Concise approach to benzisothiazol-3(2 H)-one via copper-catalyzed tandem reaction of o -bromobenzamide and potassium thiocyanate in water

Article abstract of DOI:10.1021/jo300250x

A concise approach to various benzisothiazol-3(2H)-one derivatives has been developed by copper-catalyzed the reaction of o-bromobenzamide derivatives with potassium thiocyanate (KSCN) in water. The reaction proceeds via a tandem reaction with S-C bond and S-N bond formation.

Full text of DOI:10.1021/jo300250x

Note
pubs.acs.org/joc
Concise Approach to Benzisothiazol-3(2H)-one via Copper-Catalyzed
Tandem Reaction of o-Bromobenzamide and Potassium Thiocyanate
in Water
Fei Wang,† Chao Chen,*,† Geng Deng,† and Chanjuan Xi*,†,‡
†Key Laboratory of Bioorganic Phosphorus Chemistry & Chemical Biology (Ministry of Education), Department of Chemistry,
Tsinghua University, Beijing 100084, China
‡State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, China
S
* Supporting Information
ABSTRACT: A concise approach to various benzisothiazol-3(2H)-
one derivatives has been developed by copper-catalyzed the reaction
of o-bromobenzamide derivatives with potassium thiocyanate
(KSCN) in water. The reaction proceeds via a tandem reaction
with S−C bond and S−N bond formation.
enzisothiazol-3(2H)-ones are widely used as pharmaceut-
ical agents because of their fungistatic, antimicrobial, and
copper-catalyzed tandem reaction of o-bromobenzamides and
potassium thiocyanate (KSCN) under the water as solvent.
This reaction includes new C−S bond and N−S bond
formation in one pot.
B
antipsychotic activities.1 Recently, benzisothiazol-3(2H)-one
derivatives were discovered to be a potentially antithrombotic
agent that could be developed into a drug for the first-phase
aggregation ex vivo in man.2 The traditional approaches to
benzisothiazol-3(2H)-ones generally converged on the reaction
of 2,2′-dithiosalicylic acids with amines2,3 or amination of 2-
mercaptobenzoate.4 Although these protocols provided power-
ful access to benzisothiazol-3(2H)-ones, they often suffered
limitations in scope and generality. Furthermore, some
protocols proceeded via a multistep process with harsh reaction
conditions and low yields. Because of the powerful requirement
of benzisothiazol-3(2H)-ones in medicament, development of
more practical methods to synthesize benzoisothiazol-3(2H)-
ones from easily available materials is highly desirable.
In the preliminary experiment, we used o-bromobenzamide
1a and potassium thiocyanate as the starting material and
Cs2CO3 as a base in DMF at 140 °C, and the reaction did not
proceed after 48 h (Table 1, entry 1). Then several bases were
screened under the same reaction conditions. Clearly, inorganic
bases such as Cs2CO3, K3PO4, and tBuONa were ineffective for
this reaction (entries 1−3). Organic bases such as Et3N and 1,4-
diazabicyclo[2.2.2]octane (DABCO) could promote the
reaction, and benzisothiazol-3(2H)-one 3a was observed
(entries 4 and 5). When 1,8-diazabicyclo[5.4.0]undec-7-ene
(DBU) was used as a base, the reaction did not proceed (entry
6). A range of ligands including N,N′-dimethylethylenediamine
(DMEDA), tetramethylethylenediamine (TMEDA), 2,2-bipyr-
idine, and 1,10-phenanthroline were screened (entries 7−10),
and 1,10-phenanthroline was found to gave the best result
(entry 10). We then examined the effect of different solvents,
such as toluene, dimethyl sulfoxide (DMSO), MeCN, MeOH,
and H2O (entries 10−15). Of the solvents tested, water
improved the yield to 41% (entry 15). In order to further
improve the yield, a phase-transfer catalyst such as Bu4NI was
added in the reaction. To our delight, a satisfactory yield could
be obtained when Bu4NI was used as an additive in the reaction
system (entry 16). The reaction also depended on the reaction
temperature (entries 16 and 17). When the reaction temper-
ature was decreased to 120 °C, the yield of product was
decreased to 48% (entry 17). On the other hand, without use of
CuI, the reaction did not proceed (entry 18). Furthermore, CuI
Recently, one-pot strategy for the synthesis of various useful
