A mild method for indium(III)-catalyzed 1,4-hydrosilylation of α,β-enone esters with triethylsilane and trifluoroacetic acid

Article abstract of DOI:10.1055/s-0031-1290448

A chemo- and stereoselective 1,4-hydrosilylation of α,β-enone esters was developed using triethylsilane and trifluoroacetic acid under indium chloride catalysis. Georg Thieme Verlag Stuttgart ? New York.

Full text of DOI:10.1055/s-0031-1290448

LETTER
▌2269
lAetteMr ild Method for Indium(III)-Catalyzed 1,4-Hydrosilylation of α,β-Enone
Esters with Triethylsilane and Trifluoroacetic Acid
Indium(III)-Catalyzed 1,4-Hydrosilylation
Ping Xing,a Wei Zang,a Zuo-gang Huang,b Yue-xiong Zhan,a Chuan-jun Zhu,b Biao Jiang*a,b
a
Key Laboratory of Synthetic Chemistry of Natural Substances, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences,
345 Lingling Road, Shanghai 200032, P. R. of China
Fax +86(21)64166128; E-mail: jiangb@sioc.ac.cn
b
Shanghai Advanced Research Institute, Chinese Academy of Sciences, 99 Haike Road, Shanghai 201210, P. R. of China
Received: 26.04.2012; Accepted after revision: 23.06.2012
Table 1 1,4-Hydrosilylation of α,β-Enone Ester 1ga
Abstract: A chemo- and stereoselective 1,4-hydrosilylation of α,β-
enone esters was developed using triethylsilane and trifluoroacetic
acid under indium chloride catalysis.
O
OSiEt3
CO2Et
InCl3, Et3SiH
CF3CO2H, r.t.
CO2Et
Key words: 1,4-hydrosilylation, α,β-enone ester, indium chloride,
triethylsilane, silyl enol ether
Br
Br
1g
2g
Entry Catalyst
(equiv)
Silane (equiv) Brønsted acid Time Yield (%)b
Silanes are well-known reducing regents for a variety of
functional groups. There are numerous reports on the re-
duction of aryl aldehydes or ketones to hydrocarbons us-
ing Et3SiH in the presence of Brønsted or Lewis acids,
such as MeSO3H,1 CF3CO2H(NH4F),2 pyridine·polyHF,3
BF3,4 TiCl4,5 and ZnI2.6 The reduction of conjugated
enones to α,β-saturated ketones can also proceed using si-
lanes and metal salts, such as R3SiH/TiCl4 (R = Me, Et),7
Ph2SiH2/ZnCl2/Pd(PPh3)4,8 or PhMe2SiH/Cu(I) salts.9 Si-
lanes were also used in the reduction of alkenes and im-
ines, decyanation of nitriles,10 and 1,4-hydrosilylation of
α,β-unsaturated carbonyl compounds.11
(equiv)
(h)
1
none
Et3SiH (5.0) TFA (5.0)
2
no reaction
2
InCl3 (0.2) Et3SiH (5.0) TFA (5.0)
InCl3 (0.2) Et3SiH (5.0) TFA (3.0)
InCl3 (0.2) Et3SiH (5.0) TFA (1.0)
InCl3 (0.2) Et3SiH (5.0) none
0.5
0.5
2
41
3
37
4
12
5
2
10
6
InCl3 (0.2) Et3SiH (5.0) TFA (10.0)
InCl3 (1.0) Et3SiH (5.0) TFA (5.0)
InCl3 (0.5) Et3SiH (5.0) TFA (5.0)
InCl3 (0.1) Et3SiH (5.0) TFA (5.0)
InCl3 (0.1) Et3SiH (3.0) TFA (5.0)
InCl3 (0.1) Et3SiH (1.0) TFA (5.0)
InCl3 (0.1) Et3SiH (10.0) TFA (5.0)
1
complex
42
7
0.5
0.5
0.5
0.5
0.5
0.5
0.5
8
40
O
O
ArCHO
[H]
Me
CO2R1
Ar
CO2R1
9
41
A
10
11
12
41
R23SiH
this work
Brønsted acid
27
OSiR2
O
3
base
R23SiCl
42
CO2R1
Ar
CO2R1
C (Z/E)
Ar
13c InCl3 (0.1) Et3SiH (3.0) TFA (5.0)
51
B
a Reactions were carried out under 1 atm of argon in CH2Cl2 (0.5 M)
in the presence of indicated equivalents of InCl3, Brønsted acid, and
Et3SiH.
