Biomedical Engineering Reference
In-Depth Information
S
S
S
S
S
S
HO
HO
HO
Au
+
+ 2H
+
R = Bz
21
O
O
O
OBz
70
O
OR
- Au
+
Au
THF
Au
OPMB
O
Ph
OPMB
OPMB
74
76
77
- H
+
R = H
MeOH
S
- AuOH
S
72
HO
HO
S
+ H
+
- H
+
71
O
O
S
OPMB
OPMB
H
75
SCHEME 4.23
stabilized conformer
76
, which then leads to oxonium
77
after protodemetalation and
acidic reactivation.
The same discrimination in reactivity was used by Forsyth and coworkers in
their syntheses of two spiroketal fragments of okadaic acid
82
(Scheme 4.24) [21].
The ynediol
78
was efficiently converted into spiroketal
79
by reaction with AuCl in
OPMB
15
OH
38
HO
OBn
32
HO
HO
O
PMP
28
19
34
BnO
OH
27
O
H
O
80
78
1. AuCl (19 mol%)
CH
2
Cl
2
, rt, 2 h
2.
p
-TsOH, MeOH
rt, 2 h
AuCl (10 mol%)
4 Å MS, THF
0°C, 0.5 h
84%
65%
OBn
PMBO
H
O
O
OH
28
34
38
15
19
BnO
O
O
H
27
OH
O
H
79
81
O
OH
H
H
O
15
O
HO
1
O
19
O
OH
O
H
H
28
34
38
27
OH
O
O
H
H
H
OH
Okadaic acid
82
SCHEME 4.24
Syntheses of two spiroketal fragments of okadaic acid by Forsyth and
coworkers.
Search WWH ::
Custom Search