Kinetic resolution of allyl fluorides by enantioselective allylic trifluoromethylation based on silicon-assisted c-F bond cleavage

Article abstract of DOI:10.1002/anie.201308071

Two birds, one stone! The first kinetic resolution of allyl fluorides was achieved by the development of an organocatalyzed enantioselective allylic trifluoromethylation. Two kinds of chiral fluorinated compounds, which incorporate C-F and C-CF₃ units, respectively, can thus be accessed by a single transformation.

Full text of DOI:10.1002/anie.201308071

Angewandte
Chemie
DOI: 10.1002/anie.201308071
À
C F Bond Activation
Kinetic Resolution of Allyl Fluorides by Enantioselective Allylic
À
Trifluoromethylation Based on Silicon-Assisted C F Bond Cleavage**
Takayuki Nishimine, Kazunobu Fukushi, Naoyuki Shibata, Hiromi Taira, Etsuko Tokunaga,
Akihito Yamano, Motoo Shiro, and Norio Shibata*
À
Enantioenriched fluorinated molecules play an important
role as pharmaceutically active compounds with impressive
biological activities.[1] The anti-HIV drug Efavirenz, for
allylic C F bonds and developed a palladium- or platinum-
catalyzed substitution reaction of allyl fluorides with carbon,
nitrogen, and oxygen nucleophiles.[7] Paquin et al. also
À
À
example, contains a chiral C* CF3 unit, and the broad-
described the activation of allylic C F bonds by palladium
spectrum antibiotic Levofloxacin has a chiral C* F moiety.
catalysis and hydrogen bonding.[8] Recently, we reported the
synthesis of a series of 2-fluoromethyl-oxazolidin-2-ones by
desymmetrization of non-activated aliphatic difluorides by
À
Fluorinated molecules also offer opportunities for creating
functional molecules with potential applications, such as
liquid crystals.[2] Metal- and/or organocatalyzed asymmetric
transformations for the synthesis of organofluorine com-
pounds that make use of fluorinated building blocks and
direct enantioselective fluorination or trifluoromethylation
are among the most powerful means to access chiral
fluorinated synthons.[3] However, these methods are not
always applicable to the synthesis of a desired compound,
and thus, the development of new approaches for the
synthesis of chiral organofluorine compounds remains an
area of great importance in modern organic chemistry.
Kinetic resolution is an alternative and complementary
strategy for the preparation of a wide range of enantioen-
riched organic compounds.[4] A possible drawback of this
approach is that with the exception of dynamic kinetic
resolution, a mixture of the product and unreacted starting
material is often obtained. We envisaged that if both these
compounds were potentially important fluorinated materials
and produced in high enantiomeric excess, kinetic resolution
would become a more attractive strategy, as it would allow the
synthesis of two chiral fluorinated targets by a single trans-
formation at the same time; we coined this process a “kill two
birds by one stone” strategy (TBOS strategy).
silicon-induced catalytic C F bond cleavage.[9] Our group also
À
investigated the cinchona-alkaloid-catalyzed asymmetric
allylic trifluoromethylation of Morita–Baylis–Hillman
(MBH) carbonates with the Ruppert–Prakash reagent
(Me3SiCF3) to deliver allylic trifluoromethylated com-
pounds.[10] As an application of the TBOS strategy and as
[9]
À
an extension of our research on C F bond activation and
[11]
À
the enantioselective construction of chiral C* CF3
and
C* F units,[12] we herein disclose the first kinetic resolution of
allyl fluorides by catalytic asymmetric allylic trifluoromethy-
lation of MBH-type allyl fluorides 1. Racemic allyl fluorides 1
can be converted into enantioenriched 1 and trifluoromethy-
lated allyl compounds 2 with an excellent degree of enantio-
purity by a single transformation; both compounds are
potential chiral synthons for biologically important mole-
cules. Racemate 1 was also kinetically resolved by asymmetric
allylic pentafluoroethylation and pentafluorophenylation to
furnish enantioenriched allyl fluorides 1, along with penta-
fluoroethylated 3 and pentafluorophenylated 4 with 99% ee
each. The key to these highly asymmetric transformations is
À
À
the silicon-induced cleavage of an allylic C F bond, which is
assisted by SN2’substitution with a bis(cinchona alkaloid),
namely (DHQD)2PHAL (Scheme 1). Enantioenriched allyl
fluorides 1 are produced by kinetic resolution, while the
enantioenriched trifluoromethylated allyl compounds 2 are
simultaneously formed by enantioselective trifluoromethyla-
tion. The products can be transformed into the fluorine-
À
The activation or cleavage of C F bonds has recently also
gained much attention.[5,6] As C F bonds are the strongest
À
À
bonds that carbon can form, the cleavage of C F bonds
requires rather forced conditions, and therefore, the develop-
ment of mild and effective methods for the activation of C F
bonds has become a crucial topic in general organic chemistry.
