N, N’-dimethyl formamide (DMF) mediated Vilsmeier–Haack adducts with 1,3,5-triazine compounds as efficient catalysts for the transesterification of β-ketoesters

Article abstract of DOI:10.1080/00397911.2020.1750033

N, N’-dimethyl formamide (DMF) mediated Vilsmeier–Haack (VH) adducts with 1,3,5-triazine compunds such as trichloroisocyanuric acid (TCCA) and trichlorotriazine (TCTA) were prepared by replacing classical oxy chlorides POCl₃, and SOCl₂, which were explored as efficient catalysts for the transesterification of β-ketoesters. The prepared (TCCA/DMF) and (TCTA/DMF) adducts improved greenery of the classical Vilsmeier–Haack reagents (POCl₃/DMF), and (SOCl₂/DMF), and demonstrated their better efficient catalytic ativity. Reaction times were in the range: 3.5 to 6.5 hr (SOCl₂/DMF); 2.8–5.2 hr (POCl₃/DMF); 2.5–5.2 hr (TCCA/DMF) and 2.5–5.0 hr (TCTA/DMF) catalytic systems. Ultrasonically (US) assisted protocols with these reagents further reduced the reaction times (two to three times), while microwave assisted (MW) protocols with these reagents were much more effective. The reactions could be completed in only few seconds (less than a minute) in MWassisted protocols as compared to US assited reactions, followed by good product yields.

Full text of DOI:10.1080/00397911.2020.1750033

Synthetic Communications
An International Journal for Rapid Communication of Synthetic Organic
Chemistry
ISSN: 0039-7911 (Print) 1532-2432 (Online) Journal homepage: https://www.tandfonline.com/loi/lsyc20
N, N’-dimethyl formamide (DMF) mediated
Vilsmeier–Haack adducts with 1,3,5-triazine
compounds as efficient catalysts for the
transesterification of β-ketoesters
Govardhan Duguta, Chinna Rajanna Kamatala, Satish Kumar Mukka,
Bhooshan Muddam & Yadaiah Chityala
To cite this article: Govardhan Duguta, Chinna Rajanna Kamatala, Satish Kumar Mukka,
Bhooshan Muddam & Yadaiah Chityala (2020): N, N’-dimethyl formamide (DMF) mediated
Vilsmeier–Haack adducts with 1,3,5-triazine compounds as efficient catalysts for the
transesterification of β-ketoesters, Synthetic Communications
To link to this article: https://doi.org/10.1080/00397911.2020.1750033
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https://doi.org/10.1080/00397911.2020.1750033
N, N’-dimethyl formamide (DMF) mediated Vilsmeier–Haack
adducts with 1,3,5-triazine compounds as efficient catalysts
for the transesterification of b-ketoesters
Govardhan Dugutaa,b, Chinna Rajanna Kamatalaa, Satish Kumar Mukkaa,
Bhooshan Muddama,c, and Yadaiah Chityalaa
b
aDepartment of Chemistry, Osmania University, Hyderabad, India; P. G. College, Osmania University,
c
Mirzapur (B), India; Department of Chemistry, M.V.S.R. Engineering College, Hyderabad, India
ABSTRACT
ARTICLE HISTORY
Received 29 January 2020
N, N’-dimethyl formamide (DMF) mediated Vilsmeier–Haack (VH)
adducts with 1,3,5-triazine compunds such as trichloroisocyanuric
acid (TCCA) and trichlorotriazine (TCTA) were prepared by replacing
classical oxy chlorides POCl3, and SOCl2, which were explored as effi-
cient catalysts for the transesterification of b-ketoesters. The pre-
pared (TCCA/DMF) and (TCTA/DMF) adducts improved greenery of
the classical Vilsmeier–Haack reagents (POCl3/DMF), and (SOCl2/
DMF), and demonstrated their better efficient catalytic ativity.
