Use of tridentate TsDPEN/pyridine ligands in ruthenium-catalysed asymmetric reduction of ketones

Article abstract of DOI:10.1016/j.tetlet.2013.05.141

A series of enantiomerically pure tridentate ligands based on the 1,2-diphenylethane-1,2-diamine structure, containing additional pyridine groups, was prepared and tested in asymmetric transfer hydrogenation of ketones using Ru₃(CO)₁₂ as a metal source. Alcohols were formed in up to 93% ee in the best cases, and good results were obtained with ortho-haloarylketones.

Full text of DOI:10.1016/j.tetlet.2013.05.141

Tetrahedron Letters 54 (2013) 4250–4253
Contents lists available at SciVerse ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Use of tridentate TsDPEN/pyridine ligands in ruthenium-catalysed
asymmetric reduction of ketones
⇑
Moftah O. Darwish, Alistair Wallace, Guy J. Clarkson, Martin Wills
Department of Chemistry, The University of Warwick, Coventry CV4 7AL, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of enantiomerically pure tridentate ligands based on the 1,2-diphenylethane-1,2-diamine struc-
ture, containing additional pyridine groups, was prepared and tested in asymmetric transfer hydrogena-
tion of ketones using Ru3(CO)12 as a metal source. Alcohols were formed in up to 93% ee in the best cases,
and good results were obtained with ortho-haloarylketones.
Received 30 March 2013
Revised 16 May 2013
Accepted 30 May 2013
Available online 7 June 2013
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
Asymmetric catalysis
Reduction
Transfer hydrogenation
Ruthenium
Alcohol
Asymmetric transfer hydrogenation (ATH) of ketones is a valu-
able method for the synthesis of enantiomerically pure alcohols.1–3
A large number of catalysts have been reported for this application
in recent years, of which those based on enantiomerically pure N-
tosyl-1,2-diphenylethane-1,2-diamine 1 in combination with a Ru/
arene or Rh or Ir/pentamethylcyclopentadiene have been particu-
larly successful.2 Recently, we found4 that an N-tosyl-1,2-diphenyl-
ethane-1,2-diamine (TsDPEN) modified with a triazole donor,5 that
is, 2, gave good results in the reduction of ketones when used in
conjunction with Ru3(CO)12. The results of the use of the triazole
made us consider pyridine as an alternative donor, and the results
of our study are described below.
A number of pyridine-containing ligands have been employed
in ATH reactions.1,6–17 Early examples include Schiff base 3 (the
Ir complex of which reduced acetophenone in up to 84% ee),8 the
BINOL-derived 4 (the complex with Ru(PPh3)3Cl2 gave up to 97%
ee in ATH in iPrOH),10 as well as 2-(20-pyridyl)pyridines,6 phen-
anthrolines7 and pyridines combined with phosphines in triden-
tate donor ligands.9 More recent examples include a series of
Ru(II) complexes of pyridine/phosphine tridentate ligands together
with phosphines, for example 5 (gave an alcohol of 93% ee from
acetophenone reduction in iPrOH),11a reported by Yu and co-work-
ers.11 The pyridine-containing catalysts, for example 6, reported by
Baratta, are highly active and give products of high ee in ketone
reductions in ATH using iPrOH.12 Also containing a chiral diphos-
phine, 6 gave ketone reduction products of up to 99% ee in ATH
reactions in isopropanol, and is also active in ketone
hydrogenation.12a
NBn
H
N
Ph
Ph
NH2
Ph
Ph
N
Me
Ph
N
N
N
NHTs
NHTs
3
1
2
O
OH
N
Cl
H
N
N
HN
Ph3P
N
Ru
Cl
5
N
4
Me
N
P
Josiphos
ligand
Cl
P
NH2
Ru
P
P
6
Pyridine-containing ligands have also been used extensively in
non-asymmetric hydrogen-transfer processes, and for hydrogen
generation from organic molecules.13 Other applications of pyri-
dine-containing ligands have been reported,14 as have their appli-
cations in highly active non-asymmetric hydrogenations of
⇑
Corresponding author. Tel.: +44 24 7652 3260; fax: +44 24 7652 4112.
E-mail address: m.wills@warwick.ac.uk (M. Wills).
