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OH
O
9
, h
ν
, air
quantitative
OH
O
d
6
-benzene, rt, 12 h
d
n
4
r
4
n
g
|
1
0%
N
NO
N
Ru
Cl
t
-Bu
O
O
t
-Bu
t
-Bu
t
-Bu
9
Scheme 9.12 Aerobic primary alcohol oxidation with achiral Ru(salen) catalyst in
the presence of secondary alcohols.
right-hand cycle). This explains why the complexes bearing chiral quaternary
carbons at the diamine moiety are generally favorable catalysts for the
desymmetrization of meso-diols. The quaternary methyl group at the
diamine moiety has been considered to play an important role in regulating
the conformation of meso-diols.
9.3 Asymmetric Oxidation of Phenol Derivatives
with Air
Phenol derivatives are abundant in fossil resources and plants. They are
electron rich and undergo various oxidation reactions. Therefore, their
asymmetric oxidative transformation using chiral transition metal com-
plexes as catalysts is a topic of growing interest. Especially two classes of
asymmetric oxidative reactions of phenol derivatives using ambient air have
been actively investigated: (i) asymmetric oxidative coupling (AOC) and (ii)
asymmetric oxidative dearomatization. As is well known, the complexes that
catalyze the oxidation of alcohols not infrequently also catalyze the oxidation
of phenol and its derivatives. In this section, these two types of oxidation of
phenol derivatives are described.
.
9.3.1 Asymmetric Oxidative Coupling of Phenol Derivatives
Optically active biphenols or binaphthols (BINOLs) and their derivatives
have been utilized not only as versatile ligands in asymmetric synthesis but
also as intermediates for the synthesis of natural products bearing axial
chirality.
25
Oxidative coupling of phenol derivatives is a direct and atom-
ecient tactic since it does not require any prefunctional group such as a
halogen or metal. Since the first report of the catalytic AOC of 2-naphthol
using dioxygen in the presence of a copper-diamine catalyst in 1995,
26
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