Investigation of arene-arene interaction in stereoselective MCPBA epoxidation

Article abstract of DOI:10.1039/b004098n

Effect of arene-arene interaction in stereoselective MCPBA epoxidation was investigated using 5,6-dimethyl-2-phenyl-3a,4,7,7a-tetrahydroisoindole-1,3-diones 1. From the good correlation between the stereoselectivity of the products and Hammett's coefficients of para-substituents (σ_P) on the phenyl group, it was found that polar/π interaction between the phenyl group and MCPBA is the main interaction for controlling the stereoselectivity in the reaction. Other arene-arene interactions, charge-transfer complexation and edge-to-face interaction, were assumed to be much weaker than polar/π interaction in this reaction.

Full text of DOI:10.1039/b004098n

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Investigation of arene–arene interaction in stereoselective MCPBA
epoxidation
Keiki Kishikawa,*a Mamoru Naruse,a Shigeo Kohmoto,a Makoto Yamamotoa and
Kentaro Yamaguchib
1
a Department of Materials Technology, Faculty of Engineering, Chiba University,
1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
b Chemical Analysis Center, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522,
Japan
Received (in Cambridge, UK) 22nd May 2000, Accepted 8th December 2000
First published as an Advance Article on the web 25th January 2001
Effect of arene–arene interaction in stereoselective MCPBA epoxidation was investigated using 5,6-dimethyl-2-
phenyl-3a,4,7,7a-tetrahydroisoindole-1,3-diones 1. From the good correlation between the stereoselectivity of
the products and Hammett’s coefficients of para-substituents (σP) on the phenyl group, it was found that polar/π
interaction between the phenyl group and MCPBA is the main interaction for controlling the stereoselectivity in the
reaction. Other arene–arene interactions, charge-transfer complexation and edge-to-face interaction, were assumed
to be much weaker than polar/π interaction in this reaction.
Epoxidation of alkenes with commercially available m-chloro-
perbenzoic acid (MCPBA) is one of the most important
reactions in organic synthesis and is useful for laboratory-scale
experiments.1 Moreover, the excellent face-selectivity was
reported in the epoxidation of dienes,2 sterically hindered
alkenes (steroidal olefins3), cyclic alkenones,4 and alkenes poss-
essing hydrogen-bond acceptors (allyl alcohols,5 allylamides,6
allyl carbamates,7 allyl ethers,8 bicylic diketones (α-diones),9 and
unsaturated carboxylic acids10). Recently, it has been said that
arene–arene interaction11 is important in self-assembly of
molecules to superstructures.12 Further, arene–arene interaction
has attracted synthetic scientists as an important control
element for stereoselective synthesis.13 Though MCPBA is a
unique oxidizing reagent which has a large π-system in its
molecule, arene–arene interaction has not been utilised for
stereoselective oxidation yet. In this paper we investigate the
effect of arene–arene interaction in this stereoselective reaction,
using tailor-made molecules, 5,6-dimethyl-2-phenyl-3a,4,7,7a-
tetrahydroisoindole-1,3-diones 1. To the best of our knowledge,
this is the first example of stereoselective MCPBA epoxidation
directed by arene–arene interaction.
Compounds 1 have the following significant features to allow
investigation of the arene–arene interaction in the transition
state; 1) the tetraalkyl-substituted double bond, which is highly
reactive in MCPBA epoxidation,14 2) the arrangement of a
benzene ring at the suitable position for arene–arene inter-
action with MCPBA in the reaction transition state, 3) adjust-
able π-electron density of the benzene ring by introduction of
the para-substituent group, and 4) the bicyclic structure which
makes determination of exo/endo ratios of the products easier
in NMR and HPLC analyses.
Scheme 1 Synthesis of 1.
by recrystallization from chloroform–hexane, and its stereo-
chemistry was determined by X-ray crystallography to be the
anti-form for the relationship between the imide ring and the
oxirane ring (Fig. 1). Accordingly, the other stereoisomer 5f
was determined to be the syn-form. The stereochemistry of
epoxides 4a–e and 5a–e was estimated from the 1H NMR chem-
ical shifts of Ha–Hd shown in Table 2, based on the differences
between 4f and 5f. Conformers (I and II) of 4f and 5f are shown
in Scheme 2 and the ‘flapping’ between them is so rapid because
of the small barrier (about 5 kcal molϪ1 † by AM1 calculations).
Results and discussion
Bicyclic N-phenylimides 1a–e, possessing a substituent R1
(OMe, H, Cl, CO2Me, NO2), and 1f, possessing R3(But) were
synthesized by Diels–Alder reaction of 2,3-dimethylbuta-
1,3-diene and N-phenylmaleimides 3a–f, which were in turn
prepared by condensation of anilines 2a–f and maleic
anhydride. Compound 1g was derived from 1f (Scheme 1).15
The results of the epoxidation of alkenes 1a–e are shown in
Table 1. A single crystal of tricyclic compound 4f was obtained
† 1 cal = 4.184 J.
462
J. Chem. Soc., Perkin Trans. 1, 2001, 462–468
This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b004098n

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Table 1 Epoxidation of 1a–e with MCPBAa
Starting
material
Yield
(%)b
Ratioc
4:5
Entry
R1
1
2
3
4
5
1a
1b
1c
1d
1e
OMe
H
Cl
CO2Me
NO2
69
79
81
79
79
42:58
37:63
26:74
26:74
16:84
a The reaction was carried out at room temperature for 3 h in
chloroform. b Isolated yields for a mixture of 4 and 5. c The ratios were
determined by 1H NMR spectroscopy (400 MHz).
Scheme 2 Flapping of 4f and 5f.
(R1 = NO2) in chloroform at 21 ЊC to give the relative pro-
portions of krel(4a):krel(5a):krel(4e):krel(5e) = 1.0:1.8:1.1:4.6.
Generation of 5e is about 2.6-times faster than that of 5a,
though generation of 4e is only 1.1-times faster than that of 4a.