0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2013.05.141

M. O. Darwish et al. / Tetrahedron Letters 54 (2013) 4250–4253
4251
Et3N, ethyl
H
N
R
R
R
R
NH2
chloroformate
N
+
HO
THF, 0 oC to rt
12 h
O
N
NHTs
NHTs
O
1 R=R=Ph
10
8
7 R=R=Ph 86%
9
R-R = (CH2)4
R-R = (CH2)4 90%
Scheme 1. Synthesis of ligands 7 and 9.
ketones.15 In some cases, ATH catalysts have been reported which
contain a pyridine ring, but as one of a series of tosylated diamine
(complex with Ru/
g
6-arene)16 or amino acid (complex with
RhCp⁄)17 derivatives.
In view of the encouraging precedents, we elected to study tri-
dentate ligands containing pyridine groups, with regard to their
efficiency when used in a novel complex with Ru3(CO)12.4 Towards
this end we first prepared (R,R)-pyridine-2-carboxylic acid [2-(tol-
uene-4-sulfonylamino)-1,2-diphenyl-1,2-ethylenediamine]-amide
7 in 86% yield (Scheme 1) by the reaction between pyridine-2-car-
boxylic acid 8 and (1R,2R)-TsDPEN 1 using ethyl chloroformate.
In addition, the known (R,R)-[2-(toluene-4-sulfonylamino)-
cyclohexyl]-amide 918 was prepared from pyridine-2-carboxylic
acid 8 and (R,R)-(ꢀ)-N-(4-toluenesulfonyl)-1,2-diaminocyclohex-
ane 10 (90% yield, Scheme 1). The synthesis of the reduced ana-
logues of compounds 7 and 9 was completed by reductive
amination. (R,R)-N-{1,2-Diphenyl-2-[(pyridin-2-ylmethyl)amino]-
ethyl}-4-methylbenzenesulfonamide (11) was prepared by react-
ing (1R,2R)-TsDPEN 1 in CH2Cl2 with 2-pyridinecarboxaldehyde
(12). The mixture was stirred overnight at rt to obtain the known
imine (R,R)-N-{1,2-diphenyl-2-[(pyridin-2-ylmethylene)amino]-
ethyl}-4-methylbenzenesulfonamide (81%).19,20 This was reduced
using NaBH4 to afford 11 (62% yield, Scheme 2).
Compound 11 was found to be stable over a period of weeks and
its structure was confirmed by X-ray crystallography (Fig. 1).21
The synthesis of (R,R)-4-methyl-N-{2-[(pyridin-2-ylmethyl)-
amino]cyclohexyl}benzenesulfonamide (13)16 was likewise
achieved via the corresponding imine20 from (1R,2R)-(ꢀ)-N-p-to-
syl-1,2-cyclohexanediamine (10) (Scheme 2). The synthesis of
(R,R)-{2-[(pyridin-2-ylmethyl)amino]cyclohexyl}carbamic acid
tert-butyl ester (14) was completed by treatment of mono-Boc dia-
mine 1522 with 2-pyridinecaboxaldehyde (12) in CH2Cl2 to give the
intermediate imine, which was reduced by NaBH4 (Scheme 3).
To carry out the ATH of ketone substrates, the reaction was first
optimised with respect to reaction time, concentration and catalyst
loading using compound 11 and acetophenone as a representative
ketone (Table 1). An optimum ratio of 1:3 Ru3(CO)12, that is a 1:1
ratio of Ru:ligand. Experiments were carried out using varying con-
centrations and catalyst loadings for 72 h (Table 1). In all cases, the
enantiomeric excesses decreased slightly with respect to time, pos-
sibly due to slow racemisation of the products (see Supplementary
data for full tables of conversion and ee with respect to reaction
time).
Figure 1. X-ray crystallographic structure of (R,R)-11 with thermal ellipsoids
drawn at 50% probability (ORTEP).
H
NH2
N
i) CH2Cl2, o/n, rt.
N
+
ii) NaBH4,
MeOH, 5 h
N
NHBoc
NHBoc
O
14 62% two steps
12
15
Scheme 3. Synthesis of ligand 14.
reaction was repeated using ligand 13 (Table 1), which gave a sim-
ilar trend in the results. The supplementary data shows graphical
comparisons of the ATH of acetophenone at different concentra-
tions using ligand 11, and of the ee for ATH of acetophenone at dif-
ferent concentrations using ligand 13. The reduction of
acetophenone using ligand 14 for 48 h (0.1 M concentration,
2 mol % catalyst loading) gave almost the same conversion and
ee compared to compounds 11 and 13 (Table 1, entry 9).
