Cu(I)-catalyzed enantioselective [3 + 2] cycloaddition reaction of 1-alkylallenylsilane with α-imino ester: Asymmetric synthesis of dehydroproline derivatives

Article abstract of DOI:10.1021/ol047343c

(Chemical Equation Presented) The catalytic, enantioselective [3 + 2] cycloaddition reaction of 1-alkyl-substituted allenylsilanes with α-imino ester has been achieved by means of [Cu(MeCN)₄]BF₄/(R)-DM- SEGPHOS catalyst to afford sil

Full text of DOI:10.1021/ol047343c

ORGANIC
LETTERS
2005
Vol. 7, No. 6
1051-1053
Cu(I)-Catalyzed Enantioselective [3
Cycloaddition Reaction of
+ 2]
1-Alkylallenylsilane with
Asymmetric Synthesis of
r-Imino Ester:
Dehydroproline Derivatives
Kazunori Daidouji, Kohei Fuchibe, and Takahiko Akiyama*
Department of Chemistry, Faculty of Science, Gakushuin UniVersity, Mejiro,
Toshima-ku, Tokyo 171-8588, Japan
takahiko.akiyama@gakushuin.ac.jp
Received December 24, 2004
ABSTRACT
The catalytic, enantioselective [3
+
2] cycloaddition reaction of 1-alkyl-substituted allenylsilanes with
r
-imino ester has been achieved by
means of [Cu(MeCN)4]BF4/(R)-DM-SEGPHOS catalyst to afford silyl-substituted dehydroproline derivatives in high yields and enantioselectivities.
The chiral Lewis acid-catalyzed cycloaddition reaction is a
useful method for enantioselective formation of carbocyclic
and heterocyclic compounds1 which are important building
blocks for natural product synthesis and thus attracts attention
of synthetic organic chemists. R-Substituted allenylsilanes2
are reported to work as counterparts of a cycloaddition reac-
tion.3 Their application to enantioselective reaction is limited.
For example, 1-methylallenylsilane undergoes [3 + 2] cyclo-
addition reaction with electron deficient olefins, aldehydes,
and N,O-hemiacetal to give five-membered carbocycles and
heterocycles, respectively.4 Chiral Lewis acid-catalyzed [3
+ 2] cycloaddition reaction with aldehydes leading to
dihydrofuran derivatives has been reported.5 Catalytic enan-
tioselective [3 + 2] cycloaddition reaction of allenylsilane
with imine has not been reported as far as we know.
Recently, we have reported Cu(I)-catalyzed enantioselective
[2 + 2] cycloaddition reaction of 1-methoxyallenylsilane with
R-imino ester.6 We wish to report herein enantioselective [3
+ 2] cycloaddition reaction of R-alkylallenylsilane with
R-imino ester by means of chiral Cu(I) catalyst.
At the outset, 1-methylallenylsilane 1a7 and R-imino ester
2 were treated with [Cu(MeCN)4]BF4 (10 mol %) in THF.6
Although no reaction proceeded at room temperature, [3 +
2] cycloaddition reaction took place under reflux conditions
(1) Evans, D. A.; Johnson, J. S. In ComprehensiVe Asymmetric Catalysis;
Jacobsen, E. N., Pfaltz, A., Yamamoto, H., Eds.; Springer, Berlin, 1999; p
1177. Oi, T.; Maruoka, K. In ComprehensiVe Asymmetric Catalysis;
Jacobsen, E. N., Pfaltz, A., Yamamoto, H., Eds.; Springer, Berlin, 1999; p
1237. Cycloaddition Reactions in Organic Synthesis; Kobayashi, S.,
Jørgensen, K. A., Eds.; Wiley-VCH: Weinheim, 2002.
(2) Allenylsilane has been used as a propargyl anion equivalent; see:
Yamamoto, H. In ComprehensiVe Organic Synthesis; Trost, B. M., Fleming,
I., Eds.; Pergamon Press: Oxford, 1991; Vol 2, p 81. Danheiser, R. L.;
Carini, D. J. J. Org. Chem. 1980, 45, 3925. Danheiser, R. L.; Carini, D. J.;
Kwasigroch, C. A. J. Org. Chem. 1986, 51, 3870.
(3) Panek, J. S. In ComprehensiVe Organic Synthesis; Trost, B. M.,
Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol 1, p 579. Masse, C.
E.; Panek, J. S. Chem. ReV. 1995, 95, 1293.
(4) Danheiser, R. L.; Carini, D. J.; Basak, A. J. Am. Chem. Soc. 1981,
103, 1604. Danheiser, R. L.; Fink, D. M. Tetrahedron Lett. 1985, 26, 2513.
Danheiser, R. L.; Kwasigroch, C. A.; Tsai, Y.-M. J. Am. Chem. Soc. 1985,
107, 7233.
(5) Evans, D. A.; Sweeney, Z. K.; Rovis, T.; Tedrow, J. S. J. Am. Chem.
Soc. 2001, 123, 12095.
(6) Akiyama, T.; Daidouji, K.; Fuchibe, K. Org. Lett. 2003, 5, 3691.
(7) For the preparation, see ref 5.
10.1021/ol047343c CCC: $30.25
© 2005 American Chemical Society
Published on Web 02/22/2005

