Hydrosilylation of unsaturated (hetero)aromatic aldehydes and related compounds catalyzed by transition metal complexes

Article abstract of DOI:10.1016/S0022-328X(98)00431-8

[Rh(COD)CI]₂ has been found to be a more active catalyst than Ir, Ru, Pt and Pd complexes for the hydrosilylation of unsaturated furan and aromatic aldehydes with HSiEt₃. 1,4- and 1,2-addition reactions giving unsaturated silyl ethers in cis- and trans-configurations occurred as well as the hydrogenation reactions which produce the corresponding saturated silyl ethers. The migration of the ethyl group was observed in the hydrosilylation of 3-ethyl-3-(5-nitrofuryl)acrolein. The dehydrogenative silylation occurred in the reactions of cinnamyl alcohol and furan-2-acrylic acid.

Full text of DOI:10.1016/S0022-328X(98)00431-8

Journal of Organometallic Chemistry 559 (1998) 123–130
Hydrosilylation of unsaturated (hetero)aromatic aldehydes and related
compounds catalyzed by transition metal complexes
Irina Iovel, Juris Popelis, Alexander Gaukhman, Edmunds Lukevics *
Lat6ian Institute of Organic Synthesis, 21 Aizkraukles str, Riga, LV-1006, Lat6ia
Received 5 November 1997
Abstract
[
Rh(COD)CI]2 has been found to be a more active catalyst than Ir, Ru, Pt and Pd complexes for the hydrosilylation of
unsaturated furan and aromatic aldehydes with HSiEt . 1,4- and 1,2-addition reactions giving unsaturated silyl ethers in cis- and
3
trans-configurations occurred as well as the hydrogenation reactions which produce the corresponding saturated silyl ethers. The
migration of the ethyl group was observed in the hydrosilylation of 3-ethyl-3-(5-nitrofuryl)acrolein. The dehydrogenative silylation
occurred in the reactions of cinnamyl alcohol and furan-2-acrylic acid. © 1998 Elsevier Science S.A. All rights reserved.
Keywords: Hydrosilylation; Complex catalysis; Rhodium(I); (Hetero)aromatic aldehydes
1
. Introduction
The dehydrogenative silylation to unsaturated silyl
ethers occurs as the main process in the reactions of
cinnamic (trans-3-phenylacrylic) acid with thienyl
silanes in the presence of Speier’s catalyst [7]. The
The hydrosilylation of a large number of various
unsaturated compounds with alkylsilanes has been suc-
cessfully carried out during the last decades [1]. The
investigations of this reaction are still continuing [2].
Nevertheless, up to now the hydrosilylation of unsatu-
rated (hetero)aromatic aldehydes (and related alcohols
and acids) has not been investigated in detail. The pool
of catalysts used for these processes is very limited.
The hydrosilylation of cinnamaldehyde (trans-3-
phenyl-2-propenal) with various trialkyl(aryl)silanes
was studied in the presence of homogeneous and het-
erogeneous catalysts. The reaction directions depend on
a catalyst nature. In the presence of Speier’s and
Wilkinson’s catalysts (H PtCI · 6H O solution in 2-
hydrosilylation of methyl cinnamate with HSiEt cata-
3
lyzed by RhCl(PPh ) proceeds as 1,4-addition, giving
3
3
the corresponding silyl ether [8].
To our knowledge, the hydrosilylation of heterocyclic
unsaturated carbonyl and carboxyl functionalized com-
pounds has been reported only in our previous work
[9].
trans-3-(2-Furyl)acrolein
and
trans-3-(2-
furyl)acrylic acid were studied in the hydrosilylation
2
6
2
propanol and RhCl(PPh ) , respectively) and metallic
3
3
nickel the 1,4-addition occurs giving the corresponding
silyl ethers [3–5]. The ratio of the product stereo iso-
mers cis/trans=75/25 was determined in [5]. The reac-
tion catalyzed by fluoride ion gives the trans-product of
1,2-addition to the carbonyl group [6] (Scheme 1).
*
Corresponding author. Fax: +371 7821038.
Scheme 1.
0022-328X/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved.
PII S0022-328X(98)00431-8

124
I. Io6el et al. / Journal of Organometallic Chemistry 559 (1998) 123–130
with trialkylsilanes in the presence of Speier’s catalyst,
which was not enough effective, therefore, reactions
were carried out at prolonged reflux. The correspond-
ing silyl ethers were obtained from the aldehyde in the
result of 1,4 addition. Their configurations were not
detected. The saturated compounds were prepared from
the acid via dehydrogenative silylation accompanied by
hydrogenation.
The studies of such objects in the hydrosilylation are
intriguing from both scientific and practical points of
view: as for determination of the reaction regio- and
stereoselectivity and other phenomena as well as for the
preparation of biologically active compounds [10,11].