Gouverneur and co-workers investigated the activation of
À
[*] T. Nishimine, K. Fukushi, N. Shibata, H. Taira, E. Tokunaga,
Prof. Dr. N. Shibata
Department of Frontier Materials, Nagoya Institute of Technology
Gokiso, Showa-ku, Nagoya, 466-8555 (Japan)
E-mail: nozshiba@nitech.ac.jp
A. Yamano, Dr. M. Shiro
Rigaku Corporation
3-9-12 Matsubara-cho, Akishima, Tokyo, 196-8666 (Japan)
[**] This study was financially supported in part by Kakenhi (25288045,
24105513, Project No. 2304: Advanced Molecular Transformation
by Organocatalysts) and JST (ACT-C).
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201308071.
Scheme 1. Kinetic resolution of MBH-type allyl fluorides 1 by enantio-
À
selective fluoroalkylation through C F bond activation/cleavage.
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containing isoxazolines 5 and 6, which are interesting struc-
tures from an agrochemical point of view, in a single step.
Asymmetric reactions of MBH adducts have hitherto
been studied by many groups,[13] including by ourselves.[10,14]
Rios and co-workers described an organocatalyzed kinetic
resolution of MBH carbonates,[15] as did several other
groups.[16] The basic framework of MBH adducts contains
an OR group (acetate or carbonate) at the allylic position,
which can act as a leaving group. Therefore, we surmised that
MBH-type fluorides 1[17] could also behave as conventional
MBH starting materials for asymmetric allylic substitution;
enantioselectivities of 87–96% ee. The allyl fluorides (R)-1a–
i were then recovered with excellent enantioselectivities of up
to 99% ee, which corresponds to s factors of 24–64 (entries 1–
9). The kinetic resolution of nitro-activated allyl fluoride 1j
was performed with a lower amount of Me3SiCF3 (0.7 equiv)
because of the high reactivity of 1j, and the reaction showed
good selectivity; (S)-2j was obtained in 89% ee and 52%
yield, while (R)-1j was recovered in 90% ee and 44% yield
(s = 20; entry 10). The reaction of 1k with a sterically
demanding naphthyl moiety also gave the corresponding
product in good chemical yield and selectivity (s = 22;
entry 11). We next attempted the reaction of an alkyl-
substituted compound; cyclohexyl-substituted allyl fluoride
1l was converted into the desired (S)-2l, but the reaction was
very slow.[10] Increasing the amount of (DHQD)2PHAL
(30 mol%) slightly improved the reactivity to afford (S)-2l
in 82% ee and 22% yield after 120 h (s = 18; entry 12). A
series of bulky tert-butyl esters 1m–p were converted into the
corresponding products (S)-2m–p with good selectivity (87–
96% ee, s = 14–105; entries 13–16), even though the reactivity
was lower than for the methyl esters 1a–l. The reaction of
phenyl-substituted allyl fluoride 1m proceeded particularly
well; (S)-2m was obtained in 94% ee and 48% yield, and 1m
was recovered in 93% ee and 42% yield. The highest s factor
that was observed during this study was thus measured for 1m
(s = 105; entry 13). We also succeeded in obtaining the
À
C F bond activation should be rendered possible by a silicon-
À
induced pathway. For a successful kinetic resolution, the C F
bond of 1 must nevertheless be sufficiently stable under the
selected reaction conditions.
