Pt-catalyzed regio- and stereoselective thienylthiolation of alkynes

Article abstract of DOI:10.1246/cl.2004.1148

The Pt-catalyzed decarbonylative thienylthiolation of terminal alkynes by thienylthioesters took place regio- and stereoselectively under toluene reflux to give vinylsulfides with cis-thienyl group at β-carbon in moderate to good yields.

Full text of DOI:10.1246/cl.2004.1148

1148
Chemistry Letters Vol.33, No.9 (2004)
Pt-Catalyzed Regio- and Stereoselective Thienylthiolation of Alkynes
Takayoshi Hirai, Hitoshi Kuniyasu,ꢀ and Nobuaki Kambeꢀ
Department of Molecular Chemistry & Frontier Research Center, Graduate School of Engineering,
Osaka University, Suita, Osaka 565-0871
(Received June 23, 2004; CL-040728)
The Pt-catalyzed decarbonylative thienylthiolation of termi-
nal alkynes by thienylthioesters took place regio- and stereose-
lectively under toluene reflux to give vinylsulfides with cis-
thienyl group at ꢀ-carbon in moderate to good yields.
was obtained in 88% yield together with 7% of (2-thienyl)-
(n-C6H13)C=CHCH=C(SPh)(n-C6H13) (6a) (Entry
1
in
Table 1. Pt-catalyzed thienylthiolation of 2 by 5a
Entry
Isolated Yield (%) of 4
5
2
Transition-metal catalyzed simultaneous introductions of
carbon and heteroatom functionalities to C–C unsaturated bonds
have provided straightforward strategies to produce highly func-
tionalized organic compounds. The carbosilylation,1 carbostan-
nylation,2 and carbochlorination3 of alkynes are among the most
successful examples. On the other hand, we have recently dis-
closed that the Pt-catalyzed regio- and stereoselective carbothio-
lation of terminal alkynes has been achieved by exploiting con-
trastive reactivities of C and S ligands on Pd and Pt complexes.4
The basic concept is shown in Scheme 1, comprising: (1) gener-
ation of platinum complex 1 having C–Pt–S moiety produced af-
ter the Pd-catalyzed C–S bond-forming reactions,5 (2) conver-
sion of 1 into the vinyl complex 3 possessing C–Pt–C
fragment by the cis-insertion of HCCR (2) into the Pt–S bond
of 1 with Pt bound at the terminal position,6 and (3) subsequent
C–C bond-forming reductive elimination from 3 to afford vinyl
sulfide 4 with regeneration of Pt(0) complex.7,8 For example, the
Pt-catalyzed arylthiolation and vinylthiolation of 2 were realized
using CC(O)SAr (C = aryl or vinyl) with the Pd-catalyzed
decarbonylations as model reactions.9
O
b
1
C H -n
4a
88
6
13
SPh
2a
S
5a
5a
2
3
4
Ph
2b
C H OMe-p
4b
4c
4d
80
78
85
5a
5a
6
4
2c
(CH ) CN
2 3
2d
(CH ) OH
5
6
5a
5a
4e
E
85
E
2 4
2e
E
E
SPh
S
4f
2f
68
R
c
R
4g
4h
4i
7
5a
5a
SiMe
2g
89
nd
nd
3
- Pt(0)
R
2
C
M
S
d
Pt
S
H C
7
C H
3 7
8
9
3
C
S
1
M = Pt
C
2h
d,e
3
4
5a
CH Br
2
M = Pd
2i
O
C
S
84
10
2a
4j
SPh
Scheme 1. Strategy for carbothiolation of alkynes.
5b
S
Herein we wish to report on the thienylthiolation, an extend-
ed type of Pt-catalyzed carbothiolation using thienylthioesters
(5) as substrates (Eq 1).
O
76
46
11
12
2a
2a
4k
4l
SC H OMe-p
6
4
R
cat. Pt(0)
O
S
5c
O
+
2
(1)
C
SAr
C
SAr
SC H Cl-p
5
6
4
4
S
(C = thienyl)
5d
First, the reaction of (2-thienyl)C(O)SPh (5a, 1.0 mmol)
with 1-octyne (2a, 1.2 mmol) in toluene (0.5 mL) was carried
out in the presence of Pt(PPh3)4 (0.05 mmol) under reflux for
24 h. The anticipated Z-(2-thienyl)CH=C(n-C6H13)(SPh) (4a)
a5 (1.0 mmol), 2 (1.2 mmol), and Pt(PPh3)4 (0.05 mmol) in tol-
uene (0.5 mL) at 110 ꢁC for 24 h. b7% of (2-thienyl)RC=
CHCH=C(SPh)(R) (6a). c2.5 mmol of 2g, 24 h in a sealed tube.
e
dNot detected. CH2=C(SPh)(CH2Br) (12%).
Copyright Ó 2004 The Chemical Society of Japan