This means that the epoxidation of the double bond from its
down side is accelerated more than that from its upper side. In
attack of an MCPBA molecule from the down side of 1, the
activation energy in the reaction of 1e (R1 = NO2) is 0.56 kcal
molϪ1 smaller than that in the reaction of 1a (R1 = OMe). In
other words, the transition state of 1e and MCPBA is more
stabilized than that of 1a and MCPBA by a certain interaction
between MCPBA and 1.
Fig. 1 ORTEP diagram of compound 4f.
In 4f-I Hd protons are in the diamagnetic deshielding zone of
the oxirane oxygen atom, and in 4f-II Ha protons of the methyl
groups are in the deshielding zone of the benzene ring. On the
other hand, in 5f-I and 5f-II, protons Hb and Hc are within the
deshielding zone of the O–C bonds of the oxirane ring. As a
result, chemical shifts of Ha and Hd of 4f are at lower field than
those of 5f, and Hb and Hc of 5f are at lower field than those of
4f.16 In all cases, the chemical shifts of Ha and Hd of isomers 4
are at lower field than those of isomers 5, and shifts of Hb and
Hc of isomers 5 appear at lower field than those of isomers 4,
and the coupling patterns of 4a–e and 5a–e are similar to those
of 4f and 5f, respectively.
An electron-withdrawing group increased the exo/endo ratio
of products [5/(4 ϩ 5)], while an electron-donating group
decreased the ratio. This selectivity seems to be related to the
arene–arene interaction between the N-phenyl group and
MCPBA. In the case of 1e (R1 = NO2), which has the most
electron-deficient benzene ring in this series, the epoxidation
mainly proceeded from the endo-side of 1, to give the highest
5/(4 ϩ 5) ratio. Relative rates of the epoxidation in 10% conver-
sion were measured in a solution of 1a (R1 = OMe) and 1e
The arene–arene interaction seems to consist chiefly of the
following three types of interactions: 1) charge-transfer com-
plexation,17 2) edge-to-face interaction,18 3) polar/π inter-
action.19 From PM3 calculations,20 rotational barriers of the
N–Ar bonds are only 2–3 kcal molϪ1 for 1a–e, which means that
the bond freely rotates under the reaction conditions. It was
found that the cyclohexene ring also ‘flapped’ freely at room
temperature (the barrier 19.6 kcal molϪ1 was obtained from the
coalescence temperature of the 5- and 6-methyl peaks of 2,5,6-
trimethyl-3a,4,7,7a-tetrahydroisoindole-1,3-dione 6). From the
flexibility of its molecular structure, both the face-to-face and
face-to-edge arrangements are possible between MCPBA and
1a–e. The three above mentioned arene–arene interactions were
investigated by calculations and experiments.
From PM3 calculations,20 both HOMO and LUMO energy
levels of MCPBA and N-(4-nitrophenyl)succinimide 1eЈ (a
model compound of 1e) were obtained as follows: MCPBA:
J. Chem. Soc., Perkin Trans. 1, 2001, 462–468
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Table 2 1H NMR spectraa of epoxides 4 and 5
Productsb
Ha
Hb
Hc
Hd
4a (R1 = OMe)
5a (R1 = OMe)c
1.39 (s, 6H)
1.44 (s, 6H)
2.02 (m, 2H)
2.51 (m, 2H)
2.59 (d, J 15.2 Hz, 2H)
3.13 (m, 2H)
2.90 (A) (d, J 7.2 Hz, 1H)
2.90 (B) (dd, J 1.0, 2.5 Hz, 1H)
3.11–3.20 (m, 2H)
2.93 (A) (d, J 7.3 Hz, 1H)
2.93 (B) (dd, J 1.0, 2.7 Hz, 1H)
3.15 (m, 2H)
2.92 (A) (d, J 7.2 Hz, 1H)
2.92 (B) (dd, J 1.0, 2.5 Hz, 1H)
3.17 (m, 2H)
2.93 (A) (d, J 7.0 Hz, 1H)
2.93 (B) (dd, J 1.0, 2.5 Hz, 1H)
3.20 (m, 2H)
2.97 (A) (d, J 7.1 Hz, 1H)
2.97 (B) (dd, J 1.0, 2.7 Hz, 1H)
3.13 (m, 2H)
2.20 (A) (dd, J 7.2, 15.2 Hz, 1H)
2.20 (B) (dd, J 2.5, 15.2 Hz, 1H)
1.99–2.08 (m, 2H)
2.22 (A) (dd, J 7.3, 15.3 Hz, 1H)
2.22 (B) (dd, J 2.7, 15.3 Hz, 1H)
2.02 (m, 2H)
2.19 (A) (dd, J 7.2, 15.4 Hz, 1H)
2.19 (B) (dd, J 2.5, 15.4 Hz, 1H)
2.04 (m, 2H)
2.22 (A) (dd, J 7.0, 15.2 Hz, 1H)
2.22 (B) (dd, J 2.5, 15.2 Hz, 1H)
2.04 (m, 2H)
4b (R1 = H)
5b (R1 = H)c
1.40 (s, 6H)
1.34 (s, 6H)
2.47–2.56 (m, 2H)
2.61 (d, J 15.3 Hz, 2H)
4c (R1 = Cl)
5c (R1 = Cl)c
1.40 (s, 6H)
1.33 (s, 6H)
2.51 (m, 2H)
2.59 (d, J 15.4 Hz, 2H)
4d (R1 = CO2Me)
5d (R1 = CO2Me)c
1.40 (s, 6H)
1.34 (s, 6H)
2.52 (m, 2H)
2.60 (d, J 15.2 Hz, 2H)
4e (R1 = NO2)
5c (R1 = NO2)c
1.40 (s, 6H)
1.35 (s, 6H)
2.53 (m, 2H)
2.60 (d, J 15.4 Hz, 2H)
2.25 (A) (dd, J 7.1, 15.4 Hz, 1H)
2.25 (B) (dd, J 2.7, 15.4 Hz, 1H)
2.03 (m, 2H)
4f
1.38 (s, 6H)
1.34 (s, 6H)
1.40 (s, 6H)
2.48 (m, 2H)
(R1 = H, R2 = exo-But)
5f
2.18 (A) (dd, J 7.0, 15.1 Hz, 1H)
2.18 (B) (dd, J 2.7, 15.1 Hz, 1H)
2.01 (m, 2H)
2.60 (br d, J 15.1 Hz, 2H)
2.53 (m, 2H)
2.90 (A) (d, J 7.0 Hz, 1H)
2.90 (B) (dd, J 1.0, 2.7 Hz, 1H)
3.15 (m, 2H)
(R1 = H, R2 = exo-But)c
4g
(R1 = H, R2 = endo-But)
a 1H NMR samples were prepared as dilute solutions in CDCl3. Chemical shifts (δ) are reported in parts per million (ppm) of the applied field. Me4Si
1
was used as internal standard (δH and δC = 0.00) for H and 13C nuclei. b R2 = H unless otherwise stated. c Two conformers (A and B, 1:1) were
observed in the 1H NMR spectrum.
