Asymmetric kinetic resolution of sulfides for the construction of unsymmetric sulfides and chiral 3,3-disubstituted oxindoles

Article abstract of DOI:10.1039/c9ob01065c

A range of 3,3-disubstituted oxindoles accessed using para-quinone methides derived from isatins with thiols were used for the formation of unsymmetrical disulfides, and 3,3-disubstituted oxindoles with a chiral quaternary carbon center and unsymmetric di

Full text of DOI:10.1039/c9ob01065c

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Takeharu Haino et al.
Solvent-induced emission of organogels based on tris(phenylisoxazolyl)
benzene
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DOI: 10.1039/C9OB01065C
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Asymmetric Kinetic Resolution of Sulfides for the Construction of
Unsymmetric Sulfides and Chiral 3,3-Disubstituted Oxindoles
Kaiye Wang, Yanan Xiang, Zhujun Shi, Hongyu Wang,* Na Li * and Bo Tang *
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
O
O
CO2H
A range of 3,3-disubstituted oxindoles accessed by para-quinone
methides derived from isatins with thiols was used for the
formation of unsymmetrical disulfides, and 3,3-disubstituted
oxindoles with chiral quaternary carbon center and unsymmetric
disulfides could also be directly obtained with high selectivities
catalyzed by chiral phosphines in one step.
Me
Me
O
O
N
N
H
N
N
NH
NH HN
MeO
NH
O
O
HN
H2N
N
H
O
O
NH
O
HO2C
HN
S
H
S
Istodax
Me
Me
O
HO2C
O
Me
Me
N
N
OAc
O
NH
HN
HO
OMe
O
MeO
MeO
NH
Disulfide bonds, as important structural motifs, are present in
numerous natural products and bioactive molecules, which also
play a significant role in controlling the three-dimensional
structure of protein in biological systems.1 Because disulfide
bonds can be reduced by glutathione and cysteine in cancer
cells, unsymmetrical disulfides have been widely applied in
controlled drug release and targeted drug delivery (Figure 1).2
Up to now, great efforts have been focused on the
development of efficient synthetic methods to prepare
unsymmetrical and symmetrical disulfides.3 In particular,
nucleophile substitution reactions present an simple and
convenient approach for constructing disulfides, and many
sulfonation reagents, such as 1-chlorobenzotriazole, N-
trifuoroacetyl arenesulfenamides and R-S-S-OMe, have since
been developed over the past decades.4 Although great
advances have been made over the past decades, little
attention was paid to the construction of disulfide bonds in the
discovery of new reactions for simultaneously obtaining other
useful compounds. In 1988, Yoneda and co-workers found that
5-arylidene-1,3-dimethylbarbituric acid derivative I could be
efficiently reduced by thiols to generate 1,3-dicarbonyl
compound II at high temperature, which can further react with
R-S-Cl and thiols to prepare unsymmetrical disulfides (Scheme
1a).5 Recently, our group found that para-quinone methides
derived from isatins possess excellent properties to prepare 3,3-
S
N
OH
N
N
HO2C
NH
HO
NH2
N
O
Me
S
O
S
NH
OMe
O
O
S
S
Me
Polycarpamine B
Vintafolide
Fig. 1 Representative natural products and drugs containing unsymmetrical
disulfide bonds.
a) Previous works by Yoneda and co-workers :
O
O
Me
Me
N
Et3N, n-BuSH
120~150 o
dioxane, 2 days
N
C
O
N
O
NO2
R
O
N
Me
I
O
NO2
Me
II
: 88% yield
S
R'
S
O
R
S
Me
O
N
R-S-Cl
N
O
NO2
R'-SH
Me
III
b) This work:
HO
O
t-Bu
t-Bu
t-Bu
t-Bu
Thiols
Asymmetric kinetic resolution
S
R'
O
+
S
R''
R'
S
R
O
R
N
N
Me
Me
IV
1
3
Scheme 1. Synthesis of disulfides and chiral 3,3-disubstituted oxindoles.
