Idotrimethylsilane and catalytic iodine promoted cyclization for the facile synthesis for the facile synthesis of 3-monoarylated five-membered benzosultams

Article abstract of DOI:10.3987/COM-09-11884

3-Monoarylated five-membered benzosultams with various functional groups were prepared by simple and convenient two-step procedures. N-t-Bu-benzenesulfonamides were lithiated and reacted with substituted aromatic aldehydes to form the corresponding carbinols, which were converted to the cyclic compounds via a sequence of consecutive processes mediated by TMSCl-NaI-MeCN reagent and catalytic amount of iodine. Iodine played a crucial role in the eliminating the reductive side reaction in the cyclization processes.

Full text of DOI:10.3987/COM-09-11884

HETEROCYCLES, Vol. 81, No. 3, 2010
637
HETEROCYCLES, Vol. 81, No. 3, 2010, pp. 637 - 648. © The Japan Institute of Heterocyclic Chemistry
Received, 13th December, 2009, Accepted, 15th January, 2010, Published online, 18th January, 2010
DOI: 10.3987/COM-09-11884
IODOTRIMETHYLSILANE AND CATALYTIC IODINE PROMOTED
CYCLIZATION
FOR
THE
FACILE
SYNTHESIS
OF
3-MONOARYLATED FIVE-MEMBERED BENZOSULTAMS
Yue-Hui Dong,1,2 Qiong-Wei Ni,1 Shu-Tao Ma,1 and Zhao-Peng Liu1*
1Department of Organic Chemistry, School of Pharmaceutical Sciences,
Shandong University, Jinan 250012, P.R. China. E-mail: liuzhaop@sdu.edu.cn
2Jinan Health School of Shandong Province, Jinan 250023, China
Abstract – 3-Monoarylated five-membered benzosultams with various functional
groups were prepared by simple and convenient two-step procedures.
N-t-Bu-benzenesulfonamides were lithiated and reacted with substituted aromatic
aldehydes to form the corresponding carbinols, which were converted to the
cyclic compounds via a sequence of consecutive processes mediated by
TMSCl-NaI-MeCN reagent and catalytic amount of iodine. Iodine played a
crucial role in the eliminating the reductive side reaction in the cyclization
processes.
1. INTRODUCTION
The sulfonamide functional group stands out as one of the most important pharmacophores and is widely
used by medicinal chemists for the design of a host of biologically active derivatives with
pharmacological applications.1 Recently, high interest has also been directed to their conformationally
constrained cyclic counterparts, the sultams, which display a vast array of biological activities, act as
nonsteroidal antiinflammatory agents, agonists of 5-HT1A receptors, novel serine inhibitors, zinc enzyme
carbonic anhydrase inhibitors, etc.2 3-substituted five-membered benzosultams have also received
attention as potent modulators of neurotransmitters,3 HIV-1 inhibitors,4 and serotonin antagonists.5 In
addition to their significance in the treatment of diseases, sultams have also been succesfully applied as
chiral auxiliaries in asymmetric versions of several reactions, including alkylations, acylations, aldol
reactions, Diels-Alder reactions and azidations.6 Design and synthesis of N-fluorobenzosultam based on
sultam templates have also become one of the important strategies for the development of novel
electrophilic fluorinating agents.7
As part of a program to study the biological activities of highly functionalized cyclic sulfonamides, we

638
HETEROCYCLES, Vol. 81, No. 3, 2010
are interested in the development of an efficient method for the construction of 3-monoarylated
five-membered benzosultams. An often used method for the preparation of such kind of compounds
includes two steps from saccharin: (1) the direct nucleophilic addition to the carbonyl carbon using strong
nucleophiles such as aryllithium reagents or Grignard reagents to form a cyclic N-sulfonylimine; (2)
reduction of the sulfonylimine through Pd/C catalyzed hydrogenation.8 But this method has limitations
owning to the unavailability of some of the functionalized organometallic species, or the poor reactivities
of some hindered organometallic reagents with saccharin. In addition, substituted saccharins on the
aromatic ring are not readily available and usually take several steps to prepare.9 In fact, only a limited
number of 3-monoarylated five-membered benzosultams have been prepared in this way. In recent years,
metal (Fe, Mn, Ru, Cu, Rh, Co) complexes catalyzed intramolecular CH amination and intramolecular
aziridination have been investigated for the synthesis of five- and six-membered benzosultams.10
However, a simple and general procedure to generate 3-monoarylated five-membered benzosultams,
which can tolerate a wide variety of functional groups, remains elusive. In previous researches, we
developed a novel cyclization method mediated by iodotrimethylsilane (Me3SiI, TMSI), generated in situ
by mixing chlorotrimethylsilane (TMSCl) with sodium iodide (NaI) in acetonitrile (MeCN) solution, for
the efficient construction of 3,3-disubstituted five-membered benzosultams, 3-monosubstituted and
3,3-disubstituted six-membered benzosultams.11 To study the mechanism, the scope and limitations of
this novel methodology, we want to adopt the same two-step strategy for the preparation of
3-monoarylated five-membered benzosultams (Scheme 1). We here report our new findings in the
synthesis of 3-monoarylated benzosultams.
O2
R1
R2
SO2NHBut
R1
R2
SO2NHBut
R1
R2
S
1) BuLi, THF, 0°C
2) R3CHO
cyclization
N
OH
R3
H
R3
1
2
1
2
: R ,R = H
: R ,R = -OCH2CH2O-
4
3
1
2
Scheme 1. Two-step Synthesis of 3-Monoarylated Five-membered Benzosultams
2. RESULTS AND DISCUSSION
The first step takes advantage of the powerful sulfonamide directed ortho metalation (DoM) effect.12
N-t-Butylbenzenesulfonamides 1 or 2 underwent ortho metalation, as well as N-metalation, with two
equivalents of BuLi in anhydrous THF at 0 °C for 30 min under a nitrogen atmosphere to generate
dilithiosulfonamide, which was reacted with an aldehyde to form a carbinol. Keen to test the generality of
our strategy, a variety of aromatic aldehydes with different functional groups were applied, and the
corresponding carbinol sulfonamides 3a-m were obtained in general good yields, ranging from 58 to 96%

