PEG-600 mediated one-pot reaction of 3-acetyl-2: H -chromen-2-one with heterylthiols and phenylthioureas using tetrabutylammonium tribromide as an efficient green reagent

Article abstract of DOI:10.1039/c7nj00504k

A simple method for the one-pot reaction of 3-acetyl-2H-chromen-2-one with different heterylthiols and phenylthioureas under green conditions using tetrabutylammonium tribromide (TBATB) as an efficient reagent has been described. 3-Acetyl-2H-chromen-2-one

Full text of DOI:10.1039/c7nj00504k

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The role of atropisomers on the photo-reactivity and fatigue of
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PEG-600 mediated one-pot reaction of 3-acetyl-2H-chromen-2-one with
heterylthiols and phenylthioureas using Tetrabutylammonium Tribromide as
an efficient green reagent
Devulapally Srikrishna* and Pramod Kumar Dubey
Department of Chemistry, Jawaharlal Nehru Technological University Hyderabad
College of Engineering, Kukatpally, Hyderabad, Telangana ꢀ 500 085, India.
Email ID: devulapallisrikrishna@gmail.com
Ph. No.: +91ꢀ9951306098, Fax No.: 040ꢀ23057787.
Abstract: A facile method for the oneꢀpot reaction of 3ꢀacetylꢀ2Hꢀchromenꢀ2ꢀone with different
heterylthiols and phenylthioureas has been described under green conditions using
tetrabutylammonium tribromide (TBATB) as an efficient reagent. 3ꢀacetylꢀ2Hꢀchromenꢀ2ꢀone
reacted with TBATB in acetic acid to give 3ꢀ(2ꢀbromoacetyl)ꢀ2Hꢀchromenꢀ2ꢀone. PEGꢀ600 was
found to be the effective solvent for this reaction. Thus, oneꢀpot reaction of equimolar amounts
of 3ꢀacetylꢀ2Hꢀchromenꢀ2ꢀone, TBATB & heterylthiols/phenylthioureas independently, resulted
in the formation of heterylthioacetylcoumarins and coumarinylthiazoles respectively. Effect of
solvent on these reactions has been studied. The merits of this preparation are mild reaction
conditions, easy workup, good yields and use of PEGꢀ600 as green reaction media.
Keywords: 3ꢀAcetylꢀ2Hꢀchromenꢀ2ꢀone, tetrabutylammonium tribromide, heterylthiols,
phenylthioureas and PEGꢀ600.
INTRODUCTION
Coumarin is one of the important parent compounds found in many plants and could be
used as an important component of various functional materials and shown diverse
1
2
pharmacological properties. Some of the important activities include antitumor, antiꢀ
3
4
5
inflammatory, antiꢀcoagulant, and antiꢀoxidant etc. Coumarins containing other heterocycles
1

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such as thiazole, imidazole, and oxazole have been reported to possess various biological
6
ꢀ10
activities which requires 3ꢀ(2ꢀbromoacetyl)ꢀ2Hꢀchromenꢀ2ꢀone as a starting material. Also 3ꢀ
2ꢀbromoacetyl)ꢀ2Hꢀchromenꢀ2ꢀone is a very attractive synthetic intermediate since it has been
(
11
used for a variety of organic transformations especially for the synthesis of thiadiazines ,
1
2
13
14
15
16
pyrans,
phosphates, etc.
ꢀ(2ꢀbromoacetyl)ꢀ2Hꢀchromenꢀ2ꢀone is generally prepared by the reaction of 3ꢀacetylꢀ
pyridines,
thiadiazoles,
oxadiazoles,
selenazoles,
phosphonates and
1
7
3
1
8
2
Hꢀchromenꢀ2ꢀone with liquid bromine. However, bromine is a corrosive, toxic, maintenance
of stoichiometry is difficult and special care is required for its storage and transportation, it is
very important for various organic transformations. Therefore there has been a search for benign
reagents which can act as bromine alternatives. A number of such alternatives have been
reported in literature for the synthesis of 3ꢀ(2ꢀbromoacetyl)ꢀ2Hꢀchromenꢀ2ꢀone in recent days.
1
9
Shaikh et al. reported the synthesis of 3ꢀ(2ꢀbromoacetyl)ꢀ2Hꢀchromenꢀ2ꢀone by the
reaction of 3ꢀacetylꢀ2Hꢀchromenꢀ2ꢀone with copper(II)bromide in 1:1 ethyl acetate and
2
0
chloroform under reflux conditions for 12 h in 90 % yield. Abdolali et al. reported the synthesis
of 3ꢀ(2ꢀbromoacetyl)ꢀ2Hꢀchromenꢀ 2ꢀone from 3ꢀacetylꢀ2Hꢀchromenꢀ2ꢀone by its reaction with
Nꢀbromosuccinimide in 1:5 ratio of acetonitrile and chloroform using pꢀtoluenesulfonic acid as a
2
1
catalyst under refluxing conditions in 70% yield. Wang et al. reported the treatment of 3ꢀacetylꢀ
2
Hꢀchromenꢀ2ꢀone with Nꢀbromosuccinimide in the presence of pꢀtoluenesulfonic acid in
acetonitrile at 50 °C for 5 h to give 3ꢀ(2ꢀbromoacetyl)ꢀ2Hꢀchromenꢀ 2ꢀone in 75% yield.
Among all the bromine alternatives that have been developed so far, a group of reagents
that have become popular are the quaternary ammonium tribromides which are having numerous
22,23
applications in various organic transformations such as bromination reactions,
2
synthesis of

