One-pot B(C6F5)3 catalyzed cascade synthesis of 2-substituted-2,3-dihydroquinazolin-4(1H)-ones

Article abstract of DOI:10.1080/00397911.2019.1679539

A new and efficient B(C₆F₅)₃ catalyzed domino strategy has been developed for the synthesis of 2-substituted quinazolinones. The reaction utilizes 2-aminobenzamide and aldehydes for a one-pot protocol. A wide range of substrate scope, functional group tolerance, and operational simplicity with excellent yield are synthetically useful features.

Full text of DOI:10.1080/00397911.2019.1679539

Synthetic Communications
An International Journal for Rapid Communication of Synthetic Organic
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One-pot B(C6F5)3 catalyzed cascade synthesis of 2-
substituted-2,3-dihydroquinazolin-4(1H)-ones
Achut R. Shinde, Yogesh D. Mane & Dnyanoba B. Muley
To cite this article: Achut R. Shinde, Yogesh D. Mane & Dnyanoba B. Muley (2019): One-pot
B(C6F5)3 catalyzed cascade synthesis of 2-substituted-2,3-dihydroquinazolin-4(1H)-ones, Synthetic
Communications, DOI: 10.1080/00397911.2019.1679539
To link to this article: https://doi.org/10.1080/00397911.2019.1679539
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SYNTHETIC COMMUNICATIONSV
https://doi.org/10.1080/00397911.2019.1679539
One-pot B(C6F5)3 catalyzed cascade synthesis of
2-substituted-2,3-dihydroquinazolin-4(1H)-ones
Achut R. Shindea, Yogesh D. Maneb, and Dnyanoba B. Muleyc
b
aDepartment of Chemistry, Sanjeevanee Mahavidyalaya, Chapoli, India; Department of Chemistry,
c
Shri Chhatrapati Shivaji College, Omerga, India; Department of Chemistry, Shivaji Mahavidyalaya,
Udgir, India
ABSTRACT
ARTICLE HISTORY
Received 5 August 2019
A new and efficient B(C6F5)3 catalyzed domino strategy has been
developed for the synthesis of 2-substituted quinazolinones. The
reaction utilizes 2-aminobenzamide and aldehydes for a one-pot
protocol. A wide range of substrate scope, functional group toler-
ance, and operational simplicity with excellent yield are synthetically
useful features.
KEYWORDS
Aldehyde;
2-aminobenzamide;
quinazolinone; tris(penta-
fluorophenyl)borane
GRAPHICAL ABSTRACT
Introduction
Quinazolin-4-(3H)-one is a main structural unit found in several natural products and
biologically potent compounds. Quinazolinones are considered as privileged structures
due to their immanent nature and their function as pharmacophores in drugs.[1]
Quinazolinones are known for their several pharmacological and biological activities
including antimalarial,[2] anticancer,[3] anti-inflammatory,[4] antihypertensive,[5] and
antituberculosis activities.[6] Owing to their notable significance, huge efforts have been
made toward efficient and convenient strategies for the construction of the quinazoline
skeleton from 2-aminobenzamide and aldehydes.[7–12] However, these strategies suffer
from certain drawbacks including use of coupling agents/bases, use of heavy and expen-
sive metal catalysts, harsh reaction conditions, use additives, low yields, stoichiometric
or large excess amounts of toxic oxidants. Therefore, search for a simple and efficient
cascade protocol to access quinazolinones from 2-aminobenzamide and aldehydes is
highly desirable.
CONTACT Achut R. Shinde
shindear123@gmail.com
Department of Chemistry, Sanjeevanee Mahavidyalaya,
Chapoli, Maharashtra, 413513, India.
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/lsyc.
Supplemental data for this article can be accessed on the publisher’s website.
ß 2019 Taylor & Francis Group, LLC

