Copper(I)-catalyzed addition of trifluoromethylated benzyl radicals derived from aryltrifluoroethyl bromides to terminal olefins

Article abstract of DOI:10.1016/S0022-1139(02)00002-7

Relatively unreactive aryltrifluoroethyl bromides were reacted with 1-octene in the presence of CuCl and 2,2′-bipyridyl at high temperatures. Trifluoromethylated benzyl radical was generated, and a diastereomer mixtures of radical adducts was obtained wit

Full text of DOI:10.1016/S0022-1139(02)00002-7

Journal of Fluorine Chemistry 114 ꢀ2002) 91±98
CopperꢀI)-catalyzed addition of tri¯uoromethylated benzyl radicals
derived from aryltri¯uoroethyl bromides to terminal ole®ns
Takashi Okano*,Hirokazu Sugiura,Masataka Fumoto,Hiroyoshi Matsubara,
1
Takahiro Kusukawa,Makoto Fujita
Department of Applied Chemistry, Graduate School of Engineering, Nagoya University,
Chikusa-ku, Nagoya 464-8603, Japan
Received 2 October 2001; received in revised form 18 December 2001; accepted 20 December 2001
Abstract
Relatively unreactive aryltri¯uoroethyl bromides were reacted with 1-octene in the presence of CuCl and 2,20-bipyridyl at high
temperatures. Tri¯uoromethylated benzyl radical was generated,and a diastereomer mixture of radical adducts was obtained with a
ꢀ60±70):ꢀ40±30) diastereomer ratio. Ph3SnH reduction of the adducts gave the corresponding hydrocarbons with an isolated tri¯uoromethyl
group. The reactions with styrene or aromatic and aliphatic silyl enol ethers led to the formation of tri¯uorodiphenylbutene and b-
tri¯uoromethylated ketones,respectively. # 2002 Elsevier Science B.V. All rights reserved.
Keywords: Tri¯uoromethyl compound; Radical addition; Atom-transfer reaction; CuꢀI) catalysts; Tin hydride reduction
1. Introduction
activating electron-withdrawing group for lowering the
energy level of the sÃCÀBr-orbital is only the tri¯uoromethyl
group accompanied with a generally radical-stabilizing aryl
group. Itoh and Nagashima et al. [5] reported the rate
acceleration by CuCl/2,20-dipyridyl complex for the radical
cyclization of N-alkenyltrichloroacetamides. Although bro-
mides 1 appear still less reactive than trichloroacetamides,
this catalyst system could work also in the intermolecular
reaction of bromides 1.
We report here the atom-transfer radical reaction of
aryltri¯uoroethyl bromides 1 with some terminal ole®ns
in the presence of CuꢀI) amine complex and the following
reduction of the product bromides into ꢀtri¯uoromethyl)-
aralkanes.
Synthesis of the compounds with a tri¯uoromethyl group
[1] is an active area of organic synthesis due to their potential
biological activities [2] and the utility as a structural subunit
for the functional materials such as ferroelectric liquid
crystals [3]. However,most of the reports deal with the
synthesis of tri¯uoromethylated aromatics and heteroaro-
matics. As a new synthetic pathway for the compounds
with an isolated tri¯uoromethyl group on a straight alkyl
chain,which could be useful for a substructure of ferro-
electric liquid crystals,we propose here an atom-transfer
reaction of brominated precursors 1 with terminal ole®ns. In
the reaction,tri¯uoromethylated benzyl radicals 2 are gen-
erated by single electron transfer from copperꢀI) ꢀCuꢀI))
catalyst ꢀScheme 1). CuꢀI)-catalyzed radical generation
from polyhaloalkanes is a well known process for the
polyhalogenated compounds [4]. Since the more halogen
substitution effectively lowers the energy level of the anti-
bonding sÃ-orbital of C±X bond where an electron transfer
occurs from CuꢀI),the electrophilic radical reaction of
highly halogenated substrates with electron-rich ole®ns is
faster. In the case of aryltri¯uoroethyl bromides 1,the
2. Experimental
1H and 13C NMR spectra were collected in CDCl3 in the
presence of TMS as an internal standard at 300 and
75.4 MHz,respectively unless otherwise noted. 19F NMR
spectra ꢀ282 MHz) were recorded in CDCl3,and referenced
based on internal CF3COOC2H5 whose chemical shift was
set at À75.75 ppm down®eld ꢀd) from internal CFCl3 in
CDCl3. Preparative HPLC was performed by a Jai JAIGEL
1H or 2H GPC column ꢀ20 mm ? Â 600 mm) using a UV
detector.
* Corresponding author. Tel.: ‡81-52-789-4671; fax: ‡81-52-789-3199.
E-mail address: okano@apchem.nagoya-u.ac.jp ꢀT. Okano).
1 Co-corresponding author.
0022-1139/02/$ ± see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 2 - 1 1 3 9 ꢀ 0 2 ) 0 0 0 0 2 - 7

92
T. Okano et al. / Journal of Fluorine Chemistry 114 ,2002) 91±98
was obtained as colorless solid by stirring the solution at
room temperature overnight: mp 30±31 8C; 1H NMR d
6.093 ꢀ1H,q, J ˆ 6:0 Hz),7.44±7.695 ꢀ3H,m),7.85±7.97
ꢀ4H,m); 13C NMR d 42.01 ꢀq, J ˆ 36 Hz),121.87,123.96
ꢀq, J ˆ 278 Hz),125.41,126.22,127.32,127.98,129.27,
130.18,130.57,130.65,133.70;
19F NMR d À69.2 ꢀd,
‡
J ˆ 6 Hz); MS m/z 288 ꢀM ). Anal. Calcd. for C12H8BrF3:
C,49.86; H,2.79. Found: C,49.58; H,2.73.
Scheme 1.
2.6. 4-,1-Bromo-2,2,2-trifluoroethyl)-1,10-biphenyl ,1f)
2.1. General method for the preparation
of aryltrifluoroethylbromides
As described above,from alcohol 5f ꢀ1.60 g,6.3 mmol),
NBS ꢀ1.25 g,7.0 mmol),and ꢀPhO) P ꢀ2.17 g,7.0 mmol) in
3
CH2Cl2 ꢀ50 ml), 1f ꢀ1.20 g,60%) was obtained by stirring at
room temperature overnight as colorless solid: mp 89±
An equimolar mixture of tri¯uoroethanol 5,triphenylpho-
sphite,and NBS in CH 2Cl2 was stirred at room temperature
or under re¯uxing for several hours. The solvent was removed
under reduced pressure,and then,the residue was chromato-
graphed on a silica gel column ꢀhexane±CH2Cl2) to give pure
bromide 1. The spectral data of known bromides 1b and d
were identical to the reported ones.
1
90 8C; H NMR d 5.178 ꢀ1H,q, J ˆ 7:3 Hz),7.35±7.49
ꢀ3H,m),7.56±7.63 ꢀ6H,m);
J ˆ 34 Hz),123.43 ꢀq,
13C NMR d 46.89 ꢀq,
J ˆ 278 Hz),127.17,127.59,
127.91,128.91,129.53,129.55,131.63 ꢀq,
139.95,142.98; 19F NMR d À71.2 ꢀd, J ˆ 7 Hz); MS m/z
J ˆ 1 Hz),
‡
314 ꢀM ). Anal. Calcd. for C14H10BrF3: C,53.36; H,3.20.