HETEROCYCLES, Vol. 81, No. 3, 2010
639
(Table 1). In next step, we first tested the TMSCl-NaI-MeCN reagent system to effect the cyclization.
When carbinol sulfonamides 3a and 3b were treated with two equivalents of TMSCl-NaI in acetonitrile
under reflux conditions for one hour respectively, to our surprise, in addition to the normal cyclization
products 4a and 4b, there were also the unexpected deoxygenated products 5a and 5b formed (Scheme 2),
and the ratio of 4a to 5a is 1:2, while 4b to 5b is 5:1! (Table 2, entries 1 and 2). When we run the same
reaction with substrate 3a at room temperature, the cyclic N-t-butylbenzosultam 4a’, together with the
deoxygenated N-t-butylbenzenesulfonamide 5a’ were isolated, the ratio of 4a’ to 5a’ is 1:2 (Table 2,
entriy 5). It is clear now, in the TMSCl-NaI-MeCN reagent promoted synthesis of five-membered
benzosultams, the cyclization goes first, while the removal of the t-butyl protective group runs second,
and the later needs heating to go to completion. It is also apparent that the reductive reaction is
competitive with the cyclization, but how is the reduction product generated?
Table 1. Synthesis of Carbinol 3a-m and Benzosultams 4a-m
Yields (%)
R1
R2
R3
Entry
4a-m
3a-m
a
b
c
d
e
91
58
86
90
86
96
76
88
98
80
88
90
90
82
89
86
84
75
81
91
76
84
83
80
H
H
H
H
H
H
H
H
H
H
H
H
4-chlorophenyl
4-dimethylaminophenyl
4-methylphenyl
4-methoxyphenyl
3,4-dimethoxyphenyl
3,4,5-trimethoxyphenyl
4-chlorophenyl
4-methoxyphenyl
3,4,5-trimethoxyphenyl
f
g
-OCH2O-
-OCH2O-
-OCH2O-
-OCH2O-
-OCH2O-
-OCH2O-
-OCH2O-
h
i
j
k
l
m
3,4-dimethoxyphenyl
4-methylphenyl
4-fluorophenyl
3-chlorophenyl
80
76
O2
S
SO2NHBut
OH
SO2NHR5
N R5
+
TMSCl, NaI
MeCN
4
5
4a: R4 = Cl, R5 = H
4a': R4 = Cl, R5 = But
4b: R4 = NMe2, R5 = H
5a
: R = Cl, R = H
4
4
5
t
3a
: R = Cl
5a'
: R = Cl, R = Bu
4
4
5
R4
R4
R4
3b
: R = NMe2
5b
: R = NMe2, R = H
Scheme 2. TMSCl-NaI-MeCN Reagent Mediated Cyclization of Carbinol Sulfonamides 3a and 3b
It is well known that alcohols can be converted to iodides by the iodotrimethylsilane rather rapidly.13
Therefore the novel cyclization mediated by iodotrimethylsilane can be visulised to proceed via a
sequence of consecutive processes, involving in the conversion of the hydroxy group to iodide, an
intramolecular necleophilic substitution for the cyclization, and finally the removal of the t-butyl

640
HETEROCYCLES, Vol. 81, No. 3, 2010
protective group (Scheme 3). In the formation of an iodide, an alcohol first reacts with one molecule of
iodotrimethylsilane to form trimethylsilyl ether 6, and in this process, one molecule of HI is always
generated.14 We postulate that the hydrogen iodide might account for the formation of the deoxygenated
product, as HI is known to reduce an alkyl iodide to an alkane. Comparing with 4a to 5a, the reversed
ratio of 4b to 5b also supports our hypothesis, since the dimethylamine group in the substrate 3b may trap
part of the HI, so the deoxygenated product 5b was much less than 5a, while the cyclization product 4b
was predominant.
SO2NHBut
SO2NHBut
SO2NHBut
OH
Me3SiI
Me3SiI
-HI
(1)
+ (Me3Si
)2O
OSiMe3
I
R
R
7
3
R
6
O2
S
O2
S
deprotective
N But
N
H
SO2NHBut
I
4
5
(2)
4'
R
R
SO2NHBut
SO2NH2
deprotective
7
R
5'
R
R
Scheme 3. Mechanism Considerations of Iodotrimethylsilane Promoted Cyclization Processes
Table 2. The Results of Cyclization Under Different Synthetic Conditions
Temperature
Entry
Additive
Product and Yields (%)
Substrate TMSCl-NaI
2 eq
2 eq
2 eq
3 eq
2 eq
2 eq
1
2
3
4
5
6
3a
3b
3a
3a
3a
3a
reflux
reflux
reflux
reflux
rt
4a, 32% 5a, 67%
5a, 80% 5a, 17%
4a', 21%
4a, 79% 5a, 10%
4a', 29% 5a', 60%
4a, 90%
Et3N, 1 eq
Et3N, 1 eq
I2, 0.5 eq
reflux
To prove our above assumptions, we first used triethylamine as HI scavenger. When carbinol
sulfonamides 3a was reacted with two equiv of TMSCl and NaI in acetonitrile and one equiv of
triethylamine under reflux conditions (Table 2, entry 3), indeed, there were no deoxygenated products 5a
or 5a’ detected, however, the reaction did not go completely, with 76% of 3a recovered, and the cyclic
1
product was identified by H NMR analysis as N-t-butylbenzosultam 4a’. It is clear that HI do play an
important role in the formation of the deoxygenated products and triethylamine is an effective HI
scavenger. But triethylamine can also interact directly with iodotrimethylsilane, reducing its lewis acidity
and nucleophilicity,15 thus affect the formation of the iodide 7 and the cyclization process. When one
more equiv of TMSCl-NaI were added to above reaction mixture, the transformation was completed in

