Synthesis of chiral depsipeptide building block via asymmetric hydrosilylation

Article abstract of DOI:10.1081/SCC-120002401

Asymmetric hydrosilylation of N-(α-ketoacyl)-α-amino esters was performed, catalyzed by rhodium(I) complex of chiral 2-(2-pyridyl)-4-carbomethoxy-1,3-thiazolidine or Rh(PPh₃)₃Cl. The N-(α-hydroxyacyl)-α-amino esters were synthesized

Full text of DOI:10.1081/SCC-120002401

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SYNTHESIS OF CHIRAL DEPSIPEPTIDE BUILDING BLOCK
VIA ASYMMETRIC HYDROSILYLATION
a
b
Jin-shui Yao & You-shi Wu
a
Department of Material Science & Engineering , Shandong Institute of Light Industry ,
Jinan, Shandong, 250100, China
b
College of Material Science & Engineering , Shandong University (South Part) , Jinan,
Shandong, 250061, China
Published online: 16 Aug 2006.
To cite this article: Jin-shui Yao & You-shi Wu (2002) SYNTHESIS OF CHIRAL DEPSIPEPTIDE BUILDING BLOCK VIA
ASYMMETRIC HYDROSILYLATION, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 32:4, 553-556, DOI: 10.1081/SCC-120002401
To link to this article: http://dx.doi.org/10.1081/SCC-120002401
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SYNTHETIC COMMUNICATIONS, 32(4), 553–556 (2002)
SYNTHESIS OF CHIRAL
DEPSIPEPTIDE BUILDING
BLOCK VIA ASYMMETRIC
HYDROSILYLATION
Jin-shui Yao1,2,* and You-shi Wu2
1
Department of Material Science & Engineering,
Shandong Institute of Light Industry,
Jinan, Shandong 250100, China
College of Material Science & Engineering,
2
Shandong University (South Part),
Jinan, Shandong 250061, China
ABSTRACT
Asymmetric hydrosilylation of N-(a-ketoacyl)-a-amino esters
was performed, catalyzed by rhodium(I) complex of chiral
2-(2-pyridyl)-4-carbomethoxy-1,3-thiazolidine or Rh(PPh ) Cl.
3 3
The N-(a-hydroxyacyl)-a-amino esters were synthesized in
high stereoselectivity.
Recently, asymmetric hydrosilylation of ketones, olefins and imines
1
has received very much attention. We have also reported some results in
2
this field. But, application of asymmetric hydrosilylation of functional
ketones on enantioselective synthesis has received very little attention.
*
Corresponding author.
5
53
Copyright & 2002 by Marcel Dekker, Inc.
www.dekker.com

ORDER
REPRINTS
5
54
YAO AND WU
We now report preliminary results of the asymmetric hydrosilylation
of one kind of functional ketones, N-(a-ketoacyl)-a-amino esters, which
affords the chiral depsipeptides building block, N-(a-hydroxyacyl)-a-
amino esters.
The N-(a-ketoacyl)-a-amino esters (1) were readily prepared in
high yields by the reaction of a-ketoacyl chloride with hydrogen chloride3
salts of a-amino acid methyl esters in the presence of N-methylmorphorine
(
Equation 1).
(1)
The asymmetric hyrosilylation of N-(a-ketoacyl)-a-amino esters (1)
followed by methanolysis were carried out by using diphenylsilane as redu-
cing agent and rhodium(I) complexes as catalysts (Equation 2). The ligands
(2)
using in the reaction were achiral ligand, PPh , or chiral ligand 2-(2-pyri-
3
4
dyl)-4-carbomethoxy-1,3-thiazolidine (A). The procedure was as follows:
Reaction was run with 5 mmol of 1.6 mmol of Ph SiH , 0.025 mmol of
2
2
Rh(I) catalyst at room temperature for 48 h. Methanolysis was carried out
by using 10ml of methanol containing 0.1 g of p-toluenesulphonic acid
ꢀ
(
TsOH) at 40 C for 1 h. After the solvent was removed, the residue was
submitted to short column chromatography on silica gel to give product 2.
Thus, the conversion was calculated. Since determination of the optical
1
purities of the products 2 by HNMR using shift reagent resulted in
unsatisfactory separation of key signals, all products 2 were transformed

