Asymmetrical [4+2]-cycloaddition of (-)-menthyl acrylate and (-)-menthyl methacrylate to cyclopentadiene in the presence of BBr3

Article abstract of DOI:10.1023/A:1012374828303

An asymmetrical synthesis of bicyclo[2.2.1]hept-2-enes is described performed by [4+2]-cycloaddition of (-)-menthyl acrylate and (-)-menthyl methacrylate to cyclopentadiene in the presence of BBr₃. The effect of different factors on isomer composition, yield, and enantiomeric purity of the compounds obtained was investigated. Kovatch indices were determined and boiling points were estimated with the use of gas-liquid chromatography.

Full text of DOI:10.1023/A:1012374828303

Russian Journal of Organic Chemistry, Vol. 37, No. 2, 2001, pp. 217 222. Translated from Zhurnal Organicheskoi Khimii, Vol. 37, No. 2, 2001,
pp. 230 235.
Original Russian Text Copyright
2001 by Mamedov.
Asymmetrical [4+2]-Cycloaddition of ( )-Menthyl Acrylate
and ( )-Menthyl Methacrylate to Cyclopentadiene
in the Presence of BBr3
E. G. Mamedov
Institute of Petrochemical Processes, Azerbaidzhan Academy of Sciences, Baku, 370025 Azerbaidzhan
Received January 5, 2000
Abstract An asymmetrical synthesis of bicyclo[2.2.1]hept-2-enes is described performed by [4+2]-cyclo-
addition of ( )-menthyl acrylate and ( )-menthyl methacrylate to cyclopentadiene in the presence of BBr3.
The effect of different factors on isomer composition, yield, and enantiomeric purity of the compounds
obtained was investigated. Kovatch indices were determined and boiling points were estimated with the use
of gas-liquid chromatography.
A norbornene moiety is inherent to a large number
of natural and synthetic biologically active com-
pounds. Introduction of a norbornene moiety into
pharmaceuticals improves their therapeutic effect [1].
In the synthesis of bicyclo[2.2.1]heptene derivatives
is used as diene the cyclopentadiene that is a known
by-product of ethylene and coal-tar chemical industry
[2].
[3, 4]. The application of BH2Br in combination with
chiral polymers as catalyst in asymmetrical Diels
Alder reaction of cyclopentadiene with methacrolein
afforded adducts in a good yield and with a fair
enantiomeric purity [5, 6].
In extension of our studies on asymmetrical diene
synthesis [7 11] we report here of the asymmetrical
[4+2]-cycloaddition of ( )-menthyl acrylate (II) and
( )-menthyl methacrylate (III) to cyclopentadiene (I)
in the presence of BBr3 (Scheme 1).
Since often only a single optically active isomer
possesses physiological activity the synthesis of
bicyclic compounds with a bridged structure in the
enantiomerically pure state is especially valuable. The
asymmetrical diene synthesis is among the promising
procedures leading to the above compounds in an
optically active form.
The residual chiral alcohol, L-( )-menthol (R ) in
compounds IV, V was removed by alkaline hydro-
lysis. The separation of isomeric endo-(VI, VII) and
exo-(VIII, IX) acids was performed by conversion of
the endo-isomers into lactones (Scheme 2).
On removing exo-acids VIII, IX from optically
active iodolactones XIV, XV the reduction with the
In these reactions Lewis acids (AlCl3, TiCl4,
SnCl4, BF3 OEt2) are known to be used as catalysts
Scheme 1.
R = H (II, IV, VI, VIII, X, XII), R = CH3 (III, V, VII, IX, XI, XIII); R
= L-( )-menthyl.
1070-4280/01/3702-0217$25.00 2001 MAIK Nauka/Interperiodica

218
MAMEDOV
Scheme 2.
R = H (VI, VIII, XIV), R = CH3 (VII, IX, XV).
system Zn + CH3COOH afforded the corresponding
optically endo-acids VI, VII. To avoid the con-
comitant racemization of adducts IV, V during
alkaline hydrolysis their reduction was carried out
with the use of LiAlH4 (Scheme 1). The catalytic
effect of BBr3 may be attributed to formation of its
complex with dienophiles II, III.
