whether
the thus generated zwitterionic imidide 12 is trapped in a concerted manner by the
present enone part to form the zwitterionic enolate 14, which then yields the 1,2-
dihydro-indeno-pyridines by intermolecular Hþ shift, or whether the imidide 12 has a
certain life-time, so that it can undergo intermolecular Hþ shift to the neutral 1-
azahexatriene intermediate 13, which then experiences an electrocyclic disrotatory ring
closure to the products. Boutome and Hartmann observed a comparable formation of a
complex pyridine compound by treatment of the 2-oxonaphtho[1,2-b]pyran-3-carbon-
itrile 15 with piperidine in boiling MeCN with concomitant autoxidation (Scheme 6)
[18].
3. Concluding Remarks. – We described a new reaction between 3-(dicyanome-
thylidene)indanone, and aldehydes without H-atoms at C(a) and secondary amines
that leads by a [5 þ 1] cyclocondensation to 1-substituted 3-(dialkylamino)-1,2-dihydro-
9-oxo-9H-indeno[2,1-c]pyridine-4-carbonitriles. Aldehydes with H-atoms at C(a) or
a,b-unsaturated aldehydes with H-atoms at C(g) do not undergo the [5 þ 1] cyclo-
condensation reaction. The primary 1,2-dihydro products can easily be dehydrogenated
to the pyridine forms, which show with aromatic or heteroaromatic substituents at C(1)
a blue-green fluorescence with two emission maxima of similar intensity around 460
and 480 nm.
We thank our NMR laboratory for specific and sometimes laborious NMR measurements, our MS
laboratory for mass spectra, and our laboratory for microanalysis. Financial support of this work by the
Swiss National Science Foundation is gratefully acknowledged.
Experimental Part
General. M.p.: Homemade apparatus with a heating table and microscope; uncorrected. TLC:
aluminum sheets coated with silica gel 60 F254 (Merck) or plastic sheets coated with alumina N/UV254
(POLYGRAMꢃ, Macherey-Nagel); spot visualization with UV light (254 or 366 nm) or with appropriate
spray reagents. Column chromatography (CC): silica gel C-560 (0.040 – 0.063 mm; Chemie Uetikon AG)
or on alumina, type 5016A, basic (0.05 – 0.15 mm; Fluka). UV/VIS Spectra: Lambda 19 UV/VIS/NIR
spectrophotometer (Perkin-Elmer); maxima and minima, lmax and lmin, in nm; molar extinction
coefficients e [1000 cm2 · molÀ1] in log e. Fluorescence spectra (FL): luminescence spectrometer LS 50 B
(Perkin-Elmer); maxima of emission, lem, in nm. IR Spectra: FT 1600 instrument or Spectrum One FT-IR
spectrophotometer (both Perkin-Elmer), in KBr pills (ca. 1 mg substrate/150 mg KBr); absorption bands
1
in cmÀ1; intensities as residual transmission. NMR Spectra: H-NMR on Bruker instruments (AC-300,
ARX-300, or AMX-600) in CDCl3 and TMS as internal standard; chemical shifts (d) in ppm, coupling
constants (J) in Hz; 13C-NMR on ARX-300 or AMX-600 instruments; as internal standard the

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corresponding solvent signal, i.e., CDCl3 (t, J(C,D) ¼ 31.5 Hz, d(C) ¼ 77.00 ppm), (D6)acetone (sept.,
J(C,D) ¼ 19.3 Hz, d(C) ¼ 29.73); DEPT spectra for the determination of the multiplicities of the 13C
fragments; Cq, quaternary C-atom. MS: MAT-95 instrument (Finnigan), EI at 70 eV, source temp. 2508,
CI with NH3, ions in m/z, in parentheses relative peak intensities in %. GC/MS on a GC-8000Top
apparatus (CE Instruments), coupled with a Voyager mass spectrometer (Finnigan) with combined CI/EI
source (70 eV); OV-5 capillary column (Restek; 15 m ꢁ 0.25 mm, 0.25 mm; 95% dimethyl- and 5%
diphenylpolysiloxane).
1. Formation of the 1,2-Dihydro-indeno-pyridine-carbonitriles. 1.1. 1,2-Dihydro-9-oxo-1-(1,5,6,8,10-
pentamethylheptalen-2-yl)-3-(piperidin-1-yl)-9H-indeno[2,1-c]pyridine-4-carbonitrile
(4’).
The
57:43 mixture of the heptalenecarbaldehydes 1 and 1’ (252.4 mg, 1.00 mmol) and 3-(dicyanomethylide-
ne)indan-1-one (194.2 mg 1.00 mmol) [6] were placed in dry EtOH (30 ml) in a 50 ml round-bottom
flask. Under stirring, piperidine (0.20 ml, 2.0 mmol) was added, whereby a red color appeared at once,
and the indanone dissolved slowly. The mixture was heated for 3 h at reflux, in which time the color
turned more and more to violet. EtOH and excess piperidine were distilled off in vacuo. The residue was
separated by CC (silica gel; toluene and successively increasing amounts of AcOEt (100 :1, 50 :1, 20 :1,
10 :1, 5 :1, 2 :1, 1:1, 1:2; each time 100 ml)). The first wine-red fraction gave after evaporation of the
solvent mixture a violet solid, which was crystallized from toluene at À 158 to yield pure 4’ (87.4 mg,
17%). A sample for analysis was dissolved in CH2Cl2 and precipitated by addition of pentane and then
dried in vacuo. M.p. 164 – 1668. Rf (AcOEt/MeOH 10 :1) 0.84. UV/VIS (MeCN): lmax 590 (sh, 3.50), 531
(3.80), 357(sh, 3.77), 341 (sh, 3.90), 317(sh, 4.24), 305 (4.29), 278 (4.40), 259 (4.45), 233 (4.56); lmin 413
(2.78), 295 (4.27), 276 (4.40), 248 (4.43), 213 (4.49). IR: 3424w (NÀH, free), 3287m (NÀH, ass.), 3065w,
3003w, 2938m, 2857m, 2184s (CꢀN), 1673s (C¼O), 1652 (sh), 1604s, 1578vs, 1552s, 1457s, 1445s, 1411vs,
1376s, 1364s, 1322w, 1310m, 1275m, 1252s, 1237(sh), 1186 s, 1162m, 1147m, 1118m, 1078m, 1043w, 1015m,
956w, 938w, 915w, 855m, 819w, 804w, 7 85w, 7 58m, 7 28w, 7 02w, 690w, 67 3w, 625w, 589w, 547w, 531w, 47 2w.
