Vanadium-catalyzed sulfenylation of indoles and 2-naphthols with thiols under molecular oxygen

Article abstract of DOI:10.1021/jo048758e

Vanadium oxyacetylacetonate [VO(acac)₂] works as a catalyst for the direct synthesis of 3-sulfanylindoles from indoles and thiols under an atmospheric pressure of molecular oxygen as a reoxidant. For example, the reaction of 2-phenylindole with benzenethiol in the presence of a catalytic amount of VO(acac)₂, potassium iodide, and 2,6-di-tert-butyl-p-cresol in chlorobenzene under molecular oxygen proceeds to afford 2-phenyl-3- (phenylsulfanyl)indole in 86% yield. This catalytic system can also be applied to 2-naphthols instead of indoles to give the corresponding 1-sulfanyl-2- naphthols in up to 57% yield.

Full text of DOI:10.1021/jo048758e

Va n a d iu m -Ca ta lyzed Su lfen yla tion of In d oles a n d 2-Na p h th ols
w ith Th iols u n d er Molecu la r Oxygen
Yasunari Maeda, Motonori Koyabu, Takahiro Nishimura,* and Sakae Uemura*
Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University,
Nishikyo-ku, Kyoto 615-8510, J apan
takahiro@scl.kyoto-u.ac.jp; uemura@scl.kyoto-u.ac.jp
Received J uly 20, 2004
Vanadium oxyacetylacetonate [VO(acac)2] works as a catalyst for the direct synthesis of 3-sulfan-
ylindoles from indoles and thiols under an atmospheric pressure of molecular oxygen as a reoxidant.
For example, the reaction of 2-phenylindole with benzenethiol in the presence of a catalytic amount
of VO(acac)2, potassium iodide, and 2,6-di-tert-butyl-p-cresol in chlorobenzene under molecular
oxygen proceeds to afford 2-phenyl-3-(phenylsulfanyl)indole in 86% yield. This catalytic system
can also be applied to 2-naphthols instead of indoles to give the corresponding 1-sulfanyl-2-naphthols
in up to 57% yield.
In tr od u ction
phthalic acid,8 and unique organic reactions using them
as catalysts have appeared in recent years.9 Recently, we
have reported the vanadium-complex-catalyzed oxidation
of propargylic alcohols under an atmospheric pressure
of molecular oxygen.10 During the course of our further
studies on this subject, we found that some vanadium
complexes worked as efficient catalysts for the direct
synthesis of 3-sulfanylindoles from thiols and indoles in
the presence of an atmospheric pressure of molecular
oxygen. Moreover, the use of 2-naphthols as substrates
instead of indoles resulted in a formation of the corre-
sponding 1-sulfanyl-2-naphthols, which could be used as
agricultural chemicals for powdery mildew.11 We report
herein the direct catalytic synthesis of 3-sulfanylindoles
Indole derivatives have been well-known as important
compounds such as biologically active substances and
intermediates of many pharmaceuticals. Especially, 3-su-
fanylindoles are of interest as the precursors of anti-HIV
active compounds,1 antinociceptive active compounds,2
5-lipoxygenase inhibitors,3 organic nonlinear optical ma-
terials,4 etc. Although many useful methods of sulfenyl-
ation at the 3-position of indoles have been reported using
a variety of reagents such as succinimide-sulfonium salt,
sulfenic acid chloride, acyloxysulfonium salt, sulfide,
disulfide, mono-O,S-acetal, etc., most of them need sto-
ichiometric amounts of the reagents.5 On the other hand,
direct synthetic methods of 3-sulfanylindoles from indoles
and thiols have been known, but they also need stoichio-
metric amounts of organic or inorganic reagents such as
I2,6a,b N-chlorosuccinimide,6c and phenyliodine(III)bis-
(trifluoroacetate).6d One catalytic method for substitution
by sulfur moiety at the 3-position of indole with disulfide
using AlCl3 as a catalyst has been reported, but severe
reaction conditions were required and the yield of 3-sul-
fanylindole was relatively low.7
(5) (a) Woodbridge, R. G.; Dougherty, G. J . Am. Chem. Soc. 1950,
72, 4320. (b) Harris, R. L. N. Tetrahedron Lett. 1969, 10, 4465. (c)
Kisaki, S.; Tominaga, Y.; Matsuda, Y.; Kobayashi, G. Chem. Pharm.
Bull. 1974, 22, 2246. (d) Hocker, J .; Ley, K.; Merten, R. Synthesis 1975,
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729. (f) Anzai, K. J . Heterocycl. Chem. 1979, 16, 567. (g) Raban, M.;
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F.; Ottenheijm, H. C. J . Tetrahedron 1986, 42, 4503. (i) Atkinson, J .
G.; Hamel, P.; Girard, Y. Synth. Commun. 1988, 6, 480. (j) Hartke,
K.; Teuber, D.; Gerber, H.-D. Tetrahedron 1988, 44, 3261. (k) J ain, S.;
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Copeland, J . N.; Kelly, K. E. J . Heterocycl. Chem. 1991, 28, 1025. (m)
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K.; Kita, Y. Chem. Commun. 1997, 1387. (o) J oule, J . A. In Science of
Synthesis; Thomas, J . E., Ed.; Georg Thieme Verlag: Stuttgard, New
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Murata, K.; Gotanda, K.; Nambu, H.; Kita, Y. Tetrahedron Lett. 2001,
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Anilkumar, G.; Matsumoto, K.; Kita, Y. J . Org. Chem. 2001, 66, 2434.
(r) Shevchenko, N. E.; Nenajdenko, V. G.; Balenkova, E. S. Synthesis
2003, 1191.
Vanadium compounds have been known as important
oxidation catalysts for the synthesis of acids such as
* To whom correspondence should be addressed. Tel/Fax: +81-75-
383-2517.
