InBr3-catalyzed direct alkynylation of nitrones with terminal alkynes: an efficient synthesis of N-hydroxy-propargyl amines

Article abstract of DOI:10.1016/j.tetlet.2009.03.206

An InBr₃-catalyzed direct and efficient alkynylation of nitrones with terminal alkynes was developed. The process enables practical synthesis of a wide range of synthetically useful N-hydroxy-propargyl amine derivatives in good yields under mil

Full text of DOI:10.1016/j.tetlet.2009.03.206

Tetrahedron Letters 50 (2009) 2952–2955
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InBr3-catalyzed direct alkynylation of nitrones with terminal alkynes: an
efficient synthesis of N-hydroxy-propargyl amines
*
Du-Ming Ji, Ming-Hua Xu
Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 555 Zuchongzhi Road, Shanghai 201203, China
a r t i c l e i n f o
a b s t r a c t
Article history:
An InBr3-catalyzed direct and efficient alkynylation of nitrones with terminal alkynes was developed. The
process enables practical synthesis of a wide range of synthetically useful N-hydroxy-propargyl amine
derivatives in good yields under mild conditions. The application of this method to optically active prop-
argylic N-hydroxyamines syntheses was also described. With chiral nitrones, good diastereoselectivities
were obtained. Moreover, the first chiral indium(III) complex-catalyzed asymmetric alkynylation of nit-
rone was achieved with moderate enantioselectivity.
Received 9 February 2009
Revised 27 March 2009
Accepted 31 March 2009
Available online 5 April 2009
Ó 2009 Elsevier Ltd. All rights reserved.
The catalytic in situ generation of alkynilides and their use in
carbon–carbon bond-forming processes are currently of great
interest because of the atom economy and high efficiency for prep-
aration of synthetically very useful propargylic compounds.1–4
Important progress has been made by using various transition-me-
tal catalysts, particularly with easily available zinc and copper
salts.2,3 Carreira and co-workers documented the pioneering work
of asymmetric addition of terminal alkynes to aldehydes and nitro-
nes in the presence of catalytic amount of Zn(OTf)2 and tertiary
propargyl amines that can serve as important synthetic building
blocks like the corresponding propargylic alcohols, direct alkynyla-
tion of imino substrates with terminal alkynes remains an impor-
tant and challenging topic. To our knowledge, indium salt-
mediated alkynylation of nitrones has not been described before.
Herein, we wish to present an efficient and practical process for
synthesis of N-hydroxy-propargyl amines by InBr3-catalyzed direct
alkyne addition to nitrones under mild conditions.
Our studies were initiated by screening various imines and
imine derivatives in the presence of indium(III) salt and tertiary
amine such as i-Pr2NEt which are similar to Shibasaki’s condi-
tions.8a However, unlike the catalytic alkynylation of carbonyl
compounds, most reactions did not lead to the desired product ex-
cept using nitrone as substrate. Encouraged by this finding, we
then selected the reaction of iso-butyl nitrone 1a and phenylacet-
ylene for model studies. As shown in Table 1, InBr3 was more reac-
tive than In(OTf)3 (entry 1 vs entry 3), and 15 mol % of catalyst was
found to be suitable (entries 3–5). In addition, reducing the amount
of phenylacetylene from 2 equiv to 1.5 equiv did not influence the
yield (entries 4 and 6). These results demonstrated that treatment
of nitrone and terminal alkyne with 15 mol % of InBr3 and 20 mol %
of i-Pr2NEt at room temperature could afford propargylic N-
hydroxylamine adducts in high yields. It is worth noting that, dur-
ing these early investigation, we observed the formation of cycliza-
tion product 2,3-dihydroisoxazole11 in toluene with In(OTf)3 as
catalyst (entry 2).