Found: C,53.29; H,3.17.
2.2. 1-,1-Bromo-2,2,2-trifluoroethyl)-4-chlorobenzene ,1b)
As described above,from alcohol 5b ꢀ3.50 g,16.7 mmol),
NBS ꢀ3.03 g,17.0 mmol),and ꢀPhO) P ꢀ5.28 g,17.0 mmol)
2.7. Radical reaction of arylbromotrifluoroethanes ,1) with
1-octene
3
in CH2Cl2 ꢀ20 ml), 1b ꢀ2.36 g,52%) was obtained as color-
less oil by stirring the solution under re¯uxing for 5 h:
spectral data were identical with those reported in [14].
Bromide 1 was dissolved in 1,2-dichlorobenzene, and the
solution was degassed by sonication under N2 atmosphere.
The solution was added into preliminarily degassed mixture
of 1-octene,CuCl,and 22, 0-bipyridyl in 1,2-dichloroben-
zene. The resulting solution was re¯uxed at 180 8C for 24 h.
The cooled mixture was ®ltered. The solvent of the ®ltrate
wad removed by distillation under reduced pressure. The
residue was puri®ed by preparative HPLC with a GPC
column ꢀCHCl3) directly or after distillation under reduced
pressure ꢀ150 8C,5 mmHg).
2.3. 4-,1-Bromo-2,2,2-trifluoroethyl)toluene ,1c)
As described above,from alcohol 5c ꢀ5.77 g,30.4 mmol),
NBSꢀ6.05 g,34.0 mmol),andꢀPhO) 3Pꢀ9.43 g,30.4 mmol)in
CH2Cl2 ꢀ40 ml) at room temperature, 1c ꢀ2.53 g,33%) was
obtained as colorless oil by stirring the solution under re¯ux-
1
ing for 10 h: H NMR d 2.366 ꢀ3H,s),5.098 ꢀ1H,q, J ˆ
7:5 Hz),7.196ꢀ2H,d, J ˆ 4:2 Hz),7.388ꢀ2H,d, J ˆ 4:2 Hz);
13C NMR d 21.22,47.09 ꢀq, J ˆ 34 Hz),123.44 ꢀq,
2.8. 4-Bromo-1,1,1-trifluoro-2-phenyldecane ,3a)
J ˆ 278 Hz),128.97,129.57,129.87,140.21;
19F NMR d
As described above,bromide 3a was obtained as a mixture
of 3a1 and3a2 ꢀ66:34) from bromide1aꢀ478 mg,2.00 mmol),
1-octene ꢀ898 mg,8.00 mmol),CuCl ꢀ20 mg,0.20 mmol),
2,20-bipyridyl ꢀ63 mg,0.40 mmol),21-,dichlorobenzene
‡
À71.1 ꢀd, J ˆ 8 Hz); MS m/z 252 ꢀM ). Anal. Calcd. for
C9H8BrF3: C,42.72; H,3.19. Found: C,42.61; H,3.11.
‡
2.4. 4-,1-Bromo-2,2,2-trifluoroethyl)anisole ,1d)
ꢀ8 ml): 519 mg ꢀ74%); colorless oil; MS m/z 350 ꢀM ). Anal.
Calcd. for C16H22BrF3: C,54.71; H,6.31. Found: C,55.03; H,
6.25. NMR signals for the diastereomers were assigned
by comparison of spectra obtained from partly separated
As described above,from alcohol 5d ꢀ9.42 g,47.2 mmol),
NBS ꢀ8.90 g,50.0 mmol),and ꢀPhO) 3P ꢀ15.5 g,50.0 mmol)
in CH2Cl2 ꢀ40 ml), 1d ꢀ6.59 g,54%) was obtained as colorless
oil by stirring the solution at room temperature overnight:
spectral data were identical with those reported in [15].
1
samples: 3a1 ꢀmajor component); H NMR d 0.855 ꢀ3H,t,
J ˆ 7:2 Hz),1.22±1.56 ꢀ8H,m),1.68±1.92 ꢀ2H,m),2.25±
2.40 ꢀ2H,m),3.480 ꢀ1H,tt, J ˆ 8:4,5.1 Hz),3.772 ꢀ1H,dqd,
J ˆ 9:3,9.3,5.4 Hz),7.28±7.42 ꢀ5H,m); 13C NMR d 14.00,
2.5. 1-,1-Bromo-2,2,2-trifluoroethyl)naphthalene ,1e)
As described above,from alcohol 5e ꢀ4.76 g,21.0 mmol),
NBS ꢀ3.92 g,22.0 mmol),and ꢀPhO) P ꢀ6.83 g,22.0 mmol)
22.49,27.24,28.57,31.53,37.83 ꢀq, J ˆ 1 Hz),39.66,48.71
2
ꢀq, J ˆ 27 Hz),54.21,120±135;
19F NMR d À70.0 ꢀd,
2 No rigorous assignment was achieved because of the low S/N ratios of
CF3 carbon signals.
3
in CH2Cl2 ꢀ30 ml) at room temperature, 1e ꢀ3.89 g,64%)

T. Okano et al. / Journal of Fluorine Chemistry 114 ,2002) 91±98
93
J ˆ 9 Hz): 3a2 ꢀminor component); 1H NMR d 0.874 ꢀ3H,t,
6.2 Hz),3.612 ꢀ1H,qt,
J ˆ 9:0,6.9 Hz),3.998 ꢀ1H,tt,
J ˆ 7:2 Hz),1.22±1.56 ꢀ8H,m),1.68±1.92 ꢀ2H,m),2.32±
2.46 ꢀ1H,m),2.586 ꢀ1H,dt, J ˆ 15:0,6.6 Hz),3.607 ꢀ1H,qt,
J ˆ 9:3,7.2 Hz),4.001 ꢀ1H,tt, J ˆ 6:9,6.9 Hz),7.28±7.42
ꢀ5H,m); 13C NMR d 14.01,22.51,27.05,28.48,31.55,38.06,
39.16 ꢀq, J ˆ 1 Hz),48.05 ꢀq, J ˆ 27 Hz),54.06,120±135
ꢀsee footnote 3); 19F NMR d À69.6 ꢀd, J ˆ 9 Hz).
J ˆ 7:8,6.0 Hz),7.19±7.42 ꢀ4H,m);
13C NMR d 14.00,
22.51,28.57,31.52,39.15 ꢀq, J ˆ 2 Hz),38.25,47.55 ꢀq,
J ˆ 27 Hz),53.90,121±135 ꢀsee footnote 3),133.22 ꢀq,
J ˆ 2 Hz); 19F NMR d À69.7 ꢀd, J ˆ 9 Hz).
