Highly convergent one-pot four-component regioselective synthesis of spiro-pyranopyrazoles and oxa-aza-[3.3.3]propellanes

Article abstract of DOI:10.1002/hlca.201300260

A concise and efficient route for the synthesis of spiro-pyranopyrazoles and oxa-aza-[3.3.3]propellanes by simple regioselective multicomponent reaction of ninhydrin, malononitrile, hydrazine derivatives, and β-keto esters or dimethyl acetylenedicarboxylate was developed. This protocol provides an alternative method for combinatorial and parallel syntheses in drug discovery. The value of this method lies in its simplicity, regioselectivity, and good yields. The structures of 3 and 4 were corroborated spectroscopically (IR, ¹H- and ¹³C-NMR, and EI-MS). A plausible mechanism for this type of reaction is proposed (Schemes 2 and 3). Copyright

Full text of DOI:10.1002/hlca.201300260

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Helvetica Chimica Acta – Vol. 97 (2014)
Highly Convergent One-Pot Four-Component Regioselective Synthesis of
Spiro-pyranopyrazoles and Oxa-aza-[3.3.3]propellanes
by Abdolali Alizadeh* and Fahimeh Bayat
Department of Chemistry, Tarbiat Modares University, P.O. Box 14115-175, Tehran, Iran
(phone: þ 98-21-88006631; fax: þ 98-21-88006544; e-mail: abdol_alizad@yahoo.com and
aalizadeh@Modares.ac.ir)
A concise and efficient route for the synthesis of spiro-pyranopyrazoles and oxa-aza-[3.3.3]propel-
lanes by simple regioselective multicomponent reaction of ninhydrin, malononitrile, hydrazine
derivatives, and b-keto esters or dimethyl acetylenedicarboxylate was developed. This protocol provides
an alternative method for combinatorial and parallel syntheses in drug discovery. The value of this
method lies in its simplicity, regioselectivity, and good yields. The structures of 3 and 4 were corroborated
spectroscopically (IR, 1H- and 13C-NMR, and EI-MS). A plausible mechanism for this type of reaction is
proposed (Schemes 2 and 3).
Introduction. – We have previously developed some synthetic methods for the
preparation of propellanes [1] and spiro compounds [2] via multicomponent domino
reactions. Encouraged by our past results, we became interested in producing
propellanes and spiro-pyranopyrazoles by the multicomponent reaction of ninhydrin,
malononitrile, b-keto esters or dimethyl acetylenedicarboxylate (DMAD), and
hydrazine derivatives.
Results and Discussion. – Very recently, we have reported novel multicomponent
methods for the preparation of propellanes [1]. These methods rely on the reaction of
an electron-deficient Knoevenagel adduct, resulting from ninhydrin and malononitrile,
with diverse nucleophiles such as enamines, ketene aminals, and thioureas. At the
outset of our study, we examined the multicomponent reaction of ninhydrin,
malononitrile, phenylhydrazine (1a) with methyl acetoacetate (2a), using piperidine
as catalyst. First, 1a and 2a were refluxed for 2 h in EtOH, then the mixture was cooled
to ambient temperature, and a solution of ninhydrin, malononitrile, and piperidine in
EtOH was added. The reaction afforded the desired spiro-pyranopyrazole 3a in
moderate yield. To explore the scope of this transformation, a variety of hydrazines, b-
keto esters, and DMAD were applied (Scheme 1). Surprisingly, for hydrazine
derivatives with an electron-withdrawing group close to the NHNH2 moiety, instead
of the anticipated spiro-pyranopyrazole products, we observed an unexpected process
leading to heterocyclic propellanes, 4a – 4c, in moderate yields. The results are compiled
in the Table. The reaction of H2NNH2 · H2O, DMAD, ninhydrin, and malononitrile also
led to desired spiro-pyranopyrazole 5.