(1) (a) Williams, T. M.; Ciccarone, T. M.; MacTough, S. C.; Rooney,
C. S.; Balani, S. K.; Condra, J . H.; Emini, E. A.; Goldman, M. E.;
Greenlee, W. J .; Kauffman, L. R.; O’Brien, J . A.; Sardana, V. V.; Schleif,
W. A.; Theoharides, A. D.; Anderson, P. S. J . Med. Chem. 1993, 36,
1291. (b) Silvestri, R.; De Martino, G.; La Regina, G.; Artico, M.; Massa,
S.; Vargiu, L.; Mura, M.; Loi, A. G.; Marceddu, T.; La Colla, P. J . Med.
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10.1021/jo048758e CCC: $27.50 © 2004 American Chemical Society
Published on Web 10/08/2004
7688
J . Org. Chem. 2004, 69, 7688-7693

Vanadium-Catalyzed Sulfenylation with Thiols
TABLE 1. Va n a d iu m -Ca ta lyzed Syn th esis of
3-(P h en ylsu lfa n yl)in d ole (3a ) u n d er Va r iou s Con d ition s
TABLE 2. Op tim iza tion of th e Rea ction
isolated
yield
isolated
2a
VO(acac)2 PhCl time conversion
conversion
yield
entry (mmol)
(mmol)
(mL) (h)
of 1a (%) of 3a (%)a
entry
solvent
toluene
acetonitrile
ClCH2CH2Cl
catalyst
of 1a (%) of 3a (%)a
1
2
3
2
2
1
5
2
2
2
2
2
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.05
0.01
1
0.5
1
1
1
1
1
1
1
12
12
12
12
12
48
72
48
48
60
56
51
85
9
65
90
30
0
38
32
16
33
tr
44
42
6
1
2
3
VO(acac)2
VO(acac)2
VO(acac)2
43
20
59
60
1
23
2
16
38
0
4
4
ch lor oben zen e VO(a ca c)2
5b
6
5
6
7
8
9
10
11
DMF
ethanol
VO(acac)2
VO(acac)2
V(acac)3
VO(hfac)2
VOCl3
2
tr
7
chlorobenzene
chlorobenzene
chlorobenzene
chlorobenzene
chlorobenzene
60
44
44
1
32
26
28
tr
8
9c
-
Based on 1a employed. MS3Å (250 mg) was added. c Under
a
b
VOSO4‚nH2O
V2O5
N2 (1 atm).
1
tr
a
Based on 1a employed.
and Table 1, entry 1). Among solvents examined such as
acetone, 1,2-dichloroethane, chlorobenzene, N,N-dimeth-
ylformamide, and ethanol (entries 2-6), chlorobenzene
was revealed to be the solvent of choice, and 3a was
obtained in 38% yield (entry 4). Next, we examined the
reaction in chlorobenzene using other vanadium com-
pounds as catalysts in which V(acac)3, VO(hfac)2 (hfac )
1,1,1,5,5,5-hexafluoroacetylacetonate), and VOCl3 were
slightly less effective than VO(acac)2 (entries 7-9). The
use of VOSO4‚nH2O and V2O5 did not give any 3a (entries
10 and 11). Some other transition metal compounds such
as (NH4)2Ce(NO3)6, Ti(OiPr)4, ZrCl4, MoO2(acac)2, Mn-
(OAc)2‚4H2O, Fe(OAc)2, Co(OAc)2‚4H2O, Ni(acac)2, Pd-
(acac)2, and CuCl were found to be completely ineffective
for this reaction.
SCHEME 1
and 1-sulfanyl-2-naphthols by reactions of indoles and
2-naphthols with thiols, respectively.
Resu lts a n d Discu ssion
Va n a d iu m -Ca ta lyzed Syn th esis of 3-Su lfa n ylin -
d oles fr om In d oles a n d Th iols u n d er Molecu la r
Oxygen . First, indole (1a ) and benzenethiol (2a ) were
chosen as substrates, and their reaction was examined
under various reaction conditions (Table 1). Treatment
of 1a (1 mmol) and 2a (2 mmol) in toluene (1 mL) in the
presence of a catalytic amount of VO(acac)2 (0.01 mmol)
at 60 °C for 12 h under an atmospheric pressure of
molecular oxygen gave 3-(phenylsulfanyl)indole (3a ) in
23% yield together with diphenyl disulfide (1.38 mmol,
69% yield) and some unidentified compounds (Scheme 1
Next, the effect of the amount of a catalyst and a
solvent was investigated (Table 2). The reaction in a
higher concentration of substrates did not improve the
yield of 3a (entry 2). Increasing or reducing of the amount
of 2a decreased the yield of 3a (entries 3 and 4). When
MS3Å was added as a dehydrating agent in this reaction
mixture, 3a was not obtained at all and diphenyl disulfide
was formed selectively (1.9 mmol, 95% yield) (entry 5).
Although a higher yield of 3a was attained after 48 h
(entry 6), the yield of 3a was not improved by prolonging
the reaction time further irrespective of higher conversion
of 1a (entry 7). When the amount of catalyst was
increased, the yield of 3a diminished due to the prefer-
ential formation of diphenyl disulfide (entry 8). The
reaction under nitrogen atmosphere did not afford 2a at
all, suggesting that the presence of molecular oxygen is
essential for this reaction (entry 9).
(9) For examples, see: (a) Hirao, T. Chem. Rev. 1997, 97, 2707 and
references therein. (b) Kirihara, M.; Takizawa, S.; Momose, T. J . Chem.
Soc., Perkin Trans. 1 1998, 7. (c) Hwang, D.-R.; Chen, C.-P.; Uang,
B.-J . Chem. Commun. 1999, 1207. (d) Kirihara, M.; Ochiai, Y.; Arai,
N.; Takizawa, S.; Momose, T. Nemoto, H. Tetrahedron Lett. 1999, 40,
9055. (e) Ishii, Y.; Matsunaka, K.; Sakaguchi, S. J . Am. Chem. Soc.
2000, 122, 7390. (f) Hon, S.-W.; Li, C.-H.; Kuo, J .-H.; Barhate, N. B.;
Liu, Y.-H.; Wang, Y.; Chen, C.-T. Org. Lett. 2001, 3, 869. (g) Chu, C.-
Y.; Hwang, D.-R.; Wang, S.-K.; Uang, B.-J . Chem. Commun. 2001, 980.
