Ultrasound-assisted rapid and efficient one-pot synthesis of furanyl spirooxindolo and spiroquinoxalinopyrrolizidines by 1,3-dipolar cycloaddition: a green protocol

Article abstract of DOI:10.1007/s11164-016-2703-8

Efficient synthesis of novel spirooxindolo and spiroquinoxalinopyrrolizidine derivatives was expediently accomplished with regioselectivity via one-pot, three-component 1,3-dipolar cycloaddition using ultrasonication. Chalcones derived from both heteroaryl methyl ketones and furfural were used as dipolarophiles in these reactions. The synthesized compounds were analyzed by ¹H and ¹³C nuclear magnetic resonance (NMR), mass spectrometry, and elemental (CHN) analysis. Single-crystal X-ray diffraction studies of one of the compounds (11d) proved the structure and regiochemistry of the cycloaddition. The ultrasound methodology is clearly advantageous, and the desired products were obtained in moderate to good yield in shorter reaction time compared with conventional heating and fusion methods.

Full text of DOI:10.1007/s11164-016-2703-8

Res Chem Intermed
DOI 10.1007/s11164-016-2703-8
Ultrasound-assisted rapid and efficient one-pot
synthesis of furanyl spirooxindolo and spiroquinox-
alinopyrrolizidines by 1,3-dipolar cycloaddition:
a green protocol
Venkata Bharat Nishtala1 Jagadeesh Babu Nanubolu2
•
•
Srinivas Basavoju1
Received: 19 April 2016 / Accepted: 12 August 2016
Ó Springer Science+Business Media Dordrecht 2016
Abstract Efficient synthesis of novel spirooxindolo and spiroquinoxalinopy-
rrolizidine derivatives was expediently accomplished with regioselectivity via one-
pot, three-component 1,3-dipolar cycloaddition using ultrasonication. Chalcones
derived from both heteroaryl methyl ketones and furfural were used as dipo-
larophiles in these reactions. The synthesized compounds were analyzed by 1H and
13C nuclear magnetic resonance (NMR), mass spectrometry, and elemental (CHN)
analysis. Single-crystal X-ray diffraction studies of one of the compounds (11d)
proved the structure and regiochemistry of the cycloaddition. The ultrasound
methodology is clearly advantageous, and the desired products were obtained in
moderate to good yield in shorter reaction time compared with conventional heating
and fusion methods.
Keywords Ultrasonication Á 1,3-Dipolar cycloaddition Á Azomethine ylide Á
Spirooxindolopyrrolizidines Á Spiroquinoxalinopyrrolizidines Á Dipolarophile
Introduction
Ultrasonication is an important technique that has been widely used recently in
organic synthesis, having an immense impact on organic and parallel synthesis. This
is due to the special sonochemical effects in liquids, which cause chemical reactions
in either homo- or heterogeneous systems. As ultrasonic waves travel through a
liquid, they form microbubbles or cavities which cause chemical reactions. These
&
Srinivas Basavoju
basavoju_s@yahoo.com
1
2
Department of Chemistry, National Institute of Technology Warangal, Warangal,
Telangana 506 004, India
Centre for X-ray Crystallography, CSIR-Indian Institute of Chemical Technology,
Hyderabad 500 607, India
123

V. B. Nishtala et al.
cavities produce high pressures and temperatures in their surroundings. Ultrasonic
irradiation is very effective for a large number of organic reactions to obtain higher
yield or reduce the reaction time, enabling use of milder conditions relative to
traditional thermal heating [1]. Multicomponent reactions (MCRs) are one of the
most important strategies for synthesis of heterocyclic compounds through
formation of carbon–carbon and carbon–heteroatom bonds along with stereogenic
carbon centers in one pot [2–4]. MCRs produce complex structures without isolation
of reaction intermediates. Some of the advantages of MCRs are high reaction rate,
high degree of atom economy, etc. [5, 6].
Over the last few decades, 1,3-dipolar cycloaddition reactions have been
extensively studied due to their selectivity, which can be influenced by steric and
electronic factors. The regio- and stereochemistry of such reactions can be
controlled through use of a catalyst or suitable dipole or dipolarophile [7–11].
Several spiro compounds have been synthesized via multicomponent 1,3-dipolar
cycloaddition under ultrasound irradiation [12–19]. Pyrrolizidines are important
core structures of many natural products such as alkaloids, and also occur in
synthetic compounds that exhibit a variety of remarkable bioactivities. In particular,
multifunctional polycyclic spiropyrrolizidines exhibit versatile bioactivities, such as
antimycobacterial, antitumor, antimicrobial, antibacterial, antifungal, and antiviral
properties [20, 21]. Spiropyrrolizidines can be synthesized efficiently from
azomethine ylide and electron-deficient alkenes and alkynes via 1,3-dipolar
cycloaddition reaction [22–24]. Literature survey reveals that there are reports on
regio- and stereoselective synthesis of spiropyrrolizidines using classical heating
methods via 1,3-dipolar cycloaddition [25–32].
Among various methods, one-pot, three-component, 1,3-dipolar cycloaddition
reaction of azomethine ylide with electron-deficient olefin is a convenient route for
regio- and stereoselective synthesis of various spiropyrrolizidine derivatives
[33, 34]. However, fewer reports are found on synthesis of spiropyrrolizidines
using ultrasonication [35–38], and no reports on chalcones derived from heteroaryl
methyl ketone and furfural as dipolarophiles. Hence, our aim in this work was to
synthesize novel spirooxindolo and spiroquinoxalinopyrrolizidines with dipo-
larophiles having both heterocyclic rings using MCRs via 1,3-dipolar cycloaddition
under environmentally benign conditions, i.e., using ultrasonication (method A).
However, these reactions were also carried out using conventional heating
(method B) and fusion (method C) methods.
Results and discussion
In the present study, three different dipolarophiles were synthesized via Claisen–
Schmidt reaction from furfural (Scheme 1). Furfural (1, 1 mmol) reacts with
1 mmol of 2-acetylfuran (2)/2-acetylthiophene (3)/2-acetylpyridine (4) in presence
of 10 % aq. NaOH solution at 5–10 °C to form corresponding dipolarophiles [39].
These three dipolarophiles, i.e., 1,3-di(furan-2-yl)prop-2-en-1-one (5), 3-(furan-2-
yl)-1-(thiophen-2-yl)prop-2-en-1-one (6), and 3-(furan-2-yl)-1-(pyridin-2-yl)prop-2-
en-1-one (7), were used to synthesize the novel spiropyrrolizidines.
123

