Rhodium(I)-catalyzed 1,2- and 1,4-addition of aryltriethoxysilanes to carbonyl compounds under aqueous basic conditions

Article abstract of DOI:10.1055/s-2002-25764

Aryltriethoxysilanes add to aldehydes and α,β-unsaturated carbonyl compounds in high yield in the presence of a rhodium(I) catalyst and aqueous sodium hydroxide.

Full text of DOI:10.1055/s-2002-25764

SHORT PAPER
717
Rhodium(I)-Catalyzed 1,2- and 1,4-Addition of Aryltriethoxysilanes to
Carbonyl Compounds under Aqueous Basic Conditions
1
, 2- and 1,4-Addition o
i
f
A
ryl
k
ines to Carbon
M
yl
C
ompounds urata,* Ryuta Shimazaki, Masanori Ishikura, Shinji Watanabe, Yuzuru Masuda*
Department of Materials Science, Kitami Institute of Technology, Kitami, 090-8507, Japan
Fax +81(157)264973; E-mail: muratamk@mail.kitami-it.ac.jp; E-mail: masudayz@mail.kitami-it.ac.jp
Received 15 February 2002; revised 6 March 2002
Very recently, the 1,2-additions of arylsilanes, such as
halosilanes6 and silandiols,7 have been investigated. Also,
the conjugated additions of these, such as halosilanes,8 si-
lanediols,9 and methoxysilanes,10 have been reported. In
comparison with other silicon reagents, aryltriethoxysi-
lanes 1 should have greater advantages of availability; i.e.,
several synthetic routes to 1 have been developed, e.g. the
palladium-catalyzed silylation of organic halides utilizing
triethoxysilane11 and the reaction of Grignard reagents
with tetraethyl orthosilicate.3 Therefore, the present addi-
tion of 1 should provide a synthetically useful and alterna-
tive method.
Abstract: Aryltriethoxysilanes add to aldehydes and , -unsaturat-
ed carbonyl compounds in high yield in the presence of a rhodi-
um(I) catalyst and aqueous sodium hydroxide.
Key words: rhodium, addition reactions, silicon, arylations, carbo-
nyl compounds
Hypervalent siloxane derivatives, which are obtained
from aryl(trialkoxy)silanes and tetrabutylammonium
fluoride, are versatile reagents for carbon–carbon and car-
bon–heteroatom bond formation, and provide an
alternative to the reaction of organotin or -boron com-
pounds. The palladium-catalyzed cross-coupling reaction
with organic electrophile1 and the copper-mediated ami-
nation reaction2 should proceed through a transmetalation
to transition metals. We have recently reported on a prac-
tical example of a palladium-catalyzed cross-coupling re-
action of aryltriethoxysilanes 1 with aryl bromides in the
presence of an aqueous base.3 The aqueous base as well as
fluoride ion promote the transmetalation between 1 and a
transition metal complex.
A series of reactions of phenyltriethoxysilane 1a with
benzaldehyde 2a were performed under several condi-
tions for optimization studies (Table 1). In the presence of
a rhodium(I) -hydroxo complex,12 cycloocta-1,5-diene,
and aqueous sodium hydroxide, the reaction in dioxane at
90 °C gave the desired benzhydrol 3a in a 79% yield (en-
try 1). Although commercially available -chloro and cat-
ionic complexes were also effective as catalysts (entries 3
and 4), the addition of cycloocta-1,5-diene as a ligand was
necessary to any rhodium catalyst, since the use of rhodi-
um complex alone resulted in low yield due to the decom-
position of the catalyst during the reaction (entry 2). The
present addition was achieved with the aid of an aqueous
solution of hydroxide ion analogous to the palladium-cat-
alyzed cross-coupling reaction;3 i.e., the reactions of 1a
occurred insufficiently in the presence of fluoride ion (en-
tries 7 and 8)6 or in the absence of a base (entry 5),7 even
though the cited additions of arylsilanes have been report-
ed. Several solvents including DMF and toluene were
tested, and it was observed that the reaction in ether sol-
vents afforded 3a in acceptable yield (entries 10 and 11).
