Hydroxorhodium complex-catalyzed Carbon-Carbon bond-forming reactions of silanediols with α,β-unsaturated carbonyl compounds. Mizoroki-heck-type reaction vs conjugate addition [19]

Full text of DOI:10.1021/ja015928l

10774
J. Am. Chem. Soc. 2001, 123, 10774-10775
Hydroxorhodium Complex-Catalyzed
Carbon-Carbon Bond-Forming Reactions of
Silanediols with r,â-Unsaturated Carbonyl
Compounds. Mizoroki-Heck-Type Reaction vs
Conjugate Addition
Atsunori Mori,* Yasuaki Danda, Toshinari Fujii,
Kazunori Hirabayashi, and Kohtaro Osakada
examined to date the reaction did not necessarily proceed in a
Chemical Resources Laboratory, Tokyo Institute of Technology
9
reasonable yield. A stoichiometric amount of Pd(OAc)
2
or the
with excess Cu(OAc) -
4
259 Nagatsuta, Yokohama 226-8503, Japan
combined use of catalytic Pd(OAc)
2
2
LiOAc as an oxidant is usually required.3 In contrast, rhodium
complex 3 affected the desired reaction at 3 mol % loading with
no further additives. Among several solvents examined, ethereal
solvents such as THF and 1,4-dioxane were the best.
c-e
ReceiVed April 1, 2001
ReVised Manuscript ReceiVed July 10, 2001
The development of novel carbon-carbon bond forming
reactions is a continuing goal in organic synthesis. Organome-
talloids of boron, silicon, and tin are among the most powerful
reagents employed in C-C bond forming reactions. The propen-
sity of these reagents to undergo transition metal-catalyzed cross-
coupling reactions with a variety of organic electrophiles is what
10
As shown in Table 1, the use of a silanediol as the substrate
appears to be important. Silanols, although reactive, were inferior
to silanediol 1, and afforded product 4 in only moderate yield.
Other organosilicon reagents such as PhSi(OMe) were completely
3
unreactive. The reactions of several acrylates and acryl amides
occurred in good yields, but â-substitued substrates were so far
unsuccessful under similar conditions. Silanediols such as (4-
methylphenyl)(ethyl)silanediol (1b) and (4-methoxyphenyl)(eth-
yl)silanediol (1c) also underwent MH-type reaction smoothly.
1
makes them so valuable in organic synthesis. The transmetalation
step, in which an organic group on the organometalloid becomes
bound to the transition metal catalyst, is often the key to the
success of the entire process. Of the many organometalloids
known to undergo coupling reactions, organosilicon reagents are
the most intriguing since they are inexpensive, readily prepared,
and environmentally benign.
Table 1. Rh-Catalyzed Mizoroki-Heck-Type Reaction of
R,â-Unsaturated Carbonyl Compoundsa
Organosilicon reagents bearing hydroxy groups on the silicon
atom such as silanols, silanediols, and silanetriols are particularly
R,â-unsaturated
% yield
of 4
b
substrate
PhSiEt(OH) (1a)
)SiEt(OH)
carbonyl compound
2
useful. These compounds are readily available by hydrolysis of
2
H
2
CdCHCO
2
Bu (2a)
81
99
the corresponding chlorosilanes. They are also unexpectedly stable
and easy to handle, and at the same time undergo smooth
transmetalation to palladium, which enables cross-coupling reac-
(
4-Me-C
H
6 4
2
(1b)
2a
2a
2a
2a
c
1
b
79
(4-Me-C
H
6 4
)SiMe
2
OH
34
0
83
3
,4
tions with organohalogen compounds and olefinic compounds.
PhSi(OMe)
3
5
We have recently found that rhodium is also a suitable catalyst
for the transmetalation of silanediols 1, and can catalyze the
addition of such species to R,â-unsaturated carbonyl compounds
. Interestingly, the most effective rhodium complex is hydroxo-
rhodium 3a, which has rarely been applied in organic synthesis.
c
1
b
H
2
CdCHCO
2
Et (2b)
1b
1b
1b
1b
1b
(4-MeO-C
H CdCHCO Me (2c)
2
2
2
2
2
2
61
48
d
H
H
CdCHCO
CdCHCO
CH
Bu (2e)
2
CF
3
(2d)
t
2
78
6
H CdCHCONMe (2f)
70
68
76
c
2
2
t
7,8
H
2
CdCHCONH Bu (2g)
The reaction furnishes either Mizoroki-Heck (MH) -type or 1,4-
conjugate addition5c,d product with high specificity depending on
6
H
4 2
)SiEt(OH) (1c) 2b
the reaction conditions.
