Triethylbenzylammonium chloride as a useful and efficient catalyst for the alkylation of indole/substituted indoles in water: A comparative study between conventional and microwave irradiation

Article abstract of DOI:10.1002/jccs.201400221

A green and facile method for the alkylation of indole/substituted indole in water using a phase Transfer catalyst (Triethylbenzylammonium Chloride, TEBA) to synthesise bis-indolyl methanes (BIMs) and Michael addition of indole to α,β-unsaturated carbonyl compounds is reported. The substitution of indoles occurred exclusively at the 3-position and products of N-alkylation has not been observed. However, for 3-substituted indoles, reactions were found to occur at the 2-position. A comparative study between conventional heating and microwave irradiation has also been reported. A comparative study between conventional heating and microwave irradiation for the alkylation of indole/substituted indole in water using a phase transfer catalyst (Triethylbenzylammonium Chloride, TEBA) to synthesise bis-indolyl methanes (BIMs) and Michael addition of indole to α, β-unsaturated carbonyl compounds is reported.

Full text of DOI:10.1002/jccs.201400221

JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Article
Triethylbenzylammonium Chloride as a Useful and Efficient Catalyst for the Alkylation
of Indole/substituted Indoles in Water: A Comparative Study between Conventional
and Microwave Irradiation
Shokip Tumtin, Chingrishon Kathing, Ivulho Tovishe Phucho, Ridaphun Nongrum,
Bekington Myrboh and Rishanlang Nongkhlaw*
Department of Chemistry, North-Eastern Hill University, Shillong, Meghalaya 793022, INDIA
(Received: May 15, 2014; Accepted: Sept. 26, 2014; Published Online: Mar. 16, 2015; DOI: 10.1002/jccs.201400221)
A green and facile method for the alkylation of indole/substituted indole in water using a phase Transfer
catalyst (Triethylbenzylammonium Chloride, TEBA) to synthesise bis-indolyl methanes (BIMs) and Mi-
chael addition of indole to a,b-unsaturated carbonyl compounds is reported. The substitution of indoles
occurred exclusively at the 3-position and products of N-alkylation has not been observed. However, for
3-substituted indoles, reactions were found to occur at the 2-position. A comparative study between con-
ventional heating and microwave irradiation has also been reported.
Keywords: Indoles; Triethylbenzylammonium chloride; Water; Microwave; Bis-indolylmethanes.
INTRODUCTION
The increasing attention directed towards the envi-
due to its operational simplicity, mild reaction conditions,
safe considerations and environmental concerns. Because
of these salient features, the research and developments of
novel PTC, especially to carry out rare organic reactions,
have received considerable industrial interest.8-9 However,
the prime consideration in the selection of the catalyst is the
economy of scale and the efficiency of the PTC, specifi-
cally on the industrial-scale preparation of organic com-
pounds. In this paper, we wish to report an efficient synthe-
sis of 2 and 3-methyl substituted indoles with aldehydes
and a,b-unsaturated ketones under Phase Transfer Catalyst
(PTC) conditions by using Triethylbenzylammonium chlo-
ride (TEBA). The PTC system, which is widely and suc-
cessfully employed in different branches of organic chem-
istry,10 was well suited to the microwave assisted reaction
in water. Owing to the great structural diversity of biologi-
cally active indoles, it is not surprising that the indole ring
system has become an important structural component in
many pharmaceutical agents.11(a-c) For well over a hundred
years, the synthesis and functionalization of indoles has
been a major area of the focus for synthetic organic chem-
ists, and numerous methods for the preparation of indoles
have been developed.12(a-b)
ronmental and toxicological implications associated with
commercial materials, along with the high energy inputs re-
quired for most existing processes, suggest that environ-
mentally-benign alternatives must be explored.1 While in
the past the main issue was the process economics, nowa-
days the preferred processes are mainly due to more re-
stricted environmental regulations and high costs of waste
treatment, removal and remediation.2 Nature, the most
amazing entity of the universe, assembled truly complex
molecules with astonishing efficiency from a primordial
aquatic environment. Therefore, it is not surprising that we
witness the efforts of numerous research groups to intro-
duce water as a solvent in many organic transformations.