ORDER
REPRINTS
CHIRAL DEPSIPEPTIDE BUILDING BLOCK
555
to the corresponding trifluoroacetates 3 by reacting with trifluoroacetic
anhydride in the presence of N-methyl morpholine (Equation 3). The tri-
1
fluoroacetates 3 were submitted to F NMR analysis using Eu(fod) as shift
9
3
reagent, and the optical purities were successfully determined. Results are
shown in table.
As shown in table, asymmetric induction by the Rh(I)-chiral ligand A
predominates over that by the chiral center involved in the substrate 1.
Achiral catalyst Rh(PPh ) Cl has also relatively large asymmetric induction
3
3
caused by the chiral center in the substrate 1. The predominate configura-
(3)
Table. Asymmetric Hydrosilylation Results of 1
c
2
Catalyst
Conversion (%)
(R,S)/(S,S)
% D.E.
a
HOCH(Me)CO-
Phe-OMe
HOCH(Me)CO-
Ala-OMe
HOCH(Me)CO-
Val-OMe
Rh(I)-A
Rh(PPh
Rh(I)-A
84
65
81
52
79
73
79
64
8088/12
66
86
63
84
6044/56
81
73
8091/9
67
87/13
35/65
89/11
48/52
90/10
29/71
89/11
34/66
76
50/50
90/10
23/77
92/8
12
93/7
28/72
82
28/72
78
50/50
74
30
78
4
80
42
78
32
3
)
3
Cl
a
Rh(PPh ) Cl
3
3
a
Rh(I)-A
Rh(PPh
Rh(I)-A
3
)
3
Cl
a
HOCH(Me)CO-
Leu-OMe
HOCH(Me)CO-
Rh(PPh ) Cl
3
3
3
3
a
Rh(I)-A
Rh(PPh
Rh(I)-A
Rh(PPh
Rh(I)-A
b
Gly-OMe
HOCH(Ph)CO-
Phe-OMe
3
)
Cl
Cl
0
80
54
84
a
3
)
a
HOCH(Ph)CO-
Ala-OMe
HOCH(Ph)CO-
Val-OMe
Rh(PPh ) Cl
3
3
a
Rh(I)-A
Rh(PPh
Rh(I)-A
86
44
3
)
3
Cl
a
HOCH(Ph)CO-
Leu-OMe
HOCH(Ph)CO-
Rh(PPh ) Cl
3
44
0
3
a
Rh(I)-A
Rh(PPh
8089/11
65
b
Gly-OMe
3
)
3
Cl
a
2 2
Rh(I)-A was prepared with 0.0125 mmol of [Rh(COD)Cl ] and 0.125 mmol of
b
chiral ligand A in situ. The isomer ratio was R/S, since the Glyine is an achiral
c
amino acid. Diastereomeric excess.

ORDER
REPRINTS
5
56
YAO AND WU
tions of the product 2 were (R,S) when using Rh(I)-ligand A as catalyst,
while they are (S,S) when using achiral catalyst Rh(PPh ) Cl.
3
3
ACKNOWLEDGMENT
We thank Shandong Province Natural Science Fundation Committee
for a Grant-in-Aid for Scientific Research (No. Q98B03119) for financial
support of this work.
REFERENCES
1
. a) Heldmann, D.J.; Seebach, D. Helv. Chim. Acta 1999, 62, 1096;
b) Yun, J.; Buchwald, S.L. J. Am. Chem. Soc. 1999, 121, 5640;
c) Yao, J.S.; Zhou, L.G. Chemistry (in Chinese) 1999, (7), 40;
d) Brunner, H.; Mijolovic, D. J. Organomet. Chem. 1999, 577, 346.
. a) Li, H.; Yao, J.S.; He, B.L. Science in China (Series B) 1997, 40, 485;
b) Yao, J.S.; Xu, G.Y.; Li, H.; He, B.L. Chem. J. Chinese University
2
1
1
998, 19, 1763; c) Yao, J.S.; Zhou, L.G.; Li, H.; He, B.L. Chinese J. Cat.
998, 19, 378.
3
. a-Keto acid chlorides were prepared by the reaction of a-keto acid with
dichloromethyl methyl ether: Ottenheijm, H.C.J.; de Man, J.H.M.
Synthesis 1975, 163.
4. Brunner, H.; Kurzinger, A. J. Organmet. Chem. 1988, 346, 413.
Received in the Netherlands March 19, 2001

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