disubstituted oxindoles,6 which represent important structural
motifs widely existing in natural products.7 In view of the similar
structures between I and IV (Scheme 1), we anticipated that it
will be an ideal method to construct unsymmetrical sulfides
using IV and simultaneously generate 3,3-disubstituted
oxindoles (Scheme 1b). Furthermore, chiral 3,3-disubstituted
oxindoles would be synthesized via asymmetric kinetic
resolution in one step, which would expand the applications of
a. College of Chemistry, Chemical Engineering and Materials Science, Key Laboratory
of Molecular and Nano Probes, Ministry of Education Collaborative Innovation
Center of Functionalized Probes for Chemical Imaging in Universities of Shandong,
Institute of Molecular and Nano Science, Shandong Normal University
Jinan, 250014 (P.R. China). E-mail: wanghongyu@sdnu.edu.cn, lina@sdnu.edu.cn,
tangb@sdnu.edu.cn.
Electronic Supplementary Information (ESI) available: [Experimental details and
supplementary figures. CCDC 1906989. For ESI and crystallographic data in CIF or
other electronic format. See DOI: 10.1039/x0xx00000x
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Table 1. Screening the chiral catalysts.a
DDQ, CH3CN,rt
>99% yield
View Article Online
DOI: 10.1039/C9OB01065C
R
R
S
S
Bn
OH
O
Bn
O
t-Bu
t-Bu
catalyst (5 mol%)
2a
p-BrC6H4SH ( ), toluene, r.t.
O
N
O
t-Bu
t-Bu
N
Me
1a
Me
K2CO3 (20 mol%)
TBAB (20 mol%)
1'a
a)
BnSH (4 equiv.)
Toluene, r.t.
R
R
O
Chiral Amines (5 mol%):
N
N
Me
CF3
Me
95% yield, 30 min
4b:
IV
N
4a:
R = 5-Me,
R = H,
N
S
75% yield, 20 min
NH
HO
N
N
CF3
4c:
4d:
R = 5-Br,
R = 6-Br,
58% yield, 20 min
62% yield, 20 min
OH
t-Bu
H
H
N
N
N
C
S
NH
t-Bu
A
1'a
1'a
: 53% yield, -56% ee, 18 h
B
1'a
: 95% yield, -3% ee, 18 h
S
Bn
(DHQD)2PHAL
F3C
CF3
BnSH
BnSH
O
R
1'a
: 99% yield, 0% ee, 18 h
: 63% yield, -35% ee, 18 h
N
Chiral Phosphines (5 mol%) with Methyl Acrylate (1 L):

Me
1
O2N
F3C
O2N
S
Bn
O
Bn
O
Bn
HO
OH
t-Bu
t-Bu
N
N
N
N
N
N
Bn
S
H
H
H
H
H
H
t-Bu
SH
t-Bu
PPh2
PPh2
1'a
: 34% yield, 85% ee, 30 min
D
PPh2
: 44% yield, 86% ee, 30 min
O2N
E
F
S
1'a
: 58% yield, 76% ee, 30 min
1'a
b)
+
S
+
Bn
O2N
K2CO3 (20 mol%)
TBAB (20 mol%)
Toluene, r.t.
O2N
O
O
Ph
O
O
O
N
Br
N
N
N
N
N
N
N
Br
H
H
H
H
H
H
Me
, 90% yield
Me
1a
PPh2
: 79% yield, 2% ee, 30 min
PPh2
1'a
: 67% yield, 13% ee, 30 min
PPh2
H
I
G
2a
3a
, 90% yield
4a
1'a
1'a
: 78% yield, 8% ee, 30 min
Scheme 2. Synthesis of disulfide bonds via the reduction of para-quinone
methides using thiols. The yields of the isolated products are given.
aUnless otherwise noted, all the reactions were carried out with 1a (0.1 mmol) in
the presence of chiral catalyst (5 mol%) in toluene (2.0 mL) at r.t.. The yields of the
isolated products are given, and the ee value was determined by HPLC analysis
HO
R'
S
t-Bu
R
these results and those of previous works,9 we hypothesized
that 1,6-conjugate adduct 1 may be first generated, and then
another BnSH would react with 1 via the SN2 reaction to furnish
the reduced product 4 under basic conditions. Subsequently, a
control experiment was performed using 1a and p-BrC6H4SH,
whereby 4a was successfully synthesized with 90% yield, and
the unsymmetrical disulfide 3a was also obtained with 90%
yield (Scheme 2b). Notably, 4 could easily be oxidized by DDQ
to regenerate the para-quinone methides IV.
t-Bu
K2CO3 (20 mol%)
R
R'
S
:
+
R''S-H
O
S
R''
TBAB (20 mol%), toluene, r.t.
