Synthesis of para-substituted bicyclo[2.2.1]hept-5-en-2-ylmethyl benzoates

Article abstract of DOI:10.1134/S1070428009010102

para-Substituted bicyclo[2.2.1]hept-5-en-2-ylmethyl benzoates were synthesized by the Diels-Alder reaction of cyclopentadiene with the corresponding para-substituted allyl benzoates, and optimal reaction conditions were found. The product structure was confirmed by independent synthesis and IR and ¹H NMR spectroscopy.

Full text of DOI:10.1134/S1070428009010102

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2009, Vol. 45, No. 1, pp. 74–77. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © E.G. Mamedbeili (Mamedov), T.G. Kyazimova, Z.M. Nagiev, O.B. Abdiev, K.A. Aliev, 2009, published in Zhurnal Organicheskoi
Khimii, 2009, Vol. 45, No. 1, pp. 81–84.
Synthesis of para-Substituted
Bicyclo[2.2.1]hept-5-en-2-ylmethyl Benzoates
E. G. Mamedbeili (Mamedov)a, T. G. Kyazimovab, Z. M. Nagievb,
O. B. Abdievc, and K. A. Alievb
a Institute of Petrochemical Processes, National Academy of Sciences of Azerbaidjan,
pr. Khodzhaly 30, Baku, 1025 Azerbaidjan
e-mail: eldar_mamedbeyli@mail.ru
b Institute of Chemical Problems, National Academy of Sciences of Azerbaidjan, Baku, Azerbaidjan
c Institute of Polymeric Materials, National Academy of Sciences of Azerbaidjan, Sumgaiyt, Azerbaidjan
Received January 30, 2008
Abstract—para-Substituted bicyclo[2.2.1]hept-5-en-2-ylmethyl benzoates were synthesized by the Diels–
Alder reaction of cyclopentadiene with the corresponding para-substituted allyl benzoates, and optimal reaction
1
conditions were found. The product structure was confirmed by independent synthesis and IR and H NMR
spectroscopy.
DOI: 10.1134/S1070428009010102
Compounds of the norbornene series possess vari-
ous useful properties. Molecules of these compounds
have a rigid cage-like structure with fixed orientations
of substituents and are promising models for studying
structure–property relations [1]. Some norbornene de-
rivatives were found to exhibit analgesic and antiseptic
effects [2, 3]. Accessibility of norbornene derivatives
strongly increased due to improvement of procedures
for Diels–Alder reactions involving cyclopentadiene
which is a large-scale chemical product. On the one
hand, esters derived from norbornene attract interest
from the viewpoint of their practical importance; on
the other hand, their molecules contain reactive frag-
ments capable of undergoing various chemical trans-
formations [4–7].
In the present article we report on the synthesis of
para-substituted bicyclo[2.2.1]hept-5-en-2-ylmethyl
benzoates. Previously unknown initial dienophiles IX–
XV were obtained by esterification of the correspond-
ing para-substituted benzoic acids II–VIII with allyl
alcohol (I), and Diels–Alder reaction of cyclopentadi-
ene with esters IX–XV gave compounds XVII–XXIII
(Scheme 1). The Diels–Alder reactions were carried
out at 120–180°C (reaction time 6–12 h), the diene–
Scheme 1.
H+, PhH, reflux
OH
O
R
+
RCOOH
H2C
H2C
–H2O
O
I
II–VIII
IX–XV
7
7
(XVI)
Ha
3
4
4
HA
HA
Hb
3
5
5
8
+
2
2
HX
HB
1
1
6
6
HB
OCOR
8
Ha
HX
OCOR
Hb
endo
XVII–XXIII
exo
II, IX, XVII, R = Ph; III, X, XVIII, R = p-MeC6H4; IV, XI, XIX, R = p-HOC6H4; V, XII, XX, R = p-MeOC6H4;
VI, XIII, XXI, R = p-ClC6H4; VII, XIV, XXII, R = p-BrC6H4; VIII, XV, XXIII, R = p-O2NC6H4.
74

SYNTHESIS OF para-SUBSTITUTED BICYCLO[2.2.1]HEPT-5-EN-2-YLMETHYL BENZOATES
75
Scheme 2.
II–VIII, H+, PhH, reflux
OH
OH
+
XVII–XXIII
H2C
–H2O
XVI
I
XXIV
dienophile molar ratio being 1:1 to 1:4. We examined
the effect of the reaction temperature on the yield and
isomeric composition of adduct XVII. The yield of
XVII increased from 33 to 45% as the temperature
rose from 120 to 160°C. Further raising the tempera-
ture to 180°C resulted in reduced yield and endo-selec-
tivity; the latter decreased from 94 to 83%. The op-
timal conditions were temperature 140°C, reaction
time 8 h, diene–dienophile ratio 1:1.5.
of XVII–XXIII gave bicyclo[2.2.1]hept-5-en-2-yl-
methanol (XXIV) whose isomeric composition was the
same as that of the initial esters. It is known that
alcohol XXIV prepared as described in [8, 9] consists
mainly of the endo isomer. By comparing isomeric
compositions of alcohol XXIV obtained by different
methods we determined the isomeric composition of
adducts XVII–XXIII.
