Copper catalyzed oxidative deamination of Betti bases: An efficient approach for benzoylation/formylation of naphthols and phenols

Article abstract of DOI:10.1039/c6ra04567g

An efficient route for benzoylation or formylation of naphthols/phenols is developed via oxidative deamination of Betti bases. A copper salt catalyst with TBHP as an oxidant is used. Water is used as a reagent as well as solvent. The reaction proceeds through a regioselective radical pathway. Most importantly, the position of acylation is unambiguous. The method is also applicable to non-hydroxy substrates.

Full text of DOI:10.1039/c6ra04567g

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Copper catalyzed oxidative deamination of Betti
bases: an efficient approach for benzoylation/
formylation of naphthols and phenols
Cite this: RSC Adv., 2016, 6, 40552
Received 20th February 2016
Accepted 16th April 2016
*
*
Mohit L. Deb, Choitanya Dev Pegu, Paran J. Borpatra and Pranjal K. Baruah
DOI: 10.1039/c6ra04567g
www.rsc.org/advances
An efficient route for benzoylation or formylation of naphthols/ established to be the most efficient catalysts for the a-func-
phenols is developed via oxidative deamination of Betti bases. A tionalization of tertiary amines.12 However, C–H functionaliza-
copper salt catalyst with TBHP as an oxidant is used. Water is used as tion via oxidative deamination catalyzed by metal or non-metal
a reagent as well as solvent. The reaction proceeds through a regio- is less explored.13
selective radical pathway. Most importantly, the position of acylation is
Our target was to synthesize hydroxyaryl ketones and alde-
unambiguous. The method is also applicable to non-hydroxy hydes as they are highly useful intermediates in the synthesis of
substrates.
many pharmaceuticals,14 natural products,15 and some cosmetic
products.16 Therefore, the development of simple and efficient
synthetic methods of this structural moiety is in demand. A few
bio-active derivatives of hydroxyaryl ketones are shown (Fig. 1),
where A is potent against HIV-1 reverse transcriptase,17 B is
cancer chemo-preventive15d and C is cGMP-dependent protein
kinase.15a By tradition, Friedel–Cras type acylation reactions
have been used to obtain acylated phenol or naphthol
compounds,18 but these methods have been found to be diffi-
cult in controlling product regioselectivity.18b,c Moreover, Frie-
del–Cras reaction of naphthols and phenols give low yield,18d,e
and in some cases reaction has to be performed at higher
temperature.18f Another common route to hydroxyaryl ketones
is from the corresponding naphthyl/phenyl esters via Fries-
rearrangement in the presence of Lewis acid catalyst.19
Although, the yields are good in some cases, but require pro-
longed heating using stoichiometric amount of Lewis acid.19a,b
Some reactions are reported with expensive triate catalysts like
Hf(OTf)4 and Sc(OTf)3.19c,d Moreover, Fries-rearrangement gives
mixture of o/p-acylated product,19e,f and deacylated product.19g
Recently, transition-metal catalyzed C–H functionalization
technique has been used to form aryl ketones.20 In addition,
Betti bases,1 o-(a-aminoalkyl)-naphthols or phenols have many
applications such as, they are very good precursors for the
synthesis of several nitrogen containing bio-active compounds
and key intermediates for many multistep organic syntheses.2 A
small number of Betti base derivatives are reported to have
biological activity.3 From the last two decades, Betti bases were
widely used as ligands in organometallic and asymmetric
catalysis.4 Despite these progresses, exploration in search of
more applications of Betti bases are still highly enviable. The
tertiary amine moiety of Betti bases is highly useful to incor-
porate nucleophile/functional groups into the a-CH of nitrogen
through C–H activation.1b,e
C–H functionalization has attracted great attention in the
past decades since it offers maximum step and atom economy
for the formation of carbon–carbon or carbon–hetero bond
compared to the routine cross coupling based methods where
extra steps are required for the pre-functionalization of
substrates.5 The functionalization of sp3 C–H bonds adjacent to
a nitrogen atom has usually been realized utilizing transition
metal salt catalysts with co-oxidants, such as tert-butyl hydro-
peroxide (TBHP), di-tert-butyl peroxide (DTBP), H2O2, molecular
oxygen, to generate iminium ion intermediate, which can react
with different nucleophiles.6 Metals like Pd,7 Ru,8 Fe,9 Rh,10 V,11
are oen used for this purpose. However, there are many
advantages of using copper salts, such as low cost, little toxicity,
ready availability, high-efficiency and, therefore, have
Department of Applied Sciences, GUIST, Gauhati University, Guwahati-781014,
Assam, India. E-mail: baruah.pranjal@gmail.com; mohitdd.deb@gmail.com; Fax:
+91-3612700311; Tel: +91-8876998905
Fig. 1 Few bioactive derivatives of hydroxyaryl ketones.