HETEROCYCLES, Vol. 81, No. 3, 2010
641
less than one hour, but in addition to the normal cyclic product 4a, there were still about 10%
deoxygenated products 5a produced (Table 2, entry 4). Other HI scavengers like N,N-dimethylaniline,
cyclohexene and sodium carbonate did not give any better results than triethylamine. Inspired by the
report that iodine exerts a catalytic effect in the conversion of aromatic esters with iodotrimethylsilane,16
we tested iodine as a catalyst for this reaction. When 0.5 equiv of iodine was coexistence in the
iodotrimethylsilane reagent system, the cyclization went smoothly with no reduced products 5a or 5a’
detected by TLC analysis, and the sultam 4a was obtained in 90% yield after silica gel chromatography
(Table 2, entry 6). Though the exact role of iodine needs further experiments to elucidate, it is suggested
that iodine sets up an equilibrium with TMSI to form trimethylsilyl triiodide (TMSI3).16 The
triiodide-silicon bond would be expected to be more polarizable than the silicon-iodine bond in
iodotrimethylsilane, and we suppose it would behave differently with TMSI, possibly via an alternative
pathway involving a six-centered transition state in the transformation of alcohol into the iodide, with the
release of Me3SiOH and I2, but accompanying no HI formation in this process, thus avoids the formation
of the reduction products. There is another possibility that iodine might trap HI through the direct
formation of HI-I2 complex or hydrogen triiodide,17 affecting the reductive ability of hydrogen iodide.
The scope of this novel cyclization was studied with various carbinol sulfonamides. When 3b-m were
subject to two equiv of TMSCl-NaI and 0.5 equiv of iodine in acetonitrile under reflux conditions for 1 h,
sultams 4b-m were obtained in high yields (Table 1). It was seen that the novel process mediated by
TMSI in the presence of catalytic amounts of iodine was effective and tolerant to a broad range of
functional groups. It is also of note that the five-membered polymethoxyphenolic benzosultams, the
potentially biologically interesting molecules that have the structural features to combine the important
sulfonamide pharmacophore and the common polymethoxyphenolic units existed in many bioactive
natural products, are readily prepared by this novel method.
In conclusion, we have developed a simple two-step synthesis of 3-monoarylated five-membered
benzosultams via the novel cyclization mediated by iodotrimethylsilane and a catalytic amount of iodine.
This method makes 3-monoarylated five-membered benzosultams having diverse functional groups easily
preparable in two steps.
EXPERIMENTAL
Melting points were determined on an X-6 micro-melting point apparatus (Beijing Tech. Co., Ltd) and
were uncorrected. IR spectra (cm–1) were recorded on a Perkin-Elmer 1600 spectrometer. 1H NMR (600
MHz) spectra were recorded at room temperature for CDCl3. All chemical shifts were reported as 
1
values (ppm) relative to Me4Si (0.00 ppm) as internal standards for H spectra. Electrospray-ionization
mass spectrometry (ESI-MS) was performed on an API 4000 instrument. Microanalyses were performed
with a YANAKO CHN-coder MT-5. Column chromatography was performed on silica gel (200-300

642
HETEROCYCLES, Vol. 81, No. 3, 2010
mesh). All reactions involving oxygen- or moisture-sensitive compounds were carried out under a dry N2
atmosphere. Unless otherwise noted, reagents were added by syringe. THF was distilled from
sodium/benzophenone immediately prior to use.
Typical Procedure for the Preparation of Carbinol Sulfonamide 3a-m. A 2.5 M solution of BuLi (6.5
mL, 16 mmol) in hexane was added dropwise to a stirred solution of N-t-Bu-benzenesulfonamide 1 (1.70
g, 8 mmol) in THF (8 mL) under nitrogen at 0 °C. After stirring for 30 min, another solution of
4-chlorobenzaldehyde (1.12 g, 8 mmol) in THF (5 mL) was added. The mixture was stirred for 1 h and
quenched by saturated aqueous NH4Cl. The mixture was then extracted with EtOAc, and the combined
organic layers were dried (Na2SO4), concentrated in vacuo. Crystallization from EtOAc/petroleum ether
gave 3a as a white solid (2.56 g, 91%), mp 109–111 °C; IR (KBr) 3484, 3270, 1489, 1393, 1300, 1152,
1012, 861, 762 cm–1; 1H NMR  8.05 (dd, J = 7.9, 1.2 Hz, 1H), 7.46 (td, J = 7.9, 1.2 Hz, 1H), 7.38 (td, J
= 7.7, 1.0 Hz, 1H), 7.31–7.32 (m, 4H), 7.22 (dd, J = 7.7, 1.0 Hz, 1H), 6.71 (s, 1H), 4.91 (s, 1H), 3.51 (s
1H), 1.20 (s, 9H) ; MS (ESI) m/z 376.4 [M+Na]+. Anal. Calcd for C17H20ClNO3S: C, 57.70; H, 5.70; N,
3.96. Found: C, 57.79; H, 5.81; N, 3.91.
N-t-Butyl-2-[1-(4-dimethylaminophenyl)-1-hydroxy]methylbenzenesulfonamide 3b. White solid; mp
117–118 °C; IR (KBr) 3494, 3272, 1613, 1518, 1442, 1302, 1153, 770 cm–1; 1H NMR  8.08 (dd, J = 8.3,
1.1 Hz, 1H), 7.54 (td, J = 7.5, 1.0 Hz, 1H), 7.41 (td, J = 7.7, 1.2 Hz, 1H), 7.26–7.30 (m, 3 H,), 6.75 (d, J =
1.5 Hz, 2H), 6.67 (d, J = 3.5 Hz, 1H), 4.22 (d, J = 3.5 Hz, 1H), 2.97 (s, 6 H), 1.06 (s, 9H); MS m/z 363
[M+H]+. Anal. Calcd for C19H26N2O3S: C, 62.96; H, 7.23; N, 7.73. Found: C, 62.71; H, 7.26; N, 7.68.
N-t-Butyl-2-[1-(4-methylphenyl)-1-hydroxy]methylbenzenesulfonamide 3c. White solid; mp
100–101 °C; IR (KBr) 3477, 3273, 1511, 1471,1390, 1152, 1004, 820, 767 cm–1; 1H NMR  8.07 (dd, J =
5.9, 0.9 Hz, 1H), 7.38–7.53 (m, 3H), 7.30 (d, J = 6.0 Hz, 2H), 7.19 (d, J = 5.9 Hz, 2H), 6.68 (s, 1H), 2.35
(s, 3H), 1.11 (s, 9H); MS m/z 356.5 [M+Na]+. Anal. Calcd for C18H23NO3S: C, 64.84; H, 6.95; N, 4.20.
Found: C, 64.75; H, 6.99; N, 4.15.
N-t-Butyl-2-[1-(4-methoxylphenyl)-1-hydroxy]methylbenzenesulfonamide 3d. White solid; mp
103–104 °C; IR (KBr) 3424, 3237, 1614, 1512, 1320, 1245, 1150, 1036, 841, 764 cm–1; 1H NMR  7.74
(dd, J = 4.7, 1.6 Hz, 1H), 7.42–7.46 (m, 2H), 7.33–7.37 (m, 2H), 7.02–7.04 (m, 1H), 6.84–6.87 (m, 2H),
5.60 (s, 1H), 3.78 (s, 3H), 1.45 (s, 9H); MS m/z 372.3 [M+Na]+. Anal. Calcd for C18H23NO4S: C, 61.87;
H, 6.63; N, 4.01. Found: C, 61.69; H, 6.53; N, 4.05.
N-t-Butyl-2-[1-(3,4-dimethoxylphenyl)-1-hydroxy]methylbenzenesulfonamide 3e. White solid; mp
133–135 °C; IR (KBr) 3494, 3270, 1606, 1511, 1305, 1265, 1144, 1120, 1037, 812, 757 cm–1; 1H NMR 
7.75 (dd, J = 4.4, 1.4 Hz, 1H), 7.39–7.51 (m, 3H), 7.06–7.08 (m, 1H), 6.98 (d, J = 1.5 Hz, 1H), 6.82 (d, J
= 6.0 Hz, 1H), 5.58 (s, 1H), 3.86 (s, 3H), 3.82 (s, 3H), 1.46 (s, 9H); MS m/z 402.5 [M+Na]+. Anal. Calcd
for C19H25NO5S: C, 60.14; H, 6.64; N, 3.69. Found: C, 60.01; H, 6.57; N, 3.65.
N-t-Butyl-2-[1-(3,4,5-triimethoxylphenyl)-1-hydroxy]methylbenzenesulfonamide 3f. White solid; mp

