SIAPhos: Phosphorylated sulfonimidamides and their use in iridium-catalyzed asymmetric hydrogenations of sterically hindered cyclic enamides

Article abstract of DOI:10.1002/adsc.201100692

Phosphorylated sulfonimidamides (SIAPhos) undergo ion exchange reactions with cationic complexes, [Rh(cod)₂BF₄] and [Ir(cod) ₂BarF], or neutral complexes [Rh(cod)Cl] ₂ and [Ir(cod)Cl] ₂, leading to unprecedented neutral complexes with PN- S-N chelates. Use of the resulting neutral iridium complexes in asymmetric hydrogenation reactions of tri- and tetrasubstituted enamides leads to products with high enantioselectivities (up to 92% ee).

Full text of DOI:10.1002/adsc.201100692

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DOI: 10.1002/adsc.201100692
SIAPhos: Phosphorylated Sulfonimidamides and their Use in
Iridium-Catalyzed Asymmetric Hydrogenations of Sterically
Hindered Cyclic Enamides
Frederic W. Patureau,a,d Christin Worch,b Maxime A. Siegler,c Anthony L. Spek,c
Carsten Bolm,b,* and Joost N. H. Reeka,*
a
Van’t Hoff Institute for Molecular Sciences, Postbus 94720, 1090 GE Amsterdam, The Netherlands
Fax : (+31)-20-525-5604; phone: (+31)-20-525-5265; e-mail: J.N.H.Reek@uva.nl
Institut fꢀr Organische Chemie, RWTH Aachen University, Landoltweg 1, 52056 Aachen, Germany
b
Fax : (+49)-241-809-2391, phone: (+49)-241-809-4675; e-mail: Carsten.Bolm@oc.RWTH-Aachen.de
Bijvoet Center for Biomolecular Research, Crystal and Structural Chemistry, Utrecht University, Padualaan 8, 3584CH
c
Utrecht, The Netherlands
d
Fachbereich Chemie, Technische Universitꢁt Kaiserslautern, Erwin-Schrçdinger-Straße Geb. 52, 67663 Kaiserslautern,
Germany
Received: September 2, 2011; Published online: January 12, 2012
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/adsc.201100692.
Abstract: Phosphorylated sulfonimidamides (SIA-
Phos) undergo ion exchange reactions with cationic
ways.[1,2] Because of these dogmas, neutral transition
metal-based catalysts[3] and metal complexes based on
ligands with C1 symmetry[4] are somewhat undevel-
oped, although recent examples illustrate their poten-
tial.[3,4,5] Here, we report on the first sulfonimidamido-
based phosphoramidites (SIAPhos), their rhodium
and iridium complexes and the application of these
neutral C1-symmetrical complexes in asymmetric hy-
drogenation reactions. The iridium complexes are
complexes, [Rh
neutral complexes [Rh
A
ACHTUNGTRENNUNG
N
ACHTUNGTRENNUNG
leading to unprecedented neutral complexes with P-
N-S-N chelates. Use of the resulting neutral iridium
complexes in asymmetric hydrogenation reactions
of tri- and tetrasubstituted enamides leads to prod-
ucts with high enantioselectivities (up to 92% ee).
Keywords: asymmetric hydrogenation; iridium;
phosphorylated sulfonimidamides (SIAPhos); SIA-
Phos (phosphorylated sulfonimidamides); sulfon-
ACHTUNGTRENNUNGimidamides; sulfur chirality
Metal-catalyzed asymmetric hydrogenation reactions
are among the most important transformations in ho-
mogeneous catalysis and, as such, have been widely
studied in both academia and industry.[1] Commonly,
the rhodium and iridium complexes employed in
enantioselective hydrogenations of olefins are cationic
because they prove more effective than their neutral
counterparts.[1] This has been explained in part by the
fact that the cationic metal centers display stronger
bonding of the substrate compared to the analogous
neutral centers, leading to a higher face discrimina-
tion.[1] Furthermore, the most successful ligands are
C2-symmetrical, so reducing the number of substrate
complexes and therefore competing reaction path-
Scheme 1. Synthesis of sulfonimidamide-based phosphor-
AHCTUNGTREGaNNUN midites (SIAPhos).
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59

Frederic W. Patureau et al.
