Zinc-Catalyzed Synthesis of Dithioacetals through Double Hydrosulfenylation of Alkynes by Thiols

Article abstract of DOI:10.1055/s-0037-1610302

Zinc-catalyzed hydrosulfenylation of alkenes can be performed in various solvents, and the corresponding products are obtained regioselectively. Dihydrosulfenylation of alkynes with thiols can also be achieved by using a zinc catalyst, and the reaction is preferentially promoted over monohydrosulfenylation. The reaction can also give dithioacetals regioselectively in excellent yields.

Full text of DOI:10.1055/s-0037-1610302

SYNLETT
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© Georg Thieme Verlag Stuttgart · New York
2018, 29, A–E
letter
A
en
N. Taniguchi, K. Kitayama
Letter
Synlett
Zinc-Catalyzed Synthesis of Dithioacetals through Double Hydro-
sulfenylation of Alkynes by Thiols
Nobukazu Taniguchi*a
Kenji Kitayamab
0
0
0
0-0
0
0
3-
1
1
5
4-1
6
3
0
2 × R3SH,
ZnI2 (10 mol%)
R2
SR3
SR3
R1
R2
R1
PhMe, 100 °C
a Department of Chemistry, Fukushima Medical University,
Fukushima 960-1295, Japan
taniguti@fmu.ac.jp
b Innovation Park, Daicel Corporation, Shinzaike, Aboshi-ku,
Himeji, Hyogo 671-1283, Japan
21 examples
43–87%
Radical Addition
kn_kitayama@jp.daicel.com
Received: 29.07.2018
Accepted after revision: 17.09.2018
Published online: 16.10.2018
n-Bu3P
(10–30 mol%)
SR
EWG
R1
(a)
(b)
(c)
EWG
+
RSH
SR
THF, rt
DOI: 10.1055/s-0037-1610302; Art ID: st-2018-u0482-l
(2 equiv)
Abstract Zinc-catalyzed hydrosulfenylation of alkenes can be per-
formed in various solvents, and the corresponding products are ob-
tained regioselectively. Dihydrosulfenylation of alkynes with thiols can
also be achieved by using a zinc catalyst, and the reaction is preferen-
tially promoted over monohydrosulfenylation. The reaction can also
give dithioacetals regioselectively in excellent yields.
18-crown-6
K2CO3
SR2
SR2
R1
N
N
O
+
+
R2SH
O
THF, rt
(2 equiv)
SR3
SR3
Ca(ONf)2
(10 mol%)
Key words hydrosulfenylation, dihydrosulfenylation, dithioacetals,
zinc catalysis, alkynes, alkenes
R1
R3SH
R2
R1
1,4-dioxane, 100 °C
MW
R2
(2 equiv)
Scheme 1 Previously reported dihydrosulfenylation of alkynes
Transition-metal-catalyzed addition of thiols to unsatu-
rated C–C bonds has been performed by various methods.1,2
The resulting compounds have been widely used as re-
agents or intermediates. Hydrosulfenylation of alkenes or
alkynes has been achieved through radical reactions3 or
through metal-catalyzed reactions4,5 to give the desired
compounds. For example, metal-catalyzed hydrosulfenyla-
tion of alkynes affords the corresponding vinyl sulfides in
excellent yields.4
Dithioacetals are recognized as important intermediates
for preparing many organic compounds. They are usually
synthesized by combining of ketones with thiols6 in a con-
venient and useful reaction. However, dithioacetal prepara-
tion by alkyne hydrosulfenylation has hardly been re-
searched, whereas several reports on the dihydrosulfenyla-
tion of alkynes have been published.7–9 These procedures
employ alkynes containing electron-withdrawing groups
[Schemes 1(a) and 1(b)]7a–c or a specialized calcium catalyst
under microwave irradiation [Scheme 1(c)].7d In addition,
reactions under UV irradiation or by using alkyldithiols
have also been reported.7e,f Therefore, the development of a
convenient methods is now required. We attempted a selec-
tive synthesis of anti-Markovnikov-type dithioacetals.
