The first hydroxysilylation of alkenes with triethylsilane under dioxygen catalyzed by N-hydroxyphthalimide

Article abstract of DOI:10.1002/ejoc.200300074

Catalytic hydroxysilylation of alkenes with trialkylsilane under dioxygen through a radical process was successfully achieved by the use of N-hydroxyphthalimide (NHPI) as a catalyst under mild conditions. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.

Full text of DOI:10.1002/ejoc.200300074

FULL PAPER
The First Hydroxysilylation of Alkenes with Triethylsilane under Dioxygen
Catalyzed by N-Hydroxyphthalimide
Osamu Tayama,[a] Takahiro Iwahama,[a] Satoshi Sakaguchi,[a] and Yasutaka Ishii*[a]
Keywords: Hydroxysilylation / Molecular oxygen / N-(Hydroxy)phthalimide / Alkene / Catalysts
Catalytic hydroxysilylation of alkenes with trialkylsilane
under dioxygen through a radical process was successfully
achieved by the use of N-hydroxyphthalimide (NHPI) as a
catalyst under mild conditions.
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2003)
Introduction
Thus, our effort has been focused on the first catalytic
hydroxysilylation of alkenes by the concomitant introduc-
tion of silyl and hydroxyl functions by the use of NHPI as
a key catalyst under dioxygen.[7] In this paper, we report
the first hydroxysilylations of substituted alkenes bearing
electron-withdrawing groups by reacting them with triethyl-
silane and molecular oxygen under the influence of NHPI.
The hydrosilylation of alkenes and alkynes with hydro-
silanes is a frequently used and important method for the
formation of complex organosilanes, such as vinylsilanes.
These reactions can be brought about through catalysis by
Pt and Rh compounds[1] as well as by radical processes,
both photo- and radical-initiated.[2] The latter process is
limited, however, to silanes such as HSiCl3 or MeSiCl2H,[2]
and the introduction of trialkylsilanes to alkenes is not suc- Results and Discussion
cessful. Giese et al. have reported that tris(trimethylsilyl)-
The hydroxysilylation of methyl acrylate (1a) with Et3SiH
silane (TTMSS) adds to carbonϪcarbon multiple bonds by
a free-radical chain process to form the corresponding
hydrosilanes.[3] Thus, a variety of substituted alkenes can be
hydrosilylated successfully by TTMSS in the presence of a
radical initiator, such as AIBN.[4] The simultaneous intro-
duction, however, of both silyl and hydroxyl functions to
carbonϪcarbon multiple bonds, which is referred to as
hydroxysilylation, remained an unsolved reaction.[5]
under dioxygen, which is catalyzed by NHPI combined with
a Co species, was chosen as a model reaction and was car-
ried out under various reaction conditions (Table 1).
Table 1. Hydroxysilylation of methyl acrylate (1a) with Et3SiH to
2a by NHPI under various conditions.
Run[a]
NHPI
(mol %)
Co(OAc)2
(mol %)
Co(acac)3
(mol %)
Conv.[b]
(%)
Yield[b]
(%)
1
2
10
10
0.1
63
57 (90)
Ͻ3
Ͻ4
48 (57)
73 (88)
74 (94)
Ͻ3
Ͻ4
84
83
79
3
0.1
0.1
0.1
0.1
4[c]
5
10
10
5
0.1
0.1
6[d]
Scheme 1
[a]
1a (3 mmol) was reacted with Et3SiH (15 mmol) in EtOAc
[b]
(2 mL) at 60 °C for 2 h under dioxygen (1 atm).
Based on the
amount of 1a used. Numbers in parentheses show the selectivity
Recently, we have developed a novel catalytic method for
the introduction of both alkyl and hydroxyl groups to al-
kenes by using N-hydroxyphthalimide (NHPI), which serves
as a catalyst for producing alkyl radicals from alkanes.[6]
[c]
[d]
based on the amount of 1a consumed. 3 h. 5 h.
