The first vinyl acetate mediated organocatalytic transesterification of phenols: A step towards sustainability

Article abstract of DOI:10.1039/c5nj01436k

The present report outlines our efforts toward a simple yet elegant protocol for O-acylation of a wide variety of phenols. This highly enabling and solventless method relies on vinyl acetate as an innocuous acyl donor and DABCO as an organocatalyst. Operational simplicity, excellent yields, higher and faster conversion rates without excess reagents, a simple workup and essentially no need of columns are some of the salient features of the reported protocol.

Full text of DOI:10.1039/c5nj01436k

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The first vinyl acetate mediated organocatalytic
transesterification of phenols: a step towards
sustainability†
Cite this:DOI: 10.1039/c5nj01436k
Manoj Kumar, Sourav Bagchi and Anuj Sharma*
The present report outlines our efforts toward a simple yet elegant protocol for O-acylation of a wide
variety of phenols. This highly enabling and solventless method relies on vinyl acetate as an innocuous
acyl donor and DABCO as an organocatalyst. Operational simplicity, excellent yields, higher and faster
conversion rates without excess reagents, a simple workup and essentially no need of columns are
some of the salient features of the reported protocol.
Received (in Montpellier, France)
6th June 2015,
Accepted 13th August 2015
DOI: 10.1039/c5nj01436k
www.rsc.org/njc
product side rapidly turn into the corresponding aldehydes or
ketones, enabling the system to escape from equilibrium
Introduction
Acylation of alcohols, phenols and amines is a transformation (Scheme 1).14,15 Moreover, the reactivity profile of enol esters
of fundamental interest. Acetic anhydride and acyl halide in the is also better than ordinary esters.
presence of basic1 (tertiary amines, pyridine, DMAP, PBu3), acidic2
Several catalysts, promoters and additives have been put forth
(Lewis/protic) and other catalysts3 are usually employed for this for enol ester based acylation such as Cp2-Sm(thf)2,14 SmI2,14
purpose. No doubt, most of these catalysts ensure good conver- distannoxane,15 diethyl Zinc + N-substituted diethanolamine (as
sion; however, they still suffer from many disadvantages3d such as a ligands),16 binuclear zinc,17 iminophosphoranes,18 PdCl2,19
poor selectivity, cleavage of acid sensitive groups such as acetal, Al(OTf)3,20 ytterbium complexes such as Y5(Ot-pr)13O,21
diene, epoxide (with strong acid catalysts), toxicity (pyridine, [RuCl2( p-cymene)]2,22 molecular iodine,23 N-heterocyclic
DMAP), low air stability and flammability (PBu3).
carbenes,24 nucleophilic Fe catalysts,25 lipases26 and anti-
Transesterification (acylation by esters) is an important bodies27 etc. Despite several advantages, these methods also suffer
alternative method.4 However, lower reactivity of the ester from one or the other drawback such as the use of expensive
carbonyl functionality and the reversible nature of the reaction catalysts,14,21,22 requirement of delicate reaction conditions,14 the
equilibrium resulting in partial conversion are two major use of obnoxious solvents16,18,19 and long reaction times.15,17,18
limitations associated with this class of reactions. Here also,
It is strange that most of these methods have remained
a wide range of acidic, basic and other catalysts (sulfuric acid,5 limited to non-aromatic primary and secondary alcohols.14–25
p-toluenesulfonic acid,6,7 DMAP,8 ZnO,9 sodium alkoxide,10 To the best of our knowledge, there are only a few reports of vinyl
solid K2CO3,11 KCN,12 Rasta resin-TBD,13 etc.) have been employed acetate based acylation of phenols and in all the cases, it resulted
to enhance the reactivity of ester carbonyl. These catalysts act in failure (Scheme 2).19,20,23a It was assumed that deprived
either by coordinating acyl carbonyl or by enhancing the nucleo- nucleophilic properties of the phenols could be a possible reason
philicity of the attacking species. Meanwhile, the reversibility for the failure.28 Secondly, the catalytic systems exploited
issue is customarily overcome either by using excess starting so far comprised either enzymes21 or metals/organometallic
alcohols or by continuously removing the product alcohols compounds.14–17,19–22 Interestingly, we could not find any
which are neither trivial nor economical.14,15
An effective replacement of the above strategy is the use
of enol esters such as vinyl acetate (Caution! Carcinogenic A3
and 2B) as acylating agents, since enol alcohols formed in the
Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee-247667,
India. E-mail: anujsharma.mcl@gmail.com, anujsfcy@iitr.ac.in;
Fax: +91 13 3227 3560; Tel: +91 13 3228 4751
Scheme 1 Vinyl acetate based transesterification reaction. Tautomeriza-
tion of vinyl alcohol to acetaldehyde drives the equilibrium toward the
product side.
† Electronic supplementary information (ESI) available: General experimental
details, the microwave irradiation experiment, the general procedure, 1H, 13C NMR
and HRMS spectral data and the recorded spectra. See DOI: 10.1039/c5nj01436k
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Table 1 Optimization of reaction conditionsa
Catalyst
Entry Solvent (mol%)
Temp.