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Figure 1. X-ray structure of [(Rax,R)-2·Et3NH] (ORTEP view, 50% probability level), selected atomic distances (ꢃ):
À
À
À
À
À
À
H31 N3=0.932 (19); H31 N1=2.20(2); H31 N2=2.217(19); N2 P1=1.6605(18); N2 S2=1.5541(19); S2 N1=1.5844(18);
N1 S1=1.6022(16).
À
very selective catalysts for sterically hindered tetra- 3·Et3NH] imposes pseudo-axial chirality on the tropos
substituted acetamido-alkenes, providing new routes biphenol backbone [pseudo-(S) configuration in the
to relevant products for the preparation of bioactive X-ray; Figure 2]. As evidenced by the X-ray struc-
compounds.[6] Although the resolution of various sul- tures and solution phase 31P NMR experiments, the
fonimidamides is established,[7] their applications as N-phosphorylation of the sulfonimidamides had no
chiral ligands in transition metal catalysis are still effect on the absolute configuration at sulfur.[8]
scarce. Hypothesizing that sulfonimidamides could be
N-phosphorylated, we envisioned that the chemistry with [Rh
would be compatible with that of METAMORPhos, lyst precursor), a single product was formed, which
the sulfonamide-based analogues that we have recent- was identified as neutral [Rh(Rax,R)-2(nbd)] by NMR
ly introduced.[3a,8] spectroscopy and HR-MS.[9] In this complex the
When enantiopure [(Rax,R)-2·Et3NH] was combined
AHCTUNGTRENNUNG
A
ACHTUNGTRENNUNG
Sulfonimidamido-based phosphoramidites (SIA- ligand chelates to the metal with its P-N-S-N core
Phos) were accessible by reactions between sulfonimi- forming a 5-membered ring (Scheme 2). As evidenced
damides 1 and phosphochloridites in the presence of by the 31P NMR profile (Figure 3), the complex is
Et3N (Scheme 1).[9] With enantiomerically pure sulfur configurationally stable and no isomerization to the
reagents, products 2–4 were obtained in almost quan- corresponding diastereomeric complex [Rh
ACHTUGNERTN(NUGN Sax,R)-2-
titative yields with retention of chirality. The struc- (nbd)] occurs, even after 24 h in solution (CD2Cl2) at
AHCTUNGTRENNUNG
tures of [(Rax,R)-2·Et3NH] and [(R)-3·Et3NH] were room temperature. In contrast to the coordination be-
confirmed by X-ray crystallography (Figure 1 and havior of the analogous sulfonamido-phosphoramid-
Figure 2, respectively).[9] Noticeably, in both com-
pounds one equivalent of Et3NH+ is bound to the
ites,[3a] none of the sulfonimidamido-based phosphor-
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
amidites led to dimeric m-P,NÀ-bridged dinuclear rho-
anionic core, a feature that resembles the binding dium complexes,[3a] which can be attributed to the
mode in sulfonamido-phosphoramidites.[3a] Interest- steric bulk of the SIAPhos ligands in combination
ingly, in [(Rax,R)-2·Et3NH] the ammonium proton is with their chelating capability through the second ni-
equally bound to N-1 and N-2 [2.20
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG(0.2) ꢃ, respectively), whereas in [(R)-3·Et3NH] the
H-bond is non-symmetrical in favor of N-1 [1.95(2) when [(R)-3·Et3NH] derived from the bulky 3,3’,5,5’-
versus 2.73(2) ꢃ for N-2], presumably due to the tetra-tert-butylbiphenyl-2,2’-diol was treated with cat-
steric congestion with the t-Bu groups.[9] The central ionic [Rh
N
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
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SIAPhos: Phosphorylated Sulfonimidamides and their Use in Iridium-Catalyzed Asymmetric Hydrogenations
Figure 2. X-ray structure of [(R)-3·Et3NH] (ORTEP view, 30% probability level; protons, solvent molecules and Et3NH+
À
À
À
À
moiety omitted for clarity), selected atomic distances (ꢃ): N2 P1=1.665(2); N2 S2=1.543(2); S2 N1=1.602(2); N1 S1=
À
À
À
1.6163(19); C29 O3=3.305(3); C41 C10=3.612(4); C42 C9=3.851(4).
Scheme 2. Treatment of [(Rax,R)-2·Et3NH] with the complex
[Rh(nbd)2BF4].
