Synthesis of new chiral monodentate aminophosphinites and their use in catalytic asymmetric hydrogenations

Article abstract of DOI:10.1016/S0022-328X(03)00223-7

A general synthesis of chiral 4-amino-4,5-dihydro-3H- dinaphthophosphepines 5a-f is described. The resulting monodentate chiral aminophosphinites have been tested in the rhodium-catalyzed asymmetric hydrogenation of methyl α-acetamidocinnamate and methyl

Full text of DOI:10.1016/S0022-328X(03)00223-7

Journal of Organometallic Chemistry 675 (2003) 91ꢀ96
/
www.elsevier.com/locate/jorganchem
Synthesis of new chiral monodentate aminophosphinites and their use
in catalytic asymmetric hydrogenations
Kathrin Junge a, Gunther Oehme a, Axel Monsees b, Thomas Riermeier b,
¨
Uwe Dingerdissen b, Matthias Beller a,*
a Leibniz Institut fur Organische Katalyse (IfOK), Buchbinderstrasse 5-6, 18055 Rostock, Germany
¨
b Degussa AG, Projecthouse Catalysis, Industriepark Hochst, D-65296 Frankfurt am Main, Germany
¨
Received 2 February 2003; received in revised form 10 March 2003; accepted 10 March 2003
Abstract
A general synthesis of chiral 4-amino-4,5-dihydro-3H-dinaphthophosphepines 5aꢀf is described. The resulting monodentate
/
chiral aminophosphinites have been tested in the rhodium-catalyzed asymmetric hydrogenation of methyl a-acetamidocinnamate
and methyl a-acetamidoacrylate. Enantioselectivities up to 96% ee were obtained in the presence of 5a and sodium dodecylsulfonate
in toluene.
# 2003 Elsevier Science B.V. All rights reserved.
Keywords: Chiral aminophosphinites; Enantioselectivities; Toluene
1. Introduction
genations [7]. In general, monodentate phosphites and
phosphoramidites are attracting most interest. However,
the monodentate phosphines and phosphinites are also
interesting due to their often easier synthesis compared
to the corresponding bidentate ligands.
In homogeneous catalysis the performance of the
respective metal catalyst is largely dependent on the
surrounding ligands. Despite the recent development of
new ligand classes, such as carbenes [1], still P-based
compounds constitute the most important class of
ligands for late transition metals. In asymmetric cata-
lysis especially bidentate phosphine ligands have been
found to give excellent control in a number of catalytic
asymmetric reactions [2]. Among the different transition
metal-catalyzed enantioselective reactions, hydrogena-
tions of olefins, imines and ketones are the most
important in industry. Until very recently, optically
active diphosphines were essential as chiral ligands in
order to achieve high selectivities in these reactions.
Based on the important discovery by Reetz (phosphites
1) [3], de Vries and co-workers (phosphoramidites 2) [4],
Pringle and Claver (phosphonites 3) [5] and others [6]
nowadays monodentate ligands (Scheme 1) have become
increasingly important for catalytic asymmetric hydro-
Parallel to the work of Zhang [8] and Gladiali [9], we
have introduced last year new monodentate phosphines
based on
a
4,5-dihydro-3H-dinaphtho[2,1-c;1?,2?-
e]phosphepine structure 4 [10]. Similar to phosphites
and phosphoramidites these ligands give high enantios-
electivities (up to 95% ee) in the hydrogenation of
dehydroamino acid methyl esters and methyl itaconate,
which are typical benchmark tests for asymmetric
hydrogenations.
Having a reliable synthesis route for phosphepine
ligands 4 in hand, we wondered whether related
aminophosphinites based on the structure of 4 would
be easily accessible and induce high enantioselectivities
in benchmark hydrogenation reactions. With the excep-
tion of the description of the diethylamino derivative 5b
[10], such aminophosphinites have not been disclosed in
the literature so far. Here, we report a straightforward
synthesis of six aminophosphinites 5aꢀ
data on the rhodium-catalyzed hydrogenation of methyl
a-acetamidocinnamate in the presence of 5aꢀf.
/
f and preliminary
* Corresponding author. Tel.:
4669324.
E-mail address: matthias.beller@ifok.uni-rostock.de (M. Beller).
