Electrochemical synthesis of quinazolinone: via I2-catalyzed tandem oxidation in aqueous solution

Article abstract of DOI:10.1039/d1ra02706a

The development of protocols for synthesizing quinazolinones using biocompatible catalysts in aqueous medium will help to resolve the difficulties of using green and sustainable chemistry for their synthesis. Herein, using I2 in coordination with electrochemical synthesis induced a C-H oxidation reaction which is reported when using water as the environmentally friendly solvent to access a broad range of quinazolinones at room temperature. The reaction mechanism strongly showed that I2 cooperates electrochemically promoted the oxidation of alcohols, then effectively cyclizing amides to various quinazolinones.

Full text of DOI:10.1039/d1ra02706a

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Electrochemical synthesis of quinazolinone via I2-
catalyzed tandem oxidation in aqueous solution†
Cite this: RSC Adv., 2021, 11, 17721
Huiqing Hou,a Xinhua Ma,a Yingying Lin,a Jin Lin,a Weiming Sun,a Lei Wang,c
a
ab
*
*
Xiuzhi Xu and Fang Ke
The development of protocols for synthesizing quinazolinones using biocompatible catalysts in aqueous
medium will help to resolve the difficulties of using green and sustainable chemistry for their synthesis.
Herein, using I2 in coordination with electrochemical synthesis induced a C–H oxidation reaction which
is reported when using water as the environmentally friendly solvent to access a broad range of
quinazolinones at room temperature. The reaction mechanism strongly showed that I2 cooperates
electrochemically promoted the oxidation of alcohols, then effectively cyclizing amides to various
quinazolinones.
Received 7th April 2021
Accepted 3rd May 2021
DOI: 10.1039/d1ra02706a
rsc.li/rsc-advances
The N-heterocycles are key core structures that form the basis of nitriles, or acid derivatives plus a nitrogen source.8 Moreover,
many pharmaceutical, agrochemical and natural products.1 the synthesis of quinazolinone involving transition metal cata-
Among them, quinazolinones are an important motif in several lysed reactions of o-haloarylamides with nitriles, or amines9 and
biologically relevant pharmacophores,2 such as methaqualone reaction of o-halogenated aryl acid with amides10 have been
which is famous for its effective sedative and hypnotic effects, explored (Scheme 1).
luotonin A which is a quinazolinone alkaloid with anti-
Although the above approaches solved a lot of practical
inammatory effects, and erlotinib which is an anti-tumour problems, there are still some limitations such as long reaction
agent, and all these compounds contain a quinazoline bond time, high temperature and by-products. Hence, development
in their backbone (Fig. 1).3
of greener, atom economic, synthetic approaches for the prep-
Due to their advantageous structures quinazolinones have aration of quinazolinones from inexpensive and easily available
been widely explored in numerous syntheses.4 The classical starting materials under relatively mild conditions is desirable.
method involves condensation of aldehydes and o-amino- On one hand, electrochemical-induced direct functionalization
benzamides to give aminal intermediates, which then undergo has gained signicant attention from the synthetic chemistry
oxidation to yield the nal quinazolinone product.5 Another community due to it being environmentally friendly, and
strategy is to use more benign and readily available alcohols as requiring mild conditions, and low-energy irradiation.11 With
starting materials.6 The reaction takes place through a two-step electrons as the oxidizing/reducing agent, organic electrosyn-
oxidation pathway, where the alcohols are rst oxidized to thesis could offer appropriate alternatives to traditional oxida-
aldehydes, followed by coupling with o-aminobenzamides. The tion or reduction reactions. For example, Zhao and co-workers12
catalyst needs to demonstrate high activity and selectivity as the reported an efficient electrochemical-induced C–H methyl-
reaction involves dehydrogenation of both the C–H and N–H thiolation of electron-rich aromatics via a three-component
bonds in one pot. In 2018, Sarma and co-workers7 demonstrated cross-coupling strategy. On the other hand, the non-metallic
that a magnetically recoverable iron oxide-carbon dot nano-
composite was an effective catalyst for cyclooxidative tandem
synthesis of quinazolinones in aqueous medium using alcohols
as starting materials. Furthermore, annulation reactions of o-
aminoaryl acids may be the most employed strategies, which
include the condensation of o-aminoaryl acids with amides,
aSchool of Pharmacy, Fujian Provincial Key Laboratory of Natural Medicine
Pharmacology, Fujian Medical University, Fuzhou 350004, China. E-mail: kefang@
mail.mu.edu.cn; Fax: +86-591-22862016; Tel: +86-591-22862016
bFaculty of Material and Chemical Engineering, Yibin University, Yibin 644000, China
cSchool of Science, Xuchang University, Xuchang 461000, China
† Electronic supplementary information (ESI) available. See DOI:
Fig. 1 Bioactive compounds containing quinazolinone skeleton.
