Deiodinative fluorination of alkyl iodide with p-iodotoluene difluoride

Article abstract of DOI:10.1016/S0040-4020(01)00201-0

Oxidative fluorination of alkyl iodides with p-iodotoluene difluoride (4) was carried out. In the presence of Et₃N-4HF, the fluorination reaction of prim-alkyl iodides selectively took place at the iodine position under mild conditions to give the corresponding alkyl fluorides in good yields.

Full text of DOI:10.1016/S0040-4020(01)00201-0

TETRAHEDRON
Pergamon
Tetrahedron 57.2001) 3315±3319
Deiodinative ¯uorination of alkyl iodide with
p-iodotoluene di¯uoride
Masanori Sawaguchi, Shoji Hara,p Yutaka Nakamura, Shinichi Ayuba, Tsuyoshi Fukuhara
and Norihiko Yoneda
Division of Molecular Chemistry, Graduate School of Engineering, Hokkaido University, Sapporo 060-8628, Japan
Received 27December 2000; accepted 19 February 2001
AbstractÐOxidative ¯uorination of alkyl iodides with p-iodotoluene di¯uoride .4) was carried out. In the presence of Et3N±4HF, the
¯uorination reaction of prim-alkyl iodides selectively took place at the iodine position under mild conditions to give the corresponding alkyl
¯uorides in good yields. q 2001 Elsevier Science Ltd. All rights reserved.
1. Introduction
Recently, we reported that p-iodotoluene di¯uoride .4)
reacts with 1-alkenes in the presence of an amine±HF
complex to give vic-di¯uoroalkanes .6) selectively and the
reaction can be explained by presuming the formation of
hypervalent prim-alkyliodine intermediates .5) .Scheme
2).7 This result suggested that the oxidative ¯uorination
method is applicable to the synthesis of prim-alkyl ¯uorides
by the addition of the amine±HF complex, and we investi-
gated the oxidative ¯uorination of the alkyl iodides using 4
and the amine±HF complex.
The ¯uoride ion displacement of halides or sulfonates has
been widely used for the preparation of organo¯uorine
compounds.1 However, in the reaction of metal ¯uorides,
high temperatures and/or long reaction times are generally
necessary due to the low solubility of the metal ¯uorides in
organic solvents and the low nucleophilicity of the ¯uoride
ion.1b Recently, ammonium ¯uorides2 and phosphonium
¯uorides3 have been used to convert the alkyl halides to
the corresponding ¯uorides under mild conditions.
However, anhydrous tetrabutylammonium ¯uoride
.TBAF) generates signi®cant amounts of alkenes and
alcohols as well as the desired alkyl ¯uorides in the reaction
with alkyl halides or sulfonates because TBAF behaves as a
base and hydrolyzing reagent.2a Though TBAF´5H2O2g or
F
I(F)Tol-p
p-TolIF2 (4)
F
F
Et3N-5HF / CH2Cl2
R
R
R
5
6
2h
TBAF´HF2 can suppress such side reactions, it requires
relatively high reaction temperatures.
Scheme 2.
The oxidative ¯uorination of alkyl iodides .1), including
reactive hypervalent alkyliodine di¯uoride intermediates
.2), was reported to give the alkyl ¯uorides .3) under mild
conditions, but the application of this method was limited to
methyl ¯uoride4 or bridgehead ¯uoride syntheses,5 and the
application to prim-alkyl ¯uoride synthesis resulted in poor
yield .Scheme 1).6
2. Results and discussion
The ¯uorination of decyl iodide .1a) by 4 with or without
the amine±HF complex was examined in CH2Cl2 at room
temperature .Table 1). When the reaction was carried out
without the amine±HF complex, decyl ¯uoride .3a) was
obtained only in low yield as previously reported6 .entry
1). The addition of a slightly acidic complex, Et3N±4HF,
could cause a drastic increase in the reaction rate and 1a was
consumed in 3 h to afford 3a in 74% yield .entry 3), the
expected by-products, such as the alcohol or alkene, not
being found. When a more acidic complex such as Et3N±
5HF or pyridine±6HF was used, 1a disappeared in 1 h but
3a was obtained only in lower yields with some by-products
.entries 4 and 5). The neutral complex, Et3N±3HF,8
inhibited the reaction and 1a was mostly recovered after
24 h .entry 2).
XeF2 or ArIF2
F
F
R
I
R
I
R F
1
2
3
Scheme 1.
Keywords: halogenation; hypervalent element; oxidation.
