Chiral sodium phosphate catalyzed enantioselective 1,4-addition of TMSCN to aromatic enones

Article abstract of DOI:10.1055/s-0030-1258817

A facile enantioselective 1,4-addition of TMSCN to aromatic enones has been developed using chiral sodium phosphate. Thus, in the presence of 20 mol% of sodium salt generated in situ from (R)-3,3′-di(1-adamantyl)-1,1′- binaphthyl-2,2′-diylphosphoric acid and NaOH, β-cyano ketones were obtained in high yield (86-96%) and up to 72% ee within three hours at 80 °C in toluene.

Full text of DOI:10.1055/s-0030-1258817

LETTER
2725
Chiral Sodium Phosphate Catalyzed Enantioselective 1,4-Addition of TMSCN
to Aromatic Enones
A
symmetr
i
ic 1, 4-A
n
ddition of
C
g
yanide ya Yang,a,b Shaoxiang Wu,a Fu-Xue Chen*a
a
Department of Applied Chemistry, School of Chemical Engineering & the Environment, Beijing Institute of Technology, No. 5 South
Zhongguancun Street, Haidian District, Beijing 100081, P. R. of China
Fax +86(10)68918296; E-mail: fuxue.chen@bit.edu.cn
College of Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou 730070, P. R. of China
b
Received 6 August 2010
(entries 1–6). Sodium salt of L-proline (3) exhibited cer-
tain catalytic activity but giving racemic b-cyano ketone
(2a) (entry 1).7 Similarly, the salt of D-camphor sulfonic
acid (4) also afforded a racemic product (entry 2). How-
Abstract: A facile enantioselective 1,4-addition of TMSCN to aro-
matic enones has been developed using chiral sodium phosphate.
Thus, in the presence of 20 mol% of sodium salt generated in situ
from (R)-3,3¢-di(1-adamantyl)-1,1¢-binaphthyl-2,2¢-diylphosphoric
acid and NaOH, b-cyano ketones were obtained in high yield (86– ever, the bissodium salt of L-tartaric acid (5) bearing two
96%) and up to 72% ee within three hours at 80 °C in toluene.
chiral centers yielded the product 2a in low yield and 20%
ee (entry 3). The bissodium salt of (R)-BINOL
(BINOL = 1,1¢-binaphthyl-2,2¢-diol, 6a) showed poor
chiral inductive capability (entry 4).8 To our delight, sodi-
um salt of (R)-BNPH (BNPH = 1,1¢-binaphthyl-2,2¢-
diylphosphoric acid, 7a) gave the product 2a with 31%
Key words: asymmetric catalysis, enones, 1,4-addition, nitriles,
phosphates
The catalytic asymmetric conjugate addition of a,b-unsat-
urated carbonyl compounds is one of the most powerful
carbon–carbon bond-forming reactions.1 Recently, signif-
icant achievements have been made in the catalytic asym-
metric 1,4-addition of cyanide to a,b-unsaturated
carboxylic acid derivatives.2 However, the asymmetric
1,4-addition of cyanide to enones is limited.3 The pioneer-
ing work of the enantioselective reaction was reported by
Shibasaki and co-workers in 2008.3 To develop a new
practical methodology for this useful transformation of
aromatic enones is still highly demanding.4
OH
O
HO
O
O
OH
S
COOH
N
HO
H
O
O
OH
3
4
5
R
7a R = H
7b R = Me
7c R = Me3Si
7d R = Ph
7e R = 4-MeOC6H4
7f R = 3,5-(CF3)2C6H3
7g R = 2-naphthyl
O
Previously, we reported CsF- and Cs2CO3-catalyzed 1,4-
addition of trimethylsilyl cyanide (TMSCN) to enones to
prepare racemic b-cyano ketones in excellent yield and
perfect regioselectivity.5,6 Inspired by this work, we spec-
ulated that an asymmetric variant might be achieved using
metal salts of chiral acids as catalysts. Recently, metal
salts,7–9 a kind of chiral anionic Lewis base,10,11 have been
employed as potential catalysts in asymmetric reactions.
Among them, alkali-metal salts of chiral amino acid cata-
lyzed asymmetric Michael reactions have been dis-
closed.7a–h However, chiral-salt-catalyzed 1,4-addition of
cyanide to enones, to the best of our knowledge, has not
been reported. Herein, we report a chiral sodium phos-
phate catalyzed enantioselective 1,4-addition of TMSCN
to aromatic enones.
