Direct conversion of methylarenes into dithiocarbamates, thioamides and benzyl esters

Article abstract of DOI:10.1016/j.tet.2014.04.041

A new strategy for the synthesis of a variety of dithiocarbamates and thioamides has been developed employing inexpensive and readily available methylarenes under metal-free and solvent-free conditions. The approach offers a one-pot procedure and has also been extended to the synthesis of a diverse range of benzyl esters.

Full text of DOI:10.1016/j.tet.2014.04.041

Tetrahedron 70 (2014) 3887e3892
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Direct conversion of methylarenes into dithiocarbamates,
thioamides and benzyl esters
*
Tirumaleswararao Guntreddi, Rajeshwer Vanjari, Krishna Nand Singh
Department of Chemistry, Centre of Advanced Study, Faculty of Science, Banaras Hindu University, Varanasi 221005, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A new strategy for the synthesis of a variety of dithiocarbamates and thioamides has been developed
employing inexpensive and readily available methylarenes under metal-free and solvent-free conditions.
The approach offers a one-pot procedure and has also been extended to the synthesis of a diverse range
of benzyl esters.
Received 11 March 2014
Received in revised form 12 April 2014
Accepted 13 April 2014
Available online 23 April 2014
Ó 2014 Elsevier Ltd. All rights reserved.
Keywords:
Dithiocarbamates
Thioamides
Esters
NBS
TBHP
1. Introduction
transition metals in an ample range of oxidation states.11 Conven-
tional methods for the synthesis of dithiocarbamates involve the
The development of convenient methodologies for the con-
struction of functionalized molecules from simple, readily available
and inexpensive materials has come to the forefront of current day
organic synthesis. Hydrocarbons are perhaps the nature’s most
abundant organic chemicals that are easily available. Chemists have
long desired the use of hydrocarbons as feedstock, new
materials and even pharmaceuticals. In this perspective, the se-
lective functionalization of hydrocarbons is of enormous current
importance and is highly tempting. An up-to-date literature survey
reveals that the synthesis of dithiocarbamates and thioamides us-
ing alkylarenes has not been explored so far and the synthesis of
benzyl esters using alkylarenes is rather inadequate.
Dithiocarbamates constitute an extremely important class of
organic compounds used as synthetic intermediates,1 protecting
groups in peptide synthesis,2 linkers in solid phase organic syn-
thesis,3 agrochemicals,4 biologically active compounds,5 and vul-
canisation accelerators.6 They have been nicely applied in the
controlled radical polymerization techniques,7 molecular electronic
devices,8 and in the synthesis of ionic liquids.9 In biological sys-
tems, dithiocarbamates are extensively used as inhibitors of en-
zymes and for the treatment of cancer.1c,10 Dithiocarbamates also
represent a versatile class of ligands with the ability to stabilize
reactions of amines with lethal and expensive chemicals, such as
thiophosgenes/isothiocyanates/carbonyl sulphide, and alkyl ha-
lides in organic medium using catalyst.4d,12 In this perspective, an
efficient three-component approach has been recently developed
using amines, carbon disulfide and alkyl halides,13
a,b-unsaturated
compounds,14 alkyl vinyl ethers,15 sulfamidates,16 or N-tosyl
hydrazones.17
Thioamides are another established class of biologically active
compounds found in organic chemistry.18 They are potentially
useful starting materials for the synthesis of heterocycles contain-
ing both the nitrogen and sulfur atoms.19 Although a number of
methods are available for the synthesis of thioamides, the most
frequently used ones are thionation of amides,20 and Will-
gerodteKindler reaction,21 involving aryl alkyl ketones, elemental
sulfur and amine. Despite their relevance, however, these protocols
suffer from one or other drawbacks, such as harsh reaction condi-
tions, prolonged reaction time, cumbersome product isolation and
low yields.
Benzyl esters are ubiquitous in natural and medicinal mole-
cules,22 and act as protecting groups in organic synthesis.23 Al-
though different methods are available for the preparation of
esters, tetrabutylammonium iodide (TBAI) or tert-butyl hydroper-
oxide (TBHP) catalysed oxidative esterification of carboxylic acid
with ethylbenzene,24 and palladium catalysed oxidative esterifi-
cation of carboxylic acid with toluene,25 have attracted a great deal
of recent attention. The former method, however, makes the use of
* Corresponding author. E-mail addresses: knsingh@bhu.ac.in, knsinghbhu@ya-
hoo.co.in (K.N. Singh).
0040-4020/$ e see front matter Ó 2014 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2014.04.041

3888
T. Guntreddi et al. / Tetrahedron 70 (2014) 3887e3892
no more than ethylbenzene, whereas the later one involves the use
of expensive palladium catalyst and is limited to the use of merely
toluene.