Corresponding author. Tel./fax: 181-11-706-6556;
e-mail: hara@org-mc.eng.hokudai.ac.jp
p
0040±4020/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020.01)00201-0

3316
M. Sawaguchi et al. / Tetrahedron 57 +2001) 3315±3319
Table 1. Effect of amine±HF complex on ¯uorination of decyl iodide .1a)
unstable, and in the reaction of bridgehead iodides, they
decomposed to the carbonium ion intermediates which
were attacked by the ¯uoride ion to give the alkyl ¯uorides.5
If the carbonium ions were formed from 2, the resulting
unstable prim-alkyl carbonium ions would isomerize to
more stable internal ones and sec-alkyl ¯uorides would be
formed. However, the isomers of 3 could not be found in the
products from the prim-alkyl iodides. Therefore, a reaction
mechanism including the carbonium ion intermediate can
be ruled out and the reaction must proceed via the SN2
mechanism between 2 and the ¯uoride ion .Scheme 3).9
Entry
HF±base
Reaction time .h)
Yield .%)a
1
2
3
4
5
None
24
24
3
1
1
20
3b
74
54
28
Et3N±3HF
Et3N±4HF
Et3N±5HF
Pyridine±6HF
The reaction was carried out in CH2Cl2 at room temperature using
1.5 equiv. of 4 to 1a.
a
GC yields based on 1a.
96% of 1a was recovered.
b
4, Et3N-4HF
CH2Cl2
Table 2. Oxidative ¯uorination of alkyl iodides .1b±g)
RCH2 IF2
RCH2
F
RCH2
I
Entry Alkyl iodide
Product
Yield .%)a
1
3
2
F
1
2
3
4
5
6
CH3.CH2)13±I
1b
AcO±.CH2)6±I
1c
MeOOC±.CH2)10±I
1d
Cl±.CH2)10±I
1e
p-Tol±COO.CH2)4±I
1f
AcO±.CH2)5±CHCH3±I AcO±.CH2)5±CHCH3±F 30
1g 3g
CH3.CH2)13±F
3b
AcO±.CH2)6±F
3c
MeOOC±.CH2)10±F
3d
Cl±.CH2)10±F
3e
72
75
78
68
68
Scheme 3.
For the successful conversion of prim-alkyl iodides into
¯uorides, the addition of a slightly acidic amine±HF
complex is critical, and the Et3N±4HF complex must
activate 2 by the protonation.9 However, highly acidic
complexes such as Et3N±5HF or pyridine±6HF strongly
coordinate to 2 and decompose it very rapidly. On the
other hand, the neutral Et3N±3HF cannot activate 2 by
coordination; moreover, a free Et3N, existing in Et3N±
3HF, must react with 4 to suppress the formation of 2.10
p-Tol±COO.CH2)4±F
3f
a
Isolated yields based on alkyl iodides used.
Various alkyl iodides .1b±g) were subjected to the reaction
with 4 and Et3N±4HF, and the corresponding alkyl ¯uorides
.3b±g) were obtained as shown in Table 2. Regardless of
the functional groups in the substrates, the prim-alkyl ¯uor-
ides could be obtained in good yields from the correspond-
ing alkyl iodides and the functional groups, such as an ester
and chloride, remained unchanged .entries 1±5). On the
contrary, sec-alkyl iodide gave a complex mixture of the
products and the desired sec-alkyl ¯uoride was obtained
only in low yield .entry 6).
The highly chemoselective character of our method was
demonstrated by the following examples. In spite of the
high reactivity of sulfonates and benzylic halides towards
nucleophiles, the alkyl iodides having a tosyl group .1h) and
a benzylic chloride group .1i) selectively reacted with 4 at
the iodine position to give the mono-¯uoro products .3h and
3i), and the ¯uorinated products at the tosyl or benzylic
position could not be found at all. Such selectivities could
not be observed in the conventional SN2 substitution reac-
tions. When 1h was allowed to react with 1.2 equiv. of
TBAF´5H2O, 1,6-di¯uorohexane .7) and 1-¯uoro-6-iodo-
hexane .8) were formed in a ratio of 1:2 and the formation
of 3h could not be observed. In the reaction of TBAF´5H2O
with 1i, the ¯uorination also took place non-selectively and
In the initial step of the reaction, the hypervalent alkyl-
iodines 2 must be formed by the ligand transfer from 4 to
1.6 The hypervalent alkyliodine species are known to be
4, Et3N-4HF
CH2Cl2
p-TsO-(CH2)6-I
p-TsO-(CH2)6-F
1h
3h
4, Et3N-4HF
CH2Cl2
Cl-CH2
COO-(CH2)4-F
Cl-CH2
COO-(CH2)4-I
1i
3i
TBAF 5H2O
+
F-(CH2)6-F
F-(CH2)6-I
1h
80˚C, 1 h
7
8
TBAF 5H2O
80˚C, 1 h
1i
F-CH2
COO-(CH2)4-F
9
Scheme 4.

