BAGMANOV
1636
the effect of substituent configuration in positions 2
and 3 on the reactivity of N-arylbicyclo[2.2.1]hept-
5-ene-endo- and -exo-2,3-dicarboximides I−XX.
Epoxidation of N-arylimides I−XX is stereoselec-
tive. Electrophilic oxygen atom approaches the double
bond from the side of the endo-methylene bridge,
regardless of endo or exo configuration of the imide
fragment. Negative inductive effect of the imide frag-
ment is sufficient to stabilize both epoxide ring and
norbornane skeleton, for the process is not accom-
panied by Wagner−Meerwein rearrangement [11].
In the present work we studied stereochemical
relations holding in the oxidation of N-arylbicyclo-
[2.2.1]hept-5-ene-endo- and -exo-2,3-dicarboximides
I−XX at the double bond with peroxyacetic acid
generated in situ from acetic acid and 30% hydrogen
peroxide in the presence of a catalytic amount of
sulfuric acid. We anticipated formation of stable epoxy
derivatives, taking into account that negative inductive
effect (–I) of the imide carbonyl groups should favor
stabilization of the epoxide ring [7]. However, regard-
less of the substituent in the N-aryl group and imide
ring configuration, the oxidation of imides I−XX at
room temperature led to the formation of the corre-
sponding trans-dihydroxy imides XXI−XL [8]
(Scheme 1). This means that, in contrast to the data of
[9, 10], the initially formed epoxide ring undergoes
fast opening.
The presence of a proton-donor carboxy group in
the N-aryl substituent of compounds VIII and XVIII
does not affect the stability of the oxirane ring and
stereochemistry of epoxidation. A probable reason is
formation of intramolecular hydrogen bond between
strongly electronegative imide carbonyl oxygen atom
and hydroxy proton of the carboxy group in ortho
isomers XLVIII and LVIII. The carboxy group in
para isomers X and XX is unlikely to be involved in
such intramolecular hydrogen bond.
H
O
O
O
O
O
On the other hand, the oxidation of compounds
I−XX with anhydrous peroxyacetic acid in dioxane
gave exo-epoxy derivatives XLI−LX as the only prod-
ucts (Scheme 2). Their acid hydrolysis in aqueous me-
dium leads to trans-dihydroxy compounds XXI−XL,
regardless of the configuration of the imide ring and
the nature and position of substituent in the aromatic
ring. Thus the main factors determining the direction
of oxidation of endo- and exo-imides I−XX with
peroxy acids are the reaction medium and substrate
structure.
O
N
N
O
H
O
O
O
XLVIII
LVIII
The oxidation of imides I−X with a dilute solution
of potassium permanganate in aqueous acetone (neu-
tral medium) at 10°C was strictly stereoselective, and
the products were exclusively the corresponding cis-
dihydroxy derivatives LXI−LXX with exo-oriented
hydroxy groups (Scheme 3). Thus, either cis- or trans-
dihydroxy imides can be obtained, depending on the
conditions.
Scheme 2.
O
The trans configuration of the hydroxy groups in
diols XXI−XL was proved by the presence in their IR
spectra of an absorption band at 3620 cm−1, which is
typical of stretching vibrations of free hydroxy groups
[12]. cis-Diols LXI−LXX displayed bands at 3465,
3480, and 3405 cm−1, which characterize hydroxy
groups involved in intramolecular hydrogen bond.
R
O
CH3CO3H, dioxane
I–X
N
O
XLI–L
R
O
O
The steric structure of the obtained compounds was
CH3CO3H, dioxane
1
XI–XX
confirmed by analysis of their H NMR spectra [13].
N
O
Protons in the bridging methylene group (syn-7-H
and anti-7-H) resonate as a doublet of doublets at
δ 1.25−1.75 ppm (AB spin system, 2J = 10 Hz). The syn-
7-H proton in endo-dihydroxy derivatives XXI−XXX
shows additional long-range W-coupling [14, 15] with
LI–LX
XLI, LI, R = H; XLII, LII, R = o-MeO; XLIII, LIII, R =
m-MeO; R = XLIV, LIV, p-MeO; XLV, LV, R = o-Cl;
XLVI, LVI, R = m-Cl; XLVII, LVII, R = p-Cl; XLVIII,
LVIII, R = o-HOCO; XLIX, LIX, R = m-HOCO; L, LX,
R = p-HOCO.
2-H and 3-H. Its signal is a broadened doublet (W1/2
=
5 Hz) located in a weaker field relative to the anti-7-H
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 11 2007