1H-NMR (300 MHz): 7.85 (dm, 3J(5,6) ¼ 7.0, HÀC(5)); 7.34 – 7.21 (m, 3 arom. H); 6.44 (d, 3J ¼ 11.9,
HÀC(3’)); 6.27( d, 3J ¼ 11.9, HÀC(4’)); 6.07( s, HÀC(9’)); 5.96 (s, HÀC(7’)); 5.66 (d, 3J(1,2) ¼ 3.5,
HÀC(1)); 5.40 (br. d, 3J(2,1) ¼ 3.5, HÀN(2)); 3.64 – 3.42 (m, 2 NCH2CH2); 2.16 (s, Me); 1.96 (d, 4J ¼ 1.2,
Me); 1.94 (d, 4J ¼ 1.0, Me); 1.71 (br. s, 2 NCH2CH2CH2, NCH2CH2CH2); 1.68 (s, 2 Me). EI-MS: 513 (32,
.
.
Mþ ), 511 (25, [M À H2]þ ), 496 (17), 290 (100, [M À hept]þ), 234 (25), 224 (23), 209 (18), 193 (16), 184
(50), 170 (20), 149 (13), 123 (14), 105 (15), 91 (48), 69 (30), 57 (31), 43 (31), 41 (36).
The structure of 4’ was finally established by an X-ray crystal-structure analysis (cf. Fig. 1 and
Table 5).
1.2. 1,2-Dihydro-9-oxo-1-phenyl-3-(piperidin-1-yl)-9H-indeno[2,1-c]pyridine-4-carbonitrile (6a). In
analogy to Sect. 1.1, the indanone (1.00 mmol), PhCHO (0.10 ml, 1.0 mmol), and piperidine (0.20 mmol)
were heated under reflux in EtOH during 2 h. The residue was separated by CC (silica gel; first hexane/
Et2O 1:1, then Et2O, and finally Et2O/MeOH 10 :1, then 1:1; each time 250 ml). This procedure resulted
in clean yellow and violet colored fractions, which gave dark red crystals of 6a (173.3 mg, 49%) and 7a as
a yellow solid (28.8 mg, 8%). A sample for analysis of 6a was dissolved in CH2Cl2 and precipitated by
addition of pentane and then dried in vacuo.
Data of 6a. M.p. 130 – 1338. Rf (AcOEt/MeOH 10 :1) 0.82. UV/VIS (MeCN): lmax 516 (3.85), 356
(3.79), 342 (3.81), 317 (sh, 4.03), 304 (4.11), 279 (4.30), 228 (4.49); lmin 398 (2.67), 351 (3.77), 333 (3.77),
296 (4.09), 252 (3.86), 213 (4.37). IR: 3401w (NÀH, free), 3278m (NÀH, ass.), 3062w, 3027w, 2940m,
2857m, 2184s (CꢀN), 1667s (C¼O), 1603vs, 1576vs, 1553 (sh), 1492m, 1459vs, 1443vs, 1415vs, 1367s,
1326m, 1273s, 1243s, 1189s, 1162s, 1148m, 1119s, 1078m, 1046w, 1015m, 961m, 939w, 914w, 856m, 820w,
1
796w, 7 7m1, 7 33s, 698m, 681m, 635w, 602w, 57 2w, 544m, 528w, 493w, 47 2w. H-NMR (300 MHz): 7.83
(dm, 3J(5,6) ¼ 7.0, HÀC(5)); 7.36 – 7.20 (m, 8 arom. H); 5.77 (br. d, 3J(2,1) ¼ 4.6, HÀN(2)); 5.64 (d,
3J(1,2) ¼ 4.6, HÀC(1)); 3.68 – 3.49 (m, 2 NCH2CH2); 1.73 (br. s, 2 NCH2CH2CH2, NCH2CH2CH2). EI-
.
.
MS: 367(54, Mþ ), 365 (56, [M À H2]þ ), 336 (55), 322 (24), 310 (22), 296 (14), 290 (100, [M À C6H5]þ),
282 (29), 253 (12), 234 (17), 227 (16), 161 (16), 103 (10), 91 (11), 84 (20, C5H10Nþ), 73 (15), 61 (10), 44
(20).
Data of 7a. See Sect. 2.2.
1.3. 3-(Diethylamino)-1,2-dihydro-9-oxo-1-phenyl-9H-indeno[2,1-c]pyridine-4-carbonitrile (6b). The
above described amounts of the indanone, PhCHO, and Et2NH (2.0 mmol) were heated in EtOH (25 ml)

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during 4 h under reflux. The obtained residue was separated on silica gel with 1. hexane/Et2O 1:1, 1:10;
2. Et2O; 3. Et2O/MeOH 10 :1, 5 :1, 2 :1, 1:1 (each time 200 ml). The first fraction delivered 7b (41.5 mg,
12%) as yellow solid. The following violet-colored fractions gave dark red needles of 6b (182.0 mg,
51%).
Data of 6b. M.p. 215 – 2178 (CH2Cl2). Rf (AcOEt/MeOH 10 :1) 0.78. UV/VIS (MeCN): lmax 516
(3.86), 355 (3.75), 341 (3.78), 316 (sh, 4.03), 303 (4.12), 278 (4.31), 230 (4.50); lmin 395 (2.63), 350 (3.73),
332 (3.73), 297 (4.11), 252 (3.89), 214 (4.37). IR: 3429 (sh, NÀH, free), 3341m (NÀH, ass.), 3082w,
3061w, 3030w, 2977m, 2934w, 2890 (sh), 2874w, 2171s (CꢀN), 1665vs (C¼O), 1604s, 1577vs, 1553s,
1503m, 1491m, 1457vs, 1407vs, 1380s, 1353s, 1343s, 1290m, 1264s, 1241s, 1202s, 1186m, 1170s, 1152m,
1112m, 1076m, 1047w, 1029w, 1011w, 1002w, 967m, 930w, 885w, 858w, 823w, 7 93w, 7 85w, 7 7m4, 7 59m,
1
738m, 7 11m, 696m, 684w, 647w, 631w, 587w, 57 1w, 546m, 534w, 486w, 47 8w. H-NMR (300 MHz): 7.93
(dm, 3J(5,6) ¼ 7.0, HÀC(5)); 7.38 – 7.20 (m, 8 arom. H); 5.65 – 5.62 (m, HÀC(1), HÀN(2)); 3.63 (q, 3J ¼
.
7.1, 2 NCH2Me); 1.32 (t, 3J ¼ 7.1, 2 NCH Me). EI-MS: 355 (51, Mþ ), 326 (19), 324 (27), 310 (9), 278 (100,
2
[M À C6H5]þ), 250 (14), 234 (8), 227(12), 222 (16), 86 (13), 84 (22), 77(8, C 6H5þ), 51 (15), 49 (35).