Condition (1C)
Yieldb
Time (%)
1
2
3
4
5
6
7
8
ACN
ACN
ACN
ACN
ACN
ACN
ACN
ACN
ACN
ACN
ACN
ACN
ACN
ACN
ACN
ACN
ACN
ACN
Heating
Heating
Heating
60
60
60
60
60
60
60
60
60
15 h
0
Pyridine (10)
Morpholine
3 h nd
3 h 37c
3 h 30c
3 h 34
3 h 48
3 h 55
3 h 67
5 h 68
8 h 68
5 m 68
5 m 75
5 m 75
10 m 79
15 m 80
10 m 87
10 m 95
10 m 90
10 m 86
10 m 85
10 m 86
10 m 95
Piperidine (10) Heating
DIPEA (10)
DMAP (10)
DBU (10)
Heating
Heating
Heating
Heating
Heating
Heating
MW
MW
MW
MW
MW
MW
MW
MW
MW
MW
MW
MW
DABCO (10)
DABCO (10)
DABCO (10)
DABCO (10)
DABCO (10)
DABCO (10)
DABCO (10)
DABCO (10)
DABCO (20)
DABCO (30)
DABCO (50)
9
10
11
12
13
14
15
16
17
18
19
20
21
22
60
100
140
180
140
140
140
140
140
140
140
140
140
Scheme 2 Comparison of various methods attempted for vinyl acetate
based transesterification of phenols.
Toluene DABCO (30)
Hexane DABCO (30)
THF
report of organocatalysts being ever used for entitled esterifica-
tion. The use of organocatalysts, which in many occasions are
viewed as fillers between metal- and enzyme-catalysis29a and have
shown general superiority in many similar transformations,29b
seem to be a logical choice for such studies. Other inherent
advantages associated with organocatalysts are their easy and
cheaper commercial availability, easy procedure and separation
and environmental friendliness, etc.29,30
Considering all these facts, we were keen to device an effective
yet practical protocol for vinyl ester based esterification particularly
suited for phenols under organocatalytic conditions. After a careful
survey of a number of conditions and catalysts and assessment
of the results on the basis of yield, efficiency, time, cost and
greenness; we report herein a DABCO catalyzed vinyl ester based
esterification of phenols under microwave conditions.
DABCO (30)
DABCO (30)
h = hours, m = minutes, MW = Anton Paar Monowave 300 microwave
reactor. Irradiation power: 850 W; ramp time: 1 min. 60 1C, ACN =
acetonitrile, DIPEA = N,N-diisopropylethylamine, DMAP = 4-dimethyl-
aminopyridine, DBU = 1,8-diazabicyclo[5.4.0]undec-7-ene, DABCO =
1,4-diazabicyclo[2.2.2]octane. a General conditions: phenol 1a (1 mmol);
b
vinyl acetate 1b (1.2 mmol). Isolated yields; nd = not determined.
c
The corresponding amine acetate is formed (confirmed by mass
spectroscopy of the reaction mixture).
amine acetates (confirmed by mass spectroscopy) and this might
be a reason for an unsatisfactory yield of 1c (Table 1, entries 3
and 4). This prompted us to use tertiary amines such as DIPEA,
DMAP and DBU as catalysts which resulted in further improve-
ments in the yield of 1c (Table 1, entries 5–7). Gratifyingly,
employment of DABCO in a catalytic amount increased the yield
up to 67% (Table 1, entry 8). Since DMAP, DBU and DABCO are
Results and discussion
In all the scouting experiments, 1 mmol of phenol (1a) and quite hygroscopic, compounds traces of water or moisture in the
1.2 mmol of vinyl acetate (1b) were taken as model substrates. reaction system could adversely affect the outcome, therefore,
Before anything else, the role of a catalyst was determined by these experiments were also conducted in duplicates under
performing a reaction between 1a and 1b in acetonitrile at 60 1C anhydrous conditions with special care. No significant changes
without any catalyst. Even after 15 h of continuous heating, were noticed in reaction outcomes. Since DABCO was found to
nothing new was spotted on the TLC and the starting material be better than all other catalysts probably because of its higher
remained intact, indicating that a suitable catalyst system was nucleophilicity,27 therefore, all further optimization reactions
mandatory for the reaction to occur (Table 1, entry 1). Initially, were carried out using DABCO as the catalyst.
pyridine was used as a catalyst in the above reaction which
Because of the relatively low boiling point of vinyl acetate,
unfortunately resulted in a black unidentifiable viscous mixture the next set of experiments was performed under closed micro-
and multiple spots on the TLC (Table 1, entry 2). Replacing wave conditions in anticipation of better availability of the ester
pyridine with secondary amine catalysts such as morpholine to the reacting atmosphere. Comparable results were obtained
and piperidine created a marked change in the reaction profile at relatively higher temperature (100 1C) however, notable
with the formation of the desired product. However, some of improvement in the yield occurred at 140 1C (Table 1, entries
the catalysts themselves got converted into the corresponding 11 and 12). Further optimization involving a temperature of
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140 1C, a holding time of 10 minutes and 30% catalytic loading chance to undergo a series of reactions. The presence of imines
increased the yield of 1b up to 90% (Table 1, entries 12–18). The was also confirmed by GC-MS and a similar TLC profile of a
reaction yield seemed to be independent of the solvent used standard reaction between acetaldehyde and anilines under a
(Table 1, entries 19–21) and this prompted us to perform the similar set of conditions. It was however surprising that 4-bromo
reaction under solvent-free conditions. Gratifyingly, the reaction and 4-chloroaniline did not react under the given conditions and
under neat conditions resulted in 95% of 1b (Table 1, entry 22) and only the starting material was recovered (Table 5, entries 6–10).
