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OMe
MeO
OMe
OH
OMe
in solution product
MeO
OMe
Oxone
b.m.
O
MeO
OMe
O
solvent-free product
Scheme 3.10 Mechanochemical oxidation of methoxylated aromatic compounds
with Oxone.
Solution based oxidation of 1,2,3-trimethoxybenzene using Oxone.
a
Table 3.9
Product
(2,3,4-Trimethoxy-
phenol)
(2,6-Dimethoxy-
benzoquinone)
1 0.5 d
3
-AcCN 17 77 8
2 1 d
3
-AcCN 26 69 8
3
c
2 d
3
-AcCN 55(53) 49(54) 9(10)
4 4 d
3
-AcCN 81 24 9
5 2 d
3
-MeOH 67 34 3
6 2 d
6
-Acetone 55 31 2
a
Reaction conditions: 50 mmol substrate, 1 mL of 10% (v/v) co-solvent in D
2
O (9 mL), room temp,
5h.
b
Conversion as percentage of starting material consumed.
c
Oxone
(eq)
Conversion
(%)
b
Entry
Co-solvent
Numbers in parenthesis were obtained when the reaction was degassed and run under inert
(N
2
) atmosphere.
The solid-state oxidation of cinnamic, 4-methoxy- and 3,4-dimethoxy-
cinnamic acids using CAN-MX (CAN
¼
ceric ammonium nitrate
((NH
4
)
2
Ce(NO
3
)
6
); M
¼
Li, Na; X
¼
Br, Cl) systems in a vibratory mill has
been described by Nikishin and co-workers. The oxidation led to the
b-halostyrenes in 69-91% yields after for 4 h of grinding at a frequency of
12 Hz. A similar procedure, in the absence of a metal halide, resulted in the
cleavage of the C
¼
C bond to afford the corresponding benzaldehydes in
20-60% yields (Scheme 3.11).
11
It is also possible to oxidize a tertiary amine under ball-milling conditions.
Pankrushina et al. found that the nitroxide derivative was formed from the
mechanochemical oxidation of lappaconitine using 3-chloroperbenzoic acid
(3-Cl-PBA) in a SPEX-8000 vibratory mill using a solid absorptive material
(aluminium oxide) to loosen the reaction mixture (Scheme 3.12).
12
In fact, the
mechanochemical solid-state oxidation and de-ethylation of lappaconitine
leads to the formation of lappaconitine N(20)-oxide II and N(20)-diethyl-
lappaconitine III, respectively, in good isolated yields (57% and 42%
respectively). This mechanochemical approach was also applied to the
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