Novel chiral phosphine-phosphoramidite ligands derived from 1-naphthylamine for highly efficient Rh-catalyzed asymmetric hydrogenation

Article abstract of DOI:10.1016/j.tetasy.2008.07.022

A new chiral phosphine-phosphoramidite ligand (S)-HY-Phos 1 has been prepared from 1-naphthylamine via a two-step transformation, and successfully applied in the Rh-catalyzed asymmetric hydrogenation of various functionalized olefins, including α-(acetamido)cinnamates, enamides and α-enol ester phosphonates, in which up to 98% ee, 99% ee and 99% ee were achieved, respectively.

Full text of DOI:10.1016/j.tetasy.2008.07.022

Tetrahedron: Asymmetry 19 (2008) 1862–1866
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Tetrahedron: Asymmetry
journal homepage: www.elsevier.com/locate/tetasy
Novel chiral phosphine-phosphoramidite ligands derived from
1-naphthylamine for highly efficient Rh-catalyzed asymmetric hydrogenation
Sai-Bo Yu a,b, Jia-Di Huang a,b, Dao-Yong Wang a,b, Xiang-Ping Hu a, , Jun Deng a,b, Zheng-Chao Duan a,b
,
*
Zhuo Zheng a,
*
a Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China
b Graduate School of Chinese Academy of Sciences, Beijing 100039, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A new chiral phosphine-phosphoramidite ligand (S)-HY-Phos 1 has been prepared from 1-naphthylamine
via a two-step transformation, and successfully applied in the Rh-catalyzed asymmetric hydrogenation of
Received 24 June 2008
Accepted 15 July 2008
Available online 8 August 2008
various functionalized olefins, including
a-(acetamido)cinnamates, enamides and a-enol ester phospho-
nates, in which up to 98% ee, 99% ee and 99% ee were achieved, respectively.
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
functionalized olefins.8 Due to the high cost of chiral 1,2,3,4-tetra-
hydro-1-naphthylamine, the search for an inexpensive alternative
for the synthesis of new phosphine-phosphoramidite ligands is
highly desirable. Due to the structural similarity, we therefore
surmised that 1-naphthylamine should be a good candidate.
Furthermore, the increased rigidity from 1,2,3,4-tetrahydro-1-
naphthylamine to 1-naphthylamine may also result in the signifi-
cantly different results in the catalytic asymmetric hydrogenation.
As a result, we herein report our study on the development of this
new chiral phosphine-phosphoramidite ligand [(S)-HY-Phos] from
commercially available and inexpensive starting materials, 1-
naphthylamine. The results disclose that this newly developed
phosphine-phosphoramidite ligand, despite the absence of the
central chirality in comparison with (Rc,Ra)-THNAPhos, displayed
excellent enantioselectivities in the Rh-catalyzed asymmetric
Unsymmetrical hybrid phosphine-phosphoramidite com-
pounds have recently emerged as a new class of chiral ligands
for highly efficient asymmetric catalysis.1 Due to the two different
phosphorus binding sites, this kind of ligands can offer a unique
electronic environment around the central metal, which results
in significantly improved enantioselectivities in some cases. The
first successful phosphine-phosphoramidite ligand was known as
QUINAPHOS, reported by Leitner et al. in 2000, which exhibited
good enantioselectivities in the Rh-catalyzed asymmetric hydro-
genation of dimethyl itaconate and methyl 2-acetamidoacrylate.2
Since then, a few examples of chiral phosphine-phosphoramidite
species (e.g., ferrocene-based derivatives,3 PEAPhos,4 Me-Anila-
Phos,5 IndolPhos6 and others7) have been found to be highly
efficient ligands for various asymmetric catalyses including
Rh-catalyzed asymmetric hydrogenation, Rh-catalyzed asymmet-
ric hydroformylation and Cu-catalyzed asymmetric conjugate
addition of diethylzinc to enones. In spite of these advances, the
development of new chiral phosphine-phosphoramidite ligands
in terms of easy preparation and wide substrate scope remains
an interesting and important goal. As part of our ongoing efforts to-
ward the development of new and efficient unsymmetrical hybrid
ligands for asymmetric catalysis,4,8,9 in our recent research, we
have reported a highly efficient 1,2,3,4-tetrahydro-1-naphthyl-
amine-derived phosphine-phosphoramidite ligand, (Rc,Ra)-THNA-
Phos, for the Rh-catalyzed asymmetric hydrogenation of various
hydrogenation of various functionalized olefins including
a-
(acetamido)cinnamates, enamides and -enol ester phosphonates,
a
in which up to 98% ee, 99% ee and 99% ee were achieved, respec-
tively (see Fig. 1).