hence this was selected as the optimized protocol for the ensuing
A plausible mechanism that is also in agreement with
course. It becomes apparent that the solvent effects reported in the previous reports of DABCO catalyzed transformations30 is
some previous cases for acylation of alcohols vanished under outlined in Scheme 3. The enol ester is activated by an initial
microwave conditions in the present reaction.16
nucleophilic attack by DABCO and forms intermediate ‘A’
We also examined the effectiveness of other enol esters such and enolate ‘B’. This enolate abstracts a proton from phenol
as isopropenyl acetate (2b), 1-acetoxy-1,3-butadiene (3b), 1-(tri- and subsequently tautomerises to the corresponding aldehyde.
fluoromethyl)vinyl acetate (4b) on the above mentioned trans- The phenolate thus generated attacks the nucleophilic carbon
esterification reaction. As expected other enol esters proved to of intermediate ‘A’ forming a tetrahedral complex ‘C’, which
be equally good acyl donors with nearly quantitative conver- eventually produces an O-acylated product and regenerates
sions illustrating the generality of the method. (Table 2, entries DABCO for the next cycle.
1 to 4). However, we decided to continue with vinyl acetate in
our work due to economical reasons.31
In summary, this is the first successful report of organoca-
talytic transesterification of a wide range of phenols using vinyl
With optimized conditions in hand, the substrate scope and acetate. In addition, solventless conditions, inexpensive cata-
generality of the protocol were explored and the results are lysts, operational simplicity, a simple and column free workup,
summarized in Table 3. A wide variety of substituted phenols faster and quantitative conversions and the exclusive formation
underwent facile and nearly quantitative conversions. Substrates of O-acylated products without excess reagents are some of
bearing both electron-rich (such as 4-methoxy, 4-methyl and 4-tert- the salient features of the presented protocol which renders
butylphenol) and electron-deficient (4-chloro and 3-trifluoromethyl- significant greenness to the method. Considering the bulk
phenols) groups smoothly got converted into the corresponding scale applicability, further work is currently underway in our
acetates. The reaction worked well with ortho-, meta-, para- laboratory to extend the scope and scale of this reaction.
methoxyphenols (Table 3, entries 2–4) and hydroxyphenols such
as catechol, resorcinol, hydroquinone, 2,3-dihydroxy naphthol
and 1,6- and 1,5-dihydroxy naphthol (Table 3, entries 14–16, 19,
20 and 22) and afforded the respective products in excellent yields
Experimental section
under standard conditions. In our hands, 4-methoxyphenol
resulted in a better yield than the one reported previously.20 The
present methodology was further extended to O-benzoylation of
phenols using vinyl benzoate as evident from Table 4.
General experimental details
All NMR spectra were recorded on a Jeol Resonance ECX-400II. The
chemical shifts are reported in parts per million and are refer-
enced to TMS. The spectra were processed using MestReNova6
software. Mass spectrometry (HRMS) was performed using a
Bruker daltronics microTOF-QIIs spectrometer using ESI ioni-
zation, with less than 5 ppm error for all HRMS analyses.
Analytical Thin layer chromatography (TLC) was performed
on a silica gel plate (Mercks 60F254). All solvent were distilled
prior to use and all chemicals were purchased from Sigma-
Aldrichs and used without further purification.
Having achieved success with phenols, we next turned our
attention toward acylation of anilines. As apparent from Table 5,
the presented method worked equally well with aminoazines such
as 2-aminopyridine, 2-amino-4-methylpyridine and 2-amino-5-
bromopyridine (Table 5, entries 1–5). However crude and uni-
dentifiable mixtures were obtained with unsubstituted aniline,
p-toluidine and benzylamine. We reasoned that the enolate half
(and ensuing aldehyde) generated from the cleavage of vinyl esters
might be interacting with unsubstituted aniline, p-toluidine
and benzylamine. The reactive imines thus formed, had a
Microwave irradiation experiment
All microwave experiments were carried out in a dedicated
Anton-Paar Monowave 300 reactors, operating at a frequency
of 2.455 GHz with a continuous irradiation power of 0–300 W.
The reactions were performed in a G-4 borosilicate glass vial
sealed with a Teflon septum and placed in a microwave cavity.
Initially, a microwave with the required power was used and the
temperature was ramped from room temperature to a desired
temperature. Once this temperature was attained, the process
vial was held at this temperature for the required time.
The reactions were continuously stirred. The temperature was
measured using an IR sensor. After the experiments a cooling
jet cooled the reaction vessel to ambient temperature.
Table 2 Effect of the nature of the acylating agent on the transesterification
reactiona
Entry
Enol ester
Yieldb (%)
1
2
3
4
Vinyl acetate (1b)
95
93
96
96
Isopropenyl acetate (2b)
1-Acetoxy-1,3-butadiene (3b)
1-(Trifluoromethyl)vinyl acetate (4b)
a
General conditions: phenol 1a (1 mmol); enol ester 1b–4b (1.2 mmol);
DABCO (30 mol%); solvent-less, Anton Paar Monowave 300 microwave
reactor. Irradiation power: 850 W; ramp time: 1 min. 60 1C, holding
b
time: 10 min. 140 1C. Isolated yields.