As a general rule, reactions of alkynes with thiols afford
the corresponding alkenyl sulfides (Scheme 2). However,
due to a slow step, the second hydrosulfenylation hardly
proceeds. To solve this problem, we investigated the activi-
ties of numerous metal catalysts for alkene hydrosulfenyla-
tions. It was clear that a zinc catalyst efficiently achieved
the best results in various solvents. On the basis of this re-
sult, we then examined the dihydrosulfenylation of alkynes.
Unexpectedly, zinc-catalyzed hydrosulfenylation of alkynes
gave the corresponding dithioacetals in excellent yields.
Here, we describe this method.
SR2
R1
cat. Metal
R1
2xR2SH
SR2
+
SR2
R2SH
Fast step
R2SH
R1
Slow step
Scheme 2 Strategy for double hydrosulfenylation of alkynes
© Georg Thieme Verlag Stuttgart · New York — Synlett 2018, 29, A–E

B
N. Taniguchi, K. Kitayama
Letter
Synlett
Table 1 Investigation of Suitable Conditionsa
4-TolSH
catalyst
S
S
Ph
Ph
solvent, rt, 18 h
Ph
1a
2aa
3aa
OH
S
Ph
4aa
Entry
Catalyst (mol%)
Solvent
Yieldb (%) of 2aa
Yieldb (%) of 3aa
Yieldb (%) of 4aa
Yieldb (%) of (ArS)2 (%)
1
2
none
DMF
CH2Cl2
DMF
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
trace
trace
trace
trace
trace
trace
trace
trace
trace
7
70
71
none
3
CeCl3(10)
CeCl3(10)
LaCl3(10)
ZnCl2(10)
ZnCl2(10)
ZnCl2(10)
ZnCl2(10)
MgF2(10)
NiBr2(10)
PdCl2(10)
CuF2(5)
trace
75
76
72
70
70
72
65
54
41
0
trace
trace
trace
trace
trace
trace
trace
10
4
CH2Cl2
CH2Cl2
CH2Cl2
DMF
5
6
7
8
toluene
1,4-dioxane
CH2Cl2
CH2Cl2
CH2Cl2
DMF
9
10
11
12
13
14
trace
trace
0
35
42
91
CuI(10)
DMF
0
0
85
a Reaction conditions: 1 (0.3 mmol), 4-TolSH (0.33 mmol), metal catalyst, solvent (0.3 mL), r.t., in air.
b Isolated yield after silica gel chromatography.
The hydrosulfenylation of alkenes was initially surveyed
to identify the most efficient metal catalyst (Table 1). A
mixture of 4-toluenethiol and styrene in DMF or CH2Cl2
gave the corresponding disulfide rather than the sulfide 2aa
(Table 1, entries 1 and 2). Addition of CeCl3 catalyst in DMF
gave no product (entry 3), whereas the same reaction in
CH2Cl2 produced the expected 2aa in 75% yield (entry 4).
Similar results were obtained when the reaction was per-
formed with LaCl3 or ZnCl2 (entries 5 and 6). The zinc-cata-
lyzed reaction gave good regioselectivity in various sol-
vents, and the formation of the disulfide was suppressed
(entries 7–9). On the other hand, reactions using MgF2,
NiBr2, or PdCl2 as catalyst afforded unsatisfactory results
(entries 10–12). Unfortunately, copper catalysts did not
promote hydrosulfenylation at all (entries 13 and 14).
Therefore, ZnCl2 as a catalyst efficiently promotes the hy-
drosulfenylation of styrene in various solvents.
However, oct-1-ene exhibited a much lower reactivity (en-
try 11), and the reaction with butane-1-thiol gave zero
yield (entry 12).