O
O
O
O
P
P
N
N
H
H
PPh2
PPh2
(R,R)-THNAPhos
(S)-HY-Phos 1
* Corresponding authors. Tel.: +86 411 84379206; fax: +86 411 84684746.
E-mail addresses: xiangping@dicp.ac.cn (X.-P. Hu), zhengz@dicp.ac.cn (Z. Zheng).
Figure 1. The structure of phosphine-phosphoramidite ligands (R,R)-THNAPhos
and (S)-HY-Phos 1.
0957-4166/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2008.07.022

S.-B. Yu et al. / Tetrahedron: Asymmetry 19 (2008) 1862–1866
1863
NAPNH2 3 was then converted into the corresponding phos-
phine-phosphoramidite ligand [(S)-HY-Phos 1] by the reaction
with 1 equiv of (S)-4-chloro-3,5-dioxa-4-phosphacyclohepta[2,1-
2. Results and discussion
2.1. Synthesis of chiral phosphine-phosphoramidite ligand 1
from 1-naphthylamine
a
;3,4-a0]dinaphthalene in toluene at 0 °C in the presence of Et3N
as a scavenger for the HCl eliminated (Scheme 2). This new phos-
phine-phosphoramidite ligand is air-stable and can be used in
the open air, which makes this ligand practical for general labora-
tory preparations, as well as scale-up operations.
The key to the synthesis of the target phosphine-phosphorami-
dite ligand is the preparation of an amino-phosphine intermediate,
which can be obtained by the direct ortho-lithiation of 1-naphthyl-
amine followed by the introduction of a diphenylphosphino group
as the method described by us recently.4 Thus, commercially avail-
able 1-naphthylamine 2 was treated with n-BuLi at ꢀ20 °C, fol-
lowed by the slow addition of neat ClSiMe3, which in situ
generated a monosilyated product, N-(trimethylsilyl)-1-naphthyl-
amine. The compound was further dilithiated by the addition of
3 equiv of n-BuLi at ꢀ30 °C, and then ortho-phosphinated with
ClPPh2. Since 1-naphthylamine can undergo lithiation at either
the 8-position or the 2-position, the subsequent reaction with
ClPPh2 gives rise to 1-(8-diphenylphosphino)naphthylamine 3
(NAPNH2) and 1-(2-diphenylphosphino)naphthylamine 4, respec-
tively, as shown in Scheme 1.
O
P
Cl
O
O
PPh NH
2
2
P
N
H
(S)
O
Et3N/toluene
0 oC-rt
PPh
2
NAPNH 3
(S)-HY-Phos 1
2
Scheme 2. Synthesis of chiral phosphine-phosphoramidite ligand (S)-HY-Phos 1.
NH2
n-BuLi/Et2O
-20 oC
NHSiMe3
2.2. Rh-catalyzed asymmetric hydrogenation of various
functionalized olefins with phosphine-phosphoramidite
ligand 1
ClSiMe3/Et2O
-20 o
C
2
n-BuLi/Et2O
-30 oC
With this newly developed phosphine-phosphoramidite ligand
in hand, we then examined its efficiency in the Rh-catalyzed asym-
metric hydrogenation of a-(acetamido)cinnamates 5. The hydroge-
Li
Li
Me3Si
Li
NSiMe3
N
nation was performed at room temperature under an H2 pressure
of 10 atm in the presence of 1 mol % of the Rh-catalyst prepared
in situ from [Rh(COD)2]BF4 and 1.1 equiv of chiral ligand. As shown
in Table 1, this new phosphine-phosphoramidite ligand displayed
excellent enantioselectivity for the hydrogenation of methyl (Z)-
acetamidocinnamate 5a, affording the hydrogenation product in
an ee-value of up to 98% ee (entry 2). This result is comparable
to that obtained with (R,R)-THNAPhos, although only axial chirality
Li
ClPPh2/Et2O
-30 oC-rt
ClPPh2/Et2O
-30 oC-rt
NH2
PPh2
NH2
PPh2
Table 1
Rh-catalyzed asymmetric hydrogenation of
a-(acetamido)cinnamates 5 with phos-
phine-phosphoramidite ligand 1a
NAPNH2 3
4
(30% yield)
[Rh(COD)2]BF4 (1 mol %)
(S)-HY-Phos 1 (1.1 mol %)
CO2R
NHAc
CO2R
NHAc
Scheme 1. Synthesis of amino-phosphine intermediate via direct ortho-lithiation of
1-naphthylamine followed by the introduction of a diphenylphosphino group.