HETEROCYCLES, Vol. 81, No. 3, 2010
643
1
122–124 °C; IR (KBr) 3498, 3218, 1592, 1505, 1332, 1230, 1144, 1122, 863, 810, 771 cm–1; H NMR
8.08 (dd, J = 7.9, 0.9 Hz, 1H), 7.52 (td, J = 7.5, 1.0 Hz, 1H), 7.40–7.43 (m, 2H), 6.68 (s, 2H), 6.66 (s,
1H), 3.85 (s, 3H), 3.83 (s, 6H), 1.17 (s, 9H); MS m/z 427.5 [M+NH4]+. Anal. Calcd for C20H27NO6S: C,
58.66; H, 6.65; N, 3.42. Found: C, 58.45; H, 6.78; N, 3.36.
N-t-Butyl-6-[1-(4-chlorophenyl)-1-hydroxy]methylbenzo[d][1,3]dioxole-5-sulfonamide 3g. White
solid; mp 132.5134.5 °C; IR (KBr) 3524, 3256, 1625, 1597, 1297, 1254, 1139, 814, 768 cm–1; 1H NMR
 7.70 (d, J = 8.4 Hz, 1H), 7.39 (d, J = 8.4 Hz, 2H), 7.34 (dd, J = 7.6, 2.0 Hz, 2H), 6.85 (d, J = 8.4 Hz,
1H), 6.51 (s, 1H), 6.09 (d, J = 1.2 Hz, 1H ), 6.01 (d, J = 1.2 Hz, 1H), 1.13 (s, 9H); MS m/z 396.3
[MH]Anal. Calcd for C18H20ClNO5S: C, 54.34; H, 5.07; N, 3.52. Found: C, 54.24; H, 5.15; N, 3.47.
N-t-Butyl-6-[1-(4-methoxyphenyl)-1-hydroxy]methylbenzo[d][1,3]dioxole-5-sulfonamide 3h. White
solid; mp 8486 °C; IR (KBr): 3522, 3264, 1610, 1512, 1297, 1136, 830, 768 cm–1; 1H NMR  7.45 (dd,
J = 7.7, 2.0 Hz, 2H), 7.30 (d, J = 8.1 Hz, 1H), 6.92 (d, J = 8.1 Hz, 1H), 6.86 (dd, J = 10.7, 2.0 Hz, 2H),
6.01 (d, J = 1.3 Hz, 1H), 5.92 (d, J = 1.3 Hz, 1H), 5.62 (s, 1H ), 3.80 (s, 3H), 1.43 (s, 9H); MS m/z 392.5
[MH]. Anal. Calcd for C19H23NO6S: C, 58.00; H, 5.89; N, 3.56. Found: C, 58.14; H, 5.93; N, 3.47.
N-t-Butyl-6-[1-(3,4,5-trimethoxyphenyl)-1-hydroxy]methylbenzo[d][1,3]dioxole-5-sulfonamide
3i.
White solid; mp 9698 °C; IR (KBr) 3507, 3365, 1594, 1506, 1331, 1309, 1250, 1128, 1060, 901, 759
cm–1; 1H NMR  7.71 (d, J = 8.4 Hz, 1H), 6.86 (d, J = 8.4 Hz, 1H), 6.70 (s, 2H), 6.45 (s, 1H), 6.16 (d, J =
1.4 Hz, 1H), 6.08 (d, J = 1.4 Hz, 1H), 3.85 (s, 9H), 1.08 (s, 9H); MS m/z 452.5 [MH]. Anal. Calcd for
C21H27NO8S: C, 55.62; H, 6.00; N, 3.09. Found: C, 55.45; H, 6.10; N, 3.02.
N-t-Butyl-6-[1-(3,4-dimethoxyphenyl)-1-hydroxy]methylbenzo[d][1,3]dioxole-5-sulfonamide
3j.
White solid; mp 84.586.5 °C; IR (KBr): 3573, 3274, 1593, 1518, 1304, 1258, 1132, 1000, 898, 758
cm–1; 1H NMR  7.30 (d, J = 8.1 Hz, 1H), 7.13 (d, J = 2.0 Hz, 1H), 7.09 (dd, J = 9.3, 2.0 Hz, 1H), 6.92 (d,
J = 8.1Hz, 1H), 6.84 (s, 1H), 6.82 (d, J = 8.1 Hz, 1H), 6.02 (d, J = 1.3 Hz, 1H), 5.95 (d, J = 1.3 Hz, 1H),
5.62 (s, 1H ), 3.88 (s, 3H), 3.86 (s, 3H), 1.46 (s, 9H); MS m/z 422.4 [MH]. Anal. Calcd for
C20H25NO7S: C, 56.72; H, 5.95; N, 3.31. Found: C, 56.53; H, 6.03; N, 3.19.
N-t-Butyl-6-[1-(4-methylphenyl)-1-hydroxy]methylbenzo[d][1,3]dioxole-5-sulfonamide 3k. White
solid; mp 123125 °C; IR (KBr) 3538, 3246, 1597, 1459, 1299, 1252, 1139, 1004, 901, 816, 766 cm–1; 1H
NMR 7.68 (d, J = 8.4 Hz, 1H) , 7.33 (d, J = 7.9 Hz, 2H), 7.19 (d, J = 7.9 Hz, 2H), 6.84 (d, J = 8.4 Hz,
1H), 6.48 (d, J = 10.4 Hz, 1H), 6.13 (d, J = 1.2 Hz, 1H), 6.07 (d, J = 1.2 Hz, 1H), 4.45 (d, J = 10.7 Hz,
1H), 3.53 (s, 1H), 2.35 (s, 3H), 1.02 (s, 9H); MS m/z 376.6 [MH]. Anal. Calcd for C19H23NO5S: C,
60.46; H, 6.14; N, 3.71. Found: C, 60.31; H, 6.25; N, 3.65.
N-t-Butyl-6-[1-(4-fluorophenyl)-1-hydroxy]methylbenzo[d][1,3]dioxole-5-sulfonamide 3l. White
solid; mp 127129 °C; IR (KBr) 3439, 3260, 1603, 1509, 1459, 1297, 1253, 1137, 1057, 935, 838, 764
1
cm–1; H NMR  7.70 (d, J = 8.4 Hz, 1H), 7.41 (dd, J = 8.4, 5.5 Hz, 2H), 7.05 (td, J = 7.7, 2.0 Hz, 2H),
6.85 (d, J = 8.4 Hz, 1H), 6.52 (s, 1H), 6.09 (d, J = 1.2 Hz, 1H), 6.01 (d, J = 1.2 Hz, 1H), 3.90 (s, 1H), 1.12

