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Anodic oxidation of α,β-unsaturated Sulfides to α-acetoxy ketones or α,β-diacetoxy sulfides
EIectrochimica Acta, Vol. 42, Nos. 13-14, pp. 1993-1994. 1997 0 1997 Eisevier Science Ltd. All rights reserved
Pergamon PII:
Printed in Great Britain OOlF4686/97 $17.00 + 0.00
s0013486(96)00467-7
Anodic oxidation of ar$-unsaturated sulfides to a-acetoxy ketones or a$-diacetoxy sulfides Junzo Nokami,* Satoshi Fukutake, Department
Hiroyuki Matsuura and Nobuyuki
Imai
of Applied Chemistry, Okayama University of Science, Ridai, Okayama 700, Japan
(Received 2 August 1996) Abatract-a,/I-Unsaturated sulfides can be oxidized to a-acetoxy ketones or a$-diacetoxy sulfides by electrolysis in acetic acid containing an acetate salt in an undivided cell. 0 1997 Elsevier Science Ltd. Key words: Electrolysis, a&unsaturated
sulfide, oxidation, a-acetoxy ketone, a$-diacetoxy
We have been interested in the use of organosulfur compounds in organic synthesis in view of their widespread synthetic utility, especially due to the versatile functionalization induced by the sulfur group. For example, we have succeeded in converting sulfides into a-acetoxy sulfides by electrolysis in acetic acid and, further, into a&unsaturated sulfides by thermolysis of the a-acetoxy sulfides as shown in Scheme 1 [l]. On the other hand, a few studies have been made of the two-electron electrooxidation of a&unsaturated ethers (enol ethers) and amines (enamines [2]). This background prompted us to examine the electrolysis of a&unsaturated sulfides, easily obtained via electrolysis as shown *Author to whom correspondence should be addressed.
sulfide.
above, to develop another method for versatile functionalization of sulfides (Scheme 2 [3]). For instance, ethyl 2-(phenylthio)but-2-enoate la was electrolyzed as follows. A mixture of la (141 mg, 0.6 mmol) and sodium acetate (147 mg) in acetic acid (2.2 cm’) was electrolyzed at a constant current density of 50 mA cm2 at two platinum electrodes in an undivided cell at 25°C. After passage of 5 F/mol of electricity, the solvent (acetic acid) was removed under reduced pressure, and to the residue was added ethyl acetate and then the mixture was washed with brine. The extract was dried, concentrated, and purified by column chromatography on silica gel with a mixed solvent, ethyl acetate-hexane (l/20), as an eluent to give 3-acetoxy-2-oxobutanoate 2a in 67% yield. In contrast, I-phenylthiohexene If gave 1,2-diacetoxy-1-phenylthiohexane 3f under the same reaction 2
2
thermolysis >5O’C
R1 = H, alkyl, atyl, COzEt; R2 = H, COzR, COR, CN Scheme 1
R1 = alkyl; R2 = H, CH20Ac, COzR Scheme 2. 1993
J. Nokami ec al.
1994 Table I. Electrochemical acetoxylation of a$-unsaturated Sulfide 1
OOEt
la lb
sulfides’
Electricity (Fimol)
R = CH,
5
R=n-C&t,,
5
Reaction conditionb
Products 2 or 3
A (B) A
Yield (o/.1
OOEt
2a 62(84) 2b 67
lc Id le
If
A
-Ph
vfah
3fc 57 dAc AC
5
lcl
C
AC
36
63
“The reaction was carried out as shown in the text unless otherwise noted. bA: AcONa/AcOH, B: AcONHd/AcOH, C: AcONHd/AcOH-MeCN (:2). cMixture of diastereoisomers (: 1). dSingle isomer (the geometry is not clear).
conditions in poor yield ( < 30%), but 57% yield was obtained after passage of 3.5 F/mol of electricity. The results are listed in Table 1. Further application of this type of reaction to a wide variety of a$-unsaturated sulfides and to organic synthesis of compounds such as sugars is now in progress. The reason for the difference in the product obtained from the cc-acetoxy sulfide and the a&unsaturated sulfide has not yet been clarified. ACKNOWLEDGEMENTS This work was supported by a Grant-in-Aid for Scientific Research on the Priority Area of Electroorganic Chemistry from the Ministry of Education, Science and Culture, Japan. REFERENCES J. Nokami, M. Hatate, S. Wakabayashi and R. Okawara, Tefrahedron Lett. 21, 2557 (1980); T. Fuchigami, Y. Nakagawa and T. Nonaka, ibid. 27,3869 (1986); J. Nokami, K. Ryokume and J. Inada, ibid. 36, 6099 (1995).