Scheme 1. Catalytic [3 + 2] Cycloaddition Reaction with
R-Imino Ester
Table 2. Reaction with Other Allenyl Derivatives
yield of
ee of
entry
Si
R
time (h)
3 (%)
3 (%)
to give silyl-substituted dehydroproline derivative 3a in 19%
yield. Use of benzene as a solvent improved the chemical
yield to 91% (Scheme 1).
We attempted the cycloaddition reaction of 1a with other
imine derivatives such as PhCHdNPh, PhCHdNTs, and
EtOCOCHdNC6H4(p-OMe) using [Cu(MeCN)4]BF4 as the
catalyst; no cycloadducts were obtained. It was found that
use of highly reactive aldimine 2 is essential for the present
cycloaddition reaction to proceed.
1
2
3
Si(t-Bu)Ph2
Si(t-Bu)Ph2
Si(t-Bu)Ph2
Si(t-Bu)Ph2
Si(t-Bu)Me2 Me
SiPh3
Me
7
9
24
20
3
5
1
3
74
52
50
46
90
71
92
0
85
77
78
71
75
84
84
n-Pr
i-Pr
4
cyclohexyl
5a
6
Me
Me
H
7a
8
Si(i-Pr)3
Si(t-Bu)Ph2
a [Cu(MeCN)4]PF6 was employed.
The asymmetric synthesis of silyl-substituted dehydro-
proline derivative 3a8 was investigated and the results are
shown in Table 1. Treatment of 1a (1.0 equiv) and 2 (1.2
AD-H). (R)-SEGPHOS10 (entry 3) was more effective than
(R)-Tol-BINAP (entry 2). When (R)-DM-SEGPHOS was
used as a chiral ligand, the highest enantioselectivity (85%
ee) was observed (entry 4). Use of 2.0 equiv of 2 significantly
improved the chemical yield to 74% (entry 5). Other solvents
gave inferior results (entries 6-8).
Table 1. Effect of Solvents and Chiral Ligandsa
Other allenylsilanes were examined, and the results are
shown in Table 2. Allenyl(tert-butyl)diphenylsilanes bearing
bulky silyl group afforded cycloadducts in good enantiose-
lective manner (entries 2-4). tert-Butyldimethylsilyl-, triph-
enylsilyl-, and triisopropylsilyl-subsituted allenylsilanes also
gave [3 + 2] cycloadducts (entries 5-7). It is noted that
parent allenylsilane gave no cycloadduct (entry 8). The
presence of R-alkyl group is essential for the present
cycloaddition reaction to proceed.
Treatment of 2-alkyl-substituted pyrroline esters 3 with
aqueous HI solution at room temperature for 2-3 h furnished
desilylated γ-amino ketones 4 in high yields and without
decreasing enantioselectivities (Table 3).
yield of ee of
3a (%) 3a (%)
entry
solvent
benzene
benzene
benzene
benzene
chiral ligand
(R)-BINAP
(R)-Tol-BINAP
(R)-SEGPHOS
(R)-DM-SEGPHOS
(R)-DM-SEGPHOS
1
2
3
4
48
67
65
53
74
32
55
60
58
57
67
85
78
78
73
75
5b benzene
6
7
8
1,4-dioxane
1,2-dichloromethane (R)-DM-SEGPHOS
toluene
(R)-DM-SEGPHOS
(R)-DM-SEGPHOS
Table 3. Ring-Opening Reaction
a 1.2 equiv of 2 was employed. b 2.0 equiv of 2 was employed.
equiv) with [Cu(MeCN)4]BF4/(R)-BINAP catalyst (10 mol
%)9 in refluxing benzene for 7 h afforded 3a in 48% yield
with 58% ee (entry 1). Enantiomeric excess was determined
by HPLC with a chiral stationary phase column (Chiralpak
entry
R
time (h) yield of 4 (%) ee of 4 (%)
1
2
3
Me (85% ee)
n-Pr (77% ee)
cyclohexyl (71% ee)
3
2
3
98
97
89
85
77
71
(8) For the chiral synthesis of 3-pyrroline, see: Kagoshima, H.; Okamura,
T.; Akiyama, T. J. Am. Chem. Soc. 2001, 123, 7182.
(9) For enantioselective Cu(I)-catalyzed nucleophilic addition reaction
with R-imino ester, see: Ferraris, D.; Young, B.; Dudding, T.; Lectka, T.
J. Am. Chem. Soc. 1998, 120, 4548. Drury, W. J., III; Ferraris, D.; Cox,
C.; Young, B.; Lectka, T. J. Am. Chem. Soc. 1998, 120, 11006. Yao, S.;
Fang, X.; Jørgensen, K. A. Chem. Commun. 1998, 2547. Yao, S.; Saaby,
S.; Hazell, R. G.; Jørgensen, K. A. Chem. Eur. J. 2000, 6, 2435. Ferrars,
D.; Young, B.; Cox, C.; Dudding, T.; Ryzhkov, L.; Taggi, A. E.; Lectka,
T. J. Am. Chem. Soc. 2002, 124, 67. Taggi, A. E.; Hafez, A. M.; Lectka,
T. Acc. Chem. Res. 2003, 36, 10.
The 2-pyrroline esters described in this study afforded
useful synthons. The vinylsilane functionality in pyrroline 3
(10) Saito, T.; Yokozawa, T.; Ishizaki, T.; Moroi, T.; Sayo, N.; Miura,
T.; Kumobayashi, H. AdV. Synth. Catal. 2001, 343, 264.
1052
Org. Lett., Vol. 7, No. 6, 2005

