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In-Depth Information
O
O
1) BuLi
hexane / THF
-78 °C
2) EtCOCl
O
O
O
O
O
1) LDA
THF, -78 °C
2) PhCHO
O
O
O
N
O
O
O
N
O
O
O
H
O
O
O
Me
O
O
O
O
46
48
(78% de)
47
OH
Ph
O
O
OH
O
LiBH
4
+
Ph
O
HO
H
O
O
O
49
Scheme 3.16
Propionate-type aldolization using a spiro-oxazolidinone derived from galactose
as chiral auxiliary.
However, subsequent studies have shown that the recovered spiro-oxazolidinone
auxiliary
46
undergoes epimerization about the spiro-carbon atom upon cleavage
with lithium borohydride.
To avoid the epimerization process, the same group has reported the synthesis
of oxazinone
50
in four steps starting from gulonic acid [24]. Lithium enolate
mediated aldol condensation of
51
with benzaldehyde gave only the
syn
adducts
in 88% yield and a 91 : 9 ratio in favor of the diastereoisomer
52
with (2
′
S
)
configurations. Reductive cleavage of
52
using LiBH
4
led to (1
S
,2
R
)-1-phenyl-2-
methylpropane-1,3 diol-
49,
together with recovery of the chiral auxiliary
50
with
no appreciable epimerization (Scheme 3.17) [20].
Solladié's group has studied the reaction of an imino glycinate derivative of a
carbohydrate with an aldehyde
en route
to chiral
′
S
,3
-amino acids derivatives (Scheme
3.18). The aldol condensation of diacetone-D-glucose iminoglycinate
53,
obtained
in three steps from diacetone-D-glucose, with tetradecanal under phase-transfer
α
1) BuLi
hexane / THF
-78 °C
O
O
O
O
O
O
O
O
O
1) LDA
THF, -78 °C
O
O
O
O
O
O
N
HN
O
O
O
N
2) EtCOCl
2) PhCHO
O
O
O
Me
50
O
51
52
(88% de)
O
Ph
OH
OH
Ph
HO
LiBH
4
49
Me
Scheme 3.17
Propionate-type aldolization using an oxazinone derived from gulonic acid as
chiral auxiliary.
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