II, III to their complexes with BBr3. These results
are consistent with the data reported in [12] on the
shift of the C=O absorption band in methyl acrylate
from 1720 to 1640 cm effected by AlCl3, TiCl4,
SnCl4 due to complexing between the catalysts and
dienophile.
1
The study was carried out in a wide temperature
range (from 78 to 20 C) in different solvents at
varying ratio between catalyst and dienophiles II, III.
The effect of these parameters on the yield, isomer
composition, and enantiomeric purity is presented in
Table 1.
As seen from Table 1 in contrast to noncatalyzed
reaction of asymmetrical diene synthesis where the
changing temperature weakly affects the enantiomeric
purity of compounds obtained [13], in the presence
of BBr3 this reactions at low temperature furnishes
The electron deficiency arising therefrom on the
multiple bond of the dienophiles II, III facilitates
their interaction with diene I. This assumption is
corroborated by the displacement of the (C=O)
1
from 1730 to 1630 cm on going from dienophiles
Table 1. Effect of cycloaddition reaction parameters on the yield, isomer composition, and enantiomeric purity of
compounds IV XIII
Molar Yield of Isomer ratio
Prevailing
[ ]2D0, EtOH
Solvent
ratio
com-
(IV, V), %
enantiomer, %
BBr3/
pounds
dienophil (IV, V), endo
exo VI, VIII, X, XII,
V,
VII
VIII,
IX
X,
XI
XII,
XIII
(II, III)
%
VII IX XI XIII
II
II
II
II
II
II
II
II
20 CH2Cl2
0.25
0.25
0.25
0.25
0.25
0.25
0.5
0.75
0.25
0.25
0.25
0.25
0.25
0.25
90
81
73
62
60
91
94
96
91
82
63
59
54
52
86.4 13.6
91.7 8.3 32 30 49
98.7 5.3 40 31 53
96.5 3.5 69
98.4 1.6 74
87.3 12.7
89.2 10.8
21 20 30 24 +30.28 +29.42 +22.98 +22.45
10 CH2Cl2
40 CH2Cl2
70 CH2Cl2
78 CH2Cl2
20 C6H6
+46.14 +45.13 +37.5
+57.68 +55.3
+99.5
+104.47
+40.6
+88.31
+94.36
80
84
19 19 28 27 +27.4
21 19 27 25 +27.10 +22.25 +22.19 +19.28
29 +30.28 +22.93
+24.25 +22.20 +20.45
20 C6H6
20 C6H6
80.3 9.7 27
87.2 13.8
II
20 C6H5CH5
20 CH2Cl2
10 CH2Cl2
40 CH2Cl2
70 CH2Cl2
78 CH2Cl2
20 21 30 31 +29.95 +28.76 +21.97 +20.17
19 18 28 27 +20.12 +19.13 +19.33 +12.63
28 27 47 45 +42.63 +41.09 +21.61 +20.59
III
III
III
III
III
10
11
16
13
15
90
89
84
87
85
37 36 51 50
57 56 66 65 +60.33 +56.61 +30.35 +34.19
65 64 70 67 +68.87 61.54 +32.19 +30.55
49.16 +43.45 +23.45 +22.99
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 37 No. 2 2001

ASYMMETRICAL [4+2]-CYCLOADDITION
219
Table 2. Physical constants,IR spectra and elemental analyses of compounds II XIII
Compd.
no.