N
Me
1
2
3
Br
F
Br
CO2Me
S
CO2Me
S
S
S
BocHN
S
BocHN
3c
S
3a
3b
: 2 h, 90% yield
: 10 min, 50% yield
: 10 min, 57% yield
MeO2C
O
S
S
CO2Me
S
BocHN
O
BocHN
Se
To explore the generality of the method for the construction
of unsymmetrical disulfides, a series of substituted oxindoles
and thiols were examined under mild conditions, aryl-thiols (or
selenol) and alkyl-thiols were all suitable for the catalytic system
to obtain various unsymmetrical disulfides. In addition, cysteine
and sugar derivatives could be easily functionalized via this
method (Scheme 3). Owing to the importance of chiral 3,3-
disubstituted oxindoles in natural products, we decided to
explore an enantioselective process for the above reaction via
asymmetric kinetic resolution. In this way, not only could chiral
3,3-disubstituted oxindoles be furnished, but unsymmetrical
disulfides could also be obtained in one step. First, many chiral
Brønsted bases were carefully investigated,10 however, no high
ee values were obtained (Table 1). Recently, Zhao and
coworkers found that the cooperation of chiral phosphines and
methyl acrylate provided an excellent method for asymmetric
Mannich-type reactions.11 Inspired by this, the dual-reagent
catalytic system was then tested for the reaction. The urea
moiety of these catalysts seemed better than thiourea, and the
urea catalyst E bearing a 4-nitrophenyl group turned out to be
the optimum one for the reaction. Notably, the chiral skeleton
3e
: 60 min, 60% yield
AcO
3d
: 5 min, 40% yield
O
OAc
O
S
AcO
O
CO2Me
AcO
S
S
S
S
AcO
Se
OAc
BocHN
CO2Me
AcO
OAc
BocHN
3f
3g
3h
: 15 min, 57% yield
: 10 min, 58% yield
: 10 min, 62% yield
Scheme 3. Substrate scope for the synthesis of unsymmetrical disulfides. All the
reactions were carried out with 1 (0.1 mmol) and 2 (0.2 mmol) in the presence of
K2CO3 (20 mol%) and TBAB (20 mol%) in toluene (2 mL) at r.t.. The yields of the
isolated products are given. TBAB: tetrabutylammonium bromide.
para-quinone methides derived from isatins in organic
synthesis.8
Initially, 1,6-conjugate addition reactions between IV and
BnSH were investigated under basic conditions, and the
reduced product 4 and 1,2-dibenzyldisulfane were detected in
high yield (Scheme 2a). While para-quinone methides derived
from aryl aldehydes were also examined, but no reduzates and
disulfides were observed, and only the addition product 4-
((benzylthio)(4-fluorophenyl)methyl)-2,6-di-tert-butylphenol
was obtained (see Supporting Information, Figure S1). Based on
2 | J. Name., 2012, 00, 1-3
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Table 3. Scope of thiols 2 in the asymmetric kinetic resolution.a
derived from L-phenyl-alanine was found to be crucial for
improving the enantioselectivity of this reaction after several
catalysts were screened. Via the optimization of these catalysts,
chiral phosphine E showed to be the best choice with 86% ee
and 44% yield.
View Article Online
DOI: 10.1039/C9OB01065C
Bn
R
R
R
S
S
Bn
Bn
S
E
(5 mol%)
SH
R'
O
+
O
+
+
O
S
methyl acrylate (1 L)
toluene, r.t.
N
Me
N
Me
N
R'
Me
With the optimized conditions in hand, the scope of the
enantioselective method for the generation of chiral 3,3-
disubstituted oxindoles and disulfides was then carefully
explored (Table 2). The substituents (5-Me, 5-Br, 6-Br) on the
benzene ring of the isatin skeleton were first examined, and all
gave excellent results with excellent enantioselectives in a short
time. In addition, the absolute configuration of 1’j was
determined by X-ray crystallographic analysis (CCDC
1906989).12 Moreover, different substituents on the “S” atom,
including benzyl thiols, allyl thiol, cysteine, glucoside thiol, were
all well tolerated in the reactions (up to >99% ee) (Table 3).
