Chiral sulfonimide as a bronsted acid organocatalyst for asymmetric Friedel-Crafts alkylation of indoles with imines

Article abstract of DOI:10.1021/jo2011335

Binaphthyl-based chiral sulfonimide (CSI) is demonstrated for the first time to be an efficient, strong Bronsted acid in asymmetric organocatalysis. A series of CSIs were synthesized and screened in the asymmetric Friedel-Crafts alkylation of indoles with imines. Good to excellent yields and enantioselectivities have been achieved. It was proved that it was crucial to wash the CSI catalyst with HCl before use.

Full text of DOI:10.1021/jo2011335

ARTICLE
pubs.acs.org/joc
Chiral Sulfonimide as a Brønsted Acid Organocatalyst for Asymmetric
FriedelꢀCrafts Alkylation of Indoles with Imines
Ling-Yan Chen, Hao He, Wing-Hong Chan, and Albert W. M. Lee*
Department of Chemistry, Hong Kong Baptist University, Kowloon Tong, Hong Kong, People's Republic of China
S Supporting Information
b
ABSTRACT:
Binaphthyl-based chiral sulfonimide (CSI) is demonstrated for the first time to be an efficient, strong Brønsted acid in asymmetric
organocatalysis. A series of CSIs were synthesized and screened in the asymmetric FriedelꢀCrafts alkylation of indoles with imines.
Good to excellent yields and enantioselectivities have been achieved. It was proved that it was crucial to wash the CSI catalyst with
HCl before use.
’ INTRODUCTION
acid-catalyzed transformations.10 It has been reported that the
pKa value of 3 in water is ꢀ4.1,10b and those for the correspond-
ing aliphatic cyclic sulfonimides 4 and 5 are ꢀ3.1 and ꢀ1.7,
respectively.11 We envision that a chiral version of 3 could be an
effective Brønsted acid for asymmetric organocatalysis, and
binaphthyl was selected as the chiral backbone in the design of
the chiral sulfonimide (CSI 6). It is also worth noting that
binaphthyl sulfonimide has a C2-symmetric topology, while the
corresponding BINOL-derived chiral phosphoric acid is only
pseudo-C2-symmetric.
Asymmetric organocatalysis, the use of small chiral organic
molecules to catalyze enantioselective transformations, has cap-
tured the imagination of chemists around the world in recent
years.1 It has complemented the organometallic and enzymatic
approaches to asymmetric catalysis in the construction of chiral
molecules and molecular scaffolds.2 Among various types of
organocatalysts, many believe Brønsted acid catalysts have the
potential to match up with the reactivities and selectivities
provided by metalꢀchiral ligand type asymmetric catalysts.3
In comparison with other types of organocatalysts, the struc-
tural variations of strong Brønsted acid organocatalysts are
relatively limited. For example, hundreds of Lewis base catalysts
derived from primary or secondary amines are known.1a,b
Hydrazine has also been recently explored by us and others as
a new functionality for Lewis base organocatalysis.4 In contrast,
most widely used strong Brønsted acid catalysts are still the
BINOL-derived chiral phosphoric acids (1) discovered indepen-
dently by Akiyama5 and Terada6 in 2004 or the more acidic N-
triflyl phosphoramides (2) developed by Yamamoto.7 In addi-
tion, chiral binaphthyl disulfonic acids have also been used as
Brønsted acid catalysts in organocatalysis by Ishihara.8 In this
paper, we report, for the first time, that chiral sulfonimide9 (CSI)
is an effective Brønsted acid scaffold for organocatalysis.
The synthesis of 6 was first reported by List12 and Giernoth.13
Giernoth only reported the preparation of the parent compound
with no substituents at the 3,30-positions. List and co-workers
elegantly demonstrated the use of 6a as an organocatalyst in
Mukaiyama aldol reactions of ketene silyl acetals with
aldehydes.12 Nevertheless, the actual catalyst is not Brønsted
acid 6a. It is the in situ generated silyated sulfonimine 8, which
acts as a Lewis acidic catalyst. Recently, we also reported our
synthetic approach of CSI 6.14
Our synthesis of 3,30-substituted chiral sulfonamides is slightly
different from that of List and is more convergent. In the List’s
synthesis of 6, the 3,30-diaryl substitutents are already in place in
the starting BINOL. In our approach (Scheme 1), we made use of
the sulfonyl groups at 2,20-positions as the directing groups for
functionalization of the 3,30-positions via ortho lithiation (7a to
7b) followed by bromination or iodination.14 The resulting
’ RESULTS AND DISCUSSION
Our idea on developing chiral sulfonimides as strong Brønsted
acid organocatalysts was inspired by the reports of Barbero that
o-benzenedisulfonimide (3) is a strong Brønsted acid for various
Received: June 2, 2011
Published: July 29, 2011
r
2011 American Chemical Society
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|

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ARTICLE
Scheme 1. Phosphoric and Sulfonimidic Brønsted Acidic
Organocatalysts
Table 2. HCl-Washed CSIs in Enantioselective Friedelꢀ
Crafts Alkylation of Indole with Imine
entrya
cat.b
t
yield (%)c
ee (%)d
1
2
3
4
5
6a
6b
6c
6d
6e
5 min
2 h
88
77
80
84
84
77
46
65
75
72
1 h
30 min
1 h
a Reaction conditions: 10a (0.1 mmol), 9a (3.0 equiv), 6 (10 mol %),
toluene (1.0 mL), 0 °C. b Catalysts 6aꢀe were washed with 1 M HCl
c
before use. Yield of product 11a isolated after flash chromatography.
d Determined by HPLC analysis using a Chiralcel OD column.
Brønsted acids in the asymmetric FriedelꢀCrafts alkylation of
indoles with imines.