Reaction times were in the range: 3.5 to 6.5 hr (SOCl2/DMF);
2.8–5.2 hr (POCl3/DMF); 2.5–5.2 hr (TCCA/DMF) and 2.5–5.0 hr (TCTA/
DMF) catalytic systems. Ultrasonically (US) assisted protocols with
these reagents further reduced the reaction times (two to three
times), while microwave assisted (MW) protocols with these reagents
were much more effective. The reactions could be completed in only
few seconds (less than a minute) in MWassisted protocols as com-
pared to US assited reactions, followed by good product yields.
KEYWORDS
b-Ketoesters; oxychloride/
DMF adducts; rate
enhancements; symmetric
triazine/DMF adducts;
transesterification
GRAPHICAL ABSTRACT
CONTACT Chinna Rajanna Kamatala
kcrajannaou@yahoo.com
Department of Chemistry, Osmania University,
Hyderabad 500007, India.
Supplemental data for this article can be accessed on the publisher’s website.
ß 2020 Taylor & Francis Group, LLC

2
G. DUGUTA ET AL.
Introduction
Triazine compounds (1,3,5-triazine compounds) are special class of heterocyclic com-
pounds which are known since two centuries which find their use in synthetic organic
chemistry with a special emphasis in pharmaceutical, textile, plastic, and industrial
applications. Besides, these compounds are also used as pesticides, dyestuffs, optical
bleaches, explosives, and surface active agents.[1–6] Among several symmetric triazine
derivatives, cyanuric chloride (2.4.6-trichloro 1,3,5-triazine or TCTA)), and trichloro
isocyanuric acid (TCCA) received up surging attention in synthetic organic chemistry
(Chart-I), because they are economically cheap, environmentally safe, easily available
and easy to handle.[7–10]
The field of organic synthesis is a boon to human society, which provided several
millions of useful compounds from lifesaving drugs to industrially important and day-
to-day useful items. Transesterification is one of the most important chemical transfor-
mations, which converts one organic ester (ROOR1) into another ester (ROOR2) in the
presence of alcohol (R2OH). In addition, b-ketoesters are multicoupling agents with
nucleophilic carbon, and electrophilic carbonyl moiety, which makes them as valuable
synthetic tools for the preparation of complex organic molecules. This methodology is
useful to achieve medicinally important pharmaceuticals, and polyesters used in textile
industry. But, transesterification of b-ketoesters is a highly sluggish reaction which
demands large amounts of ketoester and high boiling alcohols for effective transesterica-
tion. In view of this reaction required an efficient catalyst to accelerate transesterifica-
tion. A survey of literature revealed that several Brønsted acids, Lewis acids, Lewis
bases, enzymes, and metal ions used as efficient catalysts[11–20] to achieve transesterifica-
tion. Recently, our research group also explored economically cheap Mn(II)salts, Cs(I)
carbonate, and Prussian blue as catalysts for chemoselective transesterification of
b-ketoesters.[20]
On the other hand, since 1927, Vilsmeier–Haack (VH) reagents such as (POCl3/
DMF, SOCl2/DMF, POCl3/DMA, SOCl2/DMA, (COCl)2/DMF, etc.) have been widely
used for a broad spectrum of reactions in organic synthesis.[21–35] These reactions
include formylation,[26] acylation,[27,28] chloroformylation,[29] chloroacylation,[30] ben-
zoylation,[31] bromination,[32] nitration,[33] nitrodecarboxylation,[34] and sulfonation,[35]
under specific conditions. But the main difficulty for the preparation of classical VH
adducts is the use of hazardous, toxic oxychlorides, which is also difficult to handling.