heterocyclic compounds based on the copper-catalyzed C-X (X
= N, O, and S) bond formation have been studied.5−7 For
example, aminobenzothiazoles could be efficiently formed via a
copper(I)-catalyzed one-pot cascade process of o-haloanilines
with isothiocyanates.7e,f More recently, benzothiazole deriva-
tives could be prepared via a copper-catalyzed three-component
reaction of o-haloanilines, carbon disulfide, and nucleophiles.7k
Although the chemistry of Cu-catalyzed C−N, C−O and C−S
bond formations for the preparation of heterocyclic compounds
is well explored, the reaction involving S−N bond formation is
rare in the formation of heterocyclic compounds.8 Further-
more, the use of water as solvent in organic reactions has
attracted much attention in recent years because of its low cost,
nontoxicity, safety, and environmental friendliness compared
with organic solvents.9 As part of an ongoing program in our
laboratory to systematically synthesize a variety of heterocyclic
compounds action in a one-pot strategy, we herein report the
first example of synthesizing benzisothiazol-3(2H)-ones via
Received: February 8, 2012
Published: March 23, 2012
© 2012 American Chemical Society
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The Journal of Organic Chemistry
Note
a
Table 1. Optimization between o-Bromobenzamide and Potassium Thiocyanate
b
entry
base
ligand
solvent
temp (°C)
yield (%)
1
Cs2CO3
tBuONa
K3PO4
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
toluene
DMSO
MeCN
MeOH
H2O
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
140
120
140
140
140
140
140
trace
trace
trace
15
2
3
4
Et3N
5
DABCO
DBU
22
6
trace
25
7
DABCO
DABCO
DABCO
DABCO
DABCO
DABCO
DABCO
DABCO
DABCO
DABCO
DABCO
DABCO
DABCO
DABCO
DABCO
DABCO
DMEDA
8
TMEDA
30
9
2,2′-bipyridine
35
10
11
12
13
14
15
1,10-phenanthroline
1,10-phenanthroline
1,10-phenanthroline
1,10-phenanthroline
1,10-phenanthroline
1,10-phenanthroline
1,10-phenanthroline
1,10-phenanthroline
1,10-phenanthroline
1,10-phenanthroline
1,10-phenanthroline
1,10-phenanthroline
1,10-phenanthroline
37
22
27
30
15
41
c
16
H2O
60
c
17
H2O
48
d
18
H2O
NR
42
e
19
H2O
f
20
H2O
34
g
21
H2O
50
h
22
H2O
38
a
Unless otherwise noted, the reactions were performed in a sealed tube with 1a (0.5 mmol), 2 (1.0 mmol), base (1.0 mmol), CuI (10 mol %), and
b
c
d
e
ligand (20 mol %) in solvent (1.0 mL) for 48 h. Isolated yield. Bu4NI (20 mol %) was added. Without CuI. CuBr was added instead of CuI.
f
g
h
CuCl was added instead of CuI. CuCl2 was added instead of CuI. Cu(OAc)2 was added instead of CuI.
proved to be best choice among the screened copper salts
under the reaction conditions (entries 16 and 19−22).
potassium thiocyanate also proceeded in moderate yields
(entries 6 and 7). When substrates 1h and 1i were employed
in the reaction, the desired product 3h and 3i also formed in
good yields, respectively (entries 8 and 9). When 2-bromo-N-
phenylbenzamide 1j was treated with potassium thiocyanate
under the optimized conditions, the 2,2′-thiobis(N-phenyl-
benzamide) 4 was obtained under the reaction conditions in
35% yield without ring closure (entry 10).11 This result may be
attributed to the weaker nucleophilicity of nitrogen in aromatic
amines.
On the basis of the above observations and reported
literature,12,13 a plausible reaction mechanism was proposed
as shown in Scheme 1. The first step involves oxidative addition
of CuI catalyst into the o-bromobenzamide and ligand exchange
between Br− and −SCN to form intermediate I. Reductive
elimination then gives the aryl thiocyanate (II), which
undergoes an intramolecularly nucleophilic substitution reac-
tion13 to afford compound 3. The −CN group is hydrolyzed by
a base under the reaction conditions.11
To our delight, the crystal of 3a was suitable for single-crystal
analysis, and its structure was fully characterized by X-ray
diffraction analysis.10 The structure of 3a clearly shows the
formation of the benzisothiazol-3(2H)-one skeleton, in which
the C−S and S−N bond were formed within the five-
membered ring.