The kinetic resolution of racemic 1 with Me3SiCF3 was
successfully carried out in the presence of a catalytic amount
of (DHQD)2PHAL and molecular sieves (4 ꢀ), in 1,4-
dioxane/THF (5:1; 0.5m) at 08C, thus providing the enan-
tioenriched allyl fluoride 1 and trifluoromethylated 2
(Table 1).[18] The allyl fluorides 1 were slowly consumed by
trifluoromethylation, and the reactions were stopped at about
50% conversion of 1. A series of allyl fluorides 1a–i with
a variety of substituents on the aromatic ring, including
methyl, methoxy, chloro, and bromo moieties, were converted
into the trifluoromethylated products (S)-2a–i with excellent
Table 1: Kinetic resolution of MBH-type allyl fluorides 1 by enantioselective trifluoromethylation.[a]
Entry
1
R1
R2
t [h]
Conv.[b] [%]
2
recovered 1
ee[c] (yield[d]) [%]
ee[c] (yield[d]) [%]
s[e]
1
2
3
4
5
6
7
8
1a
1b
1c
1d
1e
1 f
1g
1h
1i
1j
1k
1l
1m
1n
1o
1p
1a
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
tBu
tBu
tBu
tBu
Me
Ph
36
60
50
48
18
16
20
19
108
3
54
53
53
55
54
54
56
55
52
55
53
23
50
44
54
55
53
95 (51)
95 (48)
96 (50)
94 (50)
89 (51)
91 (50)
89 (52)
90 (52)
87 (36)
89 (52)
91 (48)
82 (22)
94 (48)
96 (37)
87 (51)
90 (48)
À62 (44)
97 (41)
96 (40)
97 (41)
97 (40)
98 (43)
97 (41)
96 (42)
99 (41)
85 (31)
90 (44)
88 (42)
26 (54)
93 (42)
70 (47)
84 (42)
84 (43)
À77 (42)
44
50
64
36
45
42
26
50
24
20
22
18
105
33
15
14
12
4-MeC6H4
3-MeC6H4
3-MeOC6H4
4-ClC6H4
3-ClC6H4
4-BrC6H4
3-BrC6H4
2-BrC6H4
4-NO2C6H4
2-naphthyl
Cy
9
10[f]
11
12[g]
13
14
15
16
17[h]
36
120
120
120
66
5
120
Ph
3-MeC6H4
4-BrC6H4
4-NO2C6H4
Ph
[a] Reactions were carried out using rac-1 (0.1 mmol), Me3SiCF3 (1.0 equiv), (DHQD)2PHAL (10 mol%), and molecular sieves (4 ꢀ) in 1,4-dioxane/
THF (5:1; 0.2 mL, 0.5m) unless otherwise noted. [b] The conversion of 1 was determined by 19F NMR spectroscopy with an internal standard.
[c] Determined by HPLC analysis. [d] Yield of isolated product. [e] The selectivity factor (s) based on recovered 1 was determined by the equation
s=krel(fast/slow)=In[(1ÀC)(1Àee)]/In[(1ÀC)(1+ee)] (C=conversion; ee=enantiomeric excess of recovered 1). [f] Me3SiCF3 (0.7 equiv).
[g] (DHQD)2PHAL (30 mol%). [h] (DHQ)2PYR used instead of (DHQD)2PHAL. Cy=cyclohexyl, (DHQ)2PYR=hydroquinine 2,5-diphenyl-4,6-
pyrimidinediyl diether.
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opposite set of enantiomers, namely (R)-2a in 62% ee and
(S)-1a in 77% ee, in the presence of (DHQ)2PYR, rather than
(DHQD)2PHAL, as the catalyst (s = 12; entry 17). The
absolute configurations of the trifluoromethylated com-
pounds 2 were determined by a comparison with previously
reported HPLC retention times.[10] The absolute configura-
tion of recovered 1g was unambiguously assigned to be R by
X-ray crystallographic analysis[19] of the isoxazoline derivative
(1R,2R)-5g (see below and Scheme 3); the absolute stereo-
chemistry of the other allyl fluorides was tentatively assumed
to be R by analogy.
occurred. The product 2 is formed by a second SN2’
substitution reaction of E-configured I, which was generated
from (S)-1, with CF3 as the nucleophile (Figure 1).[10,14,20]
A
À
thorough investigation of the ee values of 1a and 2a at
different conversions revealed that the enantiopurity of 2a is
not related to the conversion (Figure 2). Excellent enantio-
selectivities were persistently observed and found to be
independent of the conversion and the ee of 1a. Therefore, 2a
was produced by enantioselective trifluoromethylation. On
Interestingly, a kinetic resolution of 1a was also achieved
by enantioselective allylic pentafluoroethylation and penta-
fluorophenylation. Both of the reactions proceeded smoothly
to provide the desired products, pentafluoroethylated 3 and
pentafluorophenylated 4, with excellent enantioselectivities
of 99% ee and s factors of 52 and 37, respectively (Scheme 2).