An investigation into the possibility of non-linear chirality
transfer from ligand 11 to the product was carried out using ligand
samples of varying ee from 0% to 100%. This did not indicate any
significant effect (see Supplementary data for full details), indicat-
ing a 1:1 ligand:metal ratio in the active species. A suggested
mechanism of action for the ATH of an aryl ketone using compound
11 as the ligand is illustrated in Figure 2.4 Initial decomposition of
Ru3(CO)12 with CO release, then ligation by 11 and proton transfer
form the coordinatively saturated active species 16. Aryl ketones
can be reduced by 16 via an outer sphere, concerted mechanism
as shown in transition state 17.
The orientation of approach may be influenced by a favourable
p–p interaction between the pyridine group in the ligand and the
aromatic substituent on the respective ketone. Finally, hydrogen
donation by the iPrOH solvent regenerates 18 to complete the cat-
alytic cycle.
Compound 7 was employed as a ligand in the ATH of acetophe-
none, however no reduction product was observed after two days,
as might be predicted in light of the anticipated requirement for a
basic amine in the catalyst. The amide bond functionality may pre-
vent the coordination of the corresponding nitrogen to ruthenium
to form the active catalyst, as the lone pair is not available due to
conjugation.
A series of ketone derivatives were then reduced by ATH using
ligands 11 and 13, (Table 2). Clearly, substituted aryl ketones are
highly compatible with this methodology. Near quantitative con-
version and high enantioselectivity were achieved for the majority
of the substrates tested. Most of the substituted aryl ketones gave
It was found that a reaction concentration of 0.1 M combined
with a catalyst loading of 2 mol % returned optimal results (Table 1,
entry 4). The reaction reached completion after 48 h, therefore the
H
R
R
NH2
R
R
N
i) CH2Cl2, o/n, rt.
N
+
ii) NaBH4,
MeOH, 5 h
N
NHTs
NHTs
O
11 R=R=Ph 50% two steps
1 R=R=Ph
12
13
10
R-R = (CH2)4 53% two steps
R-R = (CH2)4
Scheme 2. Synthesis of ligands 11 and 13.

4252
M. O. Darwish et al. / Tetrahedron Letters 54 (2013) 4250–4253
Table 1
Table 2
A summary of initial ATH of acetophenone with ligands 11 and 13a
ATH of ketones with ligands 11 and 13 in conjunction with Ru3(CO)12
a
11 13
11 13
or (2 mol%)
O
or
(x mol%)
O
OH
OH
R1 R2
Ru3(CO)12 (y mol%)
Ru3(CO)12 (0.66 mol%)
R1 R2
iPrOH, 80 oC, 48 h, [S]=0.1M
iPrOH, 80 °C, 48 h
O
O
O
Entry
Ligand
[Substrate] (M)
0.1
x:y
Convb (%)
eeb,c (%)
MeO
1
2
3
4
5
6
7
8
9
11
11
11
11
13
13
13
13
14
1:0.33
1:0.33
1:0.33
2:0.66
1:0.33
1:0.33
1:0.33
2:0.66
2:0.66
90
97
97
97
62
96
94
97
96
93 (R)
86 (R)
84 (R)
92 (R)
91 (R)
88 (R)
87 (R)
90 (R)
88 (R)
F3C
0.2
0.5
0.1
0.1
0.2
0.5
0.1
0.1
21
19
20
O
O
O
O
4
O
Cl
22
23
24
25
a
b
c
The reaction was carried out at 80 °C using acetophenone (1 mmol).
Enantiomeric excess and conversion determined by chiral GC.
Configuration determined by the sign of the optical rotation of the isolated
Entry
Ketone
Ligand
Convb (%)
eeb,c (%)
1
2
3
4
5
6
7
8
19
p-20
21
22
19
o-20
m-20
p-20
23
21
24
13
13
13
13
11
11
11
11
11
11
11
11
11
26
68
100
86
84
99
98
90
99
99
85
95
88
86 (R)
88 (R)
86 (R)
17 (S)
93 (R)
89 (R)
94 (R)
92 (R)
91 (R)
91 (R)
90 (R)
91 (R)
19 (S)
product.
H
N
Ph
Ph
N
9
11
NHTs
11
12
13
14
Ru3(CO)12
25
22
O
H
H
a
The reaction was carried out at 80 °C using acetophenone (1 mmol), iPrOH
Ph
Ph
N
(10 cm3).