Recently we investigated the hydrosilylation of O-, S-
and N-heterocyclic aldehydes in the presence of various
metal complex catalysts [12,13], and the asymmetric
hydrosilylation and hydrogen transfer reduction of het-
eroaromatic ketones [14]. A number of complexes has
been shown to be efficient in these processes. In the
present paper we are reporting the hydrosilylation of
Scheme 2.
by GC and GC-MS). The hydrosilylation of 3-(4-
pyridyl)acrolein, nitrofuryl derivatives and cinnamyl al-
cohol was undertaken for the first time.
2
.2. Hydrosilylation of six-membered
h,i-unsaturated(hetero)aromatic aldebydes
The hydrosilylation of cinnamaldehyde (trans-3-
phenyl-2-propenal, CA) and 3-(4-pyridyl)acrolein
trans-configuration, PA) with HSiEt were studied in
(
3
the presence of [Rh(COD)Cl] (1–2 mol.%). The reac-
2
tivity of CA was considerably higher than that of PA.
CA reacted at ambient temperature reaching the com-
plete conversion after 15 h; the product was isolated in
(
hetero)aromatic compounds, containing two reactive
sites in the side chain, with HSiEt in the presence of
3
1
various metal complexes (some results were reported in
82% yield. According to H-NMR data triethyl[(3-
[
15]).
phenyl-2-propenyl)oxy]silane (3) in cis- and trans-
configurations (isomer ratio: 77/23) was obtained.
The hydrosilylation of PA occurred only under more
vigorous conditions (at 120°C for 48 h). It proceeded
also as 1,4-addition yielding triethyl{[3-(4-pyridyl)-2-
propenyl]oxy}silane (4) but in cis-configuration only.
However, the main product in this case was the satu-
rated silyl ether 5. GC reaction control showed that the
hydrogenation occurred consecutively to the 1,4-hy-
drosilylation (Scheme 3).
The low reactivity of PA may be explained by the
formation of stable complexes of a catalyst with the
electron-donor pyridine derivatives (substrate and
products) hindering the reaction. This phenomenon has
been also observed in the hydrosilylation of pyridine-
carbaldehydes [12,13].
2
. Results and discussion
2
.1. Hydrosilylation of furylacrolein
3-(2-Furyl)acrolein (FA) is known only as a trans-
isomer. The hydrosilylation of this compound with
triethylsilane was studied in the presence of a number
of transition metal complexes: [Rh(COD)CI] (COD=
cis,cis-1,5-cyclooctadiene), Ir(CO)(PPh ) Cl, Ru(CO)
(
the presence of Speier’s catalyst for a comparison. The
complexes of bivalent Pd(II) and Pt(II) have been
found to be absolutely inactive in this process at ambi-
2
3
2
PPh ) Cl , Pd(PPh ) Cl and Pt(PPh ) Cl , as well as in
3 2 2 3 2 2 3 2 2
ent temperature. [Rh(COD)Cl] catalyzed the addition
2
reaction at the room temperature. The studied com-
plexes can be arranged according to their activity in
the order: [Rh(COD)Cl] ꢀIr(CO)(PPh ) Cl\Ru(CO)
2
.3. Hydrosilylation of nitrofurylacroleins
2
3 2
The hydrosilylation of trans-3-(5-nitro-2-furyl)-
(
PPh ) Cl \H PtCI ꢀPd(PPh ) Cl and Pt(PPh ) Cl .
3 2 2 2 6 3 2 2 3 2 2
acrolein (NFA1) and E-3-ethyl-3-(5-nitro-2-furyl)-
acrolein (NFA2) was carried out at 40°C for 20 h. Very
complicated mixtures of the products were obtained for
these substrates. They have been separated by column
chromatography. It has been found that 1,4-addition as
well as 1,2-addition took place giving the corresponding
unsaturated silyl ethers (Scheme 4). The subsequent
hydrogenation accompanied the hydrosilylation of
NFA1 yielding saturated silyl derivative. Unusual mi-
gration of Et group was observed in the reaction of
NFA2. Perhaps the complex of the substrate with a
catalyst caused such migration.
The main product in all cases was the corresponding
unsaturated silyl ether (1) in cis- and trans-configura-
tions. In the presence of monovalent Rh(I) and Ir(I)
complexes the 1,4-addition was accompanied by hydro-
genation giving saturated silyl ether (2) (Scheme 2,
Table 1).