M. Sawaguchi et al. / Tetrahedron 57 +2001) 3315±3319
3317
OHex
I
4.1.1. Preparation of iodotoluene di¯uoride /4). The
compound 4 was prepared from iodotoluene dichloride14
by a modi®cation of the reported procedure.15 Into a
300 ml three-necked round-bottomed ¯ask equipped with
a dry ice condenser, a mechanical stirrer, and an inlet tube
for the introduction of Cl2, were placed iodotoluene .21.8 g,
100 mmol) and CH2Cl2 .75 ml). The Cl2 gas generated from
MnO2 .30.5 g, 350 mmol) and conc. HCl .80 ml) was dried
by passing it through washing bottles containing conc. sul-
furic acid and water, and a CaCl2 tube, and then introduced
into the reaction mixture at 08C with stirring. After the
introduction of Cl2, the mixture was stirred for 1 h at
room temperature and then cooled to 2788C. The generated
solids were separated by ®ltration, washed with a small
amount of CHCl3 and dried in air on ®lter paper to give
iodotoluene dichloride .a pale yellow solid, 24.5 g,
85 mmol), which was used in the next step.
OHex
F
4, Et3N-4HF
OHex
CH2Cl2
10
11
50%
F
12
Scheme 5.
OHex
TBAF 5H2O
80˚C, 1 h
75%
10
13
Scheme 6.
a di¯uorinated compound .9) was isolated as the main
product .Scheme 4).
Into a 500 ml vessel made of ¯uororesin, iodotoluene
dichloride .24.5 g, 85 mmol), HgO .23.8 g, 110 mmol)
and CH2Cl2 .200 ml) were introduced and the mixture was
vigorously stirred at room temperature. Then 46% hydro-
¯uoric acid .60 ml) was added and the mixture was vigor-
ously stirred again. After 10 min, a white solid .HgCl2) was
removed by ®ltration and the ®ltrate was extracted three
times with CH2Cl2. The ®ltration and extraction were
carried out using apparatuses made of ¯uororesin. The
organic layers were dried over MgO and concentrated
under reduced pressure to give a pale yellow solid of 4
.21.3 g, 83 mmol). Borosilicate glasswares are not corroded
by 4 but a ¯uororesin vessel is recommended for storage of
4. The compound 4 can be handled in the air and stored in a
refrigerator for a few months without any change, but
quickly decomposes under basic conditions. Mp 140±
From trans-2-alkoxyiodocyclohexane .10), trans-2-alkoxy-
¯uorocyclohexane .11) was obtained in moderate yield. As
the trans-stereochemistry of 10 was completely retained in
11, the reaction may take place through an oxonium inter-
mediate .12) .Scheme 5).11
When 10 was subjected to the reaction with TBAF´5H2O,
the ¯uoro compounds could not be obtained and an elimina-
tion reaction predominantly took place to provide the allylic
ether .13) .Scheme 6).2
3. Conclusions
The oxidative ¯uorination of alkyl iodides was carried out
using iodotoluene di¯uoride 4 and Et3N±4HF. prim-Alkyl
iodides could be effectively converted to the corresponding
alkyl ¯uorides under mild conditions. The reaction was
highly chemoselective and the various functional groups
remained unchanged under the reaction conditions.
1
1428C. H NMR dˆ2.47.3H, s), 7.56 .2H, d, Jˆ8.4 Hz),
7.84 .2H, d, Jˆ8.4 Hz). 19F NMR d 2147.30 .2F, s).
4.1.2. Decyl ¯uoride /3a). A colorless oil; IR .neat):
1
1467cm 21. H NMR dˆ4.43 .2H, dt, Jˆ47.3, 6.1 Hz),
1.75±1.62 .2H, m), 1.43±1.27 .14H, m), 0.88 .3H, t, Jˆ
6.6 Hz). 19F NMR dˆ2218.5 .1F, tt, Jˆ47.3, 25.0 Hz).
HRMS.EI) Calcd for C10H21F 160.1627. Found 160.1612.
4. Experimental
4.1. General
4.1.3. Tetradecyl ¯uoride /3b). To a CH2Cl2 .1 ml)
solution of 4 .1.5 mmol, 384 mg) and Et3N±4HF .2 ml) in
a reaction vessel made of ¯uororesin, a CH2Cl2 .1 ml)
solution of tetradecyl iodide .1 mmol, 324 mg) was added at
room temperature. The reaction mixture was stirred at room
temperature until the consumption of starting substrate was
con®rmed by TLC, and poured into aqueous NaHCO3 in a
¯uororesin beaker. The product was extracted with CH2Cl2
and the combined organic phase was successively washed
with aqueous Na2S2O3 and brine, then dried over MgSO4.