OH
OH
O
O
P
OH
7h R = 1-adamantyl
R
6a
7a–h
Figure 1 Chiral acids evaluated in catalyst screening
1-adamantanol
cat. H2SO4
CH2Cl2, 0 °C to r.t.
OH
OH
OH
OH
60%
6h
6a
To optimize the reaction parameters, model reaction was
conducted with chalcone (1a) and TMSCN (Table 1). Ini-
tially, various chiral acids (20 mol%) were screened
(Figure 1), which reacted with sodium hydroxide in situ to
give the corresponding chiral sodium salts as the catalysts
1) POCl3, pyridine, r.t.
2) H2O, r.t.
O
O
O
P
OH
90%
SYNLETT 2010, No. 18, pp 2725–2728
x
x
.x
x
.2
0
1
0
Advanced online publication: 08.10.2010
DOI: 10.1055/s-0030-1258817; Art ID: W12610ST
© Georg Thieme Verlag Stuttgart · New York
7h
Scheme 1 Synthesis of phosphoric acid 7h from (R)-BINOL

2726
J. Yang et al.
LETTER
yield and 53% ee (entry 5) comparing with no reaction 88% in yield and 49% ee in enantioselectivity (entry 13
when using (R)-BNPH alone (entry 6).9
vs. entry 5). Considering significant improvement on oth-
er reactions could be realized by the addition of proton ad-
ditives,2,5b 20 mol% of 2-t-BuC6H4OH was introduced
into the reaction mixture. To our delight, higher enantio-
selectivity (63% ee) and better yield (92%) were obtained
in a short reaction time (entry 14 vs. entry 13). Further-
more, decreasing the reaction temperature from 110 °C to
80 °C, the enantioselectivity was improved to 71% ee (en-
try 15). Other reaction parameters including solvents, the
nature of metal salts, and other additives were also exam-
ined but generally inferior results were obtained.
Subsequently, several sodium salts of 3,3¢-disubstituted
BINOL-derived phosphoric acids 7a–h12 were evaluated
in terms of enantioselectivity and catalytic activity
(Table 1, entries 7–13). Thus, with sodium salt of 7b, poor
enantioselectivity (4% ee) and yield (5%) were obtained
(entry 7). Sodium salt of 7c gave 15% ee with the other
enantioisomer as major product (entry 8). Other candi-
dates (7d–g) with aromatic substituents at 3,3¢-positions
showed good catalytic activity but poor enantioselectivity
ranging 0–37% ee (entries 9–12). However, the sodium
salt of phosphoric acid 7h, synthesized from (R)-BINOL Under the optimized reaction conditions, the substrate
with the bulky 1-adamantyl substituent (Scheme 1),13 ex- generality of the chiral sodium phosphate-catalyzed 1,4-
hibited much better catalytic activity than 7a, giving 2a addition of TMSCN to enones was investigated
(Table 2).14 In general, chalcone derivatives gave excel-
lent yields (86–99%) and moderate enantioselectivities
(53–72% ee) at varying reaction rate (entries 1–10). The
reactions with electron-donating substituents proceeded
Table 1 Optimization of Reaction Conditions
1) chiral acid
(20 mol%)
NaOH
O
CN
O
Me3SiCN (2.2 equiv)
toluene,110 °C
Table 2 Substrate Scope
∗
Ph
Ph
Ph
Ph
2) 1 M HCl, r.t.
1a
2a
7h
NaOH
1)
(20 mol%)
Entrya
1
Chiral acid
Time (h)
4.5
4.5
4.5
4.5
4.5
4.5
4.5
4.5
4.5
4.5
4.5
4.5
4.5
2
Yield (%)b ee (%)c
Me3SiCN (2.2 equiv)
2-t-BuPhOH (20 mol%)
toluene, 80 °C
O
CN
*
O
3
4
5
34
75
7
0
0
R1
R2
R1
R2
2) 1 M HCl, r.t.
1a–k
2a–k
2
Entrya Product
Time Yield ee
(h) (%)b (%)c
3d
4d
5
–20
4
6a
21
31
n.r.