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Table 1 Optimization of the reaction conditionsa
Entry
Variations from the standard conditions
Yieldb (%)
1
None
92
2
0.1 mmol I2
42
3
4
5
6
MeCN/H2O (v/v ¼ 1 : 1) as solvent
In the absence of I2
In the absence of NaOH
CuI instead of I2
73
Trace
Trace
19
Scheme 1 Methods for the synthesis of quinazolinones.
7
8
TBAI instead of I2
KI instead of I2
26
42
9
Cs2CO3 instead of NaOH
KOH instead of NaOH
No current
31
73
Trace
92
28
30
64
16
71
oxidant, iodine, catalysed C–H oxidation has attracted great
interest in recent times due to its low toxicity and because it is
inexpensive compared with transition metal catalysts.13 There-
fore, the combination of electrochemical catalysis and non-
metallic oxidant iodine is a very feasible means of organic
synthesis and does not require use of the historical large doses
of iodine. In this research the possibility of combining the two
in a one-pot reaction was explored, thus avoiding the isolation
of either aldehyde or amine intermediates leading to quinazo-
linones formed from alcohols as starting materials.
10
11
12
13
14
15
16
17
Addition of Bu4NPF6 as electrolyte
0.4 mmol I2 instead of current
1.0 mmol I2 instead of current
C(+)/Pt(ꢀ)
Pt(+)/Cu(ꢀ)
40 mA
a
Standard conditions: undivided cell, Pt anode, Pt cathode, 1a (0.5
mmol), 2a (0.6 mmol), I2 (0.2 mmol), NaOH (2 mmol), H2O (3 mL), I
¼ 80 mA at room temperature (r.t.) for 6 h. b Isolated yield.
Furthermore, water as a reaction medium is generally
considered as an inexpensive, safe, and environmentally benign
alternative to organic solvents.14 Recently, Muthaiah and co-
workers15 demonstrated a catalyst system for the dehydrogen-
ative oxidation of alcohols to carbonyl compounds and dehy-
drogenative lactonization of diols in water catalyzed by a water-
soluble bifunctional iridium complex. In continuation of our
work to develop new organic transformations,16,11f herein, it is
demonstrated that I2 is an efficient catalyst for a novel, one-pot
electrochemical-induced tandem reaction in aqueous solution.
The investigation was initially begun by selecting o-amino-
benzamide 1a and benzyl alcohol 2a as the model substrate to
optimize the reaction conditions shown in Table 1. The reaction
was initially heated in water using a catalyst: I2 (0.4 equiv.) and
a base: NaOH (4 equiv.) to give the desired product 3aa with
a yield of 92% (Table 1, entry 1). The amount of catalyst used
was reduced to one-h and the separation rate of the corre-
sponding product was only 42% (Table 1, entry 2). When the
reaction mixture was placed in other solvents for 6 h, this
reaction takes place with a 73% isolated yield (Table 1, entry 3),
and for the sake of environmental protection, water was chosen
as a green and energy saving solvent. Poor yields were obtained
in the absence of I2 (Table 1, entry 4). Removal of NaOH from
the reaction system led to a disruption reaction that may be due
to the unstable or even interrupted current (Table 1, entry 5).
Other catalysts such as CuI, TBAI and KI all gave lower reactivity
or poor reactivity (Table 1, entries 6–8). Among the bases
investigated, NaOH was found to be the best choice (Table 1,
entries 9 and 10). Control experiments revealed that no reaction
occurred in the absence of current, indicating that it was
essential to the reaction (Table 1, entry 11). Also, no signicant
improvement in the product yield was observed even when
tetrabutylammonium hexauorophosphate (Bu4NPF6) was
added as the electrolyte (Table 1, entry 12). An attempt was
made to replace the current by increasing the amount of catalyst
so that a large number of imines were produced and less than
30% of 3aa was produced (Table 1, entries 13 and 14). Addi-
tionally, other electrode materials such as a graphite anode or
Cu cathode have proved less efficient (Table 1, entries 15 and
16). This may be due to the discrepancy in reactivity between the
graphite electrode and the Pt electrode which may cause the
difference in current density at the anode surface, which results
in differing concentrations of electron oxidation products,
inhibiting further oxidation of 2a and decreasing the rate of
electron transfer. In addition, the overpotential of hydrogen
evolution at the cathode (Cu electrode) is higher than that of Pt,
and the aldehydes formed by anodic oxidation may be prefer-
entially reduced to alcohols at the cathode.17 It was also
observed that the reduction in current also leads to a reduction
in yield (Table 1, entry 17).
