Chemistry Reference
In-Depth Information
OPiv
PivO
OPiv
PivO
HCO
O
HCOOH, THF
ZnCl
2
, OEt
2
+ R
1
CHO + R
2
NC
NH
2
OPiv
O
PivO
CONHR
2
N
OPiv
L-24
PivO
H
R
1
3
OPiv
PivO
Cl
-
+
H
3
N
COO
-
1. 6 M HCl, 80 °C
2. Amberlite IR 200
1. HCl/MeOH
2. H
2
O
+
H
3
N
CONHR
2
O
OH
+
PivO
H
R
1
H
R
1
OPiv
25
26
27
R' =
n
Pr, R'' =
t
Bu, 80% 94:6 dr
R' =
i
Pr, R'' =
t
Bu, 86% 95:5 dr
R' =
t
Bu, R'' =
t
Bu, 80% 96:4 dr
R' = Bn, R'' =
t
Bu, 80% 95:5 dr
R' = 2-furyl, R'' =
t
Bu, 90% 95:5 dr
R' = 2-thienyl, R'' =
t
Bu, 93% 96:4 dr
R' = Ph, R'' =
t
Bu, 81% 91:9 dr
R' =
p-
Cl-C
6
H
4
, R'' =
t
Bu, 92% 97:3 dr
R' =
p-
NO
2
-C
6
H
4
R'' =
t
Bu, 91% 94:6 dr
R' = styryl, R'' =
t
Bu, 75% 95:5 dr
R' = N
C-(CH
2
)
3
, R'' = Ph, 81% 94:6 dr
Scheme 1.9
Asymmetric Ugi reaction using a galactose-derived chiral auxiliary.
(Scheme 1.9). After acidolytic cleavage of the N-glycosidic bond the tetra-O-pivaloyl-
galactose
25
is reisolated in quantitative yield. Hydrolysis of the amino acid amides
26
and subsequent deprotonation gives the free
-d-amino acids
27
[12].
The arabinosylamine
10
also was applied in Ugi reaction by Kunz and shows a
slightly enhanced reactivity in comparison to the galactosylamine [5, 13]. At
α
25 °C,
10
reacts with aldehydes,
tert
-butyl isocyanide, and formic acid in the presence of
zinc chloride in THF to form the
N
-formyl-
N
-arabinosyl amino acid amides
28
in
almost quantitative yield. The diastereomeric ratio for the l-amino acid derivatives
28
ranges from 22 : 1 to 30 : 1. The free enantiomerically pure l-amino acids
31
can
easily be released from the carbohydrate templates by a two-step acidic hydrolysis
and the carbohydrate template can be recovered in quantitative yield (Scheme 1.10).
−
Scheme 1.10
Stereoselective synthesis of l-amino acid derivatives
31
using a d-arabinose-
derived auxiliary.
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