Catalytic asymmetric synthesis of allylsilanes through rhodium/chiral diene-catalyzed 1,4-addition of alkenyl[2-(hydroxymethyl)phenyl]dimethylsilanes

Article abstract of DOI:10.1021/ol702125q

(Chemical Equation Presented) A new synthetic method of chiral allylsilanes has been developed through a rhodium-catalyzed asymmetric 1,4-addition of alkenyl[2-(hydroxymethyl)phenyl]dimethylsilanes to β-silyl α,β-unsaturated ketones. By employing (S,S)-Ph

Full text of DOI:10.1021/ol702125q

ORGANIC
LETTERS
2007
Vol. 9, No. 22
4643-4645
Catalytic Asymmetric Synthesis of
Allylsilanes through Rhodium/Chiral
Diene-Catalyzed 1,4-Addition of
Alkenyl[2-(hydroxymethyl)phenyl]dimethylsilanes
Ryo Shintani,*,† Yoshitaka Ichikawa,† Tamio Hayashi,*,† Jinshui Chen,‡
Yoshiaki Nakao,‡ and Tamejiro Hiyama*,‡
Department of Chemistry, Graduate School of Science, Kyoto UniVersity, Sakyo, Kyoto
606-8502, Japan, and Department of Material Chemistry, Graduate School of
Engineering, Kyoto UniVersity, Nishikyo, Kyoto 606-8510, Japan
shintani@kuchem.kyoto-u.ac.jp; thayashi@kuchem.kyoto-u.ac.jp;
thiyama@npc05.kuic.kyoto-u.ac.jp
Received August 29, 2007
ABSTRACT
A new synthetic method of chiral allylsilanes has been developed through a rhodium-catalyzed asymmetric 1,4-addition of alkenyl[2-
(hydroxymethyl)phenyl]dimethylsilanes to â-silyl r,â-unsaturated ketones. By employing (S,S)-Ph-bod* as a ligand, a range of alkenyl nucleophiles
have been installed to these substrates in high yield and enantiomeric excess. The resulting allylsilanes can be used for stereoselective
intramolecular allylation reactions to control two contiguous tertiary and quaternary stereocenters.
Organic molecules containing carbon-silicon bonds are an
important class of compounds due to their wide utility in
organic synthesis.1 In particular, allylsilanes are known to
act as effective allylating agents toward various carbonyl
compounds to give homoallyl alcohol derivatives, and these
allylation processes proceed with high stereoselectivity when
stereo issues are involved.2 Therefore, the development of a
catalytic asymmetric method of constructing highly enantio-
enriched chiral allylsilanes is of high value in view of the
efficiency,3 and it would be more desirable if these com-
(2) For reviews, see: (a) Masse, C. E.; Panek, J. S. Chem. ReV. 1995,
95, 1293. (b) Fleming, I.; Barbero, A.; Walter, D. Chem. ReV. 1997, 97,
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3173. See also: (d) Suginome, M.; Ito, Y. J. Organomet. Chem. 2003, 685,
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Soc. 1982, 104, 4962. (b) Hayashi, T.; Konishi, M.; Okamoto, Y.; Kabeta,
K.; Kumada, M. J. Org. Chem. 1986, 51, 3772. (c) Hayashi, T.; Kabeta,
K.; Yamamoto, T.; Tamao, K.; Kumada, M. Tetrahedron Lett. 1983, 24,
5661. (d) Hayashi, T.; Han, J. W.; Takeda, A.; Tang, J.; Nohmi, K.;
Mukaide, K.; Tsuji, H.; Uozumi, Y. AdV. Synth. Catal. 2001, 343, 279. (e)
Matsumoto, Y.; Ohno, A.; Hayashi, T. Organometallics 1993, 12, 4051.
(f) Hayashi, T.; Ohno, A.; Lu, S.; Matsumoto, Y.; Fukuyo, E.; Yanagi, K.
J. Am. Chem. Soc. 1994, 116, 4221. (g) Hayashi, T.; Iwamura, H.; Uozumi,
Y. Tetrahedron Lett. 1994, 35, 4813. (h) Ohmura, T.; Taniguchi, H.;
Suginome, M. J. Am. Chem. Soc. 2006, 128, 13682. (i) Kacprzynski, M.
A.; May, T. L.; Kazane, S. A.; Hoveyda, A. H. Angew. Chem., Int. Ed.
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L.; Hoveyda, A. H. Org. Lett. 2007, 9, 3187.
† Graduate School of Science.
‡ Graduate School of Engineering.
(1) (a) Colvin, E. W. In Chemistry of Organic Silicon Compounds;
Rappoport, Z., Apeloig, Y., Eds.; Wiley: Chichester, 1998; Part 2, p 1667.
(b) Hiyama, T.; Shirakawa, E. In Handbook of Organopalladium Chemistry
for Organic Synthesis; Negishi, E.-i., Ed.; John Wiley & Sons: Hoboken,
2002; Vol. 1, p 285. (c) Denmark, S. E.; Sweis, R. F. In Metal-Catalyzed
Cross-Coupling Reactions, 2nd ed.; De Meijere, A., Diederich, F., Eds.;
Wiley-VCH: Weinheim, 2004; Vol. 1, p 163. (d) Jones, G. R.; Landais,
Y. Tetrahedron 1996, 52, 7599. (e) Chan, T. H.; Wang, D. Chem. ReV.
1992, 92, 995.
10.1021/ol702125q CCC: $37.00
© 2007 American Chemical Society
Published on Web 10/03/2007

