Chemistry Reference
In-Depth Information
Scheme 1.22
Diastereoselective synthesis of
β
-amino acids
73.
OPiv
PivO
OPiv
PivO
R
1
R
3
R
1
OTMS
R
3
R
3
AgOTf
2,6-lutidine
CH
2
Cl
2
-40
O
O
N
OR
4
R
2
+
N
+
PivO
PivO
R
3
OR
4
PivO
Br
PivO
R
2
74
75
76
O
20 °C
77
R
1
= Et, R
2
= Ph, R
3
= Et, R
4
= Me, 68% (R), 18% (S) 4:1 dr
R
1
= Et, R
2
= Ph, R
3
= Me, R
4
= Me, 48% (R), 17% (S) 3:1 dr
R
1
= Et, R
2
= Ph, R
3
= -(CH
2
)
5
-, R
4
= Et, 63% (R), 23% (S) 3:1 dr
R
1
= Et, R
2
= 4-NO
2
-Ph, R
3
= Et, R
4
= Me, 53% (R), 7% (S) 8:1 dr
R
1
= Et, R
2
= 3,4(MeO)
2
Ph, R
3
= Et, R
4
= Me, 68% (R), 24% (S) 3:1
dr
R
1
= Ph, R
2
= Ph, R
3
= Et, R
4
= Me, 88% 3:1 dr
R
1
= All, R
2
= Ph, R
3
= Et, R
4
= Me, 70% (R), 18% (S) 4:1 dr
R
1
= Bn, R
2
= Ph, R
3
= Et, R
4
= Me, 37% (R), 30% (S) 5:4 dr
Scheme 1.23
Diastereoselective synthesis of
β
-amino acid esters via an
in situ
glycosylation
method.
In 1989, Kunz reported the stereoselective tandem Mannich-Michael reactions
for the synthesis of piperidine alkaloids again using galactosylamine
3
as an effec-
tive chiral auxiliary [36]. A subsequent publication described how the
N
-galactosyl
aldimines
5
react with silyl dienol ether
81
in the presence of zinc chloride
in tetrahydrofuran at
20 °C to give the Mannich bases
82/83
with high
diastereoselectivities. The Michael addition then occurs to give the dehydropiperi-
dones
84/85
in high yields upon hydrolysis with 1M HCl (Scheme 1.25) [37].
−
OPiv
PivO
OPiv
PivO
Et
OTMS
75
O
O
Et
OMe
sN
+
PivO
PivO
N
PivO
O
AgOTf
2,6-lutidine,CH
2
Cl
2
PivO
Br
Et
Et
OMe
74
78
80
dr 13:1
yield: 69% (R); 6% (S)
Scheme 1.24
Diastereoselective synthesis of
β
-amino acid ester
80
from dihydroquinoline
78.
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