5
1
2
2a R1 = Ph, R2 = Ph
2b R1 = 2-MeOC6H4, R2 = Ph
2
3
2
2
2
2
1
1
1
94 71
96 63
91 67
97 70d
93 72
7a
7a
7b
7c
7d
7e
7f
53
–
6e
3
2c R1 = 3-MeOC6H4, R2 = Ph
2d R1 = 4-MeOC6H4, R2 = Ph
2e R1 = 4-MeC6H4, R2 = Ph
2f R1 = 4-MeOC6H4, R2 = 3-BrC6H4
2g R1 = 2-ClC6H4, R2 = Ph
7
4
4
8
84
71
84
94
87
88
92
94
–15
2
5
9
6
97 66 (100, S)e
99 53f
10
11
12
13
14f
15g
37
0
7
8
2h R1 = 2,4-Cl2C6H3, R2 = Ph
2i R1 = 3-O2NC6H4, R2 = Ph
99 64
7g
7h
7h
7h
2
9
99 65
49
63
71
10
11
2j R1 = 2-ClC6H4, R2 = 4-O2NC6H4 0.5 86 62
2k R1 = Me, R2 = Ph
94 50
1
2
a Reaction conditions: After stirring 1 h at 30 °C under argon, the so-
lution of 7h (0.03 mmol, 20 mol%) and NaOH (0.03 mmol, 20 mol%)
in toluene (0.5 mL) was added enones (0.15 mmol), 2-t-BuPhOH
(0.03 mmol, 20 mol%), toluene (0.5 mL), and TMSCN (0.33 mmol,
2.2 equiv) at r.t. followed by stirring for indicated reaction time at 80
°C.
a Reaction conditions: After stirring 1 h at 30 °C under argon the so-
lution of chiral acid (20 mol%) and NaOH (20 mol%) in toluene (0.5
mL) was sequentially added 1a (0.15 mmol), toluene (0.5 mL) and
TMSCN (0.33 mmol, 2.2 equiv) at r.t. followed by stirring for indi-
cated reaction time at 110 °C or otherwise noted reaction temperature.
b Isolated yield; n.r. = no reaction.
b Isolated yield.
c Determined by chiral HPLC analysis on Chiralpak AS-H.
d Conditions: 20 mol% of chiral acid and 40 mol% of NaOH were
loaded.
c Determined by chiral HPLC analysis on Chiralpak AS-H or other-
wise noted.
d Determined by chiral HPLC analysis on Chiralcel OD-H.
e In parentheses, enantiopure 2f was obtained after recrystallization
from EtOAc and PE with the absolute configuration of 2f determined
by X-ray crystal structure analysis.
e In the absence of NaOH.
f In the presence of 2-t-BuC6H4OH (20 mol%).
g The reaction was performed in the presence of 2-t-BuPhOH (20
mol%) at 80 °C.
f Determined by chiral HPLC analysis on Chiralpak AD-H.
Synlett 2010, No. 18, 2725–2728 © Thieme Stuttgart · New York

LETTER
Asymmetric 1,4-Addition of Cyanide
2727
(2) (a) Wang, J.; Li, W.; Liu, Y.; Chu, Y.; Lin, L.; Liu, X.; Feng,
X. Org. Lett. 2010, 12, 1280. (b) Mazet, C.; Jacobsen, E. N.
Angew. Chem. Int. Ed. 2008, 47, 1762. (c) Madhavan, N.;
Weck, M. Adv. Synth. Catal. 2008, 350, 419. (d) Fujimori,
I.; Mita, T.; Maki, K.; Shiro, M.; Sato, A.; Furusho, S.;
Kanai, M.; Shibasaki, M. Tetrahedron 2007, 63, 5820.
(e) Mita, T.; Sasaki, K.; Kanai, M.; Shibasaki, M. J. Am.
Chem. Soc. 2005, 127, 514. (f) Sammis, G. M.; Danjo, H.;
Jacobsen, E. N. J. Am. Chem. Soc. 2004, 126, 9928.
(g) Sammis, G. M.; Jacobsen, E. N. J. Am. Chem. Soc. 2003,
125, 4442.
(3) (a) Tanaka, Y.; Kanai, M.; Shibasaki, M. J. Am. Chem. Soc.
2008, 130, 6072. (b) Tanaka, Y.; Kanai, M.; Shibasaki, M.
J. Am. Chem. Soc. 2010, 132, 8862.
(4) Shibasaki, M.; Kanai, M.; Matsunaga, S.; Kumagai, N. Acc.