EXPERIMENTAL
Under the optimal conditions, the Diels–Alder reac-
tions of cyclopentadiene with allyl esters IX–XV gave
48–65% of the corresponding adducts XVII–XXIII.
The maximal yield (65%) was obtained in the reaction
with allyl p-nitrobenzoate (XV), and the minimal
(48%), in the reaction with allyl p-methylbenzoate (X).
The reaction of cyclopentadiene with allyl p-bromo-
benzoate (XIV) was characterized by the highest endo-
selectivity (92%).
The IR spectra were recorded in the range from
4000 to 400 cm–1 on a UR-20 spectrometer; samples
were examined as thin films or KBr pellets. The
1H NMR spectra were measured on a Tesla BS-487
spectrometer (80 MHz) from solutions in carbon tetra-
chloride using tetramethylsilane as internal reference.
Gas–liquid chromatography was performed on an
LKhM-8 MD instrument equipped with a thermal con-
ductivity detector and a 300×0.3 cm column; station-
ary phase 5% of poly(ethylene glycol succinate), car-
rier gas helium, flow rate 40 ml/min; oven temperature
150°C, injector temperature 250°C.
The structure of compounds XVII–XXIII was
proved by independent syntheses. For this purpose, by
Diels–Alder reaction of cyclopentadiene with allyl
alcohol according to the procedure described in [8] we
obtained bicyclo[2.2.1]hept-5-en-2-ylmethanol
(XXIV) which was then used to esterify p-substituted
benzoic acids II–VIII (Scheme 2). Bicyclo[2.2.1]hept-
5-en-2-ylmethyl esters XVII–XXIII thus obtained
were identical to the products synthesized according to
Scheme 1.
p-Substituted allyl benzoates IX–XV were pre-
pared by esterification of the corresponding benzoic
acids with allyl alcohol (I) in benzene in the presence
of sulfuric acid (5 wt % with respect to the entire reac-
tion mixture). The mixture was heated under reflux in
a flask equipped with a Dean–Stark trap until water no
longer separated. When the reaction was complete, the
mixture was washed first with a solution of sodium
hydrogen carbonate and then with distilled water until
neutral washings and dried over MgSO4, the solvent
was distilled off, and the residue was distilled under
reduced pressure.
The IR spectra of compounds XVII–XXIII con-
tained a strong carbonyl absorption band at 1655–
1650 cm–1; absorption bands in the regions 3070–3040
[ν(=C–H)] and 725–700 cm–1 [δ(=C–H)] indicated the
presence of a strained double C=C bond in their mole-
1
cules. In the H NMR spectra of XVII–XXIII, non-
equivalent protons at the double bond in the norbor-
nene skeleton resonated as multiplets at δ 5.85–5.70
Allyl benzoate (IX) was obtained from 5.8 g
(0.1 mol) of allyl alcohol and 12.2 g (0.1 mol) of ben-
zoic acid. Yield 13.8 g (80%), bp 74–75°C (1 mm),
nD20 = 1.5156, d420 = 0.8861. IR spectrum, ν, cm–1: 3040,
1740, 1600, 1390.
(5-H) and 6.15–5.90 ppm (6-H), respectively (J5,6
=
7.0 Hz). Signals from protons in the bridgehead posi-
tions were located at δ 2.74–2.40 (m, 1-H) and 3.00–
2.84 ppm (m, 4-H). Methylene protons in the CH2O
group (8-Ha and 8-Hb) gave rise to a multiplet in the
region δ 4.25–3.31 ppm (Ja,b = 9.0 Hz).
Allyl p-methylbenzoate (X) was obtained from
5.8 g (0.1 mol) of allyl alcohol and 13.6 g (0.1 mol) of
p-methylbenzoic acid. Yield 10.2 g (58%), bp 90–92°C
(1 mm), nD20 = 1.4950, d420 = 0.08861. IR spectrum, ν,
cm–1: 3040, 1740, 1600, 1410.
The isomeric composition of esters XVII–XXIII
was determined by GLC analysis. Alkaline hydrolysis
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 45 No. 1 2009

MAMEDBEILI et al.
