Asymmetric Ir-catalyzed hydrogenation of 1,3-dihydro-2H-1,5-benzodiazepin-2-ones using phosphoramidites

Article abstract of DOI:10.1007/s11172-018-2068-9

A series of phosphoramidite ligands was tested in the asymmetric hydrogenation of 4-arylsubstituted 1,3-dihydro-2H-benzodiazepine-2-ones and up to 52% ee was achieved. The effects of various factors (solvents, hydrogen pressure, and addition of phosphine

Full text of DOI:10.1007/s11172-018-2068-9

Russian Chemical Bulletin, International Edition, Vol. 67, No. 2, pp. 260—264, February, 2018
260
Asymmetric Irꢀcatalyzed hydrogenation
of 1,3ꢀdihydroꢀ2Hꢀ1,5ꢀbenzodiazepinꢀ2ꢀones using phosphoramidites
M. V. Sokolovskaya,a S. E. Lyubimov,a I. S. Mikhel,b K. P. Birin,b and V. A. Davankova
aA. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
28 ul. Vavilova, 119991 Moscow, Russian Federation.
Fax: +7 (499) 135 5085. Eꢀmail: lssp452@mail.ru
bA. N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences,
31/4 Leninsky prosp., 119071 Moscow, Russian Federation.
Fax: +7 (495) 952 0449. Eꢀmail: i_mikhel@rambler.ru
A series of phosphoramidite ligands was tested in the asymmetric hydrogenation of 4ꢀarylꢀ
substituted 1,3ꢀdihydroꢀ2Hꢀbenzodiazepineꢀ2ꢀones and up to 52% ee was achieved. The
effects of various factors (solvents, hydrogen pressure, and addition of phosphine ligands)
on the hydrogenation were studied.
Key words: asymmetric hydrogenation, phosphoramidites, mixed ligands, 1,5ꢀbenzoꢀ
diazepinꢀ2ꢀones.
Widely used hypnotic agents, tranquilizers, and antiꢀ
inhibitors;9 caspaseꢀ3 inhibitors;10 cholecystokinin antaꢀ
gonists11 used, in particular, to treat the gastric ulcer; and
antipyretics.12
depressant drugs are based on benzodiazepine derivatives
such as the mild tranquilizer diazepam (sibazon, seduxen
(1)) and nitrazepam (2).1,2 Grandaxin (tofisopam (3))
with anxiolytic action without a soporific effect also reꢀ
fers to benzodiazepine derivatives.3 In addition, comꢀ
pounds of this class are applied as anesthetics, muscle
relaxants, analgesics, and antiepileptic drugs.4—7
Hydrogenated benzodiazepinone derivatives, tetraꢀ
hydroꢀ1Нꢀbenzodiazepinones, including chiral ones,
represent a new, actively developed class of biologiꢀ
cally active compounds exhibiting antiasthmatic, antiꢀ
tumor, and neuroprotective properties.13—15 The existꢀ
ing approaches to the preparation of these chiral comꢀ
pounds are based on organocatalysis.16,17 Also, the apꢀ
plicability of chiral diphosphine ligands in the asymꢀ
metric hydrogenation of 4ꢀsubstituted 1,3ꢀdihydroꢀ2Hꢀ
1,5ꢀbenzodiazepinꢀ2ꢀones has been recently reported.18
For attaining high enantioselectivity, it was necessary to
use more than 5 mol.% of expensive NaBARF (BARF is
tetrakis[3,5ꢀbis(trifluoromethyl)phenyl]borate) and
the (R)ꢀDifluoroPhos chiral ligand, and the products
were obrained in the Nꢀacetyl form. Previously we briefꢀ
ly described the first examples of application of phosꢀ
phite type ligands in asymmetric hydrogenation of
1,5ꢀbenzodiazepinones.19,20 This study addresses
the effect of the ligand, metal, nature of the solvent,
and hydrogen pressure on the reactant conversion and
enantioselectivity in 1,5ꢀbenzodiazepinone hydroꢀ
genation.
Results and Discussion
We prepared a small series of known phosphoramidite
ligands (L1—L3) with cyclic and acyclic substituents for
testing in the hydrogenation of benzodiazepinones.
Among benzodiazepinones there are anticancer agents
(farnesyl protein transferase inhibitors);8 HIV replication
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 0260—0264, February, 2018.