(h) Trost, B. M.; Oi, S. J . Am. Chem. Soc. 2001, 123, 1230. (i) Hirao,
T.; Morimoto, C.; Takada, T.; Sakurai, H. Tetrahedron 2001, 57, 5073.
(j) Trost, B. M.; J onasson, C.; Wuchrer, M. J . Am. Chem. Soc. 2001,
123, 12736. (k) Hwang, D.-R.; Uang, B.-J . Org. Lett. 2002, 4, 463. (l)
Luo, Z.; Liu, Q.; Gong, L.; Cui, X.; Mi, A.; J iang, Y. Chem. Commun.
2002, 914. (m) Barhate, N. B.; Chen, C.-T. Org. Lett. 2002, 4, 2529.
(n) Chu, C.-Y.; Uang, B.-J . Tetrahedron: Asymmetry 2003, 14, 53. (o)
Trost, B. M.; J onasson, C. Angew. Chem., Int. Ed. 2003, 42, 2063. (p)
Somei, H.; Asano, Y.; Yoshida, T.; Takizawa, S.; Yamataka, H.; Sasai,
H. Tetrahedron Lett. 2004, 45, 1841.
Further, the effect of additives was examined in order
to improve the yield of 3a (Table 3). When the reaction
was carried out in the presence of 10 mol % KI under
the same reaction conditions of entry 6 of Table 2, the
yield of 3a increased up to 66% yield (entry 2).12 Other
additives such as NaI, CsI, KBr, LiCl, and n-Bu4NI were
not effective (entries 3-6). Any appreciable improvement
of the yield of 3a was not observed by increasing or
decreasing the amount of KI (entries 7 and 8).
(10) (a) Maeda, Y.; Kakiuchi, N.; Matsumura, S.; Nishimura, T.;
Uemura, S. Tetrahedron Lett. 2001, 42, 8877. (b) Maeda, Y.; Kakiuchi,
N.; Matsumura, S.; Nishimura, T.; Kawamura, T.; Uemura, S. J . Org.
Chem. 2002, 67, 6718.
(11) Magee, P. S. United States Patent 3,409,724; Chem. Abstr.
1969, 70, 95745.
(12) The combination of a stoichiometric amount of I2 and KI was
used in the synthesis of 3-sulfanylindoles from indoles and thiols; see
ref 6a and b.
J . Org. Chem, Vol. 69, No. 22, 2004 7689

Maeda et al.
TABLE 3. Effect of Ad d itive
about the reaction pathway. Surprisingly, the addition
of BHT dramatically accelerated the reaction, and 3a was
obtained in 75% yield within 12 h (entry 3). The combi-
nation of BHT and KI was revealed to be essential for
obtaining 3a in higher yield (entry 4). The presence of
BHT might prevent the radical reaction of thiols forming
diphenyl disulfide. These results show that the optimized
reaction condition is the use of indole (1 mmol) and thiol
(2 mmol) in the presence of catalytic amounts of VO-
(acac)2 (1 mol %), KI (10 mol %), and BHT (5 mol %) at
60 °C for 12 h in chlorobenzene (1 mL) under an
atmospheric pressure of molecular oxygen.
isolated
yield
additive
conversion
of 1a (%)
entry
(mmol)
of 2a (%)a
1
2
3
4
5
6
7
8
none
KI (0.1)
65
90
57
65
64
1
44
66
34
30
16
0
NaI (0.1)
KBr (0.1)
LiCl (0.1)
n-Bu4NI (0.1)
KI (0.05)
KI (0.2)
Results of the synthesis of a variety of 3-sulfanylindoles
under the above optimized reaction conditions are sum-
marized in Table 5. Reactions of 1a with some ben-
zenethiols, except for the one having a substituent at the
ortho position (entry 2), smoothly gave the corresponding
3-sulfanylindoles in good yields (entries 3-7). The use
of benzyl mercaptan (2h ) as a substrate also gave the
corresponding 3-sulfanylindole (3h ) in good yield (entry
8). This reaction system could be applied for some
alkanethiols such as 2i and 2j, giving the corresponding
3-sulfanylindole 3i and 3j in moderate yield (entries 9
and 10), whereas the treatment of 2-methyl-2-propaneth-
iol (2k ) with indole did not give any corresponding
product (entry 11). Next, we examined the reaction of
substituted indoles with 2a . In all cases, except for the
use of indole having a 2-ethoxycarbonyl group (1e), the
corresponding 3-sulfanylindoles were obtained in moder-
ate to high yield (entries 12-18).
80
69
60
57
a
Based on 1a employed.
TABLE 4. Effect of th e Am ou n t of BHT
isolated
yield
BHT
conversion
entry
(mmol)
of 1a (%)
of 3a (%)a
1
2
3
4
5
6
7
0
60
97
99
95
99
69
58
38
67
75
34b
60c
47
0.02
0.05
0.05
0.05
0.1
1
30
Va n a d iu m -Ca ta lyzed Syn th esis of 1-Su lfa n yl-2-
n a p h th ols fr om 2-Na p h th ols a n d Th iols u n d er Mo-
lecu la r Oxygen . This vanadium-catalyzed sulfenylation
was then applied to 2-naphthol (4a ). Treatment of 4a
with 2a in the presence of a catalytic amount of VO(acac)2
in toluene under an atmospheric pressure of molecular
a
b
Based on 1a employed. In the absence of KI. c For 24 h.