The asymmetric FriedelꢀCrafts alkylation reaction of indoles
with imines is an important method for the preparation of
optically active 3-substituted indole derivatives.3d,16 The result-
ing chiral 3-indolyl methanamine motif is embedded in numer-
ous biologically active indole alkaloids and synthetic indole
derivatives.17 The first BINOL-derived chiral phosphoric acid
catalyzed enantioselective FriedelꢀCrafts alkylation reaction of
indoles with imines was reported by You.18 Recently, the use of
SPINOL-derived chiral phosphoric acids in the same reaction
system has also been reported.19
Table 1. Initial Studies on Unwashed-CSI-Catalyzed Asym-
metric FriedelꢀCrafts Alkylation of Indoles with Imines
Our investigations started with the examination of the reaction
between indole 9a and imine 10a in the presence of 10 mol % of
CSI 6a in toluene. We were disappointed that the reaction
proceeded very slowly at room temperature. Only when the
temperature was raised to 60 °C could the reaction proceed
smoothly in reasonable conversion with moderate ee, along with
a significant amount of the bis-indole product 1220 (14% yield,
Table 1, entry 1). These discouraging initial results are summar-
ized in Table 1. The best ee was up to 83%, achieved by
5-methylindole with imine 10a (Table 1, entry 9).
It has been pointed out by Ishihara that BINOL-derived
phosphoric acids are readily neutralized to adventitious metal
salts such as alkali- and alkaline-earth-metal salts during purifica-
tion on silica gel and warned that such impurities might have a
substantial influence on the catalyst’s performance.21 Ding also
reported that phosphoric acid washed with HCl improved the
catalytic activity in the BaeyerꢀVilliger reaction.22 Recently, List
reported a detailed analysis of the phosphate salt impurities of a
chiral BINOL phosphoric acid and confirmed that it is easily
contaminated during synthesis and silica gel column
chromatography.23 We speculated that similar contamination
could happen with our CSI catalysts and decided to wash the
sulfonimide catalysts with dilute HCl (followed by water and
brine) before use.
entrya
R1
10 R2/R3
t (h) yield of 11 (%)b ee (%)c
1
2
3
4
5
6
7
8
9
H
H/4-MePh (10a)
H/Ph
7
10
8
84
74
74
90
46
66
55
77
87
76
76
76
76
53
77
70
81
83
H
H
H/4-BrPh
H
H/2-Nap
3
Me
H
4-MeO/4-MePh
4-Br/4-MePh
H/4-MePh
1
3
Br
9
MeO H/4-MePh
Me H/4-MePh
3
6
a Reaction conditions: 10 (0.1 mmol), 9a (3.0 equiv), 6a (10 mol %),
toluene (0.4 mL), 60 °C. b The yield was determined after flash
chromatography. c Determined by HPLC analysis using a Chiralcel
OD column.
dihalogenated 7c could serve as the common precursor for a
series of 3,30-diaryl-substituted CSIs via coupling reactions.
C2-symmetric BINOL-derived chiral sulfonimide is a new
scaffold for organocatalysis. List has demonstrated that in situ
generated silyated sulfonimine 8 is a Lewis acidic organocatalyst.
More recently, a proline-attached CSI was used as a Lewis base in
the Michael addition of ketone and aldehyde to nitroalkenes.15
However, to the best of our knowledge, there has been no report
of using chiral sulfonimide (CSI) as a Brønsted acid in organo-
catalysis. In this paper, we demonstrate that CSIs are effective
To our delight, the acid-washed CSI was much more reactive.
Using 10 mol % of HCl-washed CSI 6a, the reaction was
completed at 0 °C within 5 min with a high yield of the desired
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Table 3. Optimization of Reaction Conditions
Table 4. CSI-Catalyzed Enantioselective FriedelꢀCrafts
Alkylation of Indoles with N-Sulfonyl Iminesa
entrya amt of 6a (mol %) T (°C)
t
yield (%)b ee (%)c
1
2
3
4
5
6
7
10
10
10
10
10
5
0
ꢀ40
ꢀ50
ꢀ60
ꢀ78
ꢀ50
ꢀ50
5 min
10 min
50 min
3 h
88
90
82
86
70
90
64
77
89
92
93
93
93
93
5 h
1.5 h
5 h
2
a Reaction conditions: 10a (0.1 mmol), 9a (3.0 equiv), toluene
(1.0 mL). b Yield of product isolated after flash chromatography.
c Determined by HPLC analysis using a Chiralcel OD column.
product and no contamination of the byproduct 12 (Table 2,
entry 1). Under the same conditions, we screened several HCl-
washed CSI catalysts with different Ar groups at the 3- and 30-
positions of the binaphthyl scaffold. From the results given in
Table 2, the best-performing catalyst with regard to reactivity,
yield, and stereoselectivity was 6a. Notably, CSI 6d had similar
performance but the reactivity was slightly lower (30 min vs
5 min, Table 2, entries 4 and 1).
We then investigated the effect of the reaction temperature
and catalyst loading using CSI 6a. The results are summarized in
Table 3. In general, lower reaction temperatures decreased the
reaction rate with enhanced enantioselectivity. At ꢀ40 °C, the
reaction was still relatively fast (10 min, Table 3, entry 2) and the
ee increased to 89%. At ꢀ50 °C, the reaction could be completed
in 50 min with an increase in ee to 92% (Table 3, entry 3).
Lowering the reaction temperature to ꢀ78 °C only marginally
increased the enantioselectivity, but the reaction time was greatly
lengthened (Table 3, entries 4 and 5). By lowering the catalyst
loading to 5% or 2%, the same level of enantioselectivity could be
maintained but the reaction rate was decreased (Table 3, entries
6 and 7). Therefore, we concluded that ꢀ50 °C and 5 mol % of
6a were the optimized conditions. In addition to toluene, we also
tested other solvents such as THF, TBME, DCM, and MeCN.
However, they all resulted in a significant drop of both the
reaction rate and enantioselectivity.