Allyl p-hydroxybenzoate (XI) was obtained from
76
1
1600, 1400. H NMR spectrum, δ, ppm: 0.40 m (1H,
HA), 1.15 q (1H, anti-7-H), 1.65 m (1H, syn-7-H),
1.75 m (1H, HB), 2.1 q (1H, HX), 2.45 m (1H, 1-H),
3.0 m (1H, 4-H), 3.31 m (1H, Ha), 4.25 m (1H, Hb),
5.8 g (0.1 mol) of allyl alcohol and 13.8 g (0.1 mol) of
p-hydroxybenzoic acid. Yield 11.6 g (60%), bp 85–
87°C (1 mm), nD20 = 1.5040, d420 = 1.0348. IR spectrum,
ν, cm–1: 3060, 1750, 1600, 1440.
5.7 m (1H, 5-H), 5.9 m (1H, 6-H), JAB = –11.4, JAX
=
3.9, JBX = 8.9 Hz. Found, %: C 79.3; H 7.48. C16H18O2.
Calculated, %: C 79.04; H 7.13.
Allyl p-methoxybenzoate (XII) was obtained from
5.8 g (0.1 mol) of allyl alcohol and 15.2 g (0.1 mol) of
p-methoxybenzoate. Yield 11.5 g (60%), bp 90–91°C
(1 mm), nD20 = 1.5010, d420 = 1.0115. IR spectrum, ν,
cm–1: 3070, 1745, 1620, 1400.
Bicyclo[2.2.1]hept-5-en-2-ylmethyl p-hydroxy-
benzoate (XIX) was synthesized from 6.6 g (0.1 mol)
of cyclopentadiene and 27.7 g (0.15 mol) of ester XI.
Yield 8.15 g (53%), bp 132–135°C (1 mm), nD20
=
Allyl p-chlorobenzoate (XIII) was obtained from
5.8 g (0.1 mol) of allyl alcohol and 15.6 g (0.1 mol) of
p-chlorobenzoate. Yield 15.3 g (78%), bp 85–89°C
(1 mm), nD20 = 1.6343, d420 = 1.2055. IR spectrum, ν,
cm–1: 3070, 1730, 1620, 1400, 820.
1.5340, d420 = 1.0660. IR spectrum, ν, cm–1: 3070,
1
1735, 1620, 1495. H NMR spectrum, δ, ppm: 0.45 m
(1H, HA), 1.10 q (1H, anti-7-H), 1.60 m (1H, syn-7-H),
1.75 q (1H, HB), 2.1 q (1H, HX), 2.40 m (1H, 1-H),
2.80 m (1H, 4-H), 3.92 m (1H, Ha), 4.21 m (1H, Hb),
Allyl p-bromobenzoate (XIV) was obtained from
5.8 g (0.1 mol) of allyl alcohol and 20.1 g (0.1 mol) of
p-bromobenzoic acid. Yield 19.68 g (82%), bp 95°C
(1 mm), nD20 = 1.5546, d420 = 1.3305. IR spectrum, ν,
cm–1: 3060, 1740, 1620, 1400, 600.
5.75 m (1H, 5-H), 5.90 m (1H, 6-H); JAB = –11.3, JAX
3.9, JBX = 8.9 Hz. Found, %: C 74.6; H 6.1. C15H16O3.
Calculated, %: C 73.8; H 6.6.
=
Bicyclo[2.2.1]hept-5-en-2-ylmethyl p-methoxy-
benzoate (XX) was synthesized from 6.6 g (0.1 mol)
of cyclopentadiene and 28.8 g (0.15 mol) of allyl
p-methoxybenzoate (XII). Yield 14.96 g (58%),
bp 138–141°C (1 mm), nD20 = 1.5410, d240 = 0.9429. IR
Allyl p-nitrobenzoate (XV) was obtained from
5.8 g (0.1 mol) of allyl alcohol and 16.7 g (0.1 mol) of
p-nitrobenzoate. Yield 12 g (58%), bp 128–132°C
(1 mm), nD20 = 1.5420, d420 = 1.1278. IR spectrum, ν,
cm–1: 3040, 1740, 1620, 1500, 550.
1
spectrum, ν, cm–1: 3040, 1735, 1650, 1495. H NMR
spectrum, δ, ppm: 0.55 m (1H, HA), 1.10 q (1H, anti-
7-H), 1.50 m (1H, syn-7-H), 1.70 q (1H, HB), 2.1 q (1H,
HX), 2.65 m (1H, 1-H), 2.85 m (1H, 4-H), 3.95 m (1H,
Ha), 4.25 m (1H, Hb), 5.85 m (1H, 5-H), 6.15 m (1H,
6-H); JAB = –11.8, JAX = 3.9, JBX = 9.0 Hz. Found, %:
C 75.2; H 6.3. C16H18O3. Calculated, %: C 74.4; H 6.9.
Diels–Alder reaction of cyclopentadiene with
allyl benzoates IX–XV (general procedure). A mix-
ture of 0.1 mol of freshly distilled cyclopentadiene and
0.15 mol of ester IX–XV was heated for 8 h at 140°C
in a sealed ampule. The ampule was cooled and
opened, and esters XVII–XXIII were isolated by
vacuum distillation.