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2
4,25
26
27
28
acetals,
heterocyclic synthesis, sulfide oxidations, multiꢀcomponent reactions, oxidative
29
30,31
cyclizations, etc. Moreover, most of these tribromides are stable up to 200 °C temperatures,
and thus can be used for reactions at higher temperature, making them reagents of choice over
3
2,33
liquid bromine at elevated temperatures.
Among all these, Tetrabutylammonium tribromide
(TBATB) has drawn the attention of researchers because of its stability, easier method of
34
preparation and has certain advantages over liquid bromine. TBATB was first synthesized by
3
5
Buckles et al. from tetrabutylammonium bromide and liquid bromine.
Oneꢀpot synthesis is an important strategy to improve the efficiency of a chemical
reaction whereby a reactant is subjected to successive chemical reactions just in one reaction
vessel. This is much desired by chemists because avoiding lengthy processes and purifications of
the intermediate compounds would save time and resources with enhancing the product yield.
3
6
Rao et al. reported the oneꢀpot synthesis of aminothiazole by heating a mixture of 3ꢀ
acetylꢀ2Hꢀchromenꢀ2ꢀone, iodine and phenylthioureas on water bath for 24 h. Gouda et al.
3
7
described the oneꢀpot reaction of 3ꢀacetylꢀ2Hꢀchromenꢀ2ꢀone with iodine and thiourea to yield
3
8
the corresponding aminothiazole in refluxing ethanol for 8 h. It was reported from our
laboratory, a oneꢀpot reaction of 3ꢀacetylꢀ2Hꢀchromenꢀ2ꢀone, 1Hꢀbenzo[d]imidazoleꢀ2ꢀthiol &
iodine in isopropyl alcohol at room temperature for 4ꢀ5 h to give the corresponding condensed
products.
3
9,40
Thus, based on the above literature reports and in continuation of our research work
it was considered worthwhile to develop an alternative method which avoids the use of liquid
bromine or the use of iodine for the oneꢀpot reaction of 3ꢀacetylꢀ2Hꢀchromenꢀ2ꢀones with
heterylthiols and phenylthioureas.
3

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RESULTS AND DISCUSSION:
Commercially available salicylaldehyde was treated with ethyl acetoacetate in
triethanolamine containing catalytic amount of Lꢀproline at RT for 30 min to yield 3ꢀacetylꢀ2Hꢀ
chromenꢀ2ꢀone (1). The later, on bromination, using tetrabutylammonium tribromide (TBATB)
in acetic acid, at room temperature for 2 h afforded 3ꢀ(2ꢀbromoacetyl)ꢀ2Hꢀchromenꢀ2ꢀone (2)
(Scheme 1).
Scheme 1. Synthesis of 3ꢀ(2ꢀbromoacetyl)ꢀ2Hꢀchromenꢀ2ꢀone (2)
With a view to optimize the reaction conditions for the formation of compound 2 in
maximum yield & in shorter reaction time, the reaction of 1 with TBATB was examined by
treating equimolar amounts of the reactants in different solvents (Table 1).
Table 1. Optimization of reaction conditions for the synthesis of 2 from 1 using TBATB at RT
#
S. No.
Solvent
Acetic acid
Ethanol
Time
2 h
Yield (%)
1
2
3
4
5
6
7
92
83
78
96
86
61
70
4 h
Glycerol
2 ½ h
1 ½ h
4 h
PEG-600
Methanol
Acetonitrile
Isopropyl alcohol
3 h
5h
4

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8
9
Tetrahydrofuran
3 ½ h
6 h
81
56
1,4ꢀDioxane
1
0
Water
10 h
Nil
#
Isolated yield.
Among all these conditions PEGꢀ600 was found to be the best solvent in terms of
reaction time and yield. So, keeping this best result in hand, we have utilized PEGꢀ600 for the
oneꢀpot reaction of 3ꢀacetylꢀ2Hꢀchromenꢀ2ꢀone (1) with various nucleophiles.
Initially, the oneꢀpot reaction was performed between 3ꢀacetylꢀ2Hꢀchromenꢀ2ꢀone (1)
and xanthate salt i.e., potassium Oꢀmethyl carbonodithioate 3a (i.e., 3, R=CH ) in PEGꢀ600
3
without the use of any base or any phase transfer catalyst (PTC) to check whether the reaction is
forwarding or not. Surprisingly, the reaction completed just in 1 h to result in the formation of
corresponding condensed product Oꢀmethyl Sꢀ(2ꢀoxoꢀ2ꢀ(2ꢀoxoꢀ2Hꢀchromenꢀ3ꢀyl)ethyl)
carbonodithioate, 4a (i.e., 4, R=CH ) in good yields. It was found that in this reaction PEGꢀ600
3
4
0ꢀ
found to play the dual role as a base and also as a PTC which was reported earlier in literature.
4
1
This reaction was also extended to other xanthate salts i.e., potassium Oꢀethyl carbonodithioate
3
b (i.e., 3, R=C H ), potassium Oꢀisopropyl carbonodithioate 3c (i.e., 3, R=C(CH ) ) to obtain
2
5
3 3
the compounds 4b and 4c respectively (Scheme 2).
O
O
O
O
O
O
S
TBATB
S
+
KS
OR
PEG-600 / RT /1-1.5 h
S
OR
(1)
(3)
(4)
3
a : R=CH3,
4a : R=CH3,
4b: R=C2H5,
4c: R=C(CH3)3
3b: R=C H ,
2
5
3
c: R=C(CH3)3
Scheme 2. Oneꢀpot reaction of 3ꢀacetylꢀ2Hꢀchromenꢀ2ꢀone, TBATB & xanthate salts.
5