Figure 3. 31P NMR profile (202.3 MHz, CD2Cl2) of a diaste-
reomeric mixture of [Rh(Rax,R)-2(nbd)] and [Rh(Sax,R)-2-
(nbd)] (top), and of diastereopure [Rh(Rax,R)-2(nbd)] after
24 h in solution at room temperature (bottom), d (ppm)=
129.44 {d, 1JP, Rh =264 Hz, [Rh
(Rax,R)-2(nbd)]}, 125.48 {d,
1JP, Rh =264 Hz, [Rh
(Sax,R)-2(nbd)]}.
ACHTUNGTRENNUNG
G
R
ACHTUNGTRENNUNG
G
E
ACHTUNGTRENNUNG
[Ir(R)-3ACHTUNGTRENNUNG(cod)], respectively (Scheme 3). The chelating
G
ACHTUNGTRENNUNG
effect of the ligand was even sufficient to instantane-
ously displace chloride ions from metal complexes
G
ACHTUNGTRENNUNG
such as [RhCl
change behavior is remarkable because chloride is a
(cod)]2.[9] This ion ex-
ACHTUNGTRENNUNG(cod)]2 and [IrClACHUTNGTRENNUGN
strongly coordinating anion, and structures with m-Cl cyclic enamides. Due to potential applications in the
bridges commonly require strong alkali reagents for synthesis of bioactive compounds, the resulting prod-
chloride removal.
ucts have synthetic relevance,[6] and generally, those
The neutral rhodium and iridium complexes were transformations are reputed to be difficult. In this par-
then evaluated as catalysts in asymmetric hydrogena- ticular case, asymmetric hydrogenation of N-(3,4-di-
tion reactions. The most interesting results were ob- hydronaphthalen-2-yl)acetamide (5a) with a catalyst
tained with the iridium-based systems, which did not bearing (R)-4 as ligand led to amide 6a with a re-
give satisfactory results for benchmark substrates (see markable 75% ee (Table 1, entry 4). Also tetrasubsti-
Supporting Information)[9] but allowed enantioselec- tuted cyclic enamides reacted well affording the cor-
tive hydrogenations of conjugated, multi-substituted responding amides with high enantioselectivities.
Adv. Synth. Catal. 2012, 354, 59 – 64
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Frederic W. Patureau et al.
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Scheme 3. Treatment of SIAPhos [(R)-3·Et3NH] with rhodium and iridium complexes.
Table 1. Hydrogenation with Ir-based SIAPhos catalysts.
resulted only in trace amounts of products (Table 1,
entries 1 and 2).
In conclusion, we have prepared sulfonimidamido-
based phosphoramidites (SIAPhos) and found them
to be effective in catalyzed asymmetric hydrogena-
tions of tri- and tetra-substituted acetamido-alkenes
with neutral iridium complexes. In transformations of
5c a product with up to 92% ee was obtained, which –
to the best of our knowledge – is the highest enantio-
selectivity ever reported in a conversion of this chal-
lenging and biologically relevant substrate.[3a] Finally,
we have shown that neutral iridium catalysts based on
SIAPhos ligands are more effective in the asymmetric
hydrogenation reaction of strongly coordinating sub-
strates. We expect that future asymmetric transforma-
tions of likewise strongly coordinating substrates may
be addressed by analogous strategies, that is, by
taming the cationic character of the active metal
center.
Entry
L[a]
(Rax,R)-2
Substrate
Conv. [%][b]
ee [%][b]
1
2
3
4
5
6
7
8
G
5a
5a
5a
5a
5b
5b
5c
5c
trace
trace
>98
81
27
55
–
–
A
(R)-3
(R)-4
(R)-3
(R)-4
(R)-3
(R)-4
70
75
73
85
86
92
75
55
[a]
Ir: 0.5 mM in CH2Cl2, reaction volume: 2.5 mL.
[b]
Determined by GC (for 6a and 6c) or HPLC (5b) using
chiral stationary phases. From 5b and 5c cis-configured
products were selectively formed. Complexes bearing
(R)-3 and (R)-4 gave the same enantiomeric products
from all three substrates.