The hydrosilylation of a number of (hetero)aromatic
unsaturated aldehydes and related compounds with
HSiEt3 (molar ratio 1:1.2) has been studied in the
presence of the most active catalyst [Rh(COD)CI] . The
2
reactions were carried out at various temperatures until
complete conversion of the starting substrate (control

I. Io6el et al. / Journal of Organometallic Chemistry 559 (1998) 123–130
125
Table 1
Hydrosilylation of trans-3-(2-furyl)acrolein with HSiEt3 in the presence of metal complexes
Conversiona (%) (GC)
Total yieldb (%)
Products ratios (%)
c
Complex
r.t., 24 h
40°C
cis-1
trans-1
2
[
Rh(COD)Cl]2
100
41
30
—
82
54
50
50
51
35
63
59
37
42
37
41
12
23
0
Ir(CO)(PPh ) Cl
Ru(Co)(PPh ) Cl
2
H PtCl6 · 6H O
68 (48 h)
70 (60 h)
56 (60 h)
3
2
3
2
d
12
0
2
2
Pd(PPh ) Cl
:0
:0
3
2
2
Pt(PPh ) Cl
2
3
2
a
The reactions were carried out under argon in a solvent—0.61 g (5 mmol) of FA in 2 ml CH Cl ; molar ratio of FA to HSiEt =1:1.2; catalyst
2
2
3
amounts of [Rh(COD)Cl]2 was 1 mol.%, for others were 5 mol.%.
b
Products were isolated by vacuum distillation (69–72°C/0.1–0.2 mm).
c
Determined by means of 1H-NMR.
d
Used as 1 mol.% solution in 2-propanol.
The formation of the compounds 6–10 was confi-
(l=3.51 and 3.29 ppm, respectively). At the same time
the signals of i-CH2 protons for E-10 are shifted
downfield (by more than 0.15 ppm).
1
rmed by H-NMR and GC-MS spectra (see Experimen-
1
tal). In H-NMR spectrum of compound 6 the
additional coupling of doublets of the furan ring pro-
tons to triplets was found, that evidenced for the exis-
2.4. Hydrosilylation of unsaturated hydroxy deri6ati6es
tence of CH group in 2 position of the furan ring. The
2
values of JHCꢀCH stipulated cis- and trans-forms for
compounds 6 and 7. In the second case these values
were higher than in the first (5.7 Hz (cis) and 11.8 Hz
The hydrosilylation of furan-2-acrylic acid (FAC)
and cinnamyl alcohol (CAL), the trans-isomers both,
was studied in the presence of 1 mol.% [Rh(COD)Cl]2
in dichloromethane. The complete conversions were
reached for 15 h at 40°C and after 46 h without
heating, respectively (Scheme 5). In the reaction of
FAC the products were isolated by vacuum distillation
(70–80°C/0.1 mm) in 68% yield. The reaction products
of CAL hydrosilylation were isolated by filtration over
silica gel in 75% yield. The mixtures of the unsaturated
(in trans-configurations) and saturated compounds
(
trans) for 6 and 15.7 Hz (trans) for 7).
The product 9 was identified as E-isomer because
CH2 protons of Et group had not the long range
1
coupling with proton of CꢀCH group. The H-NMR
spectra of 10 (Z- and E-) indicated the Et group
migration from C-4 to C-3 in the side chain. In the
spectra of Z-10 and E-10 there have appeared the
signals of two CH -group protons with chemical shifts
2
1
l=3.51 and 3.29 which are close to those in spectra of
cis-6 and trans-6 (3.54 and 3.33). Besides, the addi-
tional coupling (J=0.8–1 Hz) of doublet to triplet of
the proton in 3 position of the furan ring was observed.
The similar values of l and coupling constants were
found for the compound 6, thus confirming the pres-
were detected by the H-NMR and GC-MS analysis of
the reaction products. The dehydrogenative silylation
took place in the reactions of these starting substrates
yielding the corresponding silyl ether of alcohol and
ester of acid (11 and 13). The processes of complete
additions also occurred giving the saturated products
(12 and 14).
ence of CH group in the 2 position of the furan ring.
2
The assignment of Z- and E-conformers of the 10 is
based on the analysis of the proton chemical shifts of
the h- and i-CH groups in the system:
2
It is known [16], that the change of the cisoidal
position to the transoidal one causes the decrease by
~0.2 ppm in the chemical shift of the h-methylene
protons and slight increase in l of i-CH protons. The
2
comparison of the chemical shifts of both CH groups
2
(
h- and i-) showed that Z-10 h-CH protons resonate
2
in lower field (Dl=0.22 ppm) than protons of E-10
Scheme 3.

126
I. Io6el et al. / Journal of Organometallic Chemistry 559 (1998) 123–130
Scheme 4.
3. Conclusions
4. Experimental
4
.1. Measurement
1
. [Rh(COD)Cl]2 has been found to be effective in
the hydrosilylation of unsaturated furan and ben-
zene aldehydes, acid and carbinol.
. The hydrosilylation of aldehydes proceeds mainly
as an 1,4-addition reaction yielding the corre-
sponding Z- and E-silyl ethers.
1
H-NMR spectra were registered on a Bruker AC-360
(
360 MHz) spectrometer using CDCl as a solvent and
3
2
Me Si as an internal standard. The mass spectra were
4
obtained on a Kratos MS-25 (70 eV) GC-MS instrument.
The GC analyses of the reaction mixtures were per-
formed on a chromatograph Chrom-4 equipped with a
flame-ionization detector and glass column (2.4 m ×3
mm) packed with 10% SE-30 and 2.5% Reoplex 400 on
Chromosorb W-AW (60–80 mesh); the carrier gas was
3
4
5
6
7
. The hydrosilylation of the nitro derivatives of 3-(2-
furyl)acrolein yields moreover the products of cor-
responding to a 1,2-addition.