Table 3 Epoxidation of 1f–g with MCPBAa
HOMO Ϫ10.10, LUMO Ϫ1.07 eV, 1eЈ: HOMO Ϫ10.32,
LUMO Ϫ1.33 eV, respectively. Those values indicated that the
charge transfer between MCPBA and 1e would be difficult.
A known value for edge-to-face interaction is about 0.5 kcal
molϪ1 for one hydrogen.18 From PM3 calculations,20 net atomic
Starting
material
Time
(t/h)
Yield
(%)b
Ratioc
4:5
charges of hydrogen atoms on the N-phenyl group change from
ϩ0.63 to ϩ0.67 (1b) to ϩ0.82 to ϩ0.97 (1e) in this series, and
hydrogen atoms of 1a (ϩ0.66 to ϩ0.78) are more positive than
those of 1b. The orders of the net atomic charges do not agree
with that of the product ratios. To investigate the edge-to-face
interaction, compound 1f (R1 = R2 = H, R3 = But) was syn-
thesized stereoselectively by Diels–Alder reaction of 3f with
2,3-dimethylbuta-1,3-diene. Rotation around the N–Ar single
bond is fixed by steric repulsion between the two carbonyl
and 2-tert-butyl groups at room temperature.21 The π-face of
MCPBA interacts with the hydrogen atoms of the N-phenyl
group of 1f in the transition state. In the reaction of 1f, the ratio
of 4f:5f was 69:31 (Table 3), which is larger than that of 4b:5b
(=37:63, in Table 1). This indicates that the edge-to-face
arrangement does not accelerate the generation of products
5 and weakens the arene–arene interaction. Further, the
rotational isomer (1g) also reacted with MCPBA to give 4g in
perfect stereoselectivity (>99:1). Accordingly, the steric effect is
much more dominant than the arene–arene effect in this case.
In order to investigate the polar/π interaction, the ratios
[5/(4 ϩ 5)] were plotted against the Hammett’s coefficient
Entry
R2
R3
1
2
1f
1g
H
But
H
20
29
64
61
69:31
>99:1
But
a The reaction was carried out at room temperature in chloroform.
b Isolated yields for a mixture of 4 and 5. c The ratios were determined
by 1H NMR spectroscopy (400 MHz).
σP (Fig. 2).22 The ratios were clearly correlated with σP of R1.
The results are in good accord with the precedent reports on
polar/π interaction in rotational isomerization of 1,8-biphenyl-
naphthalene which interacts as a repulsive force between two
aromatic rings.19 The stabilization energy by polar/π interaction
was 1.0–1.3 kcal molϪ1 which was measured as the difference
in rotational barriers between 8-(4-methoxyphenyl)- and 8-(4-
nitrophenyl)-1-(2-methylphenyl)naphthalene. The difference in
stabilization energy between 1a and 1e (0.56 kcal molϪ1) is
smaller than above value in the naphthalenes. This difference
may originate in the difference between the inter- and intra-
molecular relations, or between their molecular structures. The
464
J. Chem. Soc., Perkin Trans. 1, 2001, 462–468

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prepared as dilute solutions in CDCl3. Chemical shifts (δ) are
reported in parts per million (ppm) of the applied field. Me4Si
was used as internal standard (δH and δC = 0.00) for 1H and 13
C
nuclei. Compounds 3b and 3f were prepared by our previous
method.21b IR spectra were measured with the KBr method on
a Hitachi I-2000 spectrometer.
Synthesis of N-phenylmaleimides 3a and 3c–e
A para-substituted aniline 2a,c–e (1.02 mmol) was added to a
stirred solution of maleic anhydride (1.02 mmol) in acetic acid
(10 cm3) in a 100 cm3 round-bottom flask. After being stirred
for 1 h at room temperature, the solution was concentrated and
10 cm3 of benzene was added. The solution was refluxed, and
then zinc bromide (1.02 mmol) and 1,1,1,3,3,3-hexamethyl-
disilazane (HMDS) (2.04 mmol) were added and the mixture
was refluxed for 3 h with stirring. Ice–water (50 cm3) and ethyl
acetate (50 cm3) were added. The organic phase was washed
successively with 1 M hydrochloric acid (5 cm3) and brine (50
cm3), dried over anhydrous MgSO4, and concentrated in vacuo.
The residual solid was purified with silica gel column chrom-
atography and elution with ethyl acetate–hexane (1:1) and
recrystallized from chloroform–hexane.
Fig. 2 Plots of ratio of 5 against Hammett’s coefficient σP.
N-(4-Methoxyphenyl)maleimide 3a. Yield 83%; yellow
crystals (Found: C, 64.78; H, 4.32; N, 6.81. Calc. for C11H9NO3:
C, 65.02; H, 4.46; N, 6.89%); mp 148–151 ЊC (from CHCl3–
hexane); νmax/cmϪ1 1715 (C᎐O), 1515, 1400; δ 3.83 (s, 3H), 6.84
Fig. 3 Interaction between MCPBA and 4-nitrophenyl group of 1e in
the transition state. a) Dipole moment of the peracid part [-C(O)OOH],
b) dipole moment of the imide part (O᎐C–N–C᎐O), and c) polar/π
᎐
᎐
||||||||
᎐
H
interaction ( ) between the arenes.