Ultrasound-assisted rapid and efficient one-pot synthesis…
H3C
O
O
S
O
2
O
O
O
O
5
6
H3C
O
S
10% aq. NaOH
5-10 oC
O
3
4
O
H
1
H3C
N
O
N
O
O
7
Scheme 1 Synthesis of various dipolarophiles
Initially, during the synthesis of one of the target molecules (10a) under
sonication, reflux, and fusion methods, higher yield and shorter reaction time were
observed under sonication (method A). Hence, the reaction conditions were
optimized using various solvents with the sonication method to synthesize 10a
(Table 1). Among all the solvents, use of methanol as solvent was prominent under
these conditions.
In method A, i.e., ultrasound irradiation, the starting materials were dissolved in
methanol to prepare a homogeneous reaction medium. One-pot, three-component,
1,3-dipolar cycloaddition reaction of azomethine ylide generated in situ by reaction
of isatin derivatives 8a–d and L-proline (9) with dipolarophiles (5, 6, and 7) in
methanol at room temperature yielded spirooxindolopyrrolizidine derivatives within
short time (Table 2). The precipitated compounds were filtered and washed with
Table 1 Optimization of reaction conditionsa
Entry
Solvent
Temp (°C)
Yield (%)
Time (min)
1
2
3
4
5
6
7
a
Methanol
RT
RT
RT
RT
RT
RT
RT
80
1
1
1
1
1
1
1
Ethanol
79
Acetonitrile
Tetrahydrofuran
1,4-Dioxane
Water:methanol
Water
64
64
73
69
No reaction
The reaction was carried out with isatin (1.0 mmol), L-proline (1.0 mmol), and chalcone 5 (1.0 mmol)
at room temperature in solvent (5 mL) under ultrasonic power of 250 W, irradiation frequency of 25 kHz.
Isolated yield based on isatin
123

V. B. Nishtala et al.
Table 2 Yield and time required for synthesis of spirooxindolopyrrolizidines 10a–d, 11a–d, and 12a, b
S. no
Compound
Yield (%) and time
Method A
Time (s)
Method B
Time (h)
Method C
Time (min*)
1
2
3
4
5
6
7
8
9
10
10a
10b
10c
10d
11a
11b
11c
11d
12a
12b
80
82
84
78
80
82
82
77
69
64
60
50
50
73
5
73
74
76
71
71
72
73
69
58
52
1
2
2
3
8
6
6
8
3
4
60
61
59
57
60
58
58
56
48
45
2
2
2
2.5
2
7
2
7
2
15
45
45
2
2
2
Method A ultrasound irradiation in methanol at room temperature
Method B conventional heating or refluxing in methanol (80–85 °C)
Method C fusion method
* Approximate time
methanol. Pure compounds were obtained without column chromatography
(Scheme 2).
The same reactions were carried out using reflux (method B) and fusion
(method C) methods. When using method B, i.e., under reflux conditions, among
various solvents such as 1,4-dioxane, toluene, ethanol, acetonitrile, and methanol, it
was observed that the yield was moderately enhanced for methanol. A significant
temperature effect on the reaction in methanol was observed; at the particular reflux
O
O
N
R2
heteryl
5 / 6 / 7
R2
OH
+
O
O
N
H
O
Ultrasonication/reflux/fusion
N
R1
N
R1
O
10a-d
11a-d
12a-b
8-a-d
9
heteryl
heteryl:
O
heteryl:
O
S
N
heteryl:
O
12 a-b
a) R1=H,R2=H
b) R1=H,R2=Cl
5, 6 & 7
11a-d
10a-d
a) R1=H,R2=H
b) R1=Me,R2=H
c) R1=Et,R2=H
d) R1=H,R2=Cl
a) R1=H,R2=H
b) R1=Me,R2=H
c) R1=Et,R2=H
d) R1=H,R2=Cl
Scheme 2 Synthesis of various spirooxindolopyrrolizidines
123

Ultrasound-assisted rapid and efficient one-pot synthesis…
Reflux,
O
N
O
O
N
5
N
H
/
6
/
H
7
O
O
N
+
N
O
heteryl
O
O
O
N
H
O
N
H
N
H
OH
7
/
6
/
N
5
U.S., ))))
O
N
H
Scheme 3 Reaction pathway for 1,3-dipolar cycloaddition reaction
temperature, the reaction time was longer. This led us to elevate the temperature to
80–85 °C for methanol to obtain spirooxindolopyrrolizidines in 1–8 h. The crude
products were purified by column chromatography. Further, method C, i.e., fusion
was also applied as a benign method without solvent. The components were fused
without solvent, and the products were formed in 2–3 min. Therefore, from the
above results, it was found that higher yield and shorter reaction time were observed
when using the sonication method. A plausible reaction pathway [40] for the above
1,3-dipolar cycloaddition reaction (under reflux and sonication conditions) is shown
in Scheme 3. However, when these reactions were carried out at room temperature,
no target compounds were obtained. Hence, sonication was found to be a better
method for synthesis of the target molecules.
Spectral analysis
1
The synthesized compounds were characterized by IR, H NMR, 13C NMR, and
mass spectral analyses. The IR spectrum of 10a showed peaks at 1731 and
1677 cm-1 due to oxindole ring carbonyl and heteroyl carbonyl group, respectively.
In the 1H NMR spectrum of 10a, proton Ha appeared as a doublet at d 4.72
(J = 11.6 Hz) and Hb appeared as a triplet at d 4.04 (J = 10.0 Hz), clearly showing
the regiochemistry of the cycloaddition reaction. If the other possible regioisomer
1
13a had been formed (Scheme 4), the H NMR spectrum would have shown a
triplet for proton Hb at higher d value (i.e., approximately d 4.7). Literature
[23, 32, 33] shows that the –CH– proton of –CH–CO–Ar/heteryl group shows a d
value ranging from *4.7 to *5.8. Therefore, the doublet for proton Ha appearing at
d 4.72 for 10a indicates that the regioisomers formed are 10a–d, 11a–d, and 12a,
b. However, proton Hc appeared as a multiplet at d 4.29–4.23, which is more
deshielded than proton Hb. This is due to strong intramolecular C–HÁÁÁO hydrogen
bonding between proton Hc and furan ring O-atom. Later this was confirmed by
single-crystal X-ray diffraction analysis. N–H protons of oxindole appeared as a
singlet at d 7.84.
123