The optimized conditions were then applied to various
substrates to extend the scope of the method (Table 2). Various
substituted alcohols with different electronic properties and
functional groups were tested. It was observed that alcohols
bearing electron-donating or electron-withdrawing functional
groups could be smoothly converted to the desired products
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Table 2 Synthesis of quinazolinones from benzyl alcohols and o-
aminobenzamidesa,b
Scheme 2 Gram-scale experiment.
under the same reaction conditions, the product formed only
had a 46% yield (Table 2, 3bb).
Subsequently, the substrates of o-aminobenzamide were also
expanded (Table 2, 3an–3aw). Similar to the observation with
the alcohol substitution compounds, o-aminobenzamides with
electron-donating groups (–Me, –OMe) gave relatively higher
reactivity than those with electron-withdrawing groups (–NO2,
–F, –Cl, –Br). Whereas when heterocyclic amides were used as
the starting substrates, yields of 65% and 73% of the corre-
sponding products were also obtained (Table 2, 3ax and 3ay).
In order to demonstrate the practicality of this method, the
gram-scale preparation of 1a (5 mmol) and 2a (6 mmol) with
H2O (20 mL) under the optimized reaction conditions was
performed as shown in Scheme 2, which gave the desired
product 3aa with an 83% yield (1.47 g). This reveals that the new
procedure has signicant advantages over many current
methods for further practical applications.
To exclude the possibility of other reaction pathways, some
control experiments were performed (Scheme 3). Firstly, benzyl
alcohol 2a effectively gave benzaldehyde 4a using aerobic
oxidation reactions under standard conditions. In contrast, the
absence of either base or current lead to the production of trace
amounts of benzaldehyde, furthermore, the lack of catalyst lead
to the formation of 5a (Scheme 3 a and b) with a yield of 43%.
a
Standard Conditions: undivided cell, Pt anode, Pt cathode, 1a (0.5
mmol), 2a (0.6 mmol), I2 (0.2 mmol), NaOH (2 mmol) in H2O (3 mL), I
b
¼ 80 mA at room temperature for 6 h. Isolated yield.
with excellent yields of 79–94% (Table 2, 3ab–3aj). Because of
the stability of the electron donor to intermediates and free
radical electrons, it was found that the yield of electron-
donating substrates (–Et, –OMe) was slightly higher than that
of electron-withdrawing substrates (–NO2, –F, –Cl, –Br, –OH).
The highest yield of 94% was obtained with 4-methoxybenzyl
alcohol whereas the lowest yield was 79% with 2-hydroxybenzyl
alcohol (Table 2, 3ac and 3aj). It was obvious that heterocyclic
alcohols such as pyridinyl, thienyl and methylfuran were well-
tolerated in this catalytic system with 78% and 77% yields
(Table 2, 3al, 3am and 3az). Notably, long-chain aliphatic alco-
hols also yielded a corresponding product, but the yield was
dramatically lower than that of aromatic alcohols (Table 2, 3ak).
Furthermore, highly catalytic activities were found in trans-
formations of naphthalenemethanol to the corresponding
products (Table 2, 3ba). When alkenyl alcohol was employed
Scheme 3 Control experiments of alcohol oxidation and synthesis of
3aa.
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Nevertheless, the yield of 4a was reduced to 90% when nitrogen
was substituted for air (Scheme 3c). Then, the reaction of 1a and
4a under the standard conditions effectively gave 3aa with
a high yield of 93% (Scheme 3d), whereas the reaction of o-
aminobenzamide under a nitrogen atmosphere, resulted in 3aa
with a yield of 68% and 32% (Scheme 3e and f).
To gain an understanding of the reaction mechanism, cyclic
voltammetry (CV) was then conducted (Fig. 2). Using H2O as the
solvent, a glass electrode as the working electrode, platinum
wire as the opposite electrode, and SCE as the reference elec-
trode with a 0.1 V sꢀ1 scanning rate. By comparing curves c, f
Scheme 4 Proposed mechanism for this transformation.
and g, it was observed that the onset potential of the I2 oxidation
shied from 1.57 to 1.07 V vs. SCE in the presence of substrate
2a, which was more than that in the presence of NaOH, indi-
cating that I2 was more likely to react with b than dis-
proportionated with NaOH (Fig. 2, curves c, f and g). However,
a reduction peak appears in b at 0.43 V, and the reduction peak
of I2 was 0.69 V, indicating that Iꢀ is still carrying out the
reduction reaction in the presence of b (Fig. 2, curve c and g).
