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

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.

Key words

Hg(OTf)₂ - N-tosylanilinoallylic alcohol cyclization - 2-vinylindoline - 2-vinylpyrrolidine - 2-vinylpiperidine

References and Notes

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11

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^-¹. ^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.