1066ꢀ5285/18/6702ꢀ0260 © 2018 Springer Science+Business Media, Inc.

Hydrogenation of benzodiazepinones
Russ.Chem.Bull., Int.Ed., Vol. 67, No. 2, February, 2018
261
but the enantioselectivity did not exceed 8%. The replaceꢀ
ment of the solvent by ethanol markedly increased the
reaction selectivity (Table 1, entries 1—3), and L1 proved
to be the best ligand. The use of methanol produces some
increase in the asymmetric induction, whereas trifluoroꢀ
ethanol (TFE) or propanꢀ2ꢀol lead, conversely, to a proꢀ
nounced decrease in the enantioselectivity (see Table 1,
entries 4—6).
We also checked the idea of combining chiral phosꢀ
phoramidite ligands with аchiral phosphines. This apꢀ
proach is known in the hydrogenation of heterocyclic comꢀ
pounds and, in some cases, it considerably increases the
enantioselectivity.19—22 By using L1—L3 in the hydrogenaꢀ
tion of 4a in ethanol with addition of triphenylphosphine,
full conversion was achieved, but the enantioselectivity
was moderate (see Table 1, entries 7—9). The replaceꢀ
ment of ethanol by dichloromethane (see Table 1, entries 9
and 10), as in the experiments without addition of phosꢀ
phines, led to the formation of an almost racemic reacꢀ
tion product. The use of tricyclohexylphosphine resulted
in a somewhat higher selectivity (see Table 1, entries 10
and 11). The presence of methanol as the solvent slightly
improved the result (see Table 1, entry 12). The addition
of triꢀоꢀtolylphosphine in the reaction conducted in methꢀ
anol gave 52% ее (see Table 1, entry 13). A lower ee value
was provided by ethanol (see Table 1, entry 14), and with
dichloromethane the process became nonꢀselective (see
Table 1, entry 15). We also investigated the effect of the
hydrogen pressure on the reaction rate and selectivity.
A pressure decrease from 70 to 35 atm reduced both the
R =
(L1),
(L2),
(L3)
First, the ligands were tested in the Irꢀcatalyzed hydroꢀ
genation of 4ꢀphenylꢀ1,3ꢀdihydroꢀ2Hꢀ1,5ꢀbenzodiazeꢀ
pinꢀ2ꢀone (4a) (Scheme 1) in dichloromethane. The use
of any of the ligands resulted in quantitative conversion,
Scheme 1
4, 5
a
b
R1
H
H
R2
H
OMe
H
c
OMe
Table 1. IrꢀCatalyzed hydrogenation of 4а—са
Entry
Catalyst
Substrate
Solvent
Сb (%)
ee (%)c
1
2
3
4
5
6
7
8
[Ir(COD)Cl]2/4L2
[Ir(COD)Cl]2/4L3
[Ir(COD)Cl]2/4L1
[Ir(COD)Cl]2/4L1
[Ir(COD)Cl]2/4L1
4a
4a
4a
4a
4a
4a
4a
4a
4a
4a
4a
4a
4a
4a
4a
4a
4b
4c
EtOH
EtOH
EtOH
МеOH
PriOH
TFE
EtOH
EtOH
EtOH
CH2Cl2
CH2Cl2
MeOH
MeOH
EtOH
CH2Cl2
MeOH
MeOH
MeOH
131
100
100
100
100
100
100
100
100
100
100
100
100
100
100
178
173
168
22 (–)
10
30 (–)
36 (–)
14 (–)
20 (–)
18 (–)
10
13 (–)
12 (–)
14 (–)
14 (–)
52 (–)
42 (–)
10
[Ir(COD)Cl]2/4L1
[Ir(COD)Cl]2/2L2/2PPh3
[Ir(COD)Cl]2/2L3/2PPh3
[Ir(COD)Cl]2/2L1/2PPh3
[Ir(COD)Cl]2/2L1/2PPh3
[Ir(COD)Cl]2/2L1/2PСy3
[Ir(COD)Cl]2/2L1/2PСy3
[Ir(COD)Cl]2/2L1/2P(oꢀtol)3
[Ir(COD)Cl]2/2L1/2P(oꢀtol)3
[Ir(COD)Cl]2/2L1/2P(oꢀtol)3d
[Ir(COD)Cl]2/2L1/2P(oꢀtol)3
[Ir(COD)Cl]2/2L1/2P(oꢀtol)3
[Ir(COD)Cl]2/2L1/2P(oꢀtol)3
9
10
11
12
13
14
15
16
17
18
30 (–)
32 (–)
42 (–)
а T = 20 °C, τ = 18 h, P(H2) = 70 atm, 1 mol.% [Ir(COD)Cl]2.
b C is conversion.
c The specific rotation sign of the product is given in parentheses.
d P(H2) = 35 atm.

