A convenient synthesis of p-Aminobenzyl-tris(hydroxymethyl)methane as precursor of solid-supported tripodal ligands

Article abstract of DOI:10.1055/s-2002-19291

p-Aminobenzyl-tris(hydroxymethyl)methane has been prepared in 5 steps from diethylmalonate and p-nitrobenzyl bromide, with an overall yield of 23%. This compound could be grafted on silica previously derivatized with 3-isocynatopropyltriethoxysilane.

Full text of DOI:10.1055/s-2002-19291

PAPER
39
A Convenient Synthesis of p-Aminobenzyl-tris(hydroxymethyl)methane as
Precursor of Solid-Supported Tripodal Ligands
Synthesis of
p
-A
r
minobe
i
nzyl-tri
c
s(hydroxymethyl
D)methane ulière, Jacqueline Marchand-Brynaert*
Unité de chimie organique et médicinale, Université catholique de Louvain, Département de chimie, Bâtiment Lavoisier, place Louis Pa-
steur 1, 1348 Louvain-la-Neuve, Belgium
Fax +32(10)474168; E-mail: marchand@chim.ucl.ac.be
Received 25 July 2001; revised 12 October 2001
PPh2
Abstract: p-Aminobenzyl-tris(hydroxymethyl)methane has been
prepared in 5 steps from diethylmalonate and p-nitrobenzyl bro-
mide, with an overall yield of 23%. This compound could be grafted
PPh2
on silica previously derivatized with 3-isocynatopropyltriethoxysi-
Ph2P
lane.
Triphos
Key words: tris(hydroxymethyl)methane derivatives, tripodal
ligands, amino alcohols, solid-phase synthesis
X
H
H
Y
OH
Cl
PPh2
Cl
Y
a
b
c
d
e
f
H
Y
X
SO3Na
SO3Na PPh2
OH
NH2
Solid-supported reagents1,2 are increasingly used in or-
ganic synthesis with a view of promoting clean and safe
chemistry, making easier the purification steps and devel-
oping parallel or combinatorial chemistry. In this context,
several organometallic catalysts have been bound to
polymers3–5 and silica.6–8
Y
PPh2
OH
1
g
h
NH2 OPPh2
Scheme 1
The usual ligands of transition metals are phosphorous de-
rivatives,9 particularly tripodal phosphines,10 as well illus-
trated by Triphos11–13 and the related aryl derivative 1c
(Scheme 1). Recent developments in the field of polypo-
dal phosphorous ligands involve the synthesis of chiral
ligands on the one hand,14 and water-soluble ligands on
the other hand.15,16 Bianchini et al. synthesized an interest-
ing new ligand belonging to this last family, called Sul-
phos (Scheme 1, structure 1e).17 This compound allowed
the preparation of rhodium and ruthenium catalysts work-
ing in liquid biphasic systems,17,18 or in solid heteroge-
neous systems after immobilization on silica via unique
hydrogen bonding;19,20 these catalysts were used under re-
ductive conditions (hydrogenation and hydroformylation
reactions).
silica. Accordingly, we selected the corresponding ni-
trobenzene derivative (X = NO2) as a suitable precursor.
We previously established that phosphinite ligands are
more appropriate to fulfill our objective than the tradition-
al phosphine ligands, which are too easily oxidizable.23
Therefore, we designed the tripodal phosphinite ligand 1h
(Scheme 1) as synthetic target. In this paper, we describe
the preparation of the triol precursor 1g and its fixation on
silica.
We first examined a strategy similar to that of Bianchini17
which uses the known unsubstituted aryl precursor 1a24 as
the starting material; the sulfonyl substituent was intro-
duced by treatment of tris(chloromethyl) derivative 1b
with hot concentrated sulfuric acid and sodium chloride.