N
O
Ru
b
Enantiomeric excess and conversion determined by chiral GC.
Determined by the sign of optical rotation of isolated product.
N
CO
c
Ts
CO
OH
O
H
H
Table 3
Ph
Ph
N
N
Ph
Ph
ATH of aryl ketones containing a substituent at the ortho positiona
N
N
Ru
Ru
N
CO
N
CO
O
OH
11
(2 mol%)
Ts
Ts
CO
OH
CO
Ru3(CO)12 (0.66 mol%)
i PrOH, 80 oC, 48 h
R
R
Entry
R
Convb (%)
eeb,c (%)
Figure 2. Proposed mechanism of action of the catalyst derived from tridentate
ligand 11.
1
2
3
4
5
6
F
>99
>99
99.0
3.1
33.3
>99
83.7
Cl
Br
I
CF3
Me
87.6 (R)
86.2 (R)
9.1 (R)
17.6 (R)
93.8 (R)
high conversions and good enantioselectivities (Table 2). Among
the substituted aryl ketones tested, it was found that the presence
of a meta-methoxy substituent on the aromatic ring yielded opti-
mal results under the ATH conditions employed (48 h, 98% conv,
94% ee). Acetophenone was reduced completely with only 88% ee
compared to other substituted aryl ketones, which may indicate
the effect of substitution on enhancing the ee. Trifluoromethyl-
and chloro-substituted acetophenone were reduced completely
with 91% ee.
The reaction was carried out using substrate (1 mmol) in iPrOH (10 cm3), 48 h.
Enantiomeric excess and conversion determined by chiral GC.
Determined by the sign of the optical rotation of the isolated product.
a
b
c
An investigation was carried out into the reduction of ortho-
The bicyclic compounds 19 and 25 were reduced in 84% and
95% conversion with 93% and 91% ees respectively. Also the long
chain high molecular weight compound 24 was reduced in 85%
conversion with 90% ee. Acetylcyclohexane was reduced at a lower
rate compared to aryl ketones, and additionally the enantiomeric
excess was significantly lower. The reversed enantioselectivity
for acetylcyclohexane reduction, relative to acetophenone deriva-
tives, suggest that weaker steric factors were directing the reac-
tion, rather than electronic ones. The supplementary data
contains tables and graphs of the observed conversion and ee for
ketone reduction.
substituted aryl ketones (Table 3). Most of the substrates were re-
duced with near quantitative conversion and high enantioselectiv-
ity and are highly compatible with this methodology. Conversion
improved with smaller electron-withdrawing groups (fluorine
and chlorine) compared to unsubstituted acetophenone. Among
the reduced substituents, lower conversion was obtained for large
substituents such as iodide and trifluoromethyl groups. In these
cases, it is likely that that the substituents cause an unfavourable
orthogonal orientation of the arene group, which will subsequently
disrupt the proposed
p–p interaction (Fig. 2). Among the sub-
strates reduced, 20-methylacetophenone yielded optimal results

M. O. Darwish et al. / Tetrahedron Letters 54 (2013) 4250–4253
4253
Sterk, D.; Stephan, M. S.; Mohar, B. Tetrahedron: Asymmetry 2002, 13, 2605–
2608; (h) Wu, X.; Vinci, D.; Ikariya, T.; Xiao, J. Chem. Commun. 2005, 4447–
4449.
after 48 h, achieving almost quantitative conversion and an ee of
93.8%. The electron-donating effect of the methyl substituent
may encourage more favourable p–p interactions in the transition
state, whilst sterically it appears to be of optimum size to encour-
age high conversion without preventing approach to the catalyst.
The supplementary data features further information on conver-
sion and ee against time for these reductions.
In conclusion, we have described the synthesis of an effective
tridentate ligand for incorporation into an active asymmetric
4. Johnson, T. C.; Totty, W. G.; Wills, M. Org. Lett. 2012, 14, 5230–5233.
5. (a) Timmis, F.; Adolfsson, H. Org. Biomol. Chem. 2010, 8, 4536–4539; (b)
Cambreiro, X. C.; Pericas, M. A. Adv. Synth. Catal. 2011, 353, 113–124.
6. Botteghi, C.; Chelucci, G.; Chessa, G.; Delogu, G.; Gladiali, S.; Soccolini, F. J.
Organomet. Chem. 1986, 304, 217–225.
