Preparation of azide functionalized MNPs (3)
propanal to b-arylsubstituted nitroolefins. The nanoparticles
showed good stability in front of agglomeration in dichloro-
methane, and could be easily separated from the reaction media
by magnetic decantation and easily redispersed for reuse. In this
manner, the MNPs could be used in 4 consecutive runs without
any reactivation of the catalyst.
To a suspension of MNPs 1 (402 mg) in degassed toluene (10 mL)
under argon were added 3-azidopropyltrimethoxysilane (2)
(482.4 mg, 2.35 mmol), glacial acetic acid (50.3 mL, 0.87 mmol)
and ultrapure water (69 mL, 3.86 mmol). The reaction mixture
was warmed at 105 ꢂC for 24 h and then cooled at room
temperature. The MNPs were removed using an external
magnetic field, washed several times with MeOH, hexane,
acetone and dried under vacuum.
Acknowledgements
This work was supported by MICINN (grant CTQ2008-00947/
BQU) and Consolider Ingenio 2010 (grant CSD2006-0003),
DURSI (grant 2009SGR623), and the ICIQ foundation. P.R.
thanks MICINN for a Torres Quevedo posdoctoral grant. We
also thank ICIQ Support Units and Universitat Rovira i Virgili
for TEM images.
Preparation of (S)-a,a-diphenylprolinol trimethylsilyl ether
supported onto azide functionalized MNPs (5)
Azide functionalized MNPs (3) (0.17 mmol), (S)-a,a-diphenyl-
prolinol trimethylsilyl ether (4) (115 mg, 0.24 mmol), CuI (6.61
mg, 0.034 mmol), DIPEA (386 mL, 2.21 mmol) and a mixture of
dry THF/DMF (1 : 1), under argon, were warmed at 50 ꢂC for 10
h. The ligand supported onto MNPs was removed using an
external magnetic field, washed several times with MeOH,
acetone and dried under vacuum.
Notes and references
€
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€
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The corresponding nitroolefin (0.2 mmol), catalyst 5 (10 mol%),
aldehyde (0.3 mmol) and CH2Cl2 (0.5 mL) were mixed and stirred
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organic mixture was concentrated and was purified by column
chromatography (silica gel, hexane/EtOAc) to afford the Michael
adduct. The enantiomeric excess was determined by HPLC on
a chiral stationary phase (Chiralpak IC column and IC guard
column) and the diastereoisomeric ratio by 1H NMR.
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Recycling of catalyst 5
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Trans-b-nitrostyrene (0.2 mmol), catalyst 5 (10 mol%), propio-
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stirred at room temperature and monitored by TLC until
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In conclusion, we have reported for the first time the support of
C-4 propargyloxy substituted (S)-a,a-diphenylprolinol trime-
thylsilyl ether onto azide functionalized MNPs of Fe3O4 using
the CuAAC reaction for the construction of 1,2,3-triazole linkers
on the nanoparticles. The functional, magnetic nanoparticles
prepared in this manner, spherical in size and depicting a narrow
size distribution (4.8 ꢀ 0.8 nm), have been successfully used to
promote the highly enantioselective Michael addition reaction of
7354 | J. Mater. Chem., 2011, 21, 7350–7355
This journal is ª The Royal Society of Chemistry 2011