ꢁ
/
49-381-466930; fax:
ꢁ49-381-
/
/
0022-328X/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00223-7

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K. Junge et al. / Journal of Organometallic Chemistry 675 (2003) 91ꢀ96
/
Double metallation of 2,2?-dimethylbinaphthyl with
n-butyl lithium in the presence of TMEDA (tetra-
methylethylene diamine) [12] and quenching with com-
mercially available dichloro(N,N-dimethylamino)pho-
sphine or dichloro(N,N-diethylamino)phosphine gave
5aꢀ
/
b in 72ꢀ80% yield [13]. In order to access other
/
aminophoshinites, 5b was subsequently reacted with
HCl to give the corresponding chlorophosphepine 6 in
80% yield. It is worth mentioning that the chloropho-
sphepine 6 is also a useful building block for the
synthesis of a variety of substituted 4,5-dihydro-3H-
dinaphtho[2,1-c;1?,2?-e]phosphepines
4
by simple
Grignard reaction. Ligands 5cꢀf were prepared by the
/
reaction of 6 and an excess of the corresponding amine
(N,N-diisopropylamine, azetidine, piperidine, pyrrole).
However, in most reactions varying amounts of by-
products were produced, which could not be removed by
standard purification procedures. Hence, the corre-
sponding aminodichlorophosphines were prepared by
the reaction of azetidine, piperidine, pyrrole and PCl3 as
described by Harris and co-workers [13]. Next, double
lithiation of 2,2?-dimethylbinaphthyl and quenching
Scheme 1. Selection of recent developments of monodentate P-ligands.
2. Results
At the start of our investigations we envisioned the
preparation of different 4-amino-4,5-dihydro-3H-di-
naphtho[2,1-c;1?,2?-e]phosphepine ligands 5 based on
our previously established route for ligands 4. So far,
only the 4-diethylamino derivative 5b was prepared, but
has not been investigated in catalytic reactions. As
shown in Scheme 2 six different 4-amino-4,5-dihydro-
3H-dinaphtho[2,1-c;1?,2?-e]phosphepine ligands were
synthesized either directly or in a three-step sequence
from homochiral 2,2?-dimethylbinaphthyl [11].
with aminodichlorophosphines led to 5dꢀ
/
f in 62ꢀ75%
/
yield.
Having the desired ligands in hand we were interested
in their catalytic behaviour. As a model reaction the
asymmetric hydrogenation of methyl (Z)-a-acetamido-
cinnamate 7 was studied at ambient pressure (Table 1).
This reaction is generally accepted as a benchmark
Scheme 2. General synthesis of 4-amino-4,5-dihydro-3H-dinaphtho[2,1-c;1?,2?-e]phosphepine ligands 5.

K. Junge et al. / Journal of Organometallic Chemistry 675 (2003) 91ꢀ
/
96
93
Table 1
Asymmetric hydrogenation of methyl a-acetamidocinnamate 7
Entry
Liganda
Solvent
t/2 [min]b
Conv. [%]
ee [%] (R)
1
5a
5a
5a
5ac
5ad
5b
5b
5b
5cc
5c
Toluene
Ethyl acetate
THF
11
2
100
100
100
100
100
100
100
100
15
95
92
90
96
93
84
78
90
26
9
2
3
1
4
Toluene/SDS
Toluene/SDS
Toluene
10
21
5
5
6
7
Ethyl acetate
Toluene/SDS
Toluene
5
43
8
9
ꢀ/
ꢀ/
ꢀ/
5
10
11
12
13
14
15
16
17
Ethyl acetate
Toluene
43
59
5d
5d
5e
42
42
84
73
83
60
52
Ethyl acetate
Toluene
100
100
98
15
28
29
7
5e
Ethyl acetate
Toluene/SDS
Toluene
5ec
5fe
5fe
75
100
100
Ethyl acetate
4
a
Conditions: 1 mmol substrate; 0.01 mmol [Rh(COD)2]BF4; cat.:ligandꢂ1:2; 15 ml solvent; 25 8C.
/
b
c
Halftime of hydrogenation.
Conditions likeaꢁ
0.2 mmol SDS.
1 mmol: 0.005 mmol: 0.011 mmolꢁ
Prepared catalyst [Rh(COD)L2]BF4; Lꢂ5f.
/
d
e
Subst.: Rh: 5aꢂ
/
/
0.2 mmol SDS.