amine.2a–d In the same way, via
p-complexes formation with fur-
ther deprotonation, copper3 and other transition metal4 acetylides
could be generated and subsequently submitted to carbonyls and
imines to give the corresponding propargylic adducts. In the past
several years, indium(III) salts5 have also attracted considerable
attention of organic chemists in the field because of its remarkable
effectivity in activation of alkynes,6–8 great functional group toler-
ance, high stability, and low toxicity. Sakai and Konakahara have
reported an indium bromide-promoted process in Et2O for the mild
addition of terminal alkynes to aldehydes and acetals,7 however,
stoichiometric amount of indium salt had to be used. Quite re-
cently, Shibasaki and co-workers successfully developed its cata-
lytic version for alkynylation of carbonyl compounds, in which
dual activation of both terminal alkynes and carbonyls was found
in the presence of an indium(III) catalyst.8a Moreover, catalytic
asymmetric alkynylation of aldehydes could be readily achieved
using an In(III)/BINOL complex.8b,c
In comparison to the alkynylation of aldehydes and ketones,9
addition of acetylide to imines and imine derivatives is far fewer
reported due to the relatively poor electrophilicity of the azome-
thine carbon. Although there have been several methods of activa-
tion of C@N bond by Lewis acid promotion10 for the preparation of
With optimal reaction conditions being identified, we then
decided to investigate the scope of the method by evaluating this
direct alkynylation of various nitrones with terminal alkynes. To
our delight, the reaction seems to be general, as shown in Table
2, most nitrones derived from aliphatic aldehydes could react with
phenylacetylene successfully to produce propargylic N-hydroxy-
amines in good to excellent yields. Linear (entries 2–5),
branched (entries 1, 6–9), and b-branched (entry 10) aliphatic nit-
a-
* Corresponding author. Tel./fax: +86 21 5080 7388.
E-mail address: xumh@mail.sioc.ac.cn (M.-H. Xu).
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.03.206

D.-M. Ji, M.-H. Xu / Tetrahedron Letters 50 (2009) 2952–2955
2953
Table 1
Table 3
Screening and optimization of the reaction conditionsa
InBr3-catalyzed alkynylation of aromatic nitronesa
InBr3 (25 mol%)
i-Pr2NEt (25 mol%)
HO
Ar
Bn
O
Bn
H
Catalyst
N
N
HO
Bn
O
Bn
H
N
+
Ph
3 equiv
i-Pr2NEt (20 mol%)
N
CH2Cl2, 40 ºC
+
Ph
1.5 equiv
Ar
CH2Cl2, rt
Ph
1
2
Ph
1a
2a
Entry
1: Ar
Time (h)
2
Yieldb (%)
Entry
Catalyst
Mol %
Alkyne (equiv)
Solvent
Yieldb (%)
1
2
3
4
5
6
7
8
9
1k C6H5
24
24
24
24
24
24
24
24
24
24
2k
2l
74
80
74
81
66
68
74
40
55
50
1l o-MeC6H4
1m p-MeOC6H4
1n o-BrC6H4
1o m-ClC6H4
1p p-BrC6H4
1q p-FC6H4
1r 2-Furyl
1
2
3
4
5
6
7
In(OTf)3
In(OTf)3
InBr3
InBr3
InBr3
10
10
10
15
20
15
15
2
2
2
2
CH2Cl2
Toluene
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
10
11c
40
84
86
89
69
2m
2n
2o
2p
2q
2r
2
InBr3
InBr3
1.5
1.2
1s m-NO2C6H4
1t p-NO2C6H4
2s
2t
a
The reaction was performed with 0.2 mmol of nitrone in 1 mL of dry solvent at
10
rt.
a
b
The reaction was carried out with InBr3 (0.05 mmol), i-Pr2NEt (0.05 mmol),
phenylacetylene (0.6 mmol), and nitrone (0.2 mmol) in dry CH2Cl2 (1 mL) at 40 °C
for 24 h. See Ref. 12 for experimental procedure.
Isolated yield.
c
Isolated yield of cyclization product.
b
Isolated yield.
Table 2
Other aromatic nitrones bearing various electron-withdrawing or
electron-donating substituents could also be successfully applied
for alkynylation, the results are summarized in Table 3.
Additionally, as exemplified in Table 4, with heptyl nitrone 1d, a
further study of the reaction generality and scope was carried out
using some representative terminal acetylenes. In most cases, the
corresponding propargylic N-hydroxyamines 3a–f were obtained
in good yields. From the results we also observed that some func-
tional groups such as cyano and hydroxyl groups could be toler-
ated during the reaction.