262
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Sokolovskaya et al.
Table 2. Full assignment of the 1Н NMR signals fot compounds 4b,s and 5b,c (CDCl3)
Atom, gtoup
δ, J/Hz
4b
5b
4c
5c
1
3
8.55 (br.s, 1 Н)
3.57 (br.s, 2 H)
7.80 (br.s, 1 Н)
8.62 (br.s, 1 Н)
3.59 (s, 2 H)
8.05 (br.s, 1 Н)
2.88 (dd, 1 Н,
2.91 (dd, 1 Н,
J = 9.6, J = 13.8);
2.75 (br.dd, 1 Н,
J = 4.2, J = 13.8)
J = 10.2, J = 13.2);
2.76 (dd, 1 Н,
J = 2.4, J = 13.2)
4
—
4.99 (br.dd, 1 Н,
J = 3.6, J = 9.6)
—
—
5.01 (br.dd, 1 Н,
J = 2.4, J = 9.6)
5
6
—
3.80 (br.s, 1 Н)
3.86 (br.s, 1 Н)
7.50 (d, 1 Н, J = 7.8)
6.83 (d, 1 Н, J = 7.8)
7.53 (dd, 1 Н,
6.87 (d, 1 Н, J = 7.8)
J = 7.8, J = 1.2)
7
8
7.28 (br. t, 1 Н, J = 7.8)
7.05—7.09 (m, 1 Н)
6.93—6.96 (m, 1 Н)
7.27—7.31 (m, 1 Н)
7.24—7.28 (m, 1 Н)
7.08 (t, 1 Н, J = 7.2)
7.23 (dt, 1 Н,
6.93—6.97 (m, 1 Н)
J = 7.8, J = 0.6)
9
7.10 (d, 1 Н, J = 7.8)
8.10 (d, 1 Н, J = 9.0)
7.00 (d, 1 Н, J = 9.0)
—
6.94—6.97 (m, 1 Н)
7.32 (d, 1 Н, J = 8.4)
6.91 (d, 1 Н, J = 9.0)
—
7.12 (d, 1 Н, J = 7.8)
7.71 (t, 1 Н, J = 1.8)
—
6.98 (d, 1 Н, J = 7.2)
6.95 (s, 1 H)
13
14
15
—
7.07 (dd, 1 Н,
6.87 (d, 1 Н, J = 7.8)
J = 8.4, J = 2.4)
16
7.00 (d, 1 Н, J = 9.0)
8.10 (d, 1 Н, J = 9.0)
3.89 (s, 3 H)
6.91 (d, 2 Н, J = 9.0)
7.32 (d, 1 Н, J = 8.4)
3.83 (s, 3 H)
7.41 (t, 1 Н, J = 7.8)
7.68 (d, 1 Н, J = 7.8)
3.91 (s, 3 H)
7.30 (t, 1 Н, J = 7.8)
6.98 (d, 1 Н, J = 7.2)
3.82 (s, 3 H)
17
OMe
conversion and the enantioselectivity (see Table 1, enꢀ
tries 13 and 16).
In the comparison of the spectral parameters of comꢀ
pounds 4b,c and 5b,c, attention is attracted by the proꢀ
nounced (more than 95 ppm) upfield shift of the С(4)
We attempted using [Rh(COD)Cl]2 as a precatalyst.
Unlike the use of [Ir(COD)Cl]2, the application of
[Rh(COD)Cl]2 and L1 (or L1 combined with P(oꢀtol)3) in
CH2Cl2 leads to very low (below 12%) conversion and
virtually no enantioselectivity, while the same reaction in
methanol does not occur at all.