The resulting 1d was then transformed into 1e by substi-
tution with potassium diphenylposphide. Several attempts
to perform the nitration of 1b with nitric acid failed
[HNO3–H2SO4 (1:3), HOAc, 120 °C]. Using ammonium
nitrate and trifluoroacetic anhydride25 [NH4NO3–TFAA
(1:3), CH2Cl2, reflux, 24 h], we recovered a mixture of
o- and p-nitrobenzyl-tris(chloromethyl)methane. There-
fore, we preferred to prepare the target molecule from di-
ethyl malonate and p-nitrobenzyl bromide (Scheme 2).
We are interested in the development of homogeneous ru-
thenium catalysts for alcohol oxidation that could be co-
valently fixed on a solid support (heterogenization of
homogeneous catalysis).21 For that purpose, the phenyl
substituent of ligand 1 should be equipped with a func-
tional group X susceptible to make stable bonding at the
support surface. One representative of such ligands, com-
pound 1f (X = OH)22 has been prepared and fixed on a
Merrifield resin via phenolic ether bonds. Here we consid-
ered the amine function (X = NH2) as a more versatile an-
chorage point, allowing to create stable amide or urea
linkages, either on organic polymers, or on (derivatized)
Diethyl 2-(p-nitrobenzyl)malonate (2) was obtained in
52% yield and further alkylated with chloromethyl benzyl
ether.26 The crude product 3 was reduced with sodium
borohydride to furnish the diol 4 in 89% yield. Treatment
of 4 by catalytic hydrogenation transformed the nitro
function into the desired amine function 5, without affect-
ing the benzyl ether moiety. We found that the deprotec-
tion of this ether by hydrogenolysis could be performed
Synthesis 2002, No. 1, 28 12 2001. Article Identifier:
1437-210X,E;2002,0,01,0039,0042,ftx,en;E14901SS.pdf.
© Georg Thieme Verlag Stuttgart · New York
ISSN 0039-7881

40
E. Dulière, J. Marchand-Brynaert.
PAPER
the elaboration of phosphine and phosphinite tripodal
ligands of transition metals, with a possibility of solid-
support.
COOEt
COOEt
EtOOC
Br
a
+
52%
EtOOC O2N
O2N
2
a
Cl
O
Ph
Ph
OH
100%
OH
OH
OH
a
b
4
HO
Ph
107%
(crude)
OH
COOEt
49%
b
O
H2N
O
HO
1g
9
COOEt
89%
O2N
O2N
O2N
HO
c
O
3
4
c
Si
NCO
O
65%
O
F3COCO
HO
Ph
O
d
H
N
H
O
Ph
O
Si
N
OH
OH
70%
F3COCHN
O
H2N
F3COCO
HO
O
O
6
5
c
10
HO
0.45 mmol/g
62%
HO
OH
F3COCO
OH
Scheme 3 Reagents and conditions: (a) TMSCl, NaI; (b) H2, Pd–C,
H2O–acetone; (c) THF, reflux
e
90%
OH
R
N
H
OCOCF3
F3COCHN
7
8 R = CF3CO
1g R = H
Solvents were dried prior to use. Reagents and solvents (Aldrich or
Acros) were used as purchased. Melting points (uncorrected) were
f
1
determined on an electrothermal apparatus. H (200 MHz or 300
75%
MHz) and 13C (50 MHz or 75 MHz) NMR spectra were recorded on
Varian Gemini 200 or 300 spectrometers. Chemical shifts are re-
ported as values downfield from TMS. The mass spectra (FAB,
APCI or CI modes) were obtained on a Finnigan MAT TSQ-70 in-
strument. HRMS (CI mode) spectrum was performed on a VG-Au-
tospec-Q apparatus. IR spectra were obtained using Biorad FTS 135
spectrometer calibrated with polystyrene. Thermogravimetric anal-
ysis (TGA) were performed on a Mettler Toledo TGA SDTA851
apparatus. TLC were carried out using silica gel 60 F254 (Merck) and
spots were visualized by UV. Silica gel 60 mesh size 0.04–0.063
mm (Merck) was used for column chromatography.