2.11. 4-Bromo-1,1,1-trifluoro-2-,4-
methyoxyphenyl)decane ,3d)
2.9. 4-Bromo-2-,4-chlorophenyl)-1,1,1-trifluorodecane
,3b)
As described above,bromide 3d was obtained as a
mixture of 3d1 and 3d2 ꢀ68:32) from bromide 1d
ꢀ536 mg,2.00 mmol),1-octene ꢀ898 mg,8.00 mmol),CuCl
As described above,bromide 3b was obtained as a
mixture of 3b1 and 3b2 ꢀ60:40) from bromide 1b
ꢀ544 mg,2.00 mmol),1-octene ꢀ898 mg,8.00 mmol),CuCl
ꢀ20 mg,0.20 mmol),22,
1,2-dichlorobenzene ꢀ8 ml): 229 mg ꢀ30%); colorless oil;
0-bipyridyl ꢀ63 mg,0.40 mmol),
‡
ꢀ20 mg,0.20 mmol),22,
1,2-dichlorobenzene ꢀ8 ml): 673 mg ꢀ81%); colorless oil;
0-bipyridyl ꢀ63 mg,0.40 mmol),
MS m/z 380 ꢀM ). Anal. Calcd. for C17H24BrF3O: C,53.55;
H,6.34. Found: C,53.17; H,6.21. NMR signals for the
diastereomers were assigned by comparison of spectra
obtained from partly separated samples: 3d1 ꢀmajor com-
‡
MS m/z 384 ꢀM ). Anal. Calcd. for C16H21BrClF3: C,49.83;
H,5.49. Found: C,49.48; H,5.30. NMR signals for the
diastereomers were assigned by comparison of spectra
obtained from partly separated samples: 3b1 ꢀmajor com-
1
ponent); H NMR d 0.858 ꢀ3H,t, J ˆ 6:9 Hz) 1.22±1.92
ꢀ10H,m),2.16±2.42 ꢀ2H,m),3.383±3.603 ꢀ1H,m),3.64±
3.80 ꢀ1H,m),3.807 ꢀ3H,s),6.907 ꢀ2H,d, J ˆ 8:7 Hz),7.229
ꢀ2H,d, J ˆ 8:7 Hz); 13C NMR d 14.00,22.50,27.28,27.28,
31.54,37.84 ꢀq, J ˆ 2 Hz),39.67,47.92 ꢀq, J ˆ 27 Hz),
54.37,55.21,114.21,120±135 ꢀsee footnote 3),159.62; 19F
1
ponent); H NMR d 0.861 ꢀ3H,t, J ˆ 6:8 Hz) 1.23±1.52
ꢀ8H,m),1.68±1.92 ꢀ2H,m),2.17±2.40 ꢀ2H,m),3.438 ꢀ1H,
dddd, J ˆ 11:1,8.1,5.4,3.3 Hz),3.766 ꢀ1H,dqd, J ˆ 11:7,
9.3,3.9 Hz),7.19±7.42 ꢀ4H,m); 13C NMR d 14.00,22.49,
1
28.49,31.52,37.70 ꢀq,
J ˆ 27 Hz),53.89,120±135 ꢀsee footnote 3),131.63 ꢀq,
J ˆ 2 Hz),39.62,48.22 ꢀq,
NMR d À70.3 ꢀd, J ˆ 9 Hz): 3d2 ꢀminor component); H
NMR d 0.874 ꢀ3H,t, J ˆ 7:2 Hz),1.23±1.64 ꢀ8H,m),1.70±
J ˆ 2 Hz); 19F NMR d À70.1 ꢀd, J ˆ 9 Hz): 3b2 ꢀminor
1.91 ꢀ2H,m),2.17±2.40 ꢀ1H,m),2.574 ꢀ1H,dt,
J ˆ 14:9,
1
component); H NMR d 0.878 ꢀ3H,t, J ˆ 6:6 Hz),1.23±
6.2 Hz),3.64±3.80 ꢀ1H,m),3.802 ꢀ3H,s),3.982 ꢀ1H,tt,
J ˆ 7:8,6.0 Hz),6.894 ꢀ2H,d, J ˆ 8:7 Hz),7.219 ꢀ2H,d,
J ˆ 8:7 Hz); 13C NMR d 14.00,22.53,27.04,28.49,31.57,
39.09 ꢀq, J ˆ 2 Hz),39.67,47.23 ꢀq, J ˆ 26 Hz),54.02,
55.23,114.25,120±135 ꢀsee footnote 3),159.57; 19F NMR d
À70.1 ꢀd, J ˆ 9 Hz).
1.64 ꢀ8H,m),1.70±1.91 ꢀ2H,m),2.17±2.40 ꢀ1H,m),2.574
ꢀ1H,dt, J ˆ 14:9,6.2 Hz),3.612 ꢀ1H,qt, J ˆ 9:0,6.9 Hz),
3.998 ꢀ1H,tt, J ˆ 7:8,6.0 Hz),7.19±7.42 ꢀ4H,m);
13C
NMR d 14.00,22.51,28.57,31.52,39.15 ꢀq,
J ˆ 2 Hz),
38.25,47.55 ꢀq, J ˆ 27 Hz),53.90,121±135 ꢀsee footnote
3),133.22 ꢀq, J ˆ 2 Hz); 19F NMR d À69.7 ꢀd, J ˆ 9 Hz).
2.12. 4-Bromo-1,1,1-trifluoro-2-,1-naphthyl)decane ,3e)
2.10. 4-Bromo-1,1,1-trifluoro-2-,4-methylphenyl)decane
,3c)
As described above,bromide 3e was obtained as a mixture
of 3e1 and 3e2 ꢀ64:36) from bromide 1e ꢀ576 mg,
2.00 mmol),1-octene ꢀ898 mg,8.00 mmol),CuCl ꢀ20 mg,
As described above,bromide 3c was obtained as a mixture
of 3c1 and 3c2 ꢀ58:42) from bromide 1c ꢀ504 mg,
2.00 mmol),1-octene ꢀ898 mg,8.00 mmol),CuCl ꢀ20 mg,
0
0.20 mmol),2,2 -bipyridyl ꢀ63 mg,0.40 mmol),1,2-dichlor-
obenzene ꢀ8 ml): 144 mg ꢀ18%); colorless oil; MS m/z 400
‡
0
0.20 mmol),2,2 -bipyridyl ꢀ63 mg,0.40 mmol),1,2-dichlor-
obenzene ꢀ8 ml): 494 mg ꢀ68%); colorless oil; MS m/z 364
ꢀM ). Anal. Calcd. for C20H24BrF3O: C,59.86; H,6.03.
Found: C,59.94; H,5.94. NMR signals for the diastereomers
were assigned by comparison of spectra obtained from
partly separated samples: 3e1 ꢀmajor component); 1H
NMR d 0.838 ꢀ3H,t, J ˆ 6:9 Hz) 1.10±1.55 ꢀ8H,m),
1.60±1.80 ꢀ2H,m),2.46±2.64 ꢀ2H,m),3.514 ꢀ1H,tt,
‡
ꢀM ). Anal. Calcd. for C17H24BrF3: C,55.90; H,6.62.