Afterwards, many substituted nucleophiles (aryl-thiols) were
then investigated, and were also found to be well tolerated with
high ee values. Notably, benzeneselenol was also examined in
this system, which gave the product 1’a with 96% ee.
Meanwhile, the alkyl-thiol 2g could also react with 1a furnishing
the product 1’a with moderate enantioselectivity.
1a
2
1'a
3
4a
SeH
SH
SH
F
2b
2c
: 32% yield, 96% ee, 5 min
2d
: 42% yield, 90% ee, 30 min
1'a
: 46% yield, 80% ee, 40 min
1'a
1'a
3n
4a
: 35% yield, 40 min
: 53% yield, 40 min
3o
4a
: 33% yield, 5 min
: 68% yield, 5 min
3p
4a
: 32% yield, 30 min
: 58% yield, 30 min
SH
Br
SH
SH
COOMe
Cl
2e
2g
2f
: 43% yield, 86% ee, 30 min
3r
1'a
1'a
: 48% yield, 55% ee, 12 h
: 39% yield, 88% ee, 30 min
1'a
3q
4a
3s
4a
: 28% yield, 30 min
: 61% yield, 30 min
: 23% yield, 12 h
: 52% yield, 12 h
: 37% yield, 30 min
4a
: 57% yield, 30 min
aAll the reactions were carried out with 1a (0.1 mmol) with 2 (0.2 mmol) in the
presence of E (5 mol%) and methyl acrylate (1 μL) at r.t.; Yields of isolated products
are given, and the ee value was determined by HPLC analysis.
Table 4. Scope of the 3-arylthio-3-aryl-oxindoles 1.a
Ar
Ar
S
S
R
R
E
(5 mol%)
Table 2. Scope of the 3-alkylthio-3-aryl-oxindoles 1.a
methyl acrylate (1 L)
p-BrC6H4SH
X
X
O
O
N
N
R1
toluene, -40 o
C
PG
PG
R
S
R
R
SH
S
1
S
1'
R1
O
E
S
R1
(5 mol%)
+
+
O
X
+
X
L)
O
methyl acrylate (1
toluene, r.t.
X
N
N
N
Me
Entry
Ar
X
PG
Me
Me
Time
1.3 h
1.3 h
12 h
11.5 h
12 h
12 h
18 h
12 h
12 h
1’
(yield, ee)b
34%, 94%
38%, 94%
39%, 94%
42%, 90%
40%, 92%
34%, 95%
42%, 86%
30%, 92%
30%, 90%
Me
Me
Br
Br
1
2a
1'
3
4
1
2
3
4
5
6
7
8
9
4-BrC6H4
4-BrC6H4
4-BrC6H4
4-FC6H4
4-BrC6H4
5-Br
5-I
H
1’k
1’l
Bn
Bn
S
Bn
R
S
N
R
S
R
Me
Br
O
O
O
PMB
Me
Me
Me
Me
Me
Me
1’m
1’n
1’o
1’p
1’q
1’r
N
N
Me
Me
Me
H
1'b
: 42% yield, 81% ee, 30 min
: 30% yield, 30 min
1'a
1'c
: 44% yield, 86% ee, 30 min
: 29% yield, 30 min
: 35% yield, 96% ee, 15 min
: 28% yield, 15 min
3a
4b
3a
4a
3a
4c
H
: 57% yield, 30 min
Cl
: 56% yield, 30 min
: 65% yield, 15 min
Bn
4-MeC6H4
4-EtC6H4
3-BrC6H4
2-MeC6H4
H
S
R
R
R
S
S
H
O
Cl
O
N
Me
O
N
Me
Br
H
N
Me
1'd
3a
4d
: 39% yield, 95% ee, 15 min
: 32% yield, 15 min
: 60% yield, 15 min
1'f
3j
4a
: 45% yield, 76% ee, 30 min
: 27% yield, 30 min
: 54% yield, 30 min
MeO2C
1'e
3i
4a
H
1’s
: 40% yield, 94% ee, 30 min
: 33% yield, 30 min
: 59% yield, 30 min
CO2Me
aAll the reactions were carried out with 1 (0.1 mmol) with 2a (0.2 mmol) in the
presence of E (5 mol%) and methyl acrylate (1 μL) at –40 °C. bYields of isolated
products are given, and the ee value was determined by HPLC analysis.