Scheme 2 Reagents and conditions: (a) NaH, THF, 20 °C to reflux;
(b) NaBH4, EtOH, reflux; (c) H2, Pd–C, EtOAc; (d) (CF3CO)2O, py-
ridine; (e) H2O–MeCN; (f) HCl, H2O–MeCN
after masking the polar functions of 5 by acylation with
trifluoroacetic anhydride in pyridine to form 6. Catalytic
hydrogenation of 6 gave now the mono-alcohol 7, the two
other hydroxyl functions of which could be unmasked by
smooth hydrolysis to give 8. Prolonged acidic hydrolysis
of 7 furnished the final compound 1g. This first synthetic
scheme was shortened by changing the method of depro-
tection of the benzyl ether moiety from 4 (Scheme 3): nu-
cleophilic displacement with trimethylsilyl iodide
afforded the triol 9; reduction of the nitro function by cat-
alytic hydrogenation conducted to 1g with an overall yield
of 23% for five steps.
Diethyl 2-[(4-Nitrophenyl)methyl]propanedioate (2)
To a suspension of NaH (60% in oil, 2.08 g, 0.05 mol) in THF (30
mL), under Ar, was added dropwise diethyl malonate (12 mL, 0.078
mol). The mixture was stirred 30 min at 20 °C, then cooled to 0 °C
(ice bath). A solution of p-nitrobenzyl bromide (10.1 g, 46 mmol)
in THF (30 mL) was added dropwise. After the addition was com-
plete, the mixture was refluxed for 3 h. The mixture was concentrat-
ed under vacuum, the residue was dissolved in Et2O (100 mL), the
Et2O layer was washed with H2O (3 30 mL) and dried (MgSO4).
The excess of diethyl malonate was removed by horizontal distilla-
tion (3 h, 70 °C, 0.005 mbar). The yellow solid residue (9.97 g con-
taining mono- and dialkylation products) was purified by column
chromatography on silica gel (cyclohexane–EtOAc, 90:10) to fur-
nish pure 2 as white crystals; yield: 7.11 g (52%); Rf 0.17; mp 60.5–
62 °C.
The possibility of grafting 1g (and derivatives) on a solid
support has been illustrated with silica derivatized by 3-
isocyanatopropyltriethoxysilane. Such silica reacted with
aniline 1g to furnish the support 10 well characterized by
elemental analysis. The heterogeneous phosphinite ligand
of ruthenium (II), was obtained by reacting 10 with chlo-
rodiphenylphosphine and triethylamine. The correspond-
ing homogeneous ligands could be similarly prepared
from 8 or 9.
1H NMR (CDCl3, 200 MHz): = 8.15 (d, 2 Harom, J = 8.7 Hz), 7.39
(d, 2 Harom, J = 8.7 Hz), 4.18 (q, 4 H, J = 7.2 Hz, CH3CH2O), 3.66
[t, 1 H, J = 7.8 Hz, CH(CO2Et)2)], 3.32 (d, 2 H, J = 7.8 Hz, PhCH2),
1.22 (t, 6 H, J = 7.2 Hz, CH3CH2O).
Thus, the amino-functionalized triol 1g is readily accessi-
ble, as such, totally protected (6), or partially protected
(4,5,7 9). These compounds are valuable precursors for
13C NMR (CDCl3, 50 MHz):
(Carom), 145.7 (Carom), 128.8 (Carom), 123.7 (Carom), 61.8 (CH3CH2O),
53.2 [CH(COOEt)2], 34.4 (PhCH2), 14.0 (CH3CH2O).
= 168.2 [CH(CO2Et)2], 147.0
Synthesis 2002, No. 1, 39–42 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Synthesis of p-Aminobenzyl-tris(hydroxymethyl)methane
41
IR (KBr): 3055, 2987, 1731, 1523 cm–1.