. The subsequent hydrogenation accompanies the
hydrosilylation of 3-(2-furyl)acrolein, 3-(5-nitro-2-
furyl)acrolein and 3-(4-pyridyl)acrolein.
. The migration of h-ethyl group to i-position was
found in the hydrosilylation of 3-ethyl-3-(5-nitro-2-
furyl)acrolein.
. The products of dehydrogenative silylation were
obtained in the reactions of cinnamyl alcohol and
furan-2-acrylic acid.
−
1
nitrogen (60 ml min ). The temperature was pro-
grammed from 60 to 270°C (10°C min ).
−
1
. The order of the substrates reactivity in the hy-
drosilylation catalyzed by [Rh(COD)Cl] is as fol-
2
lows:
Scheme 5.

I. Io6el et al. / Journal of Organometallic Chemistry 559 (1998) 123–130
127
1
4.2. Materials
87 (65), 81 (21), 77 (15), 75 (23). H-NMR: l (ppm), J
Hz) 0.55–0.75 (6H, q, J=8.2, MeCH ), 0.98 (9 H, t,
(
2
Dichloromethane was dried over P O and distilled;
J=8.2, CH ), 3.46 (2 H, m, J =7.4, J =1.4,
2
5
3 1 2
xylene was distilled from LiAlH4 prior to use.
Rh(COD)CI] was synthesized according to procedure
FurCH ), 4.65 (1H, dt, J =7.4, J =5.5, CH CH), 6.33
2 1 2 2
[
(1 H, dt, J =5.5, J =1.4, CHOSi), protons of Fur:
2
1 2
given in [17]. The other transition metal complexes were
obtained from Fluka. Triethylsilane, cinnamaldehyde,
cinnamyl alcohol, furylacrolein and furylacrylic acid
were purchased from commercial sources (Fluka,
Aldrich). Silica gel (Kieselgel 60, 0.063–0.200 mm,
Merck) was used for column chromatography. 4-
Pyridylacrolein and two nitrofuryl derivatives were syn-
thesized following the methods [18,19].
5.97 (1H, m, H-3), 6.27 (1H, m, H-4), 7.3 (1H, m, H-5).
4.4.2. trans-triethyl{[3-(2-furyl)-2-propenyl]oxy}silane
(trans-1)
+
MS: m/z [rel. int. (%)] 238 (100, M ), 209 (86,
+
+
M
−Et), 179 (18), 153 (47), 151 (28, M −3Et), 125
+
(45), 115 (18), 107 (71, M −OSiEt ), 103 (11), 97 (15),
87 (50), 81 (22), 75 (15). H-NMR: l (ppm), J(Hz)
3
1
0
.55–0.75 (6 H, q, J=8.2, MeCH ), 0.98 (9H, t, J=
2
4.3. General procedure for hydrosilylation of
8.2, CH ), 3.22 (2H, m, J =7.6, J =1.2, FurCH );
3 1 2 2
unsaturated (hetero)aromatic aldebydes, acid and
5.12 (1H, dt, J =10.6, J =7.6, CH CH), 6.37 (1H, dt,
1 2 2
alcohol
J =10.6, J =1.2, CHOSi), protons of Fur: 6.0 (1 H,
1 2
m, H-3), 6.3 (1 H, m, H-4), 7.3 (1 H, m, H-5).
In a typical procedure 0.05–0.25 mmol of the metal
3
complex catalyst was placed in a 5-cm Pierce reaction
4.4.3. Triethyl[3-(2-furyl)propoxy]silane (2)
+
+
vial under an argon atmosphere and was dissolved in 2
ml of dry dichloromethane (or xylene in a case of PA).
Then 5 mmol of substrate and 1.2 equivalents (6 mmol,
MS: m/z [rel. int. (%)] 240 (53, M ), 211 (70, M −
+
Et), 181 (10), 155 (10), 153 (18, M −3Et), 125 (10),
+
117 (12), 108 (100, M −HOSiEt ), 91 (14), 77 (13).
3
1
1
.0 ml) of triethylsilane were added and stirred at
H-NMR: l (ppm), J (Hz) 0.55–0.75 (6 H, q, J=8.2,
ambient temperature (either at 40, or 120°C) until
almost complete conversion of the substrate (monitor-
ing by GC and GC-MS). The resulting reaction mixture
was filtered off from the catalyst over silica gel, the
solvent was removed under reduced pressure to obtain
a mixture of the reaction products-silyl derivatives,
MeCH ), 0.98 (9H, t, J=8.2, CH ), 2.78 (2H, m,
2
3
J =7.4, J =6.4, CH CH CH ), 2.98 (2H, t, J=7.4,
1
2
2
2
2
FurCH ), 3.65 (2H, t, J=6.4, CH OSi), protons of
2
2
Fur: 6.0 (1H, m, H-3), 6.3 (1H, m, H-4), 7.3 (1H, m,
H-5).
