Novel photoinduced reduction of conjugate dienes by the combination of benzenethiol and diphenyl diselenide

Article abstract of DOI:10.1246/bcsj.80.2443

By using a binary system that consisted of benzenethiol and diphenyl diselenide under photoirradiation through a Pyrex vessel with a xenon lamp (λ > 300 nm), a variety of conjugate dienes could be reduced to the corresponding internal alkenes under mild conditions.

Full text of DOI:10.1246/bcsj.80.2443

Short Articles
Bull. Chem. Soc. Jpn. Vol. 80, No. 12, 2443–2445 (2007) 2443
GSSG
ROOH
ROH
E-SeH
Novel Photoinduced Reduction
of Conjugate Dienes by the
Combination of Benzenethiol
and Diphenyl Diselenide
GSH
E-SeSG
E-SeOH
H2O
GSH
Fig. 1. Catalytic cycle for the glutathione peroxidase-
catalyzed reduction of hydroperoxides with glutathione.
Takenori Mitamura, Yoshiaki Imanishi,
Akihiro Nomoto, Motohiro Sonoda, and
ꢀ
Akiya Ogawa
Department of Applied Chemistry, Graduate School
of Engineering, Osaka Prefecture University,
1-1 Gakuen-cho, Nakaku, Sakai, Osaka 599-8531
Received July 2, 2007; E-mail: ogawa@chem.osakafu-u.ac.jp
By using a binary system that consisted of benzenethiol
and diphenyl diselenide under photoirradiation through a
Pyrex vessel with a xenon lamp (ꢀ > 300 nm), a variety of
conjugate dienes could be reduced to the corresponding
internal alkenes under mild conditions.
Fig. 2. Photoinduced reduction of 1a. — presence of
(PhSe)2, : yield of 1a; : yield of 2a; : yield of 3a.
- - - absence of (PhSe)2, : yield of 1a; : yield of 2a;
: yield of 3a.
Glutathione peroxidase (GPx), which has –SeH groups at its
active sites, catalyzes in vivo the reduction of hydroperoxides
(ROOH) with cysteine or glutathione (GSH), which has an
–SH group (Fig. 1).1
In this reduction system, selenol (RSeH), thiol (R0SH), and
selenosulfide (RSeSR0) play important roles, and therefore,
it is of great importance to clarify the reducing behavior
of chalcogen compounds bearing a Ch–H or Ch–Ch bond
(Ch ¼ S and Se) under radical conditions, especially, in the
mixed systems of them. In view of our biological and syntheti-
cal interest involving mixed systems of such chalcogen com-
pounds,2 we examined the photoinduced reduction of several
unsaturated compounds using PhSH–(PhSe)2 as a model sys-
tem by combining a Ch–H compound and a Ch–Ch compound.
This attempt led to a new reduction reaction of conjugate
dienes 1 to the corresponding alkenes 2 by using the PhSH–
(PhSe)2 mixed system under photoirradiation conditions
(Eq. 1).
Table 1. Photoinduced Reduction of 2,3-Dimethyl-1,3-
butadiene (1a)a)
hν (> 300 nm)
PhSH
(PhSe)2
+
+
1a
2a
Entry
PhSH
/mol. amt.
(PhSe)2
/mol. amt.
Yieldb)/%
1
2
3
4
5
10
0.30
1.0
10
2.0
5.0
29
45
33
50
49
2.0
2.0
3.0
3.0
a) Reaction conditions: 2,3-dimethyl-1,3-butadiene (1a, 0.1
mmol), PhSH, (PhSe)2, CDCl3 (0.5 mL), rt, hꢁ: xenon lamp
(through Pyrex). b) Determined by H NMR.
