Novel synthesis of 2-alkylquinolizinium-1-olates and their 1,3-dipolar cycloaddition reactions with acetylenes

Article abstract of DOI:10.1002/hlca.201200038

Several 2-alkylquinolizinium-1-olates 9, i.e., heterobetaines, were prepared from ketone 11, the latter being readily available either from pyridine-2-carbaldehyde via a Grignard reaction, followed by oxidation with MnO₂, or from 2-picolinic acid (=pyridine-2-carboxylic acid) via the corresponding Weinreb amide and subsequent Grignard reaction. Mesoionic heterobetaines such as quinolizinium derivatives have the potential to undergo cycloaddition reactions with double and triple bonds, e.g., 1,3-dipolar cycloadditions or Diels-Alder reactions. We here report on the scope and limitations of cycloaddition reactions of 2-alkylquinolizinium-1-olates 9 with electron-poor acetylene derivatives. As main products of the reaction, 5-oxopyrrolo[2,1,5-de]quinolizines (='[2.3.3]cyclazin-5-ones') 19 were formed via a regioselective [2+3] cycloaddition, and cyclohexadienone derivatives, formed via a Diels-Alder reaction, were obtained as side products. The structures of 2-benzylquinolizinium-1-olate (9a) and two '[2.3.3]cyclazin-5- ones' 19i and 19l were established by X-ray crystallography. Copyright

Full text of DOI:10.1002/hlca.201200038

Helvetica Chimica Acta – Vol. 95 (2012)
737
Novel Synthesis of 2-Alkylquinolizinium-1-olates and Their 1,3-Dipolar
Cycloaddition Reactions with Acetylenes
by Andreas Gebert1)a)b), Max Barth2)a), Anthony Lindena), Ulrich Widmerc),
and Heinz Heimgartner*a)
a) Organisch-Chemisches Institut der Universitꢀt Zꢁrich, Winterthurerstrasse 190, CH-8057 Zꢁrich
(phone: þ 41-44-6354282; fax: þ 41-44-6356812; e-mail: heimgart@oci.uzh.ch)
b) F. Hoffmann-La Roche Ltd., Chemical Manufacturing Basel, Grenzacherstrasse 124, CH-4070 Basel
c) F. Hoffmann-La Roche Ltd., pRED, Discovery Chemistry Basel, Grenzacherstrasse 124,
CH-4070 Basel
Dedicated to Professor Hans-Jꢀrgen Hansen on the occasion of his 75th birthday
Several 2-alkylquinolizinium-1-olates 9, i.e., heterobetaines, were prepared from ketone 11, the latter
being readily available either from pyridine-2-carbaldehyde via a Grignard reaction, followed by
oxidation with MnO2, or from 2-picolinic acid (¼ pyridine-2-carboxylic acid) via the corresponding
Weinreb amide and subsequent Grignard reaction. Mesoionic heterobetaines such as quinolizinium
derivatives have the potential to undergo cycloaddition reactions with double and triple bonds, e.g., 1,3-
dipolar cycloadditions or DielsꢀAlder reactions. We here report on the scope and limitations of
cycloaddition reactions of 2-alkylquinolizinium-1-olates 9 with electron-poor acetylene derivatives. As
main products of the reaction, 5-oxopyrrolo[2,1,5-de]quinolizines (¼ꢂ[2.3.3]cyclazin-5-onesꢃ) 19 were
formed via a regioselective [2 þ 3] cycloaddition, and cyclohexadienone derivatives, formed via a
DielsꢀAlder reaction, were obtained as side products. The structures of 2-benzylquinolizinium-1-olate
(9a) and two ꢂ[2.3.3]cyclazin-5-onesꢃ 19i and 19l were established by X-ray crystallography.
1. Introduction. – Since the formulation of the concept of 1,3-dipolar cycloadditions
([2 þ 3] cycloadditions) by Huisgen [1], this reaction type proved to be an indispensable
tool for the synthesis of five-membered heterocycles [2]. Belonging to the pericyclic
reactions, the special features of [2 þ 3] cycloadditions such as chemo-, regio-, and
stereoselectivity are nowadays well understood on the basis of the Frontier Molecular
Orbital (FMO) theory [3], and the WoodwardꢀHoffmann [4] and DewarꢀZimmerman
rules [5] allow reliable predictions of the reaction course and the structure of the
products. But an increasing number of formal 1,3-dipolar cycloadditions is known, in
which a non-concerted, two-step mechanism [6], via either a biradical [7] or a
zwitterion [8] as the crucial intermediate, leads to the five-membered products.
An important group of 1,3-dipoles often used in [2 þ 3] cycloadditions consists of
azomethine ylides, which can be generated as reactive intermediates by various
methods such as thermal and photochemical ring-opening of aziridines, deprotonation
of iminium salts, desilylation of silylated amines and imines, base-catalyzed elimination
1
)
)
Part of the Ph.D. thesis of A. G., Universitꢀt Zꢁrich, 2001.
Part of the diploma thesis of M. B., Universitꢀt Zꢁrich, 1994.
2
ꢄ 2012 Verlag Helvetica Chimica Acta AG, Zꢁrich

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Helvetica Chimica Acta – Vol. 95 (2012)
of thiophenol from 2-(phenylsulfanyl)amines, thermal decarboxylation of 1,3-oxazo-
lidin-5-ones, and dehydration of N-oxides of tertiary amines [9]. In addition, a series of
relatively stable azomethine ylides has been described, in which the formal charges are
stabilized by extended delocalization or electron-withdrawing substituents. Well-
known examples are pyridinium, quinolinium, and isoquinolinium methanides, and
mesoionic 1,3-oxazol-5-ones (ꢂMꢁnchnonesꢃ) [10], which have also been used in [2 þ 3]
cycloadditions.
A less well-known group of stabilized azomethine ylides includes mesoionic
quinolizinium-1-olates (Scheme 1). Although a few compounds of this group have been
prepared [11], they were only scarcely investigated in dipolar cycloadditions. For
example, Pastor et al. reported that 1 and dimethyl acetylenedicarboxylate (DMAD)
reacted already at room temperature, and the ꢂ[2.3.3]cyclazin-5-oneꢃ (Boekelheide
nomenclature) derivative 23) was isolated as the only product albeit in rather low yield
[11d]. It is important to note that the initially formed [2 þ 3] cycloadduct could not be
isolated, and a spontaneous dehydrogenation occurred under the reaction conditions
leading to the ꢂaromatizedꢃ product 2. Analogous reactions were observed between
quinolizinium-3-olate (3) and ethyl propiolate (¼ethyl prop-2-ynoate) leading to 4
[12], and between the non-mesoionic pyrrolo[1,2-a]pyridine (5) and DMAD in
refluxing toluene in the presence of Pd/C to yield 6 [13] (Scheme 1).
Scheme 1
In the present study, we elaborated a new synthesis of 2-alkylquinolizinium-1-olates
of type 9 and investigated their ability to undergo 1,3-dipolar cycloadditions with alkyl
3
)
The IUPAC (class) name of these compounds is pyrrolo[2,1,5-de]quinolizin-5-ones, and the semi-
trivial name 8b-azaacenapthylen-5-one has also been used in the literature.

Helvetica Chimica Acta – Vol. 95 (2012)
739
acetylenecarboxylates. As the cyclazine skeletons of type 2, 4, and 6 occur in
quinolizinium alkaloids [14], these cycloadditions may be of interest as a synthetic tool
for the preparation of these products.
2. Results and Discussion. – 2.1. Synthesis of 2-Alkylquinolizinium-1-olates 9. In
analogy to the synthesis of the quinolizinium derivative 7 via cyclization of 8 by Fozard
and Jones [11a], our approach to 9 was based on the cyclization via formation of the
CꢀN bond (Scheme 2). A suitable precursor is the aldehyde 10, which after alkylation
of 11, can be generated in situ under acidic conditions.
Scheme 2
The known ketone 11 [15] was synthesized via two different routes, both involving a
Grignard reaction (Scheme 3). Starting with 2-(2-bromoethyl)-1,3-dioxolane, the
Grignard reagent 13 was prepared at 108, followed by dropwise addition of pyridine-
2-carbaldehyde (12; route A). When the reaction was complete, an aqueous solution of
NH4Cl was added. The crude alcohol was purified by column chromatography to yield
14 (29%), which was oxidized with MnO2 to give ketone 11 in 82% yield. In the second
approach (route B), the mixed anhydride of pyridine-2-carboxylic acid (15) and
isobutyl chloroformate was formed in situ, and subsequent treatment with N,O-
dimethylhydroxylamine gave the Weinreb amide 16 [16] in 75% yield. The following
Grignard reaction with 1.5 equiv. of 13 led to 11 as white crystals in 79% yield. Route A
has the disadvantage of a low overall yield (24%), but it has to be taken into account
that the higher overall yield achieved via route B (59%) is connected with much higher
costs of the starting materials.
The alkylation of 11 in the a-position to the C¼O group was carried out by
treatment with LDA (LiN(i-Pr)2) at ꢀ 788 in THF/DMPU (1,3-dimethyltetrahydro-
pyrimidin-2(1H)-one)4), followed by addition of various alkyl halogenides at the same
temperature, to give the desired 2-alkylated products 17 (Table 1)5). After complete
addition, the mixture was allowed to warm to room temperature and was then poured
4
)
)
The yields of the alkylation were much lower in the absence of DMPU.
The temperature of the mixture had to be kept below ꢀ 558, otherwise the yields decreased
dramatically.
5

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Helvetica Chimica Acta – Vol. 95 (2012)
Scheme 3
Table 1. Formation of 17 via Alkylation of Ketone 11 and Cyclization to Give 2-Alkylquinolizinium-1-
olates 9
R
17
Yield [%]
9
Yield [%]
Bn
Me
a
b
c
d
e
11
63
55
64
18
64
a
b
87
86
69
70
21
10
CH2¼CHꢀCH2
ca)
d
i-Pr
CHꢁCꢀCH2
eb)
f [11b]
H
a) Prop-1-en-1-yl derivative. b) 2-[(1,3-Dioxolan-2-yl)methyl]-4-methylquinolizinium-1-olate.
into ice-water. The crude products were purified by column chromatography. With the
exception of 17d, the products were obtained in good yields.
For the cyclization, the respective ketones 17 were dissolved in glacial AcOH, and
the solutions were heated to reflux for 12 h. Then, the excess AcOH was removed by
azeotropic distillation with EtOH. The crude products were purified by chromatog-
raphy and recrystallization to give 9a – 9d in 69 – 87% yield (Table 1). In the case of the
allyl derivative 17c, the 1H- and 13C-NMR spectra indicated that the formed
quinolizinium-1-olate 9c was the (E)-prop-1-en-1-yl derivative. The structures of the
products 9, which were obtained as yellow or orange solids, were determined on the
basis of their analytical and spectroscopic data. They showed an intense UVabsorption
in the range of 361 – 416 nm and a bright yellow fluorescence, when solutions were

Helvetica Chimica Acta – Vol. 95 (2012)
741
irradiated with UV light (l 366 nm). In the 13C-NMR spectra (CDCl3), C(1)ꢀO
absorbed at 165.4 – 162.8 ppm, and the IR absorption (CHCl3) of the C,O group was
typically found at ca. 1550 cmꢀ1, i.e., at much lower frequencies than the normal C¼O
groups6). Finally, the structure of 9a was established by means of X-ray crystallography
(Fig. 1). The crystal structure shows that the compound has the expected zwitterionic
character: the C(1)ꢀO bond is significantly longer (1.272(2) ꢅ) than expected for C¼O
groups (ca. 1.20 ꢅ).
Fig. 1. ORTEP Plot [17] of the molecular structure of 9a (50% probability ellipsoids; arbitrary
numbering of the atoms)
We also tried to prepare the known parent compound 9f [11b] via the acid-
catalyzed cyclization of 11 under the conditions described above. The reaction was
remarkably slower than that in the previous cases, and after 40 h in refluxing glacial
AcOH and chromatographic workup, 9f was obtained in only 10% yield. A possible
explanation is the effect of a bulky substituent at the a-position on the conformation of
the intermediate for the ring closure. Such a substituent may promote a conformation
in which the acetal group is close to the pyridine N-atom, thereby favoring the
cyclization.
An unexpected result was obtained with the propargyl derivative 17e. After 12 h in
refluxing glacial AcOH, a complex mixture of products was formed. Following the
progress of the reaction by TLC showed that a new product with a yellow fluorescence
was present after ca. 2 h, but disappeared when the mixture was heated for a longer
time. After azeotropic distillation of the excess AcOH with EtOH, column
chromatography, and recrystallization, a yellow powder was isolated. Surprisingly, in
the NMR spectra, all signals of the dioxolane ring were still present. Additionally, the
1H-NMR spectrum showed the absorptions of a CH2 group at 3.18 ppm (d, J ¼ 5.2) and
a Me signal at 2.63 ppm, and, in the 13C-NMR spectrum, the signals of these groups
were observed at 35.1 and 19.3 ppm, respectively. In the CI-MS (NH3), the [M þ 1]
6
)
The C(1)ꢀO group of the analogous mesoionic 8-(ethoxycarbonyl)acenaphtho[1,2-b]quinolizinium-
1-olate absorbs at 1586 cmꢀ1 (KBr) [11d].