To overcome environmental issues, Paul Anastas and John Warner suggested to adapt
twelve (12) green chemistry principles which include prevention of hazardous materials,
design of atom economy protocols comprising the use of less hazardous chemicals, cata-
lysts, safer solvents, renewable feed stocks, and non-conventional energy sources to trig-
ger the reactions.[30] Perusal of literature shows excellent papers, reviews, and books on
the green chemistry aspects.[36] Encouraged by these aspects several research groups
including our group tried to explore easily available, less hazardous and easy handling
triazine compounds like cyanuric chloride (2.4.6-trichloro 1,3,5-triazine or TCTA)), and
trichloro isocyanuric acid (TCCA) by replacing hazardous and fuming and suffocative
oxychlorides for the preparation of VH reagents, which have been employed as efficient
reagents/catalysts for formylation,[37] acetylation,[38] chlorodehydration,[39] and nitra-
tion[40–43] reactions. In the present study, we want to explore [TCTA/DMF] and

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3
O
Cl
N
Cl
4
Cl
N
N
5
3
N
N
N
N
2
6
O
N
O
N
Cl
Cl
1
Cl
Trichloro isocyanuric acid
( TCCA) 1.3.5-trichloro
1,3,5-triazine 2.4.6-trione
Cyanuric Chloride
(TCTA) 2.4.6-trichloro
1,3,5-triazine
Symmetric
triazine (s-triazine
or 1,3,5-triazine)
Chart-I. Symmetric triazine compunds.
Table 1. Transesterification of ethyl acetoacetate (b-ketoester) with C6H5CH2OH using differ-
ent catalysts.
S.N.
Catalyst
R.T (hr)
Yield (%)
Reference
1
2
3
4
5
6
7
8
SOCl2/DMF
POCl3/DMF
TCCA/DMF
4.5
4.0
3.5
3.0
12.0
8.0
3.5
8.0
8.0
10
5.0
18
18
19
18–20
85
80
80
78
90
90
80
93
75
80
66
72
75
75
75
Present work
TCTA/DMF
I2
[44]
[14a]
[17g]
[45]
Zeolite H-FER
Montmorillonite K-10
Mn(III) salen complex
Vanadyl acetate [V(IV)]
Dealuminated H-b
Zn/I2
9
10
11
[46]
[15a]
[16a]
MnSO4
MnCO3
Prussian blue
Cs2CO3
12
13
[16b]
[16c]
[TCCA/DMF] adducts for transesterification reactions, and also compare the obtained
results with those obtained using classical VH reagents also as catalysts (Scheme-I).
Results and discussion
Initially we have studied transesterification of ethyl acetoacetate (b-ketoester) with
C6H5CH2OH using classical VH reagents (POCl3/DMF and SOCl2/DMF), and also
modified VH reagents with symmetric triazine (TCCA/DMF and TCTA/DMF) in order
to optimize the reaction conditions. Reaction mixture containing ethyl acetoacetate
(10 mmol), C6H5CH2OH (10 mmol) and one millimolar (1.0 mmol) catalyst (POCl3/
DMF, SOCl2/DMF, TCCA/DMF and TCTA/DMF) in about 20 mL solvent (toluene)
were taken in a clean round bottomed flask, and continuously stirred under reflux at
about 60–70 ꢀC temperature range. Thin layer chromatographic (TLC) method was used
to monitor progress of the reaction till the completion of reaction. After ascertaining
the completion of the reaction with periodic monitoring by TLC, products were isolated
and compared with earlier reports.[39–41] Data presented in Table 1 clearly show that
classical VH adducts and modified VH adducts with symmetric triazines exhibited bet-
ter catalytic activity with comparable product yields and comparable with few import-
ant catalysts.

4
G. DUGUTA ET AL.

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5
In view of this, we have taken up detailed study of transesterification of ethyl
acetoacetate (b-ketoester) with different hydroxy compounds, which are presented in
Table 2.