ꢀ 2014 Verlag Helvetica Chimica Acta AG, Zꢁrich

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Scheme 1. Synthesis of Spiro-pyranopyrazoles and Oxa-aza-[3.3.3]propellanes
Table. Spiro-pyranopyrazole and Oxa-aza-[3.3.3]propellane Derivatives Prepared
Entry
R1
R2
R3
Product
Yield [%]
1
2
3
4
5
6
7
Ph
Me
Me
Pr
Me
Et
Et
Et
Me
Et
3a
3b
3c
3d
4a
4b
4c
90
85
81
87
75
70
81
4-NO2ꢀC6H4
Ph
4-NO2ꢀC6H4
2-NO2ꢀC6H4
2-NO2ꢀC6H4
4-MeꢀC6H4ꢀSO2
Pr
Me
Me
Me
Me
NMR, IR, MS, and elemental-analysis data support the spiro and propellane
structures. In contrast to the unsymmetrical structure of propellanes, spiro-pyranopyr-
azoles have a plane of symmetry. These findings are reflected in corresponding
13C-NMR spectra. The mass spectra of 3a displayed the molecular-ion peak at m/z 382.
The IR spectrum of 3a clearly indicated the presence of NH2 (3375 and 3308 cmꢀ1), CN
(2202 cmꢀ1), C¼O (1716 cmꢀ1), and NC¼C (1657 cmꢀ1) as the most significant
1
functional groups of the product. The H-NMR spectrum of 3a showed two sharp
singlets at d(H) 1.5 and 7.86 arising from the Me and NH2 group, respectively. The
signals of aromatic H-atoms appeared as two triplets at d(H) 7.34 and 7.49, a doublet at
d(H) 7.73, and a singlet at d(H) 8.15. Due to the plane of symmetry of 3a, 16 signals
1
were observed in the H-decoupled 13C-NMR spectrum.
The mass spectra of 4b displayed the molecular-ion peak at m/z 473. The IR
spectrum of 4b clearly indicated the presence of NH2 and NH (at 3390 and 3201 cmꢀ1),
CN (2189 cmꢀ1), CO2 (1730 cmꢀ1), C¼O (1670 cmꢀ1), NC¼C (1632 cmꢀ1), and NO2
(1460 and 1325 cmꢀ1) as the most significant functional groups of the product. The
1H-NMR spectrum of 4b exhibited a triplet at d(H) 1.35 arising from the Me group,
three sharp singlets at d(H) 2.04, 7.48, and 9.67, attributed to Me, NH2, and NH groups,

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Helvetica Chimica Acta – Vol. 97 (2014)
respectively. The signal of the CH2 group appeared as a doublet of quartet at d(H) 4.19.
The aromatic H-atom signals were four triplets at d(H) 7.02, 7.72, 7.88, and 7.89, and four
doublets at d(H) 7.51, 7.66, 7.77, and 8.19. Observation of 24 distinct signals in the 1H-
decoupled 13C-NMR spectrum of 4b was in agreement with the proposed structure.
Wardell et al. investigated the reactions of methyl acetoacetate with a range of
simple arylhydrazines. According to their report, polarized quinonoid form of (2-
nitrophenyl)hydrazine is a significant contributor to the overall electronic structure of
compound 6, and it causes a reduction in the basicity and nucleophilicity of N(1) in (2-
nitrophenyl)hydrazine as compared with phenylhydrazine itself (Fig. 1).
The aryl ring in (2-nitrophenyl)hydrazine is almost coplanar with the chain-
extended fragment between C(1) and C(13) and the NO2 groups are nearly coplanar
with the ring. This nearly planar conformation may be influenced by the intramolecular
NꢀH ··· O H-bond, and the observed distance for N(1)ꢀH ··· O(21) in the X-ray
structure is 1.97 ꢂ (Fig. 2).
Therefore, from the reaction of methyl acetoacetate with (2-nitrophenyl)hydrazine
or phenylhydrazine acyclic and cyclic products are obtained [3].
Based on this finding, we assume that heating of NH2NH2, PhNHNH2, or (4-
nitrophenyl)hydrazine with b-keto esters 2 or DMAD at reflux initially produces the
pyrazole intermediate 7, which undergoes tautomerization to enol form 8. A
Knoevenagel condensation of ninhydrin and malononitrile is also proposed to give
adduct 9, which acts as Michael acceptor. Michael addition of pyrazole intermediate 8
to Knoevenagel adduct 9 should provide intermediate 10. Then, the intermediate 11,
which is the tautomeric form of intermediate 10, undergoes intramolecular cyclization
to give intermediate 12. In the last step, intermediate 12 tautomerizes to product 3 and 5
(Scheme 2).