644
HETEROCYCLES, Vol. 81, No. 3, 2010
(s, 9H); MS m/z 380.6 [MH]. Anal. Calcd for C18H20FNO5S: C, 56.68; H, 5.29; N, 3.67. Found: C,
56.56; H, 5.33; N, 3.53.
N-t-Butyl-6-[1-(3-chlorophenyl)-1-hydroxy]methylbenzo[d][1,3]dioxole-5-sulfonamide 3m. White
solid; mp 130132 °C; IR (KBr) 3528, 3317, 1596, 1462, 1300, 1254, 1177, 1135, 991, 900, 818, 767
cm–1; 1H NMR  7.70 (d, J = 8.4 Hz, 1H), 7.38 (d, J = 7.9 Hz, 2H), 7.31 (t, J = 7.9 Hz, 1H), 7.27 (s, 1H),
6.86 (d, J = 8.4 Hz, 1H), 6.51 (d, J = 9.5 Hz, 1H), 6.11 (d, J = 1.2 Hz, 1H), 6.02 (d, J = 1.2 Hz, 1H), 4.13
(d, J = 9.5 Hz, 1H), 3.84 (s, 1H), 1.12 (s, 9H); MS m/z 396.3 [MH]. Anal. Calcd for C18H20ClNO5S: C,
54.34; H, 5.07; N, 3.52. Found: C, 54.29; H, 5.09; N, 3.45.
TMSCl-NaI-MeCN Reagent Promoted Cyclization of 3a and 3b under Reflux Conditions.
Chlorotrimethylsilane (0.26 mL, 2 mmol) was added dropwise to a stirred solution of 3a (354 mg, 1
mmol) and sodium iodide (300 mg, 2 mmol) in MeCN (10 mL) under nitrogen at room temperature. The
mixture was heated under reflux for 1 h, after which it was cooled and 10% sodium thiosulfate solution
was added. The mixture was extracted with EtOAc, and the combined organic layers were washed with
brine, dried (Na2SO4), concentrated in vacuo. The residue was purified by preparative TLC (Hex-EtOAc,
5:1) to give 4a (90 mg, 32%) and 5a (190 mg, 67%).
In the same way, from 3b (880 mg, 2.43 mmol), chlorotrimethylsilane (0.63 mL, 4.86 mmol) and sodium
iodide (730 mg, 4.86 mmol) in MeCN (20 mL), 4b (560 mg, 80%) and 5b (120 mg, 17%) were isolated
by silica gel chromatography (CH2Cl2-Et2O, 40:1).
3-(4-Chlorophenyl)-2,3-dihydro-1,2-benzisothiazole 1,1-dioxide 4a. White solid; m.p. 181–182 °C; IR
1
(KBr) 3436, 3281, 1487, 1391, 1290, 1169, 839, 758 cm–1; H NMR  7.85 (dd, J = 5.8, 1.5 Hz, 1H),
7.56–7.59 (m, 2H), 7.37 (dd, J = 6.9, 1.1 Hz, 2H), 7.32 (d, J = 8.5 Hz, 2H), 7.13 (d, J = 6.5 Hz, 1H), 5.71
(d, J = 3.6 Hz, 1H), 4.95 (d, J = 3.6 Hz, 1H); MS m/z 280.3 [M+H]+. Anal. calcd for C13H10ClNO2S: C,
55.82; H, 3.60; N, 5.01. Found: C, 55.80; H, 3.58; N, 4.99.
2-(4-Chlorobenzyl)benzenesulfonamide 5a. White solid; mp 137–138 °C; IR (KBr) 3346, 3249, 1489,
1151, 899, 755 cm–1; 1H NMR  8.09 (dd, J = 5.9, 1.0 Hz, 1H), 7.53 (td, J = 5.7, 1.0 Hz, 1H), 7.40 (td, J =
5.6, 0.9 Hz, 1H), 7.27–7.30 (m, 3H), 7.15 (d, J = 6.3 Hz, 2H), 4.31 (s, 2H), 4.46 (s, 2H) ; MS m/z 282.0
[M+H]+. Anal. calcd for C13H12ClNO2S: C, 55.42; H, 4.29; N, 4.97. Found: C, 55.36; H, 4.23; N, 4.89.
3-(4-Dimethylaminophenyl)-2,3-dihydro-1,2-benzisothiazole 1,1-dioxide 4b. White solid; mp
137–139 °C; IR (KBr) 3437, 3259, 1623, 1532, 1450, 1324, 1302, 1278, 1164, 818, 765 cm–1; 1H NMR 
7.85 (dd, J = 7.1, 1.0 Hz, 1 H), 7.53–7.58 (m, 2 H), 7.16–7.20 (m, 3 H), 6.72 (s, 2 H), 5.66 (d, J = 3.9 Hz,
1 H), 4.70 (d, J = 3.9 Hz, 1 H), 2.98 (s, 6 H); MS m/z 289 [M+H]+. Anal. Calcd for C15H16N2O2S: C,
62.48; H, 5.59; N, 9.71. Found: C, 62.21; H, 5.56; N, 9.68.
2-(4-Dimethylaminobenzyl)benzenesulfonamide 5b. White solid; mp 209–210 °C; IR (KBr) 3494,
3269, 1511, 1463, 1389, 1305, 1285, 1143, 978, 812, 758 cm–1; 1H NMR  8.06 (dd, J = 8.2, 1.5 Hz, 1H),
7.55 (td, J = 7.5, 1.2 Hz, 1H), 7.39 (d, J = 7.0 Hz, 2H), 7.06 (d, J = 8.7 Hz, 2H), 6.69 (d, J = 8.7 Hz, 2H),