On the basis of these results, the optimal reaction conditions
involved the following parameters: CuI as a precatalyst, 1,10-
phenanthroline as a ligand, DABCO as a base, Bu4NI as an
additive, and H2O as a solvent with a reaction temperature of
140 °C. Under these optimized conditions, a study on the
substrate scope was carried out, and the results are summarized
in Table 2. First, we used o-bromobenzamide derivatives 1 to
react with potassium thiocyanate 2. The methyl group and
fluoro atom on the benzene ring performed well (entries 2 and
3). Nitro-substituted o-bromobenzamide showed a lower yield
(entry 4). Then different N-substituted o-bromobenzamide
derivatives were applied under the optimized conditions. The
behaviors of benzisothiazol-3(2H)-ones in fungistatic, anti-
microbial, and antipsychotic bioactivities could be improved
through the use of various N-substituents,1,2 and our current
work provides an easy-access procedure for the N-substituted
benzisothiazol-3(2H)-ones. It is noteworthy that in this case a
higher temperature (160 °C) was required to complete the
reaction. For example, when N-methyl-2-bromobenzamide 1e
was treated with potassium thiocyanate at 160 °C, the desired
product was obtained in 62% yield (entry 5). Other substrates
such as ethyl- or n-butyl-substituted 2-bromobenzamide with
In summary, a novel method to prepare benzisothiazol-
3(2H)-ones has been presented based on the copper-catalyzed
reaction of o-halobenzamides with potassium thiocyanate
(KSCN) in water. The reaction proceeds via a tandem reaction
with S−C bond and S−N bond formation. Further application
of this method to prepare other cyclic sulfur-containing
heterocycles is under investigation in our laboratory
EXPERIMENTAL SECTION
Unless otherwise indicated, all materials were obtained from
commercial sources and used as received. Column chromatography
■
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dx.doi.org/10.1021/jo300250x | J. Org. Chem. 2012, 77, 4148−4151

The Journal of Organic Chemistry
Note
Table 2. CuI-catalyzed One-Pot Reactions of o-
Bromobenzamides 1 with KSCN
Scheme 1. Proposed Reaction Pathway
a
CuI (0.05 mmol), 1,10-phenanthroline (0.1 mmol), DABCO (1.0
mmol), and Bu4NI (0.1 mmol) and then stirred in H2O (1 mL) at
room temperature under nitrogen atmosphere. Half an hour later, the
tube was sealed, and the mixture was allowed to stir at 140−160 °C for
the indicated time. After completion of the reaction, the mixture was
cooled to room temperature, and then H2O (5 mL) was added and the
mixture extracted with EtOAc (5 mL × 3) and dried by anhydrous
Na2SO4. Evaporation of the solvent followed by purification on silica
gel (petroleum ether/ethyl acetate = 2/1) provided the corresponding
product 3.
Benzisothiazol-3(2H)-one (3a).3d White solid, 45 mg (60%
yield). Mp: 150−151 °C (lit.3d mp 157−158 °C). H NMR (DMSO-
1
d6, 300 MHz): δ 7.41−7.44 (m, 1H), 7.59−7.62 (m, 1H), 7.87−7.98
(m, 2H), 11.42 (brs, 1H). 13C NMR (DMSO-d6, 75 MHz): δ 121.6,
124.3, 124.8, 125.0, 130.2, 147.4, 165.0. IR (KBr) νmax: 3462, 2921,
1638, 1591, 742, 605 cm−1. ESI-MS: [M + H]+ m/z 152.2.
6-Methylbenzisothiazol-3(2H)-one (3b). White solid, 39 mg
1
(48% yield). Mp: 198−200 °C. H NMR (DMSO-d6, 300 MHz): δ
2.43 (s, 3H), 7.24 (d, JH−H = 8.2 Hz, 1H), 7.72−7.76 (m, 2H), 11.19
(brs, 1H). 13C NMR (DMSO-d6, 75 MHz): δ 21.3, 121.0, 122.6, 124.0,
126.6, 140.6, 147.4, 164.9. IR (KBr) νmax: 3461, 2913, 1627, 1514, 761,
600 cm−1. ESI-MS: [M + H]+ m/z 166.3. HRMS calcd for C8H7NOS:
166.0321 (M + H)+, found 166.0324.
