Copper-amidophosphine catalyst in asymmetric addition of organozinc to imines [31]

Full text of DOI:10.1021/ja005629g

J. Am. Chem. Soc. 2000, 122, 12055-12056
12055
a very effective and general method.10 We document our
observations involving the addition of diethylzinc to CdN of a
broad range of N-sulfonylimines in the presence of catalytic (1
mol %) copper(II) triflate and a chiral amidophosphine in toluene
under mild conditions (0 °C).
Copper-Amidophosphine Catalyst in Asymmetric
Addition of Organozinc to Imines
Hidetaka Fujihara, Kazushige Nagai, and Kiyoshi Tomioka*
At the outset of our study, we examined a reaction of
Graduate School of Pharmaceutical Sciences
Kyoto UniVersity, Sakyo-ku, Kyoto 606-8501, Japan
1
diethylzinc with N-tosylimine 1a (R ) Tol), which is highly
reactive11 and readily accessible by condensation of benzaldehyde
12
ReceiVed September 21, 2000
with p-toluenesulfonamide in the presence of tetraethoxysilane.
Contrary to our expectation, the reaction of 1a in toluene was
sluggish and after 4 h at 0 °C gave the corresponding reduction
The discovery and development of new catalytic reactions that
lead to C-C bond formation by addition of organometallic
reagents to CdN of imines are of fundamental importance in the
continuing development of efficient processes for chemical
synthesis. Of greater importance, the catalytic generation of
reactive organometal-chiral ligand complexes from the corre-
sponding less reactive organometallic reagents in situ under mild
conditions would provide comfortable avenues for the develop-
ment of new, efficient asymmetric processes leading to C-C bond
1
product 3a, the desired ethylation product 2a (R ) Tol) and
starting 1a in 40, 10, and 50% yields, respectively. Copper(II)
triflate (20 mol %) was beneficial in accelerating ethylation to
afford 2a, 3a, and 1a in 46, 32, and 18% yields after 12 h at
room temperature. Upon further addition of 40 mol % of
tributylphosphine, the reaction was accelerated to afford, after 4
h at 0 °C, 2a, 3a, and 1a in 57, 15, and 22% yields. Encouraged
by the catalyzing effects of copper(II)-phosphine, some chiral
phosphines were applied into diethylzinc reaction. However, it
was very disappointing to learn that a representative chiral
bisphosphine, (R)-(+)-BINAP 4 (20 mol %), was not endowed
with good catalyzing attitude to afford, after 24 h at 0 °C, 2a and
1
formation. Reactive organolithium reagents have been activated
by a chiral amino ether ligand and applied into a catalytic
2,3
asymmetric addition to CdN of imines. Since then, considerably
energetic approaches toward catalytic asymmetric addition of
organometallic reagents to CdN of imines have appeared.4
Among these, zinc triflate-chiral amino alcohol-catalyzed acetylide
3
a in 52 and 16% yields, respectively. The enantiomeric excess
of 2a was determined to be only 2% by HPLC analysis with a
chiral stationary phase column (Daicel Chiralcel OD-H, hexane/
i-PrOH (10/1), 254 nm, 0.6 mL/min). (-)-DIOP 5 (20 mol %)
was a slightly better ligand to afford, after 24 h at 0 °C, (R)-2a
5
addition, chiral π-allylpalladium-catalyzed allylation with allyl-
6
stannane or allylsilane, and rhodium-MOP-based phosphine-
7
catalyzed arylation with arylstannanes showed impressive suc-
cess.8 However, the catalytic asymmetric addition of simple
alkylmetals that satisfies high catalytic performance in chemical
13
in 60% yield and 27% ee.
Dramatic improvement in catalytic activity, reaction-type
9
yield and enantioselectivity has not yet been achieved. This is
selectivity, and enantioselectivity was realized using an amido-
in great contrast to the chiral amino alcohol-catalyzed asymmetric
alkylation of aldehydes with organozinc reagents, which becomes
14
phosphine (S)-(-)-6 as a ligand for copper. The reaction of 3
equiv of diethylzinc (hexane solution) was conducted in toluene
in the presence of 8 mol % of copper(II) triflate and 10 mol % of
6 at 0 °C for 1 h to afford (S)-2a in 98% yield and 93% ee. It is
also surprisingly delightful to learn that only 1.3 mol % of 6 and
(
1) (a) Tomioka, K. Synthesis 1990, 541-549. (b) Noyori, R. Asymmetric
Catalysis in Organic Synthesis; John Wiley & Sons: New York, 1994. (c)
Lagasse, F.; Kagan, H. B. Chem. Pharm. Bull. 2000, 48, 315-324.