Chem. Res. 2009, 42, 1117.
slower than or comparable to that of chalcone (entries 2–
6 vs. entry 1). On the other hand, electron-deficient
enones were converted into b-cyano ketones much quick-
ly with slightly lower enantioselectivity (entries 7–10 vs.
entry 1). Therefore, 4-methyl- and 4-methoxy-substituted
chalcone derivatives had higher enantioselectivity (66–
72% ee, entries 3–6) than electron-deficient ones (53-65%
ee, entries 7–10). b-Alkyl-substituted enone 1k also gave
excellent yield and 50% ee under the same reaction con-
ditions (entry 11). Enantiopure 2f was easily obtained af-
ter simple recrystallization of a 66% ee product sample
(entry 6). Its absolute configuration was established to be
S by X-ray crystal structure analysis (Figure 2).15
(5) (a) Yang, J.; Wang, Y.; Wu, S.; Chen, F.-X. Synlett 2009,
3365. (b) Yang, J.; Chen, F.-X. Chin. J. Chem. 2010, 28,
981.
(6) Yang, J.; Shen, Y.; Chen, F.-X. Synthesis 2010, 1325.
(7) For reports using chiral alkali metal salts of amino acids,
see: (a) Yamaguchi, M.; Yokota, N.; Minami, T. J. Chem.
Soc., Chem. Commun. 1991, 1088. (b) Yamaguchi, M.;
Shiraishi, T.; Hirama, M. Angew. Chem., Int. Ed. Engl. 1993,
32, 1176. (c) Yamaguchi, M.; Shiraishi, T.; Igarashi, Y.;
Hirama, M. Tetrahedron Lett. 1994, 35, 8233.
(d) Yamaguchi, M.; Shiraishi, T.; Hirama, M. J. Org. Chem.
1996, 61, 3520. (e) Yamaguchi, M.; Igarashi, Y.; Reddy, R.
S.; Shiraishi, T.; Hirama, M. Tetrahedron 1997, 53, 11223.
(f) Kochetkov, K. A.; Harutyunyan, S. R.; Kuz’mina, N. A.;
Savel’eva, T. F.; Maleev, V. I.; Peregudov, A. S.; Vyskočil,
S.; Sagiyan, A. S. Russ. Chem. Bull. Int. Ed. 2001, 50, 1620.
(g) Xiong, Y.; Wen, Y.; Wang, F.; Gao, B.; Liu, X.; Huang,
X.; Feng, X. Adv. Synth. Catal. 2007, 349, 2156. (h) Sato,
A.; Yoshida, M.; Hara, S. Chem. Commun. 2008, 6242.
(i) Liu, X.; Qin, B.; Zhou, X.; He, B.; Feng, X. J. Am. Chem.
Soc. 2005, 127, 12224. (j) Li, P.; Yamamoto, H. Chem.
Commun. 2009, 5412.
Figure 2 X-ray crystallographic structure of (S)-2f
In summary, a catalytic enantioselective 1,4-addition of
TMSCN to aromatic enones have been developed using
chiral sodium (R)-BINOL-derived phosphate. In the pres-
ence of 20 mol% of sodium salt of 7h, the corresponding
b-cyano ketones were obtained in high yields (86–99%)
and moderate enantioselectivities (up to 72% ee). This
protocol provides a complementary substrate scope to
Shibasaki’s methodology.3 Further optimization and
mechanism elucidation are currently under way.
(8) For reports using chiral alkali metal binaphtholate salts, see:
(a) Holmes, I. P.; Kagan, H. B. Tetrahedron Lett. 2000, 41,
7453. (b) Hatano, M.; Ikeno, T.; Miyamoto, T.; Ishihara, K.
J. Am. Chem. Soc. 2005, 127, 10776. (c) Nakajima, M.;
Orito, Y.; Ishizuka, T.; Hashimoto, S. Org. Lett. 2004, 6,
3763. (d) Ichibakase, T.; Orito, Y.; Nakajima, M.
Tetrahedron Lett. 2008, 49, 4427. (e) Zhao, H.; Qin, B.;
Liu, X.; Feng, X. Tetrahedron 2007, 63, 6822. (f) Hatano,
M.; Horibe, T.; Ishihara, K. J. Am. Chem. Soc. 2010, 132, 56.
(9) For reports using chiral alkali-metal phosphate salts, see:
(a) Hatano, M.; Ikeno, T.; Matsumura, T.; Torii, S.; Ishihara,
K. Adv. Synth. Catal. 2008, 350, 1776. (b) Shen, K.; Liu,
X.; Cai, Y.; Lin, L.; Feng, X. Chem. Eur. J. 2009, 15, 6008.
