[bmIm]OH: An efficient basic catalyst for the synthesis of 4H-benzo[d][1,3-]oxazin-4-one derivatives in solvent-free conditions

Article abstract of DOI:10.1016/j.tetlet.2014.09.055

Reusable [bmIm]OH was found to be a highly efficient renewable homogenous catalyst for the rapid and convenient synthesis of benzoxazine-4-one derivatives from o-iodobenzoic-acid and benzonitrile at 75 °C in moderate to good yields. This methodology provides a facile and straightforward path to construct other related heterocycles in an eco-compatible fashion.

Full text of DOI:10.1016/j.tetlet.2014.09.055

Accepted Manuscript
[bmIm]OH: An efficient basic catalyst for the synthesis of 4H-benzo[d][1,3-]ox-
azin-4-one derivatives in solvent -free conditions
Malik Abdul Waseem, Shireen, Anjali Srivastava, Arjita Srivastava, Rahila, I.R.
Siddiqui
PII:
S0040-4039(14)01556-1
DOI:
http://dx.doi.org/10.1016/j.tetlet.2014.09.055
TETL 45149
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
3 July 2014
6 September 2014
8 September 2014
Please cite this article as: Waseem, M.A., Shireen, Srivastava, A., Srivastava, A., Rahila, Siddiqui, I.R., [bmIm]OH:
An efficient basic catalyst for the synthesis of 4H-benzo[d][1,3-]oxazin-4-one derivatives in solvent -free conditions,
Tetrahedron Letters (2014), doi: http://dx.doi.org/10.1016/j.tetlet.2014.09.055
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1
Tetrahedron Letters
jo u rn al h ome p ag e : w ww .e lse vie r .c om
[bmIm]OH: An efficient basic catalyst for the synthesis of 4H-benzo[d][1,3-
]oxazin-4-one derivatives in solvent -free conditions.
Malik Abdul Waseem, Shireen, Anjali Srivastava, Arjita Srivastava, Rahila, I.R. Siddiqui,*
a Laboratory of Green Synthesis, Department of Chemistry, University of Allahabad, Allahabad
Email: dr.irsiddiqui@gmail.com
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
Reusable [bmIm]OH was found to be a highly efficient renewable homogenous
catalyst for the rapid and convenient synthesis of benzo-oxazin-4-one derivatives
from o-iodobenzoic-acid and benzonitrile at 75°C in moderate to good yield.
This methodology provides a facile and straightforward path to construct other
related heterocycles in eco-compatible fashion.
Available online
Keywords:
Green protocol
[bmIm]OH
2009 Elsevier Ltd. All rights reserved.
intermolecular heterocyclization
benzo-oxazin-4-one
iodobenzoic acid
limitations including unsatisfactory yield, long reaction time,
limited substrate tolerance, use of expensive catalyst, toxic
organic solvents and cumbersome experimental procedure. All
As part of eco-compatible organic transformations, ionic
liquids (ILs) have received substantial attention from the
synthetic community5,6 owing to their properties like negligible
vapour pressure, lack of flammability, wide solvating ability and
high stability.. Today, ionic liquids offer their potential in
controlling a reaction as a catalyst as well as playing a role in rate
enhancement of a reaction7.The association of reactant molecules
in solvent cavities due to the internal pressure created by ionic
environment of the ionic liquid is probably responsible for the
rate enhancement8-10. Basic ionic liquids have attracted huge
interest for a longtime by virtue of their catalytic efficiency, easy
recovery and reuse as compared to the combination of a base and
IL in a base-catalyzed process11. A basic ionic liquid [BMIM]OH
(1-butyl-3-methylimidazolium hydroxide) has been successfully
employed as a catalyst for Michael addition12, Knoevenagel
these drawbacks prompted us to develop a more efficient,
28-32
convenient and eco-friendly methodology
for the synthesis
of this aesthetically appealing molecular architecture.
The processes that involve the incorporation of fragments
from different starting components and construction of multiple
chemical bonds allows a high level of complexity and diversity to
built into pharmaceutically important products and drug like
small molecules.
O
O
O
O
H
N
OMe
O
O
O
N
O
N
CF3
N
O
I
II
III
condensation 13, Markovnikov addition, and a number of other
O
N
O
N
14,15
Br
O
O
reactions
.It has very successfully replaced conventional
-
bases as it is flexible, non-volatile and non-corrosive.
O
(CH2 )
15
IV
V
4H-3,1-Benzoxazin-4-ones are ubiquitous building blocks in
medicinal chemistry and are of great interest to organic chemists
owing to their diverse biological activities.16,17 Some of the 2-
substituted 4H-3,1-benzoxan-4-ones act as chymotrypsin
inactivator18, HSV(1), protease inhibitors (II),19 inhibitors of
human leucocyte elastase (III),20 compound( IV) lower level of
plasma cholesterol and triglyceride.21 In addition, cetilistat (V),
Figure 1: Medicinally recognized compounds with
benzooxazine-4-one as a core structure.
In view of above consideration, here in we wish to report a
more practical and expedient synthesis of 4H-benzo[d][1,3-
]oxazin-4-one derivatives by using iodobenzoic acid and
benzonitrile in basic ionic liquid ([bmIm]OH) at 75oC (Scheme
1)
a
novel lipase inhibitor, showed promising anti-obesity
remedies22 ( Figure 1). Therefore, its synthesis has received
intensive attention in medicinal chemistry research. A number of
synthetic routes have been reported for the synthesis of benzo-
oxazin-4-ones 24,27. Numerous elegant protocols for the synthesis
of this scaffold involving various types of catalysts have been
reported. Despite these advances, there are still some potential
O
O
N
C
O
[bmIm]OH,20%mol%
OH
R1
R1
R2
75°C , 73-91%
N
I
R2
4a
Scheme 1: [bmIm]OH promoted synthesis of benzo-oxazin-4-one and its
derivatives

