Pd/Zn(OTf)2 Co-Catalyzed Asymmetric Hydrogenation of Imines under Normal Pressure of Hydrogen

Article abstract of DOI:10.1002/ejoc.201801123

An efficient method for the asymmetric hydrogenation of cyclic and acyclic N-sulfonylimines co-catalyzed by Pd/Zn(OTf)₂ using hydrogen gas under ambient pressure was developed. The methodology offers an easy access to generate chiral sulfonylam

Full text of DOI:10.1002/ejoc.201801123

A Journal of
Accepted Article
Title: Pd/Zn(OTf)₂ Co-catalyzed Asymmetric Hydrogenation of Imines
under Normal Pressure of Hydrogen
Authors: Yang Gao, Yang Fan, Dongdong Pu, Ronibala Devi
Laishram, Ruifeng Fan, Gouli Shen, Xuexin Zhang, Jingchao
Chen, and Baomin Fan
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To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.201801123
Link to VoR: http://dx.doi.org/10.1002/ejoc.201801123
Supported by

10.1002/ejoc.201801123
European Journal of Organic Chemistry
FULL PAPER
Pd/Zn(OTf)2 Co-catalyzed Asymmetric Hydrogenation of Imines
under Normal Pressure of Hydrogen
Yang Gao,[a] Fan Yang,[a] Dongdong Pu,[a] Ronibala Devi Laishram,*[a] Ruifeng Fan,[b] Guoli Shen,[a]
Xuexin Zhang,[a] Jingchao Chen,[a] and Baomin Fan*[a,b]
Abstract: Efficient method for the asymmetric hydrogenation of cyclic and acyclic N-sulfonylimines co-catalyzed by Pd/Zn(OTf)2 using
hydrogen gas under ambient pressure is developed. The methodology offers an easy access to generate chiral sulfonylamines in good yields
and excellent enantioselectivities.
Introduction
heterobicyclic alkenes using primary and secondary alcohol as
hydrogen source[15]
and very recently this same catalytic
system was successfully utilized in the ATH of N-sulfonylimines
with alcohol as the hydrogen source.[16] In both the reactions, we
hypothesized the generation of hydride intermediate from
alcohol by the Pd catalyst for hydrogenation. Therefore, we
anticipated this catalytic system also could lead to being an
effective catalytic system for AH of N-sulfonylimines. Herein, we
describe our attempt towards a different approach involving the
combination of Lewis acid with Pd(OAc)2/ (R)-MeO-BIPHEP
complex for the AH of various N-sulfonylimines with molecular
hydrogen under 1 bar to form the corresponding amines with
high reactivity and enantiopurity.
Chiral amines are valuable and prevalent substructures with
important biological, agrochemical and pharmacological
properties.[1]
Thus,
the
development
of
expeditious
methodologies for the preparation of chiral amines in high
enantiopurity is of great significance and highly desirable.
Amination of alcohols by the hydrogen auto transfer method has
long been recognized as a highly economical and greener
method.[2] Since then much progress has been made in the last
two decades in search for the development of efficient
methodology. Among the most explored methods,[3-5]
asymmetric hydrogenation (AH) of imines using hydrogen is the
most efficient and elegant method. However, the AH of imines
still remains a major challenge due to the poor reactivity of
imines towards hydrogenation and also difficulties in obtaining
excellent results as the E and Z isomers of acyclic imines gave
different enantioselectivity. In spite of these problems, much
progress has been made in asymmetric hydrogenation of imines
leading to the discovery of various catalytic systems.[6-11] To the
best of our knowledge, the asymmetric hydrogenation of linear
N-tosylimines has rarely been explored despite continuing
progress. Until Zhang et al. reported, the asymmetric
hydrogenation of linear N-tosylimines was not satisfactory.[12]
Then in 2007, Zhou et al. documented Pd/bisphosphines
complexes catalyzed highly effective asymmetric hydrogenation
under 600 psi of H2.[13] Very recently Zhou et al. also reported
the Pd-catalyzed highly enantioselective hydrogenation of a
series of linear and cyclic N-tosylimines with the phosphonates
group in good to excellent enantioselectivities.[14] Most of these
methodologies used high pressure to activate the reaction.
However, in our methodology, we used Pd/Zn co-catalytic
system under ambient pressure of H2 to activate the reaction.
Our group has successfully employed the co-catalytic system
of Pd/Zn in asymmetric transfer hydrogenation (ATH) of
Results and Discussion
We initiated our investigations of AH using N-sulfonylimine
(1a) as the model substrate under 1 bar H2 in DCE employing
Pd(OAc)2, Zn(OTf)2 and protonic acid CF3SO2H as a catalytic
system (Table 1). First, we studied the reaction of 1a using chiral
diphosphine ligand (R)-SEGPHOS which has found to be a good
ligand giving high yield, 90% and ee, 95%. To enhance the
reactivity we were also tested other chiral diphosphorus ligands
like (R)-Cl-MeO-BIPHEP, (R)-DTB-MeO-BIPHEP, (R)-BINAP,
(R)-BDPP, (R)-P-PHOS, (R)-SYNPHOS but no appreciable
improvement was observed. Notably, (R)-MeO-BIPHEP gave
the best result with the highest yield 94% and excellent ee 97%.