1.4. 1,2-Dihydro-9-oxo-3-(piperidino-1-yl)-1-(thien-2-yl)-9H-indeno[2,1-c]pyridine-4-carbonitrile
(6c). The same amounts as described before and thiophen-2-carbaldehyde (1.0 mmol) were heated in
EtOH (25 ml) during 4 h under reflux. The residue was separated by CC (silica gel; 1. hexane/Et2O 1:1,
1:10, 1:100; 2. Et2O; 3. Et2O/MeOH 100 :1, 10 :1, 5 :1; each time 200 ml) to yield a yellow and then a
violet-colored fraction. The oily residue of the latter was dissolved in toluene, and the soln. was cooled to
À 208 to give dark-red crystalline 6c (137.7 mg, 37%). A sample for analysis of6c was dissolved again in
CH2Cl2 and precipitated by addition of pentane. The yellow-colored fraction gave a brown-yellow solid
of 7c, which was recrystallized from cyclohexane (99.7mg, 27%).
Data of 6c. M.p. 132 – 1358. Rf (AcOEt/MeOH 10 :1) 0.78. UV/VIS (MeCN): lmax 510 (3.87), 355
(3.82), 342 (3.84), 316 (sh, 4.03), 304 (4.09), 278 (4.28), 231 (4.53); lmin 398 (2.74), 351 (3.81), 332 (3.79),
296 (4.07), 254 (3.91), 209 (4.30). IR: 3401 (sh, NÀH, free), 3276m (NÀH, ass.), 3107w, 3069w, 3014w,
2940m, 2857m, 2185s (CꢀN), 1668s (C¼O), 1603s, 1575vs, 1553 (sh), 1457vs, 1444s, 1416vs, 1369s, 1327w,
1296m, 1280m, 1246s, 1226m, 1187s, 1163m, 1145m, 1118s, 1079m, 1037w, 1014m, 954m, 938w, 854m, 834
(sh), 800w, 7 55m, 7 36m, 7 06m, 681w, 636w, 606w, 57 4w, 544w, 530 (sh), 472w. 1H-NMR (300 MHz): 7.85
(dm, 3J(5,6) ¼ 7.1, HÀC(5)); 7.41 – 7.24 (m, 3 arom. H); 7.19 (dd, 3J(5’,4’) ¼ 5.0, 4J(5’,3’) ¼ 1.2, HÀC(5’));
6.99 (dm, 3J(3’,4’) ¼ 3.6, HÀC(3’)); 6.93 (dd, 3J(4’,3’) ¼ 3.6, 3J(4’,5’) ¼ 5.0, HÀC(4’)); 5.92 (d, 3J(1,2) ¼ 4.6,
HÀC(1)); 5.72 (br. d, 3J(2,1) ¼ 4.6, HÀN(2)); 3.71 – 3.54 (m, 2 NCH2CH2); 1.76 (br. s, 2 NCH2CH2CH2,
.
.
NCH2CH2CH2). EI-MS: 373 (35, Mþ ), 371 (100, [M À H2]þ ), 342 (86), 328 (39), 316 (39), 303 (22), 288
(51), 261 (16), 245 (16), 233 (20), 215 (15), 188 (15), 97(14), 84 (75, C 5H10Nþ), 56 (19), 41 (44), 39 (20).
1.5. Attempted Formation of 1,2-Dihdro-9-oxo-3-(piperidin-1-yl)-1-(pyridin-4-yl)-9H-indeno[2,1-
c]pyridine-4-carbonitrile (6d). The reaction in EtOH was performed with freshly distilled pyridine-4-
carbaldehyde as described in 1.2 for 6a. The workup procedure yielded only 7d (45.6 mg, 25%). Yellow
solid.
Data of 7d. See Sect. 2.5.
2. Formation of the Indeno-pyridine-carbonitriles. 2.1. 9-Oxo-1-(1,5,6,8,10-pentamethylheptalen-4-yl)-
3-(piperidin-1-yl)-9H-indeno[2,1-c]pyridine-4-carbonitrile (5) and 9-Oxo-1-(1,5,6,8,10-pentamethylhep-
talen-2-yl)-3-(piperidin-1-yl)-9H-indeno[2,1-c]pyridine-4-carbonitrile (5’). Method A. Compound 4’
(25.7mg, 0.05 mmol) was dissolved in acetone (10 ml) in a 25-ml round-bottom flask. The soln. was
cooled to 08, and a 0.04m soln. of KMnO4 in acetone was added dropwise. The color of the mixture has
slowly changed to yellow-brown within 1 h stirring. MeOH (5 ml) was added, and stirring was continued
for a further h. The suspension formed was filtered through Celiteꢃ, and the filter cake was washed with
acetone. The residue of the yellow colored filtrate was purified by CC (silica gel; toluene/AcOEt 25 :1).
Evaporation of the yellow eluate gave a dark yellow oil, which crystallized on stirring with a glass rod and
a small amount of Et2O. The dried crystals (16.7mg, 65%) represented a 1:3 mixture of 5 and 5’
according to 1H-NMR analysis.
Method B. The indanone (97.1 mg, 0.50 mmol), the 57 :43 mixture 1/1’ (151.4 mg, 0.60 mmol),
piperidine (0.6 ml, 0.6 mmol), and, later, chloranil were reacted according to the analogous reaction with
PhCHO (see below, Sect. 2.2). The dark yellow oil, which was obtained after CC, was taken up in hexane/
Et2O and yielded on evaporation a conglomerate of crystals of 5 and 5’ (112.0 mg, 44%) in a ratio of 1:1

Helvetica Chimica Acta – Vol. 91 (2008)
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(1H-NMR). The conglomerate could be separated by manual selection of the differently crystallized and
colored DBS isomers 5 and 5’.
Data of 5. Yellow crystals. M.p. 206 – 2078 (hexane). Rf (toluene/AcOEt 5 :1) 0.83. UV/VIS
(cyclohexane): lmax 371 (4.13), 328 (4.30), 306 (4.32), 253 (4.58), 218 (4.59); lmin 347(4.08), 318 (4.26),
303 (4.32), 233 (4.45), 207(4.56). IR: 2936 s, 2915s, 2855m, 2209m (CꢀN), 1706vs (C¼O), 1594s, 1566vs,
1533vs, 1465s, 1444s, 1394m, 1368m, 1317w, 1289m, 1275w, 1253s, 1229m, 1208vs, 1173w, 1157m, 1144m,
1120m, 1087w, 1016m, 966w, 868m, 851m, 839m, 7 7 1m, 7 58m, 699w, 686w. 1H-NMR (300 MHz): 8.37( dm,
3
4
3J(5,6) ¼ 7.5, HÀC(5)); 7.71 (dm, 3J(8,7) ¼ 7.3, HÀC(8)); 7.58 (td, 3J(6,5) ꢂ J(6,7) ¼ 7.5, J(6,8) ¼ 1.0,
3
HÀC(6)); 7.50 (tm, 3J(7,6)ꢂ J(7,8)¼ 7.3, HÀC(7)); 6.72 (d, 3J(3’,2’) ¼ 5.9, HÀC(3’)); 6.23 (dm,
3J(2’,3’) ¼ 5.9, HÀC(2’)); 6.13 (s, HÀC(9’)); 5.97( s, HÀC(7’)); 3.85 (br. s, 2 NCH2CH2); 2.05 (s, Me); 2.02
(s, Me); 2.00 (s, Me); 1.7 5 (s, Me); 1.70 (br. s, 2 NCH2CH2CH2, NCH2CH2CH2); 1.56 (s, Me). EI-MS: 511
.