Out of different solvents tried, use of DMSO and DMF was
completely futile (entries 5 and 6), THF gave poor yield (entry 8),
while CCl4, DCM, DCE, dioxane and chlorobenzene could provide
only moderate yields (entries 2e4, 7 and 9). Changing TBHP with
another radical initiator azobisisobutyronitrile (AIBN) was found to
be ineffective at room temperature. However, when the tempera-
ture was increased to 80 ꢀC, a comparable product yield (entry 12)
to that of TBHP in acetonitrile at room temperature, was obtained,
which might be attributed to the fact that AIBN intrinsically initi-
ates radical reactions at 80 ꢀC. As a result, 20 mol % TBHP and
solvent-free conditions at room temperature were settled as the
optimum reaction conditions. Under these conditions, a variety of
methylarenes and amines were subsequently reacted to assess the
scope and versatility of the methodology and the outcome is given
in Table 2.
In light of the above facts, and as a part of our recent interest in
the activation of methylarenes,26 and development of other pro-
tocols,27 we describe herein an efficient, one-pot, metal-free con-
version of methylarenes into dithiocarbamates, thioamides and
benzyl esters by its initial treatment with N-bromosuccinimide
(NBS)/catalytic THBP, followed by the reaction with carbon disul-
fide/amine, amine/elemental sulfur and carboxylic acid/Et3N, re-
spectively (Scheme 1).
Table 2
Synthesis of dithiocarbamatesa
Scheme 1. Conversion of methylarenes to dithiocarbamates, thioamides and esters.
Entry
R
R1
R2
Product
Yield (%)
1
2
3
4
5
6
7
8
H
H
H
H
H
H
H
H
d
C6H5CH2
e(CH2)5e
e(CH2)4e
Furfuryl
Propyl
Ethyl
Methyl
Ethyl
Ethyl
e(CH2)4e
Ethyl
Ethyl
Ethyl
3a
3b
3c
3d
3e
3f
3g
3h
3i
75
85
86
73
79
86
79
2. Results and discussion
d
H
Since radical reactions play a vital role in devising synthetic
plans for many organic molecules,28 our strategy was to explore
a suitable catalytic system to firstly transform methylarenes via
radical pathway to its side-chain substituted halo derivatives,
which might be subsequently reacted to achieve the proposed class
of functionalized products under different investigated conditions.
To begin with the optimization process (Table 1), a model re-
action using toluene and NBS was undertaken in the presence of
varying amounts of TBHP in acetonitrile, followed by the addition of
carbon disulfide and diethylamine, which eventually afforded an
excellent product yield (83%) using TBHP (20 mol %) at room
temperature (entry 1). Further optimization was directed towards
the solvent effect by means of identical reaction conditions, which
lastly revealed solvent-free conditions as the most effective for the
desired conversion (entry 13).
Propyl
Ethyl
Methyl
Ethyl
Ethyl
d
2,3-Benzo
4-NO2
4-NO2
4-Br
4-Cl
3-Cl
3-Cl
2-Cl
2-Cl
4-CH3
4-CH3
4-CH3
4-CH3
3-CH3
45, 80b
0, 78c
0, 78c
57, 78c
63, 80c
50, 78c
49, 79c
60, 80c
60, 82c
84
9
10
11
12
13
14
15
16
17
18
19
20
21
3j
3k
3l
Ethyl
Ethyl
Ethyl
d
3m
3n
3o
3p
3q
3r
3s
3t
e(CH2)4e
Ethyl
e(CH2)4e
Ethyl
Ethyl
d
Ethyl
Propyl
d
Propyl
81
83
85
82
e(CH2)5e
e(CH2)4e
Ethyl
d
Ethyl
3u
a
Reaction conditions: 1 (0.5 mmol), NBS (0.55 mmol), TBHP (20 mol %), CS2
(1 mmol), amine (1 mmol). Yields after column chromatography.
b
Using CCl4.
At 80 ꢀC.
c
Table 1
Optimization of reaction conditionsa
Doubly methyl substituted arenes viz., p-xylene and m-xylene
reacted smoothly under the optimized conditions and were selec-
tively converted to their corresponding mono substituted di-
thiocarbamates in reasonably high yields. Toluene derivatives
containing halo atoms, such as o-chlorotoluene, p-chlorotoluene, m-
chlorotoluene and p-bromotoluene gave rise to 60, 63, 50 and 57%
yields, respectively at room temperature. However, when the tem-
perature was raised to 80 ꢀC, a considerable improvement in the
yields of the corresponding dithiocarbamates (80, 80, 78 and 78%,
respectively) was observed. p-Nitrotoluene failed to react under the
optimized conditions, yet, it gave rise to 76% product yield at an
increased temperature of 80 ꢀC. 1-Methylnaphthalene reacted
somewhat sluggishly and furnished 45% product yield under the
optimized conditions at room temperature and remained unaltered
by an increase in the reaction temperature, but by using carbon
tetrachloride as solvent, a creditable increase in the yield (80%) was
noticed at room temperature. To make this approach more versatile,
different amines, such as diethylamine, dimethylamine, piperidine,
Selective entries
Initiator
Solvent
Temp (ꢀC)
Yield (%)b
1
2
3
4
5
6
7
8
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
AIBN
TBHP
AIBN
TBHP
CH3CN
CCl4
DCM
DCE
DMSO
DMF
Dioxane
THF
Chlorobenzene
CH3CN
CH3CN
CH3CN
d
rt
rt
rt
rt
rt
rt
rt
rt
rt
rt
80
80
rt
83
73
63
67
0
0
55
39
59
0
83
82
86
9
10
11
12
13
a
Reaction conditions: toluene (0.5 mmol), NBS (0.55 mmol), initiator (20 mol %),
solvent (0.5 mL), CS2 (1 mmol), diethylamine (1 mmol).
b
Isolated yields after column chromatography.

