Asymmetric 1,4-addition of organosiloxanes to α,β-unsaturated carbonyl compounds catalyzed by a chiral rhodium complex

Article abstract of DOI:10.1021/ol0272904

(Matrix presented) Highly enantioselective 1,4-addition of organosiloxanes to α,β-unsaturated carbonyl compounds was found to be catalyzed by a chiral rhodium complex generated from [Rh(cod)(MeCN)₂]BF₄ and (S)-BINAP. Both (E)- and (Z)-1-alkenyl groups as well as aryl groups can be introduced enantioselectively into the β-position of a variety of ketones, esters, and amides.

Full text of DOI:10.1021/ol0272904

ORGANIC
LETTERS
2003
Vol. 5, No. 1
97-99
Asymmetric 1,4-Addition of
Organosiloxanes to r,â-Unsaturated
Carbonyl Compounds Catalyzed by a
Chiral Rhodium Complex
Shuichi Oi,* Akio Taira, Yoshio Honma, and Yoshio Inoue*
Department of Materials Chemistry, Graduate School of Engineering,
Tohoku UniVersity, Sendai 980-8579, Japan
oishu@aporg.che.tohoku.ac.jp
Received November 15, 2002
ABSTRACT
Highly enantioselective 1,4-addition of organosiloxanes to r,â-unsaturated carbonyl compounds was found to be catalyzed by a chiral rhodium
complex generated from [Rh(cod)(MeCN)2]BF4 and (S)-BINAP. Both (E)- and (Z)-1-alkenyl groups as well as aryl groups can be introduced
enantioselectively into the â-position of a variety of ketones, esters, and amides.
Transition-metal-catalyzed transformations using organome-
tallic reagents are of great importance in modern organic
chemistry.1 In particular, an asymmetric carbon-carbon
bond-forming process is being emphasized in advanced
materials and pharmaceuticals. The asymmetric 1,4-conjugate
addition of organometallic reagents to R,â-unsaturated car-
bonyl compounds is widely used for carbon-carbon bond
formation with a new stereogenic center being introduced
at the â-position of the formed saturated carbonyl com-
pounds.2 Hayashi and Miyaura proposed the highly useful
rhodium-catalyzed asymmetric 1,4-addition of organoboron
reagents with R,â-unsaturated ketones, esters, amides, and
phosphonates.3 Organosilicon reagents are playing a growing
role in organic synthesis due to their low cost, low toxicity,
ease of handling, tolerance to a variety of functional groups,
and simplicity of byproduct removal.4 A synthetical advan-
tage is that the organosilicon reagents are readily prepared
in one step by a variety of methods. For example, â-substi-
tuted (E)- and (Z)-vinylsilanes5 and R-substituted ones6 can
be prepared by regio- and stereoselective hydrosilylation of
alkynes, and acyl- alkyl-, vinyl-, and arylsilanes can be
prepared by cross-coupling reaction of corresponding organic
halides with disilanes7 or hydrosilanes.8 Regarding the
(3) (a) Takaya, Y.; Ogasawara, M.; Hayashi, T.; Sakai, M.; Miyaura, N.
J. Am. Chem. Soc. 1998, 120, 5579. (b) Takaya, Y.; Ogasawara, M.;
Hayashi, T. Tetrahedron Lett. 1998, 39, 8479. (c) Takaya, Y.; Ogasawara,
M.; Hayashi, T. Tetrahedron Lett. 1999, 40, 6957. (d) Hayashi, T.; Senda,
T.; Takaya, Y.; Ogasawara, M. J. Am. Chem. Soc. 1999, 121, 11591. (e)
Takaya, Y.; Senda, T.; Kurushima, H.; Ogasawara, M.; Hayashi, T.
Tetrahedron: Asymmetry 1999, 10, 4047. (f) Sakuma, S.; Sakai, M.; Itooka,
R.; Miyaura, N. J. Org. Chem. 2000, 65, 5951. (g) Takaya, Y.; Ogasawara,
M.; Hayashi, T. Chirality 2000, 12, 469. (h) Kuriyama, M.; Tomioka, K.
