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first oxidation step
OH
O
XH
XH
IIa
, X = O
IIb
, X = NTs
Ia
, X = O
Ib
, X = NTs
P
h
P
h
Ph
O
Ph
OH
2,6-dimethoxybenzoquinone
8
Ph
Ph
Ph
Ph
metal-macrocyclic complex
9
Ru
Ru
7a
CO
H
7b
OC
CO
CO
O
OH
X
X
second oxidation step
IVa
, X = O
IVb
, X = NTs
IIIa
, X = O
IIIb
, X = NTs
Scheme 7.5 Biomimetic aerobic oxidation of diols and amino alcohols.
O
7
(0.5 mol %)
8
(20 mol %)
OH
OH
O
9
(2 mol %)
PhCl, air (1 atm), 80 °C, 24 h
n
n
12a
, n = 1, 73%
12b
, n = 2, 95%
12c
, n = 3, 86%
12d
, n = 4, 89%
12e
, n = 5, 89%
(7.3)
11a-e
the hydroquinone moiety. As a result, milder reaction conditions with a
lower catalyst loading were ecient for the oxidation of secondary alcohols.
B¨ckvall's group also reported the biomimetic aerobic oxidation of diols
and amino alcohols to produce lactones and lactams, respectively, via a two
oxidation step mechanism (Scheme 7.5).
15,16
The first dehydrogenation of
substrate I provided hydroxy- or aminoaldehyde intermediate II, which
underwent an intramolecular cyclization affording hemi-acetal or -aminal
III, respectively; the second oxidation produced desired lactone or lactam
products IV.
The reaction of diols 11a-e provided corresponding five- to nine-
membered lactones 12a-e in good to excellent yields (Equation 7.3).
17
Conversely, the formation of 2-oxetanones, derived from 1,3-diols, was not
observed under these reaction conditions. For the formation of larger rings,
diluted reaction conditions were required to avoid the formation of oligo-
mers from intermolecular esterification.
In addition, biologically significant lactams such as 2-piperidinones,
3-morpholinones, 2-piperazinones, indolinones and isoindolinones (14a-g)
were produced in good to excellent yields from the corresponding
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