2
Tetrahedron Letters
This synthetic protocol is efficient, convergent and allows
Table2: Influence of various mol% of [bmIm]OH on
benzooxazine-4-one derivativesa 4a
easy placement of various types of substituents around the
periphery of the heterocyclic ring system. Our careful literature
survey revealed that there is no report on the use of [bmIm]OH as
a catalyst for the synthesis of benzo-oxazine derivatives.
O
N
O
I
N
C
O
[bmIm]OH, mol%
OH
75°C
In our preliminary experiments we attempted to investigate
the optimization of the reaction conditions regarding the solvent,
base, time and yield. For this, 2-iodobenzoic acid and
benzonitrile were selected as model substrates. In order to find
optimum reaction condition equimolar amounts of model
substrates were used in the absence of catalyst but no desired
product were formed (Table 1, entry 1).However, when the
reaction was carried out in presence of organic bases like NEt3,
DBU, pyridine, product was obtained but the reaction took long
time for completion with low yield .(Table 1 Entry 2, 3, 4).
Entry
Catalyst mol% Time (h)
Yieldb (%)
1
2
3
4
5
6
7
10
20
25
30
35
40
45
8.5
8
7.5
7.5
7
51
67
73
80
91
91
91
7
7
aReaction conditions: Benzonitrile (2.0 mmol) and o-iodobenzoic acid (2.0
mmol) in [bmIm]OH.
Table 1 Screening of base, solvent, tempature for the
synthesis of benzooxazine-4-one derivativesa 4a
bIsolated yields.
O
O
Next, a series of catalytic cycles were run to explore the
consistancy of the catalyst activity for the synthesis of benzo-
oxazine derivatives. After completion of reaction, the product
was extracted with ethyl acetate. The catalyst left after extraction
was used for the subsequent cycles. The results showed that there
was no appreciable loss in yield of product (4a) up to five times
of recycling of [bmIm]OH..(Table 3 Entries 1-5).
N
C
O
Solvents
OH
Base
N
I
Time(h) Yieldb%
Base
-
Mol% Temp75°C
Entry Solvent
1
2
3
4
EtOH
EtOH
EtOH
-
Reflux
Reflux
Reflux
Reflux
12
11
11
10
-
NEt3
5
7
5
23
21
19
DBU
Table 3 Reusability of catalyst for the synthesis of
benzooxazine-4-one derivatives a 4a
EtOH Pyridine
O
O
Reusability
of bmImOH
5
6
7
8
DCM NaOH,
10
5
5
100
110
75
11
12
12
7
27
23
21
91
C
N
O
OH
THF
KOH
N
Yield%
I
CH2Cl2 K2CO3
[bmIm]OH 35
75
aReaction conditions: Benzonitrile (2.0 mmol) and o-iodobenzoic acid (2.0
mmol) , Solvents, Bases, Basic [bmIm]OH.
Entry
Time (h)
Yieldb (%)
1
2
3
4
5
7
7
7
91
91
89
89
87
bIsolated yields
Replacing organic bases by inorganic bases, NaOH, KOH,
K2CO3 in different solvents like DCM, THF, CH2Cl2 in sealed
vessels, no progress in reaction time and product yield were
observed (Table1 entries 5,6,7, We then planned to exploit
[bmIm]OH as a basic catalyst. To our delight the reaction
resulted in the formation of desirable products (4a) in good yield
with appreciable reaction time, as monitored by TLC (Table 1
entry 8). With [bmIm]OH as good activator in hand, we next
intended to investigate the reaction by using different amounts of
[bmIm]OH.
7.5
7.5
aReaction conditions: Benzonitrile (2.0 mmol) and o-iodobenzoic acid (2.0
mmol) and [bmIm]OH (35mol).
bIsolated yields.
Next, to explore the robustness of the methodology, various
derivatives of o-halo benzoic acid and benzonitrile were used for
For this, we first examined the synthesis of 4a in the presence
of 10mol% of [bmIm]OH. After 8.5h, the desired product 4a was
formed in small amounts (Table 2, Entry 1). Use of 20, 25 and
30 mol% of catalyst afforded the desired product with moderate
to good yield (Table 2, Entry 2, 3, 4) while using 35mol% of
catalyst the yield of product was excellent (Table 2 entry 5).On
increasing further mol% of ionic liquid to 40 and 45mol% no
enhancement of product yield was observed (Table 2, entry 6, 7).
Finally, we noticed that 35mol% of [bmIm]OH was the most
appropriate amount of catalyst for achieving the desired
conversion .( Table 2,Entry 5)
the construction of a
corresponding functionalized benzo-oxazinone derivatives were
obtained in good yield. The results are summarized in Table 4.
library of benzo-oxazinone. The
Table 4 Scope of substrate for the synthesis of benzooxazine-
4-one derivativesa 4a
O
O
N
C
O
[bmIm]OH,35%mol%
OH
R1
R1
R2
75C, 73-91%
N
I
R2
Entry Benzonitrile o-Halobenzoic
acid
Product (a-m)
Time(h)
3
Yieldb
(%)
O
O
CO2H
1
87
C
N
I
N
4a