13
Table 3. Full assignment of the С NMR signals for comꢀ
pounds 4b,с and 5b,c (CDCl3)
According to the study of the Irꢀcatalyzed hydrogenaꢀ
tion of methoxyꢀsubstituted substrates 4b,c (see Scheme 1,
Table 1, entries 17 and 18) using L1 and P(oꢀtol)3 as an
additive, the catalysis is fairly sensitive to the nature of subꢀ
stituent. Indeed, the introduction of electronꢀdonating
methoxy groups leads to a slight decrease in the conversion
as compared with the reaction of 4a under the same reaction
conditions. In addition, more pronounced electronꢀdonatꢀ
ing effect of the 4ꢀmethoxy substituent towards the C=N
bond being hydrogenated results in lower selectivity in comꢀ
parison with that for 3ꢀmethoxyꢀsubstituted substrate 4c.
Detailed investigation of CDCl3 solutions of hydroꢀ
genation products 5b,c (as well as substrates 4b,c) by 1D
and 2D NMR techniques, namely, 1H, 13C{1H}, 13C DEPT,
Atom,
group
δ
4b
5b
4c
5c
2
3
4
6
7
8
9
167.63
139.48
158.19
128.26
125.12
126.04
121.73
129.02
140.27
130.22
129.66
114.08
162.14
114.08
129.66
155.46
171.89
141.99
62.59
167.57
139.92
158.64
128.37
125.12
126.50
121.75
129.09
139.98
139.11
112.36
159.97
117.60
129.70
120.40
155.46
172.07 (br)
141.92 (br)
163.21
121.15
126.11
121.57
122.47
127.81
138.38
146.05
111.68
160.07
113.48
130.08
118.18
155.30
121.13
126.06
121.41
122.35
127.70
138.39
136.57
127.16
114.32
159.44
114.32
127.16
155.33
10
11
12
13
14
15
16
17
OMe
1H—1H COSY, H—1H NOESY, H—13C HSQC, and
1H—13C HMBC experiments, allowed full assignment of
all resonance signals in the 1Н and 13С NMR spectra (see
Tables 2 and 3).
1
1

Hydrogenation of benzodiazepinones
Russ.Chem.Bull., Int.Ed., Vol. 67, No. 2, February, 2018
263
signal in the 13C NMR spectra, which proves the reducꢀ
tion of the C=N bond. Correspondingly, the Н NMR
4ꢀ(3ꢀMethoxyphenyl)ꢀ1Hꢀbenzo[b][1,4]diazepinꢀ2(3H)ꢀ
one (4с). Yield 0.746 g (56%). White crystals, m.p. 206 °C. Found (%):
C, 72.22; H, 5.37; N, 10.45. C16H14N2O2. Calculated (%):
C, 72.16; H, 5.30; N, 10.52.
1
spectra of 5b,c reasonably exhibit a broad singlet for the
secondary amino group at 3.80—3.86 ppm and a doublet
of doublets at 4.99—5.01 ppm for protons at С(4) as
a result of spin—spin coupling with two nonꢀequivalent
protons at С(3). The spectral parameters for the periphꢀ
eral part of molecules 5b,c (phenyl ring) change insigꢀ
nificantly with respect to those of 4b,с. Conversely, deꢀ
spite the different positions of the methoxy substituent
in the peripheral benzene ring in the hydrogenation prodꢀ
Asymmetric hydrogenation of 4а—с. A 10 mL autoclave was
charged with a solution of [Ir(COD)Cl]2 or [Rh(COD)Cl]2
(0.005 mmol) in a solvent (0.2 mL) together with ligand L1—L3
(0.02 mmol) or with a mixture of a chiral ligand (0.01 mmol)
and appropriate phosphine (0.01 mmol) (see Table 1) in CH2Cl2
(0.2 mL). The reaction mixture was stirred for 2 min, the solꢀ
vent was removed in vacuo, and the specified solvent was added
without degassing (2 mL, see Table 1). Then the substrate 4а—с
(0.5 mmol) was added. The autoclave was filled with hydrogen
(70 or 35 atm) and the reaction was conducted with magnetic
stirring. After the end of the reaction, hydrogen was released
and the solvent was removed in vacuo. The conversion was
determined by 1H NMR spectroscopy.
1
ucts 5b and 5c, the H и 13C NMR resonance signals
for the 4,5ꢀdihydrobenzodiazepinone core atoms are
largely similar.