InBr3-catalyzed alkynylation of aliphatic nitronesa
InBr3 (15 mol%)
i-Pr2NEt (20 mol%)
HO
R
Bn
O
R
Bn
H
N
N
+
Ph
1.5 equiv
CH2Cl2, rt
Ph
1
2
Entry
1: R
Time (h)
2
Yieldb (%)
1
2
3
4
5
6
7
8
1a i-C3H7
1
1
4
1
1
2a
89
87
97
92
91
95
95
84
92
89
1b n-C3H7
1c n-C4H9
1d n-C6H13
1e C2H5
2b
2c
2d
2e
2f
2g
2h
2i
The established method was also applied to synthesize optically
active propargylic N-hydroxyamines2a,d,13 that can serve as highly
valuable building blocks for asymmetric organic synthesis. Reac-
1f C2H5(CH3)CH
1g (C2H5)2CH
1h i-C4H9
1.5
1.5
1
Table 4
9
1i c-C6H11
1j c-C3H5
1
20
InBr3-catalyzed alkynylation of heptyl nitronea
10c
2j
InBr3 (15 mol%)
i-Pr2NEt (20 mol%)
a
The reaction was carried out with InBr3 (0.03 mmol), i-Pr2NEt (0.04 mmol),
phenylacetylene (0.3 mmol), and nitrone (0.2 mmol) in dry CH2Cl2 (1 mL) at rt. See
Ref. 12 for experimental procedure.
HO
Bn
O
Bn
H
N
N
+
R
CH2Cl2, 40 ºC
b
C6H13
C6H13
Isolated yield.
Stirred at 40 °C.
1.5 equiv
c
R
1d
3
Entry
Alkyne
Time (h)
3
3
Yieldb (%)
73
rones are all suitable substrates. It should be noted that, perform-
ing the same reaction with cyclopropyl nitrone 1j under optimal
conditions gave a more sluggish conversion and the nitrone could
not be consumed completely. Eventually, we were pleased to find
that the reaction was dramatically improved when elevating tem-
perature to 40 °C (entry 10). Moreover, it was found that the reac-
tion could also be accomplished well in high yield using the base
Et3N instead of i-Pr2NEt.
Next our attention was devoted to the addition of terminal al-
kyne to nitrones derived from aromatic aldehydes. Not surpris-
ingly, the reactions proceeded not so well as described above
because of the lower reactivity of aromatic nitrones in contrast
to the corresponding aliphatic ones.2a With phenyl nitrone 1k as
model substrate, the optimal reaction conditions were reinvesti-
gated. It was found that a moderate yield could be reached by
increasing the loading of the catalyst InBr3 and terminal acetylene
to 25 mol % and 3 equiv, respectively. Slight warming (40 °C) was
also effective for the smooth reaction. Finally, combining
25 mol % of InBr3 and 25 mol % of i-Pr2NEt into a solution of phen-
ylacetylene (3 equiv) and nitrone (1 equiv) in CH2Cl2 at 40 °C gave
the desired adducts in good yield (74%) after 24 h (Table 3, entry 1).
1
2
3
4
3a
H
SiMe3
3
3b
3c
3d
84
82
81
H
H
(CH2)3CH3
(CH2)3CN
1
1
H
tBu
5
6
48
1
3e
3f
44
75
H
(CH2)3OH
HO
H
a
The reaction was carried out with InBr3 (0.03 mmol), i-Pr2NEt (0.04 mmol),
phenylacetylene (0.3 mmol), and nitrone (0.2 mmol) in dry CH2Cl2 (1 mL) at 40 °C.
b
Isolated yield.

2954
D.-M. Ji, M.-H. Xu / Tetrahedron Letters 50 (2009) 2952–2955
phenylacetylene was firstly studied with Shibasaki’s In(III)/BINOL
(a)
system.8b To our disappointment, the enantioselectivity was
low.15 Several other chiral compounds such as BINOL derivatives,
amino alcohols, diamines, and salen derivatives were also exam-
ined as ligands. At this stage, salan 6 was determined to be the
best; product 2a was obtained with 47% ee though the yield was
still low (23%) (Scheme 2).
Bn
HO
O
O
N
*
InBr3 (15 mol%)
base (20 mol%)
O
H
+ Ph
1.5 equiv
O
N+
Ph
CH2Cl2, rt
Bn
O-
4
In summary, we have developed an indium(III)-catalyzed direct
and efficient alkynylation of nitrones with terminal alkynes. The
reactions could be accomplished with ease in the presence of InBr3
and simple tertiary amine under mild conditions to afford a variety
of synthetically very useful N-hydroxy-propargyl amine deriva-
tives in good yields. By applying this method to chiral nitrones,
good diastereoselectivities were observed and optically active
propargylic N-hydroxyamines could be available. In addition, the
first example of chiral indium(III) complex-catalyzed enantioselec-
tive alkynyl addition to nitrone was described. Further studies on
improving the catalytic asymmetric addition are in progress.
base: i-Pr2NEt, 85% yield, 80:20 dr
Et3N, 99% yield, 88:12 dr
(b)
HO
OBn
Ph
O
OBn
+
N
N
*
InBr3, Et3N
Ph
1.5 equiv
CH2Cl2, 40 ºC
3 h
H
5
41% yield, 86:14 dr
Acknowledgments
Scheme 1. InBr3-induced diastereoselective alkynylation of chiral nitrones.