As expected, the reaction of 1a with Et3SiH (5 equiv.)
under 1 atm of dioxygen in the presence of NHPI (10
mol %) and Co(OAc)2 (0.1 mol %) in ethyl acetate at 60 °C
for 2 h produced methyl 2-hydroxy-3-triethylsilylpropionate
(2a) in 57% yield (Run 1). We note that the hydroxysilyl-
ation of an alkene with a trialkyl silane, such as Et3SiH,
[a]
Department of Applied Chemistry, Faculty of Engineering &
High Technology Research Center,
Kansai University, Suita, Osaka 564-8680, Japan
Fax: (internat.) ϩ81-06/6339-4026
E-mail: ishii@ipcku.kansai-u.ac.jp
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 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI: 10.1002/ejoc.200300074
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Hydroxysilylation of Alkenes with Triethylsilane under Dioxygen Catalyzed by N-Hydroxyphthalimide
FULL PAPER
was first successfully achieved through a catalytic process
by using NHPI as the catalyst. The same reaction in the
absence of either NHPI or Co(OAc)2 afforded 2a in poor
yield (Runs 2 and 3). When the reaction was prolonged to
3 h, the yield of 2a decreased to 48%. This result shows that
the adduct 2a is not stable and decomposes to undesired
side products. In fact, an independent reaction of 2a under
these conditions resulted in a complex mixture of cleaved
products of 2a. When the reaction was carried out in the
presence of NHPI combined with CoII (0.1 mol %) and
CoIII (0.1 mol %), we obtained the adduct 2a in 73% yield
(Run 5). Previously, we observed a similar synergistic effect
of both the CoII and the CoIII in the NHPI-catalyzed coup-
ling reaction of alcohols with 1a leading to α-hydroxy-γ-
butyrolactones.[8] By using both CoII and CoIII as co-cata-
lysts, the amount of NHPI required was reduced to 5 mol %
(Run 6). In these reactions, oxygenated products derived
from Et3SiH, such as Et3SiOH, were formed in 15Ϫ20 %
yields based on the amount of Et3SiH.
Table 2. Hydroxysilylation of several alkenes (1bϪf) with Et3SiH
catalyzed by NHPI.
On the basis of these results, various olefinic compounds
were reacted under selected conditions with Et3SiH in the
presence of both NHPI and the Co species (Table 2).
The reaction of acrylonitrile (1b) with Et3SiH under di-
oxygen (1 atm) at 60 °C afforded 3-triethylsilyl-2-hydroxy-
propionitrile (2b) in 60% yield (Run 1). The reaction of
methyl methacrylate (1c) with Et3SiH occurred with some
difficulty, probably because of the steric hindrance resulting
from the methyl substituent on the olefinic unit of 1c, to
give hydroxysilylated product (2c) in 55% yield (Run 2). The
hydroxysilylation of diethyl fumarate (1d) with Et3SiH took
place even at room temperature to form the corresponding
adduct, 2d (Run 3). The reaction of 1a with Ph3SiH af-
forded the hydroxysilylated product 2e, while mainly hydro-
silylation occurred in the reaction with (TMS)3SiϪH to give
2f, probably because of the lower bond-dissociation energy
of (TMS)3SiϪH (i.e., BDE [Et3SiϪH] ϭ 96 kcal/mol and
BDE [(TMS)3SiϪH] ϭ 74 kcal/mol) (Runs 4 and 5).[9] It is
interesting to note that under similar conditions methacrol-
[a] Alkene (2 mmol) was reacted with Et3SiH (15 mmol) in the pres-
ence of NHPI (10 mol %) and Co(OAc)2 (0.5 mol %) in EtOAc
(2 mL) under O2 (1 atm). [b] Based on amount of alkene consumed.
[c] 1b (3 mmol), NHPI (5 mol %), Co(OAc)2 (0.1 mol %), Co(acac)3
[d]
(0.1 mol %). Et3SiH (20 mmol), NHPI (20 mol %) under N2/O2
(0.5:0.5 atm). [e] 1d (3 mmol), CH3CN (3 mL). [f] Ph3SiH (6 mmol).
[g]
[h]
1a (1 mmol), (TMS)3SiH (5 mmol) under air.
Et3SiH
[i]
[j]
(20 mmol).
Based on amount of alkene used.
1h (3 mmol),
1i (3 mmol),
[k]
Co(OAc)2 (0.1 mol %), Co(acac)3 (0.3 mol %).
Co(OAc)2 (0.1 mol %), Co(acac)3 (0.1 mol %).