(
2) (a) Tomioka, K.; Inoue, I.; Shindo, M.; Koga, K. Tetrahedron Lett.
1
mol % of copper (II) triflate were enough to catalyze the addition
of 2 equiv of diethylzinc for 2 h at 0 °C, giving 2a in 94% yield
and 90% ee (Table 1, entry 1).
The performance of copper-6 catalyst in reactivity, reaction-
type selectivity, and enantioselectivity is tunable by variation of
N-sulfonyl groups of imines 1. 4-Methoxyphenylsulfonylimine
1
990, 31, 6681-6684. (b) Taniyama, D.; Hasegawa, M.: Tomioka, K.
Tetrahedron Lett. 2000, 41, 5533-5536.
3) For a chiral ligand-catalyzed asymmetric addition of lithium enolates
to imines, see: (a) Kambara, T.; Tomioka, K. J. Org. Chem. 1999, 64, 9282-
285. For the chiral ligand-catalyzed asymmetric reactions of enolate
(
9
equivalents with imines, see: (b) Ishihara, K.; Miyata, M.; Hattori, K.; Tada,
T.; Yamamoto, H. J. Am. Chem. Soc. 1994, 116, 10520-10524. (c) Ishitani,
H.; Ueno, M.; Kobayashi, S. J. Am. Chem. Soc. 1997, 119, 7153-7154. (d)
Hagiwara, E.; Fujii, A.; Sodeoka, M. J. Am. Chem. Soc. 1998, 120, 2474-
1
b was a good acceptor to provide the same level of high catalytic
2
1
475. (e) Ferraris, D.; Young, B.; Dudding, T.; Lectka, T. J. Am. Chem. Soc.
performance as tosylimine 1a (entry 2). However, 4-nitrophenyl-
sulfonyl group 1c was less efficient in providing nosylamide 2c
in 67% yield and 65% ee after 6 h at 0 °C (entry 3).
Pentafluorophenylsulfonylimine 1d was a highly nonreactive
substrate providing 2d in only 22% yield and 6% ee after 24 h
entry 4). Steric bulkiness is another influential factor shown by
,4,6-trimethylphenylsulfonylimine 1e, affording 2e in 26% yield
and 5% ee after 24 h (entry 5). Alkylsulfonylimines are good
acceptors allowing high catalytic performance (entries 6, 7).
Methanesulfonyl (Ms) group 1f showed the highest performance
providing mesylamide in 97% yield and 94% ee after 4 h.
998, 120, 4548-4549. (f) Yamada, K.; Harwood, S. J.; Groger, H.; Shibasaki,
M. Angew. Chem., Int. Ed. 1999, 38, 3504-3506.
(
4) For excellent reviews, see: (a) Denmark, S. E.; Nicaise, O. J.-C. J.
Chem. Soc., Chem. Commun. 1996, 999-1004. (b) Enders, D.; Reinhold, U.
Tetrahedron: Asymmetry 1997, 8, 1895-1946. (c) Bloch, R. Chem. ReV. 1998,
9
8, 1407-1438. For the leading references of chiral ligand-catalyzed
(
2
asymmetric addition to imines, see: (d) Itsuno, S.; Yanaka, H.; Hachisuka,
C.; Ito, K. J. Chem. Soc., Perkin Trans. 1 1991, 1341-1342. (e) Katritzky,
A. R.; Harris, P. A. Tetrahedron: Asymmetry 1992, 3, 437-442. (f) Soai,
K.; Hatanaka, T.; Miyazawa, T. J. Chem. Soc., Chem. Commun. 1992, 1097-
1
1
5
098. (g) Nakamura, M.; Hirai, A.; Nakamura, E. J. Am. Chem. Soc. 1996,
18, 8489-8490. (h) Denmark, S. E.; Stiff, C. M. J. Org. Chem. 2000, 65,
875-5878. (i) Ukaji, Y.; Shimizu, Y.; Kenmoku, Y.; Ahmed, A.; Inomata,
K. Bull. Chem. Soc. Jpn. 2000, 73, 447-452.
2
-Trimethylsilylethanesulfonyl (SES) group 1g also showed a high
performance providing the SES-amide in 94% yield and 89% ee
after 12 h.
(
5) Frantz, D. E.; F a¨ ssler, R.; Carreira, E. M. J. Am. Chem. Soc. 1999,
21, 11245-11246.
6) (a) Nakamura, H.; Nakamura, K.; Yamamoto, Y. J. Am. Chem. Soc.
1
(
1
998, 120, 4242-4243. (b) Nakamura, K.; Nakamura, H.; Yamamoto, Y. J.