Chemistry Letters Vol.33, No.9 (2004)
1149
Table 1).10 However, neither isomer of 4a nor thioether (2-thie-
nyl)SPh (7a) was detected.11 It must be noted that Pd-complex
also possessed some catalytic ability in the present thienylthiola-
tion: 38% of 4a as well as 25% of 7a and 2% of 6a was produced
when Pd(PPh3)4 was employed as a catalyst. The scope and lim-
itations of the present Pt-catalyzed thienylthiolation of alkynes
were summarized in Table 1. Phenylacetylene and its derivative
(2b and 2c) also underwent the thienylthiolation to give the cor-
responding decarbonylative adducts 4b and 4c, which have sig-
nificantly extended ꢁ-conjugation systems in moderate yields
(Entries 2 and 3). Some functional groups such as cyano and hy-
droxy groups were tolerant toward the present transformation
(Entries 4 and 5). When an alkyne (2f) with a tethered olefin unit
was employed, the chemoselective addition took place at the tri-
ple bond (Entry 6). The reaction using trimethylsilylacetylene
(2g) gave the thienylthiolation product in good yield (Entry 7).
However, internal alkyne (2h) and propargyl bromide (2i) were
totally ineffective (Entries 8 and 9). The 3-thienylthiolation us-
ing (3-thienyl)C(O)SPh (5b) also occurred to give the corre-
sponding adduct 4j in 84% yield (Entry 10). The compounds
such as (2-thienyl)C(O)(SC6H4OMe-p) (5c) and (2-thienyl)-
C(O)(SC6H4Cl-p) (5d) also can be used as reagents for thie-
nylthiolation of 2 (Entries 11 and 12).
of carbothiolation chemistry is now under investigation.
Thanks are due to the Instrumental Analysis Center, Faculty
of Engineering, Osaka University, for assistance in obtaining
mass spectra with a JEOL JMS-DX303 instrument.
References and Notes
1
a) N. Chatani, N. Amishiro, and S. Murai, J. Am. Chem. Soc.,
113, 7778 (1991). b) N. Chatani, N. Amishiro, T. Mori, T.
Yamashita, and S. Murai, J. Org. Chem., 60, 1834 (1995). c)
Y. Obora, Y. Tsuji, and T. Kawamura, J. Am. Chem. Soc.,
115, 10414 (1993). d) Y. Obora, Y. Tsuji, and T. Kawamura,
J. Am. Chem. Soc., 117, 9814 (1995). e) S. Nii, J. Terao, and
N. Kambe, J. Org. Chem., 65, 5291 (2000). f) S. Nii, J. Terao,
and N. Kambe, J. Org. Chem., 69, 573 (2004).
2
H. Yoshida, E. Shirakawa, Y. Nakano, Y. Honda, and T.
Hiyama, Bull. Chem. Soc. Jpn., 74, 637 (2001) and references
sited therein.
3
4
K. Kokubo, K. Matsumasa, M. Miura, and M. Nomura, J. Org.
Chem., 61, 6941 (1996).
a) H. Kuniyasu and H. Kurosawa, Chem.—Eur. J., 8, 2660
(2002). b) K. Sugoh, H. Kuniyasu, T. Sugae, A. Ohtaka, Y.
Takai, A. Tanaka, C. Machino, N. Kambe, and H. Kurosawa,
J. Am. Chem. Soc., 123, 5108 (2001). c) T. Hirai, H. Kuniyasu,
T. Kato, Y. Kurata, and N. Kambe, Org. Lett., 5, 3871 (2003).
a) G. Mann, D. Barannaro, J. F. Hartwig, A. L. Rheingold, and
L. A. Guzei, J. Am. Chem. Soc., 120, 9205 (1998). b) T. Kondo
and T. Mitsudo, Chem. Rev., 100, 3205 (2000).
Although quite a few papers, describing the participation of the
insertion of alkynes into S–M (M = Pd and Pt) bonds as elemen-
tary reactions have been reported, information about the process
has been actually very limited. a) H. Kuniyasu, in ‘‘Catalytic
5
6
Pt(0)
- 4
5
O
R
Heterofunctionalization,’’ ed. by A. Togni and H. Grutzmacher,
Wiley, Zurich, Switzerland (2001), Chap. 7, p 217. b) K. Sugoh,
