Synthesis of 4-[(1R,4R)-3-oxo-p-menthan-2-ylidenemethyl]benzoic acid and its esters

Article abstract of DOI:10.1007/s11176-005-0283-1

Carbonylation of (E)-2-(4-halobenzylidene)-p-menthan-3-ones, catalyzed by PdCl₂(PPh₃)₂, gave a distereometric mixure of 4-[(1R,4R)- and (1R,4S)-3-oxo-p-menthan-2-ylidenemethyl]benzoic acids, whose reaction with phenols gave 1R,4R diastereomers of the corresponding esters. 2005 Pleiades Publishing, Inc.

Full text of DOI:10.1007/s11176-005-0283-1

Russian Journal of General Chemistry, Vol. 75, No. 4, 2005, pp. 622 627. Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 4, 2005,
pp. 659 664.
Original Russian Text Copyright
2005 by Drushlyak, Kutulya, Pivnenko, Vashchenko.
Synthesis
of 4-[(1R,4R)-3-Oxo-p-menthan-2-ylidenemethyl]benzoic Acid
and Its Esters
T. G. Drushlyak, L. A. Kutulya, N. S. Pivnenko, and V. V. Vashchenko
Institute of Monocrystals Scientific and Engineering Complex,
National Academy of Sciences of Ukraine, Kharkov, Ukraine
Received November 18, 2003
Abstract Carbonylation of (E)-2-(4-halobenzylidene)-p-menthan-3-ones, catalyzed by PdCl2(PPh3)2, gave
a distereometric mixure of 4-[(1R,4R)- and (1R,4S)-3-oxo-p-menthan-2-ylidenemethyl]benzoic acids, whose
reaction with phenols gave 1R,4R diastereomers of the corresponding esters.
4-Substituted 2-benzylidene-p-menthan-3-ones are
effective chiral components of liquid crystalline
materials used in the production of displays [1].
4-[(1R,4R)-3-oxo-p-menthan-2-ylidenemethyl]benzoic
acid esters, along with (1R,4R)-2-(4-hydroxybenzyl-
idene)-p-menthan-3-one derivatives [2] are of partic-
ular importance, since the ester group imparts to these
compounds enhanced solubility in ester liquid crystal-
line solvents that are employed in a number of prac-
tically important compositions. However, compounds
like I proved to be difficult to synthesize [6, 7] by
schemes involving crotonic or directed aldol con-
densation, that work well with other arylmethylene-p-
menthan-3-ones (see, for example, [3 5]). Therefore,
we chose another synthetic approach to (E)-4-[(1R,4R)-
3-oxo-p-menthan-2-ylidenemethyl]benzoic acid (II)
via carbonylation with carbon monoxide (III) of 2-
(4-halobenzylidene)mentan-3-ones IVa and IVb on a
palladium catalyst [scheme (1)]. This approach has
been applied to success in the synthesis of para-
substituted benzoic acids [8 12].
_
.
9
.
.
.
.
5 6
8
.
.
.
..
.
...
.
...
.
. .
7
.
a
4
1
b
.
_
.
3 2
O
O
10
(1)
O
O
O
X
11
OH
OR
IVa, IVb
II
Ia Ij
a: CO, [PdCl2(PPh3)2] or PdCl2; base (KOH or NaOH); H+ (HCl or HAc);
b: ROH, N,N -dicyclohexylcarbodiimide (V), 4-dimethylaminopyridine (VI);
I, R = CH3 (a), C6H5 (b), p-C4H9OC6H4 (c), p-C5H11OC6H4 (d), p-C6H13OC6H4 (e), p-C7H15OC6H4 (f), p-C8H17OC6H4
(g), p-C9H19OC6H4 (h), p-C10H21OC6H4 (i), 4 -C6H13-(4-C6H4C6H4) (j); IV, X = I (a), Br (b).
The mechanism of the carbonylation of halobenze-
nes, catalyzed triphenylphosphine palladium(II) com-
plexes VII, has been explored in detail by Grushin
and Alper [9]. However, the cinnamoyl groups in
compounds IVa and IVb can complicate their carbo-
nylation. We could not find examples of successful
carbonylations of such derivatives. At the same time,
it is known that the double bond in certain alkenes,
styrene, and cyclohexene is carbonylated at elevated
pressures (7 20 atm) [13]. The carbonylation of
cynnamoyl chloride, catalyzed by [PdCl2(PPh3)2],
under 50 atm resulted in quantitative formation of
4-phenyl-3-butenoic acid [14].
