One-Pot Expeditious Synthesis of 2-Amino-4,6-(disubstituted)nicotinonitriles Using Activated Fuller’s Earth as Catalyst

Full text of DOI:10.1080/00304948.2020.1858693

Organic Preparations and Procedures International
The New Journal for Organic Synthesis
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One-Pot Expeditious Synthesis of 2-Amino-4,6-
(disubstituted)nicotinonitriles Using Activated
Fuller’s Earth as Catalyst
Deelip S. Rekunge, Anil S. Mali & Ganesh U. Chaturbhuj
To cite this article: Deelip S. Rekunge, Anil S. Mali & Ganesh U. Chaturbhuj (2021) One-Pot
Expeditious Synthesis of 2-Amino-4,6-(disubstituted)nicotinonitriles Using Activated Fuller’s
Earth as Catalyst, Organic Preparations and Procedures International, 53:2, 112-119, DOI:
10.1080/00304948.2020.1858693
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ORGANIC PREPARATIONS AND PROCEDURES INTERNATIONAL
2021, VOL. 53, NO. 2, 112–119
https://doi.org/10.1080/00304948.2020.1858693
EXPERIMENTAL PAPER
One-Pot Expeditious Synthesis of 2-Amino-4,6-
(disubstituted)nicotinonitriles Using Activated Fuller’s
Earth as Catalyst
Deelip S. Rekungea , Anil S. Malib , and Ganesh U. Chaturbhuja
aDepartment of Pharmaceutical Sciences and Technology, Institute of Chemical Technology, Mumbai,
b
India; DKSS’s Institute of Pharmaceutical Science and Research Swami Chincholi, Pune, India
ARTICLE HISTORY Received 6 April 2020; Accepted 3 August 2020
Pyridine is a ubiquitous privileged heteroaromatic found in numerous natural products,
including vitamins B3 and B6, nicotine, and nicotinamide adenine dinucleotide phos-
phate (NADP).1–4 The pyridine ring is a key structural motif present in numerous drugs
with important biological activities such as anti-HIV,5 antimicrobial,6 and anti-inflam-
matory7 properties. Pyridine-containing molecules are potent phosphodiesterase 4
(PDE4) inhibitors that are beneficial for treating asthma and chronic obstructive pul-
monary disease (COPD).8,9 In addition, pyridines are applied in coordination chemis-
try,10 materials science,11 supramolecular structures,12 organocatalysis,13 polymers, non-
linear optical materials, electrical materials and agrochemicals.1 Among the pyridine
substructures, 2-amino-4,6-(disubstituted)nicotinonitriles (5, Scheme 1) are known for
their remarkable pharmacological activities, including anti-tumor,14 cardiotonic,15 and
anti-inflammatory16 characteristics.
2-Amino-4,6-(disubstituted)nicotinonitriles have conventionally been synthesized by
the four-component reactions of aldehydes, acetophenone, malononitrile, and ammo-
nium acetate17 in the presence of such promoters as diphenyl ammonium triflate,18
montmorillonite K-10,9 [EtNH3]NO3,19 microwave irradiation,20,21 Yb(PFO)3,22
FePO4,23 urease,24 Ti(dpm)(NMe2)2,25 [Bmim][BF4],26 cellulose-SO3H,27 ultrasonic
irradiation,28,29 SBTETASA,30 and trifluoroethanol.31
In keeping with our previous experiments in catalysis,32–51 we structured the present
work to investigate the suitability of activated Fuller’s earth34 as a catalyst for the syn-
thesis of 2-amino-4,6-(disubstituted)nicotinonitriles. For our initial model reaction, we
chose benzaldehyde (2 mmol), acetophenone (2 mmol), malononitrile (2 mmol), and
ammonium acetate (2.4 mmol) as reactants, and investigated solvent-free conditions in
the production of compound 5a (Tables 1 and 2).
The significance of catalyst loading on yields and time of the reaction was assessed
(Table 1, entries 2-6). In the absence of a catalyst at 90 ꢀC, the reaction occurred with
only traces of the product, even after 120 minutes (Table 1, entry 1). An increase of the
catalyst loading increased the product yield with a reduction in reaction time (Table 1,
CONTACT Ganesh U. Chaturbhuj
gu.chaturbhuj@gmail.com
Department of Pharmaceutical Sciences and
Technology, Institute of Chemical Technology, Mumbai, 400019, India
Supplemental data for this article can be accessed here.
ß 2021 Taylor & Francis Group, LLC