Furthermore, the chiral allyl fluoride 1g was smoothly
converted into the biologically interesting heterocycle 5g by
a 1,3-dipolar cycloaddition (Scheme 3). The analogous trans-
formation of chiral trifluoromethylated allyl compounds 2
into the corresponding isoxazolines 6 by the same procedure
was previously reported by our group.[10]
À
Figure 1. Proposed mechanism consisting of three steps: 1) C F bond
activation, 2) kinetic resolution, and 3) enantioselective trifluoro-
methylation. N(R1)3 =(DHQD)2PHAL.
Scheme 2. Kinetic resolution of 1a by enantioselective pentafluoro-
ethylation or pentafluorophenylation.
*
Figure 2. Kinetic resolution of 1a ( ) and enantioselective formation
^
of 2a ( ; see Table S2).
the other hand, the enantiopurity of 1a constantly increased
from 0 to 97% ee with increasing conversion. These data
strongly support the idea that the enantioenriched allyl
fluoride 1a is generated by kinetic resolution through
enantioselective trifluoromethylation.
In conclusion, the first kinetic resolution of allyl fluorides
was realized by an enantioselective allylic trifluoromethyla-
tion of MBH-type allyl fluorides 1 under organocatalysis. The
Scheme 3. Conversion of allyl fluoride (R)-1g into isoxazoline 5g.
To understand the high efficiency of the kinetic resolution
of 1 by trifluoromethylation, the postulated mechanism must
be considered. Kinetic resolution/trifluoromethylation begins
À
with C F bond activation of 1 by coordination to the silicon
atom of Me3SiCF3;[3a] this is followed by the addition of
(DHQD)2PHAL to the alkene moiety through the quinucli-
dine nitrogen atom in an SN2’ process that involves the loss of
the fluoride as Me3SiF to provide the ammonium salt I. This
step is believed to be rate-determining. The catalyst
(DHQD)2PHAL preferentially attacks (S)-1, while (R)-
1 remains intact; kinetic resolution of 1 has therefore
À
key for success was the cleavage of the strong C F bond of
(S)-1 by a cooperative system that includes the bis(cinchona
alkaloid) and the silicon atom of the trifluoromethylating
reagent, while (R)-1 remains intact. The features of the
overall transformation include: 1) asymmetric synthesis of
allyl fluorides,[21] 2) enantioselective trifluoromethylation,
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À
Y. Huang, A. Matsnev, S. Nakamura, T. Torua, D. Cahard, Org.
Biomol. Chem. 2009, 7, 3599 – 3604; c) H. Kawai, A. Kusuda, S.
Nakamura, M. Shiro, N. Shibata, Angew. Chem. 2009, 121, 6442 –
6445; Angew. Chem. Int. Ed. 2009, 48, 6324 – 6327; d) H. Kawai,
K. Tachi, E. Tokunaga, M. Shiro, N. Shibata, Org. Lett. 2010, 12,
5104 – 5107; see also Ref. [3].
3) C F bond activation by a cooperative system, 4) kinetic
resolution, and 5) allylic trifluoromethylation.[10,21c,22] Two
À
À
chiral fluorinated compounds with C* F and C* CF3 units,
respectively can be accessed at the same time by the TBOS
strategy. Further developments of this transformation to
include different nucleophiles are currently under investiga-
tion.
À
[12] For the construction of chiral C* F centers, see: a) N. Shibata, E.
Suzuki, Y. Takeuchi, J. Am. Chem. Soc. 2000, 122, 10728 – 10729;
b) N. Shibata, E. Suzuki, T. Asahi, M. Shiro, J. Am. Chem. Soc.
2001, 123, 7001 – 7009; c) N. Shibata, J. Kohno, K. Takai, T.
Ishimaru, S. Nakamura, T. Toru, S. Kanemasa, Angew. Chem.
2005, 117, 4276 – 4279; Angew. Chem. Int. Ed. 2005, 44, 4204 –
4207; d) D. S. Reddy, N. Shibata, J. Nagai, S. Nakamura, T. Toru,
S. Kanemasa, Angew. Chem. 2008, 120, 170 – 174; Angew. Chem.
Int. Ed. 2008, 47, 164 – 168.
Received: September 14, 2013
Published online: November 7, 2013
Keywords: allyl fluorides · fluorine · kinetic resolution ·
organocatalysis · trifluoromethylation
.
[13] a) D. Basavaiah, B. S. Reddy, S. S. Badsara, Chem. Rev. 2010,
110, 5447 – 5674; b) T.-Y. Liu, M. Xie, Y.-C. Chen, Chem. Soc.
Rev. 2012, 41, 4101 – 4112; c) R. Rios, Catal. Sci. Technol. 2012, 2,
267 – 278.