Org. Chem. 1999, 64, 2614-2615. (c) Bao, M.; Nakamura, H.; Yamamoto,
(10) (a) Noyori, R.; Kitamura, M. Angew. Chem., Int. Ed. Engl. 1991, 30,
49-69. (b) Soai, K.; Shibata, T.; Sato, I. Acc. Chem. Res. 2000, 33, 382-
390.
Y. Tetrahedron Lett. 2000, 41, 131-134.
(
(
7) Hayashi, T.; Ishigedani, M. J. Am. Chem. Soc. 2000, 122, 976-977.
8) For asymmetric ene-type addition to imines, see: (a) Drury, W. J., III;
(11) (a) Sisko, J.; Weinreb, S. M. J. Org. Chem. 1990, 55, 393-397. (b)
Masquelin, T.; Obrecht, D. Synthesis 1995, 276-284.
(12) Love, B. E.; Raje, P. S.; Williams, T. C., II. Synlett 1994, 493-494.
(13) The absolute configuration of 2a was determined by specific rotation.
Raban, M.; Moulin, C. P.; Lauderback, S. K.; Swilley, B. Tetrahedron Lett.
1984, 25, 3419-3422.
Ferraris, D.; Cox, C.; Young, B.; Lectka, T. J. Am. Chem. Soc. 1998, 120,
1
8
1006-11007. (b) Martin, S. F.; Lopez, O. D. Tetrahedron Lett. 1999, 40,
949-8953. (c) Johannsen, M. Chem. Commun. 1999, 2233-2234. (d) Yao,
S.; Fang, X.; Jorgensen, K. A. Chem. Commun. 1999, 2547-2548.
(
9) (a) Brandt, P.; Hedberg, C.; Lawonn, K.; Pinho, P.; Andersson, P. G.
Chem. Eur. J. 1999, 5, 1692-1699. (b) Jimeno, C.; Reddy, K. S.; Sol a` , L.;
(14) Nakagawa, Y.; Kanai, M.; Nagaoka, Y.; Tomioka, K. Tetrahedron
1998, 54, 10295-10307.
Moyano, A.; Peric a` s, M. A.; Riera, A. Org. Lett. 2000, 2, 3157-3159.
1
0.1021/ja005629g CCC: $19.00 © 2000 American Chemical Society
Published on Web 11/16/2000

12056 J. Am. Chem. Soc., Vol. 122, No. 48, 2000
Communications to the Editor
Table 1. Catalytic Asymmetric Addition of Et
N-Sulfonylimines 1 Catalyzed by 1 mol % of Cu(OTf)
of 6 in Toluene at 0 °C
2
Zn (2 equiv) to
from furfural can be converted to adducts in 98% yields and 93%
ees (entries 11, 12), which are useful intermediates for synthesis
of biologically active compounds.
2
and 1.3 mol
%
15
The mechanistic details of the asymmetric process are currently
under scrutiny to determine the nature of the reactive species and
reaction mode involved. Our current hypothesis is that a zinc
cuprate-phosphine complex is formed in situ, analogous to the
well-studied chemistry of organocuprates.16 The observation that
a bulky mesitylenesulfonyl group 1e retarded the addition reaction
implies coordination of zinc or copper with a sulfonyl oxygen
followed by 1,4-addition-type alkylation. Poor reactivity exhibited
unexpectedly by an electron-withdrawing nosyl and pentafluo-
rophenylsulfonyl groups 1c,d also suggests the above scenario,
considering the decreasing coordinating ability of a sulfonyl
oxygen.17
entry
1
R1
time/h
yield/%
ee/%
Additional studies demonstrated that the total process is
extended to asymmetric amine synthesis. The N-sulfonyl groups
used in this study can be removed by the established methods to
provide the corresponding amines. For example, although reduc-
1
2
3
4
5
6
7
a
b
c
d
e
f
6
4-MeC H
4
2
3
6
24
24
4
94
97
67
22
26
97
94
90
90
65
6
5
94
89
a
a
4-MeOC
6
H
H
4
4-NO
2
C
6
4
18
C
6
F
5
tion of mesylamide 2f with Red-Al in refluxing benzene for 12
2,4,6-Me
Me
3
C
6
H
2
h gave (S)-1-phenylpropylamine19 in 87% yield with slight
20
racemization, N-tosylamide 2a was treated with SmI
2
in a
a
g
Me
3
Si(CH
2
)
2
12
mixture of THF and HMPA under reflux for 5 h gave (S)-amine
in 84% yield without any racemization. The corresponding
N-SESamide 2g was treated with CsF21 in DMF at 95 °C for 40
h gave (S)-amine in 84% yield without any racemization.