HETEROCYCLES, Vol. 81, No. 3, 2010
645
4.14 (s, 2H), 2.93 (s, 6H); MS m/z 289.4 [M–H]–. Anal. Calcd for C15H18N2O2S: C, 62.04; H, 6.25; N,
9.65. Found: C, 62.00; H, 6.21; N, 9.67.
TMSCl-NaI-MeCN Reagent Promoted Cyclization of 3a at RT. Chlorotrimethylsilane (0.26 mL, 2
mmol) was added dropwise to a stirred solution of 3a (354 mg, 1 mmol) and sodium iodide (300 mg, 2
mmol) in MeCN (10 mL) under nitrogen at room temperature. The mixture was stirred for 1 h. 10%
sodium thiosulfate solution was added. The mixture was extracted with EtOAc, and the combined organic
layers were washed with brine, dried (Na2SO4), concentrated in vacuo. The residue was purified by
preparative TLC (Hexane-EtOAc, 5:1) to give 4a’ (100 mg, 29%) and 5a’ (200 mg, 60%).
N-t-Butyl-3-(4-chlorophenyl)-2,3-dihydro-1,2-benzisothiazole 1,1-dione 4a’. White solid; mp
135–136 °C; IR (KBr) 3323, 3281, 3251, 1487, 1300, 1291, 1169, 839, 758 cm–1; 1H NMR  8.10 (dd, J
= 4.0, 0.7 Hz, 1H), 7.50 (td, J = 3.8, 0.7 Hz, 1H), 7.43 (td, J = 3.8, 0.7 Hz, 1H), 7.38 (s, 4H), 7.27–7.29
(m, 1H), 6.73 (s, 1H), 1.23 (s, 9H); MS m/z 358.3 [M+Na]+. Anal. Calcd for C17H18ClNO2S: C, 60.80; H,
5.40; N, 4.17. Found: C, 60.73; H, 5.43; N, 4.14.
N-t-Butyl-2-(4-chlorobenzyl)benzensulfonamide 5a’. White solid; mp 102–103 °C; IR (KBr) 3301,
1
1473, 1441, 1307, 1150, 796, 760 cm–1; H NMR  8.08 (dd, J = 6.0, 0.9 Hz, 1H), 7.47 (td, J = 5.7, 1.0
Hz, 1H), 7.36 (td, J = 8.0, 0.8 Hz, 1H), 7.27–7.30 (m, 2H), 7.19 (d, J = 5.7 Hz, 1H), 7.14 (d, J = 6.3 Hz,
2H), 4.43 (s, 2H), 3.97 (s, 1H), 1.08 (s, 9H); MS m/z 360.4 [M+Na]+. Anal. Calcd for C17H20ClNO2S: C,
60.43; H, 5.97; N, 4.15. Found: C, 60.46; H, 5.99; N, 4.09..
TMSCl-NaI-MeCN Reagent Promoted Cyclization of 3a in the Presence of Et3N under Reflux
Conditions. Chlorotrimethylsilane (0.65 mL, 5 mmol) was added dropwise to a stirred solution of 3a
(900 mg, 2.55 mmol), sodium iodide (765 mg, 5.10 mmol) in MeCN (20 mL) and triethylamine (0.36 mL,
2.55 mmol) under nitrogen at room temperature. The mixture was heated under reflux for 1 h, after which
it was cooled and 10% sodium thiosulfate solution was added. The mixture was extracted with EtOAc,
and the combined organic layers were washed with brine, dried (Na2SO4), concentrated in vacuo. The
residue was purified by silica gel chromatography (CH2Cl2-Et2O, 40:1) to give 4a’ (174 mg, 21%) and
recovered 3a (684 mg, 76%).
Typical Procedure for the Preparation of 3-Monoarylated Benzosultam 4 Promoted by
Iodotrimethylsilane and Catalytic Amount of Iodine. Chlorotrimethylsilane (0.26 mL, 2 mmol) was
added dropwise to a stirred solution of 3a (0.36 g, 1 mmol), iodine (0.12 g, 0.5 mmol) and sodium iodide
(0.30 g, 2 mmol) in MeCN (10 mL) under nitrogen at room temperature. The mixture was heated under
reflux for 1 h, after which it was cooled and 10% sodium thiosulfate solution was added. The mixture was
extracted with EtOAc, and the combined organic layers were washed with brine, dried (Na2SO4),
concentrated in vacuo. Recrystallizion from EtOAc/hexane gave 4a as a white solid (0.25 g, 90%).
3-(4-Methylphenyl)-2,3-dihydro-1,2-benzisothiazole 1,1-dioxide 4c. White solid; mp 166–168 °C; IR
(KBr): 3277, 3036, 1511, 1454, 1391, 1279, 1168, 1048, 833, 751 cm–1; 1H NMR  7.84 (td, J = 2.7, 1.1

