Asymmetric Diels-Alder reaction between acrylates and cyclopentadiene in the presence of chiral catalysts

Article abstract of DOI:10.1134/S1070427206100120

Asymmetric Diels-Alder reaction between cyclopentadiene and alkyl and cycloalkyl acrylates in the presence of new chiral catalysts, BBr ₃?MentOEt, AlCl₂OMent, BBr₂OMent, and BBr(OMent)₂, was studied. Optically active bicyclo[2.2.1]hept-2-ene- 5-carboxylates were synthesized. The influence of the reaction conditions on the total and optical yields and on the stereoselectivity of the adducts synthesized was examined. Nauka/Interperiodica 2006.

Full text of DOI:10.1134/S1070427206100120

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2006, Vol. 79, No. 10, pp. 1621 1625.
Pleiades Publishing, Inc., 2006.
Original Russian Text
E.G. Mamedov, 2006, published in Zhurnal Prikladnoi Khimii, 2006, Vol. 79, No. 10, pp. 1642 1646.
ORGANIC SYNTHESIS
AND INDUSTRIAL ORGANIC CHEMISTRY
Asymmetric Diels-Alder Reaction between Acrylates
and Cyclopentadiene in the Presence of Chiral Catalysts
E. G. Mamedov
Institute of Petrochemical Processes, National Academy of Sciences of Azerbaijan, Baku, Azerbaijan
Received August 17, 2005; in final from, March 2006
Abstract Asymmetric Diels-Alder reaction between cyclopentadiene and alkyl and cycloalkyl acrylates in
the presence of new chiral catalysts, BBr3 MentOEt, AlCl2OMent, BBr2OMent, and BBr(OMent)2, was studied.
Optically active bicyclo[2.2.1]hept-2-ene-5-carboxylates were synthesized. The influence of the reaction con-
ditions on the total and optical yields and on the stereoselectivity of the adducts synthesized was examined.
DOI: 10.1134/S1070427206100120
The asymmetric catalysis is currently under rapid
development. The number of publications on this sub-
ject and the finance assigned to development of this
line tend to increase [1 3]. Organic reactions per-
formed in the presence of chiral catalysts underlie
modern asymmetric synthesis. A key issue for achieve-
ment of high results in this field is directed synthesis
of new efficient optically active catalysts [4].
[10, 11] using optically active methyloxy- and bornyl-
oxyaluminum dichlorides.
Here we report the results of examination of ADAR
between acrylates and cyclopentadiene (CPD) in
the presence of chiral catalysts, aimed at preparation
of optically active norbornene derivatives.
Chiral B- and Al-containing complex catalysts
were synthesized from natural l-( )menthol; their
characteristics are listed in Table 1.
Norbornene and its saturated analogue norbornane
are essential fragments of many important natural
compounds [5]. Today, synthesis of new compounds
containing these moieties attracts the researchers’ at-
tention [6 8]. Synthesis of representatives of this
class of compounds in the optically active form is of
certain theoretical and practical interest.
All chiral catalysts are well soluble in organic sol-
vents (CH2Cl2, CCl4, CHCl3, C6H6, C5H5Cl, C6H5CH3)
and can be used as homogenous catalysts.
Optically active norbornenecarboxylates XI XIX
are prepared by ADAR according to the scheme
Among the promising lines of synthesis of opti-
cally active norbornene derivatives is the asymmetric
Diels-Alder reaction (ADAR) in the presence of chiral
catalysts. We described the first example of ADAR
with BF3 MentOEt as chiral catalyst in [9]. That
study laid the foundations of an efficient meth-
od of synthesis of optically active derivatives of
norbornene by ADAR, which was further developed
where R = Et (II, XI), n-Pr (III, XII), i-Pr (IV, XIII),
n-Bu (V, XIV), i-Bu (VI, XV), t-Bu (VII, XVI),
Table 1. Characterization of chiral catalysts
Catalyst
Initial compound
bp, C (P, mm Hg)
[ ]2D0, deg
Reference
[10]
BBr3 MentOEt
AlCl2OMent
BBr2OMent
MentOEt
187 188 (1)
181 182 (1)
185 187 (1)
191 (1)
99.3
73.5
78.5
91.7
l-( )-MentOH
l-( )-MentOH
l-( )-MentOH
BBr(OMent)2
1621