bp (p,
mm Hg) or
mp (heptane), C
n2D0
d240
Found, %
Calculated, %
1
IR spectrum, , cm
Formula
C
H
C
H
II
III
IV
V
103 104
(11 mm Hg)
115 116
(7.5 mm Hg)
138 140
(0.5 mm Hg)
173 175
(4 mm Hg)
45 46
1.4610 0.9396 1730(C=O),3040(C=C),
1050 (C O)
1.4600 0.9271 1730 (C=O), 1375 (C H), 74.36 10.51 C14H24O2
1050 1120 (C O)
1.4878 1.009 1730 (C=O), 1373 (C H), 78.16 10.12 C18H28O2
1060 1115 (C=O)
1.4758 0.9726 1725 (C=O), 1180 (C O), 78.34 10.25 C19H30O2
3060 (C=C)
74.28 10.10 C13H22O2
74.28 10.47
75.00 10.71
78.26 10.14
78.62 10.34
VI
VII
VIII
1730 (C=O), 3055 (C=C) 69.33
1730 (C=O), 1060 (C O) 70.93
1730 (C=O), 1065 (C O), 69.38
3060 (C=C)
7.27 C8H10O2
7.67 C9H12O2
7.21 C8H10O2
69.56
71.06
69.56
7.24
7.89
7.24
98 99
38 39
IX
X
84 85
80 82
(2 mm Hg)
96
1725 (C=O), 3050 (C=C) 70.96
3300 (O H), 3065 (C=C), 77.39
1775 (C O)
3300 (O H), 3060 (C=C) 78.13 10.11 C9H14O
3300 (O H), 3050 (C=C) 76.96 9.48 C8H12O
7.23 C9H12O2
9.65 C8H12O
71.06
77.41
7.89
9.67
1.4998
1.4973
XI
XII
78.26 10.14
77.41 9.67
81 82
(2 mm Hg)
67 68
XIII
3300 (O H), 3060 (C=C) 78.10 10.12 C9H14O
78.26 10.14
compounds VI XIII of significantly higher purity: It
attains 84% for adduct IV and 70% for adduct V at
78 C. With decreasing temperature the stereo-
selectivity of reactions grows, and the overall yield
of products decreases.
We also developed in this study the preparative
GLC methods for separation of compounds obtained.
We determined the retention volumes, relative reten-
tion volumes, Kovatch indices, and estimated the
boiling points of the compounds under study. The
Kovatch indices were calculated by Kovatch formula
[14], and boiling points by Sakharov equation [15]. In
both calculations was used the retention time of the
normal paraffins om Dynochrom P with Apieson at
the temperature and analysis modes the same as used
with compounds under study (Table 4).
The increase in catalyst BBr3 amount virtually
does not affect the enantiomeric purity of compounds
VI XIII, but their overall yield grows. The data of
Table 1 also indicate that the character of solvent
hardly affects the enantiomeric purity and the overall
yield of the final products.
Optical purity and enantiomeric excess (%) of
compounds VI XIII were calculated from com-
parison of their specific rotation values with the cor-
responding figures for the enantiomerically pure
samples of these compounds described in [16]. The
relative configuration of products VI XIII was
estimated from the rule of correlation of the sign of
optical rotation with that of structurally similar
compounds of established configuration [14]: 5R for
compounds (+)-(VII), (+)-(X), and (+)-(XI); 5S for
Under conditions of this study the reaction of
dienophile II afforded predominantly endo-isomer,
and that with dienophile III mostly exo-isomer.
Isomers of alcohols X, XII and XI, XIII were
separated by preparative gas-liquid chromatography.
The GLC data show that the isomer composition of
alcohols X, XI and XI, XIII is the same as that of
the adducts IV and V respectively.
The composition and structure of compounds
synthesized were confirmed by elemental analysis,
compounds (+)-(VIII),
(+)-(XIII).
(+)-(IX), (+)-(XII),
1
IR and H NMR spectra (Tables 2, 3).
EXPERIMENTAL
Mass spectra of compounds X, XII and XI, XIII
support the structure of these compounds but are
insensitive to the isomer composition.