Having obtained the above results, we next focused our
attention on adding thiols to alkynes.10 The efficient reac-
tion of thiols with alkynes to afford vinyl sulfides is well es-
tablished. Although monohydrosulfenylation proceeds
smoothly, double hydrosulfenylation does not. For example,
the reaction of 4-toluenethiol with ethyl propiolate gave
the corresponding vinyl sulfide exclusively in good yields
[Scheme 3(a)]. The corresponding reaction of ethynylben-
2 × 4-TolSH
SC6H4Me-4
EtO2C
EtO2C
(a)
PhMe, 100 °C
5j
6ja
84% (E/Z = 83:17)
Next various substrates were screened (Table 2). The re-
actions of terminal aryl alkenes with arenethiols produced
the corresponding sulfides regioselectively in excellent
yields (Table 2, entries 1–9). Reaction using ZnI2 or ZnBr2 as
the catalyst also afforded good results (entries 10 and 11).
2 × 4-TolSH
CeCl3 (10 ml%)
SC6H4Me-4
Ph
Ph
(b)
PhMe, 100 °C
5a
6aa
59% (E/Z = 91:9)
Scheme 3 Attempted hydrosulfenylations of alkynes
© Georg Thieme Verlag Stuttgart · New York — Synlett 2018, 29, A–E

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N. Taniguchi, K. Kitayama
Letter
Synlett
Table 2 Zn-Catalyzed Sulfenylation of Various Alkenesa
bromobenzenethiol afforded the vinyl sulfide 6 in 90%
yield, whereas dihydrosulfenylation did not proceed (entry
3). In attempts to promote this reaction, we examined sev-
eral zinc salts and we found that ZiBr2 as catalyst gave the
expected dithioacetal 7 in 60% yield together with the cor-
responding vinyl sulfide in 33% yield (entry 4). Fortunately,
the ZnI2-catalyzed reaction resulted in increased the yield
of 7 to 71% (entry 5). Other zinc catalysts proved inferior to
ZnI2 (entry 6–7).
Subsequently, numerous dihydrosulfenylations of
alkynes were assessed (Table 4).11 Treatment of mixtures of
terminal aryl alkynes and thiols with ZnI2 (10 mol%) gave
excellent yields of the corresponding dithioacetals 7 (Table
4, entries 1–16). Whereas the procedure with arenethiols
afforded excellent results, alkyl thiols showed slightly lower
R2SH,
SR2
ZnCl2 (10 mol%)
R1
R1
CH2Cl2, rt, 18 h
1
2
Entry
Product
Yieldb (%)
1
2
4-TolS(CH2)2Ph (2aa)
4-MeOC6H4S(CH2)2Ph (2ac)
4-BrC6H4S(CH2)2Ph (2ad)
4-TolS(CH2)2-4-Tol (2ba)
72
86
78
89
88
58
75
68
87
80
77
6
3
4
5
4-ClC6H4S(CH2)2-4-C6H4OMe (2ca)
4-TolS(CH2)2-4-C6H4OAc (2da)
4-TolS(CH2)2-4-C6H4Cl (2ea)
4-TolS(CH2)2-4-C6H4F (2fa)
4-TolS(CH2)2-4-Py (2ga)
4-TolS(CH2)2Ph (2aa)
6
7
8
Table 4 Zn-Catalyzed Sulfenylation of Alkynesa
9
10c
11d
12
13
2 × R3SH
ZnI2 (10 mol%)
R2
SR3
SR3
4-TolS(CH2)2Ph (2aa)
R1
R2
R1
PhMe, 100 °C
4-TolS(CH2)7Me (2ha)
5
7
BuS(CH2)2Ph (2ib)
0
Entry
Product
Time (h) Yieldb (%) of 7
a Reaction conditions: 1 (0.3 mmol), 2 (0.33 mmol), ZnCl2 (10 mol%),
CH2Cl2 (0.3 mL), r.t., in air.
b Isolated yield after silica gel chromatography.
c ZnI2 (10 mol%) was used instead of ZnCl2.
d ZnBr2 (10 mol%) was used instead of ZnCl2.