The reaction is initiated by the formation of phthalimide
ein (1g) and 3-methyl-3-buten-2-one (1h) led to the same N-oxyl (PINO) from NHPI by the action of the
product, triethylsilylacetone (2g), in 52 and 42% yields, cobaltϪoxygen complex,[6,8,10] and then PINO abstracts a
respectively, and is discussed later (Runs 6 and 7). Similarly, hydrogen atom from Et3SiH to form the triethylsilyl radical
the cleavage product was obtained in the reaction of trie- Et3Si·, which then adds to the alkene to form an adduct
thoxyvinylsilane (1i) (Run 8). The reaction of a simple al- radical A. It is known that the hydrogen atom abstraction
kene, such as 1-octene, with Et3SiH was examined under from trialkyl hydrosilane by an alkyl radical, such as A,
these conditions, but no hydrosilylation product was ob- occurs with difficulty. Hence, the abstraction of a hydrogen
tained, probably because of polar effect of the Et3Si· rad- atom from Et3SiH by the carbon-centered adduct radical A
ical, which has nucleophilic character and prefers an elec- is probably a sluggish process.[3] Under the present reaction
tron-deficient alkene to an electron-rich one, such as 1-oc- conditions, in which molecular oxygen is present, the re-
tene.
sulting silylated alkyl radical A is readily trapped by dioxy-
Scheme 2 illustrates a plausible reaction pathway for the gen to form a hydroperoxide B that undergoes redox de-
present hydroxysilylation of alkenes with Et3SiH under di- composition mediated by the cobalt species to convert it
oxygen catalyzed by NHPI combined with Co species.
into an alcohol.
Eur. J. Org. Chem. 2003, 2286Ϫ2289
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 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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O. Tayama, T. Iwahama, S. Sakaguchi, Y. Ishii
FULL PAPER
To obtain further information regarding the reaction
pathway, the reaction of β-pinene (1j) was chosen to prove
the radical nature of the reaction. It is known that the rad-
ical addition of 1j proceeds through ring opening of its
cyclobutane moiety. Unfortunately, the reaction of 1j with
Et3SiH was difficult to achieve with selectivity. When the
reaction of 1j with (TMS)3SiH was carried out by the pre-
sent reaction system, however, 2-(4-trimethylsilanylmethyl-
cyclohex-3-enyl)propan-2-ol (2j) (2%) was obtained as a
minor product, together with the hydrosilylated product 3
(31%), suggesting that the adduct formed between
(TMS)3Si and 1j underwent ring opening of the cyclo-
butane ring to give D, which subsequently underwent ad-
dition of O2 to afford the corresponding adduct [Equa-
tion (2)].
In conclusion, we have achieved the first catalytic
hydroxysilylation of electron-deficient alkenes with Et3SiH
and dioxygen by the use of NHPI as the key catalyst under
mild conditions.
Scheme 2. A possible reaction pathway for the hydroxysilylation
Experimental Section
The formation of triethyl silylacetone 2g from alkenes 1g
and 1h can be explained by the β-cleavage of the resulting General Procedures: All starting materials were commercially avail-
hydroperoxide, as is shown in Scheme 3.[10]
able and used without further purification. GLC analysis was per-
formed with a flame-ionization detector using a 0.2 mm ϫ 25 m
capillary column (OV-1). 1H and 13C NMR spectra were measured
at 400 MHz and 100 MHz, respectively, in CDCl3 with Me4Si as
the internal standard. Infrared (IR) spectra were measured using
NaCl plates.
Representative Procedure for the Hydroxysilylation of 1a with
Et3SiH: Compound 1a (3 mmol) and Et3SiH (15 mmol) were ad-
ded to a solution of NHPI (0.3 mmol) and the transition metal
salts in EtOAc (2 mL). The flask was equipped with a balloon filled
with O2 (1 atm). The mixture was stirred at 60 °C for 2 h. The
Scheme 3. A possible reaction pathway for the reaction of 1g
with Et3SiH
product 2a (ca. 1.8 mmol, 390 mg) was isolated by column chroma-
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Eur. J. Org. Chem. 2003, 2286Ϫ2289

Hydroxysilylation of Alkenes with Triethylsilane under Dioxygen Catalyzed by N-Hydroxyphthalimide
FULL PAPER
tography (230Ϫ400 mesh silica gel, n-hexane/ethyl acetate ϭ 4:1).