V. B. Nishtala et al.
O
Hc
O
Hb
Ha
R2
N
heteryl
R2
O
O
O
N
R1
N
R1
8a-d
10a-d
11a-d
12a-b
Reflux/ultrasonication/fusion
OH
+
N
H
O
9
heteryl
Hc
N
Hb
O
heteryl
Ha
O
N
O
R2
O
O
5, 6 & 7
R1
13a-d
14a-d
15a-b
Scheme 4 Possible regioisomers during the synthesis of spirooxindolopyrrolizidines
The signal in the 13C NMR spectrum of 10a at d 68.80 corresponds to the spiro
carbon. The oxindole ring carbonyl and the heteroyl carbonyl resonated at d 183.77
and 207.08, respectively. Moreover, the presence of a molecular ion peak at 389.10
(M?) in the mass spectrum of 10a confirmed the structure of the cycloadduct. The
regiochemistry of the cycloaddition reaction and configurations at chiral centers of
compound 11d were determined unambiguously by single-crystal X-ray diffraction
analysis.
The above results encouraged us to extend this methodology to azomethine ylides
generated from 11H-indeno[1,2-b]quinoxalin-11-one (18) and L-proline (9) to
synthesize spiroquinoxalinopyrrolizidines. Compounds 16 and 17 were stirred in
methanol for 5–10 min to yield a yellow solid, 11H-indeno[1,2-b]quinoxalin-11-one
(18) (Scheme 5). To this compound, L-proline (9) and the three dipolarophiles (5, 6 or
7) were added without decanting the methanol. The target molecules (20a–c) were
synthesized by the above three methods (A, B, and C), as shown in Scheme 6.
However, these experiments also proved that ultrasonication was a better method, as
the yield improved from moderate to good. The reaction times and yields of the
corresponding products formed using these three methods are presented in Table 3.
1
In the H NMR spectrum of 20a, the proton Ha appeared as a doublet at d 4.87
(J = 11.2 Hz) and Hb appeared as a triplet at d 4.33 (J = 11.6 Hz), which indicates
the regiochemistry of the cycloaddition reaction. Similar to the molecule 10a, if the
1
other regioisomer 21a had been formed, then the H NMR spectrum would have
shown a triplet for proton Hb at higher d value (i.e., approximately d 4.7)
123

Ultrasound-assisted rapid and efficient one-pot synthesis…
O
N
H2N
OH
OH
methanol
N
+
H2N
room temperature
stirring
O
O
5-10minutes
17
18
16
Scheme 5 Synthesis of 11H-indeno[1,2-b]quinoxalin-11-one
O
heteryl
N
5 / 6 / 7
N
N
OH
+
N
O
N
H
Ultrasonication/reflux/fusion
O
O
N
9
18
20a-c
heteryl:
heteryl:
S
N
heteryl:
O
heteryl
O
20c
20b
20a
O
5, 6 & 7
Scheme 6 Synthesis of spiroquinoxalinopyrrolizidines
Table 3 Yields and times required for synthesis of spiroquinoxalinopyrrolizidines 20a–c
S. no. Compound Yield (%) and time
Method A Time (min) Method B Time (h) Method C Time (min*)
1
2
3
20a
20b
20c
73
78
69
2
3
3
71
68
62
6
6
4
64
59
52
4
4
3
Method A ultrasound irradiation in methanol at room temperature
Method B conventional heating or refluxing in methanol (80–85 °C)
Method C fusion method
* Approximate time
(Scheme 7). The explanation for the formation of the above regioisomers (10a–d,
11a–d, and 12a, b) is also applicable to these 20a–c isomers. However, the proton
Hc appeared as a multiplet at d 4.58–4.53, which is more deshielded than proton Hb.
This may be due to strong intramolecular C–HÁÁÁO hydrogen bonding between Hc
proton and furan O-atom as in 11d. The signal in the 13C NMR spectrum of 20a at d
69.40 corresponds to the spiro carbon. The oxindole ring carbonyl and the heteroyl
carbonyl resonated at d 164.54 and 188.66, respectively.
123

V. B. Nishtala et al.
Hc
Hb
Ha
O
N
heteryl
N
O
N
20a-c
5 / 6 / 7
N
N
OH
+
N
H
Ultrasonication/reflux/fusion
O
heteryl
O
O
Hc
Hb
9
18
Ha
N
N
O
heteryl
N
O
O
21a-c
5, 6 & 7
Scheme 7 Possible regioisomers during the synthesis of spiroquinoxalinopyrrolizidines
Crystal structure analysis of 11d
Compound 11d crystallizes in the centrosymmetric (racemate) monoclinic P21/
c space group with one molecule in the asymmetric unit. The furan moiety is located
above the mean plane of the pyrrolizidine ring and displays conformational disorder
(i.e., rotation through 90°), with site occupancy ratio of 0.529(4):0.471(4) as shown
in Fig. 1. Crystal structure analysis revealed that the molecules form an elongated
hexagonal network structure. The 21 screw axis-related molecules are connected by
N–H group of isatin moiety and thiophene attached –C=O group via N–HÁÁÁO
˚
[N(1)–H(1N)ÁÁÁO(2); D = 2.928(3) A; h = 151°] hydrogen bonds along the crys-
tallographic c-axis. Three molecules from each 21 screw axis are connected with
adjacent furan rings by C–HÁÁÁO dimer synthons [C(23)–H(23)ÁÁÁO(3);
˚
D = 2.945(13) A, h = 117°] to form an elongated hexagonal network structure
(Fig. 2). This hexagonal structure is extended along the crystallographic a-axis.
Further, the crystal structure is stabilized by weak C–HÁÁÁO hydrogen bonds. The
relevant crystal data, collection parameters, and refinement results can be found in
Table 4. The hydrogen bond parameters are given in Table 5.
Experimental
General considerations
All melting points were recorded using Stuart SMP30 melting point apparatus and
are uncorrected. IR spectra were recorded on a PerkinElmer 100S series FTIR
1
instrument. H and 13C NMR spectra were recorded in CDCl3 using tetramethyl-
silane (TMS) as internal standard on a Bruker Avance III HD 400 MHz instrument.
123

