Rhodium-catalyzed asymmetric addition of potassium organotrifluoroborates to N-sulfonyl ketimines

Article abstract of DOI:10.1021/ol200958q

A rhodium-catalyzed asymmetric addition of readily available potassium organotrifluoroborates to both N-tosyl and N-nosyl ketimines has been developed. High enantioselectivity has been achieved by using a chiral diene ligand, and the nosyl group of the ad

Full text of DOI:10.1021/ol200958q

ORGANIC
LETTERS
2011
Vol. 13, No. 12
2977–2979
Rhodium-Catalyzed Asymmetric Addition
of Potassium Organotrifluoroborates to
N-Sulfonyl Ketimines
Ryo Shintani,* Momotaro Takeda, Ying-Teck Soh, Tomoaki Ito, and Tamio Hayashi*
Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo,
Kyoto 606-8502, Japan
shintani@kuchem.kyoto-u.ac.jp; thayashi@kuchem.kyoto-u.ac.jp
Received April 12, 2011
ABSTRACT
A rhodium-catalyzed asymmetric addition of readily available potassium organotrifluoroborates to both N-tosyl and N-nosyl ketimines has been
developed. High enantioselectivity has been achieved by using a chiral diene ligand, and the nosyl group of the addition products can be easily
removed while retaining the enantiomeric purity.
Transition-metal-catalyzed asymmetric addition of or-
ganometallic reagents to imines is one of the most powerful
methods for the construction of enantioenriched chiral
amines possessing an R-carbon stereocenter.1 Most of the
existing methods in this regard employ aldimines as sub-
strates under the catalysis of copper,2 zirconium,3
rhodium,4 or palladium.5 In contrast, asymmetric addi-
tions to ketimines have been much less explored,6 and to
the best of our knowledge, only the copper-catalyzed addi-
tion of an allylboronate7 and the copper-8 or zirconium-
catalyzed9 addition of dialkylzincs have been known
until recently.10 To broaden the scope of the applicable
organometallic nucleophiles, we reported a rhodium-
catalyzed asymmetric addition of sodium tetraarylborates
(4) (a) Hayashi, T.; Ishigedani, M. J. Am. Chem. Soc. 2000, 122, 976.
(b) Hayashi, T.; Kawai, M.; Tokunaga, N. Angew. Chem., Int. Ed. 2004,
43, 6125. (c) Tokunaga, N.; Otomaru, Y.; Okamoto, K.; Ueyama, K.;
Shintani, R.; Hayashi, T. J. Am. Chem. Soc. 2004, 126, 13584.
(d) Otomaru, Y.; Tokunaga, N.; Shintani, R.; Hayashi, T. Org. Lett.
2005, 7, 307. (e) Nishimura, T.; Yasuhara, Y.; Hayashi, T. Org. Lett.
2006, 8, 979. (f) Okamoto, K.; Hayashi, T.; Rawal, V. H. Chem.
Commun. 2009, 4815. (g) Kuriyama, M.; Soeta, T.; Hao, X.; Chen, Q.;
Tomioka, K. J. Am. Chem. Soc. 2004, 126, 8128. (h) Hao, X.; Kuriyama,
M.; Chen, Q.; Yamamoto, Y.; Yamada, K.; Tomioka, K. Org. Lett.
2009, 11, 4470. (i) Duan, H.-F.; Jia, Y.-X.; Wang, L.-X.; Zhou, Q.-L.
Org. Lett. 2006, 8, 2567. (j) Jagt, R. B. C.; Toullec, P. Y.; Geerdink, D.;
de Vries, J. G.; Feringa, B. L.; Minnaard, A. J. Angew. Chem., Int. Ed.
2006, 45, 2789. (k) Wang, Z.-Q.; Feng, C.-G.; Xu, M.-H.; Lin, G.-Q.
J. Am. Chem. Soc. 2007, 129, 5336. (l) Yang, H.-Y.; Xu, M.-H. Chem.
Commun. 2010, 46, 9223. (m) Kurihara, K.; Yamamoto, Y.; Miyaura, N.
Adv. Synth. Catal. 2009, 351, 260. (n) Crampton, R. H.; Hajjaji, S. E.;
Fox, M. E.; Woodward, S. Tetrahedron: Asymmetry 2009, 20, 2497.