Ar
Ar
H2 (10 atm), solvent, rt
Fortunately, after work-up and crystallization from n-hexane, 1-
(8-diphenylphosphino)naphthylamine 3 (NAPNH2) was obtained
in 30% yield exclusively, and no 1-(2-diphenylphosphino)naph-
thylamine 4 was separated. The structure of 1-(8-diphenylphos-
5
6
Entry
Substrate (Ar, R)
Solvent
Conv.b (%)
eec (%) (config.)
1
2
3
4
5
6
7
8
9
5a (Ph, Me)
5a (Ph, Me)
5a (Ph, Me)
5a (Ph, Me)
5a (Ph, Me)
5b (Ph, Et)
5c (2-MeOC6H4, Me)
5d (4-MeOC6H4, Me)
5e (2-ClC6H4, Me)
5f (4-ClC6H4, Me)
5g (4-ClC6H4, Et)
CH2Cl2
CH2Cl2
toluene
MeOH
i-PrOH
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
100
100 (98)
100
100
100
100 (98)
100 (98)
100 (97)
100 (97)
100 (98)
100 (98)
99 (S)d
98 (R)
97 (R)
95 (R)
92 (R)
97 (R)
97 (R)
98 (R)
97 (R)
98 (R)
97 (R)
phino)naphthylamine
3 was confirmed by X-ray diffraction
analysis of its acetylated derivative (Fig. 2).
10
11
a
All reactions were carried out with 0.5 mmol of substrates, 1 mol % of catalyst
prepared from [Rh(COD)2]BF4 and 1.1 equiv of ligand for 12 h under the conditions
given in the equation.
b
Conversions were determined by GC, and the isolated yields were provided in
parentheses.
c
Enantiomeric excesses were determined by GC, using
a CP-Chiralsil-L-Val
capillary (0.25 mm ꢁ 30 m) column. The absolute configurations were determined
by comparing the GC retention times with the GC data in the literature.
Figure 2. Crystal structure of N-acetyl-1-(8-diphenylphosphinon)naphthylamine.
Hydrogen atoms are omitted for clarity (CCDC 697094).
d
The data were obtained with (R,R)-THNAPhos.

1864
S.-B. Yu et al. / Tetrahedron: Asymmetry 19 (2008) 1862–1866
Table 3
is present in (S)-HY-Phos (entry 2 vs entry 1). A solvent screening
experiment revealed that the nature of solvent had some effect on
the enantioselectivity; however, no result surpassed that obtained
in CH2Cl2 (entries 2–5). Hydrogenation of a series of substituted a-
(acetamido)cinnamates 5b–g was then performed in CH2Cl2. The
Rh-catalyzed asymmetric hydrogenation of
a
-enol ester phosphonates
9
with
phosphine-phosphoramidite ligand 1a
O
P
[Rh(COD)2]BF4 (1 mol %)
(S)-HY-Phos 1 (1.1 mol %)
O
P
OMe
OMe
OMe
OMe
*
R
R
results revealed that there was no major effect on the substitution
H2 (20 atm), CH2Cl2, rt
OBz
OBz
pattern or electronic properties of the
a-(acetamido)cinnamates,
9
10
while all of the tested substrates were hydrogenated in excellent
enantioselectivities with full conversions (entries 6–11).
Entry
Substrate
Conv.b (%)
eec (%) (config.)
We next investigated the application of this newly developed
phosphine-phosphoramidite ligand in the Rh-catalyzed asymmet-
ric hydrogenation of enamide substrates 7, and the results are
summarized in Table 2. Under the optimized hydrogenation condi-
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
9a: R = H
9a: R = H
9b: R = Me
9c: R = Et
9d: R = CH2(CH2)8CH3
9e: R = Ph
100
99 (S)d
99 (R)e
99 (R)
98 (R)e
98e
98 (R)
98
99
98
95
99
>99
98
100 (99)
100 (98)
100 (99)
100 (98)
100 (98)
100 (97)
100 (97)
100 (99)
100 (95)
100 (98)
100 (97)
100 (98)
100 (98)
100 (98)
tions as used in the hydrogenation of a-(acetamido)cinnamates, a
series of substituted N-(phenylethenyl)acetamides 7a–f were
hydrogenated in good to excellent enantioselectivities, with the
best enantioselectivity (99% ee) being achieved in the hydrogena-
tion of substrate 7b with a 4-Cl group (entries 1–6). In particular,
with the hydrogenation of trisubstituted enamides 7g–i, this ligand
also displayed good enantioselectivities, providing ee-values of
93–96% (entries 7–9). In comparison with the corresponding
(R,R)-THNAPhos, (S)-HY-Phos displayed somewhat lower enanti-
oselectivity in the hydrogenation of disubstituted substrate 7a (en-
try 1 vs entry 10). However, for the hydrogenation of trisubstituted
substrates, (S)-HY-Phos 1 showed significantly higher enantiose-
lectivities (entries 7 and 8 vs entries 11 and 12).