According to [2, 15, 16], (1R,4R)-2-arylmethylene-
p-menthan-3-ones, including IVa and IVb, can un-
dergo both acid- or base-catalyzed and thermal
epimerization (configuration inversion of the chiral C4
center) via intermediate formation of dienol VIII
[scheme (2)].
1070-3632/05/7504-0622 2005 Pleiades Publishing, Inc.

SYNTHESIS OF 4-[(1R,4R)-3-OXO-p-MENTHAN-2-YLIDENEMETHYL]BENZOIC ACID
623
(2)
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..
..
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..
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...
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...
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4
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4
1
1
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_
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O
O
H
Ar
Ar
O
Ar
cis-1R,4R
VIII
trans-1R,4R
Base-catalyzed epimerization of compounds IVa
and IVb gives rise to an equilibrium mixture of
(E)-(1R,4R)- (70 80%) and (E)-(1R,4S) diastereomers
(30 20%) [15]. In this connection we considered it
important to find out in the present work what is the
ratio of the above diastereomers, formed in carbonyla-
tion of the 1R,4R isomers of compounds IVa and IVb.
little as 10% lowed than in exp. no. 1, even though
the reaction time is increased from 5 to 50 h. Never-
theless, such conditions are much more practical in
terms of catalyst and base consumption. Note that
compounds IVa and IVb exhibit reduced reactivity,
and, therefore, they cannot be carbonylated in condi-
tions suitable for carbonylation of aryl halides with
electron-acceptor substituents, such as NO2, CN, or
Cl [solvent DMF water, catalyst Pd(OAc)2, 40 45 C]
[8]. A possible explanation for this effect is that the
electron-acceptor cinnamoyl substituent in the
benzene ring of aryl halides IVa and IVb transforms
in the basic medium into a strongly electron-acceptor
group of dienolate VIII as an actual substrate
[scheme (2)]. This suggestion is nicely consistent with
the reported fact that p-iodoanisole is carbonylated in
a much lower yield than iodobenzene in the same
conditions [9].
In view of the data in [8 12], to find conditions
for mild cabbonylation of compounds IVa and IVb
(pressure 1 atm, temperature below 100 C), we tried
three palladium catalysts: [(Ph3P)2PdCl2], Pd(OAc)2,
and PdCl2. Attempted use of Pd(OAc)2 under the
conditions described in [8] has not met with success:
No acid II was formed even when the reaction tem-
perature was raised by 20 C.
The conditions and results of the (Ph3P)2PdCl2- and
PdCl2-catalyzed carbonylations of compounds IVa
and IVb are given in the table. The best results were
obtained with (Ph3P)2PdCl2 under conditions similar
to those in [12]. The difference was that the reaction
was performed in aqueous toluene with KOH instead
of NaOH. Potassium hydroxide was preferred, since
the potassium salt of acid II is better soluble than the
sodium salt. As seen from the table, iodine derivative
IVa reacts double as fast and at a lower temperature
as bromine derivative IVb (see table, exp. nos. 1 and
4; 5, 7, and 8), which agrees with tendencies charac-
teristic of other para-substituted aryl halides [11].
With triphenylphosphine as catalyst stabilizer, the
reaction yield increases (exp. nos. 1 and 2). Decreased
catalyst (0.2% per IVa) and KOH concentrations
increase the reaction time (exp. nos. 2 and 10). At
KOH concentrations above 16.8%, more by-products
are formed [by HPLC data, 35% at a KOH concentra-
tion of 42.5%, exp. no. 3]. Therewith, isolation of the
target esterificaion products is complicated.
We also performed carbonylation in the absence of
an aromatic solvent by a procedure involving micellar
catalysis [10] (see table, exp. no. 10, system BuOH
H2O sodium lauryl sulfonate PdCl2). However, with
the system described in [10] we failed to obtain a
microemulsion with haloarene IVa, which probably
explains the unexpectedly low yield of the reaction
product.
The ratio of the 1R,4R and 1R,4S isomers resulting
from the carbonylation of compounds IVa (exp. no.
