Organocatalytic alkynylation of densely functionalized monofluorinated derivatives: C(sp3)-C(sp) coupling

Article abstract of DOI:10.1016/j.tetlet.2013.02.023

Organocatalytic alkynylation of nucleophilic fluorocarbons using hypervalent iodine compounds under cinchona-based catalysis, namely using O-allyl N-anthracenyl cinchona alkaloid derivative II, is described. The reaction gives the final fluoro-propargyl compounds in good to excellent yields (up to 91%) and with moderate to low enantioselectivity (up to 61% ee). The reaction represents the first example of the use of hypervalent iodine compounds for the construction of fluorinated compounds and opens access to the preparation of biologically attractive compounds such as 1,2,3-triazoles.

Full text of DOI:10.1016/j.tetlet.2013.02.023

Tetrahedron Letters 54 (2013) 2097–2100
Contents lists available at SciVerse ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Organocatalytic alkynylation of densely functionalized monofluorinated
derivatives: C(sp3)–C(sp) coupling
⇑
´
Martin Kamlar, Piotr Putaj, Jan Vesely
Department of Organic Chemistry, Faculty of Science, Charles University in Prague, Hlavova 2030, 128 43 Praha 2, Czech Republic
a r t i c l e i n f o
a b s t r a c t
Article history:
Organocatalytic alkynylation of nucleophilic fluorocarbons using hypervalent iodine compounds under
cinchona-based catalysis, namely using O-allyl N-anthracenyl cinchona alkaloid derivative II, is
described. The reaction gives the final fluoro-propargyl compounds in good to excellent yields (up to
91%) and with moderate to low enantioselectivity (up to 61% ee). The reaction represents the first exam-
ple of the use of hypervalent iodine compounds for the construction of fluorinated compounds and opens
access to the preparation of biologically attractive compounds such as 1,2,3-triazoles.
Ó 2013 Elsevier Ltd. All rights reserved.
Received 4 January 2013
Revised 22 January 2013
Accepted 7 February 2013
Available online 16 February 2013
Keywords:
Organocatalysis
Monofluorination
Hypervalent iodine
Alkynylation
Phenylsulfonyl derivatives
The ability of fluorine to improve molecular properties has been
convincingly demonstrated in a wide range of applications. In
many cases, the small and highly electronegative fluorine atom is
introduced following a particular rationale, based on our under-
standing of the effects of fluorination.1 In the life sciences area,
well-known effects include enhancement of metabolic stability,
conformational stabilization, and modifications of functional group
reactivity, acid/base properties, enhanced binding interactions, and
increased CNS penetration or lipophilicity. Importantly, these ef-
fects cannot be considered individually as usually a number of
properties are influenced simultaneously.2 For example, fluorina-
tion of amines in order to increase their metabolic stability also
leads to a decrease in pKa(H), an increase in their lipophilicity,
and may induce strong conformational effects.
For these reasons the development of new methodologies that
delivers fluorinated molecules in an enantioselective fashion has
experienced a significant growth in recent years.3 Organocatalysis
has emerged as a promising tool for their synthesis.4 Since the first
organocatalytic fluorination was reported, almost simultaneously,
by Enders,5 Barbas,6 MacMillan,7 and Jorgensen,8 much research
has been performed in this area. For example Shibata,9 Rios,10
Wang,11 Tan,12 and Cordova13 have reported the formal fluorome-
thylation of enones, enals, and Baylis–Hillman carbonates with
excellent results. Our group, fascinated by the use of fluorine build-
ing blocks in organocatalysis, has developed the first fluoromalo-
nate addition14 and first fluoro phenylsulfonyl nitromethane15
addition to enals catalyzed by secondary amines with excellent
results.
The unique properties of alkynes such as sp hybridized carbon
atoms and their electronic properties, impart rich reactivity.16
Moreover, triple bonds have emerged as a useful tool in nano-
sciences and chemical biology,17 as a result of the copper-catalyzed
cycloadditions of azides to acetylenes (click chemistry). Chiral mol-
ecules bearing a triple bond adjacent to a stereogenic carbon atom,
have found utility as building blocks in the synthesis of natural
products,18 and as bioactive compounds possessing antiviral
properties.19
Despite their importance in organic chemistry, there are only a
few examples of organocatalytic enantioselective syntheses of chi-
ral propargylic compounds. The majority are based on the use of
nucleophilic propargyl compounds. For example, Schreiner re-
ported the alkynylation of aldehydes and ketones under PTC condi-
tions.20 A few years later, Jørgensen developed the alkynylation of
enals using secondary amines as catalysts.21 The use of electro-
philic propargylic compounds has been less studied,22 and only
two examples have been described in an enantioselective fashion.