Scheme 2. Synthesis of Pyrrolidinone
Scheme 4. Plausible Transition Statea
is nucleophilic, and can be epoxidized with m-CPBA to
produce epoxypyrrolidine 5. Subsequent treatment with
aqueous HI solution at room temperature furnished desily-
lated 3-pyrrolidinone 6 in a high yield (Scheme 2). The
relative stereochemistry of 6 has not been determined.11
Next, the absolute stereochemistry of γ-amino ketone 4a
(R ) Me) was determined to be S by comparison of the
optical rotation of 8, which was prepared from 3a via 4a,
with that of the authentic sample prepared from D-norleucine
(Scheme 3). The absolute stereochemistry of pyrroline ester
3a was thus found to be S. We surmised that the absolute
a Methylenedioxy moieties of (R)-DM-SEGPHOS are omitted
for clarity.
stereochemistries of other γ-amino ketones and pyrrolines
to be S by analogy.
The stereochemical outcome can be rationalized by the
plausible transition state model as shown in Scheme 4.12
Because the Re-face is blocked by the pseudoequatorial
dimethyphenyl moiety, allenylsilane attacks the Si-face
preferentially to give S-isomer selectively.
In summary, we have developed the first enantioselective
[3 + 2] cycloaddition reaction of 1-alkyl-substituted alle-
nylsilanes with R-imino ester by chiral Cu(I) catalyst. Use
of (R)-DM-SEGPHOS as a chiral ligand resulted in high
enantioselective cycloaddition reaction.
Scheme 3. Determination of the Absolute Configuration
Acknowledgment. We thank the Takasago International
Corp. (Tokyo, Japan) for supplying the SEGPHOS ligands.
Supporting Information Available: Experimental pro-
cedures, spectra data, and characterization data. This material
is available free of charge via the Internet at http://pubs.acs.org.
OL047343C
(11) We could not obtain 6 as crystals. All our attempts to determine
the relative stereochemistry of 6 by NOE experiments failed.
(12) Ferraris, D.; Young, B.; Cox, C.; Drury, W. J., III; Dudding, T.;
Lectka, T. J. Org. Chem. 1998, 63, 6090. Yao, S.; Saaby, S.; Hazell, R.
G.; Jørgensen, K. A. Chem. Eur. J. 2000, 6, 2435.
Org. Lett., Vol. 7, No. 6, 2005
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