R
R
PhSH - (PhSe) -h
ν
2
1
ð1Þ
1
2
conjugate addition product, i.e., allyl sulfide derivative 3a,
was obtained in excellent yield within 6 h. On the other hand,
in the presence of (PhSe)2, 2,3-dimethyl-2-butene (2a), as a re-
duction product, was formed gradually with a decrease in the
yield of 3a by continuous photoirradiation. To increase the
yield of the reduced product 2a, the reaction of 1a with PhSH
in the presence of (PhSe)2 under photoirradiation for 24 h was
examined under several reaction conditions (Table 1).
Results and Discussion
The reaction of 2,3-dimethyl-1,3-butadiene (1a) with PhSH
(10 mol. amt.) in CDCl3 was conducted at room temperature in
the presence/absence of (PhSe)2 (0.30 mol. amt.) under irradi-
ation with a xenon lamp through a Pyrex vessel (ꢀ > 300 nm),
and was monitored by taking the 1H NMR spectra of the reac-
tion solution (Fig. 2).
The use of excess amounts of PhSH and (PhSe)2 improved
the yield of the reduction product 2a (Entries 4 and 5). Thus,
As can be seen from Fig. 2, in the absence of (PhSe)2, a
Published on the web December 13, 2007; doi:10.1246/bcsj.80.2443

2444 Bull. Chem. Soc. Jpn. Vol. 80, No. 12 (2007)
ꢀ 2007 The Chemical Society of Japan
Table 2. Photoinduced Reduction of Conjugate Dienes with
a)
PhSH/(PhSe)2
Time
/h
Yield Recovered
/%b) (PhSe)2/%e)
Entry
1
Diene
Product
96
82
45
88
77
1a
2a
2
100
1b
1c
2b
2c
3
4
70
78
0
86
80
Ph
Ph
Ph
Ph
100
1d
1e
2d
2e
time/h
5
6
96
72
62
73
83
74
Fig. 3. Photoinduced reduction of 1a. — —: 3 mol. amt.
of PhSH; 2 mol. amt. of (PhSe)2, — —: 3 mol. amt. of
PhSH; 5 mol. amt. of (PhSe)2, — —: 2 mol. amt. of
PhSH; 1 mol. amt. of (PhSe)2.
1f
2f
we examined the reaction by prolonging irradiation time, and
the results are summarized in Fig. 3. A 3/2 molar ratio of
PhSH/(PhSe)2 provided 2a in more than 80% yield.
7
8
96
81
70
79
90
1g
2g
The results of the reduction of various dienes using the
PhSH/(PhSe)2 mixed system are summarized in Table 2. Sim-
ilar conditions could be employed with isoprene (1b) and 1,3-
pentadiene (1c) (Entries 2 and 3). On the other hand, 1,4-di-
phenyl-1,3-butadiene (1d) did not undergo reduction, probably
due to the bulkiness of the phenyl groups at the terminal posi-
tions (Entry 4). The reduction of cyclic dienes 1e, 1f, and 1g
proceeded successfully, affording the corresponding cyclic al-
kenes 2e, 2f, and 2g, respectively, in high yields (Entries 5–7).
With ꢂ-myrcene (1h), the reduction took place only at the con-
jugate double bond (Entry 8). When benzeneselenol was em-
ployed in place of (PhSe)2, the reduction of diene took place
smoothly (1 h) (Entry 9).3 Next, we examined the recycling
of (PhSe)2 for this diene reduction. After the reduction of diene
1a was complete, (PhSe)2 was recovered as a dichalcogenide
mixture ((PhSe)2:(PhS)2:PhSSePh = 4:2:1). Using this dichal-
cogenide mixture, the reduction of diene 1a was attempted and
2a was obtained in 74% yield (Entry 10).