Found: C,55.64; H,6.59. NMR signals for the diastereomers
were assigned by comparison of spectra obtained from
partly separated samples: 3c1 ꢀmajor component); 1H
NMR d 0.858 ꢀ3H,t, J ˆ 6:9 Hz) 1.22±1.92 ꢀ8H,m),
1.64±1.92 ꢀ2H,m),2.16±2.42 ꢀ2H,m),3.438 ꢀ1H,dddd,
J ˆ 7:8,6.6 Hz),4.838 ꢀ1H,dqd,
J ˆ 9:0,9.0,5.7 Hz),
7.46±7.62 ꢀ4H,m),7.83±7.90 ꢀ2H,m),8.236 ꢀ1H,d,
J ˆ 8:7 Hz); 13C NMR d 13.99,22.48,27.22,28.56,
31.52,38.72 ꢀq, J ˆ 2 Hz),39.72,41.66 ꢀq, J ˆ 27 Hz),
54.19,120±135 ꢀsee footnote 3); 19F NMR d À69.8 ꢀd,
J ˆ 9 Hz): 3e2 ꢀminor component); 1H NMR d 0.832 ꢀ3H,t,
J ˆ 7:2 Hz),1.10±1.55 ꢀ8H,m),1.70±1.91 ꢀ2H,m),2.25±
2.50 ꢀ1H,m),2.574 ꢀ1H,ddd, J ˆ 15:0,7.5,5.7 Hz),4.132
ꢀ1H,tt, J ˆ 7:5,6.0 Hz),4.61±4.76 ꢀ1H,m),7.46±4.62
J ˆ 11:1,8.1,5.4,3.3 Hz),3.766 ꢀ1H,dqd,
J ˆ 11:7,9.3,
3.9 Hz),7.19±7.42 ꢀ4H,m); 13C NMR d 14.00,22.49,28.49,
31.52,37.70 ꢀq, J ˆ 2 Hz),39.62,48.22 ꢀq, J ˆ 27 Hz),
53.89,120±135 ꢀsee footnote 3),131.63 ꢀq, J ˆ 2 Hz); 19F
1
NMR d À70.1 ꢀd, J ˆ 9 Hz): 3c2 ꢀminor component); H
NMR d 0.878 ꢀ3H,t, J ˆ 6:6 Hz),1.23±1.64 ꢀ8H,m),1.70±
1.91 ꢀ2H,m),2.17±2.40 ꢀ1H,m),2.574 ꢀ1H,dt,
J ˆ 14:9,

94
T. Okano et al. / Journal of Fluorine Chemistry 114 ,2002) 91±98
ꢀ4H,m),7.83±7.90 ꢀ2H,m),8.144 ꢀ1H,d,
J ˆ 8:4 Hz); 13
C
1.74±1.87 ꢀ1H,m),1.92±2.03 ꢀ1H,m),3.188 ꢀ2H,dqd,
J ˆ 11:1,9.3,3.9 Hz),7.207 ꢀ2H,d,
NMR d 13.99,22.48,27.07,28.40,31.43,38.53,40.11
ꢀq, J ˆ 2 Hz),40.90 ꢀq, J ˆ 26 Hz),54.62,55.23,120±135
ꢀsee footnote 3); 19F NMR d À68.3 ꢀd, J ˆ 9 Hz).
J ˆ 8:7 Hz),7.328
ꢀ1H,d, J ˆ 8:7 Hz); 13C NMR d 14.06,22.64,26.69,28.60
ꢀq, J ˆ 2 Hz),29.16,29.20,29.21,31.77,50.08 ꢀq,
J ˆ 26 Hz),127.05 ꢀq,
J ˆ 280 Hz),128.00,128.58,
2.13. 4-[3-Bromo-1-,trifluoromethyl)nonyl]-1,10-biphenyl
,3f)
129.10,135.03 ꢀq, J ˆ 2 Hz); 19F NMR d À70.3 ꢀd,
‡
J ˆ 9 Hz); MS m/z 306 ꢀM ). Anal. Calcd. for C16H22ClF3:
C,62.64; H,7.23. Found: C,62.26; H,6.93.
As described above,bromide 3f was obtained as a mixture
of 3f1 and 3f2 ꢀ68:32) from bromide 1f ꢀ576 mg,
2.00 mmol),1-octene ꢀ898 mg,8.00 mmol),CuCl ꢀ20 mg,
2.16. 1,1,1-Trifluoro-2-,4-methylphenyl)decane ,4c)
0
0.20 mmol),2,2 -bipyridyl ꢀ63 mg,0.40 mmol),1,2-dichlor-
obenzene ꢀ8 ml): 147 mg ꢀ35%); colorless oil; MS m/z 426
As described above,a mixture of bromide 3c ꢀ182 mg,
0.5 mmol) and Ph3SnH ꢀ351 mg,1.0 mmol) was mixed
without solvent,and the resulting mixture was heated at
90 8C for 5 h. The mixture was distilled in a glass tube
oven ꢀ140 8C,5 mmHg) to obtain 4c: 130 mg ꢀ91%); color-
‡
ꢀM ). Anal. Calcd. for C22H26BrF3: C,61.83; H,6.13.
Found: C,61.51; H,5.99. NMR signals for the diastereomers
were assigned by comparison of spectra obtained from
partly separated samples: 3f1 ꢀmajor component); 1H
NMR d 0.852 ꢀ3H,t, J ˆ 7:2 Hz),1.20±1.55 ꢀ8H,m),
1.65±1.95 ꢀ2H,m),2.20±2.47 ꢀ2H,m),3.549 ꢀ1H,dtd,
1
less oil; H NMR d 0.858 ꢀ3H,t, J ˆ 6:9 Hz),1.13±1.27
ꢀ12H,m),1.78±1.87 ꢀ1H,m),1.89±2.02 ꢀ1H,m),2.336 ꢀ3H,
s),3.161 ꢀ1H,dqd, J ˆ 11:1,9.3,4.2 Hz),7.154 ꢀ4H,s); 13C
J ˆ 10:8,5.4,3.3 Hz),3.824 ꢀ1H,dqd,
J ˆ 9:3,9.3,
NMR d 14.05,21.08,22.63,26.72,28.60 ꢀq,
J ˆ 2 Hz),
5.4 Hz),7.33±7.62 ꢀ5H,m);
27.26,28.60,31.53,37.82 ꢀt,
13C NMR d 14.00,22.49,
J ˆ 2 Hz),36.69,48.42 ꢀq,
29.19,29.24,29.24,31.80,49.42 ꢀq, J ˆ 26 Hz),127.12 ꢀq,
J ˆ 279 Hz),128.87,129.29,131.95 ꢀq, J ˆ 2 Hz),137.70;
‡
J ˆ 27 Hz),54.27,125±142 ꢀsee footnote 3); 19F NMR d
19F NMR d À69.6 ꢀd, J ˆ 9 Hz); MS m/z 322 ꢀM ). Anal.
1
À69.9 ꢀd, J ˆ 9 Hz): 3e2 ꢀminor component); H NMR d
Calcd. for C17H25F3: C,71.30; H,8.80. Found: C,70.93; H,
8.80.
