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OH
OH
OH
tigloyl chloride
C
3
H
7
COCH
2
CO
2
Et
AlCl
3
,CS
2
/PhNO
2
CF
3
SO
3
H
HO
O
O
HO
OH
HO
O
O
1
O
OH
3-chloro-3-methyl-1-butyne, ZnCl
2
, K
2
CO
3
K
2
CO
3
2-butanone
(n-Bu
4
)NI, 2-butanone/DMF/Et
2
O (10:1:1)
O
O
O
O
2
1:1
O
O
+
O
O
O
O
O
O
O
O
3
4
NaBH
4
, CeCl
3
7H
2
O
NaBH
4
, EtOH
EtOH
O
O
D
A
B
O
OO
O
O
O
C
OH
OH
5
6
(±)-calanolide A
(±)-calanolide C
Scheme 8-1
acid-promoted Claisen rearrangement. The chromene ring was built last. Finally,
Luche reduction of the chromanone provided racemic calanolide A (
1).
One year later, Kucherenko et al.
43
reported on a novel method to synthesize
racemic calanolide A (Scheme 8-2).
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