646
HETEROCYCLES, Vol. 81, No. 3, 2010
Hz, 1H), 7.55 (td, J = 2.7, 1.1 Hz, 2H), 7.18–7.25 (m, 4H), 7.12–7.14 (m, 1H), 5.68 (d, J = 2.9 Hz, 1H),
4.77 (d, J = 2.9 Hz, 1H), 2.36 (s, 3H); MS m/z 260.3 [M+H]+. Anal. Calcd for C14H13NO2S: C, 64.84; H,
5.05; N, 5.40. Found: C, 64.67; H, 5.11; N, 5.36.
3-(4-Methoxyphenyl)-2,3-dihydro-1,2-benzisothiazole 1,1-dioxide 4d. White solid; mp 143–144 °C; IR
(KBr) 3252, 3010, 1615, 1515, 1292, 1276, 1251, 1165, 1028, 919, 838, 763 cm–1; 1H NMR  7.85 (dd, J
= 4.2, 1.8 Hz, 1H), 7.55–7.57 (m, 2H), 7.25 –7.26 (m, 2H), 7.14 (d, J = 6.5 Hz, 1H), 6.90–6.92 (m, 2H),
5.68 (d, J = 3.4 Hz, 1H), 4.77 (d, J = 3.4 Hz, 1H), 3.81 (s, 3H); MS m/z 276.5 [M+H]+. Anal. Calcd for
C14H13NO3S: C, 61.07; H, 4.76; N, 5.09. Found: C, 60.89; H, 4.87; N, 4.93.
3-(3,4-Dimethoxyphenyl)-2,3-dihydro-1,2-benzisothiazole 1,1-dioxide 4e. White solid; mp
184–185 °C; IR (KBr) 3276, 3068, 1598, 1519, 1452, 1377, 1279, 1162, 1027, 864, 752 cm–1; 1H NMR 
7.86 (dd, J = 6.7, 1.7 Hz, 1H), 7.56–7.61 (m, 2H), 7.17–7.19 (m, 1H), 6.96 (dd, J = 8.2, 2.1 Hz, 1H), 6.88
(d, J = 8.2 Hz, 1H), 6.84 (d, J = 2.1 Hz, 1H), 5.69 (d, J = 3.9 Hz, 1H), 4.86 (d, J = 3.9 Hz, 1H), 3.90 (s,
3H), 3.84 (s, 3H); MS m/z 306.4 [M+H]+. Anal. Calcd for C15H15NO4S: C, 59.00; H, 4.95; N, 4.59.
Found: C, 58.86; H, 4.97; N, 4.45.
3-(3,4,5-Trimethoxyphenyl)-2,3-dihydro-1,2-benzisothiazole 1,1-dioxide 4f. White solid; mp
192–194 °C; IR (KBr) 3213, 3006, 1597, 1507, 1467, 1342, 1285, 1165, 1062, 995, 856, 782, 756 cm–1;
1H NMR  7.85 (dd, J = 4.8, 1.4 Hz, 1H), 7.56–7.61 (m, 2H), 7.20–7.22 (m, 1H), 6.59 (s, 2H), 5.64 (s,
1H), 4.88 (s, 1H), 3.85 (s, 3H), 3.83 (s, 3H), 3.82 (s, 3H); MS m/z 336.5 [M+H]+. Anal. Calcd for
C16H17NO5S: C, 57.30; H, 5.11; N, 4.18. Found: C, 57.15; H, 5.20; N, 4.09.
3-(4-Chlorophenyl)-2,3-dihydro[1,3]dioxolo[4,5-f][1,2]benzisothiazole 1,1-dioxide 4g. White solid;
mp 188190 °C; IR (KBr) 3307, 3098, 2910, 1601, 1491, 1467, 1261, 1188, 1039, 899, 832, 743 cm–1;
1H NMR  7.37–7.43 (m, 5H), 7.02 (d, J = 8.1 Hz, 1H), 6.04 (d, J = 1.2 Hz, 1H), 5.98 (d, J = 1.2 Hz, 1H),
5.71 (d, J = 3.6 Hz, 1H), 4.86 (d, J = 3.6 Hz, 1H); MS m/z 324.4 [M+H]+. Anal. Calcd for C14H10ClNO4S:
C, 51.94; H, 3.11; N, 4.33. Found: C, 51.88; H, 3.09; N, 4.29.
3-(4-Methoxyphenyl)-2,3-dihydro[1,3]dioxolo[4,5-f][1,2]benzisothiazole 1,1-dioxide 4h. White solid;
mp 177179 °C; IR (KBr) 3224, 3010, 1613, 1514, 1468, 1269, 1251, 1187, 1140, 1031, 897, 831, 705
1
cm–1; H NMR  7.39 (d, J = 8.1 Hz, 1H), 7.35 (dd, J = 6.8, 1.9 Hz, 2H), 7.01 (d, J = 8.1 Hz, 1H), 6.92
(dd, J = 6.8, 1.9 Hz, 2H), 6.01 (d, J = 1.2 Hz, 1H), 5.98 (d, J = 1.2 Hz, 1H), 5.69 (d, J = 4.0 Hz, 1H), 4.69
(d, J = 4.0 Hz, 1H), 3.83 (s, 3H); MS m/z 320.3 [M+H]+. Anal. Calcd for C15H13NO5S: C, 56.42; H, 4.10;
N, 4.39. Found: C, 56.56; H, 4.08; N, 4.28.
3-(3,4,5-Trimethoxyphenyl)-2,3-dihydro[1,3]dioxolo[4,5-f][1,2]benzisothiazole 1,1-dioxide 4i. White
solid; mp 213.5215.5 °C; IR (KBr) 3266, 3007, 1593, 1518, 1472, 1299, 1139, 1036, 877, 773 cm–1; 1H
NMR  7.39 (d, J = 8.1 Hz, 1H), 7.02 (d, J = 8.1 Hz, 1H), 6.72 (s, 2H), 6.06 (d, J = 1.2 Hz, 1H), 6.03 (d, J
= 1.2 Hz, 1H), 5.67 (d, J = 4.0 Hz, 1H), 4.85 (d, J = 4.0 Hz, 1H), 3.86 (s, 9H); MS m/z 380.5 [M+H]+.
Anal. Calcd for C17H17NO7S: C, 53.82; H, 4.52; N, 3.69. Found: C, 53.67; H, 4.56; N, 3.56.