While (R)-DIOP gave out of the racemic product in poor yield,
and monophosporus ligand like (R)-MONOPHOS gave no
product even after 48 h. We then turned our attention to
examine the effect of Lewis acids, additives, solvent, and
reaction temperature on reactivity and enantioselectivity (Table
2). Used of the additive has no influence on the reactivity and
enantioselectivity of the reaction since without the use of it
also gave the products as high as 90% yield and ee 99%
(Table 2, entry 5). We then studied the influence of Lewis
[a]
[b]
YMU-HKBU Joint Laboratory of Traditional Natural Medicine
Yunnan Minzu University, Kunming, 650500, China
E-mail: FanBM@ynni.edu.cn; ronilais79@yahoo.com
Key Laboratory of Chemistry in Ethnic Medicinal Resources,
Yunnan Minzu University, Kunming, 650500, China
Supporting information for this article is given via a link at the end of
the document.
acids on enantioselectivities and reactivities of the reaction.
However, Lewis acids like ZnCl2, Fe(OTf)3, CuOTf,
Cu(OTf)2, AgOTf, proceeded with the low conversion of the
product albeit ee of the reaction were relatively high (Table
2
, entries
Zn(OAc)2, Yb(OTf)3, Sc(OTf)3, FeBr2 (Table
15). But, Fe(OTf)2 gave a trace amount even after the 48 h.
6
,
11
-
14) and the result were not impressive for
2
, entries 9,
7-
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10.1002/ejoc.201801123
European Journal of Organic Chemistry
FULL PAPER
Table 1. Screening of ligands for AH reaction of 1a
Under optimized conditions,
a
variety of substituted N-
sulfonylimines were subjected to investigate the AH and
summarized in Table 3. It was found that the reaction has a wide
range of functional group tolerance giving excellent
enantioselectivities regardless of the substituents being electron-
donating or electron-withdrawing but the position of the
substituent has effects on the reactivities. Electron-donating or
electron-withdrawing substituents like methyl, methoxy, fluoro,
chloro, bromo in para-position of aryl imine gave comparatively
excellent enantioselectivities (2b-2h) but the yield was highest
when the methyl substituent was in para-position 91% (2b).
Interestingly, unsubstituted aryl imine gave the highest yield
90% and ee 99% (2a), while naphthyl substituted aryl imine
gave the same ee with reduced yield (2i).
O
O
O
O
A
S
S
r
N
A
r
HN
c
Pd OA 2 / L
(
)
e
M
e
M
OTf DCE CF SO H 70 ο
C
1 b H2
n
Z
ar
,
)
2
,
,
3
,
(
3
a
1
a
2
'
R'
=
=
en
l
y
R
Cl R''
h
p
,
e
ee
ld 97
%
,
-
e
- -
12 h 79
i
R
Cl M O BIPHEP
%
,
,
y
(
)
H3CO
H3CO
PR''
PR''
'
''
=
=
en
h l
p
y
R
(
H
,
R
bi
e
i ld 97
%
,
y
ee
-
e
M
-
15 h 94
R
O BIPHEP
%
,
,
)
R'
'
''
=
-
=
-
-
- er -
1 3 di t t b t l 2
u
-
-me ox
th
en
h
R
H
,
R
l
,
e
y
yp
y
%
e
ee
-
13 h 85
,
i
ld 90
,
R
DTBM M O BIPHEP
%
,
y
(
)
O
PPh2
Table 2: Evaluation of reaction conditionsa
Ph
P
P
PPh2
PPh2
O
O
Ph
Ph
O
O
O
A
O
A
PPh2
Ph
S
S
O
r
N
r
HN
c
e
- -
M
O BIPHEP
Pd OA / R
(
)
(
)
2
e
M
e
M
-
SEGPHOS
)
R
(
-
-
PHANEPHOS
L
i
id
l
t
,
70 ο
ve
ar
dditi
C
1 b H2
, ,
R
BINAP
R
(
)
( )
ew s ac so ven
a
,
e
ee
%
12 h 90
i
ld 95
,
e
ee
%
,
17 h
7
i
l
4
e
y
9%
d
,
9
%
ee
%
,
21 h 15
,
i
ld 45
,
y
%
y
a
1
a
2
OCH3
N
Lewis
Acid
Additive Solvent Time
(h)
Yield
(%)b
ee
Entry
(%)c
H3CO
H3CO
PPh2
PPh2
PPh
2PPh2
P
P
1
2
Zn(OTf)2
CF3SO2H
DCE
15
11
94
88
97
97
N
O
O
Zn(OTf)2 CF3COOH DCE
OCH3
Benzoic
acid
DCE
-
DIOP
)
R
3
Zn(OTf)2
11
93
97
-
BDPP
(
-
-
os
R
R
P Ph
(
)
(
)
e
i ld 65
y
ee
e
ee
ld 0%
e
ee
21 h 82
21 h 21% i
y
%
%
,
,
12 h 88
i
ld 94
,
,
%
%
,
,
y
4
5
Zn(OTf)2
Zn(OTf)2
ZnCl2
L-CSA
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
THF
11
11
33
48
48
12
48
20
20
12
12
48
48
48
48
77
90
98
99
95
/
O
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
6
47
PPh2
PPh2
O
O
O
O
P
N
7
Zn(OAc)2
Yb(OTf)2
Sc(OTf)3
Fe(OTf)2
Fe(OTf)3
CuOTf
trace
trace
23
8
/
O
9
3
-
M
)
ono os
h
p
-
R
(
R
SYNPHOS
(
)
race
48 h t
,
10
11
12
13
14
15
16
17
18
trace
57
/
e
ee
%
11 h
77
i
ld 97
%
,
,
y
97
98
96
85
/
80
Reaction conditions: 1a (0.2 mmol), Pd(OAc)2 (5.0 mol%), L (6.0 mmol%),
Cu(OTf)2
AgOTf
67
Zn(OTf)2 (10.0 mmol%), CF3SO2H (5.0 mmol%) in DCE (2.0 ml) at 70 °C, H2 1
bar
60
FeBr2
trace
NR
23
/
/
Interestingly, Zn(OTf)2 was found to be the most favorable
activator with respect to enantioselectivity and turnover (Table 2,
entry 5). We also examined in absence of Lewis acid, but it does
not give product even after 48 h (Table 2, entry 16). It implied
that Lewis acid played a crucial role in activating the reaction.