Ultrasound-assisted rapid and efficient one-pot synthesis…
Fig. 1 ORTEP diagram of 11d with the atom numbering scheme. Displacement ellipsoids are drawn at
20 % probability level, and H atoms are shown as small spheres of arbitrary radius. Only major
component of the disordered furan ring atoms is shown for clarity. The configurations at chiral centers
C2, C9, C10, and C11 are R, S, S, and R, respectively
Fig. 2 Crystal structure packing diagram of 11d. Notice the elongated hexagonal network structures
formed by N–HÁÁÁO hydrogen bonds and C–HÁÁÁO dimer synthons
Mass spectra were recorded on Joel JMSD-300 spectrometer. Elemental analyses
were performed on a Carlo-Erba model EA 1108 analytical unit (Triad, NJ, USA),
and the values are within 0.4 % of theoretical values. Column chromatography
was performed on silica gel (100–120 mesh). Reaction progress and purity were
monitored by thin-layer chromatography. Unless otherwise stated, all chemicals and
solvents used were of high grade and purchased from Sigma Aldrich and
123

V. B. Nishtala et al.
Table 4 Salient
11d
crystallographic data and
structure refinement parameters
of compound 11d
Empirical formula
Formula weight
Crystal system
Space group
T (K)
C23H19ClN2O3S
438.91
Monoclinic
P21/c
293(2)
˚
a (A)
8.2305(6)
18.5917(13)
13.9102(10)
90
˚
b (A)
˚
c (A)
a (°)
b (°)
c (°)
Z
106.4740(10)
90
4
3
˚
V (A )
2041.1(3)
1.428
Dcalc (g/cm3)
F(000)
912.0
l (mm-1
h (°)
Index ranges
)
0.318
1.879–25.994
-10 B h B 10
-22 B k B 22
-17 B l B 17
21,054
N-total
N-independent
N-observed
Parameters
R1 [I [ 2r(I)]
wR2 (all data)
GOF
3996
3593
312
0.0651
0.1836
1.070
CCDC
1,470,017
Spectrochem. Ultrasonication was performed on PCi-Analytics-6.5L200H1DTC
ultrasonic cleaner whose frequency is 25 kHz, input voltage range of 170–270 VAC
at 50 Hz, and output power is 250 W (Mumbai, India). The reaction flasks were
immersed throughout the cleaner such that the surface of the reactants was slightly
lower than the water in the cleaner.
Typical procedures for synthesis of spirooxindolopyrrolizidines
and spiroquinoxalinopyrrolizidines
Ultrasound irradiation
A mixture of L-proline (1 mmol), isatin/11H-indeno[1,2-b]quinoxalin-11-one
(1 mmol), and Claisen–Schmidt adducts 5, 6, 7 (1 mmol) in methanol was stirred
123

Ultrasound-assisted rapid and efficient one-pot synthesis…
Table 5 Geometrical parameters of hydrogen bonds in compound 11d
D–H_Aa
D_A (A)
H_A (A)
D–H_A (°)
Symmetry code
˚
˚
N(1)–H(1 N)ÁÁÁO(2)
C(3)–H(3)ÁÁÁO(1)
Intra C(9)–H(9)ÁÁÁO(1)
C(10)–H(10)ÁÁÁN(1)
Intra C(11)–H(11)ÁÁÁO(3)
C(13)–H(13A)ÁÁÁO(2)
C(21)–H(21)ÁÁÁN(1)
C(23)–H(23)ÁÁÁO(3)
a
2.928(3)
3.740(3)
3.116(3)
3.710(3)
3.011(6)
3.539(6)
3.182(8)
2.945(13)
2.00
2.70
2.71
2.79
2.54
2.54
2.20
2.29
151
160
101
142
105
153
149
117
x, 1/2 - y, 1/2 ? z
x, 1/2 - y, -1/2 ? z
–
x, 1/2 - y, -1/2 ? z
–
-1 ? x, y, z
x, 1/2 - y, -1/2 ? z
1-x, 1-y, -z
˚
All C–H and N–H distances are neutron normalized to 1.083 and 1.009 A, respectively
for a few minutes. After obtaining a homogeneous solution, the mixture was
irradiated in an ultrasonic bath for the appropriate time at room temperature
(Tables 1, 2). Reaction progress was monitored by TLC. The precipitated
compound was filtered and washed with methanol and dried.
Conventional heating
A mixture of L-proline (1 mmol), isatin/11H-indeno[1,2-b]quinoxalin-11-one
(1 mmol), and Claisen–Schmidt adducts 5, 6, 7 (1 mmol) in methanol was refluxed
vigorously (maintained 80–85 °C) for an appropriate time (Tables 1, 2). Reaction
progress was monitored by TLC. After completion of the reaction, the solvent was
removed under reduced pressure and the crude product was purified by column
chromatography using petroleum ether:ethyl acetate (7:3) as eluent, followed by
recrystallization from methanol.
Fusion method
A mixture of L-proline (1 mmol), isatin/11H-indeno[1,2-b]quinoxalin-11-one
(1 mmol), and Claisen–Schmidt adducts 5, 6, 7 (1 mmol) was fused directly
without solvent for the appropriate time (Tables 1, 2). Reaction progress was
monitored by TLC.
Spectral data for all synthesized compounds
11H-Indeno[1,2-b]quinoxalin-11-one (18)
1
Color: yellow; M.p. 217–219 °C. IR (KBr, cm-1): 1724, 1616, 1570. H NMR
(400 MHz, CDCl3) d: 8.26 (d, 1H, J = 9.2 Hz), 8.14–8.11 (m, 2H), 7.94 (d, 1H,
J = 7.6 Hz), 7.86–7.75 (m, 3H), 7.62 (t, 1H, J = 7.2 Hz). 13C NMR (101 MHz,
CDCl3) d: 189.94, 156.63, 149.28, 143.14, 142.65, 141.56, 136.84, 136.68, 132.53,
132.47, 131.62, 130.30, 129.68, 124.79, 122.53. ESI mass spectrum (m/z): calcd. for
[C15H8N2O]: 232.24 (M?), obsd.: 233.10.
123

