P4S10/dimethicone tandem: Efficient reagent for thionation of various aromatic amides and esters

Article abstract of DOI:10.1016/j.tet.2010.05.100

Organosulfur compounds are valuable because of their rich and varied chemistry especially in biological field. We report a new and efficient way for thionation of various aromatic amides and esters using P₄S ₁₀/ dimethicone tandem. The ease of handling and higher yield makes this protocol economical.

Full text of DOI:10.1016/j.tet.2010.05.100

Tetrahedron 66 (2010) 5583e5588
Contents lists available at ScienceDirect
Tetrahedron
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P4S10/dimethicone tandem: efficient reagent for thionation of various
aromatic amides and esters
,b,
Dongho Cho a, Jiyoung Ahn b, Kathlia A. De Castro a, Hyunseok Ahn b, Hakjune Rhee a
*
a Hanyang University, Department of Chemistry and Applied Chemistry, 1271 Sa-3-dong, Sangrok-Gu, Ansan-si, Kyunggi-do 426-791, Republic of Korea
b Hanyang University, Department of Bionanotechnology, 1271 Sa-3-dong, Sangrok-gu, Ansan-si, Kyunggi-do 426-791, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 3 May 2010
Received in revised form 25 May 2010
Accepted 26 May 2010
Available online 1 June 2010
Organosulfur compounds are valuable because of their rich and varied chemistry especially in biological
field. We report a new and efficient way for thionation of various aromatic amides and esters using P4S10
/
dimethicone tandem. The ease of handling and higher yield makes this protocol economical.
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Thionation
Dimethicone
Phosphoruspentasulfide
Thioamide
Thioester
1. Introduction
CH3
H3C Si
CH3
CH3
CH3
O
Si
O
Si CH3
CH3
Sulfur containing compounds especially thiocarbonyls are
highly versatile intermediate or precursor, which find many ap-
plications both in synthetic and biological chemistry.1 This growing
repertoire of applications draw significant attention to develop new
and efficient methods for thionation, the widely applied method for
the synthesis of organosulfur compounds. There have been gar-
gantuan ways and modifications made on this method. Few of the
most recent and popular methods employed Lawesson’s reagent
with and without modifications,2 P4S10 in combination with other
reagents or materials, such as hexamethyldisiloxane (HMDO)3 or
Al2O3,4 PSCl3 with H2O and Et3N,5 thiourea,6 and aqueous ammo-
nium sulfide.7 Some of these methods offer various advantages and
drawbacks one way or another. To quote a few drawbacks are dif-
ficulty in separation, longer reaction time, expensive reagent, and
low yield. Herein we report dimethicone, commonly known as
silicon oil, as a new additive for P4S10 that efficiently thionates ar-
omatic amide and esters.
CH3
n
Figure 1. Structure of dimethicone.
HMDO, we hypothesized that perhaps it could also function as such
in the thionation reaction. Furthermore, dimethicone is immiscible
in methanol thus; dissolving the product in this solvent could
separate the dimethicone and possibly recycle it. Consequently, we
check this possibility using benzamide (Scheme 1).
O
S
NH2
P4S10/dimethicone
CH2Cl2, reflux
NH2
Scheme 1. Thionation of benzamide.
2. Results and discussion
Our optimization studies showed that 0.2 equiv of P4S10 in 5 mL
of dimethicone (Dow Corning Corporation 200Ò fluid, viscosity
50 cSt) using CH2Cl2 solvent is the appropriate condition. It is
necessary to use CH2Cl2 solvent to dissolve the starting benzamide.
Since dimethicone is immiscible in methanol (Fig. 2) it is possible to
extract the product to methanol layer by simple decantation8 and
Dimethicone (Fig. 1) has been explored in our laboratory for
various applications in organic synthesis. Since it is an oligomer of
* Corresponding author. Tel.: þ82 31 400 5498; fax: þ82 31 407 3863; e-mail
address: hrhee@hanyang.ac.kr (H. Rhee).