1) and IVb (exp. no. 4) was established by HPLC of
the mixture of the reaction products extracted from
the aqueous phase and esterified with methanol. It was
earlier shown that (1R,4R)-2-(4-hydroxybenzylidene)-
p-menthan-3-one is esterified under these conditions
without appreciable configuration inversion of the C4
chiral center [2]. As reference compounds in the
analysis we used the individual diastereomers ob-
tained previously by directed aldol condensation of
4-(methoxycarbonyl)benzaldehyde with ( )-menthone
The effects on the carbonylation reaction of such
factors as triphenylphosphine and base concentrations,
as well as temperature are similar to those described
in [12], namely, the yield of the target reaction
product increases in the presence of triphenylphos-
phine, the optimal concentration of KOH is 16.8%,
and the reaction slows down at temperatures below
80 C with compound IVa and 85 C with compound
IVb. Under the carbonylation conditions proposed in
[10] (see table, exp. no. 10), the yield of acids II is as
1
[6], whose structure was confirmed by H NMR [17]
and stereochemistry [(E)-(R,4S) isomer], by X-ray
diffraction analysis [18].
Thus, it was shown that carbonylation of (E)-(R,4S)-
2-(4-halobenzylidene)-p-mentan-3-ones IVa and IVb
gives a mixture of the E-1R,4R and E-1R,4S diastereo-
mers ( 2.5:1). This ratio corresponds to that in the
equilibrium mixture of the same diastereomers,
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 75 No. 4 2005

624
DRUSHLYAK et al.
Carbonylation of 2-(4-halobenzylidene)-p-menthan-3-ones IVa and IVba
Concentration
of KOH in
water, %
Exp.
no.
Time, h
(t, C)
Yield of
II, %
Substrate
Solvent (v/v)
Catalyst (concentration)
1
IVa
IVa
IVa
IVb
IVb
IVb
IVa
IVb
IVa
IVa
5(79 80) Toluene water
(75: 25)
5(79 80) Toluene water
(75: 25)
4(85 86) Toluene water
(75: 25)
10(85 86) Toluene water
(75: 25)
4(86 96) p-Xylene water
(3: 7)
9(60 64) p-Xylene water
(3: 7)
5(78 80) Benzene water
(10: 3)
10(78 80) Benzene water
(10: 3)
[(Ph3P)2PdCl2] 1 mol% perIVa + Ph3P,
16 mol/mole Pd
[(Ph3P)2PdCl2] 1 mol% per IVa
16.8
16.8
42.5
16.8
50b
50
55
46
41
34
20
1
2
3
Like in exp. no. 1
The same
4
5
[(Ph3P)2PdCl2] 1 mol% per IVa + Ph3P,
2 mol/mole Pd
Like in exp. no. 5
6
7c
8c
9d
10
Like in exp. no. 2
The same
50
21
21
19
44
50
30(80 85) BuOH water
PdCl2 (1 mol% per IVa)
[(Ph3P)2PdCl2] 0.2 mol% per IVa
2.1
(1: 10)e
50(78 82) Toluene water
(1: 2)e
1.0
a
b
c
In exp. nos. 1 6, Bu NI (5.6 mol% per IV) was used as phase-transfer catalyst. NaOH was used instead of KOH. As described
4
d
e
in [9].
As described in [10].
Sodium lauryl sulfonate was added (0.5 g per 10 ml of water).
formed upon epimerization of 2-(4-phenylbenzyl-
idene)-p-menthan-3-one in basic medium [15]. It is
indubitable that the realization under the reaction
conditions (basic medium) of the epimeric equilibrium
according to scheme (2) (with the starting halo deriva-
tives and, what is more important, with the resulting
salt of acid II) is the main reason for the formation of
the diastereomeric mixture. Similar thermal epimeriza-
tion [19] (which evidently occurs in view of increased
reaction temperature and long reaction time) can be
considered as a certain additional factor.
EXPERIMENTAL
The IR spectra were measured on a Specord M-82
1
instrument in KBr. The H NMR spectra were ob-
tained on Jeol JNM-LA-400FT-NMR (400 MHz) and
Varian Mercury VX-200 (200 MHz) spectrometers
in CDCl3 and DMSO-d6 (internal reference TMS).
The mass spectra were taken on a Finnigan-MAT-
1020 GC MS system, ionizing energy 70 eV, direct
sample inlet. The specific rotation of chiral com-
pounds ( 2D0) [(deg ml) (g dm) ] was measured on an
1
AA-10 automated polarimeter at 589 nm in chloro-
form (1 1.5 g sample/100 ml solvent).