Reaction times were in the range: 3.5–6.5 hr (SOCl2/DMF); 2.8–5.2 hr (POCl3/DMF);
2.5–5.2 hr (TCCA/DMF) and 2.5–5.0 hr (TCTA/DMF) catalytic systems followed by
very good product yields respectively. These trends further point out that VH reagents
prepared from symmetric triazines and DMF (TCCA/DMF and TCTA/DMF) are prom-
ising catalysts, which not only improved greenery of the reactions (by avoiding the use
of toxic and hazardous oxychlorides) in the preparation of VH reagents. In order to
through light into the mechanism of reactions we need to consider the active species of
catalyst. In large numbers of publications,[22–29] it has been earlier suggested that either
“chloromethyleniminium cation [(CH3)2N ¼ C(R)Cl]þ,” and dipolar oxychloride active
intermediate ([(CH3)2N ¼ C(R)Cl]þ[PO2Cl2]ꢂ in case of (DMF/POCl3) and
([(CH3)2N ¼ C(R)Cl]þ[SO2Cl]ꢂ in case of (DMF/SOCl2) respectively) are active species,
which are formed in situ during the course of reaction. Similar types of dipolar species
([(CH3)2N ¼ C(R) Cl]þ [TCCA]–or [(CH3)2N ¼ C(R) Cl]þ [TCTA]–) were considered
by us when [TCTA–DMF] or [TCCA–DMF] were used as modified VH adducts.[37–40]
These contentions were supported by infrared (IR) and nuclear magnetic resonance
(NMR) spectroscopic results obtained under different conditions. On the basis of the
foregoing discussions, we feel that mechanism of transesterification proceeds through
two steps.
Scheme-II depicts the steps involved in the formation of “chloromethyleniminium
cation” in (DMF/POCl3), (DMF/SOCl2), (TCTA/DMF) and (TCCA–DMF), while the
Scheme-III elaborates “chloromethyleniminium cation” mediated transesterification of
b-ketoester by alcohol (ROH). Chloromethyleniminium cation ([(CH3)2N 5 C(H)Cl]1
or (I)) formed here in Scheme-II further interacts with alcohol (R–OH) in the first step
to give transient species (TST-I), which in turn liberates HCl and also affords inter-
mediate alkoxymethyleniminium cation species (II). In a further step, in situ liberated
HCl most plausibly reacts with ethyl acetoacetate (b-ketoester) to give a transient
dipolar species (III). Finally, a fast rearrangement step, the reaction between two inter-
mediate species (II) and (III) afford end product (IV) as elaborated in Scheme-III.
An array of alcohols was chosen in this reaction. It is interesting to note that the
nature and size of the alcohol involved in the reaction significantly affects the rate of
transesterification. Simple aliphatic alcohols with high nucleophilicity generally facilitate
transesterification faster than bulkier alcohols. Obtained products are characterized by
physical data and spectroscopic results, which agree well with the data presented in our
earlier publications, and elsewhere.
Data presented in Table 2 further show that transesterification also depend on the
size and nature of alcohol as well as b-ketoester. Simple alcohols facilitate better transes-
terification with their higher nucleophilicity than bulkier alcohols. Reactions occurred
smoothly with primary and sterically less hindered alcohols, while reactions with sec-
ondary and tertiary alcohols slowly with relatively longer reaction times and moderate
product yields. In order to further improve the greenery of the reactions, we have taken
up the transesterification under ultrasonication and microwave irradiation. Obtained
results are compiled in Tables 3 and 4.

6
G. DUGUTA ET AL.
Scheme-I. VH Reagents as catalysts for transesterification of beta keto esters.
O
N
H
SOCl2
SO2Cl-
POCl3
H
H
-
N
PO2Cl2
N
Cl
Cl
Dipolar Imminium species
Dipolar Imminium species
SO2Cl-
-
PO2Cl2
H
N
Cl
(TCCA)-
(TCTA)-
(I)
chloromethyleniminium cation
H
H
(TCTA)-
N
(TCCA)-
N
Cl
Cl
Dipolar Imminium species
Dipolar Imminium species
TCTA
TCCA
O
H
N
Scheme-II. Formation of chloromethyleniminum cation species.