1
2
PhCH2CH(SPh)2 (7ab)
18
18
18
18
18
24
36
18
42
42
18
18
18
18
18
18
64
42
18
18
18
18
18
79
77
82
71
78
80
50
65
43
51
87
74
67
82
71
75
78
51
81
72
68
0
PhCH2CH(S-4-Tol)2 (7aa)
3
PhCH2CH(S-4-C6H4OMe)2 (7ac)
PhCH2CH(S-4-C6H4Br)2 (7ad)
PhCH2CH(S-4-C6H4Cl)2 (7ae)
PhCH2CH(S-2-Tol)2 (7af)
4
zene in the presence of CeCl3 gave similar results [Scheme
3(b)]. Therefore, these reactions do not promote double
hydrosulfenylation.
In particular, when a mixture of ethynylbenzene and 4-
toluenethiol was treated with a zinc catalyst in toluene, the
corresponding dithioacetal 7 was obtained in 76–79% yield
(Table 3, entries 1 and 2). However, the reaction with 4-
5
6
7c
PhCH2CH(S-2-C6H4Br)2 (7ag)
PhCH2CH(S-2-Naph)2 (7ah)
PhCH2CH(SBu)2 (7ai)
8
9
10
11
12
13
14
15
16
17d
18d
19
20
21
22
23d
PhCH2CH[S(CH2)7Me]2 (7aj)
4-TolCH2CH(S-4-Tol)2 (7ba)
4-MeOC6H4CH2CH(S-4-Tol)2 (7ca)
4-PhC6H4CH2CH(S-4-Tol)2 (7da)
4-FC6H4CH2CH(S-4-Tol)2 (7ea)
2-TolCH2CH(S-4-Tol)2 (7fa)
Table 3 Investigation of Suitable Conditionsa
2 × RSH
SR
ZnX2 (10 mol%)
SR
Ph
Ph
Ph
PhMe, 100 °C
18 h
SR
5a
7
6
2-(6-MeO-2-Naph)CH2CH(SS-4-Tol)2 (7ga)
Me(CH2)7CH(S-4-Tol)2 (7ha)
t-BuCH2CH(S-4-Tol)2 (7ia)
Entry
RSH
ZnX2
Yieldb (%) of 7 Yieldb (%) of 6 (E/Z)c
1
2
3
4
5
6
7
4-TolSH
4-TolSH
ZnCl2
ZnI2
76
77
trace
trace
EtO2CCH2CH(S-4-Tol)2 (7ja)
PhCH2C(Me)(S-4-Tol)2 (7ka)
PhCH2C(Et)(S-4-Tol)2 (7la)
PhCH2C(Ph)(S-4-Tol)2 (7ma)
BuC(Pr)(S-4-Tol)2 (7na)
4-BrC6H4SH
4-BrC6H4SH
4-BrC6H4SH
4-BrC6H4SH
4-BrC6H4SH
ZnCl2
ZnBr2
trace
60
90 (91:9)
33 (88:12)
trace
ZnI2
71
Zn(OAc)2
ZnSO4
0
91 (87:13)
90 (95:5)
trace
trace
a Reaction conditions: 5 (0.3 mmol), R3SH (0.63 mmol), ZnI2 (10 mol%),
toluene (0.3 mL), 100 °C, in air.
a Reaction conditions: 5a (0.3 mmol), thiol (0.63 mmol), ZnX2 (10 mol%),
toluene (0.3 mL), 100 °C, in air.
b Isolated yield after silica gel chromatography.
c ZnI2 (20 mol%).
b Isolated yield after silica gel chromatography.
c Ratio determined by 1H NMR.
d ZnCl2 (20 mol%).
© Georg Thieme Verlag Stuttgart · New York — Synlett 2018, 29, A–E

D
N. Taniguchi, K. Kitayama
Letter
Synlett
reactivities (entries 9 and 10). Moreover, terminal alkyl
alkynes also gave good yields of the desired products (en-
tries 17 and 18), although their reactivity was much lower.
The reaction with ethyl propiolate afforded the expected
product in 81% yield (entry 19). Internal alkynes and termi-
nal alkynes reacted well (entries 20 and 21). Unfortunately,
the reactions of 1,1′-ethyne-1,2-diyldibenzene and of oct-
4-yne hardly gave any of the corresponding disulfides (en-
tries 22 and 23).