(41, Mþ ), 496 (25, [M À Me]þ), 351 (17), 322 (38), 296 (18), 198 (23), 184 (100), 169 (18), 91 (12), 84 (17,
C5H10Nþ). Anal. calc. for C35H33N3O (511.67): C 82.16, H 6.50, N 8.21; found: C 82.11, H 6.49, N 8.11.
Data of 5’. Orange prisms. M.p. 177 – 1808 (cyclohexane/toluene). Rf (toluene/AcOEt 5 :1) 0.83. UV/
VIS (cyclohexane): lmax 367(4.11), 352 (4.10), 327(4.34), 307(4.32), 257(4.62), 217(4.60);
lmin 359
(4.08), 343 (4.05), 319 (4.25), 304 (4.31), 233 (4.37), 205 (4.58). IR (KBr): 2999w, 2939m, 2855m, 2213m
(CꢀN), 1707vs (C¼O), 1597m, 1570vs, 1527vs, 1489s, 1465s, 1450s, 1368s, 1315w, 1288m, 1274w, 1250s,
1208s, 1170w, 1160m, 1147m, 1120m, 1086w, 1070w, 1022m, 988w, 97 2w, 955w, 941w, 887w, 87 0m, 848w,
822w, 7 99w, 7 82w, 7 61m, 7 46w, 7 24w, 698w, 688w. 1H-NMR (300 MHz): 8.39 (dm, 3J(5,6) ¼ 7.6, HÀC(5));
3
3
3
3
3
7.71 (dm, J(8,7) ¼ 6.9, HÀC(8)); 7.60 (tm, J(6,5) ꢂ J(6,7) ¼ 7.6, HÀC(6)); 7.51 (tm, J(7,6)ꢂ J(7,8)¼
7.4, HÀC(7)); 6.38 (d, 3J ¼ 11.7, HÀC(3’ oder 4’)); 6.30 (d, 3J ¼ 11.7, HÀC(4’ oder 3’)); 6.17( s,
HÀC(9’)); 6.03 (s, HÀC(7’)); 3.95 (br. s, 2 NCH2CH2); 2.12 (s, Me); 2.02 (s, Me); 1.86 (s, Me); 1.81 (s,
Me); 1.77 (br. s, 2 NCH2CH2CH2, NCH2CH2CH2); 1.56 (s, Me). CI-MS (NH3): 512 (100, [M þ H]þ). EI-
.
MS: 511 (12, Mþ ), 198 (18), 184 (100), 169 (19), 91 (13), 84 (32, C5H10Nþ), 69 (13). Anal. calc. for
C35H33N3O (511.67): C 82.16, H 6.50, N 8.21; found: C 81.90, H 6.62, N 8.10.
The structure of 5’ was finally established by an X-ray crystal-diffraction analysis (cf. Fig. 2 and
Table 5).
2.2. 9-Oxo-1-phenyl-3-(piperidin-1-yl)-9H-indeno[2,1-c]pyridine-4-carbonitrile (7a). 3-(Dicyanome-
thylidene)indan-1-one (97.1 mg, 0.50 mmol) was dissolved in 1,4-dioxane (25 ml) in a 50-ml round-
bottom flask. Freshly distilled PhCHO (0.06 ml, 0.60 mmol) and piperidine (0.06 ml, 0.60 mmol) were
added in quick succession. The color of the soln. turned to red upon addition of piperidine. The soln. was
stirred during 14 h at r.t. Then, chloranil (¼2,3,5,6-tetrachlorocyclohexa-2,5-diene-1,4-dione; 132.5 mg,
0.55 mmol) was added to the wine-red soln., which was stirred for another 0.5 h, whereby the color
changed to a turbid yellow-black. The soln. was poured on ice, stirred for 30 min, and then extracted
several times with toluene. The combined extracts were successively washed with 4% aq. NaOH, H2O,
and finally sat. NaCl soln. The dried (MgSO4) soln. was evaporated, and the brown residue was purified
by CC (silica gel; hexane/Et2O 10 :1). The obtained yellow colored fraction gave on evaporation 7a
(121.1 mg, 66%). Yellow prisms.
Data of 7a. M.p. 161 – 1638 (cyclohexane/toluene). Rf (toluene/AcOEt 5 :1) 0.78. UV/VIS (cyclo-
hexane)5): lmax 375 (4.11), 333 (4.19), 276 (4.50), 223 (4.41); lmin 347(3.95), 325 (4.11), 239 (4.14), 216
(4.36). FL (cyclohexane): lem 477. IR: 3055w, 3029w, 3014w, 2932m, 2852m, 2207m (CꢀN), 1705vs
(C¼O), 1596s, 1567vs, 1532vs, 1492s, 1467s, 1451s, 1402m, 1386m, 1362m, 1350m, 1294m, 1275m, 1254s,
1227m, 1208vs, 1172m, 1157m, 1146m, 1123m, 1022m, 1003m, 996m, 954w, 900w, 87 0m, 854w, 815w, 7 7 8w,
754s, 7 08m, 698m, 684w, 634w, 612w, 546w, 465w, 435w. 1H-NMR (300 MHz): 8.42 (dm, 3J(5,6) ¼ 7.6,
3
3
3
HÀC(5)); 7.93 – 7.90 (m, 2 arom. H); 7.71 (dm, J(8,7) ¼ 7.4, HÀC(8)); 7.61 (td, J(6,5) ꢂ J(6,7) ¼ 7.6,
4J(6,8) ¼ 1.4, HÀC(6)); 7.52 (td, 3J(7,6)ꢂ J(7,8)¼ 7.4,4J(7,5)¼ 0.9, HÀC(7 )); 7.51 – 7.43 (m, 3 arom. H);
3
3.99 (br. s, 2 NCH2CH2); 1.78 (br. s, 2 NCH2CH2CH2, NCH2CH2CH2). 13C-NMR (75 MHz, CDCl3):
187.78 (CO); 160.70 (Cq); 160.51 (Cq); 159.21 (Cq); 138.31 (Cq); 136.49 (Cq); 135.55 (Cq); 134.00 (CH);
132.15 (CH); 130.46 (CH); 129.89 (2 CH); 127.63 (2 CH); 123.71 (CH); 123.23 (CH); 117.23 (C); 115.48
q
5
)
For 7a and the other derivatives, a number of faintly visible sh, most of them interpretable as
vibration fine structure of the main absorption bands, are recognizable. They appear for 7a at 206
(4.46), 267(4.44), 292 (4.41), 304 (4.29), 319 (4.15), 362 (4.04), 392 (3.95), 406 (3.80), and 430 (3.45).

