Synthesis of difluorinated β-ketosulfones and novel gem-difluoromethylsulfone-containing heterocycles as fluorinated building blocks

Article abstract of DOI:10.1016/j.jfluchem.2009.12.022

A series of new heterocyclic β-ketosulfides was prepared by the reaction of the corresponding heterocyclic thiols with α-bromoacetophenone and its derivatives. Oxidation of the products using m-CPBA gave the corresponding heterocyclic β-ketosulfones, whic

Full text of DOI:10.1016/j.jfluchem.2009.12.022

Journal of Fluorine Chemistry 131 (2010) 561–569
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Synthesis of difluorinated
b-ketosulfones and novel gem-difluoromethylsulfone-
containing heterocycles as fluorinated building blocks
*
Hossein Loghmani-Khouzani , Dariush Hajiheidari
Department of Chemistry, University of Isfahan, Isfahan 81746-73441, Iran
A R T I C L E I N F O
A B S T R A C T
Article history:
A series of new heterocyclic
b-ketosulfides was prepared by the reaction of the corresponding
Received 23 September 2009
Received in revised form 14 December 2009
Accepted 29 December 2009
Available online 7 January 2010
heterocyclic thiols with
a
-bromoacetophenone and its derivatives. Oxidation of the products using m-
-ketosulfones, which, on treatment with SelectfluorTM under
CPBA gave the corresponding heterocyclic
b
anhydrous condition underwent electrophilic fluorination resulting in new heterocycles with
difluoromethylene moiety adjacent to the sulfur atom and the carbonyl group. Base-induced cleavage
of the five types of the resulting products, with different heterocyclic moieties as model compounds,
afforded the difluoromethyl sulfones attached to the corresponding heterocycles. They can be
considered as interesting fluorinated building blocks for further elaborations.
Keywords:
b-Ketosulfones
gem-Difluorination
Heterocycles
SelectfluorTM
ß 2010 Elsevier B.V. All rights reserved.
b-Ketosulfides
Difluoromethyl sulfones
1. Introduction
molecules derived from CF2-synthons [15]. Direct methods for the
preparation of gem-difluorinated compounds by reacting appro-
Recently, organofluorine compounds have received much
attention due to their potential use in pharmaceutical, biological,
and material science [1]. The selective transfer of a fluorine atom
into an organic molecule has become a considerable challenge for
chemists interested in biological and medicinal applications [2].
The introduction of the difluoromethylene (CF2) moiety into
organic molecules, especially those heterocyclic compounds has
been proved to be attractive due to the potential biological
properties of such molecules [3–5]. This group has been recognized
as an isopolar–isosteric replacement for oxygen. The formation of
the C–F bond adjacent to the carbonyl or imine functionality
increases the electrophilicity of these functional groups [6],
improving their bioactivity [7]. Important efforts have been made
toward the synthesis of compounds containing a difluoromethy-
lene group adjacent to a carbonyl group [8–10]. Among organo-
fluorine compounds, gem-difluorinated compounds with CF2
adjacent to the sulfur atom have also attracted significant attention
especially in the field of medicinal chemistry [11–14].
priate substrates with fluorinating agents such as DAST [16], SF4
[17], TBAF [18], BrF3 [19], Selectfluor [20] or NFSI [21] have been
reported. Several nucleophilic gem-difluoromethylation building
blocks employing difluoromethylphenylsulfone (PhSO2CF2H) [22],
bromodifluoromethylphenylsulfone (PhSO2CF2Br) [23], (trifluor-
omethyl)trimethylsilane (CF3SiMe3) [24], [(difluoromethyl)(phe-
nylsulfonyl)]trimethylsilane (PhSO2CF2SiMe3) [25], [(difluoro-
methyl)(phenylsulfanyl)]trimethylsilane (PhSCF2SiMe3) [26],
[difluoro(phenylseleno)methyl]trimethylsilane
(PhSeCF2SiMe3)
[27], arylthiobromodifluoromethane (ArSCF2Br) [28], diethyl
bromodifluoromethylphosphonate [P(O)(OEt)CF2Br] [29], dietyl
difluoro(trimethylsilyl)methylphosphonate [P(O)(OEt)CF2Br] [30]
and diethyl difluoromethylphosphonate P(O)(OEt)2CF2H [31] have
been extensively studied.
In this article, we wish to report the synthesis of certain new
gem-difluoromethylene-containing heterocycles, which also result
in the preparation of difluoromethylsulfones attached to hetero-
cycles as new fluorinated building blocks. Possibility of at room
temperature synthesis of heterocyclic synthons, with the potential
pharmaceutical effect of interest is the main advantage of the
present method over the one proposed by Zafrani et al. [29].
The preparation of gem-difluoromethylene substituted mole-
cules falls broadly into two classes. The first involves direct gem-
difluorination, and the second draws from the construction of
2. Results and discussion
* Corresponding author. Tel.: +98 311 7932722; fax: +98 311 6689732.
E-mail addresses: h.log119@sci.ui.ac.ir, loghmani_h@yahoo.com
(H. Loghmani-Khouzani).
In an effort to prepare new fluorinated heterocyclic
ketosulfones as well as new fluorinated building blocks, a series
b-
0022-1139/$ – see front matter ß 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2009.12.022

562
H. Loghmani-Khouzani, D. Hajiheidari / Journal of Fluorine Chemistry 131 (2010) 561–569
Table 1
Table 2
Synthesis of heterocyclic
b-ketosulfides.
Sulfonation of heterocyclic b-ketosulfides.
.
Substrate
Product
Yield (%)a
.
(1a) X = H
(1b) X = Br
(1c) X = Cl
(1d) X = Me
93
96
95
88
Substrate
Product
Yield (%)a
1a
1b
1c
1d
(2a) X = H
(2b) X = Br
(2c) X = Cl
(2d) X = Me
73
80
58
55
(1e) X = H
(1f) X = Br
(1g) X = Cl
(1h) X = Me
89
95
92
85
1e
1f
(2e) X = H
(2f) X = Br
(2g) X =Cl
(2h) X = Me
70
75
68
65
1g
1h
(1i) X = H
(1j) X = Br
(1k) X = Cl
(1l) X = Me
95
95
90
88
1i
1j
(2i) X =H
(2j) X =Br
(2k) X = Cl
(2l) X =Me
70
73
66
62
1k
1l
1m
1n
1o
1p
(2m) X = H
(2n) X =Br
(2o) X = Cl
(2p) X = Me
79
82
68
56
(1m) X = H
(1n) X = Br
(1o) X = Cl
(1p) X = Me
95
96
96
89
1q
1r
1s
1t
(2q) X = H
(2r) X = Br
(2s) X = Cl
(2t) X = Me
73
77
67
57
(1q) X = H
(1r) X =Br
(1s) X = Cl
(1t) X = Me
85
87
84
86
a
Isolated yields.
a
Isolated yields.
of heterocyclic
b
-ketosulfides 1a–t was prepared by the reaction of
Fluorination of the resulted compounds 2a–t (Table 3) was
carried out using SelectfluorTM in the presence of sodium
carbonate in dry acetonitrile, under inert atmosphere. In all cases,
diflouoro derivatives were the main products when 2.5 equiv. of
SelectfluorTM was used. The product yields were 38–61% (3a–t) as
shown in Table 3. These new gem-difluorinated compounds are of
heterocyclic thiols, 2-mercaptobenzothiazol (1), 2-mercaptothia-
zoline (2), 2-mercaptobenzoxazole (3), 2-mercaptobenzimidazole
(4) and 2-mercaptopyrimidine (5), with
and its derivatives in the presence of sodium carbonate (Table 1).
The selected heterocyclic moieties have attracted special attention
in chemistry [3–5].
a-bromoacetophenone
As shown in Table 1, the product yields were 85–96% (entries
Table 3
Fluorination of heterocyclic
b-ketosulfones.
1a–t). Attempted fluorination of
b-ketosulfides 1a–t using
Selectfluor (F-TEDA-BF4) resulted in gem-difluorinated compounds
in poor yields and the corresponding disulfides as by-products. In
order to enhance activation of the methylene group adjacent to the
sulfur atom and stabilize the products [32], the heterocyclic
ketosulfides 1a–t were oxidized using m-CPBA to the correspond-
ing -ketosulfones (Table 2).
The product yields of the
as shown in Table 2. In the presence of m-CPBA as the oxidizing
agent, no competing oxidation of the heterocyclic benzothiazol
and thiazoline rings was observed.
b-
b
.
b
-ketosulfones (2a–t) were 55–80%,
Substrate
Product
Yield (%)a
2a
2b
2c
2d
(3a) X = H
(3b) X = Br
(3c) X = Cl
(3d) X = Me
48
56
50
42
It is noteworthy that the resulting
b-ketosulfones can be very
useful. -Ketosulfones are a very important group of precursors for
b
Michael and Knoevenagel reactions and are used in the preparation
of various organic compounds [33,34]. The versatile utility of
heterocyclic sulfones for the preparation of carbon–carbon double
bond from carbonyl compounds is well documented [35]. We used
2e
2f
(3e) X = H
(3f) X = Br
(3g) X =Cl
(3h) X = Me
50
52
48
45
2g
2h
the resulted
b-ketosulfones as substrates for electrophilic
fluorination. Targeting nonhazardous procedure, SelectfluorTM
was selected as a user-friendly fluorinating agent [36].