9f: R = 4-FC6H4
9g: R = 4-ClC6H4
9h: R = 4-NO2C6H4
9i: R = 4-MeOC6H4
9j: R = 3-MeOC6H4
9k: R = 3-ClC6H4
9l: R = 2-ClC6H4
9m: R = OEt
96
98
9n: R = OiPr
a
All reactions were carried out with 0.5 mmol of substrate, 1 mol % of catalyst
prepared from [Rh(COD)2]BF4 and 1.1 equiv of ligand for 24 h under the conditions
given in the equation unless otherwise specified.
b
Conversions were determined by NMR, and the isolated yields were provided in
parentheses.
c
Enantiomeric excesses were determined by HPLC on a chiral column (Chiralpak
AD, Chiralcel OD-H, or Chiralcel OJ-H, 0.46 mm ꢁ 25 cm). The absolute configura-
tions were determined by comparing the HPLC retention times with the reported
data.
Table 2
Rh-catalyzed asymmetric hydrogenation of enamides 7 with phosphine-phospho-
d
ramidite ligand 1a
The data were obtained with (R,R)-THNAPhos.
e
Hydrogenation was performed under 10 atm of H2 pressure for 12 h.
R2
R2
[Rh(COD)2]BF4 (1 mol %)
*
(S)-HY-Phos 1 (1.1 mol %)
NHAc
NHAc
tion.8,11 We found that this newly developed phosphine-phospho-
ramidite ligand was also highly efficient for the hydrogenation of
this substrate class, providing an ee-value of 99% in the rhodium-
R1
R1
H2 (10 atm), CH2Cl2, rt
7
8
catalyzed asymmetric hydrogenation of dimethyl
a-benzo-
Entry
Substrate (R1, R2)
Ligand
Conv.b (%)
eec (%) (config.)
yloxyethenephosphonate 9a, comparable to that obtained with
(R,R)-THNAPhos (entries 1 and 2). The hydrogenation of various
1
2
3
4
5
6
7
8
9
7a (H, H)
HY-Phos
HY-Phos
HY-Phos
HY-Phos
HY-Phos
HY-Phos
HY-Phos
HY-Phos
HY-Phos
100 (96)
100 (99)
100 (96)
100 (97)
100 (98)
100 (98)
100 (98)
100 (99)
100 (95)
100
96 (R)
99 (R)
98 (R)
96 (R)
98 (R)
96 (R)
96 (R)
93 (R)
94 (R)
>99 (S)
91 (S)
78 (S)
7b (4-Cl, H)
7c (4-Br, H)
7d (4-Me, H)
7e (4-CF3, H)
7f (3-OMe, H)
7g (H, Me) (E/Z, 75/25)
7h (4-Cl, Me) (E/Z, 63/37)
7i (4-OMe, Me) (E/Z, 73/27)
7a (H, H)
b-alkyl substituted
a-benzoyloxyethenephosphonates 9b–d was
then examined. The results indicated that the b-alkyl substituent
in the substrate had little effect in the enantioselectivity, and all
substrates were hydrogenated in excellent enantioselectivities (en-
tries 3–5). We next examined the Rh-catalyzed hydrogenation of a
set of structurally diverse b-aryl substituted substrates 9e–l with
this new ligand. It was found that all b-aryl substituted substrates
9e–l were hydrogenated in excellent enantioselectivity (95–99%
ee), regardless of the substitution pattern and electronic property
of the substituent in the phenyl ring of the substrates (entries 6–
13). High enantioselectivity was also observed in the hydrogena-
tion of b-alkoxy substituted substrates 9m–n, in which 96% ee
and 98% ee were obtained, respectively (entries 14 and 15).
