3 For reviews, see: (a) R. Smits, C. D. Cadicamo, K. Burger and
B. Koksch, Chem. Soc. Rev., 2008, 37, 1727; (b) X.-L. Qiu,
W.-D. Meng and F.-L. Qing, Tetrahedron, 2004, 60, 6711;
(c) M. Zanda, New J. Chem., 2004, 28, 1401. For selected papers,
see: (d) V. A. Soloshonok, I. I. Gerus and Y. L. Yagupolskii,
Zh. Org. Khim., 1986, 22, 1335.
4 (a) J. T. Welch, A. Gyenes and M. J. Jung, in General Features of
Biological Activity of Fluorinated Amino Acids: Design, Pharma-
cology and Biochemistry, ed. V. P. Kuhhar and V. A. Soloshonok,
John Wiley & Sons, Chichester, 1995, pp. 311–331; (b) R. Smits
and B. Koksch, Curr. Top. Med. Chem., 2006, 16, 1483.
5 For reviews on stereocontrolled synthesis of a-fluoroalkyl a-amino
acids, see: (a) S. Fustero, J. F. Sanz-Cervera, J. L. Acena and
M. Sanchez-Rosello, Synlett, 2009, 525, and ref. 3b. For diastereo-
Scheme 1 Determination of the absolute configuration of 3 by X-ray
crystal structure of compound 6.
selective synthesis of a-ethynyl 3,3,3-CF3 alaninate, see:
;
(b) M. Crucianelli, F. D. Angelis, F. Lazzaro, L. Malpezzi,
A. Volonterio and M. Zanda, J. Fluorine Chem., 2004, 125, 573.
During our manuscript preparation, an organocatalytic enantio-
selective Strecker synthesis of a-quaternary-a-CF3-amino acids
was reported: (c) D. Enders, K. Gottfried and G. Raabe, Adv.
Synth. Catal., 2010, 352, 3147.
6 For catalytic enantioselective synthesis of trifluoromethyl con-
taining tertiary amines, only a few examples have been reported,
see: (a) P. Fu, M. L. Snapper and A. H. Hoveyda, J. Am. Chem.
Soc., 2008, 130, 5530; (b) C. Lauzon and A. B. Charette, Org. Lett.,
2006, 8, 2743.
7 Q.-Q. Min, C.-Y. He, H. Zhou and X. Zhang, Chem. Commun.,
2010, 46, 8029.
Scheme 2 Gram-scale catalytic enantioselective synthesis of 3a and
3m and synthesis of 7.
8 (a) J. W. Corbett, S. S. Ko, J. D. Rodgers, L. A. Gearhart,
N. A. Magnus, L. T. Bacheler, S. Diamond, S. Jeffrey,
R. M. Klabe, B. C. Cordova, S. Garber, K. Logue,
G. L. Trainor, P. S. Anderson and S. K. Erickson-Viitanen,
J. Med. Chem., 2000, 43, 2019; (b) R. W. King, R. M. Klabe,
C. D. Reid and S. K. Erickson-Viitanen, Antimicrob. Agents
Chemother., 2002, 46, 1640; (c) B. Jiang and Y.-G. Si, Angew.
Chem., Int. Ed., 2004, 43, 216.
9 For reviews related to enantioselective addition of terminal alkynes
to aldimines, see: (a) B. M. Trost and A. H. Weiss, Adv. Synth.
Catal., 2009, 351, 963; (b) P. Armas, D. Tejedor and F. Garcia-
Tellado, Angew. Chem., Int. Ed., 2010, 49, 1013; (c) L. Zani and
C. Bolm, Chem. Commun., 2006, 4263.
10 For selected recent papers related to enantioselective addition of
terminal alkynes to aldimines, see: (a) S. Nakamura, M. Ohara,
Y. Nakamura, N. Shibata and T. Toru, Chem.–Eur. J., 2010,
16, 2360; (b) Y. Lu, T. C. Johnstone and B. A. Arndtsen, J. Am.
Chem. Soc., 2009, 131, 11284; (c) G. Blay, L. Cardona, E. Climent
and J. R. Pedro, Angew. Chem., Int. Ed., 2008, 47, 5593.
11 For selected recent papers on copper catalyzed alkynylation of
aldimines, see: (a) C. Wei and C.-J. Li, J. Am. Chem. Soc., 2002,
124, 5638; (b) C. Wei, J. T. Mague and C.-J. Li, Proc. Natl. Acad.