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Z.; Shi, M. Tetrahedron 2010, 66, 2619.
(1) For reviews, see: (a) Yamada, K.; Tomioka, K. Chem. Rev.
2008, 108, 2874. (b) Friestad, G. K.; Mathies, A. K. Tetrahedron 2007,
63, 2541. (c) Ding, H.; Friestad, G. K. Synthesis 2005, 2815. (d) Vilaivan,
T.; Bhanthumnavin, W.; Sritana-Anant, Y. Curr. Org. Chem. 2005, 9,
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(6) For reviews, see: (a) Riant, O.; Hannedouche, J. Org. Biomol.
Chem. 2007, 5, 873. (b) Denissova, I.; Barriault, L. Tetrahedron 2003, 59,
10105. (c) Shibasaki, M.; Kanai, M. Chem. Rev. 2008, 108, 2853.
(7) (a) Wada, R.; Shibuguchi, T.; Makino, S.; Oisaki, K.; Kanai, M.;
Shibasaki, M. J. Am. Chem. Soc. 2006, 128, 7687. (b) Kanai, M.; Wada,
R.; Shibuguchi, T.; Shibasaki, M. Pure Appl. Chem. 2008, 80, 1055.
(8) Lauzon, C.; Charette, A. B. Org. Lett. 2006, 8, 2743.
(2) For recent advances, see: (a) Bonnaventure, I.; Charette, A. B.
Tetrahedron 2009, 65, 4968. (b) Perron, Q.; Alexakis, A. Tetrahedron:
Asymmetry 2008, 19, 1871. (c) Pizzuti, M. G.; Minnaard, A. J.; Feringa,
B. L. J. Org. Chem. 2008, 73, 940. (d) Shi, M.; Lei, Z.-Y.; Xu, Q. Adv.
Synth. Catal. 2006, 348, 2237.
(3) (a) Porter, J. R.; Traverse, J. F.; Hoveyda, A. H.; Snapper, M. L.
J. Am. Chem. Soc. 2001, 123, 984. (b) Akullian, L. C.; Snapper, M. L.;
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J. F.; Hoveyda, A. H.; Snapper, M. L. Org. Lett. 2003, 5, 3273.
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r
10.1021/ol200958q
2011 American Chemical Society
Published on Web 05/16/2011

to N-tosyl ketimines in the presence of a chiral diene ligand
in 2010.11,12 Although high yield and enantioselectivity
were achieved, the major drawback of this process in a
synthetic point of view was the requirement to use
tetraarylborates13 to promote the reaction effectively. In
addition, the use of N-nosyl ketimines resulted in moderate
yields under this catalytic system. To overcome these
problems, herein we describe that readily available potas-
sium organotrifluoroborates14,15 can now be employed as
the nucleophile for the rhodium-catalyzed asymmetric
addition to both N-tosyl and N-nosyl ketimines.
in the presence of [RhCl((R,R)-L1)]2 (5 mol % Rh) and
MeOH (3.0 equiv) in dioxane at 80 °C.
As we have previously reported,11 a reaction of N-tosyl
imine of 40-chloroacetophenone (1a; 0.2 M initial con-
centration) with sodium tetraphenylborate (2.0 equiv)
smoothly proceeds in the presence of [RhCl((R,R)-
16
L1)]2 (5 mol % Rh) and MeOH (2.0 equiv) in dioxane
Table 1. Rhodium-Catalyzed Asymmetric Addition of
Potassium Phenyltrifluoroborate to N-Tosyl and N-Nosyl
Ketimines 1
at 60 °C to give addition product (S)-2a in 83% yield with
97% ee (eq 1). Under these conditions, the use of potas-
sium phenyltrifluoroborate in place of sodium tetraphe-
nylborate significantly lowered the reactivity, giving 2a
only in 36% yield, although the enantioselectivity stayed
high (98% ee). After some investigation of the reaction
conditions, we were able to find a set of conditions that can
efficiently promote this reaction. Thus, as shown in Table
1, entry 1, addition product 2a can be obtained in 84%
yield with 98% ee by reacting 1a (0.3 M initial concen-
tration) with potassium phenyltrifluoroborate (3.0 equiv)
(10) For recent examples of catalytic asymmetric Strecker- and
Mannich-type reactions with ketimines, see: (a) Shen, K.; Liu, X.;
Cai, Y.; Lin, L.; Feng, X. Chem.;Eur. J. 2009, 15, 6008. (b) Wang, J.;
Hu, X.; Jiang, J.; Gou, S.; Huang, X.; Liu, X.; Feng, X. Angew. Chem.,
Int. Ed. 2007, 46, 8468. (c) Huang, J.; Liu, X.; Wen, Y.; Qin, B.; Feng,
X. J. Org. Chem. 2007, 72, 204. (d) Wieland, L. C.; Vieira, E. M.;
Snapper, M. L.; Hoveyda, A. H. J. Am. Chem. Soc. 2009, 131, 570.
