TRANSFORMATIONS OF CYCLIC ACETALS
2
1121
1
where n = 0, R = i-Pr (I, VIII), Ph (II, IX), R =
Table 1. Oxidation of acetals I IV with Caro salt in the
presence of alumina (A) or radical XXIV (B). Solvent
CHCl3, 50 C, 2 h
3
4
1
R = R = H (I, II, VIII, IX); n = 1, R = i-Pr (III,
2
3
4
X), Ph (IV, XI), R = R = R = H (III, IV, X, XI);
1
2
1
R = i-Pr (V, XII, XV), Ph (VI, XIII, XVI), R =
Acetal
Monoester Yield of monoester, A (B), %
3
4
Me, R = R = H (V, VI, XII, XIII, XV, XVI); R =
2
3
4
Ph (VIII, XIV), R = H, R = R = Me (VII, XIV).
I
VIII
IX
X
40 (99)
76* (97)
38 (94)
II
III
IV
From V and VI, both isomeric esters XII and XV,
XIII and XVI are formed, since the C O and C
O bonds are cleaved concurrently. According to the
2
1
2
3
XI
45** (96)
1
13
H and C NMR data, under conditions of our exper-
iments, esters XII and XIII with the secondary hy-
* 13% benzaldehyde. ** 25% benzaldehyde.
droxy group are the major products.
Table 2. Oxidation of dioxacycloalkanes I IV with the
complex KCrO5Cl 2C10H20O5 in the absence (A) and in
the presence (B) of the radical. Solvent MeCN, 60 C, 2 h;
molar ratio substrate : oxidant 1 : 3, substrate : radical
1 : 0.01
2,2-Disubstituted 1,3-dioxacyclanes XVII XIX
under the action of dimethyldioxirane decompose to
the corresponding ketones XX:
Me Me
2
R3
(CH ) C O
R
Substrate
Product
Product yield, A (B), %
(CH2 ) CH
n
O
O
1
R C O + HO
2
n
O
O
I
II
III
IV
VIII
PhCHO
X
55 ( 99)
88 ( 99)
1 ( 99)
XXI XXIII
XX
1
R2
R
PhCHO
65 ( 99)
XVII XIX
1
2
3
where n = 1, R = R = Me, R = H (XVII, XX,
1
2
3
XXI); R = R = Me, R = CH OH (XVIII); n = 2,
In the series of 1,3-dioxacycloalkanes I VI, only
compounds I and II are oxidized with potassium per-
sulfate K S O to form, in the first case, ethylene
glycol monoisobutyrate VIII (yield 45%) and, in the
second case, benzaldehyde (yield 25%). In the pres-
ence of catalytic amounts of XXIV, compounds I VI
afford esters VIII XIII in quantitative yield.
2
1
2
3
R
= R = R = Me (XIX, XXII, XXIII).
2 2
8
Apparently, in the first stage compounds XVII
XIX give the corresponding unstable 4-hydroxy-1,3-
dioxacyclanes, subsequently decomposing to give
ketones XX.
It is known [5] that dimethyldioxirane is prepared
using Caro salt. We found that this agent oxidizes
2-alkyl-1,3-dioxacyclanes I and III in the presence of
alumina to the corresponding monoesters VIII and X.
However, benzaldehyde derivatives II and VI under
these conditions, along with monoesters IX and XI,
give also benzaldehyde (Table 1).
We also studied oxidation of cyclic acetals I IV
with the complex of potassium chlorodiperoxochro-
mate KCrO Cl with 15-crown-5 C H O . We found
that acetals I and III are oxidized with this complex
to the corresponding monoesters VIII and X. At the
same time, 2-phenyl derivatives II and IV are selec-
tively oxidized to benzaldehyde (Table 2). Catalytic
amounts of nitroxyl radical XXIV provide complete
conversions of acetals even in 2 h (Table 2).
5
10 20 5
We found that oxidation of cyclic acetals with Caro
salt in the presence of stable nitroxyl radical 2,2,5,5-
tetramethyl-4-phenyl-3-imidazoline-3-oxide-1-oxyl
XXIV
Thus, complex of potassium chlorodiperoxochro-
mate with 15-crown-5 can be successfully used for
removing acetal protective groups from aromatic alde-
hydes.
Ph
N
Me
Me
Me
Me
N
.
O
CONCLUSION
XXIV
allows preparation of monoesters VIII XI in quanti-
tative yield (Table 1). The catalytic effect of nitroxyl
radicals was noted previously in [10].
Dimethyldioxirane, Caro salt, and complex of
potassium chlorodiperoxochromate with 15-crown-5
efficiently oxidize polycyclic acetals to the corre-
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 75 No. 7 2002