Experimental Section
General Procedure for the Asymmetric
Hydrogenation of 5a–c
Thus, starting from N-(1-benzyl-3,4-dihydronaphtha-
len-2-yl)acetamide (5b) product 6b was obtained with
up to 85% ee (at 55% conversion) (Table 1, entry 6),
A 15-mL pressure reactor containing a glass insert was suc-
which are among the highest ee and conversions re- cessively charged, under inert conditions, with a dichlorome-
ported so far.[10] Hydrogenating N-(1-methyl-3,4-dihy-
thane (DCM) solution (1 mL) of the ligand, a DCM solution
(0.5 mL) of the metal precursor {either [Rh
ACHTUNGTRNEN(UNG nbd)2BF4] or
dronaphthalen-2-yl)acetamide (5c) led to amide 6c
with 92% ee (at 55% conversion, Table 1, entry 8),
which, to the best of our knowledge, is the highest ee
ever reported in a catalytic synthesis of this biologi-
cally relevant and challenging substrate. To our sur-
prise, complexes with sulfonimidamido-based phos-
phoramidites having two stereogenic elements, but
being less bulky than the 3,3’,5,5’-tetra-tert-butylbi-
[IrCl(coe)2]2}, and a DCM solution (1 mL) of the substrate,
AHCTUNGTRENNUNG
at the required concentrations. The resulting solution was
stirred at room temperature for 5 min and then exposed to
50 bar of H2 atmosphere (at 298 K under vortex-type stirring
with 300 rpm).
CCDC 746665 and CCDC 746666 contain the supplemen-
tary crystallographic data for 2 and 3. These data can be ob-
tained free of charge from The Cambridge Crystallographic
phenyl-2,2’-diol-based backbones of (R)-3 and (R)-4, Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
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SIAPhos: Phosphorylated Sulfonimidamides and their Use in Iridium-Catalyzed Asymmetric Hydrogenations
Zheng, Tetrahedron: Asymmetry 2005, 16, 1233; k) J. D.
Acknowledgements
Huang, X. P. Hu, Z. C. Duan, Q. H. Zeng, S. B. Yu, J.
Deng, D. Y. Wang, Z. Zheng, Org. Lett. 2006, 8, 4367;
l) D. Y. Wang, X. P. Hu, J. D. Huang, J. Deng, S. B. Yu,
Z. C. Duan, X. F. Xu, Z. Zheng, Angew. Chem. 2007,
119, 7956; Angew. Chem. Int. Ed. 2007, 46, 7810; m) M.
Qiu, X. P. Hu, D. Y. Wang, J. Deng, J. D. Huang, S. B.
Yu, Z. C. Duan, Z. Zheng, Adv. Synth. Catal. 2008, 350,
1413; n) S. B. Yu, J.-D. Huang, D. Y. Wang, X. P. Hu, J.
Deng, Z. C. Duan, Z. Zheng, Tetrahedron: Asymmetry
2008, 19, 1862; o) K. A. Vallianatou, I. D. Kostas, J.
Holz, A. Bçrner, Tetrahedron Lett. 2006, 47, 7947; p) Y.
Yan, X. Zhang, J. Am. Chem. Soc. 2006, 128, 7198;
q) X. Zhang, B. Cao, Y. Yan, S. Yu, B. Ji, X. Zhang,
Chem. Eur. J. 2010, 16, 871; r) Z. C. Duan, X. P. Hu, J.
Deng, S. B. Yu, D. Y. Wang, Z. Zheng, Tetrahedron:
Asymmetry 2009, 20, 588; s) M. Qiu, D. Y. Wang, X. P.
Hu, J. D. Huang, S. B. Yu, J. Deng, Z. C. Duan, Z.
Zheng, Tetrahedron: Asymmetry 2009, 20, 210; t) S. B.
Yu, X. P. Hu, J. Deng, D. Y. Wang, Z. C. Duan, Z.
Zheng, Tetrahedron: Asymmetry 2009, 20, 621; u) J.
Wassenaar, J. N. H. Reek, Dalton Trans. 2007, 3750;
v) J. Wassenaar, M. Kuil, J. N. H. Reek, Adv. Synth.
Catal. 2008, 350, 1610; w) J. Wassenaar, J. N. H. Reek,
J. Org. Chem. 2009, 74, 8403; x) C. Darcel, D. Moulin,
J-C. Henry, M. Lagrelette, P. Richard, P. D. Harvey, S.
Juge, Eur. J. Org. Chem. 2007, 2078; y) J. Wassenaar, E.