3
O
N
CO2H
I
2
3
91
C
N
N
N
O
OH
4b
O
C
O
C
N
N
N
O
N
CO2H
I
3
4
4
5
89
85
O
C
N
O
OH
O
OH
4c
O
I
I
O
CO2H
I
C
N
F
O
N
4d
F
O
CO2H
5
6
7
8
4
3
3
4
80
85
83
75
C
N
O
O
Cl
I
Cl
N
4f
O
N
N
O
O
CO2
I
H
O
OH
I
N
C
C
N
N
O
O
O
N
O
O
CO2H
I
O
O
N
N
4g
CO2H
I
O
F
C
N
F
O
N
Scheme 2: Tentative mechanism for 4H-benzo[d][1,3-]oxazin-4-ones
4h
O
CO2
I
H
Cl
9
5
5
80
83
C
N
Cl
O
On the basis of above results, a plausible mechanism for the
formation benzo-oxazin-4-ones derivatives 4(a-m) can be
tentatively presented , (scheme 2.) Presumably the reaction is
triggered by proton abstraction from carboxylic group of o-
iodobenzoic acid by hydroxyl group of [bmIm]OH. Then
nucleophilic attack of generated carboxylate anion on activated
nitrile group, followed by intramolecular nucleophilic attack of
the C=N- on the I of o-iodobenzoic acid provides the target
heterocyclic compounds 4(a-m). Scheme 2
N
4i
O
N
CO2H
I
10
O
C N
O
4j
O
O
CO2H
I
11
4
76
O2N
C N
O
N
4k
NO2
O
N
CO2
I
H
F3
C
In summary, we have disclosed a convenient ,efficient and
straightforward two -component one-pot approach for the
synthesis of 4H-benzo[d][1,3-]oxazin-4-one framework using
the environmentally benign catalyst [bmIm]OH under metal-free
conditions. In this experimentally simple process two new bonds
are formed in a single operation with all reactants efficiently
utilized. Further no by-product formation was observed .The
short reaction time, excellent yield and more importantly
recyclability without losing catalytic activity prove that the
protocol is a good alternative to the previously reported
methods.
12
13
5
5
73
81
F3
C
C
N
O
4l
O
N
CO2
H
F3
C
C
N
O
I
4m
CF3
aReaction conditions: Benzonitrile (2.0 mmol) and o-iodobenzoic acid (2.0
mmol) and [bmIm]OH (35mol) was stirred at room temperature for (3-5) h.
bIsolated yields.
When benzonitrile and its derivatives were
used under
optimized conditions, the compounds with electron-donating
group on the benzene furnished the corresponding products in
higher yields than the substrates with electron withdrawing
substitutents.(Table 4, entry 1,2,3,4,10,11,13)..When several
derivatives of iodobenzoic acid were used in this reaction,
compounds containing electron donating groups gave high
yields (Table 4 entries 6,7) and componds with electron
withdrawng groups furnished the products in low yield (Table 4
entries 5,8,9,12).
Acknowledgement
The authors gratefully acknowledge UGC, New Delhi for
financial grant in the form of junior research fellowship and
Department of Chemistry, University of Allahabad, Allahabad.
The authors would also like to thank SAIF, Chandigarh for
spectral analysis.
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GRAPHICAL ABSTRACT
[bmIm]OH: An efficient basic catalyst for the synthesis of 4H-benzo[d][1,3-
]oxazin-4-one derivatives in solvent free condition.
Malik Abdul. Waseem, Shireen, Arjita Srivastava, Anjali Srivastava, Rahila, I.R. Siddiqui,*
Laboratory of Green synthesis, Department of Chemistry, University of Allahabad, Allahabad, 211002,
India.
E-mail: dr.irsiddiqui@gmail.com
O
O
N
N
20mol%
OH
N
C
O
OH
R1
R1
R2
N
I
rt , 73-91%
R2