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Helvetica Chimica Acta – Vol. 95 (2012)
peak appeared at m/z 246, i.e., indicating the same mass as the starting material 17e.
The IR spectrum showed the characteristic band at 1551 cmꢀ1, suggesting the presence
of a quinolizinium-1-olate. On the basis of these data, the structure 9e was proposed for
the product.
A reaction mechanism for the formation of 9 is proposed in Scheme 4. Under the
acidic conditions, the dioxolane ring is opened to give intermediate A. A bulky
substituent R may favor conformation B, which is suitable for the ring closure to give C
via nucleophilic addition of the pyridine N-atom. Finally, elimination of ethyleneglycol
and rearomatization yields the mesoionic product 9.
Scheme 4
The formation of 9c with a (E)-prop-1-en-1-yl side chain can be rationalized by a
secondary isomerization of the initially formed 1-hydroxyquinolizidinium derivative D
via the intermediate E (Scheme 5). In the case of the propargyl derivative 17e, a
protonation of the acetylenic group may lead to cation F, which is prone to undergo the
ring closure to G. Aromatization of the latter via enolization and 1,3-H shift gives the
isolated product 9e. It is important to note that the acetal unit remains unreacted under
the acidic reaction conditions, and the formal 6-endo-dig cyclization is the preferred
ring closure.
2.2. 1,3-Dipolar Cycloadditions of 9 with Acetylenes. As mentioned in the
Introduction, quinolizinium-olates 1 and 3 can undergo 1,3-dipolar cycloadditions with
electron-deficient acetylenes [11d][12]. Having in hand the quinolizinium-1-olates 9a –
9f (Table 1), we studied their reactions with acetylene dicarboxylates 18. For this
purpose, solutions of 1 equiv. of 9 and 2 equiv. of 18 in THF were stirred at room
temperature. After ca. 30 min, 9 was completely consumed (TLC), and chromato-
graphic workup gave the main product as an orange oil or powder (Table 2). On the
basis of the analytical and spectroscopic data, the structure of 4-substituted
[2.3.3]cyclazin-5-ones 19 (1,2-bis(alkoxycarbonyl)pyrrolo[2,1,5-de]quinolizinium-5-
olates) was proposed (Scheme 6). For example, the IR spectrum (CHCl3) of 19b
showed a strong band at 1584 cmꢀ1, and in the 13C-NMR spectrum (CDCl3), the
C(5)ꢀO group absorbed at 175.2 ppm, indicating a less pronounced dipolar character
compared with 9a. The CI-MS with [M þ 1]þ at m/z 376 as well as the elemental analysis

Helvetica Chimica Acta – Vol. 95 (2012)
743
Scheme 5
Table 2. Formation of Compounds 19 via [2 þ 3] Cycloaddition of 9 with Acetylene Dicarboxylates 18a
and 18b
9
a
R
18
R1
Procedure
19
Yield [%]
Bn
a
b
a
b
b
b
b
Et
Me
Et
Me
Me
Me
Me
Aa)
A
A
A
A
a
b
c
d
e
f
36 (45b))
orange oil
orange powder, m.p. 169 – 1708
orange oil
orange powder, m.p. 148 – 1498
orange oil
orange oil
40
29
39
33
41
19
b
Me
c
d
f
MeꢀCH¼CH
i-Pr
H
A
A
g
orange oil
a) Reaction in THF at room temperature. b) Reaction in toluene, 17 min reflux, 18 h at r.t.
supported this structure. Furthermore, 9a exhibited an intense UV absorption at
473 nm (log e ¼ 4.01, MeOH) and a bright yellow fluorescence.
The formation of the products 19 can be rationalized by a [2 þ 3] cycloaddition of 9
and 18 to give H, which spontaneously undergoes a dehydrogenation to yield the final
product (Scheme 6). It is important to note that, in all experiments, the initially formed
cycloadduct of type H could neither be isolated nor detected. This is in accordance with
the results of the reaction 1 ! 2 reported in [11d], whereas the reactions 3 ! 4 [12] and
5 ! 6 [13] (Scheme 1) have been carried out under dehydrogenation conditions.

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Helvetica Chimica Acta – Vol. 95 (2012)
Scheme 6
For the next series of reactions with 9, unsymmetrical acetylenecarboxylates 18c –
18f were used. The reaction with ethyl 4,4,4-trifluorobut-2-ynoate (18c) occurred
smoothly in THF at room temperature to yield a single product with the characteristic
spectroscopic properties of compounds of type 19 in 43% yield (Scheme 7). The exact
structure of 19l was established by X-ray crystallography (Fig. 2,b).
Scheme 7
The C(1)ꢀO bond length is 1.234(3) ꢅ and is slightly longer than a normal C¼O
bond but shorter than the C,O bond in 9a (1.272(2) ꢅ), indicating a higher C¼O bond
character. On the other hand, the IR (1542 cmꢀ1) and 13C-NMR spectra (175.8 ppm)
point to a pronounced dipolar character of the C,O bond [18]. The molecule 19l is
highly planar with all ring atoms being within 0.05 ꢅ of the mean plane. The C¼C bonds
are completely delocalized in the five-membered ring, but tend to be slightly more
localized within the six-membered rings. This is in accordance with the observation that
the C(1),C(2) bond of 8b-azaacenaphthylenium ions do not show olefinic character,
i.e., they do not undergo [2 þ 4] cycloadditions with, e.g., 1,3-diphenylisobenzofuran, in
contrast to the isoelectronic acenaphthylene [12].

Helvetica Chimica Acta – Vol. 95 (2012)
745
Fig. 2. ORTEP Plots [17] of the molecular structures a) of 19i and b) of 19l (50% probability ellipsoids;
arbitrary numbering of the atoms)
Similar to 9a, quinolizinium-1-olates 9b – 9d also reacted with 18c in THF at room
temperature to give the corresponding products 19 in a regioselective manner
(Table 3). In contrast, the reactions of 9a and 9b with ethyl and methyl prop-2-ynoate
(18d and 18e, resp.) were sluggish at room temperature and, therefore, were carried out
in boiling toluene. After 10 – 20 h, the corresponding products of type 19 were obtained
in 27 – 29% yield, again as single regioisomers (Table 3).
Table 3. Formation of Compounds 19 via [2 þ 3] Cycloaddition Reaction of 9 with Unsymmetrical
Acetylene Carboxylates 18c – 18f
9
a
R
18
R1
R2
Procedure
19
Yield [%]
Bn
c
d
e
f
c
e
f
Et
Et
Me
Et
Et
CF3
H
H
Me
CF3
H
Me
H
Aa)
Bb)
B
Cc)
A
B
C
C
A
h
i
j
k
l
m
n
o
p
q
43
24
27
32
41
29
28
27
33
36
b
Me
Me
Et
Acd)
Et
c
d
MeꢀCH¼CH
c
c
CF3
CF3
i-Pr
Et
A
a) Reaction in THFat room temperature. b) Reaction in boiling toluene. c) Reaction in toluene at 1408 in
d
a sealed tube. ) Ac instead of R1O2C in the formula 19h – 19q (Scheme 7); reaction with but-3-yn-2-one.
The product of the reaction of 9a with 18d was obtained as dark-yellow oil (27%),
which crystallized as orange prisms after treatment with Et2O. The most characteristic
spectroscopic data were the IR absorption at 1577 cmꢀ1 (CHCl3), the 13C-NMR signal

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Helvetica Chimica Acta – Vol. 95 (2012)
at 174.9 ppm, and the Mþ peak at m/z 331 in the EI-MS. The proposed structure 19i was
finally established by X-ray crystallography (Fig. 2,a). The molecule lies on a
crystallographic mirror plane and is completely planar, except for the Ph ring, which
is perpendicular to the mirror plane. The length of the C(1)ꢀO bond is 1.241(2) ꢅ, i.e.,
in the same range as in the case of 19l.
Even less reactive than 18d and 18e were ethyl but-2-ynoate (18f) and but-3-yn-2-
one. In these cases, the reactions with 9a and 9b were performed in toluene in a sealed
tube at 1408. After ca. 60 h, the expected products 19k, 19n, and 19o were obtained in
27 – 31% yield (Table 3). Even under the most drastic conditions and with the most
reactive acetylenes, no reaction of 9e leading to products of type 19 could be observed,
but decomposition occurred.
2.3. Formation of Side Products. In the reactions of quinolizinium-1-olates 9 with
acetylenes described above, the formation of minor side products was observed, in
addition to the desired compounds 19. Therefore, some of the reactions were repeated
aiming at the isolation and structure determination of some of the side products.
Repeated chromatography of the mixture of side products of the reaction of 9a with
18a in toluene (17 min reflux, 18 h at r.t.) furnished a pure substance as a yellow oil (ca.
1
8%). The CI-MS showed the [M þ 1]þ peak at m/z 406, and both H- and 13C-NMR
spectra indicated an adduct of 9a and 18a. Strong absorptions in the IR spectrum
(CHCl3) at 1753, 1714, and 1668 cmꢀ1 evidenced the presence of three C¼O groups, one
of them exhibiting a 13C-NMR signal at 194.4 ppm. In addition, the product was
characterized by a UV absorption (EtOH) at 326 nm (log e ¼ 3.21), typical for
cyclohexa-2,4-dien-1-ones [19]. On the basis of these data, we proposed structure 20a
for this side product (Scheme 8)7). Analogous side products 20b – 20d were obtained
from the reactions of 9a with 18b and 18d, and of 9b with 18b. An additional side
product, methyl 3-benzyl-2-hydroxy-6-(pyridin-2-yl)benzoate (21), could be isolated in
the case of the reaction of 9a with 18d, whereas dimethyl 3-hydroxy-4-methylbenzene-
1,2-dicarboxylate (22) was obtained from the reaction of 9b and 18b.
A mechanistic proposal for the formation of the identified side products is outlined
in Scheme 8. The initial reaction step is a DielsꢀAlder addition to yield I, which
undergoes a spontaneous rearrangement to give the cyclohexadienone 20. In the case of
R2 ¼ H, i.e., the product of the reaction with methyl prop-2-ynoate, a second
rearrangement could lead to 2-hydroxy-3-(pyridin-2-yl)benzoate 21. The mechanism
of the formation of 22 is not clear, and I as well as 20 may be the precursor. It is worth
emphasizing that quinolizinium-1-olates 9 undergo [2 þ 3] as well as [2 þ 4] cyclo-
additions. There is only one other known example of a reaction occurring via similar
dual pathways, which was described by McEwen et al. and by Schmitt et al. [20]. On
treatment with HBF4, the Reissert compound 2-benzoyl-1,2-dihydroisoquinoline-1-
carbonitrile forms a reactive 1,3-oxazolium intermediate, which reacts with acetylenes
and acrylates to give products via 1,3-dipolar cycloaddition and DielsꢀAlder reactions,
respectively. On the other hand, [2 þ 4] cycloadditions with aromatic N-heterocycles
are well-known [21], including acridizinium salts [22] and a quinolizinium salt [23].
2.4. Attempted 1,3-Dipolar Cycloadditions of 9 with Alkenes. The attempted
reaction of 9b with electron-poor alkenes such as diethyl fumarate (23a), maleic
7
)
The same product 20a was formed under the usual reaction conditions (THF, r.t.; TLC evidence).

Helvetica Chimica Acta – Vol. 95 (2012)
747
Scheme 8
anhydride, N-phenylmaleimide, fumaronitrile (23b), etc., in THF at room temperature
failed. Even after several days, only starting materials could be detected (TLC).
Heating of a mixture of 9b and 23a in toluene or mesitylene to reflux for some days led
only to traces of product 19d. The initially formed cycloadduct could not be detected.
Therefore, mixtures of 1 equiv. of 9b, 4 equiv. of 23a or 23b, and a small amount of Pd/
C in toluene were heated to reflux for 4 – 5 d. After chromatographic workup,
pyrrolo[2,1,5-de]quinolizinones 19d and 19r, respectively, were obtained in 8 and 14%
yield (Scheme 9). With other C¼C dipolarophiles, no analogous products were
formed8).
Scheme 9
These results are in accordance with the observation of Alvarez-Builla and co-
workers that only acetylenes undergo the 1,3-dipolar cycloaddition with quinolizinium-
1-olates, but reactions with alkenes and isocyanates failed [11d]. In our hands, even
thiobenzophenone and thiofluorenone, which are known as ꢂsuperdipolarophilesꢃ [24],
did not undergo the cycloaddition with 9.
8
)
At a higher temperature or after a longer reaction time, only decomposition of 9b was observed.