H. Loghmani-Khouzani, D. Hajiheidari / Journal of Fluorine Chemistry 131 (2010) 561–569
563
Table 3 (Continued )
heterocyclic moieties were selected as model compounds and
were treated these compounds with aqueous alkali. Under this
condition, these compounds underwent base-induced cleavage to
afford difluoromethyl sulfones attached to the corresponding
heterocycles (4b, 4f, 4j, 4n and 4r) in high yields (Table 4). Such
fluorinated synthons can be very useful for introducing fluorinat-
ed building blocks directly into a variety of organic molecules. Our
literature survey showed that only one of the resulted difluor-
omethylsulfone-containing heterocycle has been prepared. Calata
et al. [15c] synthesized difluoromethylsulfone (4b) from decar-
boxylation reaction of realated ethyldifluoromethyl-benzothiaa-
zolylsulfone in five steps (from mercaptoaryl as a starting
material). The most advantage of our research work over the
work above mentioned is working at room temperature, no
expensive catalytic material, no by-product and fast reaction
times.
Substrate
Product
Yield (%)a
2i
2j
(3i) X = H
(3j) X = Br
(3k) X = Cl
(3l) X = Me
47
46
45
38
2k
2l
2m
2n
2o
2p
(3m) X = H
(3n) X = Br
(3o) X = Cl
(3p) X = Me
54
63
53
46
2q
2r
2s
2t
(3q) X = H
(3r) X = Br
(3s) X = Cl
(3t) X = Me
59
61
57
41
3. Conclusions
a
Isolated yields.
We have prepared heterocyclic
The corresponding -keto heterocyclic sulfones were obtained
after oxidation of the resulted -ketosulfides using m-CPBA.
Electrophilic fluorination of these -ketosulfones by the use of
b-ketosulfides in high yields.
b
Table 4
Synthesis of difluoromethyl sulfones.
b
b
SelectfluorTM resulted in the corresponding heterocycles with
difluoromethylene moiety adjacent to the sulfur atom and the
carbonyl group as possible bioactive molecules. We have
successfully prepared difluoromethyl sulfones via base-induced
cleavage of the corresponding gem-difluorinated sulfones. The
present synthetic methodology provides a convenient way for the
.
preparation of new heterocyclic
fones as well as difluorinated
potential bioactive compounds. The ease and efficiency of the
conversion at room temperature of -keto heterocyclic sulfones
b
-ketosulfides and
b-ketosul-
Substrate
Product
Yield (%)a
b
-keto heterocyclic sulfones as
3b
(4b) 98
b
to the corresponding fluorinated building blocks is another
advantage of this method. The resulted heterocyclic difluoro-
methyl sulfones are expected to be useful fluorinated building
blocks and the study of them as fluoroalkylating agents is
underway in our laboratory.
3f
(4f) 97
4. Experimental
Melting points were determined using a Linkam HF591 heating
stage, used in conjunction with a TC92 controller, and are
uncorrected. The 1H NMR spectra were recorded on either Bruker
DPX-300 (300 MHz), Bruker 400 MHz or Bruker Avance-500
(500 MHz) spectrometer in CDCl3 using tetramethylsilane as an
internal standard. 13C NMR spectra were recorded at 125 MHz. The
19F NMR spectra were recorded on a Bruker Avance-500 (470 MHz)
3j
(4j) 97
3n
(4n) 94
spectrometer, in which the chemical shifts (d) were measured with
fluorotrichloromethane ( = 0) as an internal standard. The IR
d
spectra were recorded on either a Jasco A-302 or a Perkin Elmer
683 infrared spectrometer. Elemental analyses were performed on
a Perkin Elmer Elemental Analyzer 2400 CHN.
3r
(4r) 96
4.1. Typical procedure for the synthesis of
b-ketosulfide (1a)
Sodium carbonate (4.5 mmol) was added to a solution of 2-
mercaptobenzothiazol (3 mmol) in mixture of ethanol
(15 mL) and water (15 mL). The reaction mixture was stirred
at room temperature for 30 min and then -bromoacetophe-
1
a
a
Isolated yields.
a
none (3 mmol) was added, and the reaction mixture was stirred
at room temperature for another 1 h. The reaction was
monitored by TLC and after 1 h showed the complete
disappearance of the starting materials. The resulting mixture
was poured into 100 mL of 1 M HCl containing 50 g of crushed
ice. The crude product was filtered and the filtrate was washed
interest due to the potential biological properties of such
molecules.
The fluorination of these compounds encouraged us to
examine the preparation of the corresponding fluorinated
synthons. Therefore, 3b, 3f, 3j, 3n and 3r with different

564
H. Loghmani-Khouzani, D. Hajiheidari / Journal of Fluorine Chemistry 131 (2010) 561–569
with a mixture of ethanol (10 mL) and water (10 mL). The crude
product was purified by recrystallization from petroleum ether
to give product 1a as a pale yellow solid.
Calcd for C11H10ClNOS2: C, 48.61; H, 3.71; N, 5.15. Found: C, 48.52;
H, 3.68; N, 5.22.
4.1.8. 2-(4,5-Dihydrothiazol-2-ylthio)-1-p-tolylethanone (1h)
4.1.1. 2-(Benzo[d]thiazol-2-ylthio)-1-phenylethanone (1a)
White solid; m.p.: 75–76 8C; 1H NMR (400 MHz; CDCl3):
d
8.12 (d, 2H, J = 7.8 Hz), 7.27 (d, 2H, J = 7.8 HZ), 4.80 (s, 2H), 3.96
(t, 2H, J = 7.5 Hz), 3.38 (t, 2H, J = 7.5 Hz), 2.63 (s, 3H). 13C NMR
Pale yellow solid; m.p.: 114–115 8C; 1H NMR (400 MHz; CDCl3):
d
8.15-7.75 (m, 4H), 7.55–7.32 (m, 5H), 5.10 (s, 2H). 13C NMR
(126 MHz; CDCl3):
d
194.2 (C55O), 162.1, 151.8, 135.3, 134.2, 131.1,
(126 MHz; CDCl3): d 194.1 (C55O), 161.8, 161.9, 142.1, 128.2,
126.7, 126.5, 124.7, 124.1, 119.8, 119.6, 37.5. IR (KBr, cmÀ1): 3055,
2820, 1676(C55O), 1580, 1420, 1371, 1318, 1283, 1182, 996, 750,
672. Anal. Calcd for C15H11NOS2: C, 63.13; H, 3.89; N, 4.91. Found:
C, 63.07; H, 3.86; N, 4.93.
127.8, 54.9, 36.9, 31.2, 23.8. IR (KBr, cmÀ1): 3112, 2891, 1688
(C55O), 1556, 1374, 1362, 1259, 1187, 1070, 963, 818. Anal. Calcd
for C12H13NOS2: C, 57.34; H, 5.21; N, 5.57. Found: C, 57.32; H,
5.21; N, 5.52.
4.1.2. 2-(Benzo[d]thiazol-2-ylthio)-1-(4-bromophenyl)ethanone (1b)
4.1.9. 2-(Benzo[d]oxazol-2-ylthio)-1-phenylethanone (1i)
White solid; m.p.: 153–154 8C; 1H NMR (400 MHz; CDCl3):
d
Colorless solid; m.p.: 124–125 8C; 1H NMR (400 MHz; CDCl3):
d
8.15–7.45 (m, 8H), 5.23 (s, 2H). 13C NMR (126 MHz; CDCl3):
d
193.9
7.86–7.21 (m, 9H), 4.58 (s, 2H). 13C NMR (126 MHz; CDCl3):
d 194.1
(C55O), 162.2, 151.5, 134.7, 133.3, 129.7, 129.2, 126.1, 123.9, 123.2,
121.7, 121.4, 37.4. IR (KBr, cmÀ1): 3027, 2943, 1683 (C55O), 1569,
1432, 1375, 1319, 1273, 1076, 986, 764. Anal. Calcd for
(C55O), 164.3, 148.9, 140.8, 136.1, 132.6, 128.0, 127.8, 124.1, 122.9,
118.3, 109.6, 37.3. IR (KBr, cmÀ1): 3027, 2581, 1671 (C55O), 1593,
1492, 1447, 1382, 1326, 1291, 1230, 1182, 1025, 993, 738. Anal.
Calcd for C15H11NO2S: C, 66.89; H, 4.12; N, 5.20. Found: C, 66.96; H,
4.06; N, 5.17.
C
15H10BrNOS2: C, 49.46; H, 2.77; N, 3.85. Found: C, 49.34; H,
2.81; N, 3.84.
4.1.3. 2-(Benzo[d]thiazol-2-ylthio)-1-(4-chlorophenyl)ethanone (1c)
Pale yellow solid; m.p.: 139–140 8C; 1H NMR (400 MHz; CDCl3):
4.1.10. 2-(Benzo[d]oxazol-2-ylthio)-1-(4-bromophenyl)ethanone
(1j)
d
8.15–7.42 (m, 8H), 5.23 (s, 2H). 13C NMR (126 MHz; CDCl3):
d
White solid; m.p.: 138–139 8C; 1H NMR (400 MHz; CDCl3):
7.75–7.21 (m, 9H), 4.58 (s, 2H). 13C NMR (126 MHz; CDCl3):
d 193.7
d
193.7 (C55O), 162.2, 151.5, 137.6, 133.3, 129.3, 129.1, 125.2, 123.9,
123.2, 121.6, 121.4, 37.4. IR (KBr, cmÀ1): 3070, 2908, 1685 (C55O),
1582, 1432, 1292, 1205, 1097, 986, 805, 750. Anal. Calcd for
(C55O), 164.1, 148.9, 140.7, 135.1, 127.2, 125.8, 125.2, 124.2, 122.8,
118.3, 109.5, 36.8. IR (KBr, cmÀ1): 3035, 2976, 1684 (C55O), 1582,
1490, 1458, 1195, 1117, 982, 807, 730. Anal. Calcd for
C
15H10ClNOS2: C, 56.33; H, 3.15; N, 4.38. Found: C, 56.28; H, 3.15;
N, 4.46.
