Rh-catalyzed selective synthesis of 1,5-dimethylhexahydro-1H-inden-4(2H)-one via hydroformylation of (R)-carvone

Article abstract of DOI:10.1016/j.catcom.2018.04.018

This work reports domino hydroformylation, hydrogenation and intramolecular keto-aldol condensation reactions for the selective synthesis of 1,5-dimethylhexahydro-1H-inden-4(2H)-one obtained from (R)-carvone and dihydrocarvone under homogeneous hydroformy

Full text of DOI:10.1016/j.catcom.2018.04.018

CatalysisCommunications112(2018)21–25
Contents lists available at ScienceDirect
Catalysis Communications
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Short communication
Rh-catalyzed selective synthesis of 1,5-dimethylhexahydro-1H-inden-4(2H)-
one via hydroformylation of (R)-carvone
Sachin S. Bhagade, Bhalchandra M. Bhanage⁎
Department of Chemistry, Institute of Chemical Technology, N. P. Marg, Matunga, Mumbai 400019, India
A R T I C L E I N F O
A B S T R A C T
Keywords:
Hydroformylation
Hydrogenation
Intra-molecular keto-aldol reaction
Rhodium catalyst
This work reports domino hydroformylation, hydrogenation and intramolecular keto-aldol condensation reac-
tions for the selective synthesis of 1,5-dimethylhexahydro-1H-inden-4(2H)-one obtained from (R)-carvone and
dihydrocarvone under homogeneous hydroformylation condition. The synthesis of the desired product was
achieved by using conventional rhodium/1,3-bis(diphenylphosphino)propane (Rh/dppp) catalyst and PPTS
(pyridinium p-toluenesulfonate) as an acidic co-catalyst. The reaction conditions were optimized with respect to
various reaction parameters like time, temperature, synthesis gas (CO/H2) pressure, solvents, catalyst and co-
catalyst loading. The experimental results showed that less planner carbon backbone in dihydrocarvone in-
creases the steric hindrance around the reaction site and responsible for the reactivity difference between (R)-
carvone and dihydrocarvone.
Homogeneous catalysis
1. Introduction
= 1,5-cyclooctadiene) [7]. Vieira et al. have developed a protocol for
the synthesis of fragrance ingredient 4,8-dimethyl-bicyclo[3.3.1]non-7-
Hydroformylation of olefins is one of the excellent tool for the
synthesis of industrially important alkanals. These alkanals are im-
portant intermediates in the pharmaceuticals, agrochemicals, fra-
grances, in fuels, and for the synthesis of organic solvents [1]. Ac-
cording to techsci research report the global market of fine chemicals
obtained via hydroformylation, estimated to exceed US$ 33.27 billion
by 2025 published as “Global Oxo Chemicals Market By End Use, By
Region, Forecast & Opportunities 2011-2025” in the year october 2016
[2]. The phosphine modified cobalt or rhodium metal-based complexes
are used as a homogeneous or heterogeneous catalyst for hydro-
formylation reaction [3]. The tandem hydroformylation reaction is
known for the synthesis of compounds like acetals, amines, alcohols,
amides and amino acids [4]. Apart from various advantages of using
such integrated processes, designing of the multifunctional or multi-
catalytic system is also a challenging task for the chemists to achieve
multistep synthesis in one pot. The use of additives such as modified
cyclodextrins [5,6], surfactant and ionic liquids in enhancing the ac-
tivity, selectivity, solubility of reactant and interfacial area between
two solvents is well known in the literature. Even such systems can also
be adopted for consecutive secondary reactions in the tandem process
in hydroformylation reaction. Tetrafluoroboric acid (HBF4) was used as
an additive to increase the conversion and selectivity towards branched
amine in hydroaminomethylation of styrene with aniline catalyzed by
Rh(COD)2BF4 /dppf (1,1′-bis(diphenylphosphino)ferrocene) (COD
en-2-ol via hydroformylation followed by an intramolecular carbonyl-
ene reaction, catalyzed by rhodium complexes with PPTS as co-catalyst
[8]. Fang et al. reported the effect of acid-base co-catalyst on the con-
version and selectivity for the synthesis of ketones via hydroformyla-
tion/aldol condensation/hydrogenation using [Rh(CO)2(acac)]/naphos
(2,2′-bis(diphenylphosphinomethyl)-1,1′-binaphthyl) as a suitable cat-
alytic system [9]. Limonene aldehyde, vertral and florhydral was used
as an ingredient in perfumes, flavours, and foodstuffs industries
through hydroformylation reaction [10]. Asakawa et al. reported a
protocol for the synthesis and degradation of intense mossy odorous
liverwort sesquiterpene alcohol “tamariscol” and studied its stereo-
chemistry and absolute configuration [11]. They have success-
