Synlett 2008(11): 1719-1723  
DOI: 10.1055/s-2008-1077881
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Hg(OTf)2-Catalyzed Cyclization of N-Tosylanilinoallylic Alcohols to 2-Vinylindolines

Kosuke Namba*, Yuki Nakagawa, Hirofumi Yamamoto, Hiroshi Imagawa, Mugio Nishizawa*
Faculty of Pharmaceutical Sciences, Tokushima Bunri University, Yamashiro-cho, Tokushima 770-8514, Japan
Fax: +81(88)6553051; e-Mail: mugi@ph.bunri-u.ac.jp;
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Publikationsverlauf

Received 21 March 2008
Publikationsdatum:
11. Juni 2008 (online)

Abstract

The Hg(OTf)2-catalyzed cyclization of N-tosylanilino­allylic alcohols giving rise to vinyl-substituted indolines has been developed. The reaction takes place with a highly efficient catalytic turnover (up to 1000 times) under mild conditions. The hydroxyl group of the organomercuric intermediate is protonated by in situ formed TfOH generating an oxonium cation, which regenerates the catalyst after demercuration.

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Typical Experiment Procedure: To a solution of 5 (20 mg, 0.063 mmol) in CH2Cl2 (0.6 mL) was added mercury triflate (0.01 M solution in MeCN, 6.3 µL, 0.063 µmol) at r.t., and the mixture was stirred for 24 h. After addition of sat. NaHCO3 solution, the dried and concentrated residue was subjected to a column chromatography on silica gel using hexane-EtOAc (12:1) as eluent to give 6 (18.4 mg, 98%) as a colorless powder; mp 111 ˚C. IR (neat): 3066, 1598, 1354, 1165 cm. ¹H NMR (300 MHz, CDCl3): δ = 7.65 (d, J = 8.1 Hz, 1 H), 7.57 (d, J = 8.1 Hz, 2 H), 7.21 (m, 1 H), 7.17 (d,
J = 8.1 Hz, 1 H), 7.01-7.07 (m, 2 H), 6.99 (dd, J = 0.9, 7.5 Hz, 1 H), 5.91 (ddd, J = 6.3, 10.2, 16.8 Hz, 1 H), 5.39 (dt,
J = 1.2, 16.8 Hz, 1 H), 5.15 (dt, J = 1.5, 10.2 Hz, 1 H), 4.74 (m, 1 H), 2.95 (dd, J = 9.9, 15.9 Hz, 1 H), 2.64 (dd, J = 3.3, 15.9 Hz, 1 H), 2.36 (s, 3 H). ¹³C NMR (75 MHz, CDCl3):
δ = 143.8, 141.4, 137.6, 135.3, 131.2, 129.5, 127.7, 127.1, 125.1, 124.5, 116.8, 115.7, 63.8, 34.9, 21.5. HRMS (EI):
m/z [M]+ calcd for C17H19NO3S+: 299.0980; found: 299.0999.