Synthesis of new chiral amidophosphite ligands and their application in hydrogenation of benzodiazepinones and enamides

Article abstract of DOI:10.1007/s11172-017-1875-8

New chiral amidophosphites were synthesized and tested in the Ir-catalyzed hydrogenation of 4-substituted 1,3-dihydro-2H-1,5-benzodiazepin-2-ones and Rh-catalyzed hydrogenation of dehydro amino acid derivatives. The triphenylphosphine additive can considerably increase the enantioselectivity of both processes.

Full text of DOI:10.1007/s11172-017-1875-8

Russian Chemical Bulletin, International Edition, Vol. 66, No. 7, pp. 1213—1216, July, 2017
1213
Synthesis of new chiral amidophosphite ligands and their application
in hydrogenation of benzodiazepinones and enamides
M. V. Sokolovskaya, S. E. Lyubimov, and V. A. Davankov
A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences,
2
8 ul. Vavilova, 119991 Moscow, Russian Federation.
Fax: +7 (499) 135 6471. Eꢀmail: lssp452@mail.ru
New chiral amidophosphites were synthesized and tested in the Irꢀcatalyzed hydrogenation
of 4ꢀsubstituted 1,3ꢀdihydroꢀ2Hꢀ1,5ꢀbenzodiazepinꢀ2ꢀones and Rhꢀcatalyzed hydrogenation
of dehydro amino acid derivatives. The triphenylphosphine additive can considerably increase
the enantioselectivity of both processes.
Key words: enantioselective hydrogenation, rhodium complexes, iridium complexes,
enamides, benzodiazepinones, amidophosphites.
Lately, much attention is paid to the development of
catalyst systems based on metal complexes for carrying
out asymmetric hydrogenation reactions.1 Inexpensive
hydrogen and small amounts of catalyst make this proꢀ
cess promising. The known examples of metal complex
hydrogenation of unsaturated precursors mainly include
the use of expensive chiral phosphine ligands.2 A conꢀ
venient alternative to phosphine systems are phosphiteꢀ
type ligands, which can be obtained over several tens of
minutes from available reagents. Chiral phosphites and
amidophosphites showed bright results in a number of
amidophosphite ligands, as well as on their application in
asymmetric hydrogenation, which yielded nonnatural
amino acids and tetrahydroꢀ1Hꢀbenzodiazepinones exꢀ
hibiting asthmatic, anticancer, neuroprotective properꢀ
6
—9
ties.
Note that the information on the synthesis of
tetrahydroꢀ1Hꢀbenzodiazepinones by asymmetric hydroꢀ
genation is absent in the scientific literature. There are
only examples of their preparation by hydrosilylation and
Hantzsch reduction.1
—4
0,11
Results and Discussion
5
processes of asymmetric hydrogenation. In this connecꢀ
tion, the search for simple, but efficient metal complex
catalysts based on such ligands for asymmetric hydroꢀ
genation of unsaturated precursors seems an actual issue.
In the present work, we report on the synthesis of new
The reaction of the chiral phosphorylating agent 1
with NꢀbenzylꢀNꢀisopropylamine or NꢀisopropylꢀNꢀ(2ꢀ
phenylethyl)amine in CH Cl was used to synthesize new
2
2
amidophosphite ligands L1 and L2 (Scheme 1).
Scheme 1
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1213—1216, July, 2017.
066ꢀ5285/17/6607ꢀ1213 © 2017 Springer Science+Business Media, Inc.
1

1
214
Russ. Chem. Bull., Int. Ed., Vol. 66, No. 7, July, 2017
Sokolovskaya et al.
Table 2. Metal complex hydrogenation of compound 2ba
The efficiency of these amidophosphites was initially
tested in the Irꢀcatalyzed hydrogenation of benzodiazeꢀ
pinone 2a (Scheme 2). When ligands L1 and L2 were
Entry Catalyst systemb
Solvent
Conversion
%)
ee
(%)
c
(
used in CH Cl as the solvent, the conversion was moderate
2
2
(
Table 1, entries 1 and 2). The hydrogenation in ethanol
1
2
3
4
5
6
7
8
A/4L1
A/4L2
A/4L1
CH Cl
100
100
95
100
100
100
100
100
22(+)
12(+)
6(+)
50(+)
26(+)
47(+)
0
2
2
2
provided a complete conversion when L1 was used (entry 3).