Jansen, W. J. van Zeist, F. M. Bickelhaupt, M. A. Sie-
gler, A. L. Spek, J. N. H. Reek, Nature Chem. 2010, 2,
417; z) J. Wassenaar, M. Kuil, M. Lutz, A. L. Spek,
J. N. H. Reek, Chem. Eur. J. 2010,16, 6509.
Fatna Ait El Maate (preparation of 5c) and Han Peeters
(HR-MS) are acknowledged. The NRSC-C, BASF, EZ and
the Fonds der Chemischen Industrie are acknowledged for fi-
nancial support. This work was also supported in part
(A.L.S.) by the Council for the Chemical Sciences of The
Netherlands Organization for Scientific Research (CW-
NWO).
References
[1] a) J. G. de Vries and C. J. Elsevier, The Handbook of
Homogeneous Hydrogenation, Wiley-VCH, Weinheim,
2007; b) H.-U. Blaser, B. Pugin, F. Spindler, M. Thom-
men, Acc. Chem. Res. 2007, 40, 1240; c) H.-U. Blaser,
C. Malan, B. Pugin, F. Spindler, H. Steiner, M. Studer,
Adv. Synth. Catal. 2003, 345, 103; d) I. D. Gridnev, T.
Imamoto, Chem. Commun. 2009, 7447; e) J. K. White-
sell, Chem. Rev. 1989, 89, 1581; f) J.-H. Xie, S.-F. Zhu,
Q.-L. Zhou, Chem. Rev. 2011, 111, 1713.
[2] J. M. Brown, P. L. Evans, Tetrahedron 1988, 44, 4905.
[3] For successful neutral rhodium and iridium complexes,
see: a) F. W. Patureau, S. de Boer, M. Kuil, J. Meeuwis-
sen, P-A. B. Breuil, M. A. Siegler, A. L. Spek, A. J.
Sandee, B. de Bruin, J. N. H. Reek, J. Am. Chem. Soc.
2009, 131, 6683; b) F. Giacomina, A. Meetsma, L. Pan-
ella, L. Lefort, A. H. M. de Vries, J. G. de Vries,
Angew. Chem. 2007, 119, 1519; Angew. Chem. Int. Ed.
2007, 46, 1497. For analogous strategies in Ir asymmet-
ric hydrogenation, see also: c) G. Erre, S. Enthaler, K.
Junge, D. Addis, M. Beller, Adv. Synth. Catal. 2009,
351, 1437; d) S. Enthaler, G. Erre, K. Junge, K. Schrçd-
er, D. Addis, D. Michalik, M. Hapke, D. Redkin, M.
Beller, Eur. J. Org. Chem. 2008, 3352. For Ir asymmet-
ric hydrogenation examples of cyclic enamides with C2-
symmetrical phosphoramidites see also: e) G.-H. Hou,
J.-H. Xie, P.-C. Yan, Q-L. Zhou, J. Am. Chem. Soc.
2009, 131, 1366. For indicative examples of phosphora-
midites in IrCl-based neutral catalysis, see also: f) T.
Ohmura, J. F. Hartwig, J. Am. Chem. Soc. 2002, 124,
15164; g) F. Lopez, T. Ohmura, J. F. Hartwig, J. Am.
Chem. Soc. 2003, 125, 3426; h) C. A. Kiener, C. Shu, C.
Incarvito, J. F. Hartwig, J. Am. Chem. Soc. 2003, 125,
14272; i) A. Leitner, S. Shekhar, M. J. Pouy, J. F. Hart-
wig, J. Am. Chem. Soc. 2005, 127, 15506; j) G. Lipow-
sky, N. Miller, G. Helmchen, Angew. Chem. 2004, 116,
4695; Angew. Chem. Int. Ed. 2004, 43, 4595.
[4] For reviews, see: a) V. A. Pavlov, Tetrahedron 2008, 64,
1147; b) K. C. Bhowmick, N. N. Joshi, Tetrahedron:
Asymmetry 2006, 17, 1901; c) J. Wassenaar, J. N. H.
Reek, Org. Biomol. Chem. 2011 ,9, 1704; d) H. Fernan-
dez-Perez, P. Etayo, A. Panossian, A. Vidal-Ferran
Chem. Rev. 2011, 111, 2119; e) F. Boeda, T. Beneyton,
C. Crꢄvisy, Mini-Rev. Org. Chem. 2008, 5, 96; f) H. A.
McManus, P. J. Guiry, Chem. Rev. 2004, 104, 4151. For
some examples: g) G. Francio, F. Faraone, W. Leitner,
Angew. Chem. 2000, 112, 1486; Angew. Chem. Int. Ed.