A wide range of substituted indoles and imines have been tested
under the optimized conditions. The scope of the substrates is
summarized in Table 4. Several substituted indoles, containing
either electron-donating groups or electron-withdrawing groups,
have been examined. The enantioselectivities were found to be
sensitive to the electronic property of the indole rings. 5-Methy-
lindole has the best performance, with an ee value up to 95%
(Table 4, entry 2). When 5-methoxyindole was used, the reaction
proceeded very quickly and gave 93% ee with 94% yield in 1 h
(Table 4, entry 3). Even with 2 mol % of catalyst, good enantios-
electivity and yield could be maintained, though a slightly longer
reaction time was needed (Table 4, entry 4). However, the
introduction of an electron-withdrawing group onto the indole ring
led to a decrease in enantioselectivity (5-Br, Table 4, entry 5).
a Unless otherwise noted, all reactions were carriedout using6a(5 mol %),
10(0.1 mmol), and 9 (3.0 equiv) in toluene (1.0 mL) atꢀ50 °C. b Yield of
product isolated after flash chromatography. c Determined by HPLC
analysis using a Chiralcel OD column. d Using 2 mol % 6a. e The absolute
configuration was determined by comparison of the optical rotation with
the known compounds in the literature.18,20 f Reaction at ꢀ78 °C.
When the sulfonyl group in 10 was changed from 4-methyl-
phenyl to other sulfonyl groups such as phenyl, 4-bromophenyl,
and 2-naphthyl, the enantioselectivities were slightly decreased
(Table 4, entries 1 and 6ꢀ8).
N-4-Methylphenyl sulfonyl arylimines with various R2 groups
reacted smoothly to afford the corresponding products in good
to excellent yields and enantioselectivities. The enantioselectiv-
ities were not very sensitive to the electronic properties of the
arylimines. An electron-withdrawing group such as Cl at the 3- or
4-position gave a slightly higher ee value than an electron-
donating group such as MeO (Table 4, entries 11, 13 and 14,
15). The bromo-substituted arylimine reacted much more slowly
with decreased enantioselectivity because of poor solubility
(Table 4, entry 12). In addition, the enantioselectivities for
furylimine and alkylimine were poor (Table 4, entries 16 and 17).
On the basis of the transition state models of BINOL-phos-
phoric acids24 and the L-proline-based binaphthyl sulfonimides,15
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ARTICLE
(d, J = 8.4 Hz, 2H), 7.30 (d, J = 8.0 Hz, 1H), 7.24ꢀ7.15 (m, 7H), 7.11
(d, J = 8.0 Hz, 2H), 7.02ꢀ6.98 (m, 1H), 6.68 (d, J = 2.0 Hz, 1H), 5.85
(d, J = 6.8 Hz, 1H), 5.05 (d, J = 6.8 Hz, 1H), 2.37 (s, 3H); 13C NMR
(100 MHz, CDCl3) δ 143.0, 140.2, 137.4, 136.5, 129.2, 128.3, 127.3,
127.2, 127.1, 125.3, 123.8, 122.5, 119.9, 119.2, 116.3, 111.2, 55.0,
21.4; HRMS (MALDI-TOF) C22H20N2NaO2S (M + Na)+ m/z calcd
399.1138, found 399.1125.
11b: white solid, 88% yield, 95% ee (Daicel Chiralcel OD column
guarded with Chiracel OD Guard column, n-hexane/i-PrOH 60/40,
flow rate 0.75 mL/min, λ 254 nm, TR(1) = 8.944 min (major), TR(2) =
21
19.030 min (minor)); mp 159ꢀ160 °C; [R]D = +21.0° (c 0.91,
Figure 1. Plausible transition state.
acetone); 1H NMR (400 MHz, CDCl3) δ 7.91 (br, 1H), 7.59 (d, J = 8.3
Hz, 2H), 7.28ꢀ7.20 (m, 5H), 7.15 (t, J = 8.6 Hz, 3H), 6.97 (dd, J1 = 1.2
Hz, J2 = 8.3 Hz, 1H), 6.85 (d, J = 0.6 Hz, 1H), 6.53 (d, J = 2.3 Hz, 1H),
5.78 (d, J = 6.4 Hz, 1H), 5.07 (d, J = 6.4 Hz, 1H), 2.38 (s, 3H), 2.30 (s,
3H); 13C NMR (100 MHz, CDCl3) δ 143.0, 140.4, 137.3, 134.7, 129.3,
129.2, 128.2, 127.3, 127.2, 127.1, 125.5, 124.2, 124.1, 118.5, 115.8, 110.9,
54.8, 21.5, 21.3; HRMS (MALDI-TOF) C23H21N2O2S (M ꢀ H)ꢀ m/z
calcd 389.1329, found 389.1347.
we propose a plausible transition state model as depicted in
Figure 1. As a strong Brønsted acid, CSI is assumed to link the
two substrates together by hydrogen bonds, leading to an efficient
attack from the Si face of the imine transition state and thus giving
R configuration products.
11c: white solid, 94% yield, 93% ee (Daicel Chiralcel OD column
guarded with Chiracel OD Guard column, n-hexane/i-PrOH 60/40,
flow rate 0.75 mL/min, λ 254 nm, TR(1) = 8.842 min (major), TR(2) =
’ CONCLUSIONS
In conclusion, we have demonstrated for the first time that
chiral sulfonimides (CSIs) are effective Brønsted acids for
organocatalysis: in particular, the enantioselective Friedelꢀ
Crafts alkylation of indoles with imines. Considering the reaction
time, catalyst loadings, and enantioselectives, CSIs exhibited
excellent activities comparable to those of phosphoric acids.
Together with the results of the List group, our results have
shown that CSIs are effective Lewis and Brønsted acids in
organocatalysis. Further explorations of this new chiral sulfoni-
mide scaffold in other asymmetric transformations are in
progress.
22
25.673 min (minor)); mp 142ꢀ143 °C; [R]D = +38.4° (c 0.62,
acetone); 1H NMR (400 MHz, CDCl3) δ 7.93 (br, 1H), 7.55 (d, J = 8.3
Hz, 2H), 7.24ꢀ7.16 (m, 6H), 7.08 (d, J = 8.0 Hz, 2H), 6.82 (dd, J1 = 2.4
Hz, J2 = 8.8 Hz, 1H), 6.78 (d, J = 2.4 Hz, 1H), 6.59 (d, J = 2.5 Hz, 1H),
5.82 (d, J = 7.0 Hz, 1H), 5.17 (d, J = 7 Hz, 1H), 3.72 (s, 3H), 2.35 (s,
3H); 13C NMR (100 MHz, CDCl3) δ 139.4, 139.2, 135.1, 131.8, 128.6,
128.5, 127.9, 127.4, 127.1, 127.0, 125.6, 125.1, 121.7, 115.5, 113.5, 112.8,
55.0; HRMS (MALDI-TOF) C23H21N2O3S (M ꢀ H)ꢀ calcd m/z
405.1278, found 405.1290.
