Chemistry Reference
In-Depth Information
Oxidations of racemic secondary alcohols ArCH(R)OH by
system in the presence of HC1 proceed with some
kinetic resolution
138
. The smaller molecules were oxidized with larger
selectivity. Thus oxidation of when carried out
to ~50% of conversion, yielded ~ 50% methylphenylketone, and the
remaining alcohol was enantiomerically enriched (24%
ee
). Similarly,
oxidation of alcohol gave 32% of ketone, with the
ee
of
remaining alcohol being 10%;
yielded 25%
of ketone, and 25%
ee
for the remaining alcohol; and
yielded 41% of ketone, and 2%
ee
for residual alcohol
138
.
3.7
Oxidative dehydrogenation of amines
The oxidation of amines is important biologically
7,178,179
. In particular,
oxidative
N
-dealkylation (eq. 37) is one specific reaction catalyzed by
cytochrome P-450 monooxygenase (Section 1)
7,180
, and several models
mimicking this reactivity have been reported using iron porphyrins
181
and Ru
non-porphyrin
182
systems. More generally, oxidation of amines catalyzed by
transition metal complexes can lead to this dealkylation, formation of amine
or dehydrogenation
183-185
. Ruthenium(II) precursors have been
used with a variety of oxidizing agents, including oxygen
186
,
t
BuOOH
182, 187
,
PhIO
188, 189
,
and bromamine-T
190
.
Reports
utilizing high-valent
Ru-oxo
complexes include the use of
(L = N- and P- donors)
191
,
species (see below); it is this last mentioned type of the system that is the
focus of this Section.
As first shown in the laboratory here, can
oxidatively dehydrogenate primary and secondary amines under
stoichiometric and catalytic conditions in benzene at 50°C (with as
oxidant)
185
. For the former, the reaction stoichiometry depends on the
number of H-atoms in the of the amine, and for primary amines
can be presented primarily by eqs. 38 and 39 (
Ru =
Ru(TMP)): imines or
nitriles are formed with generation of isolable Ru(II)-bis(amine) complexes,
and an X-ray structure of
was determined
185
.
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