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(Cq, CN); 83.95 (Cq); 49.50 (2 NCH2CH2); 26.09 (2 CH2); 24.42 (CH2). CI-MS (NH3): 366 (100, [M þ
.
H]þ). EI-MS: 365 (100, Mþ ), 336 (77), 322 (37), 309 (33), 296 (34), 282 (36), 253 (13), 227 (14), 84
(20, C5H10Nþ), 56 (13). Anal. calc. for C24H19N3O (365.44): C 78.88, H 5.24, N 11.50; found: C 78.88, H
5.33, N 11.56.
The structure of 7a was further secured by an X-ray crystal-diffraction analysis (see Fig. 4 and
Table 5).
2.3. 3-(Diethylamino)-9-oxo-1-phenyl-9H-indeno[2,1-c]pyridine-4-carbonitrile (7b). The indanone
(0.5 mmol), PhCHO (0.6 mmol), and Et2NH (0.6 mmol) were reacted as described in 2.2. A red solid
precipitated in the course of the reaction, which later on dissolved again. The crude product was purified
by CC (silica gel; hexane/Et2O 10 :1) to give 7b. (111.3 mg, 63%). Yellow solid.
Data of 7b. M.p. 139 – 1408 (EtOH/H2O). Rf (toluene/AcOEt 5 :1) 0.74. UV/VIS (cyclohexane): lmax
373 (4.10), 332 (4.19), 275 (4.48), 223 (4.39); lmin 345 (3.92), 323 (4.10), 241 (4.13), 216 (4.34). FL
(cyclohexane): lem 475, 454. IR: 3062w, 2982m, 2935m, 2210m (CꢀN), 1700vs (C¼O), 1596m, 1564vs,
1531vs, 1492m, 1468s, 1454m, 1434m, 1404w, 1384w, 1373w, 1357s, 1310w, 1295m, 1254m, 1230s, 1197m,
1151m, 1120m, 1075m, 1036w, 1024w, 1010m, 924w, 866m, 812w, 7 80w, 7 49s, 7 08m, 697m, 686w, 67 4w,
1
3
635w, 515w, 468w, 446w. H-NMR (300 MHz): 8.49 (dm, J(5,6) ¼ 7.6, HÀC(5)); 7.93 – 7.89 (m, 2 arom.
H); 7.7 1 (dm, 3J(8,7) ¼ 7.3, HÀC(8)); 7.61 (td, 3J(6,5) ꢂ J(6,7) ¼ 7.6, 4J(6,8) ¼ 1.4, HÀC(6)); 7.52 (td,
3
3J(7,6)ꢂ J(7,8)¼ 7.3, 4J(7,5)¼ 0.9, HÀC(7 )); 7.51 – 7.43 (m, 3 arom. H); 3.91 (q, J ¼ 7.0, 2 NCH2Me);
3
3
1.41 (t, J ¼ 7.0, 2 NCH Me). 13C-NMR (75 MHz, CDCl3): 187.80 (C , CO); 160.67(C q); 159.37(C q);
3
2
q
158.39 (Cq); 138.41 (Cq); 136.64 (Cq); 135.64 (Cq); 133.90 (CH); 132.00 (CH); 130.35 (CH); 129.80 (2
CH); 127.59 (2 CH); 123.59 (CH); 123.37 (CH); 117.80 (C); 114.45 (Cq, CN); 81.81 (Cq); 45.08 (2
q
.
NCH2Me); 13.73 (2 Me). EI-MS: 353 (33, Mþ ), 324 (100, [M À Et]þ), 310 (29), 281 (7), 252 (7),
72 (8, C4H10Nþ). Anal. calc. for C23H19N3O (353.43): C 78.16, H 5.42, N 11.89; found: C 77.87, H 5.45,
N 11.74.
2.4. 9-Oxo-3-(piperidin-1-yl)-1-(thien-2-yl)-9H-indeno[2,1-c]pyridine-4-carbonitrile (7c). The pro-
cedure for the reaction with thiophen-2-carbaldehyde (0.6 mmol) was the same as described in 1.5 for
PhCHO. The usual purification by CC (silica gel; hexane/Et2O and then CH2Cl2) gave 7c (111.5 mg,
60%). Yellow solid.
Data of 7c. M.p. 218 – 2208 (cyclohexane). Rf (toluene/AcOEt 5 :1) 0.83. UV/VIS (cyclohexane):
lmax 390 (4.22), 336 (4.38), 308 (4.27), 283 (4.41), 212 (4.40); lmin 371 (4.18), 315 (4.20), 303 (4.26), 243
(4.01), 204 (4.36). FL (cyclohexane): lem 487, 463. IR: 3106w, 3082w, 3012w, 2988w, 2941m, 2932m, 2853m,
2208m (CꢀN), 1691s (C¼O), 1598s, 1572vs, 1524 (sh), 1516vs, 1492s, 1464s, 1449s, 1425s, 1395m, 1369m,
1341w, 1318w, 1286m, 1269m, 1258m, 1242m, 1208s, 1167m, 1161m, 1124s, 1086w, 1059m, 1024m, 957w,
868m, 860m, 854m, 839w, 809w, 7 63s, 7 22s, 684w, 618w, 546w, 47 6w. 1H-NMR (300 MHz): 9.08 (dd,
3J(3’,4’) ¼ 4.0, 4J(3’,5’) ¼ 1.1, HÀC(3’)); 8.39 (dm, 3J(5,6) ¼ 7.5, HÀC(5)); 7.74 (dm, 3J(8,7) ¼ 7.1,
3
4
HÀC(8)); 7.59 (td, 3J(6,5) ꢂ J(6,7) ¼ 7.5, J(6,8) ¼ 1.4, HÀC(6)); 7.55 – 7.50 (m, HÀC(7), HÀC(5’);
3
3
7.19 (dd, J(4’,3’) ¼ 4.0, J(4’,5’) ¼ 5.1, HÀC(4’)); 3.96 (br. s, 2 NCH2CH2); 1.78 (br. s, 2 NCH2CH2CH2,
NCH2CH2CH2). 13C-NMR (75 MHz, CDCl3): 187.91 (C , CO); 160.77 (Cq); 159.91 (Cq); 151.47(C q);
q
143.48 (Cq); 138.09 (Cq); 135.52 (Cq); 133.90 (CH); 133.07(CH); 132.11 (CH); 131.66 (CH); 128.67
(CH); 123.62 (CH); 123.21 (CH); 117.16 (C ); 113.60 (Cq, CN); 83.98 (Cq); 49.52 (2 NCH2CH2); 26.02 (2
q
.
CH2); 24.41 (CH2). EI-MS: 371 (100, Mþ ), 342 (73), 328 (43), 316 (32), 315 (32), 303 (26), 288 (44,
[M À C4H3S]þ), 260 (14), 233 (14), 188 (15), 175 (25), 133 (22), 131 (28), 101 (21), 89 (77), 87 (76), 84
(70, C5H10Nþ), 75 (22), 73 (21), 59 (22), 57 (23), 56 (25). Anal. calc. for C22H17N3OS (371.46): C 71.14, H
4.61, N 11.31, S 8.63; found: C 71.10, H 4.58, N 11.33, S 8.72.