10
11
12
THNAPhos
THNAPhos
THNAPhos
7g (H, Me) (E/Z, 75/25)
7h (4-Cl, Me) (E/Z, 63/37)
100
100
a
All reactions were carried out with 0.5 mmol of substrates, 1 mol % of catalyst
prepared from [Rh(COD)2]BF4 and 1.1 equiv of ligand for 12 h under the conditions
given in the equation.
b
Conversions were determined by GC, and the isolated yields were provided in
parentheses.
c
Enantiomeric excesses were determined by GC, using a Chiral Select 1000
capillary (0.25 mm ꢁ 30 m) column. The absolute configurations were determined
3. Conclusion
by comparing the GC retention times with the GC data in the literature.
In conclusion, a new chiral phosphine-phosphoramidite ligand
(S)-HY-Phos 1 has been prepared from commercially available
and inexpensive 1-naphthylamine through a two-step transforma-
tion and successfully applied in the Rh-catalyzed asymmetric
hydrogenation of various functionalized C@C double bonds includ-
To further demonstrate the efficiency of this new phosphine-
phosphoramidite ligand in the catalytic asymmetric hydrogena-
tion, we applied it to the Rh-catalyzed asymmetric hydrogenation
of various
a
-enol ester phosphonates 9 (Table 3). The catalytic
ing a-(acetamido)cinnamates, enamides and a-enol ester phos-
asymmetric hydrogenation of
a
-enol ester phosphonates remains
phonates. Despite the absence of the central chirality, this newly
developed phosphine-phosphoramidite ligand showed excellent
a rarely explored area.10 It is only very recently that some unsym-
metrical hybrid bidentate phosphorus ligands have been found to
show good to excellent enantioselectivities in this transforma-
enantioselectivities in the hydrogenation of
a-(acetamido)cinna-
mates and -enol ester phosphonates, comparable to those ob-
a

S.-B. Yu et al. / Tetrahedron: Asymmetry 19 (2008) 1862–1866
1865
tained with the corresponding (R,R)-THNAPhos derived from chiral
4.3. Preparation of N-[1-(8-diphenylphosphino)naphthyl]-(S)-
1,10-bi-2-naphthylphosphoramidite [(S)-HY-Phos 1]
1,2,3,4-tetrahydro-1-naphthylamine. In the hydrogenation of
disubstituted enamides, (S)-HY-Phos gave somewhat lower enanti-
oselectivity than (R,R)-THNAPhos. However, higher enantioselec-
tivities were observed in the hydrogenation of trisubstituted
enamides by the use of (S)-HY-Phos instead of (R,R)-THNAPhos.
Further investigations on other catalytic asymmetric reactions
with this ligand are underway, and progress will be reported in
due time.
(S)-4-Chloro-3,5-dioxa-4-phosphacyclohepta[2,1-a
;3,4-a0]di-
naphthalene (350.5 mg, 1.0 mmol) was dissolved in 2.0 mL of dried
toluene, which was cooled to 0 °C. A solution of 1-(8-diphenylphos-
phino)naphthylamine 3 (327 mg, 1.0 mmol) and Et3N (303 mg,
3.0 mmol) in 4.0 mL of toluene was added to the above solution
for 30 min. The resulting mixture was left standing at room temper-
ature overnight. The precipitate was filtered, and the filtrate col-
lected, and concentrated under reduced pressure. The residue was
purified by column chromatography to give the target phosphine-
phosphoramidite ligand, (S)-HY-Phos 1 (280 mg, 44% yields). Mp
4. Experimental
4.1. General
94–96 °C; ½a 2D0
ꢂ
¼ þ53:7 (c 0.56, CHCl3); 1H NMR (400 MHz, CDCl3):
d 7.00–7.16 (m, 8H), 7.26–7.32 (m, 10 H), 7.40–7.44 (m, 4H), 7.53–
7.63 (m, 2H), 7.76–7.93 (m, 4H); 13C NMR (100 MHz, CDCl3): d
119.2, 124.9, 125.1, 126.2, 126.4, 127.3, 127.3, 128.5, 128.6, 128.7,
128.8, 128.9, 129.1, 133.9, 134.1, 134.7, 134.8, 134.9; 31P NMR
(162 MHz, CDCl3): d ꢀ4.7, 145.5; HRMS (EI) calcd for C42H30NO2P2
[M+H]: 642.1752, found 642.1771.
All synthetic reactions and manipulations were performed in a
nitrogen or argon atmosphere using standard Schlenk techniques.