The reaction in the presence of a radical inhibitor such
as 2,6-di-tert-butyl-p-cresol (butylhydroxytoluene, BHT)
was next examined in order to obtain some information
TABLE 5. Va n a d iu m -Ca ta lyzed Syn th esis of 3-Su lfa n ylin d oles u n d er Molecu la r Oxygen
isolated
yield
conversion
of 1 (%)
entry
R
R′
time (h)
product
of 2 (%)a
1
2
3
4
5
6
7
8
H (1a )
H (1a )
H (1a )
H (1a )
H (1a )
H (1a )
H (1a )
H (1a )
H (1a )
H (1a )
H (1a )
N-Me (1b)
2-Me (1c)
2-Ph (1d )
2-CO2Et (1e)
3-Me (1f)
5-Me (1g)
5-Cl (1h )
Ph (2a )
12
12
12
12
12
12
12
48
48
48
48
48
12
12
48
12
12
48
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3n
3o
3p
3q
3r
99
57
91
79
98
80
92
58b
99
15
49
93
86
22
24
54
99
80
75
29
80
65
74
70
75
77
43b
45
0
2-MeC6H4 (2b)
3-MeC6H4 (2c)
4-MeC6H4 (2d )
4-ClC6H4 (2e)
4-MeOC6H4 (2f)
4-NO2C6H4 (2g)
PhCH2 (2h )
C8H17 (2i)
9
10
11
12
13
14
15
16
17
18
(CH2)2COOEt (2j)
tBu (2k )
Ph (2a )
Ph (2a )
Ph (2a )
Ph (2a )
Ph (2a )
Ph (2a )
Ph (2a )
26
85
86
0
47c
70
60
a
b
Based on indole employed. Isolated by HPLC. c 3-Methyl-2-(phenylsulfanyl)indole.
7690 J . Org. Chem., Vol. 69, No. 22, 2004

Vanadium-Catalyzed Sulfenylation with Thiols
TABLE 6. Solven t Effect
TABLE 8. Va n a d iu m -Ca ta lyzed Syn th esis of
1-Su lfa n yl-2-n a p h th ol u n d er Molecu la r Oxygen
isolated
yield
time
(h)
conversion
of 4a (%)
entry
solvent
tolu en e
chlorobenzene
DMF
CH3CN
DMSO
of 5a (%)a
isolated
yield
1
2
3
4
24
24
21
21
42
19
93
96
100
45
7
62
20
0
28
25
0
time
entry
R
R′
Ph (2a )
4-MeC6H4 (2d )
4-ClC6H4 (2e)
tBu (2k )
C8H17 (2i)
Cy (2l)
Ph (2a )
(h) product of 2 (%)a,b
1
2
3
4
5
6
7
8
H (4a )
H (4a )
H (4a )
H (4a )
H (4a )
H (4a )
6-Br (4b)
16
26
19
27
24
18
19
19
5a
5b
5c
5d
5e
5f
44
27
25
26
24
24
57
47
2
5
tr
10
-
6
ClCH2CH2Cl
ethanol
7b
a
b
Based on 4a employed. At 70 °C.
5g
5h
7-MeO (4c) Ph (2a )
TABLE 7. Op tim iza tion of th e Rea ction
a
b
Based on 4 employed. 4 was consumed completely in all
reactions.
SCHEME 3
isolated
yield
2a
(mmol)
VO(acac)2
(mol %)
time
(h)
conversion
of 4a (%)
entry
of 5a (%)a
1
2
3
4
2
2
2
2
1
5
2
2
1
2
5
10
5
5
24
16
16
23
26
23
26
24
96
100
100
95
91
100
93
28
34
44
36
20
39
5
5
6
7b
8c
5
5
5
tr
a
b
Based on 4a employed. KI (0.1 mmol) was added. c Under
N2 (1 atm).
react with indole, reacted to give 1-(tert-butylsulfanyl)-
2-naphthol (5e) (entry 5). Next, the reaction of some
2-naphthol derivatives with benzenethiol (2a ) was ex-
amined. Thus, from 6-bromo-2-naphthol (4b) and 7-meth-
oxy-2-naphthol (4c), 6-bromo-1-(phenylsulfanyl)-2-naph-
thol (5g) and 7-methoxy-1-(phenylsulfanyl)-2-naphthol
(5h ) were obtained in moderate yields (entries 7 and 8).
3,5-Dimethoxyphenol (6) could be used as a substrate
instead of 2-naphthol, and the reaction of 6 with ben-
zenethiol or 2-methyl-2-propanethiol gave the corre-
sponding 3,5-dimethoxy-2-sulfanylphenol, respectively,
but the yield was low (Scheme 3).
P la u sible Rea ction P a th w a y. The reaction seems
to be electrophilic in nature since (i) the reactivity as well
as the orientation of the substituted indoles are similar
to those of other known electrophilic substitution reac-
tions of indoles6a and (ii) a radical scavenger such as BHT
does not inhibit this reaction. A proposed catalytic cycle
mechanism is shown in Figure 1 that is a similar to one
assumed by Uang9k for a vanadium-catalyzed Mannich-
type reaction. First, a vanadium(IV) species (A) reacts
with thiol and molecular oxygen to form a vanadium(V)
species (B). An electrophilic sulfur moiety in species B
reacts with indoles or 2-naphthols to give the correspond-
ing 3-sulfanylindoles or 1-sulfanyl-2-naphthols and a
hydroxyvanadium(III) species (C). Dehydration from
species C gives an oxovanadium(III) species (D). The
species D is transformed to dioxovanadium(V) species (E)
by oxidation with molecular oxygen, and the successive
reaction of E with thiols reproduces species B, furnishing
a catalytic cycle in vanadium.
SCHEME 2
oxygen at 80 °C for 24 h gave 1-(phenylsulfanyl)-2-
naphthol (5a ) in 28% yield (Scheme 2 and Table 6, entry
1). Among solvents examined, toluene was revealed to
be the solvent of choice. Similarly to the sulfenylation of
indoles, VO(acac)2 was the most efficient catalyst within
a variety of vanadium salts examined, such as V(acac)3,
VO(hfac)2, VO(tfac)2, VO(hfdm)2, VOSO4‚nH2O, VO(C2O4),
and V2O5.
Attempts to optimize this reaction are summarized in
Table 7. The reaction in the presence of 5 mol % of VO-
(acac)2 gave 5a in 44% yield (entries 1-4). Increasing or
decreasing of the amount of 2a did not improve the yield
of 3a (entries 5 and 6). Although the addition of KI was
beneficial in the case of indole sulfenylation, a decrease
in the yield was observed in the naphthol sulfenylation
case (entry 7). When this reaction was carried out under
nitrogen atmosphere, 4a was not converted to 5a at all
(entry 8). This result shows that the presence of molec-
ular oxygen is essential for this reaction as well.