Puri®cation by column chromatography .silica gel/hexane)
gave tetradecyl ¯uoride in 78% yield as a colorless oil; IR
.neat): 1467.C±F) cm 21. 1H NMR dˆ4.44 .2H, dt, Jˆ47.3,
6.3 Hz), 1.75±1.62 .2H, m), 1.40±1.26 .22H, m), 0.88 .3H,
t, Jˆ7.0 Hz). 19F NMR dˆ2218.3 .1F, tt, Jˆ47.3,
25.0 Hz). HRMS.EI) Calcd for C14H29F 216.2253. Found
216.2254. Anal.: C, 77.71; H, 13.51. Found: C, 77.64; H,
13.46.
The IR spectra were recorded using a JASCO FT/IR-410.
The 1H NMR .400 MHz) and 19F NMR .376 MHz) spectra
were recorded in CDCl3 on a JEOL JNM-A400II FT NMR
and the chemical shifts, d, are referred to TMS .1H) and
CFCl3 .19F), respectively. The EI low- and high-resolution
mass spectra were measured on a JEOL JMS-700TZ, JMS-
FABmate or JMS-HX110. The elemental micro-analyses
were done using a Yanagimoto CHN Corder MT-5. The
Et3N±nHF and pyridine±nHF complexes were prepared
by the addition of freshly distilled amine to anhydrous HF
at 08C.10 TBAF was purchased from Aldrich as a 1 M solu-
tion of THF and used after removing the solvent under
reduced pressure. The alkyl iodides 1b±e were prepared
by iodination of the corresponding alcohols with chlorotri-
methylsilane and sodium iodide.12 The iodo esters 1f±i were
prepared by esteri®cation of the corresponding iodo
alcohols and 10 was prepared from cyclohexene by the
reported method.13
4.1.4. 1-Acetoxy-6-¯uorohexane /3c). Colorless oil; IR

3318
M. Sawaguchi et al. / Tetrahedron 57 +2001) 3315±3319
.neat): 1740 .CvO), 1239 .C±OR), 1041.C±OR) cm21. 1H
NMR dˆ4.45 .2H, dt, Jˆ47.3, 6.1 Hz), 4.07 .2H, t,
Jˆ6.8 Hz), 2.05 .3H, s), 1.76±1.63 .4H, m), 1.49±1.36
.4H, m). 19F NMR dˆ2218.3 .1F, tt, Jˆ47.3, 25.0 Hz).
HRMS.EI) Calcd for C8H16FO2 .M111) 163.1134. Found
163.1132.
sealed and the reaction mixture was stirred at 808C for 1 h.
After cooling to room temperature, pentane .1 mol) was
added and GLPC analysis showed the formation of 7 and
8 in a ratio of 1:2.
4.1.12. 4-/Fluoromethyl)benzoic acid 4-¯uorobutyl ester
/9). Colorless oil; IR .neat): 1719 .CvO), 1276 .C±OR)
1
cm21. H NMR dˆ8.06 .2H, d, Jˆ7.8 Hz), 7.44 .2H, d,
4.1.5. Methyl 11-¯uoroundecanoate /3d). Colorless oil; IR
.neat): 1741 .CvO), 1437.C±F), 1172 .C±OCH 3) cm21
.
Jˆ7.8 Hz), 5.45 .2H, d, Jˆ47.1 Hz), 4.60±4.45 .2H, m),
4.38 .2H, t, Jˆ6.3 Hz), 1.97±1.81 .4H, m). 19F NMR
dˆ2213.4 .1F, Jˆ47.1 Hz), dˆ2219.3±2219.6 .1F, m).
HRMS.EI) Calcd for C12H14F2O2 228.0962. Found
228.0977. Anal.: C, 63.15; H, 6.18. Found: C, 62.92; H,
6.27.
1H NMR dˆ4.44 .2H, dt, Jˆ47.6, 6.2 Hz), 3.67 .3H, s),
2.30 .2H, t, Jˆ7.6 Hz), 1.75±1.60 .4H, m), 1.39±1.29
.12H, m). 19F NMR dˆ2218.3 .1F, tt, Jˆ47.6, 25.0 Hz).
HRMS.EI) Calcd for C12H23FO2 218.1682. Found
218.1669. Anal.: C, 66.02; H, 10.62. Found: C, 66.04; H,
10.65.
