The synthesis of cyclopenta[c]pyridine (2-Pyrindene) derivatives

Article abstract of DOI:10.1007/s00706-007-0784-1

Ethyl 2-(N-morpholinyl)cyclopent-1-ene-1-carboxylate reacted smoothly with cyanothioacetamide to give morpholinium 4-cyano-1-oxo-2,5,6,7-tetrahydro-1H- cyclopenta[c]pyridine-3-thiolate; the former when treated with N-benzyl-α-chloroacetamide gave either a S-alkyl derivative or cyclopenta[d]thieno[2,3-b]pyridine, depending on the reaction conditions. Under Mannich-type aminomethylation with primary amines and formaldehyde the above thiolate afforded derivatives of the previously unknown heterocyclic system, cyclopenta[g]pyrido[2,1-b][1,3,5]thiadiazine in 81-90% yields.

Full text of DOI:10.1007/s00706-007-0784-1

Monatsh Chem 139, 271–275 (2008)
DOI 10.1007/s00706-007-0784-1
Printed in The Netherlands
The Synthesis of Cyclopenta[c]pyridine (2-Pyrindene) Derivatives
Victor V. Dotsenko1;ꢀ, Sergey G. Krivokolysko1, and Victor P. Litvinov2;y;z
1
‘‘ChemEx’’ Laboratory, Vladimir Dal’ East Ukrainian National University, Lugansk, Ukraine
2
Russian Academy of Sciences, Zelinsky Institute of Organic Chemistry, Moscow, Russian Federation
Received June 18, 2007; accepted August 13, 2007; published online February 12, 2008
# Springer-Verlag 2008
Summary. Ethyl 2-(N-morpholinyl)cyclopent-1-ene-1-car-
boxylate reacted smoothly with cyanothioacetamide to give
morpholinium 4-cyano-1-oxo-2,5,6,7-tetrahydro-1H-cyclo-
penta[c]pyridine-3-thiolate; the former when treated with
N-benzyl-ꢀ-chloroacetamide gave either a S-alkyl derivative
or cyclopenta[d]thieno[2,3-b]pyridine, depending on the reac-
tion conditions. Under Mannich-type aminomethylation with
primary amines and formaldehyde the above thiolate afforded
derivatives of the previously unknown heterocyclic system,
cyclopenta[g]pyrido[2,1-b][1,3,5]thiadiazine in 81–90%
yields.
an active cat attractant derived from valerian root
and a pheromone for a variety of insects. Some
cyclopenta[c]pyridine species showed affinity for
the central nicotinic receptor [6] and also were found
to be effective precursors for synthesis of anti-cancer
alkaloid camptothecin analogues [7].
Only a few methods are known to be useful for
construction of the cyclopenta[c]pyridine ring system
[8]. One of the most concise and handy approaches
to 2-pyrindene derivatives based on the Guareschi-
Thorpe-type reaction of cyanoacetamide with cyclic
ꢁ-ketoester 1 was proposed for the first time by
Prelog and Metzler [9]. In continuation of our work
on the chemistry of cyanothioacetamide [10] and 3-
cyanopyridine-2(1H)-thiones [11] we report here the
synthesis of new cyclopenta[c]pyridine derivatives
using a modified Prelog and Metzler procedure.
In the Guareschi-Thorpe synthesis [12], formation
of a pyridine ring occurs through the reaction of
ethyl cyanoacetate and ammonia (or their condensa-
tion product, cyanoacetamide) with 1,3-bielectrophi-
lic species, usually 1,3-diketones and ꢁ-ketoesters.
In most cases, however, enamines derived from 1,3-
dicarbonyl compounds (ꢁ-enamino ketones and
esters) should be preferred over 1,3-dicarbonyl com-
pounds itselves due to the milder reaction conditions
and higher yields [11, 13, 14].
Keywords. Heterocycles; Thorpe-Ziegler cyclization;
Mannich reaction; Pyridine-2-thiolates; Guareschi-Thorpe
cyclization.
