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i) Et
2
Zn (2 equiv.)
ClCH
2
I(4equiv.)
ca. 92% de (quant)
2steps
TMSI
O
O
O
O
O
O
76%
ii) Crystallized, 96% de
54%
I
34
35
36
O
H
N
O
O
O
O
S
9N H
2
SO
4
LiHMDS
37
Cl
O
H
OH
N
O
O
S
S
Cl
Cl
38
39
O
O
Oxone, KHCO
3
,
aq. acetone
i) Oxalyl chloride
i
i) 2-aminopyrazine,pyridine
N
N
OH
76%
42% over 4 steps
O
O
S
N
S
O
O
O
O
Cl
Cl
33
(Piragliatin)
40
TMSI = Trimethylsilyliodide
Scheme 3.1
Stereoselective synthesis of piragliatin (33)
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