CH Cl
2
EtOH
A/2L1/2PPh3
A/2L2/2PPh3
A/2L1/2PPh3
A/2L1/2PСу3
B/2L1
CH Cl
2
2
2
Scheme 2
CH Cl
2
EtOH
CH Cl
2
2
2
CH Cl
44(+)
2
a
b
c
T = 25 °C, P(H ) = 55 atm, τ = 24 h, [Ir(COD)Cl] /2b = 1/200.
2
2
A = [Ir(COD)Cl] , B = [Ir(COD) ]BARF.
2
2
The sign of the product specific rotation is given in parenꢀ
theses.
R = Ph (a), Me (b)
selectivity being shown by amidophosphite L1 (Table 2,
entries 1 and 2). In ethanol, L1 gave almost racemic prodꢀ
uct (entry 3). The addition of triphenylphosphine to L1
and L2 considerably increased the enantioselectivity
(cf. entries 1, 2 and 4, 5). The use of ethanol in the case of
L1 in the combination with triphenylphosphine showed
similar results (see Table 2, entry 6). The use of a mixture
of L1 and tricyclohexylphosphine gave a racemate (see
Table 2, entry 7). The involvement of an alternative preꢀ
We checked a suggestion of using a combination of chiral
phosphite ligands with achiral phosphines in hydrogenaꢀ
tion of compound 2a. Such an approach has been already
used in hydrogenation and in a number of cases considerꢀ
12—14
ably increased enantioselectivity.
of ligands L1 or L2 in a combination with triphenylphosꢀ
phine in CH Cl gave the product with 24% ee, while a
The use of a mixture
2
2
better conversion was shown by ligand L1 (see Table 1,
entries 4 and 5). In the case of L1, replacement of CH Cl
2
2
catalyst [Ir(COD) ]BARF and L1 gave the product with
with ethanol allowed us to reach 50% ee (entry 6). The
use of tricyclohexylphosphine as an additive to L1 led to a
decrease in enantioselectivity (see Table 1, entries 7 and
2
4
4% ee without phosphine additives.
Ligands L1 and L2 were tested in the Rhꢀcatalyzed
hydrogenation of methyl (Z)ꢀ2ꢀacetamidoꢀ3ꢀ(3,4ꢀdimethꢀ
oxyphenyl)acrylate (4) which yielded an LꢀDOPA derivaꢀ
tive (Scheme 3).
8
). The compound [Ir(COD) ]BARF (BARF is the tetꢀ
2
rakis[3,5ꢀbis(trifluoromethyl)phenyl]borate) was also
tested as a precatalyst and showed a low efficiency (see
Table 1, entry 9).
A complete conversion was reached in the Irꢀcatalyzꢀ
ed hydrogenation of benzodiazepinone 2b (see Scheme 2)
Scheme 3
involving ligands L1 and L2 in CH Cl , with the higher
2
2
Table 1. Metal complex hydrogenation of compound 2aa
Entry
Catalyst
systemb
Solvent
Conversion
(%)
ee
(%)
c
1
2
3
4
5
6
7
8
9
A/4L1
A/4L2
A/4L1
CH Cl
30
26
100
63
21
67
43
27
20
0
0
0
2
2
2
CH Cl
2
EtOH
A/2L1/2PPh3
A/2L2/2PPh3
A/2L1/2PPh3
A/2L1/2PСу3
CH Cl
24(+)
24(+)
50(+)
8(+)
6(+)
28(+)
2
2
2
CH Cl
2
EtOH
EtOH
A/2L1/2PСу3
CH Cl
2
2
2
Like in the case with heterocyclic substrates 2a,b, amiꢀ
dophosphite L2 showed a lower efficiency (Table 3, entries 1
and 2). The use of L1 in a combination with triphenylphosꢀ
phine increased the enantioselectivity (see Table 3, cf. enꢀ
tries 1 and 3), similarly to the case of hydrogenation of
substrates 2a,b.
B/2L1
CH Cl
2
a
T = 25 °C, P(H ) = 55 atm, τ = 24 h, [Ir(COD)Cl] /2a = 1/200.
2
2
b
c
A = [Ir(COD)Cl] , B = [Ir(COD) ]BARF.
2
2
The sign of the product specific rotation is given in parenꢀ
theses.