Reaction times in ultrasonic assisted transesterification (USATEST), and microwave
assisted transesterification (MWATEST) protocols (Tables 3 and 4) substantially reduced
from the reaction times recorded in conventional method as shown below in table:
Among all the studied transesterification protocols, microwave assisted transesterifica-
tion (MWATEST) protocols exhibited highly noticeable rate accelerations with the reac-
tion times reduced from few hours (in conventional and USATEST) to few seconds,
followed by very good yield of products. In ultrasonic assisted transesterification
(USATEST), protocols also, the reaction times reduced two to three times as compared
to conventional methods. Accelerating rates in ultrasonic assisted transesterification

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7
R
H
R
H
N
N
N
O
+
O
R
Cl
O
Cl
H
Cl
H
H
(TST-I)
HCl
(TST-I)
(I)
Alcohol
N
Where R = Alkyl or Aryl group;
(I) Chloromethyleniminium cation;
(II) Alkoxymethyleniminium cation;
EAA= Ethyl acetoacetate
R
O
H
(II)
EAA
(I)
O
O
HO
O
Cl
OH
Ethylalcohol
+
O
R
O
(II)
(IV) Beta-Ketoester
Dipolar species ( III)
Scheme-III. Transesterification of b-Ketoesters with R-OH using Iminium on species as catalyst.
reactions could be attributed to the larger fraction of molecules getting activated by
absorbing the “cavitation energy” released due to the collapse of “cavitation bubbles”.
When ultrasound waves are propagated through the reaction mixture small cavitation
bubbles are formed initially, which gradually increase in size and collapse when the size
of the bubble unassumingly larger.[47–49] On the other hand, enormous microwave
catalysis could be explained due to the bulk activation of molecules which is due to the
rapid super heating of all reactant species, polar solvents and pressure effects.[50,51] We
have done microwave assisted (MWA) transesterification experiments without using
500 mg of silica gel. We noticed about 4–5% decrease in the product yield. There is not
much difference in the reaction time.
Conclusion
In this part of the study we have synthesized modified VH adducts with symmetric tria-
zine (1,3,5-triazine) compounds such as trichloroisocyanuric acid (TCCA) and trichloro-
triazine (TCTA) along with DMF (TCCA/DMF, and TCTA/DMF), which are used as
green catalysts for efficient transesterification of b-ketoesters with different alcohols.
The developed green Vilsmeier–Haack adducts such as (TCCA/DMF), and (TCTA/
DMF)] are found superior over classical VH reagents (POCl3/DMF), and (SOCl2/DMF)
in terms of easy handling and environmentally safety. Observed reaction times were in
the range: 3.5–6.5 hr (SOCl2/DMF);2.8–5.2 hr (POCl3/DMF); 2.5–5.2 hr (TCCA/DMF)
and 2.5–5.0 hr (TCTA/DMF) catalytic systems. These reaction times were further
reduced by two to three times under ultrasonication, while microwave assisted protocols

8
G. DUGUTA ET AL.
Table 3. Ultrasonic Assisted Transesterification (USTEST) of b-ketoesters using VH reagents
as catalysts.