Next, the solvents effects were extensively studied and found
that it also played an important role in promoting the
hydrogenation. Other than DCE, solvents like THF, toluene, and
1,4-dioxane were also tested but failed to promote the
conversion of the products. Gratifyingly, DCE was proved to be
the best solvent with excellent ee and good yield at 70 ºC (Table
2, entry 5). To further improved the reaction efficiency we
studied the effect of reaction temperature, instead of increasing
the reactivity of the reaction it leads to the lower conversion of
products when the temperature was either increased to 80 ºC or
decreased to 60 ºC.
Zn(OTf)2
Zn(OTf)2
95
93
Toluene
38
1,4-
Dioxane
19
Zn(OTf)2
48
17
91
20
Zn(OTf)2
Zn(OTf)2
Zn(OTf)2
/
/
/
CH3OH
DCE
12
36
26
25
85
77
95
97
95
22d
23e
DCE
Reaction conditionsa: 1a (0.2 mmol), Pd(OAc)2 (5.0 mmol%), (R)-MeO-
BIPHEP (6.0 mmol%), Lewis acid (10.0 mmol%), additive (5 mmol%) in
solvent (2 mL) at 70 ºC, H2 1 bar. bIsolated yield of the products. Determined
by HPLC with a Chiralcel OD-H column. dReaction carried out at 60 ºC.
eReaction carried out at 80 ºC. NR-no reaction.
c
Nevertheless, imine bearing
moderate yield 90% with good ee 95% (2j). The
a thiophenyl group gave
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10.1002/ejoc.201801123
European Journal of Organic Chemistry
FULL PAPER
enantioselectivity was lowest when the methyl group was
replaced by ethyl group (2k). In addition, imines with substitution
in the sulfonyl group were also subjected to AH, fortunately; it
gave good yields and enantioselectivities (2l-2p). Electronic
effects of the substituents on the aryl of the sulfonyl group have
no significant effect on the yields and ees of the reactions.
Encouraged with the generality of these results we tried with
other non-activated imines but the results were not appreciable
(2q, 2r). The absolute configurations of 2a-2p were established
as ‘‘R’’ by comparing the HPLC spectra with that reported in the
literature.[16]
substructural units of biological and pharmaceutical products.[17]
Pleasingly, our methodology fits well for those cyclic
sulfonylimines 3, and they were successfully converted to the
corresponding cyclic sulfonamides, sultams 4 with good to
excellent yield and ee (Table 4). It is noteworthy that the
electronic effects of the substituents on the aromatic ring have
little influence on the ees and the yields of the reaction. With, the
fluro substituent on the phenyl ring gave the highest yield 92%
with comparable ee 85% (4e). However, the positions of the
substituents have great influenced on the ees and yields of the
reaction. Among the ortho-, meta-, and the para-substituent
substrates, the ortho-methyl substituent on the phenyl ring gave
the lowest ee and yield (4b) while the para-methyl substituent
gave the highest ee 90% with 89 % yield (4d). Ethyl phenyl
substituted imine also gave good yield 93% and moderate ee
71% (4h). Simple alkyl substituted imine gave moderate yield
and ee (4f). But, ee and yield of the neo butyl substituent was
not appreciable. The absolute configurations of 4a-4h were
established as ‘’S’’ by comparing the HPLC spectra with that
reported in the literature.[18] The plausible mechanism of the
catalytic cycle of the AH is shown in Scheme 1.