C15H10BrNO2S: C, 51.74; H, 2.89; N, 4.02. Found: C, 51.71; H,
2.87; N, 4.15.
4.1.4. 2-(Benzo[d]thiazol-2-ylthio)-1-p-tolylethanone (1d)
Pale yellow solid; m.p.: 121–122 8C; 1H NMR (400 MHz; CDCl3):
4.1.11. 2-(Benzo[d]oxazol-2-ylthio)-1-(4-chlorophenyl)ethanone
(1k)
d
8.15–7.23 (m, 8H), 5.22 (s, 2H), 2.65 (s, 3H). 13C NMR (126 MHz;
CDCl3):
d
194.4 (C55O), 162.2, 151.4, 141.5, 133.2, 132.9, 128.0,
Pale yellow solid; m.p.: 129–130 8C; 1H NMR (400 MHz; CDCl3):
127.7, 123.9, 123.1, 121.6, 121.5, 37.4, 23.7. IR (KBr, cmÀ1): 3086,
2924, 1680 (C55O), 1579, 1418, 1296, 1194, 1090, 991, 817, 747.
Anal. Calcd for C16H13NOS2: C, 64.18; H, 4.38; N, 4.68. Found: C,
64.19; H, 4.35; N, 5.78.
d d
7.80–7.20 (m, 9H), 4.58 (s, 2H). 13C NMR (126 MHz; CDCl3):
193.3 (C55O), 164.2, 148.9, 140.8, 134.2, 131.2, 130.4, 127.0, 124.2,
122.7, 118.2, 109.6, 36.6. IR (KBr, cmÀ1): 3073, 2618, 1687 (C55O),
1595, 1486, 1455, 1182, 993, 818, 714. Anal. Calcd for
C15H10ClNO2S: C, 59.31; H, 3.32; N, 4.61. Found: C, 59.22; H,
4.1.5. 2-(4,5-Dihydrothiazol-2-ylthio)-1-phenylethanone (1e)
3.27; N, 4.61.
Pale yellow solid; m.p.: 58–60 8C; 1H NMR (500 MHz; CDCl3):
d
8.20–7.55 (m, 5H), 4.82 (s, 2H), 4.05 (t, 2H, J = 7.5 Hz), 3.42 (t, 2H,
4.1.12. 2-(Benzo[d]oxazol-2-ylthio)-1-p-tolylethanone (1l)
White solid; m.p.: 127–128 8C; 1H NMR (400 MHz; CDCl3):
d
J = 7.5 Hz). 13C NMR (126 MHz; CDCl3):
d
194.1 (C55O), 161.2, 135.5,
132.4, 127.9, 127.3, 54.9, 36.2, 31.3. IR (KBr, cmÀ1): 3117, 2912,
7.74–7.11 (m, 8H), 5.22 (s, 2H), 2.63 (s, 3H). 13C NMR (126 MHz;
1678 (C55O), 1544, 1263, 1159, 971, 776. Anal. Calcd for
CDCl3): d 194.4 (C55O), 164.2, 148.8, 142.1, 140.8, 133.2, 128.6,
C
11H11NOS2: C, 55.67; H, 4.67; N, 5.90. Found: C, 55.56; H, 4.64;
128.2, 124.1, 122.8, 118.4, 109.6, 36.9, 23.8. IR (KBr, cmÀ1): 3094,
2711, 1681 (C55O), 1578, 1497, 1436, 1172, 981, 802, 727. Anal.
Calcd for C16H13NO2S: C, 67.82; H, 4.62; N, 4.94. Found: C, 67.75; H,
4.63; N, 4.89.
N, 27.03.
4.1.6. 2-(4,5-Dihydrothiazol-2-ylthio)-1-(4-bromophenyl)ethanone
(1f)
Pale yellow solid; m.p.: 110–111 8C; 1H NMR (400 MHz; CDCl3):
4.1.13. 2-(1H-benzo[d]imidazol-2-ylthio)-1-phenylethanone (1m)
d
8.15–7.26 (m, 4H), 4.82 (s, 2H), 4.05 (t, 2H, J = 7.5 Hz) 3.42 (t, 2H,
White solid; m.p.: 168–170 8C; 1H NMR (300 MHz; DMSO):
d
J = 7.5 Hz). 13C NMR (126 MHz; CDCl3):
d
193.7 (C55O), 161.2, 134.9,
12.1 (s, 1H), 7.79–7.18 (m, 9H), 3.92 (s, 2H). 13C NMR (126 MHz;
130.7, 130.1, 126.8, 54.9, 36.1, 31.2. IR (KBr, cmÀ1): 3081, 2902,
CDCl3): d 193.2 (C55O), 146.9, 137.8, 137.5, 134.8, 131.3, 126.5,
1690 (C55O), 1558, 1276, 1166, 963, 788. Anal. Calcd for
126.3, 122.7, 122.5, 11.3.3, 113.1, 36.5. IR (KBr, cmÀ1): 3048,
C
11H10BrNOS2: C, 41.78; H, 3.19; N, 4.43. Found: C, 41.78; H,
1670 (C55O), 1455, 1412, 1273, 970, 744. Anal. Calcd for
3.23; N, 4.38.
C15H12N2OS: C, 67.14; H, 4.51; N, 10.44. Found: C, 66.27; H,
4.13; N, 4.78.
4.1.7. 2-(4,5-Dihydrothiazol-2-ylthio)-1-(4-chlorophenyl)ethanone
(1g)
4.1.14. 2-(1H-benzo[d]imidazol-2-ylthio)-1-(4-
bromophenyl)ethanone (1n)
White solid; m.p.: 87–88 8C; 1H NMR (500 MHz; CDCl3):
d
8.19–
7.78 (m, 4H), 4.82 (s, 2H), 4.05 (t, 2H, J = 7.5 Hz), 3.42 (t, 2H,
White solid; m.p.: 212–214 8C; 1H NMR (300 MHz; DMSO):
d
J = 7.5 Hz). 13C NMR (126 MHz; CDCl3):
d
193.6 (C55O), 161.8, 137.7,
12.4 (s, 1H), 7.68–7.18 (m, 8H), 3.89 (s, 2H). 13C NMR (126 MHz;
133.9, 129.6, 128.2, 54.9, 35.9, 31.3. IR (KBr, cmÀ1): 3072, 2850,
CDCl3):
d 192.4 (C55O), 145.1, 136.8, 136.7, 133.7, 129.5, 129.0,
1694 (C55O), 1560, 1386, 1351, 1272, 1195, 1082, 960, 811. Anal.
125.4, 121.0, 120.8, 113.1, 112.9, 36.4. IR (KBr, cmÀ1): 3046, 1687

H. Loghmani-Khouzani, D. Hajiheidari / Journal of Fluorine Chemistry 131 (2010) 561–569
565
(C55O), 1448, 1403, 1285, 966, 750. Anal. Calcd for C15H11BrN2OS:
C, 51.89; H, 3.19; N, 8.07. Found: C, 51.22; H, 3.27; N, 8.21.
4.2.1. 2-(Benzo[d]thiazol-2-ylsulfonyl)-1-phenylethanone (2a)
White solid; m.p.: 150–151 8C; 1H NMR (400 MHz; CDCl3):
8.17–7.76 (m, 4H), 7.56–7.33 (m, 5H), 5.53 (s, 2H). 13C NMR
(126 MHz; CDCl3): 188.1 (C55O), 153.9, 151.8, 135.4, 134.3, 131.1,
126.8, 126.5, 124.7, 124.0, 119.9, 119.6, 59.7. IR (KBr, cmÀ1): 3034,
2818, 1678 (C55O), 1593, 1412, 1330, 1141, 1137, 964, 787, 748.
Anal. Calcd for C15H11NO3S2: C, 56.76; H, 3.49; N, 4.41. Found: C,
56.72; H, 3.49; N, 4.46.
d
4.1.15. 2-(1H-benzo[d]imidazol-2-ylthio)-1-(4-
chlorophenyl)ethanone (1o)
d
White solid; m.p.: 189–191 8C; 1H NMR (300 MHz; DMSO):
d
12.3 (s, 1H), 7.72–7.17 (m, 8H), 4.93 (s, 2H). 13C NMR (126 MHz;
CDCl3):
d 192.3 (C55O), 145.1, 136.9, 136.7, 136.5, 132.9, 128.2,
126.8, 121.1, 120.9, 113.3, 113.1, 36.5. IR (KBr, cmÀ1): 3057, 1689
(C55O), 1447, 1407, 1289, 960, 754. Anal. Calcd for C15H11ClN2OS: C,
59.50; H, 3.66; N, 9.25. Found: C, 60.03; H, 3.54; N, 9.37.
