Biomedical Engineering Reference
In-Depth Information
syn
:
anti
> 19:1
CO
2
H
H
O
O
OH
O
9
2
(10 mol%)
+
PMBO
H
H
PMBO
5
H
DMSO, 4°C
48% (75% brsm)
anti
:
syn
= 12:1
Me
Me
Me
Me
22
23
24
(ee = 99%)
Zn
HCCCH
2
Br
THF
OTBS
Me
OH
OH
5
Me
2
CO
2
Me
PMBO
O
H
OMe
Me
Me
O
H
9
21
25
SCHEME 6.5
Synthesis of the C1-C9 unit of callipeltoside C.
The C3 stereogenic center, on the other hand, was controlled through a proline-
catalyzed asymmetric
a
-aminoxylation (see 6.3.2.).
The original procedure [6] of the proline-catalyzed aldol reaction of furfural
(
) in DMF was not practical for large-scale synthesis as it
required large amounts of furfural (10 equivalents) and resulted in both low yields
(up to 10%) and low diastereoselectivities (
anti
/
syn
33
) and propanal (
23
1:1). After some optimization,
¼
diol
could eventually be obtained in good yield and diastereoselectivity by
conducting the reaction without solvent and using the surfactant-proline conjugated
catalyst
34
was water soluble, these solvent-free
conditions also enabled easyworkup. Protection of diol
17
(Scheme 6.7). Since diol
34
34
as a
p
-methoxybenzylidene
OTES
OMe
CO
2
H
H
O
OH
O
OH
O
2
(10 mol%)
28
TIPSO
H
DMF
75%
H
MgBr
2
·OEt
2
CH
2
Cl
2
47%
TIPSO
OMe
OTIPS
TIPSO
OTIPS
OH
26
27
(ee = 99%)
29
(dr > 20:1)
Me
O
O
NH
Me
O
OBn
CCl
3
TIPSO
TIPSO
OMe
OMe
HO
Me
O
20
30
SCHEME 6.6
Synthesis of the sugar moiety of callipeltoside C.
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