1H NMR (CDCl3, 300 MHz): = 7.3 (m, 5 Harom), 6.9 (d, 2 Harom
,
J = 8 Hz), 6.6 (d, 2 Harom, J = 8 Hz), 4.5 (s, 2 H, PhCH2O), 3.6 (s, 4
H, OH), 3.4 (s, 2 H CCH2O), 2.6 (s, 2 H, PhCH2C).
13C NMR (CDCl3, 50 MHz): = 144.4, 138.0, 131.0, 128.2, 127.4,
127.3, 126.8, 114.8 (Carom), 73.3, 72.5 (CH2OCH2), 65.3 (CH2OH),
44.0 (PhCH2C), 34.9 (PhCH2C).
MS (FAB): m/z (%) = 296.1 (100), 249.9 (10), 203.9 (32).
Anal. Calcd for C14H17NO6: C 56.94; H 5.80; N 4.74. Found: C
57.29; H 5.80; N 4.62.
Diethyl 2-(Benzyloxymethyl)-2-[(4-nitrophenyl)methyl]-pro-
panedioate (3)
IR (KBr): 3457, 3382, 3052, 2923, 2871 cm–1.
To a suspension of NaH (60% in oil, 1.06 g, 26 mmol) in THF (30
mL), under Ar, was added dropwise a solution of 2 (7.06 g, 24
mmol) in THF (30 mL). After 10 min, chloromethyl benzyl ether26
(3 mL, 29 mmol) was added and the mixture was refluxed for 5 h.
Aq NH4Cl (5%, 50 mL) was added and the aqueous phase was ex-
tracted with Et2O (3 30 mL). The combined organic phases were
dried (MgSO4) and concentrated to give crude 3 as a yellow solid;
yield: 10.3 g ( 100%). An analytically pure sample was obtained by
column chromatography on silica gel neutralized with NEt3 (cyclo-
hexane –EtOAc, 90:10); Rf 0.29; mp 53.2–55.1°C.
1H NMR (CDCl3, 200 MHz): = 8.05 (d, 2 Harom, J = 8.8 Hz), 7.4–
7.3 (m, 5 Harom), 7.19 (d, 2 Harom, J = 8.8 Hz), 4.53 (s, 2H, PhCH2O),
4.19 (q, 4 H, J = 7.1 Hz, CH3CH2O), 3.69 (s, 2 H, CCH2O), 3.46 (s,
2 H, PhCH2C), 1.23 (t, 6 H, J = 7.1 Hz, CH3CH2O).
MS (FAB): m/z (%) = 301 (35, M; C18H23NO3), 196 (100), 106 (45),
91 (60).
2-(Benzyloxymethyl)-2-{[4-(2,2,2-trifluoroacetamido)-phenyl]-
methyl}-1,3-di(2,2,2-trifluoroacetoxy)propane (6)
To a solution of 5 (0.90 g, 3.0 mmol) in pyridine (5 mL) at 0 °C was
added Ac2O (2 mL, 14 mmol) over 10 min. The mixture was stirred
at 20 °C for 20 h. CH2Cl2 (20 mL) was added, the solution was
washed with dil HCl (1 mol/L, 5 15 mL), dried (MgSO4) and con-
centrated under vacuum. Crude 6 was purified by column chroma-
tography on silica gel (cyclohexane–EtOAc 85:15) to furnish a
product still contaminated with partially deprotected derivatives;
yield: 1.18 g (70%); Rf 0.23.
1H NMR (CDCl3, 300 MHz): = 8.2 (s, 1 H, NH), 7.5 (d, 2 Harom
,
13C NMR (CDCl3, 50 MHz): = 168.9 (CO2Et), 147.1, 144.1,
137.2, 130.9, 128.4, 127.9, 127.8, 123.3 (Carom), 73.4 (PhCH2O),
68.4 (CCH2O), 61.7 (CH3CH2O), 59.4 (PhCH2C), 36.0 (PhCH2C),
14.0 (CH3CH2O).