4.2.2. 2-(Benzo[d]thiazol-2-ylsulfonyl)-1-(4-bromophenyl)ethanone
(2b)
White solid; m.p.: 196–198 8C; 1H NMR (400 MHz; CDCl3):
8.16–7.47 (m, 8H), 5.67 (s, 2H). 13C NMR (126 MHz; CDCl3):
d 188.1
d
4.1.16. 2-(1H-benzo[d]imidazol-2-ylthio)-1-p-tolylethanone (1p)
White solid; m.p.: 184–186 8C; 1H NMR (300 MHz; DMSO):
d
(C55O), 154.1, 151.5, 134.8, 133.2, 129.7, 129.1, 126.2, 123.9, 123.1,
121.7, 121.2, 59.8. IR (KBr, cmÀ1): 3010, 2800, 1684 (C55O), 1570,
1401, 1328, 1150, 1122, 970, 803, 752. Anal. Calcd for
C15H10BrNO3S2: C, 45.46; H, 2.54; N, 3.53. Found: C, 45.49; H,
2.50; N, 3.43.
12.0 (s, 1H), 7.66–7.08 (m, 8H), 4.94 (s, 2H), 2.53 (s, 3H). 13C NMR
(126 MHz; CDCl3): 193.5 (C55O), 145.1, 140.8, 136.9, 136.7, 131.8,
d
127.0, 126.7, 121.2, 121.0, 113.3, 113.1, 36.6, 21.8. IR (KBr, cmÀ1):
3041, 1683 (C55O), 1441, 1408, 1371, 1269, 965, 740. Anal. Calcd
for C16H14N2OS: C, 68.06; H, 5.00; N, 9.92. Found: C, 67.91; H, 5.14;
N, 9.76.
4.2.3. 2-(Benzo[d]thiazol-2-ylsulfonyl)-1-(4-chlorophenyl)ethanone
(2c)
4.1.17. 1-Phenyl-2-(pyrimidin-2-ylthio)ethanone (1q)
White solid; m.p.: 181–182 8C; 1H NMR (400 MHz; CDCl3):
d
White solid; m.p.: 98–99 8C; 1H NMR (300 MHz; CDCl3):
d
7.79–
195.2
8.15–7.45 (m, 8H), 5.63 (s, 2H). 13C NMR (126 MHz; CDCl3):
d 187.9
7.19 (m, 8H), 3.91 (s, 2H). 13C NMR (126 MHz; CDCl3):
d
(C55O), 154.1, 151.5, 137.5, 133.2, 129.4, 129.1, 125.2, 123.8, 123.2,
121.5, 121.3, 61.3. IR (KBr, cmÀ1): 3062, 2814, 1686 (C55O), 1582,
1418, 1333, 1147, 1135, 961, 812, 744. Anal. Calcd for
(C55O), 169.9, 154.9, 134.8, 131.2, 126.8, 126.6, 114.3, 36.8. IR (KBr,
cmÀ1): 3029, 2583, 1674 (C55O), 1439, 1410, 1269, 973, 740. Anal.
Calcd for C12H10N2OS: C, 62.59; H, 4.38; N, 12.16. Found: C, 62.51;
H, 4.53; N, 12.28.
C15H10ClNO3S2: C, 51.21; H, 2.86; N, 3.98. Found: C, 51.17; H,
2.78; N, 4.03.
4.1.18. 1-(4-Bromophenyl)-2-(pyrimidin-2-ylthio)ethanone (1r)
4.2.4. 2-(Benzo[d]thiazol-2-ylsulfonyl)-1-p-tolylethanone (2d)
White solid; m.p.: 166–167 8C; 1H NMR (400 MHz; CDCl3):
d
White solid; m.p.: 108–110 8C; 1H NMR (300 MHz; CDCl3):
d
8.00–7.09 (m, 7H), 3.87 (s, 2H). 13C NMR (126 MHz; CDCl3):
d
194.8
8.15–7.27 (m, 8H), 5.70 (s, 2H), 2.65 (s, 3H). 13C NMR (126 MHz;
(C55O), 169.9, 154.9, 133.8, 129.6, 129.1, 125.5, 114.3, 36.8. IR (KBr,
cmÀ1): 3038, 2971, 1692 (C55O), 1449, 1401, 1271, 959, 738. Anal.
Calcd for C12H9BrN2OS: C, 46.62; H, 2.93; N, 9.06. Found: C, 46.03;
H, 2.81; N, 9.27.
CDCl3): d 189.2 (C55O), 154.1, 151.3, 141.5, 133.3, 132.9, 128.1,
127.7, 123.8, 123.1, 121.6, 121.5, 42.5, 23.8. IR (KBr, cmÀ1): 3074,
2950, 1681 (C55O), 1569, 1392, 1318, 1153, 1139, 968, 817, 754.
Anal. Calcd for C16H13NO3S2: C, 57.99; H, 3.95; N, 4.23. Found: C,
57.93; H, 4.03; N, 4.23.
4.1.19. 1-(4-Chlorophenyl)-2-(pyrimidin-2-ylthio)ethanone (1s)
White solid; m.p.: 101–102 8C; 1H NMR (300 MHz; CDCl3):
d
4.2.5. 2-(4,5-Dihydrothiazol-2-ylsulfonyl)-1-phenylethanone (2e)
8.03–7.06 (m, 7H), 3.92 (s, 2H). 13C NMR (126 MHz; CDCl3):
d
194.4
White solid; m.p.: 89–91 8C; 1H NMR (400 MHz; CDCl3):
d
8.22–
(C55O), 169.9, 154.8, 136.6, 132.9, 128.2, 126.8, 114.2, 36.7. IR (KBr,
cmÀ1): 3078, 2621, 1691 (C55O), 1451, 1411, 1292, 965, 743. Anal.
Calcd for C12H9ClN2OS: C, 54.44; H, 3.43; N, 10.58. Found: C, 54.32;
H, 3.51; N, 10.76.
7.58 (m, 5H), 5.36 (s, 2H), 4.08 (t, 2H, J = 7.5 Hz), 3.44 (t, 2H,
J = 7.5 Hz). 13C NMR (126 MHz; CDCl3):
d 189.0 (C55O), 162.1, 135.4,
132.5, 127.9, 127.2, 60.9, 54.9, 31.4. IR (KBr, cmÀ1): 3056, 2927,
1682 (C55O), 1541, 1328, 1262, 1142, 976, 768. Anal. Calcd for
C11H11NO3S2: C, 49.05; H, 4.12; N, 5.20. Found: C, 49.17; H, 4.23; N,
4.1.20. 2-(Pyrimidin-2-ylthio)-1-p-tolylethanone (1t)
5.07.
White solid; m.p.: 97–98 8C; 1H NMR (300 MHz; CDCl3):
d
7.73–
7.08 (m, 7H), 3.95 (s, 2H), 2.54 (s, 3H). 13C NMR (126 MHz; CDCl3):
d
4.2.6. 2-(4,5-Dihydrothiazol-2-ylsulfonyl)-1-(4-
bromophenyl)ethanone (2f)
195.5 (C55O), 169.9, 155.0, 140.8, 131.8, 127.0, 126.7, 114.3, 36.8,
22.3. IR (KBr, cmÀ1): 3099, 2718, 1685 (C55O), 1432, 1412, 1361,
1270, 961, 731. Anal. Calcd for C13H12N2OS: C, 63.91; H, 4.95; N,
11.47. Found: C, 63.75; H, 4.63; N, 11.26.
White solid; m.p.: 141–142 8C; 1H NMR (400 MHz; CDCl3):
d
8.16–7.64 (m, 4H), 5.38 (s, 2H), 4.08 (t, 2H, J = 7.5 Hz), 3.45 (t, 2H,
J = 7.5 Hz). 13C NMR (126 MHz; CDCl3):
199.2 (C55O), 162.2, 134.8,
d
130.7, 129.9, 126.8, 54.8, 41.3, 31.3. IR (KBr, cmÀ1): 3078, 2917,
1698 (C55O), 1563, 1314, 1165, 1149, 1100, 958, 744. Anal. Calcd
for C11H10BrNO3S2: C, 37.94; H, 2.89; N, 4.02. Found: C, 37.79; H,
2.78; N, 4.14.
4.2. Typical procedure for the synthesis of
b-ketosulfone (2a)
To a stirred solution of -ketosulfide 1a (1 mmol) in CH2Cl2
b
(20 mL) at 0 8C, m-CPBA (3 mmol) was added. After 10 min, the
cold bath was removed and the reaction was stirred for 1 h. The
progress of the reaction was monitored by TLC. After completion of
the reaction, saturated aqueous sodium sulfite solution (50 mL)
was added and the reaction mixture was stirred at room
temperature for another 1 h. The CH2Cl2 layer was washed with
water, dried over MgSO4 and the solvent was evaporated under
reduced pressure. Purification of the crude mixture by flash silica
gel chromatography (AcOEt/petroleum ether = 3:7) afforded the
sulfone 2a as a white solid.
4.2.7. 2-(4,5-Dihydrothiazol-2-ylsulfonyl)-1-(4-
chlorophenyl)ethanone (2g)
Pale yellow solid; m.p.: 134–135 8C; 1H NMR (500 MHz; CDCl3):
d
8.20–7.79 (m, 4H), 5.32 (s, 2H), 4.05 (t, 2H, J = 7.5 Hz), 3.41 (t, 2H,
J = 7.5 Hz). 13C NMR (126 MHz; CDCl3):
d
198.6 (C55O), 162.7, 137.7,
133.8, 129.5, 128.2, 60.8, 54.9, 31.3. IR (KBr, cmÀ1): 3066, 2864,
1701 (C55O), 1536, 1379, 1348, 1286, 1189, 1073, 802. Anal. Calcd
for C11H10ClNO3S2: C, 43.49; H, 3.32; N, 4.61. Found: C, 43.63; H,
3.32; N, 4.67.