Esterification of the diastereomeric mixture of
acids II with methanol, phenol, and substituted
phenols was performed in the presence of the system
V + VI according to [20, 21]. Individual (1R,4R)-
esters (98 99% pure) were isolated in 18 27% (per
starting phenol) by double crystallization from
2-propanol. Thus prepared methyl benzoate II is
identical to the major product of the directed aldol
condensation of 4-(methoxycarbonyl)benzaldehyde
with ( )-menthone with subsequent mild dehydration
[6].
High-performance liquid chromatography was
performed on a Milikhrom-5 microcolumn chromato-
graph in the direct and reversed-phase modes on
Silasorb-600 and Diasorb-C16T (5 m), respectively.
The eluents were 5% butyl acetate in heptane and
acetonitrile water (80:20, v/v). Detection was
performed at
260, 280, and 330 nm.
( )-Menthone was synthesized as described in [22],
p-iodobenzaldehyde was prepared from 1-(bromo-
methyl)-4-iodobenzene by the Sommelet reaction [23]
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 75 No. 4 2005

SYNTHESIS OF 4-[(1R,4R)-3-OXO-p-MENTHAN-2-YLIDENEMETHYL]BENZOIC ACID
625
and 1-(bromomethyl)-4-iodobenzene, by bromination
of p-iodotoluene with N-bromosuccinimide [24].
trum (DMSO-d6, 200 MHz), , ppm: 0.899 d, 0.961 d
(6H, C9H3, C10H3), 1.176 d (3H, C7H3), 1.865 d (4H,
C5H2, C6H2), 2.251 m (1H, H4), 2.543 m (1H, H8),
3.373 m (1H, H1), 7.088 s (1H, H11), 7.427 d (2H,
Hm), 8.105 d (2H, Ho), 9.490 s (1H, OH).
p-(n-Alkoxy)phenols (n-CnH2n+1OC6H4OH,
n = 4 10) were synthesized by a procedure similar
to that described in [25] and modified for alkyla-
tion of phenols [26], using, instead of sodium al-
coholate, 28% aqueous KOH (15 ml), that was
added dropwise over the course of 5 h to a boiling
solution of 0.1 mol of hydroquinone and 0.1 mol of
n-alkyl bromide in 25 ml of ethanol. Yield 15 25%
(yield of n-C10H21OC6H4OH 2%). n-C9H19OC6H4OH
and n-C10H21OC6H4OH were isolated from the pre-
cipitate that, like in the synthesis of n-C8H17O
C6H4OH, contains diester, after acidification and ex-
traction with chloroform. The extract was dried over
magnesium sulfate, the solvent was removed, and the
residue was distilled in a vacuum [in the case of
n-C9H19OC6H4OH, bp 186 C (8 10 mm)] and re-
crystallized from hexane. For further purification,
n-C10H21OC6H4OH was applied to Al2O3, washed
with heptane until a negative Beilstein test of
washings, eluted with 2-propanol and 5% acetic acid
in 2-propanol, freed of the solvent, and dried in a
vacuum (8 20 mm Hg).
Synthesis of a mixture of diastereomeric oxo-
menthanylidenemethylbenzoic acids II from 2-(4-
bromobenzylidene)-p-menthan-3-one (IVb). To a
solution of 2 g of compound IVb in 15 ml of toluene,
257 mg of triphenylphosphine, 128 mg of tetrabutyl-
ammonium iodide, 43 mg of [(Ph3P)2PdCl2] (1 mol%
per IVb), and 4.7 ml of 16.7% aqueous KOH were
added in succession. The system was purged with CO
in triplicate and then heated with vigorous stirring at
86 C under CO until reaction completion (8 10 h,
control by TLC). Further workup was performed as
described above. Yield 34%.
Esterification of 4-[(1R,4R)-3-oxo-p-menthan-2-
ylidenemethyl]benzoic acid (II) with methanol.
Stereoisomeric mixture II and 20 mg of compound
VI were added to a solution of 0.06 ml of dry me-
thanol in 7.5 ml of dry dichloromethane. After cooling
to 0 C, diimide V, 317 mg, was added, and the mix-
ture was stirred in moisture-proof conditions for 1 h
at 0 C, for 6 h without cooling, left to stand for 14 h
at room temperature, filtered through a bed (1 cm) of
silica gel, and the solvent was removed by distillation.