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other methods for their synthesis have also been developed. For
Encouraged by the results of Maycock et al., where they ob-
instance, transformation from ortho-functionalized diaryl tained dihydro-1,3-oxazines along with traces of ketones from
ketones21 or chromones,22 acylation of benzoquinone,23 or Betti bases (Scheme 1)1b and in continuation of our work27 on
related arenes,24 coupling reactions of nitriles with boronic the application of Betti bases in organic synthesis, herein we
acids,25 and addition of lithium or magnesium reagents to report an efficient method for benzoylation/formylation of
carboxylic derivatives.26 Though these methods are effective for naphthols and phenols from Betti bases via oxidative deami-
the acylation, few of the reactions experience harsh reaction nation under Cu(OAc)2$H2O/TBHP catalytic system using water
conditions,26 inconvenient operation24a,26 and handling as reagent and solvent (Scheme 1). We used sodium dodecyl
hazardous substances.24a
sulphate (SDS) in the reaction to solubilize organic materials
into water via micelle formation.28 To the best of our knowledge
there is no such report of transformation of Betti bases to
hydroxyaryl ketones in the literature. Betti bases were efficiently
prepared by the 3-component Mannich reaction of naphthol/
phenol, aldehydes, and amines and obtained solely ortho-
substituted naphthol/phenol product (1, Scheme 1).1
To test our hypothesis, we initiated a model study by
considering the transformation of 1a to 2a as a representative
example. Diverse solvents, metal catalysts and oxidants were
screened (Table 1). We found that most of the organic solvents
were inefficient for the successful reaction. When we performed
the reaction in water as solvent, no product was indeed formed
which might be due to insolubility of organic substrates in
water. We obtained the best result while performing the reac-
tion in presence of Cu(OAc)2$H2O (0.1 eq.), TBHP (2 eq.) and
SDS (0.2 eq.) in water at 120 ꢀC (entry 6, Table 1). Among the two
types of sp3 C–H bonds adjacent to the nitrogen atom, a-
Scheme 1 Synthesis of hydroxyaryl ketones.
Table 1 Optimization of the reaction conditionsa
Entry
Catalyst (eq.)
Oxidant/additive (eq.)
H2O (eq.)
Solventb
Temp. ꢀ
C
Time (h)
Yield,c 2a (3a)%
1
2
3
4
5
6
7
8
Cu(OAc)2$H2O (0.1)
Cu(OAc)2$H2O (0.1)
Cu(OAc)2$H2O (0.1)
Cu(OAc)2$H2O (0.1)
Cu(OAc)2$H2O (0.08)
Cu(OAc)2$H2O (0.1)
Cu(OAc)2$H2O (1.0)
—
Cu(OAc)2$H2O (0.1)
Cu(OAc)2$H2O (0.1)
Cu(OAc)2$H2O (0.1)
Cu(OAc)2$H2O (0.1)
CuSO4$5H2O (0.1)
CuBr (0.1)
—
—
5
10
10
—
—
—
—
—
—
—
—
—
—
—
—
10
10
10
p-Xylene
p-Xylene
p-Xylene
H2O
H2O
H2O
H2O
H2O
H2O
H2O
130
130
130
120
120
120
120
120
100
120
120
120
120
120
120
120
120
120
2
2
2
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
5 (85)
5 (85)
15 (70)
NR
70 (trace)
90 (5)
15 (ND)
NR
40 (trace)
60 (5)
90 (5)
20 (5)
50 (trace)
55 (ND)
40 (5)
10 (ND)
10 (ND)
15 (60)
TBHP (2)
TBHP (2)
TBHP (2), SDS (0.2)
TBHP (2), SDS (0.2)
SDS (0.2)
TBHP (2), SDS (0.2)
TBHP (2), SDS (0.2)
TBHP (1), SDS (0.2)
TBHP (3), SDS (0.2)
H2O2 (2), SDS (0.2)
TBHP (2), SDS (0.2)
TBHP (2), SDS (0.2)
TBHP (2), SDS (0.2)
TBHP (2), SDS (0.2)
TBHP (2), SDS (0.2)
TBHP (2), SDS (0.2)
9
10
11
12
13
14
15
16
17
18
H2O
H2O
H2O
H2O
FeCl3$6H2O (0.1)
Cu(OAc)2$H2O (0.1)
Cu(OAc)2$H2O (0.1)
Cu(OAc)2$H2O (0.1)
H2O
DMF
DMSO
Toluene
a
Unless otherwise mentioned, all the reactions were performed by using 1a (1 mmol, 303 mg). b 3 ml of solvent was used in each case. c Products
were puried by column chromatography using silica gel (100–200 mesh) and yields are of isolated products. NR ¼ No Reaction. ND ¼ Not Detected.