/
hydrogenation test for new chiral ligands. Most catalytic
tests were run with 1.0 mmol of substrate in 15 ml
solvent in the presence of 1.0 mol% of rhodium catalyst
at 25 8C and 1 bar of hydrogen. In general a P/Rh ratio
of 2:1 was employed. In most cases the hydrogenations
were finished within 1 h, showing the reasonable
activities of the catalyst systems.
From the different solvents tested in the asymmetric
hydrogenation of methyl a-acetamidocinnamate in the
presence of 5a (Table 1, entries 1ꢀ5) toluene gave the
/
best enantioselectivities. However, faster reactions were
observed in ethyl acetate and THF. The addition of a
tenside (sodium dodecylsulfateꢂ
solution improved the enantioselectivity further on [14].
Next, the combination of [Rh(COD)2]BF4/5aꢀf was
/SDS) to the toluene
/
Although there is a close structural relationship
used as catalyst precursor in asymmetric hydrogenations
of methyl a-acetamidoacrylate 9 (Table 2). Except for 5c
all ligands led to excellent conversion. Best enantios-
electivities (up to 71% ee) were obtained in the presence
of 5a in THF as solvent. In contrast to the hydrogena-
tion of methyl a-acetamidocinnamate 7 (Table 1) only
low ee’s were obtained for methyl a-acetamidoacrylate 9
using toluene as solvent. Hence, most experiments were
carried out in THF and ethyl acetate.
between 5aꢀf and our recently synthesized ligand class
/
4 [10], ligands with similar steric dimension behave quite
different, e.g. 5a gave 95% ee (Table 1, entry 1), while
the corresponding (and sterically related) 4-isopropyl-
4,5-dihydro-3H-dinaphtho[2,1-c;1?,2?-e]phosphepine
gave only 46% ee under similar conditions. As can be
seen from Table 1 only aminophosphonites with small
alkyl groups attached to the nitrogen atom gave good to
very good enantioselectivities in the model reaction. In
contrast ligands 4 with alkyl groups attached to the
phosphorus atom gave low enantioselectivities. Some-
what surprisingly the azetidinyl-substituted aminopho-
sphinite 5d gave a low enantioselectivity, which we
cannot explain at present. In general, the new ligands
5 resemble in their catalytic behavior much more the
synthesized phosphoramidates 2 of de Vries and Fer-
3. Conclusion
There is a continuing interest in the synthesis and
application of new monodentate P-ligands, which can be
modularly designed. Here, we describe for the first time
a general synthesis of chiral 4-amino-4,5-dihydro-3H-
dinaphthophosphepines 5 from 2,2?-dimethylbinaphthyl
inga. Hence, the presence of PÃ
/
N bond has a significant
influence on the enantioselectivity of the reaction.

94
K. Junge et al. / Journal of Organometallic Chemistry 675 (2003) 91ꢀ96
/
Table 2
Asymmetric hydrogenation of methyl a-acetamidoacrylate 9
Entry
Liganda
Solvent
t/2 [min]b
Conv. [%]
ee [%]
1
5a
5a
5b
5b
5c
5c
5d
5d
5e
5e
5fc
5fc
THF
Ethyl acetate
THF
4
100
100
100
100
21
71 (R)
62 (R)
62 (R)
57 (R)
1 (S)
2
2
3
8
10
4
Ethyl acetate
THF
5
ꢀ
ꢀ
540
600
20
25
3
/
6
Ethyl acetate
THF
/
29
91
14 (R)
40 (R)
32 (R)
53 (R)
52 (R)
58 (R)
58 (R)
7
8
Ethyl acetate
THF
90
9
100
100
100
100
10
11
12
Ethyl acetate
THF
Ethyl acetate
2
a
Conditions: 1 mmol substrate; 0.01 mmol [Rh(COD)2]BF4; cat.:ligandꢂ1:2; 15 ml solvent; 25 8C.
Halftime of hydrogenation.