Individual methyl (E)-4-[(1R,4R)-3-oxo-p-menthan-2-
ylidenemethyl]benzoate (Ia) was isolated by double
crystallization from methanol; yield 19%, purity 99%
(by HPLC). The melting point (73 74 C) and spectral
data are consistent with those reported in [6].
n-C6H13C6H4C6H4OH was synthesized as descri-
bed in [27].
(E)-(1R,4R)-2-(4-iodobenzylidene)-p-menthan-3-
one (IVa) was synthesized like bromo derivative IVb
[5, 15] by condensation of p-iodobenzaldehyde with
( )-menthone in DMSO CsOH H2O or DMSO
Bu4NOH (30% aqueous) (0.1 mol base/mole
menthone) at 18 C, yield 48% (after crystallization
from ethanol), mp 87 88 C.
Esterification of 4-[(1R,4R)-3-oxo-p-menthan-2-
ylidenemethyl]benzoic acid (II) with phenols. A
mixture of 2.3 mmol of stereisomeric mixture II and
0.25 mmol of compound VI were added to a solution
of 2.3 mmol of phenol in 7.5 ml of dry dichloro-
methane. After cooling to After cooling to 0 C, di-
imide V, 2.53 mmol, was added, and the mixture was
stirred in moisture-proof conditions for 1 h at 0 C,
6 8 h without cooling, left to stand for 14 h at room
temperature, and filtered through a bed (1 cm) of
silica gel. The solvent was removed from the filtrate
ba distillation, and the residue was doubly crystallized
from 2-propanol.
Synthesis of a mixture of diastereomeric oxo-
menthanylidenemethylbenzoic acids II from (E)-
(1R,4R)-2-(4-iodobenzylidene)-p-menthan-3-one
(IVa). To a solution of 4 g of compound IVa in 28
ml of toluene, 448 mg of triphenylphosphine, 224 mg
of tetrabutylammonium iodide, 76 mg of dichlorobis-
(triphenylphosphine)palladium (1 mol% per IVa),
8.2 ml of 16.8% aqueous KOH were added in succes-
sion. The system was purged with CO in triplicate and
then heated with vigorous stirring at 79 80 C under
CO until reaction completion (4 5 h, control by
TLC). The layers were separated, and the aqueous
layer was acidified with acetic acid to pH 4. The pre-
cipitate that formed was filtered off, washed with
water and benzene, and dried at a temperature of no
higher than 30 C, yield 55%. The reaction product
was brought into esterification without further purifica-
tion. Individual acid II was isolated from the resulting
stereoisomeric mixture by crystallization from
p-(Decyloxy)phenyl ester Ii was prepared from
individual (1R,4R)-II and isolated by double crystal-
lization from methanol hexane (4:1).
Phenyl (E)-4-[(1R,4R)-3-oxo-p-menthan-2-
ylidenemethyl]benzoate (Ib). Yield 21%, mp 129
1
130 C. IR spectrum, , cm : 1727 (ester C=O), 1678
1
benzene, yield 14%, mp 169 170 C. H NMR spec-
(ketone C=O), 1618; 1602 (aryl C=C). Mass spectrum,
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 75 No. 4 2005

626
DRUSHLYAK et al.
m/z: 362 [M]+, 269, 241, 227, 198, 183, 171, 155,
p-(Heptyloxy)phenyl (E)-4-[(1R,4R)-3-oxo-p-
menthan-2-ylidenemethyl]benzoate (Id). Yield 37%,
mp 88 89 C. H NMR spectrum, , ppm (DMSO-d6,
20
1
141, 128, 115, 94, 77, 65.
118.45 . H NMR
spectrum, , ppm (CDCl3, 400DMHz), , ppm: 0.981,
0.919 t (6H, C9H3, C10H3, J 6.8 Hz), 1.195 t (3H,
C7H3, J 7.0 Hz), 1.784 1.960 m (4H, C5H2, C6H2),
2.269 m (1H, C4H, J 12.3, 6.2, 3.4 Hz), 2.559 sept.d
(1H, C8H, J 6.8, 3.4 Hz), 3.407 m (1H, C1H, J 7.0,
4.2, 2.2 Hz), 7.118 s (1H, 11H), 7.218 d (2H, Ho , J
8.5 Hz), 7.286 t (1H, Hp ), 7.446 t (2H, Hm , J 8.5 Hz),
7.467 d (2H, Ho, J 8.5 Hz), 8.205 d (2H, Hm, J
8.5 Hz).
1
200 MHz), , ppm : 0.879 t (3H, CH3), 0.944 d,
0.862 d (6H, C9H3, C10H3), 1.112 d (3H, C7H3),
1.294 m (8H, (CH2)4), 1.726 m (2H, CH2), 1.824 m
(4H, C5H2, C6H2), 2.338 m (2H, C4H, C8H), 3.379
m (1H, C1H), 3.984 t (2H, OCH2), 6.980 d (2H, Hm ),
7.016 s (1H, C11H), 7.177 d (2H, Ho ), 7.590 d (2H,
Hm), 8.135 d (2H, Ho).