pounds could be synthesized through the formation of new
carbon-carbon bonds.3a,b,i,j Herein we describe that a rhodium/
chiral diene catalyst is highly effective for asymmetric 1,4-
addition of alkenyl[2-(hydroxymethyl)phenyl]dimethylsi-
lanes4,5 to â-silyl R,â-unsaturated ketones, providing a new
and useful method for the construction of chiral allylsilanes
in high yield and ee.
Table 1. Rhodium-Catalyzed Asymmetric 1,4-Addition of
(2-Propenyl)[2-(hydroxymethyl)phenyl]dimethylsilane (2a) to
(E)-4-Dimethylphenylsilyl-3-buten-2-one (1a)
In 2005, we reported a rhodium-catalyzed asymmetric 1,4-
addition of arylboronic acids to â-silyl R,â-unsaturated
carbonyl compounds for the synthesis of chiral organosilanes
and demonstrated that high yield and enantioselectivity could
be achieved by the use of a chiral diene ligand such as (R,R)-
Bn-bod*.6 On the basis of this study, we envisioned that the
use of alkenyl nucleophiles would lead to the formation of
enantio-enriched chiral allylsilanes. To implement this
strategy, because some alkenylboronic acids are known to
be unstable, we decided to focus on the employment of
alkenyl[2-(hydroxymethyl)phenyl]dimethylsilanes as the nu-
cleophile. Although these reagents are known to function as
nucleophiles in the rhodium-catalyzed 1,4-addition reactions,
their usage has been limited to the addition to simple R,â-
unsaturated ketones so far.5
entry
ligand
yield (%)
ee (%)a
1
2
3
4
5
(S,S)-Bn-bod*
(S,S)-Ph-bod*
(R)-binap
(R)-phosphoramidite
(R)-MeO-mop
96
96
10
54
<2
93
93
22
16
-
a ee was determined by chiral HPLC on a Chiralpak AS column with
hexane/2-propanol ) 98/2.
In an initial investigation, we examined the effect of ligand
by using â-dimethylphenylsilyl enone 1a as a model substrate
in the 1,4-addition of 2-propenylsilyl reagent 2a with 5 mol
% rhodium at 50 °C (Table 1). As was the case with the
addition of arylboronic acids,6 the use of chiral diene ligands
such as (S,S)-Bn-bod*7,8 and (S,S)-Ph-bod*7 gave the desired
1,4-adduct (3aa) in high yield and ee (96% yield, 93% ee;
Table 1, entries 1 and 2). In comparison, typical phosphorus-
based chiral ligands, such as (R)-binap,9 (R)-phosphoramid-
ite,10 and (R)-MeO-mop,11 turned out to be much less
effective, giving 3aa in lower yield and enantioselectivity
(Table 1, entries 3-5).
Under the conditions using (S,S)-Ph-bod* as a ligand, the
scope of the substrate and the nucleophile is illustrated in
Table 2. Thus, not only dimethylphenylsilyl group but also
other silyl groups such as the tert-butyldimethylsilyl group
can be employed at the â-position of the substrate (Table 2,
entry 2). With respect to the substituent adjacent to the car-
bonyl group, primary alkyl, secondary alkyl, and aryl groups
are all tolerated to give the corresponding allylsilanes in high
yield and enantioselectivity (88-95% yield, 92-97% ee;
Table 2, entries 3-5). In addition to 2-propenyl group,
various other alkenyl groups are also successfully installed
with high efficiency (90-98% yield, 91-94% ee; Table 2,
entries 6-10). Unfortunately, somewhat lower enantiose-
lectivity is observed by the use of a linear alkenyl nucleophile
under the present reaction conditions (Table 2, entry 11).
(4) (a) Nakao, Y.; Imanaka, H.; Sahoo, A. K.; Yada, A.; Hiyama, T. J.
Am. Chem. Soc. 2005, 127, 6952. (b) Nakao, Y.; Sahoo, A. K.; Yada, A.;
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Y.; Imanaka, H.; Chen, J.; Yada, A.; Hiyama, T. J. Organomet. Chem.
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T. Chem. Lett. 2007, 606. (e) Nakao, Y.; Imanaka, H.; Chen, J.; Yada, A.;
Hiyama, T. J. Organomet. Chem. 2007, 692, 585. See also: (f) Hudrlik, P.
F.; Abdallah, Y. M.; Hudrlik, A. M. Tetrahedron Lett. 1992, 33, 6747. (g)
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Can. J. Chem. 2000, 78, 1421.
(5) Nakao, Y.; Chen, J.; Imanaka, H.; Hiyama, T.; Ichikawa, Y.; Duan,
W.-L.; Shintani, R.; Hayashi, T. J. Am. Chem. Soc. 2007, 129, 9137.
(6) Shintani, R.; Okamoto, K.; Hayashi, T. Org. Lett. 2005, 7, 4757.
(7) (a) Tokunaga, N.; Otomaru, Y.; Okamoto, K.; Ueyama, K.; Shintani,
R.; Hayashi, T. J. Am. Chem. Soc. 2004, 126, 13584. (b) Otomaru, Y.;
Okamoto, K.; Shintani, R.; Hayashi, T. J. Org. Chem. 2005, 70, 2503. (c)
Shintani, R.; Kimura, T.; Hayashi, T. Chem. Commun. 2005, 3213. (d)
Shintani, R.; Okamoto, K.; Hayashi, T. Chem. Lett. 2005, 1294. (e) Shintani,
R.; Okamoto, K.; Hayashi, T. Org. Lett. 2005, 7, 4757. (f) Nishimura, T.;
Yasuhara, Y.; Hayashi, T. Org. Lett. 2006, 8, 979. (g) Shintani, R.; Duan,
W.-L.; Hayashi, T. J. Am. Chem. Soc. 2006, 128, 5628. (h) Tokunaga, N.;
Hayashi, T. AdV. Synth. Catal. 2007, 349, 513. (i) Duan, W.-L.; Imazaki,
Y.; Shintani, R.; Hayashi, T. Tetrahedron 2007, 63, 8529.
The absolute configuration of 1,4-adduct 3ea (Table 2,
entry 5) was determined as shown in Scheme 1. Thus,
Scheme 1. Derivatization of Compound 3ea
(8) (a) Shintani, R.; Okamoto, K.; Otomaru, Y.; Ueyama, K.; Hayashi,
T. J. Am. Chem. Soc. 2005, 127, 54. (b) Shintani, R.; Tsurusaki, A.;
Okamoto, K.; Hayashi, T. Angew. Chem., Int. Ed. 2005, 44, 3909. (c)
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4644
Org. Lett., Vol. 9, No. 22, 2007

