Chemistry Reference
In-Depth Information
S
n
-Bu
OTf
n
-BuSH, KO
t
-Bu
Pd(OAc)
2
, tol-BINAP
2.608
2.609
Scheme 2.181
CO
2
Me
Me
CO
2
Me
HS
S
I
Me
(Ph
3
P)
4
, Et
3
N
H
H
2.610
2.611
Scheme 2.182
2.12.4 Formation of Other C-X bonds
Thiols have been employed as nucleophiles in palladium-catalysed coupling reactions (Scheme 2.181). An
aryl thioether could be formed from an aryl triflate using a strong base, a bidentate ligand and a nonpolar
solvent to suppress competitive triflate decomposition.
220
An intramolecular thiol coupling with an iodoindole
was a key step in a synthesis of chuangxinmycin (Scheme 2.182).
221
Carbon-phosphorus bonds may also be formed.
222
Chemists at Merck developed a synthesis of either
enantiomer of the valuable ligand BINAP
1.33
from the more easily resolved BINOL
2.612
,usinga
triflate-phosphine coupling reaction (Scheme 2.183).
223
They reasoned that nickel catalysis would be more
effective as this metal is harder than palladium and, therefore, less susceptible to catalyst poisoning by the
product. BINAP
1.33
could be obtained with no loss of chirality. They also reported a resolution procedure
for BINOL
2.612
.
224
Triarylphosphines can add an additional aryl group to form tetraarylphosphonium salts
2.613
by reaction
with an aryl halide and a transition-metal catalyst (Scheme 2.184).
225
This is one cause of ligand destruction
during coupling and Heck reactions.
226
OH
OH
dppeNiCl
2
, Ph
2
PH
DABCO, DMF
PPh
2
PPh
2
2.612
1.33
Scheme 2.183
NiBr
2
Ph
3
P + PhBr
Ph
4
P Br
2.613
Scheme 2.184
