Enantioselective aldol reaction of tin enolates with aldehydes catalyzed by BINAP·silver(I) complex

Full text of DOI:10.1021/ja970203w

J. Am. Chem. Soc. 1997, 119, 9319-9320
9319
Table 1. Enantioselective Aldol Reaction of Tin Enolates with
Enantioselective Aldol Reaction of Tin Enolates
with Aldehydes Catalyzed by BINAP‚Silver(I)
Complex
Aldehydes Catalyzed by BINAP‚AgOTf Complexa
Akira Yanagisawa, Yukari Matsumoto, Hiroshi Nakashima,
Kenichi Asakawa, and Hisashi Yamamoto*
Graduate School of Engineering, Nagoya UniVersity
CREST, Japan Science and Technology Corporation (JST)
Chikusa, Nagoya 464-01, Japan
ReceiVed January 22, 1997
The catalytic asymmetric aldol reaction has been extensively
studied during the past decade since it provides a favorable route
to optically active â-hydroxy carbonyl compounds.1 Although
numerous successful methods have been developed, most of
these are the chiral Lewis acid-catalyzed Mukaiyama aldol
reactions using silyl enol ethers or ketene silyl acetals,2-7 and
there has been no report which includes enol stannanes. We
report herein the first example of catalytic enantioselective aldol
addition of tributyltin enolates to aldehydes employing BINAP‚
silver(I) complex as a catalyst (eq 1).
The tributyltin enolate is easily prepared from the corre-
sponding enol acetate and tributyltin methoxide in the absence
of solvent.8 The tin enolate thus obtained exists in O-Sn form
and/or C-Sn form; however, both species can be used for the
aldol reaction of the present system. The tin enolate itself
possesses adequate reactivity toward an aldehyde,8b for example,
treatment of the tin enolate of acetone (R1 ) CH3, C-Sn form,
eq 1) with benzaldehyde (R2 ) Ph) in dry THF at room
temperature for 14 h gave the aldol adduct in 84% yield. In
the presence of 10 mol % of (R)-BINAP‚AgOTf complex,9
however, the reaction proceeded much faster even at -20 °C
and afforded the aldol product in 73% yield and 77% ee with
R-configuration.10 Several different solvents were tested for the
reaction and THF was found to provide the best result.11
(1) Reviews: (a) Bach, T. Angew. Chem., Int. Ed. Engl. 1994, 33, 417.
(b) Hollis, T. K.; Bosnich, B. J. Am. Chem. Soc. 1995, 117, 4570.
(2) Chiral boron catalysts: (a) Furuta, K.; Maruyama, T.; Yamamoto,
H. J. Am. Chem. Soc. 1991, 113, 1041. (b) Furuta, K.; Maruyama, T.;
Yamamoto, H. Synlett 1991, 439. (c) Parmee, E. R.; Tempkin, O.;
Masamune, S.; Abiko, A. J. Am. Chem. Soc. 1991, 113, 9365. (d) Parmee,
E. R.; Hong, Y.; Tempkin, O.; Masamune, S. Tetrahedron Lett. 1992, 33,
1729. (e) Kiyooka, S.; Kaneko, Y.; Kume, K. Tetrahedron Lett. 1992, 33,
4927. (f) Corey, E. J.; Cywin, C. L.; Roper, T. D. Tetrahedron Lett. 1992,
33, 6907. (g) Ishihara, K.; Maruyama, T.; Mouri, M.; Gao, Q.; Furuta, K.;
Yamamoto, H. Bull. Chem. Soc. Jpn. 1993, 66, 3483.
(3) Chiral titanium catalysts: (a) Mukaiyama, T.; Inubushi, A.; Suda,
S.; Hara, R.; Kobayashi, S. Chem. Lett. 1990, 1015. (b) Mikami, K.;
Matsukawa, S. J. Am. Chem. Soc. 1993, 115, 7039. (c) Mikami, K.;
Matsukawa, S. J. Am. Chem. Soc. 1994, 116, 4077. (d) Carreira, E. M.;
Singer, R. A.; Lee, W. J. Am. Chem. Soc. 1994, 116, 8837. (e) Keck, G.
E.; Krishnamurthy, D. J. Am. Chem. Soc. 1995, 117, 2363. (f) Carreira, E.
M.; Lee, W.; Singer, R. A. J. Am. Chem. Soc. 1995, 117, 3649. (g) Singer,
R. A.; Carreira, E. M. J. Am. Chem. Soc. 1995, 117, 12360. (h) Mikami,
K.; Takasaki, T.; Matsukawa, S.; Maruta, M. Synlett 1995, 1057. (i)
Matsukawa, S.; Mikami, K. Tetrahedron: Asymmetry 1995, 6, 2571. (j)
Mikami, K.; Yajima, T.; Takasaki, T.; Matsukawa, S.; Terada, M.;
Uchimaru, T.; Maruta, M. Tetrahedron 1996, 52, 85.