Interestingly, the addition of 1a and NaOH further decreases
the onset potential of I2 complex oxidation to 0.99 V vs. SCE
(Fig. 2, curve e). In contrast, the oxidation potential increased
when NaOH was added individually, and this may be evidence
that NaOH does not interact with 2a and I2 (Fig. 2, curve d).
By considering the whole of the experimental ndings,
a
plausible mechanistic pathway for the formation of
compound 3aa is outlined in Scheme 4. First of all, benzyl
alcohol 2a is rst oxidized to benzaldehyde 4a by I2, which is
generated in situ on the anode.6a,18 The iodine undergoes
cathodic reduction by regenerating the iodide ion for the cata-
lytic cycle. Next, 4a can readily react with 1a to obtain the imine
D, imine D is then converted to E in the presence of a base, and
thus E oxidizes and dehydrogenates to give the desired product
3aa.19 Finally, H+ removed from E combines with O2 to form
H2O at the cathode.20
Lots of nuclear nitrogen heterocycles, such as pteridine
which is a widely existing aromatic compound, similar to qui-
nazolines, which are tyrosine kinase inhibitors, which have
good specicity and inhibitory activity on tumour cells. It is
Fig. 2 Cyclic voltammetry measurements were performed at room Scheme
5
Synthesis
of
N-(4-methoxyphenyl)-6-(2,2,2-tri-
temperature with standard three electrode systems.
fluoroethoxy) pteridin-4-amine (A3).
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mmol), NaOH (2.0 mmol) and water (3 mL). The mixture was
stirred at room temperature for 6 h in a 80 mA circuit. Aer the
reaction was completed the solution containing the crude
product was concentrated under vacuum, and the residue was
puried by column chromatography on a silica gel (petroleum
ether/ethyl acetate ¼ 3/1) to give the target product as a white
solid.
Conflicts of interest
There are no conicts to declare.
Fig. 3 In vitro inhibitory data of target compounds against A549, HCT-
Acknowledgements
116 and SGC-7901 cell line.
This work was supported by the Fujian Provincial Foundation
(Grant No. FJNMP-201902, FJNMP-2020004, 2019R11020034-1,
2020J01622, 2020J01627).
thought that many uorine-containing drugs have been widely
used in clinical situations. The introduction of uorine atoms
and uorine-containing groups into drugs can improve the
clinical efficacy of drugs and reduce their side effects. Based on
this, the electrocatalytic system was applied to the synthesis of
the structure of the trexine and the synthesis of getinib
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analogues.
For
example,
N-(4-methoxyphenyl)-6-(2,2,2-
triuoroethoxy)pteridin-4-amine A3 was synthesized from 3-
amino-6-(2,2,2-triuoroethoxy) pyrazine-2-carboxamide with
a yield of 56% (see Scheme 5). The compounds were then tested
using the MTT assay and the results are shown in Fig. 3. The A3
inhibited human non-small-cell lung carcinoma cells, A549,
human colon cancer cells, HCT-116, and human gastric cancer
cells, SGC-7901 to different degrees. As shown in Fig. 3, the
results showed that the IC50 value of A3 in HCT116 cells (IC50 ¼
14.79 mg mLꢀ1 in A549 cells, IC50 ¼ 34.52 mg mLꢀ1 in HCT116
cells, IC50 ¼ 36.44 mg mLꢀ1 in SCG-7901 cells) was just sur-
passed by that of getinib.
Conclusions
In summary, it is demonstrated that simple and commercially
available I2 could be used as an electrocatalyst for the selective
oxidation of a range of activated C–H bonds in alcohols. It is
also demonstrated that I2 together with electrochemistry is
a mild catalyst to efficiently promote C–H oxidation reactions.
Oxidative tandem cyclization is of importance in the synthesis
of heteropolycyclic skeletons and has a high atom economy.
Furthermore, use of both electrocatalysis as a reaction process
and water as a green solvent was consistent with the concept of
green synthesis. This catalytic protocol avoids using toxic
reagents and shows a broad substrate scope, providing consis-
tently good yields of quinazolinones under constant current at
room temperature for 6 h. Further extension of this electro-
chemical protocol to the synthesis of other heterocycles is
underway.
Experimental section
General procedure (for Tables 1 and 2)
To a dried 10 mL quartz tube equipped with 80 mA current was
added benzamide (0.5 mmol), alcohol (0.6 mmol), I2 (0.2
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