6-Fluorobenzisothiazol-3(2H)-one (3c). White solid, 44 mg
1
(52% yield). Mp: 213-215 °C. H NMR (DMSO-d6, 600 MHz): δ
7.27−7.30 (m, 1H), 7.87−7.91 (m, 2H), 11.56 (brs, 1H). 13C NMR
(DMSO-d6, 150 MHz): δ 108.3 (d, JF−C = 27.3 Hz), 114.4 (d, JF−C
=
24.4 Hz), 122.2, 126.7 (d, JF−C = 10.0 Hz), 150.0, 163.8 (JF−C = 245.6
Hz), 164.6. IR (KBr) νmax: 3457, 3069, 1642, 1465, 754, 605 cm−1.
ESI-MS: [M + H]+ m/z 170.2. HRMS calcd for C7H4FNOS: 170.0070
(M + H)+, found 170.0067.
6-Nitrobenzisothiazol-3(2H)-one (3d).4d Light yellow solid, 34
mg (35% yield). Mp: 272−274 °C (lit.4d mp 275−280 °C). 1H NMR
a
Unless otherwise noted, the reactions were performed in a sealed
(DMSO-d6, 300 MHz): δ 8.07 (d, JH−H = 8.9 Hz, 1H), 8.19 (d, JH−H
=
tube with 1 (0.5 mmol), 2 (1.0 mmol), DABCO (1.0 mmol), CuI (10
8.9 Hz, 1H), 9.06 (s, 1H), 12.44 (brs, 1H). 13C NMR (DMSO-d6, 75
MHz): δ 118.0, 119.6, 124.9, 128.5, 148.0, 148.4, 163.3. IR (KBr) νmax
mol %), ligand (20 mol %), and Bu4NI (20 mol %) in H2O (1 mL).
:
b
2,2′-Thiobis(N-phenylbenzamide) 4 was obtained under the reaction
3464, 3093, 1643, 1339, 721, 608 cm−1. ESI-MS: [M + H]+ m/z 197.2.
2-Methylbenzisothiazol-3(2H)-one (3e).4c White solid, 51 mg
(62% yield). Mp: 46−47 °C (lit.4c mp 50−51 °C). 1H NMR
(methanol-d4, 300 MHz): δ 3.43 (s, 3H), 7.40−7.46 (m, 1H), 7.62−
7.68 (m, 1H), 7.76 (d, JH−H = 8.2 Hz, 1H), 7.92 (d, JH−H = 8.2 Hz,
1H). 13C NMR (methanol-d4, 75 MHz): δ 30.7, 122.1, 125.2, 126.7,
126.8, 133.2, 142.1, 167.3; IR (KBr) νmax: 3065, 1640, 1337, 740, 667
cm−1. ESI-MS: [M + H]+ m/z 166.2.
c
conditions without ring closure. Isolated yields.
was performed on silica gel. H NMR and 13C NMR spectra were
1
recorded on a 300 or 600 MHz spectrometer at ambient temperature
with DMSO-d6 or methanol-d4 as the solvent. Chemical shifts (δ) were
given in ppm, referenced to the residual proton resonance of DMSO
(2.50) or methanol (3.31), to the carbon resonance of DMSO-d6
(39.52) or methanol-d4 (39.00). Coupling constants (J) are given in
hertz (Hz). The terms m, t, d, and s refer to multiplet, triplet, doublet,
and singlet. The melting points were measured on an X-4 digital
melting point apparatus and are uncorrected. Mass spectra were
obtained using an ion-trap mass spectrometer in positive mode. IR
spectra were recorded on AVATAR 360 FT-IR.
2-Ethylbenzisothiazol-3(2H)-one (3f).14 Colorless oil, 40 mg
(45% yield). 1H NMR (methanol-d4, 300 MHz): δ 1.35 (t, JH−H = 7.2
Hz, 3H), 3.94 (q, JH−H = 7.2 Hz, 2H), 7.42−7.47 (m, 1H), 7.64−7.69
(m, 1H), 7.78 (d, JH−H = 8.2 Hz, 1H), 7.93 (d, JH−H = 7.9 Hz, 1H).
13C NMR (methanol-d4, 75 MHz): δ 14.9, 40.2, 122.2, 125.7, 126.8,
126.8, 133.2, 142.2, 166.8. IR (KBr) νmax: 2975, 1652, 1447, 741, 673
cm−1. ESI-MS: [M + H]+ m/z 180.1.