T. Guntreddi et al. / Tetrahedron 70 (2014) 3887e3892
3889
Table 4
pyrrolidine, dipropylamine, benzylamine and furfurylamine have
Synthesis of benzyl estersa
been effectively employed. The structure of a representative di-
thiocarbamate 3p has been conclusively proved by single crystal
XRD (Fig. 1).29
Entry
R
R3
Product
Yield (%)
1
2
3
4
5
6
7
8
9
H
4-CH3
4-Cl
2,3-Benzo
2-Cl
3-CH3
4-Br
C6H5
5a
5b
5c
5d
5e
5f
5g
5h
5i
83
85
81
73b
79
80
76
75
78
C6H5(CH)2
4-CH3C6H4
C6H5
4-NO2C6H4
4-ClC6H4
2-CH3C6H4
3-C5H4N
C6H5CH2
4-NO2
4-Br
a
Reaction conditions: 1 (0.5 mmol), NBS (0.55 mmol), TBHP (20 mol %), Et3N
(1 mmol), carboxylic acid (0.5 mol), at 80 ꢀC, 1 h. Isolated yields by column
chromatography.
Fig. 1. X-ray crystal structure of 3p.
b
Using CCl4.
Taking advantage of the earlier optimized conditions for con-
version of toluene to benzylbromide, the process was directed to
achieve the synthesis of thioamides by investigating the second
step using morpholine as a reacting partner, which finally gave the
maximum yield (71%) of the corresponding thioamide in the
presence of elemental sulfur at 120 ꢀC in 24 h. Under these studied
conditions, a choice of methylarenes and amines were then made
to react to afford diverse thioamides (Table 3).
4. Experimental section
All the reagents were purchased from SigmaeAldrich Corpora-
tion, USA and were used as received. The reactions were monitored
by thin-layer chromatography (TLC) and visualized using UV light;
products purification was done using silica gel column chroma-
tography. 1H and 13C NMR were recorded on a JEOL FT-NMR spec-
trometer at 300 and 75.45 MHz, respectively using CDCl3 solution.
Table 3
Synthesis of thioamidesa
Chemical shifts are given in
d parts per million and are measured
relative to tetramethylsilane (TMS) as an internal standard.
4.1. General synthetic procedure for dithiocarbamates 3
A mixture of methylarene (0.5 mmol), NBS (0.55 mmol) and
TBHP (0.1 mmol) was stirred at room temperature for 2 h. To it were
then added CS2 (1.0 mmol) and amine (1.0 mmol) and the stirring
was continued at room temperature for another 5 h. After com-
pletion of reaction (TLC), the mixture was quenched with water and
then extracted with ethyl acetate. The combined organic phase was
dried over anhyd Na2SO4, filtered, dried under reduced pressure
and purified by column chromatography using n-hexane and ethyl
acetate as eluent to afford the product 3. The product 3h required
the use of CCl4 as solvent, whereas the products 3iep required an
initial heating cum stirring at 80 ꢀC using the mixture of methyl-
arene, NBS and TBHP.
Entry
R
R1
R2
Product
Yieldb (%)
1
2
3
4
5
6
7
8
9
H
H
H
H
d
H
H
H
H
H
H
d
H
(CH2)2O(CH2)2
C6H5(CH2)2
Cyclohexyl
Butyl
4a
4b
4c
4d
4e
4f
4g
4h
4i
71
69
66
67
68
67
68
73
65
H
Hexyl
3-Cl
4-Cl
4-Me
3-Cl
C6H5(CH2)2
C6H5(CH2)2
(CH2)2O(CH2)2
Cyclohexyl
a
Reaction conditions: 1 (0.5 mmol), NBS (0.55 mmol), TBHP (20 mol %), sulfur
(1.5 mmol), amine (1 mmol), 120 ꢀC, 24 h.
b
Isolated yield after column chromatography.
