2011, 47, 632; (b) A. Cordova, Catalytic Asymmetric Conjugate
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K. A. Jørgensen, Chem. Soc. Rev., 2009, 38, 2178.
7 For early reports, see: (a) M. Marigo, T. C. Wabnitz,
D. Fielenbach and K. A. Jørgensen, Angew. Chem., Int. Ed.,
2005, 44, 794; (b) Y. Hayashi, H. Gotoh, T. Hayashi and
M. Shoji, Angew. Chem., Int. Ed., 2005, 44, 4212.
8 N. Ishikawa, M. G. Koh, T. Kitazume and S. K. Choi, J. Fluorine
Chem., 1984, 24, 419.
9 For early reports on the enantioselective Friedel–Crafts alkylation
of pyrroles and indoles with MacMillan catalyst, see:
(a) J. F. Austin and D. W. C. MacMillan, J. Am. Chem. Soc.,
2002, 124, 1172; (b) N. A. Paras and D. W. C. MacMillan, J. Am.
Chem. Soc., 2001, 123, 4370; For the report with Jørgensen–Hayashi
catalyst, see: (c) L. Hong, L. Wang, C. Chen, B. Zhang and
R. Wang, Adv. Synth. Catal., 2009, 351, 772.
10 Recently, Soloshonok revealed that compounds containing a
trifluoromethyl group directly bonded to a stereogenic carbon
center are prone to an enantiomer self-disproportionation effect
on achiral silica gel. We therefore confirmed that the optical purity
of selected products, 6a, 9b and 11, do not change even after
chromatographic purification using achiral silica gel. For the self-
disproportionation effect of the enanatiomers, see: (a) H. Ueki,
M. Yasumoto and V. A. Soloshonok, Tetrahedron: Asymmetry,
2010, 21, 1396; (b) V. A. Soloshonok, H. Ueki, M. Yasumoto,
S. Mekala, J. S. Hirschi and D. A. Singleton, J. Am. Chem. Soc.,
2007, 129, 12112; (c) V. A. Soloshonok and D. O. Berbasov,
J. Fluorine Chem., 2006, 127, 597; (d) V. A. Soloshonok, Angew.
Chem., Int. Ed., 2006, 45, 766.
Scheme 4 Asymmetric synthesis of befloxatone. Reaction conditions:
(a) Pd(OH)2 (20 mol% Pd), MeOH, H2, rt, 3 h; (b) TsCl (1.5 equiv.),
pyridine, rt, 24 h; (c) K2CO3 (3 equiv.), DMF, reflux, 3 h; (d) Pd/C
(10 mol% Pd), MeOH, H2 (1 atm), rt, 3 h; (e) K2CO3 (2 equiv.), DMF,
85 1C, 6 h.
various nucleophiles such as alkylthiols, pyrroles, indoles,
triazoles, and aldoximes afforded a variety of trifluoromethylated
chiral stereogenic centers in a highly enantioselective manner.
We also demonstrated the application of this method to the
asymmetric synthesis of an MAO-A inhibitor, befloxatone.
This study was supported by the Takeda Science Foundation
and a Grant-in-Aid for Young Scientists (B) (23750111) from
MEXT. The partial support from the Asahi Glass Foundation
is also acknowledged.
11 N. A. Paras and D. W. C. MacMillan, J. Am. Chem. Soc., 2002,
124, 7894.
12 For the addition of alkylthiols, see: (a) S. Brandau, E. Maerten and
K. A. Jørgensen, J. Am. Chem. Soc., 2006, 128, 14986;
(b) M. Marigo, T. Schulte, J. Franzen and K. A. Jørgensen,
J. Am. Chem. Soc., 2005, 127, 15710; For the addition of triazoles,
see: (c) P. Diner, M. Nielsen, M. Marigo and K. Anker Jørgensen,
Angew. Chem., Int. Ed., 2007, 46, 1983; For the addition of
succinimide and N-methoxycarbamates, see: (d) H. Jiang,
J. B. Nielsen, M. Nielsen and K. A. Jørgensen, Chem.–Eur. J.,
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Y. Xu and A. Cordova, Tetrahedron Lett., 2007, 48, 2193; (f) For
the addition of aldoximes, see: (g) S. Bertelsen, P. Diner,
R. L. Johansen and K. A. Jørgensen, J. Am. Chem. Soc., 2007,
129, 1536.
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13 For selected papers on the pharmacology of befloxatone or
11C]befloxatone, see: (a) M. Bottlaender, H. Valette, J. Delforge,
[
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4 For the catalytic asymmetric reaction with 4,4,4-trifluorocrotonates,
see: (a) K. Shibatomi, F. Kobayashi, A. Narayama, I. Fujisawa
and S. Iwasa, Chem. Commun., 2012, 48, 413; (b) X.-Q. Dong,
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5 There are four reports describing the synthesis of 1. All of them
mentioned the difficulty involved in the isolation of 1:
(a) D. M. Pearson, N. R. Conley and R. M. Waymouth, Organo-
metallics, 2011, 30, 1445; (b) L. Dumitrescu, D. T. M. Huong,
N. V. Hung, B. Crousse and D. Bonnet-Delpon, Eur. J. Med.
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6 For recent reviews, see: (a) M. Nielsen, D. Worgull, T. Zweifel,
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see: (a) T. Yamazaki, N. Okamura and T. Kitazume, Tetrahedron:
Asymmetry, 1990, 1, 521; (b) T. Kitazume, J. T. Lin and
T. Yamazaki, Tetrahedron: Asymmetry, 1991, 2, 235; (c) See also
ref. 13e.
15 The absolute configuration of 12 was determined to be R by
comparing the optical rotation with a value described in ref. 14a.
16 S. Jegham, A. Nedelec, Ph. Burnier, Y. Guminski, F. Puech,
J. J. Koenig and P. George, Tetrahedron Lett., 1998, 39, 4453.
c
7382 Chem. Commun., 2012, 48, 7380–7382
This journal is The Royal Society of Chemistry 2012