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Helvetica Chimica Acta – Vol. 95 (2012)
3. Conclusions. – We reported on a new approach to mesoionic heterocycles of type
9, i.e., quinolizinium-1-olates, in reasonable yields, via a four-step synthesis with
commercially available starting materials. The key intermediate, ketone 11, was
prepared via two different routes, both involving a Grignard reaction. The cyclization
of the alkylated ketones 17 to give 9 was carried out under acidic conditions. In the case
of the allyl derivative, a secondary isomerization was observed, whereas an unexpected
cyclization occurred with the propargyl derivative.
The quinolizinium-1-olates 9 are stabilized, aromatic azomethine ylides, which
reacted with electron-poor acetylenes to give ꢂ[2.3.3]cyclazin-5-onesꢃ 19 in moderate
yields as the result of a 1,3-dipolar cycloaddition, followed by a spontaneous
dehydrogenation. Depending on the reactivity of the acetylene, the reaction was
performed in THF at room temperature, in boiling toluene, or at higher temperature in
a sealed tube. With unsymmetrical acetylenes as dipolarophiles, the cycloaddition
occurred regioselectively, and only one regioisomer was obtained. Compared with the
mesoionic 1,3-oxazol-5-ones (ꢂMꢁnchnonesꢃ), the reactivity of 2-alkylquinolizinium-1-
olates 9 is much lower. In some cases, cyclohexa-2,4-dien-1-ones 20 and phenols 21 and
22 were isolated as minor products. Their formation was proposed to occur via a
competitive [2 þ 4] cycloaddition (DielsꢀAlder reaction) and subsequent rearrange-
ments. The failure of the reactions with 9e can be rationalized by steric hindrance of the
cycloaddition step by the Me group at C(4) and by the impossibility of aromatization of
the adduct.
The scope of the 1,3-dipolar cycloaddition of 9 is limited to reactions with
acetylenes. With other dipolarophiles, such as electron-poor olefins or thioketones, no
reaction was observed. Most likely, the aromatization of the initially formed cyclo-
adducts to give ꢂ[2.3.3]cyclazin-5-onesꢃ 19 is the driving force. Therefore, the reactions
of 9 with fumaronitrile and ethyl fumarate as dipolarophiles, in the presence of Pd/C as
dehydrating catalyst, led to the corresponding aromatized products, albeit in low yield.
We thank Mrs. Annick Hartmann for skillful technical assistance, the analytical sections of our
institute for spectra and analyses, and the Swiss National Science Foundation and F. Hoffmann-La Roche
AG, Basel, for financial support.
Experimental Part
1. General. TLC: Merck 60 F254 SiO2-coated Al-plates, 0.2 mm; detection of the substances on the
TLC plates under UV light (l 254 nm) or with KMnO4 soln. Prep. TLC: Merck 60 F254 SiO2-coated glass-
plates, 2 mm. Column chromatography (CC): Merck 60 SiO2, 0.040 – 0.63 mm. M.p.: Mettler-FP-5
instrument; uncorrected. UV/VIS Spectra: Uvikon instrument; in MeOH; lmax in nm (log e). IR Spectra:
1
PerkinꢀElmer-1600 FT-IR spectrophotometer; in CHCl3; cmꢀ1. H- and 13C-NMR spectra: Bruker-AC-
300 or Bruker-ARX-300 instrument (at 300 and 75.5 MHz, resp.) or Bruker-AMX 600 instrument (at 600
and 150 MHz, resp.), in CDCl3; multiplicity of C-atoms from DEPT spectra; d in ppm rel. to Me4Si as
internal standard, J in Hz. MS: Finnigan MAT-90 (EI, 70 eV) or CI (NH3 or isobutene)), Finnigan SSQ-
700 (EI and CI), or Finnigan TSQ-700 (ESI) instrument; in m/z (rel. %). Elemental analyses were
performed by the Mikroanalytisches Laboratorium des Organisch-chemischen Instituts der Universitꢀt
Zꢁrich (Elementar Vario EL instrument).
2. Starting Materials. All chemicals were commercially available (Fluka, Aldrich, and Merck).
Solvents were purified as follows: hexane by distillation from CaH2; AcOEt and CH2Cl2 by distillation
from K2CO3 and storing over molecular sieves (4 ꢅ); THF (purum, Fluka) and Et2O, dried over Na and
distilled; toluene (p.a., Merck), stored over Na; MeOH (p.a., Merck) and AcOH (p.a., Merck) were
directly used.

Helvetica Chimica Acta – Vol. 95 (2012)
749
3. Synthesis of 2-Alkylquinolizinium-1-olates 9. 3.1. Synthesis of 3-(1,3-Dioxolan-2-yl)-1-(pyridin-2-
yl)propan-1-one (11). Route A: 3-(1,3-Dioxolan-2-yl)-1-(pyridin-2-yl)propan-1-ol (14). In a three-
necked flask flushed with Ar and equipped with thermometer, mechanical stirrer, and dropping funnel,
Mg pieces (2.34 g, 0.10 mol), THF (5 ml), an I2 crystal, and 2-(2-bromoethyl)-1,3-dioxolane (2 ml) were
mixed and intensively stirred. When the reaction started, the mixture was cooled to 108, and a soln. of 2-
(2-bromoethyl)-1,3-dioxolane (12 ml, 0.10 mmol) in 100 ml of dry THF was added dropwise, while
keeping the temp. at 108. After stirring for another 0.5 h, a soln. of pyridine-2-carbaldehyde (12; 10.5 ml,
0.11 mol) in THF (100 ml) was added within 0.5 h. Then, the temp. was allowed to increase to r.t., and the
mixture was stirred for 19 h. The mixture was cooled with ice, hydrolyzed by addition of 20% aq. NH4Cl
soln. (100 ml), and extracted with Et2O. The org. phase was washed with H2O (200 ml) and brine
(100 ml), dried (MgSO4), and the solvent was evaporated. The crude product was purified by CC
(AcOEt) to give 14 (6.02 g, 29%). Yellow oil. IR (film): 3370w (br.), 2947m, 2912m, 2871m, 1590m,
1568m, 1470m, 1406m, 1431m, 1305w, 1211w, 1179w, 1135s, 1105m, 1068m, 1027s, 997m, 970m, 941m,
748m, 703w. 1H-NMR: 8.53 (d, J ¼ 4.8, HꢀC(6) (Py)); 7.68 (td, J ¼ 7.7, 1.7, HꢀC(4) (Py)); 7.30 (d, J ¼ 7.8,
HꢀC(3) (Py)); 7.19 (dd, J ¼ 7.4, 5.0, HꢀC(5) (Py)); 4.91 (t, J ¼ 4.4, OCHO); 4.80 (t, J ¼ 7.0, HꢀC(1)); 4.38
(br. s, OH); 3.82 – 3.99 (m, OCH2CH2O); 1.97 – 2.04, 1.75 – 1.88 (2m, 2 CH2). 13C-NMR: 162.1 (s, C(2)
(Py)); 148.2 (d, C(6) (Py)); 136.6 (d, C(4) (Py)); 122.2 (d, C(3) (Py)); 120.3 (d, C(5) (Py)); 104.3 (d,
OCHO); 72.5 (d, C(1)), 64.9, 64.8 (2t, OCH2CH2O); 32.4, 29.5 (2t, 2 CH2). CI-MS: 211 (11), 210 (100,
[M þ 1]þ), 166 (5).
3-(1,3-Dioxolan-2-yl)-1-(pyridin-2-yl)propan-1-one (11) [15]. To a soln. of 14 (6.0 g, 29 mmol) in
THF (70 ml) was added MnO2 (36 g, 414 mmol), and the mixture was heated to reflux for 2 h. After
cooling to r.t., filtration through Celite (Et2O, 50 ml), and evaporation of the solvent, the product
crystallized and was dried (h.v.): 11 (4.89 g, 82%). Pale yellow crystals. M.p. 65.9 – 668. IR (KBr): 3062w,
2960m, 2939m, 2873m, 1690s, 1608w, 1580s, 1569m, 1480w, 1462m, 1439s, 1411s, 1397s, 1368s, 1354s,
1314w, 1299m, 1282s, 1247m, 1225m, 1203m, 1175m, 1131s, 1059s, 1022s, 987s, 958s, 931s, 881s, 808m,
1
789m, 760s, 704w, 663m, 612s. H-NMR: 8.68 (d, J ¼ 4.8, HꢀC(6) (Py)); 8.03 (d, J ¼ 7.6, HꢀC(3) (Py));
7.83 (td, J ¼ 7.6, 1.4, HꢀC(4) (Py)); 7.46 (dd, J ¼ 7.4, 5.2, HꢀC(5) (Py)); 5.03 (t, J ¼ 4.3, OCHO); 4.00 –
3.80 (m, OCH2CH2O); 3.37 (t, J ¼ 7.3, CH2); 2.20 – 2.10 (m, CH2). 13C-NMR: 201.1 (s, C¼O); 153.4 (s,
C(2) (Py)); 148.9 (d, C(6) (Py)); 136.8 (d, C(4) (Py)); 126.9 (d, C(5) (Py)); 121.7 (d, C(3) (Py)); 103.6 (d,
OCHO); 65.0 (t, OCH2CH2O); 31.9, 28.0 (2t, 2 CH2). CI-MS: 209 (11), 208 (100, [M þ 1]þ). Anal. calc.
for C11H13NO3 (207.22): C 63.75, H 6.32, N 6.76; found: C 64.02, H 6.56, N 6.79.
Route B: N-Methoxy-N-methylpyridine-2-carboxamide (16). To a suspension of pyridine-2-carbox-
ylic acid (15; 30.78 g, 0.25 mol) in CH2Cl2 (100 ml) at 08, N-methylmorpholine (100 ml, 0.50 mol) was
added dropwise. Then, the clear soln. was cooled to ꢀ 108, and isobutyl chloroformate (32.75 ml
(0.25 mol) was added slowly, the mixture stirred for 0.5 h, and the precipitate was filtered off. In another
flask, N,O-dimethylhydroxylamine hydrochloride (24.38 g, 0.25 mol) was suspended in CH2Cl2 (100 ml),
Et3N (40 ml, 0.5 mol) was added, and the formed Et3N · HCl was filtered off. The soln. of the amine was
added dropwise to the soln. of the mixed anhydride at ꢀ 108, and the mixture was stirred until no amine
was left (TLC). The mixture was washed with 5% aq. Na2CO3 (3 ꢂ 100 ml) and brine (100 ml), and the
org. phase was dried (MgSO4). The crude product was distilled (bulb-to-bulb) to give 16 (31.87 g, 75%).
Colorless oil. IR (film): 2936m, 1658s, 1586s, 1567s, 1439s, 1415s, 1384s, 1288m, 1226m, 1150m, 1073m,
1045m, 995s, 883w, 805m, 750s, 709m. 1H-NMR: 8.62 (d, J ¼ 4.8, 1 arom. H); 7.85 – 7.75 (m, 1 arom. H);
7.65 (br. s, 1 arom. H); 7.40 – 7.30 (m, 1 arom. H); 3.75 (br. s, MeO); 3.41 (br. s, MeN). 13C-NMR: 153.0 (s,
C(2) (Py)); 148.3 (d, C(6) (Py)); 136.6 (d, C(4) (Py)); 124.7 (d, C(5) (Py)); 123.1 (d, C(3) (Py)); 61.3 (q,
MeO); 33.7 (br. q, MeN). CI-MS: 167 (100, [M þ 1]þ), 135 (20).
3-(1,3-Dioxolan-2-yl)-1-(pyridin-2-yl)propan-1-one (11). A soln. of 16 (16.6 g, 0.10 mol) in dry THF
(120 ml) was cooled to ꢀ 58, and 1.5 equiv. of the Grignard reagent 13 were added dropwise. After
complete addition, the mixture was stirred for 2 h at 08 and then hydrolyzed by addition of 3% HCl in
EtOH (100 ml) at 08. The mixture was poured into a mixture of brine and Et2O/CH2Cl2 (1:1), the org.
phase was separated and dried (MgSO4), and the solvent was evaporated to give 11 (16.35 g, 79%).
3.2. Alkylation of 11 to 2-Alkyl-3-(1,3-dioxolan-2-yl)-1-(pyridin-2-yl)propan-1-ones 17. 2-Benzyl-3-
(1,3-dioxolan-2-yl)-1-(pyridin-2-yl)propan-1-one (17a). A soln. of LDA (37 ml, 1.5m, 56 mmol) in dry
THF (150 ml) was cooled to ꢀ 788, and a mixture of 11 (4.87 g, 23.5 mmol), dissolved in 1,3-

