Stereoselection in asymmetric PTC alkylation
Russ.Chem.Bull., Int.Ed., Vol. 51, No. 11, November, 2002 2089
Table 1. Efficiency of catalysts based on various metal ionsa
previously described procedure.13 The optical purity of the isoꢀ
lated amino acid was determined by enantiomeric GLC analysis.
Run
Complex
type
M
Amino acid
This work was financially supported by the Internaꢀ
tional Scientific and Technical Center (Grant ISTC
Aꢀ356), the American Civil Research and Development
Foundation (Grant CRDF RCꢀ1ꢀ2205), and the Russian
Foundation for Basic Research (Project No. 02ꢀ03ꢀ
32050).
Yield (%) eeb (%)
1
3 (5)
CuII (CuI)c
>95
90
2
3
4
5
6
7
8
9
10
11
12
13
3
3
3
3
3
3
3
7
6
4
5
8
NiII
ZnII
PdII
SnII
FeII
CoII
MnII
TiIV
VIV
36
62
50
35
38
84
28
0
60
31
20
5
6 d
17
15
3
—
31
0
References
1. E. N. Jacobsen, A. Pfaltz, and H. Yamamoto, Comprehenꢀ
sive Asymmetric Catalysis, Springer—Ferlag, Berlin, 2000.
2. M. J. O´Donnell, W. D. Bennet, and S. Wu, J. Am. Chem.
Soc., 1989, 111, 2353.
3. J. Casas, C. Nájera, J. Sansano, J. González, J. Saá, and
M. Vega, Tetrahedron Asymmetry, 2001, 12, 699.
4. T. Abellán, R. Chinchilla, N. Galindo, C. Nájera, and
J. Sansano, Eur. J. Org. Chem., 2000, 2689.
5. B. Lygo, J. Crosby, and J. A. Peterson, Tetrahedron Lett.,
1999, 40, 1385.
6. B. Lygo, Tetrahedron Lett., 1999, 40, 1389.
7. E. J. Corey, F. Xu, and M. C. Noe, J. Am. Chem. Soc., 1997,
119, 12414.
8. M. Horikawa, J. BuschꢀPetersen, and E. J. Corey, Tetraꢀ
hedron Lett., 1999, 40, 3843.
9. T. Ooi, M. Kameda, and K. Maruoka, J. Am. Chem. Soc.,
1999, 121, 6519.
10. T. Ooi, M. Takeuchi, M. Kameda, and K. Maruoka, J. Am.
Chem. Soc., 2000, 121, 5228.
11. Y. N. Belokon, K. A. Kochetkov, T. D. Churkina, N. S.
Ikonnikov, O. V. Larionov, S. R. Haratynyan, Š. Vysko il,
M. North, and H. Kagan, Angew. Chem., Int. Ed. Engl.,
2001, 40, 1948.
CoIII
AgI
LaIII
21
>95
>95
0
0
a Reaction conditions: 1 equiv. of Schiff´s base 1, 1.5 equiv. of
BnBr, 5 mol.% of the catalyst, 2.2 equiv. of NaH. The change in
the amount of the chiral catalyst from 0.5 to 10 mol.% does not
change the chemical yield or the stereochemical outcome of the
reaction. When comparing the efficiency of various chiral salen
complexes in alkylation, 5 mol.% of the catalyst was always used.
b Determined by chiral GLC.
c During alkylation, the catalyst is rapidly (over ∼20 min) oxiꢀ
dized to give a CuII complex, which can be easily detected by a
typical coloring.
d The reaction catalyzed by the SnII complex with (R,R)ꢀcycloꢀ
hexaneꢀ1,2ꢀdiamine afforded (S)ꢀαꢀmethylphenylalanine,
whereas catalysis by complexes of other metals with the same
diamine gave rise to (R)ꢀamino acid.
N, 6.59. C20H20N2O2Mn•0.4 CHCl3. Calculated (%): C, 57.91;
H, 4.86; N, 6.62.
Complex 6. M.p. 345—346 °C (dec.), [α]D25 –816 (s, 0.024,
CHCl3). Found (%): C, 60.12; H, 5.21; N, 6.98.
12. Y. N. Belokon, M. North, V. S. Kublitski, N. S. Ikonnikov,
P. E. Krasik, and V. I. Maleev, Tetrahedron Lett., 1999,
40, 6105.
13. Y. N. Belokon, M. North, T. D. Churkina, N. S. Ikonnikov,
and V. I. Maleev, Tetrahedron, 2001, 57, 2491.
14. C. Girard and H. Kagan, Angew. Chem., Int. Ed. Engl., 1998,
37, 2923.
15. E. N. Jacobsen, Y. Gao, Y. Hong, X. Nie, and C. Zepp,
J. Org. Chem., 1994, 59, 1939.
C
20H20N2O3V•2/3 H2O. Calculated (%): C, 60.15;
H, 5.38; N, 7.01.
Alkylation catalyzed by complexes 3 (M = CoII, FeII, SnII,
ZnII), 5 (M = CuI, AgI), and 8 was preceded by preparation of the
catalysts in situ under argon from Co(OAc)2•4 H2O, FeCl2,
SnCl2•2 H2O, Zn(OAc)2, CuBr•MeCN, AgNO3, and LaCl3,
respectively.
16. A. R. Amundsen, J. Whelan, and B. Bosnich, Inorg. Chem.,
1979, 18, 206.
Complex 4 was prepared in situ similarly to complex 3
(M = CoII) but with bubbling air through the reaction mixture.
Complexes 7 and 9 used in the work were prepared previꢀ
ously.17,18
17. Y. N. Belokon, S. CavedaꢀCepas, B. Green, N. S. Ikonnikov,
V. N. Khrustalev, V. S. Larichev, M. A. Moscalenko,
M. North, C. Orizu, V. I. Tararov, M. Tasinazzo, G. I.
Timofeeva, and L. V. Yashkina, J. Am. Chem. Soc., 1999,
121, 118.
18. Yu. N. Belokon', V. M. Belikov, M. M. Dolgaya, I. I.
Kruman, S. B. Nikitina, and P. V. Petrovskii, Izv. Akad.
Nauk SSSR, Ser. Khim., 1973, 1836 [Bull. Acad. Sci. USSR,
Div. Chem. Sci., 1973, 22 (Engl. Transl.)].
Catalytic asymmetric alkylation (general procedure). Cataꢀ
lyst (0.0228 mmol) was placed in a roundꢀbottom twoꢀnecked
flask filled with argon, the flask was evacuated three times and
filled with argon with heating by a torch flame. The flask was
cooled in an argon flow, and a solution of compound 1 (100 mg,
0.457 mmol) and BnBr (0.1 mL) in 2 mL of anhydrous toluene
was added, followed by the addition of NaH (40 mg, 1 mmol).
The reaction mixture was stirred for 24 h under argon. After
completion of the reaction, the precipitate was filtered off; the
amino acid was isolated by workup of the filtrate according to a
Received December 21, 2001
in revised form May 15, 2002