Optimal conditions were established using THF as solvent,
and we then employed these conditions in catalytic enantio-
selective aldol reaction of a variety of tributyltin enolates with
typical aromatic, R,â-unsaturated, and aliphatic aldehydes. The
results are summarized in Table 1, and the characteristic features
are as follows: (1) All reactions proceeded to furnish satisfactory
yield in the presence of 10 mol % of (R)-BINAP‚AgOTf
complex at -20 °C for 8 h except reactions of acetophenone-
derived tin enolate which gave relatively low yield (entries 7-9)
and no dehydrated aldol adduct was observed; (2) with an R,â-
unsaturated aldehyde, the 1,2-addition reaction took place
exclusively (entries 2, 5, and 8); (3) a bulky alkyl substituent
of tin enolate increased the enantioselectivity of the aldol
reaction. For instance, the highest ee (95% ee) was obtained
(4) Chiral tin catalysts: (a) Kobayashi, S.; Fujishita, Y.; Mukaiyama, T.
Chem. Lett. 1990, 1455. (b) Mukaiyama, T.; Furuya, M.; Ohtsubo, A.;
Kobayashi, S. Chem. Lett. 1991, 989. (c) Kobayashi, S.; Furuya, M.;
Ohtsubo, A.; Mukaiyama, T. Tetrahedron: Asymmetry 1991, 2, 635. (d)
Kobayashi, S.; Harada, T.; Han, J. S. Chem. Exp. 1991, 6, 563. (e)
Kobayashi, S.; Uchiro, H.; Shiina, I.; Mukaiyama, T. Tetrahedron 1993,
49, 1761. (f) Kobayashi, S.; Kawasuji, T. Synlett 1993, 911. (g) Kobayashi,
S.; Kawasuji, T.; Mori, N. Chem. Lett. 1994, 217. (h) Kobayashi, S.;
Hayashi, T.; Kawasuji, T. Tetrahedron Lett. 1994, 35, 9573.
(5) Chiral zinc reagents: (a) Mukaiyama, T.; Takashima, T.; Kusaka,
H.; Shimpuku, T. Chem. Lett. 1990, 1777. See also: (b) Nakagawa, M.;
Nakao, H.; Watanabe, K. Chem. Lett. 1985, 391.
(8) (a) Pereyre, M.; Bellegarde, B.; Mendelsohn, J.; Valade, J. J.
Organomet. Chem. 1968, 11, 97. (b) Labadie, S. S.; Stille, J. K. Tetrahedron
1984, 40, 2329. (c) Kobayashi, K.; Kawanisi, M.; Hitomi, T.; Kozima, S.
Chem. Lett. 1984, 497. Tributyltin enolates should be purified by distillation
immediately before use.
(6) Chiral transition metal and lanthanoid catalysts were also utilized
for the catalytic asymmetric Mukaiyama aldol reactions. Chiral rhodium
catalysts: (a) Reetz, M. T.; Vougioukas, A. E. Tetrahedron Lett. 1987, 28,
793. Chiral palladium catalysts: (b) Sodeoka, M.; Ohrai, K.; Shibasaki,
M. J. Org. Chem. 1995, 60, 2648. Chiral copper catalysts: (c) Evans, D.
A.; Murry, J. A.; Kozlowski, M. C. J. Am. Chem. Soc. 1996, 118, 5814.
(d) Evans, D. A.; Kozlowski, M. C.; Tedrow, J. S. Tetrahedron Lett. 1996,
37, 7481. Chiral lanthanoid catalysts: (e) Uotsu, K.; Sasai, H.; Shibasaki,
M. Tetrahedron: Asymmetry 1995, 6, 71.
(7) Chiral quarternary ammonium fluoride was found to catalyze the aldol
reaction, see: (a) Ando, A.; Miura, T.; Tatematsu, T.; Shioiri, T. Tetrahedron
Lett. 1993, 34, 1507. (b) Shioiri, T.; Bohsako, A.; Ando, A. Heterocycles
1996, 42, 93.
(9) Yanagisawa, A.; Nakashima, H.; Ishiba, A.; Yamamoto, H. J. Am.
Chem. Soc. 1996, 118, 4723.
(10) The absolute configuration was determined by comparison of the
[R]D value with reported data; R-enriched product (78% ee), [R]23D +56.7
(c 1.1, CHCl3): Matsumoto, Y.; Hayashi, T.; Ito, Y. Tetrahedron 1994,
50, 335. Observed [R]D value (77% ee): [R]20 +32.4 (c 1.0, CHCl3).