[1] a) K. L. Kirk, J. Fluorine Chem. 2006, 127, 1013 – 1029; b) K. L.
Kirk, Org. Process Res. Dev. 2008, 12, 305 – 321; c) I. Ojima,
Fluorine in Medicinal Chemistry and Chemical Biology, Wiley-
Blackwell, Oxford, 2009.
[2] a) M. Hird, Chem. Soc. Rev. 2007, 36, 2070 – 2095; b) Z. Hong,
S. G. Weber, Teflon AF Materials in Topics in Current Chemistry,
Vol. 308 (Ed.: I. T. Horvꢁrth), Springer, Berlin, 2012, pp. 307 –
377.
[3] a) K. Uneyama, Organofluorine Chemistry, Blackwell, Oxford,
2006; b) J.-A. Ma, D. Cahard, Chem. Rev. 2008, 108, PR1 – PR43;
c) N. Shibata, S. Mizuta, H. Kawai, Tetrahedron: Asymmetry
2008, 19, 2633 – 2644; d) J. Nie, H.-C. Guo, D. Cahard, J.-A. Ma,
Chem. Rev. 2011, 111, 455 – 529; e) C. Hollingworth, V. Gouver-
neur, Chem. Commun. 2012, 48, 2929 – 2942; f) T. Liang, C. N.
Neumann, T. Ritter, Angew. Chem. 2013, 125, 8372 – 8423;
Angew. Chem. Int. Ed. 2013, 52, 8214 – 8264.
[14] T. Furukawa, J. Kawazoe, W. Zhang, T. Nishimine, E. Tokunaga,
T. Matsumoto, M. Shiro, N. Shibata, Angew. Chem. 2011, 123,
9858 – 9862; Angew. Chem. Int. Ed. 2011, 50, 9684 – 9688.
[15] X. Companyꢄ, G. Valero, V. Ceban, T. Calvet, M. Font-Bardꢅa,
A. Moyano, R. Rios, Org. Biomol. Chem. 2011, 9, 7986 – 7989.
[16] a) J. N. Kim, H. J. Lee, J. H. Gong, Tetrahedron Lett. 2002, 43,
9141 – 9146; b) M. G. Nascimento, S. P. Zanotto, S. P. Melegari,
L. Fernandes, M. M. Sꢁ, Tetrahedron: Asymmetry 2003, 14,
3111 – 3115; c) C.-W. Cho, J.-R. Kong, M. J. Krische, Org. Lett.
2004, 6, 1337 – 1339; d) C. E. Aroyan, M. M. Vasbinder, S. J.
Miller, Org. Lett. 2005, 7, 3849 – 3851; e) C. ꢆ. Dꢁlaigh, S. J.
Connon, J. Org. Chem. 2007, 72, 7066 – 7069; f) F. Wang, S. Li, M.
Qu, M.-X. Zhao, L.-J. Liu, M. Shi, Chem. Commun. 2011, 47,
12813 – 12815; g) Y. Wang, X. Feng, H. Du, Org. Lett. 2011, 13,
4954 – 4957; h) B. Hu, M. Meng, S. Jiang, W. Deng, Chin. J.
Chem. 2012, 30, 1289 – 1294.
[17] a) E. Farrington, M. Comes-Franchini, J. M. Brown, Chem.
Commun. 1998, 277 – 278; b) L. Bernardi, B. F. Bonini, M.
Comes-Franchini, M. Fochi, M. Folegatti, S. Grilli, A. Mazzanti,
A. Ricci, Tetrahedron: Asymmetry 2004, 15, 245 – 250.
[18] For the optimization of the reaction conditions, see the
Supporting Information, Table S1 and Scheme S1.
[19] CCDC 959849 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.
cam.ac.uk/data_request/cif.
[20] M. Baidya, G. Y. Remennikov, P. Mayer, H. Mayr, Chem. Eur. J.
2010, 16, 1365 – 1371. See also the Supporting Information,
Figure S1.
[21] a) T. Ishimaru, N. Shibata, T. Horikawa, N. Yasuda, S. Naka-
mura, T. Toru, M. Shiro, Angew. Chem. 2008, 120, 4225 – 4229;
Angew. Chem. Int. Ed. 2008, 47, 4157 – 4161; b) M. H. Katcher,
A. Sha, A. G. Doyle, J. Am. Chem. Soc. 2011, 133, 15902 – 15905;
c) E. Benedetto, M. Tredwell, C. Hollingworth, T. Khotavivat-
tana, J. M. Brown, V. Gouverneur, Chem. Sci. 2013, 4, 89 – 96,
and references therein.