11d: white solid, 87% yield, 88% ee (Daicel Chiralcel OD column
guarded with Chiracel OD Guard column, n-hexane/i-PrOH 60/40,
flow rate 0.75 mL/min, λ 254 nm, TR(1) = 8.142 min (major), TR(2) =
’ EXPERIMENTAL SECTION
22
15.051 min (minor)); mp 184ꢀ185 °C; [R]D = +21.4° (c 0.74,
acetone); 1H NMR (400 MHz, CDCl3) δ 8.11 (br, 1H), 7.59 (d, J = 8.2
Hz, 2H), 7.26ꢀ7.20 (m, 5H), 7.17ꢀ7.11 (m, 5H), 6.71 (d, J = 2.3 Hz,
1H), 5.72 (d, J = 6.4 Hz, 1H), 5.08 (d, J = 6.4 Hz, 1H), 2.39 (s, 3H); 13C
NMR (100 MHz, CDCl3) δ 143.4, 140.1, 137.0, 135.1, 129.5, 128.5,
127.6, 127.1, 127.0, 125.4, 125.2, 121.5, 116.1, 113.3, 112.7, 54.6, 21.6;
HRMS (MALDI-TOF) C22H19BrN2NaO2S (M + Na)+ m/z calcd
479.0224, found 479.0241.
General Information. Unless otherwise noted, solvents and
starting materials were obtained from commercial suppliers. All chemi-
cals used were of reagent grade, without further purification before use.
1H NMR and 13C NMR spectra were recorded (400 MHz for 1H and
100 MHz for 13C) in CDCl3 or acetone-d6. Chemical shifts were
recorded in ppm (δ) relative to CHCl3 at 7.26 or to TMS at 0.00 for
1H NMR and 77.0 for 13C NMR or to acetone at 2.05 for 1H NMR and
29.8 for 13C NMR. Melting points were determined with a melting point
apparatus and are reported in degrees Celsius (uncorrected). Optical
rotations were taken on a digital polarimeter. Enantiomeric excesses of
compounds were determined by HPLC using a Daicel Chiralpak OD
(0.46 cm ꢁ 25 cm) column with OD guard (UV detection monitored at
254 nm). High-resolution mass spectra (HRMS) were recorded on a
MALDI-TOF MS instrument. Organocatalysts 6aꢀe were prepared
according to the procedure13 we reported recently.
General Procedure for CSI-Catalyzed FriedelꢀCrafts Alky-
lation of Indoles with Imines. To a solution of N-sulfonyl imine
(0.1 mmol) in 1.0 mL of dry toluene in a Schlenk tube under N2 was
added CSI ((R)-6a, 0.005 mmol). The solution was stirred at ꢀ50 °C for
15 min, and indole (0.3 mmol) was added in one portion. The reaction
mixture was kept stirring at ꢀ50 °C until consumption of the N-sulfonyl
imine. After the reaction was complete, the mixture was purified by flash
column chromatography with petroleum ether/ethyl acetate (3/1, v/v)
as eluent to afford the product.
11e: white solid, 60% yield, 90% ee (Daicel Chiralcel OD column
guarded with Chiracel OD Guard column, n-hexane/i-PrOH 60/40,
flow rate 0.75 mL/min, λ 254 nm, TR(1) = 11.084 min (major), TR(2) =
20
21.859 min (minor)); mp 133ꢀ135 °C; [R]D = +75.6° (c 1.0,
acetone); 1H NMR (400 MHz, acetone-d6) δ 10.13 (br, 1H), 7.56 (d,
J = 8.4 Hz, 2H), 7.47ꢀ7.42 (m, 3H), 7.38ꢀ7.34 (m, 4H), 7.20 (d, J = 5.6
Hz, 3H), 7.09 (t, J = 7.4 Hz, 1H), 6.94 (t, J = 7.4 Hz, 1H), 6.83 (s, 1H),
5.95 (d, J = 8.4 Hz, 1H); 13C NMR (100 MHz, acetone-d6) δ 142.1,
142.0, 137.9, 132.3, 129.5, 128.9, 128.2, 127.8, 126.7, 126.6, 124.9, 122.5,
120.1, 119.8, 116.5, 112.2, 56.0; HRMS (MALDI-TOF) C21H17BrN2NaO2S
(M + Na)+ m/z calcd 465.0067, found 465.0070.
11f: white solid, 93% yield, 90% ee (Daicel Chiralcel OD column
guarded with Chiracel OD Guard column, n-hexane/i-PrOH 60/40,
flow rate 0.75 mL/min, λ 254 nm, TR(1) = 10.564 min (major), TR(2) =
22
15.734 min (minor)); mp 130ꢀ132 °C; [R]D = +16.5° (c 1.50,
acetone); 1H NMR (400 MHz, CDCl3) δ 8.01 (br, 1H), 7.62 (d, J = 8.5
Hz, 2H), 7.40 (t, J = 7.4 Hz, 1H), 7.29ꢀ7.23 (m, 4H), 7.19ꢀ7.12 (m,
6H), 6.99 (t, J = 7.2 Hz, 1H), 6.57 (d, J = 2.1 Hz, 1H), 5.86 (d, J = 7.2 Hz,
1H), 5.34 (d, J = 7.2 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 140.3,
140.0, 136.5, 132.2, 128.6, 128.3, 127.4, 127.1, 127.0, 125.3, 123.8, 122.4,
119.9, 119.2, 116.1, 111.3, 55.0; HRMS (MALDI-TOF) C21H18N2O2S
(M+) m/z calcd 362.1084, found 362.1072.