4.1.1. Benzyl benzylaminocarbodithioate (3a).13 Yield 75%. Yellow
The studies were lastly directed to look into the conditions for
the synthesis of benzyl esters using methylarenes and benzoic acid
as reacting components. The prospective trial of different bases like
Et3N, K2CO3 and t-BuOK to promote the second step, lastly revealed
the use of triethyamine at 80 ꢀC as the best fit to afford utmost yield
(83%) of benzyl benzoate in 1 h. Under these developed conditions,
the reaction of different methylarenes and carboxylic acids were
afterwards undertaken to afford a variety of benzyl esters (Table 4).
oil; 1H NMR (CDCl3, 300 MHz):
d 7.59 (br, 1H), 7.32e7.17 (m, 10H),
4.79 (s, 2H), 4.48 (s, 2H); 13C NMR (CDCl3, 75 MHz):
135.7, 128.6, 128.3, 128.2, 127.6, 127.4, 127.0.
d 197.0, 135.9,
4.1.2. Benzyl piperidine-1-carbodithioate (3b).13 Yield 85%. Yellow
oil; 1H NMR (CDCl3, 300 MHz):
7.34e7.18 (m, 5H), 4.52 (s, 2H), 4.21
(br, 2H), 4.17 (br, 2H), 1.59 (br, 6H); 13C NMR (CDCl3, 75 MHz):
194.4, 135.7, 128.8, 128.0, 126.9, 52.3, 50.8, 41.7, 25.2, 23.8.
d
d
3. Conclusion
4.1.3. Benzyl pyrrolidine-1-carbodithioate (3c).13 Yield 86%. Yellow
oil; 1H NMR (CDCl3, 300 MHz):
7.38e7.25 (m, 5H), 4.57 (s, 2H),
3.94e3.90 (m, 2H), 3.61e3.57 (m, 2H), 2.03e1.93 (m, 4H); 13C NMR
In conclusion, a variety of methylarenes have been efficiently
transformed to dithiocarbamates, thioamides and benzylic esters
by its treatment with NBS/TBHP (20 mol %), followed by the re-
action with carbon disulfide/amine, amine/elemental sulfur and
carboxylic acid/Et3N, respectively. The methodology offers a one-
pot, practical, green and metal-free approach under solvent-free
conditions from readily available and inexpensive starting
materials.
d
(CDCl3, 75 MHz):
25.9, 24.1.
d 192.0, 136.3, 129.0, 128.3, 127.2, 54.8, 50.3, 41.0,
4.1.4. Benzyl furfurylaminocarbodithioate (3d).12e Yield 73%. Yellow
oil; 1H NMR (CDCl3, 300 MHz):
7.84 (br, 1H), 7.33e7.23 (m, 6H),
6.31e6.26 (m, 2H), 4.83 (s, 2H), 4.50 (s, 2H); 13C NMR (CDCl3,
d

3890
T. Guntreddi et al. / Tetrahedron 70 (2014) 3887e3892
75 MHz):
43.6, 39.9.
d
197.4, 148.9, 142.5, 136.2, 128.9, 128.5, 127.3, 110.4, 108.8,
2H), 3.74e3.67 (m, 2H), 1.28e1.24 (m, 6H); 13C NMR (CDCl3,
75 MHz): 194.7, 134.3, 134.2, 131.4, 129.3, 128.7, 126.7, 49.5, 46.6,
d
39.4, 12.3, 11.4.
4.1.5. Benzyl dipropylcarbamodithioate (3e).10c Yield 79%. Yellow
oil; 1H NMR (CDCl3, 300 MHz):
7.30e7.20 (m, 5H), 4.48 (s, 2H),
d
4.1.16. 2-Chlorobenzyl pyrrolidine-1-carbodithioate (3p).13 Yield
3.89e3.84 (m, 2H), 3.56e3.51 (m, 2H),1.79e1.60 (m, 4H), 0.88e0.86
82%. Light yellow solid; 1H NMR (CDCl3, 300 MHz):
d 7.51e7.48 (m,
(m, 6H); 13C NMR (CDCl3, 75 MHz):
127.2, 56.6, 54.1, 42.1, 20.5, 19.4, 11.0.
d
195.6, 135.9, 129.2, 128.3,
1H), 7.27e7.24 (m, 1H), 7.14e7.08 (m, 2H), 4.63 (s, 2H), 3.85e3.80
(m, 2H), 3.54e3.49 (m, 2H), 1.96e1.83 (m, 4H); 13C NMR (CDCl3,
75 MHz):
38.5, 25.8, 24.0.
d 191.6, 134.5, 134.1, 131.2, 129.2, 128.6, 126.7, 54.9, 50.3,
4.1.6. Benzyl diethylcarbamodithioate (3f).13 Yield 86%. Yellow oil;
1H NMR (CDCl3, 300 MHz):
7.36e7.21 (m, 5H), 4.53 (s, 2H),
4.01e3.95 (m, 2H), 3.67e3.61 (m, 2H), 1.26e1.20 (m, 6H); 13C NMR
d
4.1.17. 4-Methylbenzyl diethylcarbamodithioate (3q).10c Yield 84%.