(s, 2H), 6.98 (d, J 9.0 Hz, 2H), 7.23 (d, J 9.0 Hz, 2H); δC 55.47,
repulsive Cl/π interaction between the chlorine atom of
MCPBA and the benzene ring may be suggested as one of the
reasons.
114.46, 123.73, 127.58, 134.11, 159.13, 169.82.
N-(4-Chlorophenyl)maleimide (3c). Yield 83%; yellow solid
(Found: C, 57.87; H, 2.73; N, 6.61. Calc. for C10H6ClNO2: C,
57.85; H, 2.91; N, 6.75%); mp 116–117 ЊC (from CHCl3–
hexane); νmax/cmϪ1 1720 (C᎐O), 1505, 1390; δ 6.84 (s, 2H), 7.30
The following mechanism is postulated for this stereo-
selective MCPBA epoxidation on the basis of ‘butterfly’
models1a,13d,23,24 (Fig. 3). The dipole moments of model com-
pounds, viz. peracetic acid and N-methylsuccinimide, were
calculated by PM3 as 2.5 and 2.1 debyes, respectively. There-
fore, the dipole–dipole interaction between the peracid moiety
[-C(O)OOH)] of MCPBA and the imide part (O᎐C–N᎐C᎐O) of
᎐
H
(d, J 8.9 Hz, 2H), 7.42 (d, J 8.9 Hz, 2H); δC 127.09, 129.32,
129.73, 133.64, 134.29, 169.14.
N-[4-(Methoxycarbonyl)phenyl]maleimide 3d. Yield 86%;
yellow crystals (Found: C, 62.47; H, 3.82; N, 5.95. Calc. for
C12H9NO4: C, 62.34; H, 3.92; N, 6.06%); mp 170–171 ЊC (from
᎐
᎐ ᎐
compounds 1 acts as an attractive force which is almost
constant [net atomic charges of the imide oxygen atoms are
from Ϫ0.33 (1a) to Ϫ0.31 (1e) in PM3 calculations)20] in the
series of compounds 1a–e. The polar/π interaction is known to
act as a repulsive force which correlates the product ratios with
the σP values.19 Repulsive (polar/π) interaction of 1a with
MCPBA is larger than that of 1e, and the attractive (dipole–
dipole) interactions are almost constant and stronger than the
polar/π interactions. Accordingly, epoxidation of 1e is faster
than that of 1a. Thus, stereoselectivity in this epoxidation can
be explained from the balance of these two interactions. The
edge-to-face arrangement of the arenes seems to prevent the
approach of the MCPBA molecule because of the steric
repulsion.
CHCl3–hexane); νmax/cmϪ1 3100, 1715 (C᎐O), 1605, 1515, 1445,
᎐
1395; δH 3.94 (s, 3H), 6.89 (s, 2H), 7.51 (d, J 8.9 Hz, 2H), 8.14
(d, J 8.9 Hz, 2H); δC 52.24, 125.15, 129.06, 130.39, 134.34,
135.34, 166.17, 168.90.
N-(4-Nitrophenyl)maleimide 3e. Yield 88%; yellow crystals
(Found: C, 54.95; H, 2.61; N, 12.73. Calc. for C10H6N2O4: C,
55.05; H, 2.77; N, 12.84%); mp 168–169 ЊC (from CHCl3–
hexane); νmax/cmϪ1 3080, 1720 (C᎐O), 1605, 1525, 1390, 1355;
᎐
δH 6.91 (s, 2H), 7.66 (d, J 8.9 Hz, 2H), 8.31 (d, J 8.9 Hz, 2H);
δC 124.48, 125.47, 134.60, 137.07, 147.23, 168.48.
Synthesis of bicyclic imides 1a–f
Conclusions
In a two-necked 100 cm3-flask equipped with a reflux condenser
capped with a calcium chloride drying tube and a rubber
septum was stirred a solution of an imide 3 (0.493 mmol)
in toluene (10 cm3). Then, 2,3-dimethylbuta-1,3-diene (1.48
mmol) was added and the mixture was heated at 70 ЊC for 2 h
with stirring. After cooling, the solution was concentrated
in vacuo and the products were separated by column chrom-
atography on silica gel and elution with ethyl acetate to give the
corresponding bicycle 1. Further, crystals were obtained by
recrystallization from chloroform–hexane.
We conclude that epoxidation of alkenes 1a–g with MCPBA
has the following features; 1) the stereoselectivity in MCPBA
epoxidation of alkenes can be explained from a balance of the
arene–arene and dipole–dipole interactions, 2) an edge-to-face
interaction was not observed in the reaction of substrates 1,
and 3) a polar/π interaction is the main arene–arene interaction
for controlling the stereoselectivity. In this paper, we demon-
strate that arene–arene interaction of MCPBA with a substrate
can be utilised as a control element of the stereoselective
epoxidation.
2-(4-Methoxyphenyl)-5,6-dimethyl-3a,4,7,7a-tetrahydroiso-
indole-1,3-dione 1a. Yield 88%; yellow crystals (Found: C,
71.56; H, 6.67; N, 4.82. Calc. for C17H19NO3: C, 71.56; H, 6.71;
N, 4.91%); mp 143–144 ЊC (from CHCl3–hexane); νmax/cmϪ1
Experimental
General methods
1H NMR (400 MHz) and 13C NMR (100 MHz) samples were
2930, 1710 (C᎐O), 1515, 1440, 1390, 1310; δH 1.70 (d, J 1.0 Hz,
᎐
J. Chem. Soc., Perkin Trans. 1, 2001, 462–468
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6H), 2.29 (br d, J 15.2 Hz, 2H), 2.52 (d, J 15.2 Hz, 2H), 3.17
(br d, J 2.4 Hz, 2H), 3.79 (s, 3H), 6.93 (d, J 9.0 Hz, 2H), 7.07 (d,
J 9.0 Hz, 2H); δC 19.21, 30.96, 40.01, 55.46, 114.43, 124.77,
127.02, 127.58, 159.41, 179.58.