Using 5 mol % catalyst, the reactions of 2-naphthol
with some thiols were carried out (Table 8). Although
2-naththol was consumed completely in all cases, the
yields of the corresponding 1-sulfanyl-2-naphthols were
low (entries 2-6). Interestingly, thiol 2k , which could not
J . Org. Chem, Vol. 69, No. 22, 2004 7691

Maeda et al.
Florisil. For isolation of the product, the solvent was evapo-
rated and the residue was purified by column chromatography
(n-hexane-ethyl acetate as an eluent). Isolation of 3i was
carried out using preparative HPLC after column chromatog-
raphy because a small amount of unidentified products could
not be separated from the major product by column chroma-
tography.
3-(m -Tolylsu lfa n yl)in d ole6a (3c; Ta ble 5, En tr y 3). White
1
solid; mp 124.4-125.0 °C; H NMR (300 MHz, CDCl3) δ 2.18
(s, 3H), 6.85 (t, J ) 7.0 Hz, 2H), 7.00-7.03 (m, 2H), 7.13 (td,
J ) 7.4, 1.1 Hz, 1H), 7.22 (td, J ) 7.4, 1.1 Hz, 1H), 7.31 (dd,
J ) 5.4, 2.6 Hz, 2H), 7.60 (d, J ) 8.0 Hz, 1H), 8.12 (br s, 1H,
NH); 13C NMR (75.5 MHz, CDCl3) δ 21.3, 102.6, 111.6, 119.5,
120.8, 122.9, 122.9, 125.7, 126.4, 128.6, 129.0, 130.7, 136.3,
138.4, 138.9.
3-(p-Tolylsu lfa n yl)in d ole6a (3d ; Ta ble 5, En tr y 4). White
1
solid; mp 125.0-126.0 °C; H NMR (300 MHz, CDCl3) δ 2.21
(s, 3H), 6.94 (d, J ) 8.0 Hz, 2H), 7.02 (d, J ) 8.0 Hz, 2H), 7.13
(td, J ) 1.2, 8.0 Hz, 1H), 7.23 (td, J ) 1.2, 8.0 Hz, 1H), 7.31-
F IGURE 1. Plausible reaction pathway.
7.34 (m, 2H), 7.60 (d, J ) 8.0 Hz, 1H), 8.14 (br s, 1H, NH); 13
C
NMR (75.5 MHz, CDCl3) δ 20.9, 103.1, 111.5, 119.5, 120.7,
122.8, 126.1, 128.9, 129.4, 130.4, 134.5, 135.3, 136.3.
Con clu sion
3-(4-Ch lor op h en ylsu lfa n yl)in d ole6a (3e; Ta ble 5, En tr y
5). White solid; mp 127.5-128.3 °C; 1H NMR (300 MHz,
CDCl3) δ 7.00 (dt, J ) 8.8, 2.4 Hz, 2H), 7.09 (dt, J ) 8.8, 2.4
Hz, 2H), 7.16 (td, J ) 7.2, 1.1 Hz, 1H), 7.26 (td, J ) 7.2, 1.1
Hz, 1H), 7.38-7.43 (m, 2H), 7.56 (d, J ) 7.2 Hz, 1H), 8.33 (br
s, 1H, NH); 13C NMR (75.5 MHz, CDCl3) δ 102.3, 111.6, 119.4,
121.0, 123.2, 127.0, 128.7, 128.7, 130.5, 136.4, 137.7.
We found that vanadium oxyacetylacetonate [VO-
(acac)2] was an effective catalyst for the direct synthesis
of 3-sulfanylindoles (up to 86% yield) and 1-sulfanyl-2-
naphthols (up to 57% yield) from the reaction of indoles
and 2-naphthols with thiols, respectively, in chloroben-
zene or toluene under an atmospheric pressure of mo-
lecular oxygen. The addition of catalytic amounts of
potassium iodide and 2,6-di-tert-butyl-p-cresol improved
the yield of 3-sulfanylindoles. This catalytic reaction did
not proceed at all under a nitrogen atmosphere. The
reaction mechanism appears to be electrophilic in nature.
3-(n -Octylsu lfa n yl)in d ole5e (3i; Ta ble 5, En tr y 9). Pale
yellow liquid; 1H NMR (300 MHz, CDCl3) δ 0.86 (t, J ) 6.2
Hz, 3H), 1.23-1.35 (m, 10H), 1.53 (quint, J ) 7.3 Hz, 2H),
2.69 (t, J ) 7.3 Hz, 2H), 7.17-7.34 (m, 4H), 7.77 (d, J ) 6.6
Hz, 1H), 8.13 (br s, 1H, NH); 13C NMR (75.5 MHz, CDCl3) δ
14.1, 22.7, 28.6, 29.2, 29.9, 31.8, 36.5, 106.1, 111.4, 119.3, 120.2,
122.5, 129.1, 129.3, 136.1; IR (neat, cm-1) 3408, 2925, 2853,
1453, 1406, 1340, 1235, 1091, 1008, 1023, 743. Anal. Calcd
for C16H23NS: C, 73.51; H, 8.87. Found: C, 73.80; H, 9.04.
Eth yl 3-(3-in d oylth io)p r op ion a te15 (3j; Ta ble 5, En tr y
Exp er im en ta l Section
Gen er a l Meth od s. 1H NMR spectra were obtained in
CDCl3 at 270, 300, or 400 MHz with Me4Si as an internal
standard. 13C NMR spectra were obtained at 67.5, 75.5, or 100
MHz.
1
10). Pale green liquid; H NMR (300 MHz, CDCl3) δ 1.21 (t,
J ) 7.2 Hz, 3H), 2.53 (t, J ) 7.2 Hz, 2H), 2.93 (t, J ) 7.2 Hz,
2H), 4.08 (t, J ) 7.2 Hz, 2H), 7.19-7.24 (m, 2H), 7.29 (d, J )
2.6 Hz, 1H), 7.33-7.37 (m, 1H), 7.76-7.79 (m, 1H), 8.45 (br s,
1H, NH); 13C NMR (75.5 MHz, CDCl3) δ 14.1, 31.0, 35.1, 60.6,
104.3, 111.5, 119.1, 120.5, 122.7, 129.3, 130.1, 136.3, 172.2
(CdO); IR (neat, cm-1) 3401, 2979, 1719, 1453, 1410, 1339,
1236, 1094, 1009, 745. Anal. Calcd for C13H15NO2S: C, 62.62;
H, 6.06. Found: C, 62.88; H, 6.11.