1622
MAMEDOV
Table 2. Constants and elemental analysis data for compounds of optically active norbornenecarboxylates XI XIX
Found, %
Calculated, %
bp
C
Compound
n2D0
d2D0
Formula
(P, mm Hg)
C
H
C
H
XI
XII
127 128 (15)
130 132 (25)
100 101 (10)
115 117 (10)
104 105 (10)
101 103 (10)
115 117 (20)
118 120 (20)
144 146 (5)
1.4805
1.4795
1.4630
1.4602
1.4615
1.4645
1.5521
1.5526
1.5261
1.038
71.19
73.02
72.90
73.91
73.50
75.22
74.16
75.69
76.53
8.97
8.10
8.30
9.56
8.89
8.99
8.13
9.24
8.20
C10H14O2
C11H16O2
C11H16O2
C12H18O2
C12H18O2
C12H18O2
C13H18O2
C14H20O2
C14H18O2
72.28
73.33
73.33
74.23
74.23
74.23
75.72
76.36
77.06
9.03
8.89
8.89
9.28
9.28
9.28
8.73
9.09
8.25
1.0262
0.9958
0.9771
0.9794
0.9889
0.9780
0.9789
0.9785
XIII
XIV
XV
XVI
XVII
XVIII
XIX
Table 3. Isomeric composition and total and optical yields of XI XIX in relation to the reaction conditions
Catalyst : di- Yield of Isomeric composition, %
[ ]2D0,
EtOH,
deg
Dieno-
phile
T,
C
Optical
yield
Solvent
Catalyst
enophile
XI XIX,
molar ratio
%
endo
exo
III
20
10
40
70
78
20
20
20
20
20
20
20
20
10
10
70
70
70
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
BBr2OMent
BBr2OMent
BBr2OMent
BBr2OMent
BBr2OMent
BBr2OMent
AlCl2OMent
AlCl2OMent
AlCl2OMent
AlCl2OMent
AlCl2OMent
AlCl2OMent
AlCl2OMent
BBr2OMent
BBr2OMent
AlCl2OMent
0.25
0.25
0.25
0.25
0.25
0.25
0.25
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
0.25
88
87
87
85
82
88
89
89
89
89
88
89
88
88
89
86
85
85
84
83
84
83
94
95
96
99
99
96
96
95
95
95
96
96
95
96
97
98
98
98
97
98
98
97
6
5
4
1
1
4
4
5
5
5
4
4
5
4
3
2
2
2
3
2
2
3
35
45
50
92
94
35
35
36
35
36
36
36
35
45
45
90
91
91
45
45
45
45
+24.8
+31.9
+35.3
+67.5
+68.2
+24.8
+24.8
+25.5
+24.8
+25.5
+25.5
+25.5
+24.8
+31.9
+31.9
+63.8
+64.8
+64.8
+31.9
+31.9
+31.9
+31.9
III
III
III
III
II
IV
V
VI
VII
VIII
IX
X
III
III
III
III
III
IV
IV
IV
IV
CH2Cl2 BBr3MentOEt
CH2Cl2
BBr(OMent)2
BBr2OMent
BBr2OMent
BBr2OMent
BBr2OMent
20 C6H5CH3
20
20
20
CCl4
CHCl3
C6H5Cl
cyclopentyl (VIII, XVII), cyclohexyl (IX, XVIII),
and cyclohex-3-enyl (X, XIX).
and chemical yields of the compounds synthesized.
The results are summarized in Table 3.
The reaction was run in a wide temperature range
from 78 to 20 C in a CH2Cl2 or C6H5CH3 solution.
The catalyst-to-dienophile molar ratio was varied from
0.25 to 0.75. The physicochemical characteristics of
adducts XI XIX synthesized are listed in Table 2.
A mixture of endo and exo isomers of XI XIX was
separated by preparative chromatography. The amount
of exo isomers was negligible; therefore, only endo
isomers of the adducts were collected, and their opti-
cal activity was examined.
We examined how various reaction parameters
affect the isomeric composition, as well as optical
Table 3 shows that, in contrast to the noncatalyzed
asymmetric Diels-Alder reaction of CPD with acrylic
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 79 No. 10 2006