(d, J 15.0 Hz, 2H), 3.22 (m, 2H), 6.79 (dd, J 7.7, 1.5 Hz, 1H),
7.26 (td, J 7.7, 1.5 Hz, 1H), 7.36 (td, J 7.7, 1.5 Hz, 1H), 7.53 (dd,
J 7.7, 1.5 Hz, 1H); δC 19.36, 30.46, 31.08, 35.05, 40.05, 127.36,
127.42, 128.17, 129.54, 130.85, 131.90, 148.63, 180.74.
5,6-Dimethyl-2-phenyl-3a,4,7,7a-tetrahydroisoindole-1,3-
dione 1b. Yield 74%; white crystals (Found: C, 75.16; H, 6.71;
N, 5.49. Calc. for C16H17NO2: C, 75.28; H, 6.71; N, 5.49%); mp
86–87 ЊC (from CHCl3–hexane); νmax/cmϪ1 3070, 2930, 2840,
1700 (C=O), 1600, 1440; δH 1.73 (d, J 0.9 Hz, 6H), 2.33 (dm,
J 15.4 Hz, 2H), 2.55 (d, J 15.4 Hz, 2H), 3.21 (m, 2H), 7.18 (d,
J 7.7 Hz, 2H), 7.43 (m, 3H); δC 19.12, 30.88, 40.01, 126.32,
126.94, 128.97, 129.69, 132.08, 179.22.
MCPBA epoxidation of 1a–g
In a 100 cm3 round-bottom flask equipped with a dropping
funnel capped with a calcium chloride drying tube was slowly
added a solution of MCPBA (0.588 mmol) in chloroform
(5 cm3) to a solution of 1 (0.392 mmol) in chloroform (10 cm3)
via the dropping funnel within 20 min. The solution was stirred
at room temperature for 3 h, washed successively with 20% aq.
NaHSO3 (100 cm3), saturated aq. NaHCO3 (100 cm3), and
water (50 cm3), and dried over anhydrous MgSO4. The products
were separated by column chromatography on silica gel and
elution with ethyl acetate–hexane (1:1) to give a mixture of
2-(4-Chlorophenyl)-5,6-dimethyl-3a,4,7,7a-tetrahydroiso-
indole-1,3-dione 1c. Yield 96%; colorless crystals (Found: C,
66.41; H, 5.49; N, 4.72. Calc. for C16H16ClNO2: C, 66.32; H,
5.57; N, 4.83%); mp 123–125 ЊC (from CHCl3–hexane);
νmax/cmϪ1 2850, 1715 (C᎐O), 1630, 1495, 1385; δ 1.695 [s, 3H
1
diastereoisomers 4 and 5. The ratio 4:5 was obtained by H
NMR (400 MHz) spectroscopy. The products were separated
by HPLC [Merck, Lichrosorb Si 60; ethyl acetate–hexane
(1:1)] to give pure 4 and 5.
᎐
H
(conformer A)], 1.697 [s, 3H (conformer B)], 2.25 (br d, J 14.6
Hz, 2H), 2.52 (d, J 14.6 Hz, 2H), 3.18 (br t, J 2.4 Hz, 2H), 7.14
(d, J 9.1 Hz, 2H), 7.40 (d, J 9.1 Hz, 2H); δC 19.14, 30.81, 39.98,
126.94, 127.00, 127.52, 129.17, 130.49, 134.10, 134.18, 178.95.
9-(4-Methoxyphenyl)-3,5-dimethyl-4-oxa-9-azatricyclo-
[5.3.0.03,5]decane-8,10-dione 4a. Yield 29%; colorless crystals
(Found: C, 67.81; H, 6.42; N, 4.51. Calc. for C17H19NO4: C,
67.76; H, 6.35; N, 4.65%); mp 144–145 ЊC (from CHCl3–
hexane); νmax/cmϪ1 1715 (C᎐O), 1520, 1400; δ 1.39 (s, 6H), 2.02
Methyl 4-(5,6-dimethyl-1,3-dioxo-1,3,3a,4,7,7a-hexahydro-
2H-isoindol-2-yl) benzoate 1d. Yield 97%; colorless crystals
(Found: C, 69.11; H, 6.05; N, 4.40. Calc. for C18H19NO4: C,
69.00; H, 6.11; N, 4.47%); mp 152–153 ЊC (from CHCl3–
hexane); νmax/cmϪ1 1715 (C᎐O), 1635; δ 1.703 [s, 3H (con-
᎐
H
(m, 2H), 2.51 (m, 2H), 3.13 (m, 2H), 3.82 (s, 3H), 6.97 (d, J 9.0
Hz, 2H), 7.17 (d, J 9.3 Hz, 2H); δC 18.49, 30.23, 36.81, 55.48,
59.19, 114.48, 124.36, 127.58, 159.41, 179.06.
᎐
H
former A)], 1.705 [s, 3H (conformer B)], 2.31(br d, J 14.9 Hz,
2H), 2.53 (d, J 14.9 Hz, 2H), 3.20 (br t, J 2.5 Hz, 2H), 3.91 (s,
3H), 7.31 (d, J 8.5 Hz, 2H), 8.10 (d, J 8.5 Hz, 2H); δC 19.25,
30.93, 40.12, 52.29, 126.09, 127.05, 129.87, 130.37, 136.01,
166.08, 178.89.
9-(4-Methoxyphenyl)-3,5-dimethyl-4-oxa-9-azatricyclo-
[5.3.0.03,5]decane-8,10-dione 5a. Yield 40%; colorless crystals
(Found: C, 67.51; H, 6.32; N, 4.51%); mp 179–181 ЊC
(from CHCl3–hexane); νmax/cmϪ1 2920, 1710 (C᎐O), 1630, 1520;
᎐
δH 1.33 (s, 6H), 2.20 [dd, J 7.2, 15.2 Hz, 1H (conformer A)], 2.20
[dd, J 2.5, 15.2 Hz, 1H (conformer B)], 2.59 (d, J 15.2 Hz, 2H),
2.90 [d, J 7.2 Hz, 1H (conformer A)], 2.90 [dd, J 1.0, 2.5 Hz, 1H
(conformer B)], 3.82 (s, 3H), 6.97 (d, J 9.0 Hz, 2H), 7.22 (d,
J 9.0 Hz, 2H); δC 18.48, 29.55, 36.75, 55.46, 61.06, 114.43,
125.38, 127.93, 159.40, 180.09.