ORGANIC PREPARATIONS AND PROCEDURES INTERNATIONAL
113
Scheme 1. Schematic representation of activated Fuller’s earth catalyzed synthesis of 2-amino-4,6-
diphenylnicotinonitrile.
Table 1. Effect of catalyst loading.a
Entry
Catalyst (wt %)
Temperature (ꢀC)
Time (min.)
Yieldb (%)
1
2
3
4
5
6
7
8
9
10
–
5
90
90
90
90
90
90
rt
50
70
110
120
15
Traces
35
58
78
93
93
Traces
60
68
94
10
15
20
30
20
20
20
20
15
15
15
15
120
15
15
15
aReaction conditions: benzaldehyde (2 mmol), acetophenone (2 mmol), malononitrile
(2 mmol), and ammonium acetate (2.4 mmol).
bIsolated yield.
Table 2. Effect of the solvents for the synthesis of 2-amino-4,6-
diphenylnicotinonitrile.a
Entry
Solvent
Temperature (ꢀC)
Time (min.)
Yieldb (%)
1
2
3
4
5
6
7
Solvent-free
H2O
90
90
reflux
reflux
reflux
90
15
93
29
68
53
61
25
78
120
120
120
120
120
120
EtOH
THF
MeCN
Toluene
DMF
90
aReaction conditions: benzaldehyde (2 mmol), acetophenone (2 mmol), malononitrile
(2 mmol), ammonium acetate (2.4 mmol), and activated Fuller’s earth (20 wt. %).
bIsolated yield.
entries 2-5). However, catalyst loading beyond 20 wt. % was not advantageous (Table 1,
entries 5 and 6), so 20 wt. % catalyst loading was chosen for further work. Temperature
also played an important role in our model reaction. The best results were obtained at
90 ꢀC (Table 1, entry 5).
The effect of several solvents on time and yield of the reaction was ascertained
(Table 2). None of the solvents had an advantage of time and yield over the solvent-free
conditions. Hence, the solvent-free protocol was regarded as the best for cost and envir-
onmental acceptability.
Table 3 shows a comparison of catalysts reported in the literature for the preparation
of the title compounds. The present method ranks among the best in terms of reaction
conditions, workup procedure, time and yields.

114
D. S. REKUNGE ET AL.
Table 3. Comparison of the efficiency of activated Fuller’s earth with literature catalysts.
Entry
Catalyst
Reaction conditions
Time
Yielda (%)
Ref.
1
2
3
4
5
6
7
8
9
10
11
12
Activated Fuller’s earth
Fe3O4@Niacin) microwave
Fe3O4@TiO2@O2PO2(CH2)NHSO3H
Perchlorated Al-MCM-41 nanoparticles
Ultrasound irradiation
{Fe3O4@SiO2@(CH2)3Im}C(CN3
Nano-Cu2O–MFR
TBAB
Cellulose–SO3H
FePO4
Solvent free/90 ꢀC
15 min.
10 min.
20 min.
20 min.
25 min.
40 min.
1 h
2 h
2.5 h
4 h
93
86
90
73
91
86
92
92
95
93
91
90
96
91
This work
52
53
54
28, 29
55
56
H2O/70 ꢀC
Solvent free/90 ꢀC
Solvent free/100 ꢀC
CH3COONH4
Solvent free/100 ꢀC
EtOH/ H2O/reflux
H2O/reflux
57
27
23
58
22
59
60
H2O/60 ꢀC
EtOH/reflux
EtOH/reflux
SnO2/SiO2 nanocomposite
[Yb(PFO)3]
Graphene oxide
4 h
4 h
5 h
6 h
EtOH/reflux
13
H2O/80 ꢀC
14
Copper nanoparticles on charcoal (Cu/C)
MeCN/80 ꢀC
aIsolated yield.
Table 4. Substrate scope.
Entry
Aldehydes (R1)
Ketones (R2)
Product
Time (min)
Yielda (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
4-CH3O-C6H4
4-HO-C6H4
4-Br-C6H4
4-Cl-C6H4
3-Br-C6H4
3-NO2-C6H4
4-Br-C6H4
4-Br-C6H4
4-Br-C6H4
3-Br-C6H4
3-Br-C6H4
3-Br-C6H4
5a
5b
5c
5d
5e
5f
5g
5h
5i
5j
5k
5l
5m
5n
5o
5p
5q
5r
15
15
20
15
15
15
15
20
25
30
30
40
20
20
15
15
20
25
20
15
15
20
20
25
93
87
85
92
91
90
89
87
86
82
80
85
86
84
92
90
88
86
91
92
89
90
92
86
4-CH3O-C6H4
4-HO-C6H4
4-Br-C6H4
4-Cl-C6H4
4-CH3-C6H4
4-NO2-C6H4
3-Br-C6H4
3-NO2-C6H4
2-Cl-C6H4
2-NO2-C6H4
Thien-2-yl
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
4-CH3O-C6H4
4-Cl-C6H4
4-CH3-C6H4
4-CH3O-C6H4
4-CH3-C6H4
3-Br-C6H4
5s
5t
5u
5v
5w
5x
24
aIsolated yield.
Table 4 shows the results of applying our procedure more broadly. We prepared
numerous 2-amino-4,6-(disubstituted)nicotinonitriles in very good to excellent yields
(82-93%) in short reaction times. The nature of substitution has no significant effect on
reaction time and yields. This protocol tolerates a variety of substituents on substituted
aldehydes and substituted acetophenones. Table 5 provides melting points and litera-
ture references.
The reusability of the catalyst in the model reaction under solvent-free conditions at
90 ꢀC was evaluated. We found that the recovered catalyst could be recycled as many as
four times with no significant loss in catalytic activity (fourth run 89% yield).
In summary, the present work describes the scope of activated Fuller’s earth as a cata-
lyst for the formation of 2-amino-4,6-(disubstituted)nicotinonitriles in the reaction of