J = 8.7 Hz), 7.4–7.3 (m, 5 Harom), 7.1 (d, 2 Harom, J = 8.7 Hz), 4.5 (s,
2 H, PhCH2O), 4.3 (s, 2 H, CH2OCOCF3), 3.5 (s, 2 H, CH2OH), 3.3
(s, 2 H, CCH2O), 2.7 (s, 2 H, PhCH2C).
13C NMR (CDCl3, 50 MHz): = 137.1, 134.4, 132.7, 131.2, 128.6,
128.1, 127.8, 120.7 (Carom), 73.7 (PhCH2O), 67.8 (CCH2O), 67.0
(CH2OCOCF3), 43.0 (PhCH2C), 34.9 (PhCH2C) (CF3CO not visi-
ble).
IR (KBr): 3055, 2986, 1731, 1524, 1349 cm–1.
MS (FAB): m/z (%) = 416.1 (95), 91 (100).
Anal. Calcd for C22H25NO7: C 63.9; H 6.06; N 3.37. Found: C
64.14; H 6.17; N 3.38.
IR (KBr): 3412, 3055, 2987, 1786, 1734, 1168 cm–1.
MS (FAB): m/z (%) = 588 (100, M-1; C24H20NO6F9), 492 (35), 396
2-(Benzyloxymethyl)-2-[(4-nitrophenyl)methyl]propan-1,3-diol
(4)
(2), 113 (55).
To a suspension of NaBH4 (17.1 g, 442 mmol) in EtOH (200 mL),
under Ar, was added dropwise a solution of 3 (14.8 g, 30 mmol) in
EtOH (100 mL) and the mixture was refluxed for 16 h. After addi-
tion of aq NH4Cl in small portions (5%,150 mL), the crude solution
was distilled under vacuum to remove EtOH. CH2Cl2 (200 mL) was
added and the mixture filtered. The two layers were separated, the
aqueous phase was extracted with CH2Cl2 (3 50 mL), the com-
bined organic phases were washed with aq NaHCO3 (5% 100 mL),
dried (MgSO4) and concentrated under vacuum. Crude 4 was isolat-
ed as an orange solid; yield; 8.8 g (89%). An analytically pure sam-
ple was obtained by column chromatography on silica gel
(cyclohexane–EtOAc, 60:40); Rf 0.28; mp 85.5–86.7 °C.
2-(Hydroxymethyl)-2-{[4-(2,2,2-trifluoroacetamido)-phenyl]-
methyl}-1,3-di(2,2,2-trifluoroacetoxy)propane (7)
A solution of 6 (2.74 g, 5.6 mmol) in EtOAc (50 mL) was stirred for
5 h at 50 °C under an atmosphere of H2 with 10% Pd/C (1.06 g, 1.0
mmol) as catalyst. The mixture was filtered and concentrated under
vacuum. Crude 7 was purified by column chromatography on silica
gel (cyclohexane–EtOAc, 50:50); yield: 1.39 g (62%).
1H NMR (CDCl3, 300 MHz): = 8.5 (br s, 1 H, NH), 7.5 (d, 2 Harom
J = 8.4 Hz), 7.2 (d, 2 Harom, J = 8.4 Hz), 3.7 (s, 4 H, CH2O), 3.5 (s,
2 H, CH2O), 2.7 (s, 2 H, PhCH2).
,
13C NMR (CDCl3, 50 MHz): = 135.0, 133.7, 131.1, 120.5 (Carom),
64.8, 62.3 (CH2O), 38.2 (PhCH2), 36.3 (PhCH2C) (CF3CO not vis-
ible).
