Difluorocarbene chemistry: Synthesis of gem-difluorocyclopropenylalkynes and 3,3,3′,3′-tetrafluorobicyclopropyl-1,1′-dienes

Article abstract of DOI:10.1016/j.jfluchem.2004.10.012

A series of gem-difluorocyclopropenylalkynes are easily obtained in good yields by the Sonogashira reaction of 3,3-difluoro-1-iodocyclopropenes with terminal alkynes. Onto these new alkynes addition of difluorocarbene, generated from the decomposition of

Full text of DOI:10.1016/j.jfluchem.2004.10.012

Journal of Fluorine Chemistry 126 (2005) 93–97
www.elsevier.com/locate/fluor
Difluorocarbene chemistry: synthesis of gem-difluorocyclopropenylalk-
ynes and 3,3,30,30-tetrafluorobicyclopropyl-1,10-dienes
*
Zhan-Ling Cheng, Qing-Yun Chen
Key Laboratory of Organofluorine Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences,
354 Fenglin Lu, 200032 Shanghai, China
Received 12 August 2004; accepted 26 October 2004
Available online 2 December 2004
Abstract
A series of gem-difluorocyclopropenylalkynes are easily obtained in good yields by the Sonogashira reaction of 3,3-difluoro-1-
iodocyclopropenes with terminal alkynes. Onto these new alkynes addition of difluorocarbene, generated from the decomposition of
FSO2CF2COOTMS in diglyme in the presence of 10 mol% anhydrous NaF at 120 8C, gives 3,3,30,30-tetrafluorobicyclopropyl-1,10-dienes.
Acid hydrolysis of gem-difluorocyclopropenylalkynes in refluxing CH3OH affords the corresponding methoxycarbonylenynes.
# 2004 Elsevier B.V. All rights reserved.
Keywords: 3,3-Difluoro-1-iodocyclopropenes; Sonogashira reaction; 3,3,30,30-Tetrafluorobicyclopropyl-1,10-dienes; Difluorocarbene
1. Introduction
phenylacetylene, turns black quickly and loses fluorine on
standing when exposed to air at room temperature [7].
However, this situation has been improved to a great
extent when an iodine atom was introduced into the
difluorocyclopropene [7]. Thus, 3,3-difluoro-1-iodocyclo-
propenes (1), readily prepared by the reaction of trimethyl-
The insertion difluorocarbene into hydrogen–oxygen,
hydrogen–sulfur, hydrogen–nitrogen, carbon–carbon dou-
ble, and carbon–carbon triple bonds is one of the most
convenient methods for synthesizing of organic fluoride
compounds [1]. Among them gem-difluorocyclopropanes
formed by addition of difluorocarbene to carbon–carbon
bonds are versatile intermediates, from which a quite variety
of difluoromethylene substituted compounds are prepared
either by anionic or by radical ring opening [2]. As
compared with this, the chemistry difluorocyclopropenes
has been much less investigated, probably due to their
synthetic difficulties [3]. The difficulties come not only from
preparing difluorocarbene precursors, harsh reaction con-
ditions (e.g. (CH3)3SnCF3/150 8C [4]; (CF3)3PF2/100 8C
[5]; ClCF2CO2Na/160 8C [6]; (C6H5)3P+CF2BrBr-/KF/18-
crown-6/25 8C [3]) but also from unstability of the initiated
products. For example, 3,3-difluorophenylcyclopropene-1,
readily obtained through addition of difluorocarbene to
silylfluorosulfonyldifluoroacetate
(FSO2CF2CO2SiMe3,
TFDA), with iodoalkynes, are rather stable: they can be
stored at room temperature without decomposition for
several hours and much longer in a solvent in refrigerator
[7]. Utilizing just their comparable stability, these iodides
have been trifluoromethylated and functionalized with a,b-
unsaturated carbonyl compounds via Heck reaction. In order
to expand the application of the iodides in difluorocarbene
chemistry, their Sonogashira reaction were carried out. We
present, herein, the results.