750
Helvetica Chimica Acta – Vol. 95 (2012)
dimethyltetrahydropyrimidin-2(1H)-one (DMPU; 48.7 ml) was added, keeping the temp. below ꢀ 558.
The mixture was stirred for 2 – 3 h, and a soln. of BnBr (3 ml, 17.8 mmol) in THF (40 ml) was added. The
mixture was allowed to reach r.t. slowly and was stirred for 40 h. Then, H2O (10 ml) was added, and the
mixture was poured into ice water, extracted with Et2O (3 ꢂ 100 ml), dried (MgSO4), and evaporated.
The crude product was separated by CC (hexane/AcOEt 4 :1) to afford 17a (4.4 g, 64%). Brownish oil.
IR (film): 3055w, 3021w, 2920m, 2880m, 1690s, 1599w, 1580m, 1563w, 1491w, 1450m, 1432m, 1366m,
1
1227m, 1135s, 1024m, 992s, 975s, 943m, 877w, 850w, 793m, 746s, 698s, 616s. H-NMR: 8.65 (d, J ¼ 4.7,
HꢀC(6) (Py)); 8.00 (d, J ¼ 7.6, HꢀC(3) (Py)); 7.76 (td, J ¼ 7.6, 1.5, HꢀC(4) (Py)); 7.35 (ddd, J ¼ 7.4, 4.5,
1.2, HꢀC(5) (Py)); 7.30 – 7.00 (m, 5 arom. H); 4.87 (t, J ¼ 4.3, OCHO); 4.75 – 4.60 (m, HꢀC(2)); 3.90 –
3.51 (m, OCH2CH2O); 3.10 (dd, J ¼ 13.6, 6.6, 1 H, PhCH2); 2.75 (dd, J ¼ 13.6, 8.2, 1 H, PhCH2); 2.35
(ddd, J ¼ 14.2, 9.8, 4.4, 1 HꢀC(3)); 1.90 (dt, J ¼ 14.0, 3.9, 1 HꢀC(3)). 13C-NMR: 203.7 (s, C¼O); 153.3 (s,
C(2) (Py)); 148.8 (d, C(6) (Py)); 139.3 (s, C(1) (Ph)); 136.7 (d, C(4) (Py)); 129.2, 128.2 (2d, 4 arom. CH);
126.7 (d, C(5) (Py)); 126.1 (d, 1 arom. CH); 122.3 (d, C(3) (Py)); 103.0 (d, OCHO); 64.8, 64.6 (2t,
OCH2CH2O); 40.9 (d, C(2)); 38.4 (t, PhCH2); 34.9 (t, C(3)). CI-MS: 299 (15), 298 (100, [M þ 1]þ). Anal.
calc. for C18H19NO3 (297.34): C 72.71, H 6.44, N 4.71; found: C 72.68, H 6.59, N 4.88.
3-(1,3-Dioxolan-2-yl)-2-methyl-1-(pyridin-2-yl)propan-1-one (17b). As described for 17a: LDA
(56 ml, 2m, 112 mmol) in THF (150 ml), 11 (9.74 g, 47 mmol) in DMPU (97.4 ml), MeI (24 ml,
400 mmol) in THF (60 ml); 20 h. Yield: 5.70 g (55%). Brownish oil. IR (film): 3054w, 2969m, 2880m,
1697s, 1582m, 1568m, 1459m, 1435m, 1353m, 1266m, 1228m, 1143s, 1029s, 984s, 809m, 748m, 701m, 664w.
1H-NMR: 8.69 (d, J ¼ 4.2, HꢀC(6) (Py)); 8.05 (d, J ¼ 7.5, HꢀC(3) (Py)); 7.83 (td, J ¼ 7.6, 1.5, HꢀC(4)
(Py)); 7.45 (ddd, J ¼ 7.6, 4.5, 1.3, HꢀC(5) (Py)); 4.95 (t, J ¼ 4.9, OCHO); 4.40 – 4.30 (m, HꢀC(2)); 4.00 –
3.70 (m, OCH2CH2O); 2.36 (ddd, J ¼ 14.0, 9.4, 4.6, 1 HꢀC(3)); 1.96 (dt, J ¼ 14.0, 4.6, 1 HꢀC(3)); 1.24 (d,
J ¼ 6.9, Me). 13C-NMR: 204.5 (s, C¼O); 152.9 (s, C(2) (Py)); 148.8 (d, C(6) (Py)); 136.7 (d, C(4) (Py));
126.7 (d, C(5) (Py)); 122.3 (d, C(3) (Py)); 103.0 (d, OCHO); 64.7, 64.6 (2t, OCH2CH2O); 36.9 (t, C(3));
34.3 (d, C(2)); 17.8 (q, Me). CI-MS: 223 (12), 222 (100, [M þ 1]þ), 208 (5). Anal. calc. for C12H15NO3
(221.26): C 65.14, H 6.83; found: C 65.46, H 6.83.
2-[(1,3-Dioxolan-2-yl)methyl]-1-(pyridin-2-yl)pent-4-en-1-one (17c). As described for 17a: LDA
(28 ml, 2m, 56 mmol) in THF (100 ml), 11 (4.87 g, 23.5 mmol) in DMPU (48.7 ml), allyl bromide (10 ml,
100 mmol) in THF (40 ml); 25 h. Yield: 3.71 g (64%). Brown oil. IR (film): 2943m, 1668s, 1495s, 1446s,
1375s, 1285s, 1214m, 1132s, 1084m, 995m, 759m, 665w. 1H-NMR: 8.69 (d, J ¼ 3.7, HꢀC(6) (Py)); 8.04 (d,
J ¼ 7.2, HꢀC(3) (Py)); 7.82 (td, J ¼ 7.6, 1.5, HꢀC(4) (Py)); 7.45 (ddd, J ¼ 7.5, 4.5, 1.3, HꢀC(5) (Py)); 5.83 –
5.60 (m, CH2¼CH); 5.04, 4.99 (2d, J ¼ 1.5, CH2¼CH); 4.92 (t, J ¼ 4.4, OCHO); 4.50 – 4.40 (m, HꢀC(2));
3.90 – 3.60 (m, OCH2CH2O); 2.57 – 2.47 (m, 1 H, CH2¼CHꢀCH2); 2.40 – 2.16 (m, 1 H, CH2¼CHꢀCH2),
1 HꢀC(3)); 1.94 (dt, J ¼ 14.0, 4.0, 1 HꢀC(3)). 13C-NMR: 203.7 (s, C¼O); 153.4 (s, C(2) (Py)); 148.8 (d,
C(6) (Py)); 136.8 (d, C(4) (Py)); 135.5 (d, CH2¼CH); 126.8 (d, C(5) (Py)); 122.3 (d, C(3) (Py)); 116.9 (t,
CH2¼CH); 103.0 (d, OCHO); 64.9, 64.7 (2t, OCH2CH2O); 38.7 (d, C(2)); 36.8 (t, CH2¼CHꢀCH2); 35.0
(t, C(3)). CI-MS: 249 (59), 248 (100, [M þ 1]þ), 208 (22), 129 (23). Anal. calc. for C14H17NO3 (247.29): C
68.00, H 6.93, N 5.66; found: C 68.29, H 7.06, N 5.73.
2-[(1,3-Dioxolan-2-yl)methyl]-3-methyl-1-(pyridin-2-yl)butan-1-one (17d). As described for 17a:
LDA (28 ml, 2m, 56 mmol) in THF (100 ml), 11 (4.87 g, 23.5 mmol) in DMPU (48.7 ml), i-PrI (15 ml,
150 mmol) in THF (40 ml); 42 h. Yield: 1.04 g (18%). Brownish oil. IR (Film): 3054w, 2962s, 2876s,
1732m, 1693s, 1582s, 1568m, 1465s, 1435s, 1388s, 1371s, 1223s, 1140s, 1045s, 994s, 979s, 871m, 789m, 694m,
676m. 1H-NMR: 8.69 (d, J ¼ 4.4, HꢀC(6) (Py)); 8.06 (d, J ¼ 7.7, HꢀC(3) (Py)); 7.82 (td, J ¼ 7.6, 1.5,
HꢀC(4) (Py)); 7.42 (ddd, J ¼ 7.5, 4.5, 1.3, HꢀC(5) (Py)); 4.88 (t, J ¼ 4.1, OCHO); 4.28 – 4.20 (m, HꢀC(2));
3.70 – 3.50 (m, OCH2CH2O); 2.40 (ddd, J ¼ 13.9, 11.3, 4.0, 1 HꢀC(3)); 2.04 (sept., J ¼ 6.7, Me2CH); 1.90
(dt, J ¼ 13.8, 3.8, 1 HꢀC(3)); 0.95, 0.89 (2d, J ¼ 6.8, Me2CH). 13C-NMR: 204.4 (s, C¼O); 154.1 (s, C(2)
(Py)); 148.8 (d, C(6) (Py)); 136.8 (d, C(4) (Py)); 126.5 (d, C(5) (Py)); 122.2 (d, C(3) (Py)); 103.4 (d,
OCHO); 64.9, 64.7 (2t, OCH2CH2O); 44.3 (d, C(2)); 32.4 (t, C(3)); 30.5 (d, Me2CH); 20.9, 19.3 (2q,
Me2CH). CI-MS: 251 (19), 250 (100, [M þ 1]þ). Anal. calc. for C14H19NO3 (249.31): C 67.45, H 7.68, N
5.62; found: C 67.81, H 7.60, N 5.49.
2-[(1,3-Dioxolan-2-yl)methyl]-1-(pyridin-2-yl)pent-4-yn-1-one (17e). As described for 17a: LDA
(12 ml, 2m, 24 mmol) in THF (100 ml), 11 (2.0 g, 10 mmol) in DMPU (20 ml), propargyl bromide (7.4 ml,
11.4 mmol) in THF (25 ml); 20 h. Yield: 1.50 g (64%). Brown oil. IR (Film): 3280m, 3054w, 2887m,

Helvetica Chimica Acta – Vol. 95 (2012)
751
2117w, 1697s, 1583s, 1568m, 1465m, 1436s, 1368s, 1269m, 1221m, 1140s, 1025s, 995s, 981s, 945m, 803m,
746m. 1H-NMR: 8.68 (d, J ¼ 4.8, HꢀC(6) (Py)); 8.06 (d, J ¼ 7.8, HꢀC(3) (Py)); 7.84 (td, J ¼ 7.7, 1.8,
HꢀC(4) (Py)); 7.46 (ddd, J ¼ 7.5, 4.8, 1.3, HꢀC(5) (Py)); 4.97 (t, J ¼ 4.2, OCHO); 4.51 – 4.43 (m,
HꢀC(2)); 3.90 – 3.65 (m, OCH2CH2O); 2.70 – 2.58 (m, CHꢁCꢀCH2); 2.41 (ddd, J ¼ 14.3, 8.9, 4.3,
1 HꢀC(3)); 2.14 (dt, J ¼ 14.3, 4.5, 1 HꢀC(3)); 1.95 (t, J ¼ 2.7, CHꢁ). 13C-NMR: 201.8 (s, C¼O); 152.8 (s,
C(2) (Py)); 148.7 (d, C(6) (Py)); 136.8 (d, C(4) Py); 126.8 (d, C(5) (Py)); 122.3 (d, C(3) (Py)); 102.7 (d,
OCHO); 81.5 (s, CHꢁC); 70.0 (d, CHꢁC); 64.8, 64.5 (2t, OCH2CH2O); 38.7 (d, C(2)); 33.9 (t, C(3));
21.2 (t, CHꢁCꢀCH2). CI-MS: 247 (14), 246 (100, [M þ 1]þ), 208 (7), 168 (6), 140 (20), 136 (7). Anal.
calc. for C14H15NO3 (245.28): C 68.56, H 6.16, N 5.71; found: C 68.33, H 6.16, N 5.52.
3.3. Cyclization of 17 to 2-Alkylquinolizinium-1-olates 9. 2-Benzylquinolizinium-1-olate (9a). A soln.
of 17a (4.40 g, 14.8 mmol) in glacial AcOH (130 ml) was heated to reflux for 12 h. The excess AcOH was
removed by azeotropic distillation with EtOH, the residue was purified by CC (CH2Cl2/MeOH 12 :1),
and the product was dried (h.v., 808) to give 9a (3.01 g, 87%). Yellow powder. Recrystallization from
EtOH/Et2O gave yellow crystals. M.p.159 – 1608. UV (MeOH): 393 (3.65). IR (CHCl3): 2960m, 1551s,
1512m, 1477s, 1462s, 1420w, 1356w, 1331m, 1310w, 1260w, 1187w, 1160w, 1136w, 1097w, 1026w, 698w, 659w.
1H-NMR: 8.73 (d, J ¼ 8.7, 1 arom. H); 8.22 (d, J ¼ 6.8, 1 arom. H); 7.54 (d, J ¼ 6.3, 1 arom. H); 7.40 – 7.16
(m, 7 arom. H); 7.12 (d, J ¼ 6.3, 1 arom. H); 4.17 (s, PhCH2). 13C-NMR: 164.1 (s, C(1)); 140.2, 138.1, 134.5
(3s, C(2), C(9a), C(1) Ph); 131.8, 129.4, 128.5, 126.2, 126.1, 125.5, 125.4, 121.4, 114.3 (9d, C(3) – C(9),
5 CH Ph); 36.1 (t, PhCH2). CI-MS: 237 (19), 236 (100, [M þ 1]þ). Anal. calc. for C16H13NO (235.27): C
81.68, H 5.57, N 5.59; found: C 81.35, H 5.51, N 5.81.
Suitable crystals of 9a for the X-ray crystal-structure determination were obtained by crystallization
from THF/hexane.
2-Methylquinolizinium-1-olate (9b). As described for 9a: 17b (5.70 g, 25.7 mmol) in glacial AcOH
(140 ml); 10 h. Yield: 3.54 g (86%). Yellow crystals. M.p. 149 – 1508 (EtOH/Et2O). UV (MeOH): 361
(3.86). IR (CHCl3): 2966w, 2476w, 1763w, 1601w, 1555s, 1516m, 1478s, 1464s, 1417m, 1376m, 1349m,
1322s, 1269m, 1160m, 1141w, 1099w, 1050w, 1026w, 932w, 881w, 658m. 1H-NMR: 8.69 (d, J ¼ 8.7, 1 arom.
H); 8.13 (d, J ¼ 6.8, 1 arom. H); 7.48 (d, J ¼ 6.1, 1 arom. H); 7.40 – 7.20 (m, 3 arom. H); 2.39 (s, Me).
13C-NMR: 165.4 (s, C(1)); 132.1, 131.4 (2s, C(2), C(9a)); 126.4, 125.6, 125.4, 121.1, 113.4 (5d, C(3) – C(9));
17.2 (q, Me). ESI-MS: 181 (20), 160 (100, [M þ 1]þ).
2-(Prop-1-en-1-yl)quinolizinium-1-olate (9c). As described for 9a: 17c (4.80 g, 19.4 mmol) in glacial
AcOH (140 ml); 12 h. Yield: 2.50 g (69%). Yellow crystals. M.p. 129 – 1308 (EtOH/Et2O). UV (MeOH):
416 (4.05). IR (CHCl3): 2964m, 1760w, 1549s, 1409m, 1470s, 1456s, 1422m, 1358m, 1328s, 1261s, 1139m,
1099m, 1026m, 813m, 658m. 1H-NMR: 8.68 (d, J ¼ 8.7, 1 arom. H); 8.18 (d, J ¼ 6.8, 1 arom. H); 7.47 (d,
J ¼ 6.5, 1 arom. H); 7.40 – 7.15 (m, 3 arom. H); 6.95 – 6.73 (m, CH¼CH); 1.94 (d, J ¼ 5.4, Me). 13C-NMR:
163.4 (s, C(1)); 139.1, 128.3 (2s, C(2), C(9a)); 132.0, 128.7, 126.6, 126.3, 125.4, 122.0, 120.9, 114.0 (8d,
C(3) – C(9), CH¼CH); 19.2 (q, Me). CI-MS: 186 (100, [M þ 1]þ), 170 (7).
2-(1-Methylethyl)quinolizinium-1-olate (9d). As described for 9a: 17d (1.0 g, 4.0 mmol) in glacial
AcOH (75 ml); 12 h. Yield: 0.52 g (70%). Yellow crystals. M.p. 139 – 1408 (EtOH/Et2O). IR (CHCl3):
2965m, 2872m, 2479w, 2361w, 1764s, 1639m, 1548s, 1512m, 1457s, 1421s, 1368s, 1337s, 1308s, 1288m, 1262s,
1164s, 1099s, 1014s, 924m, 894m, 867m, 806s, 658m, 629m. 1H-NMR: 8.75 (d, J ¼ 8.7, 1 arom. H); 8.11 (d,
J ¼ 6.8, 1 arom. H); 7.51 (d, J ¼ 8.7, 1 arom. H); 7.4 – 7.3 (m, 2 arom. H); 7.25 – 7.20 (m, 1 arom. H); 3.68
(sept., J ¼ 6.9, Me2CH); 1.27 (d, J ¼ 6.9, Me2CH). 13C-NMR: 162.8 (s, C(1)); 141.7, 137.5 (2s, C(2), C(9a));
131.9, 126.3, 125.1, 124.3, 121.1, 115.5 (6d, C(3) – C(9)); 26.7 (d, Me2CH); 21.7 (q, Me2CH). CI-MS: 189
(13), 188 (100, [M þ 1]þ).
2-[(1,3-Dioxolan-2-yl)methyl]-4-methylquinolizinium-1-olate (9e). As described for 9a: 17e (1.5 g,
6.1 mmol) in glacial AcOH (80 ml), 2.5 h. Yield: 0.30 g (21%). Yellow powder. IR (CHCl3): 2963m,
1691w, 1612w, 1551s, 1508w, 1476m, 1448m, 1415m, 1327w, 1307w, 1261s, 1099s, 1013s, 806s, 658w.
1H-NMR: 8.83 – 8.79 (m, 1 arom. H); 8.21 – 8.18 (m, 1 arom. H); 7.50 – 7.42 (m, 2 arom. H); 7.41 (s,
HꢀC(3)); 5.31 (t, J ¼ 5.2, OCHO); 4.10 – 3.70 (m, OCH2CH2O); 3.18 (d, J ¼ 5.2, CH2); 2.63 (s, Me).
13C-NMR: 163.6 (s, C(1)); 138.3, 129.1 (2s, C(2), C(9a)); 128.8, 127.5, 125.6, 125.3, 121.9 (5d, C(3), C(6) –
C(9)); 120.1 (s, C(4)); 102.4 (d, OCHO); 64.7, 64.5 (2t, OCH2CH2O); 35.1 (t, CH2); 19.3 (q, Me). CI-MS:
278 (9), 262 (38, [M þ NH3]þ), 247 (14), 246 (100, [M þ 1]þ).