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Encouraging with the above positive result, oneꢀpot reaction between 3ꢀacetylꢀ2Hꢀ
chromenꢀ2ꢀone (1), TBATB and different heterylthiols performed independently in PEGꢀ600.
Reaction was completed successfully in 2ꢀ3 h at RT itself to give the corresponding condensed
products, i.e., 6(a-c) (Scheme 3).
Scheme 3. Oneꢀpot reaction of 1, TBATB & 5 to give 6
In order to check the effect of solvent on this reaction, we have optimized the reaction
conditions for the reaction between 3ꢀacetylꢀ2Hꢀchromenꢀ2ꢀone (1), TBATB & 1Hꢀ
benzo[d]imidazoleꢀ2ꢀthiol (5a) using different solvents (Table 2). Form the optimization studies
it was found that PEGꢀ600 as the best reaction medium for the reaction to occur in lesser time
and in maximum product yield.
Table 2. Optimization of reaction conditions for the synthesis of 6a from 1, 5a & TBATB at RT
#
S. No.
Solvent
Ethanol
Glycerol
PEG-600
Methanol
DMF
Time
6 h
Yield (%)
1
2
3
4
5
63
78
84
60
64
4 h
2 ½ h
7 h
4 ½ h
6

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6
7
8
9
Isopropyl alcohol
5 h
6 ½ h
8 h
57
70
Tetrahydrofuran
1,4ꢀDioxane
Acetic acid
Water
51
10 h
10 h
Nil
Nil
10
#
Isolated yield.
The above products 6 could also be prepared alternatively by the reaction of 4a with each
of oꢀphenylenediamine (7a), oꢀaminophenol (7b) & oꢀaminothiophenol (7c) independently in
refluxing ethanol for 2ꢀ4 h, but in lower yields. Thus, these compounds 6, prepared in this route
were found to be identical with the ones that obtained in the earlier route in all respects such as
mp, mmp and coꢀTLC (Scheme 4).
Scheme 4. Alternative method for the preparation of 6.
From the above set of reactions, TBATB has been found to be an effective reagent for the
direct reaction of 3ꢀacetylꢀ2Hꢀchromenꢀ2ꢀone (1) with sulfur nucleophiles. The efficiency of this
reagent was extended to test a reaction between 3ꢀacetylꢀ2Hꢀchromenꢀ2ꢀone (1) and
phenylthiourea 8a (i.e., 8, Ar=C H ) under the same reaction conditions. Thus a mixture of
6
5
equimolar amounts of 1, TBATB, phenylthiourea in PEGꢀ600 was stirred at RT. Interestingly,
the reaction was completed just in 2 h to yield a product which was characterized as 3ꢀ(2ꢀ
7

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(phenylamino)thiazolꢀ4ꢀyl)ꢀ2Hꢀchromenꢀ2ꢀones (9) that was found to be identical with the
product obtained by the reaction of 3ꢀ(2ꢀbromoacetyl)ꢀ2Hꢀchromenꢀ2ꢀone (2) with
phenylthiourea in ethanol under reflux conditions, a reaction that is usually known as Hantzsch
thiazole synthesis. Thus, this oneꢀpot reaction of 1 with TBATB and phenylthiourea in PEGꢀ600
was found to be a general one and was extended to other substituted phenylthioureas (Scheme 5).
Scheme 5. Oneꢀpot synthesis of 3ꢀ(2ꢀ(phenylamino)thiazolꢀ4ꢀyl)ꢀ2Hꢀchromenꢀ2ꢀones (9)
The scope of formation of product 9a in maximum yield & in lesser reaction time was
further studied using various solvents (Table 3). From this optimization study, we came to a
conclusion that PEGꢀ600 is the best reaction medium for the oneꢀpot reaction of 3ꢀacetylꢀ2Hꢀ
chromenꢀ2ꢀone (1), TBATB & various nucleophiles in terms of reaction time & product yield.
Table 3. Optimization of reaction conditions for the synthesis of 9a from 1, 8a & TBATB at RT
#
S. No.
Solvent
Ethanol
Glycerol
PEG-600
Methanol
DMF
Time
7 ½ h
6 ½ h
3 h
Yield (%)
1
2
3
4
5
61
65
88
58
60
9 h
7 ½ h
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6
7
8
9
Isopropyl alcohol
7 h
8 h
57
53
Tetrahydrofuran
1,4ꢀDioxane
Acetic acid
Water
9 h
46
10 h
10 h
Nil
Nil
10
#
Isolated yield.
The mechanism for these oneꢀpot reactions was studied and it was found from literature
that TBATB known to release anhydrous HBr in an alcoholic medium and in other organic
4
2ꢀ44
solvents.
brominations that ordinarily performed with molecular bromine. Thus, it reacts with 3ꢀacetylꢀ
Hꢀchromenꢀ2ꢀone (1) in PEGꢀ600 to give the corresponding 3ꢀ(2ꢀbromoacetyl)ꢀ2Hꢀchromenꢀ2ꢀ
TBATB can be considered as a general brominating agent which can be used in
2
one (2), HBr and tetrabutylammonium bromide (TBAB). 2, thus formed reacts inꢀsitu with
heterylthiols (5) or phenylthioureas (8) to give the corresponding products 6 or 9. The beauty of
this reaction is, TBATB during its reaction generates TBAB and will be in the reaction mass, act
as a Phase Transfer Catalyst and further enhances the progress of reaction inꢀsitu (Scheme 6).
9