IR spectra were recorded on spectrophotometer
1
UR-20 in the region of 4000 400 cm from thin film
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 37 No. 2 2001

220
MAMEDOV
1
Table 3. H NMR spectra of compounds VI XIII, , ppm, coupling constants, Hz
R1 = COOH, R2 = H (VI), R1 = COOH, R2 = CH3 (VII), R1 = H, R2 = COOH (VIII), R1 = CH3, R2 = COOH
(IX), R1 = CH2OH, R2 = H (X), R1 = CH2OH, R2 = CH3 (XI), R1 = H, R2 = CH2OH (XII), R1 = CH3, R2 =
CH2OH (XIII)
No. CH3 CH2O OH COOH H1 H2 H3 H4 H5endo He5xo
H6n H6x H7s H7an
J, Hz
VI
11.8 2.85 6
5.85 2.71
2.85 1.30 1.71 1.30 1.30 J2.3 5.7, J2.1 3.0, J3.4
2.7, J6 n 12.0
,6
x
VII 1.15
VIII
11.65 2.75 5.95 5.95 2.75
12.0 3.1 6.05 6.05 2.85 1.4
11.60 2.75 5.95 5.95 2.77
2.81 6.15 5.9 2.71
1.4 1.92 1.45 1.45 J2.3 5.8, J2.1 2.1, J3.4
2.8, J6 n 11.5
,6
x
1.4 1.85 1.4
1.4 J2.3 5.7, J2.1 2.0, J3.4
2.7, J6 n 12.0
,6
x
IX 1.12
X
1.4 1.92 1.47 1.47 J2.3 5.4, J2.1 3.2, J3.4
2.7, J6 n 11.9
,6
x
3.20 3.81
2.18 1.31 1.71 1.30 1.30 J2.3 5.5, J2.1 2.5, J3.4
2.8, J6 n 12.0
,6
x
XI 0.8 3.65 3.35
XII 3.35 3.81
XIII 0.88 3.41 3.95
2.90 5.85 6.15 2.65
1.35 1.50 1.35 1.35 J2.3 5.4, J2.1 2.1, J3.4
2.8, J6 n 11.8
,6
x
3.15 6
5.85 2.85 1.52
1.3 1.82 1.3
1.30 J2.3 5.8, J2.1 2.5, J3.4
2.8, J6 11.8
,6
x
2.75 5.94 5.94 2.5
1.15 1.82 1.42 1.42 J2.3 5.4,n J2.1 2.5, J3.4
2.7, J6 n 12.0
,6
x
Table 4. Retention volumes (Vr), relative retention volumes (menthol standard), Kovatch indices (Ik), and boiling
points of compounds under study
Compound
Relative retention volume
Retention volume
PEGS Apiezon
logVr
Ik
bp,
C
PEGS
Apiezon
(on Apiezon)
Menthol
II
III
V
IV
V
V
X
XI
1
1
288
446
1.13
1.18
7.95
6.02
5.92
5.27
1.58
1.42
1.81
1.72
0.75
0.78
2.45
2.45
2.65
2.65
0.55
0.57
0.55
0.57
300
2820
2136
2100
1872
480
432
540
513
348
1152
1152
1244
1244
216
224
216
224
60
2.62
3.06
3.06
3.30
3.30
2.38
2.46
2.38
2.46
1.78
1.99
2.23
2.43
2.72
2.95
3.22
1174
1430
1430
1544
1544
1050
1089
1050
1089
800
210
242
242
260
260
185
191
185
191
125
151
174
196
216
235
253
XII
XIII
Octane
Nonane
Decane
Undecane
Dodecane
Tridecane
Tetradecane
99
900
168
266
528
888
1668
1000
1100
1200
1300
1400
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 37 No. 2 2001

ASYMMETRICAL [4+2]-CYCLOADDITION
221
1
or KBr pellets. H NMR spectra were registered on
7.4 g of adduct V (52%). MRD found 83.04, calc.
20
spectrometer Tesla BS-487 (operating frequency
80 MHz) from solutions in CCl4, internal references
HMDS or TMS. Mass spectra were run on mass
spectrometer MKh-1303 with the input from a gas
bulb (ionizing voltage 30 and 12 eV). The optical
rotation was measured on polarimeters Perkin
Elmer-141, Polamat A (546 nm), and spectropolari-
meter Spectrol-1. Preparative separation was carried
out on a column 900 0.8 cm packed with porovin
with 5% PEGA [poly(ethylene glycole) adipate],
evaporizer temperature 250 C, oven temperature
170 C, carrier gas nitrogen, gas flow rate
84.07, [ ]
54.48 (c 7.93 EtOH).
589
The other runs for preparation of compound V
were performed similarly (the reaction conditions and
results are listed in Table 1).