p-(Octyloxy)phenyl (E)-4-[(1R,4R)-3-oxo-p-
menthan-2-ylidenemethyl]benzoate (Ig). Yield 28%,
p-Butoxyphenyl (E)-4-[(1R,4R)-3-oxo-p-
menthan-2-ylidenemethyl]benzoate (Ic). Yield 33%,
1
mp 79 80 C. IR spectrum, , cm : 1725 (ester C=O),
1
1680 (ketone C=O), 1602 (aryl C=C). Mass spectrum,
mp 108 109 C. H NMR spectrum, , ppm (DMSO-
m/z: 490 [M]+, 269, 241, 227, 198, 171, 155, 141,
d6, 200 MHz), , ppm : 0.946 t (3H, CH3), 0.964 d,
0.864 d (6H, C9H3, C10H3), 1.116 d (3H, C7H3),
1.445 m (4H, CH2CH2), 1.837 m (4H, C5H2, C6H2),
2.350 m (2H, C4H, C8H), 3.383 m (1H, C1H), 3.995 t
(2H, OCH2), 6.997 d (2H, Hm ), 7.013 s (1H, C11H),
7.184 d (2H, Ho ), 7.595 d (2H, Hm), 8.136 d (2H, Ho).
20
D
1
128, 115, 69.
56.46. H NMR spectrum, , ppm
(DMSO-d6, 400 MHz), , ppm : 0.883 t (3H, CH3),
0.944 d, 0.948 d (6H, C9H3, C10H3), 1.120 d (3H,
C7H3), 1.297 m [10H, (CH2)5], 1.725 m (2H, CH2),
1.828 m (4H, C5H2, C6H2), 2.355 m (2H, C4H, C8H),
3.387 m (1H, C1H), 3.988 t (2H, OCH2), 6.990 d (2H,
Hm ), 7.024 s (1H, C11H), 7.182 d (2H, Ho ), 7.595 d
(2H, Hm), 8.140 d (2H, Ho).
p-Pentyloxyphenyl (E)-4-[(1R,4R)-3-oxo-p-
menthan-2-ylidenemethyl]benzoate (Id). Yield 66%,
purity 99% (by HPLC), mp 107 108 C. IR spectrum,
1
p-(Nonyloxy)phenyl (E)-4-[(1R,4R)-3-oxo-p-
menthan-2-ylidenemethyl]benzoate (Ih). Yield 42%,
, cm : 1726 (ester C=O), 1675 (ketone C=O), 1599
(aryl C=C). Mass spectrum, m/z: 448 [M]+, 269, 241,
1
20
mp 76 78 C. H NMR spectrum, , ppm (DMSO-d6,
227, 198, 171, 155, 141, 128, 115, 91, 81, 69.
96.75 . 1H NMR spectrum, , ppm (CDClD3,
400 MHz), , ppm : 0.941 t (3H, CH3, J 7.0 Hz),
0.980 d, 0.918 d (6H, C9H3, C10H3, J 6.8 Hz), 1.189 d
(3H, C7H3, J 7.0 Hz), 1.426 m (4H, CH2CH2),
1.800 m (2H, CH2, 1.866 1.937 m (4H, C5H2, C6H2),
2.267 m (1H, C4H, J 12.3, 6.2, 3.4 Hz), 2.554 sept.d
(1H, C8H, J 6.8, 3.4 Hz), 3.400 m (1H, C1H, J 7.0,
4.2, 2.2 Hz), 3.963 t (2H, OCH2, J 6.7 Hz), 6.931 d
(2H, Hm , J 8.5 Hz), 7.111 d (2H, Ho , J 8.5 Hz),
7.114 s (1H, C11H), 7.456 d (2H, Ho, J 8.5 Hz),
8.186 d (2H, Hm, J 8.5 Hz).