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Table 3 Scope of the transesterification reactiona
Entry
1
Substrate
Product
Yieldb (%)
99
Entry
12
Substrate
Product
Yieldb (%)
96
1c
12c
2
3
2c
3c
98
97
13
14
13c
14c
98
92c
4
5
4c
5c
98
98
15
16
15c
16c
94c
92c
6
7
6c
7c
99
96
17
18
17c
18c
90
99
8
9
8c
9c
96
97
19
20
19c
20c
98c
97c
10
10c
11c
95
94
21
22
21c
22c
96
11
99c
a
General conditions: substrate 1a–22a (1 mmol); vinyl acetate 1b (1.2 mmol); DABCO catalyst loading (30 mol%), Anton Paar Monowave 300
b
c
reactor. Irradiation power: 850 W; ramp time: 1 min. 70 1C. Holding time: 10 min. 140 1C. Isolated yield. 2.5 mmols of vinyl acetate were used.
at 70 1C. The temperature was then increased to 140 1C with a
holding time of 10 minutes. The reaction mixture was brought
to room temperature by cooling jet and dissolved in 10 ml
General procedure for the vinyl acetate based
transesterification of phenols
Under solvent-free conditions, phenol 1a (1.0 mmol), vinyl acetate of ethyl acetate. This organic layer was washed with water,
1b (1.2 mmols) and 1,4-diazabicyclo[2.2.2]octane (30 mol%) were saturated brine solution and dried over anhydrous MgSO4
mixed well in a G-4 process vial capped with a Teflon septum. and finally evaporated under reduced pressure to give corre-
After pre-stirring for 1 or 2 minutes, the vial was subjected sponding ester 1c. Product 1c was pure enough for spectral
1
to microwave irradiation with an initial ramp time of 1 minute elucidation by H NMR, 13C NMR and HRMS.
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Table 4 Benzoylation of phenol using vinyl benzoatea
Table 5 Transesterification of amines using vinyl estersa
Entry Substrate Enol ester Product
Yieldb
97
1
Entry
1
Substrate
Product
Yieldb (%)
2
96
97
3
4
98
92
2
95
3
4
95
98
5
90
6
7
8
9
nd
nd
0
5
93c
a
General conditions: substrate phenol (1 mmol); vinyl benzoate 1b
(1.2 mmol); DABCO catalyst loading (30 mol%), Anton Paar Monowave
300 reactor. Irradiation power: 850 W; ramp time: 1 min. 70 1C. Holding
b
c
time: 10 min. 140 1C. Isolated yield. 2.5 mmols of vinyl benzoate
were used.
0
Phenyl acetate (1c). Yield: 99%; whitish yellow solid; mp:
52 1C; 1H NMR (400 MHz, DMSO-d6): d (ppm) 2.29 (s, 3H), 7.01
(dd, 2H, J = 6.0 & 1.0 Hz), 7.14 (tt, 1H, J = 6.0 & 1.1 Hz), 7.23
(t, 2H, J = 5.9 Hz). 13C NMR: (100 MHz, DMSO-d6): d (ppm) 20.9,
121.0, 125.2, 129.9, 150.5, 169.7. HRMS (ESI) m/z calcd for
(C8H8O2) [M + Na]+: 159.0422, found: 159.0419.
2-Methoxyphenyl acetate (2c). Yield: 98%; yellow liquid;
1H NMR (400 MHz, DMSO-d6): d (ppm) 2.30 (s, 3H), 2.80
(s, 3H), 6.91–6.97 (m, 2H), 7.05 (dd, 1H, J = 7.8 & 1.8 Hz),
10
nd
a
General conditions: substrate amine 23a–30a (1 mmol); vinyl ester 1b
or 5b (1.2 mmol); DABCO catalyst loading (30 mol%), Anton Paar
Monowave 300 reactor. Irradiation power: 850 W; ramp time: 1 min.
b
70 1C. Holding time: 10 min. 140 1C. Isolated yields; nd = not determined.
7.16–7.23 (m, 1H). 13C NMR: (100 MHz, DMSO-d6): d (ppm) J = 7.7 Hz). 13C NMR: (100 MHz, DMSO-d6): d (ppm) 21.0, 60.4,
20.7, 55.9, 112.5, 120.8, 122.9, 127.0, 139.9, 151.3, 169.1. HRMS 118.6, 122.2, 126.6, 129.2, 139.5, 150.7, 169.6. HRMS (ESI) m/z
(ESI) m/z calcd for (C9H10O3) [M + Na]+: 189.0528, found: calcd for (C9H10O3) [M + Na]+: 189.0528, found: 189.0525.
189.0522.
4-Methoxyphenyl acetate (4c). Yield: 98%; yellow liquid;
3-Methoxyphenyl acetate (3c). Yield: 97%; yellow liquid; 1H NMR (400 MHz, DMSO-d6): d (ppm) 2.24 (s, 3H), 3.75 (s,
1H NMR (400 MHz, DMSO-d6): d (ppm) 2.22 (s, 3H), 2.31 3H), 6.86 (dt, 2H, J = 9.1 & 3.6 Hz), 6.98 (dt, 2H, J = 9.2 & 3.5 Hz).