General Procedure for the Synthesis of Benzisothiazol-
3(2H)-one. A sealed tube was charged with the mixture of o-
halobenzamide 1 (0.5 mmol), potassium thiocyanate 2 (1.0 mmol),
2-Butylbenzisothiazol-3(2H)-one (3g).3c Colorless oil, 57 mg
(55% yield). 1H NMR (methanol-d4, 300 MHz): δ 0.96 (t, JH−H = 7.6
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The Journal of Organic Chemistry
Note
Hz, 3H), 1.34−1.41 (m, 2H), 1.69−1.76 (m, 2H), 3.90 (t, JH−H = 7.2
Hz, 2H), 7.42−7.47 (m, 1H), 7.63−7.68 (m, 1H), 7.77 (d, JH−H = 8.2
Hz, 1H), 7.93 (d, JH−H = 7.9 Hz, 1H). 13C NMR (methanol-d4, 75
MHz): δ 13.9, 20.7, 32.6, 44.7, 122.1, 125.6, 126.8, 126.9, 133.2, 142.2,
167.1. IR (KBr) νmax: 2958, 1662, 1447, 740, 674 cm−1. ESI-MS: [M +
H]+ m/z 208.3.
bryakov, E. A.; Kislitsin, P. G.; Semenov, V. V.; Zlotin, S. G. Synthesis
2001, 1659.
(5) Recent one-pot reactions based on copper-catalyzed C−N
coupling, for example: (a) Zou, B.; Yuan, Q.; Ma, D. Angew. Chem., Int.
Ed. 2007, 46, 2598. (b) Zheng, N.; Buchwald, S. L. Org. Lett. 2007, 9,
4749. (c) Martín, R.; Rivero, M. R.; Buchwald, S. L. Angew. Chem., Int.
2,6-Dimethylbenzisothiazol-3(2H)-one (3h). White solid, 38
mg (45% yield). Mp: 79−80 °C. 1H NMR (methanol-d4, 300 MHz): δ
2.46 (s, 3H), 3.40 (s, 3H), 7.25 (d, JH−H = 8.2 Hz, 1H), 7.53 (s, 1H),
7.79 (d, JH−H = 7.9 Hz, 1H). 13C NMR (methanol-d4, 75 MHz): δ
21.9, 30.7, 121.7, 122.9, 126.5, 128.4, 142.4, 144.5, 167.4. IR (KBr)
νmax: 2923, 1642, 1331, 754, 669 cm−1. ESI-MS: [M + H]+ m/z 180.1.
HRMS calcd for C9H9NOS: 180.0478 (M + H)+, found 180.0480.
2-Butyl-6-methylbenzisothiazol-3(2H)-one (3i). Colorless oil,
55 mg (50% yield). 1H NMR (methanol-d4, 300 MHz): δ 0.95 (t, JH−H
= 7.2 Hz, 3H), 1.33−1.41 (m, 2H), 1.67−1.75 (m, 2H), 2.46 (s, 3H),
3.87 (t, JH−H = 6.9 Hz, 2H), 7.26 (d, JH−H = 8.2 Hz, 1H), 7.55 (s, 1H),
7.80 (d, JH−H = 8.2 Hz, 1H). 13C NMR (methanol-d4, 75 MHz): δ
13.9, 20.7, 21.9, 32.6, 44.6, 121.8, 123.3, 126.6, 128.4, 142.5, 144.5,
167.1. IR (KBr) νmax: 2959, 1662, 1457, 760, 671 cm−1. ESI-MS: [M +
H]+ m/z 222.1. HRMS calcd for C12H15NOS: 222.0947 (M + H)+,
found 222.0949.
́ ́
Ed. 2006, 45, 7079. (d) Vina, D.; del Olmo, E.; Lopez-Perez, J. L.;
̃
Feliciano, A. S. Org. Lett. 2007, 9, 525. (e) Cacchi, S.; Fabrizi, G.;
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8719. (i) Lv, X.; Bao, W. J. Org. Chem. 2009, 74, 5618. (j) Wang, F.;
Cai, S.; Liao, Q.; Xi, C. J. Org. Chem. 2011, 76, 3174.
(6) For recent one-pot reactions based on copper-catalyzed C−O
coupling, see: (a) Lu, B.; Wang, B.; Zhang, Y.; Ma, D. J. Org. Chem.
2007, 72, 5337. (b) Nordmann, G.; Buchwald, S. L. J. Am. Chem. Soc.
2003, 125, 4978. (c) Viirre, R. D.; Evindar, G.; Batey, R. A. J. Org.
Chem. 2008, 73, 3452.