Tetrahedron Lett. 2001, 42, 921. (i) Reetz, M. T.; Moulin, D.; Gosberg, A.
Org. Lett. 2001, 3, 4083. (j) Sakuma, S.; Miyaura, N. J. Org. Chem. 2001,
66, 8944. (k) Hayashi, T.; Takahashi, M.; Takaya, Y.; Ogasawara, M. J.
Am. Chem. Soc. 2002, 124, 5052.
(4) (a) Ojima, I.; Li, Z.; Zhu, J. In The Chemistry of Organosilicon
Compounds; Rappoport, S., Apeloig, Y., Eds.; Wiley: New York, 1998.
(b) Langkopf, E.; Schinzer, D. Chem. ReV. 1995, 95, 1375.
(5) (a) Ojima, I.; Kumagai, M.; Nagai, Y. J. Organomet. Chem. 1974,
66, C14. (b) Hill, J. E.; Nile, T. A. J. Organomet. Chem. 1977, 137, 293.
(c) Watanabe, H.; Kitahara, T.; Motegi, T.; Nagai, Y. J. Organomet. Chem.
1977, 139, 215. (d) Tanke, R. S.; Crabtree, R. H. J. Am. Chem. Soc. 1990,
112, 7984. (e) Ojima, I.; Clos, N.; Donovan, R. J.; Ingallina, P. Organo-
metallics 1990, 9, 3127. (f) Takeuchi, R.; Tanouchi, N. J. Chem. Soc., Perkin
Trans. 1 1994, 2909. (g) Takeuchi, R.; Nitta, S.; Watanabe, D. J. Org.
Chem. 1995, 60, 3045. (h) Mori, A.; Takahisa, E.; Kajiro, H.; Hirabayashi,
K.; Nishihara, Y.; Hiyama, T. Chem. Lett. 1998, 443. (i) Na, Y.; Chang,
S. Org. Lett. 2000, 2, 1887. (j) Faller, J. W.; D′Alliessi, D. G. Organome-
tallics 2002, 21, 1743. (k) Katayama, H.; Taniguchi, K.; Kobayashi,
M.; Sagawa, T.; Minami, T.; Ozawa, F. J. Organomet. Chem. 2002, 645,
192.
(1) Knight, D. W. In ComprehensiVe Organic Synthesis; Trost, B. M.,
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10.1021/ol0272904 CCC: $25.00 © 2003 American Chemical Society
Published on Web 12/12/2002

Table 1. Rhodium-Catalyzed Asymmetric 1,4-Addition of
Phenyltrimethoxysilane (1a) to Cyclohexenone (2a)a
Table 2. Rhodium-Catalyzed Asymmetric 1,4-Addition of
Organosiloxanes to R,â-Enonesa
entry
ligand (mmol)
yield,b %
ee, %
1
2
3
4
5
6
7
8
9c
10d
(S)-(R)-BPPFA (0.02)
(S)-(R)-BPPFOAc (0.02)
(R)-DIOP (0.02)
(S)-Tol-BINAP (0.02)
(S)-BINAP (0.02)
(S)-BINAP (0.025)
(S)-BINAP (0.03)
(S)-BINAP (0.04)
(S)-BINAP (0.03)
(S)-BINAP (0.06)
72
33
77
59
88
75
58
38
72
76
0
0
0
12
25
35
97
97
98
98
a Common reaction conditions: 1a (2.0 mmol), 2a (1.0 mmol),
[Rh(cod)(MeCN)2]BF4 (0.02 mmol), 2.2 mL of dioxane/H2O (10:1), 90 °C,
20 h, N2 atmosphere. b Isolated yield. c Reaction for 40 h. d 0.04 mmol of
[Rh(cod)(MeCN)2]BF4 was used.