Scheme 1 Synthesis of 2-siloxy-2-alkenoates
For α,β-enone ester substrates, as shown in Scheme 1, the
hydrogenation of A to B, and following enolization and si-
lylation afforded 2-siloxy-2-alkenoate C, but the stereose-
lectivity of the double bond remained undetermined.12
Herein, we would like to report a mild method using
Et3SiH/TFA and a catalytical amount of InCl3 for the che-
mo- and stereoselective direct 1,4-hydrosilylation of α,β-
enone ester A to give the silyl enol ether C.
b Isolated yields and 1H NMR spectra indicated a single isomer.
c In toluene.
gating the influence of various reaction parameters, and
the results are summarized in Table 1. There was no reac-
tion when the mixture of 1g and Et3SiH was treated with
TFA without any Lewis acid catalyst added (Table 1, en-
try 1). In the presence of 20 mol% of InCl3, the reaction
took place and an isolated 41% yield was obtained (Table
1, entry 2).13 With fewer amounts of TFA, the reaction
yields were also decreased (Table 1, entries 3–5), while
increasing the amount of Brønsted acid, the reaction re-
sulted in a complex (Table 1, entry 6). At higher loadings
of InCl3, or with 10 mol% of InCl3, the yields did not
The 1,4-hydrosilylation of (E)-ethyl-4-(2-bromophenyl)-
2-oxobut-3-enoate (1g) was used as a model for investi-
SYNLETT 2012, 23, 2269–2273
Advanced online publication: 24.08.2012
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6
DOI: 10.1055/s-0031-1290448; Art ID: ST-2012-W0369-L
© Georg Thieme Verlag Stuttgart · New York

2270
P. Xing et al.
LETTER
change much (Table 1, entries 7–9). With slightly lower lents of Et3SiH, the yield did not improve much (Table 1,
amounts (3 equiv) of Et3SiH, the yield was not affected, entry 12).14 A screening of solvents revealed that 52%
while the yield dropped to 27% with only one equivalent yield could be obtained in toluene (Table 1, entry 13), and
of Et3SiH (Table 1, entries 10 and 11). With ten equiva- 30–40% yields for hexane, THF, and MeCN.
Table 2 Scope of the 1,4-Hydrosilylation of α,β-Enone Estersa
Entry
1
Substrate
Product
Yield (%)b
O
O
O
OSiEt3
CO2Et
CO2Et
53
F
F
1a
2a
O
OSiEt3
CO2Et
F
F
CO2Et
2
3
56
62
1b
2b
OSiEt3
CO2Et
O
CO2Et
F
F
1c
2c
OSiEt3
CO2Et
CO2Et
4
5
6
57
52
61
Cl
Cl
1d
2d
OSiEt3
CO2Et
O
Cl
Cl
CO2Et
1e
2e
OSiEt3
CO2Et
O
CO2Et
Cl
Cl
1f
2f
OSiEt3
CO2Et
CO2Et
7
8
9
51
57
59
Br
Br
1g
2g
O
OSiEt3
CO2Et
Br
Br
CO2Et
2h
1h
O
OSiEt3
CO2Et
CO2Et
Br
Br
1i
2i
Synlett 2012, 23, 2269–2273
© Georg Thieme Verlag Stuttgart · New York

LETTER
Indium(III)-Catalyzed 1,4-Hydrosilylation
2271
Table 2 Scope of the 1,4-Hydrosilylation of α,β-Enone Estersa (continued)
Entry
10
Substrate
Product
Yield (%)b
O
OSiEt3
CO2Et
CO2Et
54
MeO
MeO
1j
2j
O
OSiEt3
CO2Et
CO2Et
11
12
60
51
2k
1k
O
OSiEt3
CO2Et
CO2Et
O2N
O2N
1l
2l
O
13c
14c
15c
60
2m
1m
1n
O
60
2n
O
OEt
–
no reaction
1o
O
O
CO2Et
CO2Et
16
17
–
–
complex mixture
unstable
1p
O
S
1q
a Reactions were carried out under 1 atm of argon at r.t. in toluene (0.5 M) in the presence of 10 mol% of InCl3, 3 equiv of Et3SiH, and 5 equiv
of TFA for 0.5 h.
b Isolated yields and 1H NMR spectra indicated a single isomer.
c Reaction time 20–30 h.