0.870 ꢀ3H,t, J ˆ 6:6 Hz),1.20±1.55 ꢀ8H,m),1.65±1.95
ꢀ2H,m),2.25±2.50 ꢀ1H,m),2.619 ꢀ1H,dt,
6.6 Hz),3.659 ꢀ1H,qt,
J ˆ 15:0,
J ˆ 9:3,7.2 Hz),4.044 ꢀ1H,tt,
2.17. 1,1,1-Trifluoro-2-,4-methoxyphenyl)decane ,4d)
J ˆ 7:2,6.3 Hz),7.33±7.62 ꢀ5H,m);
13C NMR d 14.02,
22.53,27.06,28.51,31.53,38.11,39.19 ꢀq, J ˆ 2 Hz),47.73
ꢀq, J ˆ 26 Hz),54.08,125±145 ꢀsee footnote 3); 19F NMR d
À69.5 ꢀd, J ˆ 9 Hz).
As described above,a mixture of bromide 3d ꢀ114 mg,
0.3 mmol) and Ph3SnH ꢀ211 mg,0.6 mmol) was mixed
without solvent,and the resulting mixture was heated at
90 8C for 9 h. The mixture was distilled in a glass tube oven
ꢀ140 8C,5 mmHg) to obtain 4d: 91 mg ꢀquantity); colorless
2.14. 1,1,1-Trifluoro-2-phenyldecane ,4a)
1
oil; H NMR d 0.860 ꢀ3H,t, J ˆ 6:8 Hz),1.13±1.26 ꢀ12H,
A mixture of bromide 3a ꢀ351 g,1.0 mmol) and Ph SnH
3
m),1.76±1.88 ꢀ1H,m),1.91±2.01 ꢀ1H,m),3.150 ꢀ1H,dqd,
J ˆ 11:1,9.6,3.9 Hz),3.798 ꢀ3H,s),6.881 ꢀ2H,d,
ꢀ702 mg,2.0 mmol) was mixed without solvent,and the
resulting mixture was heated at 90 8C for 8 h. The mixture
was distilled in a glass tube oven ꢀ140 8C,5 mmHg) to
obtain 4a: 270 mg ꢀquantity); colorless oil; 1H NMR d 0.858
ꢀ3H,t, J ˆ 6:6 Hz),1.13±1.27 ꢀ12H,m),1.79±2.04 ꢀ2H,m),
3.202 ꢀ1H,dqd, J ˆ 10:8,9.6,4.2 Hz),7.24±7.39 ꢀ5H,m);
13C NMR d 14.06,22.64,26.69,28.6 ꢀq, J ˆ 2 Hz),29.16,
J ˆ 9:0 Hz),7.190 ꢀ3H,d,
J ˆ 9:0 Hz); 13C NMR d
J ˆ 2 Hz),29.17,29.20,
14.06,22.62,26.68,28.55 ꢀq,
29.24,31.78,49.20 ꢀq, J ˆ 26 Hz),55.16,113.95,126.91
ꢀq, J ˆ 2 Hz),127.12 ꢀq, J ˆ 280 Hz),130.02,159.27; 19F
‡
NMR d À70.7 ꢀd, J ˆ 9 Hz); MS m/z 302 ꢀM ). Anal.
Calcd. for C17H25F3: C,67.53; H,8.33. Found: C,67.35;
H,8.15.
29.20,29.21,31.77,50.08 ꢀq,
J ˆ 26 Hz),127.05 ꢀq,
J ˆ 280 Hz),128.00,128.58,129.01,135.03 ꢀq,
J ˆ 2 Hz); 19F NMR d À70.3 ꢀd, J ˆ 9 Hz); MS m/z 272
2.18. 1,1,1-Trifluoro-2-,1-naphthyl)decane ,4e)
‡
ꢀM ). Anal. Calcd. for C16H23F3: C,70.56; H,8.51. Found:
C,70.20; H,8.42.
As described above,a mixture of bromide 3e ꢀ80 mg,
0.2 mmol) and Ph3SnH ꢀ140 mg,0.4 mmol) was mixed
without solvent,and the resulting mixture was heated at
90 8C for 11 h. The mixture was distilled in a glass tube oven
ꢀ160 8C,5 mmHg) to obtain 4d: 0.058 g ꢀ90%); colorless
2.15. 2-,4-Chlorophenyl)-1,1,1-trifluorodecane ,4b)
As described above,a mixture of bromide 3b ꢀ246 mg,
0.5 mmol) and Ph3SnH ꢀ351 mg,1.0 mmol) was mixed
without solvent,and the resulting mixture was heated at
90 8C for 5 h. The mixture was distilled in a glass tube oven
ꢀ140 8C,5 mmHg) to obtain 4b: 154 mg ꢀquantity); colorless
oil; 1H NMRd 0.860ꢀ3H,t, J ˆ 6:6 Hz),1.09±1.27ꢀ12H,m),
1
oil; H NMR d 0.831 ꢀ3H,t, J ˆ 6:6 Hz),1.00±1.30 ꢀ12H,
m),1.96±2.08 ꢀ1H,m),2.11±2.25 ꢀ1H,m),4.15±4.34 ꢀ1H,
m),7.41±7.66 ꢀ4H,m),7.835 ꢀ1H,d,
J ˆ 8:1 Hz),7.886
ꢀ1H,d, J ˆ 8:5 Hz),8.062 ꢀ1H,d, J ˆ 8:4 Hz); 13C NMR d
14.05,22.58,26.68,29.10,29.15,29.36,29.44,31.71,42.76

T. Okano et al. / Journal of Fluorine Chemistry 114 ,2002) 91±98
95
ꢀq, J ˆ 26 Hz),122±135 ꢀsee footnote 3),122.56,125.32,
125.60,126.84,128.50,129.09,129.14,131.24ꢀq, J ˆ 2 Hz),
136.13,136.19; 19F NMR d À69.6 ꢀd, J ˆ 9 Hz); MS m/z 322
ketone 9 was obtained by distillation ꢀ150 8C/5 mmHg)
followed by GPC ꢀCHCl3) as colorless oil: 521 mg
1
ꢀ94%); mp 63±4 8C; H NMR d 3.592 ꢀ1H,dd, J ˆ 18:0,
‡
ꢀM ). Anal. Calcd. for C20H25F3: C,74.51; H,7.82. Found: C,
4.5 Hz),3.704 ꢀ1H,dd, J ˆ 18:0,9.9 Hz),4.248 ꢀ1H,qdd,
J ˆ 10:0,9.9,4.5 Hz),7.25±7.47 ꢀ7H,m),7.565 ꢀ1H,tt,
74.18; H,7.48.
J ˆ 7:5,1.5 Hz),7.90±7.94 ꢀ2H,m);
13C NMR d 38.25
ꢀq, J ˆ2 Hz),44.76 ꢀq, J ˆ 27 Hz),126.94 ꢀq, J ˆ 279 Hz),
2.19. 4-[1-,Trifluoromethyl)nonyl]-1,1'-biphenyl ,4f)
128.01,128.27,128.67,128.70,129.01,131.53,134.56
ꢀq, J ˆ 2 Hz),136.26,195.25;
As described above,a mixture of bromide 3f ꢀ85 mg,
0.2 mmol) and Ph3SnH ꢀ140 mg,0.4 mmol) was mixed
without solvent,and the resulting mixture was heated at
90 8C for 9 h. The mixture was distilled in a glass tube oven
ꢀ160 8C,5 mmHg) to obtain 4d: 70 mg ꢀquantity); colorless
19F NMR d À70.21
‡
ꢀd, J ˆ 11 Hz); MS m/z 278 ꢀM ). Anal. Calcd. for
C16H13F3O: C,69.06; H,4.71. Found: C,68.93; H,4.64.