chiral building blocks for further derivatizations. For ex-
ample, treatment of 1,4-adduct 3dc with TiCl4 at -78 °C
rapidly gave intramolecular allylation product 6 in 89% yield
as a single diastereomer with retaining the enantiomeric
excess (eq 1).15 Similarly, compound 3dd was converted to
compound 7 with complete stereoselectivity in 75% yield
(eq 2).
Table 2. Rh/(S,S)-Ph-bod*-Catalyzed Asymmetric 1,4-Addition
of Alkenyl[2-(hydroxymethyl)phenyl]dimethylsilanes 2 to
â-Silyl R,â-Unsaturated Ketones 1
In summary, we have developed a new synthetic method
of chiral allylsilanes through a rhodium-catalyzed asymmetric
1,4-addition of alkenyl[2-(hydroxymethyl)phenyl]dimethyl-
silanes to â-silyl R,â-unsaturated ketones. By employing
(S,S)-Ph-bod* as a ligand, we have efficiently installed a
range of alkenyl nucleophiles to these substrates in high yield
and enantiomeric excess. The resulting allylsilanes can be
used in the context of stereoselective intramolecular allylation
reactions to control two contiguous tertiary and quaternary
stereocenters.
Acknowledgment. Support has been provided in part by
a Grant-in-Aid for Scientific Research, the Ministry of
Education, Culture, Sports, Science, and Technology, Japan
(21 COE on Kyoto University Alliance for Chemistry).
Supporting Information Available: Experimental pro-
cedures and compound characterization data. This material
is available free of charge via the Internet at http://pubs.acs.org.
a ee was determined by chiral HPLC with hexan/2-propanol. b (S,S)-Bn-
bod* was used as a ligand. c The reaction was conducted at 60 °C.
OL702125Q
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hydrogenation of the olefin by Wilkinson’s catalyst, followed
by Tamao oxidation,12,13 gave 3-hydroxy-4-methyl-1-phe-
nylpentan-1-one (5), retaining its stereochemical information.
By comparing the optical rotation with the literature value,14
the absolute configuration of compound 5 was assigned as
(R), which determined the configuration of 3ea to be (R).
Highly enantio-enriched chiral allylsilanes obtained through
these rhodium-catalyzed 1,4-addition reactions are useful
Org. Lett., Vol. 9, No. 22, 2007
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