Fig. 1. The polarized quinonoid form of intermediate 6 (according to [3])
Fig. 2. Intramolecular NꢀH ··· O H-bond (dashed line) in compound 6 (according to [3])

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Scheme 2. Proposed Mechanism of the Synthesis of 3 and 5
For the preparation of propellane, it is conceivable that initially the ninhydrin
undergoes piperidine-promoted Knoevenagel condensation with malononitrile to give
adduct 9, which acts as Michael acceptor. The formation of intermediate 13 occurs
through condensation of (2-nitrophenyl)hydrazine or tosylhydrazine with the C¼O
group of b-keto ester 2. Then, the intermediate 14, which is the tautomeric form of 13,
attacks the Knoevenagel adduct 9 in a Michael-type addition to produce an open-chain
intermediate 15, which is transformed to intermediate 16 through the migration of the
H-atom. At this stage, the regioselective nucleophilic addition of the amino group to
the C¼O bond affords intermediate 17, which is transformed to intermediate 18 through
the O-cyclization. Then tautomerization of the imino group to the amino group could
lead to product 4 (Scheme 3).
In conclusion, we have described a chemoselective four-component reaction for the
synthesis of spiro-pyranopyrazoles and oxa-aza-[3.3.3]propellanes by taking advantage
of the effect of an electron-withdrawing group on the reactivity of hydrazine
derivatives. These reactions employ piperidine as catalyst. The advantages of this
protocol include high yields, operational simplicity, regioselectivity, simple filtration,

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Scheme 3. Proposed Mechanism of the Synthesis of 4
and needing no metal catalyst. No extraction or separation by column chromatography
is necessary.
Financial support of this research from Tarbiat Modares University, Iran, is gratefully acknowledged.
Experimental Part
General. The b-keto esters, hydrazine derivatives, ninhydrin, and malononitrile were obtained from
Merck (Germany) and Fluka (Switzerland) and were used without further purification. M.p.:
Electrothermal 9100. IR Spectra: as KBr pellets on a NICOLET FT-IR 100 spectrometer; ˜n in cmꢀ1
.
1H- (300, 400, and 500 MHz) and 13C-NMR (75, 100, and 125 MHz) spectra: Bruker DRX-400
AVANCE and Bruker DRX-500 AVANCE spectrometers. EI-MS: FINNIGAN-MAT 8430 mass

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699
spectrometer; at an ionization potential of 70 eV. Elemental analyses for C, H, and N: Heraeus
CHNꢀOꢀRapid analyzer.
General Procedure (exemplified for 3a). A soln. of methyl acetoacetate (2a; 1 mmol) and
phenylhydrazine (1a; 1 mmol) in EtOH (4 ml) was heated to reflux for 30 min. The soln. was cooled
to ambient temp., and then a mixture of ninhydrin (1 mmol), malononitrile (1 mmol), and piperidine
(one drop) in EtOH (4 ml) was added to the mixture. The resulting mixture was stirred at r.t. Upon
completion (1 h), monitored by TLC, the mixture was filtered, and the precipitate was washed with
EtOH (4 ml) to afford the pure product 3a.
General Procedure (exemplified for 4b). A soln. of ethyl acetoacetate (2b; 1 mmol) and (2-
nitrophenyl)hydrazine (1b; 1 mmol) in EtOH (4 ml) was heated to reflux for 30 min. The soln. was
cooled to r.t., and then a mixture of ninhydrin (1 mmol), malononitrile (1 mmol), and piperidine (one
drop) in EtOH (4 ml) was added. The resulting mixture was stirred at r.t. Upon completion (48 h),
monitored by TLC, the mixture was filtered, and the precipitate was washed with EtOH (4 ml) to afford
the pure product 4b.
General Procedure (exemplified for 5). A soln. of dimethyl acetylenedicarboxylate (DMAD;
1 mmol) and NH2NH2 · H2O (0.32 g, 1 mmol) in EtOH (4 ml) was stirred for 15 min at r.t. The soln. was
cooled to r.t., and then a mixture of ninhydrin (1 mmol), malononitrile (1 mmol), and piperidine (one
drop) in EtOH (4 ml) was added. The resulting mixture was stirred at r.t. Upon completion (1 h),
monitored by TLC, the mixture was filtered, and the precipitate was washed with EtOH (4 ml) to afford
the pure product 5.