We then studied a variety of α,β-enone ester substrates, 4–9). For 1j and 1k, the reactions were also applicable and
and the results are summarized in Table 2. The 1,4-hydro- gave products 2j and 2k in 54–60% yield (Table 2, entries
silylation reactions of 1a–c with different fluorine-substi- 10 and 11). For 1l with a strong electron-withdrawing
tuted positions all preceded smoothly and gave products group (NO2), the reactions afforded product 2l in 51%
2a–c in moderate yields (53–62%, Table 2, entries 1–3). yield (Table 2, entry 12). However, for α,β-enone sub-
For substrates with a weaker electron-withdrawing group stances 1m and 1n, the reduction of carbonyl to methylene
(Cl, Br), the 1,4-hydrosilylation reactions also afforded occurred instead of 1,4-hydrosilylation (Table 2, entries
products 2d–i in similar yields (51–61%, Table 2, entries 13 and 14), and for the α,β-unsaturated ester 1o, the reduc-
© Georg Thieme Verlag Stuttgart · New York
Synlett 2012, 23, 2269–2273

2272
P. Xing et al.
LETTER
tion did not proceed (Table 2, entry 15).15 Using furan or
thiophene derivatives as substrates, the reaction resulted
in a mess or unstable products (Table 2, entries 16 and 17).
(Z)-Ethyl 4-(4-Fluorophenyl)-2-[(triethylsilyl)oxy]but-2-enoate
(2c)
Yellow oil. 1H NMR (300 MHz, CDCl3): δ = 7.16 (dd, J = 8.4, 5.7
Hz, 2 H), 6.97 (t, J = 8.7 Hz, 2 H), 6.13 (t, J = 7.5 Hz, 1 H), 4.21 (q,
J = 7.2 Hz, 2 H), 3.49 (d, J = 6.3 Hz, 1 H), 1.30 (t, J = 7.2 Hz, 3 H),
1.02 (t, J = 7.8 Hz, 9 H), 0.75 (q, J = 7.8 Hz, 6 H). 13C NMR (75
MHz, CDCl3): δ = 164.8, 161.4 (d, J = 243 Hz), 141.2, 135.3 (d, J
= 3 Hz), 129.8 (d, J = 8 Hz), 120.3, 115.2 (d, J = 21 Hz), 61.1, 31.0,
14.2, 6.8, 5.4. ESI-MS: m/z = 361.0 [M + Na]+. ESI-HRMS: m/z
calcd for C18H27FNaO3Si: 361.1611; found: 361.1611. IR: 2957,
2912, 2877, 1723, 1646, 1586, 1017, 978, 754 cm–1.
OSiEt3
HMBC:
δ (C1) = 165.5
δ (H3) = 6.13
CO2Et
H
3JCH = 3.3 Hz
Br
Figure 1
(Z)-Ethyl 4-(2-Chlorophenyl)-2-[(triethylsilyl)oxy]but-2-eno-
ate (2d)
Since only one single isomer of all the above products had
been generated, we then selected 2i and used the HMBC
method to determine the geometry of its double bond
(Figure 1). The resulted 3JCH of the carbonyl carbon (C1)
and the β-hydrogen (H3) is 3.3 Hz (see Supporting Infor-
mation); thus, the trisubstituted double bond could be as-
signed to be of Z-configuration.16
1
White oil. H NMR (300 MHz, CDCl3): δ = 7.37–7.17 (m, 4 H),
6.14 (t, J = 7.2 Hz, 1 H), 4.21 (q, J = 6.9 Hz, 2 H), 3.63 (d, J = 7.2
Hz, 2 H), 1.30 (t, J = 6.9 Hz, 3 H), 1.00 (t, J = 7.5 Hz, 9 H), 0.77 (q,
J = 7.5 Hz, 6 H). 13C NMR (75 MHz, CDCl3): δ = 164.7, 141.8,
137.4, 134.0, 130.2, 129.4, 127.7, 126.9, 118.7, 61.1, 29.6, 14.2,
6.8, 5.5. ESI-MS: m/z = 377.0 [M + Na]+. ESI-HRMS: m/z calcd for
C18H27ClNaO3Si: 377.1316; found: 377.1326. IR: 3426, 3067,
2956, 2876, 1723, 1371, 1051, 905, 745 cm–1.