1
which were analyzed by means of H-NMR and GC-
4.5. Reaction of cinnamaldehyde (CA)
MS. Some reaction mixtures were distilled in vacuum,
some of them were separated by column chromatogra-
phy (silica gel 60, eluents: hexane–ethyl ether 9:1 or
benzene–hexane 9:1).
In a Pierce vial the catalyst [Rh(COD)Cl] (25 mg,
0.05 mmol), dichloromethane (2 ml), CA (0.66 g, 5
2
mmol), HSiEt (1 ml, 6 mmol) were placed and stirred
3
at room temperature. The complete conversion was
reached after 15 h (analysis by GC and GC-MS). The
reaction mixture was filtered over silica gel, and the
solvent was removed. The obtained product (1.02 g,
4
.4. Reaction of 3-(2-furyl)acrolein (FA)
In a Pierce vial the catalyst [Rh(COD)Cl] (25 mg,
.05 mmol), dichloromethane (2 ml), FA (0.61 g, 5
2
1
0
82% yield) was analyzed by means of H-NMR and
mmol), HSiEt (1 ml, 6 mmol) were placed and stirred
GC-MS, and the silyl ether 3 (in cis- and trans-configu-
rations, ratio 77/23) was found.
3
at ambient temperature. The complete conversion was
reached after 24 h (analysis by GC and GC-MS). The
reaction mixture was filtered over silica gel and the
solvent was removed. The product was isolated by
vacuum distillation at 69-72°C/0.1-0.2 mm in yield 1.05
g (87%). The mixture of silyl ethers 1 (in cis- and
trans-configurations) and 2 (in ratio 51/37/12) was de-
4.5.1. cis-triethyl[(3-phenyl-2-propenyl)oxy]silane (cis-3)
+
MS: m/z [rel. int. (%)] 248 (42, M ), 219 (100,
+
+
M
−Et), 163 (29), 135 (25), 117 (59, M −OSiEt3),
1
115 (20), 103 (20), 91 (18), 87 (19), 77 (5). H-NMR: l
(ppm), J(Hz) 0.68(6H, q, J=8.0, MeCH ), 1.00 (9H, t,
2
1
tected in this product by means of H-NMR and GC-
J=8.0, CH ), 3.45 (2H, dd, J =7.5, J =1.7, PhCH ),
3
1
2
2
MS analysis.
4.66 (1 H, dt, J =7.5, J =5.8, CH CH), 6.33 (1H, dt,
1 2 2
J =5.8, J =1.7, CHOSi), 7.22–7.26 (5H, m, Ph).
1
2
4.4.1. cis-triethyl{[3-(2-furyl)-2-propenyl]oxy}silane
(
cis-1)
4.5.2. trans-triethyl[(3-phenyl-2-propenyl)oxy]silane
(trans-3)
+
MS: m/z [ref. int. (%)] 238 (100, M ), 209 (93,
+
+
+
M
(
−Et), 179 (12), 153 (55), 151 (29, M -3Et), 125
MS: m/z [rel. int. (%)] 248 (40, M ), 219 (100,
+
+
+
50), 115 (22), 107 (93, M −OSiEt ), 103 (15), 97 (20),
M −Et), 194 (10), 163 (28), 135 (28), 117 (67, M −
3

128
I. Io6el et al. / Journal of Organometallic Chemistry 559 (1998) 123–130
OSiEt ), 115 (20), 103 (18), 91 (18), 87 (20), 77 (2).
H-NMR: l (ppm), J(Hz) 0.67 (6 H, q, J=8.2,
4.7.1. cis-Triethyl{[3-(5-nitro-2-furyl)-2-
propenyl]oxy}silane (cis-6)
MS: m/z [rel. int. (%)] 283 (5, M ), 254 (100, M −
3
1
+
+
MeCH ), 0.98 (9H, t, J=8.2, CH ), 3.23 (2 H, dd,
2
3
J =7.5, J =1.4, PhCH ), 5.16 (1H, dt, J =11.5, J =
Et), 195 (8), 167 (15), 151 (8), 132 (13), 115 (15), 103
(13), 91 (15), 87 (43), 75 (35), 63 (14), 59 (46), 45 (16).
H-NMR: (ppm), J (Hz) 0.67 (6 H, q, J=8.2, MeCH2),
1
2
2
1
2
7
.5, CH CH), 6.34 (1H, dt, J =11.5, J =1.4, CHOSi),
2
1
2
1
7.15–7.20 (5H, m, Ph).
0
4
.97 (9H, t, J=8.2, CH ), 3.54 (2H, m, J =7.1, CH ),
3 1 2
.64 (1 H, dt, J =5.7, J =7.1, CH CH), 6.41 (1H, dt,
1
2
2
4.6. Reaction of 3-(4-pyridyl)acrolein (PA)
J =5.7, J =1.3, CHOSi), ring protons: 6.25 (1H, dt,
1
2
J =3.6, J =1.0, H-3), 7.24 (1H, dt, J =3.6, J B0.2,
H-4).