Enol ethers: R. Couture and B. Belleau, Can. J. Chem. 50, 3424 (1972); D. Koch, H. Schafer and E. Steckhan, Chem. Ber. 107,364O(1974); T. Shono, Y. Matsumura, T. Imanishi and K. Yoshida, Bull. Chem. Sot. Jpn. 51, 2179 (1978); M. Cariou, J. Simonet and J. Toupet, Tetrahedron L.ett. 28, 1275 (1987); M. Katz, P. Riemenschneider and H. Wendt, Electrochim. Acta 17, 1595 (1972); K. Fujimoto, Y. Tokuda, Y. Matsubara, H. Maekawa, T. Mizuno and I. Nishiguchi, Tetrahedron Lett. 36, 7483 (1995). En01 acetates: T. Shono, Y. Matsumura and Y. Nakagawa, J. Am. Chem. Sot. 96, 3532 (1974); T. Shono, M. Okawa and I. Nishiguchi, ibid. 97,6144 (1975); L. C. Lin, L. L. Chueh, S.-C. Tsay and J. R. Hwu, Tetrahedron Lett. 36, 4093 (1995). Enamines: For a review, E. S&khan, in Organic Electrochemistry (Edited by H. Lund and M. M. Baizer), pp. 597-599, Marcel Dekker, New York (1991). It has been reported that electrolysis of 2-phenyl-lphenylthioethene gives 2-phenyl-2-phenylthioethanal in wet acetonitrile or its dimethylacetal in methanol and that of 2-cyano-2-phenyl-1-phenylthioethene gives 1.2-dimethoxy-2-cyano-2-phenyl-l-phenylthio-ethane (A. Matsumoto, K. Suda and C. Yijima, J. Chem. Sot. Chem. Commun. 263 (1981); G. IX Guillanton and J. Simonet, Acta Chem. &and. B37, 437 (1983)). However, application of the electrolysis of a$unsaturated sulfides to organic synthesis has not been studied.
Pergamon PII:
Printed in Great Britain OOlF4686/97 $17.00 + 0.00
s0013486(96)00467-7
Anodic oxidation of ar$-unsaturated sulfides to a-acetoxy ketones or a$-diacetoxy sulfides Junzo Nokami,* Satoshi Fukutake, Department
Hiroyuki Matsuura and Nobuyuki
Imai
of Applied Chemistry, Okayama University of Science, Ridai, Okayama 700, Japan
(Received 2 August 1996) Abatract-a,/I-Unsaturated sulfides can be oxidized to a-acetoxy ketones or a$-diacetoxy sulfides by electrolysis in acetic acid containing an acetate salt in an undivided cell. 0 1997 Elsevier Science Ltd. Key words: Electrolysis, a&unsaturated
sulfide, oxidation, a-acetoxy ketone, a$-diacetoxy
We have been interested in the use of organosulfur compounds in organic synthesis in view of their widespread synthetic utility, especially due to the versatile functionalization induced by the sulfur group. For example, we have succeeded in converting sulfides into a-acetoxy sulfides by electrolysis in acetic acid and, further, into a&unsaturated sulfides by thermolysis of the a-acetoxy sulfides as shown in Scheme 1 [l]. On the other hand, a few studies have been made of the two-electron electrooxidation of a&unsaturated ethers (enol ethers) and amines (enamines [2]). This background prompted us to examine the electrolysis of a&unsaturated sulfides, easily obtained via electrolysis as shown *Author to whom correspondence should be addressed.
sulfide.