In summary, we have developed a mild method for the
chemo- and stereoselective 1,4-hydrosilylation of α,β-
enone esters with triethylsilane and trifluoroacetic acid
with a catalytic amount of indium chloride. Moderate
yields of 50–60% have been obtained for a variety of sub-
strates with different substitution groups.
(Z)-Ethyl 4-(3-Chlorophenyl)-2-[(triethylsilyl)oxy]but-2-eno-
ate (2e)
1
Yellow oil. H NMR (300 MHz, CDCl3): δ = 7.22–7.07 (m, 4 H),
6.11 (t, J = 7.2 Hz, 1 H), 4.21 (q, J = 6.9 Hz, 2 H), 3.49 (d, J = 7.2
Hz, 2 H), 1.31 (t, J = 7.2 Hz, 3 H), 1.00 (t, J = 7.2 Hz, 9 H), 0.75 (q,
J = 7.2 Hz, 6 H). 13C NMR (75 MHz, CDCl3): δ = 164.6, 141.7,
141.6, 134.2, 129.7, 128.6, 126.6, 126.4, 119.4, 61.1, 31.4, 14.2,
6.8, 5.5. ESI-MS: m/z = 376.9 [M + Na]+. ESI-HRMS: m/z calcd for
C18H27ClNaO3Si: 377.1316; found: 377.1314. IR: 2957, 2911,
2877, 1724, 1644, 1371, 979, 766, 742, 68 cm–1.
General Experimental Procedure
A mixture of α,β-enone ester (1.0 mmol), InCl3 (0.10 mmol), and
Et3SiH (3.0 mmol, 0.48 mL) in toluene (2.0 mL) was treated with
TFA (5.0 mmol, 0.38 mL) at r.t. dropwise. The solution was stirred
at r.t. until no α,β-enone ester was detected by TLC. The solution
was diluted with EtOAc (10 mL), NaHCO3 (aq, 10 mL), and H2O
(10 mL), the organic solution was separated, and the aqueous layer
was extracted by EtOAc (2 × 10 mL). The combined organic layer
was dried over anhyd Na2SO4, concentrated to dryness, and the res-
idue was purified by flash chromatography on silica gel to give the
product.
(Z)-Ethyl 4-(4-Chlorophenyl)-2-[(triethylsilyl)oxy]but-2-eno-
ate (2f)
Yellow oil. 1H NMR (300 MHz, CDCl3): δ = 7.18 (dd, J = 37.8, 8.4
Hz, 4 H), 6.11 (t, J = 7.8 Hz, 1 H), 4.21 (q, J = 7.2 Hz, 2 H), 3.49 (d,
J = 7.5 Hz, 2 H), 1.30 (t, J = 7.2 Hz, 3 H), 1.00 (t, J = 7.8 Hz, 9 H),
0.77 (q, J = 7.8 Hz, 6 H). 13C NMR (75 MHz, CDCl3): δ = 164.7,
141.5, 138.2, 131.9, 129.8, 128.6, 119.8, 61.1, 31.1, 14.2, 6.8, 5.5.
ESI-MS: m/z = 377.0 [M + Na]+. ESI-HRMS: m/z calcd for
C18H27ClNaO3Si: 377.1316; found: 377.1318. IR: 2957, 2911,
2877, 1723, 1645, 1371, 784, 763, 702 cm–1.
(Z)-Ethyl 4-(2-Fluorophenyl)-2-[(triethylsilyl)oxy]but-2-enoate
(Z)-Ethyl 4-(2-Bromophenyl)-2-[(triethylsilyl)oxy]but-2-enoate
(2a)
1
(2g)
Yellow oil. H NMR (300 MHz, CDCl3): δ = 7.23–7.00 (m, 4 H),
1
Yellow oil. H NMR (300 MHz, CDCl3): δ = 7.56–7.05 (m, 4 H),
6.12 (t, J = 7.5 Hz, 1 H), 4.21 (q, J = 7.2 Hz, 2 H), 3.55 (d, J = 7.5
Hz, 2 H), 1.30 (t, 7.2 Hz, 3 H), 1.00 (t, J = 8.1 Hz, 9 H), 0.75 (q, J
= 8.1 Hz, 6 H). 13C NMR (75 MHz, CDCl3): δ = 164.7, 160.9 (d, J
= 183 Hz), 141.6, 130.5 (d, J = 3 Hz), 127.9 (d, J = 6 Hz), 126.6 (d,
J = 12 Hz), 124.1 (d, J = 2 Hz), 119.0, 115.2 (d, J = 16.2 Hz), 61.0,
25.0 (d, J = 3 Hz), 14.2, 6.7, 5.5. ESI-MS: m/z = 361.0 [M + Na]+.