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O
O
O
O
O
+
Bu NBr PEG-600
Bu
TBAB
acts as a PTC &
4
NBr
+
HBr
4
3
O
+
(
TBATB)
(2)
Br
(1)
enhances the progress of
reaction in-situ
N
X
S
S H
K S
8)
PEG-600
OR
(
(5)
O
O
O
O
O
O
S
PEG-600
X
S
OR
S
N
S
PEG-600
HS
(4)
(6)
NH
Ar
NH
Ar
H N
HN
2
(3)
O
O
O
O
O
O
O
O
S
S
N
S
N
(9)
NH
Ar
HN Ar
H N
Ar
HN
2
O
O
N
O
O
N
O
O
S
S
N
S
O
HO
N
N
Ar
H
H
H
N
Ar
Ar
Scheme 6. Plausible mechanism for the oneꢀpot reaction.
Characterization of TBATB:
Even though the formation of the reagent was compared with the available literature data,
further characterization is always an added advantage. Keeping this in view, we characterized the
reagent with SEM–EDX analysis, powder XRD analysis.
SEM–EDX analysis of TBATB:
To study the surface morphology of the reagent, i.e., TBATB, SEM micrograph of the
reagent was recorded. The SEM images of the reagent (Fig. 1) showed an even distribution and
in a proper alignment which was recorded at 10 µm. Further, EDX analysis (Fig. 2) is generally
1
0

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carried out to know the elemental composition of the material of our interest. For TBATB, EDX
analysis showed the presence of C, N and Br elements.
Fig. 1 SEM image of TBATB at different magnifications
1
1

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Fig. 2: EDX analysis of TBATB
Powder X-ray diffraction (XRD) analysis of TBATB:
The nature of the prepared reagent (TBATB) was identified by powder XRD. Xꢀray
patterns of the reagent was recorded at 2 theta = 10–80° range (Fig. 3). A broad peak centered at
2
theta angle showed strong crystalline peaks in the range 10–60° confirmed the nature of the
TBATB reagent as crystalline.
Fig. 3: Powder Xꢀray diffraction analysis of TBATB
1
2