2.5. 9-Oxo-3-(piperidin-1-yl)-1-(pyridin-4-yl)-9H-indeno[2,1-c]pyridine-4-carbonitrile (7d). 3-(Di-
cyanomethylidene)indan-1-one (97.1 mg, 0.5 mmol), freshly distilled pyridine-4-carbaldehyde (0.06 ml,
0.6 mmol), and piperidine (0.06 ml, 0.6 mmol) were reacted as described in 2.2. A red solid, which did not
dissolve again during the reaction and also not after the addition of chloranil, was precipitated. The
purification of the crude product by CC (SiO2; hexane/Et2O 10 :1), followed by recrystallization from
cyclohexane (and a small amount of toluene), gave pure 7d (47.5 mg, 26%). Yellow solid.
Data of 7d. M.p. 195 – 1978. Rf (toluene/AcOEt 5 :1) 0.18. UV/VIS (cyclohexane): lmax 380 (4.10),
336 (4.10), 308 (4.16), 267(4.45), 225 (4.43); lmin 349 (3.93), 318 (4.01), 305 (4.15), 235 (4.23), 212 (4.26).
FL (cyclohexane): lem 476, 459. IR: 3068w, 3033w, 3009w, 2940m, 2859w, 2208w (CꢀN), 1706s (C¼O),

Helvetica Chimica Acta – Vol. 91 (2008)
281
1596m, 1567vs, 1551s, 1529vs, 1506 (sh), 1488s, 1467s, 1453s, 1416m, 1366m, 1314w, 1293m, 1280w, 1256s,
1206s, 1165w, 1148w, 1123m, 1065w, 1028w, 1005m, 87 2m, 855w, 836w, 7 60s, 7 22w, 7 09w, 686w, 682w, 542w.
1H-NMR (300 MHz): 8.76 (dm, 3J ¼ 4.5, 2 arom. H); 8.43 (dm, 3J(5,6) ¼ 7.5, HÀC(5)); 7.78 (dm, 3J ¼ 4.5,
3
2 arom. H); 7.73 (dm, 3J(8,7) ¼ 7.3, HÀC(8)); 7.64 (td, 3J(6,5) ꢂ J(6,7) ¼ 7.5,4J(6,8) ¼ 1.4, HÀC(6)); 7.55
3
(td, 3J(7,6)ꢂ J(7,8)¼ 7.3, 4J(7,5)¼ 1.0, HÀC(7)); 4.00 (br. s, 2 NCH2CH2); 1.80 (br. s, 2 NCH2CH2CH2,
NCH2CH2CH2). 13C-NMR (75 MHz, CDCl3): 187.43 (C , CO); 160.57(2 C q); 156.42 (Cq); 149.52 (2
q
CH); 143.76 (Cq); 138.20 (Cq); 135.40 (Cq); 134.31 (CH); 132.48 (CH); 123.95 (CH); 123.69 (2 CH);
123.44 (CH); 116.82 (Cq); 115.60 (Cq, CN); 84.91 (Cq); 49.55 (2 NCH2CH2); 26.07(2 CH 2); 24.31 (CH2).
.
EI-MS: 366 (100, Mþ ), 337(81), 323 (44), 311 (30), 298 (21), 283 (46), 254 (20), 91 (51), 84 (5,7
C5H10Nþ), 75 (18), 56 (17). Anal. calc. for C23H18N4O (366.42): C 75.39, H 4.95, N 15.29; found: C 75.45,
H 4.97, N 15.17.
2.6. 9-Oxo-1-phenyl-3-(pyrrolidin-1-yl)-9H-indeno[2,1-c]pyridine-4-carbonitrile (7e). The proce-
dure as described in 2.2 was applied with pyrrolidine instead of piperidine to give 7e (120.8 mg, 68%).
Yellow solid.
Data of 7e. M.p. 201 – 2028 (cyclohexane/toluene). Rf (toluene/AcOEt 5 :1) 0.71. UV/VIS (cyclo-
hexane): lmax 373 (4.13), 332 (4.20), 275 (4.50), 223 (4.40); lmin 345 (3.93), 323 (4.10), 241 (4.15), 216
(4.34). FL (cyclohexane): lem 475, 452. IR: 3049w, 3000w, 2969m, 2870m, 2215m (CꢀN), 1701vs (C¼O),
1639w, 1594s, 1564vs, 1539vs, 1512vs, 1492vs, 1478s, 1457s, 1406m, 1346m, 1330s, 1316m, 1293m, 1281m,
1262s, 1240s, 1223s, 1200s, 1179m, 1149m, 1127m, 1088w, 1070w, 1044w, 1034w, 1022w, 1008m, 998w, 980w,
967w, 921w, 87 0m, 858m, 819w, 7 7 w9, 7 7 m1 , 7 54s, 7 11m, 697m, 689m, 67 5m, 539w. 1H-NMR (600 MHz):
3
3
8.39 (dm, J(5,6) ¼ 7.6, HÀC(5)); 7.93 – 7.90 (m, 2 arom. H); 7.69 (dm, J(8,7) ¼ 7.4, HÀC(8)); 7.57 (td,
3J(6,5) ꢂ J(6,7) ¼ 7.6, 4J(6,8) ¼ 1.3, HÀC(6)); 7.50 (td, 3J(7,6)ꢂ J(7,8)¼ 7.4, 4J(7,5)¼ 0.9, HÀC(7));
7.51 – 7.43 (m, 3 arom. H); 3.98 (br. s, 2 NCH2CH2); 2.02 (br. s, 2 NCH2CH2). 13C-NMR (75 MHz,
CDCl3): 187.64 (C , CO); 160.13 (Cq); 159.76 (Cq); 157.22 (C ); 138.21 (Cq); 136.63 (Cq); 135.69 (Cq);
3
3
q
q
133.84 (CH); 132.01 (CH); 130.37(CH); 129.90 (2 CH); 12.753 (2 CH); 123.54 (CH); 123.23 (CH);
117.89 (C ); 114.24 (Cq, CN); 82.25 (Cq); 49.80 (2 NCH2CH2); 25.32 (2 CH2). CI-MS (NH3): 352 (100,
q
.
[M þ H]þ). EI-MS: 351 (33, Mþ ), 322 (95), 296 (50), 154 (42), 128 (21), 84 (100), 70 (32, C4H8Nþ).
Anal. calc. for C23H17N3O (351.41): C 78.61, H 4.88, N 11.96; found: C 78.43, H 4.64, N 11.95.
2.7. 9-Oxo-1-[(E)-2-phenylethenyl]-3-(piperidin-1-yl)-9H-indeno[2,1-c]pyridine-4-carbonitrile (7f).