0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.05.100

5584
D. Cho et al. / Tetrahedron 66 (2010) 5583e5588
Table 2 (continued )
recovered the dimethicone for possible reuse. Test tube A shows the
crude reaction mixture containing dimethicone after the removal
of CH2Cl2 solvent. First extraction was tried by shaking the mixture
with methanol (test tube B) and standing it for a while clearly
separated the methanol layer (upper) and the dimethicone layer
(lower) as shown in test tube C. Further extractions were done to
ensure that no more product remained in the dimethicone layer
(test tubes EeG). It was noticeable that further extractions led to
the recovery of dimethicone as a viscous transparent liquid (test
tube G lower layer), that is, ready for reuse.
Entry
Starting material
Product
Time
Isolated yield (%)
Dimethicone
With
Without
O
S
4
5
6
7
1.5 h
5 h
96
74
N
H
N
H
O
S
91
71
90
62
NH
NH
O
N
S
15 min 99
N
O
S
6 h
96
90
NH2
NH2
O
O
S
8
NH2 3 h
40
NH2
Figure 2. Reaction mixture (A) and extraction (B and C: first, D: second, E: third, F:
fourth, G: fifth extraction) of product using methanol (upper layer).
Cl
Cl
S
Recycle test (Table 1) showed that certain volume of dimethi-
cone was consumed during the reaction. These results demon-
strated that it acts in the same manner as HMDO as previously
studied by some group.3b Even though dimethicone was consumed
(0.60e1.2 mL in every run) during the reaction it can still be reuse
up to four times without considerable loss of reactivity. Further-
more its immiscibility in methanol was an advantage because it
makes the separation easy. To further validate this observation
several amides were tested for thionation (Table 2) with and
without dimethicone.
9
NH2 8 h
84
68
89
67
56
41
NH2
NH2
NH2
Br
Br
O
S
NH2
10
2.5 h
H3CO
H3CO
O
S
11b
12 h
NH2
O2N
O2N
a
Procedure: Reflux starting material (3.0 mmol), P4S10 (0.6 mmol), and dime-
Table 1
thicone (5 mL) in CH2Cl2 solvent (10 mL).
Dimethicone recovery test for thionation of benzamidea
b
Used 45 mL solvent.
Run
Volume (mL)
Yield (%)
First
5.0
4.4
3.6
2.4
87
85
90
89
Table 2 revealed that thionation yield is much higher using P4S10
with dimethicone compared to that of without. Previous study3
described that during the thionation with P4S10, the reaction en-
vironment becomes more electrophilic due to the successive re-
placement of sulfur by oxygen on the phosphorus atom. It produces
highly electrophilic species that may act as potent electrophile
capable of promoting undesirable side reactions with the carbonyl
and thiocarbonyl compounds present in the reaction mixture
thereby giving lower yield.
We presumed that dimethicone acted as scavenger of these
electrophilic species by simply entrapping them perhaps via en-
capsulation and also via reaction like HMDO. This is probably the
reason for the good to excellent yield of thionated product. In ad-
dition, the short reaction time probably makes some of the dime-
thicone to simply act as adsorbent of the produced electrophilic
species that intervenes in the reaction progress.
Moreover, our results showed that an increase in the electron
density on the oxygen atom of the amido group favors thionation
such that tertiary amide (entry 6) reacts faster than secondary
(entry 2) and primary (entry 1). Furthermore, the presence of
electron withdrawing group on the ring, such as nitro group (entry
11) also supports this observation. However, the presence of
methoxy substituent gave lower yield presumably because of the
competition between the carbonyl oxygen and the more basic ox-
ygen for electrophilic phosphorus in the active thionating species.
Second
Third
Fourth
a
Reaction conditions: Reflux benzamide (3.0 mmol), P4S10 (0.6 mmol), and
dimethicone (5 mL) in CH2Cl2 solvent (10 mL) for 1.5 h. Reuse the dimethicone for
the succeeding trials. Independently, using 0.6 mL of dimethicone gave 83% yield.