566
H. Loghmani-Khouzani, D. Hajiheidari / Journal of Fluorine Chemistry 131 (2010) 561–569
4.2.8. 2-(4,5-Dihydrothiazol-2-ylsulfonyl)-1-p-tolylethanone (2h)
White solid; m.p.: 117–118 8C; 1H NMR (400 MHz; CDCl3):
8.14 (d, 2H, J = 7.8 Hz), 7.27 (d, 2H, J = 7.8 Hz), 5.34 (s, 2H), 3.92 (t,
2H, J = 7.5 Hz), 3.33 (t, 2H, J = 7.5 Hz), 2.65 (s, 3H). 13C NMR
4.2.15. 2-(1H-benzo[d]imidazol-2-ylsulfonyl)-1-(4-
chlorophenyl)ethanone (2o)
d
White solid; m.p.: 157–159 8C; 1H NMR (300 MHz; DMSO):
d
12.7 (N–H, 1H), 7.76–7.36 (m, 8H), 5.51 (s, 2H). 13C NMR (126 MHz;
(126 MHz; CDCl3):
d
199.1 (C55O), 162.8, 162.0, 142.1, 128.3, 127.8,
CDCl3): d 197.5 (C55O), 139.7, 136.8, 136.6, 136.4, 132.9, 128.2,
56.1, 54.9, 36.8, 23.7. IR (KBr, cmÀ1): 3106, 2912, 1696 (C55O),
126.7, 121.4, 121.1, 113.6, 113.2, 61.2. IR (KBr, cmÀ1): 3059, 1698
1546, 1367, 1351, 1181, 1027, 954, 816. Anal. Calcd for
(C55O), 1440, 1422, 1314, 1269, 963, 734. Anal. Calcd for
C
12H13NO3S2: C, 50.86; H, 4.62; N, 4.94. Found: C, 51.03; H,
C15H11N2O3S: C, 53.82; H, 3.31; N, 8.37. Found: C, 53.79; H,
4.71; N, 4.96.
3.22; N, 8.51.
4.2.9. 2-(Benzo[d]oxazol-2-ylsulfonyl)-1-phenylethanone (2i)
White solid; m.p.: 132–133 8C; 1H NMR (400 MHz; CDCl3):
4.2.16. 2-(1H-benzo[d]imidazol-2-ylsulfonyl)-1-p-tolylethanone
(2p)
d
8.02–7.26 (m, 9H), 5.16 (s, 2H). 13C NMR (126 MHz; CDCl3):
d
199.4
White solid; m.p.: 149–151 8C; 1H NMR (300 MHz; DMSO):
d
(C55O), 150.7, 148.8, 140.8, 136.2, 132.5, 128.1, 127.8, 124.1, 122.9,
118.3, 109.7, 61.9. IR (KBr, cmÀ1): 3118, 2612, 1676 (C55O), 1589,
1483, 1539, 1380, 1342, 1329, 1293, 1199, 1012, 992. Anal. Calcd
for C15H11NO4S: C, 59.79; H, 3.68; N, 4.65. Found: C, 59.84; H, 3.75;
N, 4.62.
12.3 (N–H, 1H), 7.70–7.27 (m, 8H), 5.57 (s, 2H), 2.66 (s, 3H). 13C
NMR (126 MHz; CDCl3):
d 197.6 (C55O), 140.8, 139.1, 136.9, 136.6,
131.8, 127.0, 126.7, 121.3, 121.0, 113.2, 113.0, 61.3, 22.2. IR (KBr,
cmÀ1): 3046, 1691 (C55O), 1446, 1417, 1372, 1322, 1275, 978, 747.
Anal. Calcd for C16H14N2O3S: C, 61.13; H, 4.49; N, 8.91. Found: C,
61.85; H, 4.27; N, 8.73.
4.2.10. 2-(Benzo[d]oxazol-2-ylsulfonyl)-1-(4-
bromophenyl)ethanone (2j)
4.2.17. 1-Phenyl-2-(pyrimidin-2-ylsulfonyl)ethanone (2q)
Pale yellow solid; m.p.: 145–146 8C; 1H NMR (400 MHz; CDCl3):
White solid; m.p.: 103–104 8C; 1H NMR (300 MHz; CDCl3):
d
d
7.76–7.23 (m, 9H), 5.18 (s, 2H). 13C NMR (126 MHz; CDCl3):
d
9.01–7.47 (m, 8H), 5.41 (s, 2H). 13C NMR (126 MHz; CDCl3):
d 201.6
198.8 (C55O), 150.9, 148.9, 140.7, 135.0, 127.3, 125.8, 125.3, 124.3,
122.7, 118.3, 109.6, 60.7. IR (KBr, cmÀ1): 3084, 2993, 1688 (C55O),
1586, 1477, 1462, 1317, 1197, 1132, 992, 823, 712. Anal. Calcd for
(C55O), 165.0, 156.2, 134.8, 131.1, 126.7, 126.5, 123.9, 61.6. IR (KBr,
cmÀ1): 3120, 2611, 1680 (C55O), 1443, 1412, 1314, 1263, 969, 736.
Anal. Calcd for C12H10N2O3S: C, 54.95; H, 3.84; N, 10.68. Found: C,
55.12; H, 3.68; N, 10.47.
C
15H10BrNO4S: C, 47.38; H, 2.65; N, 3.68. Found: C, 47.54; H, 2.65;
N, 3.57.
4.2.18. 1-(4-Bromophenyl)-2-(pyrimidin-2-ylsulfonyl)ethanone (2r)
4.2.11. 2-(Benzo[d]oxazol-2-ylsulfonyl)-1-(4-chlorophenyl)ethanone
White solid; m.p.: 115–117 8C; 1H NMR (300 MHz; CDCl3):
d
(2k)
9.01–7.67 (m, 7H), 5.54 (s, 2H). 13C NMR (126 MHz; CDCl3):
d 200.8
White solid; m.p.: 143–144 8C; 1H NMR (400 MHz; CDCl3):
198.4
d
(C55O), 165.2, 156.1, 133.8, 129.6, 129.0, 125.5, 123.8, 61.6. IR (KBr,
cmÀ1): 3087, 2986, 1692 (C55O), 1433, 1407, 1301, 1259, 961, 731.
Anal. Calcd for C12H9BrN2O3S: C, 42.24; H, 2.66; N, 8.21. Found: C,
42.21; H, 2.58; N, 8.34.
7.80–7.22 (m, 9H), 5.07, (s, 2H). 13C NMR (126 MHz; CDCl3):
d
(C55O), 150.6, 148.9, 140.8, 134.3, 131.4, 130.4, 127.1, 124.2, 122.8,
118.2, 109.8, 60.7. IR (KBr, cmÀ1): 3043, 2611, 1694 (C55O), 1599,
1403, 1450, 1316, 1191, 980, 820, 724. Anal. Calcd for C15H10ClNO4S:
C, 53.66; H, 3.00; N, 4.17. Found: C, 53.48; H, 3.12; N, 4.21.
4.2.19. 1-(4-Chlorophenyl)-2-(pyrimidin-2-ylsulfonyl)ethanone (2s)
White solid; m.p.: 113–115 8C; 1H NMR (300 MHz; CDCl3):
d
4.2.12. 2-(Benzo[d]oxazol-2-ylsulfonyl)-1-p-tolylethanone (2l)
9.03–7.48 (m, 7H), 5.22 (s, 2H). 13C NMR (126 MHz; CDCl3):
d 200.6
White solid; m.p.: 136–137 8C; 1H NMR (400 MHz; CDCl3):
d
(C55O), 165.0, 156.2, 136.7, 132.9, 128.2, 126.8, 123.7, 61.5. IR (KBr,
cmÀ1): 3048, 2617, 1699 (C55O), 1442, 1425, 1312, 1270, 961, 737.
Anal. Calcd for C12H9ClN2O3S: C, 48.57; H, 3.06; N, 9.44. Found: C,
48.45; H, 3.09; N, 9.58.
7.76–7.11 (m, 8H), 5.75 (s, 2H), 2.63 (s, 3H). 13C NMR (126 MHz;
CDCl3): 199.6 (C55O), 150.5, 148.7, 141.2, 140.8, 133.0, 128.6,
d
128.1, 124.2, 122.8, 118.3, 109.7, 60.3, 23.8. IR (KBr, cmÀ1): 3078,
2720, 1687 (C55O), 1566, 1484, 1430, 1327, 1154, 977, 815, 748.
Anal. Calcd for C16H13NO4S: C, 60.94; H, 4.16; N, 4.44. Found: C,
60.85; H, 4.17; N, 4.22.
4.2.20. 2-(Pyrimidin-2-ylsulfonyl)-1-p-tolylethanone (2t)
White solid; m.p.: 106–108 8C; 1H NMR (300 MHz; CDCl3):
d
8.98–7.27 (m, 7H), 5.56 (s, 2H), 2.65 (s, 3H). 13C NMR (126 MHz;
CDCl3): 201.8 (C55O), 164.9, 156.2, 140.8, 131.7, 127.0, 126.7,
4.2.13. 2-(1H-benzo[d]imidazol-2-ylsulfonyl)-1-phenylethanone
d
(2m)
123.9, 61.6, 22.1. IR (KBr, cmÀ1): 3081, 2717, 1691 (C55O), 1449,
1421, 1362, 1320, 1267, 973, 751. Anal. Calcd for C13H12N2O3S: C,
56.51; H, 4.38; N, 10.14. Found: C, 56.37; H, 4.17; N, 10.31.