V. B. Nishtala et al.
20-(Furan-2-carbonyl)-10-(furan-2-yl)-10,20,50,60,70,7a0-hexahydrospiro[indoline-3-30-
pyrrolizin]-2-one (10a) Color: white. M.p. 215–217 °C. IR (KBr, cm-1): 3335,
1
3123, 2871, 1731, 1677, 1393, 768. H NMR (400 MHz, CDCl3) d: 7.84 (s, 1H),
7.39 (d, 1H, J = 2.4 Hz), 7.31 (d, 1H, J = 2.8 Hz), 7.24 (d, 1H, J = 7.6 Hz), 7.14
(t, 1H, J = 7.6 Hz), 7.06 (d, 1H, J = 3.2 Hz), 7.00 (t, 1H, J = 7.6 Hz), 6.69 (d, 1H,
J = 7.6 Hz), 6.33–6.32 (dd, 1H, J1,2 = J3,4 = 1.6 Hz), 6.26–6.25 (dd, 1H,
J1,2 = J3,4 = 1.6 Hz), 6.16 (d, 1H, J = 3.6 Hz), 4.72 (d, 1H, J = 11.6 Hz),
4.29–4.23 (m, 1H), 4.04 (t, 1H, J = 10 Hz), 2.70–2.57 (m, 2H), 2.15–1.79 (m, 4H).
13C NMR (101 MHz, CDCl3) d: 207.08, 183.77, 180.50, 153.02, 147.05, 141.78,
140.38, 129.56, 127.70, 124.81, 122.42, 118.65, 112.24, 110.18, 106.17, 73.54,
68.80, 61.49, 48.13, 45.52, 30.96, 30.59, 27.15. ESI mass spectrum (m/z): calcd. for
[C23H20N2O4]: 389.10 (M?), obsd.: 388.42; Anal. calcd. for C23H20N2O4: C, 71.12;
H, 5.19; N, 7.21; found: C, 70.94; H, 5.42; N, 7.49.
20-(Furan-2-carbonyl)-10-(furan-2-yl)-1-methyl-10,20,50,60,70,7a0-hexahydrospiro[in-
doline-3-30-pyrrolizin]-2-one (10b) Color: white. M.p. 184–186 °C. IR (KBr,
1
cm-1): 3319, 3111, 2872, 1727, 1668, 1372, 757. H NMR (400 MHz, CDCl3) d
7.36 (d, 1H, J = 2.4 Hz), 7.30 (d, 1H, J = 2.8 Hz), 7.24–7.18 (m, 2H), 7.03–6.97
(m, 2H), 6.61 (d, 1H, J = 7.6 Hz), 6.33–6.31 (dd, 1H, J1,2 = J3,4 = 2.0 Hz),
6.26–6.25 (dd, 1H, J1,2 = J3,4 = 1.6 Hz), 6.15 (d, 1H, J = 3.2 Hz), 4.68 (d, 1H,
J = 11.6 Hz), 4.32–4.26 (m, 1H), 4.02 (t, 1H, J = 10 Hz), 3.06 (s, 3H), 2.70–2.54
(m, 2H), 2.15–1.81 (m, 4H). 13C NMR (101 MHz, CDCl3) d 188.38, 178.72,
153.02, 143.96, 143.10, 141.78, 134.46, 132.31, 129.56, 127.66, 124.37, 122.51,
110.20, 108.14, 106.18, 73.89, 69.03, 62.99, 50.82, 48.33, 45.66, 30.88, 27.34,
26.24. ESI mass spectrum (m/z): calcd. for [C24H22N2O4]: 403.15 (M?), obsd.:
402.44; Anal. calcd. for C24H22N2O4: C, 71.63; H, 5.51; N, 6.96; found: C, 71.35;
H, 5.79; N, 6.73.
1-Ethyl-20-(furan-2-carbonyl)-10-(furan-2-yl)-10,20,50,60,70,7a0-hexahydrospiro[indo-
line-3-30-pyrrolizin]-2-one (10c) Color: white. M.p. 193–195 °C. IR (KBr, cm-1):
1
3315, 3130, 2870, 1720, 1667, 1371, 757. H NMR (400 MHz, CDCl3) d: 7.36 (d,
1H, J = 1.2 Hz), 7.30 (d, 1H, J = 2.0 Hz), 7.26–7.18 (m, 2H), 7.06–6.99 (m, 2H),
6.65 (d, 1H, J = 7.6 Hz), 6.33–6.32 (dd, 1H, J1,2 = J3,4 = 1.6 Hz), 6.26–6.25 (dd,
1H, J1,2 = J3,4 = 2.0 Hz), 6.15 (d, 1H, J = 3.2 Hz), 4.71 (d, 1H, J = 11.6 Hz),
4.30–4.25 (m, 1H), 4.04 (t, 1H, J = 10 Hz), 3.76–3.54 (m, 2H), 2.64–2.53 (m, 2H),
2.14–1.79 (m, 4H), 1.06 (t, 3H, J = 7.2 Hz). 13C NMR (101 MHz, CDCl3) d:
183.77, 178.08, 153.10, 152.05, 147.05, 142.40, 141.79, 129.54, 127.54, 124.59,
122.18, 119.01, 112.07, 110.17, 108.31, 106.12, 73.39, 68.84, 61.48, 48.16, 45.44,
34.84, 30.58, 27.17, 12.43. ESI mass spectrum (m/z): calcd. for [C25H24N2O4]:
417.20 (M?), obsd.:416.47; Anal. calcd. for C25H24N2O4: C, 72.10; H, 5.81; N,
6.73; found: C, 72.31; H, 5.55; N, 6.49.
5-Chloro-20-(furan-2-carbonyl)-10-(furan-2-yl)-10,20,50,60,70,7a0-hexahydrospiro[in-
doline-3-30-pyrrolizin]-2-one (10d) Color: white. M.p. 212–214 °C. IR (KBr,
1
cm-1): 3280, 3107, 2863, 1729, 1651, 1393, 781. H NMR (400 MHz, CDCl3) d:
7.88 (s, 1H), 7.42 (d, 1H, J = 2.4 Hz), 7.30 (d, 1H, J = 2.4 Hz), 7.22 (d, 1H,
J = 2.0 Hz), 7.15–7.12 (dd, 1H, J1,2 = J3,4 = 2.0 Hz), 7.09 (d, 1H, J = 3.2 Hz),
123