fully synthesized tamariscol by utilizing carbonyl compound
i.e. (1R,3aS,5R,7aS)-1,5-dimethylhexahydro-1H-inden-4(2H)-one (A)
(Scheme 1) obtained via multiple synthetic steps from (R)-carvone. This
process can be made more efficient and sustainable if one can minimize
the multiple synthetic steps using the multifunctional catalytic system
through tandem reaction. In this regard, herein we report the selective
synthesis of 1,5-dimethylhexahydro-1H-inden-4(2H)-one (1d) (Scheme
2) from (R)-carvone and dihydrocarvone using Rh/dppp as a catalyst in
the presence of PPTS co-catalyst through tandem reactions. The de-
veloped catalytic system proceeds through various reaction sequence in
one pot fashion i.e.(A) selective hydroformylation of (R)-carvone gives
(1a); (B) hydrogenation of α,β-unsaturated C]C bond of enone (1a);
⁎
Corresponding author.
E-mail address: bm.bhanage@ictmumbai.edu.in (B.M. Bhanage).
https://doi.org/10.1016/j.catcom.2018.04.018
Received 7 March 2018; Received in revised form 18 April 2018; Accepted 19 April 2018
Availableonline21April2018
1566-7367/©2018ElsevierB.V.Allrightsreserved.

S.S. Bhagade, B.M. Bhanage
CatalysisCommunications112(2018)21–25
It has been observed that change in reaction temperature significantly
affects the net conversion and selectivity of the desired product. When
the reaction was carried out at 120 °C it gave 100% conversion with
91% selectivity for compound (1d) (Table 1, entry 4). Further increase
in temperature up to 130 °C had no significant impact (Table 1, entry
5). However at 140 °C, the conversion remains same but the rate of
substrate hydrogenation was increased and gives (1e) (Table 1, entry
6). The effect of reaction temperature and pressure on the conversion
and selectivity of products under hydroformylation condition for (R)-
carvone was not studied in earlier reports [12]. In the catalyst
screening, the performance of different rhodium metal sources for
better selectivity with conversion towards desired product was tested. It
is been found that the use of [RhCl3] and [Rh(COD)Cl]2 (Table 1, en-
tries 7, 8) are not ideal for the given set of reaction sequences and gives
low i.e. 40% and 70% conversion respectively. With [RhCl3] and [Rh
(COD)Cl]2 complexes, an inhibition period always observed before
hydroformylation began. Such inhibition period in [RhCl3] and [Rh
(COD)Cl]2 complexes may be responsible for a slow formation of cat-
alytically active Rh-hydride species by hydrogenolysis and less re-
activity in the developed catalytic system. Desire results for compound
(1d) were obtained only by using [Rh(CO)2(acac)] as a rhodium metal
precursor and gives the highest selectivity up to 91% with 100% con-
version (Table 1, entry 4). The appropriate choice of ligand ancillary
was found to be a crucial step as it plays an important role in conversion
and selectivity towards formation of (1d) (Table 1, entries 9–14). The
phosphine containing aryl (PPh3 (triphenylphosphine); Table 1, entry
10), alkyl (PBu3 (tributylphosphine); PCy3 (tricyclohexylphosphine);
Table 1, entries 11, 12) backbone gave acceptable conversion but high
reactivity towards the hydrogenation leads to the generation of (1e) in
the final product and hence it eliminates their applicability for the
synthesis of (1d). Whereas the use of dppp ligand gives 97% selectivity
for (1d) shows similar conversion as of dppe (Table 1, entries 9). Use of
wide bite angle containing bulky bidentate phosphine ligand like
xantphos (4,5-bis(diphenylphosphino)-9,9-dimethylxanthene) is well-
known ligand reported for the hydroformylation chemistry and known
for its excellent selectivity towards normal aldehyde product. And
hence use of xantphos as phosphine ancillary displays very high se-
lectivity for the hydroformylation reaction and gives (1a) in the highest
ratio (Table 1, entry 13) but retards next consecutive hydrogenation
reaction of (1a) to form intermediate product (1b). The low conversion
and highest percent composition of side product (1e) in reaction mix-
ture disclose the importance of phosphine ancillary in the developed in
the present catalytic system (Table 1, entry 14). The diphosphine li-
gands are reported in the literature for hydroformylation of various
olefins and their performance in terms of conversion and selectivity is
correlated with their bite angle. We also observed results which are in
line with the reported results for other olefins. i.e. increase in conver-
sion and selectivity ratio with respect bite angle [13,14].
