10.1002/anie.201708440
Angewandte Chemie International Edition
COMMUNICATION
Acknowledgements
Ad
N(iPr)2
N(CH2)5
tBu
Ts
15
16
17
18
19
3pa
3qa
3ra
H
91
60
74
92
85
85
90
81
42
61
72
43
98:2
84.5:15.5
78.5:21.5
98:2
Ts
Ts
H
This work is supported by the Swiss National Science
Foundation (no 157741). We thank Dr. R. Scopelliti and Dr. F.
Fadaei Tirani for X-ray crystallographic analysis of compound
3aa.
H
o-Ns
3bb
3bc
H
tBu
p-Ns
H
98:2
Keywords: Asymmetric Catalysis • C‒H Activation • Iridium •
Chiral Cp Ligand • P-Chirality
20[c] 3bd
H
99:1
tBu
p-Cl-C6H4SO2
p-MeO-C6H4SO2
Ms
tBu
21
22
3be
3bf
H
98.5:1.5
98:2
[1]
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Synthesis, (Eds.: P. C. J. Kamer, P. W. N. M. v. Leeuwen), Wiley,
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tBu
H
23[c] 3ib
24[c] 3id
25[c] 3ie
26[c] 3if
p-Cl
p-Cl
p-Cl
p-Cl
97:3
tBu
o-Ns
[2]
[3]
[4]
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tBu
p-Cl-C6H4SO2
p-MeO-C6H4SO2
Ms
99:1
tBu
98:2
D. Parmar, E. Sugiono, S. Raja, M. Rueping, Chem. Rev. 2014, 114,
9047.
tBu
95:5
[5]
[6]
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[a] Conditions: 0.1 mmol 1x, 0.11 mmol of 2y, 2.00ꢀµmol Ir1, 8.50ꢀµmol
AgNTf2, 24.0ꢀµmol (S)-A1, 0.1 M in tAmOH/dioxane (4:1), 0 °C for 36 h; [b]
Isolated yield; [c] with 4.00 μmol Ir1 and 17.0 μmol AgNTf2.
[7]
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Removal of the o-nosyl group of 3bb proceeded smoothly
under Fukuyama-conditions,[21] providing free aniline 4 in 88%
yield with a preservation of the enantiomeric purity (Scheme 4).
An enantiospecific reduction of the phosphine oxide functionality
of 3ba was achieved in a two-step procedure.[22] Methylation,
followed by treatment with MeOTf and LiAlH4 gave P-chiral
phosphine (isolated as its borane adduct 5) without loss of
enantiomeric purity.
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[9]
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1892.
Scheme 4. o-Nosyl-deprotection of 3bb and enantiospecific reduction of 3ba.
In summary, we have developed a highly enantioselective C-H
amidation of phosphine oxides showcasing the potential of our
chiral Cpx ligand for iridium(III) catalyzed C-H functionalizations.
A very strong cooperative effect between the chiral Cpx ligand
and the readily available phthaloyl tert-leucine enabled this
transformation. We have shown that matched-mismatched
cases of the different acid enantiomers can dramatically
enhance yield and selectivity. Enantiospecific reduction provides
access to valuable P-chiral phosphines for potential application
as ligands and catalysts.
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