2.22. 1,1,1-Trifluoro-2-phenyl-4-nonanone ,10)
1
oil; H NMR d 0.857 ꢀ3H,t, J ˆ 6:9 Hz),1.14±1.35 ꢀ12H,
m),1.885 ꢀ1H,ddt, J ˆ 14:1,10.8,7.5 Hz),2.012 ꢀ1H,dtd,
As described as above a mixture of bromide 2a ꢀ478 mg,
0-bipyridyl ꢀ63 mg,
J ˆ 14:1,7.8,4.5 Hz),3.249 ꢀ1H,dqd,
J ˆ 10:8,9.6,
2 mmol),CuCl ꢀ20 mg,0.2 mmol),22,
4.5 Hz),7.30±7.61 ꢀ9H,m);
26.73,28.61 ꢀq, J ˆ 2 Hz),29.18,29.23,31.78,49.75 ꢀq,
J ˆ 26 Hz),127.05 ꢀq, J ˆ 280 Hz),127.06,127.28,
127.40,128.77,129.12,129.39,133.99 ꢀq,
13C NMR d 14.07,22.62,
0.4 mmol),and 2-heptanone trimethylsilyl enol ether
ꢀ1.489 g,8 mmol) in 12, -dichlorobenzene ꢀ8 ml) accompa-
nied with molecular sieves 4A ꢀ2 g) ketone 10 as colorless
1
J ˆ 2 Hz),
oil: 257 mg ꢀ48%); H NMR d 0.835 ꢀ3H,t, J ˆ 7:5 Hz),
136.18; 19F NMR d À70.2 ꢀd, J ˆ 9 Hz); MS m/z 348
1.04±1.25 ꢀ4H,m),1.483 ꢀ2H,tt,
J ˆ 7:8,7.5 Hz),2.277
‡
ꢀM ). Anal. Calcd. for C22H27F3: C,75.83; H,7.81. Found:
C,76.04; H,7.41.
ꢀ1H,dt, J ˆ 16:5,7.2 Hz),2.392 ꢀ1H,dt, J ˆ 16:5,7.5 Hz),
3.039 ꢀ2H,d, J ˆ 6:9 Hz),4.031 ꢀ1H,qt, J ˆ 9:5,6.9 Hz),
7.28±7.39 ꢀ5H,m); 13C NMR d 13.76,22.29,23.14,31.08,
42.03 ꢀq, J ˆ 2 Hz),43.30,44.59 ꢀq, J ˆ 28 Hz),126.74 ꢀq,
J ˆ 279 Hz),128.26,128.63,128.91,134.47 ꢀq, J ˆ 2 Hz),
2.20. ,E)-1,1,1-Trifluoro-2,4-diphenyl-3-butene ,8)
A freshly degassed mixture of bromide 1a ꢀ478 mg,
‡
206.26; 19F NMR d À70.5 ꢀd, J ˆ 9 Hz); MS m/z 272 ꢀM ).
2 mmol),CuCl ꢀ20 mg,0.2 mmol),22,
0-bipyridyl ꢀ63 mg,
Anal. Calcd. for C15H19F3O: C,66.16H,7.03. Found: C,
65.88; H,6.92.
0.4 mmol),and styrene ꢀ833 mg,8 mmol) in 12, -dichloro-
benzene ꢀ8 ml) was re¯uxed under nitrogen for 24 h. After
®ltration of the mixture,the solvent was removed under
reduced pressure. The residue was distilled ꢀ200 8C/
5 mmHg) and ®nally ole®n 8 was isolated by GPC ꢀCHCl3)
3. Results and discussion
1
as colorless oil: 412 mg ꢀ79%); H NMR d 4.129 ꢀ1H,qd,
3.1. Preparation of aryltrifluoroethylbromides ,1)
J ˆ 9:0,8.4 Hz),6.447 ꢀ1H,dd,
J ˆ 15:9,8.4 Hz),6.582
ꢀ1H,d, J ˆ 15:9 Hz),7.15±7.38 ꢀ10H,m); 13C NMR d 53.41
While bromotri¯uorophenylethane 1a is a known com-
pound,the bromination of the corresponding alcohol 5a with
PBr5 [6] was sluggish and,in some cases,unexpected
reduction of bromide was observed. We modi®ed the pro-
cedure for bromination of the starting materials 5b±f to
obtain bromides 1b±f ꢀTable 1). The reaction of alcohols
5b±f with triphenyl phosphite and NBS in CH2Cl2 [7] at
room temperature or under re¯uxing gave the bromides 1b±f
in moderate yields.
ꢀq, J ˆ 28 Hz),122.61 ꢀq,
J ˆ 2 Hz),126.04 ꢀq,
J ˆ 281 Hz),126.53,128.14,128.22,128.60,128.82,
128.98,134.70 ꢀq, J ˆ 2 Hz),135.48,136.12; 19F NMR d
‡
À69.4 ꢀd, J ˆ 9 Hz); MS m/z 262 ꢀM ). Anal. Calcd. for
C16H13F3: C,73.27; H,5.00. Found: C,72.94; H,4.90.
2.21. 1,1,1-Trifluoro-2,4-diphenyl-4-butanone ,9)
A freshly degassed mixture of bromide 1a ꢀ478 mg,
2 mmol),CuCl ꢀ20 mg,0.2 mmol),22,
0-bipyridyl ꢀ63 mg,
3.2. Cu,I) catalyzed radical reaction of aryltrifluoroethyl
bromides
0.4 mmol),and acetophenone trimethylsilyl enol ether
ꢀ1.537 g,8 mmol) in 12, -dichlorobenzene ꢀ8 ml) accompa-
nied with molecular sieves 4A ꢀ2 g) was stirred in a sealed
tube at 180 8C for 33 h. After ®ltration of the mixture,the
solvent was removed under reduced pressure. Then,the
residue was dissolved to a mixture of Et2O ꢀ5 ml),AcOH
ꢀ5 ml),12 M HCl ꢀ1 ml). The mixture was stirred at room
temperature overnight. The mixture was extracted with
CHCl3. The combined extracts were dried over Na2SO4,
and the solvents were removed under reduced pressure. Pure
Radical reaction of bromide 1a with an excess amount of
1-octene was examined in various reaction conditions
ꢀTable 2). The reaction conditions previously used by Burton
and Kehoe [8],i.e. CuCl with ethanolamine as an additive in
t-BuOH,resulted in low yield ꢀ29%) of the atom-transfer
product 3a. Use of DMF as solvent gave a complex mixture
of ole®ns 6. While employing Itoh's catalyst system ꢀCuCl/
2,20-bipyridyl) [5] was not so successful for the reaction of

96
T. Okano et al. / Journal of Fluorine Chemistry 114 ,2002) 91±98
Table 1
Preparation of substituted aryltrifluoroethyl bromides 1
Entry
Ar
Product
Yield ꢀ%)
1
2
3
4
5
4-Cl±C6H4Cl±
1b
1c
1d
1e
1f
52
33
54
64
60
4-CH3Cl±C6H4Cl±
4-CH3OCl±C6H4Cl±
1-naphthyl±
4-C6H5Cl±C6H4Cl±
1a at room temperature,higher reaction temperatures ꢀ24 h
re¯uxing in 1,2-dichlorobenzene; 180 8C) improved the
yield of the products 3a1,2 up to 74% along with contam-
ination of a small amount of chlorinated products. The
mixture of 3a was also obtained by using tetraethylenedia-
mine ꢀTMEDA) as an additive in somewhat lower yield
although it was reported that TMEDA was superior to 2,20-
bipyridyl for the addition of CCl4 to styrene [9]. Other
copper catalysts were also used. To avoid formation of a
small amount of halogen-mixed products ꢀchlorinated pro-
ducts),CuBr is better,whereas the yield ꢀ63%) was lower
than the reaction with CuCl. Based on the reaction mechan-
ism that involves the initial electron transfer from CuꢀI)
catalyst to bromide 1,the presence of CuꢀI) is required.