Ultrasound-assisted rapid and efficient one-pot synthesis…
6.65 (d, 1H, J = 8.4 Hz), 6.36–6.35 (dd, 1H, J1,2 = J3,4 = 1.6 Hz), 6.27–6.25 (dd,
1H, J1,2 = J3,4 = 2.0 Hz), 6.16 (d, 1H, J = 3.2 Hz), 4.72 (d, 1H, J = 11.6 Hz),
4.28–4.22 (m, 1H), 4.00 (t, 1H, J = 10 Hz), 2.64–2.61 (m, 2H), 2.16–1.75 (m, 4H).
13C NMR (101 MHz, CDCl3) d: 188.07, 183.39, 180.51, 152.62, 152.05, 147.18,
141.89, 138.98, 129.68, 127.98, 127.82, 126.68, 118.79, 112.41, 111.08, 110.24,
106.36, 73.67, 68.85, 61.54, 48.00, 45.54, 30.65, 27.40. ESI mass spectrum (m/z):
calcd. for [C23H19N2O4Cl]: 423.10 (M?), obsd.: 422.86; Anal. calcd. For
C23H19N2O4Cl: C, 65.33; H, 4.53; N, 6.62; found; C, 65.61; H, 4.29; N, 6.36.
10-(Furan-2-yl)-20-(thiophene-2-carbonyl)-10,20,50,60,70,7a0-hexahydrospiro[indoline-
3-30-pyrrolizin]-2-one (11a) Color: white. M.p. 231–232 °C. IR (KBr, cm-1):
1
3300, 3063, 2874, 1730, 1660, 1325, 751. H NMR (400 MHz, CDCl3) d: 7.63 (d,
1H, J = 3.6 Hz), 7.48 (d, 1H, J = 4.0 Hz), 7.31 (d, 1H,J = 1.6 Hz), 7.16–6.96 (m,
4H), 6.61 (d, 1H, J = 7.6 Hz), 6.26–6.25 (dd, 1H, J1,2 = J3,4 = 1.6 Hz), 6.15 (d,
1H, J = 3.2 Hz), 4.83 (d, 1H, J = 11.6 Hz), 4.30–4.24 (m, 1H),4.02 (t, 1H,
J = 7.2 Hz), 2.68–2.58 (m, 2H), 2.17–1.79 (m, 4H). 13C NMR (101 MHz, DMSO)
d: 188.55, 179.74, 153.72, 143.99, 142.65, 136.38, 133.30, 129.81, 129.01, 127.99,
124.91, 121.66, 110.90, 110.11, 106.38, 73.19, 69.06, 61.84, 47.91, 45.91, 31.17,
30.27, 27.18. ESI mass spectrum (m/z): calcd. for [C23H20N2O3S]: 405.10 (M?),
obsd.: 404.48; Anal. calcd. For C23H20N2O3S: C, 68.30; H, 4.98; N, 6.93; found: C,
68.07; H, 5.76; N, 6.69.
10-(Furan-2-yl)-1-methyl-20-(thiophene-2-carbonyl)-10,20,50,60,70,7a0-hexahydrospiro[in-
doline-3-30-pyrrolizin]-2-one (11b) Color: white. M.p. 191–193 °C. IR (KBr,
1
cm-1): 3280, 3111, 2872, 1717, 1650, 1416, 755. H NMR (400 MHz, CDCl3) d:
7.5 (d, 1H, J = 2.8 Hz), 7.44 (d, 1H, J = 4.0 Hz), 7.31 (d, 1H, J = 2.4 Hz),
7.24–7.17 (m, 2H), 7.04 (t, 1H, J = 7.6 Hz), 6.95 (t, 1H, J = 4.0 Hz), 6.54 (d, 1H,
J = 7.6 Hz), 6.26–6.25 (dd, 1H, J1,2 = J3,4 = 2.0 Hz), 6.16 (d, 1H, J = 3.2 Hz),
4.78 (d, 1H, J = 11.6 Hz), 4.31–4.26 (m, 1H), 4.0 (t, 1H, J = 11.2 Hz), 2.95 (s,
3H), 2.68–2.55 (m, 2H), 2.17–1.81 (m, 4H). 13C NMR (101 MHz, CDCl3) d:
183.82, 178.66, 153.09, 152.07, 146.84, 143.27, 141.76, 129.58, 127.19, 124.34,
122.41, 118.41, 112.03, 110.18, 108.10, 106.14, 73.45, 68.84, 61.92, 48.31, 45.30,
30.56, 27.11, 26.37. ESI mass spectrum (m/z): calcd. for [C24H22N2O3S]: 419.10
(M?), obsd.: 418.51; Anal. calcd. For C24H22N2O3S: C, 68.88; H, 5.30; N, 6.69;
found: C, 68.64; H, 5.53; N, 6.93.
1-Ethyl-10-(furan-2-yl)-20-(thiophene-2-carbonyl)-10,20,50,60,70,7a0-hexahydrospiro[in-
doline-3-30-pyrrolizin]-2-one (11c) Color: white. M.p. 198–200 °C. IR (KBr,
1
cm-1): 3276, 3112, 2869, 1716, 1650, 1354, 754. H NMR (400 MHz, CDCl3) d:
7.57 (d, 1H, J = 3.6 Hz), 7.44 (d, 1H, J = 4.8 Hz), 7.31–7.18 (m, 3H), 7.04 (t, 1H,
J = 7.6 Hz), 6.94 (t, 1H, J = 4.4 Hz), 6.6 (d, 1H, J = 8 Hz), 6.25 (s, 1H), 6.15 (d,
1H, J = 2.8 Hz), 4.84 (d, 1H, J = 11.6 Hz), 4.30–4.24 (m, 1H), 4.03 (t, 1H,
J = 10.4 Hz), 3.67–3.45 (m, 2H), 2.64–2.54 (m, 2H), 2.15–1.78 (m, 4H), 0.95 (t,
3H, J = 7.2 Hz). 13C NMR (101 MHz, CDCl3) d: 188.40, 178.10, 153.07, 144.12,
142.28, 141.80, 134.53, 132.74, 129.49, 127.90, 124.61, 122.23, 110.18, 108.32,
106.12, 73.69, 69.02, 62.35, 50.86, 48.17, 45.84, 34.83, 30.86, 27.36, 12.08. ESI
mass spectrum (m/z): calcd. for [C25H24N2O3S]: 433.15 (M?), obsd.: 432.53; Anal.
123