(10) For reviews on Lewis base catalysis, see: (a) Denmark, S.
E.; Beutner, G. L. Angew. Chem. Int. Ed. 2008, 47, 1560.
(b) Gawronski, J.; Wascinska, N.; Gajewy, J. Chem. Rev.
2008, 108, 5227.
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synlett.
Acknowledgment
The authors thank Beijing Institute of Technology and NSFC
(20972016) for financial support.
References and Notes
(1) (a) Ji, J.-X.; Chan, A. S. C. In Catalytic Asymmetric
Synthesis, 3rd ed.; Ojima, I., Ed.; Wiley: New Jersey, 2010,
439–495. (b) Shintani, R.; Hayashi, T. In New Frontiers in
Asymmetric Catalysis; Mikami, K.; Lautens, M., Eds.;
Wiley: New Jersey, 2007, 59–100. (c) Brock, S.; Hose, D.
R. J.; Moseley, J. D.; Parker, A. J.; Patel, I.; Williams, A. J.
Org. Process Res. Dev. 2008, 12, 496. (d) Hayashi, T.;
Yamasaki, K. Chem. Rev. 2003, 103, 2829.
(11) For reviews on chiral anion, see: (a) Lacour, J.; Hebbe-
Viton, V. Chem. Soc. Rev. 2003, 32, 373. (b) Lacour, J.;
Moraleda, D. Chem. Commun. 2009, 7073.
(12) The (R)-BINOL-derived phosphoric acids 7a–g were
synthesized according to the literature methods
(a) Uraguchi, D.; Terada, M. J. Am. Chem. Soc. 2004, 126,
5356. (b) Yamanaka, M.; Itoh, J.; Fuchibe, K.; Akiyama, T.
J. Am. Chem. Soc. 2007, 129, 6756. (c) Akiyama, T.;
Katoh, T.; Mori, K. Angew. Chem. Int. Ed. 2009, 48, 4226.
(13) Preparation of 6h
(e) Harutyunyan, S. R.; Hartog, T.; Geurts, K.; Minnaard, A.
J.; Feringa, B. L. Chem. Rev. 2008, 108, 2824. (f) López,
F.; Minnaard, A. J.; Feringa, B. L. Acc. Chem. Res. 2007, 40,
179.
To a stirred solution of (R)-BINOL (6a; 1.431 g, 5.0 mmol)
and 1-adamantanol (1.522 g, 10.0 mmol) in CH2Cl2 (25 mL),
Synlett 2010, No. 18, 2725–2728 © Thieme Stuttgart · New York

2728
J. Yang et al.
LETTER
concd H2SO4 (0.8 mL) was added dropwise at 0 °C over 5
min. After stirring at 0 °C for 30 min the ice bath was
removed. The suspension was stirred at r.t. for an additional
6 h before aq NaOH (5%) was added to neutralize H2SO4
thus to quench the reaction. The resulting mixture was
extracted by CH2Cl2 twice. The combined organic phase was
washed with brine, dried over Na2SO4, and concentrated.
The crude solid was purified by silica gel chromatography
using PE–EtOAc (10:1, v/v) as the eluent to yield (R)-3,3¢-
di(1-adamantyl)-1,1¢-binaphthyl-2,2¢-diol (6h) as a white
solid (1.670 g, 3.01 mmol); 60% yield, mp 207–209 °C;
[a]D17 –82.5 (c 0.114, CHCl3). 1H NMR (500 MHz, CDCl3):
d = 1.79–1.85 (dd, J = 21.0, 12.0 Hz, 12 H, CHCH2CH),
2.00 (s, 12 H, CCH2CH), 2.15 [s, 6 H, CH(CH2)3], 7.17 (d,
J = 9.0 Hz, 2 H, ArH), 7.37–7.43 (m, 4 H, ArH), 7.80 (s, 2
H, ArH), 7.97 (d, J = 9.0 Hz, 2 H, ArH) ppm. 13C NMR (125
MHz, CDCl3): d = 29.0, 36.1, 36.8, 43.1, 110.7, 117.5,
123.5, 124.0, 125.7, 129.5, 131.4, 131.6, 147.0, 152.3 ppm.
Preparation of 7h
(R)-3,3¢-Di(1-adamantyl)-1,1¢-binaphthyl-2,2¢-diol (6h; 555
mg, 1 mmol) was dissolved in pyridine (3 mL) in a 50 mL
Schlenk tube. Phosphorous oxychloride (185 mL, 2 mmol)
was added dropwise at r.t. After stirring for 10 h at r.t., H2O
(3 mL) was added. The resulting mixture was stirred for
additional 6 h at r.t. followed by addition of CH2Cl2. All
pyridine was removed by reverse extraction with 1 M HCl.