ESI-HRMS: m/z calcd for C18H27FNaO3Si: 361.1611; found:
361.1620. IR: 2957, 2912, 2877, 1723, 1646, 1586, 978, 754 cm–1.
6.14 (t, J = 7.2 Hz, 1 H), 4.21 (q, J = 6.9 Hz, 2 H), 3.64 (d, J = 7.2
Hz, 2 H), 1.30 (t, J = 6.9 Hz, 3 H), 1.00 (t, J = 7.8 Hz, 9 H), 0.75 (q,
J = 7.8 Hz, 6 H). 13C NMR (75 MHz, CDCl3): δ = 164.6, 141.7,
139.1, 132.7, 130.2, 127.9, 127.5, 124.5, 118.8, 61.1, 32.3, 14.2,
6.8, 5.5. ESI-MS: m/z = 423.0 [M + Na]+. ESI-HRMS: m/z calcd for
C18H27BrNaO3Si: 421.0811; found: 421.0801. IR: 2957, 2911,
2877, 1723, 1644, 1250, 978, 786, 745, 704 cm–1.
(Z)-Ethyl 4-(3-Bromophenyl)-2-[(triethylsilyl)oxy]but-2-enoate
(Z)-Ethyl 4-(3-Fluorophenyl)-2-[(triethylsilyl)oxy]but-2-enoate
(2h)
(2b)
1
1
White oil. H NMR (300 MHz, CDCl3): δ = 7.36–7.14 (m, 4 H),
White oil. H NMR (300 MHz, CDCl3): δ = 7.22–6.90 (m, 4 H),
6.11 (t, J = 7.8 Hz, 1 H), 4.21 (q, J = 7.2 Hz, 2 H), 3.49 (d, J = 7.8
Hz, 2 H), 1.31 (t, J = 7.2 Hz, 3 H), 1.00 (t, J = 7.8 Hz, 9 H), 0.75
( q, J = 7.8 Hz, 6 H). 13C NMR (75 MHz, CDCl3): δ = 164.6, 142.1,
141.6, 131.5, 130.0, 129.3, 127.1, 122.5, 119.3, 61.1, 31.4, 14.2,
6.7, 5.5. ESI-MS: m/z = 421.0 [M + Na]+. ESI-HRMS: m/z calcd for
C18H27BrNaO3Si: 421.0811; found: 421.0802. IR: 2956, 2910,
2877, 1723, 1644, 1392, 1017, 765, 742, 669 cm–1.
6.13 (t, J = 7.5 Hz, 1 H), 4.21 (q, J = 6.9 Hz, 2 H), 3.51 (d, J = 7.5
Hz, 2 H), 1.30 (t, J = 6.9 Hz, 3 H), 1.00 (t, J = 7.8 Hz, 9 H), 0.75 (q,
J = 7.8 Hz, 6 H). 13C NMR (75 MHz, CDCl3): δ = 164.7, 162.9 (d,
J = 167 Hz), 142.3 (d, J = 7 Hz), 141.6, 129.9 (d, J = 8 Hz), 124.1
(d, J = 3 Hz), 119.5, 115.3 (d, J = 21 Hz), 113.6 (d, J = 21 Hz), 61.1,
31.4, 14.2, 6.8, 5.5. ESI-MS: m/z = 361.0 [M + Na]+. ESI-HRMS:
m/z calcd for C18H27FNaO3Si: 361.1611; found: 361.1610. IR:
2957, 2912, 2877, 1723, 1645, 1077, 769, 742, 691 cm–1.