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Experimental Section
Melting points are uncorrected and were determined in open capillary tubes using hot
sulphuric acid bath. TLC analyses were done on silica gelꢀG coated sheets supplied by Merck
Company and visualization was done using UV lamp and iodine. IR spectra were recorded using
1
Perkin Elmer modelꢀ446 FTIR in KBr. H NMR spectra were recorded in DMSO–d using TMS
6
as an internal standard using Varian 400ꢀMHz spectrometer instrument. Mass spectra were
recorded on AgilentꢀLCMS instrument. Starting materials salicyladehydes, ethyl acetoacetate,
liquid bromine and solvents like PEGꢀ600 were obtained from commercial suppliers and were
used as such.
General procedure for the preparation of 1 from salicylaldehyde:
A mixture of a salicylaldehyde (10 mM), ethyl acetoacetate (12 mM) and 25 mol% of Lꢀproline
in triethanolamine (5 mL) was stirred at RT for 30 min. The progress of the reaction was
monitored by TLC. After the completion of reaction, the mixture was poured into iceꢀcold water
(30 mL). The separated solid was filtered, washed and dried. The crude product was
recrystallized from a methanol to obtain pure 1.
Yield 1.80 g (96%). m.p.121ꢀ123 °C.
General procedure for the preparation of 4 from 1:
A mixture of 1 (1.88 g, 10 mmol), tetrabutylammonium tribromide (TBATB) (4.82 g, 10 mmol),
xanthate salt (3) (10 mmol) and PEGꢀ600 (30 mL) was stirred at RT for 1ꢀ1½ h. After
completion of reaction, as indicated by TLC, the mixture was poured into iceꢀcold water
(100 mL). The separated solid was filtered, washed with water (2×30 mL) and airꢀdried at RT.
The crude product was recrystallized from suitable solvent to obtain pure 4.
O-methyl S-(2-oxo-2-(2-oxo-2H-chromen-3-yl)ethyl) carbonodithioate (4a)
1
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ꢀ1
Yield = 2.58 g (88%); mp 196–198 °C (Chloroform); IR (KBr): 1263 cm (strong, sharp, ꢀC=S),
ꢀ1
ꢀ1
1
1
690 cm (strong, sharp, ꢀCO of ꢀCOCH ), 1715 cm (strong, sharp, ꢀCO of coumarin ring); Hꢀ
3
NMR (400 MHz, DMSOꢀd / TMS): δ 3.72 (s, 3H, OCH ), 4.90 (s, 2H, ꢀCH ), 4.80 (s, 2H, ꢀ
6
3
2
1
3
CH ), 7.43ꢀ8.08 (m, 4H, ArꢀH), 8.84 (s, 1H, ArꢀH); C NMR (100 MHz, DMSOꢀd ): 52.261,
2
6
55.211, 119.088, 119.255, 124.649, 128.892, 131.597, 134.409, 152.261, 158.761, 139.084,
+
1
94.649, 208.741; HRMS calculated for C H O S [M+H] : 295. 0098, Found: 295.0103.
1
3
10
4 2
O-ethyl S-(2-oxo-2-(2-oxo-2H-chromen-3-yl)ethyl) carbonodithioate (4b)
0
ꢀ1
Yield = 2.64 g (86%); M.P: 131–133 C (Methanol); IR (KBr): 1236 cm (strong, sharp, ꢀC=S),
ꢀ1
ꢀ1
1
1
695 cm (strong, sharp, ꢀCO of ꢀCOCH ), 1733 cm (strong, sharp, ꢀCO of coumarin ring); Hꢀ
3
NMR (400 MHz, DMSOꢀd /TMS): δ 1.28 (t, 3H, CH ), 4.58 (q, 2H, ꢀOCH ), 4.80 (s, 2H, ꢀCH ),
6
3
2
2
1
3
7
7
1
.41ꢀ8.08 (m, 4H, ArꢀH), 8.80 (s, 1H, ArꢀH); C NMR (100 MHz, DMSOꢀd ): 22.322, 51.340,
6
3.478, 116.543, 118.180, 125.049, 127.291, 128.345, 131.257, 137.300, 153.061, 159.881,
+
97.208, 210.171; HRMS calculated for C H O S [M+H] : 309.0255, Found: 309.0390
1
4
12
4 2
O-isopropyl S-(2-oxo-2-(2-oxo-2H-chromen-3-yl)ethyl) carbonodithioate (4c)
0
Yield = 2.89 g (90%); M.P: 173–175 C (Ethanol); IR (KBr): 1236 (strong, sharp, ꢀC=S), 1695
ꢀ1
ꢀ1
1
cm (strong, sharp, ꢀCO of ꢀCOCH ), 1724 cm (strong, sharp, ꢀCO of coumarin ring); HꢀNMR
3
(
400 MHz, DMSOꢀd /TMS): δ 1.30 (d, 6H, ꢀCH ), 4.75 (s, 2H, ꢀCH ), 5.60 (m, 1H, ꢀCH), 7.43ꢀ
6 3 2
1
3
8
5
1
3
.02 (m, 4H, ArꢀH), 8.79 (s, 1H, ArꢀH); C NMR (100 MHz, DMSOꢀd ): 21.512, 21.536,
6
2.234, 67.098, 110.165, 118.567, 125.438, 127.954, 128.398, 131.271, 137.092, 154.042,
+
58.976, 196.841, 209.897; HRMS calculated for C H O S [M+H] : 323.0411, Found:
1
5
14
4 2
23.0398
General procedure for the preparation of 6 from 1:
A mixture of 1 (1.88 g, 10 mmol), tetrabutylammonium tribromide (TBATB) (4.82 g, 10 mmol),
1
4