After the reaction was complete, GC and GC-MS analyses were
performed. The conversions and yields of products were estimated
from the peak areas, based on the internal-standard technique, ob-
served using GC. Products 2f and 3 have been reported pre-
viously.[3,4]
(s, 27 H) ppm. 13C NMR: δ ϭ 137.2, 118.5, 72.7, 44.8, 31.4, 27.5,
27.0, 26.3, 24.1, 17.5, 1.35 ppm.
Acknowledgments
This work was supported partially by a Grant-in-Aid for Scientific
Research (KAKENHI) (S) (No.13853008) from the Japan Society
for Promotion of Science.
Methyl 2-Hydroxy-3-triethylsilylpropionate (2a): 1H NMR: δ ϭ
4.29Ϫ4.23 (m, 1 H), 3.77 (s, 3 H), 2.46 (br., 1 H), 1.26Ϫ1.11 (m, 2
H), 0.93 (t, J ϭ 7.9 Hz, 9 H), 0.61 (q, J ϭ 7.9 Hz, 6 H) ppm. 13C
NMR: δ ϭ 177.0, 68.4, 52.3, 18.4, 7.2, 3.6 ppm. C10H22O3Si
(218.4): calcd. C 55.00, H 10.15, O 21.98; Si 12.86; found C 54.95,
H 10.06.
[1] [1a]
J. Y. Corey, J. Braddock-Wilking, Chem. Rev. 1999, 99,
[1b]
175Ϫ292.
K. A. Horn, Chem. Rev. 1995, 95, 1317Ϫ1350.
[1c]
P. Braunstein, M. Knorr, J. Organomet. Chem. 1995, 500,
2-Hydroxy-3-triethylsilylpropionitrile (2b): 1H NMR: δ ϭ 4.53 (t,
J ϭ 7.8 Hz, 1 H), 3.72 (br., 1 H), 1.27 (d, J ϭ 2.4 Hz, 2 H), 0.97
(t, J ϭ 7.8 Hz, 9 H), 0.63 (q, J ϭ 7.8 Hz, 6 H) ppm. 13C NMR:
δ ϭ 121.3, 58.6, 20.0, 7.2, 3.4 ppm.
[1d]
21Ϫ38.
B. Marciniec, J. Gulinski, J. Organomet. Chem.
1993, 446, 15Ϫ23.
[2] [2a]
L. H. Sommer, E. W. Pietrusza, F. C. Whitmore, J. Am.
Chem. Soc. 1947, 69, 188Ϫ188. [2b] C. A. Barkhard, R. H. Krie-
ble, J. Am. Chem. Soc. 1947, 69, 2687Ϫ2689. [2c] A. J. Barry, L.
Methyl 2-Hydroxy-2-methyl-3-triethylsilylpropionate (2c): 1H
NMR: δ ϭ 3.77 (s, 3 H), 3.09 (br., 1 H), 1.45 (s, 3 H), 1.23 (d, J ϭ
14.8 Hz, 1 H), 1.16 (d, J ϭ 14.8 Hz, 1 H), 0.93 (t, J ϭ 7.9 Hz, 9
H), 0.55 (q, J ϭ 7.9 Hz, 6 H) ppm. 13C NMR: δ ϭ 178.7, 74.0,
52.5, 29.6, 24.5, 7.26, 4.06 ppm.
DePree, J. W. Gilkey, D. E. Hook, J. Am. Chem. Soc. 1947, 69,
[2d]
2916Ϫ2916.
F. W. Pietrusza, L. H. Sommer, F. C. Whit-
more, J. Am. Chem. Soc. 1948, 70, 484Ϫ486. [2e] C. Eaborn, M.
R. Harrison, D. R. M. Walton, J. Organomet. Chem. 1971, 31,
43Ϫ46.
[2f]
J. W. Wilt, in Reactive Intermediates, Vol. 3 (Ed.:
R. A. Abramovitch), Pergamon Press, New York, 1983, pp.
143Ϫ151. [2g]K. Miura, K. Oshima, K. Uchimoto, Bull. Chem.