11a: white solid, 90% yield, 93% ee (Daicel Chiralcel OD column
guarded with Chiracel OD Guard column, n-hexane/i-PrOH 60/40,
flow rate 0.75 mL/min, λ 254 nm, TR(1) = 10.138 min (major),
TR(2) = 15.717 min (minor)); mp 162.5ꢀ163.5 °C; [R]D22 = +12.5°
(c 1.35, acetone); 1H NMR (400 MHz, CDCl3) δ 7.99 (br, 1H), 7.56
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11g: white solid, 83% yield, 90% ee (Daicel Chiralcel OD column
guarded with Chiracel OD Guard column, n-hexane/i-PrOH 60/40,
flow rate 0.75 mL/min, λ 254 nm, TR(1) = 12.716 min (major), TR(2) =
TR(2) = 17.290 min (minor)); mp 183ꢀ184 °C; [R]D22 = +16.5° (c 1.0,
1
acetone); H NMR (400 MHz, CDCl3) δ 8.02 (br, 1H), 7.57 (d, J =
12.2 Hz, 2H), 7.32 (d, J = 8.5 Hz, 2H), 7.21ꢀ7.14 (m, 8H), 7.02 (t, J =
7.1 Hz, 1H), 6.64 (d, J = 2.4 Hz, 1H), 5.82 (d, J = 6.6 Hz, 1H), 5.04 (d, J =
6.6 Hz, 1H), 2.40 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 143.3, 138.8,
137.2, 136.5, 133.2, 129.4, 128.6, 128.4, 127.2, 125.1, 123.7, 122.8, 120.2,
119.1, 115.9, 111.3, 54.4, 21.5; HRMS (MALDI-TOF) C22H19ClNa-
N2O2S (M + Na)+ m/z calcd 433.0748, found 433.0722.
21
21.536 min (minor)); mp 179ꢀ180 °C; [R]D = ꢀ8.5° (c 0.70,
1
acetone); H NMR (400 MHz, CDCl3) δ 8.20 (br, 1H), 7.94ꢀ7.89
(m, 1H), 7.83 (d, J = 8.0 Hz, 1H), 7.78ꢀ7.72 (m, 2H), 7.63ꢀ7.53 (m,
3H), 7.27ꢀ7.21 (m, 3H), 7.14ꢀ7.06 (m, 4H), 6.95ꢀ6.92 (m, 1H), 6.86
(s, 1H), 6.63 (d, J = 2.1 Hz, 1H), 5.93 (d, J = 7.0 Hz, 1H), 5.24 (d, J = 7.0
Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 139.9, 137.2, 136.5, 134.6,
131.9, 129.2, 128.9, 128.6, 128.5, 128.3, 127.7, 127.5, 127.2, 127.1, 125.3,
123.8, 122.6, 122.4, 120.0, 119.3, 116.1, 111.2, 55.2; HRMS (MALDI-
TOF) C25H20KN2O2S (M + K)+ m/z calcd 451.0877, found 451.0860.
11h: white solid, 60% yield, 88% ee (Daicel Chiralcel OD column
guarded with Chiracel OD Guard column, n-hexane/i-PrOH 60/40,
flow rate 0.75 mL/min, λ 254 nm, TR(1) = 11.729 min (major), TR(2) =
11m: white solid, 91% yield, 87% ee (Daicel Chiralcel OD column
guarded with Chiracel OD Guard column, n-hexane/i-PrOH 60/40,
flow rate 0.75 mL/min, λ 254 nm, TR(1) = 11.622 min (major), TR(2) =
20
15.989 min (minor)); mp 164ꢀ165 °C; [R]D = +9.1° (c 0.77,
1
acetone); H NMR (400 MHz, CDCl3) δ 8.01 (br, 1H), 7.56 (d, J =
8.1 Hz, 2H), 7.30ꢀ7.26 (m, 2H), 7.18ꢀ7.10 (m, 4H), 7.02ꢀ6.98 (m,
1H), 6.74ꢀ6.69 (m, 3H), 5.82 (d, J = 6.8 Hz, 1H), 5.10 (d, J = 6.8 Hz,
1H), 3.68 (s, 3H), 2.37 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 159.5,
143.0, 141.8, 137.4, 136.5, 129.3, 127.2, 125.3, 123.8, 122.5, 119.9, 119.6,
119.2, 116.2, 113.0, 112.6, 111.2, 55.1, 55.0, 20.5; HRMS (MALDI-
TOF) C23H22NaN2O3S (M + Na)+ m/z calcd 429.1243, found
429.1267.
25
18.329 min (minor)); mp 185ꢀ187 °C; [R]D = +19.8° (c 1.03,
CH2Cl2); 1H NMR (400 MHz, CDCl3) δ 8.05 (br, 1H), 7.55 (d, J = 15.6
Hz, 2H), 7.32ꢀ7.29 (m, 3H), 7.22ꢀ7.17 (m, 2H), 7.16ꢀ7.10 (m, 4H),
7.03ꢀ6.99 (m, 1H), 6.62 (d, J = 1.9 Hz, 1H), 5.78 (d, J = 6.8 Hz, 1H),
5.18 (d, J = 6.8 Hz, 1H), 2.40 (s, 3H); 13C NMR (100 MHz, CDCl3) δ
143.3, 139.3, 137.2, 136.5, 131.3, 129.3, 128.9, 127.1, 125.1, 123.7, 122.7,
121.3, 120.1, 119.1, 115.7, 111.3, 54.4, 21.5; HRMS (MALDI-TOF)
C22H19BrNaN2O2S (M + Na)+ m/z calcd 479.0224, found 479.0200.