White solid; m.p.: 148–150 8C; 1H NMR (300 MHz; DMSO):
d
12.4 (N–H, 1H), 7.85–7.37 (m, 9H), 5.41 (s, 2H). 13C NMR (126 MHz;
CDCl3):
d 197.4 (C55O), 139.5, 137.9, 137.6, 134.8, 131.2, 126.8,
126.5, 121.1, 120.9, 113.0, 112.8, 61.3. IR (KBr, cmÀ1): 3038, 1682
4.3. Typical procedure for fluorination of b-ketosulfone (2b)
(C55O), 1441, 1408, 1311, 1270, 972, 741. Anal. Calcd for
C
15H12N2O3S: C, 59.99; H, 4.03; N, 9.33. Found: C, 60.14; H,
Under N2 atmosphere, Na2CO3 (2.2 mmol) was added to a 50-
mL Schlenk flask containing 2b (1 mmol), and dry acetonitrile
(20 mL) at room temperature. The reaction mixture was stirred for
2 h. SelectfluorTM (2.5 mmol) was added and the mixture was
stirred at ambient temperature overnight. The progress of the
reaction was monitored by TLC. After the completion of the
reaction, the reaction mixture was quenched by the addition of
water and was extracted with methylene chloride (3Â 20 mL). The
organic phase was separated, dried over MgSO4, filtered, and
evaporated under reduced pressure. The crude product was further
purified by silica gel column chromatography using AcOEt/
petroleum ether (3:7) as eluent to give product 3b as a white solid.
4.17; N, 9.15.
4.2.14. 2-(1H-benzo[d]imidazol-2-ylsulfonyl)-1-(4-
bromophenyl)ethanone (2n)
White solid; m.p.: 160–162 8C; 1H NMR (300 MHz; DMSO):
d
12.8 (N–H, 1H), 7.71–7.36 (m, 8H), 5.55 (s, 2H). 13C NMR (126 MHz;
CDCl3):
d 197.8 (C55O), 139.5, 137.0, 136.8 133.8, 129.5, 129.0,
125.6, 122.0, 121.2, 113.8, 113.4, 61.1. IR (KBr, cmÀ1): 3045, 1695
(C55O), 1438, 1411, 1305, 1267, 969, 739. Anal. Calcd for
C
3.04; N, 7.45.
15H11BrN2O3S: C, 47.51; H, 2.92; N, 7.39. Found: C, 47.46; H,

H. Loghmani-Khouzani, D. Hajiheidari / Journal of Fluorine Chemistry 131 (2010) 561–569
567
4.3.1. 2-(Benzo[d]thiazol-2-ylsulfonyl)-2,2-difluoro-1-
phenylethanone (3a)
NMR (126 MHz; CDCl3): d 194.7 (C55O), 162.5, 137.6, 133.8, 128.9,
128.1, 114.3 (t, J = 301.7 Hz, CF2), 53.9, 31.2. 19F NMR (470 MHz;
White solid; m.p.: 161–162 8C; 1H NMR (400 MHz; CDCl3):
d
CDCl3):
d
À99.93 (s, 2F). IR (KBr, cmÀ1): 3058, 2853, 1716 (C55O),
7.82–6.96 (m, 9H). 13C NMR (126 MHz; CDCl3):
d
184.2 (C55O),
153.7, 151.8, 135.5, 134.1, 131.0, 126.7, 126.2, 124.5, 123.2, 119.3,
118.9, 112.2 (t, J = 301.1 Hz, CF2). 19F NMR (470 MHz; CDCl3):
1555, 1393, 1347, 1269, 1202, 1183, 1081, 971, 823. Anal. Calcd for
C11H8ClF2NO3S2: C, 38.88; H, 2.37; N, 4.12. Found: C, 38.79; H,
d
2.38; N, 4.08.
À99.82 (s, 2F). IR (KBr, cmÀ1): 3078, 1695 (C55O), 1568, 1412, 1372,
1315, 1271, 1246, 982, 743. Anal. Calcd for C15H9F2NO3S2: C, 50.98;
H, 2.57; N, 3.96. Found: C, 51.93; H, 2.46; N, 4.12.
4.3.8. 2-(4,5-Dihydrothiazol-2-ylsulfonyl)-2,2-difluoro-1-p-
tolylethanone (3h)
White solid; m.p.: 112–113 8C; 1H NMR (400 MHz; CDCl3):
d
4.3.2. 2-(Benzo[d]thiazol-2-ylsulfonyl)-1-(4-bromophenyl)-2,2-
7.64–7.14 (m, 4H), 4.15 (t, 2H, J = 7.5 Hz), 3.75 (s, 3H), 3.43 (t, 2H,
J = 7.5 Hz). 13C NMR (126 MHz; CDCl3):
196.7 (C55O), 162.8, 162.1,
difluoroethanone (3b)
d
Whitesolid;m.p.:189–191 8C;1HNMR(400 MHz;CDCl3):
d
d
7.82–
184.2
141.8, 128.3, 127.7, 109.5 (t, J = 301.3 Hz, CF2), 54.1, 36.7, 23.7. 19
F
7.78 (m, 4H), 7.65–7.43 (m, 4H). 13C NMR (126 MHz; CDCl3):
NMR (470 MHz; CDCl3):
d
À100.12 (s, 2F). IR (KBr, cmÀ1): 3084,
(C55O), 153.8, 151.5, 134.9, 133.0, 129.5, 128.8, 126.2, 123.0, 122.9,
120.9, 119.8, 112.7 (t, J = 301.8 Hz, CF2). 19FNMR(470 MHz;CDCl3):
À99.73 (s, 2F). IR (KBr, cmÀ1): 3068, 1698 (C55O), 1573, 1440, 1366,
1321, 1279, 1215, 1061, 983. Anal. Calcd for C15H8BrF2NO3S2: C,
41.68; H, 1.87; N, 3.24. Found: C, 41.59; H, 1.76; N, 3.32.
2894, 1708 (C55O), 1568, 1368, 1359, 1260, 1226, 1172, 1083, 947,
802. Anal. Calcd for C12H11F2NO3S2: C, 45.13; H, 3.47; N,4.39.
Found: C, 45.12; H, 3.41; N, 4.35.
d
4.3.9. 2-(Benzo[d]oxazol-2-ylsulfonyl)-2,2-difluoro-1-
phenylethanone (3i)
4.3.3. 2-(Benzo[d]thiazol-2-ylsulfonyl)-1-(4-chlorophenyl)-2,2-
White solid; m.p.: 156–157 8C; 1H NMR (400 MHz; CDCl3):
d
difluoroethanone (3c)
7.89–7.22 (m, 9H). 13C NMR (126 MHz; CDCl3):
d 195.5 (C55O),
White solid; m.p.: 171–172 8C; 1H NMR (400 MHz; CDCl3):
d
150.8, 148.6, 141.1, 136.2, 132.1, 128.2, 127.7, 125.2 (t,
J = 301.2 Hz, CF2), 124.1, 122.0, 118.1, 109.6. 19F NMR (470 MHz;
7.82–7.78 (m, 4H), 7.70–7.27 (m, 4H). 13C NMR (126 MHz; CDCl3):
183.9 (C55O), 154.2, 151.4, 137.2, 133.0, 129.1, 128.7, 125.2,
d
CDCl3):
d
À99.41 (s, 2F). IR (KBr, cmÀ1): 3143, 2617, 1689 (C55O),
123.6, 123.1, 121.3, 120.9, 114.2 (t, J = 301.7 Hz, CF2). 19F NMR
1598, 1497, 1544, 1383, 1321, 1280, 1215, 1176, 1017, 987, 714.
Anal. Calcd for C15H9F2NO4S: C, 53.41; H, 2.69; N, 4.15. Found: C,
53.34; H, 2.74; N, 4.09.
(470 MHz; CDCl3):
d
À99.69 (s, 2F). IR (KBr, cmÀ1): 3076, 1700
(C55O), 1593, 1423, 1289, 1218, 1214, 1092, 991, 812. Anal. Calcd
for C15H8ClF2NO3S2: C, 46.46; H, 2.08; N, 3.61; Found: C, 46.52; H,
2.15; N, 3.53.
4.3.10. 2-(Benzo[d]oxazol-2-ylsulfonyl)-1-(4-bromophenyl)-2,2-
difluoroethanone (3j)
4.3.4. 2-(Benzo[d]thiazol-2-ylsulfonyl)-2,2-difluoro-1-p-
White solid; m.p.: 183–184 8C; 1H NMR (400 MHz; CDCl3):
d
tolylethanone (3d)
7.65–7.43 (m, 4H), 7.35–7.10 (m, 4H). 13C NMR (126 MHz; CDCl3):
d 194.9 (C55O), 150.9, 148.8, 140.2, 135.2, 127.0, 125.3, 124.9,
White solid; m.p.: 168–169 8C; 1H NMR (400 MHz; CDCl3):
d
7.82–7.78 (m, 4H), 7.64–7.06 (m, 4H), 2.35 (s, 3H). 13C NMR
(126 MHz; CDCl3): 183.7 (C55O), 154.1, 151.3, 141.2, 133.5, 132.7,
123.7, 122.7, 118.3, 113.8 (t, J = 301.8 Hz, CF2), 109.5. 19F NMR
d
(470 MHz; CDCl3):
(C55O), 1581, 1488, 1463, 1204, 1187, 996, 823, 746. Anal. Calcd for
d
À99.35 (s, 2F). IR (KBr, cmÀ1): 3102, 1704
128.2, 127.7, 123.9, 122.8, 122.2, 121.5, 111.6 (t, J = 301.3 Hz, CF2),
23.7. 19F NMR (470 MHz; CDCl3):
3121, 1699 (C55O), 1587, 1420, 1286, 1222, 1201, 1077, 986, 807.