HETEROCYCLES, Vol. 81, No. 3, 2010
647
3-(3,4-Dimethoxyphenyl)-2,3-dihydro[1,3]dioxolo[4,5-f][1,2]benzisothiazole 1,1-dioxide 4j. White
solid; mp 175177 °C; IR (KBr) 3265, 3006, 1593, 1518, 1472, 1298, 1265, 1139, 1035, 907, 877, 817,
1
758 cm–1; H NMR  7.39 (d, J = 8.1 Hz, 1H), 7.00-7.02 (m, 2H), 6.97 (d, J = 2.1 Hz, 1H), 6.87 (d, J =
8.1 Hz, 1H), 6.03 (d, J = 1.2 Hz, 1H), 5.99 (d, J = 1.2 Hz, 1H), 5.68 (d, J = 4.0 Hz, 1H), 4.79 (d, J = 4.0
Hz, 1H), 3.89 (s, 3H), 3.87 (s, 3H,); MS m/z 350.4 [M+H]+. Anal. Calcd for C16H15NO6S: C, 55.01; H,
4.33; N, 4.01. Found: C, 54.89; H, 4.41; N, 3.89.
3-(4-Methylphenyl)-2,3-dihydro[1,3]dioxolo[4,5-f][1,2]benzisothiazole 1,1-dioxide 4k. White solid;
1
mp 218220 °C; IR (KBr) 3426, 3213, 3095, 1498, 1471, 1287, 1139, 1037, 899, 827, 741 cm–1; H
NMR  7.39 (d, J = 8.1 Hz, 1H), 7.33 (dd, J = 7.9, 4.2 Hz, 2H), 7.21 (d, J = 8.1 Hz, 2H), 7.01 (d, J =
8.1Hz, 1H), 6.01 (d, J = 1.2 Hz, 1H), 5.97 (d, J = 1.2 Hz, 1H), 5.69 (d, J = 4.0 Hz, 1H), 4.72 (d, J = 4.0
Hz, 1H), 2.38 (s, 3H); MS m/z 304.4 [M+H]+. Anal. Calcd for C15H13NO4S: C, 59.39; H, 4.32; N, 4.62.
Found: C, 59.21; H, 4.29; N, 4.65.
3-(4-Fluorophenyl)-2,3-dihydro[1,3]dioxolo[4,5-f][1,2]benzisothiazole 1,1-dioxide 4l. White solid; mp
195.5197.5 °C; IR (KBr) 3422, 3187, 1604, 1512, 1473, 1292, 1144, 1029, 898, 841, 820, 741 cm–1; 1H
NMR  7.447.46 (m, 2H), 7.40 (d, J = 8.1 Hz, 1H), 7.09 (td, J = 8.1, 2.3 Hz, 2H), 7.02 (d, J = 8.1 Hz,
1H), 6.03 (d, J = 1.2 Hz, 1H), 5.98 (d, J = 1.2 Hz, 1H), 5.72 (d, J = 4.0 Hz, 1H), 4.82 (d, J = 4.0 Hz, 1H);
MS m/z 308.6 [M+H]+. Anal. Calcd for C14H10FNO4S: C, 54.72; H, 3.28; N, 4.56. Found: C, 54.68; H,
3.29; N, 4.52.
3-(3-Chlorophenyl)-2,3-dihydro[1,3]dioxolo[4,5-f][1,2]benzisothiazole 1,1-dioxide 4m. White solid;
1
mp 146148 °C; IR (KBr) 3289, 1593, 1500, 1465, 1290, 1184, 1146, 1035, 899, 796 cm–1; H NMR 
7.46 (d, J = 8.1 Hz, 1H), 7.387.39 (m, 1H), 7.367.37 (m, 1H), 7.347.35 (m, 2H), 7.02 (d, J = 8.1 Hz,
1H), 6.05 (d, J = 1.2 Hz, 1H), 6.00 (d, J = 1.2 Hz, 1H), 5.70 (d, J = 4.5 Hz, 1H), 4.99 (d, J = 4.5 Hz, 1H);
MS m/z 324.4 [M+H]+. Anal. Calcd for C14H10ClNO4S: C, 51.94; H, 3.11; N, 4.33. Found: C, 51.78; H,
3.09; N, 4.36.
ACKNOWLEDGEMENTS
This work was supported by the Natural Science Foundation of China (Grant No. 30873134) and Natural
Science Foundation of Shandong Province (Y2007C125).
REFERENCES (AND NOTES)
1. J. Drew, Science, 2000, 287, 1960; C. T. Supuran, A. Scozzafava, and A. Casini, Med. Res. Rev.,
2003, 23, 146; C. T. Supuran, A. Casini, and A. Scozzafava, Med. Res. Rev., 2003, 23, 535; J.-Y.
Winum, A. Scozzafava, J.-L. Montero, and C. T. Supuran, Med. Res. Rev., 2006, 26, 767.
2. P. Dauban and R. H. Dodd, Org. Lett., 2000, 2, 2327.
3. G. H. Merriman, PCT Int Appl WO 9828925, 1998.

648
HETEROCYCLES, Vol. 81, No. 3, 2010
4. D. C. Baker, A. Mayasundai, J. Mao, S. C. Johnson, and S. Yan, US Patent, US 6 562 850, 2003.
5. M.-T. Comte, Eur Patent, EP 0 433 149, 1991.
6. See a review: Z. Liu and Y. Takeuchi, Heterocycles, 2002, 56, 693.
7. Y. Takeuchi, T. Suzuki, A. Satoh, T. Shiragami, and N. Shibata, J. Org. Chem., 1999, 64, 5708; Y.
Takeuchi, Z. Liu, M. Suzuki, N. Shibata, and K. L. Kirk, J. Fluorine Chem., 1999, 97, 65; N. Shibata,
Z. Liu, and Y. Takeuchi, Chem. Pharm. Bull., 2000, 48, 1954; H. M. Sun, Z. P. Liu, and L. Q. Tang,
Chin. Chem. Lett., 2008, 19, 907.
8. W. Oppolzer, M. Wills, C. Starkemann, and G. Bernardinelli, Tetrahedron Lett., 1990, 31, 4117; K.
H. Ahn, C. Ham, S. K. Kim, and C.-W. Cho, J. Org. Chem., 1997, 62, 7047.
9. J. Blanchet, T. Macklin, C. Metallinos, and V. Snieckus, J. Org. Chem., 2007, 72, 3199.
10. See a review: Z. Liu and Y. Takeuchi, Heterocycles, 2009, 78, 1387; C. Fruit and P. Müller, Helv.
Chim. Acta., 2004, 87, 1607; J. V. Ruppel, R. M. Kamble, and X. P. Zhang, Org. Lett., 2007, 9,
4889; J.-L. Liang, S.-X. Yuan, J.-S. Huang, and C.-M. Che, J. Org. Chem., 2004, 69, 3610.
11. Z. Liu, N. Shibata, and Y. Takeuchi, J. Chem. Soc., Perkin Trans. 1, 2002, 302; Z. Liu, N. Shibata,
and Y. Takeuchi, J. Org. Chem., 2000, 65, 7583; Z. Liu, Heterocycles, 2007, 71, 1843; F. Fang, R.
Wang, Z.-P. Liu, and A.-G. Ji, Heterocycles, 2007, 71, 2377; R. Wang, F. Fang, L.-Q. Tang, and
Z.-P. Liu, Lett. Org. Chem., 2008, 5, 461.
12. See a review: O. B. Familoni, Synlett, 2002, 1181.
13. For a review, see: G. A. Olah and S. C. Narang, Tetrahedron, 1982, 38, 2225.
14. M. E. Jung and P. L. Ornstein, Tetrahedron Lett., 1977, 18, 2659.
15. T.-L. Ho, Synth. Commun., 1979, 9, 665.
16. R. A. Benkeser, E. C. Mozdzen, and C. L. Muth, J. Org. Chem., 1979, 44, 2185.
17. J. A. Maguson and J. H. Wolfenden, J. Phys. Chem., 1956, 60, 1665.