decompose to unidenti®ed byproducts at high reaction
temperature ꢀ180 8C). In the low-boiling temperature sol-
vents such as 1,2-dichloroethane ꢀbp 83 8C),the reaction of
1a was sluggish ꢀ34% yield; 7 days) although the product
ratio ꢀ3a1:3a2) was improved up to 84:16. This suggests that
the radical addition reaction occurs selectively at low tem-
perature. However,at the higher temperatures,the products
equilibrated to afford the ꢀ60±70):ꢀ40±30) mixture of 3a1
and 3a2. Actually,when a 73:27 diastereomer mixture of 3a
was heated in re¯uxing 1,2-dichlorobenzene for 26 h in the
presence of CuCl ꢀ0.1 equivalents) and 2,20-bipyridyl ꢀ0.2
equivalents),it was converted into a 66:34 diastereomer
mixture.
The related aryltri¯uoroethyl bromides 1b±f were also
reacted with 1-octene in the presence of CuCl ꢀ0.1 equiva-
lents) and 2,20-bipyridyl ꢀ0.2 equivalents) in re¯uxing 1,2-
dichlorobenzene as shown in Table 3. Electron-withdrawing
4-chlorophenyl derivative 1b is a superior electron acceptor
andgave theproduct 3bin 81%yieldin a shorter reactiontime
ꢀ4 h). p-Tolyl derivative 1c reacted with 1-octene in a com-
parable yield to that of the reaction of 1a,whereas electron-
Interestingly,CuCl [10] was also effective presumably
2
because a CuꢀI) species was generated by the reduction
of CuꢀII) in situ. CuI was not a superior catalyst. Since
bromide 3a was converted into the corresponding iodide in
low yield at 180 8C on treatment with CuI in a blank
experiment,CuI exchange halogen with bromides 1a and/
or 3a to give the corresponding unstable iodides,which
Table 2
CuꢀI)-catalyzed radical reaction of 1a with 1-octene
Entry
Substrate ratio
ꢀ1a:1-octene)
Products
Catalysts ꢀmol%)
Solvent
Temperature
ꢀ8C)
Reaction
time
Yield
ꢀ%)
Product ratio
ꢀ3a1:3a2)
1
2
3
4
5
6
7
8
1:2
1:2
1:4
1:4
1:4
1:4
1:4
1:4
3a1 ‡ 3a2
6
CuCl ꢀ3); H2NCH2CH2OH ꢀ50) t-BuOH
120a
160a
180b
180b
180b
180b
180b
83b
3 days
3 days
24 h
29
41
74
47
62
63
53
34
67:33
±
CuCl ꢀ3); H2NCH2CH2OH ꢀ50) DMF
CuCl ꢀ10); 2,20-bipyridyl ꢀ20)
3a1 ‡ 3a2
3a1 ‡ 3a2
3a1 ‡ 3a2
3a1 ‡ 3a2
3a1 ‡ 3a2
3a1 ‡ 3a2
1,2-Cl2C6H4
64:36
67:33
64:36
66:34
63:37
84:16
CuCl ꢀ10); TMEDA ꢀ20)
1,2-Cl2C6H4
1,2-Cl2C6H4
1,2-Cl2C6H4
1,2-Cl2C6H4
ClCH2CH2Cl
24 h
24 h
CuBr ꢀ10); 2,20-bipyridyl ꢀ20)
CuCl2 ꢀ10); 2,20-bipyridyl ꢀ20)
CuCl ꢀ10); 2,20-bipyridyl ꢀ20)
CuCl ꢀ10); 2,20-bipyridyl ꢀ20)
24 h
24 h
7 days
a Reaction was conducted in a sealed tube.
b Reaction was carried out under refluxing condition.

T. Okano et al. / Journal of Fluorine Chemistry 114 ,2002) 91±98
97
Table 3
Preparation of 1-ꢀtrifluoromethyl)nonylarenes 4
Entry
Ar
1
Products ꢀyield ꢀ%))
Product ratio ꢀ3a1:3a2)
4
Yield ꢀ%)
1
2
3
4
5
6
C6H5±
1a
1b
1c
1d
1e
1f
3a1 ‡ 3a2 ꢀ74)
3b1 ‡ 3b2 ꢀ81)
3c1 ‡ 3c2 ꢀ68)
3d1 ‡ 3d2 ꢀ30)
3e1 ‡ 3e2 ꢀ18)
3f1 ‡ 3f2 ꢀ35)
64:36
60:40
58:42
68:32
64:36
68:32
4a
4b
4c
4d
4e
4f
Quantity
Quantity
91
4-Cl±C6H4±
4-CH3±C6H4±
4-CH3O±C6H4±
1-naphthyl±
4-C6H4±C6H4±
Quantity
90
Quantity
rich p-anisyl ꢀ1d), a-naphthyl ꢀ1e),and 4-diphenyl ꢀ 1f)
derivatives were less reactive substrates. The brominated
products 3a±f were reduced by heating at 90 8C with a
twofold amount of Ph3SnH to the corresponding tri¯uor-
oarylnonanes 4a±f in high yields as shown in Table 3.
Scheme 2.
3.3. Stereochemistry determination of adducts 3a±f with
NOESY spectra
1
The H NMR spectra of all products 3a±f show char-
the open face ꢀb-face in Scheme 2) of unfavorable 7a2,
which is 0.8 kcal/mol less stable than 7a1 at the level of
semi-empirical MNDO/PM3 calculation [12],5 leads to the
minor 3a2.
acteristic coupling pattern in the region between d 2.0 and d
4.3 assignable to H1±H4 to identify the two diastereomers.
The NOESY spectrum of the minor isomer 3a2 showed cross
peaks between H1 ꢀd 3.60) and H4 ꢀd 4.00) while no cross
peak was found in that of the major isomer 3a1. MM2
3.4. Radical reactions of bromide 1a with other olefins
3
molecular mechanics calculation [11] was performed for
4
each two possible conformers ꢀFig. 1). Conformer 3a1syn
The radical reactions of bromide 1a with several elec-
tron-rich ole®ns ꢀ4 M amount) in the presence of CuCl ꢀ0.1
equivalents) and 2,20-dipyridyl ꢀ0.2 equivalents) in re¯ux-
ing 1,2-dichlorobenzene were attempted and the results
were shown in Scheme 3. The reaction with styrene gave
no brominated products,but the obtained product was
tri¯uorodiphenylbutene 8 in 79% yield. This shows that
a stable diphenylallyl cation formed by the oxidation of the
radical intermediate with CuꢀII) species after addition of
electron-de®cient alkyl radical to styrene. As we pre-
viously reported [13],silyl enol ethers are good acceptors
for the electron-de®cient polyhalogenated alkyl radicals.