Synlett 2012, 23, 2269–2273
© Georg Thieme Verlag Stuttgart · New York

LETTER
Indium(III)-Catalyzed 1,4-Hydrosilylation
2273
(Z)-Ethyl 4-(4-Bromophenyl)-2-[(triethylsilyl)oxy]but-2-enoate
(2i)
Acknowledgment
Yellow oil. 1H NMR (300 MHz, CDCl3): δ = 7.40 (d, J = 8.7 Hz, 2
H), 7.08 (d, J = 8.7 Hz, 2 H), 6.11 (t, J = 7.2 Hz, 3 H), 4.21 (q, J =
7.1 Hz, 2 H), 3.47 (d, J = 7.2 Hz, 2 H), 1.3 (t, 7.1 Hz, 3 H), 1.00 (t,
J = 7.8 Hz, 9 H), 0.75 (q, J = 7.8 Hz, 6 H). 13C NMR (75 MHz,
CDCl3): δ = 164.6, 141.5, 138.7, 131.5, 130.2, 119.9, 119.6, 61.1,
31.2, 14.2, 6.7, 5.5. ESI-MS: m/z = 420.9 [M + Na]+. ESI-HRMS:
m/z calcd for C18H27BrNaO3Si: 421.0811; found: 421.0815. IR:
2956, 2911, 2876, 1723, 1645, 1371, 1250, 782, 742, 700 cm–1.
We are grateful for the National Basic Research Program of China
(2010CB833200).
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synlett.SnuIpofoiprmntgirStanoIuifpog
r
t
iornat
References and Notes
(Z)-Ethyl 4-(4-Methoxyphenyl)-2-[(triethylsilyl)oxy]but-2-eno-
ate (2j)
(1) Olah, G. A.; Arvanaghi, M.; Ohannesian, L. Synthesis 1986,
770.
(2) (a) Mayr, H.; Dogan, B. Tetrahedron Lett. 1997, 38, 1013.
(b) West, C. T.; Donnelly, S. J.; Kooistra, D. A.; Doyle, M.
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(6) Li, Z.; Deng, G.; Li, Y.-C. Synlett 2008, 3053.
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Bull. 1977, 25, 1468.
1H NMR (300 MHz, CDCl3): δ = 7.12 (d, J = 8.7 Hz, 2 H), 6.84 (d,
J = 8.7 Hz, 2 H), 6.15 (t, J = 7.8 Hz, 1 H), 4.20 (q, J = 7.2 Hz, 2 H),
3.78 (s, 3 H), 3.47 (d, J = 7.5 Hz, 2 H), 1.29 (t, J = 7.2 Hz, 3 H), 1.01
(t, J = 5.2 Hz, 9 H), 0.75 (q, J = 5.2 Hz, 6 H). 13C NMR (75 MHz,
CDCl3): δ = 164.8, 158.0, 140.9, 131.8, 129.4, 121.2, 113.9, 60.9,
55.2, 31.0, 14.2, 6.8, 5.4. ESI-MS: m/z = 373.0 [M + Na]+. ESI-
HRMS: m/z calcd for C19H30NaO4Si: 373.1811; found: 373.1810.
IR: 2956, 2876, 2835, 1722, 1644, 1512, 1318, 1106, 978, 807 cm–1.
(Z)-Ethyl 4-Phenyl-2-[(triethylsilyl)oxy]but-2-enoate (2k)
1
White oil. H NMR (300 MHz, CDCl3): δ = 7.63–7.11 (m, 5 H),
6.19 (t, J = 7.2 Hz, 1 H), 4.22 (q, J = 6.9 Hz, 2 H), 3.55 (d, J = 7.5
Hz, 2 H), 1.31 (t, J = 7.2 Hz, 3 H), 1.03 (t, J = 7.2 Hz, 9 H), 0.79 (q,
J = 7.8 Hz, 6 H). 13C NMR (75 MHz, CDCl3): δ = 164.8, 141.1,
139.7, 128.6, 126.1, 120.6, 61.0, 31.8, 14.2, 6.7, 5.5. ESI-MS: m/z
= 343.2 [M + Na]+. ESI-HRMS: m/z calcd for C18H28NaO3Si:
343.1700; found: 343.1710. IR: 2956, 2877, 1723, 1645, 1372,
1253, 1138, 742 cm–1.
(8) Keinan, E.; Greenspoon, N. J. Am. Chem. Soc. 1986, 108,
7314.
