Rhodium-catalyzed hydroarylation and hydroalkenylation of alkynes using organo [2-(hydroxymethyl)phenyl]dimethylsilanes

Article abstract of DOI:10.1055/s-2008-1042812

The title reaction was found to proceed in the presence of a rhodium/1,2-bis(diphenylphosphino)benzene catalyst. Variously substituted arylethenes and 1,3-dienes were obtained in good yields. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2008-1042812

774
CLUSTER
Rhodium-Catalyzed Hydroarylation and Hydroalkenylation of Alkynes Using
Organo[2-(hydroxymethyl)phenyl]dimethylsilanes
H
ydroarylation and
o
H
ydroalken
s
ylation of
h
A
lkynes iaki Nakao,* Masahide Takeda, Jinshui Chen, Tamejiro Hiyama*
Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 615-8510, Japan
Fax +81(75)3832443; E-mail: nakao@npc05.kuic.kyoto-u.ac.jp; E-mail: thiyama@npc05.kuic.kyoto-u.ac.jp
Received 30 November 2007
We first examined the reaction of [2-(hydroxymeth-
Abstract: The title reaction was found to proceed in the presence of
a rhodium/1,2-bis(diphenylphosphino)benzene catalyst. Variously
substituted arylethenes and 1,3-dienes were obtained in good yields.
yl)phenyl]phenyldimethylsilane (1a: 1.5 mmol) with 4-
octyne (2a: 1.0 mmol) in the presence of [Rh(OH)(cod)]2
(3.0 mol% Rh) in toluene at 100 °C using various bisphos-
phine ligands1a and found that 1,2-bis(diphenylphosphi-
no)benzene (DPPBz) was effective to afford (E)-4-
phenyl-4-octene (3aa) in 59% yield (Table 1, entry 1).6
Other rhodium complexes such as [RhCl(cod)]2 and
[RhCl(ethylene)2]2 were completely ineffective. Absence
of a phosphine ligand resulted in a slightly decreased
yield, and the effect of a small amount of water was neg-
ligible,4 because the hydroxy group of 1 acts as an effi-
cient proton donor in our system. Whereas arylsilanes
having an electron-donating 4-methoxy (1b) and 2-meth-
yl (1d) groups, though the latter being sterically demand-
ing, enhanced the reaction rates and yields of the reaction
with 2a (entries 2 and 4), the addition of less nucleophilic
(4-fluorophenyl)silane 1c was sluggish (entry 3). We then
turned our attention to the reaction of alkenylsilanes. (E)-
Octenylsilane (1e) added across 2a smoothly in an exclu-
sive cis fashion to give highly substituted 1,3-diene 3ea in
an excellent yield (entry 5). Silyl-protected hydroxy, cy-
ano, and ester functionalities with an acidic hydrogen
were tolerated (entries 7–9), whereas the yield of chloro-
substituted 1,3-diene 3fa was modest due to low conver-
sions of substrates (entry 6). (Z)-Propenylsilane 1j and
isomeric styrylsilanes, 1k and 1l, underwent the addition
reaction in stereo- and regiospecific manners (entries 10–
12). Since a wide variety of alkenylsilanes with various
substitution patterns are readily available in a predictable
manner by rich hydrosilylation chemistry,7 the present
protocol is apparently a promising alternative to that using
alkenylboronic acids, some of which are known to be ther-
mally unstable.8 The scope of alkynes was also briefly in-
vestigated using 1e as a coupling partner. The addition
across diphenylacetylene (2b) was sluggish to give the
corresponding adduct in a modest yield due to incomplete
conversion of the alkyne (entry 13). Unsymmetrical
alkynes 2c and 2d underwent the reaction in good yields
but to give a mixture of regioisomers (entries 14 and 15).
