Biomedical Engineering Reference
In-Depth Information
O
OPiv
O
(
S
)-Carvone
1. LDA, PhNTf
2
, -78°C
2. Me
8
Sn
2
, Pd(PPh
3
)
4
then NIS
78%
47%
OH
1
-BuLi, THF, -78°C
2. PPTS, MeOH
64%
. t
I
OHC
+
O
TMS
O
TMS
OMe
OMe
OHC OTIPS
BF
3
.Et
2
O, CH
2
Cl
2
-65°C to -20°C
79%
H
H
H
CHO
H
O
O
HO
AcO
OTIPS
TMS
(-)-7-Deacetoxyalcyonin acetate
SCHEME 8.25
Synthesis of (
)-7-deacetoxyalcyonin acetate.
Ts
N
Ts
N
Ts
N
SnCl
4
(1 equiv)
CH
2
Cl
2
, 8 min, 0°C
96%
HO
aza-Prins
Pinacol
OMe
N
Ts
Ph
Ph
CHO
Ph
OH
OH
Ph
SCHEME 8.26
7-Azabicyclo[2.2.1]heptane via aza-Prins-pinacol rearrangement.
fact, coupled with simple and mild reaction conditions (use of protic or Lewis acid
such as SnCl
4
in nitromethane or dichloromethane as the solvent), has prompted the use
of this rearrangement in the synthesis of variously substituted annulated polycyclic
ethers of biological interest, such as briarellin F [140], (
)-magellaninone [141],
(
)-7-
Deacetoxyalcyonin acetate was also synthesized using a Prins-pinacol rearrangement
staring from (
S
)-carvone [145] (Scheme 8.25). This synthesis was later optimized by
Overman and Pennington [144].
The Prins-pinacol rearrangement can also involve iminium species. The so-
called aza-Prins-pinacol rearrangement was used by Armstrong and Shanahan [146]
in their synthesis of 7-azabicyclo[2.2.1]heptane ring system present in epibatidine, an
alkaloid with high biological and pharmacological interest [147] (Scheme 8.26).
)-citreoviral [142], (
þ
)-shahamin K [143], or (
)-sclerophytin A [144]. (
8.7. THE [1,2]- AND [2,3]-WITTIG REARRANGEMENTS
TheWittig rearrangement comprises the thermal [1,2]-rearrangement of an aryl alkyl
ether to the corresponding secondary or tertiary alcohol, which was discovered by
Search WWH ::
Custom Search