Chemistry Reference
In-Depth Information
Grubbs II, 40 °C; then
H
2
(100 psi), 70°C
N
i
-Pr
N
i
-Pr
O
O
8.467
8.468
Scheme 8.125
O
O
Grubbs II
+
Ph
Ph
8.469
add
NH
2
add H
2
, 70 °C
H
2
N
H
2
, NaOH
O
OH
Ph
Ph
8.470
8.471
Scheme 8.126
Advantage was taken of the tandem reactivity of the Grubbs catalysts in a synthesis of lycoflexine
8.477
(Scheme 8.127).
146
An ene-yne-ene metathesis reaction established a five- and a nine-membered ring in
a single step. Addition of hydrogen then converted the metathesis catalyst to a hydrogenation catalyst that
showed selectivity for the less hindered of the two double bonds, giving tricycle
8.474
. The remaining double
bond could then be used to introduce a second ketone by hydroboration, followed by oxidation with IBX,
rather than a more traditional oxidant. The synthesis was completed by a transannular Mannich reaction.
H
H
Grubbs II,
then H
2
O
O
O
N
t
-Boc
8.473
N
t
-Boc
8.474
N
t
-Boc
8.472
H
H
H
1. BH
3
.THF
2. IBX
HCHO,
HCl
O
O
OH
N
O
O
O
N
8.475
8.476
8.477
N
t
-Boc
Scheme 8.127