2. Results and discussion
2.1. Sonogashira reaction of 1 with alkynes
* Corresponding author. Tel.: +86 2154925196; fax: +86 64166128.
E-mail addresses: chenqy@mail.sioc.ac.cn, chenqy@mail.sioc.ac.cn
(Q.-Y. Chen).
In order to find suitable reaction conditions using 1a and
2a as an example, various factors, such as catalyst, solvent,
0022-1139/$ – see front matter # 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2004.10.012

94
Z.-L. Cheng, Q.-Y. Chen / Journal of Fluorine Chemistry 126 (2005) 93–97
Table 2
Sonogashira reaction of 1 with alkynesa
Entry
1
2
3
Yield (%)b
1
2
1a
1a
1a
1a
1b
1b
1c
1c
1d
1e
1f
2a
2b
2c
2d
2a
2d
2a
2d
2a
2a
2a
3aa
3ab
3ac
3ad
3ba
3bd
3ca
3cd
3da
3ea
3fa
70
67
40
58
90
67
74
85
60
40
33
3
4
5
6
7
8
9
10
11
a
1:2:Ag2CO3:PdCl2(PPh3)2:CuI = 1:1.2:1.5:0.05:0.1.
Isolated yield.
Scheme 1.
b
and temperature were investigated [8] (Scheme 1). It was
found that treatment of 1a with 2a (1.2 equiv.) in benzene,
dioxane or THF in the presence of PdCl2(PPh3)2, CuI, amine
at room temperature or 50 8C gave the cross-coupling
product 3aa in poor yield. But when Ag2CO3 was used
instead of amine, the yield could be improved significantly
(entry 14 in Table 1). The results are listed in Table 1.
Based on the reaction conditions, a series of 3,3-
difluorocyclopropenylalkynes (3) were synthesized (Table 2).
The results in Table 2 shows that when R1 in 1 or R2 in 2 is
alkyl or phenyl with electron-donating group such as 4-
OMe, 4-Me, the yields of 3 were lower than those substrates
with an electron-withdrawing substituted phenyl group
(such as 4-Br, 4-NO2). (Table 2, entries 11, 10, 9 versus 5, 7,
8 and entries 3, 4 versus 1, 2).
Scheme 2.
gave dienes 4 from moderate to good yields (Scheme 2). The
results are listed in Table 3.
Notably, when R1 = 4-NO2C6H4, R2 = Ph, the addition
reaction of difluorocarbene did not occur under the similar
conditions, probably due to large reduction of electron
density on the carbon–carbon triple bond through conjuga-
tion effect by the strong electron-withdrawing 4-NO2C6H4
group.
2.2. Synthesis of 3,3,30,30-tetrafluorobicyclopropyl-1,
10-dienes (4)
Treatment of conjugated enynes 3 with TFDA in diglyme
in the presence of 10 mol% anhydrous NaF at 120 8C for 2 h
2.3. Acid hydrolysis of 3
Because the unexpected results were observed for the
hydrolysis of 1 in air or with acid [7], we were interested in
investigating the behavior of 3 under similar conditions. It
was found that 3 was inert toward 2N aqueous HCl in MeOH
at room temperature, but converted to methoxycarbonyle-
nynes (5) in moderate yields at refluxing temperature
(Scheme 3). The results are listed in Table 4.
Table 1
The reaction of 1a and 2a under various conditions
Entry Solvent Catalysta Base
Temperature (8C)b Yield (%)c
1
2
Benzene
Benzene
Benzene
Benzene
Dioxane
Dioxane
THF
A
A
A
A
A
B
A
A
B
A
A
A
A
A
A
TEA
Piperidine r.t.
TEA 50
Piperidine 50
r.t.
16
0
3
8
4
0
1
The structures of 5 were determined by H, 19F NMR,
5
TEA
r.t.
r.t.
r.t.
r.t.
r.t.
27
0
6
TEA
MS, elementary analysis as well as X-ray analysis for 5ab1
(Fig. 1).