11i: white solid, 87% yield, 92% ee (Daicel Chiralcel OD column
guarded with Chiracel OD Guard column, n-hexane/i-PrOH 60/40,
flow rate 0.75 mL/min, λ 254 nm, TR(1) = 9.760 min (major), TR(2) =
11n: white solid, 88% yield, 84% ee (Daicel Chiralcel OD column
guarded with Chiracel OD Guard column, n-hexane/i-PrOH 60/40,
flow rate 0.75 mL/min, λ 254 nm, TR(1) = 12.089 min (major), TR(2) =
21
20.999 min (minor)); mp 135ꢀ136 °C; [R]D = ꢀ32.7° (c 0.50,
acetone); 1H NMR (400 MHz, CDCl3) δ 8.01 (br, 1H), 7.57 (d, J = 8.3
Hz, 2H), 7.30 (d, J = 8.2 Hz, 1H), 7.16ꢀ7.21 (m, 1H), 7.14ꢀ7.12 (m,
5H), 6.99 (td, J1 = 0.9 Hz, J2 = 8.0 Hz, 1H), 6.75ꢀ6.71 (m, 3H), 5.79 (d,
22
15.349 min (minor)); mp 164ꢀ165 °C; [R]D = +12.3° (c 0.56,
J = 6.7 Hz, 1H), 5.01 (d, J = 6.7 Hz, 1H), 3.77 (s, 3H), 2.38 (s, 3H); 13
C
acetone); 1H NMR (400 MHz, CDCl3) δ 7.97 (br, 1H), 7.57 (d, J = 8.3
Hz, 2H), 7.29 (dd, J1 = 0.7 Hz, J2 = 8.2 Hz, 1H), 7.22 (d, J = 8.0 Hz,
1H), 7.17 (dd, J1 = 1.0 Hz, J2 = 7.1 Hz, 1H), 7.11ꢀ7.14 (m, 4H),
7.02ꢀ6.97 (m, 3H), 6.74 (d, J = 2.5 Hz, 1H), 5.81 (d, J = 6.7 Hz, 1H),
4.96 (d, J = 6.7 Hz, 1H), 2.38 (s, 3H), 2.30 (s, 3H); 13C NMR (100
MHz, CDCl3) δ 142.9, 137.6, 137.4, 137.1, 136.6, 129.2, 129.0, 127.2,
127.1, 125.4, 123.7, 122.5, 119.9, 119.4, 116.6, 111.2, 54.9, 21.4, 21.0;
HRMS (MALDI-TOF) C23H22NaN2O2S (M + Na)+ m/z calcd
413.1294, found 413.1311.
NMR (100 MHz, CDCl3) δ 158.8, 142.9, 137.4, 136.6, 132.4, 129.2,
128.4, 127.2, 125.3, 123.7, 122.5, 119.9, 119.3, 116.6, 113.6, 111.2, 55.2,
54.6, 21.5; HRMS (MALDI-TOF) C23H22KN2O3S (M + K)+ m/z calcd
445.0983, found 445.0953.
11o: white solid, 90% yield, 40% ee (Daicel Chiralcel OD column
guarded with Chiracel OD Guard column, n-hexane/i-PrOH 60/40,
flow rate 0.75 mL/min, λ 254 nm, TR(1) = 9.426 min (major), TR(2) =
1
15.636 min (minor)); H NMR (400 MHz, CDCl3) δ 8.08 (br, 1H),
11j: white solid, 83% yield, 92% ee (Daicel Chiralcel OD column
guarded with Chiracel OD Guard column, n-hexane/i-PrOH 60/40,
flow rate 0.75 mL/min, λ = 254 nm, TR(1) = 11.971 min (major), TR(2) =
7.57 (d, J = 8.2 Hz, 2H), 7.40 (d, J = 8.0 Hz, 1H), 7.29 (d, J = 6.6 Hz, 1H),
7.22 (q, J = 0.8 Hz, 1H), 7.17 (td, J1 = 1.0 Hz, J2 =7.2 Hz, 1H), 7.11 (d, J =
8.1 Hz, 2H), 7.04 (td, J1 = 0.9 Hz, J2 = 7.1 Hz, 1H), 6.92 (d, J = 2.2 Hz,
1H), 6.19 (q, J = 2.2 Hz, 1H), 6.09 (d, J = 3.2 Hz, 1H), 5.92 (d, J = 7.4 Hz,
1H), 5.19 (d, J = 7.4 Hz, 1H), 2.36 (s, 3H); 13C NMR (100 MHz,
CDCl3) δ 152.5, 142.9, 142.1, 137.3, 136.3, 129.2, 127.0, 125.2, 123.3,
122.5, 120.0, 119.3, 113.7, 111.2, 110.2, 107.7, 49.1, 21.4; HRMS
(MALDI-TOF) C20H18NaN2O3S (M + Na)+ m/z calcd 389.0899,
found 389.0899.
11p: white solid, 44% yield, 10% ee (Daicel Chiralcel OD column
guarded with Chiracel OD Guard column, n-hexane/i-PrOH 60/40,
flow rate 0.75 mL/min, λ = 254 nm, TR(1) = 6.798 min (major), TR(2) =
9.043 min (minor)); 1H NMR (400 MHz, CDCl3) δ 7.83 (br, 1H), 7.40
(d, J = 8.2 Hz, 3H), 7.23 (d, J = 8.1 Hz, 1H), 7.13 (td, J1 = 0.9 Hz, J2 = 7.1
Hz, 1H), 7.01 (td, J1 = 1.0 Hz, J2 = 8.0 Hz, 1H), 6.90 (d, J = 8.0 Hz, 2H),
6.72 (d, J = 2.4 Hz, 1H), 4.86 (d, J = 7.9 Hz, 1H), 4.33 (d, J = 7.9 Hz, 1H),
2.24 (s, 3H), 2.05ꢀ1.73 (m, 3H), 1.46ꢀ1.15 (m, 4H), 1.12ꢀ0.85 (m,
4H); 13C NMR (100 MHz, CDCl3) δ 142.4, 137.4, 136.2, 129.7, 128.7,
126.8, 122.4, 122.1, 119.6, 119.2, 111.1, 57.3, 42.8, 30.0, 29.9, 26.2, 26.0,
21.5, 21.3.
22
13.349 min (minor)); mp 155ꢀ157 °C; [R]D = +14.9° (c 0.70,
acetone); 1H NMR (400 MHz, CDCl3) δ 8.03 (br, 1H), 7.54 (d, J = 8.2
Hz, 2H), 7.32ꢀ7.23 (m, 2H), 7.18ꢀ7.10 (m, 7H), 7.01 (t, J = 7.6 Hz,
1H), 6.61 (d, J = 2.4 Hz, 1H), 5.81 (d, J = 6.8 Hz, 1H), 5.14 (d, J = 6.8 Hz,
1H), 2.37 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 143.3, 142.3, 137.2,
136.5, 134.2, 129.6, 129.3, 127.5, 127.4, 127.1, 125.5, 125.2, 123.7, 122.7,
120.1, 119.1, 115.8, 111.4, 54.5, 21.4; HRMS (MALDI-TOF)
C22H19ClKN2O2S (M + K)+ m/z calcd 449.0487, found 449.0474.