Hydrogenations were carried out in a stainless steel autoclave. Sol-
vents were reagent grade, dried and distilled before use, following
the standard procedures. (S)-4-Chloro-3,5-dioxa-4-phosphacyclo-
hepta[2,1-
the literature procedure.12
mides 714 and -enol ester phosphonates 910 are known com-
a
;3,4-a0]din-aphthalene was synthesized according to
-(Acetamido)cinnamates 5,13 ena-
a
4.4. General procedure for asymmetric hydrogenation
a
pounds, which were prepared according to the literature
methods. All other chemicals were obtained commercially.
1H, 13C and 31P NMR spectra were recorded on BRUKER DEX-400
spectrometer. Chemical shift values (d) are denoted in ppm and are
referenced to residue protons in deuterated solvents for 1H NMR
(CDCl3: 7.27 ppm), to CDCl3 (77.0 ppm) for 13C NMR and to exter-
nal H3PO4 (85% solution in D2O, 0 ppm) for 31P NMR. Optical rota-
In a nitrogen-filled glovebox, a stainless steel autoclave was
charged with [Rh(COD)2]BF4 (2.0 mg, 0.5 ꢁ 10ꢀ2 mmol) and (S)-
HY-Phos 1 (3.5 mg, 0.55 ꢁ 10ꢀ2 mmol) in 1.5 mL of a degassed
CH2Cl2. After stirring for 10 min at room temperature, the substrate
(0.5 mmol) in 1.5 mL of the same solvents was added to the reac-
tion mixture. The hydrogenation was performed at room tempera-
ture under an H2 pressure of 10 atm for 12 h. The reaction mixture
was passed through a short silica gel column to remove the cata-
lyst. After evaporating the solvent, the crude product was sub-
jected to determine the conversions by GC or 1H NMR and the
enantiomeric excesses by GC or HPLC.
tions were recorded using
a JASCO P-1020 high sensitive
polarimeter. Enantiomeric excesses were determined by capillary
GC analysis with a CP-Chiralsil-L-Val column (0.25 mm ꢁ 30 m)
for 6, a chiral Select 1000 column (0.25 mm ꢁ 30 m) for 8 and by
HPLC analysis with a chiral column (Chiralpak AD, Chiralcel OD-
H, and Chiralcel OJ-H, 0.46 mm ꢁ 25 cm) for 10.
Acknowledgement
4.2. Preparation of 1-(8-diphenylphosphino)naphthylamine 3
[NAPNH2]
We are grateful for financial support from the National Natural
Science Foundation of China (20472083).
To a solution of 1-naphthylamine (1.43 g, 10 mmol) in 10 mL of
ether at ꢀ20 °C was dropwise added 5.8 mL (1.7 M in n-hexane) of
n-BuLi. The resulting solution was stirred at ꢀ20 °C for 30 min, and
then 1.4 mL (1.1 equiv) of Me3SiCl was added slowly at the same
temperature. The reaction mixture was stirred for another 1 h,
and then 17.6 mL (1.7 M in hexane) of n-BuLi was dropwise at
ꢀ30 °C. After the addition was completed, the reaction mixture
was stirred at ꢀ30 °C for 3 h. The reaction mixture was slowly
warmed to room temperature and stirred overnight. The reaction
mixture was cooled to ꢀ30 °C again, and a solution of chlorodi-
phenylphosphine (2.2 g, 10 mmol) in 10 mL of ether was added
dropwise. After holding at the same temperature for 3 h, the reac-
tion mixture was warmed to room temperature for another 4 h. A
solution of 1 M of aqueous HCl was added slowly until the reaction
mixture became clear in both phases. The aqueous phase was ex-
tracted with ether (3 ꢁ 30 mL). The combined organic layers were
dried over Na2SO4 and concentrated under reduced pressure. The
residue was purified by silica gel column chromatography (hex-
anes/acetate, 20/1) to give 0.98 g (30% yields) of 1-(8-diphenyl-
phosphino)naphthylamine 3 as a pale-yellow solid. Mp 92–94 °C;
1H NMR (400 MHz, CDCl3): d 5.42 (br, 2H), 6.69–6.71 (m, 1H),
7.01–7.03 (m, 1H), 7.22–7.28 (m, 7H), 7.30–7.34 (m, 6H), 7.75–
7.77 (m, 1H); 13C NMR (100 MHz, CDCl3): d 113.1, 119.8, 125.0,
126.4, 128.5, 128.6, 128.7, 128.9, 130.9, 133.8, 134.0, 134.1, 136.1,
136.2, 137.0, 137.1, 145.4; 31P NMR (162 MHz, CDCl3): d ꢀ4.0.
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