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Scheme 2 Screening of tert-amine groups of Betti base.
functionalization occurred regioselectively at the benzylic
carbon. A trace amount of dihydro-1,3-oxazine (3a) was also
obtained as side product through the intramolecular a-func-
tionalization of non-benzylic carbon. We next examined the
effect of catalyst/oxidant loading on the reaction. Decrease in
the loading of TBHP from two to one equivalent reduces the
product yield whereas, increasing the amount from two to three
equivalents could not further improve the yield (entry 10 & 11,
Table 1). Also 0.1 equivalent of Cu(OAc)2$H2O was established
to be the lowest level of catalyst loading to offer good yield
(Table 1). A series of tert-amine moieties of the Betti bases were
screened to obtain the best possible yield of the product. We
used various aliphatic cyclic, acyclic, aromatic amines, and
found that Betti bases prepared from pyrrolidine furnished
highest yield (Scheme 2), which was also observed in our
previous report.27
With the optimized conditions in hand, we next investigated
the substrate scope of the reaction (Scheme 3). We used a variety
of Betti base derivatives of naphthol and phenol. The resultant
acylated products which contain a broad range of substituents
could be obtained in moderate to excellent yield. o/m-
Substituted aryl ring of Betti base (R in 1, Scheme 1) offered
relatively lower yield of product with longer time (2h–i and 2p–
q, Scheme 3). Electron withdrawing group on the R of Betti base
increases the product yield, whereas electron releasing group
decreases the yield (Scheme 3). We did not observe signicant
reactivity difference between the substrates containing electron
donating and withdrawing groups on the aromatic ring bearing
the –OH group. We then attempted our model reaction under 3-
component one pot protocol using b-naphthol, benzaldehyde
and pyrrolidine in water using the optimized conditions.
Unfortunately, we obtained only 30% of yield of 2a (Scheme 4).
There are two possible mechanisms for the reaction: either
a radical mechanism or an ionic mechanism.29 To establish the
reaction mechanism, we performed our model reaction under
the optimized conditions in presence of couple of radical
scavengers such as, 2,6-di-tert-butyl-4-methyl phenol (BHT, 2
eq.) and (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO, 2 eq.).
When we used BHT, there was no formation of product at all
and we completely recovered the unreacted Betti base, while
a signicant drop in the product yield was noticed using
TEMPO and only a trace of product 2a was isolated, which
suggest that the reaction follows a radical pathway. We also
looked for the feasibility of the reaction without using TBHP or
copper catalyst (entry 1, 2 and 8, Table 1). Without TBHP, the
reaction gave dihydro-1,3-oxazine with trace of ketone whereas,
Scheme 3 Substrate scope for the synthesis of hydroxyaryl ketones.
Reaction conditions: 1 (1 mmol), Cu(OAc)2$H2O (0.1 eq.), TBHP (2 eq.,
70% in H2O), SDS (0.2 eq.) and H2O (3 ml) at 120 ꢀC. Products were
purified by column chromatography and yields are of isolated
products.
without copper catalyst no reaction was indeed observed. A
tentative mechanism for the reaction was proposed on the basis
of these experiments and some relevant reports on a-C–H
functionalization of tert-amine (Scheme 5).1b,5f The benzylic
Scheme 4 Three-component route to hydroxyaryl ketone.
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method would offer an efficient procedure to obtain this
important class of compounds.
Experimental
General method
All the commercially available reagents were used as received.
NMR spectra were recorded on a Bruker Avance DPX-400 NMR
spectrometer with TMS as the internal standard at room
temperature. Chemical shis (d) are quoted in ppm and
coupling constants (J) are measured in Hertz (Hz). Mass spectra
were recorded in Bruker Daltonics ESQUIRE 3000 LC ESI ion
trap mass spectrometer. All the experiments were monitored by
thin layer chromatography (TLC) on pre-coated silica gel plates
(Merck) and visualized under UV lamp at 254 nm for UV active
materials. Further visualization was achieved by staining
KMnO4 warming in a hot air oven or by iodine vapour. Column
chromatography was performed on silica gel (100–200 mesh),
using ethyl acetate : hexane as eluent.