7. Gladiali, S.; Pinna, L.; Delogu, G.; De-Martin, S.; Zassinovich, G.; Mestroni, G.
Tetrahedron: Asymmetry 1990, 1, 635–648.
8. Zassinovich, G.; Bettella, R.; Mestroni, G.; Bresciani-Pahor, N.; Geremia, S.;
Randaccio, L. J. Organomet. Chem. 1989, 370, 187–202.
transfer hydrogenation catalyst upon combination with Ru3(CO)12
We are currently investigating further applications of this system.
.
9. Jiang, Q.; Van Plew, D.; Murtuza, S.; Zhang, X. Tetrahedron Lett. 1996, 37, 797–
800.
10. Brunner, H.; HenningWeber, F.; Weber, M. Tetrahedron: Asymmetry 2002, 13,
37–42.
11. (a) Ye, W.; Zhao, M.; Yu, A. Chem. Eur. J. 2012, 18, 10843–10846; (b) Du, W.;
Wang, L.; Wu, P.; Yu, Z. Chem. Eur. J. 2012, 18, 11550–11554; (c) Zeng, F.; Yu, Z.
Organometallics 2008, 27, 2898–2901; (d) Ye, W.; Zhao, M.; Du, W.; Jiang, Q.;
Wu, K.; Wu, P.; Yu, Z. Chem. Eur. J. 2011, 17, 4737–4741.
12. (a) Baratta, W.; Chelucci, G.; Magnolia, S.; Siega, K.; Rigo, P. Chem. Eur. J. 2009,
15, 726–732; Baratta, W.; Benedetti, F.; Del Zotto, A.; Lidia, L.; Fulvia Felluga, F.;
Magnolia, S.; Putignano, E.; Rigo, P. Organometallics 2010, 29, 3563–3570; (c)
Baratta, W.; Ballico, M.; Chelucci, G.; Siega, K.; Rigo, P. Angew. Chem., Int. Ed.
2008, 47, 4362–4365; (d) Baratta, W.; Chelucci, G.; Gladiali, S.; Siega, K.;
Toniutti, M.; Zanette, M.; Zangrando, E.; Rigo, P. Angew. Chem., Int. Ed. 2005, 44,
6214–6219; (e) Putignano, E.; Bossi, G.; Rigo, P.; Baratta, W. Organometallics
2012, 31, 1133–1142; (f) Baratta, W.; Ballico, M.; del Zotto, A.; Herdweck, E.;
Magnolia, S.; Peloso, R.; Siega, K.; Tuniutti, M.; Zangrando, E.; Rigo, P.
Organometallics 2009, 28, 4421–4430.
13. (a) Langer, R.; Leitus, G.; Ben-David, Y.; Milstein, D. Angew. Chem., Int. Ed. 2011,
50, 2120–2124; (b) Montag, M.; Zhang, J.; Milstein, D. J. Am. Chem. Soc. 2012,
134, 10325–10328; (c) Gnanaprakasam, B.; Zhang, J.; Milstein, D. Angew. Chem.,
Int. Ed. 2010, 49, 1468–1471; (d) Kohl, S. W.; Weiner, L.; Schwartsburd, L.;
Konstantinovski, L.; Shimon, L. J. W.; Ben-David, Y.; Iron, M. A.; Milstein, D.;
Kohl, S. W. Nature 2009, 324, 74–77.
Acknowledgments
We thank the Libyan Ministry for Higher Education and Scien-
tific Research for financial support (to M.O.D.), and Warwick Uni-
versity for support of A.W. The X-ray diffractometer was funded
through the Advantage West Midlands Science City Advanced
Materials project and ERDF support.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.tetlet.2013.05.
141.
References and notes
14. Kwong, H.-L.; Yeung, H.-L.; Yeung, C.-T.; Lee, W.-S.; Lee, C.-S.; Wong, W.-L.
Coord. Chem. Rev. 2007, 251, 2188–2222.
15. (a) Prakash, O.; Singh, P.; Mukherjee, G.; Singh, A. K. Organometallics 2012, 31,
3379–3388; (b) Nieto, I.; Livings, M. S.; Sacci, J. B., III; Reuther, L. E.; Zeller, M.;
Papish, E. T. Organometallics 2011, 30, 6339–6342; (c) Spasyuk, D.; Gusev, D. G.
Organometallics 2012, 31, 5239–5242.