Thus, a series of phosphoramidite ligands was tested
in asymmetric hydrogenation of 4ꢀsubstituted 1,3ꢀdiꢀ
hydroꢀ2Hꢀ1,5ꢀbenzodiazepinꢀ2ꢀones. The addition of triꢀ
orthoꢀtolylphosphine markedly increases the enantioꢀ
selectivity. Methanol was found to be the solvent of choice
for hydrogenation, while in dichloromethane, virtually
no enantioselectivity is observed in all cases. A combinaꢀ
tion of [Ir(COD)Cl]2, chiral phosphoramidite L1, and
triꢀorthoꢀtolylphosphine shows the best values of both
conversion and enantioselectivity for the same reaction
conditions.
4ꢀ(4ꢀMethoxyphenyl)ꢀ4,5ꢀdihydroꢀ1Hꢀbenzo[b][1,4]diazeꢀ
pinꢀ2(3H)ꢀone (5b). White crystals, m.p. 150—152 °C. Found (%):
C, 71.91; H, 6.29; N, 10.27. C16H16N2O2. Calculated (%):
C, 71.62; H, 6.01; N, 10.44. The enantiomeric excess of 5b was
determined by HPLC on a Kromasil 5ꢀTBB column, 1 mL min–1
,
219 nm, hexane—propanꢀ2ꢀol (95 : 5); the retention time of
the (+)ꢀisomer of 5b was 18 min, that of the (–)ꢀisomer of 5b
was 19 min.
4ꢀ(3ꢀMethoxyphenyl)ꢀ4,5ꢀdihydroꢀ1Hꢀbenzo[b][1,4]diazeꢀ
pinꢀ2(3H)ꢀone (5c). White crystals, m.p. 80—81 °C. Found (%):
C, 71.90; H, 6.27; N, 10.18. C16H16N2O2. Calculated (%):
C, 71.62; H, 6.01; N, 10.44. The enantiomeric excess for 5с
was determined by HPLC on a Chiralcel ADꢀH column,
1 mL min–1, 219 nm, hexane—propanꢀ2ꢀol (7 : 3), the retenꢀ
tion time of the (–)ꢀisomer of 5с was 14 min, that of the (+)ꢀisoꢀ
mer of 5с was 19 min.
Experimental
31
13
Р, 1H, and С NMR spectra were recorded on Bruker
Avance 400 (161.98, 400.13, and 100.61 MHz) and Bruker
Avance III 600 (242.94, 600.13, 150.90 MHz) instruments, with
This work was financially supported by the Russian
Foundation for Basic Research (Project No. 17ꢀ03ꢀ00483).
85% Н РО in D2О and Me4Si, respectively, as the standards.
3
4
Enantiomeric analysis of the products of catalytic reacꢀ
tions was performed by HPLC using an Agilent HPꢀ1100 chroꢀ
matograph. (Sa)ꢀ2ꢀ(4ꢀTetrahydrooxazinꢀ1ꢀyl)ꢀdinaphthoꢀ
[2,1ꢀd:1´,2´ꢀf][1,3,2]dioxaphosphepine (L1),23 (Sa)ꢀ2ꢀ(pyrrolidꢀ
inꢀ1ꢀyl)ꢀdinaphtho[2,1ꢀd:1´,2´ꢀf][1,3,2]dioxaphosphepine (L2),24
(Sa)ꢀ2ꢀ(diphenylamino)ꢀdinaphtho[2,1ꢀd:1´,2´ꢀf][1,3,2]diꢀ
oxaphosphepine (L3),25 [Ir(COD)Cl]2,26 [Rh(COD)Cl]2,27
and 4ꢀphenylꢀ1Hꢀbenzo[b][1,4]diazepinꢀ2(3H)ꢀone (4a)28
were prepared by reported procedures. The spectral characterꢀ
istics of 4ꢀphenylꢀ1,3ꢀdihydroꢀ2Hꢀ1,5ꢀbenzodiazepinꢀ2ꢀone
(4a) correspond to literature data.28 The enantiomeric excess
for reaction product 5a was determined using a Kromasil
3ꢀAmyCoat column and a reported procedure.19
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Received October 19, 2017;
in revised form November 27, 2017;
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