Chemistry Reference
In-Depth Information
OH
n
R
2
Pd
ligand
n
R
R
1
R
2
R
R
1
O
X
Primary Alcohols
P(tBu)
2
P(tBu)
2
P(tBu)
2
CH
3
P(tBu)
2
P(tBu)
2
Fe
Ph
Ph
Ph
Ph
N
H
3
C
Ph
4
8
22
13
23
Secondary Alcohols
P(tBu)
2
PPh
2
P(tBu)
2
CH
3
P(tBu)
2
P(tBu)
2
Fe
Ph
Ph
Ph
Ph
Fe
N
H
3
C
PPh
2
Ph
4
8
19
22
24
Tertiary Alcohols
P(tBu)
2
P(tBu)
2
PPh
2
P(
p
-tol)
Fe
Ph
Ph
Ph
Ph
P
Fe
Fe
P(
p
-tol)
PPh
2
Ph
1
7
8
19
25
Scheme 6.8
categories of primary, secondary and tertiary alcohols. Palladium complexes
ligated by 4,
47
8,
36
22,
39
13
47
and 23
39
promote intramolecular carbon-
oxygen bond formation of primary alcohols with aryl halides, whereas
complexes with 4,
47
8,
45
19,
48
22
47
and 24
47
and complexes with 7,
30
8,
36
19
48
and 25
48
are good catalysts for intramolecular reactions of aryl halides with
secondary and tertiary alcohols, respectively. Once again, bulky, electron-
rich phosphine ligands dominate the general ligand class. Intramolecular
etherification reactions of primary and secondary alcohols typically proceed
smoothly despite the presence of b-hydrogens in the intermediate alkoxide
palladium complexes because this elimination from a cyclic palladium
alkoxide intermediate complex is slow.
6.3 Copper-Catalyzed Cross-Coupling Reactions of
Carbon-Oxygen Bonds
Although the palladium-catalyzed formation of carbon-oxygen bonds is
broad in scope, the development of copper catalysts for etherification re-
actions is an important and growing area of research. Copper catalysts are
cheaper and less toxic than palladium catalysts, hence the development
of copper catalysts is of interest to synthetic chemists. One challenge in
developing copper-catalyzed cross-coupling reactions is the increased
complexity of the corresponding reaction mechanism. For instance, the
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