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OPiv
PivO
OPiv
PivO
OPiv
PivO
M
N
OPiv
O
O
O
R
R
N
OPiv
NH
2
OPiv
PivO
PivO
PivO
SnCl
4
, THF
M = SiMe
3
, SnBu
3
5
58
3
β
β
Scheme 1.18
Asymmetric synthesis of
(S)-
configured homoallyl amines using galactosyl amine
3
.
OPiv
RCHO/AcOH
heptane
r.t., 30min
OPiv
OPiv
N
SiMe
3
O
R
O
O
R
1.2 eq.
THF, 2.2 eq. SnCl
4
H
2
N
N
OPiv
OPiv
OPiv
PivO
PivO
PivO
59
60
61
Scheme 1.19
Asymmetric synthesis of
(R)
-configured homoallyl amines using fucosyl amine
58.
of allyl trimethylsilane in the allylic addition of the corresponding
β
-L-fucosyl
imines
60
(R
n
Pr).
Schiff bases derived from glucosyl amines and aliphatic aldehydes do not react
with allyltrimethylsilane under the same conditions. Even at low temperature
(
=
78 °C), only anomerization and decomposition occurred. However, these imines
could be converted into the corresponding homoallylamines using allyltributyls-
tannane instead of the silane at
−
−
78 °C, and SnCl
4
(1.2 equiv) was used to activate
the imine.
The homoallylamines
62
can be released from the carbohydrate template using
aqueous HCl in methanol. Homoallylamine hydrochlorides
62
could easily be N-
protected and were subsequently oxidized to yield the N-protected
β
-amino acid
64,
which was finally deprotected to the corresponding
-amino acid
65
(Scheme 1.20).
A tentative reaction mechanism was proposed by the authors. In the transition
state the tin atom of the Lewis acid SnCl
4
has octahedral coordination, with sites
occupied by chlorine atoms, the imine nitrogen and the carbonyl oxygen of the
β
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