In summary, we have reported a novel copper(II)-chiral
amidophosphine 6-catalyzed asymmetric process for the addition
of diethylzinc to N-sulfonylimines. The asymmetric addition
process affords N-sulfonylamides in excellent ee’s and yields in
toluene under mild conditions. In our working model, we postulate
that the process proceeds through the intermediacy of a zinc
cuprate in a 1,4-conjugate addition manner.
a
The reaction was conducted in the presence of 3 mol % of Cu(OTf)
2
and 3.9 mol % of 6.
Table 2. Catalytic Asymmetric Addition of Et
N-Sulfonylimines 1
2
Zn to
entry
1
R2
R3 Cu-6/mol % time/h yield/% ee /%
a
Acknowledgment. We gratefully acknowledge financial support from
Japan Society for Promotion of Science (RFTF-96P00302) and the
Ministry of Education, Science, Sports and Culture, Japan.
1
2
3
4
5
6
7
8
9
a
f
g
h
i
j
k
l
m
n
o
p
Ph
Ph
Ph
Ts
Ms
SES
8
1
8
5
1
5
1
8
1
5
1
8
1
4
2
16
8
24
8
2
3
1
3
98
97
98
79
94
83
95
99
95
95
98
98
93
94
90
92
93
92
94
93
90
92
93
93
1-naphthyl Ms
2-naphthyl Ms
4-MeOC
4-ClC
4-ClC
3-ClC
2-ClC
2-Furyl
2-Furyl
Supporting Information Available: General procedure and spec-
troscopic and analytical data for the products 2 (PDF). This material is
available free of charge via the Internet at http://pubs.acs.org.
6
H
4
Ms
Ms
SES
Ms
Ms
Ms
SES
6
H
6
H
6
H
6
H
4
4
4
4
JA005629G
(
15) (a) Zhou, W.-S.; Lu, Z.-H.; Wang, Z.-M. Tetrahedron 1993, 49, 2641-
10
11
12
2
654. (b) Hopman, J. C. P.; van den Berg, E.; Ollero, L. O.; Hiemstra, H.;
Speckamp, W. N. Tetrahedron Lett. 1995, 36, 4315-4318. (c) Koulocheri,
1
S. D.; Magiatis, P.; Skaltsounis, A.-L.; Haroutounian, S. A. Tetrahedron 2000,
5
6, 6135-6141.
(
a
The ee’s of mesylamides were determined by NMR in the presence
judged by the integration of methyl groups. The ee’s of
16) (a) Rossiter, B. E.; Swingle, N. M. Chem. ReV. 1992, 92, 771-806.
of Eu(hfc)
SES amides were determined by HPLC.
3
(b) Krause, N. Angew. Chem., Int. Ed. 1998, 37, 283-285. (c) Nakamura, E.;
Yamanaka, M.; Mori, S. J. Am. Chem. Soc. 2000, 122, 1826-1827. (d)
Tomioka, K.; Nagaoka, Y. In ComprehensiVe Asymmetric Catalyst; Jacobsen,
E. N., Pfaltz, A., Yamamoto, H., Eds.; Elsevier: New York, 1999; Chapter
When a solution of N-mesyl and SES-imines (1 mmol) derived
from arylaldehydes and furfural is treated with 2 equiv of
diethylzinc (1 M hexane solution) and 1-8 mol % of copper(II)
triflate-6 (6/Cu ) 1.3) in toluene (8 mL) at 0 °C for 0.5-24 h,
ethyl N-sulfonamides are isolated in excellent % ee’s (up to 94%
ee) and yields (up to 99%) (Table 2). In general, N-sulfonylimines
derived from arylaldehydes bearing an electron-withdrawing
substituent are more reactive than the corresponding parent
counterpart (entry 6). It is advantageous that imines 1o,p derived
3
1, Vol. III. (e) Tomioka, K. In Modern Carbonyl Chemistry; Otera, J., Ed.;
Wiley-VCH: Germany, 2000; Chapter 12.
(17) Our initial expectation was acceleration of the reaction through
increasing electrophilicity of CdN of the sulfonylimine by an electron-
withdrawing 4-nitrophenyl group.
(
18) Gold, E. H.; Babad, E. J. Org. Chem. 1972, 37, 2208-2210.
(19) Yang, T.-K.; Chen, R.-Y.; Lee, D.-S.; Peng, W.-S.; Jiang, Y.-Z.; Mi,
A.-Q.; Jong, T.-T. J. Org. Chem. 1994, 59, 914-921.
(
20) Vedejs, E.; Lin, S. J. Org. Chem. 1994, 59, 1602-1603.
(
21) Weinreb, S. M.; Demko, D. M.; Lessen, T. A. Tetrahedron Lett. 1986,
27, 2099-2102.