Table 3: Asymmetric hydrogenation of acyclic N-sulfonyliminesa
O
O
O
O
S
S
HN
R1
c
e
- -
M O BIPHEP
N
Pd OA
/
R
(
r
A
(
)
2
)
r
A
o
R2
n
Z
ar
R1
R2
OTf DCE 70 C 1 b H2
,
)
2
,
,
(
a-r
1
a-r
2
O
O
e
O
O
e
O
O
e
S
S
S
HN
HN
HN
M
M
M
b
eec
b
e
ld 96
,
%
a
e
i
eec
e
i
y
eec
b
ld 98
,
%
2
15 h 90
ld 99
,
2b 10 h 91
,
,
%
%
,
,
%
y
c
2
36 h 78
,
i
y
,
%
O
O
O
O
O
O
S
S
S
HN
HN
HN
e
M
Table 4: Asymmetric hydrogenation of cyclic N-sulfonyliminesa
e
M
e
M
F
e
M
O
eec
eec
%
b
e
2d 60 h 62
i
ld 99
,
2
11
,
h
,
86
%
i
ld 98
eec
b
b
e
e
e
,
,
%
%
y
,
2f 24 h 81%
i
ld 97%
y
,
,
,
O
O
y
O
O
S
S
c
-
R M
( )
e
-
O
O
Pd OA
/
O BIPHEP
O
O
O
O
S
(
)
2
N
NH
S
S
HN
HN
HN
OTf DCE 70 ο
C
1 b H2
n
Z
ar
,
)
2
,
,
(
R
R
e
M
e
M
e
M
a-
4
h
r
B
a-
3
h
Cl
eec
b
ld 99
,
%
e
eec
e
eec e 2i 48 h 70
b
b
,
e
i
%
y
2
,
g
24 h 79
,
i
y
ld 98
,
2h 48 h 68
%
i
y
ld 97
%
,
,
%
%
,
,
,
O
O
O
O
O
O
O
O
O
S
S
O
O
S
O
S
HN
HN
S
S
HN
NH
NH
NH
S
e
M
e
M
eec
d
,
b
e
eec 2k 60 h 85
i
y
ld 96
,
%
b
b
d
,
e
i ld
y
eec
e
2
,
j
48 h 90
i
y
ld 95
,
,
,
%
,
%
%
2l
,
36
h
,
72
%
9
7
%
,
eec
e
i
eec
c
eec
%
b
b
b
e
a
e
4
24 h 91
%
i
y
ld 88
,
4b 48 h 50
,
ld 81
4
24 h 90
,
i ld 89
,
y
O
O
,
,
%
,
%
y
,
%
,
%
O
O
O
O
S
S
S
HN
HN
HN
e
M
O
O
S
Cl
e
M
e
M
O
O
S
NH
NH
O
O
S
eec
%
b
2
11 h 94
i
y
ld 97
o
e
eec
b
m
e
eec
,
,
%
,
2
36 h 87
,
i
y
ld 97
b
n
e
%
,
%
2
36 h 82
i
y
ld 98
,
,
,
%
,
%
NH
O
O
O
S
HN
F
HN
HN
eec
4f 48 h 84
i
y
ld 85
,
e
eec
b
b
e
eec
4
24 h 92
,
,
,
%
%
b
e
e
i ld 85
%
,
y
,
%
4d 24 h 89
%
i
y
ld 90
,
,
,
%
e
M
e
M
e
M
O
O
O
O
eec
e
eec
%
2
b
b
e
2
,
p
66 h 82
i
y
ld 95
2
,
q
26 h 35
i
y
ld 75
r
race
h t
,
,
%
,
%
,
%
,
4
8
,
S
S
NH
NH
eec
e
eec
b
b
e
4
,
g
48 h 54
i
y
ld 59
4h 26 h 93
i
y
ld 71
,
%
,
%
,
,
%
,
%
Reaction conditionsa: 1a-r (0.2 mmol), Pd(OAc)2 (5.0 mmol%), (R)-MeO-
BIPHEP (6.0 mmol%), Zn(OTf)2 (10.0 mmol%), in DCE (2 mL) at 70 ºC, H2
1
bar. bIsolated yield of the products. cDetermined by HPLC. dUsed protonic acid,
CF3SO2H (5.0 mmol%). eUsed 4Å MS (50.0 mg).
Reaction conditionsa: 3a-h (0.2 mmol), (R)-MeO-BIPHEP (6.0 mmol%),
Pd(OAc)2 (5.0 mmol%), Zn(OTf)2 (10.0 mmol %), in DCE (2 mL) at 70 ºC, H2
1 bar. bIsolated yield of the products. cDetermined by HPLC.
Furthermore, in order to demonstrate the versatility of our
methodology, a series of cyclic imines were subjected to AH to
offered sulfonamides. The cyclic sulfonamides, sultams are
important organic synthetic intermediates and privileged
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10.1002/ejoc.201801123
European Journal of Organic Chemistry
FULL PAPER
TLC monitoring until the complete consumption of 1a. The
residue was purified by chromatography on a silica gel column
to afford the desired product 2a (47 mg, 90% yield).
c
+
L
Pd OA
(
)
2
H2
O
O
S
N
r
A
c
+
c
HOA
(R)-N-(1-phenylethyl)benzenesulfonamide (2a)
HPdL OA
(
)
Pd
R1
R2
n
Z
OTf
)
2
(
20
White solid, 90% yield, 99% ee. Mp 92-95 oC. [α]D = +84 (c = 0.3,
O
S
O
CH2Cl2). 1H NMR (400 MHz, CDCl3) δ 7.75–7.69 (m, 2H), 7.50–7.43 (m,
1H), 7.36 (dd, J = 10.9, 4.5 Hz, 2H), 7.20–7.12 (m, 3H), 7.10–7.05 (m,
2H), 5.42 (d, J = 7.2 Hz, 1H), 4.53–4.44 (m, 1H), 1.42 (d, J = 6.9 Hz, 3H).
The ee of 2a was determined by HPLC analysisusing Daicel Chiralcel
OJ-H columns (25 cm × 0.46 cm ID), conditions: n-Heptane/i-PrOH =
70/30, 1.0 mL/min, 240 nm; tminor = 13.3 min, tmajor = 20.8 min.
HN
R1
r
A
+
n2
+
+
n2
Z
c
A
OH
R2
Z
c
HPdL OA
O
(
)
O
S
+
n2
N
r
A
Z
R1
R2
c
PdL OA
(
O
O
)
S
HN
R1
r
A
(R)-N-(1-(p-tolyl)ethyl)benzenesulfonamide (2b)
R2
White solid, 91% yield, 98% ee. Mp 133-135 oC. [α]D20 = +113.1 (c = 0.54,
CH2Cl2). 1H NMR (400 MHz, CDCl3) δ 7.70–7.62 (m, 2H), 7.40 (d, J = 7.4
Hz, 1H), 7.30 (t, J = 7.7 Hz, 2H), 6.90 (s, 4H), 5.03 (s, 1H), 4.37 (t, J =
6.9 Hz, 1H), 2.19 (s, 3H), 1.34 (d, J = 6.9 Hz, 3H). The ee of 2b was
determined by HPLC analysis using Daicel Chiralcel OD-H column (25
Scheme 1. Proposed mechanism for Pd(II)/Zn-catalyzed asymmetric
hydrogenation.
cm
× 0.46 cm ID), conditions: n-Heptane/i-PrOH = 85/15, 0.5 mL/min,
240 nm; tmajor = 16.7 min, tminor = 19.9 min.