¨
¨
C
Pt SAr
Pt
SAr
8
H. Kuniyasu, and H. Kurosawa, Chem. Lett., 2002, 106.
a) P. J. Stang and M. Kowalski, J. Am. Chem. Soc., 111, 3356
(1989). b) R. K. Merwin, R. C. Schnabel, and J. D. Koola,
D. M. Roddick, Organometallics, 11, 2972 (1992) and refer-
ences therein.
C
7
10
- CO
2
C Pt SAr
(C = thienyl)
8
9
For the synthetic utility of vinyl sulfides, see: a) B. M. Trost
and A. C. Lavoie, J. Am. Chem. Soc., 105, 5075 (1983). b) P.
Magnus and D. Quagliato, J. Org. Chem., 50, 1621 (1985).
K. Osakada, T. Yamamoto, and A. Yamamoto, Tetrahedron
Lett., 28, 6321 (1987).
9
Scheme 2. A Plausible reaction route.
A plausible reaction route is shown in Scheme 2, which in-
cludes the oxidative addition of 5 to Pt(0) to form Pt(C)[C(O)-
SAr] (C = thienyl) (8), decarbonylation to give the complex 9,
insertion of 2 into the Pt–S bond to furnish 10, and subsequent
reductive elimination of 4 from 10 with regeneration of Pt(0).
In fact, when the reaction of 5a (0.01 mmol) with Pt(PPh3)4
(0.01 mmol) was carried out in toluene-d8 (0.5 mL), the oxida-
tive addition of 5a to Pt(PPh3)4 proceeded at ambient tempera-
ture to give a mixture of trans-Pt(SPh)[C(O)(2-thienyl)](PPh3)2
(8a) (45%) and it’s dimeric (PPh3)[(2-thienyl)C(O)]Pt(ꢂ-
SPh)2Pt[C(O)(2-thienyl)](PPh3) (8a0) (55%) after 1.5 h. The de-
carbonylation required more stringent conditions; leaving the so-
lution of 8a and 8a0 at 110 ꢁC for 1 h afforded decarbonylated
complexes trans-Pt(SPh)(2-thienyl)(PPh3)2 (9a) (30%) and (2-
thinyl)(PPh3)Pt(ꢂ-SPh)2Pt(2-thienyl)(PPh3) (9a0) (70% based
on Pt). Finally, heating the solution for 6 h after the addition
of 2a (0.012 mmol) at 110 ꢁC resulted in the formation of 4a
in 89% yield.
10 General procedure: Into a two-necked flask were placed 5a
(1.0 mmol), Pt(PPh3)4 (0.05 mmol), toluene (0.5 mL), and then
2a (1.2 mmol). After the reaction mixture was vigorously re-
fluxed for 24 h, the reaction mixture was separated by PTLC us-
ing hexane as an eluent to provide 4a and 6a in 88% and 7%
(based on 5), respectively. (Z)-4a (run 1, Table 1): light yellow
oil; 1H NMR (400 MHz, CDCl3) ꢃ 7.40–7.39 (m, 2H), 7.38–7.12
(m, 5H), 6.99 (s, 1H), 6.96–6.89 (m, 1H), 2.29 (t, J ¼ 7:6 Hz,
2H), 1.58–1.50 (m, 2H), 1.28–1.17 (m, 6H), 0.85 (t, J ¼ 6:8
Hz, 3H); NOE experiment: Irradiation of the aryl triplet at ꢃ
2.29 resulted in a 7.8% enhancement of the signal at ꢃ 6.99
(C-1 vinyl singlet); 13C NMR (100 MHz, CDCl3) ꢃ 139.77,
134.00, 132.49, 129.95, 129.10, 128.72, 127.37, 126.36,
126.19, 125.79, 38.30, 31.64, 28.86, 28.59, 22.62, 14.19; IR
(NaCl) 3071, 2954, 2928, 2855, 1582, 1476, 1439, 1377,
1361, 1315, 1216, 1068, 1050, 1024, 1000, 854, 818, 741,
699 cmꢂ1; mass spectrum (EI) m=z 302 (Mþ, 100); Anal. Calcd
for C18H22S2: C, 71.47; H, 7.33; S, 21.20. Found: C, 71.38; H,
7.33; S, 20.96. The regiochemistry was determined by C–C
2-D NMR experiment.
In conclusion, this paper revealed that the Pt-catalyzed
carbothiolation prototype also could be successfully applied to
the novel thienylthiolation. Further study to testify the generality
11 Pt(PPh3)4 did not catalyze the decarbonylation of 5a at all under
toluene reflux for 24 h.
Published on the web (Advance View) August 7, 2004; DOI 10.1246/cl.2004.1148