Table 2
Thionation of various aromatic amidesa
Entry
Starting material
Product
Time
Isolated yield (%)
Dimethicone
With
Without
O
S
1
2
1.5 h
2 h
87
67
NH2
NH2
O
S
94
87
82
N
H
N
H
O
S
N
H
N
H
3
10 min 93

D. Cho et al. / Tetrahedron 66 (2010) 5583e5588
5585
Table 4
Significantly, we obtained higher thionation yield at a shorter re-
Thionation of various aromatic estersa
action time for most of the common substrate also tested with
other thionating agents aforementioned especially P4S10/HMDO
tandem.3b
Entry
Starting
material
Product
Yield (%)
toluene/xylene
To further expound on the validity of this protocol, we also
considered the thionation reaction of esters by testing methyl-
benzoate (Scheme 2). Thionation of esters are usually difficult and
gave lower yield due to the generally lower reactivity of carbonyl
ester toward the electrophilic thionating agents. Several groups
have demonstrated this. For instance, thionation of esters with
Lawesson’s reagent9a and P4S10/HMDO required refluxing condition
with either toluene or p-xylene at a prolong time while thionation
of amides required shorter time and lower temperature.3 Further-
more, thionation of esters sometimes gave mixtures9b sub-
stantiating its lower reactivity.
S
O
1
2
3
15/81
OCH3
O
OCH3
S
55/82
63/81
OCH3
OCH3
O
S
OCH3
OCH3
O
S
OCH3
OCH3
O
4
29/71
S
OCH3
P4S10/dimethicone
OCH3
toluene or xylene, reflux
O
S
Cl
Br
I
Cl
Br
I
5
6
7
6/70
8/39
8/25
Scheme 2. Thionation of methylbenzoate.
OCH3
O
OCH3
S
At first, we considered exactly the same conditions however;
using CH2Cl2 solvent gave lower yield due to reaction temperature.
Thus, we opted to change the solvent to a higher boiling point one,
such as toluene and p-xylene. p-Xylene gave much better results for
every cases.
Dimethicone recovery test was also done using methyl 4-
methoxybenzoate (Table 3).10 The yield is almost the same all
throughout however; it is visible that the volume of dimethi-
cone quickly decreases. Presumably at longer reaction time
(12 h) and higher temperature some of the dimethicone reacts
with the electrophilic species produced during the thionation
reaction leading to the decrease in the volume of dimethicone
recovered.
OCH3
S
OCH3
O
OCH3
O
OCH3
S
F3C
H2N
N
F3C
H2N
N
8
23/51
8/9
OCH3
OCH3
S
O
9
OCH3
O
OCH3
S
10
23/86
OCH3
O
OCH3
S
Table 3
Dimethicone recovery test for thionation of methyl 4-methoxybenzoatea
Run
Volume (mL)
Yield (%)
11
12
13
O2N
HO
O2N
HO
4/28
First
Second
Third
5.0
4.4
2.8
95
95
94
OCH3
O
OCH3
S
a
10/15
52/95
Reaction Conditions: Reflux methyl 4-methoxybenzoate (3.0 mmol), P4S10
(0.75 mmol), and dimethicone (5 mL) in p-xylene solvent (10 mL) for 12 h. Reuse the
dimethicone for the succeeding trials.
OCH3
O
OCH3
S
H3CO
H3CO
OCH3
O
OCH3
S
As depicted in Table 4, thionation of esters using our protocol
gave fairly good results. The presence of electron donating sub-
stituents on the ring (entries 2e4, 10, and 13) gave higher yield
compared to those with electron withdrawing substituents (entries
5, 8, and 11). Noticeably substituents on the ring having free hy-
droxyl and amino group (entries 9, 12) likewise gave lower yield. In
the case of halogen substituents on the ring (entries 5e7), the yield
of reaction was descending from chloro to iodo substituent. It is
presumed that the lone pair of halogen atom may interact with the
electrophilic phosphorus and iodine atom can coordinate better
than chlorine and bromine atom toward the electrophilic phos-
O
O
14
94/quant
a
Reaction Conditions: Reflux starting material (3.0 mmol), P4S10 (0.75 mmol),
and dimethicone (5 mL) in toluene or p-xylene solvent (10 mL) for 12 h.
time.11 To check the effect of microwave irradiation in our pro-
tocol we considered checking the thionation of representative
sample of amide and ester. As shown in Table 5, the yield was
almost the same but the reaction time was dramatically de-
creased. Indeed, this protocol could also be applied under mi-
crowave condition leading to the same reaction yield but shorter
reaction time.
phorus species. The
a,b-unsaturated carbonyl group (entry 14)
increases the rate of reaction.