Introduction
Cyclopenta[c]pyridine (2-pyrindine; IUPAC has
recommended the name ‘‘2-pyrindene’’) derivatives
have proven to be a class of compounds of great
practical interest. Thus, the 2-pyrindene ring is the
key structural unit of certain monoterpenoid alka-
loids, namely, (ꢁ)-plectrodorine and (þ)-oxerine
[1], tecomanine [2], anti-androgenic and anti-cancer
alkaloids louisianins A–D [3], skytanthine [4], and
actinidine [5] (Scheme 1); the former is known as
y
z
Deceased
This paper is dedicated to the blessed memory of our
Thus, we became interested in the synthesis of
ethyl 2-(N-morpholinyl)cyclopent-1-ene-1-carboxyl-
ate (2) with cyanothioacetamide (3) as the method of
choice to build the 2-pyrindene ring.
colleague, Prof. Victor Petrovich Litvinov (Dec 24, 1932–
Feb 26, 2007)
ꢀ
Correspondingauthor. E-mail:Victor_Dotsenko@bigmir.net

272
V. V. Dotsenko et al.
Scheme 1
Results and Discussions
line, t-butylamine, or 2,6-dimethylaniline, remained
unrewarded. It should be noted that aminomethyla-
tion of 2-thioxopyridine species or related pyridine-
2-thiolates may proceed by different pathways
depending on the substrate structure. Thus, 2-(ami-
nomethyl)thiopyridines [17], pyrido[2,1-b][1,3,5]-
thiadiazines [18], pyrido[1,2-a][1,3,5]triazines [19],
3,5,7,11-tetraazatricyclo[7.3.1.02,7]tridec-2-ene deri-
vatives [20] or bispidines (3,7-diazabicyclo[3.3.1]-
nonanes) [21] were obtained by this method.
Ethyl 2-(N-morpholinyl)cyclopent-1-ene-1-carbox-
ylate (2) was obtained via the general protocol intro-
duced in common practice by Stork et al. [15].
Enamine 2 reacted readily with cyanothioacetamide
(3) under mild conditions to afford thiolate 4 in
57% yield (Scheme 2). The formation of 4 was
found to be in a good agreement with the behavior
of other ꢁ-enaminoester species which also give pyr-
idine-2(1H)-one derivatives when treated with ac-
tive methylene (thio)amides [13, 14]. Thiolate 4 is
thought to be a promising and versatile reagent
for heterocyclic synthesis and allowed a number
of interesting transformations. Thus, alkylation of
4 with N-benzyl-ꢀ-chloroacetamide afforded the
expected sulfide 5. When treated with excessive
KOH, 5 underwent a Thorpe-Ziegler heterocycli-
zation to give isomeric thieno[2,3-b]pyridine 6
(method A), which also could be obtained di-
rectly from thiolate 4 under rather harsh conditions
(method B).
The structures of all obtained compounds were
confirmed by means of elemental analysis for C,
1
H, and N, as well as IR- and H NMR data. The
IR-spectra of compounds (4, 5, 7) showed the char-
acteristic conjugated bands of a CꢂN group stretch-
ing at ꢂꢀ¼ 2210–2200 cmꢁ1, such a band was absent
in the IR-spectrum of thieno[2,3-b]pyridine 6. In
the spectra of all compounds, the intensive bands
at ꢂꢀ¼ 1635–1620 cmꢁ1 corresponding to the lactam
1
C¼O groups stretches were observed. The H NMR
spectra of all synthesized 4–7 revealed a mul-
tiplet and two broadened triplets (with coupling
Derivatives of a new heterocyclic system, cyclo-
penta[g]pyrido[2,1-b][1,3,5]thiadiazines 7 [16], were
easily obtained in a one-pot reaction by Mannich-
type reaction of 4 with formaldehyde and primary
amines. Both aromatic and aliphatic amines reacted
under these conditions; however, all efforts in
extending the scope of this reaction for certain steri-
cally hindered substrates, such as 2-ethyl-6-methylani-
3
constants of J ¼ 7.0–7.6 Hz) at ꢃ ¼ 1.94–3.24 ppm
corresponding to the six protons of the three-methy-
lene bridge. In addition to IR data, the broad peaks
of NH-protons at ꢃ ¼ 10.18–12.20 ppm in the spec-
tra of 4–6 revealed that the latter exist both in
solid state and solution in a form of lactam tautomers
rather than 2-hydroxypyridine species. In the 1H NMR

The Synthesis of Cyclopenta[c]pyridine (2-Pyrindene) Derivatives
273
Scheme 2
(ꢃ0.2%). IR spectra were recorded on an IKS-29 spectropho-
tometer in Nujol mulls. The 1H NMR spectra were performed
on Varian Mercury VX-200 (199.97MHz) spectrometer on
DMSO-d6 solutions with Me4Si as the internal standard. The
purity of all obtained compounds was checked by TLC on
Silufol+ UV 254 plates (sorbent – Silpearl, large-pore silica
gel after Pitra with luminescent indicator for UV 254 on the
aluminum foil, binder – starch) in the acetone:heptane (1:1)
system; spots were visualized with iodine vapors and UV
light. Ethyl 2-oxocyclopentanecarboxylate (1) (technical grade,
90%) was purchased from Acros. Cyanothioacetamide (3) was
obtained by the known method [22].