7
TEA
iPr2NH
iPr2NH
20
44
0
8
THF
The formation of 5 may be rationalized as followed:
proton attack on the carbon–carbon double bond of 3, gives
carbionium intermediate, followed by the simultaneous
collapse of the cyclopropyl ring and hydrolysis of the
resultant difluoromethylcarbonium (Scheme 4).
In conclusion, we have developed a simple method for the
synthesis of conjugated enynes containing a gem-difluor-
9
THF
10
11
12
13
14
15
THF
Piperidine r.t.
0
THF
iPr2NH
iPr2NH
iPr2NH
Ag2CO3
r.t.
50
50
r.t.
49
0
THF
Dioxane
THF
0
70
0
THF
Piperidine r.t.
a
b
c
A = PdCl2(PPh3)2: 5%, CuI: 10%. B = PdCl2(PhCN)2: 5%, CuI: 10%.
Oil bath temperature.
Isolated yield.
1
CCDC reference number 244669.

Z.-L. Cheng, Q.-Y. Chen / Journal of Fluorine Chemistry 126 (2005) 93–97
95
Table 3
Addition of difluorocarbene to 3a
Entry
3
4
Conversion
(%)
Yield
(%)b
R1
R2
1
2
3
4
5
6
7
a
Ph(a)
Ph(a)
4aa
4ba
4ca
4da
4fa
77
50
0
80
70
0
4-BrC6H4(b)
4-NO2C6H4(c)
4-MeC6H4(d)
nC5H11(f)
Ph(a)
Ph(a)
Ph(a)
Ph(a)
75
72
55
80
85
50
80
50
Ph(a)
4-BrC6H4(b)
nC5H11(d)
4ba
4fa
Ph(a)
The mole ratio 3:NaF:TFDA = 1:0.1:3.
Isolated yield based on compound 3.
b
Scheme 4.
ocyclopropenyl group. Addition of difluorocarbene to these
enynes gives unique conjugated dienes.
Scheme 3.
3. Experimental
1H NMR spectra were recorded on a Bruker AM-300
(300 MHz) spectrometer with TMS as an internal standard
(negative for upfield). 19F NMR spectra were recorded on a
Bruker AM-300 (282 MHz) using CFCl3 as an external
standard (positive for upfield). The solvent for NMR
measurement was CDCl3 or CD3COCD3. Diglyme, THF
was dried over sodium, FSO2CF2COOSiMe3(TFDA) was
prepared according to literature [9]. Phenylacetylene, 1-
octyne are commercially available, whereas all other
alkynes used were prepared following published procedures
[10,11].
Table 4
Acid hydrolysis of 3 with 2N HCl in MeOHa
Entry
3
5
Yield (%)b
R1
R2
1
2
3
4
5
a
Ph(a)
Ph(a)
5aa
5ab
5ba
5bd
5ca
70
74
66
64
32
Ph(a)
4-BrC6H4(b)
4-BrC6H4(b)
4-BrC6H4(b)
4-NO2C6H4(c)
Ph(a)
nC5H11(d)
Ph(a)
At refluxing temperature.
b
Isolated yield.
˚
Fig. 1. X-ray analysis of 5ab. Selected bond length (A), bond angle (8), and torsion angle (8): C(10)–C(11), 1.513(5); C(10)–C(13), 1.486(5); C(9)–C(10),
1.313(5); C(8)–C(9), 1.428(5); C(7)–C(8), 1.181(5); C(6)–C(7), 1.435(5); C(9)–C(10)–C(11), 116.2(3); C(7)–C(8)–C(9), 177.7(4); C(8)–C(7)–C(6), 174.2(4);
C(5)–C(6)–C(7), 119.7(3); C(4)–C(5)–C(6)–C(7), 179.0(4); C(5)–C(6)–C(7)–C(8), ꢀ19(4); C(1)–C(6)–C(7)–C(8), 160(4); C(6)–C(7)–C(8)–C(9), ꢀ43(13);
C(7)–C(8)–C(9)–C(10), 66(11); C(8)–C(9)–C(10)–C(13), 0.9(6); C(8)–C(9)–C(10)–C(11), ꢀ178.9(3); C(9)–C(10)–C(13)–C(18), 131.5(4); C(11)–C(10)–
C(13)–C(18), ꢀ48.7(4).