(9) Mori, A.; Fujita, A.; Hiroshi, K.; Nishihara, Y.; Hiyama, T.
Tetrahedron 1999, 55, 4573.
(10) (a) Hog, D. T.; Oestreich, M. Eur. J. Org. Chem. 2009, 5047.
(b) Lee, O.-Y.; Law, K.-L.; Yang, D. Org. Lett. 2009, 11,
3302. (c) Fernandes, A. C.; Romao, C. Tetrahedron Lett.
2005, 46, 8881. (d) Tobisu, M.; Nkamura, R.; Kita, Y.;
Chatani, N. Bull. Korean Chem. Soc. 2010, 31, 582.
(11) (a) Anada, M.; Tanaka, M.; Suzuki, K.; Nambu, H.;
Hashimoto, S. Chem. Pharm. Bull. 2006, 54, 1622.
(b) Blackwell, J. M.; Morrison, D. J.; Piers, W. E.
Tetrahedron 2002, 58, 8247. (c) Mori, A.; Kato, T. Synlett
2002, 1167.
(12) (a) Hoffman, R. V.; Johnson, M. C.; Okonya, J. F. J. Org.
Chem. 1997, 62, 2458. (b) Okonya, J. F.; Johnson, M. C.;
Hoffman, R. V. J. Org. Chem. 1998, 63, 6409.
(13) (a) Other indium salts like InF3, InBr3, InI3, and In(OTf)3
resulted in no reaction or complex mixtures. (b) Using TiCl4
or BF3·OEt2 instead of InCl3 resulted in only 12–23% yields.
(14) Other silanes like Ph2SiH2, (MeO)3SiH, (EtO)3SiH, and
Cl3SiH resulted in no reaction or complex mixtures.
(15) For a Rh-catalyzed 1,4-hydrosilylation of α,β-enone to
generate Z/E intermediates, see: Anada, M.; Tanaka, M.;
Washio, T.; Yamawaki, M.; Abe, T.; Hashimoto, S. Org.
Lett. 2007, 9, 4559.
(Z)-Ethyl 4-(4-Nitrophenyl)-2-[(triethylsilyl)oxy]but-2-enoate
(2l)
Yellow oil. 1H NMR (300 MHz, CDCl3): δ = 8.15 (d, J = 8.7 Hz, 1
H), 7.36 (d, J = 8.8 Hz, 1 H), 6.10 (t, J = 7.5 Hz, 1 H), 4.22 (q, J =
7.1 Hz, 2 H), 3.61 (d, J = 7.5 Hz, 2 H), 1.31 (t, J = 7.2 Hz, 3 H), 0.99
(t, J = 8.1 Hz, 9 H), 0.75 (t, J = 8.1 Hz, 6 H). 13C NMR (75 MHz,
CDCl3): δ = 164.4, 147.6, 142.3, 129.2, 123.8, 117.7, 61.3, 31.6,
14.2, 6.7, 5.5. ESI-MS: m/z = 388.0 [M + Na]+. ESI-HRMS: m/z
calcd for C18H27NNaO5Si: 388.1551; found: 388.1554. IR: 2961,
1727, 1519, 1347, 1260, 1110, 1074, 1018 cm–1.
(E)-But-1-en-1-ylbenzene (2m)
White oil. 1H NMR (300 MHz, CDCl3): δ = 7.28 (m, 5 H), 6.33 (m,
2 H), 2.25 (p, J = 7.2 Hz, 2 H), 1.11 (t, J = 7.8 Hz, 3 H).
(E)-1-(But-1-en-1-yl)-4-methylbenzene (2n)
White oil. 1H NMR (300 MHz, CDCl3): δ = 7.26 (d, J = 7.5 Hz, 2
H), 7.11 (d, J = 8.4 Hz, 2 H), 6.26 (m, 2 H), 2.34 (s, 3 H), 2.24 (p, J
= 7.2 Hz, 2 H), 1.10 (t, J = 7.2 Hz, 3 H).
(16) (a) Seneci, P.; Leger, I.; Souchet, M.; Nadler, G.
Tetrahedron 1997, 53, 17097. (b) Grison, C.; Petek, S.;
Coutrot, P. Synlett 2005, 331.
© Georg Thieme Verlag Stuttgart · New York
Synlett 2012, 23, 2269–2273