(CDCl3, 75 MHz):
12.1, 11.1.
d
194.5, 135.7, 128.9, 128.1, 126.9, 49.0, 46.3, 41.7,
Yellow oil; 1H NMR (CDCl3, 300 MHz):
d
7.28 (d, J¼7.8 Hz, 2H), 7.12
(d, J¼7.8 Hz, 2H), 4.5 (s, 2H), 4.06e4.0 (m, 2H), 3.75e3.67 (m, 2H),
2.32 (s, 3H), 1.28e1.24 (m, 6H); 13C NMR (CDCl3, 75 MHz):
d 195.4,
4.1.7. Benzyl dimethylcarbamodithioate (3g).39 Yield 79%. Yellow
137.2, 132.7, 129.5, 129.3, 49.3, 46.6, 42.0, 21.1, 12.4, 11.5.
oil; 1H NMR (CDCl3, 300 MHz):
d 7.33e7.18 (m, 5H), 4.48 (s, 2H),
3.47 (s, 3H), 3.26 (s, 3H); 13C NMR (CDCl3, 75 MHz):
129.1, 128.4, 127.3, 45.1, 42.4, 41.2.
d
196.6, 135.9,
4.1.18. 4-Methylbenzyl dipropylcarbamodithioate (3r).10c Yield 81%.
Yellow oil; 1H NMR (CDCl3, 300 MHz):
d
7.27 (d, J¼7.8 Hz, 2H), 7.12
(d, J¼7.5 Hz, 2H), 4.48 (s, 2H), 3.93e3.88 (m, 2H), 3.61e3.56 (m, 2H),
4.1.8. Naphthalen-1-ylmethyl diethylcarbamodithioate (3h). Yield
80%. Light yellow solid; 1H NMR (CDCl3, 300 MHz):
8.08 (d,
2.32 (s, 3H), 1.80e1.68 (m, 4H), 0.96e0.90 (m, 6H); 13C NMR (CDCl3,
d
75 MHz): d 195.9, 137.1, 132.6, 129.2, 129.2, 56.6, 54.2, 42.1, 21.0,
J¼8.1 Hz, 1H), 7.81e7.72 (m, 2H), 7.55e7.33 (m, 4H), 4.96 (s, 2H),
20.5, 19.5, 11.1.
4.03e3.97 (m, 2H), 3.62e3.54 (m, 2H), 1.27e1.12 (m, 6H); 13C NMR
(CDCl3, 75 MHz):
126.2, 125.7, 125.2, 123.8, 49.2, 46.5, 40.2, 12.2, 11.4.
d
194.9, 133.6, 131.6, 131.2, 128.5, 128.4, 128.0,
4.1.19. 4-Methylbenzyl piperidine-1-carbodithioate (3s).10c Yield
83%. Yellow oil; 1H NMR (CDCl3, 300 MHz):
d
7.26 (d, J¼7.8 Hz, 2H),
7.11 (d, J¼7.5 Hz, 2H), 4.5 (s, 2H), 4.26 (br, 2H), 3.82 (br, 2H), 2.3 (s,
4.1.9. 4-Nitrobenzyl diethylcarbamodithioate (3i).13 Yield 78%. Yel-
3H), 1.66 (br, 6H); 13C NMR (CDCl3, 75 MHz):
129.1, 127.6, 52.6, 51.2, 41.9, 25.5, 24.1, 21.0.
d 195.2, 137.0, 132.7,
low oil; 1H NMR (CDCl3, 300 MHz):
d
8.15 (d, J¼8.4 Hz, 2H), 7.58 (d,
J¼8.1 Hz, 2H), 4.68 (s, 2H), 4.07e4.0 (m, 2H), 3.79e3.72 (m, 2H),
1.32e1.27 (m, 6H); 13C NMR (CDCl3, 75 MHz):
d
193.5, 146.8, 144.8,
4.1.20. 4-Methylbenzyl pyrrolidine-1-carbodithioate (3t).10c Yield 85%.
Light yellow powder; 1H NMR (CDCl3, 300 MHz):
129.8, 123.3, 49.8, 46.7, 40.3, 12.3, 11.3.
d
7.28 (d, J¼7.8 Hz,
2H), 7.12 (d, J¼7.8 Hz, 2H), 4.53 (s, 2H), 3.95e3.91 (m, 2H), 3.63e3.58
4.1.10. 4-Nitrobenzyl pyrrolidine-1-carbodithioate (3j).13 Yield 78%.
Light yellow solid; 1H NMR (CDCl3, 300 MHz):
(m, 2H), 2.31 (s, 3H), 2.06e1.93 (m, 4H); 13C NMR (CDCl3, 75 MHz):
d
8.15 (d, J¼7.8 Hz,
d 192.4, 137.0, 133.2, 129.2, 129.1, 54.8, 50.4, 41.0, 25.9, 24.2, 21.0.
2H), 7.58 (d, J¼8.1 Hz, 2H), 4.69 (s, 2H), 3.96e3.92 (m, 2H),
3.67e3.63 (m, 2H), 2.19e1.97 (m, 4H); 13C NMR (CDCl3, 75 MHz):
4.1.21. 3-Methylbenzyl diethylcarbamodithioate (3u). Yield 82%.