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A. R. SHINDE ET AL.
Table 1. Screening of catalyst for the synthesis of 3a.
Entry
Catalyst (mol%)
Temp (ꢀC)
Yielda (%)
1
2
3
4
5
6
7
8
–
100
100
100
100
100
100
100
100
100
100
100
00
20
25
45
60
80
80
40
49
58
62
B(C6F5)3 (1)
B(C6F5)3 (5)
B(C6F5)3 (10)
B(C6F5)3 (15)
B(C6F5)3 (20)
B(C6F5)3 (25)
Fe2O3 (20)
ZnCl2 (20)
BiCl3 (20)
9
10
11
FeCl3 (20)
aYield refers to an isolated yield after column chromatography.
Moderate Lewis acidic nature of Tris(pentafluorophenyl)Borane (BCF) facilitates its
usage in organic synthesis. In recent times, BCF has evolved as a mild, nontoxic, envir-
onmentally benign, moisture-tolerant, air-stable, heat-stable, inherently electrophilic,
moderate and versatile Lewis acid imparting high chemo-, region- and stereoselectivity
in many organic transformation.[13] Low catalytic loading and moisture-tolerance,
makes BCF superior acid catalyst than traditional Lewis acids. Herein, we report one-
pot B(C6F5)3 catalyzed convenient synthetic protocol for the synthesis of 2-substituted-
quinazolin-4-(3H)-ones from cost-effective and easily available 2-aminobenzamide and
aldehydes in DMSO as a solvent.
Results and discussion
To demonstrate our methodology, we purchased BCF, substituted aromatic/hetero-
aromatic aldehydes and 2-aminobenzamide commercially and used without any
purification. Synthesis of quinazolin-4-(3H)-ones (3a–j) has been achieved from 2-ami-
nobenzamide (1), and aldehyde (2a–j) in the presence of B(C6F5)3 as a solid acid cata-
lyst at 110–120 ꢀC. The structure of products (3a–j) was confirmed by comparing
spectroscopic data with literature values. To optimize reaction conditions, we initially
examined the role of catalyst and screened several solid acid catalysts. 2-aminobenza-
mide (1), and benzaldehyde (2a) were selected as model starting materials and the reac-
tion was carried out in DMSO at 100–120 ꢀC using 20 mol % of B(C6F5)3 as a catalyst.
The progress of the reaction was checked by TLC and after 20 h the product 3a was
obtained in 80% yield (Table 1, entry 6). The formation of compound 3a was confirmed
1
by comparing H, 13C-NMR and mass spectroscopic data with literature data.
To know the effectiveness of BCF, we repeated the same reaction with 1, 5, 10, 15,
20, and 25 mol % of BCF and we got product 3a in 80% yield after 20 h when 20 mol %
of BCF was used as catalyst (Table 1, entry 6). To realize the efficiency of BCF, same
reaction was repeated with different solid acid catalysts such as Fe3O4, ZnCl2, FeCl3,

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Table 2. Screening of solvent for synthesis of 3a.
Entry
Solvent
Temp (ꢀC)
Yielda (%)
1
2
3
4
5
6
7
8
DMSO
THF
Toluene
CH3CN
CHCl3
EtOH
H2O
100
66
110
82
50
80
80
40
28
50
35
39
n.d.
30
100
100
–
aYield refers to an isolated yield after column chromatography.
BiCl3, and B(C6F5)3. Among these tested solid acid catalysts, BCF was found as excellent
catalysts in terms of reaction time and chemical yield (Table 1, entry 6). To know the
effect of solvent on chemical yield of this reaction, we performed same reaction with
different solvents such as tetrahydrofuran, toluene, DMSO, acetonitrile, chloroform,
ethanol, and water and found that DMSO provides the best results (Table 2, entry 1).
Therefore, the use of 20 mol% of B(C6F5)3 in DMSO is superior for this conversion.
Under the optimized reaction conditions, we synthesized several quinazolin-4-(3H)-
ones (3a–j) in 62–92% yield. All mentioned reactions proceeded smoothly to give corre-
sponding product in excellent yields and accommodated multifunctional aldehydes also.
However, sterically hindered aldehyde (Table 3, entry 3e) gave poor yields in longer
reaction times than those of unhindered aldehydes.
Based on the above results and literature reports,[14] a plausible mechanism for the
synthesis of 2-substituted-2,3-dihydroquinazolin-4(1H)-ones is illustrated in Scheme 1.
B(C6F5)3 coordinates with the carbonyl oxygen of aldehyde and makes it more suscep-
tible towards the nucleophilic attack by amino group of 2-aminobenzamide giving
imine. Imine cyclizes in the presence of B(C6F5)3 to give the final product (3a–j).
Antioxidant and antibacterial activity
Above prepared 2-substituted-2,3-dihydroquinazolin-4(1H)-ones (3a–j) were evaluated
for their antioxidant (DPPH and hydroxy radical scavenging assay) and antibacterial
potency against Escherichia coli and Staphylococcus aureus and the results are shown in
Table 4. Among these compounds, 3i and 3j depicted excellent antioxidant activity
while compounds 3c and 3h effectively inhibited S. Aureus and E. coli respectively.
Experimental
General procedure for the synthesis of 2-phenyl-2,3-dihydroquinazolin-4(1H)-one
(3a): A mixture of 2-aminobenzamide (1) (0.136 mg, 1 mmol), B(C6H5)3 (20 mol %),
and benzaldehyde (2a) (0.60 mg, 5 mmol) in DMSO (2 ꢁ 4 mL) was heated at

4
A. R. SHINDE ET AL.
Table 3. Synthesis of 2-substituted quinazolin-4-(3H)-ones (3a–j) under
B(C6F5)3 catalysis.
Entry
Aldehyde
Product
Time (h)
20
Yielda (%)
80
3a
18
19
85
82
3b
3c
17
24
90
62
3d
3e
22
72
3f
16
21
23
92
76
70
3g
3h
3i
21
75
3j
aYield refers to an isolated yield after column chromatography.