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corresponding heterylthiol (5) (10 mmol) and PEGꢀ600 (30 mL) was stirred at RT for 2ꢀ3 h.
After completion of reaction, as indicated by TLC, the mixture was poured into iceꢀcold water
(
100 mL). The separated solid was filtered, washed with water (2×30 mL) and airꢀdried at RT.
The crude product was recrystallized from suitable solvent to obtain pure 6.
-(2-((1H-benzo[d]imidazol-2-yl)thio)acetyl)-2H-chromen-2-one (6a): Yield = 2.82 g (84%);
3
0
ꢀ1
ꢀ1
M.P: 161–163 C (Ethanol); IR (KBr): 1684 cm (strong, sharp, ꢀCO of –COCH ), 1745 cm
2
ꢀ1
1
(
strong, sharp, ꢀCO of coumarin ring), 3420ꢀ3440 cm (broad, medium, ꢀNH group); HꢀNMR
(
400 MHz, DMSOꢀd /TMS): δ 4.82 (s, 2H, ꢀCH ), 7.04ꢀ8.16 (m, 8H, ArꢀH), 8.33 (s, 1H, ArꢀH),
6
2
1
3
1
1.02 (s, 1H, ꢀNH); CꢀNMR (100 MHz, DMSOꢀd /TMS): 49.0, 119.8, 120.0, 126.1, 126.2,
6
126.9, 127.5, 128.0, 128.8, 129.6, 134.1, 135.2, 139.8, 147.0, 152.4, 161.2, 196.1; HRMS
+
calculated for C H N O S [M+H] : 337.0646, Found: 337.0650
1
8
12
2
3
3-(2-(Benzo[d]oxazol-2-ylthio)acetyl)-2H-chromen-2-one (6b): Yield = 2.93 g (87%); M.P:
0
ꢀ1
ꢀ1
1
57–159 C (Methanol); IR (KBr): 1684 cm (strong, sharp, ꢀCO of –COCH ), 1727 cm
2
1
(
strong, sharp, ꢀCO of coumarin ring); HꢀNMR (400 MHz, DMSOꢀd /TMS): δ 5.16 (s, 2H, ꢀ
6
1
3
CH ), 7.11ꢀ8.03 (m, 8H, ArꢀH), 8.86 (s, 1H, ArꢀH); C NMR (100 MHz, DMSOꢀd ): 45.621,
2
6
110.642, 116.178, 118.196, 119.429, 123.988, 124.286, 125.690, 127.900, 128.316, 131.231,
137.685, 141.290, 151.873, 153.084, 159.465, 165.023, 197.031; HRMS calculated for
+
C H NO S [M+H] : 338.0487, Found: 338.0518.
18
11
4
3-(2-(Benzo[d]thiazol-2-ylthio)acetyl)-2H-chromen-2-one (6c): Yield = 2.83 g (80%); M.P:
0
ꢀ1
ꢀ1
2
38–240 C (Acetone); IR (KBr): 1675 cm (strong, sharp, ꢀCO of –COCH ), 1725 cm (strong,
2
1
sharp, ꢀCO of coumarin ring); HꢀNMR (400 MHz, DMSOꢀd /TMS): δ 5.20 (s, 2H, ꢀCH ), 7.15ꢀ
6
2
1
3
8
.03 (m, 8H, ArꢀH), 8.88 (s, 1H, ArꢀH); C NMR (100 MHz, DMSOꢀd ): 46.082, 109.487,
6
115.998, 118.763, 120.193, 123.075, 124.656, 126.560, 127.785, 128.676, 131.441, 139.993,
1
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1
42.054, 152.873, 154.128, 160.002, 166.163, 196.987; HRMS calculated for C H NO S
18 11 3 2
+
[
M+H] : 354.0253, Found: 354.0258.
Alternative method for the preparation of 6 from 4a:
A mixture of 4a (1.88 g, 5 mmol), 5 mmol each of oꢀphenylenediamine (7a), oꢀaminophenol (7b)
oꢀaminothiophenol (7c) independently was refluxed in ethanol (30 mL) for a period of 2ꢀ4 h
&
on a water bath. After completion of reaction, as indicated by TLC, the mixture was poured into
iceꢀcold water (60 mL). The separated solid was filtered, washed with water (2×30 mL) and airꢀ
dried at RT. The crude product was recrystallized from suitable solvent to obtain pure 6.
6a: Yield = 0.65 g (39%);
6b: Yield = 0.74 g (42%);
6c: Yield = 0.74 g (44%);
General procedure for the preparation of 9 from 1:
A mixture of 1 (1.88 g, 10 mmol), tetrabutylammonium tribromide (TBATB) (4.82 g, 10 mmol),
corresponding phenylthiourea (8) (10 mmol) and PEGꢀ600 (30 mL) was stirred at RT for 2ꢀ4 h.
After completion of reaction, as indicated by TLC, the mixture was poured into iceꢀcold water
(
100 mL). The separated solid was filtered, washed with water (2×30 mL) and airꢀdried at RT.
The crude product was recrystallized from suitable solvent to obtain pure 9.
-(2-(Phenylamino)thiazol-4-yl)-2H-chromen-2-one (9a)