Isomeric bicyclo[2.2.1]hept-2-ene-5-carboxylic
acids (VI, VIII). Compound IV (13.8 g, 0.05 mol)
was boiled for 2 h in 30 ml of 5% KOH solution in
methanol. On removing methanol the residue was
dissolved in 30 ml of water, the products were
extracted into ether. The water layer was treated with
diluted HCl and repeatedly extracted with ether. The
extract was washed with water, and dried on MgSO4.
On removing ether we obtained 5.6 g (89%) of iso-
mers VI and VIII mixture. The separation of endo
VI and exo VIII isomers was carried out as in [17].
6.3 g of isomer mixture of VI and VIII was neutra-
lized with 10% solution of KOH, treated with 76 ml
of iodine solution (15 g of I2, 30 g of KI were
dissolved in 90 ml of water). The precipitated iodo-
lactone XIV was extracted into ether, the water layer
was acidified with diluted HCl, the extraction was
repeated, the extract was washed with 5% sodium
thiosulfate solution, then with water, and dried with
MgSO4. On removing the solvent by distillation we
obtained exo-acid VIII. Its constants are given in
Table 2.
200 cm3 min , sample introduced 100 l, flame-
1
ionization detector, chromatograph Varian Aerog-
raph. The chromatographic analysis and purity check
of the compounds synthesized was performed with the
use of columns 300 0.3 cm packed with Dynochrom
P with 5% of Apiezon and PEGS [poly(ethylene
glycol) succinate], carrier gas helium, gas flow rate
40 cm3 min , oven temperature 140 150 C,
1
chromatograph LKhM-8MD, thermal conductivity
detector.
( )-Menthyl acrylate (II) was prepared by
20
546
procedure [12], [ ]
127 (c 4.4, MeOH). Cf.:
[ ]2D0 77 [12].
( )-Menthyl methacrylate (III) was prepared by
20
546
the same procedure, [ ]
113 (c 5.72 , MeOH).
Cf.: [ ]2D0 91.75 [12].
Iodolactone XIV, isolated from the first extract,
is a colorless crystalline substance, mp 59 60 C
(from aqueous ethanol); cf.: mp 55 58 C [18]. endo-
Acid VI was obtained from iodolactone XIV by
procedure [17]. The constants of acid VI are given in
Table 2.
( )-Menthyl bicyclo[2.2.1]hept-2-ene-5-carb-
oxylate (IV). To a solution of 10.52 g (0.05 mol) of
compound II in 30 ml of anhydrous dichloromethane
at 10 C was added dropwise 3.12 g (0.01 mol) of
BBr3 in 20 ml of dichloromethane. The mixture was
cooled to 78 C, and then was added 3.96 g
(0.06 mol) of cyclopentadiene (I) in 10 ml of di-
chloromethane. Then the mixture was stirred for
30 min at 78 C. The mixture was treated first with
diluted HCl, then with 5% solution of NaHCO3,
washed with water, and dried on MgSO4. On remov-
ing the solvent the residue was distilled in vacuo. We
obtained 8.31 g (60%) of adduct IV, MDD 79.50,
Isomeric 5-methylbicyclo[2.2.1]hept-2-ene-5-
carboxylic acids (VII, IX). Compound V (14.5 g)
was boiled for 2 h in 30 ml of 5% KOH solution.
Further hydrolysis was similar to that with adduct IV.
We obtained 6.2 g (89.8%) of a mixture of endo VII
and exo IX isomers. The separation thereof was
carried out as above.
Iodolactone XV is a colorless crystalline com-
calc. 80.39, [ ]2D0 48.18 (c 4.5, EtOH).
pound, mp 86 87 C (from aqueous ethanol) (83
1
The other runs for preparation of compound IV
were carried out similarly (the reaction conditions and
results are listed in Table 1).
85 C [17]). IR spectrum, , cm 1730 (C=O); 1100
(C O). Found, %: C 38.21; H 3.9; I 45.51.
C9H10IO2. Calculated, %: C 38.84; H 3.98; I 45.68.
By reduction of 6.95 g of iodolactone XV along
procedure [17] we obtained 3.2 g of endo-acid VII.