Ma ter ia ls. Commercially available organic and inorganic
compounds were used without further purification except for
the solvent, which was distilled by the usual method before
use. VO(tfac)2, VO(hfac)2, and VO(hfdm)2 were synthesized by
literature methods.13 All indoles, 2-naphthols, thiols, and 3,5-
dimethoxyphenol were commercial products. Sulfanylindoles
3a , 3h , and 3m were commercial products. Other sulfanylin-
doles and 1-sulfanyl-2-naphthols 5a 14 and 5e11 are known
compounds and characterized by their spectral data. 1-Sul-
fanyl-2-naphthols 5b, 5c, 5d , 5f, 5g, and 5h and 3,5-dimeth-
oxysulfanylphenols 7a , 7b, and 8 are new compounds. Some
selected spectral data of sulfanylindoles and 1-sulfanyl-2-
naphthols are shown below.
Gen er a l P r oced u r e for Va n a d iu m -Ca ta lyzed Syn th e-
sis of 3-Su lfa n ylin d oles fr om In d oles a n d Th iols u n d er
Molecu la r Oxygen . To a solution of VO(acac)2 (2.65 mg,
0.0100 mmol) in chlorobenzene (0.500 mL) in a 20-mL Schlenk
flask were added potassium iodide (16.7 mg, 0.100 mmol) and
2,6-di-tert-butyl-p-cresol (11.0 mg, 0.0500 mmol). Next, indole
(1.00 mmol) and thiol (2.00 mmol) in chlorobenzene (0.5 mL)
were added, and the resulting mixture was stirred. Oxygen
gas was then introduced into the flask from an O2 balloon
under atmospheric pressure, and then the mixture was stirred
vigorously for 12 h at 60 °C under oxygen. The mixture was
cooled to room temperature and filtered through a pad of
3-Meth yl-2-(p h en ylsu lfa n yl)in d ole5o (3p ; Ta ble 5, En tr y
16). White solid; mp 73.8-74.8 °C; 1H NMR (300 MHz, CDCl3)
δ 2.40 (s, 3H), 7.03-7.31 (m, 8H), 7.60 (d, J ) 7.8 Hz, 1H),
7.97 (br s, 1H, NH); 13C NMR (75.5 MHz, CDCl3) δ 9.4, 110.8,
119.4, 119.6, 119.9, 121.5, 123.5, 125.7, 126.5, 128.5, 129.1,
136.8, 137.1; IR (KBr, cm-1) 3375, 3056, 2908, 1579, 1476,
1448, 1330, 1288, 1239, 1082, 1022, 975, 964, 752, 739, 687,
651, 580, 485. Anal. Calcd for C15H13NS: C, 75.27; H, 5.47.
Found: C, 74.98; H, 5.43.
5-Meth yl-3-(p h en ylsu lfa n yl)in d ole16 (3q; Ta ble 5, En tr y
17). White solid; mp 153.0-154.0 °C; 1H NMR (300 MHz,
CDCl3) δ 7.01-7.18 (m, 6H), 7.28 (d, J ) 8.0 Hz, 1H), 7.38-
7.40 (m, 2H), 8.21 (br s, 1H, NH); 13C NMR (75.5 MHz, CDCl3)
δ 21.4, 101.8, 111.2, 119.1, 124.6, 124.7, 125.6, 128.7, 129.3,
130.4, 130.9, 134.7, 139.4.
5-Ch lor o-3-(p h en ylsu lfa n yl)in d ole17 (3r ; Ta ble 5, En tr y
18). White solid; mp 112.5-113.5 °C; 1H NMR (300 MHz,
CDCl3) δ 7.04-7.24 (m, 6H), 7.33 (d, J ) 8.6 Hz, 1H), 7.48 (d,
J ) 2.6 Hz, 1H), 7.58 (d, J ) 1.5 Hz, 1H), 8.43 (br s, 1H, NH);
13C NMR (75.5 MHz, CDCl3) δ 102.8, 112.7, 119.1, 123.5, 125.0,
(13) (a) Su, C.-C.; Reed, J . W.; Gould, E. S. Inorg. Chem. 1973, 12,
337. (b) Pesiri, D. R.; Morita, D. K.; Walker, T.; Tumas, W. Organo-
metallics 1999, 18, 4916.
(14) Voronkov, M. G.; Deryagina, E. N.; Papernaya, L. K. Russian
Patent 997407; Chem. Abstr. 1985, 103, 104695.
(15) Hamel, P.; Girard, M. J . Heterocycl. Chem. 1996, 33, 1695.
(16) Wieland, T.; Ru¨hl, K. Chem. Ber. 1963, 96, 260.
(17) Hary, U.; Roettig, U.; Paal, M. Tetrahedron Lett. 2001, 42, 5187.
7692 J . Org. Chem., Vol. 69, No. 22, 2004

Vanadium-Catalyzed Sulfenylation with Thiols
125.8, 126.9, 128.8, 130.3, 132.0, 134.8, 138.7; IR (KBr, cm-1
3401, 3106, 1581, 1477, 1442, 1098, 1024, 890, 870, 803, 743,
735, 689, 585, 515, 496, 425. Anal. Calcd for C14H10ClNS: C,
64.73; H, 3.88. Found: C, 64.49; H, 3.99.
)
523. Anal. Calcd for C14H16OS: C, 72.37; H, 6.94. Found: C,
72.29; H, 6.94.
1-Cycloh exylsu lfa n yl-2-n a p h th ol (5f; Ta ble 8, En tr y 6).