[22] a) A. T. Parsons, S. L. Buchwald, Angew. Chem. 2011, 123, 9286 –
9289; Angew. Chem. Int. Ed. 2011, 50, 9120 – 9123; b) X. Wang,
Y. Ye, S. Zhang, J. Feng, Y. Xu, Y. Zhang, J. Wang, J. Am. Chem.
Soc. 2011, 133, 16410 – 16413; c) Y. Li, F. Liang, Q. Li, Y.-C. Xu,
Q.-R. Wang, L. Jiang, Org. Lett. 2011, 13, 6082 – 6085; d) L. Chu,
F.-L. Qing, Org. Lett. 2012, 14, 2106 – 2109; e) R. Shimizu, H.
Egami, Y. Hamashima, M. Sodeoka, Angew. Chem. 2012, 124,
4655 – 4658; Angew. Chem. Int. Ed. 2012, 51, 4577 – 4580; f) S.
Mizuta, O. Galicia-Lꢄpez, K. M. Engle, S. Verhoog, K. Wheel-
house, G. Rassias, V. Gouverneur, Chem. Eur. J. 2012, 18, 8583 –
8587, and references therein.
[4] a) E. Vedejs, M. Jure, Angew. Chem. 2005, 117, 4040 – 4069;
Angew. Chem. Int. Ed. 2005, 44, 3974 – 4001; b) H. Pellissier,
Adv. Synth. Catal. 2011, 353, 1613 – 1666.
[5] a) H. Amii, K. Uneyama, Chem. Rev. 2009, 109, 2119 – 2183;
b) T. Stahl, H. F. T. Klare, M. Oestreich, ACS Catal. 2013, 3,
1578 – 1587.
À
[6] For examples of the activation of allylic C F bonds, see: a) K.
Hirano, H. Yorimitsu, K. Oshima, Org. Lett. 2004, 6, 4873 – 4875;
b) K. Hirano, K. Fujita, H. Yorimitsu, H. Shinokubo, K. Oshima,
Tetrahedron Lett. 2004, 45, 2555 – 2557; c) L. Hintermann, F.
Lꢂng, P. Maire, A. Togni, Eur. J. Inorg. Chem. 2006, 1397 – 1412;
d) M. Bergeron, T. Johnson, J.-F. Paquin, Angew. Chem. 2011,
123, 11308 – 11312; Angew. Chem. Int. Ed. 2011, 50, 11112 –
11116; e) D. Watanabe, M. Koura, A. Saito, H. Yanai, Y.
Nakamura, M. Okada, A. Sato, T. Taguchi, J. Fluorine Chem.
2011, 132, 327 – 338; f) M. Bergeron, D. Guyader, J.-F. Paquin,
Org. Lett. 2012, 14, 5888 – 5891.
[7] a) A. Hazari, V. Gouverneur, J. M. Brown, Angew. Chem. 2009,
121, 1322 – 1325; Angew. Chem. Int. Ed. 2009, 48, 1296 – 1299;
b) E. Benedetto, M. Keita, M. Tredwell, C. Hollingworth, J. M.
Brown, V. Gouverneur, Organometallics 2012, 31, 1408 – 1416.
[8] a) X. Pigeon, M. Bergeron, F. Barabꢃ, P. Dubꢃ, H. N. Frost, J.-F.
Paquin, Angew. Chem. 2010, 122, 1141 – 1145; Angew. Chem. Int.
Ed. 2010, 49, 1123 – 1127; b) J.-F. Paquin, Synlett 2011, 289 – 293.
[9] G. Haufe, S. Suzuki, H. Yasui, C. Terada, T. Kitayama, M. Shiro,
N. Shibata, Angew. Chem. 2012, 124, 12441 – 12445; Angew.
Chem. Int. Ed. 2012, 51, 12275 – 12279.
[10] Alkyl-substituted compounds with less bulky groups, such as
methyl substituents, are poor substrates for this transformation;
see: T. Furukawa, T. Nishimine, E. Tokunaga, K. Hasegawa, M.
Shiro, N. Shibata, Org. Lett. 2011, 13, 3972 – 3975; see also
Ref. [14].
À
[11] For the construction of chiral C* CF3 centers, see: a) S. Mizuta,
N. Shibata, S. Akiti, H. Fujimoto, S. Nakamura, T. Toru, Org.
Lett. 2007, 9, 3707 – 3710; b) S. Noritake, N. Shibata, Y. Nomura,
520
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