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anisole, selectivity to form either 4-MeOPhOH or PhOH depends greatly on the
concentration of pyridine: selective formation of 4-MeOPhOH and PhOH at low and
high concentrations of pyridine, respectively. In the oxygenations of p-D-toluene
and p-xylene, NIH shifts of p-D and p-Me groups were observed in the fairly high
values (55 and 35 %, respectively).
415
The oxygenation of the methyl group to form
benzyl alcohols and aldehydes was promoted by the high pyridine concentration.
The system was used for the hydroxylation of
tert
-butylphenol to form selectively 4-
tert
-butylcatechol as a model reaction for tyrosine hydroxylase.
416
Alkane and
alkene were also monooxygenated by the same catalytic system.
417,418
Cyclohexane,
cyclohexene, and n- and isoalkanes produced highly selectively alcohols at the low
pyridine concentration (Table 4).
417,418
This is very characteristic and different from
other systems that produce ketones selectively, and supports the high-valent iron-
oxo species as an active species. The formation of ketone was promoted
with the increasing pyridine concentration and became dominant in the pyridine
solution. The effect of the pyridine concentration is due to the change of iron
complexes from a catecholate iron complex to a pyridine iron complex, as supported
by the same results with using Not only catalytic activity but also
selectivity was greatly dependent on the substituent on hydroquinones. This
suggests that coordination of hydroquinones to iron is involved in the oxygenation
process
416 417,4I8
Takai
et al.
developed an excellent catalytic system for epoxidation of olefins
by tris(l,3-diketonato)iron(III) complexes and
aldehydes
as a reductant.
419
A
number of olefinic compounds including styrene analogues and olefinic alcohols
were converted to corresponding epoxides in good to quantitative yields with
combined use of molecular oxygen and an aldehyde (
e.g.
2-ethylbutyraldehyde) at
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