In this paper, we describe a rhodium-catalyzed addition of
1 to aldehydes 2 under aqueous basic condition
(Scheme 1). The rhodium-catalyzed 1,2- and 1,4-addi-
tions of organometallic reagents, such as organotin4 and -
boron5 reagents, to carbonyl compounds have been recog-
nized as useful methods for carbon–carbon bond forma-
tion, and the transmetalation between such organometallic
reagents and a rhodium complex has been proposed as a
key step of the catalytic cycle.
[Rh(OH)(cod)]2 / COD
OH
O
NaOH aq.
+
Ar Si(OEt)3
Generally, the role of negatively charged bases, such as
fluoride and hydroxide ion, on the transition metal-cata-
lyzed reaction of organosilanes is recognized to increase
its nucleophilicity due to the coordination of the base to
the silicon atom.13 Although there is no clear experimental
evidence, we speculated that the present addition involved
the transmetalation between a rhodium complex and the
hypervalent siloxanes, which was obtained from aryltri-
ethoxysilanes 1 and aqueous sodium hydroxide.
dioxane
Ar
R
H
R
1
2
3
Ar=
R=
Ph (2a)
Ph (1a)
4-MeC6H4 (1b)
4-F3CC6H4 (2b)
4-MeOC6H4 (2c)
cyclo-C6H11 (2d)
4-ClC6H4 (1c)
4-tBuO2CC6H4 (1d)
Scheme 1
The results obtained with representative arylsilanes 1 and
aldehydes 2, which gave the product 3 in a similar manner
to the above, are listed in Table 2. In the presence of aque-
ous sodium hydroxide, aryltriethoxysilanes 1 were more
efficient arylating substances; i.e., replacing the arylating
Synthesis 2002, No. 6, 29 04 2002. Article Identifier:
1437-210X,E;2002,0,06,0717,0719,ftx,en;F01902SS.pdf.
© Georg Thieme Verlag Stuttgart · New York
ISSN 0039-7881

718
M. Murata et al.
SHORT PAPER
Table 1 Reaction of Phenyltriethoxysilane 1a with Benzaldehyde
2a under Various Conditionsa
Table 2 Addition of 1 to 2
Entry Arylsilane 1
Aldehyde 2
Yield of 3 (%)a
Entry
1
Catalyst
Base
Solvent
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
DMF
Yield (%)b
1
PhSi(OMe)3
2a
2a
2a
2a
2a
2a
2b
2c
2d
(55)
(13)
(0)
(13)
71
[RhOH(cod)]2
[RhOH(cod)]2
[RhCl(cod)]2
[Rh(cod)2]BF4
[RhOH(cod)]2
[RhOH(cod)]2
[RhOH(cod)]2
[RhOH(cod)]2
[RhOH(cod)]2
[RhOH(cod)]2
[RhOH(cod)]2
[RhOH(cod)]2
NaOH
NaOH
NaOH
NaOH
noned
KOH
KF
79
16
72
78
4
2
PhSi(OMe)2Me
2c
3
3
PhSiCl2Me
4
PhSiMe3
4
5
1b
1c
1a
1a
1a
5
6
83
6
57
19
25
10
48
51
34
7
74
7
8b
9c
70
8
CsF
50
9
NaOH
NaOH
NaOH
NaOH
a Isolated yields are based on 2. Yields in parentheses are GC yields.
b Cycloocta-1,5-diene (0.6 equiv) was used.
10
11
12
DME
c The reaction was carried out at 120 °C in the presence of 1.0 equiv
of cycloocta-1,5-diene.
Diglyme
Toluene
a Reactions of 1a (0.50 mmol) with 2a (0.25 mmol) were carried out
at 90 °C for 16 h in 1 mL of the solvent using a catalyst (3 mol% of
rhodium metal), cycloocta-1,5-diene (0.075 mmol), and an aq base
(2.5 M, 0.25 mmol).