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Z.-L. Cheng, Q.-Y. Chen / Journal of Fluorine Chemistry 126 (2005) 93–97
3.1. Typical procedure for Sonogashira coupling reaction
3ca: Solid, IR (film) (cmꢀ1) 2201, 1762, 1598, 1521,
1
1442, 1344, 1272. H NMR (CDCl3) d 8.36–8.40 (m, 2H),
Under nitrogen atmosphere, in a 10 ml side-armed Pyrex
tube with a magnetic stirring bar was placed 1-iodo-3,3-
difluorocyclopropene (1a) (278 mg, 1 mmol), phenylacety-
lene (0.13 ml, 1.2 equiv.), Ag2CO3 (414 mg, 1.5 equiv.) and
THF (5 ml). After frozened by dry ice–ethanol bath,
PdCl2(PPh3)2 (35 mg, 5 mol%) and CuI (19 mg,
10 mol%) were added. The mixture was degassed and
slowly warmed to room temperature and stirred for 8 h. The
reaction mixture was filtered and solvent was removed under
reduced pressure. The residue was purified by flash
chromatography on a silica gel column to give the cross-
coupling compound (3aa) (177 mg, yield 70%).
7.88–7.92 (m, 2H), 7.60–7.66 (m, 2H), 7.40–7.49 (m, 3H).
19F NMR (CDCl3) d ꢀ107.10 (s, 2F). MS m/z (relative
intensity) 297 (M+, 100), 251 (96.95), 247 (25.90), 200
(99.48), 100 (17.46). Anal. Calcd. for C17H9F2NO2: C,
68.69, H, 3.05, N, 4.71, F, 12.07. Found: C, 68.66, H, 3.06,
N, 4.54, F, 12.78. mp 140–142 8C.
3cd: Solid, IR (film) (cmꢀ1) 2959, 2935, 2864, 2228,
1
1768, 1602, 1526, 1467, 1426. H NMR (CDCl3) d 8.33–
8.37 (m, 2H), 7.80–7.84 (m, 2H), 2.57 (t, J = 7.5 Hz, 2H),
1.66–1.71 (m, 2H), 1.37–1.48 (m, 4H), 0.95 (t, J = 6.9 Hz,
3H). 19F NMR (CDCl3) d ꢀ107.24 (s, 2F). MS m/z (relative
intensity) 276 (M+ ꢀ 15, 4.45), 235 (100), 201 (52.80), 188
(63.39), 82 (58.07). Anal. Calcd. for C16H15F2NO2: C,
65.97, H,5.19, N, 4.81, F, 13.04. Found: C, 65.96, H, 5.20, N,
4.43, F, 12.91.
3da: Solid, 1H NMR (CDCl3) d 7.65–7.59 (m, 4H), 7.45–
7.41 (m, 3H), 7.30–7.34 (m, 2H), 2.45 (s, 3H). 19F NMR
(CDCl3) d ꢀ106.72 (s, 2F). MS m/z (relative intensity) 266
(M+, 100), 251 (M+ ꢀ 15, 92.65). Anal. Calcd. for C18H12F2:
C, 81.19, H, 4.54, F, 14.27. Found: C, 81.20, H, 4.41, F,
13.79.
3aa: Solid, 1H NMR (CDCl3) d 7.73–7.77 (m, 2H), 7.60–
7.63 (m, 2H), 7.51–7.54 (m, 3H), 7.40–7.47 (m, 3H). 19F
NMR (CDCl3)d ꢀ107.04 (s, 2F). MS m/z (relative intensity)
252 (M+, 100), 251 (M+ ꢀ 1, 93.75), 233 (22.64), 202
(61.19), 175 (6.38), 150 (6.47), 101 (2.15). Anal. Calcd. for
C17H10F2: C, 80.94, H, 4.00, F, 15.06. Found: C, 80.63, H,
4.24, F, 15.23.