Ultrasonic Assisted Transesterification
SOCl2/DMF
POCl3/DMF
TCCA/DMF
TCTA/DMF
Time Yield Time Yield Time Yield Time Yield
Entry
1
Substrate
Propane-1-ol
Product
Propyl 3-
(hr)
1.2
(%)
79
(hr)
1.0
(%)
81
(hr)
1.0
(%)
82
(hr)
0.9
(%)
84
oxobutanoate
Allyl 3-oxobutanoate
Butyl 3-oxobutanoate
Isopropyl 3-
2
3
4
Prop-2-en-1-ol
Butan-1-ol
Propan-2-ol
1.5
1.8
1.5
80
78
75
1.0
1.5
1.0
82
80
78
1.0
1.5
1.0
83
82
79
1.0
1.2
0.8
85
82
86
oxobutanoate
5
6
7
8
2-Methylpropane-2-ol
Cyclohexanol
Tert-butyl 3-
oxobutanoate
Cyclohexyl 3-
oxobutanoate
Isobutyl 3-
oxobutanoate
2-Isopropyl-5-
1.8
2.0
1.8
2.2
78
80
78
79
1.5
1.5
1.6
2.0
82
82
80
80
1.5
1.2
1.5
2.0
84
82
80
82
1.2
1.0
1.2
1.5
85
85
81
83
2-methylpropane-1-ol
2-Isopropyl-5-
methylcyclohexanol
methylcyclohexyl-3-
oxobutanoate
9
10
Phenyl methanol
(E)-3-Phenylprop-2-en- Cinnamyl 3-
Benzyl 3-oxoutanoate
1.5
2.5
80
80
2.0
2.0
80
82
1.0
2.0
82
85
1.0
1.5
86
87
1-ol
p-Cresol
oxobutanoate
p-tolyl 3-
oxobutanoate
Phenyl 3-
oxobutanoate
11
12
13
14
15
16
17
18
19
ꢁ
1.6
1.5
2.0
2.0
2.2
2.4
2.5
2.0
2.2
81
78
80
81
79
81
81
82
78
1.5
1.5
1.5
1.8
2.0
2.2
2.2
1.8
2.0
82
80
82
84
80
83
82
82
80
1.5
1.0
1.5
1.5
1.5
2.0
2.0
1.5
1.8
85
82
82
85
82
85
84
83
81
1.0
1.0
1.3
1.2
1.3
1.8
1.3
1.5
1.6
86
84
85
87
83
85
84
85
84
Phenol
4-Cholrophenol
Furan-2-yl methanol
Quinolin-8-ol
4-Chlorophenyl 3-
oxobutanoate
Furan-2-ylmethyl 3-
oxobutanoate
Quinolin -8-yl 3-
oxobutanoate
2-Oxo-2H-chromen-7-
yl 3-oxobutanoate
2-Oxo-2H-chromen-4-
yl 3-oxobutanoate
Naphthalen-2-yl 3-
oxobutanoate
7-Hydroxy-2H-
chromen-2-one
4-Hydroxy-2H-
chromen-2-one
Naphthalen-2-ol
Naphthalen-1-ol
Naphthalen-1-yl 3-
oxobutanoate
Products are purified by column chromatography.
dramatically reduced the reaction times from few hours to only few seconds (less than a
minute) followed by very good product yields. The developed methods allowed rapid
access to diverse esters (–OR) without using large excess of the corresponding alcohol
(often as a solvent). The compounds TCCA, TCTA and DMF used for catalysts are
inexpensive, operationally simple laboratory desktop chemicals.
Experimental
Chemicals used in this study are obtained from laboratory desk, which are supplied by
SD, Loba, and Finar Chemicals (India). Sonicator bath with a frequency of 33 kHz and
100 W electric power rating (Optics Technology, Shakurpur, Delhi) for ultrasonically
assisted reactions, and “Bench mate” model Micro-wave oven (CEM-908010, 300 W) for
microwave assisted reactions were used in this study. Classical Vilsmeier Haack reagents

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9
Table 4. Microwave Assisted Transesterification (MWTEST) of b-ketoesters using VH reagents
as catalysts.