6’-Amino-1,3-dihydro-3’-methyl-1,3-dioxo-1’-phenyl-1’H-spiro[indene-2,4’-pyrano[2,3-c]pyrazole]-
5’-carbonitrile (3a). Yield: 0.34 g (90%). Yellow powder. M.p. 205 – 2078. IR: 3375, 3308 (NH2), 2202
1
(CN), 1716 (C¼O), 1657 (NC¼C), 1590, 1518 (Ar), 1455 (Me), 1265 (CꢀO). H-NMR (500.1 MHz,
(D6)DMSO): 1.50 (s, 3 H); 7.34 (t, J ¼ 7.4, 1 H); 7.49 (t, J ¼ 7.9, 2 H); 7.73 (d, J ¼ 7.9, 2 H); 7.86 (s, 2 H);
8.15 (s, 4 H). 13C-NMR (125 MHz, (D6)DMSO): 13.6; 53.4; 54.0; 94.5; 118.3; 121.4; 124.9; 127.9; 130.4;
137.7; 139.0; 141.5; 144.1; 146.3; 162.7; 199.7. EI-MS: 382 (100, Mþ), 249 (60), 193 (18), 77 (44). Anal.
calc. for C22H14N4O3 (382.38): C 69.11, H 3.69, N 14.65; found: C 69.18, H 3.62, N 14.58.
6’-Amino-1,3-dihydro-3’-methyl-1’-(4-nitrophenyl)-1,3-dioxo-1’H-spiro[indene-2,4’-pyrano[2,3-
c]pyrazole]-5’-carbonitrile (3b). Yield: 0.36 g (85%). Green powder. M.p. 2408 (dec.). IR: 3440, 3345
(NH2), 2197 (CN), 1711 (C¼O), 1657 (NC¼C), 1594, 1519 (Ar), 1518, 1339 (NO2), 1265 (CꢀO).
1H-NMR (500.1 MHz, (D6)DMSO): 1.54 (s, 3 H); 7.99 (s, 2 H); 8.05 (d, J ¼ 8.8, 2 H); 8.15 (s, 4 H); 8.29
(d, J ¼ 8.8, 2 H). 13C-NMR (125 MHz, (D6)DMSO): 13.7; 53.4; 53.8; 95.7; 118.0; 120.8; 125.0; 125.9;
137.0; 139.0; 141.4; 142.6; 146.0; 147.2; 162.5; 199.3. EI-MS: 427 (4, Mþ), 354 (25), 208 (100), 152 (95),
104 (93), 76 (74), 50 (40). Anal. calc. for C22H13N5O5 (427.37): C 61.83, H 3.07, N 16.39; found: C 61.75, H
3.15, N, 16.43.
6’-Amino-1,3-dihydro-1,3-dioxo-1’-phenyl-3’-propyl-1’H-spiro[indene-2,4’-pyrano[2,3-c]pyrazole]-
5’-carbonitrile (3c). Yield: 0.33 g (81%). Yellow powder. M.p. 206 – 2088. IR: 3383, 3320 (NH2), 2201
(CN), 1712 (C¼O), 1655 (NC¼C), 1593, 1518 (Ar), 1260 (CꢀO). 1H-NMR (500.1 MHz, (D6)DMSO):
0.45 (t, J ¼ 8.0, 3 H); 1.11 (sext., J ¼ 7.3, 2 H); 1.75 (t, J ¼ 7.6, 2 H); 7.34 (t, J ¼ 7.4, 1 H); 7.49 (t, J ¼ 7.9,
2 H); 7.73 (d, J ¼ 7.9, 2 H), 7.86 (s, 2 H), 8.16 (s, 4 H). 13C-NMR (125 MHz, (D6)DMSO): 14.2; 22.1; 30.1;
53.5; 54.2; 89.2; 118.4; 121.5; 124.9; 127.9; 130.4; 138.1; 139.0; 141.5; 143.3; 146.1; 162.6; 200.1. EI-MS: 410
(58, Mþ), 217 (33), 167 (37), 149 (57), 129 (39), 105 (37), 93 (38), 81 (57), 69 (78), 55 (100). Anal. calc.
for C24H18N4O3 (410.43): C 70.23, H 4.42, N 13.65; found: C 70.15, H 4.49, N 13.55.