Both aryl and alkyl silyl enol ethers reacted with bromide
1a in the presence of CuCl. Since some unidenti®ed
trimethylsilyl species remained in the reaction mixture,
the reaction mixture was treated with hydrochloric acid to
give the desired ketones 9 and 10,respectively. However,
because of the labile nature of ketone silyl acetal at high
temperature,the formation of a small amount of ester was
only con®rmed by GC±MS analysis. Instead,the major
product was a mixture of tri¯uoro-a-phenethyl radical
dimers.
was 4.4 kcal/mol more stable than 3a1anti due to unfavorable
CF3±Br alignment. However,energy difference of 3a2syn and
3a2anti was small ꢀ0.3 kcal/mol). Accordingly,the plausible
stable conformation of the major isomer is 3a1syn in which
NOE between H1 and H4 is not expected. On the other hand,
that between H1 and H4 in the minor isomer 3a2syn is
expected. The major isomer 3a1syn is slightly more stable
ꢀ1.5 kcal/mol) than the minor one 3a2syn,and the product
ratios re¯ect this energy difference. Since equilibration of 3a
is slow at lower temperatures,the stereoselectivity is much
better,e.g. 84:16 for the adduct obtained at 83 8C ꢀTable 2,
entry 8),than estimated one based on the relative thermo-
dynamic stabilities. This kinetic preference to give 3a1 is
explained by considering the conformation of carbocation
intermediate 7a which would be given by oxidation of the
formed radical intermediate 2a with CuꢀII)BrX ꢀX ˆ Cl or
Br). Approach of BrÀ from an open face ꢀb-face in
Scheme 2) to favorable cation conformer 7a1 leads to the
major product 3a1. On the other hand,approach of Br À from
3 MM2 calculations were performed using a software package Cache1
Release 3.7 Cache Scientific, Inc.).
4 The suffixes syn/anti indicate stereochemistry between phenyl and
1-bromohexyl groups.
5 Semi-empirical MNDO/PM3 calculation was performed using a
software package Cache1 Release 3.7 Cache Scientific, Inc.).

98
T. Okano et al. / Journal of Fluorine Chemistry 114 ,2002) 91±98
Scheme 3.
References
[1] ꢀa) A.S. Kiselyov,L. Strekowski,Org. Prep. Proced. Int. 28 ꢀ1996)
289±318;
ꢀb) M.A. McClinton,D.A. McClinton,Tetrahedron 48 ꢀ1992) 6555±
6666.
[2] ꢀa) G. Resnati,Tetrahedron 49 ꢀ1993) 9385±9445;
ꢀb) J.T. Welch,Tetrahedron 43 ꢀ1987) 3123±3197;
ꢀc) J.T. Welch,S. Eswarakrishnan,Fluorine in Bioorganic Chem-
istry,Wiley,New York,1990.
[3] ꢀa) K. Mikami,T. Yajima,J. Kojima,M. Terada,S. Kawauchi,H.
Shirasaki,K. Okuyama,Y. Suzuki,I. Kobayashi,Y. Takanishi,H.
Takezoe,Mol. Cryst. Liq. Cryst. Sci. Technol.,Sect. A 346 ꢀ2000)
41±49;
ꢀb) Y. Aoki,H. Nohira,Liq. Cryst. 23 ꢀ1997) 87±92;
ꢀc) S. Yoshida,B. Jin,Y. Takanishi,K. Ishikawa,H. Takezoe,A.
Fukuda,T. Nakai,S. Miyajima,Mol. Cryst. Liq. Cryst. Sci. Technol.,
Sect. A 301 ꢀ1997) 203±208.
[4] ꢀa) J. Iqbal,B. Bhatia,N.K. Nayyer,Chem. Rev. 84 ꢀ1994) 519±564;
È
ꢀb) B. Giese,B. Kopping,T. Go bel,J. Dickhaut,G. Thoma,K.J.
Kulicke,F. Trach,Org. React. 48 ꢀ1996) 301±880;
ꢀc) D.P. Curran,in: B.M. Trost,I. Fleming ꢀEds.),Comprehensive
Organic Synthesis,Vol. 4,Pergamon,Oxford,1991,pp. 715±777.
[5] ꢀa) H. Nagashima,H. Wakamatsu,K. Itoh,J. Chem. Soc.,Chem.
Commun. ꢀ1984) 652±653.;
ꢀb) H. Nagashima,N. Ozaki,M. Ishii,K. Seki,M. Washiyama,K.
Itoh,J. Org. Chem. 58 ꢀ1993) 464±470;
ꢀc) H. Nagashima,Y. Isono,S. Iwamatsu,J. Org. Chem. 66 ꢀ2001)
315±319.
Fig. 1. Possible conformers of 3a1,2 and the MM2 relative energies.
[6] R.J. Dannley,J.R. Weschler,G.R. Jackson,J. Am. Chem. Soc. 77
ꢀ1955) 3643±3643.
[7] A.J. Bose,B. Lal,Tetrahedron Lett. 14 ꢀ1973) 3937±3940.
[8] D.J. Burton,L.J. Kehoe,J. Org. Chem. 35 ꢀ1970) 1339±1342.
[9] M. Aslam,W.F. Stansbury,R.J. Reiter,D.R. Larkin,J. Org. Chem. 62
ꢀ1997) 1550±1552.
4. Conclusion
We have demonstrated that only a tri¯uoromethyl group is
required for activation of a bromide to generate a tri¯uor-
omethylated benzyl radical in the presence of amine-coor-
dinated CuCl catalyst. Terminal ole®ns as well as silyl enol
ethers trapped the generated radical. Reduction of the bro-
minated products with Ph3SnH gave a class of compounds
with an isolated tri¯uoromethyl group on a long straight
alkyl chain,which may be important substructure for the
ferroelectric liquid crystals.
[10] M. Asscher,D. Vofsi,J. Chem. Soc. ꢀ1963) 1887±1896.
[11] N.L. Allinger,J. Am. Chem. Soc. 99 ꢀ1977) 8127±8134.
[12] J.J.P. Stewart,J. Comput. Chem. 10 ꢀ1989) 209±220.
[13] ꢀa) T. Okano,T. Uekawa,S. Eguchi,Bull. Chem. Soc. Jpn. 62
ꢀ1989) 2575±2579;
ꢀb) T. Okano,T. Shimizu,K. Sumida,S. Eguchi,J. Org. Chem. 58
ꢀ1993) 5163±5166.
[14] A.S. Dneprovskii,E.V. Eliseenkov,S.A. Mil'tsov,Zh. Org. Khim. 18
ꢀ1982) 365±373.
[15] J.P. Richard,J. Am. Chem. Soc. 108 ꢀ1986) 6819±6820.