Pale yellow liquid; 1H NMR (300 MHz, CDCl3) δ 1.19-1.94
(m, 10H), 2.90 (tt, J ) 10.9, 3.7 Hz, 1H), 7.28 (d, J ) 8.3 Hz,
1H), 7.35 (ddd, J ) 8.3, 6.9, 1.3 Hz, 1H), 7.43 (s, 1H, OH),
7.55 (ddd, J ) 8.3, 6.9, 1.3 Hz, 1H), 7.90 (d, J ) 8.3 Hz, 2H),
8.35 (d, J ) 8.3 Hz, 1H); 13C NMR (75.5 MHz, CDCl3) δ 25.5,
26.1, 33.8, 48.2, 110.3, 116.3, 123.4, 125.0, 127.3, 128.5, 129.3,
131.4, 135.9, 156.7; IR (neat, cm-1) 3368, 2929, 1618, 1595,
1384, 1200, 1127, 816, 749. Anal. Calcd for C16H18OS: C, 74.38;
H, 7.02. Found: C, 74.36; H, 7.25.
Gen er a l P r oced u r e for Va n a d iu m -Ca ta lyzed Syn th e-
sis of 1-Su lfa n yl-2-n a p h th ols fr om 2-Na p h th ol a n d Th iols
u n d er Molecu la r Oxygen . To a solution of VO(acac)2 (13.3
mg, 0.0500 mmol) in toluene (1.0 mL) in a 20-mL Schlenk flask
were added 2-naphthol (1.00 mmol) and a solution of thiol (2.00
mmol) in toluene (1.0 mL), and the resulting mixture was
stirred. Oxygen gas was then introduced into the flask from
an O2 balloon under atmospheric pressure, and then the
mixture was stirred vigorously for 16-24 h at 80 °C under
oxygen. The mixture was then cooled to room temperature and
then filtered through a pad of Florisil. Isolation of the product
was carried out as in the case of the reaction using indole as
a substrate. Isolation of 5g was carried out using preparative
HPLC after column chromatography.
6-Br om o-1-p h en ylsu lfa n yl-2-n a p h th ol (5g; Ta ble 8, En -
1
tr y 7). White solid, mp ) 97.5-98.5 °C; H NMR (300 MHz,
CDCl3) δ 6.97 (tt, J ) 6.8, 1.7 Hz, 2H), 7.04-7.16 (m, 4H),
7.31 (d, J ) 9.0 Hz, 1H), 7.48 (dd, J ) 9.0, 2.0 Hz, 1H), 7.73
(d, J ) 9.0 Hz, 1H), 7.90 (d, J ) 2.0 Hz, 1H), 8.03 (d, J ) 9.0
Hz, 1H); 13C NMR (75.5 MHz, CDCl3) δ 108.4, 117.7, 118.0,
126.0, 126.3, 126.6, 129.2, 130.4, 130.5, 131.0, 131.7, 134.0,
134.9, 157.1; IR (KBr, cm-1) 3370, 1610, 1587, 1209, 1187,
1131, 934, 815, 734, 687. Anal. Calcd for C16H11BrOS: C, 58.02;
H, 3.35. Found: C, 57.76; H, 3.14.
1-P h en ylsu lfa n yl-2-n a p h th ol14 (5a ; Ta ble 8, En tr y 1).
1
White solid, mp ) 61.5-62.5 °C; H NMR (300 MHz, CDCl3)
δ 7.00-7.18 (m, 6H), 7.33 (d, J ) 8.8 Hz, 1H), 7.35 (ddd, J )
8.1, 6.9, 1.2 Hz, 1H), 7.47 (ddd, J ) 8.1, 6.9, 1.2 Hz, 1H), 7.79
(d, J ) 8.8 Hz, 1H), 7.89 (d, J ) 8.8 Hz, 1H), 8.22 (d, J ) 8.8
Hz, 1H); 13C NMR (75.5 MHz, CDCl3) δ 108.0, 116.8, 123.8,
124.7, 125.9, 126.3, 127.9, 128.5, 129.1, 129.5, 132.8, 135.3,
135.4, 157.0.
7-Meth oxy-1-p h en ylsu lfa n yl-2-n a p h th ol (5h ; Ta ble 8,
En tr y 8). Pale yellow liquid; 1H NMR (300 MHz, CDCl3) δ
3.78 (s, 3H), 6.97-7.19 (m, 8H), 7.53 (d, J ) 2.4 Hz, 1H), 7.67
(d, J ) 8.9 Hz, 1H), 7.78 (d, J ) 8.9 Hz, 1H); 13C NMR (75.5
MHz, CDCl3) δ 55.2, 103.7, 107.2, 114.1, 116.0, 124.6, 125.9,
126.5, 129.1, 130.1, 132.4, 135.1, 137.1, 157.4, 159.4; IR (neat,
cm-1) 3397, 1620, 1513, 1426, 1221, 1194, 1034, 835, 739, 689.
Anal. Calcd for C17H14O2S: C, 72.31; H, 5.00. Found: C, 72.02;
H, 5.02.
1-(p-Tolylsu lfa n yl)-2-n a p h th ol (5b; Ta ble 8, En tr y 2).
Yellow solid, mp ) 72.5-73.5 °C; 1H NMR (400 MHz, CDCl3)
δ 2.22 (s, 3H), 6.95 (q, J ) 8.3 Hz, 4H), 7.21 (s, 1H, OH), 7.32
(d, J ) 8.8 Hz, 1H), 7.35 (d, J ) 7.2 Hz, 1H), 7.47 (t, J ) 7.2
Hz, 1H), 7.79 (d, J ) 7.8 Hz, 1H), 7.87 (d, J ) 8.8 Hz, 1H),
8.22 (d, J ) 8.8 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 21.0,
108.6, 116.7, 123.6, 124.6, 126.5, 127.7, 128.4, 129.3, 129.8,
131.6, 132.4, 135.2, 135.7, 156.6; IR (KBr, cm-1) 3377, 1617,
1591, 1492, 1458, 1386, 1194, 1120, 811, 745, 561, 491. Anal.
Calcd for C17H14OS: C, 76.66; H, 5.30. Found C, 76.52; H, 5.30.