( )Menthyl 5-methylbicyclo[2.2.1]hept-2-ene-5-
carboxylate (V). From 11.2 g (0.05 mol) of com-
pound III and 3.92 g (0.06 mol) of cyclopentadiene
(I) along the above procedure at 78 C we obtained
Physical constants of acids VII and IX are given
in Table 2.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 37 No. 2 2001

222
MAMEDOV
Isomeric 5-hydroxymethylbicyclo[2.2.1]hept-2-
Tetrahedron, 1963, vol. 19, no. 12, pp. 2333 2339.
4. Sauer, J. and Kredel, J., Tetrahedron Lett., 1966,
vol. 7, no. 51, pp. 6359 6363.
5. Itsuno, S., Kamahori, K., Watanabe, K., Koizumi, T.,
and Ito, K., Tetrahedron: Asymmetry, 1994, vol. 5,
no. 4, pp. 523 526.
6. Kamahori, K., Tada, S., Ito, K., and Itsuno, S.,
Tetrahedron: Asimmetry, 1995, vol. 6, no. 10,
pp. 2547 2555.
7. Guseinov, M.M., Akhmedov, I.M., and Mame-
dov, E.G., Azerb. Khim. Zhurn., 1976, no. 1,
pp. 46 49.
8. Mamedov, E.G., Akhmedov, I.M., and Gusei-
nov, M.M., Dokl. Akad. Nauk Azerb. SSR, 1977,
vol. 33, pp. 34 37.
9. Mamedov, E.G., Akhmedov, I.M., Guseinov, M.M.,
Piloyan, S.R., and Klabunovskii, E.I., Izv. Akad.
Nauk SSSR, Ser. Khim., 1978, no. 4, pp. 883 886.
10. Akhmedov, I.M., Mamedov, E.G., Guseinov, M.M.,
and Mamedov, A.A., Zh. Org. Khim., 1978, vol. 14,
no. 6, pp. 1197 1199.
11. Akhmedov, I.M., Peynircioglu, Mamedov, E.H.,
Tanyeli, C., and Demir, S.A., Tetrahedron, 1994,
vol. 50, no. 7, pp. 2099 2106.
12. Williamson, K.L. and Li Hsu, Y., J. Am. Chem. Soc.,
1970, vol. 92, no. 16, pp. 7385 7389.
13. Farmer, R.F. and Harmer, J., J. Org. Chem., 1966,
vol. 31, no. 5, pp. 2418 2426.
enes (X, XII). To a dispersion of 4 g of LiAlH4 in
200 ml of anhydrous ethyl ether was added dropwise
6.6 g of adduct IV solution in 50 ml of anhydrous
ether. The mixture was stirred for 2 h at 20 C. The
excess LiAlH4 was hydrolyzed with water, then to the
mixture was slowly added cooled diluted HCl. The
ether layer was separated, washed with 5% solution
of NaHCO3 and with water till neutral, and then dried
with MgSO4. On removing ether we obtained 6.1 g
of a mixture containing menthol and compounds
X, XII. The mixture was separated by preparative
chromatography. Physical constants of compounds X
and XII are presented in Table 2. Mass spectra of
both isomers are identical and have the following
characteristics (relative intensity at 30 and 12 eV, %):
M+ 124 (17;67), 106 (10;40), 93 (5;09), 66 (100;
100).
5-Methyl- 5-hydroxymethylbicyclo[2.2.1]hept-2-
enes (XI, XIII). From 7.3 g of adduct V by reduction
with LiAlH4 along the above procedure was obtained
6.9 g of mixture containing menthol and alcohols
XI, XIII that was separated by preparative chromato-
graphy. Physical constants of compounds XI and
XIII are presented in Table 2.
Mass spectra of both isomers are identical and
have the following characteristics (relative intensity at
30 and 12 eV, %): M+ 138 (95: 32), 107 (12: 14), 95
(24: 26), 81 (26: 50), 66 (100: 100), 55 (21: 5).
14. Kovatch, E., Helv. Chim. Acta, 1958, vol. 41, no. 5,
pp. 1915 1921.
15. Sakharov, V.M., Leont,
eva, S.A., and Lulova, N.I.,
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