The reaction of phenyl(ethyl)silanediol (1a) with n-butyl
acrylate (2a) catalyzed by 3 mol % of [Rh(OH)(cod)] (3) afforded
2
n-butyl 3-phenylacrylate (4aa) in 81% yield along with only a
trace amount of conjugate adduct 5aa (eq 1).
a
Unless noted all reactions were carried out in THF with 3 mol %
of 3 and 2.5-3.0 equiv of unsaturated carbonyl compound (relative to
the substrate, respectively) at 70 °C for 24 h. b Isolated yield. The
reaction was carried out in 1,4-dioxane at 100 °C. d Conjugate adduct
c
5
bd was obtained in 7% yield.
Silanols and organostannanes both undergo Mizoroki-Heck-
As noted in eq 1, trace amounts of the product of conjugate
type reactions with Pd complexes, but under the conditions
addition 5 were observed under the standard conditions. However,
simply changing the solvent from THF to THF/H O, gave the
,4-conjugate addition product 5 as the major product. As shown
(
1) Metal-catalyzed Cross-coupling Reactions; Diederich, F., Stang, P. J.,
Eds.; Wiley-VCH: Weinheim, Germany, 1999.
2) (a) Chan, T. H.; Chen, L. M.; Wang, D. J. Chem. Soc., Chem. Commun.
2
1
(
10
in Table 2, the amount of the 1,4-adduct increased as more water
was added to the reaction solvent. Optimum conditions for the
1
1
1
1
988, 1280. (b) Takaku, K.; Shinokubo, H.; Oshima, K. Tetrahedron Lett.
996, 37, 6781. (c) Takaku, K.; Shinokubo, H.; Oshima, K. Tetrahedron Lett.
997, 38, 5189. (d) Hirabayashi, K.; Mori, A.; Hiyama, T. Tetrahedron Lett.
997, 38, 461.
2
production of 5 were found to be THF-H O (2:1) as a solvent
system (eq 2). Under these conditions, ethyl 3-(4-methylphenyl)-
propanoate (5bb) was obtained in 53% yield along with only 5%
(3) (a) Hirabayashi, K.; Kawashima, J.; Nishihara, Y.; Mori, A.; Hiyama,
T. Org. Lett. 1999, 1, 299. (b) Hirabayashi, K.; Mori, A.; Kawashima, J.;
Suguro, M.; Nishihara, Y.; Hiyama, T. J. Org. Chem. 2000, 65, 5342. (c)
Hirabayashi, K.; Nishihara, Y.; Mori, A.; Hiyama, T. Tetrahedron Lett. 1998,
(6) Uson, R.; Oro, L. A.; Cabeza, J. A. Inorg. Synth. 1985, 23, 126.
(7) (a) Heck, R. F. Org. React. 1982, 27, 345. (b) Tsuji, J. Palladium
Reagents and Catalysts; InnoVations in Organic Synthesis; Wiley: Chichester,
UK, 1996.
(8) Palladium-catalyzed MH-type reactions of boronic acids and organotin
compounds: (a) Cho, C. S.; Uemura, S. J. Organomet. Chem. 1994, 465, 85.
(b) Hirabayashi, K.; Ando, J.; Nishihara, Y.; Mori, A.; Hiyama, T. Synlett
1999, 99.
3
9, 7893. (d) Hirabayashi, K.; Ando, J.; Kawashima, J.; Nishihara, Y.; Mori,
A.; Hiyama, T. Bull. Chem. Soc. Jpn. 2000, 73, 1409. (e) Hirabayashi, K.;
Kondo, T.; Toriyama, F.; Nishihara, Y.; Mori, A. Bull. Chem. Soc. Jpn. 2000,
7
3, 749.
(
4) See also: Denmark, S. E.; Wu, Z. Org. Lett. 2000, 2, 565.
5) (a) Sakai, M.; Hayashi, H.; Miyaura, N. Organometallics 1997, 16,
(
4
6
229. (b) Sakuma, S.; Sakai, M.; Itooka, R.; Miyaura, N. J. Org. Chem. 2000,
5, 5951. (c) Takaya, Y.; Ogasawara, M.; Hayashi, T.; Sakai, M.; Miyaura,
(9) Although we also examined the Pd-mediated MH-type reactions of
silanediols, a remarkable difference from those of silanols was not observed;
unpublished results.
N. J. Am. Chem. Soc. 1998, 120, 5579. (d) Oi, S.; Moro, M.; Ono, S.; Inoue,
Y. Chem. Lett. 1998, 83. (e) Oi, S.; Moro, M.; Inoue, Y. Chem. Commun.
1
997, 1621. (f) Li, C.-J.; Meng, Y. J. Am. Chem. Soc. 2000, 122, 9538.
(10) Additional examples are shown in the Supporting Information.
