Biomedical Engineering Reference
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[(I
t
-Bu)AuCl]/AgSbF
6
(2 mol%)
THF/ H
2
O, 60°C, 8 h
[(I
t
-Bu)AuCl]/AgSbF
6
(2 mol%)
THF/ H
2
O, 60°C, 8 h
H
n
-Bu
AcO
O
O
R
98%
90%
Ph
Ph
Ph
(for R = H)
(for R =
n
-Bu)
N
N
(I
t
-Bu)AuCl =
Au
Cl
SCHEME 8.36
[(NHC)Au(I)]-catalyzed Meyer-Schuster rearrangement of propargylic
acetates.
OX
O
O
Ph
3
PAuCl/AgSbF
6
(5 mol%)
Ph
3
PAuCl/AgSbF
6
(5 mol%)
O
OPiv
OAc
CH
2
Cl
2
, rt, 30 min
CH
2
Cl
2
, rt, 30 min
85% (X = OPiv)
70% (X = OAc)
SCHEME 8.37
Meyer-Schuster rearrangement of (3-acyloxyprop-1-ynyl)oxiranes.
intermediates used in the total synthesis of complex natural products. The aggre-
gation pheromone of male boll weevil
Anthonomus grandis
Boheman, for example,
was formed by coupling four monoterpenes, three of them (
E
)-2-(3,3-dimethylcy-
clohexylidene)acetaldehyde, (
Z
)-2-(3,3-dimethylcyclohexylidene)acetaldehyde and
(
Z
)-2-(3,3-dimethylcyclohexylidene)ethanol synthesized using a Meyer-Schuster
rearrangement as the key step (Scheme 8.38) [172]. Hence, the reaction of
3-methylcyclohex-2-en-1-one with lithium dimethylcopper followed by treatment
with acetylide-ethylenediamine complex led to 1-ethynyl-3,3,-dimethylcyclohexanol.
The latter was then acetylated, and the resulting acetylated product was treated with
acetic acid and hydrolyzed to afford (
E
)-2-(3,3-dimethylcyclohexylidene)acetalde-
hyde and (
Z
)-2-(3,3-dimethylcyclohexylidene)acetaldehyde as a quasi 1:1 mixture.
Final reduction with sodium borohydride provided (
E
)-2-(3,3-dimethylcyclohexyli-
dene)ethanol and the natural product (
Z
)-2-(3,3-dimethylcyclohexylidene)ethanol in
almost quantitative yield.
The Rupe rearrangement has also been applied to the total synthesis of both
natural and unnatural molecules of biological and commercial interest. In 1980, Yates
and Stevens reported the synthesis of (3
R
,3a
R
,7
R
,8a
S
)-3,8,8-trimethyltetrahydro-
1
H
-3a,7-methanoazulene-4,6(5
H
,7
H
)-dione [173], a key intermediate in the
O
1. Li(CH
3
)
2
Cu, Et
2
O
HO
≡
2.
LiC
CH·NH
2
(CH
2
)NH
2
94%
1. Ac
2
O
2. 80% AcOH
3. 5% aq NaHCO
3
79%
HOH
2
C
CH
2
OH
OHC
CHO
NaBH
4
EtOH, rt, 1 h
+
+
99%
(47:53)
SCHEME 8.38
Synthesis of some components of the pheromone of male boll weevil.
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