Conclusions
(R)-N-(1-(m-tolyl)ethyl)benzenesulfonamide (2c)
In summary, we have developed an efficient method for the
synthesis of chiral amine and chiral sultams employing
20
Colorless oil, 78% yield, 96% ee. [α]D = +4.1 (c = 0.16, CH2Cl2). 1H
NMR (400 MHz, CDCl3) δ 7.70–7.61 (m, 2H), 7.38 (t, J = 7.4 Hz, 1H),
7.27 (t, J = 7.7 Hz, 2H), 6.97 (t, J = 7.6 Hz, 1H), 6.84 (dd, J = 19.6, 7.6
Hz, 2H), 6.75 (s, 1H), 5.37 (d, J = 7.2 Hz, 1H), 4.42–4.31 (m, 1H), 2.10 (s,
3H), 1.33 (d, J = 6.9 Hz, 3H). The ee of 2c was determined by HPLC
analysis using Daicel Chiralcel OD-H column (25 cm × 0.46 cm ID),
conditions: n-Heptane/i-PrOH = 80/20, 0.5 mL/min, 240 nm; tmajor = 12.6
min, tminor = 14.7 min.
Pd/Zn(OTf)2
hydrogenation of
co-catalytic system via the asymmetric
wide range of acyclic and cyclic N-
a
sulfonylimines under ambient pressure of hydrogen. The
methodology offered good to excellent yields and
enantioselectivities.
(R)-N-(1-(o-tolyl)ethyl)benzenesulfonamide (2d)
White solid, 62% yield, 99% ee. Mp 101-104 oC. [α]D20 = +39.3 (c = 0.6,
CH2Cl2). 1H NMR (400 MHz, CDCl3) δ 7.74–7.66 (m, 2H), 7.44 (d, J = 7.4
Hz, 1H), 7.33 (t, J = 7.7 Hz, 2H), 7.09 (d, J = 7.3 Hz, 1H), 7.07–6.96 (m,
3H), 5.29 (d, J = 6.8 Hz, 1H), 4.76 (t, J = 6.8 Hz, 1H), 2.19 (s, 3H), 1.39
(d, J = 6.8 Hz, 3H). The ee of 2d was determined by HPLC analysis
using Daicel Chiralcel OJ-H column (25 cm × 0.46 cm ID), conditions: n-
Experimental Section
Heptane/i-PrOH = 70/30, 1.0 mL/min, 240 nm; tminor = 8.4 min, tmajor
=
13.1 min.
General information:
The reactions and manipulations were performed under an atmosphere
of argon by using standard Schlenk techniques and Dry box (Mikrouna,
Supper 1220/750). Anhydrous toluene was distilled from sodium
benzophenone ketyl prior to use. Anhydrous DCE was distilled from
calcium hydride and stored under argon. 1H NMR spectra were recorded
on Bruker-Avance 400 MHz spectrometer. CDCl3 was used as solvent.
Chemical shifts (δ) were reported in ppm with tetramethylsilane as
internal standard, and J values were given in Hz. The enantioselective
excesses were determined by Agilent 1260 Series HPLC using Daicel
AD-H、AS-H、OJ-H and OD-H chiral columns eluted with a mixture of
isopropyl alcohol and hexane. Column chromatography was performed
with silica gel (200-300 mesh) with petroleum ether and ethyl acetate as
eluents.
(R)-N-(1-(4-methoxyphenyl)ethyl)benzenesulfonamide (2e)
White solid, 86% yield, 98% ee. Mp 95-97 oC. [α]D20 = +88.7 (c = 0.68,
CH2Cl2). 1H NMR (400 MHz, CDCl3) δ 7.65 (dt, J = 8.6, 1.7 Hz, 2H),
7.48–7.35 (m, 1H), 7.31 (dt, J = 7.4, 1.7 Hz, 2H), 7.02–6.82 (m, 2H),
6.75–6.48 (m, 2H), 5.19 (d, J = 6.9 Hz, 1H), 4.36 (m, 1H), 3.66 (s, 3H),
1.33 (d, J = 6.9 Hz, 4H). The ee of 2e was determined by HPLC analysis
using Daicel Chiralcel OD-H column (25 cm × 0.46 cm ID), conditions: n-
Heptane/i-PrOH = 90/10, 0.8 mL/min, 240 nm; tmajor = 21.3 min, tminor
25.0 min.
=
(R)-N-(1-(4-fluorophenyl)ethyl)benzenesulfonamide (2f)
White solid, 81% yield, 97% ee. Mp 136-138 C. [α]D20 = +62.3 (c = 0.52,
CH2Cl2). 1H NMR (400 MHz, CDCl3) δ 7.71 (dt, J = 8.6, 1.7 Hz, 2H),
7.52–7.45 (m, 1H), 7.38 (dt, J = 7.4, 1.7 Hz, 2H), 7.09–7.01 (m, 2H),
6.86–6.79 (m, 2H), 5.46 (d, J = 7.1 Hz, 1H), 4.48 (t, J = 7.0 Hz, 1H), 1.39
(d, J = 6.9 Hz, 3H). The ee of 2f was determined by HPLC analysis using
Daicel Chiralcel OD-H column (25 cm × 0.46 cm ID), conditions: n-
o
Typical procedure for the asymmetric hydrogenation reaction of N-
tosylimine:
Heptane/i-PrOH = 80/20, 0.5 mL/min, 240 nm; tmajor = 14.5 min, tminor
17.3 min.
