Chemistry Reference
In-Depth Information
5.143
, could also be prepared by a modification of the post-Heck sequence. While the right-hand ring of the
molecule was constructed by a condensation reaction, the central ring was formed by an asymmetric Heck
reaction of iodide
5.140
, forming a challenging quaternary centre in the process. In this Heck reaction, it was
found that the
Z
-isomer of the alkene
5.140
underwent the Heck reaction with good e.e. under either neutral
conditions or with an added silver reagent. Both sets of conditions gave the same sense of enantioselectivity.
The
E
-isomer underwent Heck cyclization with lower e.e., and with the two sets of conditions giving opposite
stereochemical outcomes.
The same strategy was used for the synthesis of the more complex, polycyclic alkaloids quadrigemine C
and psycholeine (Scheme 5.42).
40
A double Stille coupling between diiodide
5.145
and stannane
5.146
was
I
Me
N
H
N
TfO
Bn
Sn
n
-Bu
3
Pd
2
(dba)
3
.CHCl
3
,
(2-Fu)
3
P, C u I
N
O
NMeTs
N
5.146
H
H
Me
I
5.145
Bn
NMeTs
O
O
N
NMeTs
N
Me
Me
N
H
N
H
TfO
Bn
N
N
Pd(OAc)
2
,
(
R
)-Tol-BINAP
pempidine
1. H
2
, Pd(OH)
2
2. Na, NH
3
(l)
N
Me
N
Me
TfO
Bn
H
H
H
H
N
NMeTs
N
O
O
NMeTs
Bn
5
1
5
1
Me
Me
H
H
H
N
N
N
NH
MeN
Me
N
H
H
N
N
N
H
3
O
+
H
NMe
HN
5.150
N
Me
H
N
Me
N
H
H
N
H
N
5.149
H
Me
Scheme 5.42