Chiral amidophosphite ligands
Russ. Chem. Bull., Int. Ed., Vol. 66, No. 7, July, 2017
1215
Table 3. Metal complex hydrogenation of compound 4*
relative to Me Si and 85% H PO in D O, respectively. The
4 3 4 2
phosphorylating agent (R )ꢀ2ꢀchlorodinaphtho[2,1ꢀd:1´,2´ꢀf]ꢀ
a
1
5
16
[
1,3,2]dioxaphosphepane (1), NꢀbenzylꢀNꢀisopropylamine,
NꢀisopropylꢀNꢀ(2ꢀphenylethyl)amine,
Ir(COD) ]BARF, [Rh(COD) ]BF , 4ꢀphenylꢀ1,3ꢀdihydroꢀ
2 2 4
2Hꢀ1,5ꢀbenzodiazepinꢀ2ꢀone (2a), methyl (Z)ꢀ2ꢀacetamidoꢀ
3ꢀ(3,4ꢀdimethoxyphenyl)acrylate (4), and methyl (Z)ꢀ2ꢀacetꢀ
amidoꢀ4ꢀ(4ꢀfluorophenyl)acrylate (6)2 were obtained according
to the procedure described in the literature.
Entry
Catalyst system
Conversion
%)
ee
(%)
1
7
18
(
[Ir(COD)Cl]2,
1
9
20
[
2
1
1
2
3
[Rh(COD) ]BF /2L1
100
50
100
58 (S)
54 (S)
72 (S)
2
4
2
2
[Rh(COD) ]BF /2L2
2
4
3
[Rh(COD) ]BF /L1, PPh
3
2
4
*
=
T = 50 °C, P(H ) = 55 atm, τ = 2 h, CH Cl , [Rh(COD) ]BF /4 =
2 2 2 2 4
1/100.
Synthesis of ligands L1 and L2 (general procedure). NꢀBenzylꢀ
Nꢀisopropylamine or NꢀisopropylꢀNꢀ(2ꢀphenylethyl)amine
(
1.4 mmol) and NEt (1.6 mmol, 0.22 mL) in CH Cl (10 mL)
3 2 2
were added to a solution of (Rax)ꢀ2ꢀchlorodinaphtho[2,1ꢀ
d:1´,2´ꢀf][1,3,2]dioxaphosphepane (1) (0.5 g, 1.4 mmol) in
This effect was also confirmed for the structurally simiꢀ
lar substrate, namely, methyl (Z)ꢀ2ꢀacetamidoꢀ4ꢀ(4ꢀfluoroꢀ
phenyl)acrylate (6, Scheme 4). Thus, the use of L1 providꢀ
ed 58% ee, which grew to 80% when triphenylphosphine
was added (Table 4).
CH Cl (10 mL). The reaction mixture was stirred for 20 min at
2
2
room temperature and washed with water (20 mL) to remove
HNEt Cl. The organic layer was separated, dried with Na SO ,
3
2
4
and passed through a layer of silica gel, the solvent was reꢀ
moved in vacuo.
(
R )ꢀ2ꢀ(NꢀBenzylꢀNꢀisopropylamino)dinaphtho[2,1ꢀd:1´,2´ꢀ
a
Scheme 4
f][1,3,2]dioxaphosphepane (L1). The yield was 0.526 g (81%),
a white powder, m.p. 110—111 °C. [α]D = 441.2 (c 1.0, CHCl ).
3
Found (%): C, 77.78; H, 5.61; N, 2.96. C30H26NO P. Calcuꢀ
2
3
1
lated (%): C, 77.74; H, 5.65; N, 3.02. P{H} NMR (CDCl ),
δ: 147.43. H NMR (CDCl ), δ: 1.18 (d, 3 H, J = 8 Hz); 1.31
3
1
3
(
d, 3 H, J = 8 Hz); 3.47 (m, 1 H); 3.67 (m, 1 H); 4.21 (m, 1 H);
7
8
.23—7.52 (m, 12 H); 7.63 (d, 1 H, J = 8 Hz); 7.94—7.99 (m, 3 H);
.02 (d, 1 H, J = 8 Hz). 1 C NMR (CDCl ), δ: 23.01 (d, J
3
=
3
C,P
=
10 Hz); 23.68 (d, JC,P = 6 Hz); 39.53; 46.85 (d, JC,P = 6 Hz);
4
1
1
1
8.53 (d, JC,P = 20 Hz); 121.91, 122.32, 123.33, 124.12, 124.17,
24.57, 124.81, 126.08, 126.79, 127.06, 127.12, 127.83, 128.16,
28.28, 128.38, 130.00, 130.29, 130.72, 131.45, 132.70, 132.89,
40.76, 149.7; 150.14 (d, JC,P = 4 Hz).