11k: white solid, 65% yield, 87% ee (Daicel Chiralcel OD column
guarded with Chiracel OD Guard column, n-hexane/i-PrOH 60/40,
flow rate 0.70 mL/min, λ 254 nm, TR(1) = 9.554 min (major), TR(2) =
22
17.904 min (minor)); mp 190ꢀ192 °C; [R]D = +60° (c 0.74,
1
acetone); H NMR (400 MHz, CDCl3) δ 8.02 (br, 1H), 7.71 (d,
J = 1.6 Hz, 2H), 7.55 (dd, J1 = 1.6 Hz, J2 = 7.7 Hz, 1H), 7.45 (dd, J1 =
1.2 Hz, J2 = 6.8 Hz, 1H), 7.32 (d, J = 8.2 Hz, 1H), 7.25ꢀ7.21 (m, 3H),
7.19ꢀ7.15 (m, 2H), 7.09 (td, J1 = 1.7 Hz, J2 = 7.8 Hz, 1H), 7.0 (td, J1 =
0.9 Hz, J2 = 7.2 Hz, 1H), 6.54 (d, J = 2.5 Hz, 1H), 6.18 (d, J = 5.7 Hz,
1H), 5.09 (d, J = 5.7 Hz, 1H), 2.41 (s, 3H); 13C NMR (100 MHz,
CDCl3) δ 143.4, 139.4, 136.8, 132.9, 129.5, 129.0, 128.8, 127.4, 127.3,
125.4, 124.1, 122.7, 118.9, 115.1, 111.3, 54.2, 21.5; HRMS (MALDI-
TOF) C22H19ClKN2O2S (M + K)+ m/z calcd 494.9963, found
494.9948.
11q: white solid, 94% yield, 90% ee (Daicel Chiralcel OD column
guarded with Chiracel OD Guard column, n-hexane/i-PrOH 60/40,
flow rate 0.75 mL/min, λ 254 nm, TR(1) = 9.289 min (major), TR(2) =
22
19.855 min (minor)); mp 184ꢀ185 °C; [R]D = +11.5° (c 0.50,
acetone); 1H NMR (400 MHz, CDCl3) δ 7.94 (br, 1H), 7.60 (d, J = 8.2
Hz, 2H), 7.26ꢀ7.17 (m, 7H), 7.00ꢀ6.98 (m, 1H), 6.80 (s, 1H), 6.51 (d,
J = 2.4 Hz, 1H), 5.74 (d, J = 6.1 Hz, 1H), 5.04 (d, J = 6.1 Hz, 1H), 2.41 (s,
3H), 2.31 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 143.4, 139.1, 137.2,
11l: white solid, 65% yield, 93% ee (Daicel Chiralcel OD column
guarded with Chiracel OD Guard column, n-hexane/i-PrOH 60/40,
flow rate 0.75 mL/min, λ 254 nm, TR(1) = 11.268 min (major),
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ARTICLE
134.7, 133.1, 129.4, 128.6, 128.4, 127.2, 125.3, 124.3, 124.0, 118.3, 115.4,
110.0, 54.1, 21.5, 21.3; HRMS (MALDI-TOF) C23H21ClNaN2O2S
(M + Na)+ m/z calcd 447.0904, found 447.0903.
(4) (a) Cavill, J.; Peters, J.; Tomkinson, N. Chem. Commun.
2003, 728–729. (b) Lemay, M.; Aumand, L.; Ogilvie, W. W. Adv. Synth.
Catal. 2007, 349–441. (c) He, H.; Pei, B.-J.; Chou, H. -H.; Tian, T.;
Chan, W. -H.; Lee, A. W. M. Org. Lett. 2008, 10, 2421–2424.
(d) Langlois, Y.; Petit, A.; Rꢀemy, P.; Scherrmann, M. C.; Kouklovsky,
C. Tetrahedron Lett. 2008, 49, 5576–5579. (e) Tian, T.; Pei, B.-J.; Li,
Q. H.; He, H.; Chen, L.-Y.; Zhou, X.; Chan, W.-H.; Lee, A. W. M. Synlett
2009, 2115–2118. (f) Chen, L.-Y.; He, H.; Pei, B.-J.; Chan, W.-H.; Lee,
A. W. M. Synthesis 2009, 1573–1577. (g) Li, Q. H.; Wong, W.-Y.; Chan,
W.-H.; Lee, A. W. M. Adv. Synth. Catal. 2010, 352, 2142–2146.
(5) Akiyama, T.; Itoh, J.; Yokota, K.; Fuchibe, K. Angew. Chem., Int.
Ed. 2004, 43, 1566–1568.
11r: white solid, 81% yield, 94% ee (Daicel Chiralcel OD column
guarded with Chiracel OD Guard column, n-hexane/i-PrOH 60/40,
flow rate 0.75 mL/min, λ 254 nm, TR(1) = 8.503 min (major), TR(2) =
21
17.847 min (minor)); mp 155ꢀ156 °C; [R]D = +28.9° (c 0.45,
acetone); 1H NMR (400 MHz, CDCl3) δ 7.94 (br, 1H), 7.59 (d, J = 8.2
Hz, 2H), 7.16ꢀ7.13 (m, 5H), 7.03 (d, J = 7.1 Hz, 2H), 6.97 (dd, J1 = 1.3
Hz, J2 = 8.3 Hz, 1H), 6.86 (d, J = 0.7 Hz, 1H), 6.56 (d, J = 1.9 Hz, 1H),
5.74 (d, J = 6.5 Hz, 1H), 5.10 (d, J = 6.5 Hz, 1H), 2.39 (s, 3H), 2.31 (s,
6H); 13C NMR (100 MHz, CDCl3) δ 142.9, 137.5, 137.3, 136.9, 134.7,
129.2, 129.0, 128.9, 127.2, 127.0, 125.5, 124.1, 124.0, 118.5, 115.8, 110.9,
54.6, 21.4, 21.3, 21.0; HRMS (MALDI-TOF) C24H23N2O2S (M ꢀ H)ꢀ
m/z calcd 403.1486, found 403.1491.