above, to develop another method for versatile functionalization of sulfides (Scheme 2 [3]). For instance, ethyl 2-(phenylthio)but-2-enoate la was electrolyzed as follows. A mixture of la (141 mg, 0.6 mmol) and sodium acetate (147 mg) in acetic acid (2.2 cm’) was electrolyzed at a constant current density of 50 mA cm2 at two platinum electrodes in an undivided cell at 25°C. After passage of 5 F/mol of electricity, the solvent (acetic acid) was removed under reduced pressure, and to the residue was added ethyl acetate and then the mixture was washed with brine. The extract was dried, concentrated, and purified by column chromatography on silica gel with a mixed solvent, ethyl acetate-hexane (l/20), as an eluent to give 3-acetoxy-2-oxobutanoate 2a in 67% yield. In contrast, I-phenylthiohexene If gave 1,2-diacetoxy-1-phenylthiohexane 3f under the same reaction 2
2
thermolysis >5O’C
R1 = H, alkyl, atyl, COzEt; R2 = H, COzR, COR, CN Scheme 1
R1 = alkyl; R2 = H, CH20Ac, COzR Scheme 2. 1993
J. Nokami ec al.
1994 Table I. Electrochemical acetoxylation of a$-unsaturated Sulfide 1
OOEt
la lb
sulfides’
Electricity (Fimol)
R = CH,
5
R=n-C&t,,
5
Reaction conditionb
Products 2 or 3
A (B) A
Yield (o/.1
OOEt
2a 62(84) 2b 67
lc Id le
If
A
-Ph
vfah
3fc 57 dAc AC
5
lcl
C
AC
36
63
“The reaction was carried out as shown in the text unless otherwise noted. bA: AcONa/AcOH, B: AcONHd/AcOH, C: AcONHd/AcOH-MeCN (:2). cMixture of diastereoisomers (: 1). dSingle isomer (the geometry is not clear).
conditions in poor yield ( < 30%), but 57% yield was obtained after passage of 3.5 F/mol of electricity. The results are listed in Table 1. Further application of this type of reaction to a wide variety of a$-unsaturated sulfides and to organic synthesis of compounds such as sugars is now in progress. The reason for the difference in the product obtained from the cc-acetoxy sulfide and the a&unsaturated sulfide has not yet been clarified. ACKNOWLEDGEMENTS This work was supported by a Grant-in-Aid for Scientific Research on the Priority Area of Electroorganic Chemistry from the Ministry of Education, Science and Culture, Japan. REFERENCES J. Nokami, M. Hatate, S. Wakabayashi and R. Okawara, Tefrahedron Lett. 21, 2557 (1980); T. Fuchigami, Y. Nakagawa and T. Nonaka, ibid. 27,3869 (1986); J. Nokami, K. Ryokume and J. Inada, ibid. 36, 6099 (1995).
Enol ethers: R. Couture and B. Belleau, Can. J. Chem. 50, 3424 (1972); D. Koch, H. Schafer and E. Steckhan, Chem. Ber. 107,364O(1974); T. Shono, Y. Matsumura, T. Imanishi and K. Yoshida, Bull. Chem. Sot. Jpn. 51, 2179 (1978); M. Cariou, J. Simonet and J. Toupet, Tetrahedron L.ett. 28, 1275 (1987); M. Katz, P. Riemenschneider and H. Wendt, Electrochim. Acta 17, 1595 (1972); K. Fujimoto, Y. Tokuda, Y. Matsubara, H. Maekawa, T. Mizuno and I. Nishiguchi, Tetrahedron Lett. 36, 7483 (1995). En01 acetates: T. Shono, Y. Matsumura and Y. Nakagawa, J. Am. Chem. Sot. 96, 3532 (1974); T. Shono, M. Okawa and I. Nishiguchi, ibid. 97,6144 (1975); L. C. Lin, L. L. Chueh, S.-C. Tsay and J. R. Hwu, Tetrahedron Lett. 36, 4093 (1995). Enamines: For a review, E. S&khan, in Organic Electrochemistry (Edited by H. Lund and M. M. Baizer), pp. 597-599, Marcel Dekker, New York (1991). It has been reported that electrolysis of 2-phenyl-lphenylthioethene gives 2-phenyl-2-phenylthioethanal in wet acetonitrile or its dimethylacetal in methanol and that of 2-cyano-2-phenyl-1-phenylthioethene gives 1.2-dimethoxy-2-cyano-2-phenyl-l-phenylthio-ethane (A. Matsumoto, K. Suda and C. Yijima, J. Chem. Sot. Chem. Commun. 263 (1981); G. IX Guillanton and J. Simonet, Acta Chem. &and. B37, 437 (1983)). However, application of the electrolysis of a$unsaturated sulfides to organic synthesis has not been studied.