spectra of 7a–7d, the signals of C(2)H2NC(4)H2
protons appeared as two broadened singlets at
ꢃ ¼ 5.43–5.56 and 5.63–5.77 ppm.
Experimental
Melting points were measured on a Kofler hot stage apparatus.
Elemental analyses for C, H, and N were conducted using
a Perkin-Elmer C, H, and N analyzer; their results were
found to be in good agreement with the calculated values

274
V. V. Dotsenko et al.
Ethyl 2-(N-morpholinyl)cyclopent-1-ene-1-carboxylate (2)
To the solution of 10 cm3 of ketoester 1 (90% purity, about
0.06mol) and 6 cm3 morpholine (0.069mol) in 60cm3 ben-
zene, catalytic amounts of HCO2H (3–5 drops) were added.
The mixture was refluxed in a round bottom flask equipped
with a Dean-Stark water separator until no further separation
of water was observed. The theoretical amount of water
(1.1cm3) required approximately 0.5 h to separate. The sol-
vent was removed by distillation in vacuo, the dark red oily
residue (15.0 g of crude 2, nearly quantitatively) was used in a
next step without any purification.
Method B
To a suspension of 0.5 g thiolate 4 (1.79 mmol) in 10cm3
EtOH, 1 cm3 10% aqueous KOH solution (1.79 mmol) and
0.33g N-benzyl-ꢀ-chloroacetamide (1.8 mmol) were added
in succession. The solution formed was stirred for 0.5 h, trea-
ted with another 1 cm3 10% KOH (1.79 mmol) whereupon
the mixture was refluxed for 5 min, filtered through a paper
filter and left to stand overnight. The filtrate was acidified
with 2 cm3 AcOH, a white precipitate formed, which was
separated by filtration and washed with EtOH to afford
0.56 g (71%) of thienopyridine 6, identical to the one
1
obtained by method A. Mp 307–310ꢄC (dec, AcOH); H
NMR (200 MHz, DMSO-d6): ꢃ ¼ 2.14 (m, C(7)H2), 2.68 (br
Morpholinium 4-cyano-1-oxo-2,5,6,7-tetrahydro-1H-cyclo-
penta[c]pyridine-3-thiolate (4, C13H17N3O2S)
t, 3J ¼ 7.3 Hz, C(6)H2), 3.24 (br t, 3J ¼ 7.0 Hz, C(8)H2),
3
4.37 (d, J ¼ 5.7 Hz, NHCH2), 6.45 (br s, NH2), 7.27 (m,
To 15.0g of crude enamine 2 (about 0.06 mol) dissolved
in 30 cm3 of absolute EtOH, 6.0 g (0.06 mol) of cyanothioa-
cetamide 3 was added under vigorous stirring. The mixture
was stirred for 5 h at 20ꢄC and left to stand overnight. A white
crystalline precipitate formed, which was filtered off and
washed twice with absolute EtOH and acetone to afford
3
Ph), 7.85 (t, J ¼ 5.7 Hz, NHCH2), 12.20 (very br s, NH)
ppm; IR (nujol): ꢂꢀ¼ 3200–3350 (NH, NH2), 1640, 1630
(2C¼O) cmꢁ1
.