Bicyclo[2.2.1]hept-5-en-2-ylmethyl p-chloroben-
zoate (XXI) was synthesized from 6.6 g (0.1 mol) of
cyclopentadiene and 29.5 g (0.15 mol) of ester XIII.
Yield 13.79 g (60%), bp 149–151°C (1 mm), nD20
=
Bicyclo[2.2.1]hept-5-en-2-ylmethyl benzoate
(XVII) was synthesized from 6.6 g (0.1 mol) of cyclo-
pentadiene and 24.3 g (0.15 mol) of allyl benzoate
(IX). Yield 10.26 g (45%), bp 125–126°C (1 mm),
nD20 = 1.5265, d420 = 1.0058. IR spectrum, ν, cm–1: 3070,
1.5435, d420 = 1.2814. IR spectrum, ν, cm–1: 3070,
1
1735, 1660, 1390, 795. H NMR spectrum, δ, ppm:
0.45 m (1H, HA), 1.10 q (1H, anti-7-H), 1.50 m (1H,
syn-7-H), 1.70 q (1H, HB), 2.1 q (1H, HX), 2.40 m
(1H, 1-H), 2.90 m (1H, 4-H), 3.97 m (1H, Ha), 4.45 m
1
1745, 1655, 1390. H NMR spectrum, δ, ppm: 0.45 m
(1H, HA), 1.15 q (1H, anti-7-H), 1.6 m (1H, syn-7-H),
1.7 m (1H, HB), 2.1 m (1H, HX), 2.5 m (1H, 1-H),
2.9 m (1H, 4-H), 3.91 m (1H, Ha), 4.25 m (1H, Hb),
(1H, Hb), 5.75 m (1H, 5-H), 6.00 q (1H, 6-H); JAB
=
–11.9, JAX = 3.9, JBX = 9.0 Hz. Found, %: C 68.45;
H 5.25; Cl 13.20. C15H15 ClO2. Calculated, %: C 69.57;
H 5.72; Cl 13.22.
Bicyclo[2.2.1]hept-5-en-2-ylmethyl p-bromoben-
zoate (XXII) was synthesized from 6.6 g (0.1 mol) of
cyclopentadiene and 36 g (0.15 mol) of allyl p-bromo-
benzoate (XIV). Yield 17.74 g (58%), bp 178–180°C
(1 mm), nD20 = 1.5632, d420 = 1.5150. IR spectrum, ν,
cm–1: 3070, 1730, 1660, 1395, 650. 1H NMR spectrum,
δ, ppm: 0.50 m (1H, HA), 1.15 q (1H, anti-7-H),
5.7 m (1H, 5-H), 5.95 m (1H, 6-H); JAB = –11.4, JAX
=
3.9, JBX = 9.2 Hz. Found, %: C 78.9; H 5.86. C15H16O2.
Calculated, %: C 79.5; H 6.07.
Bicyclo[2.2.1]hept-5-en-2-ylmethyl p-methylben-
zoate (XVIII) was synthesized from 6.6 g (0.1 mol) of
cyclopentadiene and 26.4 g (0.15 mol) of ester X.
Yield 11.65 g (48%), bp 125–127°C (1 mm), nD20
=
1.5010, d420 = 1.035. IR spectrum, ν, cm–1: 3070, 1740,
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SYNTHESIS OF para-SUBSTITUTED BICYCLO[2.2.1]HEPT-5-EN-2-YLMETHYL BENZOATES
77
1.55 m (1H, syn-7-H), 1.70 q (1H, HB), 2.1 q (1H, HX),
2.74 m (1H, 1-H), 2.84 m (1H, 4-H), 3.98 m (1H, Ha),
4.45 m (1H, Hb), 5.70 m (1H, 5-H), 6.10 m (1H, 6-H);
JAB = –11.9, JAX = 4.7, JBX = 8.1 Hz. Found, %:
C 58.24; H 4.36; Br 27.4. C15H15 BrO2. Calculated, %:
C 58.63; H 4.89; Br 26.67.
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cyclopentadiene and 31 g (0.15 mol) of compound XV.
Yield 17.74 g (65%), mp 135°C. IR spectrum, ν, cm–1:
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1
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Hb), 5.85 m (1H, 5-H), 6.15 m (1H, 6-H); JAB = –11.4,
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esterification of the corresponding p-substituted ben-
zoic acids II–VIII with bicyclic alcohol XXIV accord-
ing to the procedure described above for the prepara-
tion of esters IX–XV. The products obtained by the
two methods were identical in physical constants and
spectral parameters. Bicyclo[2.2.1]hept-5-en-2-ylmeth-
anol (XXIV) was prepared by the Diels–Alder reaction
of cyclopentadiene with allyl alcohol [8].
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