(s, 3H), 6.81–6.92 (m, 2H), 7.0 (d, 1H, J = 7.6 Hz), 7.21 (t, 1H, 13C NMR: (100 MHz, DMSO-d6): d (ppm) 21.1, 55.6, 114.5, 122.4,
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J = 8.2 Hz), 7.22–7.24 (m, 1H), 7.24–7.26 (m, 3H), 7.27–7.33 (m, 2H),
7.35 (dt, 2H, J = 7.6 & 0.6 Hz). 13C NMR: (100 MHz, DMSO-d6): d
(ppm) 21.0, 36.6, 115.6, 120.6, 122.7, 126.4, 126.5, 127.8, 128.7,
129.0, 131.2, 133.1, 139.8, 149.2, 169.7. HRMS (ESI) m/z calcd for
(C15H14O2) [M + Na]+: 249.0892, found: 249.0882.
4-Benzylphenyl acetate (11c). Yield: 94%; brown liquid;
1H NMR (400 MHz, DMSO-d6): d (ppm) 2.35 (s, 3H), 4.08
(s, 2H), 7.15 (dt, 2H, J = 8.6 & 2.7 Hz), 7.29–7.36 (m, 5H),
7.39–7.45 (m, 2H). 13C NMR: (100 MHz, DMSO-d6): d (ppm)
21.3, 41.5, 115.6, 121.8, 126.5, 128.8, 129.2, 130.1, 139.0, 141.0,
149.2, 170.0. HRMS (ESI) m/z calcd for (C15H14O2) [M + Na]+:
249.0892, found: 249.0887.
4-(Benzyloxy)phenyl acetate (12c). Yield: 96%; whitish solid;
1
mp: 120 1C (decomp); H NMR (400 MHz, DMSO-d6): d (ppm)
2.29 (s, 3H), 5.05 (s, 2H), 7.0 (qt, 4H, J = 10.1 & 2.9 Hz), 7.34
(tt, 1H, J = 7.0 & 1.6 Hz), 7.37–7.47 (m, 4H). 13C NMR: (100 MHz,
DMSO-d6): d (ppm) 21.2, 70.5, 115.5, 122.5, 127.6, 128.1, 128.7,
136.9, 144.5, 156.5, 170.0. HRMS (ESI) m/z calcd for (C15H14O3)
[M + Na]+: 263.0841, found: 263.0836.
Scheme 3 Proposed mechanism of the reaction.
Benzo[d][1,3]dioxol-5-yl acetate (13c). Yield: 98%; brown
1
144.3, 157.3, 170.0. HRMS (ESI) m/z calcd for (C9H10O3)
[M + Na]+: 189.0528, found: 189.0523.
solid; mp: 106–109 1C; H NMR (400 MHz, DMSO-d6): d (ppm)
2.19 (s, 3H), 5.88 (s, 2H), 6.48 (dd, 1H, J = 8.4 & 2.4 Hz), 6.58
(d, 1H, J = 2.32 Hz), 6.72 (d, 1H, J = 8.4 Hz). 13C NMR: (100 MHz,
DMSO-d6): d (ppm) 21.0, 101.8, 103.8, 108.0, 114.0, 145.1, 145.4,
148.1, 169.8. HRMS (ESI) m/z calcd for (C9H8O4) [M + Na]+:
203.0321, found: 203.0318.
1,2-Benzenediol 1,2-diacetate (14c). Yield: 92%; brown
liquid; 1H NMR (400 MHz, DMSO-d6): d (ppm) 2.25 (s, 6H),
7.13–7.19 (m, 2H), 7.19–7.25 (m, 2H). 13C NMR: (100 MHz,
DMSO-d6): d (ppm) 20.7, 123.5, 126.5, 142.2, 168.4. HRMS (ESI)
m/z calcd for (C10H10O4) [M + Na]+: 217.0477, found: 217.0470.
1,3-Benzenediol 1,3-diacetate (15c). Yield: 94%; yellow
liquid; 1H NMR (400 MHz, DMSO-d6): d (ppm) 2.27 (s, 6H),
6.86 (t, 1H, J = 1.1 Hz), 6.92 (dd, 2H, J = 6.0 & 1.2 Hz), 7.22 (t, 1H,
J = 6.0 Hz). 13C NMR: (100 MHz, DMSO-d6): d (ppm) 20.9, 115.4,
119.2, 131.2, 151.6, 169.7. HRMS (ESI) m/z calcd for (C10H10O4)
[M + Na]+: 217.0477, found: 217.0471.
1,4-Benzenediol 1,4-diacetate (16c). Yield: 92%; brown
liquid; 1H NMR (400 MHz, DMSO-d6): d (ppm) 2.26 (s, 6H),
7.07 (s, 4H). 13C NMR: (100 MHz, DMSO-d6): d (ppm) 21.1,
122.5, 148.1, 169.4. HRMS (ESI) m/z calcd for (C10H10O4)
[M + Na]+: 217.0477, found: 217.0468.
Naphthalen-1-yl acetate (17c). Yield: 90%; brown solid; mp:
88 1C; 1H NMR (400 MHz, DMSO-d6): d (ppm) 2.48 (s, 3H), 7.31
(d, 1H, J = 8.0 Hz), 7.50 (t, 1H, J = 8.0 Hz), 7.52–7.60 (m, 2H),
7.78 (d, 1H, J = 8.2 Hz), 7.92 (t, 2H, J = 7.3 Hz). 13C NMR: (100
MHz, DMSO-d6): d (ppm) 21.2, 118.3, 121.3, 125.6, 126.2, 126.6,
126.9, 128.2, 134.7, 146.7, 169.7. HRMS (ESI) m/z calcd for
(C12H10O2) [M + Na]+: 209.0579, found: 209.0573.