ORGANIC PREPARATIONS AND PROCEDURES INTERNATIONAL
115
Table 5. Physical constants of 2-amino-4,6-(disubstituted)nicotinonitriles, 5a-x.
Observed
M. P. (ꢀC)
Literature
Observed
M. P. (ꢀC)
Literature
M. P. (ꢀC)
Entry
M. P. (ꢀC)
Entry
5a
5b
5c
5d
5e
5f
5g
5h
5i
183-185
178-180
219-221
197-198
228-229
168-170
231-233
166-168
190-192
193-195
140-142
189-191
184-18653
177-17853
22161
5m
5n
5o
5p
5q
5r
5s
5t
5u
5v
5w
5x
168-170
231-233
172-174
248-250
145-147
190-192
181-183
112-114
235-237
180-182
178-180
170-172
167-16959
233-23555
174-17663
247-24953
NA
195-19755
228-23059
170-17259
230-23253
165-16753
190-19353
194-19755
NA
190-19353
180-18227
11258
236-23756
NA
5j
5k
5l
NA
NA
190-19262
NA ¼ not available in the literature.
aldehydes, acetophenones, malononitrile, and ammonium acetate products in very good
to excellent yields under solvent-free conditions.
Experimental section
All the chemicals and solvents used were of LR grade and purchased from SD Fine,
Avra Synthesis, and Spectrochem and used as received. The purity determination of the
starting materials and the reaction monitoring was accomplished by thin-layer chroma-
tography (TLC) on Merck silica gel G F254 plates, with ethyl acetate:hexane as the elut-
ing solvent. Melting points of all the compounds were recorded on an Analab
1
ThermoCal melting point apparatus in open capillary tubes and are uncorrected. H
NMR spectra were recorded on an MR400 Agilent Technology NMR spectrometer using
tetramethylsilane as an internal standard and DMSO-d6 or CDCl3 as a solvent. HRMS
was recorded on a Shimadzu LCMS-QTOF-9030 instrument by the direct infusion
1
method. All compounds were characterized by melting points, H NMR and HRMS
spectroscopy. Characterization data are provided below for the novel compounds. For
the novel compounds, complete copies of the original spectra were submitted for review
and are available in the supplementary material in the online version of this article or
from the corresponding author upon request. Covid-19 restrictions precluded reliance
on the customary elemental analysis. Known compounds were identified by matching
their melting points with the values in the literature references cited in Table 5.
Preparation of activated Fuller’s earth catalyst
Commercial grade Fuller’s earth (10 g) was stirred with 100 ml of distilled water to sep-
arate any water-soluble material. The suspended solid was filtered, washed with distilled
water, and dried in an oven at 100 ꢀC for 1h. To a 250 ml round bottom flask contain-
ing 50 ml of 5% HCl solution was added 5 g of solid obtained from the above treatment.
The mixture was heated at 100 ꢀC for 4h, cooled to room temperature, and filtered; the
residue was washed with distilled water to neutrality. The resultant activated Fuller’s
earth was dried at 100 ꢀC to constant weight.