200 MHz), , ppm : 0.870 t (3H, CH3), 0.946 d,
0.964 d (6H, C9H3, C10H3), 1.117 d (3H, C7H3),
1.288 m [12H, (CH2)6], 1.727 m (2H, CH2), 1.830 m
(4H, C5H2, C6H2), 2.356 m (2H, C4H, C8H), 3.383 m
(1H, C1H), 3.982 t (2H, OCH2), 6.982 d (2H, Hm ),
7.020 s (1H, C11H), 7.178 d (2H, Ho ), 7.594 d (2H,
Hm), 8.137 d (2H, Ho).
p-(Decyloxy)phenyl (E)-4-[(1R,4R)-3-oxo-p-
menthan-2-ylidenemethyl]benzoate (Ii). Yield 55%,
1
mp 78 79 C. H NMR spectrum, , ppm (DMSO-d6,
200 MHz), , ppm : 0.865 t (3H, CH3, J 6.5 Hz),
0.948 d, 0.867 d (6H, C9H3, C10H3, J 6.9 Hz), 1.120 d
(3H, C7H3, J 7.0), 1.272 m [14H, (CH2)7], 1.713 m
(2H, CH2), 1.658 1.856 m (4H, C5H2, C6H2),
2.354 m (2H, C4H, C8H), 3.384 m (1H, C1H), 3.984 t
(2H, OCH2, J 6.4 Hz), 6.981 d (2H, Hm , J 8.5 Hz),
7.023 s (1H, C11H), 7.185 d (2H, Ho , J 8.5 Hz),
7.596 d (2H, Hm, J 8.5 Hz), 8.137 d (2H, Ho, J
8.5 Hz).
p-(Hexyloxy)phenyl (E)-4-[(1R,4R)-3-oxo-p-
menthan-2-ylidenemethyl]benzoate (Ie). Yield 21%,
1
mp 96 97.5 C. IR spectrum, , cm : 1730 (ester
C=O), 1678 (ketone C=O), 1599 (aryl C=C). Mass
spectrum, m/z: 462 [M]+, 269, 241, 227, 198, 171,
20
D
1
155, 128, 115, 69.
92.91. H NMR spectrum, ,
ppm (CDCl3, 400 MHz), , ppm : 0.911 t (3H, CH3,
J 6.9 Hz), 0.980 d, 0.917 d (6H, C9H3, C10H3),
1.188 d (3H, C7H3, J 7.0 Hz), 1.790 m (2H, CH2),
1.865 1.937 m (4H, C5H2, C6H2), 2.265 m (1H, C4H,
J 12.3, 6.2, 3.4 Hz), 2.553 sept.d (1H, C8H, J 6.8,
3.4 Hz), 1.343 1.504 m (6H, CH2CH2CH2), 3.402 m
(1H, C1H, J 7.0, 4.2, 2.2 Hz), 3.961 t (2H, OCH2, J
6.7 Hz), 7.110 d (2H, Ho , J 8.5 Hz), 7.114 s (1H,
C11H), 7.456 d (2H, Ho, J 8.5 Hz), 7.930 d (2H, Hm ,
J 8.5 Hz), 8.185 d (2H, Hm, J 8.5 Hz).
p-[p-(Hexylphenyl]phenyl (E)-4-[(1R,4R)-3-oxo-
p-menthan-2-ylidenemethyl]benzoate (Ij). Yield
1
22%, mp 104 172 C (meso phase). H NMR spec-
trum (CDCl3, 200 MHz), , ppm : 0.898 t (3H, CH3),
0.978 d, 0.916 d (6H, C9H3, C10H3), 1.193 d (3H,
C7H3), 1.330 m [6H, (CH2)3], 1.622 m (2H, CH2),
1.885 m (4H, C5H2, C6H2), 2.270 m (1H, C4H),
2.560 m (1H, C8H), 2.649 t (2H, CH2), 3.411 m (1H,
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 75 No. 4 2005

SYNTHESIS OF 4-[(1R,4R)-3-OXO-p-MENTHAN-2-YLIDENEMETHYL]BENZOIC ACID
627
C1H), 7.120 s (1H, C11H), 7.477 d (2H, Hm ), 7.507 d
(2H, Hm), 7.633 d (2H, Ho ), 8.221 d (2H, Ho).
14. Yamamoto, A., Bull. Chem. Soc. Jpn., 1995, vol. 68,
no. 2, p. 433.
15. Vashchenko, V.V., Cand. Sci. (Chem.) Dissertation,
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