1. (a) Gladiali, S.; Alberrico, E. Chem. Soc. Rev. 2006, 35, 226–236; (b) Ikariya, T.;
Murata, K.; Noyori, R. Org. Biomol. Chem. 2006, 4, 393–406; (c) Ikariya, T.;
Blacker, A. J. Acc. Chem. Res. 2007, 40, 1300–1308; (d) Clapham, S. E.; Hadzovic,
A.; Morris, R. H. Coord. Chem. Rev. 2004, 248, 2201–2237; (e) Hashiguchi, S.;
Noyori, R. Acc. Chem. Res. 1997, 30, 97–102.
2. (a) Fujii, A.; Hashiguchi, S.; Uematsu, N.; Ikariya, T.; Noyori, R. J. Am. Chem. Soc.
1996, 118, 2521–2522; (b) Murata, K.; Okano, K.; Miyagi, M.; Iwane, H.; Noyori,
R.; Ikariya, T. Org. Lett. 1999, 1, 1119–1121; (c) Haack, K. J.; Hashiguchi, S.; Fujii,
A.; Ikariya, T.; Noyori, R. Angew. Chem., Int. Ed. 1997, 36, 285–288; (d) Alonso, D.
A.; Brandt, P.; Nordin, S. J. M.; Andersson, P. G. J. Am. Chem. Soc. 1999, 121,
9580–9588; (e) Handgraaf, J.-W.; Meijer, E. J. J. Am. Chem. Soc. 2007, 129, 3099–
3103; (f) Soni, R.; Cheung, F. K.; Clarkson, G. C.; Martins, J. E. D.; Graham, M. A.;
Wills, M. Org. Biomol. Chem. 2011, 9, 3290–3294; (g) Steward, K. M.; Gentry, E.
C.; Johnson, J. S. J. Am. Chem. Soc. 2012, 134, 7329–7332.
3. (a) Mashima, K.; Abe, T.; Tani, K. Chem. Lett. 1998, 1199–1200; (b) Murata, K.;
Ikariya, T.; Noyori, R. J. Org. Chem. 1999, 64, 2186–2187; (c) Hamada, T.; Torii,
T.; Izawa, K.; Noyori, R.; Ikariya, T. Org. Lett. 2002, 4, 4373–4376; (d) Hamada,
T.; Torii, T.; Izawa, K.; Ikariya, T. Tetrahedron 2004, 60, 7411–7417; (e) Hamada,
T.; Torii, T.; Onishi, T.; Izawa, K.; Ikariya, T. J. Org. Chem. 2004, 69, 7391–7394;
(f) Thorpe, T.; Blacker, J.; Brown, S. M.; Bubert, C.; Crosby, J.; Fitzjohn, S.;
Muxworthy, J. P.; William, J. M. J. Tetrahedron Lett. 2001, 42, 4041–4143; (g)
16. Cortez, N. A.; Flores-López, C. Z.; Rodriguez-Apodaca, R.; Flores-López, L. Z.;
Parra-Hake, M.; Somanathan, R. ARKIVOC 2005, vi, 162–171.
17. Ahlford, K.; Livendahl, M.; Adolfsson, H. Tetrahedron Lett. 2009, 50, 6321–6324.
18. (a) Bisai, A.; Prasad, B.; Singh, V. ARKIVOC 2007, v, 20–37; (b) Trost, B. M.;
Zhang, Y. Chem. Eur. J. 2011, 17, 2916–2922.
19. Liu, B.; Zhong, Y.; Li, X. Chirality 2009, 21, 595–599.
20. Mei, W.; Wang, S.; Chungu, X.; Wei, S. Chin. J. Chem. 2010, 28, 1424–1428.
21. Compound 11 CCDC 929339; C27H27N3O2S, M = 457.58, monoclinic, space
group P2(1)2(1)2(1), a = 11.9961(2), b = 18.3565(3), c = 22.6663(3) Å,
b = 90°,
= 90°, U = 4991.26(13) Å3 (by least squares refinement on 14229
reflection positions), T = 150(2)K, k = 0.71073 A, Z = 8, D(cal) = 1.218 Mg/m3,
F(000) = 1936. mu(MoK-
) = 0.158 mmꢀ1. Crystal character: colourless block.
a = 90°,
c
a
Crystal dimensions 0.45 ꢁ 0.45 ꢁ 0.40 mm.
22. Lee, D. W.; Ha, H. Synth. Commun. 2007, 737–742.