1H NMR (CDCl3, 300 MHz): = 8.09 (d, 2 Harom, J = 8.8 Hz), 7.36
(d, 2 Harom, J = 8.8 Hz), 7.4–7.3 (m, 5 Harom), 4.50 (s, 2 H, PhCH2O),
3.61 and 3.53 (ABq, 4 H, J = 10.9, 11 Hz, CH2OH), 3.31 (s, 2 H,
CCH2O), 2.85 (s, 2 H, PhCH2C).
MS (FAB): m/z (%) = 306 (36, C13H16F3NO4), 236 (24), 188 (100).
3-(4-Nitrophenyl)-2-(hydroxymethyl)propan-1,3-diol (9)
To a solution of 4 (3.0 g, 9.1 mmol) and Et3N (1.4 mL, 19 mmol) in
MeCN (50 mL) was added trimethylsilyl chloride (9.5 mL, 73
mmol) and the mixture was refluxed for 90 min, NaI (8.30 g, 55
mmol) was then added and the mixture was further refluxed for 20
h. CH2Cl2 (20 mL) was added, the mixture was filtered and concen-
trated under vacuum. The brown solution was washed with aq
(NH4)2SO3 (5%, 3 25 mL), which caused decoloration. The or-
ganic phase was further extracted with H2O (5 25 mL). Evapora-
tion of H2O under vacuum furnished crude 9 as a yellow solid (2.36
g, 107%).
13C NMR (CDCl3, 50 MHz): = 147.5, 145.5, 137.8, 131.3, 128.6,
128.0, 127.8, 123.2 (Carom), 73.7 (PhCH2O), 72.1 (CCH2O), 65.1
(CH2OH), 44.9 (PhCH2C), 35.3 PhCH2C).
IR (KBr): 3616, 3501, 3055, 2985, 1521, 1348, 1098 cm–1.
MS (FAB): m/z (%) = 332 (20), 91 (100).
Anal. Calcd for C18H21NO5: C 65.24; H 6.39; N 4.23. Found: C
64.90; H 6.28; N 4.14.
2-(Benzyloxymethyl)-2-[(4-aminophenyl)methyl]propan-1,3-
diol (5)
1H NMR (D2O, 300 MHz): = 8.1 (d, 2 Harom, J = 8 Hz), 7.4 (d, 2
A solution of 4 (0.234 g, 0.710 mmol) in EtOAc (10 mL) was hy-
drogenated in a Parr apparatus (2750 mbar H2), with 10% Pd/C as
the catalyst (0.023 g, 0.02 mmol), for 3 h. The mixture was filtered
and concentrated under vacuum, crude 5 was recovered as a yellow
oil; yield: 0.132 g (65%).
Harom, J = 8 Hz), 3.4 (s, 6 H, CH2OH), 2.8 (s, 2 H, PhCH2).
13C NMR (D2O, 75 MHz): = 146.2, 131.5, 123.4 (Carom), 61.8
(CH2OH), 45.1 (PhCH2), 34.7 (PhCH2C) (quat Carom not visible).
Synthesis 2002, No. 1, 39–42 ISSN 0039-7881 © Thieme Stuttgart · New York

42
E. Dulière, J. Marchand-Brynaert.
PAPER
MS (APCI): m/z (%) = 242 (100, M; C11H15NO5), 206 (45), 188
(37), 176 (17), 142 (15).
Anal. Calcd for (SiO2)nC15H23N2O4 3H2O: C 6.55; H 1.06; N 1.02.
Found: C 6.38; H 1.13; N 0.76.
3-(4-Aminophenyl)-2-(hydroxymethyl)propan-1,3-diol (1g)
From 7: A solution of 7 (0.45 g, 0.9 mmol) in a H2O–acetone (2:1)
mixture (15 mL) was stirred at 20 °C for 4 h with concd HCl (2.5
mL). The solution was concentrated under vacuum, CH2Cl2 (15
mL) was added, the organic phase was extracted with H2O (3 10
mL) and the water evaporated under vacuum, 1g was recovered
from the aqueous phase as a yellow oil (0.188 g, 75%). If acid was
omitted, 8 was recovered instead of 1g.