1
2
1
2
In a Pierce vial the catalyst [Rh(COD)CI] (50 mg,
.10 mmol), xylene (2 ml), PA (0.66 g, 5 mmol), HSiEt3
2
0
(
1 ml, 6 mmol) were placed and stirred at 120°C. The
complete conversion was reached after 48 h (monitor-
ing by GC and GC-MS). The reaction mixture was
filtered over silica gel, and the solvent was removed.
4.7.2. trans-Triethyl{[3-(5-nitro-2-furyl)-2
-propenyl]oxy}silane (trans-6)
MS: m/z [rel. int. (%)] 283 (4, M ), 254 (100, M
+
+
−
1
The product (0.56 g, 45%) was analyzed by H-NMR
Et), 195 (8), 167 (16), 151 (8), 132 (14), 115 (16), 91
(16), 87 (44), 75 (33), 59 (45), 45 (13). H-NMR: l
1
and GC-MS, and the formation of the mixture of silyl
ethers 4 (in cis-configuration) and 5 (the ratio 22/78)
was obtained.
(ppm), J (Hz) 0.69(6H, q, J=8.0, MeCH ), 0.99 (9H, t,
2
J=8.0, CH ), 3.33 (2H, m, J =7.6, J =1.0, CH CH),
3
1
2
2
5
.08 (1H, dt, J =11.8, J =7.6, CH CH), 6.45 (1H, dt,
1 2 2
J =11.8, J =1.0, CHOSi), ring protons: 6.27 (1H, dt,
1
2
4
(
.6.1. cis-Triethyl{[3-(4-pyridyl)-2-propenyl]oxy}silane
cis-4)
MS: m/z [rel. int. (%)] 249 (45, M ), 220 (100,
J =3.6, J =1.0, H-3), 7.24 (1 H, dt, J =3.6, J B0.2,
1
2
1
2
H-4).
+
+
+
M
−Et), 164 (10), 136 (25), 118 (40, M −OSiEt3),
1
03 (14), 96 (13), 87 (25), 82 (14), 75 (15), 59 (32).
4.7.3. trans-Triethyl{[3-(5-nitro-2-furyl)-3-
1
H-NMR: l (ppm), J (Hz) 0.68 (6H, q, J=7.9,
MeCH ), 0.98 (9H, t, J=7.9, CH ), 3.43 (2 H, dt,
propenyl]oxy}silane (trans-7)
+
+
MS: m/z [rel. int. (%)] 283 (27, M ), 254 (89, M
−
2
3
J =7.4, J =1.5, PyCH ), 4.62 (1H, dt, J =7.4, J =
Et), 195 (11), 167 (6), 151 (34), 132 (100), 115 (48), 106
(24), 104 (47), 91 (16), 87 (92), 79 (12), 78 (44), 75 (51),
66 (18), 59 (48), 45 (28), 30 (30). H-NMR: l (ppm), J
1
2
2
1
2
5
.8, CH CH), 6.38 (1H, dt, J =5.8, J =1.5, CHOSi),
2 1 2
1
Py protons: 7.24 (2H, m, H-3, 5), 8.46 (2 H, m, H-2, 6).
(
Hz) 0.67 (6 H, q, J=8.0, MeCH ); 0.99 (9H, t, J=8.0,
2
CH ), 4.39 (2H, dd, J =3.8, J =2.1, CH OSi), 6.54
3
1
2
2
4
.6.2. Triethyl[3-(4-pyridyl)propoxy]silane (5)
(
1H, dt, J =15.7, J =2.1, ring-CH), 6.67 (1H, dt,
+
1 2
MS: m/z [rel. int. (%)] 222 (100, M −Et), 194 (7),
J =15.7, J =3.8, CHCH ), ring protons: 6.41 (1H, d,
+
1
2
2
1
20 (9, M −OSiEt ), 106 (2), 97 (5), 92 (5), 83 (5), 75
3
J=3.8, H-3), 7.30 (1H, d, J=3.8, H-4).
1
(
10), 47 (4). H-NMR: l (ppm), J (Hz) 0.52 (6 H, q,
J=7.7, MeCH ), 0.93 (9H, t, J=7.7, CH ), 2.82 (2H,
2
3
t, J=7.2, PyCH ), 2.95 (2H, m, CH CH CH ), 3.65
4.7.4. Triethyl[3-(5-nitro-2-furyl)propoxy]silane (8)
MS: m/z [rel. int. (%)] 256 (100, M −Et), 169 (16),
2
2
2
2
+
(
2H, t, J=6.5, CH OSi), Py protons: 7.13 (2H, m, H-3,
2
5), 8.50 (2H, m, H-2, 6).