Ar
O
O
[Rh(OH)(cod)]2
NaOH aq.
R3
R3
R1
R1
1
+
THF
b GC yields of 3a are based on 2a.
R2
5
R2
c The reaction was carried out in the absence of cycloocta-1,5-diene.
d Water (0.1 mL) was used in place of the aq base.
4
R1= H, R2= H, R3= OtBu (4a)
R1= H, R2= Me, R3= OtBu (4b)
R1= Me, R2= H, R3= OtBu (4c)
R1= H, R2= H, R3= NHiPr (4d)
R1, R3= –(CH2)3–, R2= H (4e)
agent with other silicon compounds gave lower yields of
3 (entries 1-4). The differences in the yields among elec-
tronic characteristics of the substituent on 1 were not par-
ticularly large (entries 5 and 6). Although 1 added to 2
having the electron-withdrawing group without any diffi-
culty (entry 7), the reaction of electron-rich aldehydes re-
quired more amount of cycloocta-1,5-diene as a ligand
and/or more elevated temperature (entries 8 and 9).
Scheme 2
Table 3 Conjugated Addition of 1 to 2a
Entry
Arylsilane 1
Carbonyl
Yield (%)b
Compounds 4
Finally, results for the 1,4-addition of aryltriethoxysilanes
1 to , -unsaturated carbonyl compounds 4 are shown in
Scheme 2 and Table 3. Under the similar reaction condi-
tion to that used for the above 1,2-addition to 2, the reac-
tion of 4, such as , -unsaturated esters 4a–c, amide 4d,
and ketone 4e, with 1 gave the desired the corresponding
adducts 5 in 64–84% yields (entries 1 and 3–7). The addi-
tion of sodium hydroxide in such a case was also effective
(entry 2), although the conjugated additions of arylsilanes
without a basic activator have been reported.9,10
1
2c
3
4
5
6
7
1a
1a
1d
1a
1a
1a
1a
4a
4a
4a
4b
4c
4d
4e
(78)
(53)
83
84
88
64
In conclusion, in the presence of aqueous sodium hydrox-
ide, aryltriethoxysilane 1 was one of the most accessible
alternative arylating reagents for the rhodium-catalyzed
addition to carbonyl compounds 2 and 4. Investigations
on the mechanistic studies and additions to other carbonyl
compounds are currently in progress in our laboratory.
81
a Reactions of 1 (0.50 mmol) with 4 (0.25 mmol) were carried out at
90 °C for 16 h in THF (1 mL) using [Rh(OH)(cod)]2 (3 mol% of rhod-
ium metal), cycloocta-1,5-diene (0.075 mmol), and NaOH (2.5 M aq
solution, 0.25 mmol).
b Isolated yields are based on 4. Yields in parentheses are GC yields.
c Water (0.1 mL) was used in place of the aq NaOH.
Synthesis 2002, No. 6, 717–719 ISSN 0039-7881 © Thieme Stuttgart · New York

SHORT PAPER
1,2- and 1,4-Addition of Aryltriethoxysilanes to Carbonyl Compounds
719
1,2- And 1,4-Additions of Aryltriethoxysilanes to Carbonyl
Compounds; General Procedure
(4) (a) Oi, S.; Moro, M.; Inoue, Y. Chem. Commun. 1997, 1621.
(b) Oi, S.; Moro, M.; Ono, S.; Inoue, Y. Chem. Lett. 1998,
83. (c) Oi, S.; Moro, M.; Fukuhara, H.; Kawanishi, H.;
Inoue, Y. Tetrahedron Lett. 1999, 40, 9259.