/
b
c
Catalyst [Rh(COD)L2]BF4; Lꢂ
/5f.
via double metallation and subsequent quenching with
aminodichlorophosphines. Applying this straightfor-
obtained in general in pure form. If necessary further
purification can be achieved by recrystallization from
toluene.
ward sequence ligands 5aꢀf are accessible in good yields
/
in g-quantities. Preliminary catalytic testing of the new
ligands in two well-known asymmetric hydrogenation
reactions reveal the usefulness of these ligands. For
example ligand 5a induces one of the highest enantios-
electivities ever reported with monodentate ligands for
this benchmark reactions. In addition, having ligands 5
available, a missing link between ligand classes 2 and 4
has been closed. Hence, it should be possible in future to
understand and develop more rationally new ligands
based on the actual dinaphtho[2,1-c;1?,2?-e]phosphepine
structure.
4.1.1. 4-Dimethylamino-4,5-dihydro-3H-dinaphtho[2,1-
c;1?,2?-e]phosphepine (5a)
Pale yellow solid, 80% yield. 1H-NMR (25 8C,
CD2Cl2): dꢂ
2.93 (d, CH2, 1H); 3.01 (d, CH2, 1H); 7.08 (d, 1H), 7.17ꢀ
7.21 (m, 4H), 7.36ꢀ7.42 (m, 1H), 7.55ꢀ7.61 (m, 2H),
7.87ꢀ 32.3
7.93 (m, 4H). 13C-NMR (25 8C, CD2Cl2): dꢂ
(d, CH2, Jꢂ 17.2 Hz), 35.7 (d, CH2, Jꢂ31.5 Hz), 41.8
(d, CH3N, Jꢂ14.35 Hz), 125.1 (d), 126.1 (d), 126.9 (d),
128.1 (d), 128.3, 128.5 (d), 129.3 (d), 132.5 (d), 133.2 (d),
136.0 (d). 31P-NMR (25 8C, CD2Cl2): dꢂ
76.8. MS (ES,
70 eV): m/zꢂ
355 [Mꢁ], 312, 265, 184, 132, 76, 60.
/2.50 (d, CH3, 6H), 2.80 (t, CH2, 2H),
/
/
/
/
/
/
/
/
/
/
4. Experimental
4.1.2. 4-Diethylamino-4,5-dihydro-3H-dinaphtho[2,1-
c;1?,2?-e]phosphepine (5b)
4.1. General procedure for the synthesis of ligands 5aꢀf
/
White solid, 72% yield. 1H-NMR (25 8C, CD2Cl2):
Metallation of chiral 2,2?-dimethylbinaphthyl with n-
BuLi/TMEDA affords the crystalline dilithio species in
dꢂ
Hz), 2.82ꢀ
Jꢂ11.5 Hz); 7.12ꢀ
7.56 (d, 1H), 7.89ꢀ
CD2Cl2): dꢂ15.3 (CH3), 33.5 (d, CH2Ã
38.2 (d, CH2ÃP, Jꢂ30.5 Hz), 44.1 (d, CH2Ã
/
1.01 (t, CH3, 6H), 2.63ꢀ
2.88 (m, CH2, 5H); 3.03ꢀ
7.24 (m, 4H), 7.37ꢀ
7.95 (m, 4H). 13C-NMR (25 8C,
P, Jꢂ 18.1 Hz),
N, Jꢂ13.3
/
2.71 (q, CH2, 1H, Jꢂ
3.06 (d, CH2, 1H,
7.44 (m, 2H),
/
14.5
/
/
60ꢀ/70% yield. Starting from 12.0 mmol dilithium salt of
/
/
/
chiral 2,2?-dimethylbinaphthyl in 35 ml hexane 13.6
mmol of the corresponding amino dichlorophosphine in
15 ml hexane was added at 0 8C. After 2 h of reflux,
hexane was replaced by 40 ml toluene to separate the
formed LiCl. The obtained filtrate was evaporated. The
residue was diluted with 10 ml dry acetone and 40 ml
hexane were added to produce a small precipitate. After
filtration and evaporation of the solvent ligands 5 were
/
/
/
/
/
/
/
/
Hz), 125.0 (d), 126.1 (d), 126.9, 128.2 (d), 128.5 (d),
128.7 (d), 132.5 (d), 133.4 (d), 134.3 (d) 136.1 (d). 31P-
NMR (25 8C, CD2Cl2): dꢂ
/
73.2. MS (ES, 70 eV): m/zꢂ
/
383 [Mꢁ], 340, 312, 297, 276, 265, 183, 138, 102, 74, 58,
46, 28.