Scheme 1. Synthesis of tamariscol.
Scheme 2. Hydroformylation of (R)-carvone and dihydrocarvone.
(C) intramolecular keto-aldol condensation of (1b) catalyzed by PPTS;
(D) hydrogenation of α,β-unsaturated C]C bond of newly formed
enone (1c); (E) hydrogenation of both C]C bonds of carvone gives by-
product (1e); (F) hydroformylation of dihydrocarvone gives keto-al-
dehyde (1b) and (G) hydrogenation of C]C bond of dihydrocarvone
gives by-product (1e) as shown in (Scheme 2).
2. Experimental
2.1. Materials and instruments
All the materials i.e. (R)-carvone, dihydrocarvone, PPTS, rhodium
metal precursor, phosphine ligand etc. were procured from the reputed
chemical supplier and used without further purification. The quanti-
tative analysis and qualitative product formation were confirmed by
using GC–MS-QP 2010 instrument (Rtx-17, 30 m × 25 mm ID, the film
thickness(df) = 0.25 μm) (column flow 2 mL min−1, 65 °C to 240 °C at
10 °C min−1 rise). The FT-IR (Fourier Transform Infrared) spectra were
recorded on Brucker Perkin Elmer-100 spectrometer in the wavelength
range from 400 to 4000 cm−1. 1H NMR spectra of the final product (1d)
were obtained with a Bruker Avance 400 MHz NMR spectrometer with
CDCl3 as the solvent [15].
3. Results and discussion
In the next set of experiments, the effect of metal to ligand ratio was
studied (Table 1, entries 15, 16). It was observed that the decrease in
Rh/dppp ratio from 1:4 to 1:2 considerably brings down the net con-
version up to 91% and selectivity (Table 1, entry 15). However when
metal to ligand ratio increased from 1:4 to 1:6, hydrogenation reactions
get decelerate and gives intermediate (1a) and (1c) in notable con-
centration (Table 1, entry 16). From above observations, it can be
concluded that metal to ligand ratio of 1:4 is necessary for the optimal
conversion and selectivity.
The pyridinium-based organic salts like pyridinium chloride
(Py.HCl), pyridinium sulfate (Py.H2SO4) and pyridinium nitrate
(Py.HNO3) were also examined. But the promising result was obtained
with PPTS as co-catalyst (Table 2, entries 1–4). When the reaction was
carried out in the absence of co-catalyst considerable amount of inter-
mediate aldehyde (1b) was detected in the final product, this indicates
that co-catalyst is necessary to accelerate intramolecular keto-aldol
reaction to give intermediate (1c) (Table 2, entry 5). Further, it has
been observed that ligand to co-catalyst ratio in reaction medium
In the initial stage, we have optimized the reaction parameters for
the hydroformylation reaction. The hydroformylation reaction was
performed by taking (R)-carvone (600 mg, 4 mmol), Rh(CO)2(acac)
(2.58 mg, 0.01 mmol), dppe (1,2-bis(diphenylphosphino)ethane,
15.92 mg, 0.04 mmol; M/L 1:4), PPTS (5.00 mg, 0.02 mmol), synthesis
gas (CO/H2, 1:1) pressure ranging from 550 psi to 750 psi in toluene
(10 mL) at 110 °C for 24 h at 700 rpm stirring speed (Table 1, entries
1–3). At 550 psi of synthesis gas pressure, only 60% of conversion and
selectivity was observed with considerable amount intermediates (1a)
and (1c) (Table 1, entry 1). With the increase in synthesis gas pressure
from 550 psi to 650 psi, the conversion was enhanced up to 96% with
90% selectivity for 1d (Table 1, entry 2). With further increase in the
synthesis gas pressure to 750 psi leads to double hydrogenation of
starting material and gives tetrahydrocarvone (1e) (Table 1, entry 3) as
a side product. Next, the effect of temperature towards conversion of
(R)-carvone and selectivity for (1d) was studied (Table 1, entries 4–6).