(11) Results using other solvents (solvent,Dyield, enantioselectivity):
DME, 53% yield, 64% ee; (MeO)2CO-THF (1:1), 46% yield, 55% ee;
(EtO)2CO, 75% yield, 55% ee; DMF, 37% yield, 34% ee; CH3CN, 39%
yield, 12% ee; C2H5NO2, 16% yield, 46% ee.
S0002-7863(97)00203-5 CCC: $14.00 © 1997 American Chemical Society

9320 J. Am. Chem. Soc., Vol. 119, No. 39, 1997
Communications to the Editor
Table 2. Diastereo- and Enantioselective Aldol Reaction of Tin
Enolates with Aldehydes Catalyzed by BINAP‚AgOTf Complexa
Figure 1. Probable cyclic transition-state structures.
acid catalysts.2a,g,3b The anti isomer indicated 93% ee (entry
2). Noteworthy was the fact that even if the amount of catalyst
was reduced to 1 mol %, the anti selective aldol reaction still
proceeded to provide high yield without any loss of the
enantioselectivity (entry 3). The cyclopentanone and cyclo-
heptanone derivatives also showed high anti selectivity (entries
1 and 4). In contrast, the Z-enolate derived from tert-butyl ethyl
ketone provided the syn aldol adduct nearly exclusively with
95% ee in combination with benzaldehyde and hydrocinnam-
aldehyde (entries 5 and 6). Similarly, a remarkable syn
selectivity was observed for the tin enolate of tert-butyl propyl
ketone (entry 7).
These results clearly show that the diastereoselectivity
depends on the geometry of enol stannane and that cyclic
transition-state structures (A and B, Figure 1) are probable
models. Thus, from the E-enolate, the anti-aldol product can
be obtained via a cyclic transition state model A, and another
model B connects the Z-enolate to the syn product. Similar
six-membered cyclic models containing a BINAP-coordinated
silver atom instead of tributylstannyl group are also possible
alternatives when the transmetalation to silver enolate is
sufficiently rapid.
The reaction reported herein represents a new class of highly
enantioselective aldol reaction of aldehydes with tributyltin
enolates using a catalytic amount of BINAP‚Ag(I) complex.
The reaction can be performed on a substantial scale using
ordinary laboratory equipment, since no complex preparation
of catalysts is required. Further work is now in progress on
application of the catalytic asymmetric aldol addition and the
detailed reaction mechanism.
when the tin enolate prepared from pinacolone was added to
benzaldehyde (entry 4).
Employment of substituted enol stannanes for the present
catalytic aldol reaction is quite attractive from the viewpoint of
diastereoselectivity (anti/syn selectivity). In general, silyl enol
ethers have been found to react with aldehydes with syn
(erythro) selectivity irrespective of the stereochemistry (E or
Z) in the presence of a catalytic amount of chiral Lewis
acid.2a,g,3b Denmark et al. recently reported that the opposite
anti aldol products were selectively obtained with excellent
enantioselectivity in the chiral phosphoramide-catalyzed aldol
reaction of a trichlorosilyl enolate of cyclohexanone with
aldehydes.12 We examined the BINAP‚silver(I) catalyzed
reaction of (E)- and (Z)-tin enolates (Table 2). Addition of the
cyclohexanone-derived enol tributylstannane (E-enolate) to
benzaldehyde under the influence of 10 mol % of (R)-BINAP‚
AgOTf in THF at -20 °C produced the optically active anti
aldol adduct preferentially with an anti/syn ratio of 92/8,13
contrary to the syn selectivity shown by typical chiral Lewis
Supporting Information Available: Experimental data for com-
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JA970203W
(12) (a) Denmark, S. E.; Winter, S. B. D.; Su, X.; Wong, K.-T. J. Am.
Chem. Soc. 1996, 118, 7404. After submitting our manuscript, the second
paper on the catalytic asymmetric aldol reaction has appeared in which the
E f anti and Z f syn correlation for silyl enol ethers is demonstrated: (b)
Denmark, S. E.; Wong, K.-T.; Stavenger, R. A. J. Am. Chem. Soc. 1997,
119, 2333.
(13) (1-Cyclohexenyloxy)tributyltin reacted with benzaldehyde at -45
°C in the absence of catalyst to give the anti isomer selectively, while at
45 °C the syn isomer predominated.8b See also: Yamamoto, Y.; Yatagai,
H.; Maruyama, K. J. Chem. Soc., Chem. Commun. 1981, 162.