Over the last decade, a substantial contribution was in fact
made by the endeavors of green chemistry.3,4 Generally,
water is considered as a solvent in a reaction when it par-
tially solubilizes the reactants prone to react. This indicates
reactions of organic substances that are not soluble yet re-
act well or even considerably faster in water than in organic
solvents.5(a-c) Furthermore, the small size and high polarity
of a water molecule provide some unique properties, among
which the large cohesive energy density (about 550 cal/
cm3), a large surface tension (72 dyn/cm), and a large heat
capacity are particularly noteworthy.6-7
Numerous methods for the preparation of (bis-indolyl
methanes) BIMs employing protic acids or Lewis acids as
catalysts have been reported in the literature, but as far as
our knowledge is concerned, syntheses using PTCs are not
well documented. Hence, we turned our attention to the ef-
Phase transfer catalysis (PTC) has been recognized as
an effective practical methodology for organic synthesis
* Corresponding author. Tel: +91-9436101349; Email: rlnongkhlaw@nehu.ac.in
Supporting information for this article is available on the www under http://dx.doi.org/10.1002/jccs.201400221
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Tumtin et al.
fective catalysis of TEBA in water for the direct and conju-
gate alkylation of indole/substituted indoles. A compara-
tive study between the conventional synthesis and micro-
wave irradiation is also carried out in view of the signifi-
cance of microwave irradiations in saving time which is
fast developing as a convenient and eco-friendly mode of
synthesis.
Proposed mechanism for formation of BIM
Scheme 2
via Azafulven 9
RESULTS AND DISCUSSION
Our present study mainly focuses on the synthesis of
2 and 3-substituted bis-indolyl alkanes in water and their
relative comparison with microwave assisted synthesis.
For these one pot reactions of indole/substituted indoles
with aldehydes/substituted benzaldehydes, it is noteworthy
that most of these reactions have been carried out in aceto-
nitrile.13(a-b) Since acetonitrile is a polar solvent miscible in
water, we expect that it should work in water as well. And
true to our proposition, the reactions were not only success-
ful in water (Scheme 1) but also clean, easy to handle and
most importantly, the yields were excellent. The conven-
tional synthesis was carried out in refluxing condition in
one pot till the completion of reaction. At first, the reactants
were not properly miscible in water but as the reaction pro-
gressed, it was found that the miscibility increased up to a
favorable extent.
to a,b-unsaturated ketones. However, when the 3-position
of the indole moiety is blocked, attack first occurred at the
3-position followed by subsequent shift to the 2-position
(Scheme 3). Formation of 11 and its rearrangement to 12 is
followed by elimination of water to yield the intermediate
13. 13 then reacts with 3-substituted indole which leads to
the formation of 2,3¢-BIM 14. Afinal rearrangement would
then give the 2,2¢-BIM 15.14 Reactions with indole and 2-
substituted indoles gave predominantly 3-alkylated prod-
ucts (Scheme 1) without any N-alkylation, however, when
the 3-position of indole was blocked, 2-alkylated product
was observed (Scheme 1), without any N-alkylation.
Rearrangement of substituent’s from posi-
tion 3 to position 2
Scheme 3
Alkylation of indole/substituted indole at
the 2- and 3-position
Scheme 1
An investigation on the use of different phase-trans-
fer catalysts, such as hexadecyl trimethyl ammonium bro-
mide (HTMAB), 4-dodecylbenzenesulfonic acid (DBSA),
and triethylbenzylammonium chloride (TEBA) on our
present reaction scheme was also carried out and it was
found that they all had catalytic activity but triethylbenzyl-
ammonium chloride (TEBA) displayed the best catalytic
effect. The result is shown in Table 1.
The mechanism of BIM formation is not very clear
but a realistic hypothesis can be formulated as follows: The
mechanism (Scheme 2) has been proposed where azafulven
9 is produced. 9 can undergo further addition with a second
indole molecule to produce BIMs. For the reaction of in-
dole with a,b-unsaturated ketones, the reaction proceed by
simple Michael type mechanism aided by the catalyst.