Microwave irradiation has been considered as well. There have
been reports on the efficiency of microwave irradiation on thio-
nation such that it enhanced the yield at a shorter reaction

5586
D. Cho et al. / Tetrahedron 66 (2010) 5583e5588
Table 5
Microwave (MW) reaction versus thermal reaction of selected compoundsa
Entry
Starting material
Product
Time
Isolated yield (%)
MW
MW (min)
Thermal (h)
1.5 h
Thermal
87
O
S
1
5 min
92
NH2
NH2
O
S
2
40 min
12 h
81
81
OCH3
OCH3
a
Reaction Conditions: Reflux starting material (3.0 mmol), P4S10 (0.75 mmol), and dimethicone (5 mL) in CH2Cl2 (entry 1) and p-xylene (entry 2) solvent (10 mL) for
specified time using MW and thermal condition.
3. Conclusion
7.87 (d, J¼6.9 Hz, 2H, ArH), 7.79 (d, J¼7.8 Hz, 2H, ArH), 7.32e7.52
(m, 7H, ArH).
In summary, we have investigated and presented a valuable
alternative for thionation. This protocol necessitate only minimum
amount of P4S10 to facilitate thionation. The use of dimethicone as
scavenger of electrophilic species that hinders the reaction and as
facilitator for reaction rate is very economical. Thus, this new
protocol for thionation is facile and practical.
4.1.5. 3,4-Dihydroquinoline-2(1H)-thione (Table 2, entry 5)14. Pale
yellow solid purified using n-hexane/EtOAc (3:1 v/v; Rf¼0.50) as
eluent system in silica gel column chromatography. 1H NMR
(CDCl3):
d 9.72 (br s, 1H, NH), 7.07e7.20 (m, 2H, ArH), 7.09 (t,
J¼7.4 Hz, 1H, ArH), 6.86 (d, J¼7.8 Hz, 1H, ArH), 3.12 (dd, J¼8.4,
6.3 Hz, 2H, CH2), 2.90 (t, J¼7.5 Hz, 2H, CH2).
4. Experimental section
4.1.6. N,N-Dimethylthiobenzamide (Table 2, entry 6)15. Pale yellow
solid purified using n-hexane/EtOAc (20:1 v/v; Rf¼0.10) as eluent
system in silica gel column chromatography. 1H NMR (CDCl3):
4.1. General procedure for thionation of amides
d
7.31e7.35 (m, 5H, ArH), 3.62 (s, 3H, CH3), 3.18 (s, 3H, CH3).
The amide starting material (3.0 mmol), P4S10 (0.6 mmol), and
dimethicone (5 mL; Dow Corning Corporation 200Ò fluid, viscosity
50 cSt) were reflux in 10 mL of CH2Cl2 solvent. The reaction mixture
was continuously stirred until completion based on TLC monitoring.
If the starting spot never disappeared we varied the reaction time to
find the maximum yield possible. Upon completion, CH2Cl2 solvent
was evaporated using rotary evaporator. Methanol was added to the
residue several times necessary to extract the product from dime-
thicone. The methanol was evaporated and the crude mixture was
purified by silica gel column chromatography using n-hexane/EtOAc
(either 3:1 or 20:1 v/v) as eluent system. The same procedure was
applied for trials without dimethicone. The dimethicone was simply
omitted so as the methanol addition during work-up.
4.1.7. 4-Methylthiobenzamide (Table 2, entry 7)12. Pale yellow solid
purified using n-hexane/EtOAc (3:1 v/v; Rf¼0.18) as eluent system
in silica gel column chromatography. 1H NMR (CDCl3):
d 7.80 (d,
J¼8.4 Hz, 2H, ArH), 7.65 (br s, 1H, NH), 7.22 (d, J¼8.1 Hz, 2H, ArH),
7.18 (br s, 1H, NH), 2.40 (s, 3H, CH3).