R
R
S
R
S
NHBoc
S
O
N
Me
O
O
N
Me
N
Me
1'g
: 38% yield, 86% ee, 15 min
1'h
3c
4a
: 30% yield, >99% ee, 5 min
: 31% yield, 5 min
: 70% yield, 5 min
To further expand the generality of this reaction, 3-arylthio-
3-aryl-oxindoles were then investigated under the dual-reagent
catalytic system (Table 4). In virtue of their instability under
basic conditions, the reactions were carried out at -40 °C. Then,
a range of substituted 3-arylthio-3-aryl-oxindoles 1 was
screened, and all the reactions performed well and gave the
desired products with excellent enantioselectivities.
In summary, we developed an enantioselective method for
preparing unsymmetrical disulfides and chiral 3,3-disubstituted
oxindoles in one step. Many substituted thiols and 3,3-
disubstituted oxindoles were well tolerated, and produced high
yields and enantioselectivities under mild conditions, which
enriched the disulfide bond chemistry and open new avenues
1'i
3l
4a
: 21% yield, 98% ee, 5 min
: 33% yield, 5 min
: 79% yield, 5 min
a
3k
4a
: - yield, 15 min
: 60% yield, 15 min
OAc
O
AcO
AcO
R
S
OAc
O
N
Me
: 37% yield, 99% ee, 5 min
1'j
3m
4a
: 23% yield, 5 min
: 60% yield, 5 min
1'j (CCDC
1906989)
aAll the reactions were carried out with 1 (0.1 mmol) with 2a (0.2 mmol) in the
presence of E (5 mol%) and methyl acrylate (1 μL) at r.t.; Yields of isolated products
are given, and the ee value was determined by HPLC analysis; Supplementary
crystallographic data for 1j can be found in CCDC 1906989.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
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9
(a) W.-D. Chu, L.-F. Zhang, X. Bao, X.-H. Zhao, C. Zeng, J.-Y. Du,
to the synthesis of unsymmetrical disulfides and chiral 3,3-
disubstituted oxindoles.
View Article Online
G.-B. Zhang, F.-X. Wang, X.-Y. Ma and C.-A. Fan, Angew. Chem.
Int. Ed., 2013, 52, 9229; (b) Z. Wang,DYO. IF: .10W.10o3n9g/Ca9nOdB0J.10S6u5nC,
Angew. Chem. Int. Ed., 2015, 54, 13711; (c) K. Zhao, Y. Zhi, T.
Shu, A. Valkonen, K. Rissanen and D. Enders, Angew. Chem.
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Financial support from the National Natural Science
Foundation of China (21535004, 91753111, 21874086,
21602125, and 21390411), the Key Research and Development
Program of Shandong Province (2018YFJH0502), the Natural
Science Foundation of Shandong Province (ZR2016BQ38), and
the China Postdoctoral Science Foundation (40411585) is
gratefully acknowledged.
10 (a) C. Palomo, M. Oiarbide, R. López, Chem. Soc. Rev. 2009, 38,
632; (b) X. Fang, C.-J. Wang, Chem. Commun. 2015, 51, 1185;
(c) F. Giacalone, M. Gruttadauria, P. Agrigento, R. Noto, Chem.
Soc. Rev. 2012, 41, 2406.
11 (a) H.-Y. Wang, K. Zhang, C.-W. Zheng, Z. Chai, D.-D. Cao, J.-X.
Zhang and G. Zhao, Angew. Chem. Int. Ed., 2015, 54, 1775; (b)
Y.-P. Lou, C.-W. Zheng, R.-M. Pan, Q.-W. Jin and G. Zhao, Org.
Lett., 2015, 17, 688; (c) H.-Y. Wang, C.-W. Zheng, Z. Chai, J.-X.
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Conflicts of interest
The authors declare no competing financial conflicts.
12 CCDC 1906989 (1’j) contains the supplementary
crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic
Data Center via www.ccdc.cam.ac.uk/data_request/cif.
Notes and references
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