932
J. H. Poupaert et al.: Montmorillonite K10 Catalyzed Michael Addition
and 13C NMR spectra were recorded on a Bruker AC-300 spectrometer. This layer chromatography
conditions: silica gel Si60 (E. Merck, Darmstadt, Germany), ethyl acetate/acetone (60/40, v/v). High
performance liquid chromatography (HPLC) was performed using a Spectra Physics solvent delivery
system (P 2000) ®tted with a RP-18 (10 m, 250Â4.7 mm, 5 mm) column. The isocratic elution solvent
was a methanol:water mixture (65:35, v/v). The solvent rate was 1.5 cm3/min. The detection
wavelength was 260 nm. Under these conditions, compounds reported in Table 1 were found to be
homogenous. Montmorillonite K10 was purchased from Aldrich. Different other samples of K10
Á
were generous gifts of Dr. A. Mathy from the University of Liege (ULg), Belgium. K10 was activated
at 120ꢂC overnight before use. CH2Cl2 and CH3NO2 were redistilled over a bed of P2O5.
The yields reported in Table 1 were obtained after running the reaction on 10 mmol of indole and
isolating the product by column chromatography (conditions: hexane/dichloromethane (50/50 v/v)
and silica gel Si60 (particle size 0.040±0.060 mm)).
3-(3-Oxobutyl)-indole
To a solution of 30.0 g of indole (258 mmol) in 250 cm3 of CH3NO2, 22 cm3 of MVK (0.26 mol;
Aldrich), 20 cm3 of 2-C3H7OH (0.26 mol, spectrophotometric grade; Acros), and 10 g of
Montmorrillonite K10 (Aldrich) were added. The reaction mixture was stirred at room temperature
for 2 h and then heated and stirred at 40ꢂC for another 2 h in a thermostatited water bath. After
cooling, the mixture was ®ltered, K10 was washed with 100 cm3 of CH2Cl2, and the ®ltrates were
evaporated in vacuo to give a yellow residue which was recrystallized from toluene:petroleum ether
(3:1, v/v) to give 38.1 g (79%) of analytically pure material (m.p.: 94±95ꢂC; Refs. [7, 8]: m.p.: 93±
94ꢂC). From a second crop, additional 4.0 g (8%, m.p.: 91±94ꢂC) were recovered. The material from
1
the ®rst crop had IR, H, and 13C NMR spectra identical to those reported previously by Dujardin
and Poirier [7].
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Received November 23, 1998. Accepted (revised) January 12, 1999