Microwave Assisted Transesterification
SOCl2/DMF
POCl3/DMF
TCCA/DMF
TCTA/DMF
Time Yield Time Yield Time Yield Time Yield
ꢁ
Entry
1
Substrate
Propane-1-ol
Product
Propyl 3-
(sec)
45
(%)
79
(sec)
40
(%)
80
(sec)
36
(%)
82
(sec)
30
(%)
83
oxobutanoate
Allyl 3-oxobutanoate
Butyl 3-oxobutanoate
Isopropyl 3-
2
3
4
Prop-2-en-1-ol
Butan-1-ol
Propan-2-ol
48
45
55
81
78
77
40
40
50
83
81
79
38
35
45
85
81
80
35
32
42
87
82
83
oxobutanoate
5
6
7
8
2-Methylpropane-2-ol
Cyclohexanol
Tert-butyl 3-
oxobutanoate
Cyclohexyl 3-
oxobutanoate
Isobutyl 3-
oxobutanoate
2-Isopropyl-5-
46
55
48
46
80
81
79
79
42
52
45
45
82
83
80
79
40
50
45
42
83
84
81
83
35
45
40
40
85
87
82
84
2-methylpropane-1-ol
2-Isopropyl-5-
methylcyclohexanol
methylcyclohexyl-3-
oxobutanoate
9
10
Phenyl methanol
(E)-3-Phenylprop-2-en- Cinnamyl 3-
Benzyl 3-oxoutanoate
50
55
80
81
50
55
80
82
45
50
82
86
45
45
82
87
1-ol
p-Cresol
oxobutanoate
p-tolyl 3-
oxobutanoate
Phenyl 3-
oxobutanoate
11
12
13
14
15
16
17
18
19
ꢁ
50
55
58
45
55
50
50
50
50
78
79
80
80
78
81
83
78
79
50
50
55
45
55
50
50
50
50
80
82
81
82
79
82
85
80
82
45
50
50
40
50
45
45
45
48
82
83
82
83
84
85
85
84
86
42
40
45
40
45
40
40
40
40
82
85
84
86
88
86
89
86
89
Phenol
4-cholrophenol
Furan-2-yl methanol
Quinolin-8-ol
4-Chlorophenyl 3-
oxobutanoate
Furan-2-ylmethyl 3-
oxobutanoate
Quinolin-8-yl 3-
oxobutanoate
2-Oxo-2H-chromen-7-
yl 3-oxobutanoate
2-Oxo-2H-chromen-4-
yl 3-oxobutanoate
Naphthalen-2-yl 3-
oxobutanoate
7-Hydroxy-2H-
chromen-2-one
4-Hydroxy-2H-
chromen-2-one
Naphthalen-2-ol
Naphthalen-1-ol
Naphthalen-1-yl 3-
oxobutanoate
Products are purified by column chromatography.
(DMF/POCl3, and DMF/SOCl2) were prepared as detailed in earlier publications,[21–29]
while modified Vilsmeier Haack reagents (DMF/TCCA, and DMF/TCTA) were synthe-
sized according to the suggested methods given in our recent publications.[35–40]
General procedure for transesterification under conventional method
Ethyl acetoacetate (10 mmol), C6H5CH2OH (10 mmol) and one millimolar (1.0 mmol)
catalyst (POCl3/DMF, SOCl2/DMF, TCCA/DMF and TCTA/DMF) were suspended in a
round bottomed flask containing 20 mL solvent (toluene), and stirred continuously at
room temperature till the completion of reaction. Progress and completion of the reac-
tion was monitored by thin layer chromatographic (TLC) method. After completion,
reaction mixture was treated with sodium bicarbonate solution followed by ethylacetate

10
G. DUGUTA ET AL.
or ether. Organic layer was then separated, dried over sodium sulfate (Na2SO4) and
purified with column on silica gel (ethyl acetate: petroleum ether) to afford the ester as
a viscous liquid in very good yields.