=
Pd(OAc)2 (2.3 mg, 0.01 mmol), (R)-MeO-BIPHEP (6.9 mg, 0.012 mmol)
(R)-N-(1-(4-chlorophenyl)ethyl)benzenesulfonamide (2g)
and 1.0 mL DCE were added to a Schlenk tube under argon atmosphere.
The resulting solution was stirred at room temperature for 30
min, then Zn(OTf)2 (7.3 mg, 0.02 mmol) was added and stirred
for additional 10 min, then DCE (1.0 mL) was added followed by
the addition of N-tosylimine 1a (51.8 mg, 0.2 mmol). The whole
mixture was stirred at 70 °C under H2 (1 bar) atmosphere with
White solid, 79% yield, 98% ee. Mp 147-150 oC. [α]D20 = +79.8 (c = 0.94,
CH2Cl2).1H NMR (400 MHz, CDCl3) δ 7.72 (d, J = 7.5 Hz, 2H), 7.53 (s,
1H), 7.41 (d, J = 7.8 Hz, 2H), 7.14 (d, J = 8.4 Hz, 2H), 7.04 (d, J = 8.5 Hz,
2H), 5.30 (s, 1H), 4.49 (s, 1H), 1.41 (d, J = 6.9 Hz, 3H). The ee of 2g was
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201801123
European Journal of Organic Chemistry
FULL PAPER
determined by HPLC analysis using Daicel Chiralcel OJ-H column (25
cm × 0.46 cm ID), conditions: n-Heptane/i-PrOH = 80/20, 0.5 mL/min,
240 nm; tmajor = 14.9 min, tminor = 17.5 min.
(R)-4-chloro-N-(1-phenylethyl)benzenesulfonamide (2o)
White solid, 87% yield, 97% ee. Mp 104-105 oC. [α]D20 = +57.4 (c = 0.92,
CH2Cl2). 1H NMR (400 MHz, CDCl3) δ 7.65–7.56 (m, 2H), 7.33–7.26 (m,
2H), 7.21–7.13 (m, 3H), 7.10–7.03 (m, 2H), 5.48 (d, J = 7.2 Hz, 1H),
4.58–4.42 (m, 1H), 1.43 (d, J = 6.9 Hz, 3H). The ee of 2o was
determined by HPLC analysis using Daicel Chiralcel OJ-H column (25
cm × 0.46 cm ID), conditions: n-Heptane/i-PrOH = 70/30, 1.0 mL/min,
240 nm; tminor = 8.8 min, tmajor = 14.6 min.
(R)-N-(1-(4-bromophenyl)ethyl)benzenesulfonamide (2h)
White solid, 68% yield, 97% ee. Mp 151-154 oC. [α]D20 = +43.5 (c = 0.2,
CH2Cl2).1H NMR (400 MHz, CDCl3) δ 7.68–7.58 (m, 2H), 7.44 (t, J = 7.5
Hz, 1H), 7.31 (s, 2H), 7.20 (d, J = 8.3 Hz, 2H), 6.89 (d, J = 8.4 Hz, 2H),
5.22 (d, J = 7.0 Hz, 1H), 4.43–4.33 (m, 1H), 1.31 (d, J = 6.9 Hz, 3H). The
ee of 2h was determined by HPLC analysis using Daicel Chiralcel AS-H
column (25 cm × 0.46 cm ID), conditions: n-Heptane/i-PrOH = 70/30, 1.0
mL/min, 240 nm; tmajor = 13.8 min, tminor = 20.1 min.
(R)-N-(1-phenylethyl)methanesulfonamide (2p)
Colorless oil, 82% yield, 97% ee. [α]D20 = +56.2 (c = 0.24, CH2Cl2). 1H
NMR (400 MHz, CDCl3) δ 7.33–7.30 (m, 1H), 7.29 (t, J = 2.7 Hz, 2H),
7.27–7.18 (m, 2H), 4.97 (d, J = 6.4 Hz, 1H), 4.58 (s, 1H), 2.53 (s, 3H),
1.47 (s, 3H).The ee of 2p was determined by HPLC analysis using Daicel
Chiralcel AS-H column (25 cm × 0.46 cm ID), conditions: n-Heptane/i-
PrOH = 80/20, 1.0 mL/min, 220 nm; tmajor = 12.7 min, tminor = 18.1 min.
(R)-N-(1-(naphthalen-1-yl)ethyl)benzenesulfonamide (2i)
White solid, 70% yield, 99% ee. Mp 161-163 oC. [α]D20 = -2.5 (c = 0.58,
CH2Cl2). 1H NMR (400 MHz, CDCl3) δ 7.91 (dd, J = 5.4, 4.3 Hz, 1H), 7.78
(dd, J = 6.8, 2.7 Hz, 1H), 7.71–7.60 (m, 3H), 7.49–7.40 (m, 2H), 7.36 (dd,
J = 14.9, 7.4 Hz, 2H), 7.24 (dt, J = 12.9, 6.5 Hz, 3H), 5.56 (d, J = 6.9 Hz,
1H), 5.38–5.27 (m, 1H), 1.57 (d, J = 6.8 Hz, 3H). The ee of 2i was
determined by HPLC analysis using Daicel Chiralcel OD-H column (25
cm × 0.46 cm ID), conditions: n-Heptane/i-PrOH = 80/20, 0.5 mL/min,
240 nm; tmajor = 17.7 min, tminor = 23.8 min.