Yellow oil; 1H NMR (CDCl3, 300 MHz):
7.18e7.07 (m, 4H), 4.5 (s,
2H), 4.06e4.0 (m, 2H), 3.74e3.67 (m, 2H), 2.33 (s, 3H),1.27e1.24 (m,
6H); 13C NMR (CDCl3, 75 MHz):
195.2, 138.1, 135.6, 130.0, 128.4,
d
190.8, 146.9, 145.1, 129.9, 123.5, 55.4, 50.6, 39.7, 26.0, 24.2.
d
4.1.11. 4-Bromobenzyl diethylcarbamodithioate (3k).3c Yield 86%.
d
Light yellow powder; 1H NMR (CDCl3, 300 MHz):
d
7.41 (d, J¼7.8 Hz,
128.2, 126.3, 49.3, 46.6, 42.2, 21.3, 12.3, 11.0.
2H), 7.26 (d, J¼8.1 Hz, 2H), 4.49 (s, 2H), 4.04e3.98 (m, 2H),
3.73e3.66 (m, 2H), 1.28e1.13 (m, 6H); 13C NMR (CDCl3, 75 MHz):
4.2. General synthetic procedure for thioamides 4
d
194.4, 135.4, 131.3, 130.8, 121.0, 49.4, 46.6, 40.9, 12.3, 11.4.
To a stirred (2 h) mixture of methylarene (0.5 mmol), NBS
(0.55 mmol) and TBHP (0.1 mmol) were added elemental sulfur
(1.5 mmol) and amine (1.0 mmol) and then heated at 120 ꢀC for 24 h.
After completion of reaction (TLC), the mixture was cooled to room
temperature and the resulting crude product was purified by silica gel
column chromatographyusing n-hexane andethyl acetateaseluent. To
achieve utmost conversion to products 4feg & 4i, the starting mixture
of methylarene, NBS and TBHP was heated under stirring at 80 ꢀC.
4.1.12. 4-Chlorobenzyl diethylcarbamodithioate (3l).3c Yield 80%.
Yellow oil; 1H NMR (CDCl3, 300 MHz):
d
7.33e7.25 (m, 4H), 4.52 (s,
2H), 4.06e3.99 (m, 2H), 3.75e3.68 (m, 2H), 1.30e1.25 (m, 6H); 13C
NMR (CDCl3, 75 MHz):
41.1, 12.5, 11.5.
d 194.7, 134.9, 133.2, 130.6, 128.6, 49.6, 46.7,
4.1.13. 3-Chlorobenzyl diethylcarbamodithioate (3m).30 Yield 78%.
Yellow oil; 1H NMR (CDCl3, 300 MHz):
7.36 (s, 1H), 7.26e7.19 (m,
3H), 4.52 (s, 2H), 4.04e3.98 (m, 2H), 3.74e3.67 (m, 2H), 1.29e1.24
(m, 6H); 13C NMR (CDCl3, 75 MHz):
194.2,138.4,133.9,129.5,129.1,
d
4.2.1. Morpholino(phenyl)methanethione (4a).21d Yield 71%. Pale
d
yellow crystals; 1H NMR (300 MHz, CDCl3):
d 7.34e7.27 (m, 5H),
127.3, 127.2, 49.5, 46.6, 40.9, 12.3, 11.4.
4.44 (t, J¼5.1 Hz, 2H), 3.88 (t, J¼4.5 Hz, 2H), 3.62e3.58 (m, 4H); 13
C
NMR (75 MHz, CDCl3):
52.3, 49.4.
d 200.8, 142.3, 128.7, 128.4, 125.7, 66.6, 66.3,
4.1.14. 3-Chlorobenzyl pyrrolidine-1-carbodithioate (3n).30 Yield
79%. Yellow oil; 1H NMR (CDCl3, 300 MHz):
d
7.36 (s, 1H), 7.26e7.18
(m, 3H), 4.55 (s, 2H), 3.92e3.87 (m, 2H), 3.61e3.57 (m, 2H),
2.04e1.90 (m, 4H); 13C NMR (CDCl3, 75 MHz):
191.1, 138.8, 133.7,
4.2.2. N-Phenethylbenzothioamide (4b).21d Yield 69%. Pale yellow
d
crystals; 1H NMR (300 MHz, CDCl3):
d 7.62e7.23 (m, 11H), 4.09 (q,
129.4, 128.8, 127.1, 127.0, 54.9, 50.2, 39.9, 25.7, 23.9.
J¼6.6 Hz, 2H), 3.07 (t, J¼6.9 Hz, 2H); 13C NMR (75 MHz, CDCl3):
d
199.1, 141.7, 138.1, 130.9, 128.8, 128.6, 128.3, 126.8, 126.4, 47.3, 33.7.
4.1.15. 2-Chlorobenzyl diethylcarbamodithioate (3o).13 Yield 80%.
Yellow oil; 1H NMR (CDCl3, 300 MHz):
d
7.56e7.53 (m, 1H),
4.2.3. N-Cyclohexylbenzothioamide (4c).31 Yield 66%. Yellow mi-
crocrystals; 1H NMR (300 MHz, CDCl3):
7.69e7.66 (m, 2H),
7.36e7.33 (m, 1H), 7.20e7.17 (m, 2H), 4.68 (s, 2H), 4.06e3.98 (m,
d

T. Guntreddi et al. / Tetrahedron 70 (2014) 3887e3892
3891
7.44e7.25 (m, 4H), 4.55e4.46 (m, 1H), 2.18e2.14 (m, 2H), 1.78e1.66
144.9,138.0,134.3,132.9,130.2,129.2,128.8,128.4,128.0,117.9, 66.2,
21.1.