6’-Amino-1,3-dihydro-1’-(4-nitrophenyl)-1,3-dioxo-3’-propyl-1’H-spiro[indene-2,4’-pyrano[2,3-c]-
pyrazole]-5’-carbonitrile (3d). Yield: 0.40 g (87%). Yellow powder. M.p. 2088 (dec.). IR: 3350, 3300
(NH2), 2195 (CN), 1708 (C¼O), 1657 (NC¼C), 1593, 1520 (Ar), 1519, 1394 (NO2), 1262 (CꢀN), 1109
(CꢀO). 1H-NMR (400.1 MHz, (D6)DMSO): 0.51 (t, J ¼ 8.0, 3 H); 1.18 (sext., J ¼ 7.3, 2 H); 1.83 (t, J ¼ 7.6,
2 H); 8.07 (s, 2 H); 8.12 (d, J ¼ 8.8, 2 H); 8.23 (s, 4 H); 8.35 (d, J ¼ 8.8, 2 H). 13C-NMR (100 MHz,
(D6)DMSO): 13.3; 21.0; 29.2; 53.8; 54.6; 94.5; 118.0; 120.1; 124.1; 125.1; 137.7; 138.3; 140.5; 141.6; 145.0;
149.0; 161.5; 198.9. EI-MS: 455 (15, Mþ), 354 (29), 247 (42), 185 (100), 105 (92), 76 (57). Anal. calc. for
C24H17N5O5 (455.43): C 63.30, H 3.76, N 15.38; found: C 63.36, H 3.71, N 15.44.
Methyl 10-Amino-11-cyano-2-methyl-1-[(2-nitrophenyl)amino]-4-oxo-1H,4H-8b,3a-(epoxyethe-
no)indeno[1,2-b]pyrrole-3-carboxylate (4a). Yield: 0.34 g (75%). Green powder. M.p. 241 – 2448. IR:

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3361, 3255 (NH2), 2186 (CN), 1729 (CO2), 1690 (C¼O), 1640 (NC¼C), 1565, 1325 (NO2), 1272, 1210
(CꢀO of ester) 1148 (CꢀN), 1069 (CꢀO). 13H-NMR (300.1 MHz, (D6)DMSO): 2.03 (s, 3 H); 3.68 (s,
3 H); 7.00 (t, J ¼ 7.6, 1 H); 7.48 (s, 2 H); 7.49 (d, J ¼ 8.4, 1 H); 7.64 (d, J ¼ 8.0, 1 H); 7.69 (d, J ¼ 8.4, 1 H);
7.74 (t, J ¼ 7.8, 1 H); 7.87 (t, J ¼ 7.7, 2 H); 8.17 (d, J ¼ 8.3, 2 H); 9.65 (s, 1 H). 13C-NMR (75 MHz,
(D6)DMSO): 11.6; 49.9; 53.8; 66.9; 99.6; 108.8; 115.1; 117.8; 119.0; 124.7; 125.9; 126.1; 131.5; 132.1; 135.9;
136.4; 136.8; 142.6; 144.5; 160.6; 164.8; 167.1; 195.1. EI-MS: 459 (4, Mþ), 416 (38), 279 (32), 247 (100),
138 (35). Anal. calc. for C23H17N5O6 (459.41): C 60.13, H 3.73, N 15.24; found: C 60.21, H 3.81, N 15.15.