In 2010, Waser reported the addition of b-keto esters to ethynyl-
1,2-benziodoxol-3(1H)-one (EBX) under PTC conditions,23 and
Jørgensen developed a highly enantioselective addition of b-keto
esters to haloalkynes with excellent results.24
Based on these previous results and our experience in organoc-
atalysis14–16,25 and the synthesis of fluorine compounds, we envi-
sioned an easy entry into fluoro-propargyl compounds based on
the addition of fluoronitrosulfones26 and other fluorinated sub-
strates to hypervalent iodine compounds.
⇑
Corresponding author. Tel.: +420 221 951 305; fax: +420 221 951 226.
E-mail address: jxvesely@natur.cuni.cz (J. Vesely´).
0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2013.02.023

2098
M. Kamlar et al. / Tetrahedron Letters 54 (2013) 2097–2100
Table 1
Alkynylation of fluoronitrosulfone
F
R
PhO2S
NO2
catalyst (10 mol%)
solvent, rt
PhO2S
NO2
+
I
F
TfO
2a, b
1a
3a
Entry
Solvent
Catalyst
R
Time (h)
Conversion (%)
eea (%)
Yieldb (%)
1
2
3
4
Toluene
CHCl3
Toluene
Toluene
I
TMS
TMS
TMS
TIPS
16
16
24
24
50
50
0
0
0
—
—
42
38
—
II
IX
I
0
—
a
Determined by chiral HPLC.
Isolated yield.
b
Table 2
Screening of the catalyst for the alkynylation of fluoronitrosulfone 1a
H
Cl-
Br-
N
H
N
O
N
N
H
O
H3CO
OH
O
N
N
I
II
III
H
H
Cl-
N
N
N
HO
N
HO
HO
H
H
OH H3CO
H3CO
N
IV
N
V
N
VI
N
VII
H3C
H3C
O
H
H
N
N
CF3
CF3
N
H
N
O
S
H
H3CO
OCH3
F3C
N
H
N
CF3
H
N
N
IX
VIII
O
F
O
I
PhO2S
NO2
PhO2S
NO2
catalyst (10 mol%)
toluene, rt
+
F
1a
2c
3a
TMS
Entry
Catalyst
Time (h)
eea (%)
Yieldb (%)
1
2
3
4
5
6
7
8
I
II
16
16
16
48
16
48
16
72
48
16
22
0
88
91
89
65
65
60
75
25
61
12
0
III
IV
V
VI
VII
VIII
IX
II
3
À2
À15
À5
—
61
56
9
10
11
n.d.
92c
75d
II
Experimental conditions: a mixture of 1a (0.1 mmol), catalyst (10 mol %), and 2c (0.2 mmol) in toluene (1 mL) was stirred at rt for the time shown in the table. After full
conversion, the crude product was purified by column chromatography.
a
Determined by Chiral HPLC.
Isolated yield.
5% Catalyst loading.
2% Catalyst loading.
b
c
d

M. Kamlar et al. / Tetrahedron Letters 54 (2013) 2097–2100
2099
Table 4
When fluoronitrosulfone 1a was treated with iodonium triflate
2a in the presence of quinine (10 mol %), the desilylated -fluoro-
acetylene 3a was obtained in 50% conversion, but in an unaccept-
Substrate scope of the organocatalytic alkynylation
a
O
able yield (42%) (Table 1, entry 1).
F
R1
R2
R1
R2
O
Next, we decided to use the more reactive 1-[(trimethyl-
silyl)ethynyl]-1,2-benziodoxol-3(1H)-one (TMS-EBX, 2c), previ-
ously reported by Waser et al., as a highly active alkynylation
reagent under PTC conditions. The use of TMS-EBX under catalysis
with quinine led to the formation of the corresponding product 3a
in high yield (88%). Unfortunately, no enantiocontrol was observed
with quinine as the catalyst (Table 2, entry 1).
Subsequently, various organocatalysts (I–IX) were screened.