To a soln. of the indanone (194.2 mg, 1.00 mmol) in 1,4-dioxane (40 ml) were added successively freshly
distilled cinnamaldehyde (0.16 ml, 1.2 mmol) and piperidine (0.12 ml, 1.2 mmol), and the mixture was
stirred for 18 h at r.t. All volatile material was removed by evaporation in high vacuum without warming.
The brown residue was separated by CC (silica gel; hexane/AcOEt 25 :1, 10 :1, 5 :1, 2 :1). The fluorescing
yellow fractions were collected, and the solvents were removed in a rotatory evaporator at 308 in vacuo.
The residue was dissolved in a small amount of CH2Cl2, and crystallization was induced by slow addition
of cyclohexane and by evaporation to yield 7f (46.7mg, 12%). Yellow needles.
Data of 7f. M.p. 225 – 2278. Rf (toluene/AcOEt 5 :1) 0.79. UV/VIS (cyclohexane): lmax 392 (4.27),
351 (4.47), 339 (4.48), 307 (4.41), 295 (4.41), 286 (4.40), 225 (4.37); lmin 374 (4.24), 348 (4.46), 315 (4.31),
303 (4.39), 289 (4.40), 248 (4.17), 213 (4.29). FL (cyclohexane): lem 487, 462. IR: 3058w, 3024w, 2936m,
2850m, 2212m (CꢀN), 1691vs (C¼O), 1632s, 1593m, 1570vs, 1544vs, 1498s, 1466s, 1447s, 1407m, 1388m,
1366m, 1347w, 1322m, 1275s, 1260m, 1227m, 1214s, 1203s, 1175w, 1158w, 1132m, 1121s, 1087w, 1076w,
1028m, 1017m, 980m, 959w, 910w, 900m, 858m, 7 63s, 7 35w, 691s, 665w, 611w. 1H-NMR (300 MHz): 8.29
(dm, 3J(5,6) ¼ 7.5, HÀC(5)); 8.19 (d, 3J ¼ 15.7, HÀC(1’)); 7.92 (d, 3J ¼ 15.7, HÀC(2’)); 7.70 (dm, 3J(8,7) ¼
3
7.4, HÀC(8)); 7.68 – 7.65 (m, 2 arom. H); 7.56 (td, 3J(6,5) ꢂ J(6,7) ¼ 7.5, 4J(6,8) ¼ 1.4, HÀC(6)); 7.49 (td,
3
3J(7,6)ꢂ J(7,8)¼ 7.4, 4J(7,5)¼ 1.3, HÀC(7 )); 7.43 – 7.34 (m, 3 arom. H); 3.93 (br. s, 2 NCH2CH2); 1.78
(br. s, 2 NCH2CH2CH2, NCH2CH2CH2). 13C-NMR (75 MHz, CDCl3): 189.20 (Cq, CO); 160.80 (Cq);
159.04 (Cq); 154.38 (Cq); 138.87(CH); 138.55 (C q); 136.04 (Cq); 135.91 (Cq); 133.90 (CH); 132.00 (CH);
129.37(CH); 128.68 (2 CH); 128.15 (2 CH); 123.50 (CH); 123.34 (CH); 122.46 (CH); 117.18 (C q); 115.10
.
(Cq, CN); 84.99 (Cq); 49.58 (2 NCH2CH2); 25.97(2 CH 2); 24.46 (CH2). EI-MS: 391 (100, Mþ ), 362 (74),
348 (41), 336 (26), 335 (25), 323 (18), 307(21), 281 (26), 279 (20), 251 (15), 126 (16), 107(10), 84 (48,
C5H10Nþ), 77 (11, C6H5þ), 56 (11). Anal. calc. for C26H21N3O (391.47): C 79.77, H 5.41, N 10.73; found: C
79.66, H 5.54, N 10.74.

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Helvetica Chimica Acta – Vol. 91 (2008)
3. Crystal-Structure Determinations of 4’, 5’, and 7a6). The data collection and refinement parameters
for each compound are summarized in Table 5. All measurements were conducted at low-temp. on a
Rigaku AFC5R diffractometer using graphite-monochromated MoKa radiation (l ¼ 0.71069 Š) and a 12-
kW rotating anode generator. The intensities were collected using w/2q scans, and three standard
reflections measured after every 150 reflections showed negligible variation in intensity. The intensities
Table 5. Crystallographic Data for Compounds 4’, 5’, and 7a
4’
5’
7a
Crystallized from
EtOH
AcOEt
cyclohexane/toluene
C24H19N3O
365.43
Empirical formula
Formula weight [g molÀ1
Crystal color, habit
Crystal dimensions [mm]
Temp. [K]
Crystal system
Space group
Z
C35H35N3O · EtOH C35H33N3O
559.75
]
511.66
orange, prism
red, prism
0.40 ꢁ 0.45 ꢁ 0.50
173(1)
monoclinic
P21/c
yellow, prism
0.25 ꢁ 0.40 ꢁ 0.50 0.18 ꢁ 0.25 ꢁ 0.32
173(1)
monoclinic
P21/n
4
173(1)
triclinic
¯
P1
4
2
Reflections for cell determination
2q Range for cell determination [8]
25
25
25
35 – 40
18.213(3)
12.531(2)
14.348(2)
90
100.49(1)
90
3219.9(8)
1200
32 – 38
12.791(1)
11.707(2)
18.352(3)
90
98.31(1)
90
2719.1(6)
1088
37– 40
10.186(2)
11.771(2)
8.881(2)
94.00 (1)
111.05(1)
68.06(1)
919.2(3)
384
Unit cell parameters
a [Š]
b [Š]
c [Š]
a [8]
b [8]
g [8]
V [Š3]
F(000)
Dx [g cmÀ3
]
1.155
0.0714
w/2q
1.250
0.0756
w/2q
1.320
0.0824
w/2q
m(MoKa) [mmÀ1
Scan type
]
2q(max) [8]
55
55
55
Total reflections measured
8038
6831
4459
Symmetry-independent reflections
Rint
7398
0.022
4580
7398
421; 57357 254
0.0618
0.1956
0.0981; 0.704
1.045
6236
0.031
4078
4221
0.024
2647
4221
Reflections with I > 2s (I)
Reflections used in refinement
Parameters refined; restraints
Final R(F) [I > 2s (I) reflections]
wR(F2) (all data)
6236
0.0503
0.1368
0.0516; 0.5839
1.023
0.0483
0.1300
0.0506; 0.1601
1.010
Weighting parametersa) [a; b]
Goodness-of-fit
Secondary extinction coefficient
0.0032(9)
0.002
0.64; À 0.48
–
0.005(2)
0.001
0.26; À 0.22
Final Dmax/s
D1 (max; min) [e Š
0.001
0.25; À 0.24
À3
]
a) wÀ1 ¼ s2(F2o ) þ (aP)2 þ bP where P ¼ (Fo2 þ 2F2c )/3.