Cyclopenta[g]pyrido[2,1-b][1,3,5]thiadiazines (7). General
Procedure
1
9.5 g (57%) of thiolate 4. Mp 248–250ꢄC (dec); H NMR
To 0.5 g thiolate 4 (1.79 mmol) and 1.8 mmol of the corre-
sponding primary amine suspended in 10–12 cm3 EtOH,
2 cm3 37% aqueous HCHO (27 mmol) were added. The mix-
ture was heated to reflux under vigorous stirring, and a crys-
talline solid started to precipitate from the formed solution
within 1–2 min. The mixture was stirred for 5 h at 25ꢄC and
left to stand overnight. Solid product was filtered off and
washed twice with EtOH to give the corresponding thiadia-
zines 7a–7d as colorless crystals.
(200 MHz, DMSO-d6): ꢃ ¼ 1.97 (m, C(6)H2), 2.50 (br t,
3
3J ¼ 7.0 Hz, C(7)H2), 2.68 (br t, J ¼ 7.3 Hz, C(5)H2), 3.12
(m, N(CH2)2), 3.76 (m, O(CH2)2), 10.18 (br s, NH) ppm.
Signal of NHþ-protons was not detected due to proton-deute-
rium exchange; IR (nujol): ꢂꢀ¼ 3315 (NH), 2200 (CꢂN), 1630
(C¼O) cmꢁ1
.
N-Benzyl-2-[(4-cyano-1-oxo-2,5,6,7-tetrahydro-1H-cyclo-
penta[c]pyridine-3-yl)thio]acetamide (5, C18H17N3O2S)
To a suspension of 0.5 g of thiolate 4 (1.79 mmol) in 10cm3
EtOH, 1 cm3 of 10% aqueous KOH solution (1.79 mmol) was
added. The solution formed was stirred for 0.5 h and filtered
through a paper filter into the solution of 0.33 g (1.8mmol) of
N-benzyl-ꢀ-chloroacetamide in 10cm3 EtOH. The mixture
was stirred for 5 h and left to stand overnight. To the resulting
mixture 5 cm3 water and 2 cm3 AcOH were added portion-
wise under vigorous stirring. The precipitate was filtered
off and washed with cold EtOH and ether to afford 0.39 g
of 5 (64%) as a white powder. Mp 227–229ꢄC (dec,
EtOH); 1H NMR (200 MHz, DMSO-d6): ꢃ ¼ 2.14 (m,
6-Oxo-3-phenyl-3,4,6,7,8,9-2H-cyclopenta[g]pyrido[2,1-b]-
[1,3,5]thiadiazine-10-carbonitrile (7a, C17H15N3OS)
Yield 90%; mp 209–211ꢄC (dec, DMF:EtOH¼ 1:4); 1H NMR
(200MHz, DMSO-d6): ꢃ ¼ 1.94 (m, C(8)H2), 2.65 (br t,
3
3J ¼ 7.3 Hz, C(7)H2), 2.78 (br t, J ¼ 7.5 Hz, C(9)H2), 5.56,
5.77 (both br s, C(2)H2NC(4)H2), 6.91–7.34 (m, Ph) ppm; IR
.
(nujol): ꢂꢀ¼ 2207 (CꢂN), 1630 (C¼O) cmꢁ1
3-(4-Methylphenyl)-6-oxo-3,4,6,7,8,9-2H-cyclopenta[g]-
pyrido[2,1-b][1,3,5]thiadiazine-10-carbonitrile
(7b, C18H17N3OS)
3
3
C(6)H2), 2.76 (br t, J ¼ 7.4 Hz, C(7)H2), 2.95 (br t, J ¼
7.6 Hz, C(5)H2), 3.90 (br s, SCH2), 4.35 (d, 3J ¼ 5.3 Hz,
NHCH2), 7.27 (m, Ph), 8.55 and 11.70 (both very br s,
2 NH) ppm; IR (nujol): ꢂꢀ¼ 3315 (N–H), 2210 (CꢂN),
Yield 88%; mp 223–225ꢄC (dec, DMF:acetone¼ 1:4); 1H
NMR (200MHz, DMSO-d6): ꢃ ¼ 2.07 (m, C(8)H2), 2.27 (s,
3
3
Ar–CH3), 2.73 (br t, J ¼ 7.3 Hz, C(7)H2), 2.84 (br t, J ¼
1660, 1620 (2 C¼O) cmꢁ1
.