K. Junge et al. / Journal of Organometallic Chemistry 675 (2003) 91ꢀ
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96
95
4.1.3. 4-Diisopropylamino-4,5-dihydro-3H-
dinaphtho[2,1-c;1?,2?-e]phosphepine (5c)
Yellow oil, 68% yield. H-NMR (25 8C, CDCl3): dꢂ
4.1.7. 4-Chloro-4,5-dihydro-3H-dinaphtho[2,1-c;1?,2?-
e]phosphepine (6)
1
/
White solid, 80% yield. 1H-NMR (25 8C, CDCl3): dꢂ
/
1.21 (d, CH3, 12H), 2.40 (d, CH2, 2H), 2.64ꢀ
CH2, 2H), 3.03ꢀ3.12 (sept, CH, 2H), 7.13ꢀ7.31 (m, 4H),
7.37ꢀ7.43 (m, 2H), 7.55 (d, 1H), 7.63 (d, 1H), 7.88ꢀ7.95
(m, 4H). 13C-NMR (25 8C, CDCl3): dꢂ
23.9 (CH3, Jꢂ
4.5 Hz), 32.8 (d, CH2, Jꢂ 17.2 Hz), 36.8 (d, CH2, Jꢂ
28.6 Hz), 46.7 (d, CH, Jꢂ5.7 Hz), 124.8, 125.9 (d),
126.0, 127.1 (d), 127.9, 128.2 (d), 128.4 (d), 132.4 (d),
132.6 (d) 134.2 (d). 31P-NMR (25 8C, CDCl3): dꢂ
46.0.
MS (ES, 70 eV): m/zꢂ
411 [Mꢁ], 354, 312, 282, 265,
185, 126, 86, 44.
/
2.87 (m,
2.65ꢀ
7.18 (m, 4H), 7.32ꢀ
13C-NMR (25 8C, CDCl3): dꢂ
Hz), 41.4 (d, CH2, Jꢂ 71.5 Hz), 124.8, 125.6, 126.0,
127.4, 127.9, 128.3, 128.7, 131.9, 132.2, 132.7. 31P-NMR
(25 8C, CDCl3): dꢂ115,1. MS (CI, Isobutan): m/zꢂ
347 [Mꢁꢁ
1], 329, 311, 283, 275, 154, 93, 67.
/
2.71 (m, CH2, 2H), 2.92ꢀ
7.43 (m, 4H), 7.80ꢀ
40.3 (d, CH2, Jꢂ
/
3.25 (m, CH2, 2H), 7.11ꢀ
7.84 (m, 4H).
72.4
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
4.2. Preparation of the Rh(II) complex of 5f
A solution of ligand 5f (2.4 mmol) in THF (7 ml) was
added dropwise to a stirred solution of Rh(COD)acac
(1.2 mmol) in the same solvent (5 ml). After 1 h at 20 8C
etheric HBF4 (1.2 mmol) is added and the solution is
stirred for an additional hour. The solvent was removed
4.1.4. 4-Azetidinyl-4,5-dihydro-3H-dinaphtho[2,1-
c;1?,2?-e]phosphepine (5d)
Yellow solid, 65% yield. H-NMR (25 8C, CDCl3):
1
dꢂ
3.61 (m, CH2, 4H); 7.04 (d, 1H), 7.12ꢀ
7.35ꢀ7.42 (m, 2H), 7.51 (d, 1H), 7.57 (d, 2H), 7.84ꢀ
(m, 3H). 13C-NMR (25 8C, CDCl3): dꢂ
19.8 (d, CH2,
Jꢂ 14.3 Hz), 30.1 (d, CH2ÃP, Jꢂ 17.2 Hz), 35.8 (d,
CH2ÃP, Jꢂ26.7 Hz), 51.0 (d, CH2, Jꢂ6.7 Hz), 124.7
/
2.18 (m, CH2, 2H), 2.51ꢀ
/
2.89 (m, CH2, 4H), 3.45ꢀ
7.25 (m, 3H),
7.91
/
/
and the residue was extracted in methanol to give redꢀ
/
brown solid (54% yield). 31P NMR (25 8C, Acetone-d6):
/
/
/
dꢂ
/
97.5 J(P,Rh)ꢂ
/
169.2 Hz. MS (FAB pos.): m/zꢂ965
/
[Mꢁ -BF4], 875 [Mꢁ -BF4 -108].