[Rh(OH)(cod)]2 (0.0038 mmol) was placed in a test tube capped
with a septum rubber. The test tube was flushed with argon and then
charged with 1,4-dioxane (1 mL), cycloocta-1,5-diene (0.075
mmol), and aq 2.5 M NaOH (0.1 mL, 0.25 mmol). Aryltriethoxysi-
lane 1 (0.5 mmol) and carbonyl compounds 2 or 4 (0.25 mmol) were
added successively. After stirring at 90 °C for 16 h, the reaction
mixture was diluted with Et2O and the organic phase was dried by
passing through a column of Na2SO4 (5 g). The solvent was evapo-
rated and the product 3 or 5 was isolated by bulb-to-bulb distillation
(Tables 1 and 2). The products obtained were identified by compar-
ison with authentic samples.
(5) (a) Sakai, M.; Hayashi, H.; Miyaura, N. Organometallics
1997, 16, 4229. (b) Sakai, M.; Ueda, M.; Miyaura, N.
Angew. Chem., Int. Ed. 1998, 37, 3279. (c) Ueda, M.;
Miyaura, N. J. Organomet. Chem. 2000, 595, 31.
(6) Oi, S.; Moro, M.; Inoue, Y. Organometallics 2001, 20, 1036.
(7) Fujii, T.; Koike, T.; Mori, A.; Osakada, K. Synlett 2002, 298.
(8) Huang, T. S.; Li, C. J. Chem. Commun. 2001, 2348.
(9) (a) Mori, A.; Danda, Y.; Fujii, T.; Hirabayashi, K.; Osakada,
K. J. Am. Chem. Soc. 2001, 123, 10774. (b) Koike, T.; Du,
X.; Mori, A.; Osakada, K. Synlett 2002, 301. (c) Fujii, T.;
Koike, T.; Mori, A.; Osakada, K. Synlett 2002, 295.
(10) Oi, S.; Honma, Y.; Inoue, Y. Org. Lett. 2002, 4, 669.
(11) (a) Murata, M.; Suzuki, K.; Watanabe, S.; Masuda, Y. J.
Org. Chem. 1997, 62, 8569. (b) Murata, M.; Watanabe, S.;
Masuda, Y. Tetrahedron Lett. 1999, 40, 9255. (c) Manoso,
A. S.; DeShong, P. J. Org. Chem. 2001, 66, 7455.
(12) (a) Usón, R.; Oro, L. A.; Cabeza, J. A. Inorg. Synth. 1985,
23, 126. (b) Agarawal, S. K.; Mehrotra, R. C. J. Indian
Chem. Soc. 1985, 62, 805.
References
(1) (a) Tamao, K.; Kobayashi, K.; Ito, Y. Tetrahedron Lett.
1989, 30, 6051. (b) Shibata, K.; Miyazawa, K.; Goto, Y.
Chem. Commun. 1997, 1309. (c) Mowery, M. E.; DeShong,
P. J. Org. Chem. 1999, 64, 1684. (d) Mowery, M. E.;
DeShong, P. Org. Lett. 1999, 1, 2140. (e) Lee, H. M.;
Nolan, S. P. Org. Lett. 2000, 2, 2053.
(2) (a) Lam, P. Y. S.; Deudon, S.; Averill, K. M.; Li, R.; He, M.
Y.; DeShong, P.; Clark, C. G. J. Am. Chem. Soc. 2000, 122,
7600. (b) Lam, P. Y. S.; Deudon, S.; Hauptman, E.; Clark, C.
G. Tetrahedron Lett. 2001, 42, 2427.
(13) (a) Hatanaka, Y.; Hiyama, T. Synlett 1991, 845.
(b) Hiyama, T. In Metal-Catalyzed Cross-Coupling
Reactions; Diederich, F.; Stang, P. J., Eds.; Wiley-VCH:
Weinhein, 1998, 421.
(3) Murata, M.; Shimazaki, R.; Watanabe, S.; Masuda, Y.
Synthesis 2001, 2231.
Synthesis 2002, No. 6, 717–719 ISSN 0039-7881 © Thieme Stuttgart · New York