5,6-Dimethyl-2-(4-nitrophenyl)-3a,4,7,7a-tetrahydroisoindole-
1,3-dione 1e. Yield 90%; yellow crystals (Found: C, 63.46; H,
5.28; N, 9.27. Calc. for C16H16N2O4: C, 63.99; H, 5.37; N,
9.33%); mp 117–118 ЊC (from CHCl3–hexane); νmax/cmϪ1 1710
(C᎐O), 1630, 1350; δH 1.726 [s, 3H (conformer A)], 1.729 [s, 3H
᎐
(conformer B)], 2.35 (br d, J 14.8 Hz, 2H), 2.56 (d, J 14.8 Hz,
2H), 3.26 (br t, J 2.1 Hz, 2H), 7.51 (d, J 8.9 Hz, 2H), 8.32 (d,
J 8.9 Hz, 2H); δC 19.25, 30.87, 40.16, 124.32, 126.77, 127.10,
137.54, 146.88, 178.56.
3,5-Dimethyl-9-phenyl-4-oxa-9-azatricyclo[5.3.0.03,5]decane-
8,10-dione 4b. Yield 29%; colorless crystals (Found: C, 70.63;
H, 6.40; N, 5.18. Calc. for C16H17NO3: C, 70.83; H, 6.32; N,
5.16%); mp 169–171 ЊC (from CHCl3–hexane); νmax/cmϪ1 2950,
exo-2-(2-tert-Butylphenyl)-5,6-dimethyl-3a,4,7,7a-tetra-
hydroisoindole-1,3-dione 1f. Yield 72%; white crystals (Found:
C, 77.19; H, 8.20; N, 4.43. Calc. for C20H25NO2: C, 77.13; H,
1710 (C᎐O), 1505, 1450, 1390; δ 1.40 (s, 6H), 1.99–2.08 (m,
᎐
H
2H), 2.47–2.56 (m, 2H), 3.11–3.20 (m, 2H), 7.25–7.27 (m, 2H),
7.39 (dd, J 7.4, 7.4 Hz, 1H), 7.45–7.49 (m, 2H); δC 18.43, 30.19,
36.84, 59.13, 126.32, 128.53, 129.09, 178.71.
8.09; N, 4.50%); mp 124–125 ЊC (from CHCl3–hexane); νmax
/
cmϪ1 2966, 2912, 1715 (C᎐O), 1495, 1380, 1315; δ 1.29 (s, 9H),
᎐
H
1.76 (d, J 1.1 Hz, 6H), 2.39 (dm, J 15.0 Hz, 2H), 2.59 (d, J 15.0
Hz, 2H), 3.21 (m, 2H), 6.51 (dd, J 7.7, 1.5 Hz, 1H), 7.25 (td,
J = 7.7, 1.5 Hz, 1H), 7.36 (td, J = 7.7, 1.5 Hz, 1H), 7.54 (dd,
J 7.7, 1.5 Hz, 1H); δC 18.91, 30.28, 31.20, 35.14, 40.06, 127.09,
128.11, 128.44, 129.24, 130.38, 130.91, 147.56, 180.17.
3,5-Dimethyl-9-phenyl-4-oxa-9-azatricyclo[5.3.0.03,5]decane-
8,10-dione 5b. Yield 50%; colorless crystals (Found: C; 71.02,
H; 6.32, N; 5.24%); mp 180–183 ЊC (from CHCl3–hexane); νmax
/
cmϪ1 2920, 1706 (C᎐O), 1598, 1504, 1402; δH 1.34 (s, 6H), 2.22
᎐
[dd, J 7.3, 15.3 Hz, 1H (conformer A)], 2.22 [dd, J 2.7, 15.3 Hz,
1H (conformer B)], 2.61 (d, J 15.3 Hz, 2H), 2.93 [d, J 7.3 Hz, 1H
(conformer A)], 2.93 [dd, J 1.0, 2.7 Hz, 1H (conformer B)],
7.30–7.33 (m, 2H), 7.38 (dd, J 7.5, 7.5 Hz, 1H), 7.44–7.48 (m,
2H); δC 18.40, 29.50, 36.75, 61.01, 126.68, 128.32, 128.97,
128.97, 132.70, 179.72.
Synthesis of bicyclic imide 1g
Imide 1f (2.22 g, 7.13 mmol) was dissolved in toluene (50 cm3)
and the solution was refluxed for 29 h. After cooling, the solu-
tion was concentrated in vacuo. The residue was separated by
column chromatography on silica gel and elution with hexane–
ethyl acetate (9:1) to give 1f (1.09 g, 49% recovery; Rf 0.25) and
1g (1.13 g, 51%; Rf 0.1).
9-(4-Chlorophenyl)-3,5-dimethyl-4-oxa-9-azatricyclo-
[5.3.0.03,5]decane-8,10-dione 4c. Yield 24%; colorless crystals
(Found: C; 62.82, H; 5.26, N; 4.43. Calc. for C16H16ClNO3: C;
62.85, H; 5.27, N; 4.58%); mp 214–215 ЊC (from CHCl3–
hexane); νmax/cmϪ1 1710 (C᎐O), 1635; δ 1.40 (s, 6H), 2.02 (m,
exo-2-(2-tert-Butylphenyl)-5,6-dimethyl-3a,4,7,7a-tetra-
hydroisoindole-1,3-dione 1g. Yield 51%; white crystals (Found:
C, 76.81; H, 7.89; N, 4.44%); mp 178–179 ЊC (from CHCl3–
hexane); νmax/cmϪ1 2938, 1710 (C᎐O), 1445, 1379; δ 1.22
᎐
H
2H), 2.51 (m, 2H), 3.15 (m, 2H), 7.24 (d, J 8.8 Hz, 2H) , 7.44
(d, J 8.8 Hz, 2H); δC 18.46, 30.17, 36.84, 59.12, 127.53, 129.32,
130.14, 134.33, 178.47.