Same mechanism applies to the 2-substituted indole
in both direct addition to aldehydes and conjugate addition
Mention may be made regarding the stoichiometry of
the catalyst and the reactants for the formation of BIMs in
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Triethylbenzylammonium Chloride: Alkylation of Indole
Table 1. Comparision of catalytic activity of phase transfer
catalysts in aqueous conditions for the synthesis of
compound 3c under microwave conditions
Table 2. Comparative study of formation of bis-indolyl com-
pounds from different aldehydes and indole/substituted
indoles under Reflux and Microwave conditions
Amount of
Reflux
Microwave
condition
Entry
Catalyst
catalyst
(mmol)
Time (s)
Yield (%)
condition
Entry R1
R2
R3
Time Yield Time Yield
1
2
3
4
5
6
7
HTMABa
DBSAb
TEBA
4.0
4.0
150
150
150
100
120
120
120
68
57
92
93
95
35
22
(hr)
(%)
(sec)
(%)
3a
3b
3c
H
H
H
H
H
H
H
2
2
2
85
86
86
120
120
120
97
94
95
4.0
CH3
TEBA
2
TEBA
HTMABa
DBSAb
1.06
1.06
1.06
OCH3
3d
3e
H
H
H
H
2
84
88
120
60
94
97
a Hexadecyl trimethyl ammonium bromide
b 4-Dodecylbenzenesulfonic acid
NO2
1.5
Cl
3f
H
H
1.5
86
60
96
our present strategy. Only a catalytic amount (0.25 equiv.)
of TEBA has been used to standardize our reaction condi-
tions. The reaction requires excess of indole (2 equiv.), but
at the end of the reaction, a small quantity of indole is al-
ways found to be left unreacted even though all the alde-
hyde has been consumed. It is recovered by column chro-
matography. One aspect of such type of reaction is that,
BIMs were formed even when 1 equivalent of indole was
used, indicating the high reactivity of indole as well as the
stability of the product. Hence for our reactions, 0.62 equiv.
of indole was just sufficient to react with 1 equiv. of alde-
hyde to form the bis-product.
OH
3g
3h
H
H
H
H
2
2
85
87
120
120
97
96
H3CO
3i
H
H
H
CH3
CH3
CH3
H
1.5
1.5
1.5
65
63
67
120
120
120
85
84
86
3j
3k
CH3
4a
4b
4c
CH3
CH3
CH3
H
H
H
H
3
3
3
66
67
63
180
180
180
84
85
86
CH3
3xa
H
H
1
46
120
50
CHO
As shown in Table 2, aliphatic as well as aromatic al-
dehydes underwent smooth direct addition to the corre-
sponding bis-indolylmethanes with high to excellent yield
in relatively short reaction times. It is observed that the
electronic properties of the aromatic ring have an effect on
the rate of this electrophilic substitution reaction. The pres-
ence of electron withdrawing group (NO2, Cl) (entries 3e,
3f) enhances the electrophillic substitution reaction with a
lesser reaction time, but the aromatic aldehyde with elec-
tron-donating and electron-withdrawing groups and even
heteroaromatic aldehyde have no significant effect on the
reaction yields. This indicates that the TEBA catalytic
system has wide functional group tolerance.
3yb
----
----
2
87
240
97
----
a The reaction was carried out with 1.24 equiv. of indole and 1
equiv. terephthaladehyde.
b This product formed when 2.24 equiv. of indole was used.
R4 = H
of aldehydes with 2-methylindole is shorter as compared to
indole under the same reaction condition. But the reaction
of 3-methyl indole took a little more time than the other
indoles. As shown in Scheme 4, reaction of terephthal-
aldehyde (3z) (Table 2, entries 3x, 3y) with indole (1a)
gave the corresponding products 3x and 3y. We initially
presumed that since 0.62 equiv. of indole gave the corre-
sponding BIM with an aldehyde, we used 1.24 equiv. of
indole with 1 equiv. of terephthaladehyde (3z) to get com-
pound 3y. But the 1H NMR spectra showed a strong aldehy-
dic peak at d 9.89 and confirmed the formation of 3x in-
stead. Hence, 2.24{1.24 + (0.25 ´ 4)} equiv. of indole was
To prove the generality of this protocol, the reaction
was extended to a variety of aliphatic and aromatic a,b-un-
saturated ketones (Table 3). In conjugate addition reac-
tions, 2-methylindole was found to be more reactive than
indole, giving the corresponding products in excellent
yield.
As shown in Table 3, the reaction time for the reaction
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Tumtin et al.