3ab: Solid, IR (film) (cmꢀ1) 2203, 1763, 1597, 1583,
1
1494, 1482, 1465, 1449, 1270. H NMR (CDCl3) d 7.72–
7.77 (m, 2H), 7.45–7.58 (m, 7H). 19F NMR (CDCl3) d
ꢀ106.92 (s, 2F). MS m/z (relative intensity) 332 (M+ + 2,
4.41), 330 (M+, 4.68), 251 (48.88), 200 (100), 174 (29.14),
100 (34.19). Anal. Calcd. for C17H9BrF2: C, 61.66, H, 2.74,
F, 11.47. Found: C, 61.58, H, 3.00, F, 11.40. mp100–102 8C.
3ac: Solid, 1H NMR (CDCl3, 300 MHz) d 7.71–7.75 (m,
3ea: Solid, 1H NMR (CDCl3) d 7.71–7.41 (m, 7H), 7.04–
7.01 (m, 2H), 3.90 (s, 3H). 19F NMR (CDCl3) d ꢀ106.99 (s,
2F). MS m/z (relative intensity) 282 (M+, 100), 267
(M+ ꢀ 15, 39.98), 251 (M+ ꢀ 31, 23.42), 238 (66.45), 189
(71.30). HRMS Calcd. for C18H12F2O: 282.0856. Found:
282.0831.
3fa: Liquid, 1H NMR (CDCl3) d 7.60–7.36 (m, 5H), 2.61
(m, 2H), 1.72 (t, J = 7.2 Hz, 2H), 1.48–1.38 (m, 4H), 0.96 (t,
J = 7.2 Hz, 3H). 19F NMR (CDCl3) d ꢀ102.63 (s, 2F). MS
m/z (relative intensity) 246 (M+, 7.50), 231 (M+ ꢀ 15,
20.92), 203 (64.13), 139 (100). HRMS Calcd. for C16H16F2:
246.1220. Found: 246.1205.
2H), 7.48-7.53 (m, 5H), 7.21–7.24 (m, 2H), 2.41 (s, 3H). 19
F
NMR (CDCl3) d ꢀ107.36 (s, 2F). MS m/z (relative intensity)
266 (M+, 100), 251 (M+ ꢀ 15, 85.95). Anal. Calcd. for
C18H12F2: C, 81.19, H, 4.54, F, 14.27. Found: C, 81.23, H,
4.46, F, 14.15.
3ad: Liquid, IR (film) (cmꢀ1) 2960, 2935, 2231, 1772,
1494, 1467, 1451, 1268. 1H NMR (CDCl3) d 7.65–7.70 (m,
2H), 7.47–7.50 (m, 3H), 2.54 (t, J = 7.2 Hz, 2H), 1.64–1.70
(m, 2H), 1.37–1.49 (m, 4H), 0.95 (t, J = 6.9 Hz, 3H). 19F
NMR (CDCl3) d ꢀ107.25 (s, 2F). MS m/z (relative intensity)
246 (M+, 12.56), 190 (100), 183 (70.29), 164 (61.78), 139
(56.44). HRMS for C16H16F2: 246.1220. Found: 246.1220.
3ba: Solid, IR (film) (cmꢀ1) 2202, 1767, 1584, 1494,
3.2. Difluorocarbene addition to 3
Under nitrogen atmosphere in a Schlenk tube with a
stirring bar was placed 3aa (150 mg, 0.6 smmol), NaF
(2.5 mg, 0.06 mmol), and DG (1 ml). At the temperature of
120 8C TFDA (450 mg, 1.8 mmol) was added dropwise via a
syringe. The mixture was stirred for 2 h at this temperature.
Then the mixture was cooled to room temperature and
directly purified by flash chromatography on a silica gel
column. 3aa (35 mg) was recycled and 4aa (112 mg) was
obtained as white solid.