110
2h
2a
2a
1h
1a
1a
9cÞ
10dÞ
1
>95
—
58
72
74
a) Reaction conditions: conjugate diene (0.1 mmol), PhSH (0.3
mmol), (PhSe)2 (0.2 mmol), CDCl3 (0.5 mL), rt, hꢁ: xenon lamp
(through Pyrex). b) Determined by 1H NMR. c) Use of PhSeH
(0.4 mmol) in place of (PhSe)2 (0.2 mmol). d) Use of recovered
(PhSe)2 instead of pure (PhSe)2. e) Along with 10%–20% of
PhSSePh.
h
ν
(> 300 nm)
SPh
+
PhSH + (PhSe)2
ð3Þ
CDCl3, 96 h
3a
3 mol. amt. 2 mol. amt.
2a, 70%
To clarify the reaction pathway for this reduction, 2,3-
dimethyl-2-butenyl phenyl sulfide (3a)4 and selenide (4a) as
plausible intermediates were synthesized by the reaction of
the corresponding diene 1a with PhSH and PhSeH, respective-
ly. Thus, we examined the reduction of these adducts under
several conditions, as shown in Eqs. 2–4. When the reaction
of allyl sulfide derivative (3a) with 1 molar amount of ben-
zenethiol was conducted with photoirradiation, the reduction
did not occur efficiently (Eq. 2).
In the case of allyl selenide derivative 4a, the photoinduced
reduction took place very smoothly (1 h) to afford 2a quantita-
tively (Eq. 4).
hν
(> 300 nm)
SePh
+
PhSH
ð4Þ
CDCl3, 1 h
4a
1 mol. amt.
2a, quant
These results prompted us to propose a possible pathway for
this photoinduced reduction using a PhSH–(PhSe)2 binary
system (Scheme 1).
Under irradiation with a xenon lamp through a Pyrex vessel
(ꢀ > 300 nm), (PhSe)2 (ꢀaxi ¼ 330 nm) mainly undergoes
homolytic dissociation to generate PhSeꢁ,5 which adds to con-
jugate diene 1a, forming seleno group-substituted allyl radical.
The allyl radical abstracts a hydrogen from PhSH6 to produce
an allyl selenide derivative 4a with the generation of phenyl-
h
ν
(> 300 nm)
SPh
+
PhSH
ð2Þ
CDCl3, 24 h
3a
1 mol. amt.
2a, < 5%
However, addition of (PhSe)2 to this reaction system and pro-
longed photoirradiation (96 h) resulted in the formation of the
reduction product 2a in 70% yield (Eq. 3).

T. Mitamura et al.
Bull. Chem. Soc. Jpn. Vol. 80, No. 12 (2007) 2445
mmol), and then the solution was stirred for 10 min under the
atmosphere at ambient temperature. The resulting solution was
path through the silica pad (eluent: hexane) and concentrated in
vacuo, yielding 2.90 g (85%) of 2,3-dimethyl-2-butenyl phenyl
selenide (4a) as a yellow oil.
hν
(> 300 nm)
(PhSe)2
PhSe
This work was supported by a Grant-in-Aid for Scientific
Research on Priority Areas ‘‘Advanced Molecular Transforma-
tions of Carbon Resources’’ (Area 444, No. 19020061) and
Scientific Research (B, No. 19350095), from the Ministry of
Education, Culture, Sports, Science and Technology, Japan.
1a
SePh
SPh
PhSH
PhS
PhSH
PhS
References
1
Selenium in Biology and Human Health, ed. by R. F. Burk,
Springer-Verlag, New York, 1994.
a) A. Ogawa, H. Tanaka, H. Yokoyama, R. Obayashi, K.
SePh
PhCh
SPh
2
4a
3a
Yokoyama, N. Sonoda, J. Org. Chem. 1992, 57, 111. b) A.
Ogawa, R. Obayashi, N. Sonoda, T. Hirao, Tetrahedron Lett.
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Doi, T. Hirao, J. Org. Chem. 1999, 64, 86. f) K. Tsuchii, Y.
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Yamamoto, K. Oshima, Wiley-VCH, Weinheim, 2004, Vol. 2,
p. 813.
PhSe
PhSeChPh
(Ch = S, Se)
PhSeSPh
PhSH
PhSe
PhSe
SePh
PhS
4a
2a
Scheme 1.
