Chemistry Reference
In-Depth Information
H
O
BnO
O
O
O
Ph
O
BnO
OTBS
2.256
H
2.254
1. KHMDS
2. (PhO)
2
POCl
9-BBN
H
O
O
BnO
O
O
Ph
B
(PhO)
2
P
O
O
H
BnO
OTBS
2.257
2.255
dppfPdCl
2
,
NaHCO
3
H
O
O
BnO
O
Ph
O
BnO
O
H
TBS
2.258
H
H
OAc
H
H
H
OAc
H
H
H
O
O
BnO
O
BnO
O
Me
3
Al
F
G
H
OAc
OAc
H
BnO
O
BnO
O
H
H
Me
H
EtO
2
S
2.259
2.260
Scheme 2.85
A Suzuki coupling was employed to connect the F and H rings of the marine polyether toxin Gambierol
(Scheme 2.85).
91
The borane component
2.255
was prepared by hydroboration of an exocyclic enol ether
2.254
, while the other partner was an enol phosphate
2.257
, prepared by enolate chemistry. Coupling of these
two fragments to give enol ether
2.258
proceeded even at room temperature. Manipulation of the functional
and protecting groups then allowed formation of the in-between G ring, with installation of the angular methyl
group by sulfone displacement.
2.6.3 Aryl Borane Coupling Reactions
The Suzuki coupling of aryl boronic acids is a widely used method for the synthesis of functionalized arenes,
including biaryls (Scheme 2.86).
92
ortho
-Metallation can be an effective method for introduction of the
boronic acid group.
O
O
NEt
2
O
Br
1.
n
-BuLi
2. B(OMe)
3
3. HO
-
Pd(PPh
3
)
4
,
Na
2
CO
3
O
NEt
2
B(OH)
2
N
i
-Pr
2
N
O
i
-Pr
2
N
O
i
-Pr
2
N
O
N
2.262
2.263
2.261
Scheme 2.86