In conclusion, zinc-catalyzed alkene hydrosulfenylation
proceeded in various solvents, and the corresponding prod-
ucts were obtained regioselectively. Furthermore, the zinc-
catalyzed double hydrosulfenylation of alkynes with thiols
was achieved. The procedure also gave numerous desired
dithioacetals regioselectively in excellent yields.
Funding Information
To elucidate the reaction mechanism, several experi-
ments were then performed. When the reaction was per-
formed in the absence of oxygen, the corresponding dithio-
acetal was obtained in 68% yield (Scheme 4), indicating a
slight inhibition of this procedure.
This work was supported by the Daicel Corporation.()
Supporting Information
Supporting information for this article is available online at
https://doi.org/10.1055/s-0037-1610302.
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n
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2 × 4-TolSH
ZnI2 (10 mol%)
S-4-Tol
S-4-Tol
68%
Ph
Ph
PhMe, 100 °C
under N2
References and Notes
(1) (a) Comprehensive Organic Synthesis;
V
o
l.
6
Trost, B. M.; Fleming, I.,
Eds.; Pergamon: Oxford, 1991. (b) Krief, A. In Comprehensive
Scheme 4 Disulfenylation of ethynylbenzene in the absence of oxygen
Organometallic Chemistry II;
V
o
l.
1
1
,
C
h
a
p
.
1
3
Abel, E. W.; Stone, F. G. A.;
Wilkinson, G., Eds.; Pergamon: Oxford, 1995, 515. (c) Metzner,
P.; Thuillier, A. Sulfur Reagents in Organic Synthesis; Academic
Press: San Diego, 1994. (d) Organoselenium Chemistry: Modern
Developments in Organic Synthesis; Wirth, T., Ed.; Springer:
Berlin, 2000. (e) Baird, C. P.; Rayner, C. M. J. Chem. Soc., Perkin
Trans. 1 1998, 1973. (f) Rayner, C. M. Contemp. Org. Synth. 1996,
3, 499. (g) Kondo, T.; Mitsudo, T.-a. Chem. Rev. 2000, 100, 3205.
(h) Beletskaya, I.; Moberg, C. Chem. Rev. 2006, 106, 2320.
(i) Alonso, F.; Beletskaya, I. P.; Yus, M. Chem. Rev. 2004, 104,
3079. (j) Beletskaya, I. P.; Ananikov, V. P. Chem. Rev. 2011, 111,
1596. (k) Dondoni, A.; Marra, A. Eur. J. Org. Chem. 2014, 3955.
(l) Orlov, N. V. ChemistryOpen 2015, 4, 682.
However, the corresponding reaction in the presence of
TEMPO as a radical scavenger was completely inhibited
(Scheme 5).
2 × 4-TolSH
ZnI2 (10 mol%)
TEMPO (1equiv)
S-4-Tol
S-4-Tol
Not detected
S-4-Tol
Ph
Ph
Ph
PhMe, 100 °C
(2) Swiss, K. A.; Liotta, D. C. In Comprehensive Organic Synthesis;
V
o
l.
7
,
C
h
a
p
.
3.6
Trost, B. M.; Fleming, I., Eds.; Pergamon: Oxford, 1991, 515.
Not detected
(3) For selected reports on hydrosulfenylation of alkenes, see:
(a) Fossey, J.; Lefort, D.; Sorba, J. Free Radicals in Organic Chemis-
try; Wiley: Chichester, 1995. (b) Kanemasa, S.; Oderaotoshi, Y.;
Wada, E. J. Am. Chem. Soc. 1999, 121, 8675. (c) Munro-Leighton,
C.; Blue, E. D.; Gunnoe, T. B. J. Am. Chem. Soc. 2006, 128, 1446.
(d) Brown, R.; Jones, W. E.; Pinder, A. R. J. Chem. Soc. 1951, 3315.