(6) (a) Uraguchi, D.; Terada, M. J. Am. Chem. Soc. 2004,
126, 5356–5357. (b) Terada, M. Synthesis 2010, 12, 1929–1982.
(7) Nakashima, D.; Yamamoto, H. J. Am. Chem. Soc. 2006, 128,
9626–9627.
11s: white solid, 95% yield, 93% ee (Daicel Chiralcel OD column
guarded with Chiracel OD Guard column, n-hexane/i-PrOH 60/40,
flow rate 0.75 mL/min, λ 254 nm, TR(1) = 8.889 min (major), TR(2) =
(8) (a) Hatano, M.; Maki, T.; Moriyama, K.; Arinobe, M.; Ishihara,
K. J. Am. Chem. Soc. 2008, 130, 16858–16860. (b) Hatano, M.; Sugiura,
Y.; Ishihara, K. Tetrahedron: Asymmetry 2010, 21, 1311–1314.
(c) Hatano, M.; Sugiura, Y.; Akakura, M.; Ishihara, K. Synlett 2011,
1247–1250.
(9) In recent literature reports, the functional group ꢀSO2NHSO2ꢀ
was called disulfonimide. Since ꢀCO2NHCO2ꢀ is called imide,
we suggest that ꢀSO2NHSO2ꢀ should be named sulfonimde. For
ꢀCO2NHSO2ꢀ, it can be called either acylated sulfonamide or sulfonyl
amide. In any event, CF3SO2NHSO2CF3 (Tf2NH, CAS No. 82113-65-
3) is called trifluoromethanesulfonimide.
(10) (a) Barbero, M.; Cadamuro, S.; Dughera, S.; Venturello, P. Synlett
2007, 2209–2212. (b) Barbero, M.; Cadamuro, S.; Dughera, S.; Venturello,
P. Synthesis 2008, 1379–1388. (c) Barbero, M.; Cadamuro, S.; Dughera, S.;
Venturello, P. Synthesis 2008, 3625–3632. (d) Barbero, M.; Bazzi, S.;
Cadamuro, S.; Dughera, S. Eur. J. Org. Chem. 2009, 430–436. (e) Barbero,
M.; Cadamuro, S.; Deagostino, A.; Dughera, S.; Larini, P.; Occhiato, E. G.;
Prandi, C.; Tabasso, S.; Vulcano, R.; Venturello, P. Synthesis 2009,
2260–2266. (f) Barbero, M.; Bazzi, S.; Cadamuro, S.; Dughera, S.; Piccinini,
C. Synthesis 2010, 315–319.
22
27.446 min (minor)); mp 170ꢀ171 °C; [R]D = +20.7° (c 0.44,
acetone); 1H NMR (400 MHz, CDCl3) δ 7.91 (br, 1H), 7.56 (d, J = 8.2
Hz, 2H), 7.18 (d, J = 8.8 Hz, 1H), 7.12ꢀ7.09 (m, 4H), 7.01 (d, J = 8.0
Hz, 2H), 6.99 (dd, J1 = 2.4 Hz, J2 = 8.8 Hz, 1H), 6.75 (d, J = 2.3 Hz, 1H),
6.64 (d, J = 2.4 Hz, 1H), 5.78 (d, J = 6.8 Hz, 1H), 5.06 (d, J = 6.8 Hz, 1H),
3.73 (s, 3H), 2.43 (s, 3H), 2.30 (s, 3H); 13C NMR (100 MHz, CDCl3) δ
154.1, 142.9, 137.5, 137.2, 137.0, 131.5, 129.2, 128.9, 127.1, 127.07,
125.8, 124.4, 116.2, 112.8, 111.9, 100.9, 55.7, 54.8, 21.4, 21.0; HRMS
(MALDI-TOF) C24H24NaN2O3S (M + Na)+ m/z calcd 443.1400,
found 443.1419.
’ ASSOCIATED CONTENT
S
Supporting Information. Figures giving NMR spectra
b
and HPLC chromatograms. This material is available free of
charge via the Internet at http://pubs.acs.org.
(11) King, J. F. In The Chemistry of Sulphonic Acids, Esters and their
Derivatives; Patai, S., Ed.; Wiley: New York, 1991; Chapter 6, pp
249ꢀ259.
’ AUTHOR INFORMATION
ꢀ
ꢀ
(12) (a) Garcιa-Garcιa, P.; Lay, F.; Rabalakos, C.; List, B. Angew.
Corresponding Author
*E-mail: alee@hkbu.edu.hk.
ꢀ
ꢀ
Chem., Int. Ed. 2009, 48, 4363–4366. (b) Ratjen, L.; Garcιa-Garcιa, P.;
Lay, F.; Beck, M. E.; List, B. Angew. Chem., Int. Ed. 2010, 49, 1–6.
(13) Treskow, M.; Neud€orfl, J.; Giernoth, R. Eur. J. Org. Chem.
2009, 3693–3697.
(14) He, H.; Chen, L.-Y.; Wong, W.-Y.; Chan, W.-H.; Lee, A. W. M.
Eur. J. Org. Chem. 2010, 4181–4184.
’ ACKNOWLEDGMENT
We thank the Faculty Research Grant (FRG/08-09/II-45)
and the Research Grant Council for financial support.
(15) (a) Ban, S.-R.; Du, D.-M.; Liu, H.; Yang, W. Eur. J. Org. Chem.
2010, 5160–5164. (b) Luo, C.; Du, D.-M. Synthesis 2011, 1968–1973.
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A. Angew. Chem., Int. Ed. 2004, 43, 550–556. (b) Bandini, M.; Melloni,
A.; Tommasi, S.; Umani-Ronchi, A. Synlett 2005, 1199–1222.
(c) Terrasson, V.; Figueiredo, R. M. d.; Campagne, J. M. Eur. J. Org.
Chem. 2010, 2635–2655.
(17) (a) Bosch, J.; Bennasar, M.-L. Synlett 1995, 587–596.
(b) Faulkner, D. J. Nat. Prod. Rep. 2002, 19, 1–48. (c) Somei, M.;
Yamada, F. Nat. Prod. Rep. 2004, 21, 278–311.
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7147
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