4.1.8. 4-Chlorothiobenzamide (Table 2, entry 8)16. Pale yellow solid
purified using n-hexane/EtOAc (3:1 v/v; Rf¼0.23) as eluent system
in silica gel column chromatography. 1H NMR (CDCl3):
d 7.83 (dt,
J¼8.7, 2.3 Hz, 2H, ArH), 7.69 (br s,1H, NH), 7.39 (dt, J¼8.7, 2.2 Hz, 2H,
ArH), 7.17 (br s, 1H, NH).
4.1.9. 4-Bromothiobenzamide (Table 2, entry 9)17. Pale yellow solid
purified using n-hexane/EtOAc (3:1 v/v; Rf¼0.18) as eluent system
4.1.1. Thiobenzamide (Table 2, entry 1)12. Pale yellow solid purified
using n-hexane/EtOAc (3:1 v/v; Rf¼0.23) as eluent system in silica
in silica gel column chromatography. 1H NMR (CDCl3):
d 7.75 (dt,
gel column chromatography. 1H NMR (CDCl3):
d
7.89 (d, J¼7.8 Hz,
J¼8.7, 2.3 Hz, 2H, ArH), 7.69 (br s, 1H, NH), 7.55 (dt, J¼8.1,2.2 Hz, 2H,
ArH), 7.16 (br s, 1H, NH).
2H, ArH), 7.64 (br s, 1H, NH), 7.53 (t, J¼7.4 Hz, 1H, ArH), 7.42 (t,
J¼7.7 Hz, 2H, ArH), 7.22 (br s, 1H, NH).
4.1.10. 4-Methoxythiobenzamide (Table 2, entry 10)16. Pale yellow
solid purified using n-hexane/EtOAc (3:1 v/v; Rf¼0.13) as eluent
4.1.2. N-Methylthiobenzamide (Table 2, entry 2)7. Pale yellow solid
purified using n-hexane/EtOAc (3:1 v/v; Rf¼0.30) as eluent system
system in silica gel column chromatography. 1H NMR (CDCl3):
d 7.91
in silica gel column chromatography. 1H NMR (CDCl3):
d 7.76 (d,
(dt, J¼9.3, 2.7 Hz, 2H, ArH), 7.54 (br s, 1H, NH), 7.12 (br s, 1H, NH),
6.91 (dt, J¼9.3, 2.7 Hz, 2H, ArH), 3.87 (s, 3H, OCH3).
J¼7.5 Hz, 2H, ArH), 7.77 (br s, 1H, NH), 7.39e7.47 (m, 3H, ArH), 3.37
(d, J¼4.8 Hz, 3H, CH3).
4.1.11. 4-Nitrothiobenzamide (Table 2, entry 11)16. Pale yellow solid
purified using n-hexane/EtOAc (3:1 v/v; Rf¼0.14) as eluent system
4.1.3. N-Benzylthiobenzamide (Table 2, entry 3)7. Pale yellow solid
purified using n-hexane/EtOAc (20:1 v/v; Rf¼0.10) as eluent system
in silica gel column chromatography. 1H NMR (CDCl3):
d 8.28 (dt,
in silica gel column chromatography. 1H NMR (CDCl3):
d 7.77 (d,
J¼8.7, 2.1 Hz, 2H, ArH), 8.00 (dt, J¼9.3, 2.1 Hz, 2H, ArH), 7.71 (br s,
1H, NH), 7.22 (br s, 1H, NH).
J¼7.2 Hz, 2H, ArH), 7.69 (br s, 1H, NH), 7.36e7.48 (m, 8H, ArH), 5.01
(d, J¼5.1 Hz, 2H, CH2).
4.2. General procedure for thionation of esters
4.1.4. Thiobenzanilide (Table 2, entry 4)13. Pale yellow solid purified
using n-hexane/EtOAc (3:1 v/v; Rf¼0.45) as eluent system in silica
The ester starting material (3.0 mmol), P4S10 (0.75 mmol), and
gel column chromatography. 1H NMR (CDCl3):
d
9.01 (br s, 1H, NH),
dimethicone (5 mL; Dow Corning Corporation 200Ò fluid, viscosity

D. Cho et al. / Tetrahedron 66 (2010) 5583e5588
5587
50 cSt) were reflux in toluene and p-xylene solvent (10 mL) in
different trials. The reaction mixture was continuously stirred for
12 h. Upon completion, all solvent was evaporated using rotary
evaporator. Methanol was added to the residue several times nec-
essary to extract the product from dimethicone. All methanol was
evaporated and the crude mixture was purified by silica gel column
chromatography using n-hexane/EtOAc (either of the following
ratio: 60:1, 30:1, 20:1, 10:1 or 5:1 v/v) as eluent system.