Scheme 5 A tentative mechanism for the reaction.
General procedure for the synthesis of 1a–m1
To a solution of naphthol (2.0 mmol) in 5 ml ethanol, aldehyde
(2.5 mmol) and amine (2.5 mmol) were added. The reaction
mixture was stirred at room temperature for 12–15 h (1a–k) and
2 h (1l–m). The precipitate was ltered and washed with 20%
ethanol in hexane to isolate the pure compound.
Scheme 6 Reaction without ortho-hydroxyl group.
radical 4 could be formed through H-abstraction by tert-butoxy
radical (formed by copper catalyzed decomposition of TBHP),5f
which followed by a single-electron transfer (SET) from 4 to
generate the benzylic iminium carbocation 5. Subsequently, the
intermediate 5 was attacked by a molecule of water giving
ketone 2. On the other hand, the intermediate 5 can undergo
tautomerization to the less stable non-benzylic iminium car-
bocation 6. In absence of water or if water is present in less
amount (entries 1–3, Table 1), the intermediate 6 can intra-
molecularly cyclise to the dihydro-1,3-oxazine 3. According to
Maycock et al., copper catalyst alone provides dihydro-1,3-
oxazines through the formation of intermediate ammoniumyl
radical cation 7.1b
From the proposed mechanism it is obvious that ortho-
hydroxyl group does not play any role in obtaining the product.
To justify this, we performed two experiments where the
substrates do not contain ortho-hydroxyl group (Scheme 6). In
both the cases we obtained good yield of oxidative deaminated
product, indicating that the method is equally applicable to
non-ortho-hydroxyl substrates as well. 4a and 4b were prepared
according to the reported procedure.30a,b
General procedure for the synthesis of 1n–v1
A mixture of phenol (2.0 mmol), aldehyde (2.5 mmol) and amine
(2.5 mmol) was stirred at 80 ꢀC for 4–5 h (1n–t) and 60 ꢀC for 2 h
(1u–v). The reaction mixture was brought to room temperature
and puried by column chromatography using silica gel (100–
200 mesh), and ethyl acetate–hexane as eluent.
The representative example of the synthesis of 2a
To a mixture of 1a (1.0 mmol, 303 mg), Cu(OAc)2$H2O (0.1
mmol, 20 mg), TBHP (2.0 mmol, 70% in H2O, 257 mg) and SDS
(0.2 mmol, 58 mg) added 3 ml water. The reaction mixture was
ꢀ
then reuxed at 120 C. Aer 3 h, the reaction was completed
(monitored by TLC). Then the reaction mixture was brought to
room temperature and extracted with ethyl acetate (2 ꢁ 50 ml).
Dried the organic fraction with anhydrous sodium sulphate and
concentrated in rotavapor under vacuum. Puried the product
by column chromatography using silica gel (100–200 mesh),
and ethyl acetate–hexane as eluent.
2a1b
Conclusion
White solid; 1H NMR (400 MHz, CDCl3): d 11.22 (s, 1H), 7.95 (d, J
¼ 8.8 Hz, 1H), 7.76 (d, J ¼ 7.9 Hz, 1H), 7.64–7.62 (m, 2H), 7.58–
7.55 (m, 1H), 7.43–7.39 (m, 2H), 7.32–7.24 (m, 3H), 7.18–7.14
(m, 1H); MS: m/z ¼ 249.1 [M + H]+.
In conclusion we have developed a simple and efficient method
for the benzoylation/formylation of naphthols and phenols. The
reaction neither uses any hazardous metal, Lewis acid catalyst
nor the corrosive and irritant acyl halide reagent is required.
Moreover, water is used as solvent. The method gives sole
acylated product and most importantly the position of acylation
2b30c
is unambiguous. A most plausible mechanism is proposed White solid; 1H NMR (400 MHz, CDCl3) d 11.02 (s, 1H), 7.91 (d, J
based on some control experiments. We anticipate that this ¼ 8.8 Hz, 1H), 7.75 (d, J ¼ 8.0 Hz, 1H), 7.54 (d, J ¼ 8.0 Hz, 2H),
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2l30h
7.36 (d, J ¼ 8.8 Hz, 1H), 7.29–7.15 (m, 5H), 2.41 (s, 3H); MS: m/z
¼ 263.1 [M + H]+.