References
(1) Bhalay, G.; Dunstan, A.; Glen, A. Synlett 2000, 1846.
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Raspolli Galetti, A. M.; Sbrana, G. J. Mol. Catal. A:
Chemical 1999, 139, 177.
(4) Yao, Q. Angew. Chem. Int. Ed. 2000, 39, 3896.
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(6) Kröcher, O.; Köppel, R. A.; Baiker, A. Chem Commun.
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(11) Bianchini, C.; Meli, A.; Peruzzini, M.; Vizza, F.; Frediani,
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8
1H NMR (D2O, 200 MHz): = 10.2 (br s, 1 H, NH), 7.6 (d, 2 Harom
,
J = 9 Hz), 7.4 (d, 2 Harom, J = 9 Hz), 3.5 (s, 6 H, CH2OH), 2.3 (s, 2
H, PhCH2).
13C NMR (aceton-d6, 50 MHz): = 132.2, 121.2 (Carom), 64.8
(CH2OH), 45.5 (PhCH2), 35.0 (PhCH2C) (CF3CO and quat. Carom
not visible).
From 9: A solution of 9 in a H2O–acetone (5:1) mixture (30 mL)
was hydrogenated in a Parr apparatus (2000 mbar H2) for 15 h with
Pd 10% on charcoal (0.023 g, 0.02 mmol) as catalyst. The mixture
was filtered, concentrated under vacuum and 1g was obtained;
yield: 0.037 g (49%).
1H NMR (D2O, 200 MHz): = 7.3 (d, 2 Harom, J = 9 Hz), 7.1 (d, 2
Harom, J = 9 Hz), 3.3 (s, 6 H, CH2OH), 2.5 (s, 2 H, PhCH2).
13C NMR (D2O, 50 MHz): = 138, 135, 134, 124 (Carom), 65
(CH2OH), 47 (PhCH2), 36 (PhCH2C).
MS (APCI): m/z (%) = 212 (98), 195 (19), 194 (100), 177 (14), 166
(15)
HRMS (CI): m/z calcd for C11H18NO3: 212.1287, Found: 212.1294
Silica Grafted with (Propyl)[3-phenyl-2,2-di(hydroxymethyl)-
propan-1-ol]urea (10)
(17) Bianchini, C.; Frediani, P.; Sernau, V. Organometallics
1995, 14, 5458.
Silica Merck type 10184, 70–230 mesh (2 g, 5 mmol of silanol func-
tions) was washed with MeOH in a Soxhlet apparatus for 2 d, dried
under vacuum (0.005 mbar) at 70 °C for 5 h and reacted with 3-iso-
cyanatopropyltriethoxysilane (1.52 g, 6.2 mmol) in THF (60 mL) at
20 °C for 3 h and then refluxed for 20 h. (The modified silica was
filtered, washed with THF (10 mL) and immediately introduced in
the next step.
(18) Rojas, I.; Lopez Limares, F.; Valencia, N.; Bianchini, C. J.
Mol. Catal. A: Chemical 1999, 144, 1.
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Functionalization, 1.2 mmol/g of modified silica as measured by
TGA: To a suspension of silica grafted with propylisocyanate (2 g,
ca 2.4 mmol isocyanate function) in THF (50 mL) was added a so-
lution of 1g (0.27 g, 1.3 mmol) in pyridine (3 mL). The mixture was
refluxed for 2 d. After filtration, crude 10 was washed with CH2Cl2
for 24 h in a Soxhlet apparatus to furnish 10 as a yellow powder.
Functionalization, 0.45 mmol/g of modified silica as measured by
TGA: weight loss = 13.36%.
IR (KBr): 2944, 1517 cm–1.
Synthesis 2002, No. 1, 39–42 ISSN 0039-7881 © Thieme Stuttgart · New York