116
D. S. REKUNGE ET AL.
General procedure for the synthesis of 2-Amino-4,6-(disubstituted)nicotinonitriles
(5a-x)
A mixture of substituted aldehyde (2 mmol), substituted acetophenone (2 mmol), malo-
nonitrile (2 mmol), ammonium acetate (2.4 mmol), and activated Fuller’s earth (20 wt.
%) was heated at 90 ꢀC in an oil bath. The reaction was monitored by thin-layer chro-
matography. After completion of the reaction, the reaction mass was treated with hot
ethanol (5 mL) dissolving the organic product and leaving the Fuller’s earth insoluble.
The Fuller’s earth was removed by hot filtration. The filtrate was evaporated to get the
product. The product was purified by recrystallization from ethanol.
2-Amino-4-(2-nitrophenyl)-6-phenylnicotinonitrile (5k)
1H NMR (400 MHz, DMSO-d6) d 8.23 (d, J ¼ 8.2 Hz, 1H), 8.12 – 8.02 (m, 2H), 7.94 –
7.85 (m, 1H), 7.79 (dd, J ¼ 17.7, 9.6 Hz, 1H), 7.64 (d, J ¼ 7.6 Hz, 1H), 7.45 (d, J ¼
3.1 Hz, 3H), 7.24 (s, 1H), 7.10 (s, 2H). HRMS calculated for C18H12N4O2: 316.09602;
found: (MHþ) 317.10234 m/z.
2-Amino-6-(3-bromophenyl)-4-phenylnicotinonitrile (5q)
1H NMR (400 MHz, DMSO-d6) d 8.33 (s, 1H), 8.11 (d, J ¼ 8.0 Hz, 1H), 7.65 (m, 3H),
7.52 (d, J ¼ 6.8 Hz, 3H), 7.41 (t, J ¼ 7.6 Hz, 1H), 7.32 (s, 1H), 7.04 (s, 2H). HRMS calcu-
lated for C18H12BrN3: 349.02145; found: (MHþ) 350.02764 m/z.
2-Amino-6-(3-bromophenyl)-4-(4-methoxyphenyl)nicotinonitrile (5v)
1H NMR (400 MHz, DMSO-d6) d 8.32 (m, 1H), 8.10 (s, 1H), 7.65-7.63 (m, 2H), 7.43-
7.41 (m, 1H), 7.08-6.98 (m, 4H), 3.81 (s, 3H). HRMS calculated for C19H14BrN3O:
379.03202; found: (MHþ) 382.03616 m/z.
2-Amino-6-(3-bromophenyl)-4-(p-tolyl)nicotinonitrile (5w)
1H NMR (400 MHz, DMSO-d6) d 8.35 (s, 1H), 8.13 (d, J ¼ 7.8 Hz, 1H), 7.67 (d,
J ¼ 7.9 Hz, 1H), 7.59 (d, J ¼ 7.9 Hz, 2H), 7.45 (t, J ¼ 7.9 Hz, 1H), 7.36 (d, J ¼ 7.9 Hz, 2H),
7.32 (s, 1H), 7.06 (s, 2H), 2.40 (s, 3H). HRMS calculated for C19H14BrN3: 363.03710;
found: (MHþ) 364.04324 m/z.
2-Amino-4,6-bis(3-bromophenyl)nicotinonitrile (5x)
1H NMR (400 MHz, DMSO-d6) d 8.34 (s, 1H), 8.13 (d, J ¼ 8.8 Hz, 1H), 7.86 (s, 1H),
7.71 (d, J ¼ 8.0 Hz, 1H), 7.65 (t, J ¼ 7.2 Hz, 2H), 7.50-7.42 (m, 2H), 7.35 (s, 1H), 7.09 (s,
2H). HRMS calculated for C18H11Br2N3: 426.93196; found: (MHþ) 429.3570 m/z.
Acknowledgment
The authors are grateful to the University Grant Commission, New Delhi, for their finan-
cial support.

ORGANIC PREPARATIONS AND PROCEDURES INTERNATIONAL
117
ORCID
Deelip S. Rekunge
http://orcid.org/0000-0003-4629-1483
Anil S. Mali
http://orcid.org/0000-0001-9568-385X
Ganesh U. Chaturbhuj
http://orcid.org/0000-0002-6263-8777
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