(m, 3H), 1.51e1.22 (m, 5H); 13C NMR (75 MHz, CDCl3):
d 197.5, 142.2,
130.7, 128.3, 126.5, 54.8, 54.7, 31.5, 25.3, 24.6.
4.3.3. 4-Chlorobenzyl 4-methylbenzoate (5c).38 Yield 81%. Yellow
4.2.4. N-Butylbenzothioamide (4d).32 Yield 67%. Yellow solid; 1H
NMR (300 MHz, CDCl3):
7.91 (s, 1H), 7.61 (d, J¼7.5 Hz, 2H),
liquid; 1H NMR (300 MHz, CDCl3):
d
7.97 (d, J¼7.8 Hz, 2H), 7.40e7.32
d
(m, 4H), 7.24 (d, J¼7.8 Hz, 2H), 5.30 (s, 2H); 13C NMR (75 MHz,
7.36e7.24 (m, 3H), 3.70e3.63 (m, 2H), 1.67e1.60 (m, 2H), 1.37e1.31
CDCl3):
d 166.3, 143.8, 134.6, 133.9, 129.6, 129.4, 129.1, 128.7, 127.1,
(m, 2H), 0.92 (t, J¼6.9, 3H); 13C NMR (75 MHz, CDCl3):
d 198.5, 141.4,
65.6, 21.5.
130.6, 128.0, 126.3, 43.3, 29.7, 19.9, 13.5.
4.3.4. Naphthalen-1-ylmethyl benzoate (5d).36 Yield 73%. Yellow
liquid; 1H NMR (300 MHz, CDCl3):
8.09e7.08 (m, 3H), 7.88 (s, 2H),
7.63e7.39 (m, 7H), 5.84 (s, 2H); 13C NMR (75 MHz, CDCl3):
166.3,
4.2.5. N-Hexylbenzothioamide (4e).42 Yield 68%. Yellow crystals; 1H
NMR (300 MHz, CDCl3):
7.90 (s, 1H), 7.70 (d, J¼7.8 Hz 2H),
d
d
d
7.42e7.28 (m, 3H), 3.76e3.70 (m, 2H), 1.74e1.65 (m, 2H), 1.39e1.28
133.6, 132.8, 131.6, 131.4, 129.6, 129.2, 128.6, 128.2, 127.3, 126.5,
125.8, 125.2, 123.8, 123.5, 65.0.
(m, 6H), 0.91 (t, J¼6.9, 3H); 13C NMR (75 MHz, CDCl3):
d 198.6, 141.6,
130.6, 128.1, 126.4, 46.7, 31.2, 27.7, 26.5, 22.3, 19.9, 13.5.
4.3.5. 2-Chlorobenzyl 4-nitrobenzoate (5e).38 Yield 79%. Yellow
4.2.6. 3-Chloro-N-phenethylbenzothioamide (4f).31 Yield 67%. Yel-
solid; 1H NMR (300 MHz, CDCl3):
d
8.30e8.22 (m, 4H), 7.50e7.43
(m, 2H), 7.33e7.26 (m, 2H), 5.51 (s, 2H); 13C NMR (75 MHz, CDCl3):
164.3, 150.6, 135.3, 134.1, 132.9, 130.8, 130.3, 130.0, 129.8, 127.0,
low solid; 1H NMR (300 MHz, CDCl3):
d 7.73 (s, 1H), 7.55 (s, 1H),
7.36e7.20 (m, 8H), 4.01 (q, J¼6.3 Hz, 2H), 3.04 (t, J¼6.9 Hz, 2H); 13
C
d
NMR (75 MHz, CDCl3):
d
197.1, 143.0, 137.8, 134.2, 130.6, 129.5, 128.7,
123.6, 65.0.
128.5, 126.8, 126.7, 124.3, 47.4, 33.4.
4.3.6. 3-Methylbenzyl 4-chlorobenzoate (5f).35 Yield 80%. Yellow
4.2.7. 4-Chloro-N-phenethylbenzothioamide (4g).43 Yield 68%. Yel-
liquid; 1H NMR (300 MHz, CDCl3):
d
8.0 (d, J¼8.4 Hz, 2H), 7.38 (d,
low solid; 1H NMR (300 MHz, CDCl3):
7.66 (s,1H), 7.51 (d, J¼8.1 Hz,
2H), 7.34e7.21 (m, 7H), 4.05 (q, J¼6.8 Hz, 2H), 3.05 (t, J¼6.9 Hz, 2H);
13C NMR (75 MHz, CDCl3):
197.4, 139.8, 137.9, 137.1, 128.7, 128.6,
128.4, 127.7, 126.7, 47.4, 33.5.
d
J¼6 Hz, 2H), 7.26e7.12 (m, 4H), 5.30 (s, 2H), 2.35 (s, 3H); 13C NMR
(75 MHz, CDCl3):
d 165.4, 139.3, 138.2, 135.6, 131.0, 129.0, 128.9,
d
128.5, 125.2, 124.82, 66.9, 21.3.