(S)-3-phenyl-2,3-dihydrobenzo[d]isothiazole-1,1-dioxide (4a)
White solid, 91% yield, 88% ee. Mp 128-131 oC. [α]D20 = +85.2 (c = 0.46,
CH2Cl2). 1H NMR (400 MHz, CDCl3) δ 7.87–7.81 (m, 1H), 7.57 (dd, J =
6.4, 2.8 Hz, 2H), 7.40 (d, J = 4.2 Hz, 5H), 7.18–7.12 (m, 1H), 5.74 (d, J =
4.1 Hz, 1H), 5.14 (d, J = 3.2 Hz, 1H). The ee of 4a was determined by
HPLC analysis using Daicel Chiralcel OD-H column (25 cm × 0.46 cm ID),
conditions: n-Heptane/i-PrOH = 70/30, 0.8 mL/min, 230 nm; tmajor = 18.5
min, tminor = 21.0 min.
(R)-N-(1-(thiophen-2-yl)ethyl)benzenesulfonamide (2j)
White solid, 90% yield, 95% ee. Mp 92-95 oC. [α]D20 = +49.0 (c = 0.2,
CH2Cl2). 1H NMR (400 MHz, CDCl3) δ 7.84 (d, J = 7.4 Hz, 2H), 7.55 (s,
1H), 7.47 (d, J = 7.8 Hz, 2H), 7.11 (d, J = 5.1 Hz, 1H), 6.88–6.72 (m, 2H),
5.35 (d, J = 7.1 Hz, 1H), 4.79 (s, 1H), 1.55 (d, J = 6.8 Hz, 3H). The ee of
2j was determined by HPLC analysis using Daicel Chiralcel OD-H
column (25 cm × 0.46 cm ID), conditions: n-Heptane/i-PrOH = 90/10, 1.0
mL/min, 240 nm; tmajor = 12.7 min, tminor = 14.6 min.
(S)-3-(p-tolyl)-2,3-dihydrobenzo[d]isothiazole-1,1-dioxide (4b)
White solid, 89% yield, 90% ee. Mp 169-171 oC. [α]D20 = +66.5 (c = 0.52,
CH2Cl2). 1H NMR (400 MHz, CDCl3) δ 7.83 (dd, J = 5.9, 2.8 Hz, 1H),
7.61–7.51 (m, 2H), 7.30–7.24 (m, 2H), 7.21 (d, J = 8.0 Hz, 2H), 7.15 (dd,
J = 5.4, 2.9 Hz, 1H), 5.70 (d, J = 3.9 Hz, 1H), 5.06 (d, J = 3.3 Hz, 1H),
2.37 (s, 3H). The ee of 4b was determined by HPLC analysis using
Daicel Chiralcel AS-H column (25 cm × 0.46 cm ID), conditions: n-
(R)-N-(1-phenylpropyl)benzenesulfonamide (2k)
White solid, 85% yield, 96% ee. Mp 117-120 oC. [α]D20 = +62.9 (c = 0.88,
CH2Cl2). 1H NMR (400 MHz, CDCl3) δ 7.63–7.55 (m, 2H), 7.33 (d, J = 7.5
Hz, 1H), 7.21 (dd, J = 15.0, 7.5 Hz, 2H), 7.04 (dd, J = 4.2, 2.3 Hz, 3H),
6.92 (dd, J = 6.6, 2.9 Hz, 2H), 5.32 (d, J = 7.6 Hz, 1H), 4.14 (q, J = 7.4
Hz, 1H), 1.74 (dd, J = 14.1, 7.0 Hz, 1H), 1.68–1.60 (m, 1H), 0.72 (t, J =
7.4 Hz, 3H). The ee of 2k was determined by HPLC analysis using Daicel
Chiralcel AD-H column (25 cm × 0.46 cm ID), conditions: n-Heptane/i-
PrOH 95/5, 0.5 mL/min, 240 nm; tminor = 51.6 min, tmajor = 54.8 min.
Heptane/i-PrOH = 70/30, 0.5 mL/min, 230 nm; tmajor = 17.4 min, tminor
23.0 min.
=
(S)-3-(4-fluorophenyl)-2,3-dihydrobenzo[d]isothiazole-1,1-dioxide
(4c)
White solid, 92% yield, 85% ee. Mp 163-67 oC. [α]D20 = +66.9 (c = 0.76,
CH2Cl2). 1H NMR (400 MHz, CDCl3) δ 7.89–7.81 (m, 1H), 7.58 (d, J = 2.8
Hz, 2H), 7.37 (dd, J = 8.6, 5.2 Hz, 2H), 7.15 (dd, J = 7.6, 5.8 Hz, 1H),
7.10 (d, J = 8.6 Hz, 2H), 5.75 (d, J = 4.1 Hz, 1H), 5.23 (d, J = 3.3 Hz,
1H).The ee of 4c was determined by HPLC analysis using Daicel
Chiralcel OD-H column (25 cm × 0.46 cm ID), conditions: n-Heptane/i-
PrOH = 70/30, 1.0 mL/min, 230 nm; tmajor = 9.8 min, tminor = 15.6 min.