Formation of recoverable and reusable silicon residue 45
Key words: silicon, alkyne, rhodium, addition reaction
Construction of multisubstituted ethenes with a defined
stereochemistry is of significant importance in organic
synthesis. Of many protocols, rhodium-catalyzed addition
of organometallic reagents across alkynes provides a
chemo- and stereoselective access to trisubstituted
ethenes.1,2 Arylboronic acids have been extensively em-
ployed in this transformation in view of ready availability,
stability, and chemoselectivity, little attention being paid
to other organometallic reagents.3 Despite an increasing
importance of the silicon-based protocol with respect to
inherent stability, availability, and nontoxicity associated
with organosilicon compounds, the use of labile organosi-
lanediols by Mori and co-workers has been a single exam-
ple ever reported on the rhodium-catalyzed reaction of
alkynes.4 We report herein organo[2-(hydroxymeth-
yl)phenyl]dimethylsilanes (1) as highly stable and reus-
able alternative organometallic reagents for the rhodium-
catalyzed addition reaction across alkynes (Equation 1).5
HO
R1 Si
O
Si
Me2
Me2
(1.5 equiv)
+
1
[Rh(OH)(cod)]2 (3 mol% Rh)
DPPBz (3 mol%)
4
+
R1
R2
H
toluene, 100 °C
R2
R3
R3
2
3
R1 = Ph (1a)
4-MeOC6H4 (1b)
R2, R3 = Pr, Pr (2a)
Ph, Ph (2b)
Me, t-Bu (2c)
Me, Ph (2d)
4-FC6H4 (1c)
2-MeC6H4 (1d)
(E)-HexCH=CH (1e)
(E)-Cl(CH2)3CH=CH (1f)
(E)-TBSO(CH2)3CH=CH (1g)
(E)-NC(CH2)3CH=CH (1h)
(E)-(MeO2C)2CHCH2CH=CH (1i)
(Z)-MeCH=CH (1j)
(E)-PhCH=CH (1k)
H2C=CPh (1l)
1
in good yields was confirmed by H NMR and/or GC
analyses of crude products of the respective reaction run.
Equation 1
The catalytic cycle should involve organorhodium species
A, which then carbometalate alkynes to give alkenylrhod-
ium intermediate B (Scheme 1). Protonolysis of the C–Rh
bond of B and/or C, which is derived from 1,4-shift of
SYNLETT 2008, No. 5, pp 0774–0776
Advanced online publication: 26.02.2008
DOI: 10.1055/s-2008-1042812; Art ID: Y0207ST
© Georg Thieme Verlag Stuttgart · New York
x
x.
x
x.
2
0
0
8

CLUSTER
Hydroarylation and Hydroalkenylation of Alkynes
775
rhodium,1a by the hydroxy group of 1 gives adduct 3 and
rhodium alkoxide D. Intramolecular transmetalation in D
would be responsible for regeneration of A, giving reus-
able silicon residue 4.5a A similar sequence involving the
reaction of 1 with Rh–OH to form D followed by the in-
tramolecular transmetalation to generate A would be re-
sponsible for the initiation of the catalytic cycle.
Table 1 Addition of Organo[2-(hydroxymethyl)phenyl]dimethyl-
silanes 1 across Alkynes 2
Entry
1
2
Time
(h)
Product
Yield
(%)a
R
Pr
The C–Rh bond in alkenylrhodium intermediate B partic-
ipates in another C–C bond-forming event, as is the case
with the reactions of arylboronic acids.2 Thus, the reaction
of diyne 5 with 1a gave substituted 1,3-diene 6
(Equation 2).2t In this particular transformation, the use of
a phosphine-free rhodium catalyst showed higher reactiv-
ity due presumably to the ability of diynes to chelate to a
rhodium catalyst as a bidentate ligand and, thus, show a
greater reactivity than simple alkynes.
Pr
1
2
3
4
1a
1b
1c
1d
2a
2a
2a
2a
3
R = H: 3aa
59
85
26
78
1
4-MeO: 3ba
4-F: 3ca
2-Me: 3da
Hex
6
0.5
Pr
5
1e
2a
0.5
97
In summary, we have demonstrated that organo[2-(hy-
droxymethyl)phenyl]dimethylsilanes undergo 1,2-addi-
tion reaction across alkynes to give a wide range of
substituted ethenes in highly chemo- and stereoselective
manners. This protocol provides us with an attractive al-
ternative to the boron-based one in view of the diversity
of available alkenylsilanes and the reusability of a silicon
residue.