(7) Recent results based on copper-catalyzed C−S coupling:
(a) Bates, C. G.; Gujadhur, R. K.; Venkataraman, D. Org. Lett. 2002,
4, 2803. (b) Gonzalez-Arellano, C.; Luque, R.; Macquarrie, D. J. Chem.
Commun. 2009, 1410. (c) Jammi, S.; Sakthivel, S.; Rout, L.;
Mukherjee, T.; Mandal, S.; Mitra, R.; Saha, P.; Punniyamurthy, T. J.
Org. Chem. 2009, 74, 1971. (d) Gan, J.; Ma, D. Org. Lett. 2009, 11,
2788. (e) Ding, Q.; He, X.; Wu, J. J. Comb. Chem. 2009, 11, 587.
(f) Shen, G.; Lv, X.; Bao, W. Eur. J. Org. Chem. 2009, 5897. (g) Zhao,
Q.; Li, L.; Fang, Y.; Sun, D.; Li, C. J. Org. Chem. 2009, 74, 459.
(h) Murru, S.; Ghosh, H.; Sahoo, S. K.; Patel, B. K. Org. Lett. 2009, 11,
4254. (i) You, W.; Yan, X.; Liao, Q.; Xi, C. Org. Lett. 2010, 12, 3930.
(j) Guo, Y.-J.; Tang, R.-Y.; Zhao, P.; Li, J.-H. Tetrahedron Lett. 2010,
51, 649. (k) Ma, D.; Lu, X.; Shi, L.; Zhang, H.; Jiang, Y.; Liu, X. Angew.
Chem., Int. Ed. 2011, 50, 1118.
2,2′-Thiobis(N-phenylbenzamide) (4). Light yellow solid, 37 mg
1
(35% yield). Mp: 219−220 °C. H NMR (DMSO-d6, 300 MHz): δ
7.06−7.11 (m, 2H), 7.25−7.32 (m, 6H), 7.35−7.42 (m, 4H), 7.59−
7.62 (m, 4H), 7.70 (d, JH−H = 7.9 Hz, 2H), 10.45 (s, 2H). 13C NMR
(DMSO-d6, 75 MHz): δ 119.7, 123.7, 127.3, 127.9, 128.7, 130.6,
132.6, 134.2, 139.0, 139.3, 166.3. IR (KBr) νmax: 3054, 1649, 1437,
751, 688 cm−1. ESI-MS: [M + Na]+ m/z 447.3. HRMS calcd for
C26H20N2O2S: 447.1138 (M + Na)+, found 447.1140.
ASSOCIATED CONTENT
■
S
* Supporting Information
(8) (a) Suzuki, H.; Abe, H. Synth. Commun. 1996, 26, 3413.
(b) Bhakuni, B. S.; Balkrishna, S. J.; Kumar, A.; Kumar, S. Tetrahedron
Lett. 2012, 53, 1354.
1H NMR and 13C NMR spectra for compounds 3a−i and 4 and
X-ray data for 3a (CIF). This material is available free of charge
via the Internet at http://pubs.acs.org.
(9) For recent reviews, see: (a) Li, C.-J. Chem. Rev. 2005, 105, 3095.
(b) Dallinger, D.; Kappe, C. O. Chem. Rev. 2007, 107, 2563.
(c) Chanda, A.; Fokin, V. V. Chem. Rev. 2009, 109, 725.
(10) X-ray data for 3a: empirical formula: C7H5NOS; unit cell
parameters: a = 6.9074(14) Å, b = 8.0365(16) Å, c = 12.211(2) Å, α =
101.66(3)°, β = 92.96(3)°, γ = 96.79(3)°; space group P-1.
(11) Ke, F.; Qu, Y.; Jiang, Z.; Li, Z.; Wu, D.; Zhou, X. Org. Lett. 2011,
13, 454.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: (C.C.) chenchao01@mails.tsinghua.edu.cn; (C.X.)
cjxi@tsinghua.edu.cn.
Notes
(12) (a) Clark, J. H.; Jones, C. W.; Duke, C. V. A.; Miller, J. M. J.
Chem. Soc., Chem. Commun. 1989, 81. (b) Sayyahi, S. Synlett 2009,
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The authors declare no competing financial interest.
ACKNOWLEDGMENTS
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This work was supported by the National Natural Science
Foundation of China (20972085 and 21032004) and the
National Basic Research Program of China (2012CB933402).
(14) Uchida, Y.; Kozuka, S. Bull. Chem. Soc. Jpn. 1982, 55, 1183.
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