1
Light brown solid; H NMR (400 MHz, CDCl3) d 13.12 (s, 1H),
10.80 (s, 1H), 8.35 (d, J ¼ 8.4 Hz, 1H), 7.96 (d, J ¼ 8.8 Hz, 1H),
7.81 (d, J ¼ 8.5 Hz, 1H), 7.61–7.58 (m, 1H), 7.46–7.44 (m, 1H),
7.12 (d, J ¼ 8.9 Hz, 1H); MS: m/z ¼ 172.0 [M + H]+.
2c30c
Brownish solid; 1H NMR (400 MHz, CDCl3) d 10.58 (s, 1H), 7.91
(d, J ¼ 9.2 Hz, 1H), 7.75 (d, J ¼ 9.2 Hz, 1H), 7.68–7.65 (m, 2H),
7.43–7.42 (d, J ¼ 8.8 Hz, 1H), 7.29–7.17 (m, 3H), 6.89–6.86 (m,
2H), 3.86 (s, 3H). MS: m/z ¼ 279.1 [M + H]+.
2m30i
White solid; 1H NMR (400 MHz, CDCl3) d 13.11 (s, 1H), 10.79 (s,
1H), 8.22 (d, J ¼ 8.8 Hz, 1H), 7.98 (d, J ¼ 2.4 Hz, 1H), 7.91 (d, J ¼
9.2 Hz, 1H), 7.71–7.69 (m, 1H), 7.21 (d, J ¼ 9.2 Hz, 1H); MS: m/z
¼ 251.0 [M + H]+ (100%), 253.0 [M + H]+ (100%).
2d30c
1
White powder; H NMR (400 MHz, CDCl3) d 11.08 (s, 1H), 7.95
(d, J ¼ 8.8 Hz, 1H), 7.76–7.73 (m, 1H), 7.57–7.54 (m, 2H), 7.38–
7.36 (m, 2H), 7.30–7.18 (m, 4H); MS: m/z ¼ 283.0 [M + H]+.
2n30j
1
2e30d
Low melting solid; H NMR (400 MHz, CDCl3): d 12.01 (s, 1H),
7.69–7.67 (m, 2H), 7.61–7.58 (m, 2H), 7.53–7.50 (m, 3H), 7.10–
7.07 (m, 1H), 6.89–6.85 (m, 1H); MS: m/z ¼ 197.0 [M ꢂ H]+.
1
Brownish powder; H NMR (400 MHz, CDCl3) d 11.07 (s, 1H),
7.93 (d, J ¼ 8.8 Hz, 1H), 7.75–7.73 (m, 1H), 7.53–7.46 (m, 4H),
7.29–7.26 (m, 2H), 7.23–7.16 (m, 2H); MS: m/z ¼ 327.0 [M + H]+
(100%), 329.0 [M + H]+ (100%).
2o30d
1
Yellow solid; H NMR (400 MHz, CDCl3): d 12.04 (s, 1H), 7.61–
2f30e
7.56 (m, 3H), 7.51–7.48 (m, 1H), 7.33 (d, J ¼ 7.8 Hz, 2H), 7.08–
7.05 (m, 1H), 6.91–6.85 (m, 1H), 2.44 (s, 3H); MS: m/z ¼ 213.1 [M
+ H]+.
1
ꢀ
Brownish solid; mp ¼ 186–188 C; H NMR (400 MHz CDCl3)
d 11.25 (s, 1H), 8.32–8.29 (m, 2H), 8.06–8.04 (m, 2H), 7.98 (d, J ¼
8.8 Hz, 1H), 7.79–7.75 (m, 1H), 7.46–7.24 (m, 4H); MS: m/z ¼
316.0 [M + Na]+.
2p30k
1
Low melting solid; H NMR (400 MHz, CDCl3): d 11.82 (s, 1H),
2g30c,f
7.70 (d, J ¼ 7.2 Hz, 2H), 7.65–7.61 (m, 1H), 7.54 (t, J ¼ 8.8 Hz,
2H), 7.38–7.34 (m, 2H), 7.0 (d, J ¼ 8.4 Hz, 1H), 2.28 (s, 3H); MS:
m/z ¼ 213.1 [M + H]+.