22

S.S. Bhagade, B.M. Bhanage
CatalysisCommunications112(2018)21–25
Table 1
Study of CO/H2 pressure, temperature, catalyst and ligand/ratio.a
Entry
CO/H2, (1:1)psi
Temp. (°C)
Catalyst (M) (0.01 mmol)
Ligand (L) (M:L) ratio
Conv. (%)b
Selectivity(%)b
(1a)/(1b)/(1c)
(1d)
(1e)
1
2
3
4
5
6
7
8
550
650
750
650
650
650
650
650
650
650
650
650
650
650
650
650
110
110
110
120
130
140
120
120
120
120
120
120
120
120
120
120
Rh(CO)2(acac)
Rh(CO)2(acac)
Rh(CO)2(acac)
Rh(CO)2(acac)
Rh(CO)2(acac)
Rh(CO)2(acac)
RhCl3
[Rh(COD)Cl]2
Rh(CO)2(acac)
Rh(CO)2(acac)
Rh(CO)2(acac)
Rh(CO)2(acac)
Rh(CO)2(acac)
Rh(CO)2(acac)
Rh(CO)2(acac)
Rh(CO)2(acac)
dppe (1:4)
dppe (1:4)
dppe (1:4)
dppe (1:4)
dppe (1:4)
dppe (1:4)
dppe (1:4)
dppe (1:4)
dppp (1:4)
PPh3 (1:4)
PBu3 (1:4)
PCy3 (1:4)
Xantphos (1:4)
00 (00:00)
dppp (1:2)
dppp (1:6)
60
96
96
100
100
100
40
70
100
91
95
95
85
10
91
90
15:03:20
00:00: 05
00:00: 05
00:00: 00
00:00: 00
00:00: 00
02:08:15
02:03:09
00:00:00
00:00:00
00:00:00
00:00:00
80:05:00
07:10:00
05:10:05
10:05:20
60
90
85
91
91
82
61
81
97
88
83
85
10
00
65
63
02
05
10
09
09
18
14
05
03
12
17
15
05
83
15
02
9
10
11
12
13
14
15
16
a
Reaction condition: (R)-carvone (600 mg, 4 mmol), PPTS (5.00 mg, 0.02 mmol), for 24 h in solvent toluene (10 mL) with 700 rpm stirring speed.
conversion and selectivity determined using GC–MS.
b
dramatically varies reactivity and selectivity of the catalytic system.
such coordination, the rhodium catalyst remains in close vicinity with
substrate (R)-carvone and accelerates the hydroformylation reaction.
Employing NMP and DMF as a reaction media, may form monodentate
coordination with active rhodium catalyst, and reduce the reach of the
substrate with rhodium catalyst, which results in lower conversions.
Use of protic polar solvents like methanol and ethanol as reaction
medium shows good conversion (59% and 60%) and selectivity (75%
and 74%) for the expected product (1d) (Table 2, entries 13, 14).
Among toluene and 1,4-dioxane as the reaction medium, toluene pro-
vides maximum yield with 100% conversion and 97% selectivity
(Table 2, entry 4) whereas 1,4-dioxane gives only 85% conversion and
80% selectivity (Table 2, entry 10). To study time duration the reaction
was operated at different time intervals and it was found that 22 h time
is enough to carry out the 100% conversion with 97% selectivity for
desired product (Table 2, entries 15, 16).