Yellow solid, Yield = 2.81 g (88%); mp 244–246 °C (Methanol); IR(KBr) νmax/ cm : 1728 cm
3
ꢀ1
ꢀ1
ꢀ1
1
(
strong, sharp, ꢀCO of coumarin ring), 3390ꢀ3430 cm (broad, medium, ꢀNH group); H NMR
(
400 MHz, DMSOꢀd / TMS): δ 6.98 (d, 2H, ArꢀH) 7.39ꢀ7.68 (complex, m, 6H, ArꢀH), 7.72 (s,
6
1
3
1
H, ArꢀH), 7.96 (d, 1H, ArꢀH), 8.67 (s, 1H, ArꢀH), 10.15 (s, 1H, ꢀNH); C NMR (100 MHz,
DMSOꢀd ): 110.366, 116.336, 117.570, 119.754, 120.792, 121.925, 125.162, 129.470, 129.601,
6
1
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132.140, 139.084, 141.440, 144.088, 152.775, 159.291, 162.993; HRMS calculated for
+
C H O N S [M+H] : 321.0697, Found: 321.0707.
18
12
2
2
3-(2-((4-Chlorophenyl)amino)thiazol-4-yl)-2H-chromen-2-one (9b)
ꢀ1
ꢀ1
Yellow solid, Yield = 2.86 g (81%); mp > 250 °C (Ethanol); IR(KBr) νmax/ cm : 1701 cm
ꢀ1
1
(
strong, sharp, ꢀCO of coumarin ring), 3380ꢀ3460 cm (broad, medium, ꢀNH group); H NMR
(
400 MHz, DMSOꢀd / TMS): δ 7.13 (t, 1H, ArꢀH), 7.36ꢀ7.66 (m, 5H, ArꢀH), 7.82 (s, 1H, ArꢀH),
6
1
3
7
.92 (d, 1H, ArꢀH), 8.48 (d, 1H, ArꢀH), 8.71 (s, 1H, ArꢀH) and 9.79 (s, 1H, ꢀNH); C NMR (100
MHz, DMSOꢀd ): 115.035, 115.334, 115.823, 118.820, 118.984, 119.276, 120.624, 124.213,
6
127.952, 130.844, 136.960, 138.273, 143.706, 152.363, 156.010, 159.196, 159.341, 163.057;
+
HRMS calculated for C H O N SCl [M+H] : 355.0308, Found: 355.0321.
1
8
11
2
2
3-(2-((2-Chlorophenyl)amino)thiazol-4-yl)-2H-chromen-2-one (9c)
ꢀ1
ꢀ1
Yellow solid, Yield = 279 g (79%); mp 154ꢀ156 °C (Ethanol); IR(KBr) νmax/ cm : 1720 cm
ꢀ1
1
(
strong, sharp, ꢀCO of coumarin ring), 3390ꢀ3450cm (broad, medium, ꢀNH group); H NMR
(
400 MHz, DMSOꢀd / TMS): δ 7.11 (t, 1H, ArꢀH), 7.37ꢀ7.65 (complex, m, 5H, ArꢀH), 7.82 (s,
6
1H, ArꢀH), 7.91 (d, 1H, ArꢀH), 8.48 (d, 1H, ArꢀH ), 8.61 (s, 1H, ArꢀH) and 9.81 (s, 1H, ꢀNH);
1
3
C NMR (100 MHz, DMSOꢀd ): 109.473, 115.574, 118.147, 119.033, 120.364, 124.051,
6
1
1
3
25.445, 127.819, 128.265, 130.707, 136.960, 137.077, 138.120, 139.308, 143.537, 152.136,
+
59.056, 162.153; HRMS calculated for C H ClN O S [M+H] : 355.0308, Found: 355.0310.
1
8
11
2
2
-(2-((2-chloro-4-fluorophenyl)amino)thiazol-4-yl)-2H-chromen-2-one (9d)
ꢀ1
ꢀ1
Yellow solid, Yield = 3.08 g (83%); mp 124ꢀ126 °C (Ethanol); IR(KBr) νmax/ cm : 1713 cm
ꢀ1
1
(
strong, sharp, ꢀCO of coumarin ring), 3360ꢀ3450 cm (broad, medium, ꢀNH group); H NMR
(
400 MHz, DMSOꢀd / TMS): δ 6.98 (d, 2H, ArꢀH), 7.40 (t, 1H, ArꢀH), 7.47 (s, 1H, ArꢀH), 7.61ꢀ
6
1
3
7
.68 (complex, m, 3H, ArꢀH), 7.72 (s, 1H, ArꢀH), 8.67 (s, 1H, ArꢀH) and 10.15 (s, 1H, ꢀNH); C
1
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NMR (100 MHz, DMSOꢀd ): 117.731, 118.595, 119.698, 120.685, 125.219, 129.245, 132.189,
6
138.627, 139.653, 139.850, 143.921, 151.210, 152.773, 153.600, 159.189, 162.633; HRMS
+
calculated for C H ClFN O S [M+H] : 373.0213, Found: 373.0402.
1
8
10
2
2
3-(2-(4-Tolylamino)thiazol-4-yl)-2H-chromen-2-one (9e)
ꢀ1
Yellow solid, Yield = 2.83 g (81%); mp 201ꢀ203 °C (Acetonitrile); IR(KBr) νmax/ cm : 1716
ꢀ1
ꢀ1
1
cm (strong, sharp, ꢀCO of coumarin ring), 3404ꢀ3450 cm (broad, medium, ꢀNH group); H
NMR (400 MHz, DMSOꢀd / TMS): δ 2.15 (s, 3H, ꢀCH ), 7.40ꢀ7.67 (m, 5H, ArꢀH), 7.72 (s, 1H,
6
3
13
ArꢀH), 7.79ꢀ7.98 (complex, m, 3H, ArꢀH), 8.71 (s, 1H, ArꢀH) and 10.50 (s, 1H, ꢀNH); C NMR
100 MHz, DMSOꢀd ): 21.243, 110.012, 115.322, 119.123, 119.854, 120.839, 125.055, 128.152,
(
6
1
3
3
28.460, 133.223, 139.228, 140.126, 144.074, 152.456, 159.569, 162.243; LCMS (CI): m/z =
