Lewis Acid Catalyzed Reaction of α-Organylsulfanyl/selanyl Carbenium Ions
SHORT COMMUNICATION
Scheme 5. Catalytic cycle of nucleophilic addition reaction of α-organylsulfanyl and α-organylselanyl carbenium ions.
roacetate (7.20 g, 51.3 mmol) was added to the reaction mix-
tions are very clean and proceed under milder conditions
than previous stoichiometric methods. High regioselectivity
of the reactions between the α-fluoro-α-organylsulfanyl or
α-fluoro-α-organylselanyl moieties and Lewis acids was suc-
cessfully achieved; therefore, the new reaction can be ap-
plied to the synthesis of more complicated compounds.
Planned future work in this area includes scandium-cata-
lyzed intramolecular or intermolecular cyclization via α-or-
ganylsulfanyl or α-organylselanyl carbenium ions. These re-
sults will be reported elsewhere.
ture. The whole mixture was stirred for 1 h at room tempera-
ture and poured into water (300 mL). The organic layer was
separated, and the aqueous layer was extracted with Et2O. The
combined organic layers were dried with MgSO4. The solvent
was then removed under reduced pressure. The residue was
purified by column chromatography on silica gel, being eluted
with AcOEt/n-hexane (1:20) to give ethyl 2-fluoro-2-(phenylsel-
anyl)acetate (3)[10] (11.0 g, 82%) as a yellow oil. IR (KBr): =
1
1752 cm–1 (CO). H NMR (500 MHz, CDCl3, 25 °C, TMS): δ
= 7.65–7.67 (m, 2 H, ArH), 7.32–7.41 (m, 3 H, ArH), 6.38 [d,
3J(H,F) = 52 Hz, 1 H, CHF], 4.08–4.13 (m, 2 H, OCH2), 1.17
[t, 3J(H,H) = 7 Hz, 3 H, Me] ppm. 19F NMR (CDCl3,
CF3CO2H): δ = –88.85 [d, 3J(H,F) = 52 Hz, 1 F] ppm. MS
(70 eV): m/z (%) = 262 (7) [M+]. C10H11FO2Se: calcd. C 45.99,
H 4.25; found C 45.92, H 4.24. The compound 3 can be stored
in the refrigerator for one year.
References
[9] Typical experimental procedure: Under argon, scandium tri-
flate (9.0 mg, 0.02 mmol) was added to a dichloromethane
(1.0 mL) solution of 3 (0.10 g, 0.38 mmol) and allyltrimethylsi-
lane (0.13 g, 1.2 mmol) at room temperature. The reaction mix-
ture was stirred for 1.5 h and poured into a saturated NaHCO3
solution (100 mL). The organic layer was separated, and the
aqueous layer was extracted with CHCl3. The combined or-
ganic layers were dried with MgSO4 and concentrated under
reduced pressure. The residue was purified by preparative TLC
on silica gel, being eluted with AcOEt/n-hexane (1:50) to give
ethyl 2-(phenylselanyl)pent-4-enoate (4a) (94.0 mg, 87%) as a
pale yellow oil. 4a: IR (KBr): = 1727 cm–1 (CO). 1H NMR
Acknowledgements
We thank Gifu University and the Endo Seijiro Memorial Founda-
tion for financial support of part of this work.
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3
3752.
(500 MHz, CDCl3, 25 °C, TMS): δ = 7.60 [d, J(H,H) = 7 Hz,
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2 H, ArH], 7.26–7.35 (m, 3 H, ArH), 5.75–5.83 (m, 1 H, ole-
finic H], 5.07–5.12 (m, 2 H, olefinic H), 4.08 [q, 3J(H,H) =
7 Hz, 2 H, OCH2], 3.66 [dd, 3J(H,H) = 6 and 9 Hz, 1 H,
SeCH], 2.63–2.69 (m, 1 H, CH2), 2.49–2.55 (m, 1 H, CH2),
3
1.16 [t, J(H,H) = 7 Hz, 3 H, Me) ppm. 13C NMR (125 MHz,
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CDCl3, 25 °C, TMS): δ = 172.5 (s), 135.8 (2 d), 134.8 (d), 129.1
(2 d), 128.6 (d), 127.8 (s), 117.7 (t), 61.1 (t), 42.6 (d), 36.1 (t),
14.1 (q) ppm. MS (70 eV): m/z (%) = 284 (2.5) [M+].
C13H16O2Se: calcd. C 55.13, H 5.69; found C 55.27, H 5.72.
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[8] Preparation of ethyl 2-fluoro-2-(phenylselanyl)acetate (3): To
ethanol (120 mL) and diphenyl diselenide (8.00 g, 25.6 mmol)
was added sodium borohydride (1.94 g, 51.3 mmol). When the
yellow solution changed color to colorless, ethyl chlorofluo-
Received: March 10, 2005
Published Online: May 27, 2005
Eur. J. Org. Chem. 2005, 2884–2887
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2887