1
0.1021/ja015928l CCC: $20.00 © 2001 American Chemical Society
Published on Web 10/05/2001

Communications to the Editor
J. Am. Chem. Soc., Vol. 123, No. 43, 2001 10775
Scheme 1. A Plausible Mechanism for the Rh-Catalyzed MH-Type Reaction and Conjugate Addition
of 4bb in the reaction of 1b with 2b. Thus, the course of the
reaction (MH-type reaction vs conjugate addition) can be
controlled by the use of water as a cosolvent.10 Preference of the
conjugate addition appears to improve when the substrate has a
more electron-deficient carbonyl group. Accordingly, the reaction
of the electron-donationg unsaturated amide 2f and 2g resulted
in a mixture of 4 and 5. In contrast, an unsaturated ketone such
as methyl vinyl ketone with less electron density on the carbonyl
oxygen atom gave only the 1,4-adduct even under nonaqueous
conditions.11
Table 2. Rhodium Complex 3a-Catalyzed Reaction of 1b with
R,â-Unsaturated Carbonyl Compoundsa
% yield of
MH product
% yield of
1,4-adduct
Y
solvent
THFb
OEt (2b)
74
55
26
5
trace
8
b
THF-H O (180:1)
2
THF-H
THF-H
2
O (5:1)b
2
O (2:1)
40
53
83
61
73
11
OBu (2a)
OMe (2c)
5
4
9
13
26
0
t
O Bu (2e)
NMe
2
(2f)
t
c
NH Bu (2g)
46
Me
THF
56
a
Unless noted, the reaction was carried out with 3 mol % of 3 and
1
.0 equiv of unsaturated carbonyl compound (to silanediol, respectively)
at 70 °C for 24 h. After chromatography, yields of MH product and
1
b
1
,4-adduct were estimated by H NMR. The ratio of 1b/2b was 1:3.
c
3
An additional 0.5 mL of Et N was used in the solvent system.
method for the catalytic formation of carbon-carbon bonds with
innocuous organosilicon reagents.
A plausible mechanism for the reactions described herein is
given in Scheme 1; transmetalation of the aryl group of the
silanediol to the hydroxorhodium complex 3 gives arylrhodium
species 6. Insertion of butyl acrylate (2a) forms 7, which would
be in equilibrium with the rhodium enolate 8. When water is
absent from the reaction system, 7 undergoes â-hydride elimina-
tion to afford MH-type product 4a along with hydridorhodium
species 9. The rhodium complex 9 reacts with 2a to form enolate
Acknowledgment. This work was supported by Asahi Glass Founda-
tion. The authors thank Professor Cathleen M. Crudden of the University
of New Brunswick for her valuable suggestion.
Note Added in Proof. After submission of this manuscript
the following papers concerning refs 5 and 6 appeared: Lautens,
M.; Roy, A.; Fukuoka, K.; Fagnou, K.; Martin-Matute, B. J. Am.
Chem. Soc. 2001, 123, 5358 (ref 5) and Itooka, R.; Iguchi, Y.;
Miyaura, N. Chem. Lett. 2001, 722 (ref 6).
10, which is transmetalated with silanediol 1 to generate enolsilane
11 and complete the catalytic cycle A. In support of this proposed
Supporting Information Available: Experimental procedures for
rhodium-catalyzed reactions and additional results for Tables 1 and 2
2
mechanism, EtCO Bu, the protonated version of 11, is obtained
in 53% under anhydrous reaction conditions. In the presence of
water, the intermediate rhodium enolate 8 is readily protonated
to form the conjugate adduct 5a and at the same time regenerate
hydroxorhodium 3 (cycle B).12
(PDF). This material is available free of charge via the Internet at
http://pubs.acs.org.
JA015928L
The rhodium-catalyzed reaction of silanediols with R,â-
unsaturated esters can be directed toward the Mizoroki-Heck-
type reaction and/or conjugate addition depending on the solvent
system and the electronic nature of the carbonyl substrate. Among
various organosilicon reagents, this interesting reactivity seems
to be specific to silanediols. By contrast, other silyl species were
unreactive or considerably less reactive. The present reactions
expand the synthetic versatility of silanediols and provide a new
(
11) The reaction with methyl methacrylate in 1,4-dioxane at 100 °C
(nonaqueous conditions) also gave 1,4-adduct in 56% yield along with 11%
of the MH product.
(
12) In the presence of a certain amount of water, immediate protonation
of enolate 8 would be preferred to the â-elimination as cycle A. An alternative
possibility to afford the conjugate adduct 5 via sequential â-elimination and
conjugate reduction with the formed H-Rh (9) species was found to be
unlikely by the following experiment: the reaction of 1b to tert-butyl acrylate
(
2e) in the presence of ethyl cinnamate (4ab) afforded 5be in 64% yield along
with 97% recovery of 4ab. (No scrambling to give 5ab occurred.)