2000, 39, 1428; h) X. P. Hu, Z. Zheng, Org. Lett. 2004,
6, 3585; i) X. P. Hu, Z. Zheng, Org. Lett. 2005, 7, 419;
j) Q. H. Zeng, X. P. Hu, Z. C. Duan, X. M. Liang, Z.
[5] For an indicative example of a neutral hydrogenation
catalyst employing a C1-symmetrical chiral ligand see:
W. S. Knowles, M. J. Sabacky, J. Chem. Soc. Chem.
Commun. 1968, 1445.
[6] a) W. Tang, Y. Chi, X. Zhang, Org. Lett. 2002, 4, 1695;
b) Z. Zhang, G. Zhu, Q. Jiang, D. Xiao, X. Zhang, J.
Org. Chem. 1999, 64, 1774; c) J. L. Renaud, P. Dupau,
A-E. Hay, M. Guingouain, P. H. Dixneuf, C. Bruneau,
Adv. Synth. Catal. 2003, 345, 230; d) X-B. Jiang, L.
Lefort, P. E. Goudriaan, A. H. M. de Vries, P. W. N. M.
van Leeuwen, J. G. de Vries, J. N. H. Reek, Angew.
Chem. 2006, 118, 1245; Angew. Chem. Int. Ed. 2006, 45,
1223; e) P. Dupau, C. Bruneau, P. H. Dixneuf, Adv.
Synth. Catal. 2001, 343, 331; f) M. C. Jetter, M. A.
Youngman, J. J. McNally, M. E. McDonnell, S-P.
Zhang, A. E. Dubin, N. Nasser, E. E. Codd, C. M.
Flores, S. L. Dax, Bioorg. Med. Chem. Lett. 2007, 17,
6160; g) M. A. Youngman, N. M. Willard, S. L. Dax,
J. J. McNally, Synth. Commun. 2003, 33, 2215; h) J.
Meeuwissen, M. Kuil, A. M. van der Burg, A. J.
Sandee, J. N. H. Reek, Chem. Eur. J. 2009, 15, 10272.
[7] a) C. Liang, F. Collet, F. Robert-Peillard, P. Mꢀller,
R. H. Dodd, P. Dauban, J. Am. Chem. Soc. 2008, 130,
343; b) C. Liang, F. Robert-Peillard, C. Fruit, P. Mꢀller,
R. H. Dodd, P. Dauban, Angew. Chem. 2006, 118, 4757;
Angew. Chem. Int. Ed. 2006, 45, 4641; c) C. Fruit, F.
Robert-Peillard, G. Bernardinelli, P. Mꢀller, R. H.
Dodd, P. Dauban, Tetrahedron: Asymmetry 2005, 16,
3484; d) C. Worch, C. Bolm, Synthesis 2007, 1355; e) C.
Worch, C. Bolm, Synthesis 2008, 739; f) S. Azzaro, L.
Fensterbank, E. Lacote, M. Malacria, Synlett 2008,
Adv. Synth. Catal. 2012, 354, 59 – 64
ꢂ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
63

Frederic W. Patureau et al.
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2253; g) C. Worch, I. Atodiresei, G. Raabe, C. Bolm,
Chem. Eur. J. 2010, 16, 677. h) For an asymmetric orga-
nocatalysis, see: C. Worch, C. Bolm, Synlett 2009, 2425.
[8] a) F. W. Patureau, M. Kuil, A. J. Sandee, J. N. H. Reek,
Angew. Chem. 2008, 120, 3224; Angew. Chem. Int. Ed.
2008, 47, 3180. Highlight: b) H. Yamamoto, P. Li, Syn-
facts 2008, 7, 0721; c) P-A. R. Breuil, F. W. Patureau,
J. N. H. Reek, Angew. Chem. 2009, 121, 2196; Angew.
Chem. Int. Ed. 2009, 48, 2162.
[9] See the Supporting Information.
[10] For example, at 100 bar of H2 pressure a Ru catalyst in
MeOH led to full conversion and 52% ee at 308C for
20 h. For details see ref.[6e]
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