V. B. Nishtala et al.
calcd. For C25H24N2O3S: C, 69.42; H, 5.59; N, 6.48; found: C, 69.69; H, 5.85; N,
6.19.
5-Chloro-10-(furan-2-yl)-20-(thiophene-2-carbonyl)-10,20,50,60,70,7a0-hexahydrospiro[in-
doline-3-30-pyrrolizin]-2-one (11d) Color: white. M.p. 220–222 °C. IR (KBr,
1
cm-1): 3296, 3107, 2857, 1729, 1635, 1408, 738. H NMR (400 MHz, CDCl3) d:
7.62 (d, 1H, J = 4.0 Hz), 7.51 (d, 1H, J = 4.0 Hz), 7.44 (s, 1H), 7.31 (d, 1H,
J = 1.2 Hz), 7.24 (dd, 1H, J = 1.0 Hz), 7.15–7.13 (dd, 1H, J1,2 = J3,4 = 2.0 Hz),
6.98–6.96 (dd, 1H, J1,2 = J3,4 = 4.0 Hz), 6.58 (d, 1H, J = 8.4 Hz), 6.26–6.25 (dd,
1H, J1,2 = J3,4 = 2.0 Hz), 6.16 (d, 1H, J = 3.2 Hz), 4.83 (d, 1H, J = 11.6 Hz),
4.29–4.23 (m, 1H), 3.99 (t, 1H, J = 10 Hz), 2.64–2.61 (m, 2H), 2.18–1.75 (m, 4H).
13C NMR (101 MHz, CDCl3) d: 207.11, 187.90, 180.16, 152.61, 144.08, 141.90,
138.82, 134.93, 132.64, 129.61, 128.06, 127.97, 126.73, 110.97, 110.23, 106.33,
73.95, 68.96, 62.38, 47.99, 46.03, 30.96, 27.55. ESI mass spectrum (m/z): calcd. for
[C23H19N2O3ClS]: 439.05 (M?), obsd.: 438.93; Anal. calcd. for C23H19N2O3ClS: C,
62.94; H, 4.36; N, 6.38; found: C, 62.68; H, 4.57; N, 6.67.
10-(Furan-2-yl)-20-picolinoyl-10,20,50,60,70,7a0-hexahydrospiro[indoline-3-30-pyrroli-
zin]-2-one (12a) Color: white. M.p. 212–214 °C. IR (KBr, cm-1): 3376, 3004,
1
2869, 1743, 1697, 1320, 760. H NMR (400 MHz, CDCl3) d: 8.50–8.48 (m, 1H),
8.35 (s, 1H), 7.54–7.50 (m, 2H), 7.32 (d, 1H, J = 2.0 Hz), 7.22–7.24 (m, 1H),
7.03–6.94 (m, 2H), 6.80 (t, 1H, J = 7.6 Hz), 6.53 (d, 1H, J = 7.6 Hz), 6.28–6.27
(dd, 1H, J1,2 = J3,4 = 1.6 Hz), 6.21 (d, 1H, J = 3.2 Hz), 5.32 (d, 1H,
J = 11.2 Hz), 4.35–4.29 (m, 1H), 3.98 (t, 1H, J = 10.4 Hz), 2.82–2.54 (m, 2H),
2.19–1.86 (m, 4H). 13C NMR (101 MHz, CDCl3) d: 198.19, 182.03, 154.01, 152.48,
148.23, 141.59, 136.33, 129.13, 126.97, 126.90, 125.72, 121.49, 121.34, 110.15,
109.84, 105.86, 72.52, 68.59, 61.26, 48.70, 45.55, 29.79, 26.36. ESI mass spectrum
(m/z): calcd. for [C24H21N3O3]: 399.44 (M?), obsd.: 400.35; Anal. calcd. for
C24H21N3O3: C, 72.16; H, 5.30; N, 10.52; found: C, 72.42; H, 5.49; N, 10.26.
5-Chloro-10-(furan-2-yl)-20-picolinoyl-10,20,50,60,70,7a0-hexahydrospiro[indoline-3-30-
pyrrolizin]-2-one (12b) Color: white. M.p. 209–211 °C. IR (KBr, cm-1): 1H NMR
(400 MHz, CDCl3) d: 9.44 (s, 1H), 8.49 (d, 1H, J = 3.6 Hz), 7.55–7.62 (m, 3H),
7.22–7.33 (m, 2H), 7.01–6.96 (m, 2H), 6.29 (d, 1H, J = 3.2 Hz), 6.22 (d, 1H,
J = 3.2 Hz), 5.31(d, 1H, J = 11.2 Hz) 4.34–4.28 (m, 1H), 3.97 (t, 1H,
J = 10.4 Hz), 2.57–2.79 (m, 2H), 2.18–1.84 (m, 4H). 13C NMR (101 MHz,
CDCl3) d: 197.80, 182.17, 153.66, 152.36, 148.27, 141.67, 140.37, 136.58, 129.16,
127.63, 127.17, 126.89, 121.57, 110.97, 110.20, 106.03, 72.54, 68.54, 61.31, 48.55,
45.46, 29.66, 26.50. ESI mass spectrum (m/z): calcd. for [C24H20N3O3Cl]: 434.10
(M?), obsd.: 433.89; Anal. calcd. For C24H20N3O3Cl: C, 66.44; H, 4.65;N, 9.68;
found: C, 66.17; H, 4.90; N, 9.43.
Furan-2-yl(10-(furan-2-yl)-10,20,50,60,70,7a0-hexahydrospiro[indeno[1,2-b]quinoxaline-
11,30-pyrrolizin]-20-yl)methanone (20a) Color: yellow. M.p. 181–183 °C. IR (KBr,
1
cm-1): H NMR (400 MHz, CDCl3) d: 8.37–7.16 (m, 10H), 6.61–6.22 (m, 4H),
4.87 (d, 1H, J = 11.2 Hz), 4.58–4.53 (m, 1H), 4.33 (t, 1H, J = 11.6 Hz), 2.80–2.47
(m, 2H), 2.30–1.86 (m, 4H). 13C NMR (101 MHz, CDCl3) d: 188.66, 164.54,
123