᎐
H
(s, 9H), 1.70 (d, J 1.1 Hz, 6H), 2.36 (dm, J 15.0 Hz, 2H), 2.56
466
J. Chem. Soc., Perkin Trans. 1, 2001, 462–468

View Online
9-(4-Chlorophenyl)-3,5-dimethyl-4-oxa-9-azatricyclo-
which were used in all calculations. The final R and wR were
0.059 and 0.061.
CCDC reference number 207/503. See http://www.rsc.org/
suppdata/p1/b0/b004098n/ for crystallographic files in .cif
format.
[5.3.0.03,5]decane-8,10-dione 5c. Yield 57%; colorless crystals;
high-resolution FAB MS (Found: m/z, 306.0872. Calc. for
C16H16ClNO3: MHϩ, 306.7682); mp 205–207 ЊC (from CHCl3–
hexane); νmax/cmϪ1 1710 (C᎐O), 1500, 1405; δ 1.33 (s, 6H),
᎐
H
2.19 [dd, J 7.2, 15.4 Hz, 1H (conformer A)], 2.19 [dd, J 2.5,
15.4 Hz, 1H (conformer B)], 2.59 (d, J 15.4 Hz, 2H), 2.92 [d,
J 7.2 Hz, 1H (conformer A)], 2.92 [dd, J 1.0, 2.5 Hz, 1H
(conformer B)], 7.27 (d, J 8.8 Hz, 2H), 7.43 (d, J 8.5 Hz, 2H);
δC 18.42, 29.55, 36.82, 61.11, 128.02, 129.23, 131.18, 134.17,
179.53.
9-(2-tert-Butylphenyl)-3,5-dimethyl-4-oxa-9-azatricyclo-
[5.3.0.03,5]decane-8,10-dione 5f. Yield 20%; colorless crystals
(Found: C, 73.39; H, 7.88; N, 4.37%); mp 156–157 ЊC (from
CHCl3–hexane); νmax/cmϪ1 2920, 1715 (C᎐O), 1450, 1385;
᎐
δH 1.26 (s, 9H), 1.34 (s, 6H), 2.18 [dd, J 7.0, 15.1 Hz, 1H (con-
former A)], 2.18 [dd, J 2.7, 15.1 Hz, 1H (conformer B)], 2.60 (br
d, J 15.1 Hz, 2H), 2.90 [d, J 7.0 Hz, 1H (conformer A)], 2.90
[dd, J 1.0, 2.7 Hz, 1H (conformer B)], 7.13 (dd, J 2.0, 7.6 Hz,
1H), 7.28 (dt, J 1.7, 7.6 Hz, 1H), 7.33 (dt, J 1.7, 7.8 Hz, 1H),
7.50 (dd, J 1.7, 7.8 Hz, 1H); δC 18.46, 29.34, 31.39, 35.18, 37.03,
61.07, 127.42, 127.74, 129.24, 130.55, 131.69, 147.64, 180.62.
Methyl
4-(3,5-dimethyl-8,10-dioxo-4-oxa-9-azatricyclo-
[5.3.0.03,5]decan-9-yl)benzoate 4d. Yield 19%; colorless crystals;
high-resolution FAB MS (Found: m/z, 330.1337. Calc. for
C18H19NO5 MHϩ, 330.1342); mp 184–186 ЊC (from CHCl3–
hexane); νmax/cmϪ1 1720 (C᎐O), 1445, 1380; δ 1.40 (s, 6H), 2.04
᎐
H
(m, 2H), 2.52 (m, 2H), 3.17 (m, 2H), 3.93 (s, 3H), 7.40 (d, J 8.8
Hz, 2H), 8.13 (d, J 8.7 Hz, 2H); δC 18.44, 30.16, 36.90, 59.11,
126.05, 129.93, 130.39, 135.72, 166.14, 178.31.
9-(2-tert-Butylphenyl)-3,5-dimethyl-4-oxa-9-azatricyclo-
[5.3.0.03,5]decane-8,10-dione 4g. Yield 61%; colorless crystals
(Found: C, 73.26; H, 7.67; N, 4.23%); mp 172–174 ЊC (from
CHCl3–hexane); νmax/cmϪ1 2926, 1711 (C᎐O), 1442, 1376;
Methyl
4-(3,5-dimethyl-8,10-dioxo-4-oxa-9-azatricyclo-
᎐
[5.3.0.03,5]decan-9-yl)benzoate 5d. Yield 60%; colorless crystals
(Found: C, 65.66; H, 5.82; N, 4.13. Calc. for C18H19NO5: C,
65.64; H, 5.81; N, 4.25%); mp 173–175 ЊC (from CHCl3–
δH 1.31 (s, 9H), 1.40 (s, 6H), 2.01 (m, 2H), 2.53 (m, 2H), 3.15 (m,
2H), 6.81 (dd, J 1.5, 7.8 Hz, 1H), 7.27 (dt, J 1.6, 7.5 Hz, 1H),
7.38 (ddd, J 1.5, 7.3, 7.8 Hz, 1H), 7.57 (dd, J 1.5, 8.2 Hz, 1H);
δC 18.36, 29.80, 31.72, 35.78, 37.34, 59.08, 127.55, 128.71,
129.74, 130.64, 130.76, 147.99, 179.74.
hexane); νmax/cmϪ1 2930, 1715 (C᎐O), 1605, 1445, 1385; δH 1.34
᎐
(s, 6H), 2.22 [dd, J 7.0, 15.2 Hz, 1H (conformer A)], 2.22 [dd,
J 2.5, 15.2 Hz, 1H, (conformer B)], 2.60 (d, J 15.2 Hz, 2H),
2.93 [d, J 7.0 Hz, 1H (conformer A)], 2.93 [dd, J 1.0, 2.5 Hz,
1H (conformer B)], 3.92 (s, 3H), 7.44 (d, J 8.7 Hz, 2H), 8.13
(d, J 8.8 Hz, 2H); δC 18.42, 29.57, 36.88, 52.24, 61.12, 126.49,
129.79, 130.35, 136.75, 166.32, 179.31.