Financial support from the National Natural Science Foundation
of China (20672123, 20721003), the Shanghai Rising-Star Program
(08QH14027), the Chinese Academy of Sciences, and Shanghai
Institute of Materia Medica is acknowledged.
tion of phenylacetylene and chiral N-benzyl-D-glyceraldehyde-de-
rived nitrone 4 was firstly examined. As summarized in Scheme
1a, good diastereoselectivities (up to 88:12) as well as excellent
yields (99%) were observed, especially when simply switching
the base from i-Pr2NEt to Et3N. While lowering the reaction tem-
perature led to no desired improvement on the diastereoselectivi-
ty. It is worth noting that, when compared to the Zn(OTf)2-involved
procedure developed by Carreira,2d less catalyst loading and reac-
tion time (2 h) were required. Moreover, the reaction could be
run under air atmosphere, rendering unnecessary the need for N2
protection.
References and notes
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Pinet, S.; Pandya, S. U.; Chavant, P. Y.; Ayling, A.; Vallée, Y. Org. Lett. 2002, 4,
1463; (c) Weil, T.; Schreiner, P. R. Eur. J. Org. Chem. 2005, 2213; (d) Ishikawa, T.;
Mizuta, T.; Hagiwara, K.; Aikawa, T.; Kudo, T.; Saito, S. J. Org. Chem. 2003, 68,
3702.
2. (a) Frantz, D. E.; Fässler, R.; Carreira, E. M. J. Am. Chem. Soc. 1999, 121, 11245;
(b) Anand, N. K.; Carreira, E. M. J. Am. Chem. Soc. 2001, 123, 9687; (c) Frantz, D.
E.; Fässler, R.; Tomooka, C. S.; Carreira, E. M. Acc. Chem. Res. 2000, 33, 373; (d)
Fässler, R.; Frantz, D. E.; Oetiker, J.; Carreira, E. M. Angew. Chem., Int. Ed. 2002,
41, 3054; (e) Jiang, B.; Si, Y.-G. Adv. Synth. Catal. 2004, 346, 669; (f) Yamashita,
M.; Yamada, K.; Tomioka, K. Adv. Synth. Catal. 2005, 347, 1649; (g) Ramu, E.;
Varala, R.; Sreelatha, N.; Adapa, S. R. Tetrahedron Lett. 2007, 48, 7184.
3. (a) Motoki, R.; Kanai, M.; Shibasaki, M. Org. Lett. 2007, 9, 2997; (b) Hatano, M.;
Asai, T.; Ishihara, K. Tetrahedron Lett. 2008, 49, 379; (c) Wei, C.; Mague, J. T.; Li,
C.-J. Proc. Natl. Acad. Sci. U.S.A. 2004, 101, 5749; (d) Taylor, A. M.; Schreiber, S. L.
Org. Lett. 2006, 8, 143; (e) Lu, G.; Li, X.; Li, Y.-M.; Kwong, F. Y.; Chan, A. S. C. Adv.
Synth. Catal. 2006, 348, 1926; (f) Li, Z.-P.; Macleod, P. D.; Li, C.-J. Tetrahedron:
Asymmetry 2006, 17, 590; (g) Asano, Y.; Hara, K.; Ito, H.; Sawamura, M. Org. Lett.
2007, 9, 3901; (h) Colombo, F.; Benaglia, M.; Orlandi, S.; Usuelli, F.; Celentano,
G. J. Org. Chem. 2006, 71, 2064.
4. (a) Wei, C.; Li, Z.; Li, C.-J. Org. Lett. 2003, 5, 4473; (b) Ji, J.-X.; Au-Yeung, T. L.;
Wu, J.; Yip, C. W.; Chan, A. S. C. Adv. Synth. Catal. 2004, 346, 42; (c) Fischer, C.;
Carreira, E. M. Org. Lett. 2001, 3, 4319; (d) Lo, V. K.-Y.; Liu, Y.; Wong, M.-K.; Che,
C.-M. Org. Lett. 2006, 8, 1529.