Ultrasound-assisted rapid and efficient one-pot synthesis…
153.56, 153.03, 143.79, 143.46, 142.77, 142.12, 141.79, 137.28, 134.10, 132.03,
131.07, 129.82, 129.75, 128.97, 128.66, 128.24, 127.04, 122.14, 110.25, 109.70,
106.09, 75.47, 69.40, 65.50, 63.81, 47.82, 45.86, 31.34, 27.95. ESI mass spectrum
(m/z): calcd. for [C30H23N3O3]: 473.17 (M?), obsd.: 473.95. Anal. calcd. for
C30H23N3O3: C, 76.09; H, 4.90; N, 8.87; found: C, 75.87; H, 4.65; N, 8.64.
(10-(Furan-2-yl)-10,20,50,60,70,7a0-hexahydrospiro[indeno[1,2-b]quinoxaline-11,30-pyr-
rolizin]-20-yl)(thiopnen-2-yl)methanone (20b) Color: yellow. M.p. 192–194 °C. IR
1
(KBr, cm-1): 3103, 2942, 2853, 1657. H NMR (400 MHz, CDCl3) d: 7.16–8.37
(m, 10H), 6.61–6.22 (m, 4H), 4.77 (d, 1H, J = 11.2 Hz), 4.59–4.52 (m, 1H), 4.32 (t,
1H,J = 11.6 Hz), 2.70–2.49 (m, 2H), 2.28–1.91 (m, 4H). 13C NMR (101 MHz,
CDCl3) d: 188.66, 164.54, 153.56, 153.03, 143.79, 143.46, 142.77, 142.12, 141.79,
137.28, 134.10, 132.03, 131.07, 129.82, 129.75, 128.97, 128.66, 128.24, 127.04,
122.14, 110.25, 109.70, 106.09, 75.47, 69.40, 65.50, 63.81, 47.82, 45.86, 31.34,
27.95. ESI mass spectrum (m/z): calcd. for [C30H23N3O2S]: 490.20 (M?), obsd.:
489.59; Anal. calcd. for C30H23N3O2S: C, 73.60; H, 4.74; N, 8.58; found: C, 73.34;
H, 4.44; N, 8.78.
(10-(Furan-2-yl)-10,20,50,60,70,7a0-hexahydrospiro[indeno[1,2-b]quinoxaline-11,30-pyr-
rolizin]-20-yl)(pyridin-2-yl)methanone (20c) Color: yellow. M.p. 193–195 °C. IR
1
(KBr, cm-1): 3113, 2942, 2883, 1692. H NMR (400 MHz, CDCl3) d: 8.36–8.38
(m, 1H), 8.08–8.03 (m, 1H), 7.78–7.73 (m, 3H), 7.53–7.21 (m, 7H), 6.89–6.86 (m,
1H), 6.31–6.27 (m, 2H), 5.80 (d, 1H, J = 3.6 Hz), 4.66–4.60 (m, 1H), 4.24 (t, 1H,
J = 11.6 Hz), 2.78–2.48 (m, 2H), 2.27–1.93 (m, 4H). 13C NMR (101 MHz, CDCl3)
d: 198.27, 165.84, 154.29, 152.75, 152.32, 147.22, 144.07, 142.59, 142.42, 141.58,
137.67, 136.23, 130.64, 130.16, 129.33, 129.19, 128.70, 128.63, 127.57, 126.47,
121.85, 121.44, 110.18, 105.85, 74.30, 69.37, 62.69, 47.83, 45.27, 30.56, 27.31. ESI
mass spectrum (m/z): calcd. for [C31H24N4O2]: 485.20 (M?), obsd.: 484.55; Anal.
calcd. for C31H24N4O2: C, 76.84; H, 4.99; N, 11.56; found: C, 76.57; H, 4.71; N,
11.76.
Single-crystal X-ray diffraction study of 11d
X-ray data for the compound were collected at room temperature using a Bruker
Smart Apex CCD diffractometer with graphite-monochromated Mo Ka radiation
˚
(k = 0.71073 A) with x-scan method. Preliminary lattice parameters and orienta-
tion matrices were obtained from four sets of frames. Unit cell dimensions were
determined using 5371 reflections. Integration and scaling of intensity data were
accomplished using SAINT program [41]. The structure was solved by direct
methods using SHELXS97, and refinement was carried out by full-matrix least-
squares technique using SHELXL-2014/7 [42]. Anisotropic displacement param-
eters were included for all nonhydrogen atoms. H bound to N atom was located
from the difference Fourier map. All other H atoms were positioned geometrically
˚
and treated as riding on their parent C atoms with C–H distances of 0.93–0.97 A,
and with Uiso(H) = 1.2Ueq (C) or 1.5Ueq for methyl atoms. The furan ring atoms are
found to be disordered over two sites, with 0.531(4) site occupancy for C22/C23/
123

V. B. Nishtala et al.
C24/O3 atoms (representing the major component) and 0.469(4) site occupancy for
C22D/C23D/C24D/O3D (minor component). PART and FVAR instructions were
used for modeling the sulfur atom disorder, and DFIX instruction for restraining the
C–C and C–O bond distance to their expected values. The anisotropic displacement
parameters of the disordered atoms were restrained to be similar (SIMU instruction),
and the direction of motion along the axis between these atoms was also restrained
(DELU instruction) [43]. The software used to prepare material for publication was
Mercury 2.3 (build RC4), ORTEP-3, and X-Seed [44–46].
Conclusions
Various spirooxindolopyrrolizidines and spiroquinoxalinopyrrolizidines were syn-
thesized by 1,3-dipolar cycloaddition with isatin/11H-indeno[1,2-b]quinoxalin-11-
one with L-proline and different dipolarophiles using ultrasonication, reflux, and
fusion methods. The green, ultrasonication method was followed, obtaining
moderate to good yield with reduced reaction time compared with the conventional
1
heating and fusion methods. The synthesized compounds were analyzed by H
NMR, 13C NMR, and mass spectrometric methods. Finally, the structure of
compound 11d was confirmed by single-crystal X-ray diffraction analysis.
Acknowledgments S. B. thanks the MHRD, India for the Research Seed Grant. V. B. N. thanks the
MHRD, India for the fellowship. S. B. and V. B. N. also thank the Prof. T. Srinivasa Rao, Director,
NITW for providing the facilities.
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