(
R )ꢀ2ꢀ[NꢀIsopropylꢀNꢀ(2ꢀphenylethyl)amino]dinaphthoꢀ
a
[
0
2,1ꢀd:1´,2´ꢀf][1,3,2]dioxaphosphepane (L2). The yield was
.528 g (79%), a white powder, m.p. 105—106 °C. [α] = 438.0 (c1.0,
D
CHCl ). Found (%): C, 77.92; H, 5.98; N, 2.89. C31H28NO P.
Calculated (%): C, 77.97; H, 5.91; N, 2.93. P{H} NMR
3
2
Table 4. Metal complex hydrogenation of compound 6*
3
1
1
(
(
(
(
(
CDCl ), δ: 153.22. H NMR (CDCl ), δ: 1.39 (s, 3 H); 1.41
3
3
Entry
Catalyst system
Conversion
%)
ee
(%)
s, 3 H); 2.74 (m, 1 H); 3.01 (m, 3 H); 3.79 (m, 1 H); 6.79—7.68
m, 13 H); 7.96—8.10 (m, 4 H). 1 C NMR (CDCl ), δ: 23.38
d, JC,P = 6 Hz); 23.6 (d, JC,P = 7 Hz); 39.53; 44.8; 48.53
d, JC,P = 30 Hz); 122.21, 122.29, 122.41, 124.19, 124.22,
(
3
3
1
2
[Rh(COD) ]BF /2L1
100
100
58 (S)
80 (S)
2
4
[Rh(COD) ]BF /L1, PPh
3
2
4
1
24.62, 124.9, 126.00, 126.24, 126.27, 127.06, 127.15, 128.24,
*
T = 50 °C, P(H ) = 55 atm, τ = 2 h, CH Cl , [Rh(COD) ]BF /6 =
128.45, 128.51, 128.51, 130.06, 130.41, 130.83, 131.52, 133.02,
2
2
2
2
4
=
1/100.
139.78, 149.91; 150.53 (d, JC,P = 6 Hz).
4
ꢀMethylꢀ1,3ꢀdihydroꢀ2Hꢀ1,5ꢀbenzodiazepinꢀ2ꢀone (2b). Triꢀ
ethylamine (16.7 mL, 0.12 mol) was added dropwise to a soluꢀ
tion of acetyl chloride (7.8 g, 0.1 mol) in diethyl ether (100 mL)
cooled with an iceꢀwater bath under argon over 30 min and the
resulting mixture was stirred for 1 h. A solution of 1,2ꢀdiaminoꢀ
benzene (4.3 g, 0.04 mol) in acetonitrile (50 mL) was added
dropwise to the diketene formed, which is unstable at room
temperature and toxic. After stirring over 1 h in an iceꢀwater
bath, the mixture was allowed to stand at room temperature for
In conclusion, we accomplished the synthesis of new
chiral amidophosphites, tested them in the reactions of
Irꢀcatalyzed hydrogenation of 1,5ꢀbenzodiazepinones and
Rhꢀcatalyzed hydrogenation of dehydro amino acid deꢀ
rivatives. We showed that the addition of triphenylphosꢀ
phine can considerably increase the enantioselectivity of
hydrogenation of the substrates tested.
8
h. Then, the reaction mixture was workedꢀup with water
(
30 mL), the product was extracted with ethyl acetate (3×25 mL).
Experimental
The organic phase was dried with sodium sulfate, the solvent
was removed in vacuo. The product was purified by recrystalꢀ
ization from ethyl acetate. The yield was 38%. The spectral
characteristics of 2b correspond to the literature data.24
1H, 31P, and 13C NMR spectra were recorded on a Bruker
Avance 400 spectrometer (400.13, 161.98, and 100.6 MHz)

1
216
Russ. Chem. Bull., Int. Ed., Vol. 66, No. 7, July, 2017
Sokolovskaya et al.