Pr
3ea
FG
Pr
Pr
6
7
8
1f
2a
2a
2a
20
1
FG = Cl: 3fa
OTBS: 3ga
CN: 3ha
58b
74
1g
1h
1
89
MeO2C
Pr
Acknowledgment
9
10
11
1i
2a
2a
2a
0.5
2
91
MeO2C
Pr
We thank Mr. Hidekazu Imanaka for experimental elaboration at
the initial stage. This work has been supported financially by a
Grant-in-Aid for Creative Scientific Research and that for Priority
Areas ‘Synergy of Elements’ from MEXT.
3ia
Pr
1jc
1k
79d
63
Me
Pr
3ja
Ph
References and Notes
Pr
3
Pr
(1) (a) Hayashi, T.; Inoue, K.; Taniguchi, N.; Ogasawara, M. J.
Am. Chem. Soc. 2001, 123, 9918. (b) Lautens, M.; Yoshida,
M. Org. Lett. 2002, 4, 123. (c) Murakami, M.; Igawa, H.
Helv. Chim. Acta 2002, 85, 4182. (d) Lautens, M.; Yoshida,
M. J. Org. Chem. 2003, 68, 762. (e) Genin, E.; Michelet,
V.; Genêt, J.-P. J. Organomet. Chem. 2004, 689, 3820.
(f) Genin, E.; Michelet, V.; Genêt, J.-P. Tetrahedron Lett.
2004, 45, 4157.
3ka
Ph
12
1l
2a
0.5
69
Pr
Pr
3la
Hex
Ph
Me
Ph
54e
84f
64g
(2) For rhodium-catalyzed arylation of alkynes followed by
intra- and intermolecular trap with electrophiles or another
unsaturated bond, see: (a) Lautens, M.; Marquardt, T. J.
Org. Chem. 2004, 69, 4607. (b) Shintani, R.; Okamoto, K.;
Otomaru, Y.; Ueyama, K.; Hayashi, T. J. Am. Chem. Soc.
2005, 127, 54. (c) Miura, T.; Shimada, M.; Murakami, M. J.
Am. Chem. Soc. 2005, 127, 1094. (d) Miura, T.; Sasaki, T.;
Nakazawa, H.; Murakami, M. J. Am. Chem. Soc. 2005, 127,
1390. (e) Miura, T.; Shimada, M.; Murakami, M. Synlett
2005, 667. (f) Shintani, R.; Hayashi, T. Org. Lett. 2005, 7,
2071. (g) Miura, T.; Nakazawa, H.; Murakami, M. Chem.
Commun. 2005, 2855. (h) Shintani, R.; Tsurusaki, A.;
Okamoto, K.; Hayashi, T. Angew. Chem. Int. Ed. 2005, 44,
3909. (i) Matsuda, T.; Makino, M.; Murakami, M. Angew.
Chem. Int. Ed. 2005, 44, 4608. (j) Miura, T.; Murakami, M.
Org. Lett. 2005, 7, 3339. (k) Shintani, R.; Okamoto, K.;
Hayashi, T. Chem. Lett. 2005, 34, 1294. (l) Matsuda, T.;
Makino, M.; Murakami, M. Chem. Lett. 2005, 34, 1416.
(m) Miura, T.; Shimada, M.; Murakami, M. Angew. Chem.
Int. Ed. 2005, 44, 7598. (n) Miura, T.; Shimada, M.;
13
14
15
1e
1e
1e
2b
2c
2d
102
2
Ph
3eb
Hex
t-Bu
Me
3ec
Hex
17
3ed
a Isolated yields based on 2.
b Conversions of 1f and 2a were about 60% based on GC and 1H NMR
analyses of a crude mixture.
c E/Z = 12:88.
d 2E/2Z = 9:91.
e Conversion of 2b was 89% based on recovered 2b.
f Regioselectivity was 69:31.
g Regioselectivity was 76:24.