1
1481, 1445, 1258. H NMR (CDCl3) d 7.57–7.69 (m, 6H),
7.40–7.48 (m, 3H). 19F NMR (CDCl3) d ꢀ107.11 (s, 2F). MS
m/z (relative intensity) 332 (M+ + 2, 24.84), 330 (M+, 25.48),
282 (20.85), 280 (21.32), 251 (100), 200 (37.00). Anal.
Calcd. for C17H9BrF2: C, 61.66, H, 2.74, F, 1.47. Found: C,
61.58, H, 3.00, F, 11.40.
4aa: Solid, 1H NMR (CDCl3) d 7.54–7.60 (m, 6H), 7.77–
7.80 (m, 4H). 19F NMR (CDCl3) d ꢀ109.1. MS m/z (relative
intensity) 302 (M+, 97.06), 282 (20.66), 262 (6.33), 251
(100.00), 233 (21.140), 202 (25.07), 151 (10.09). Anal.
Calcd. for C18H10F4: C, 71.52; H, 3.33; F, 25.14. Found: C,
71.44; H, 3.32; F, 25.22.
3bd: Liquid, IR (film) (cmꢀ1) 2959, 2935, 2231, 1772,
1
1587, 1488, 1467, 1356, 1280. H NMR (CDCl3) d 7.60–
7.65 (m, 2H), 7.50–7.55 (m, 2H), 2.53 (t, J = 7.5 Hz, 2H),
1.63–1.69 (m, 2H), 1.36–1.48 (m, 4H), 0.95 (t, J = 6.9 Hz,
3H). 19F NMR (CDCl3) d ꢀ107.25 (s, 2F). MS m/z (relative
intensity) 326 (M+ + 2, 11.19), 324 (M+, 11.87), 270 (66.44),
268 (70.38), 201 (69.33), 188 (100), 183 (45.59). HRMS
Calcd. for C16H15BrF2: 324.0325. Found: 324.0311.
4ba: Solid, IR (film) (cmꢀ1) 1723, 1585, 1483, 1450,
1
1307, 1280, 1243. H NMR (CDCl3) d 7.79–7.54 (m, 9H).
19F NMR (CDCl3) d ꢀ109.50 (s, 4F). MS m/z (relative

Z.-L. Cheng, Q.-Y. Chen / Journal of Fluorine Chemistry 126 (2005) 93–97
97
intensity) 382 (M+ + 2, 73.33), 380 (M+, 75.98), 300 (41.07),
251 (100), 200 (28.98). HRMS Calcd. for C18H9BrF4:
379.9823. Found: 379.9786.
261 (M+ ꢀ 79, 9.67), 202 (100). Anal. Calcd. for
C18H13O2Br: C, 63.36, H, 3.84. Found: C, 63.55, H, 4.11.
5bd: Liquid, 1H NMR (CDCl3) d 7.30–7.50 (m, 4H), 6.94
(t, J = 2.7 Hz, 1H), 3.79 (s, 3H), 1.24–1.47 (m, 6H), 0.86–
0.91 (t, J = 6.6 Hz, 3H). MS m/z (relative intensity) 336
(M+ + 2, 41.73), 334 (M+, 44.27), 319 (M+ ꢀ 15), 263
(47.26), 239 (93.84), 237 (100), 139 (73.55). HRMS
(MALDI) Calcd. for C17H20O2Br+ 335.0656. Found:
335.0641.
4da: Solid, IR (film) (cmꢀ1) 1723, 1608, 1491, 1450,
1
1317, 1278, 1245. H NMR (CDCl3) d 7.79–7,35 (m, 9H),
2.46 (s, 3H). 19F NMR (CDCl3) d ꢀ109.509 (s, 2F),
ꢀ109.591 (s, 2F). MS m/z (relative intensity) 316 (M+, 100),
300 (22.60), 265 (24.11), 251 (44.46). HRMS Calcd. for
C19H12F4: 316.0875. Found: 316.0864.