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Helvetica Chimica Acta – Vol. 95 (2012)
Quinolizinium-1-olate (9f) [11b]. As described for 9a: 11 (1.0 g, 4.8 mmol) in glacial AcOH (75 ml);
40 h. Yield: 70 mg (10%). Brownish powder. M.p. 183 – 1848. IR (CHCl3): 2924m, 2852m, 1568s, 1500m,
1
1471m, 1448m, 1453m, 1352w, 1310w, 1162w, 899w, 700w, 658w. H-NMR: 8.69 (d, J ¼ 8.6, 1 arom. H);
8.14 (d, J ¼ 6.8, 1 arom. H); 7.39 – 7.44 (m, 2 arom. H); 7.29 – 7.33 (m, 2 arom. H); 6.96 (d, J ¼ 8.7, 1 arom.
H). 13C-NMR: 163.9 (s, C(1)); 136.9 (s, C(9a)); 133.0, 128.1, 125.7, 124.4, 122.2, 118.9, 116.3 (7d, C(2) –
C(9)). CI-MS: 147 (8), 146 (100, [M þ 1]þ).
4. [2 þ 3] Cycloadditions of 9 with Acetylenes. General Procedures. General Procedure 1 (GP 1). To a
soln. of 1 equiv. of 9 in abs. THF (10 ml) under N2, the respective acetylene derivative 18 (2 equiv.) was
added, and the mixture was stirred at r.t., until 9 was consumed (TLC). The crude products were purified
by CC (hexane/AcOEt 4 :1 or 2 :1) and, if necessary, followed by prep. TLC (hexane/AcOEt 1:1).
General Procedure 2 (GP 2). In toluene (10 ml) under N2 , 1 equiv. of 9 was suspended
(sonification), and the respective acetylene 18 (2 equiv.) was added at r.t. Then, the mixture was heated
to reflux, until 9 was consumed. The crude products were purified by CC (hexane/AcOEt 4 :1 or 2 :1)
and, if necessary, followed by prep. TLC (hexane/AcOEt 1:1).
General Procedure 3 (GP 3). A mixture of 9 (1 equiv.), 18 (2 equiv.), and toluene (3 – 5 ml) in an
evacuated and sealed tube was heated to 1408 for 50 – 60 h. The crude products were purified by CC
(hexane/AcOEt 4 :1 or 2 :1) and, if necessary, followed by prep. TLC (hexane/AcOEt 1:1).
4-Benzyl-1,2-bis(ethoxycarbonyl)-8b-azaacenaphthylenium-5-olate (¼1,2-Bis(ethoxycarbonyl)-4-
(phenylmethyl)pyrrolo[2,1,5-de]quinolizinium-5-olate; 19a). According to GP 1: 9a (120 mg, 0.51 mmol)
and diethyl acetylenedicarboxylate (18a; 176 mg, 1.03 mmol). Yield: 76 mg (36%). Orange oil. IR
(CHCl3): 3001m, 2925m, 2854w, 1725s, 1710s, 1633m, 1582s, 1498m, 1474s, 1408m, 1383m, 1304s, 1273s,
1
1239s, 1215s, 1182m, 1143m, 1082s, 1051w, 1022m, 856w, 810w, 699w. H-NMR: 8.76 (d, J ¼ 8.6, HꢀC(6/
8)); 8.55 (d, J ¼ 7.6, HꢀC(8/6)); 7.93 (s, HꢀC(3)); 7.86 (t, J ¼ 8.1, HꢀC(7)); 7.16 – 7.28 (m, 5 arom. H);
4.43 – 4.34 (m, 2 MeCH2O); 4.05 (s, PhCH2); 1.37, 1.27 (2t, J ¼ 7.1, 2 MeCH2O). 13C-NMR: 175.2 (s, C(5));
163.5, 163.0 (2s, 2 EtOCO); 139.0, 138.6, 136.0, 132.0 (4s, C(4), C(5a), C(8a), C(1) Ph); 129.4, 128.7,
127.4, 126.6, 126.5, 124.6, 119.2 (7d, C(3), C(6), C(7), C(8), 5 CH (Ph)); 124.9, 119.8, 111.0 (3s, C(1),
C(2), C(2a)); 62.0, 61.1 (2t, 2 MeCH2O); 36.2 (t, PhCH2); 14.3, 14.1 (2q, 2 MeCH2O). CI-MS: 405 (24),
404 (100, [M þ 1]þ), 298 (21).
4-Benzyl-1,2-bis(methoxycarbonyl)-8b-azaacenaphthylenium-5-olate (¼1,2-Bis(methoxycarbonyl)-
4-(phenylmethyl)pyrrolo[2,1,5-de]quinolizinium-5-olate; 19b). According to GP 1: 9a (120 mg,
0.51 mmol) and 18b (150 mg, 1.06 mmol). Yield: 96 mg (40%). Orange powder. M.p. 169 – 1708. UV
(MeOH): 473 (4.01). IR (CHCl3): 3000w, 2954w, 1713s, 1636w, 1584s, 1499m, 1473m, 1442m, 1396w,
1307s, 1274s, 1240s, 1216s, 1177m, 1143m, 1087s, 1052w, 1000w, 940, 809w, 700w. 1H-NMR: 8.79 (d, J ¼ 8.3,
HꢀC(6/8)); 8.59 (d, J ¼ 7.5, HꢀC(8/6)); 8.05 (s, HꢀC(3)); 7.91 (t, J ¼ 8.2, HꢀC(7)); 7.37 – 7.23 (m, 5 arom.
H); 4.11 (s, PhCH2); 4.00 (s, 2 MeO). 13C-NMR: 175.2 (s, C(5)); 164.0, 163.4 (2s, 2 MeOCO); 139.1, 138.7,
135.9, 132.1 (4s, C(4), C(5a), C(8a), C(1) Ph); 129.3, 128.6, 127.4, 126.5, 124.5, 119.9 (6d, C(3), C(6),
C(7), C(8), 5 CH (Ph)); 126.6, 124.4, 110.6 (3s, C(1), C(2), C(2a)); 52.6, 52.2 (2q, 2 MeO); 36.3 (t,
PhCH2). CI-MS: 377 (24), 376 (100, [M þ 1]þ), 362 (17), 288 (30). Anal. calc. for C22H17NO5 (375.38): C
70.39, H 4.56, N 3.73; found: C 70.07, H 4.61, N 3.59.
1,2-Bis(ethoxycarbonyl)-4-methyl-8b-azaacenaphthylenium-5-olate (¼1,2-Bis(ethoxycarbonyl)-4-
methylpyrrolo[2,1,5-de]quinolizinium-5-olate; 19c). According to GP 1: 9b (160 mg, 1.0 mmol) and
18a (349 mg, 2.05 mmol). Yield: 96 mg (29%). Orange oil. IR (CHCl3): 3026m, 2986m, 1727s, 1638m,
1585m, 1501m, 1475m, 1444m, 1410m, 1377m, 1277s, 1241s, 1210w, 1191m, 1194m, 1089s, 1022s, 860w,
813w, 674m. 1H-NMR: 8.77 (dd, J ¼ 8.6, 0.9, HꢀC(6/8)); 8.55 (dd, J ¼ 7.7, 1.0, HꢀC(8/6)); 8.15 (d-like, J ¼
0.9, HꢀC(3)); 7.86 (t, J ¼ 7.9, HꢀC(7)); 4.47, 4.41 (2q, J ¼ 7.2, 2 MeCH2O); 2.33 (d, J ¼ 0.9, Me); 1.41 – 1.38
(2t, J ¼ 7.2, 2 MeCH2O). 13C-NMR: 175.8 (s, C(5)); 163.9, 163.0 (2s, 2 EtOCO); 135.9, 135.7, 131.4 (3s,
C(4), C(5a), C(8a)); 127.3, 126.3, 124.4, 119.6 (4d, C(3), C(6), C(7), C(8)); 123.2, 118.5, 110.6 (3s, C(1),
C(2), C(2a)); 62.1, 61.1 (2t, 2 MeCH2O); 17.0 (q, Me); 14.4, 14.3 (2q, 2 MeCH2O). EI-MS: 328 (19), 327
(100, Mþ), 299 (9), 282 (12), 255 (10), 254 (22), 227 (14), 182 (12).
4-Methyl-1,2-bis(methoxycarbonyl)-8b-azaacenaphthylenium-5-olate (¼1,2-Bis(methoxycarbonyl)-
4-methylpyrrolo[2,1,5-de]quinolizinium-5-olate; 19d).According to GP 1: 9b (164 mg, 1.03 mmol) and
18b (286 mg, 2.00 mmol). Yield: 117 mg (39%). Orange powder. M.p. 148 – 1498. IR (CHCl3): 3030w,
3007w, 2955m, 1734s, 1636s, 1586s, 1499m, 1444m, 1396w, 1377w, 1300s, 1278s, 1243s, 1198m, 1179m,