4.1.13. 1-Fluoro-2-hexyloxycyclohexane /11). Colorless
1
oil; IR .neat): 1455 .C±F), 1112 .C±OR) cm21. H NMR
4.1.6. 1-Chloro-10-¯uorodecane /3e). Colorless oil; IR
.neat): 1467.C±F) cm
21
.
1H NMR dˆ4.44 .2H, dt,
dˆ4.37.1H, dm, Jˆ50.4 Hz), 3.61±3.52 .2H, m), 3.33±
3.24 .1H, m), 2.09±1.98 .2H,m), 1.68±1.20 .14H, m),
0.89 .3H, t, Jˆ6.8 Hz). 19F NMR dˆ2179.4±2179.9
.1F, dm, Jˆ50.4 Hz). HRMS.EI) Calcd for C12H23FO
202.1733. Found 202.1743. Anal.: C, 71.24; H, 11.46.
Found: C, 71.39; H, 11.56.
Jˆ47.3, 6.1 Hz), 3.53 .2H, t, Jˆ6.8 Hz), 1.62±1.80 .4H,
m), 1.27±1.44 .12H, m). 19F NMR dˆ2218.3 .1F, tt,
Jˆ47.3, 25.0 Hz). MS m/z 174 .M12HF), 158
.M12HCl), 91 .M12103), 69 .M12125), 55 .M12139),
41 .M12153). Anal. Calcd for C10H20ClF: C, 61.68; H,
10.35. Found: C, 61.66; H, 10.31.
4.1.14. 3-Hexyloxycyclohexene /13). Colorless oil; IR
1
.neat): 1099 .C±OR) cm21. H NMR dˆ5.86±5.74 .2H,
4.1.7. 4-Methylbenzoic acid 4-¯uorobutyl ester /3f).
Colorless oil; IR .neat): 1717 .CvO), 1612 .Ph), 1275
m), 3.85±3.79 .1H, m), 3.53±3.41 .2H, m), 2.08±1.91
.8H, m), 1.84±1.49 .6H, m), 0.89 .3H, t, Jˆ6.8 Hz).
HRMS.EI) Calcd for C12H22O 182.1671. Found 182.1673.
1
.C±OR), 1109 .C±OR) cm21. H NMR dˆ7.93 .2H, d,
Jˆ8.1 Hz), 7.24 .2H, d, Jˆ8.1 Hz), 4.58±4.46 .2H, m),
4.36 .2H, t, Jˆ6.2 Hz), 2.41 .3H, s), 1.94±1.80 .4H, m).
19F NMR dˆ2218.9±2219.3 .1F, m). HRMS.EI) Calcd
for C12H15FO2 210.1056. Found 210.1052. Anal.: C,
68.55; H, 7.19. Found: C, 68.43; H, 7.27.
References
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4.1.8. 1-Acetoxy-6-¯uoroheptane /3g). Colorless oil; IR
.neat): 1740 .CvO), 1464 .C±F), 1241 .C±OR), 1041
1
.C±OR) cm21. H NMR dˆ4.75±4.55 .1H, m), 4.06 .2H,
t, Jˆ6.7Hz), 2.05 .3H, s), 1.71±1.28 .11H, m). 19F NMR
dˆ2172.65±2173.10 .1F, m). HRMS.EI) Calcd for
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1
oil; IR .neat): 1359 .±SO2±), 1176 .±SO2±) cm21. H
NMR dˆ7.79 .2H, d, Jˆ8.3 Hz), 7.35 .2H, d, Jˆ8.3 Hz),
4.40 .2H, dt, Jˆ47.3, 6.1 Hz), 4.03 .2H, t, Jˆ6.3 Hz), 2.45
.3H, s), 1.69±1.59 .4H, m), 1.38±1.34 .4H, m). 19F NMR
dˆ2219.1 .1F, tt, Jˆ47.3, 25.0 Hz). HRMS.EI) Calcd for
C13H19FSO3 274.1039. Found 274.1040. Anal.: C, 56.91; H,
6.98. Found: C, 56.91; H, 6.99.
4.1.10. 4-/Chloromethyl)benzoic acid 4-¯uorobutyl ester
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cm21. H NMR dˆ8.03 .2H, d, Jˆ8.3 Hz), 7.47 .2H, d,
Jˆ8.3 Hz), 4.62 .2H, s), 4.60±4.45 .2H, m), 4.38 .2H, t,
Jˆ6.2 Hz), 1.95±1.80 .4H, m). 19F NMR dˆ2219.2±
2219.6 .1F, m). HRMS.EI) Calcd for C12H14ClFO2
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