rhodium-catalyzed reaction of the organosilicon reagents, we
reported addition of phenylmethyldifluorosilane to alde-
hydes.9 Addition of diaryldichlorosilanes to unsaturated
carbonyl compounds,10 and addition of arylmethylsilanediols
to unsaturated carbonyl compounds and aldehydes11 also
occur. The 1,4-addition of organotrialkoxysilanes to unsatur-
ated carbonyl compounds was recently reported to be
catalyzed by rhodium complexes.12 In this paper, we wish
to report a highly enantioselective 1,4-addition of aryl- and
alkenyltrialkoxysilanes to R,â-unsaturated carbonyl com-
pounds catalyzed by a BINAP-rhodium complex.
Initially, various chiral phosphine ligands were examined
(P/Rh ) 2) in the reaction of phenyltrimethoxysilane (1a)
with cyclohexenone (2a) under the conditions reported before
(Table 1, entries 1-5).12a Although ferrocene-based ligands
(entries 1 and 2) and DIOP (entry 3) did not show any
enantioselectivity, modest ees were obtained when binaph-
thyl-based ligands were used (entries 4 and 5). Then, other
conditions were examined using (S)-BINAP as a ligand
(Table 1, entries 6-10). The amount of BINAP affected both
chemical and optical yields. When the amount of BINAP
was increased to 0.025 mmol (P/Rh ) 2.5) or 0.03 mmol
(P/Rh ) 3), the chemical yield decreased to 75 and 55%,
respectively, and the optical yield increased to 35 and 97%
a Common reaction conditions: 1 (2.0 mmol), 2 (1.0 mmol), [Rh(cod)-
(MeCN)2]BF4 (0.04 mmol), (S)-BINAP (0.06 mmol), 2.2 mL of dioxane/
H2O (10:1), 90 °C, 20 h, N2 atmosphere. b Isolated yield. c Absolute
configuration is shown in parentheses.
ee, respectively (entries 5-7). Further addition of BINAP
(0.04 mmol) caused the chemical yield to only decrease
(entry 8). The chemical yield could be improved by
lengthening the reaction time and by increasing the amount
of catalyst loaded without loss of the optical yield (entries 9
and 10).
With the optimized reaction conditions (Table 1, entry 10),
asymmetric 1,4-addition of various organosiloxanes to enones
were examined. Results are summarized in Table 2. As in
the reaction of cyclohexenone (2a, entry 1), cyclopentenone
(2b) also underwent the asymmetric 1,4-addition of phenyl-
trimethoxysilane (1a) with high enantioselectivity affording
the (S)-form product (3b) in good yield (entry 2). The
reaction of 1a with linear enones also proceeded enantiose-
lectively, but afforded the (R)-form producs. Enantioselec-
tivity and reactivity were affected by bulkiness of the
substituent on the â-position of the enones. With the
(7) (a) Yamamoto, K.; Suzuki, S.; Tsuji, J. Tetrahedron Lett. 1980, 21,
1653. (b) Eaborn, C.; Griffiths, R. W.; Pidcock, A. J. Organomet. Chem.
1982, 225, 331. (c) Matsumoto, H.; Kasahara, M.; Takahashi, M.; Arai, T.;
Nakao, T.; Nagai, Y. J. Organomet. Chem. 1983, 250, 99. (d) Hatanaka,
Y.; Hiyama, T. Tetrahedron Lett. 1987, 28, 4715.
(8) (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, 7449. (d) Murata, M.; Ishikura, M.; Nagata, M.; Watanabe, S.; Masuda,
Y. Org. Lett. 2002, 4, 1843.
(9) Oi, S.; Moro, M.; Inoue, Y. Organometallics 2001, 20, 1036.
(10) Huang, T. S.; Li, C. J. Chem. Commun. 2001, 2348.
(11) (a) Mori, A.; Danda, Y.; Fujii, T.; Hirabayashi, K.; Osakada, K. J.