2,3-Dimethylphenyl acetate (5c). Yield: 98%; brown liquid;
1H NMR (400 MHz, DMSO-d6): d (ppm) 2.26 (d, 6H, J = 6.0 Hz),
2.29 (s, 3H), 6.84 (dd, 1H, J = 8.0 & 2.4 Hz), 6.90 (br s, 1H), 7.14
(d, 2H, J = 8.1 Hz). 13C NMR: (100 MHz, DMSO-d6): d (ppm) 19.3,
20.0, 21.2, 118.7, 122.6, 130.5, 134.3, 138.0, 148.7, 170.0. HRMS
(ESI) m/z calcd for (C10H12O2) [M + Na]+: 187.0735, found:
187.0730.
4-tert-Butylphenyl acetate (6c). Yield: 99%; brown liquid;
1H NMR (400 MHz, DMSO-d6): d (ppm) 1.25 (s, 9H), 2.22 (s, 3H),
6.90–6.99 (m, 2H), 7.28–7.38 (m, 2H). 13C NMR: (100 MHz,
DMSO-d6): d (ppm) 14.2, 31.4, 34.5, 120.9, 126.3, 148.4, 171.5.
HRMS (ESI) m/z calcd for (C12H16O2) [M + Na]+: 215.1048,
found: 215.1041.
4-Chlorophenyl acetate (7c). Yield: 96%; yellow liquid;
1H NMR (400 MHz, DMSO-d6): d (ppm) 2.21 (s, 3H), 6.97 (dt,
2H, J = 8.7 & 3.2 Hz), 7.27 (dt, 2H, J = 8.8 & 3.2 Hz). 13C NMR:
(100 MHz, DMSO-d6): d (ppm) 20.1, 123.0, 129.5, 131.1, 149.2,
169.2. HRMS (ESI) m/z calcd for (C8H7ClO2) [M + Na]+: 193.0033,
found: 193.0028.
2,6-Dichlorophenyl acetate (8c). Yield: 96%; yellow solid;
1
mp: 108–110 1C; H NMR (400 MHz, DMSO-d6): d (ppm) 2.32
(s, 3H), 7.05 (d, 1H, J = 8.7 Hz), 7.23 (dd, 1H, J = 8.7 & 2.4 Hz),
7.43 (d, 2H, J = 2.4 Hz). 13C NMR: (100 MHz, DMSO-d6): d (ppm)
20.6, 124.7, 128.0, 129.2, 130.2, 132.0, 135.8, 168.4. HRMS (ESI)
m/z calcd for (C8H6Cl2O2) [M + Na]+: 226.9643, found: 226.9638.
3-(Trifluoromethyl)phenyl acetate (9c). Yield: 97%; yellow
liquid; 1H NMR (400 MHz, DMSO-d6): d (ppm) 2.30 (s, 3H),
7.24–7.30 (m, 1H), 7.37 (br s, 1H), 7.48 (d, 2H, J = 5.2 Hz). 13C
NMR: (100 MHz, DMSO-d6): d (ppm) 21.0, 119.0 (q, J = 3.8 Hz),
122.3, 122.7 (q, J = 3.8 Hz), 125.0, 125.3 (q, J = 1.0 Hz), 130.1,
150.8, 169.2. HRMS (ESI) m/z calcd for (C9H7F3O2) [M + Na]+:
227.0296, found: 227.0290.
Naphthalen-2-yl acetate (18c). Yield: 99%; brown solid; mp:
96–98 1C; H NMR (400 MHz, DMSO-d6): d (ppm) 2.37 (s, 3H),
1
7.26 (dd, 1H, J = 6.5 & 2.4 Hz), 7.45–7.54 (m, 2H), 7.59 (d, 1H,
J = 2.2 Hz), 7.80–7.90 (m, 3H). 13C NMR: (100 MHz, DMSO-d6):
d (ppm) 21.3, 118.7, 121.3, 125.9, 126.7, 127.8, 127.9, 129.6,
131.6, 133.9, 148.4, 169.9. HRMS (ESI) m/z calcd for (C12H10O2)
[M + Na]+: 209.0579, found: 209.0574.
2-Benzylphenyl acetate (10c). Yield: 95%; yellow liquid; 1H NMR
(400 MHz, DMSO-d6): d (ppm) 2.25 (s, 3H), 3.99 (s, 2H), 7.14 (d, 1H,
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2,3-Naphthalenediol-2,3-diacetate (19c). Yield: 98%; white
Paper
1,4-Benzenediol 1,4-dibenzoate (27c). Yield: 93%; yellow
solid; mp: 110–112 1C; H NMR (400 MHz, DMSO-d6): d (ppm) liquid; 1H NMR (400 MHz, DMSO-d6): d (ppm) 7.19 (s, 4H),
2.34 (s, 6H), 7.45–7.50 (m, 2H), 7.68 (s, 2H), 7.76–7.82 (m, 2H). 7.44 (t, 4H, J = 6.0 Hz), 7.52 (tt, 2H, J = 6.0 & 1.2 Hz), 8.03 (dd,
13C NMR: (100 MHz, DMSO-d6): d (ppm) 20.9, 121.1, 126.6, 4H, J = 6.0 & 1.0 Hz). 13C NMR: (100 MHz, DMSO-d6): d (ppm)
127.6, 131.7, 141.1, 168.8. HRMS (ESI) m/z calcd for (C14H12O4) 123.0, 129.8, 130.5, 131.7, 134.4, 149.9, 167.9. HRMS (ESI) m/z
1
[M + Na]+: 267.0634, found: 267.0621.
calcd for (C20H14O4) [M + Na]+: 341.0790, found: 341.0784.