5. For a recent review on indium salt-promoted organic reactions: Fringuelli, F.;
Piermatti, O.; Pizzo, F.; Vaccaro, L. Curr. Org. Chem. 2003, 7, 1661.
6. (a) Tsuchimoto, T.; Maeda, T.; Shirakawa, E.; Kawakami, Y. Chem. Commun.
2000, 1573; (b) Tsuchimoto, T.; Hatanaka, K.; Shirakawa, E.; Kawakami, Y.
Chem. Commun. 2003, 2454; (c) Sakai, N.; Annaka, K.; Konakahara, T. Org. Lett.
2004, 6, 1527.
On the other hand, we investigated another type of chiral nit-
rone (5)14 with a (R)-valinol-derived chiral auxiliary, transferring
the chiral center from
a-carbon to the carbon close to nitrogen
atom (Scheme 1b). Surprisingly, the alkynylation did not proceed
well under the above-optimized conditions even at 40 °C, only
gave a trace formation of product. When both the catalyst and base
loading of InBr3 and Et3N were increased to 25 mol %, the yield of
reaction was promoted to 41%, and a similar good diastereoselec-
tivity (86:14) as using D-glyceraldehyde derived nitrone 4 was ob-
served. By changing the solvent further to toluene or THF did not
help to improve the result.
In an attempt to extend our exploration of asymmetric alkyny-
lation further, we then envisioned the possibility of enantioselec-
tive addition of alkynes to nitrones by
a chiral indium(III)
complex. Catalytic asymmetric addition of alkynylzinc reagents
to nitrones has been recently reported,2a,13a but direct alkyne addi-
tion using a chiral indium catalyst remains unrealized. Accord-
ingly, the reaction between iso-butyl nitrone 1a and
7. (a) Sakai, N.; Hirasawa, M.; Konakahara, T. Tetrahedron Lett. 2003, 44, 4171; (b)
Sakai, N.; Kanada, R.; Hirasawa, M.; Konakahara, T. Tetrahedron 2005, 61, 9298.
8. (a) Takita, R.; Fukuta, Y.; Tsuji, R.; Ohshima, T.; Shibasaki, M. Org. Lett. 2005, 7,
1363; (b) Takita, R.; Yakura, K.; Ohshima, T.; Shibasaki, M. J. Am. Chem. Soc.
2005, 127, 13760; (c) Harada, S.; Takita, R.; Ohshima, T.; Matsunaga, S.;
Shibasaki, M. Chem. Commun. 2007, 948.
9. For recent reviews, see: (a) Cozzi, P. G.; Hilgraf, R.; Zimmermann, N. Eur. J. Org.
Chem. 2004, 4095; (b) Pu, L. Tetrahedron 2003, 59, 9873; (c) Si, Y.-G.; Huang, H.;
Jiang, B. Chin. J. Org. Chem. 2004, 24, 1389.
InBr3 (20 mol%)
ligand (20 mol%)
HO
Bn
O
Bn
H
N
*
N
Ph
2 equiv
+
i-Pr2NEt (50 mol%)
4A MS, CH2Cl2
40 ºC
Ph
1a
2a
10. (a) Wee, A. G. H.; Zhang, B. Tetrahedron Lett. 2007, 48, 4135; (b) Jiang, B.; Si, Y.-
G. Tetrahedron Lett. 2003, 44, 6767.
11. Aschwanden, P.; Frantz, D. E.; Carreira, E. M. Org. Lett. 2000, 2, 2331.
12. Typical procedure: Under nitrogen atmosphere, InBr3 (0.03–0.05 mmol) was
added to a dry flask, then CH2Cl2 (0.5 mL), phenylacetylene (0.3 mmol), and i-
Pr2NEt (0.04–0.05 mmol) were successively added. After stirring for 5 min at
room temperature, nitrone (0.2 mmol) in CH2Cl2 (0.5 mL) was added. Then the
reaction mixture was stirred at room temperature or at 40 °C until the nitrone
was consumed. A saturated aqueous solution of NH4Cl was added and the
mixture was extracted with CH2Cl2. The combined organic phase was dried
ligand:
6
NH HN
OH
HO
Scheme 2. Catalytic enantioselective alkynylation of nitrone.

