Biomedical Engineering Reference
In-Depth Information
R
2
R
2
R
1
R
1
R
1
R
1
R
1
N
R
2
H
R
2
R
2
N
N
N
N
Au
- Au
O
O
-
[Au]
[Au]
-
O
O
O
[Au]
[Au]
156
157
158
159
1.
TsO
Cs
2
CO
3
, NaI
CH
3
CN, 80°C, 5 h
(Ph
3
P)AuNTf
2
(5 mol%)
H
O
H
N
N
N
2.
m
-CPBA (1 equiv)
4 Å MS, CH
2
Cl
2
1 h, 0°C
63% (3 steps)
H
O
-
Cl
-
1. (CH
2
S)
2
, BF
3
·OEt
2
CH
2
Cl
2
, rt, 2 h
2. Raney Ni, MeOH
65°C, 2 h
43%
OH
H
H
O
t
-Bu
O
[43]
OH
N
N
O
t
-Bu
N
(+)-Lentiginosine
161
(±)-Cermizine C
160
SCHEME 4.44
Synthesis of (
)-cermizine C and (
þ
)-lentiginosine by Zhang and
coworkers.
been used in the total synthesis of natural products possessing a nitrogen-containing
heterocycle in their structure. For example, Zhang and coworkers recently reported a
newmethod for the synthesis of piperidin-4-ones
159
based on the reactivity of
a
-oxo
gold carbenes
(Scheme 4.44) [42]. Hence, by treatment with an electrophilic
gold complex,
N
-butynyl
N
-oxide
157
undergoes an intramolecular oxidation of
the alkyne followed by a formal 1,5-hydride shift to produce the intermediate gold
enolate
156
.This
efficient methodology (54-75% yield) was successfully applied to the total synthesis
of the alkaloids (
158
. A final ring closure affords the corresponding piperidin-4-one
159
[42,43].
The same authors also reported a synthetic approach to the structurally related
piperidin-4-ols
)-cermizine C
160
and (
þ
)-lentiginosine
161
165
(Scheme 4.45) [44]. However, the chemistry involved in this
R
2
R
2
R
2
O
B
H
CatB
(Ph
3
P)AuNTf
2
(5 mol%)
MsOH (1.2 equiv)
CH
2
Cl
2
, 4Å MS
N
O
HN
O
O
N
O
R
1
(= CatBH)
R
1
AuL
R
1
162
163
164
R
2
R
2
R
2
O
B
H
CatB
CatB
O
N
N
HN
R
1
then hydrolysis
R
1
O
R
1
O
OH
47- 83%
165
SCHEME 4.45
Synthetic approach to piperidin-4-ols.
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