2,6-Naphthalenediol-2,6-diacetate (20c). Yield: 97%; yellow
N-(Pyridine-2yl)acetamide (28c). Yield: 97%; brown solid;
liquid; 1H NMR (400 MHz, DMSO-d6): d (ppm) 2.34 (s, 6H), 7.24 mp: 108–109 1C; H NMR (400 MHz, DMSO-d6): d (ppm) 2.17
(dd, 2H, J = 6.6 & 2.1 Hz), 7.56 (d, 2H, J = 2.3 Hz), 7.80 (d, 2H, J = (s, 3H), 6.97–7.06 (m, 1H), 7.68 (td, 1H, J = 7.9 & 2.0 Hz), 8.15–
8.8 Hz). 13C NMR: (100 MHz, DMSO-d6): d (ppm) 21.2, 118.6, 8.32 (m, 2H), 9.38 (s, 1H). 13C NMR: (100 MHz, DMSO-d6): d
122.1, 129.2, 131.8, 148.4, 169.7. HRMS (ESI) m/z calcd for (ppm) 24.7, 114.6, 119.8, 138.7, 147.5, 151.9. HRMS (ESI) m/z
1
(C14H12O4) [M + Na]+: 267.0634, found: 267.0630.
calcd for (C7H8N2O) [M + Na]+: 159.0535, found: 159.0529.
6-Bromonaphthalen-2-yl acetate (21c). Yield: 96%; white
N-(Pyridine-2yl)benzamide (29c). Yield: 96%; brown solid;
solid; mp: 112 1C; H NMR (400 MHz, DMSO-d6): d (ppm) 2.35 mp: 118 1C; 1H NMR (400 MHz, DMSO-d6): d (ppm) 7.55 (td, 1H,
(s, 3H), 7.22 (dd, 1H, J = 8.9 & 2.3 Hz), 7.49–7.54 (m, 2H), 7.62 J = 6.0 & 1.1 Hz), 7.73 (t, 2H, J = 5.5 Hz), 7.78 (tt, 1H, J = 5.8 & 1.4
(d, 1H, J = 8.9 Hz), 7.71 (d, 1H, J = 8.9 Hz), 7.96 (d, 1H, J = 1.8 Hz). Hz), 7.99 (td, 1H, J = 6.0 & 1.1 Hz), 8.15 (dd, 2H, J = 5.9 & 1.2 Hz),
13C NMR: (100 MHz, DMSO-d6): d (ppm) 21.3, 118.8, 119.7, 122.4, 8.35 (dd, 1H, J = 6.0 & 1.1 Hz), 8.73 (dd, 1H, J = 6.0 & 1.3 Hz),
128.6, 129.4, 129.9, 130.1, 132.2, 132.5, 148.6, 169.7. HRMS (ESI) 9.38 (s, 1H). 13C NMR: (100 MHz, DMSO-d6): d (ppm) 116.9,
m/z calcd for (C12H9BrO2) [M + Na]+: 286.9684, found: 286.9682. 120.0, 129.2, 129.6, 132.7, 136.0, 140.7, 148.9, 153.2, 168.5.
1,5-Naphthalenediol-1,5-diacetate (22c). Yield: 99%; white HRMS (ESI) m/z calcd for (C12H10N2O) [M + Na]+: 221.0691,
1
1
solid; mp: 128–130 1C; H NMR (400 MHz, DMSO-d6): d (ppm) found: 221.0687.
2.27 (s, 6H), 6.82 (dd, 2H, J = 6.0 & 1.1 Hz), 7.25 (t, 2H, J =
N-(4-Methylpyridine-2yl)actamide (30c). Yield: 98%; brown
1
6.0 Hz), 7.44 (dd, 2H, J = 5.9 & 1.1 Hz). 13C NMR: (100 MHz, solid; mp: 122–124 1C; H NMR (400 MHz, DMSO-d6): d (ppm)
DMSO-d6): d (ppm) 20.9, 117.5, 121.2, 125.1, 125.6, 145.4, 170.2. 2.63 (s, 3H), 2.85 (s, 3H), 7.47 (dd, 1H, J = 6.0 & 1.1 Hz), 8.65 (d,
HRMS (ESI) m/z calcd for (C14H12O4) [M + Na]+: 267.0634, 1H, J = 1.1 Hz), 8.82 (d, 1H, J = 6.0 Hz), 9.38 (s, 1H). 13C NMR:
found: 267.0630.
(100 MHz, DMSO-d6): d (ppm) 21.2, 23.8, 114.8, 121.8, 149.4,
Phenyl benzoate (23c). Yield: 97%; yellow liquid; 1H NMR 155.2, 170.5. HRMS (ESI) m/z calcd for (C8H10N2O) 173.0691
(400 MHz, DMSO-d6): d (ppm) 7.03 (tt, 1H, J = 5.9 & 1.3 Hz), 7.17 [M + Na]+, found: 173.0689.