High efficiency for other quinine-based catalysts (I–III) was ob-
served, but on the other hand, lower conversions were obtained
with other cinchona-based catalysts (IV–VII) and the Sharpless
catalyst (VIII). The best results were obtained with the bulky qua-
catalyst II (10 mol%)
I
+
toluene, rt
F
1a-i
2c
3a-i
TMS
Entry
R1
R2
Time (h)
Product
eea (%)
Yieldb (%)
1
2
3
4
5
6
7
8
9
SO2Ph
SO2Ph
SO2Ph
SO2Ph
SO2Ph
SO2Ph
SO2Ph
pNO2Ph
CO2Et
NO2
CN
16
18
16
16
16
16
16
24
24
3a
3b
3c
3d
3e
3f
61
30
25
19
37
0
91
88
83
58
77
65
COPh
COMe
CO2Me
PO(OEt)2
SO2Ph
pNO2Ph
CO2Et
3g
3h
3i
—
n.d.
n.d.
70c
n.d.c
n.d.c
ternary cinchona-based catalyst II; the corresponding
a-fluoro-
acetylene 3a was obtained in excellent yield (91%) and with
satisfactory enantioselectivity (61% ee, entry 2). We studied the
dependence of the reaction efficiency on the catalyst loading. Inter-
estingly, no change in terms of the enantioselectivity and conver-
sion was observed when 5 mol % of II was used (entry 10). On
the other hand, using 2 mol % of the catalyst led to a lower conver-
sion as well as a slight drop in the enantioselectivity (entry 11).
Next, the influence of the solvent and temperature was investi-
gated (Table 3). Using THF as the solvent at room temperature, the
reaction reached full conversion in 2 h with excellent yield, but in
only poor enantiomeric excess. Interestingly, a decrease in the
temperature did not improve the enantioselective induction to-
ward the product (entries 2–4). The best results in terms of effi-
ciency and selectivity were obtained in toluene at room
temperature.27 Other solvents, such as propan-2-ol or dichloro-
methane were tested, but in spite of the high yields obtained only
poor enantioselectivity was observed (entries 5 and 6).
Experimental conditions: a mixture 1a–i (0.1 mmol), catalyst II (10 mol %), and 2c
(0.2 mmol) in toluene (1 mL) was stirred at rt for the time shown in the table. After
full conversion, the crude product was purified by column chromatography.
a
Determined by chiral HPLC.
Isolated yield.
Performed with I as the catalyst.
b
c
the corresponding a-fluoroacetylene 3a in 77% yield and low enanti-
oselectivity (37% ee). Unfortunately, switching the sulfonyl group
for a p-nitrophenyl or ester group did not lead to the corresponding
alkynylated products (entries 8 and 9). As shown in Scheme 1, using
non-fluorinated carbon nucleophiles 4a–i did not lead to formation
of the corresponding acetylene derivatives 5.
Next, the effect of the silyl group on the alkynyl moiety of the
hypervalent iodine species 2 was studied. More bulky and acid-sta-
ble silyl groups were found to be unsuitable for this transforma-
tion. In the case of sterically demanding silyl groups, such as
tert-butyldiphenylsilyl and tri-isopropylsilyl, no reaction was ob-
served even after three days (Table 5, entries 3–5). On the other
hand, hypervalent iodine species 2 with less bulky silyl moieties,
in particular triethylsilyl and trimethyl, afforded the desired prod-
ucts in good to high yields (entries 1 and 2).
Subsequently we studied the reactions with fluorocarbon nucle-
ophiles 1a–g (Table 4). Changing the nitro functionality in 3a to
cyano, benzoyl, acetyl, methyl carboxylate, or diethylphosphoryl
led to formation of the corresponding
a-fluoroacetylenes 3b–g in
good to excellent yields (58–88%), but generally with lower enanti-
oselectivities (Table 4, entries 2–6). For example O-allyl N-anthrace-
nyl cinchona alkaloid derivative II catalyzed the alkynylation
reaction between methyl phenylsulfonyl acetate 1e and 1-[(tri-
methylsilyl)ethynyl]-1,2-benziodoxol-3(1H)-one (2c) to furnish
The prepared
a-fluoroacetylenes 3 can be converted into vari-
ous structural motifs, for example, via Huisgen cycloaddition, a
reaction that has found many applications in life sciences and
materials chemistry.28,29 For example, treatment of nitrophenyl-
sulfonyl
a-fluoroacetylene (3a) with p-bromobenzyl azide in the
presence of copper(II) sulfate and sodium ascorbate led to the for-
mation of 1,2,3-triazole derivative 6a in good yield (55%) with no
change in the enantioselectivity (Scheme 2).