123 (8), 115 (7), 103 (11), 91 (17), 87 (13), 75 (26),
1
6
3 (15), 59 (16), 47 (16), 45 (13). H-NMR: l (ppm),
J (Hz) 0.60 (6H, q, J=8.2, MeCH ), 0.96 (9H, t,
2
4
.7. Reaction of 3-(5-nitro-2-furyl)acrolein (NFA1)
J=8.2, CH3), 1.93 (2H, m, J1=7.6, J2=6.0,
CH CH CH ), 2.83 (2H, bt, J=7.6, ring-CH ), 3.67
2
2
2
2
In a Pierce vial the catalyst [Rh(COD)Cl] (50 mg,
2
(
2H, t, J=6.0, CH OSi), ring protons: 6.27 (1H, dt,
2
0
.10 mmol), dichloromethane (2 ml), NFA1 (0.83 g, 5
J =3.6, J =0.8, H-3), 7.24 (1H, dt, J =3.6, J B0.2,
1
2
1
2
mmol), HSiEt (1 ml, 6 mmol) were placed and stirred
3
H-4).
at 40°C. The complete conversion was reached after 20
h (analysis by GC and GC-MS). The reaction mixture
was filtered over silica gel and the solvent was removed.
The product was obtained by vacuum distillation at
4.8. Reaction of 3-ethyl-3-(5-nitro-2-furyl)acrolein
(NFA2)
120–130°C/0.1–0.2 mm in isolated yield 0.86 g (61%).
The obtained mixture has been separated by column
chromatography (silica gel 60, eluent: hexane–ethyl
ether 9:1), and all four individual compounds were
In a Pierce vial the catalyst [Rh(COD)Cl] (50 mg,
0.10 mmol), dichloromethane (2 ml), NFA2 (0.97 g, 5
2
mmol), HSiEt (1 ml, 6 mmol) were placed and stirred
3
1
analyzed by means of H-NMR and MS.
at 40°C. The almost complete conversion was reached

I. Io6el et al. / Journal of Organometallic Chemistry 559 (1998) 123–130
129
after 20 h (analysis by GC and GC-MS). The reac-
4.9.1. trans-Triethyl[(3-phenyl-3-propenyl)oxy]silane
(trans-11)
tion mixture was filtered over silica gel and the sol-
vent was removed. The product was prepared in
isolated yield 0.82 g (53%). The mixture has been
separated by column chromatography (silica gel 60,
eluent: benzene–hexane 9:1).
+
MS: m/z [rel. int. (%)] 248 (28, M ), 219 (89,
+
+
M
−Et), 117 (100, M −OSiEt ), 115 (29), 103
3
1
(12), 91 (15), 77 (2). H-NMR: l (ppm), J (Hz) 0.65
(6H, q, J=7.8, MeCH ), 0.99 (9H, t, J=7.8, CH ),
2
3
4
.34 (2H, dd, J =5.1, J =1.7, CH OSi), 6.29 (1 H,
1 2 2
4
.8.1. E-Triethyl{[3-ethyl-3-(5-nitro-2-furyl)-3-pro-
dt, J =15.9, J =5.1, CHCH ), 6.60 (1H, dt, J =
1
1
2
2
1
penyl]oxy}silane (E-9)
5.9, J =1.7, PhCH), 7.15–7.38 (5H, m, Ph).
2
+
MS: m/z [rel. int. (%)] 311 (22, M ), 282 (100,
+
M
1
−Et), 254 (10), 238 (11), 223 (10), 179 (10),
4
.9.2. Triethyl(3-phenylpropoxy)silane (12+)
32 (21), 115 (46), 103 (20), 91 (25), 87 (53), 75
1
MS: m/z [rel. int. (%)] 250 (2, M ), 221 (100,
(
30), 59 (23), 47 (10). H-NMR: l (ppm), J (Hz)
+
+
M
1
0
−Et), 163 (2, M −3Et), 118 (22), 117 (18),
0
8
.66 (6 H, q, J=8.2, MeCH Si), 0.99 (9 H, t, J=
2
1
03 (10), 91 (35), 77 (2). H-NMR: l (ppm), J (Hz)
.2, CH CH Si), 1.16 (3H, t, J=7.6, CH ), 2.43
3
2
3
.60 (6 H, q, J=7.9, MeCH ), 0.96 (9H, t, J=7.9,
(
2H, q, J=7.6, MeCH ), 4.24 (2H, d, J=1.9,
2
2
CH ), 1.85 (2 H, m, CH CH CH ), 2.68 (2H, dd,
J1=8.0, J2=7.8, PhCH2), 3.64 (2H, t, J=6.5,
CH OSi), 7.15–7.38 (5H, m, Ph).
CH OSi), 6.42 (1H, t, J=1.9, C(Et)ꢀCH), ring pro-
tons: 6.41 (1H, d, J=3.8, H-3), 7.33 (1H, d, J=
3
2
2
2
2
3.8, H-4).