Table 3. Comparative study of reaction of indole/substituted indoles with á,â-
unsaturated ketones under Reflux and Microwave condition
Microwave
condition
Reflux condition
Entry R1
R2
R5
R6
Time
(hr)
Yield
(%)
Time
Yield
(%)
(sec)
7a
7b
7c
7d
7e
7f
H
H
H
H
H
H
CH3
C2H5
C6H5
CH3
1.5
1.5
80
83
85
75
78
74
67
68
120
120
120
100
100
100
240
240
96
98
97
94
91
92
85
86
H
H
C6H5
H
1.5
H
CH3
CH3
CH3
H
1.20
1.20
1.20
2.5
H
H
C2H5
C6H5
C2H5
C6H5
H
C6H5
H
8a
8b
CH3
CH3
H
C6H5
2.5
Formation of BIM from indole and Schiff
Scheme 5
Formation of bis- and tetra-indolyl methane
upon variation of the amount of indole
Scheme 4
base 17
heated too strongly. So, water was used as the medium for
conventional as well as microwave irradiation. All obser-
vations in both conventional heating as well as microwave
irradiation were similar except in the reaction time and
yields.
employed to get 3y, a tetraindolylmethane.
In our quest to arrive at more diversification, our
present work was further expanded. It is a well known fact
that Schiff bases are important biomimics. The immine car-
bon is found to undergo electrophilic reactions at times
much more electrophilic in nature than carbonyl carbon.
Hence BIMs were also successfully prepared (Scheme 5)
by the combination of indoles and various Schiff bases
which were readily prepared by neat mixing of amines and
aldehydes under microwave irradiation. (Table 4).
Another intention of our study was to investigate the
reusability of the catalyst. After the reaction, the products
were extracted from the reaction mixture with ethyl acetate
and the remaining aqueous part was reused without further
treatment. As shown in Figure 1, the catalytic activities
gradually decreased in the following cycles. However,
even after three cycles, it still has moderate yields. It im-
plied that the TEBA/water catalytic system can be reused at
least three times without significant loss of activity. It may
be noted here that some amount of product formed without
the use of catalyst also but not to an appreciable extent.
Hence the catalyst, TEBAwas used to successfully catalyse
the reaction to completion.
During the past two decades, many publications have
described the successful combination of microwave irradi-
ation as a non-classical energy source with alternative reac-
tion media. In continuation of our previous work18 on un-
conventional methods for organic synthesis, we have car-
ried out microwave reactions without the use of solvent. It
was successful but with some drawbacks like charring of
the reaction mixture and danger of combustion when
In summary, this paper demonstrates the versatility of
the condensation of indoles with aldehydes and other
aliphatic as well as aromatic a,b-unsaturated ketones with
324
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Triethylbenzylammonium Chloride: Alkylation of Indole
Table 4. Formation of BIM via Schiff base intermediate under
MWI
EXPERIMENTAL
Microwave reactions were carried out in a CEM Discover
Benchmate microwave digester. Melting points were determined
in open capillary tubes and are uncorrected. Infrared spectra were
recorded on a BOMEM DA-8 FT-IR instrument and the frequen-
cies are expressed in cm-1. 1H and 13C NMR spectra were recorded
on a Bruker Avance II-400 MHz spectrometer using CDCl3 as the
solvent. Chemical shifts are reported in ppm downfield from in-
ternal tetramethylsilane and are given on the d scale. Mass spec-
tral data were obtained with a JEOL D-300 (EI) mass spectrome-
ter. Elemental analyses were carried out on a Heraeus CHN-O-
Rapid analyzer. All compounds give satisfactory elemental anal-
yses within ± 0.4% of the theoretical values. All reactions were
monitored by TLC using precoated aluminum sheets (silica gel 60
F 254 0.2 mm thickness) and developed in an iodine chamber or un-
der UVGL-15 mineral light 254 lamp. Column chromatographic
separations were carried out using ACME silica gel (60-120
mesh).
Intermediate
Time Yield
Entry
R7
H
H
H
H
R8
H
(17a-17h)
(sec)
(%)
N
150
87
N
4-CH3
4-OCH3
4-C2H5
150
120
150
88
85
87
CH3
3c
N
OCH3
N
C2H5
H3CO
N
4-OCH3
H
120
180
180
84
85
85
H3CO
N
4-OCH3 4-CH3
4-OCH3 4-OCH3
CH3
3d
H3CO
N
OCH3
H3CO
N
Procedure for the synthesis of (3a-3k) and (4a-4c) under
Reflux conditions: To a stirring solution of indole/substituted
indole (6.83 mmol) and aldehyde (4.27 mmol) in water (10 mL),
TEBA(1.06 mmol) was added. The reaction mixture was refluxed
at 100 oC for 1-2 hrs (Table 2). After the completion of the reac-
tion (monitored by TLC), the resultant mixture was extracted
with ethyl acetate (3 ´ 10 mL) and the solvent removed under re-
duced pressure. The crude product was purified by column chro-
matography using ethyl acetate/hexane as eluent to afford pure
products in good to excellent yields.