In summary, we have developed an alkynylation of nucleophilic
fluorocarbons using hypervalent iodine compounds under cin-
chona-based catalysis. The reaction affords the products in good
Table 3
Temperature and solvent screening
O
F
O
PhO2S
NO2
catalyst II (10 mol%)
PhO2S
NO2
I
+
solvent,
temperature
F
O
TMS
1a
2c
3a
H
R1 R2
R1 R2
H
O
catalyst I (10 mol%)
Entry
Solvent
Temp (°C)
Time (h)
eea (%)
Yieldb (%)
I
+
1
2
3
4
5
6
Toluene
THF
THF
THF
Propan-2-ol
CH2Cl2
20
20
0
À20
20
20
16
2
7
16
12
12
61
27
26
23
12
9
91
92
88
82
87
90
toluene, rt
2c
5a-i
4a-g:
TMS
R1 = SO2Ph
R2 =NO2, CN, COPh, COMe, CO2Me, PO(OEt)2, SO2Ph
4h:
R1 = R2= pNO2Ph
4i:
Experimental conditions: a mixture of 1a (0.1 mmol), catalyst II (10 mol %), and 2c
(0.2 mmol) in the selected solvent (1 mL) was stirred at rt for the time shown in the
table. After full conversion, the crude product was purified by column
chromatography.
R1 = R2= CO2Et
a
Determined by chiral HPLC.
Isolated yield.
Scheme 1. Reaction of non-fluorinated substrates with hypervalent iodine com-
pound 2c.
b

2100
M. Kamlar et al. / Tetrahedron Letters 54 (2013) 2097–2100
2. (a) O’Hagan, D. Chem. Soc. Rev. 2008, 37, 308; (b) Hunter, L. Beilstein J. Org. Chem.
Table 5
2010, 6, 38; (c) Zimmer, L. E.; Sparr, C.; Gilmour, R. Angew. Chem., Int. Ed. 2011,
50, 11860.
3. Cahard, D.; Xu, X.; Couve-Bonnaire, S.; Pannecoucke, X. Chem. Soc. Rev. 2010, 39,
558.
4. (a) Zhao, Y.; Pan, Y.; Sim, S.; Tan, C. Org. Biomol. Chem. 2012, 10, 479; (b) Valero,
G.; Companyó, X.; Rios, R. Chem. Eur. J. 2011, 17, 2018.
5. Enders, D.; Huttl, M. R. M. Synlett 2005, 991.
Effect of the silyl group on the organocatalytic alkynylation
O
F
O
PhO2S
NO2
catalyst (10 mol%)
solvent, rt
PhO2S
NO2
I
+
F
6. Steiner, D. D.; Mase, N.; Barbas, C. F., III Angew. Chem., Int. Ed. 2005, 44, 3706.
7. Beeson, T. D.; MacMillan, D. W. C. J. Am. Chem. Soc. 2005, 127, 8826.
8. Franzen, J.; Marigo, M.; Fielenbach, D.; Wabnitz, T. C.; Kjaersgaad, A.; Jorgensen,
K. A. J. Am. Chem. Soc. 2005, 127, 18296.
9. (a) Furukawa, T.; Shibata, N.; Mizuta, S.; Nakamura, S.; Toru, T.; Shiro, M.
Angew. Chem., Int. Ed. 2008, 47, 8051; (b) Furukawa, T.; Goto, Y.; Kawazoe, J.;
Tokunaga, E.; Nakamura, S.; Yang, Y.; Du, H.; Kakehi, A.; Shiro, M.; Shibata, N.
Angew. Chem., Int. Ed. 2010, 49, 1642; (c) Nomura, Y.; Tokunaga, E.; Shibata, N.
Angew. Chem., Int. Ed. 2011, 50, 1885.
10. (a) Alba, A.-N.; Companyó, X.; Moyano, A.; Rios, R. Chem. Eur. J. 2009, 15, 7035;
(b) Companyó, X.; Valero, G.; Ceban, V.; Calvet, T.; Font-Bardia, M.; Moyano, A.;
Rios, R. Org. Biomol. Chem. 2011, 9, 7986; (c) Wang, B.; Companyó, X.; Li, J.;
Moyano, A.; Rios, R. Tetrahedron Lett. 2012, 53, 4124.