Helvetica Chimica Acta – Vol. 95 (2012)
753
1162m, 1143m, 1091m, 1021w, 1003w, 943w, 832w, 667m. 1H-NMR: 8.60 (dd, J ¼ 8.6, 0.9, HꢀC(6/8)); 8.38
(dd, J ¼ 7.5, 1.0, HꢀC(8/6)); 8.06 (d-like, J ¼ 0.9, HꢀC(3)); 7.78 (t, J ¼ 7.7, HꢀC(7)); 4.06, 3.99 (2s, 2 MeO);
2.31 (d, J ¼ 0.7, Me). 13C-NMR: 175.5 (s, C(5)); 163.9, 163.2 (2s, 2 MeOCO); 135.9, 135.3, 131.1 (3s, C(4),
C(5a), C(8a)); 127.1, 126.3, 124.2, 119.6 (4d, C(3), C(6), C(7), C(8)); 123.5, 119.6, 110.1 (3s, C(1), C(2),
C(2a)); 52.9, 52.4 (2q, 2 MeO); 16.9 (q, Me). EI-MS: 300 (17), 299 (100, Mþ), 285 (13), 284 (26), 268
(40), 254 (25), 253 (16), 252 (22), 238 (13), 182 (15), 181 (10), 167 (50), 113 (9), 43 (19). Anal. calc. for
C16H13NO5 (299.28): C 64.21, H 4.38, N 4.68; found: C 63.97, H 4.29, N 4.43.
1,2-Bis(methoxycarbonyl)-4-(prop-1-en-1-yl)-8b-azaacenaphthylenium-5-olate (¼1,2-Bis(methoxy-
carbonyl)-4-(prop-1-en-1-yl)pyrrolo[2,1,5-de]quinolizinium-5-olate; 19e). According to GP 1: 9c
(186 mg, 1.0 mmol) and 18b (279 mg, 1.96 mmol). Yield: 108 mg (33%). Orange oil. IR (CHCl3):
1
3008m, 2956m, 1730s, 1640m, 1591s, 1501m, 1476m, 1437m, 1396m, 1084m. H-NMR: 8.72 (dd, J ¼ 8.6,
1.0, HꢀC(6/8)); 8.55 (dd, J ¼ 7.6, 1.1, HꢀC(8/6)); 8.20 (s, HꢀC(3)); 7.87 (t, J ¼ 7.6, HꢀC(7)); 6.85 – 6.70 (m,
CH¼CH); 4.08, 4.00 (2s, 2 MeO); 1.98 (d, J ¼ 5.3, Me). 13C-NMR: 174.2 (s, C(5)); 164.2, 163.3 (2s,
2 MeOCO); 135.9, 133.7, 132.5 (3s, C(4), C(5a), C(8a)); 131.1, 126.6, 125.0, 124.5, 123.5, 120.1 (6d, C(3),
C(6), C(7), C(8), CH¼CH); 124.3, 119.6, 110.1 (3s, C(1), C(2), C(2a)); 52.9, 52.1 (2q, 2 MeO); 16.9 (q,
Me). CI-MS: 327 (17), 326 (100, [M þ 1]þ).
1,2-Bis(methoxycarbonyl)-4-(1-methylethyl)-8b-azaacenaphthylenium-5-olate (¼1,2-Bis(methoxy-
carbonyl)-4-(1-methylethyl)pyrrolo[2,1,5-de]quinolizinium-5-olate; 19f). According to GP 1: 9d
(97 mg, 0.51 mmol) and 18b (158 mg, 1.11 mmol). Yield: 68 mg (41%). Orange oil. IR (CHCl3):
2994m, 2956m, 2872m, 1712s, 1637s, 1590s, 1495m, 1465m, 1397m, 1368m, 1354m, 1317s, 1148s, 1107m,
999m, 978m, 859m. 1H-NMR: 8.79 (dd, J ¼ 8.6, 1.0, HꢀC(6/8)); 8.59 (dd, J ¼ 7.6, 1.1, HꢀC(8/6)); 8.13 (s,
HꢀC(3)); 7.91 (t, J ¼ 7.7, HꢀC(7)); 4.09, 4.02 (2s, 2 MeO); 3.52 (sept., J ¼ 6.8, Me2CH); 1.32 (d, J ¼ 6.9,
Me2CH). 13C-NMR: 175.2 (s, C(5)); 164.5, 163.5 (2s, 2 MeOCO); 145.9, 135.7, 132.0 (3s, C(4), C(5a),
C(8a)); 126.4, 124.4, 124.1, 119.8 (4d, C(3), C(6), C(7), C(8)); 120.0, 110.1 (2s, C(1), C(2), C(2a)); 53.0,
52.1 (2q, 2 MeO); 27.5 (d, Me2CH); 21.6 (q, Me2CH). CI-MS: 330 (5), 329 (19), 328 (100, [M þ 1]þ), 314
(17), 288 (9), 232 (5). Anal. calc. for C18H17NO5 (327.34): C 66.05, H 5.23, N 4.28; found: C 65.74, H 5.18,
N 4.46.
1,2-Bis(methoxycarbonyl)-8b-azaacenaphthylenium-5-olate (¼1,2-Bis(methoxycarbonyl)pyrro-
lo[2,1,5-de]quinolizinium-5-olate; 19g). According to GP 1: 9f (70 mg, 0.48 mmol) and 18b (76 mg,
0.55 mmol). Yield: 24 mg (19%). Orange oil. IR (KBr): 3072w, 2953m, 2924m, 2853m, 1719s, 1649m,
1606m, 1501m, 1468m, 1439m, 1395m, 1353m, 1344m, 1316m, 1277s, 1247s, 1149m, 1132m, 1096m, 1070m,
995m, 922w, 872w, 841w, 806m, 761w, 725w, 710w. 1H-NMR: 8.85 (d, J ¼ 8.6, HꢀC(6/8)); 8.60 (d, J ¼ 7.6,
HꢀC(8/6)); 8.30 (d, J ¼ 9.9, HꢀC(3)); 7.97 (t, J ¼ 8.1, HꢀC(7)); 7.16 (d, J ¼ 9.9, HꢀC(4)); 4.07, 4.02 (2s,
2 MeO). 13C-NMR: 176.1 (s, C(5)); 163.9, 163.3 (2s, 2 MeOCO); 136.4, 133.3 (2s, C(5a), C(8a)); 130.0,
127.2, 126.2, 125.0, 119.9 (5d, C(3), C(4), C(6), C(7), C(8)); 125.1, 120.2, 111.2 (3s, C(1), C(2), C(2a));
53.0, 52.3 (2q, 2 MeO). CI-MS: 286 (100, [M þ 1]þ).
4-Benzyl-1-(ethoxycarbonyl)-2-(trifluoromethyl)-8b-azaacenaphthylenium-5-olate (¼4-Benzyl-1-
(ethoxycarbonyl)-2-(trifluoromethyl)pyrrolo[2,1,5-de]quinolizinium-5-olate; 19h). According to GP 1:
9a (59 mg, 0.25 mmol) and ethyl 4,4,4-trifluorobut-2-ynoate (18c, 87 mg, 0.51 mmol). Yield: 43 mg (43%).
Orange oil. IR (CHCl3): 3026w, 2962m, 2928m, 1738s, 1639m, 1593s, 1504w, 1475m, 1410m, 1386m,
1
1311m, 1261s, 1236s, 1151m, 1127m, 1085s, 1019m, 809m, 699w. H-NMR: 9.00 (dd, J ¼ 8.7, 0.9, HꢀC(6/
8)); 8.64 (dd, J ¼ 7.5, 1.0, HꢀC(8/6)); 8.14 (s, HꢀC(3)); 7.96 (t, J ¼ 7.7, HꢀC(7)); 7.40 – 7.21 (m, 5 arom. H);
4.49 (q, J ¼ 7.1, MeCH2O); 4.12 (s, PhCH2); 1.47 (t, J ¼ 7.1, MeCH2O). CI-MS: 401 (18), 400 (100, [M þ
1]þ).
4-Benzyl-1-(ethoxycarbonyl)-8b-azaacenaphthylenium-5-olate (¼4-Benzyl-1-(ethoxycarbonyl)pyr-
rolo[2,1,5-de]quinolizinium-5-olate; 19i). According to GP 2: 9a (120 mg, 0.51 mmol) and ethyl prop-
2-ynoate (18d; 101 mg, 1.03 mmol). Yield: 41 mg (24%). Yellow-orange powder. M.p. 140.3 – 1418. IR
(CHCl3): 3000m, 1700s, 1634w, 1577s, 1529m, 1513m, 1492w, 1450m, 1417m, 1384m, 1335w, 1304s, 1237s,
1220s, 1175w, 1149s, 1116m, 1074s, 1028w, 1017w, 960w, 915w, 863w, 810w, 699w, 658w. 1H-NMR: 8.79 (dd,
J ¼ 8.4, 0.9, HꢀC(6/8)); 8.57 (dd, J ¼ 7.7, 0.8, HꢀC(8/6)); 7.87 (t, J ¼ 8.0, HꢀC(7)); 7.84, 7.72 (2s, HꢀC(2),
HꢀC(3)); 7.29 – 7.17 (m, 5 arom. H); 4.39 (q, J ¼ 7.1, MeCH2O); 4.06 (s, PhCH2); 1.38 (t, J ¼ 7.1,
MeCH2O). 13C-NMR: 174.9 (s, C(5)); 163.8 (s, EtOCO); 139.0, 137.6, 136.9, 132.2 (4s, C(4), C(5a),
C(8a), C(1) (Ph)); 129.4, 128.2, 126.4, 125.9, 123.2, 122.2, 118.7 (7d, C(2), C(3), C(6), C(7), C(8), 5 CH

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(Ph)); 120.2, 112.7 (2s, C(1), C(2a)); 60.5 (t, MeCH2O); 36.0 (t, PhCH2); 14.4 (q, MeCH2O). EI-MS: 332
(23), 331 (100, Mþ), 330 (27), 303 (10), 302 (38), 286 (20), 258 (29), 257 (13), 228 (8), 169 (17), 69 (10).
Anal. calc. for C21H17NO3 (331.38): C 76.11, H 5.17, N 4.23; found: C 75.77, H 5.41, N 3.89.
Suitable crystals of 19i for the X-ray crystal-structure determination were obtained by crystallization
from EtOH/Et2O.
4-Benzyl-1-(methoxycarbonyl)-8b-azaacenaphthylenium-5-olate (¼4-Benzyl-1-(methoxycarbonyl)-
pyrrolo[2,1,5-de]quinolizinium-5-olate; 19j). According to GP 2: 9a (120 mg, 0.51 mmol) and methyl
prop-2-ynoate (18e; 97 mg, 1.15 mmol). Yield: 43.5 mg (27%). Yellow-orange powder. M.p. 146.5 –
147.78. IR (CHCl3): 3003m, 2954w, 1709s, 1633w, 1579s, 1531m, 1515s, 1494w, 1453s, 1435s, 1412w,
1391m, 1336m, 1304s, 1241s, 1150s, 1117s, 1080s, 1030w, 994w, 938w, 870w, 810w, 700m, 660w. 1H-NMR:
8.87 (d, J ¼ 8.3, HꢀC(6/8)); 8.64 (d, J ¼ 7.6, HꢀC(8/6)); 7.97 (t, J ¼ 8.2, HꢀC(7)); 7.89, 7.80 (2s, HꢀC(2),
HꢀC(3)); 7.36 – 7.15 (m, 5 arom. H); 4.13 (s, PhCH2); 4.00 (s, MeO). 13C-NMR: 175.2 (s, C(5)); 164.5 (s,
MeOCO); 139.3, 138.0, 137.3, 132.5 (4s, C(4), C(5a), C(8a), C(1) (Ph)); 129.7, 129.0, 128.5, 126.8, 126.3,
123.5, 122.4, 119.0 (8d, C(2), C(3), C(6), C(7), C(8), 5 CH (Ph)); 120.5, 112.6 (2s, C(1), C(2a)); 51.9 (q,
MeO); 36.3 (t, PhCH2). CI-MS: 319 (18), 318 (100, [M þ 1]þ).
4-Benzyl-1-(ethoxycarbonyl)-2-methyl-8b-azaacenaphthylenium-5-olate (¼4-Benzyl-1-(ethoxycar-
bonyl)-2-methylpyrrolo[2,1,5-de]quinolizinium-5-olate; 19k). According to GP 3: 9a (97 mg, 0.41 mmol)
and ethyl but-2-ynoate (18f; 100 mg, 0.43 mmol). Yield: 23 mg (32%). Orange powder. M.p. 134.5 – 1358.
IR (CHCl3): 3007w, 2359w, 1698m, 1573s, 1530w, 1496m, 1480m, 1435w, 1405w, 1384w, 1354w, 1295s,
1261s, 1154m, 1086s, 1046w, 1015w, 810m, 688w. 1H-NMR: 8.79 (dd, J ¼ 8.4, 0.9, HꢀC(6/8)); 8.59 (dd, J ¼
7.7, 1.0, HꢀC(8/6)); 7.90 (t, J ¼ 8.2, HꢀC(7)); 7.88 (s, HꢀC(3)); 7.40 – 7.20 (m, 5 arom. H); 4.48 (q, J ¼ 7.2,
MeCH2O); 4.16 (s, PhCH2); 2.79 (s, Me); 1.49 (t, J ¼ 7.2, MeCH2O). 13C-NMR: 174.6 (s, C(5)); 164.5 (s,
EtOCO); 139.3, 137.4, 136.4, 135.9, 131.9 (5s, C(2), C(4), C(5a), C(8a), C(1) (Ph)); 129.2, 128.6, 128.4,
126.3, 126.0, 122.3, 117.9 (7d, C(3), C(6), C(7), C(8), 5 CH (Ph)); 120.5, 110.3 (2s, C(1), C(2a)); 60.2 (t,
MeCH2O); 36.2 (t, PhCH2); 14.4 (q, MeCH2O); 11.7 (q, Me). CI-MS: 347 (11), 346 (100, [M þ 1]þ).
1-(Ethoxycarbonyl)-4-methyl-2-(trifluoromethyl)-8b-azaacenaphthylenium-5-olate (¼1-(Ethoxycar-
bonyl)-4-methyl-2-(trifluoromethyl)pyrrolo[2,1,5-de]quinolizinium-5-olate; 19l). According to GP 1: 9b
(40 mg, 0.25 mmol) and 18c (85 mg, 0.51 mmol). Yield: 33 mg (41%). Orange powder. IR (CHCl3):
3019m, 1730s, 1640m, 1542s, 1504m, 1474s, 1443m, 1409m, 1378m, 1281s, 1239s, 1199s, 1151s, 1091s,
1
1025m, 899w, 815m, 665w. H-NMR (600 MHz): 8.99 (dd, J ¼ 8.6, 1.1, HꢀC(6/8)); 8.63 (dd, J ¼ 7.5, 1.1,
HꢀC(8/6)); 8.29 (d-like, J ¼ 1.0, HꢀC(3)); 7.96 (t, J ¼ 7.5, HꢀC(7)); 4.50 (q, J ¼ 7.1, 2 MeCH2O); 2.41 (d,
J ¼ 1.1, Me); 1.48 (t, J ¼ 7.1, MeCH2O). 13C-NMR: 175.8 (s, C(5)); 162.3 (s, EtOCO); 147.4 (q, 2J(C,F) ¼
29.5, C(2)); 138.6, 136.5, 131.6 (3s, C(4), C(5a), C(8a)); 127.5, 126.7, 125.1, 120.0 (4d, C(3), C(6), C(7),
C(8)); 125.4 (q, 1J(C,F) ¼ 286.5, CF3); 122.9, 118.4 (2s, C(1), C(2a)); 61.3 (t, MeCH2O); 17.2 (q, Me); 14.1
(q, MeCH2O). 19F-NMR (600 MHz, CDCl3; Cl3CF as reference): ꢀ 55 (s, CF3). CI-MS: 325 (15), 324
(100, [M þ 1]þ), 323 (38).
Suitable crystals of 19l for the X-ray crystal-structure determination were obtained by crystallization
from AcOEt.
1-(Methoxycarbonyl)-4-methyl-8b-azaacenaphthylenium-5-olate (¼1-(Methoxycarbonyl)-4-methyl-
pyrrolo[2,1,5-de]quinolizinium-5-olate; 19m). According to GP 2: 9b (157 mg, 1.0 mmol) and 18e
(173 mg, 2.06 mmol). Yield: 71 mg (29%). Yellow powder. M.p. 137.5 – 138.98. IR (CHCl3): 3022m, 3007s,
2955m, 2927m, 1705s, 1635m, 1582s, 1530s, 1516s, 1488m, 1455s, 1435s, 1419m, 1390s, 1379m, 1343m,
1331m, 1305s, 1244s, 1195m, 1180m, 1150s, 1118s, 1085s, 1050m, 1019m, 972m, 944w, 935w, 904m, 871w,
815m, 609m. 1H-NMR: 8.83 (d, J ¼ 8.4, HꢀC(6/8)); 8.59 (d, J ¼ 7.6, HꢀC(8/6)); 8.02 (s, HꢀC(3)); 7.00 (t,
J ¼ 7.4, HꢀC(7)); 4.01 (s, MeO); 2.39 (s, Me). 13C-NMR: 175.8 (s, C(5)); 164.4 (s, MeOCO); 136.9, 134.6,
131.8 (3s, C(4), C(5a), C(8a)); 128.4, 125.9, 123.1, 121.6, 118.6 (5d, C(2), C(3), C(6), C(7), C(8)); 120.2,
112.1 (2s, C(1), C(2a)); 51.7 (q, MeO); 17.0 (q, Me). CI-MS: 242 (100, [M þ 1]þ). Anal. calc. for
C14H11NO3 (241.25): C 69.70, H 4.60, N 5.81; found: C 69.55, H 4.64, N 5.62.
1-(Ethoxycarbonyl)-2,4-dimethyl-8b-azaacenaphthylenium-5-olate (¼1-(Ethoxycarbonyl)-2,4-dime-
thylpyrrolo[2,1,5-de]quinolizinium-5-olate; 19n). According to GP 3: 9b (80 mg, 0.50 mmol) and 18f
(131 mg, 1.2 mmol). Yield: 38 mg (28%). Orange powder. M.p. 150.6 – 151.88. IR (CHCl3): 3003m, 1703s,
1
1572s, 1530m, 1479m, 1434m, 1383m, 1292s, 1272s, 1239s, 1169m, 1153m, 1090s, 814w, 663w. H-NMR:
8.70 (dd, J ¼ 8.4, 1.0, HꢀC(6/8)); 8.48 (dd, J ¼ 7.7, 1.0, HꢀC(8/6)); 7.99 (d-like, J ¼ 0.9, HꢀC(3)); 7.80 (t,