(e) Sukach, V. A.; Golovach, N. M.; Pirozhenko, V. V.; Rusanov, E. B.;
Vovk, M. V. Tetrahedron: Asymmetry 2008, 19, 761. (f) Tang, C.; Liu,
X.; Wang, L.; Wang., J.; Feng, X. Org. Lett. 2008, 10, 5305. (g) Du, Y.;
Xu, L.-W.; Shimizu, Y.; Oisaki, K.; Kanai, M.; Shibasaki, M. J. Am.
Chem. Soc. 2008, 130, 16146. (h) Yazaki, R.; Nitabaru, T.; Kumagai,
N.; Shibasaki, M. J. Am. Chem. Soc. 2008, 130, 14477. (i) Suto, Y.;
Kanai, M.; Shibasaki, M. J. Am. Chem. Soc. 2007, 129, 500.
(11) Shintani, R.; Takeda, M.; Tsuji, T.; Hayashi, T. J. Am. Chem.
Soc. 2010, 132, 13168.
(12) For reviews on chiral diene ligands, see: (a) Shintani, R.;
€
Hayashi, T. Aldrichimica Acta 2009, 42, 31. (b) Defieber, C.; Grutzmacher,
H.; Carreira, E. M. Angew. Chem., Int. Ed. 2008, 47, 4482.
(13) For examples of the use of sodium tetraarylborates in rhodium-
catalyzed addition reactions, see: (a) Ueda, M.; Miyaura, N. J. Orga-
nomet. Chem. 2000, 595, 31. (b) Miura, T.; Sasaki, T.; Nakazawa, H.;
Murakami, M. J. Am. Chem. Soc. 2005, 127, 1390. (c) Ueura, K.;
Miyamura, S.; Satoh, T.; Miura, M. J. Organomet. Chem. 2006, 691,
2821. (d) Shintani, R.; Tsutsumi, Y.; Nagaosa, M.; Nishimura, T.;
Hayashi, T. J. Am. Chem. Soc. 2009, 131, 13588. (e) Shintani, R.; Isobe,
S.; Takeda, M.; Hayashi, T. Angew. Chem., Int. Ed. 2010, 49, 3795.
(f) Shintani, R.; Soh, Y.-T.; Hayashi, T. Org. Lett. 2010, 12, 4106.
(g) Shintani, R.; Hayashi, T. Org. Lett. 2011, 13, 350. (h) Chen, J.; Chen,
J.; Lang, F.; Zhang, X.; Cun, L.; Zhu, J.; Deng, J.; Liao, J. J. Am. Chem.
Soc. 2010, 132, 4552.
(14) For reviews, see: (a) Molander, G. A; Canturk, B. Angew. Chem.,
Int. Ed. 2009, 48, 9240. (b) Darses, S.; Genet, J.-P. Chem. Rev. 2008, 108,
288. (c) Stefani, H. A.; Cella, R.; Vieira, A. S. Tetrahedron 2007, 63, 3623.
(d) Molander, G. A.; Ellis, N. Acc. Chem. Res. 2007, 40, 275.
(15) For early examples of the use of potassium organotrifluorobo-
rates in rhodium-catalyzed addition reactions, see: (a) Batey, R. A.;
Thadani, A. N.; Smil, D. V. Org. Lett. 1999, 1, 1683. (b) Pucheault, M.;
Darses, S.; Genet, J.-P. Tetrahedron Lett. 2002, 43, 6155.
a Isolated yield. b Determined by chiral HPLC with hexane/2-propa-
nol. c The reaction was conducted at 90 °C. d The reaction was conducted
for 48 h. e The reaction was conducted with 4.0 equiv of PhBF3K and
4.0 equiv of MeOH.