3
The diene reduction using PhSeH may proceed via (i) the
thio radical, which adds to diene 1a. Similar hydrogen abstrac-
tion by the thio group-substituted allyl radical yields an allyl
sulfide derivative 3a. Both allyl chalcogenide derivatives 3a
and 4a undergo a SH2 reaction with seleno and/or thio radi-
cal(s) to generate an allyl radical, which is captured by thiol
affording the reduction product 2a. In this reaction system,
(PhSe)2, which has excellent carbon radical capturing ability,7
inhibits the polymerization of dienes.8
In summary, a new reduction system by combining PhSH
and (PhSe)2 was developed, which is useful for the reduction
of conjugate dienes. We are now investigating the reduction
behavior of this system in the presence of oxidizing reagents,
such as H2O2 or O2.
addition of the selenol to diene to form allylic selenide; (ii) the
generation of allylic radical from allylic selenide upon photo-
irradiation or by the attack of seleno radical; (iii) hydrogen
abstraction from PhSe–H. For the radical trapping abilities of
PhSe–H: kPhSe{H ¼ 2:0 ꢂ 109 Mꢃ1 sꢃ1, see: M. Newcomb, M. B.
Manek, J. Am. Chem. Soc. 1990, 112, 9662.
4
For the synthesis of 2,3-dimethyl-2-butenyl phenyl sulfide
(3a), see for example: A. A. Oswald, K. Griesbaum, W. A. Thaler,
B. E. Hudson, Jr., J. Am. Chem. Soc. 1962, 84, 3897.
5
405.
6
U. Schmidt, A. Muller, K. Markau, Chem. Ber. 1964, 97,
¨
The capturing rate constant of PhSH to Barton PTOC ester:
kPhS{H ¼ 1:1 ꢂ 108 Mꢃ1 sꢃ1. See for example: J. A. Franz, B. A.
Bushaw, M. S. Alnajjar, J. Am. Chem. Soc. 1989, 111, 268.
7
Experimental
The rate constants for the SH2 reaction of 5-hexenyl radical
,
General Procedure for the Photoinduced Reduction of Con-
jugate Dienes with Benzenethiol and Diphenyl Diselenide. In a
Pyrex glass tube (ꢃ ¼ 5 mm, length = 180 mm) were placed
2,3-dimethyl-1,3-butadiene (1a, 11 mL, 0.1 mmol), benzenethiol
(31 mL, 0.3 mmol), diphenyl diselenide (62.4 mg, 0.2 mmol), and
CDCl3 (0.5 mL) under nitrogen atmosphere. After irradiation with
a xenon lamp (500 W) at ambient temperature for 96 h, 2,3-
dimethyl-2-butene (2a) was obtained in 82% yield.
with (PhS)2 and (PhSe)2 are 7:6 ꢂ 104 and 1:2 ꢂ 107 Mꢃ1 sꢃ1
respectively. See for example: a) G. A. Russell, H. Tashtoush,
J. Am. Chem. Soc. 1983, 105, 1398. b) M. J. Perkins, E. S. Turner,
J. Chem. Soc., Chem. Commun. 1981, 139. c) G. A. Russell, P.
Ngoviwatchai, H. I. Tashtoush, A. Pla-Dalmau, R. K. Khanna,
J. Am. Chem. Soc. 1988, 110, 3530.
8
The photoinduced reaction of conjugate dienes with (PhS)2
causes the polymerization of dienes, whereas the same reaction in
the presence of (PhSe)2 successfully afforded the thioselenated
dienes without the formation of any polymerization products (see:
Ref. 2b).
Synthesis of 2,3-Dimethyl-2-butenyl Phenyl Selenide (4a).
In a two-necked flask (30 mL) were placed 2,3-dimethyl-1,3-buta-
diene (1a, 1.2 mL, 11 mmol) and benzeneselenol (1.1 mL, 5.0