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Quaternisation of an indole; Compound name: 2,3,3-Trimethyl-1-(4-sulfobutyl)-3H-indolium inner salt

SyntheticPage 892
DOI: 10.1039/SP892
Submitted Apr 23, 2019, published Apr 25, 2019
Robert Smith (, Megan Critchley (), Charnete Casimero (), James Davis (
A contribution from Smith Group

			Reaction Scheme: <IMG src="/images/empty.gif"><IMG src="/images/empty.gif">Quaternisation of an indole<IMG src="/images/empty.gif"><IMG src="/images/empty.gif">

Chemicals Used

2,2,3-Trimethylindolenine (Alfa Aesar)

1,4-Butansultone (Alfa Aesar)

Toluene (Fisher Scientific)


To a round bottom flask* charged with 2,2,3-trimethylindolenine (1.59 g, 10 mmol) was added 1,4-butansultone (4.09 g, 30 mmol) and toluene (20 mL).  The red solution was heated to reflux for 5 hours, with constant stirring.  Upon completion, the dark reaction mixture was allowed to cool, and the solid was isolated by vacuum filtration on a Buchner funnel, washed with ethyl acetate and air dried to yield the target compound (0.52 g, 17.63 %) as a lilac solid.

Author's Comments

*A round-bottomed flask fitted with a reflux condenser was used which fitted snugly into a metal heating block.  A thermocouple was used to control the temperature and the reaction was open to the air (no inert gasses were required).  Stirring was accomplished using a stirring bar, which was controlled from the hot plate.  The whole reaction was accomplished in the open air without the need of dry/inert conditions.


1H NMR (300 MHz, DMSO-d6) δ 8.10 – 7.99 (m, 1H), 7.90 – 7.78 (m, 1H), 7.68 – 7.56 (m, 2H), 4.49 (t, J = 7.7 Hz, 2H), 2.85 (s, 3H), 2.60 – 2.43 (m, 3H), 1.96 (q, 2H), 1.74 (q, J = 7.5 Hz, 2H), 1.53 (s, 6H).   13C NMR (101 MHz, DMSO) δ 196.96, 142.35, 141.67, 129.84, 129.42, 123.85, 116.10, 54.61, 50.62, 47.87, 26.51, 22.66, 22.53, 14.31. LCMS m/z: 294.1 [M -1]

Lead Reference

A.R. Tyler et al. European Journal of Medicinal Chemistry, 64 (2013) 222-227

Supplementary Information

13C vs 135DEPT.pdf
1H1H COSY.pdf

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Get structure file (.cdx, .sk2, .mol)

Keywords: alkylation, amines, heterocyclic compounds, sulfonates

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