D.-M. Ji, M.-H. Xu / Tetrahedron Letters 50 (2009) 2952–2955
2955
over Na2SO4, filtered, and concentrated. The crude product was purified by
silica gel flash chromatography to afford the corresponding propargylic N-
hydroxyamine. Spectroscopic data for selected products: Compound 2c:1H
NMR (300 MHz, CDCl3): d 0.92 (t, J = 7.2 Hz, 3H), 1.30–1.41 (m, 2H), 1.43–1.53
(m, 2H), 1.80–1.89 (m, 2H), 3.74 (t, J = 7.2 Hz, 1H), 3.94 and 4.16 (2d, AB,
JAB = 13.2 Hz, 2H), 4.95 (br s, 1H, OH), 7.25–7.50 (m, 10H); 13C NMR (100 MHz,
CDCl3): d 14.0, 22.4, 28.6, 33.0, 86.1, 86.9, 122.9, 127.4, 128.1, 128.2, 128.3,
129.6, 131.8, 137.1; MS (ESI) m/z: 294.1 (M+H+). Compound 2h: 1H NMR
(300 MHz, CDCl3): d 0.92 (t, J = 5.7 Hz, 6H), 1.73 (t, J = 7.2 Hz, 2H), 1.89–1.96 (m,
1H), 3.83 (t, J = 7.2 Hz, 1H), 3.95 and 4.10 (2d, AB, JAB = 12.9 Hz, 2H), 5.37 (s, 1H,
OH), 7.24–7.51 (m, 10H); 13C NMR (100 MHz, CDCl3): d 22.1, 22.8, 25.1, 42.0,
86.0, 86.9, 122.9, 127.4, 128.1, 128.2, 128.3, 129.6, 131.8, 137.1; MS (ESI) m/z:
294.0 (M+H+). Compound 2l: 1H NMR (300 MHz, CDCl3): d 2.35 (s, 3H), 4.03
and 4.12 (2d, AB, JAB = 12.9 Hz, 2H), 4.80 (s, 1H), 5.18 (s, 1H), 7.18–7.84 (m,
14H); 13C NMR (100 MHz, CDCl3): d 19.1, 84.8, 88.3, 122.8, 125.7, 127.5, 128.1,
128.2, 128.3, 129.6, 129.8, 130.5, 131.9, 135.6, 136.9; MS (ESI) m/z: 350.0
(M+Na+). Compound 2p: 1H NMR (300 MHz, CDCl3): d 4.03 and 4.11 (2d, AB,
JAB = 12.9 Hz, 2H), 4.91 (s, 1H), 4.94 (s, 1H), 7.26–7.58 (m, 14H); 13C NMR
(100 MHz, CDCl3): d 83.7, 89.1, 122.0, 122.4, 127.6, 128.3, 128.4, 128.6, 129.5,
130.5, 131.4, 131.9, 136.7, 137.0; MS (ESI) m/z: 392.0 (M+H+). Compound 3c:
1H NMR (300 MHz, CDCl3): d 0.88 (t, J = 6.0 Hz, 3H), 1.22–1.33 (m, 6H), 1.35–
1.44 (m, 2H), 1.54–1.76 (m, 2H), 1.87–1.99 (m, 2H), 2.49 (t, J = 6.6 Hz, 2H), 2.55
(t, J = 7.2 Hz, 2H), 3.47 (t, J = 6.6 Hz, 1H), 3.81 and 4.00 (2d, AB, JAB = 12.9 Hz,
2H), 5.22 (s, 1H, OH), 7.26–7.35 (m, 5H); 13C NMR (100 MHz, CDCl3): d 14.0,
16.1, 17.9, 22.5, 24.7, 26.3, 28.9, 31.7, 33.4, 78.9, 83.8, 119.2, 127.4, 128.3,
129.5,137.1; MS (ESI) m/z: 313.2 (M+H+).
13. (a) Konishi, A.; Wei, W.; Kobayashi, M.; Fujinami, S.; Ukaji, Y.; Inomata, K.
Chem. Lett. 2007, 36, 44; (b) Wei, W.; Kobayashi, M.; Ukaji, Y.; Inomata, K.
Chem. Lett. 2006, 35, 176.
14. For synthesis, see: Patel, S. K.; Murat, K.; Py, S.; Vallée, Y. Org. Lett. 2003, 5,
4081.
15. Both InBr3 and In(OTf)3 were examined with BINOL, only around 20% ee was
observed though the yields were good (ꢀ90%).