Anal. Calcd for C16H11F2NO3S2: C, 52.31; H, 3.02; N, 3.81. Found: C,
52.32; H, 2.94; N, 3.75.
d
À99.97 (s, 2F). IR (KBr, cmÀ1):
C15H8BrF2NO4S: C, 43.29; H, 1.94; N, 3.37. Found: C, 43.31; H, 2.01;
N, 3.26.
4.3.11. 2-(Benzo[d]oxazol-2-ylsulfonyl)-1-(4-chlorophenyl)-2,2-
difluoroethanone (3k)
4.3.5. 2-(4,5-Dihydrothiazol-2-ylsulfonyl)-2,2-difluoro-1-
White solid; m.p.: 152–153 8C; 1H NMR (400 MHz; CDCl3):
d
phenylethanone (3e)
7.70–7.12 (m, 8H). 13C NMR (126 MHz; CDCl3):
d
194.4 (C55O),
150.5, 148.9, 140.6, 134.3, 131.3, 130.4, 127.0, 124.4, 124.0 (t,
J = 301.7 Hz, CF2) 121.9, 118.2, 109.5. 19F NMR (470 MHz; CDCl3):
White solid; m.p.: 93–94 8C; 1H NMR (400 MHz; CDCl3):
d
7.76–
7.48 (m, 4H), 4.15 (t, 2H, J = 7.5 Hz), 3.43 (t, 2H, J = 7.5 Hz). 13C NMR
(126 MHz; CDCl3): 185.2 (C55O), 162.2, 135.4, 132.2, 127.5, 127.1,
114.0 (t, J = 301.2 Hz, CF2), 53.9, 31.3. 19F NMR (470 MHz; CDCl3):
d
d
À99.28 (s, 2F). IR (KBr, cmÀ1): 3089, 2627, 1706 (C55O), 1581, 1473,
1458, 1214, 1159, 979, 812, 713. Anal. Calcd for C15H8ClF2NO4S: C,
48.46; H, 2.17; N, 3.77. Found: C, 48.46; H, 2.12; N, 3.68.
d
À100.02 (s, 2F). IR (KBr, cmÀ1): 3113, 2901, 1687 (C55O), 1551,
1273, 1186, 1160, 964, 770. Anal. Calcd for C11H9F2NO3S2: C, 43.27;
H, 2.97; N, 4.59. Found: C, 43.31; H, 2.97; N, 4.47.
4.3.12. 2-(Benzo[d]oxazol-2-ylsulfonyl)-2,2-difluoro-1-p-
tolylethanone (3l)
4.3.6. 2-(4,5-Dihydrothiazol-2-ylsulfonyl)-1-(4-bromophenyl)-2,2-
White solid; m.p.: 157–158 8C; 1H NMR (400 MHz; CDCl3):
d
difluoroethanone (3f)
7.64–7.14 (m, 4H), 7.35–7.10 (m, 4H), 2.35 (s, 3H). 13C NMR
(126 MHz; CDCl3): 193.5 (C55O), 150.4, 148.7, 140.8, 140.7, 133.2,
White solid; m.p.: 159–160 8C; 1H NMR (400 MHz; CDCl3):
7.65–7.43 (m, 4H), 4.15 (t, 2H, J = 7.5 Hz), 3.43 (t, 2H, J = 7.5 Hz). 13
d
C
d
129.4 (t, J = 301.3 Hz, CF2), 128.5, 124.2, 122.8, 118.1, 109.7, 23.7.
NMR (126 MHz; CDCl3):
d
195.4 (C55O), 162.2, 134.4, 130.8, 129.5,
19F NMR (470 MHz; CDCl3):
2703, 1711 (C55O), 1571, 1493, 1437, 1217, 1163, 982, 827, 718.
Anal. Calcd for C16H11F2NO4S: C, 54.70; H, 3.16; N, 3.99. Found: C,
54.57; H, 3.05; N, 3.87.
d
À99.48 (s, 2F). IR (KBr, cmÀ1): 3098,
126.8, 94.3 (t, J = 301.8 Hz, CF2) 53.7, 31.3. 19F NMR (470 MHz;
CDCl3):
d
À99.98 (s, 2F). IR (KBr, cmÀ1): 3102, 2921, 1712 (C55O),
1563, 1271, 1193, 1158, 983, 727. Anal. Calcd for C11H8BrF2NO3S2:
C, 34.39; H, 2.10; N, 3.65. Found: C, 34.28; H, 2.08; N, 3.69.
4.3.13. 2-(1H-benzo[d]imidazol-2-ylsulfonyl)-2,2-difluoro-1-
4.3.7. 2-(4,5-Dihydrothiazol-2-ylsulfonyl)-1-(4-chlorophenyl)-2,2-
phenylethanone (3m)
difluoroethanone (3g)
White solid; m.p.: 128–130 8C; 1H NMR (300 MHz; DMSO):
d
White solid; m.p.: 147–148 8C; 1H NMR (400 MHz; CDCl3):
7.60–7.28 (m, 4H), 4.15 (t, 2H, J = 7.5 Hz), 3.43 (t, 2H, J = 7.5 Hz). 13
d
C
12.9 (N–H, 1H), 7.82–7.37 (m, 9H). 13C NMR (126 MHz; CDCl3):
d
192.5 (C55O), 139.5, 137.0, 136.8, 134.8, 131.2, 126.8, 126.5, 121.2

568
H. Loghmani-Khouzani, D. Hajiheidari / Journal of Fluorine Chemistry 131 (2010) 561–569
(t, J = 301.3 Hz, CF2), 121.0, 120.8, 113.6, 113.0. 19F NMR (470 MHz;
4.3.20. 2,2-Difluoro-2-(pyrimidin-2-ylsulfonyl)-1-p-tolylethanone
(3t)
CDCl3):
d
À99.45 (s, 2F). IR (KBr, cmÀ1): 3051, 1675 (C55O), 1463,
1427, 1320, 1281, 972, 746. Anal. Calcd for C15H10F2N2O3S: C,
53.57; H, 3.00; N, 8.33. Found: C, 53.22; H, 3.17; N, 8.14.
White solid; m.p.: 127–128 8C; 1H NMR (300 MHz; CDCl3):
d
8.96–7.38 (m, 7H), 2.67 (s, 3H). 13C NMR (126 MHz; CDCl3):
d
194.8
(C55O), 165.2, 156.3, 140.8, 131.8, 127.6 (t, J = 301.1 Hz, CF2), 127.0,
126.7, 123.8, 22.5. 19F NMR (470 MHz; CDCl3):
4.3.14. 2-(1H-benzo[d]imidazol-2-ylsulfonyl)-1-(4-bromophenyl)-
d
À99.51 (s, 2F). IR
2,2-difluoroethanone (3n)
(KBr, cmÀ1): 3103, 1715 (C55O), 1466, 1420, 1361, 1327, 1272, 961,
735. Anal. Calcd for C13H10F2N2O3S: C, 50.00; H, 3.23; N, 8.97.
Found: C, 50.21; H, 3.17; N, 8.86.
White solid; m.p.: 155–157 8C; 1H NMR (300 MHz; DMSO):
d
d
13.2 (N–H, 1H), 7.76–7.36 (m, 8H). 13C NMR (126 MHz; CDCl3):
189.8 (C55O), 139.8, 136.8, 136.6, 133.6, 129.4, 129.0, 125.5, 121.2,
120.9, 113.3, 113.0, 109.7 (t, J = 302.4 Hz, CF2). 19F NMR (470 MHz;
4.4. Typical procedure for the synthesis of difluoromethyl sulfone (4b)
CDCl3):
d
À99.41 (s, 2F). IR (KBr, cmÀ1): 3064, 1689 (C55O), 1458,
1420, 1315, 1277, 964, 735. Anal. Calcd for C15H9BrF2N2O3S: C,
43.39; H, 2.18; N, 6.75. Found: C, 43.35; H, 2.12; N, 6.68.
To a solution of 10% aqueous NaOH (5 mL) was added the
difluoromethyl sulfone 3b (1 mmol) at room temperature and the
mixture was stirred for 30 min. After completion of the reaction as
monitored by TLC, the reaction mixture was extracted with diethyl
ether after the addition of water. The organic extract was dried
over anhydrous MgSO4 and evaporated to give the crude product,
which was purified by chromatography on silica gel (hexane/ethyl
acetate = 8:2) to afford the heterocyclic difluoromethyl sulfone 4b
as a white solid.
4.3.15. 2-(1H-benzo[d]imidazol-2-ylsulfonyl)-1-(4-chlorophenyl)-
2,2-difluoroethanone (3o)
White solid; m.p.: 126–128 8C; 1H NMR (300 MHz; DMSO):
d
d
13.2 (N–H, 1H), 7.71–7.35 (m, 8H). 13C NMR (126 MHz; CDCl3):
191.5 (C55O), 139.2, 137.0, 136.8, 136.6, 132.9, 128.2, 126.8,
121.5, 121.2, 120.1 (t, J = 303.1 Hz, CF2), 113.3, 113.0. 19F NMR
(470 MHz; CDCl3):
(C55O), 1455, 1441, 1323, 1270, 958, 728. Anal. Calcd for
d
À99.32 (s, 2F). IR (KBr, cmÀ1): 3077, 1691
4.4.1. 2-(Difluoromethylsulfonyl)benzo[d]thiazol (4b)
C
15H9ClF2N2O3S: C, 48.59; H, 2.45; N, 7.56. Found: C, 48.33; H,
White solid; m.p.: 149 8C; 1H NMR (400 MHz; CDCl3):
d
8.4–7.7
2
2.54; N, 7.50.