4-OCH3 4-C2H5
180
86
C2H5
good yields. This method also offers several significant ad-
vantages such as green and sustainable, high conversions,
easy handling, cleaner reaction profiles, and short reaction
time in case of microwave irradiation, which makes it a
useful and attractive process for the rapid synthesis of
substituted indoles. We have also reported a diversified
approach towards the synthesis of BIMs from Schiff
bases. Due to the versatile application possibilities of
BIMs and their derivatives, there is a continuous quest for
more efficient methods for indole derivative synthesis and
we believe to have provided a cleaner and greener strat-
egy.
Procedure for the synthesis of (3a-3k) and (4a-4c) under
microwave conditions: A mixture of indole/substituted indole
(6.83 mmol), aldehyde (4.27 mmol) and TEBA (1.06 mmol) in
water (3 mL) was irradiated in a microwave digester at 100 oC,
5–10 bar, 80–120 W for 180–250 seconds (Table 2). After the re-
action was completed (monitored by TLC) the resultant mixture
was purified by column chromatography using ethyl acetate/hex-
ane as eluent to afford the pure compounds.
Procedure for the synthesis of (7a-7f) and (8a-8c) under
Reflux conditions: To a stirring solution of indole/substituted
indole (6.83 mmol) and a,b-unsaturated carbonyl compounds
(5a-5c) (6.83 mmol) in water (10 mL), TEBA (1.69 mmol) was
added. The reaction mixture was refluxed at 100 oC for 1-2.5 hrs
(Table-3). After the completion of the reaction (monitored by
TLC), the resultant mixture was extracted with ethyl acetate (3 ´
10 mL) and the solvent removed under reduced pressure. The
crude product was purified by column chromatography using
ethyl acetate/hexane as eluent to afford pure products in good to
excellent yields.
Fig. 1. Preparation of compound 3c using recycled
TEBA.
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325

Article
Tumtin et al.
Procedure for the synthesis of (7a-7f) and (8a-8c) under
ArH), 7.87 (s, 1H, NH); 13C NMR (CDCl3, 100 MHz): d 6.75,
18.40, 35.06, 41.76, 110.12, 114.32, 117.66, 118.25, 120.44,
120.99, 126.15, 135.26, 210.46; MS: m/z = 202 [M+1]+, 224
[M+Na]+; Anal. Calcd. For C13H15NO: C, 77.58; H, 7.51; N,
6.96%; Found: C, 77.52; H, 7.57; N, 6.99%. 3-(1H-indol-3-yl)-
1,3-bisphenylpropan-1-one (7c): mp 130-133 oC;IR (KBr) cm-1:
3309, 3017, 1672; 1H NMR (CDCl3, 400 MHz): d 3.65 (dd, 1H,
CH), 3.75 (dd, 1H, CH), 5.00 (t, 1H, CH), 6.93 (s, 1H, ArH),
7.05-7.87 (m, 14H, ArH), 7.89 (s, 1H, NH); 13C NMR (CDCl3,
100 MHz): d 38.21, 45.20, 111.10, 119.34, 119.42, 119.56,
121.40, 122.56, 126.29, 126.63, 127.83, 128.10, 128.43, 128.57,
133.00, 136.61, 137.12, 144.21, 198.55; MS: m/z =348 [M+Na]+;
Anal. Calcd. For C23H19NO: C, 84.89; H, 5.89; N, 4.30%; Found:
C, 84.85; H, 5.92; N, 4.34%. 4-(bis(1H-indol-3-yl)methyl)benz-
aldehyde (3x): mp 197-199 oC; IR (KBr) cm-1: 3381, 3045, 1715;
1H NMR (CDCl3, 400 MHz): d 5.89 (s, 1H, CH), 6.59 (s, 2H, 2 ´
ArH), 6.92-7.71 (m, 12H, ArH), 7.93 (s, 2H, 2 ´ NH), 9.89 (s, 1H,
CHO); 13C NMR (CDCl3, 100 MHz): d 41.16, 112.11, 119.32,
119.90, 121.48, 122.97, 123.46, 125.61, 127.44, 129.21, 134.23,
135.71, 143.71, 189.85; MS: m/z =351 [M+1]+; Anal. Calcd. For
C24H18N2O: C, 82.26; H, 5.18; N, 7.99%; Found: C, 82.22; H,
5.21; N, 7.96%. 3-((4-(bis(1H-indol-3-yl)methyl)phenyl)(1H-
microwave conditions: A mixture of indole/substituted indole
(6.83 mmol), a,b-unsaturated carbonyl compounds (5a-5c) (6.83
mmol) and TEBA (1.69 mmol) in water (3 mL) was irradiated in a
microwave digester at 100 oC, 5–10 bar, 80–120 W for 100–240
seconds (Table 3). After the reaction was completed (monitored
by TLC) the resultant mixture was purified by column chroma-
tography using ethyl acetate/hexane as eluent to afford the pure
compounds.