2
4
.8.2. Z-Triethyl{[2-ethyl-3-(5-nitro-2-furyl)-2-pro-
4
.10. Reactions of 3-(2-furyl)acrylic acid (FAC)
penyl]oxy}silane (Z-10)
+
MS: m/z [rel. int. (%)] 311 (45, M ), 282 (100,
In a Pierce vial the catalyst [Rh(COD)Cl] (25 mg,
+
2
M
1
−Et), 223 (12), 199 (12), 195 (12), 179 (10),
0
.05 mmol), dichloromethane (2 ml), FAC (0.69 g, 5
49 (11), 138 (18), 115 (30), 103 (18), 91 (21), 87
mmol), HSiEt3 (1 ml, 6 mmol) were placed and
stirred at 40°C. The complete conversion was
reached after 15 h (analysis by GC and GC-MS).
The reaction mixture was filtered over silica gel and
the solvent was removed. The product was obtained
by vacuum distillation at 70–80°C/0.1 mm in a yield
1
(
62), 75 (34), 59 (49). H-NMR: l (ppm), J (Hz)
0
8
.66 (6H, q, J=8.2, MeCH Si), 0.96 (9 H, t, J=
2
.2, CH CH Si), 0.98 (3H, t, J=7.4, CH ), 1.96
3
2
3
(
2H, dq, J =7.4, J =1.3, MeCH ), 3.51 (2H, bs,
1 2 2
ring-CH ), 6.27 (1H, t, J=1.3, CHOSi), ring pro-
tons: 6.22 (1H, dt, J =3.6, J =1.0, H-3), 7.23 (1H,
d, J=3.6, H-4).
2
1
2
0
.86 g (68%). The mixture of silyl esters 13 and 14
(
in ratio 27/73) was found in this product by means
1
of H-NMR and GC-MS analysis.
4.8.3. E-Triethyl{[2-ethyl-3-(5-nitro-2-furyl)-2-pro-
penyl]oxy}silane (E-10)
+
MS: m/z [rel. int. (%)] 311 (45, M ), 282 (100,
4
.10.1. trans-Triethylsilyl ester of 3-(2-furyl)acrylic
acid (trans-13)
MS: m/z [rel. int. (%)] 252 (6, M ), 223 (100,
+
M
−Et), 195 (13), 132 (16), 115 (33), 103 (13), 91
1
(
22), 87 (70), 75 (33), 59 (62). H-NMR: l (ppm), J
+
(
Hz) 0.67 (6H, q, J=8.2, MeCH Si), 0.99 (9H, t,
+
+
2
M −Et), 179 (27), 151 (12), 121 (55, M −
OSiEt ), 103 (8), 92 (3), 75 (12), 65 (20). H-NMR:
J=8.2, CH CH Si), 0.93 (3H, t, J=7.5, CH ), 2.11
1
3
2
3
3
(
2H, dq, J =7 5. J =0.7, MeCH ), 3.29 (2H, bs,
1 2 2
l (ppm), J (Hz) 0.72–0.86 (6H, q, J=8.2, MeCH2),
ring-CH ), 6.24 (1H, t, J=0.7, CHOSi), ring pro-
tons: 6.25 (1 H, dt, J =3.6, J =0.8, H-3), 7.24
(
2
1.00 (9H, t, J=8.2, CH ), 6.30 (1 H, d, J=15.6,
3
1
2
CHCOO), 7.37 (1H, d, J=15.6, FurCH), protons of
Fur: 6.60 (1H, m, H-3), 6.46 (1H, m, H-4), 7.47
1H, d, J=3.6, H-4).
(
1H, m, H-5).
4.9. Reaction of cynnamyl alcohol (CAL)
In a Pierce vial the catalyst [Rh(COD)Cl] (25 mg,
.05 mmol), dichloromethane (2 ml), CAL (0.67 g, 5
4.10.2. Triethylsilyl ester of 3-(2-furyl)propionic acid
(14)
2
0
+
mmol), HSiEt3 (1 ml, 6 mmol) were placed and
stirred at room temperature. The complete conver-
sion was reached after 46 h (analysis by GC and
GC-MS). The reaction mixture was filtered over sil-
ica gel, and the solvent was removed. The obtained
product (0.94 g, 75% yield) was analyzed by means
MS: m/z [rel. int. (%)] 254 (11, M ), 225 (100,
+
M
−Et), 183 (8), 115 (5), 103 (33), 94 (21), 87
1
(10), 81 (49), 75 (28). H-NMR: l (ppm), J (Hz)
0.75–0.84 (6H, q, J=7.4, MeCH ), 0.96 (9 H, t,
2
J=7.4, CH ), 2.67 (2 H, t, J=7.4, FurCH ), 2.94
3
2
(2H, t, J=7.4, CH COO), protons of Fur: 6.01
2
1
of H-NMR and GC-MS, and two silyl ethers (in
(1H, m, H-3), 6.26 (1 H, m, H-4), 7.28 (1H, m,
H-5).
ratio 55/45) were detected.

1
30
I. Io6el et al. / Journal of Organometallic Chemistry 559 (1998) 123–130
11.
1
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