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Screening of catalyst for synthesis of 3a.
Screening of solvent for synthesis of 3a.
Synthesis of 2-substitutedquinazolin-4-(3H)-ones (3a-j) under B(C6F5)3 catalysis
Scheme 1. Plausible mechanism for formation of 3a–j.
100 ꢁ 120 ꢀC for 16 ꢁ 24 h in a sealed tube. After cooling, the reaction mixture was
poured into water and extracted with EtOAc. The organic layer was washed with brine,
dried over MgSO4, and concentrated in vacuum. The residue was purified by flash col-
umn chromatography (silica gel, hexanes/EtOAc) to give desired product. The Rf value
for this compound is 0.5. White solid (90 mg (80%) yield), m.p. 100–102 ꢀC TLC Rf ¼
1
0.5 (EtOAc:Hexane ¼ 2:8); IR ꢀmax (KBr, cmꢁ1): 1620, 1662, 2990, 3165, 3190, 3320; H
NMR (400 MHz, CDCl3 and DMSO-d6): d 5.77 (1H, s), 6.74 (2H, t), 7.12 (1H, s),
7.25–7.40 (4H, t), 7.50–7.64 (3H, dd), 8.30 (1H, s); 13CMR (100 MHz, CDCl3 and
DMSO-d6): d 67.06, 114.89, 115.44, 117.60, 127.35,127.84, 128.81, 128.94, 133.79,
142.11, 148.35; MS (ESI): m/z 225 [M þ H]þ; Anal. Calcd for C14H12N2O: C, 74.98%, H,
5.39%, N, 12.49%; Found: C, 74.87%, H, 5.26%, N, 12.34% (Supplementary material).
2-(4-Methoxyphenyl)-2,3-dihydroquinazolin-4(1H)-one (3c): White solid (93 mg
(82%) yield), m.p. 125–127 ꢀC, TLC Rf ¼ 0.6 (EtOAc: Hexane ¼ 2:8); IR ꢀmax (KBr,
1
cmꢁ1): 1059, 1475, 1600, 1680, 2925, 3190, 3310, 3445; H NMR (400 MHz, CDCl3 and
DMSO-d6): d 3.76 (3H, s), 5.71 (1H, s), 6.64–6.92 (5H, m) , 7.19–7.22 (1H, t), 7.42–7.45
(2H, d) , 7.63–7.65 (1H, d), 8.06 (1H, s); 13CNMR (100 MHz, CDCl3 and DMSO-d6): d
55.48, 67.10, 113.91, 114.79, 114.82, 117.57, 127.75,128.67, 133.47, 133.57,148.45, 159.98,

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A. R. SHINDE ET AL.
Table 4. Antioxidant and antibacterial potency of compounds (3a–j).
Antimicrobial activity (mm)
Antioxidant activity
DPPH
Entry
Compound
E. coli
S. aureus
OH
1
2
3
4
5
6
7
8
3a
3b
3c
3d
3e
3f
3g
3h
3i
–
02
03
–
04
–
06
08
–
–
02
04
–
–
–
–
03
–
09.25 0.85
19.01 0.71
11.25 0.69
10.99 0.25
02.87 0.65
07.29 0.67
25.67 0.44
0.87 0.45
08.17 0.87
3.39 0.77
19.89 0.15
19.89 0.15
33.25 0.96
0.98 0.01
3.71 0.65
14.12 0.15
27.19 0.34
26.87 0.89
9
10
36.87 0.87
41.25 0.98
3j
–
–
164.36; MS (ESI): m/z 255 [M þ H]þ; Anal. Calcd for C15H14N2O2: C, 70.85%, H,
5.55%, N, 11.02%; Found: C, 70.62%, H, 5.44%, N, 10.94%.
Conclusion
In conclusion, we have developed an BCF catalyzed direct one pot, simple, efficient,
synthetic protocol for the synthesis of 2-substituted-2,3-dihydroquinazolin-4(1H)-ones
from 2-aminobenzamide and aldehyde in good to excellent yields. High yields, easy
workup, high atom-economy, low cost and easy handling of the catalyst are important
highlights of this protocol.
Acknowledgments
The authors are grateful to the Department of Postgraduate Studies and Research centre in
Chemistry, Shivaji Mahavidyalay, Udgir, and Sanjeevanee Mahavidyalaya, Chapoli, India, for pro-
viding laboratory facilities and Indian Institute of Chemical Technology, Hyderabad, for spec-
tral analysis.
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