Ethyl 10-Amino-11-cyano-2-methyl-1-[(2-nitrophenyl)amino]-4-oxo-1H,4H-8b,3a-(epoxyetheno)in-
deno[1,2-b]pyrrole-3-carboxylate (4b). Yield: 0.33 g (70%).Green powder. M.p. 237 – 2408. IR: 3390,
3201 (NH and NH2), 2189 (CN), 1730 (CO2), 1670 (CO), 1632 (NC¼C), 1616, 1523, 1489 (Ar), 1460,
1325 (NO2), 1273 (CꢀN), 1210, 1150 (CꢀO). 13H-NMR (400.1 MHz, (D6)DMSO): 1.35 (t, J ¼ 7.0, 3 H);
2.04 (s, 3 H); 4.19 (dq, 2J ¼ 26.8, 3J ¼ 7.0, 2 H); 7.02 (t, J ¼ 7.8, 1 H); 7.48 (s, 2 H), 7.51 (d, J ¼ 8.8, 1 H); 7.66
(d, J ¼ 7.6, 1 H); 7.72 (t, J ¼ 7.2, 1 H); 7.77 (d, J ¼ 7.6, 1 H); 7.88 (t, J ¼ 7.2, 1 H); 7.89 (t, J ¼ 7.6, 1 H); 8.19
(d, J ¼ 8.4, 1 H); 9.67 (s, 1 H). 13C-NMR (100 MHz, (D6)DMSO): 11.6; 14.3; 53.8; 58.9; 70.0; 99.9; 108.7;
115.1; 117.9; 119.0; 124.7; 125.9; 126.0; 131.4; 132.1; 135.8; 136.5; 136.8; 142.5; 144.5; 160.5; 164.3; 167.1;
195.0. EI-MS: 473 (1, Mþ), 430 (21), 310 (33), 264 (37), 249 (67), 138 (96), 65 (100). Anal. calc. for
C24H19N5O6 (473.44): C 60.89, H 4.04, N 14.79; found: C 60.93, H 3.97, N 14.73.
Methyl 10-Amino-11-cyano-2-methyl-1-[(4-methylphenyl)sulfonyl]-4-oxo-1H,4H-8b,3a-(epoxyethe-
no)indeno[1,2-b]pyrrole-3-carboxylate (4c). Yield: 0.40 g (81%). Yellow powder. M.p. 185 – 1868. IR:
1
3570, 3441, 3337 (NH and NH2), 2195 (CN), 1718 (C¼O), 1653 (NC¼C), 1337, 1157 (S¼O). H-NMR
(400.1 MHz, (D6)DMSO): 1.68 (s, 3 H); 2.45 (s, 3 H); 3.66 (s, 3 H); 7.49 (s, 2 H); 7.54 (d, J ¼ 7.6, 2 H); 7.56
(d, J ¼ 7.6, 1 H); 7.74 (t, J ¼ 6.4, 1 H); 7.84 (d, J ¼ 6.8, 3 H); 7.90 (t, J ¼ 7.2, 1 H); 10.22 (s, 1 H). 13C-NMR
(100 MHz, (D6)DMSO): 11.2; 21.1; 51.1; 53.1; 53.1; 70.4; 101.4; 108.5; 117.5; 124.7; 126.6; 127.6; 130.1;
131.7; 135.7; 135.8; 135.9; 142.2; 144.4; 158.4; 164.3; 170.1; 194.9. EI-MS: 492 (2, Mþ), 449 (13), 294 (98),
262 (38), 139 (46), 91 (100), 65 (58). Anal. calc. for C24H20N4O6S (492.5): C 58.53, H 4.09, N 11.38; found:
C 58.11, H 3.79, N 11.80.
Methyl 6’-Amino-5’-cyano-1,3-dihydro-1,3-dioxo-1’H-spiro[indene-2,4’-pyrano[2,3-c]pyrazole]-3’-
carboxylate (5a). Yield: 0.28 g (78%). Yellow powder. M.p. 2488 (dec.). IR: 3436, 3298, 3185 (NH
and NH2), 2189 (CN), 1718 (C¼O), 1636 (NC¼C), 1583, 1487 (Ar), 1244 (CꢀN), 1066 (CꢀO). 1H-NMR
(400.1 MHz, (D6)DMSO): 3.22 (s, 3 H); 7.71 (s, 2 H); 8.12 (s, 4 H); 14.22 (s, 1 H). 13C-NMR (100 MHz,
(D6)DMSO): 51.8; 52.4; 54.0; 97.6; 117.6; 123.6; 128.3; 137.2; 140.8; 156.5; 157.5; 162.2; 198.6. EI-MS: 350
(83, Mþ), 318 (67), 178 (48), 151 (38), 84 (67), 73 (100). Anal. calc. for C17H10N4O5 (350.29): C 58.29, H
2.88, N 15.99; found: C 58.33, H 2.94, N 15.91.
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Received June 26, 2013