11. Zhang, S.; Zhang, Y.; Ji, Y.; Li, H.; Wang, W. Chem. Commun. 2009, 4886.
12. Yang, W.; Wei, X.; Pan, Y.; Lee, R.; Zhu, B.; Liu, H.; Yan, L.; Huang, K.; Jiang, Z.;
Tan, C. Chem. Eur. J. 2011, 17, 8066.
1a
2
3a
R
Entry
Solvent
R
Catalyst
Time (h)
eea (%)
Yieldb (%)
1
2
3
4
5
Toluene
Toluene
Toluene
THF
TMS
TES
TIPS
TIPS
TBDP
II
II
I
16
120
24
24
24
61
60
—
—
—
91
65
—
—
—
I
I
Toluene
Experimental conditions: a mixture of 1a (0.1 mmol), catalyst (10 mol %), and 2
(0.2 mmol) in toluene (1 mL) was stirred at rt for the time shown in the table. After
full conversion, the crude product was purified by column chromatography.
a
Determined by chiral HPLC.
Isolated yield.
b
13. Ullah, F.; Zhao, G.-L.; Deiana, L.; Zhu, M.; Dziedzic, P.; Ibrahem, I.; Hammar, P.;
Sun, J.; Córdova, A. Chem. Eur. J. 2009, 15, 10013.
14. Companyó, X.; Hejnová, M.; Kamlar, M.; Vesely´, J.; Moyano, A.; Rios, R.
Tetrahedron Lett. 2009, 50, 5021.
15. Kamlar, M.; Bravo, N.; Alba, A. N. R.; Hybelbauerova, S.; Cisarova, I.; Vesely, J.;
Moyano, A.; Rios, R. Eur. J. Org. Chem. 2010, 28, 5464.
16. (a) Patai, S. The Chemistry of the Carbon–Carbon Triple Bond; Wiley: New York,
1978. Part 1–2; (b) Stang, P. J.; Diederich, F. Modern Acetylene Chemistry; VCH:
Weinheim, 1995; (c) Diederich, F.; Stang, P. J.; Tykwinski, R. R. Acetylene
Chemistry; VCH: Weinheim, 2005.
N
F
N
N
PhO2S
NO2
i)
Br
O2N
F
SO2Ph
6a
3a
17. See, for example: (a) Speers, A. E.; Adam, G. C.; Cravatt, B. F. J. Am. Chem. Soc.
2003, 125, 4686; (b) Prescher, J. A.; Bertozzi, C. R. Nat. Chem. Biol. 2005, 1, 13;
(c) Burley, G. A.; Gierlich, J.; Mofid, M. R.; Nir, H.; Tal, S.; Eichen, Y.; Carell, T. J.
Am. Chem. Soc. 2006, 128, 1398; (d) Dichtel, W. R.; Miljanic, O. S.; Spruell, J. M.;
Heath, J. R.; Stoddart, J. F. J. Am. Chem. Soc. 2006, 128, 10388.
18. See, for example: (a) Denmark, S. E.; Yang, S.-M. J. Am. Chem. Soc. 2002, 124,
15196; (b) Bode, J. W.; Carreira, E. M. J. Am. Chem. Soc. 2001, 123, 3611.
19. See, for example: (a) Jiang, B.; Si, Y.-G. Angew. Chem., Int. Ed. 2004, 43, 216; (b)
Corbett, J. W.; Ko, S. S.; Rodgers, J. D.; Gearhart, L. A.; Magnus, N. A.; Bacheler, L.
T.; Diamond, S.; Jeffrey, S.; Klabe, R. M.; Cordova, B. C.; Garber, S.; Logue, K.;
Trainor, G. L.; Anderson, P. S.; Erickson-Viitanen, S. K. J. Med. Chem. 2000, 43,
2019.
20. Weil, T.; Schreiner, P. R. Eur. J. Org. Chem. 2005, 11, 2213.
21. Nielsen, M.; Jacobsen, Ch. B.; Paixao, M. W.; Holub, N.; Jorgensen, K. A. J. Am.
Chem. Soc. 2009, 30, 10581.
22. For an excellent review, see: Brand, J. P.; Waser, J. Chem. Soc. Rev. 2012, 41,
4165.
yield 55%
ee = 60%
Scheme 2. An example of the transformation of alkynylated product 3a. (i) To a
stirred solution of 3a (0.1 mmol) and p-bromobenzyl azide (0.12 mmol) in
tBuOH:H2O (1:1) (1 mL) was added copper(II) sulfate (0.02 mmol) and sodium
ascorbate (0.4 mmol) and the mixture was stirred overnight. After full conversion,
the crude product was purified by column chromatography.
yields and low enantioselectivities. Mechanistic studies and syn-
thetic applications of this new methodology, as well as the inves-
tigation of new reactions based on this concept, are currently
underway in our laboratory.