Helvetica Chimica Acta – Vol. 95 (2012)
755
J ¼ 8.0, HꢀC(7)); 4.41 (q, J ¼ 7.1, MeCH2O); 2.78 (s, MeꢀC(2)); 2.34 (d, J ¼ 0.8, MeꢀC(4)); 1.43 (t, J ¼ 7.1,
MeCH2O). 13C-NMR: 175.5 (s, C(5)); 164.6 (s, EtOCO); 137.3, 135.3, 133.3, 131.4 (4s, C(2), C(4), C(5a),
C(8a)); 126.1, 125.7, 122.1, 117.7 (4d, C(3), C(6), C(7), C(8)); 120.3, 110.1 (2s, C(1), C(2a)); 60.2 (t,
MeCH2O); 17.1 (q, MeꢀC(4)); 14.5 (q, MeCH2O); 11.6 (q, MeꢀC(2)). CI-MS: 271 (26), 270 (100, [M þ
1]þ). Anal. calc. for C16H15NO3 (269.30): C 71.36, H 5.61, N 5.20; found: C 71.19, H 5.32, N 5.27.
1-Acetyl-4-methyl-8b-azaacenaphthylenium-5-olate (¼1-Acetyl-4-methylpyrrolo[2,1,5-de]quinolizi-
nium-5-olate; 19o). According to GP 3: 9b (80 mg, 0.50 mmol) and but-3-yn-2-one (102 mg, 1.5 mmol).
Yield: 37 mg (27%). Orange oil. IR (CHCl3): 3006m, 2954m, 1711w, 1602s, 1579s, 1536m, 1511w, 1386m,
1304m, 1150m, 1153m, 965w. 1H-NMR: 9.05 (dd, J ¼ 8.3, 0.6, HꢀC(6/8)); 8.61 (dd, J ¼ 7.7, 1.0, HꢀC(8/6));
8.02 (br. s, HꢀC(3)); 7.95 (t, J ¼ 8.0, HꢀC(7)); 7.81 (s, HꢀC(2)); 2.69 (s, MeCO); 2.40 (d, J ¼ 0.5, Me).
13C-NMR: 193.5 (s, MeCO); 175.7 (s, C(5)); 136.3, 134.6, 131.5 (3s, C(4), C(5a), C(8a)); 128.3, 126.9,
124.2, 121.0, 118.9 (5d, C(2), C(3), C(6), C(7), C(8)); 120.3, 119.9 (2s, C(1), C(2a)); 16.9 (q, Me). CI-
MS: 296 (9), 227 (15), 226 (100, [M þ 1]þ).
1-(Ethoxycarbonyl)-4-(prop-1-en-1-yl)-2-(trifluoromethyl)-8b-azaacenaphthylenium-5-olate (¼1-
(Ethoxycarbonyl)-4-(prop-1-en-1-yl)-2-(trifluoromethyl)pyrrolo[2,1,5-de]quinolizinium-5-olate; 19p).
According to GP 1: 9c (102 mg, 0.55 mmol) and 18c (224 mg, 1.35 mmol). Yield: 63 mg (33%). Orange
oil. IR (CHCl3): 3011m, 2956m, 1734s, 1640m, 1591s, 1504m, 1476m, 1443m, 1393m, 1238s, 1199s, 1152s,
1081m, 1025m, 899w, 815m, 667w. 1H-NMR: 8.91 (d, J ¼ 8.6, HꢀC(6/8); 8.56 (dd, J ¼ 7.6, 0.9, HꢀC(8/6));
8.27 (s, HꢀC(3)); 7.88 (t, J ¼ 7.7, HꢀC(7)); 6.90 – 6.65 (m, CH¼CH); 4.43 (q, MeCH2O); 1.93 (d, J ¼ 5.5,
Me); 1.41 (t, J ¼ 7.1, MeCH2O). CI-MS: 352 (9), 351 (23), 350 (100, [M þ 1]þ), 276 (7).
1-(Ethoxycarbonyl)-4-(1-methylethyl)-2-(trifluoromethyl)-8b-azaacenaphthylenium-5-olate (¼1-
(Ethoxycarbonyl)-4-(1-methylethyl)-2-(trifluoromethyl)pyrrolo[2,1,5-de]quinolizinium-5-olate; 19q).
According to GP 1: 9d (100 mg, 0.53 mmol) and 18c (171 mg, 1.03 mmol). Yield: 67 mg (36%). IR
(CHCl3): 3011m, 1733s, 1641m, 1547s, 1504m, 1473s, 1453m, 1410m, 1378m, 1282s, 1237s, 1199s, 1161s,
1
1086s, 1023s, 812m, 695m. H-NMR: 8.92 (dd, J ¼ 8.6, 0.9, HꢀC(6/8)); 8.56 (dd, J ¼ 7.5, 1.0, HꢀC(8/6));
8.16 (s, HꢀC(3)); 7.89 (t, J ¼ 7.6, HꢀC(7)); 4.43 (q, J ¼ 7.1, MeCH2O); 3.30 (sept., J ¼ 6.8, Me2CH); 1.22 (t,
J ¼ 7.1, MeCH2O); 1.10 (d, J ¼ 6.8, Me2CH). CI-MS: 353 (24), 352 (100, [M þ 1]þ).
5. Isolation of Side Products, Diethyl 5-Benzyl-6-oxo-1-(pyridin-2-yl)cyclohexa-2,4-diene-1,2-dicar-
boxylate (20a). A suspension of 9a (300 mg, 1.27 mmol) and 18a (607 mg, 3.57 mmol) in toluene (5 ml)
was heated to reflux for 17 min and then stirred at r.t. for 18 h. Evaporation of the solvent and CC
(hexane/AcOEt 3 :1) of the residue gave 19a (234 mg, 45%) and 138 mg of a brown oil. CC of the latter
(CH2Cl2/hexane 3 :1) yielded 20a (42 mg, 8%). Dark yellow oil. UV (EtOH): 326 (3.21). IR (CHCl3):
2984m, 2937w, 1753s, 1714s, 1668s, 1585m, 1496w, 1465m, 1432m, 1371m, 1274s, 1137m, 1099m, 1030m,
999w, 864w, 700w. 1H-NMR: 8.34 (ddd, J ¼ 4.8, 1.7, 0.6, HꢀC(6) (Py)); 7.88 (d, J ¼ 8.2, HꢀC(3) (Py)); 7.63
(td, J ¼ 7.8, 1.9, HꢀC(4) (Py)); 7.42 (d, J ¼ 6.6, HꢀC(5) (Py)); 7.23 – 7.14 (m, 4 arom. H); 7.05 – 7.02 (m, 1
arom. H, HꢀC(3)); 6.74 (dt, J ¼ 6.6, 1.4, HꢀC(4)); 4.24 – 4.13 (m, 2 MeCH2O); 3.64 (s, PhCH2); 1.19, 1.18
(2t, J ¼ 7.1, 2 MeCH2O). 13C-NMR: 194.4 (s, C(6)); 167.4, 164.3 (2s, 2 EtOCO); 155.4 (s, C(2) (Py)); 148.0
(d, C(6) Pyr); 139.6 (s, C(1) (Ph)); 138.1, 137.7 (2s, C(2), C(5)); 136.6 (d, C(4) (Py)); 136.0 (d, CH¼C);
129.0, 128.3 (2d, 4 CH (Ph)); 129.3, 126.3, 125.6, 123.0 (4d, 1 CH (Ph), C(3) (Py), C(5) (Py), CH¼C);
69.0 (s, C(1)); 62.0, 61.0 (2t, 2 MeCH2O); 35.2 (t, PhCH2); 13.9, 13.8 (2q, 2 MeCH2O). CI-MS: 407 (23),
406 (100, [M þ 1]þ).
Dimethyl 5-Benzyl-6-oxo-1-(pyridin-2-yl)cyclohexa-2,4-diene-1,2-dicarboxylate (20b). A suspension
of 9a (300 mg, 1.27 mmol) and 18b (650 mg, 4.57 mmol) in toluene (5 ml) was heated to reflux for 2 h and
then stirred at r.t. for 10 h. Evaporation of the solvent and CC (hexane/AcOEt/CH2Cl2, 3 ꢂ ) of the
residue gave 19b (160 mg, 33%) and 110 mg of a brown oil. CC of the latter (CH2Cl2/hexane 3 :1) yielded
20b (29 mg, 6%). Yellow oil. IR (CHCl3): 2983m, 1754s, 1711s, 1667s, 1582m, 1489w, 1432m, 1368m,
1275s, 1137m, 1099m, 1031m, 995w, 864w, 698w. 1H-NMR: 8.34 (d, J ¼ 4.1, HꢀC(6) (Py)); 7.83 (d, J ¼ 8.0,
HꢀC(3) (Py)); 7.63 (td, J ¼ 7.8, 1.7, HꢀC(4) (Py)); 7.40 (d, J ¼ 6.6, HꢀC(5) (Py)); 7.29 – 7.15 (m, 4 arom.
H); 7.05 – 7.02 (m, 1 arom. H, HꢀC(3)); 6.70 (dt, J ¼ 6.4, 1.4, HꢀC(4)); 3.73 (s, 2 MeO); 3.64 (s, PhCH2).
13C-NMR: 194.5 (s, C(6)); 168.0, 165.0 (2s, 2 MeOCO); 155.2 (s, C(2) (Py)); 148.2 (d, C(6) (Py)); 140.0 (s,
C(1) (Ph)); 137.6 (s, C(2), C(5)); 136.5 (d, C(4) (Py)); 136.3 (d, CH¼C); 129.1, 128.5 (2d, 4 CH (Ph));
129.7, 126.5, 125.7, 123.2 (4d, 1 CH (Ph), C(3) (Py), C(5) (Py), CH¼C); 69.0 (s, C(2)); 53.1, 52.2 (2q,
2 MeO); 35.3 (t, PhCH2). CI-MS: 379 (20), 378 (89, [M þ 1]þ).