The increase in PPTS loading from 1 to 3 equivalent with respect to the
phosphine ancillary results to deactivation of the catalytic system
(Table 2, entries 6–8). The use of excess PPTS it may undergo counter
ion-exchange (pyridine) with electron-rich phosphine ancillary in the
reaction medium which results in the formation of phosphonium p-to-
luenesulphonate salt and reduces hydroformylation activity of the
catalyst. Hence to eliminate the risk of such precipitation and to achieve
high yield, use of phosphine to PPTS in 2:1 (0.04:0.02 mmol) ratio
found desirable. The reaction works in a medium aprotic polar solvent
like tetrahydrofuran (THF) and it shows acceptable conversion and
selectivity up to 80% for (1d) (Table 2, entry 9). In N-methylpyrroli-
done (NMP) and N,N-dimethylformamide (DMF) as a reaction media,
only hydrogenated product (1e) was observed with low conversion
(Table 2, entries 11, 12). A coordination ability of the unsaturated
carbonyl compounds with rhodium catalysts in reaction medium could
account for the desired conversion in developed system. Because of
Next, the evaluation of catalyst to substrate molar ratio was carried
out (Table 3, entry 1–3). The increase in Rh/substrate molar ratio from
Table 2
Effect of co-catalyst/ratio, solvent and time study.a
Entry
Rh/dppp (ratio)
Co-catalyst (mmol)
Solvent (10 mL)
Time (h)
Conv. (%)b
Selectivity(%)b
(1a)/(1b)/(1c)
(1d)
(1e)
1
2
3
4
5
6
7
8
1:4
1:4
1:4
1:4
1:4
1:4
1:4
1:4
1:4
1:4
1:4
1:4
1:4
1:4
1:4
1:4
Py.HCl (0.02)
Py.H2SO4(0.02)
Py.HNO3 (0.02)
PPTS (0.02)
–
PPTS (0.04)
PPTS (0.08)
PPTS (0.12)
PPTS (0.02)
PPTS (0.02)
PPTS (0.02)
PPTS (0.02)
PPTS (0.02)
PPTS (0.02)
PPTS (0.02)
PPTS (0.02)
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
THF
1,4-Dioxane
NMP
DMF
MeOH
EtOH
24
24
24
24
24
24
24
24
24
24
24
24
24
24
22
20
90
91
88
100
100
60
20
00
89
85
05
13
59
60
100
91
00:02:10
00:02:10
03:05:10
00:00:00
00:75:10
00:00:05
00:00:05
00:00:00
03:05:10
03:03:11
00: 00:00
00: 00:00
14:00:06
12:00:07
00: 00:00
00: 00:00
85
86
79
97
12
92
70
00
80
80
00
00
75
74
97
97
03
02
03
03
03
03
25
00
02
03
100
100
05
07
03
03
9
10
11
12
13
14
15
16
Toluene
Toluene
a
Reaction condition: (R)-carvone (600 mg, 4 mmol), Rh(CO)2(acac) (2.58 mg, 0.01 mmol), dppp (16.50 mg, 0.04 mmol), CO/H2 (1:1, 650 psi) at temperature
120 °C with 700 rpm stirring speed.
b
conversion and selectivity determined using GC–MS.
23

S.S. Bhagade, B.M. Bhanage
CatalysisCommunications112(2018)21–25
Table 3
10 h of reaction period at different time interval qualitatively. FT-IR
data clearly reveals that after 10 h, C]CH2 bending frequency near
900 cm−1 and C]CeH stretching frequency near 3100–3000 cm−1 of
the substrate (R)-carvone was near to disappear. The broad band due to
hydrogen bonded eOH group stretching (3200–3600 cm−1) appeared
which can be attributed to β-hydroxy carbonyl intermediate generated
by intramolecular keto-aldol reaction in tandem sequence.
Study of substrate to catalyst ratio and hydroformylation of dihydrocarvone.a
Entry Rh /substrate
(ratio)
Time (h) Conv. (%)b Selectivity(%)b
(1a)/(1b)/(1c)
(1d) (1e)
1c
2c
3c
4d
5d
6d
7d
1:450
1:500
1:600
1:500
1:500
1:500
1:500
22
22
22
24
28
32
36
100
100
89
75
87
00:00:00
00:00:00
00:00:07
00:15:20
00:00:12
00:00:00
00:00:00
97
97
90
60
82
91
91
03
03
03
05
06
09
09
3.1. General procedure for the synthesis of 1,5-dimethylhexahydro-1H-
inden-4(2H)-one
97
97
a
In a typical experiment, a 100 mL high-pressure reactor charged
with (R)-carvone (750 mg, 5 mmol), Rh(CO)2(acac) (2.58 mg
0.01 mmol), dppp (16.50 mg, 0.04 mmol, L/Rh 4:1), PPTS (0.02 mmol
in 1 mL toluene) in 9 mL toluene. Was pressurized to 650 psi CO/H2
(1:1) and heated to 120 °C for 22 h with a stirring speed of 700 rpm.