Asymmetric hydrogenation of compounds 2a,b. A correspondꢀ
ing ligand (0.012 mmol or 0.024 mmol) or a chiral and an achiral
ligands (0.012 mmol each) in CH Cl (0.5 mL) were added to
6. S. E. Lyubimov, I. V. Kuchurov, V. A. Davankov, S. G.
Zlotin, J. Supercritical Fluids, 2009, 50, 118.
7. J. Liu, A.C. Cheng, H. L. Tang, J. C. Medina, ACS Med.
Chem. Lett., 2011, 2, 515.
2
2
a solution of [Ir(COD) ]BARF (7.6 mg, 0.006 mmol) or dimerꢀ
2
ic [Ir(COD)Cl] (4 mg, 0.006 mmol) and the resulting mixture
was stirred for 5 min with a magnetic stirrer. The solvent was
8. A. M. Taylor, A. Cote, M. C. Hewitt, R. Pastor, Y. Leblanc,
C. G. Nasveschuk, F. A. Romero, T. D. Crawford,
N. Cantone, H. Jayaram, J. Setser, J. Murray, M. H.
Beresini, G. de Leon Boenig, Z. Chen, A. R. Conery, R. T.
Cummings, L. A. Dakin, E. M. Flynn, O. W. Huang,
S. Kaufman, P. J. Keller, J. R. Kiefer, T. Lai, Y. Li, J. Liao,
W. Liu, H. Lu, E. Pardo, V. Tsui, J. Wang, Y. Wang, Z. Xu,
F. Yan, D. Yu, L. Zawadzke, X. Zhu, X. Zhu, R. J. Sims III,
A. G. Cochran, S. Bellon, J. E. Audia, S. Magnuson, B. K.
Albrecht, ACS Med. Chem. Lett., 2016, 7, 531.
9. H. Zou, A. S. Limpert, J. Zou, A. Dembo, P. S. Lee,
D. Grant, R. Ardecky, A. B. Pinkertone, G. K. Manguson,
M. E. Goldman, J. Rong, P. Teriete, D. J. Sheffler, J. C.
Reed, N. D. Cosford, ACS Chem. Neurosi, 2015, 6, 464.
10. M. Rueping, E. Merino, R. M. Koenigs, Adv. Synth. Catal.,
2010, 352, 2629.
2
removed in vacuo. Ethanol or CH Cl (4 mL and 2a or 2b
2
2
(
0.3 mmol) were added to the obtained catalyst, an autoclave
was filled with hydrogen (55 atm) and the experiments were
carried out at room temperature with stirring using with a magꢀ
netic stirrer. After decompression, the reaction mixture was
diluted with CH Cl (2 mL) and purified from the catalyst by
2
2
filtration through a short layer of silica gel, the solvents were
removed in vacuo. The enantiomeric composition was deterꢀ
mined by HPLC, using a Kromasil 3ꢀAmyCoat column (UV
2
19 nm, hexane/isopropyl alcohol = 90/10, 1 mL min–1).
The retention times for the enantiomers of 4ꢀphenylꢀ1,3,4,5ꢀ
tetrahydroꢀ2Hꢀ1,5ꢀbenzodiazepinꢀ2ꢀone are 17.4 ((–)ꢀ3a) and
1
9.3 min ((+)ꢀ3a) and for 4ꢀphenylꢀ1,3ꢀdihydroꢀ2Hꢀ1,5ꢀ
benzodiazepinꢀ2ꢀone (2a) it is 9.1 min. The retention times for
the enantiomers of 4ꢀmethylꢀ1,3,4,5ꢀtetrahydroꢀ2Hꢀ1,5ꢀbenzoꢀ
diazepinꢀ2ꢀone are16.5 ((–)ꢀ3b) and 23.4 min ((+)ꢀ3b) and for
11. X. Chen, Y. Zheng, Chang Shu, W. Yuan, B. Liu, X. Zhang,
J. Org. Chem., 2011, 76, 9109.
1
b it is 6.6 min. The conversion of 2a and 2b was determined
12. M. T. Reetz, H. Guo, Beilstein, J. Org. Chem., 2005, 1, 1.
13. M.ꢀT. Reetz, X. Li, Chem. Commun., 2006, 2159.
14. N. Mrsic, L. Lefort, J. A. F. Boogers, A. J. Minnaard, B. L.
Feringa, J. G. de Vries, Adv. Synth. Catal., 2008, 350, 1081.
15. G. Francio, C. G. Arena, F. Faraone, C. Graiff, M. Lanꢀ
franchi, A. Tiripicchio, Eur. J. Inorg. Chem., 1999, 1219.