6
)
CCDC-663490 – 663492 contain the supplementary crystallographic data for this paper. These data
can be obtained free of charge from the Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.

Helvetica Chimica Acta – Vol. 91 (2008)
283
were corrected for Lorentz and polarization effects, but not for absorption, and equivalent reflections
were merged. Each structure was solved by direct methods using SHELXS86 [21] or SIR92 [22], which
revealed the positions of all non-H-atoms. The non-H-atoms were refined anisotropically. For 4’, in
addition to the expected org. substrate, the asymmetric unit also contains a disordered EtOH molecule.
Two sets of overlapping positions were defined for the atoms of the EtOH molecule, and the site
occupation factor of the major conformation was refined to 0.761(6). Similarity restraints were applied to
the chemically equivalent bond lengths and angles involving all disordered atoms, while neighboring
atoms within and between each conformation of the disordered EtOH molecule were restrained to have
similar atomic displacement parameters. The amine H-atom in 4’ was placed in the position indicated by a
difference electron-density map, and its position was allowed to refine together with an isotropic
displacement parameter. All of the other H-atoms in each structure were placed in geometrically
calculated positions and refined by using a riding model where each H-atom was assigned a fixed
isotropic displacement parameter with a value equal to 1.2 Ueq of its parent atom (1.5 Ueq for the Me
groups). The refinement of each structure was carried out on F2 by using full-matrix least-squares
procedures, which minimized the function Sw(Fo2 À Fc2 )2. A correction for secondary extinction was
applied in the cases of 4’ and 7a. Neutral atom scattering factors for non-H-atoms were taken from [23a]
and the scattering factors for H-atoms from [24]. Anomalous dispersion effects were included in Fc [25];
the values for f ’ and f’’ were taken from [23b]. The values of the mass attenuation coefficients are those
of [23c]. All calculations were performed using the SHELXL97program [26] and the crystallographic
diagrams were drawn using ORTEPII [27].
REFERENCES
[1] A. A. S. Briquet, P. Uebelhart, H.-J. Hansen, Helv. Chim. Acta 1996, 79, 2282.
[2] S. El Houar, H.-J. Hansen, Helv. Chim. Acta 1997, 80, 253; S. Maillefer-El Houar, P. Uebelhart, H.-J.
Hansen, Helv. Chim. Acta, to be submitted.
[3] P. Ott, H.-J. Hansen, Helv. Chim. Acta 2001, 84, 2670.
[4] T. Landmesser, H.-J. Hansen, Helv. Chim. Acta, to be submitted.
[5] K. A. Bello, L. Cheng, J. Griffiths, J. Chem. Soc., Perkin Trans. 2 1987, 815.
[6] P. P. Fu, R. G. Harvey, Chem. Rev. 1978, 78, 317.
[7] J.-J. Godfroid, Bull. Soc. Chim. Fr., Ser. 5, 1964, 2953; J. V. Crivello, J. L. Lee, Macromolecules 1981,
14, 1141.
[8] R. C. Fuson, J. J. Miller, J. Am. Chem. Soc. 1957, 79, 3477.
[9] C. Mayor, C. Wentrup, J. Am. Chem. Soc. 1975, 97, 7467.
[10] D. Lin-Vien, N. B. Colthup, W. G. Fateley, J. G. Grasselli, ꢀThe Handbook of Infrared and Raman
Characteristic Frequencies of Organic Moleculesꢁ, Academic Press, Inc., San Diego, 1991, p. 341.
[11] J. F. Ireland, in ꢀAdvances in Physical Organic Chemistryꢁ, Eds. V. Gold, D. Bethell, Academic Press,
Ltd., London, 1975, Vol. 12, p. 131.
[12] ꢀ Handbook of Chemistry and Physicsꢁ, 70th edn., CRC Press, Inc., 1989, p. D-161.
[13] A. Huth, R. Schmiechen, I. Motoc, I. Beetz, A. Breitkopf, E. Frost, I. Schumann, K. Thielert, Arch.
Pharm. 1988, 321, 297.
[14] M.-J. Shiao, K.-H. Liu, P.-Y. Lin, Heterocycles 1993, 36, 507.
[15] H. Fischer-Colbrie, H. Aigner, H. Junek, Monatsh. Chem. 1975, 106, 743.
[16] N. S. Kozlov, V. D. Pak, Z. Z. Nugumanov, Khim. Geterotsikl. Soedin (Engl. Transl.) 1970, 6, 17 9;
N. S. Kozlov, K. N. Gusak, Dokl. Chem. (Engl. Transl.) 1990, 314, 300.
[17] H. Junek, M. Klade, H. Sterk, Monatsh. Chem. 1989, 120, 781.
[18] H. Boutome, H. Hartmann, Monatsh. Chem. 1997, 128, 7 1.
[19] M. Mishriky, F. A. Asaad, Y. A. Ibrahim, A. S. Girgis, Recl. Trav. Chim. Pays-Bas 1994, 113, 35.
[20] H. Hellmann, K. Seegmüller, Chem. Ber. 1958, 91, 2420.
[21] G. M. Sheldrick, SHELXS86, Acta Crystallogr., Sect. A 1990, 46, 467.
[22] A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, M. C. Burla, G. Polidori, M. Camalli,
SIR92, J. Appl. Crystallogr. 1994, 27, 435.

284
Helvetica Chimica Acta – Vol. 91 (2008)
[23] a) E. N. Maslen, A. G. Fox, M. A. OꢁKeefe, in ꢀInternational Tables for Crystallographyꢁ, Ed. A. J. C.
Wilson, Kluwer Academic Publishers, Dordrecht, 1992, Vol. C, Table 6.1.1.1, pp. 477 – 486; b) D. C.
Creagh, W. J. McAuley, in ꢀInternational Tables for Crystallographyꢁ, Ed. A. J. C. Wilson, Kluwer
Academic Publishers, Dordrecht, 1992, Vol. C, Table 4.2.6.8, pp. 219 – 222; c) D. C. Creagh, J. H.
Hubbell, in ꢀInternational Tables for Crystallographyꢁ, Ed. A. J. C. Wilson, Kluwer Academic
Publishers, Dordrecht, 1992, Vol. C, Table 4.2.4.3, pp. 200 – 206.
[24] R. F. Stewart, E. R. Davidson, W. T. Simpson, J. Chem. Phys. 1965, 42, 3175.
[25] J. A. Ibers, W. C. Hamilton, Acta Crystallogr. 1964, 17, 781.
[26] G. M. Sheldrick, SHELX97, Program for the Refinement of Crystal Structures, University of
Gçttingen, Gçttingen, 1997.
[27] C. K. Johnson, ORTEPII, Report ORNL-5138, Oak Ridge National Laboratory, Oak Ridge,
Tennessee, 1976.
Received November 26, 2007