4fa: Liquid, IR (film) (cmꢀ1) 2962, 2935, 2866, 1729,
1599, 1579, 1494, 1452, 1303, 1284, 1270. 1H NMR
(CDCl3) d 7.73–7.51 (m, 5H), 2.72–2.67 (m, 2H), 1.77 (t,
J = 6.9Hz, 2H), 1.47–1.37 (m, 4H), 0.93 (t, J = 7.2 Hz, 3H).
19F NMR (CDCl3) d ꢀ107.004 (s, 2F), ꢀ109.148 (s, 2F). MS
m/z (relative intensity) 296 (M+, 18.12), 240 (100), 188
(52.03), 41 (99.41). HRMS Calcd. for C17H16F4: 296.1188.
Found: 296.1192.
5ca: Solid, 1H NMR (CDCl3) d 8.27–8.31 (m, 3H), 7.72–
7.75 (m, 2H), 7.30–7.38 (m, 5H), 3.86 (s, 3H). MS m/z
(relative intensity) 307 (M+, 50.91), 276 (M+ ꢀ MeO,
12.24), 202 (100), 200 (86.95), 189 (78.35). Anal. Calcd.
for C18H13O4N: C, 70.35, H, 4.26, N, 4.56; C, 70.35, H, 4.60,
N, 4.38.
Acknowledgement
3.3. Hydrolysis reaction of compound 3
We thank the Natural Science Foundation (Nos.
20272026, D20032010) of China for support of this work.
Typical procedure: To a 25 ml round bottom flask was
placed 3aa (125 mg, 0.5 mmol), 2N aqueous HCl (2 ml),
MeOH (10 ml), the mixture was refluxed and monitored by
TLC until the reaction completed. Water (10 ml) was added
to the mixture and extracted with ether (2 ꢁ 10 ml). The
organic layer was dried over Na2SO4. After removal of
solvent under reduced pressure, the residue was purified by
flash chromatography on a silica gal column. Compound 5aa
(91 mg, 70%) was obtained as a white solid.
5aa: Solid, 1H NMR (CDCl3) d 7.54–7.57 (m, 2H), 7.41–
7.44 (m, 3H), 7.27–7.30 (m, 5H), 7.13 (s, 1H), 3.84 (s, 1H).
MS m/z (relative intensity) 262 (M+, 51.38), 231 (45.77), 202
(100), 191 (22.62). Anal. Calcd. for C18H14O2: C, 82.42, H,
5.38. Found: C, 82.48, H, 5.40.
5ab: Solid, 1H NMR (CDCl3) d 7.51–7.52 (m, 2H), 7.41–
7.44 (m, 5H), 7.09–7.15 (m, 3H), 3.84 (s, 3H). MS m/z
(relative intensity) 342 (M+ + 2, 42.66), 340 (M+, 42.60),
309 (M+ ꢀ MeO, 29.24), 202 (100). Anal. Calcd. for
C18H13O2Br: C, 63.36, H, 3.84. Found: C, 63.40, H, 3.82.
X-ray crystallographic data: crystal system, Orthorhombic;
References
[1] (a) M. Hudlicky, A.E. Pavlath (Eds.), Chemistry of Organic Fluorine
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(b) W.R. Dolbier Jr., B.H. Al-Sader, S.F. Sellers, H. Koroniak, J. Am.
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[7] W. Xu, Q.-Y. Chen, J. Org. Chem. 67 (2002) 9421–9427.
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˚
space group, Pbcn; unit cell dimensions: a = 21.582(3) A,
˚
˚
b = 7.4776(11) A, c = 19.076(3) A, a = 908, b = 908,
g = 908.
5ba: Solid, 1H NMR (CDCl3) d 7.28–7.59 (m, 9H), 7.16
(s, 1H), 3.85 (s, 3H). MS m/z (relative intensity) 342
(M+ + 2, 19.51), 340 (M+, 19.85), 309 (M+ ꢀ MeO, 6.29),
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(b) K. Yoshikazu, L. Steven, J. Org. Chem. (1982) 2493–2494.
[11] E.J. Corey, P.L. Fuchs, Tetrahedron Lett. (1972) 3769–3772.