7.5 Hz, C(9)H2), 5.48, 5.67 (both br s, C(2)H2NC(4)H2),
7.03 (dd, J ¼ 8.6Hz, Ar) ppm; IR (nujol): ꢂꢀ¼ 2205 (CꢂN),
3
1620 (C¼O) cmꢁ1
.
1-Amino-N-benzyl-5-oxo-5,6,7,8-tetrahydro-4H-cyclopenta-
[d]thieno[2,3-b]pyridine-2-carboxamide (6, C18H17N3O2S)
3-(4-Fluorophenyl)-6-oxo-3,4,6,7,8,9-2H-cyclopenta[g]-
pyrido[2,1-b][1,3,5]thiadiazine-10-carbonitrile
Method A
To a suspension of 0.5g 2-pyrindene derivative 5 (1.47 mmol)
in 10cm3 EtOH, an excess of 10% aqueous KOH solution
(1cm3, 1.79 mmol) was added. The deep yellow solution
formed was refluxed for 5 min under vigorous stirring and
allowed to cool to ambient temperature, whereupon 2 cm3
AcOH were added. A white solid was filtered off and washed
with EtOH to afford 0.40 g (80%) of thienopyridine 6.
(7c, C17H14FN3OS)
Yield 82%; mp 215–217ꢄC (dec, DMF:EtOH¼ 1:3); 1H
NMR (200MHz, DMSO-d6): ꢃ ¼ 2.02 (m, C(8)H2), 2.70 (br
t, 3J ¼ 7.4 Hz, C(7)H2), 2.82 (br t, 3J ¼ 7.6 Hz, C(9)H2), 5.43,
5.63 (both br s, C(2)H2NC(4)H2), 7.00 (m, 4-FC6H4) ppm; IR
(nujol): ꢂꢀ¼ 2200 (CꢂN), 1635 (C¼O) cmꢁ1
.

The Synthesis of Cyclopenta[c]pyridine (2-Pyrindene) Derivatives
275
Khimiya, tom 17 (Results in Science and Technology.
Organic Chemistry, Vol. 17). VINITI, Moscow, p 72 (in
Russian)
3-(4-Chlorophenyl)-6-oxo-3,4,6,7,8,9-2H-cyclopenta[g]-
pyrido[2,1-b][1,3,5]thiadiazine-10-carbonitrile
(7d, C17H14ClN3OS)
Yield 81%; mp 225–227ꢄC (dec, acetone); 1H NMR
(200 MHz, DMSO-d6): ꢃ ¼ 2.02 (m, C(8)H2), 2.70 (br t,
[12] Jie-Jack L (ed) (2005) Name Reactions in Heterocyclic
Chemistry, Wiley Interscience, p 307
3
3J ¼ 7.3 Hz, C(7)H2), 2.81 (br t, J ¼ 7.4 Hz, C(9)H2), 5.47,
[13] a) Litvinov VP, Sharanin YuA, Promonenkov VK,
Rodinovskaya LA, Shestopalov AM, Mortikov VYu
(1984) Russ Chem Bull 33: 1706; b) Dyachenko VD,
Sharanin YuA, Shestopalov AM, Rodinovskaya LA,
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[14] For review see: Rodinovskaya LA, Promonenkov VK,
Sharanin YuA, Litvinov VP, Shestopalov AM (1989)
ꢁ-Enaminocarbonyl compounds in the synthesis of 3-
cyano-2(1H)-pyridones. In: Itogi Nauki I Tekhniki
Organicheskaya Khimiya, tom 17 (Results in Science
and Technology. Organic Chemistry, Vol. 17). VINITI,
Moscow, p 3 (in Russian)
3
5.66 (both br s, C(2)H2NC(4)H2), 7.13 (dd, J ¼ 9.0 Hz, Ar)
ppm; IR (nujol): ꢂꢀ¼ 2205 (CꢂN), 1635 (C¼O) cmꢁ1
.
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