.
+
35 [M +1].
-(2-((4-Fluorophenyl)amino)thiazol-4-yl)-2H-chromen-2-one (9f)
ꢀ1
ꢀ1
Yellow solid, Yield = 2.70 g (80%); mp 126–128 °C (Methanol); IR(KBr) νmax/ cm : 1728 cm
ꢀ1
1
(
strong, sharp, ꢀCO of coumarin ring), 3385ꢀ3445 cm (broad, medium, ꢀNH group); H NMR
(
400 MHz, DMSOꢀd / TMS): δ 7.41ꢀ7.47 (complex, m, 4H, ArꢀH),7.62 (d, 1H, ArꢀH), 7.64 (s,
6
1
1
1
1
3
H, ArꢀH), 7.67 (d, 1H, ArꢀH),7.81(t, 3H, ArꢀH), 7.97 (d, 1H, ArꢀH), 8.71 (s, 1H, ArꢀH) and
1
3
0.50 (s, 1H, ꢀNH); C NMR (100 MHz, DMSOꢀd ): 110.373, 115.847, 117.009, 117.222,
6
18.135, 119.114, 120.201, 124.711, 128.743, 131.691, 138.128, 138.562, 143.420, 152.273,
.
+
58.676, 162.114; LCMS (CI): m/z = 339 [M +1].
-(2-((4-Methoxyphenyl)amino)thiazol-4-yl)-2H-chromen-2-one (9g)
ꢀ1
Yellow solid, Yield = 2.83 g (81%); mp 192ꢀ194 °C (Acetonitrile); IR(KBr) νmax/ cm : 1716
ꢀ1
ꢀ1
1
cm (strong, sharp, ꢀCO of coumarin ring), 3386ꢀ3448 cm (broad, medium, ꢀNH group); H
NMR (400 MHz, DMSOꢀd / TMS): δ 3.18 (s, 1H, OCH ), 6.98 (d, 1H, ArꢀH), 7.39ꢀ7.68 (m, 5H,
6
3
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1
3
ArꢀH), 7.72 (s, 1H, ArꢀH), 7.95 (d, 1H, ArꢀH ), 8.67 (s, 1H, ArꢀH) and 10.17 (s, 1H, ꢀNH); C
NMR (100 MHz, DMSOꢀd ): 55.211, 109.235, 114.336, 115.821, 119.088, 119.253, 120.246,
6
124.649, 128.892, 131.597, 134.409, 138.488, 143.342, 152.261, 154.333, 158.767, 163.234;
+
HRMS calculated for C H N O S [M+H] : 351.0803, Found: 351.0809.
1
9
14
2
3
3-(2-((4-Nitrophenyl)amino)thiazol-4-yl)-2H-chromen-2-one (9h)
ꢀ1
ꢀ1
Yellow solid, Yield = 3.17 g (75%); mp 170–172 °C (Methanol); IR(KBr) νmax/ cm : 1728 cm
ꢀ1
1
(
strong, sharp, ꢀCO of coumarin ring), 3404ꢀ3430 cm (broad, medium, ꢀNH group); H NMR
(
400 MHz, DMSOꢀd / TMS): δ 7.11 (t, 1H, ArꢀH), 7.37ꢀ7.65 (complex, m, 5H, ArꢀH), 7.82 (s,
6
1H, ArꢀH), 7.91 (d, 1H, ArꢀH ), 8.48 (d, 1H, ArꢀH ), 8.61 (s, 1H, ArꢀH) and 9.81 (s, 1H, ꢀNH);
1
3
C NMR (100 MHz, DMSOꢀd ): 110.789, 116.347, 119.048, 119.754, 120.690, 125.155,
6
129.352, 129.460, 132.183, 139.228, 140.326, 144.074, 152.796, 159.269, 162.633; LCMS (CI):
.
+
m/z = 366 [M +1].
CONCLUSION:
In summary, we have demonstrated a simple and efficient oneꢀpot method for the direct
reaction of 3ꢀacetylꢀ2Hꢀchromenꢀ2ꢀone with different heterylthiols, phenylthioureas & their
derivatives by employing TBATB as a reagent in PEGꢀ600. The notable advantages of the
present protocol are excellent yields, shorter reaction times, easy & safe handling of reagent. Due
to its operational simplicity, generality and efficacy this method is expected to have wider
applicability for the preparation of various other compounds with other acetophenone
derivatives. Thus, TBATB was found to be the most benign alternative for the toxic bromine and
are capable of facilitating a host of organic transformation reagents on a wide variety of
substrates.
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2
3

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PEG-600 mediated one-pot reaction of 3-acetyl-2H-chromen-2-one with
heterylthiols and phenylthioureas using Tetrabutylammonium Tribromide as
an efficient green reagent
Devulapally Srikrishna* and Pramod Kumar Dubey
Department of Chemistry, Jawaharlal Nehru Technological University Hyderabad
College of Engineering, Kukatpally, Hyderabad, Telangana - 500 085, India.
Email ID: devulapallisrikrishna@gmail.com
Ph. No.: +91-9951306098, Fax No.: 040-23057787
GRAPHICAL ABSTRACT
1