Am. Chem. Soc. 2001, 123, 10774. (b) Fujii, T.; Koike, T.; Mori, A.;
Osakada, K. Synlett 2002, 298. (c) Koike, T.; Du, X.; Mori, A.; Osakada,
K. Synlett 2002, 301.
(12) (a) Oi, S.; Honma, Y.; Inoue, Y. Org. Lett. 2002, 4, 667. (b) Murata,
M.; Shimazaki, R.; Ishikura, M.; Watanabe, S.; Masuda, Y. Synthesis 2002,
717.
98
Org. Lett., Vol. 5, No. 1, 2003

The reaction mechanism (Scheme 1) probably involves
the generation of an organorhodium intermediate 5 by the
transmetalation between the silicon reagent 1 and a rhodium
complex 4 and the addition of the organorhodium intermedi-
ate 5 to the R,â-unsaturated carbonyl compound 2 as we
reported.12 The stereochemical pathway of the addition of
the Rh-C bond to the enones should be similar to that in
the asymmetric 1,4-addition of arylboronic acids reported
by Hayashi and Miyaura.3 We considered that the chiral
rhodium species would be an 1:1 complex of rhodium and
BINAP, although addition of 1.5-fold excess of BINAP was
needed to obtain high enantioselectivity, which would be
necessary to complete the complexation. The (E)-enones
coordinates to the Rh-(S)-BINAP complex (Figure 1) on
Scheme 1. Presumed Reaction Pathway
substituent on the â-position was changed from methyl (2c)
to propyl (2e) and to isopropyl (2f), the optical yield
increased from 75% to 91% ee, and then to 98% ee, while
the chemical yield decreased from 90% to 87%, and then
67% (entries 3, 5, and 6). On the other hand, the substituent
on the carbonyl carbon had no influence on either enanti-
oselectivity or reactivity, in that methyl ketone 2c and phenyl
ketone 2d gave similar results (entries 3 and 4). Aryltri-
alkoxysilanes bearing either an electron-donating or an
electron-withdrawing group, 1b and 1c, also added to
cyclohexenone (2a) enantioselectively affording the corre-
sponding products of over 95% ee (entries 7 and 8). Asym-
metric 1,4-addition of 1-alkenyltrialkoxysilanes was also
successful. Vinylsilane 1d added to 2a to give (S)-3-
vinylcyclohexanone (3i) in an excellent ee of 96%. The
reaction of both E- and Z-styrylsilane, 1e and 1f, proceeded
without isomerization of styryl moiety affording the products
in good yield with high ees of 91% and 87%, respectively
(entries 10 and 11).
Figure 1.
their 2re face to avoid the steric interaction with the edges
of two pseudoequatorial phenyl groups to afford the (R)-
products. Cyclic enones, i.e., (Z)-enones, coordinate to the
Rh-(S)-BINAP complex in the same manner but on their
2si face to afford the (S)-products.
To expand the scope of the reaction, the asymmetric
addition of 1a to R,â-unsaturated esters and amides was
examined. As a result, the reactions with methyl crotonate
(2g) and crotonamide (2h) proceeded as in the reaction of
3-penten-2-on (2c) giving the phenylated (R)-form adducts,
3l and 3m, in good yield with high enantioselectivity.
In conclusion, highly enantioselective 1,4-addition of
organosiloxanes to R,â-unsaturated carbonyl compounds was
catalyzed by a chiral rhodium complex generated from [Rh-
(cod)(MeCN)2]BF4 and (S)-BINAP. Both (E)- and (Z)-1-
alkenyl groups as well as aryl groups can be introduced
enantioselectively into â-position of a variety of ketones,
esters, and amides. Further studies to expand the scope and
to clarify mechanistic details are underway.
Supporting Information Available: Experimental details
and characterization data for 3a-m. This material is available
free of charge via the Internet at http://pubs.acs.org.
OL0272904
Org. Lett., Vol. 5, No. 1, 2003
99