16. K. Orito, M. Miyazawa, T. Nakamura, A. Horibata, H. Ushito,
H. Nagasaki, M. Yuguchi, S. Yamashita, T. Yamazaki,
M. Tokuda, J. Org. Chem., 2006, 71, 5951.
1
using H NMR spectroscopy. Spectral characteristics of prodꢀ
ucts 3a and 3b correspond to those published earlier.2
Asymmetric hydrogenation of compounds 4 and 6. A solution of
5
[
Rh(COD) ]BF (2 mg, 0.005 mmol) in a solvent (0.5 mL) and
2 4
ligand L1, L2 (0.01 mmol) or a mixture of a chiral ligand
(
(
0.005 mmol) and triphenylphosphine (0.005 mmol) in CH Cl
2 2
1 mL) were placed into a 10ꢀmL autoclave, the reaction mixꢀ
ture was stirred for 2 min, followed by the addition of the subꢀ
strate 4 or 6 (0.5 mmol) in the corresponding solvent (2 mL).
The autoclave was filled with hydrogen (55 atm) and heated to
17. S. Bhattacharyya, U. Pathak, S. Mathur, S. Vishnoia,
R. Jainb, RSC Adv., 2014, 4, 18229.
5
0 °C (10 min). The process was carried out for 2 h with magꢀ
18. J. L. Herde, J. C. Lambert, C. V. Senoff, Inorg. Synth., 1974,
15, 18.
19. V. Semeniuchenko, V. Khilya, U. Groth, Synlett, 2009,
20, 271.
20. T. V. RajanBabu, T. A. Ayers, G. A. Halliday, K. K. You,
J. C. Calabrese, J. Org. Chem., 1997, 62, 6012.
21. H. Mtiraoui, R. Gharbi, M. Msaddek, Y. Bretonniиre,
C. Andraud, C. Sabot, P.ꢀY. Renard, J. Org. Chem., 2016,
81, 4720.
netic stirring. After the reaction reached completion, the autoꢀ
clave was cooled to room temperature, the reaction mixture
was purified from the catalyst by filtration through a short layer
of silica gel, the solvent was removed in vacuo. Spectral characꢀ
teristics of products 5 and 7 correspond to the literature data.26
The enantiomeric excess of 5 and 7 was determined by HPLC
on Chiralcel OJꢀH and Kromasil 5ꢀAmycoat columns accordꢀ
6
,22
ing to the procedure described in the literature.
2
2. S. E. Lyubimov, P. V. Petrovskii, E. A. Rastorguev, V. A.
Davankov, Russ. Chem. Bull., 2010, 59, 1761.
This work was financially supported by the Russian
Foundation for Basic Research (Project No. 17ꢀ03ꢀ00483).
23. S. E. Lyubimov, E. A. Rastorguev, T. A. Verbitskaya, P. V.
Petrovskii, E.HeyꢀHawkins, V. N. Kalinin, V. A. Davankov,
Polyhedron, 2011, 30, 1258.
2
2
References
4. A. Alizadeh, N. Zohreh, Helv. Chim. Acta, 2010, 93, 1221.
5. H. Mtiraoui, R. Gharbi, M. Msaddek, Y. Bretonniиre,
C. Andraud, C. Sabot, P.ꢀY. Renard, J. Org. Chem., 2016,
1
2
3
4
5
. A. Boerner, Phosphorus Ligands in Asymmetric Catalysis,
WileyꢀVCH, Weinheim, 2008.
. B. Weiner, W. Szymanski, D. B. Janssen, A. J. Minnaard,
B. L. Feringa, Chem. Soc. Rev., 2010, 39, 1656.
8
1, 4720.
2
6. B. Mohar, M. Stephan, Adv. Synth. Catal., 2013, 355, 594.
. D. J. Ager, A. H. de Vries, J. G. de Vries, Chem. Soc. Rev.,
2
012, 41, 3340.
. J.ꢀH. Xie, S.ꢀF. Zhu, Q.ꢀL. Zhou, Chem. Rev., 2011,
11, 1713.
1
. P. van Leeuwen, P. Kamer, C. Claver, O. Pamies, M. Dieꢀ
Received March 20, 2017;
in revised form June 8 , 2017
guez, Chem. Rev., 2011, 111, 2077.