Procedure for the synthesis of 3y under Reflux condi-
tions: To a stirring solution of indole (4.48 mmol) and tere-
phthaladehyde (2 mmol) in water (10 mL), TEBA(1.0 mmol) was
o
added. The reaction mixture was refluxed at 100 C for 1-2 hrs
(Table-2). After the completion of the reaction (monitored by
TLC), the resultant mixture was extracted with ethyl acetate (3 ´
10 mL) and the solvent removed under reduced pressure. The
crude product was purified by column chromatography using
ethyl acetate/hexane as eluent to afford pure products in good to
excellent yields.
Procedure for the synthesis of 3y under microwave con-
ditions: A mixture of indole (4.48 mmol), terephthaladehyde (2
mmol) and TEBA (1.0 mmol) in water (3 mL) was irradiated in a
microwave digester at 100 oC, 5–10 bar, 80–120 W for 180–250
seconds (Table 2). After the reaction was completed (monitored
by TLC) the resultant mixture was purified by column chroma-
tography using ethyl acetate/hexane as eluent to afford the pure
compounds.
o
indol-3-yl)methyl)-1H-indole (3y): mp 197-200 C; IR (KBr)
cm-1: 3386, 3089, 2930; 1H NMR (CDCl3, 400 MHz): d 5.70 (s,
2H, CH), 6.27 (s, 4H, 4 ´ ArH), 6.92-7.34 (m, 20H, ArH), 7.44 ( s,
4H, 2 ´ NH); 13C NMR (CDCl3, 100 MHz): d 39.86, 11.09,
118.99, 119.68, 119.97, 121.75, 123.64, 127.06, 128.54, 136.60,
141.55; MS: m/z = 567 [M+1]+; Anal. Calcd. For C40H30N4: C,
84.78; H, 5.34; N, 9.89%; Found: C, 84.73; H, 5.39; N, 9.83%.
Procedure for preparation of Schiff base (17a-17h): A
mixture of aniline (5 mmol) and aromatic aldehyde (5 mmol)
o
were mixed together at 0 C and brought to room temperature.
TLC was checked. If it showed completion of reaction, the crude
mixture was recrystallised from hot ethanol. If not, then it was ir-
radiated at 5 bars, 100 watt, 100 oC for 60-180 sec and recrystal-
lised in the same manner.
ACKNOWLEDGEMENTS
Financial assistance from UGC in the form of fellow-
ship and Spectral analysis by SAIF, NEHU, Shillong are
greatly acknowledged.
Analytical data for some selected compounds: 4-(bis-
(1H-indol-3-yl)methyl)-2-methoxyphenol (3g): mp 110-112
1
REFERENCES
oC; IR (KBr) cm-1: 3312, 3018, 2917; H NMR (CDCl3, 400
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6.57 (s, 2H, 2 ´ ArH), 6.70-7.33 (m, 11H, ArH), 7.84 (s, 2H, 2 ´
NH); 13C NMR (CDCl3, 100 MHz): d 38.81, 54.83, 109.99,
110.36, 112.94, 118.15, 118.90, 120.24, 120.86, 122.51, 126.00,
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400 MHz): d 0.97 (t, 3H, CH3), 2.34 (q, 2H, CH2), 2.75 (t, 2H,
CH2), 2.99 (t, 2H, CH2), 6.92 (s, 1H, ArH), 7.03-7.53 (m, 4H,
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