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Helvetica Chimica Acta – Vol. 95 (2012)
Methyl 5-Benzyl-6-oxo-1-(pyridin-2-yl)cyclohexa-2,4-diene-1-carboxylate (20c). A mixture of 9a
(242 mg, 1.03 mmol) and 18e (174 mg, 2.07 mmol) in toluene (10 ml) was heated to reflux for 30 min.
Evaporation of the solvent and CC (hexane/AcOEt/CH2Cl2) of the residue gave 19j (74 mg, 23%), 20c
(9 mg, 3%) as a yellow oil, and methyl 3-benzyl-2-hydroxy-6-(pyridin-2-yl)benzoate (21; 3 mg, 1%).
Data of 20c. IR (CHCl3): 3005w, 2956w, 1740s, 1664m, 1645m, 1588m, 1495w, 1467m, 1453m, 1431s,
1396w, 1370m, 1220br, 1175m, 1076w, 1030w, 1017w, 993w, 700w. 1H-NMR: 8.53 (d, J ¼ 3.7, HꢀC(6) (Py));
7.64 (td, J ¼ 7.7, 1.9, HꢀC(4) (Py)); 7.32 – 7.16 (m, 7 arom. H); 6.71 (dd, J ¼ 9.5, 0.9, HꢀC(2) or HꢀC(4));
6.65 (dd, J ¼ 6.6, 1.1, HꢀC(4) or HꢀC(2)); 6.39 (dd, J ¼ 9.5, 6.2, HꢀC(3)); 3.74 (s, MeO); 3.69, 3.61 (2d,
J ¼ 17.2, PhCH2). 13C-NMR: 195.1 (s, C(6)); 169.0 (s, MeOCO); 157.1 (s, C(2) (Py)); 149.1 (d, C(6) (Py));
138.5 (s, C(1) (Ph)); 138.0, 137.4, 136.7 (3d, C(4) (Py), C(2), C(4)); 136.5 (s, C(5)); 129.3, 128.4, 126.3,
123.8, 122.9, 122.5 (6d, C(3), C(3) (Py), C(5) (Py), 5 CH (Ph)); 69.1 (s, C(1)); 53.4 (q, MeO); 35.1 (t,
PhCH2). CI-MS: 321 (15), 320 (100, [M þ 1]þ), 262 (21), 261 (25).
Data of 21. IR (CHCl3): 3001w, 2963w, 1726m, 1673m, 1599s, 1495m, 1435s, 1374m, 1272m, 1240m,
1216s, 1091w, 993w, 960w, 827w, 699w. 1H-NMR: 10.71 (br. s, OH); 8.60 (dd, J ¼ 4.2, 0.7, HꢀC(6) (Py));
7.74 (td, J ¼ 7.8, 1.8, HꢀC(4) (Py)); 7.40 – 7.10 (m, 8 arom. H); 6.85 (d, J ¼ 7.7, 1 arom. H); 4.06 (s, PhCH2);
3.45 (s, MeO). 13C-NMR: 171.2 (s, MeOCO); 160.0, 158.9 (2s, C(2) (Py), CꢀOH); 148.4 (d, C(6) (Py));
141.2, 140.0, 129.9, 111.8 (4s, 4 arom. C)); 136.0, 134.2, 128.9, 128.3, 126.0, 122.7, 121.6, 121.2 (8d, C(4)
(Py), C(3) (Py), C(5) (Py), 7 arom. CH); 51.8 (q, MeO); 35.5 (t, PhCH2). CI-MS: 641 (11), 640 (37), 639
(82, [2M þ 1]þ), 322 (12), 321 (23), 320 (100, [M þ 1]þ).
Dimethyl 5-Methyl-6-oxo-1-(pyridin-2-yl)cyclohexa-2,4-diene-1,2-dicarboxylate (20d). A soln. of 9b
(300 mg, 1.9 mmol) and 18b (675 mg, 4.75 mmol) in THF (10 ml) was stirred at r.t. for 1 h. Evaporation of
the solvent, CC and prep. TLC of the residue gave 19d (213 mg, 38%), 20d (21 mg, 5%) as a yellow oil,
and dimethyl 3-hydroxy-4-methylbenzene-1,2-dicarboxylate (22; 22 mg, 4%).
Data of 20d. IR (CHCl3): 3391w, 3030m, 2953m, 2926w, 2848w, 2456w, 2359w, 1758s, 1718s, 1667s,
1584m, 1572m, 1499w, 1464m, 1437s, 1380m, 1370m, 1350m, 1283s, 1248s, 1138s, 1104m, 1075w, 1057w,
1
1037w, 1016w, 997w, 899w, 869w, 694w, 657w, 640w, 614w. H-NMR: 8.29 (ddd, J ¼ 4.8, 1.8, 1.1, HꢀC(6)
(Py)); 7.90 (d, J ¼ 8.2, HꢀC(3) (Py)); 7.63 (td, J ¼ 7.7, 1.7, HꢀC(4) (Py)); 7.35 (d, J ¼ 6.5, HꢀC(3)); 7.12 (dt,
J ¼ 6.4, 1.0, HꢀC(5) (Py)); 6.88 (dd, J ¼ 6.5, 1.5, HꢀC(4)); 3.67 (s, 2 MeO); 1.86 (d, J ¼ 1.4, Me).
13C-NMR: 195.4 (s, C(6)); 169.1, 165.3 (2s, 2 MeOCO); 155.9 (s, C(2) (Py)); 149.0 (d, C(6) (Py)); 137.5,
136.8 (2s, C(2), C(5)); 135.9, 134.2, 130.1, 123.0, 120.6 (5d, C(4) (Py), C(3) (Py), C(5) (Py)), C(3),
C(4)); 63.4 (s, C(1)); 51.6, 50.7 (2q, MeO); 16.8 (q, Me). CI-MS: 303 (17), 302 (100, [M þ 1]þ), 206 (23),
188 (10).
Data of 22. IR (CHCl3): 3446 m (br.), 2955m, 2361w, 1733s, 1677s, 1584m, 1436s, 1417m, 1282s,
1201s, 1156s, 1076m, 1031m, 1004m, 916w, 875m, 835m, 802m, 756m, 734m. 1H-NMR: 10.69 (s, OH); 7.26
(d, J ¼ 7.4, 1 arom. H); 6.82 (d, J ¼ 7.5, 1 arom. H); 3.84, 3.80 (2s, 2 MeO); 2.21 (s, Me). 13C-NMR: 167.0 (s,
MeOCO); 159.1 (s, CꢀOH); 134.8, 122.1 (2d, 2 arom. CH); 130.1, 128.9, 118.8 (3s, 3 arom. C); 50.6, 50.0
(2q, 2 MeO); 11.9 (q, Me). CI-MS: 226 (10), 225 (100, [M þ 1]þ), 195 (10), 193 (19).
6. Attempted [2 þ 3] Cycloadditions of 9 to Alkenes. A mixture of 9b (50 mg, 0.31 mmol),
fumaronitrile (100 mg, 1.28 mmol), and a small amount of Pd/C in toluene (10 ml) was heated to reflux
for 4 d9). Then, the mixture was filtered through Celite and the solvent was evaporated. The crude
product and starting materials were separated by CC to give 1,2-Dicyano-4-methyl-8b-azaacenaphthy-
lenium-5-olate (¼1,2-Dicyano-4-methylpyrrolo[2,1,5-de]quinolizinium-5-olate; 19r, 11 mg, 14%).
1H-NMR: 8.56 (dd, J ¼ 7.5, 1.0, HꢀC(6/8)); 8.38 (dd, J ¼ 8.7, 0.9, HꢀC(8/6)); 8.04 (s, HꢀC(3)); 7.96 (t,
J ¼ 7.5, HꢀC(7)); 2.36 (s, Me). EI-MS: 235 (7), 234 (16), 233 (100, Mþ), 232 (27), 205 (10), 204 (55), 203
(7), 169 (47), 150 (11), 147 (12), 119 (11), 100 (6), 69 (29).
The analogous reaction of 9b, dimethyl fumarate, and Pd/C in toluene gave 9d (7.5 mg, 8%). All
attempts with other dipolarophiles (e.g., dimethyl maleate, N-phenylmaleimide, tetracyanoethene,
thiobenzophenone, thiofluorenone, etc.) were unsuccessful.
9
)
In the absence of Pd/C, only traces of 19r could be detected.

Helvetica Chimica Acta – Vol. 95 (2012)
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7. X-Ray Crystal-Structure Determination of 9a, 19i, and 19l (Table 4 and Figs. 1 and 2)10). All
measurements were performed on a Rigaku AFC5R diffractometer using graphite-monochromated
MoKa radiation (l 0.71069 ꢅ) and a 12-kW rotating anode generator. The data collection and refinement
parameters are given in the Table, and views of the molecules are shown in Figs. 1 and 2. The intensities
were corrected for Lorentz and polarization effects, but not for absorption. Equivalent reflections were
merged. Each structure was solved by direct methods using SHELXS-86 [25], which revealed the
positions of all non-H-atoms. The non-H-atoms were refined anisotropically. All of the H-atoms were
located in difference electron-density maps, and their positions were allowed to refine together with
Table 4. Crystallographic Data of Compounds 9a, 19i, and 19l
9a
19i
19l
Crystallized from
Empirical formula
Formula weight
THF/hexane
C16H13NO
235.28
EtOH/Et2O
C21H17NO3
331.37
AcOEt
C16H12F3NO3
323.27
Crystal color, habit
Crystal dimensions [mm]
Temp. [K]
yellow, prism
0.22 ꢂ 0.38 ꢂ 0.43
173(1)
orange, prism
0.25 ꢂ 0.30 ꢂ 0.52
173(1)
orange, prism
0.30 ꢂ 0.35 ꢂ 0.48
173(1)
Crystal system
Space group
orthorhombic
Pbca
monoclinic
C2/m
monoclinic
P21/n
Z
8
4
4
Reflections for cell determination
25
25
25
2q Range for cell determination [8]
36 – 40
38 – 40
39 – 40
Unit cell parameters:
a [ꢅ]
b [ꢅ]
c [ꢅ]
24.982(2)
13.317(1)
7.171(1)
90
2385.6(4)
1.310
20.015(5)
6.764(7)
13.684(3)
114.60(1)
1684(2)
1.307
0.0880
w – 2q
60
6.760(6)
12.410(4)
16.610(4)
97.64(4)
1381(1)
1.555
0.134
w/2q
55
b [8]
V [ꢅ3]
Dx [g cmꢀ3
]
m(MoKa) [mmꢀ1
Scan type
]
0.0818
w
2q(max) [8]
60
Total reflections measured
Symmetry-independent reflections
Reflections used in refinement
[I > 2q(I)]a)
4683
3480
2062
2715
2646
1845
3594
3171
2471
Parameters refined
Final R(F)
wR(F)
Weighting parameter [a]b)
Goodness-of-fit
Secondary extinction coefficient
Final Dmax
D1(max; min) [e ꢅꢀ3
216
0.0443
0.0375
0.005
187
257
0.0445
0.0421
0.005
0.0560
0.0625
0.005
1.487
2.539
3.263
2.3(3) ꢂ 10ꢀ7
2.01 ꢂ 10ꢀ7
0.0002
0.29; ꢀ 0.21
5.80 ꢂ 10ꢀ7
0.0006
0.31; ꢀ 0.30
0.0004
]
0.26; ꢀ 0.21
b
a) [I > 3s(I) reflections] for 19i. ) wꢀ1 ¼ s2(Fo) þ (pFo)2.
10
)
CCDC-863882 – 863884 contain the supplementary crystallographic data for this article. These data
can be obtained free of charge from the Cambridge Crystallographic Data Centre via http://
www.ccdc.cam.ac.uk/data_request/cif.

758
Helvetica Chimica Acta – Vol. 95 (2012)
individual isotropic displacement parameters. The refinement of each structure was carried out on F
using full-matrix least-squares procedures [26], which minimized the function Sw(j Fo jꢀj Fc j )2. A
correction for secondary extinction was applied in each case. Neutral atom-scattering factors for non-H-
atoms were taken from [27a], and the scattering factors for H-atoms were taken from [28]. Anomalous
dispersion effects were included in Fc [29]; the values for f ’ and f ’’ were those of [27b]. The values of the
mass attenuation coefficients are those of [27c]. All calculations were performed using the TEXSAN
crystallographic software package [30].
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Received January 27, 2012