4.3.7. 4-Bromobenzyl 2-methylbenzoate (5g).37 Yield 76%. Yellow
4.2.8. Morpholino(p-tolyl)methanethione (4h).41 Yield 73%. Pale
yellow crystals; 1H NMR (300 MHz, CDCl3):
7.17 (d, J¼7.1 Hz, 4H),
liquid; 1H NMR (300 MHz, CDCl3):
d
7.93e7.91 (m, 1H), 7.56e7.45
(m, 2H), 7.38e7.20 (m, 5H), 5.25 (s, 2H), 2.58 (s, 3H); 13C NMR
(75 MHz, CDCl3): 166.9, 140.3, 135.1, 132.1, 131.6, 130.8, 130.5,
d
4.42 (t, J¼3.9 Hz, 2H), 3.86 (t, J¼3.9 Hz, 2H), 3.62e3.55 (m, 4H), 2.34
d
(s, 3H); 13C NMR (75 MHz, CDCl3):
66.4, 66.2, 52.3, 49.4, 21.0.
d
200.9, 139.4, 138.7, 128.7, 125.7,
129.7, 129.1, 125.6, 122.1, 65.5, 21.7.
4.3.8. 4-Nitrobenzyl nicotinate (5h).40 Yield 75%. White solid; 1H
4.2.9. 3-Chloro-N-cyclohexylbenzothioamide (4i).31 Yield 65%. Yel-
low solid; 1H NMR (300 MHz, CDCl3):
NMR (300 MHz, CDCl3): d 9.27 (s, 1H), 8.82e8.81 (m, 1H), 8.35e8.25
d
7.64 (s,1H), 7.51 (d, J¼7.8 Hz,
(m, 3H), 7.63 (d, J¼8.1, 2H), 7.45e7.41 (m, 1H), 5.49 (s, 2H); 13C NMR
1H), 7.37 (d, J¼8.1 Hz, 1H), 7.25 (t, J¼7.8 Hz, 1H), 4.50e4.41 (m, 1H),
(75 MHz, CDCl3): d 164.8, 153.8, 150.9, 147.8, 147.2, 142.6, 137.1,
2.15e2.12 (m, 2H), 1.79e1.66 (m, 3H), 1.49e1.20 (m, 5H); 13C NMR
128.5, 125.4, 123.9, 123.4, 65.5.
(75 MHz, CDCl3):
54.9, 31.3, 25.3, 24.6.
d 195.7, 143.6, 134.2, 130.5, 129.5, 126.8, 124.5,
4.3.9. 4-Bromobenzyl 2-phenylacetate (5i).34 Yield 78%. Yellow liq-
uid; 1H NMR (300 MHz, CDCl3):
d
7.45 (d, 2H, J¼8.1 Hz), 7.30e7.27
(m, 5H), 7.15 (d, 2H, J¼8.1 Hz), 5.05 (s, 2H), 3.65 (s, 2H); 13C NMR
4.3. General synthetic procedure for benzyl esters 5
(75 MHz, CDCl3):
122.1, 65.7, 41.2.
d 171.1, 134.8,133.7, 131.6, 129.6, 129.2, 128.5, 127.1,
A mixture of methylarene (0.5 mmol), NBS (0.55 mmol) and
TBHP (0.1 mmol) was stirred at room temperature for 2 h. After-
wards, carboxylic acid (0.5 mmol) and triethylamine (1.0 mmol)
were added to it followed by heating at 80 ꢀC for 1 h. After the
reaction was over (TLC), the mixture was quenched with water
and then extracted with ethyl acetate. The organic phase was
dried over anhyd Na2SO4, filtered and concentrated under reduced
pressure. The crude product was purified by column chromatog-
raphy using n-hexane and ethyl acetate as eluent. In case of
products 5c, 5e and 5gei, the mixture of methylarene, NBS and
TBHP was heated under stirring at 80 ꢀC, whereas the product 5d
required the use of CCl4.
Acknowledgements
We are thankful to the Department of Science and Technology,
Government of India, New Delhi for providing financial assistance
(Grant No. SR/S1/OC-78/2012). T.G. and R.V. are thankful to the CSIR
for their fellowships.
Supplementary data
1H and 13C NMR spectra for all compounds are available online.
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.tet.2014.04.041.
4.3.1. Benzyl benzoate (5a).33 Yield 83%. Yellow liquid; 1H NMR
(300 MHz, CDCl3):
d
8.13 (d, J¼8.4 Hz, 2H), 7.57e7.35 (m, 8H), 5.39
(s, 2H); 13C NMR (75 MHz, CDCl3):
128.5, 128.2, 128.1, 128.0, 66.5.
d 166.2, 135.9, 132.9, 130.0, 129.6,
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