/
/
/
/
/
/
(d), 125.8 (d), 126.7 (d), 127.6 (d), 128.2 (d), 128.7, 132.1
(d), 132.7 (d) 133.9 (d), 135.4 (d). 31P-NMR (25 8C,
4.3. Catalytic experiments
CDCl3): dꢂ
/
68.0. MS (ES, 70 eV): m/zꢂ
367 [Mꢁ], 311,
297, 282, 265, 239, 183, 132, 101, 88, 70, 58, 42.
/
Hydrogenation was performed under normal pressure
at 25 8C. A mixture of 0.005 mmol [Rh(COD)2]BF4,
0.055 mmol ligand 5aꢀf and 0.5 mmol methyl a-
/
4.1.5. 4-Piperidinyl-4,5-dihydro-3H-dinaphtho[2,1-
c;1?,2?-e]phosphepine (5e)
acetamidocinnamate 7 or methyl a-acetamidoacrylate
9 was stirred for 15 min in 12.5 ml solvent. The
hydrogenation flask was flushed several times with
hydrogen. The reaction was followed by a volumetric
White solid, 62% yield. 1H-NMR (25 8C, CD2Cl2):
dꢂ
2.79ꢀ
1H), 7.12ꢀ
(q, 2H), 7.86ꢀ
dꢂ24.2 (CH2), 25.1 (CH2), 32.4 (d, CH2Ã
Hz), 36.7 (d, CH2ÃP, Jꢂ
/
1.14ꢀ
/
1.56 (m, CH2, 6H), 2.51ꢀ
/
2.63 (q, CH2, 1H),
/2.91 (m, CH2, 4H), 3.02 (d, CH2, 1H), 7.07 (d,
measurement at 2590.5 8C. The enantiomeric excess
/
/
7.22 (m, 3H), 7.39ꢀ
/
7.41 (m, 2H), 7.54ꢀ
/
7.60
was determined by GC (XE 60) or HPLC (Chiracel OD-
H).
/
7.92 (m, 4H). 13C-NMR (25 8C, CD2Cl2):
/
/
P, Jꢂ
/
18.1
/
/30.5 Hz), 57.4 (CH2), 125.0
(d), 126.1 (d), 126.9 (d), 128.1 (d), 128.5 (d), 128.9, 132.6
(d), 132.9 (d) 134.1 (d), 136.1 (d). 31P-NMR (25 8C,
Acknowledgements
CD2Cl2): dꢂ
/
74.4. MS (ES, 70 eV): m/zꢂ
395 [Mꢁ],
340, 312, 297, 276, 265, 184, 160, 132, 98, 84, 60.
/
We thank Mrs A. Lehmann and Mrs M. Heyken for
excellent technical assistance. We are also thankful to
Professor Serafino Gladiali for sharing some unpub-
lished work with us. We are grateful to the BMBF,
Degussa AG, and the State Mecklenburg-Western
Pommerania for funding of this project.
4.1.6. 4-Pyrrolyl-4,5-dihydro-3H-dinaphtho[2,1-c;1?,2?-
e]phosphepine (5f)
White solid, 75% yield. 1H-NMR (25 8C, CDCl3): dꢂ
/
2.71ꢀ
6.14 (m, CH2, 2H), 6.46ꢀ
1H), 7.07ꢀ7.20 (m, 4H), 7.28ꢀ
1H), 7.74ꢀ
7.89 (m, 4H). 13C-NMR (25 8C, CDCl3): dꢂ
33.8 (d, CH2ÃP, Jꢂ 15.3 Hz), 35.8 (d, CH2ÃP, Jꢂ24.8
Hz), 111.0 (CH2Ä), 124.8 (d), 125.6 (d), 126.4, 127.0 (d),
127.6, 128.5 (CH2Ä), 128.9 (d), 129.3, 132.0 (d), 133.0
(d) 134.3. 31P-NMR (25 8C, CDCl3): dꢂ
61.5. MS (ES,
70 eV): m/zꢂ
377 [Mꢁ], 356, 328, 311, 296, 282, 229,
163, 132, 114, 91, 65, 58, 39.
/
2.86 (m, CH2, 2H), 3.05ꢀ
6.50 (m, CH2, 2H), 6.96 (d,
7.40 (m, 2H), 7.51 (d,
/
3.19 (m, CH2, 2H), 6.09ꢀ
/
/
/
/
/
/
References
/
/
/
/
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