(dd, 2H, J = 6.1 & 1.2 Hz), 7.30 (t, 2H, J = 6.0 Hz), 7.42 (t, 2H,
N-(5-Bromopyridine-2yl)actamide (31c). Yield: 92%; brown
1
J = 6.1 Hz), 7.50 (tt, 1H, J = 5.9 & 1.2 Hz), 8.10 (dd, 2H, J = 6.0 & solid; mp: 126 1C; H NMR (400 MHz, DMSO-d6): d (ppm) 2.21
1.0 Hz). 13C NMR: (100 MHz, DMSO-d6): d (ppm) 123.7, 128.1, (s, 3H), 8.25 (dd, 1H, J = 6.0 & 1.1 Hz), 8.54 (d, 1H, J = 6.0 Hz), 8.59
132.0, 132.6, 132.7, 133.8, 136.5, 153.9, 170.0. HRMS (ESI) m/z (d, 1H, J = 1.1 Hz), 9.38 (s, 1H). 13C NMR: (100 MHz, DMSO-d6): d
calcd for (C13H10O2) [M + Na]+: 221.0579, found: 221.0575.
(ppm) 20.2, 106.9, 115.3, 134.9, 147.3, 148.9, 166.8. HRMS (ESI)
4-Chlorophenyl benzoate (24c). Yield: 95%; yellow liquid; m/z calcd for (C7H7BrN2O) [M + Na]+: 236.9640, found: 236.9636.
1H NMR (400 MHz, DMSO-d6): d (ppm) 7.13 (d, 2H, J = 6.0 Hz),
N-(5-Bromopyridine-2yl)benzamide (32c). Yield: 90%; brown
1
7.39 (d, 2H, J = 6.0 Hz), 7.50 (t, 2H, J = 6.0 Hz), 7.57 (tt, 1H, J = 6.0 solid; mp: 132–134 1C; H NMR (400 MHz, DMSO-d6): d (ppm)
& 1.1 Hz), 8.17 (dd, 2H, J = 5.9 & 1.2 Hz). 13C NMR: (100 MHz, 7.44 (t, 2H, J = 5.8 Hz), 7.49 (tt, 1H, J = 5.8 & 1.2 Hz), 7.86 (dd,
DMSO-d6): d (ppm) 123.5, 131.0, 131.5, 131.7, 132.9, 133.3, 2H, J = 5.8 & 1.0 Hz), 8.09 (dd, 1H, J = 6.0 & 1.1 Hz), 8.32 (d, 1H, J
135.6, 152.1, 169.1. HRMS (ESI) m/z calcd for (C13H9ClO2) = 6.0 Hz), 8.54 (d, 1H, J = 1.1 Hz), 9.44 (s, 1H). 13C NMR: (100
[M + Na]+: 255.0189, found: 255.0183.
MHz, DMSO-d6): d (ppm) 113.2, 121.8, 128.5, 128.8, 132.0,
Benzo[d][1,3]dioxol-5-yl benzoate (25c). Yield: 95%; brown 135.2, 139.7, 150.4, 151.7, 167.7. HRMS (ESI) m/z calcd for
1
solid; mp: 120–121 1C; H NMR (400 MHz, DMSO-d6): d (ppm) (C12H9BrN2O) [M + Na]+: 298.9796, found: 298.9792.
5.90 (s, 2H), 6.67 (dd, 1H, J = 6.0 & 1.1 Hz), 6.72 (d, 1H, J =
1.2 Hz), 6.76 (d, 1H, J = 6.0 Hz), 7.43 (t, 2H, J = 6.0 Hz), 7.50 (tt,
1H, J = 6.0 & 1.1 Hz), 8.11 (dd, 2H, J = 5.9 & 1.2 Hz). 13C NMR:
(100 MHz, DMSO-d6): d (ppm) 102.1, 102.6, 110.9, 115.3, 129.1,
129.7, 131.0, 133.6, 146.8, 147.8, 149.8, 167.2. HRMS (ESI) m/z
calcd for (C14H10O4) [M + Na]+: 265.0477, found: 265.0472.
Naphthalen-2-yl benzoate (26c). Yield: 98%; brown solid;
mp: 126–127 1C; 1H NMR (400 MHz, DMSO-d6): d (ppm) 7.2
(t, 1H, J = 1.1 Hz), 7.36–7.48 (m, 5H), 7.53 (tt, 1H, J = 6.0 & 1.1
Hz), 7.58 (dd, 1H, J = 6.0 & 1.0 Hz), 7.78 (tt, 2H, J = 5.3 & 1.2 Hz),
8.14 (dd, 2H, J = 5.9 & 1.2 Hz). 13C NMR: (100 MHz, DMSO-d6): d
(ppm) 117.9, 122.7, 125.4, 128.6, 128.7, 130.1, 130.5, 130.6,
131.1, 132.3, 132.5, 133.0, 136.5, 151.7, 168.6. HRMS (ESI) m/z
calcd for (C17H12O2) [M + Na]+: 271.0735, found: 271.0730.
Acknowledgements
This work was financially supported by Department of Science
and Technology (DST), New Delhi, Govt of India (Grant No. SR/
FT/CS-55/2011). M. K. and S. B. would like to thank CSIR and
MHRD for the award of research fellowship.
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