Rf¼0.48) as eluent system in silica gel column chromatography. 1H
NMR (CDCl3):
d
8.15 (d, J¼9.3 Hz, 2H, ArH), 6.60 (d, J¼9.0 Hz, 2H,
ArH), 4.26 (s, 3H, OCH3), 3.07 (s, 6H, NMe2).
4.2.11. Methyl 4-nitrobenzenecarbothioate (Table 4, entry 11)18. Or-
ange solid purified using n-hexane/EtOAc (10:1 v/v; Rf¼0.50) as
eluent system in silica gel column chromatography. 1H NMR
(CDCl3):
2H, ArH), 4.35 (s, 3H, OCH3).
d
8.34 (dt, J¼9.3, 2.2 Hz, 2H, ArH), 8.24 (dt, J¼8.7, 2.1 Hz,
4.2.1. Methyl thiobenzoate (Table 4, entry 1)18. Orange liquid puri-
fied using n-hexane/EtOAc (60:1 v/v; Rf¼0.50) as eluent system in
4.2.12. Methyl 4-hydroxybenzenecarbothioate (Table 4, entry 12)23
.
silica gel column chromatography. 1H NMR (CDCl3):
d 8.20 (d,
Orange liquid purified using n-hexane/EtOAc (10:1 v/v; Rf¼0.18) as
J¼8.1 Hz, 2H, ArH), 7.55 (t, J¼7.2 Hz, 1H, ArH), 7.40 (t, J¼6.9 Hz, 2H,
eluent system in silica gel column chromatography. 1H NMR
ArH), 4.31 (s, 3H, OCH3).
(CDCl3):
d
8.17 (d, J¼9.0 Hz, 2H, ArH), 7.81 (d, J¼9.0 Hz, 2H, ArH),
4.2.2. Methyl 4-methylbenzenecarbothioate (Table 4, entry 2)18. Or-
ange liquid purified using n-hexane/EtOAc (60:1 v/v; Rf¼0.38) as
eluent system in silica gel column chromatography. 1H NMR
5.39 (br s, 1H, OH), 4.28 (s, 3H, OCH3).
4.2.13. Methyl 4-methoxybenzenecarbothioate (Table 4, entry 13)18
.
Orange liquid purified using n-hexane/EtOAc (60:1 v/v; Rf¼0.23) as
(CDCl3):
d
8.11 (d, J¼8.1 Hz, 2H, ArH), 7.20 (d, J¼7.8 Hz, 2H, ArH),
eluent system in silica gel column chromatography. 1H NMR
4.30 (s, 3H, OCH3), 2.40 (s, 3H, ArCH3).
(CDCl3):
d
8.20 (d, J¼8.7 Hz, 2H, ArH), 6.88 (d, J¼8.7 Hz, 2H, ArH),
4.2.3. Methyl 4-tert-butylbenzenecarbothioate (Table 4, entry 3)19
.
4.28 (s, 3H, S]CeOCH3), 3.87 (s, 3H, ArOCH3).
Orange liquid purified using n-hexane/EtOAc (30:1 v/v; Rf¼0.43) as
eluent system in silica gel column chromatography. 1H NMR
4.2.14. 2H-Chromene-2-thione (Table 4, entry 14)2b. Orange liquid
purified using n-hexane/EtOAc (60:1 v/v; Rf¼0.15) as eluent system
(CDCl3):
d
8.13 (d, J¼9.0 Hz, 2H, AreH), 7.41 (d, J¼8.4 Hz, 2H, ArH),
in silica gel column chromatography. 1H NMR (CDCl3):
d 7.63e7.50
4.30 (s, 3H, OCH3), 1.34 (s, 9H, C(CH3)3).