For instance, 2-hydroxyphenyl-3-oxobutanoate is obtained from the transesterification
ethylacetoacetate(1.4 ml, 11 mmol), by 2-hydroxyphenol (1.2 g, 11 mmol), VHR [TCCA
(0.23 g, 1 mmol), TCTA (0.18 g, 1 mmol), SOCl2 (0.7 ml, 10 mmol), POCl3 (0.9 ml,
10 mmol), DMF (0.39 ml, 5 mmol). Yield: Given in Tables 1–3. 1H NMR (CDCl3,
400 MHz) d 7.32–7.30 (d, J ¼ 8.0 Hz, 2H, Ar-H), 6.59 (s, 1H, -Ar-H), 6.01 (s, 1H, -Ar-
H), 3.93 (s, 2H, -CH2), 3.35 (s, 3H, –COCH3). 13 C NMR (CDCl3, 101.6 MHz) (d ppm)
165.8, 162.7, 160.4, 151.4, 144.7, 127.0, 126.8, 125.9, 41.6, 34.0. LCMS: m/z calcd for
C10H10O4 (Mþþ1): 195.15. Anal calcd for C10H10O4 (in %): C-61.9; H-5.2. Found: C-
61.7; H-5.0.
In another case, p-tolyl-3-oxobutanoate is obtained as the product from the transes-
terification of ethyl acetoacetate (1.4 ml, 11 mmol), p-Cresol (1.2 g, 11 mmol), VHR
[TCCA (0.23 g, 1 mmol), TCTA (0.18 g, 1 mmol), SOCl2 (0.7 ml, 10 mmol), POCl3
(0.9 ml, 10 mmol), DMF (0.39 ml, 5 mmol). Yield: Given in Tables 1–3. 1H NMR
(CDCl3, 400 MHz) d 7.74–7.72 (d, J ¼ 8.0 Hz, 2H, Ar-H), 7.44–7.42 (d, J ¼ 8.0 Hz, 2H,
Ar-H), 4.02 (s, 2H, -CH2), 3.44 (s, 3H, Ar-CH3), 3.02 (s, 3H, –COCH3). 13 C NMR
(CDCl3, 101.6 MHz) (d ppm) 166.4, 161.8, 150.7, 144.5, 129.2, 128.1, 41.5, 34.0, 28.5.
LCMS: m/z calcd for C11H12O3 (Mþ þ1): 193.00. Anal calcd for C11H12O3 (in %): C-
68.7; H-6.3. Found: C-68.6; H-6.2.
General procedure for ultrasonically assisted transesterification
In ultrasonically assisted transesterification (USATEST), a flask containing mixture of
b-ketoesters (0.1 mol), alcohol (0.1 mol) and catalysts (0.01 mol) in toluene (20 mL) was
placed in a Sonicator bath with a frequency of 33 kHz and 100 W electric power rating
(Optics Technology, Shakurpur, Delhi) and stirred at room temperature and the pro-
gress of the reaction was monitored by thin layer chromatography (TLC) till completion
of the reaction. After a similar workup procedure to obtain final product as dis-
cussed above.
General procedure for microwave assisted (MWA) transesterification (MWATEST)
under solvent free conditions
Reaction mixture containing b-ketoesters (0.1 mol), alcohol (0.1 mol), catalyst (0.01 mol)
along with 500 mg of silica gel were mixed thoroughly in a microwave reaction vial and
placed in a beaker containing silica gel powder. The beaker was then placed in a labora-
tory microwave oven (CEM-908010, benchmate model 300 W laboratory microwave
reactor) till the reaction is completed as ascertained by TLC. The reaction mixture (con-
tents of the test tube) was treated with sequentially with aqueous sodium bicarbonate
and ethyl acetate. SiO2 gets precipitated in aqueous layer, while the end product is
extracted in organic layer. After a regular work-up final product could be obtained.
Elemental analysis, and spectroscopic (1H NMR, 13C NMR, and mass) data of certain
isolated products for this article can be accessed on the publisher’s website..

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SYNTHETIC COMMUNICATIONSV
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Acknowledgments
We greatly acknowledge Head of the Chemistry Department, Osmania University Hyderabad for
laboratory facilities and Professor P.K. Saiprakash (former Dean, Science Faculty, O.U.) for con-
stant encouragement.
Disclosure statement
Authors declare that they do not have any conflict of interest.
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