Off white solid; 1H NMR (400 MHz, CDCl3) d 10.65 (s, 1H), 7.90
(d, J ¼ 9.2 Hz, 1H), 7.76 (d, J ¼ 8.4 Hz, 1H), 7.63–7.58 (m, 2H),
7.43–7.41 (m, 1H), 7.31–7.19 (m, 3H), 6.84–6.81 (m, 2H); MS: m/z
¼ 265.1 [M + H]+.
2q30k
Brown liquid; 1H NMR (400 MHz, CDCl3): d 12.27 (s, 1H), 7.52 (t,
J ¼ 7.6 Hz, 1H), 7.45–7.41 (m, 1H), 7.33–7.28 (m, 4H), 7.07 (d, J ¼
8.6 Hz, 1H), 6.84 (t, J ¼ 7.8 Hz, 1H), 2.32 (s, 3H); MS: m/z ¼ 213.0
[M + H]+.
2h30g
White solid; 1H NMR (300 MHz, CDCl3) d 11.18 (s, 1H), 7.98 (d, J
¼ 7.5 Hz, 1H), 7.82–7.78 (m, 1H), 7.56–7.52 (m, 2H), 7.42–7.38
(m, 2H), 7.31–7.20 (m, 4H); MS: m/z ¼ 283.0 [M + H]+.
2r30l
2i30g
1
Yellow solid; H NMR (400 MHz, CDCl3): d 11.88 (s, 1H), 7.71–
1
White solid; H NMR (300 MHz, CDCl3) d 11.21 (s, 1H), 7.99–
7.32 (m, 7H), 7.02 (d, J ¼ 8.6 Hz, 1H), 2.22 (s, 3H); MS: m/z ¼
7.86 (m, 2H), 7.71 (s, 1H), 7.62–7.51 (m, 2H), 7.50–7.42 (m, 2H),
7.32–7.24 (m, 2H); MS: m/z ¼ 362.8 [M + H]+.
213.1 [M + H]+.
2s30j
2j30c
1
White solid; 1H NMR (400 MHz, CDCl3) d 11.13 (s, 1H), 7.86 (s,
1H), 7.81 (d, J ¼ 8.4 Hz, 1H), 7.62–7.55 (m, 3H), 7.42–7.39 (m,
2H), 7.26–7.12 (m, 3H); MS: m/z ¼ 327.0 [M + H]+ (100%), 329.0
[M + H]+ (100%).
Light yellow solid; H NMR (400 MHz, CDCl3): d 11.61 (s, 1H),
7.71–7.68 (m, 2H), 7.62–7.58 (m, 1H), 7.53–7.50 (m, 2H), 7.16–
7.13 (m, 1H), 7.07–7.01 (m, 2H), 3.71 (s, 3H); MS: m/z ¼ 229.1 [M
+ H]+.
2k30c
2t30j
Reddish brown solid; 1H NMR (400 MHz, CDCl3) d 11.62 (s, 1H), Brown solid; 1H NMR (400 MHz, CDCl3): d 11.98 (s, 1H), 8.49 (d,
7.85 (d, J ¼ 8.4 Hz, 1H), 7.63–7.61 (m, 3H), 7.58–7.54 (m, 1H), J ¼ 2.8 Hz, 1H), 8.44–8.42 (m, 1H), 7.85–7.83 (m, 2H), 7.76–7.72
7.45–7.42 (m, 2H), 7.09 (d, J ¼ 8.8 Hz, 1H), 6.89 (d, J ¼ 8.8 Hz, (m, 1H), 7.65–7.62 (m, 2H), 7.26 (d, J ¼ 8.8 Hz, 1H); MS: m/z ¼
1H), 6.58 (s, 1H), 3.28 (s, 3H). MS: m/z ¼ 279.1 [M + H]+.
244.1 [M + H]+.
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2u30m
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Gummy; 1H NMR (400 MHz, CDCl3): d 10.82 (s, 1H), 9.83 (s, 1H),
7.33–7.30 (m, 2H), 6.91 (d, J ¼ 9.2 Hz, 1H), 2.26 (s, 3H), MS: m/z
¼ 137.1 [M + H]+.
Acknowledgements
MLD is thankful to Science and Engineering Research Board
(SERB), India, for nancial support (Grant No. SB/FT/CS-073/
2014) under Fast Track Scheme. PKB is thankful to DBT, New
Delhi (Grant No. BCIL/NER-BPMC/2015-230) and DST, New
Delhi, (Grant No. SB/FT/CS-100/2012) for nancial support. CDP
is thankful to DST for research fellowship. PJB is thankful to
DBT for research fellowship.
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