ASYMMETRIC DIELS-ALDER REACTION BETWEEN ACRYLATES AND CYCLOPENTADIENE 1623
diphenophiles, for which a temperature change in-
significantly affects the optical yield of the adducts
[12], the optical yield of XI XIX significantly in-
creases at lower temperatures in the presence of
the chiral catalysts of interest. The optical yield of
adduct XII with endo configuration, synthesized at
78 C, is as high as 94%.
be attributed to formation of their complex with di-
enophiles II X. The resulting electron deficiency on
the multiple bond in dienophiles facilitates their reac-
tion with CPD:
On lowering the temperature, the stereoselectivity
of the reaction increases, and the total yield of the ad-
ducts decreases. An increase in the content of chiral
catalysts does not noticeably affect the optical yield
of XI XIX, but the total yield increases insignifi-
cantly. Table 3 also shows that the optical and total
yields of the end products are virtually unaffected
by the solvent.
Here Cat.* is a chiral catalyst.
This is confirmed by a shift of the absorption band
1
(C=O) from 1730 to 1640 cm on passing from
dienophiles to their complexes with chiral catalysts.
These data are consistent with our observation that
the absorption band of the C=O group of methacrylate
1
is shifted from 1730 to 1630 cm under the action
At the reaction parameters within the limits ex-
amined, endo isomers of the adducts are preferential-
ly formed. The isomeric composition of these adducts
was determined by gas liquid chromatography. We
found that all the Diels-Alder reactions between CPD
and acrylates yield adducts with a positive rotation
sign, as in the case of ADAR in the presence of Lewis
acids [13]. The catalytic action of chiral catalysts can
of BBr3, which suggests complexing between the cata-
lysts and dienophiles.
All the physicochemical data for adducts XI XIX
synthesized by different procedures are identical.
The composition and structure of the compounds
synthesized were confirmed by independent synthesis:
where R = Et, n-Pr, i-Pr, n-Bu, i-Bu, t-Bu, cyclopentyl, cyclohexyl, cyclohex-3-enyl.
The composition and structure of adducts XI XIX
cause of the spatial remoteness from magnetically
1
were confirmed by their IR and H NMR spectra.
anisotropic groups of the substituent. The signals from
endo isomers are significantly nonequivalent because
of the shorter distance from the substituent situated
on the rear side of the bicyclic moiety. The bridge-
head protons appear at 2.6 2.9 ppm as a multiplet.
In the IR spectra of the norbornenecarboxylates syn-
thesized, the absorption bands of the ethylene moiety
1
are observed at 1575 1550 and 3064 3040 cm
[ (C=C), (C H)]. The unusual position of the first
absorption band is attributed to the strained state of
the double bond [14]. The (C H) absorption is char-
acteristic of norbornenes, which distinguishes them
both from alkenes with the terminal double bond
To determine the optical yield of the chiral com-
pounds XI XIX, they were converted either to XXIV
by base hydrolysis or to XXV by reduction with
LiAlH4:
1
1
(3080 cm ) and from cyclohexene (3024 cm ).
More information can be derived from the 1H NMR
spectra of nonbornenes derivatives. The spectra of
the esters synthesized contain characteristic signals
due to protons of the double bond of the norbornene
moiety at 5.8 6.2 ppm. The signals from protons of
the olefin moieties of the exo isomers are close be-
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 79 No. 10 2006

1624
MAMEDOV
The optical yield of XI XIX was determined by com-
paring the specific rotation of the endo-bicyclo[2.2.1]-
hept-5-ene-2-carboxylic acid XXIV or 2-hydroxy-
methylbicyclo[2.2.1]hept-5-ene XXV synthesized with
those of the corresponding enantiomerically pure sam-
ple described by Berson et al. [15]. Based on the cor-
relation of the optical rotation sign of compounds with
the known configuration [15], the relative configura-
tion of XI XIX was determined to be 2R (+) for all
the adducts with endo configuration.
evaporated, the residue was vacuum-distilled (for con-
ditions and results see Table 3).
Independent synthesis. Bicyclo[2.2.1]hept-2-ene-
5-carboxylic acid chloride XXI [17] and bicyclo-
[2.2.1]hept-2-ene-5-carboxylic acid XXIII [19] were
prepared by known procedures. Independent synthesis
of XI XIX was carried out by the reactions of chlo-
ride XXI or acid XXIII with the corresponding
alcohols. All the physicochemical characteristics of
compounds XI XIX prepared by independent syn-
thesis are identical to those of the compounds pre-
pared by condensation of CPD with acrylates II X
(Table 2).
EXPERIMENTAL
The IR spectra were measured on a UR-20 spec-
1
1
trophotometer at 4000 400 cm , and the H NMR
spectra, on a Tesla BS-48 (80 MHz) spectrometer in
CCl4 with hexamethyldisiloxane as internal reference.
The optical rotation was measured on a Perkin Elmer-
141 polarimeter and on a Spektropol-1 spectropolar-
imeter. Preparative separation was carried out on
900 0.8-cm columns packed with Porovina + 5%
polyethylene glycol adipate; evaporator and column
temperature, 240 and 170 C, respectively; carrier gas
CONCLUSIONS
(1) Asymmetric Diels-Alder reaction of alkyl and
cycloalkyl acrylates with cyclopentadiene in the pres-
ence of chiral catalysts BBr3 MentOEt, AlCl2OMent,
BBr2OMent, and BBr(OMent)2 yields optically active
norbornenecarboxylates with R (+) configuration.
(2) As temperature is lowered, the optical yield
of norbornenecarboxylates tends to grow and reaches
94% at 78 C; with increasing temperature, the total
yield tends to grow, and the stereoselectivity, to fall.
1
(nitrogen) flow rate 200 cm3 min ; flame-ionization
detector; a Varian-Aerograph chromatograph. Chro-
matographic analysis of the compounds we synthe-
sized was performed and their purity was determined
with an LKhM-8MD chromatograph with a thermal-
conductivity detector; 300 0.3-cm column with 5%
Porovina on Dinokhrom II; carrier gas (helium) flow
(3) An increase in the content of the chiral cata-
lyst does not noticeably affect the optical yield,
but the total yield tends to increase; the solvent only
slightly affects the optical and total yields of the ad-
ducts.
1
rate 40 cm3 min ; column and evaporator tempera-
ture, 145 and 240 C, respectively.
Acryloyl chloride XX was prepared by the known
procedure [16].
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