Under these newly established conditions, several other
N-tosyl ketimines 1bꢀ1d effectively undergo phenylation
to give products 2 in high yields with excellent enantios-
electivities (88ꢀ97% yield, g99% ee; entries 2ꢀ4). Fur-
thermore, in contrast to our previous reactions using
sodium tetraarylborates as the nucleophile,11 the present
catalysis is also effective for the reaction of N-nosyl keti-
mines. For example, N-nosyliminesofvarious (hetero)aryl
(16) Otomaru, Y.; Okamoto, K.; Shintani, R.; Hayashi, T. J. Org.
Chem. 2005, 70, 2503.
2978
Org. Lett., Vol. 13, No. 12, 2011

methyl ketones (1eꢀ1i) are efficiently converted to pheny-
lation products 2 in good to excellent yields with high ee
(71ꢀ91% yield, 92ꢀ95% ee; entries 5ꢀ9). Of course, the
nosyl group of the products thus obtained can be readily
deprotected under mild reaction conditions while retaining
the enantiomeric excesses as demonstrated in eq 2.17
of using potassium organotrifluoroborates over sodium
tetraarylborates.19
The stereochemical outcome in the reaction of 1a with
potassium phenyltrifluoroborate under the catalysis of
Rh/(R,R)-L1 can be rationalized as follows (Figure 1).
To minimize the unfavorable steric interaction between the
sulfonyl moiety on the nitrogen of 1a and the aryl group on
the olefin of (R,R)-L1, 1a approaches phenylrhodium
species with its si-face, thereby leading to the formation
of 2a with an S configuration.4c,f
With regard to the nucleophilic component, various
potassium aryltrifluoroborates including 2-naphthyl- and
5-indolylborates can be used in the reaction with N-nosyl
imine of acetophenone (1j) to give the corresponding
adducts 2 in high yield with g95% ee (Table 2, entries
1ꢀ7).18 In addition to these aryl nucleophiles, an alkenyl-
trifluoroborate can also be employed to form a highly
Table 2. Rhodium-Catalyzed Asymmetric Addition of Potas-
sium Organotrifluoroborates to N-Nosyl Ketimine 1j
Figure 1. Proposed stereochemical pathway for the rhodium-
catalyzed addition of potassium phenyltrifluoroborate to 1a.
In summary, we have disclosed that readily available
potassium organotrifluoroborates can be employed as the
nucleophile for the rhodium-catalyzed asymmetric addi-
tion toboth N-tosyl and N-nosyl ketimines. Highenantios-
electivity has been achieved by using chiral diene (R,R)-L1
as the ligand, and the nosyl group of the addition products
can be easily removed while retaining the enantiomeric
purity.
Acknowledgment. Support has been provided in part by
a Grant-in-Aid for Scientific Research (S) (19105002), the
Ministry of Education, Culture, Sports, Science and Tech-
nology, Japan.
a Isolated yield. b Determined by chiral HPLC with hexane/2-propa-
nol. c The reaction was conducted for 48 h at 90 °C. d The reaction was
conducted for 48 h at 100 °C.
substituted allylamine derivative with high enantioselec-
tivity (entry 8). This example also highlights the advantage
Supporting Information Available. Experimental pro-
cedures and compound characterization data. This ma-
terial is available free of charge via the Internet at http://
pubs.acs.org.
(17) (a) Fukuyama, T.; Jow, C.-K.; Cheung, M. Tetrahedron Lett.
1995, 36, 6373. (b) Kan, T.; Fukuyama, T. Chem. Commun. 2004, 353.
(c) Wuts, P. G. M.; Greene, T. W. Greene’s Protective Groups in Organic
Synthesis, 4th ed.; Wiley: NJ, 2007; p 860.
(18) Potassium trifluoroborates of 4-methoxycarbonylphenyl, 3-thie-
nyl, and 2-furyl are not suitable nucleophiles in the present catalysis.
(19) Attempts to prepare sodium tetraalkenylborates were unsuc-
cessful (unpublished results).
Org. Lett., Vol. 13, No. 12, 2011
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