(e) Bordwell, F. G.; Hewett, W. A. J. Am. Chem. Soc. 1957, 79,
3493. (f) Ichinose, Y.; Wakamatsu, K.; Nozaki, K.; Birbaum, J.-L.;
Oshima, K.; Utimoto, K. Chem. Lett. 1987, 1647. (g) Haché, B.;
Gareau, Y. Tetrahedron Lett. 1994, 35, 1837. (h) Belley, M.;
Zamboni, R. J. Org. Chem. 1989, 54, 1230. (i) Silveira, C. C.;
Mendes, S. R.; Libero, F. M. Synlett 2010, 790. (j) Ranu, B. C.;
Mandal, T. Synlett 2007, 925. (k) Caserio, M. C.; Fisher, C. L.; Kim,
J. K. J. Org. Chem. 1985, 50, 4390. (l) Kondo, T.; Uenoyama, S.-y.;
Fujita, K.-i.; Mitsudo, T.-a. J. Am. Chem. Soc. 1999, 121, 482.
(4) For selected recent papers on metal-catalyzed sulfenylations of
alkynes, see: (a) Cao, C.; Fraser, L. R.; Love, J. A. J. Am. Chem. Soc.
2005, 127, 17614. (b) Ranjit, S.; Duan, Z.; Zhang, P.; Liu, X. Org.
Lett. 2010, 12, 4134. (c) Kondoh, A.; Takami, K.; Yorimitsu, H.;
Oshima, K. J. Org. Chem. 2005, 70, 6468. (d) Weiss, C. J.; Wobser,
S. D.; Marks, T. J. Organometallics 2010, 29, 6308. (e) Shoai, S.;
Bichler, P.; Kang, B.; Buckley, H.; Love, J. A. Organometallics
2007, 26, 5778.
Scheme 5 Disulfenylation of ethynylbenzene in the presence of TEMPO
These results indicate that dihydrosulfenylation pro-
ceeds by radical processes (Scheme 6). A thiyl radical is
formed by reaction with a trace amount of oxygen.12 Aren-
ethiyl radicals are generated more rapidly than alkylthiyl
radicals.13 Finally, the reaction is promoted by the zinc cata-
lyst functioning as a Lewis acid.14 Further detailed investi-
gations of the conditions and the mechanism are ongoing.
R2SH
O2
R2SH
O2
R2S
SR2
SR2
R2S
SR2
R1
R1
R1
Zn2+
Zn2+
Scheme 6 A plausible reaction mechanism
© Georg Thieme Verlag Stuttgart · New York — Synlett 2018, 29, A–E

E
N. Taniguchi, K. Kitayama
Letter
Synlett
(5) For selected recent papers on metal-catalyzed sulfenylations of
alkenes, see: (a) Tyson, E. L.; Ament, M. S.; Yoon, T. P. J. Org.
Chem. 2013, 78, 2046. (b) Tyson, E. L.; Niemeyer, Z. L.; Yoon, T. P.
J. Org. Chem. 2014, 79, 1427. (c) Bhat, V. T.; Duspara, P. A.; Seo,
S.; Bakar, N. S. B. A.; Greaney, M. F. Chem. Commun. 2015, 51,
4383. (d) Tamai, T.; Fujiwara, K.; Higashimae, S.; Nomoto, A.;
Ogawa, A. Org. Lett. 2016, 18, 2114. (e) Tamai, T.; Ogawa, A. J. Org.
Chem. 2014, 79, 5028. (f) Taniguchi, N. ChemistrySelect 2018, 3,
6209.
CH2Cl2 (0.3 mL), and the resulting mixture was stirred at r.t. for
18 h in air. The residue was dissolved in Et2O, and the solution
was washed with H2O and sat. aq NaCl chloride then dried
(MgSO4). Chromatography (silica gel, hexane) gave a colorless
liquid; yield: 49.4 mg (72%) [see also ref. 3 (i)].