Sci. U. S. A., 2004, 101, 5749; (c) J.-X. Ji, J. Wu and A. S. C. Chan,
Proc. Natl. Acad. Sci. U. S. A., 2005, 102, 11196.
enantiomeric excesses up to 98%, providing feasibility for further
functionalizations (entries 11–12).
It should be pointed out that for most of the reactions shown in
Tables 1 and 2, we presented two ee values that were determined
before and after column chromatography in view of the fact that
trifluoromethyl group containing compounds are more prone to
self-disproportionation of enantiomers (SDE) under the conditions
of achiral chromatography reported by the Soloshonok group
recently.15,16 From the results illustrated in Tables 1 and 2, we
can see the ee values obtained before column chromatography
are similar to those obtained after (the sample used for
determining ee is a mixture of all of the collected product after
silica gel column chromatography), suggesting that the ee values
obtained after purification are not influenced by the SDE effect.
The absolute configuration of 3 was determined to be R by
the X-ray crystal structure of 6, which was synthesized from 3l
in 2 steps (Scheme 1).
12 (a) M. Shibasaki and M. Kanai, Chem. Rev., 2008, 108, 2853;
(b) M. Bella and T. Gasperi, Synthesis, 2009, 1583; (c) O. Riant and
J. Hannedouche, Org. Biomol. Chem., 2007, 5, 873.
13 For Me2Zn mediated alkynylation of aldimines in the absence of
ligands, see: (a) L. Zani, S. Alesi, P. G. Cozzi and C. Bolm, J. Org.
Chem., 2006, 71, 1558. For Me2Zn mediated enantioselective
alkynylation of aldimines, see: (b) L. Zani, T. Eichhorn and
C. Bolm, Chem.–Eur. J., 2007, 13, 2587.
14 For selected review on zinc/BINOL catalyzed reactions, see: (a) L. Pu
and H.-B. Yu, Chem. Rev., 2001, 101, 757. For Zn/BINOL catalyzed
enantioselective alkynylation of aldimines, see ref. 10c. For selected
papers, see: (b) G. Lu, X. Li, X. Jia, W. L. Chan and A. S. C. Chan,
Angew. Chem., Int. Ed., 2003, 42, 5057; (c) Y. Zhou, R. Wang, Z. Xu,
W. Yan, L. Liu, Y. Kang and Z. Han, Org. Lett., 2004, 6, 4147.
15 (a) V. A. Soloshonok, Angew. Chem., Int. Ed., 2006, 45, 766;
(b) V. A. Soloshonok and D. O. Berbasov, Chim. Oggi/Chem.
Today, 2006, 24, 44; (c) V. A. Soloshonok, H. Ueki, M. Yasumoto,
S. Mekala, J. S. Hirschi and D. A. Singleton, J. Am. Chem. Soc.,
2007, 129, 12112; (d) V. A. Soloshonok and D. O. Berbasov,
J. Fluorine Chem., 2006, 127, 597.
It is noteworthy that gram-scale reactions of catalytic
asymmetric synthesis of 3a and 3m were also performed in
compatible yields and ee values, indicating the good reliability
of the process (Scheme 2, eqn (1)). From the viewpoint of
synthetic application, a derivative of 2-amino-4-phenylbutanoic
acid 7 with 99% ee was easily prepared via hydrogenation of 3a,
followed by treatment with cerium(IV) diammonium nitrate
(Scheme 2, eqn (2)).
The NSFC (Nos 20902100, 20852003, 20832008), the
Shanghai Rising-Star Program (09QA1406900) and SIOC
are warmly acknowledged for funding this work.
Notes and references
1 A. Giannis and T. Kolter, Angew. Chem., Int. Ed. Engl., 1993,
32, 1244.
2 For selected recent reviews, see: (a) L. Gentilucci, A. Tolomelli and
F. Squassabia, Curr. Med. Chem., 2006, 13, 2449; (b) D. Seebach
and J. Gardiner, Acc. Chem. Res., 2008, 41, 1366.
16 The SDE tests of compounds 3a and 3h were also performed
(please see Supporting Information Tables S3 and S4).
c
This journal is The Royal Society of Chemistry 2011
Chem. Commun., 2011, 47, 5587–5589 5589