Synthesis of 2,5,6-trimethyl-3a,4,7,7a-tetrahydroisoindole-1,3-
dione 6
In a two-necked 100 cm3 flask equipped with a reflux condenser
capped with a calcium chloride drying tube and a rubber
septum was stirred a solution of N-methylmaleimide (300 mg,
2.70 mmol) in toluene (20 cm3). Then, 2,3-dimethylbuta-1,3-
diene (0.915 cm3, 8.10 mmol) was added and the mixture was
heated at 70 ЊC for 3 h with stirring. After cooling, the solution
was concentrated in vacuo and compound 6 was separated by
column chromatography on silica gel and elution with ethyl
acetate. The solid was recrystallized from chloroform–hexane
to afford a colorless solid (351.8 mg, 68%) (Found: C, 68.21; H,
7.74; N, 7.24. Calc. for C11H15NO2: C, 68.37; H, 7.82; N,
7.25%); mp 73–74 ЊC (from CHCl3–hexane); νmax/cmϪ1 2940,
3,5-Dimethyl-9-(4-nitrophenyl)-4-oxa-9-azatricyclo-
[5.3.0.03,5]decane-8,10-dione 4e. Yield 14%; yellow crystals;
high-resolution FAB MS (Found: m/z, 317.1136. Calc. for
C16H16N2O5: MHϩ, 317.1138); mp 184–184.5 ЊC (from CHCl3–
hexane); νmax/cmϪ1 1710 (C᎐O), 1630; δ 1.40 (s, 6H), 2.04 (m,
᎐
H
2H), 2.53 (m, 2H), 3.20 (m, 2H), 7.57 (d, J 9.3 Hz, 2H), 8.33
(d, J 9.3 Hz, 2H); δC 18.43, 30.15, 36.93, 59.07, 124.36, 126.74,
137.41, 146.90, 177.96.
3,5-Dimethyl-9-(4-nitrophenyl)-4-oxa-9-azatricyclo-
1770, 1700 (C᎐O), 1440, 1385, 1330; δ 1.66 [s, 3H (con-
᎐
H
[5.3.0.03,5]decane-8,10-dione 5e. Yield 66%; colorless crystals
(Found: C, 60.66; H, 4.98; N, 8.75. Calc. for C16H16N2O5: C,
60.76; H, 5.10; N, 8.86%); mp 198–199 ЊC (from CHCl3–
formerA)], 1.67 [s, 3H (conformerB)], 2.24 (br d, J 15.8 Hz,
2H), 2.42 (d, J 14.7 Hz, 2H), 2.94 (s, 3H), 3.02 (t, J 2.4 Hz, 2H);
δC 19.21, 24.90, 30.48, 39.82, 126.70, 180.33.
hexane); νmax/cmϪ1 2920, 1715 (C᎐O), 1625, 1525, 1350; δH 1.35
᎐
(s, 6H), 2.25 [dd, J 7.1, 15.4 Hz, 1H (conformer A)], 2.25 [dd,
J 2.7, 15.4 Hz, 1H (conformer B)], 2.60 (d, J 15.4 Hz, 2H), 2.97
[d, J 7.1 Hz, 1H (conformer A)], 2.97 [dd, J 1.0, 2.7 Hz, 1H
(conformer B)], 7.59 (d, J 9.0 Hz, 2H), 8.32 (d, J 9.3 Hz, 2H);
δC 18.37, 29.60, 36.93, 61.22, 124.24, 127.24, 138.33, 146.91,
178.98.
Competitive oxidation of 1a and 1e
Compounds 1a (7.0 mg, 0.025 mmol) and 1e (7.4 mg, 0.025
mmol) were dissolved in chloroform (5 cm3). A solution of
MCPBA [0.0025 mmol, 0.50 mg (purity 80%)] in chloroform
(0.1 cm3) was added and the mixture stirred at 21 ЊC for 23 h.
The proportions of epoxides 4a (retention time 38 min) 5a
(retention time 112 min), 4e (retention time 33 min), and 5e
(retention time 134 min) were determined by HPLC [hexane–
ethyl acetate (2.5:1), detection 254 nm] comparison of their
peak areas calibrated with their ε-values at 254 nm.
9-(2-tert-Butylphenyl)-3,5-dimethyl-4-oxa-9-azatricyclo-
[5.3.0.03,5]decane-8,10-dione 4f. Yield 44%; colorless crystals
(Found: C, 73.41; H, 7.71; N, 4.23. Calc. for C20H25NO3: C,
73.37; H, 7.70; N, 4.28%); mp 164–166 ЊC (from CHCl3–
hexane); νmax/cmϪ1 2968, 1713 (C᎐O), 1559, 1491, 1440, 1373;
᎐
δH 1.25 (s, 9H), 1.38 (s, 6H), 2.03 (m, 2H), 2.48 (m, 2H), 3.13 (m,
2H), 6.74 (dd, J 1.4, 7.8 Hz, 1H), 7.26 (dt, J 1.5, 7.6 Hz, 1H),
7.37 (dt, J 1.5, 7.8 Hz, 1H), 7.55 (dd, J 1.5, 8.0 Hz, 1H); δC
18.50, 18.54, 29.89, 31.49, 31.53, 35.51, 37.17, 59.17, 127.34,
128.79, 129.74, 130.16, 130.60, 147.98, 179.90.
An X-ray crystal structure was obtained: C20H25NO3,
M = 327.42, colorless prismatic crystal, crystal dimensions
0.30 × 0.40 × 0.40 mm, monoclinic, space group P21/c (no. 14),
a = 11.665(1), b = 9.667(1), c = 16.100(1) Å, β = 98.060(7)Њ,
V = 1797.7(3) Å3, Z = 4, Dx = 1.210 g cmϪ3, µ(CuKα) = 6.46
cmϪ1, 3603 reflections measured, 3428 unique (Rint = 0.037)
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