23. Gonzalez, D. F.; Brand, J. P.; Waser, J. Chem. Eur. J. 2010, 16, 9457.
24. Poulsen, T. B.; Bernardi, L.; Alemán, J.; Overgaard, J.; Jorgensen, K. A. J. Am.
Chem. Soc. 2007, 129, 441.
Acknowledgments
ˇ
´
25. (a) Remeš, M.; Vesely, J. Eur. J. Org. Chem. 2012, 20, 3747; (b) Cíhalová, S.;
´
Jan Vesely gratefully acknowledges the Ministry of Education of
ˇ
Dziedzic, P.; Córdova, A.; Vesely´, J. Adv. Synth. Catal. 2011, 7, 1096; (c) Cíhalová,
the Czech Republic (Grant No. MSM0021620857) and Czech Sci-
ence Foundation (Grant No. P207/10/0428) for financial support.
This publication is a result of the project implementation: Support
of establishment, development and mobility of quality research
teams at Charles University, project number CZ.1.07/2.3.00/
30.0022, supported by the Education for Competitiveness Opera-
tional Programme (ECOP) and co-financed by the European Social
Fund and the state budget of the Czech Republic.
ˇ
S.; Valero, G.; Schimer, J.; Humpl, M.; Dracínsky´, M.; Moyano, A.; Rios, R.
Tetrahedron 2011, 67, 8942.
26. For recent reviews on sulfone derivatives as nucleophiles, see: (a) Alba, A.;
Companyó, X.; Rios, R. Chem. Soc. Rev. 2010, 39, 2018; (b) Nielsen, M.; Jacobsen,
C.; Holub, N.; Paixao, M.; Jorgenesen, K. A. Angew. Chem., Int. Ed. 2010, 49, 2668.
27. To a stirred solution of catalyst (0.1 equiv) in toluene (1 mL) was added sulfone
(1.0 equiv) and the alkynyl benziodoxolone reagent (1.5 equiv). The mixture
was stirred at rt and the reaction monitored by TLC. After completion of the
reaction, the crude was transferred directly to a silica-gel column and eluted
with a mixture of hexane and EtOAc (in 3:1 ratio) to afford the alkynylated
product 3a. Compound 3a: White solid. Yield 91%, 61% ee. The ee was
determined by HPLC analysis using a Chiralpak IB column (95/5 heptane/i-
PrOH, flow rate 1.0 mL/min; k = 190 nm, Rt major = 14.3 min, Rt
minor = 16.0 min); 1H NMR (600 MHz, CDCl3): d = 8.01 (d, J = 7.6 Hz, 2H),
7.87–7.84 (m, 1H), 7.69–7.66 (m, 2H), 3.33 (d, J = 5.5 Hz, 1H) ppm; 13C NMR
(151 MHz, CDCl3): d = 136.76, 131.50 (2C), 130.81, 129.68 (2C), 111.90 (d,
J = 333.6 Hz, 1C), 85.97 (d, J = 7.8 Hz), 68.73 (d, J = 34.1 Hz) ppm; 19F NMR
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.tetlet.2013.02.
023.
(282 MHz, CDCl3): d = À111.44 ppm;
[
a
]
D
+3.7 (c = 0.6, CHCl3); IR (KBr):
m
= 3276, 3069, 2905, 2128, 1586, 1446, 1365, 1314, 1169, 1045, 722,
588 cmÀ1; HRMS (ESI) m/z [M+Na]+ calcd for C9H6FNO4SNa: 265.9889, found:
265.9894.
References and notes
28. Finn, M. G.; Fokin, V. V. Chem. Soc. Rev. 2010, 39, 1231.
29. Menendez, Ch.; Chollet, A.; Rodriguez, F.; Inard, C.; Pasca, M.-R.; Lherbet, Ch.;
Baltas, M. Eur. J. Med. Chem. 2012, 52, 275.
1. (a) Purser, S.; Moore, P. R.; Swallow, S.; Gouverneur, V. Chem. Soc. Rev. 2008, 37,
320; (b) Kirsch, P. Modern Fluoroorganic Chemistry: Synthesis, Reactivity,
Applications; Wiley-VCH: Weinheim, 2004.