The organic phase was washed with brine, dried over
Na2SO4, and concentrated. The crude solid was purified by
flash silica gel chromatography CH2Cl2–MeOH (5:1, v/v) as
the eluent to yield (R)-3,3¢-di(1-adamantyl)-1,1¢-binaphthyl-
2,2¢-diylphosphoric acid (7h) as a white solid (555 mg, 0.9
mmol); 90% yield; mp >300 °C; [a]D21 –283.3 (c 0.240,
CHCl3). 1H NMR (400 MHz, DMSO-d6): d = 1.75 (s, 12 H,
CHCH2CH), 1.95 (s, 12 H, CCH2CH), 2.07 [s, 6 H,
CH(CH2)3], 7.21–7.23 (m, 2 H, ArH), 7.41–7.42 (m, 4 H,
ArH), 7.87 (s, 2 H, ArH), 8.01 (d, J = 8.8 Hz, 2 H, ArH) ppm.
13C NMR (100 MHz, DMSO-d6): d = 28.5, 35.9, 36.4, 42.7,
121.6, 122.4, 123.4, 124.3, 126.0, 130.0, 130.3, 130.8,
147.1, 149.3 ppm. 31P NMR (162 MHz, DMSO-d6): d = 3.5
(s) ppm.
(14) Typical Procedure for the Asymmetric 1,4-Addition of
TMSCN to Enones
After (R)-3,3¢-di(1-adamantyl)-1,1¢-binaphthyl-2,2¢-diyl
phosphoric acid (7h, 18.5 mg, 0.03 mmol, 20 mol%) and
NaOH (1.2 mg, 0.03 mmol, 20 mol%) were placed in a dry
Schlenk tube under argon. Toluene (0.5 mL) was added, and
the mixture was stirred at 30 °C for 1 h. Then, chalcone (1a,
31.2 mg, 0.15 mmol), 2-t-BuPhOH (0.03 mmol, 20 mol%),
additional toluene (0.5 mL), and TMSCN (0.33 mmol, 2.2
equiv) were added at r.t. Equipped with cold finger, the
reaction mixture was stirred at 80 °C until the reaction was
completed (monitored by TLC). The reaction was quenched
with 1 M HCl (0.3 mL) followed by diluting with dioxane (2
mL) and stirring for additional 30 min at r.t. To work it up,
H2O (2 mL) was added, and the resulting mixture was
extracted with EtOAc (5 mL) (Caution! HCN possibly
generated in the reaction mixture is highly toxic. Those
operations should be conducted in a well-ventilated hood).
The extract was washed with H2O (2 mL), brine (3 mL),
dried over Na2SO4, and concentrated under reduced
pressure. The crude product was purified by flash column
chromatography on silica gel (PE–EtOAc, 20:1, v/v) to
afford pure product 2a as a white solid in 94% yield and 71%
ee.
4-Oxo-2,4-diphenylbutanenitrile (2a)
1H NMR (400 MHz, CDCl3): d = 3.52 (dd, J = 18.0, 6.0 Hz,
1 H, NCCHCHAHBCO), 3.74 (dd, J = 18.0, 8.0 Hz, 1 H,
NCCHCHAHBCO), 4.57 (dd, J = 8.0, 6.0 Hz, 1 H,
NCCHCHAHBCO), 7.34–7.49 (m, 7 H, ArH), 7.58–7.62 (m,
1 H, ArH), 7.92–7.94 (m, 2 H, ArH) ppm. 13C NMR (100
MHz, CDCl3): d = 31.9, 44.5, 120.6, 127.5, 128.1, 128.4,
128.8, 129.3, 133.9, 135.3, 135.8, 194.6 ppm. IR (KBr):
n = 1681, 2236 cm–1. HPLC [Chiralpak AS-H, 254 nm, n-
hexane–2-PrOH (70:30), 1.0 mL/min]: tR(major) = 13.3 min,
tR(minor) = 21.4 min; [a]D17 –20.0 (c 0.100, CH2Cl2, 71%
ee).
(15) CCDC-787260 contains the supplementary crystallographic
data of 2f 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.
Synlett 2010, No. 18, 2725–2728 © Thieme Stuttgart · New York

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