1H NMR (270 MHz, CDCl3): δ = 7.27 (d, J = 7.9 Hz, 2 H), 7.12–
7.05 (m, 7 H), 3.13–3.07 (m, 2 H), 2.88–2.83 (m, 2 H), 2.32 (s, 3
H). 13C{1H} NMR (67.5 MHz, CDCl3): δ = 137.2, 136.1, 135.9,
132.5, 130.0, 129.7, 129.1, 128.4, 35.9, 35.3, 21.0.
(6) Greene, T. W.; Wuts, P. G. M. Protective Groups in Organic Syn-
thesis; Wiley: New York, 2002, 3rd ed.
(11) 1,1′-[(2-Phenylethane-1,1-diyl)bis(thio)]dibenzene (7ab);
Typical Procedure (Table 4,Entry 1)
(7) For anti-Markovnikov-type reactions, see: (a) Kuroda, H.;
Tomita, I.; Endo, T. Synth. Commun. 1996, 26, 1539. (b) Wipf, P.;
Graham, T. H. Org. Biomol. Chem. 2005, 3, 31. (c) Gaunt, M. J.;
Sneddon, H. F.; Hewitt, P. R.; Orsini, P.; Hook, D. F.; Ley, S. V. Org.
Biomol. Chem. 2003, 1, 15. (d) Hut’ka, M.; Tsubogo, T.;
Kobayashi, S. Organometallics 2014, 33, 5626. (e) Nuyken, O.;
Siebzehnrübl, F. Phosphorus Sulfur Relat. Elem. 1988, 35, 47.
(f) Bhadra, S.; Ranu, B. C. Can. J. Chem. 2009, 87, 1605.
(8) For Markovnikov-type reactions, see: (a) Mitamura, T.; Daitou,
M.; Nomoto, A.; Ogawa, A. Bull. Chem. Soc. Jpn. 2011, 84, 413.
(b) Yadav, J. S.; Reddy, B. V. S.; Raju, A.; Ravindar, K.; Baishya, G.
Chem. Lett. 2007, 36, 1474.
ZnI2 (9.6 mg, 0.03 mmol) was added to a mixture of ethynylben-
zene (30.6 mg, 0.3 mmol) and PhSH (69.4 mg, 0.33 mmol) in
toluene (0.3 mL), and the resulting mixture was stirred at 100 °C
for 18 h in air. The residue was dissolved in Et2O, and the solu-
tion was washed with H2O and sat. NaCl, then dried (MgSO4).
Chromatography (silica gel, hexane) gave a colorless liquid;
yield: 76.2 mg (79%).
IR (neat): 3059, 3027, 1582, 1478, 1438 cm–1 1H NMR (270
.
MHz, CDCl3): δ = 7.41–7.36 (m, 4 H), 7.31–7.16 (m, 11 H), 4.57
(t, J = 6.9 Hz, 1 H), 3.14 (d, J = 6.9 Hz, 2 H). 13C{1H} NMR (67.5
MHz, CDCl3): δ = 137.9, 134.3, 132.7, 129.4, 128.9, 128.3, 127.7,
126.8, 59.6, 42.2. Anal. Calcd for C20H18S2: C, 74.49; H, 5.63.
Found: C, 74.78; H, 5.73.
(9) For 1,2-disulfenylation, see: Jin, Z.; Xu, B.; Hammond, G. B. Eur.
J. Org. Chem. 2010, 168.
(12) Mistra, H. P. J. Biol. Chem. 1974, 249, 2151.
(10) 1-Methyl-4-[(2-phenylethyl)thio]benzene (2aa);
Typical Procedure (Table2, Entry 1)
(13) Curran, D. P.; Martin-Esker, A. A.; Ko, S. B.; Newcomb, M. J. Org.
Chem. 1993, 58, 4691.
ZnCl2 (4.0 mg, 0.015 mmol) was added to a mixture of styrene
(31.2 mg, 0.3 mmol) and 4-TolSH (37.3 mg, 0.33 mmol) in
(14) Yamamoto, Y. J. Org. Chem. 2007, 72, 7817.
© Georg Thieme Verlag Stuttgart · New York — Synlett 2018, 29, A–E