(R)-2-methyl-N-(1-phenylethyl)benzenesulfonamide (2l)
White solid, 72% yield, 95% ee. Mp 87-90 oC. [α]D20 = +61.2 (c = 0.76,
CH2Cl2.1H NMR (400 MHz, CDCl3) δ 7.86 (d, J = 7.8 Hz, 1H), 7.37 (s, 1H),
7.17 (dd, J = 14.1, 4.9 Hz, 5H), 7.09–6.99 (m, 2H), 5.13 (s, 1H), 4.43 (s,
1H), 2.52 (s, 3H), 1.45 (d, J = 6.8 Hz, 3H). The ee of 2l was determined
by HPLC analysis using Daicel Chiralcel OJ-H column (25 cm × 0.46 cm
(S)-3-methyl-2,3-dihydrobenzo[d]isothiazole-1,1-dioxide (4d)
ID), conditions: n-Heptane/i-PrOH = 80/20, 0.5 mL/min, 240 nm; tminor
15.2 min, tmajor = 26.6 min.
=
White solid, 84% yield, 81% ee. Mp 92-95 oC. [α]D20 = -20 (c = 0.38,
CH2Cl2). 1H NMR (400 MHz, CDCl3) δ 7.77 (d, J = 7.4 Hz, 1H), 7.64 (t, J
= 7.5 Hz, 1H), 7.53 (t, J = 7.4 Hz, 1H), 7.40 (d, J = 7.7 Hz, 1H), 5.12 (d, J
= 27.5 Hz, 1H), 4.87–4.75 (m, 1H), 1.61 (dd, J = 6.6, 2.6 Hz, 3H). The ee
of 4d was determined by HPLC analysis using Daicel Chiralcel OD-H
column (25 cm × 0.46 cm ID), conditions: n-Heptane/i-PrOH = 80/20, 0.5
mL/min, 230 nm; tmajor = 23.0 min, tminor = 29.5 min.
(R)-3-methyl-N-(1-phenylethyl)benzenesulfonamide (2m)
White solid, 82% yield, 98% ee. Mp 145-147 oC. [α]D20 = +75.0 (c = 0.58,
CH2Cl2). 1H NMR (400 MHz, CDCl3) δ 7.61–7.54 (m, 1H), 7.50 (s, 1H),
7.28 (dd, J = 3.9, 1.6 Hz, 2H), 7.24–7.15 (m, 3H), 7.14–7.07 (m, 2H),
5.25 (d, J = 7.1 Hz, 1H), 4.51 (s, 1H), 2.32 (s, 3H), 1.46 (d, J = 6.9 Hz,
3H). The ee of 2n was determined by HPLC analysis using Daicel
Chiralcel OD-H column (25 cm × 0.46 cm ID), conditions: n-Heptane/i-
PrOH = 90/10, 1.0 mL/min, 240 nm; tmajor = 10.9 min, tminor = 12.3 min.
(S)-3-phenethyl-2,3-dihydrobenzo[d]isothiazole-1,1-dioxide (4e)
White solid, 93% yield, 71% ee. Mp 111-114 oC. [α]D20 = -32.8 (c = 0.6,
CH2Cl2). 1H NMR (400 MHz, CDCl3) δ 7.78 (d, J = 7.7 Hz, 1H), 7.62 (s,
1H), 7.53 (s, 1H), 7.34 (dd, J = 21.6, 7.5 Hz, 3H), 7.24 (dd, J = 7.0, 4.8
Hz, 3H), 5.19 (d, J = 5.2 Hz, 1H), 4.79–4.64 (m, 1H), 2.84 (t, J = 7.7 Hz,
2H), 2.28 (d, J = 3.5 Hz, 1H), 2.18–2.05 (m, 1H). The ee of 4e was
determined by HPLC analysis using Daicel Chiralcel AS-H column (25
cm × 0.46 cm ID), conditions: n-Heptane/i-PrOH = 70/30, 0.5 mL/min,
230 nm; tmajor = 43.0 min, tminor = 52.2 min.
(R)-4-methyl-N-(1-phenylethyl)benzenesulfonamide (2n)
White solid, 94% yield, 97% ee. Mp 99-102 oC. [α]D20 = +68.5 (c = 0.26,
CH2Cl2). 1H NMR (400 MHz, CDCl3) δ 7.62 (d, J = 8.3 Hz, 2H), 7.16 (dd,
J = 4.8, 3.1 Hz, 5H), 7.10 (dt, J = 5.1, 3.9 Hz, 2H), 5.23 (d, J = 7.1 Hz,
1H), 4.53–4.38 (m, 1H), 2.37 (s, 3H), 1.41 (d, J = 6.9 Hz, 3H). The ee of
2m was determined by HPLC analysis using Daicel Chiralcel OJ-H
column (25 cm × 0.46 cm ID), conditions: n-Heptane/i-PrOH = 70/30, 1.0
mL/min, 240 nm; tminor = 12.6 min, tmajor = 18.9 min.
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201801123
European Journal of Organic Chemistry
FULL PAPER
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Acknowledgements
We gratefully thank the National Natural Science Foundation of
China (21572198), the Applied Basic Research Project of
Yunnan Province (2018FB021, 2017FA004) and the Department
of Education of Yunnan Province (2017ZDX046) for financial
support.
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Keywords: Palladium
•
co-catalyst
•
asymmetric
•
hydrogenation • imine
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10.1002/ejoc.201801123
European Journal of Organic Chemistry
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This article is protected by copyright. All rights reserved.

10.1002/ejoc.201801123
European Journal of Organic Chemistry
FULL PAPER
This article is protected by copyright. All rights reserved.