Angewandte
Chemie
van den Berg, A. J. Minnaard,
Table 2: Ligand screening for the asymmetric hydrogenation of ortho-substituted aryl enamides and
1-naphthylenamides 4h–n.[a]
R. M. Haak, M. Leeman, E. P.
Schedde, A. Meetsma, B. L. Fer-
inga, A. H. M. de Vries, C. E. P.
Maljaars, C. E. Williams, D. Hyett,
J. A. F. Boogers, H. J. W. Hender-
ickx, J. G. de Vries, Adv. Synth.
Catal. 2003, 345, 308; d) R. Hoen,
J. A. F. Boogers, H. Bernsmann,
A. J. Minnaard, A. Meetsma, T. D.
Entry Substrate Ar
ee [%] (config.)[b]
L2[c] 1a[c]
The best reported ee [%]
L1[c]
1b[c]
1
4h
2-Me-C6H4
51.8 (S) 52.6 (R) 84.0 (R) 87.2 (R)
91.0 (R)[e]
74.8[12a]
2
3
4
4i
4j
4k
4l
4m
4n
2-MeO-C6H4 54.4 (R) 51.4 (R) 99.4 (R) 99.0 (R)
2-F-C6H4
2-Cl-C6H4
83.1[12d]
95.7[12a]
85[12j]
–
Tiemersma-Wegman,
A. H. M.
de Vries, J. G. de Vries, B. L. Fer-
inga, Angew. Chem. 2005, 117,
4281; Angew. Chem. Int. Ed. 2005,
44, 4209; e) A.-G. Hu, Y. Fu, J.-H.
Xie, H. Zhou, L.-X. Wang, Q.-L.
Zhou, Angew. Chem. 2002, 114,
2454; Angew. Chem. Int. Ed. 2002,
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Zhang, X. Zhang, Org. Lett. 2004,
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Chem. Soc. 2005, 127, 10488.
95.8 (R) 80.8 (R) 99.0 (R) 97.0 (R)
9.4 (R) 55.6 (R) 99.6 (R) 98.2 (R)
5[d]
6[d]
7
2-NO2-C6H4 88.0 (À) 85.8 (À) 98.2 (À) 98.2 (À)
2-CF3-C6H4
1-naphthyl
68.8 (+) 88.4 (+) 93.8 (+) 94.2 (+)
74.8 (S) 51.8 (R) 91.0 (R) 92.8 (R)
92.4 (R)[f] 93.8 (R)[g]
–
91.2[12f]
[a] Unless mentioned otherwise, all reactions were carried out with an S/C ratio of 100:1 in CH2Cl2 under
5 bar hydrogen pressure at RT for 24 h. In all cases, 100% conversion was achieved. [b] Determined by
chiral GC. The absolute configuration was assigned by comparison of observed optical rotation with
literature data. [c] [Rh(nbd)L1]SbF6 (nbd=2,5-norbornadiene) , [Rh(cod)L2]BF4, Rh[(cod)1a]BF4, and
Rh[(cod)1b]BF4 were used. [d] Absolution configurations were not determined. [e] T=08C, PH =25 bar.
2
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[f] T=08C, PH =50 bar. [g] 2,2,2-Trifluoroethanol (TFE) was used as solvent.
2
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donors. Synthesis and application of analogous triphospho-
rous bidentate ligands will be reported in due course.
Experimental Section
General procedure for the hydrogenation: A stock solution of [Rh/
1a] or [Rh/1b] complex (2 10À3 molLÀ1) was prepared by stirring
[Rh(cod)2]BF4 and 1a or 1b at a 1:1.1 molar ratio in CH2Cl2 at room
temperature for 1 h in a nitrogen-filled glovebox. The required
amount of catalyst solution (0.5 mL, 0.001 mmol) was transferred by
syringe into the vial charged with substrate (0.1 mmol), and the
solvent (2.5 mL) was added. All the vials were placed together in a
steel autoclave into which hydrogen gas was charged at the desired
pressure. After stirring at room temperature for 24 h, the hydrogen
was released carefully and the solution was concentrated and
subjected to a short column of silica gel to remove the metal complex.
The purified solution was analyzed by chiral GC or HPLC to
determine the ee value.
Received: April 15, 2006
Published online: August 7, 2006
Keywords: asymmetric catalysis · enamides · enantioselectivity ·
.
hydrogenation · rhodium
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[9] If only one phosphine group is attached to the ortho position of
the BINOL unit, two diastereomeric phosphine–phosphorami-
dite ligands will be obtained as a result of the creation of a P-
stereogenic center; this principle was applied to the preparation
of a series of single ortho-substituted monodentate ligands, see:
M. T. Reetz, J.-A. Ma, R. Goddard, Angew. Chem. 2005, 117,
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[10] See the Supporting Information for details.
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E. F. Nemeth, US Patent 2001, 6211244; b) N. Franceschini,
Angew. Chem. Int. Ed. 2006, 45, 5515 –5518
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
5517