1-(4-Ch lor op h en ylsu lfa n yl)-2-n a p h th ol11 (5c; Ta ble 8,
3,5-Dim eth oxy-2-(p h en ylsu lfa n yl)p h en ol (7a ). White
1
solid, mp ) 66.5-67.5 °C; H NMR (270 MHz, CDCl3) δ 3.78
(s, 3H), 3.82 (s, 3H), 6.13 (d, J ) 2.4 Hz, 1H), 6.30 (d, J ) 2.5
Hz, 1H), 6.91 (s, 1H, OH) 7.04-7.23 (m, 5H); 13C NMR (67.5
MHz, CDCl3) δ 55.5, 56.2, 91.9, 92.2, 95.6, 125.4, 125.8, 128.8,
135.9, 159.4, 161.7, 163.3; IR (KBr, cm-1) 3395, 1599, 1578,
1477, 1467, 1453, 1439, 1425, 1361, 1312, 1210, 1193, 1157,
1102, 936, 818, 739, 690, 568, 483, 465. Anal. Calcd for
1
En tr y 3). Yellow solid, mp ) 105.0-106.0 °C; H NMR (270
MHz, CDCl3) δ 6.93 (d, J ) 8.6 Hz, 2H), 7.10 (s, 1H, OH), 7.13
(d, J ) 8.6 Hz, 2H), 7.32 (d, J ) 8.4 Hz, 1H), 7.37 (t, J ) 7.1
Hz, 1H), 7.59 (t, J ) 7.1 Hz, 1H), 7.81 (d, J ) 8.4 Hz, 1H),
7.91 (d, J ) 8.4 Hz, 1H), 8.15 (d, J ) 8.4 Hz, 1H); 13C NMR
(67.5 MHz, CDCl3) δ 107.4, 116.7, 123.8, 124.3, 127.4, 127.9,
128.5, 129.1, 129.3, 131.7, 132.9, 133.7, 135.0, 156.8.
C
14H14O3S: C, 64.10; H, 5.38. Found: C, 63.88; H, 5.27.
1-(ter t-Bu tylsu lfa n yl)-3,5-d im eth oxyp h en ol (7b). White
1
solid, mp ) 82.5-83.5 °C; H NMR (270 MHz, CDCl3) δ 1.29
(s, 9H), 3.81 (s, 3H), 3.81 (s, 3H), 6.07 (d, J ) 2.5 Hz, 1H),
6.24 (d, J ) 2.5 Hz, 1H), 7.31 (s, 1H, OH); 13C NMR (67.5 MHz,
CDCl3) δ 31.0, 49.1, 55.4, 55.7, 91.4, 91.6, 97.4, 160.0, 162.3,
162.6; IR (KBr, cm-1) 2932, 2856, 2211, 1709, 1671, 1450, 1243,
1165, 974, 894, 725. Anal. Calcd for C12H18O3S: C, 59.47; H,
7.49. Found: C, 59.24; H, 7.78.
1-(n -Octylsu lfa n yl)-2-n a p h th ol (5d ; Ta ble 8, En tr y 4).
1
Yellow liquid; H NMR (400 MHz, CDCl3) δ 0.86 (t, J ) 6.8
Hz, 3H), 1.21-1.35 (m, 10H), 1.54 (quint, J ) 7.2 Hz, 2H),
2.69 (t, J ) 7.2 Hz, 2H), 7.25 (d, J ) 8.8 Hz, 1H), 7.35 (t, J )
7.6 Hz, 1H), 7.40 (s, 1H, OH), 7.55 (t, J ) 7.6 Hz, 1H), 7.77 (d,
J ) 8.8 Hz, 2H), 8.34 (d, J ) 8.8 Hz, 1H); 13C NMR (100 MHz,
CDCl3) δ 14.2, 22.7, 28.9, 29.2, 29.2, 30.0, 31.8, 36.0, 111.2,
116.2, 123.3, 124.5, 127.2, 128.5, 129.2, 131.2, 135.2, 156.1;
IR (neat, cm-1) 3371, 2925, 1619, 1595, 1460, 1384, 1202, 1127,
817. 750. Anal. Calcd for C18H24OS: C, 74.95; H, 8.39. Found:
C, 74.70; H, 8.38.
3,5-Dim eth oxy-2,4-d i-(p h en ylsu lfa n yl)p h en ol (8). Col-
1
orless liquid; H NMR (400 MHz, CDCl3) δ 3.76 (s, 3H), 3.82
(s, 3H), 6.57 (s, 1H), 7.05-7.25 (m, 11H); 13C NMR (100 MHz,
CDCl3) δ 56.5, 62.5, 95.1, 103.5, 106.3, 124.8, 125.9, 126.1,
126.4, 128.6, 129.1, 135.6, 138.1, 160.6, 164.0, 165.7; IR (neat,
cm-1) 3388, 2936, 1586, 1478, 1397, 1299, 1193, 1114, 1023,
926, 824, 738, 689. Anal. Calcd for C20H18O3S2: C, 64.84; H,
4.90. Found: C, 65.04; H, 4.91.
1-(ter t-Bu tylsu lfa n yl)-2-n a p h th ol (5e; Ta ble 8, En tr y 5).
Pale yellow liquid; 1H NMR (270 MHz, CDCl3) δ 1.33 (s, 9H),
7.26 (d, J ) 8.3 Hz, 1H), 7.33 (ddd, J ) 8.3, 7.1, 1.1 Hz, 1H),
7.51 (ddd, J ) 8.3, 7.1, 1.1 Hz, 1H), 7.55 (s, 1H, OH), 7.75 (d,
J ) 8.3 Hz, 1H), 7.82 (d, J ) 8.3 Hz, 1H), 8.43 (d, J ) 8.3 Hz,
1H); 13C NMR (75.5 MHz, CDCl3) δ 31.5, 50.4, 110.0, 116.2,
123.2, 125.8, 126.9, 128.2, 129.1, 131.9, 136.8, 157.3; IR (neat,
cm-1) 3363, 2960, 1618, 1595, 1384, 1207, 1127, 819, 750, 588,
Ack n ow led gm en t. We thank Toray Co., Ltd. for an
Award in Synthetic Organic Chemistry, J apan for the
financial support to T.N.
J O048758E
J . Org. Chem, Vol. 69, No. 22, 2004 7693