(m, 3H, ArH), 7.46 (d, J¼9.3 Hz, 1H, C-2), 7.34 (t, J¼7.5 Hz, 1H, ArH),
4.2.4. Methyl 3,5-dimethylbenzenecarbothioate (Table 4, entry 4).
Orange liquid purified using n-hexane/EtOAc (60:1 v/v; Rf¼0.38) as
eluent system in silica gel column chromatography. 1H NMR
7.24 (d, J¼9.0 Hz, 1H, C-1).
4.3. General procedure for thionation using Microwave
(CDCl3): d 7.82 (s, 2H, ArH), 7.19 (s, 1H, ArH), 4.29 (s, 3H, OCH3), 2.37
(s, 6H, ArCH3); 13C NMR (CDCl3):
d 213.2, 138.5, 137.9, 134.8, 126.8,
The starting material (3.0 mmol), P4S10 (0.6 mmol), dimethicone
(5 mL; Dow Corning Corporation 200Ò fluid, viscosity 50 cSt), and
10 mL of solvent (CH2Cl2 for amide and p-xylene for ester) were put
together in a long neck round bottom flask attached to a reflux con-
denser. The condenser was attached to a balloon filled with Ar. This
set-up was placed on the microwave reactor (CEM Discover System,
Model 908005). The temperature was set to the boiling point of the
solvent used plus 20 ꢁC at 300 W power. The reaction mixture was
continuously stirred until completion based onTLC monitoring. Upon
completion, all solvent was evaporated using rotary evaporator.
Methanol was added to the residue several times necessary to extract
the product from dimethicone. The methanol wasevaporated and the
crude mixture was purified by silica gel column chromatography
using n-hexane/EtOAc (either 3:1 or 60:1 v/v) as eluent system.
59.5, 21.5; IR (neat): 2938, 1448, 1223, 1200 cmꢀ1; HRMS m/z calcd
for C10H12OS 180.0609, found 180.0610.
4.2.5. Methyl 4-chlorobenzenecarbothioate (Table 4, entry 5)18. Yel-
low solid purified using n-hexane/EtOAc (60:1 v/v; Rf¼0.40) as el-
uent system in silica gel column chromatography. 1H NMR (CDCl3):
d
8.14 (dt, J¼8.7, 2.1 Hz, 2H, ArH), 7.37 (dt, J¼8.7, 2.2 Hz, 2H, ArH),
4.30 (s, 3H, OCH3).
4.2.6. Methyl 4-bromobenzenecarbothioate (Table 4, entry 6)20. Or-
ange solid purified using n-hexane/EtOAc (60:1 v/v; Rf¼0.50) as
eluent system in silica gel column chromatography. 1H NMR
(CDCl3):
ArH), 4.30 (s, 3H, OCH3).
d
8.06 (dt, J¼8.4, 2.1 Hz, 2H, ArH), 7.54 (dt, J¼8.7, 2.0 Hz, 2H,
4.2.7. Methyl 4-iodobenzenecarbothioate (Table 4, entry 7). Orange
solid purified using n-hexane/EtOAc (60:1 v/v; Rf¼0.50) as eluent
system in silica gel column chromatography. Mp: 63e64 ꢁC; 1H
Acknowledgements
J.A., K.A.D.C., and H.A. acknowledged the financial support from
the Korean Ministry of Education through the second stage of the
BK21 project for the Hanyang University graduate program.
NMR (CDCl3):
d
7.91 (d, J¼8.4 Hz, 2H, ArH), 7.76 (d, J¼8.4 Hz, 2H,
ArH), 4.29 (s, 3H, OCH3); 13C NMR (CDCl3):
d 211.1,137.7, 137.6,130.4,
101.3, 59.7; IR (neat): 2930, 1577, 1220, 821 cmꢀ1; HRMS m/z calcd
for C8H7OSI 277.9262, found 277.9259.
Supplementary data
4.2.8. Methyl 4-trifluoromethylbenzenecarbothioate (Table 4, entry
8)20. Orange liquid purified using n-hexane/EtOAc (60:1 v/v;
Rf¼0.50) as eluent system in silica gel column chromatography. 1H
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tet.2010.05.100.
NMR (CDCl3):
d
8.29 (d, J¼8.1 Hz, 2H, ArH), 7.66 (d, J¼8.4 Hz, 2H,
References and notes
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