After completion of the reaction, the heater was stopped and reactor
allowed cool to room temperature and existing synthesis gas was
carefully vented. The crude reaction product mixture was analyzed by
gas chromatography and mass spectrometry, concentrated under va-
cuum washed three times with 50 mL water and extracted with pet-
ether. Column chromatography with pet ether and ethyl acetate (99:1)
as running phase turn out to be excellent to obtain pure compound
(1d).
Reaction condition: Rh(CO)2(acac) (2.58 mg, 0.01 mmol), dppp (16.50 mg,
0.04 mmol, Rh/L 1:4), PPTS (5.00 mg, 0.02 mmol), CO/H2 (1:1, 650 psi) at
temperature 120 °C with 700 rpm stirring speed in solvent toluene (10 mL).
b
conversion and selectivity determined using GC–MS.
(R)-carvone as substrate.
dihydrocarvone as substrate.
c
d
400 to 500 has no significant effect and provides 100% conversion with
97% selectivity for the product (1d). However, with the extended cat-
alyst to substrate molar ratio to 1:600 lowers substrate conversion. This
difference in conversion could be due to a decreased amount of catalyst
from 0.01 mmol (Rh/(R)-carvone molar ratio 1: 500) to 0.008 mmol
(Rh/(R)-carvone molar ratio 1: 600). Hence the optimized reaction
conditions for synthesis of 1,5-dimethylhexahydro-1H-inden-4(2H)-one
(1d) are; (R)-carvone (750 mg, 5 mmol), Rh(CO)2(acac) (2.58 mg,
0.01 mmol), dppp (16.50 mg, 0.04 mmol; Rh/L 1:4), PPTS (0.02 mmol),
CO/H2 (1:1, 650 psi), time (22 h) at temperature 120 °C with 700 rpm
in 10 mL of toluene as solvent. Under the optimized reaction condition,
dihydrocarvone (a mixture of isomers) was subjected to hydro-
formylation reaction for the synthesis of 1,5-dimethylhexahydro-1H-
inden-4(2H)-one (1d) (Scheme 1). It was observed that both (R)-car-
vone and dihydrocarvone were hydroformylated regiospecifically. But
time requires to accomplishing reaction sequence for dihydrocarvone is
quite high compared to (R)-carvone. The less planner carbon backbone
could be responsible to increase steric hindrance around the reaction
site and causes longer reaction time i.e. 32 h with highest conversion
(97%) and selectivity (91%) (Table 3, entry 4–7) (Fig. 1).
4. Conclusions
In summary, this work reports an efficient and sustainable protocol
for the synthesis 1,5-dimethylhexahydro-1H-inden-4(2H)-one from (R)-
carvone using homogeneous Rh/dppp catalyst and mild acidic PPTS co-
catalyst for the first time. The developed catalytic system proceeds
through one pot (R)-carvone hydroformylation, intramolecular keto-
aldol condensation, and hydrogenation reactions sequentially. The
utilization of mild acidic pyridinium p-toluenesulfonate (PPTS) as a co-
catalyst accelerates the intramolecular keto-aldol condensation without
any unusual effect on Rh/dppp catalyst. Dihydrocarvone having less
planner carbon skeletone creats steric hindrance around the reaction
site could reduce the catalytic activity towards hydroformylation step
and takes a longer time to complete reaction sequence as compared to
(R)-carvone.
FTIR analyses of the reaction mixture were done to monitor the
intramolecular keto-aldol reaction pathway catalyzed by PPTS after
Fig. 1. FT-IR spectra of reaction mixture at different time interval.
24

S.S. Bhagade, B.M. Bhanage
CatalysisCommunications112(2018)21–25
Acknowledgment
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The author (Sachin. S. Bhagade) is grateful to acknowledge
University Grant Commission (UGC, India) for providing senior re-
search fellowship (SRF).
Appendix A. Supplementary data
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densation / hydrogenation catalysis : highly selective synthesis of ketones from
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[15] 1HNMR data of reaction product (1d) 1,5-Dimethylhexahydro-1H-inden-4(2H)-one
(1d); 1H NMR (400 MHz, CDCl3) δ 2.82–2.77 (m, 1H), 2.51–2.46 (m, 1H), 2.38–2.
31 (m, 3H), 2.24–2.19 (m, 1H), 2.14–2.04 (m, 2H), 1.76–1.70 (m, 2H), 1.44–1.31
(m, 2H), 1.15–1.01 (m, 6H).
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