(m, 4H), 6.61 (t, 1H JH–F = 53.2 Hz, –CF2H). 13C NMR (126 MHz;
CDCl3):
d 158.7, 152.9, 137.9, 129.1, 128.3, 126.3, 122.4, 114.4 (t,
4.3.16. 2-(1H-benzo[d]imidazol-2-ylsulfonyl)-2,2-difluoro-1-p-
tolylethanone (3p)
J = 286 Hz, –CF2H). 19F NMR (470 MHz; CDCl3):
d
À121.8 (d, 2F 2JH–
F = 52.9 Hz). IR (KBr, cmÀ1): 3050, 2611, 1678, 1568, 1410, 1290,
1255, 1043, 885, 738, 708. Anal. Calcd for C8H5F2NO2S2: C, 38.55; H,
2.02; N, 5.62. Found: C, 38.46; H, 2.14; N, 5.48.
White solid; m.p.: 131–132 8C; 1H NMR (300 MHz; DMSO):
d
12.7 (N–H, 1H), 7.70–7.36 (m, 8H), 2.37 (s, 3H). 13C NMR (126 MHz;
CDCl3):
d 190.4 (C55O), 140.8, 139.5, 136.9, 136.7, 131.8, 127.0,
126.7, 125.5 (t, J = 302.1 Hz, CF2), 113.3, 113.1, 121.4, 121.0, 22.3.
4.4.2. 2-(Difluoromethylsulfonyl)-4,5-dihydrothiazol (4f)
19F NMR (470 MHz; CDCl3):
d
À99.54 (s, 2F). IR (KBr, cmÀ1): 3065,
White solid; m.p.: 131 8C; 1H NMR (400 MHz; CDCl3):
d
6.60 (t,
2
1686 (C55O), 1465, 1429, 1375, 1332, 1270, 979, 740. Anal. Calcd
for C16H12F2N2O3S: C, 54.85; H, 3.45; N, 8.00. Found: C, 54.78; H,
3.51; N, 8.12.
1H JH–F = 53.2 Hz, –CF2H), 4.41 (t, 2H, J = 7.5 Hz), 3.42 (t, 2H,
J = 7.5 Hz). 13C NMR (126 MHz; CDCl3):
–CF2H), 54.1, 31.7. 19F NMR (470 MHz; CDCl3):
F = 51.2 Hz). IR (KBr, cmÀ1): 2856, 1687, 1562, 1412, 1383, 1274,
1056, 879, 740, 702. Anal. Calcd for C4H5F2NO2S2: C, 23.88; H, 2.50;
N, 6.96. Found: C, 23.74; H, 2.57; N, 6.87.
d 165.8, 113.3 (t, J = 284 Hz,
d
À122.6 (d, 2F 2JH–
4.3.17. 2,2-Difluoro-1-phenyl-2-(pyrimidin-2-ylsulfonyl)ethanone
(3q)
White solid; m.p.: 126–128 8C; 1H NMR (300 MHz; CDCl3):
d
9.02–7.56 (m, 8H). 13C NMR (126 MHz; CDCl3):
165.0, 156.2, 134.8, 131.3, 126.7, 126.3, 123.9, 122.3 (t,
J = 301.4 Hz, CF2). 19F NMR (470 MHz; CDCl3):
IR (KBr, cmÀ1): 3145, 1693 (C55O) 1465, 1432, 1327, 1277, 969,
751. Anal. Calcd for C12H8F2N2O3S: C, 48.32; H, 2.70; N, 9.39.
Found: C, 48.49; H, 2.63; N, 9.43.
d
196.7 (C55O),
4.4.3. 2-(Difluoromethylsulfonyl)benzo[d]oxazole (4j)
White solid; m.p.: 155 8C; 1H NMR (400 MHz; CDCl3):
d
8.7–7.6
2
d
À99.43 (s, 2F).
(m, 4H), 6.63 (t, 1H JH–F = 53.2 Hz, –CF2H). 13C NMR (126 MHz;
CDCl3):
d 158.8, 153.0, 137.8, 129.1, 128.2, 126.2, 122.4, 114.5 (t,
J = 286 Hz, –CF2H). 19F NMR (470 MHz; CDCl3):
d
À149.2 (d, 2F 2JH–
F = 24.2 Hz). IR (KBr, cmÀ1): 3045, 2625, 1680, 1567, 1409, 1296,
1255, 1062, 880, 746, 707. Anal. Calcd for C8H5F2NO3S: C, 41.20; H,
2.16; N, 6.01. Found: C, 41.12; H, 2.23; N, 6.18.
4.3.18. 1-(4-Bromophenyl)-2,2-difluoro-2-(pyrimidin-2-
ylsulfonyl)ethanone (3r)
White solid; m.p.: 153–154 8C; 1H NMR (300 MHz; CDCl3):
d
4.4.4. 2-(Difluoromethylsulfonyl)-1H-benzo[d]imidazole (4n)
White solid; m.p.: 218 8C; 1H NMR (300 MHz; DMSO): 13.2 (N–
H, 1H), 8.7–8.26 (m, 4H), 6.68 (t, 1H 2JH–F = 51.2 Hz, –CF2). 13C NMR
9.01–7.69 (m, 7H). 13C NMR (126 MHz; CDCl3):
165.8, 156.0, 133.8, 129.4, 129.1, 125.5, 123.7, 110.4 (t,
J = 301.7 Hz, CF2). 19F NMR (470 MHz; CDCl3):
d 196.1 (C55O),
d
À99.38 (s, 2F).
(126 MHz; CDCl3): d 145.5, 142.9, 142.2, 127.3, 127.1, 119.5, 119.3,
IR (KBr, cmÀ1): 3107, 1708 (C55O), 1460, 1423, 1317, 1281, 960,
736. Anal. Calcd for C12H7BrF2N2O3S: C, 38.21; H, 1.87; N, 7.43.
Found: C, 38.02; H, 1.80; N, 7.27.
114.23 (t, J = 281 Hz, –CF2H). 19F NMR (470 MHz; CDCl3):
d
À134.3
(d, 2F JH–F = 23.8 Hz). IR (KBr, cmÀ1): 3058, 1456, 1423, 1319,
1274, 970, 743. Anal. Calcd for C8H6F2N2O2S: C, 41.38; H, 2.60; N,
12.06. Found: C, 41.29; H, 2.71; N, 12.01.
2
4.3.19. 1-(4-Chlorophenyl)-2,2-difluoro-2-(pyrimidin-2-
ylsulfonyl)ethanone (3s)
4.4.5. 2-(Difluoromethylsulfonyl)pyrimidine (4r)
White solid; m.p.: 122–124 8C; 1H NMR (300 MHz; CDCl3):
d
White solid; m.p.: 142 8C; 1H NMR (300 MHz; CDCl3): 9.98–8.72
9.07–7.74 (m, 7H). 13C NMR (126 MHz; CDCl3):
165.0, 156.2, 136.7, 132.9, 128.2, 126.8, 123.9, 122.3 (t,
J = 301.5 Hz, CF2). 19F NMR (470 MHz; CDCl3):
IR (KBr, cmÀ1): 3095, 1710 (C55O), 1459, 1440, 1320, 1271, 953,
723. Anal. Calcd for C12H7ClF2N2O3S: C, 43.32; H, 2.12; N, 8.42.
Found: C, 43.28; H, 2.14; N, 8.53.
d
196.5 (C55O),
(m, 3H), 6.71 (t, 1H JH–F = 52.4 Hz, –CF2H). 13C NMR (126 MHz;
2
CDCl3):
(470 MHz; CDCl3):
3138, 1460, 1428, 1329, 1267, 963, 750. Anal. Calcd for
C5H4F2N2O2S: C, 30.93; H, 2.08; N, 14.43. Found: C, 30.74; H,
2.21; N, 14.36.
d
171.5, 162.1, 129.8, 114.03 (t, J = 278 Hz, –CF2H). 19F NMR
d
À99.30 (s, 2F).
d
À131.4 (d, 2F 2JH–F = 24.1 Hz). IR (KBr, cmÀ1):

H. Loghmani-Khouzani, D. Hajiheidari / Journal of Fluorine Chemistry 131 (2010) 561–569
569
(2005) 529–534;
Acknowledgments
(d) M.F. Greaney, W.B. Motherwell, Tetrahedron Lett. 41 (2000) 4467–4470;
(e) S. Gouault, C. Gue´rin, L. Lemoucheux, T. Lequeux, J.C. Pommelet, Tetrahedron
Lett. 44 (2003) 5061–5064;
The authors wish to thank the University of Isfahan Research
Council and the Office of Graduate Studies of the University of
Isfahan for financial support of this work.
(f) A. Konno, T. Fuchigami, J. Org. Chem. 62 (1997) 8579–8581.
[14] (a) R.C. Terrell, T. Ucciardi, J.F. Vitcha, J. Org. Chem. 30 (1965) 4011–4013;
(b) A. Hagooly, I. Ben-David, S. Rozen, J. Org. Chem. 67 (2002) 8430–8434;
(c) C. Jouen, J.C. Pommelet, Tetrahedron 53 (1997) 12565–12574;
(d) T. Fuchigami, M. Shimojo, A. Konno, J. Org. Chem. 60 (1995) 3459–3464;
(e) S. Ayuba, N. Yoneda, T. Fukuhara, S. Hara, Bull. Chem. Soc. Jpn. 75 (2002)
1597–1603.
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