Soc., Jpn. 1993, 66, 2348Ϫ2355.
Diethyl 2-Hydroxy-3-triethylsilylsuccinate (2d): 1H NMR: δ ϭ
4.23Ϫ4.11 (m, 5 H), 3.82 (br., 1 H), 2.74 (d, J ϭ 2.8 Hz, 1 H), 1.26
(q, J ϭ 7.2 Hz, 6 H), 0.99 (t, J ϭ 7.6 Hz, 9 H), 0.74 (q, J ϭ 7.6 Hz,
6 H) ppm. 13C NMR: δ ϭ 174.8, 174.0, 69.4, 61.3, 60.1, 38.2, 14.2,
7.1, 3.4 ppm.
[3]
B. Kopping, C. Chatgilialoglu, M. Zehnder, B. Giese, J. Org.
Chem. 1992, 57 3994Ϫ4000.
[4] [4a]
M. Ballestri, C. Chatgilialoglu, K. B. Clark, D. Griller, B.
[4b]
Giese, B. Kopping, J. Org. Chem. 1991, 56, 678Ϫ683.
Chatgilialoglu, Acc. Chem. Res. 1992, 25, 188Ϫ194.
Chatgilialoglu, Chem. Rev. 1995, 95, 1229Ϫ1251.
C.
C.
Methyl 2-Hydroxy-3-triphenylsilylpropionate (2e): 1H NMR: δ ϭ
7.68Ϫ7.43 (m, 6 H), 7.43Ϫ7.23 (m, 9 H), 4.42Ϫ4.25 (m, 1 H), 3.43
(s, 3 H), 2.95 (br., 1 H), 1.24Ϫ1.86 (m, 2 H) ppm. 13C NMR: δ ϭ
175.8, 135.5, 134.1, 129.3, 127.6, 67.9, 51.9, 20.4 ppm. C22H22O3Si
(362.5): calcd. C 72.89, H 6.12, O 13.24, Si 7.75; found C 72.76,
H 6.20.
[4c]
[5]
[6]
[7]
The oxysulfuration has been reported previously: A. L. J.
Beckwith, R. D. Wagner, J. Org. Chem. 1981, 46, 3638Ϫ3645.
T. Hara, T. Iwahama, S. Sakaguchi, Y. Ishii, J. Org. Chem.
2001, 66, 6425Ϫ6431.
Quite recently, the aerobic oxidation of silanes to silanols cata-
lyzed by NHPI and Co salts was reported. See: F. Minisci, F.
Recupero, C. Punta, C. Guidarini, F. Fontana, G. F. Pedullic,
Synlett 2002, 1173Ϫ1175.
T. Iwahama, S. Sakaguchi, Y. Ishii, Chem. Commun. 2000,
613Ϫ614.
J. J. Lucas, P. M. Laarhoven, D. M. W. Danial, Acc. Chem.
Res. 1999, 32, 342Ϫ349.
Triethylsilylacetone (2g): 1H NMR: δ ϭ 2.24 (s, 2 H), 2.12 (s, 3 H),
0.98 (t, J ϭ 7.8 Hz, 9 H), 0.63 (q, J ϭ 7.8 Hz, 6 H) ppm. 13C NMR:
δ ϭ 207.9, 34.3, 31.8, 7.0, 3.5 ppm.
[8]
[9]
1
Methyl Triethylsilylacetate: H NMR: δ ϭ 3.62 (s, 2 H), 1.89 (s, 2
H), 0.96 (t, J ϭ 7.9 Hz, 9 H), 0.62 (q, J ϭ 7.9 Hz, 6 H) ppm. 13C
NMR: δ ϭ 173.6, 51.1, 21.7, 7.0, 3.5 ppm.
[10]
K. Hirano, T. Iwahama, S. Sakaguchi, Y. Ishii, Chem. Com-
mun. 2000, 2687Ϫ2688.
2-(4-Trimethylsilanylmethylcyclohex-3-enyl)propan-2-ol (2j): 1H
NMR: δ ϭ 5.30 (m, 1 H), 2.08Ϫ1.24 (m, 10 H), 1.18 (s, 6 H), 0.13
Received February 7, 2003
Eur. J. Org. Chem. 2003, 2286Ϫ2289
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