Synlett 2008, No. 5, 774–776 © Thieme Stuttgart · New York

776
Y. Nakao et al.
CLUSTER
Me
Me
[Rh(OH)(cod)]2
(3 mol% Rh)
EtO2C
EtO2C
Me
Me
EtO2C
EtO2C
Ph
H
1a
+
toluene, 35 °C, 1 h
(1.5 equiv)
5
6, 78%
Equation 2
O
R2
R3
Si
RhLn
2
Me2
A
4
LnRh
O
H
RhLn
H
RhLn
R3
Si
Me2
R2
R2
R3
D
B
C
HO
H
Si
Me2
R2
R3
3
1
Scheme 1 Plausible mechanism
Murakami, M. Chem. Asian J. 2006, 1, 868. (o) Miura, T.;
Sasaki, T.; Harumashi, T.; Murakami, M. J. Am. Chem. Soc.
2006, 128, 2516. (p) Kurahashi, T.; Shinokubo, H.; Osuka,
A. Angew. Chem. Int. Ed. 2006, 45, 6336. (q) Miura, T.;
Shimada, M.; Murakami, M. Tetrahedron 2007, 63, 6131.
(r) Shintani, R.; Takatsu, K.; Hayashi, T. Angew. Chem. Int.
Ed. 2007, 46, 3735. (s) Miura, T.; Shimada, M.; Ku, S.-Y.;
Tamai, T.; Murakami, M. Angew. Chem., Int. Ed. 2007, 46,
7101. (t) Miura, T.; Yamauchi, M.; Murakami, M. Synlett
2007, 2029. (u) Miura, T.; Takanishi, Y.; Murakami, M.
Org. Lett. 2007, 9, 5075. (v) Harada, Y.; Nakanishi, J.;
Fujihara, H.; Tobisu, M.; Fukumoto, Y.; Chatani, N. J. Am.
Chem. Soc. 2007, 129, 5766. (w) For a review, see: Miura,
T.; Murakami, M. Chem. Commun. 2007, 217.
(5) For rhodium-catalyzed 1,4-addition reactions using 1, see:
(a) Nakao, Y.; Chen, J.; Imanaka, H.; Hiyama, T.; Ichikawa,
Y.; Duan, W.-L.; Shintani, R.; Hayashi, T. J. Am. Chem. Soc.
2007, 129, 9137. (b) Shintani, R.; Ichikawa, Y.; Hayashi, T.;
Chen, J.; Nakao, Y.; Hiyama, T. Org. Lett. 2007, 9, 4643.
(6) General Experimental Procedure
A solution of [Rh(OH)(cod)]2 (6.8 mg, 30 mmol Rh) and
DPPBz (13.4 mg, 30 mmol) in toluene (1.0 mL) were added
1 (1.50 mmol), 2 (1.00 mmol), and tridecane (an internal
standard, 92 mg, 0.50 mmol) sequentially, and the resulting
mixture was stirred at 100 °C. After the time specified in
Table 1, the mixture was filtered through a silica gel pad and
concentrated in vacuo. The residue was purified by flash
chromatography on silica gel to afford the corresponding
adducts in yields listed in Table 1.
(3) For use of organozinc reagents, see: (a) Shintani, R.;
Hayashi, T. Org. Lett. 2005, 7, 2071. (b) Shintani, R.;
Yamagami, T.; Hayashi, T. Org. Lett. 2006, 8, 4799.
(4) (a) Fujii, T.; Koike, T.; Mori, A.; Osakada, K. Synlett 2002,
295. (b) For rhodium-catalyzed hydrophosphination of
alkynes using silylphosphines, see: Hayashi, M.; Matsuura,
Y.; Watanabe, Y. J. Org. Chem. 2006, 71, 9248.
(7) For reviews, see: (a) Hiyama, T.; Kusumoto, T. In
Comprehensive Organic Synthesis, Vol. 8; Trost, B. M.;
Fleming, I., Eds.; Pergamon: Oxford, 1991, 763–792.
(b) Trost, B. M.; Ball, Z. T. Synthesis 2005, 853. (c) For
hydrosilylation to synthesize 1, see: (d) Nakao, Y.;
Imanaka, H.; Chen, J.; Yada, A.; Hiyama, T. J. Organomet.
Chem. 2007, 692, 585.
(8) Peyroux, E.; Berthiol, F.; Doucet, H.; Santelli, M. Eur. J.
Org. Chem. 2004, 1075.
Synlett 2008, No. 5, 774–776 © Thieme Stuttgart · New York

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