Synthesis of chiral 2-(anilinophenylmethyl)pyrrolidines and 2-(anilinodiphenylmethyl)pyrrolidine and their application to enantioselective borane reduction of prochiral ketones as chiral catalysts

Article abstract of DOI:10.1016/j.tet.2012.12.024

Chiral diamines, 2-(anilinophenylmethyl)pyrrolidines and 2-(anilinodiphenylmethyl)pyrrolidine, were prepared from N-(tert-butoxycarbonyl) pyrrolidine or (S)-proline as a starting material, respectively. These chiral diamines were efficient for the catalytic enantioselective borane reduction of acetophenone. Using (S)-2-(anilinodiphenylmethyl)pyrrolidine, chiral secondary alcohols were obtained from prochiral ketones with good to excellent enantiomeric excesses (up to 98% ee).

Full text of DOI:10.1016/j.tet.2012.12.024

Tetrahedron 69 (2013) 1739e1746
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Synthesis of chiral 2-(anilinophenylmethyl)pyrrolidines and
2-(anilinodiphenylmethyl)pyrrolidine and their application to
enantioselective borane reduction of prochiral ketones as chiral
catalysts
*
Naoya Hosoda, Hideaki Kamito, Miki Takano, Yoshitaka Takebe, Yoshitaka Yamaguchi, Masatoshi Asami
Department of Advanced Materials Chemistry, Graduate School of Engineering, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Chiral diamines, 2-(anilinophenylmethyl)pyrrolidines and 2-(anilinodiphenylmethyl)pyrrolidine, were
prepared from N-(tert-butoxycarbonyl)pyrrolidine or (S)-proline as a starting material, respectively.
These chiral diamines were efficient for the catalytic enantioselective borane reduction of acetophenone.
Using (S)-2-(anilinodiphenylmethyl)pyrrolidine, chiral secondary alcohols were obtained from prochiral
ketones with good to excellent enantiomeric excesses (up to 98% ee).
Received 15 November 2012
Received in revised form 6 December 2012
Accepted 10 December 2012
Available online 21 December 2012
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Pyrrolidine
Diamine
Enantioselective reduction
Chiral catalyst
1. Introduction
enantiomeric excesses.11e Since the reduction of acetophenone
using (S)-valinol afforded (R)-1-phenylethanol with low ee (49%
Asymmetric synthesis of enantiomerically enriched secondary
alcohols has been widely studied, because chiral secondary alcohols
are important synthetic intermediates for various other function-
alities such as halide, amine, ester, and ether, and involved in many
natural products and pharmaceuticals. A catalytic enantioselective
borane reduction of prochiral ketones is one of the useful methods
to obtain chiral secondary alcohols.1 Since Itsuno et al. reported
enantioselective reduction of aromatic ketones in the presence of
(S)-diphenylvalinol,2 borane reduction using various chiral amino
alcohols has been studied extensively.3,4 Other chiral catalysts, such
as sulfoximines,5 phosphinamides,6 a mercapto alcohol,7 sulfon-
amides,8 BINOL derivatives,9 and a bis-hydroxyamide,10 have also
been employed for asymmetric borane reduction.
ee)14 whereas the use of (S)-diphenylvalinol resulted in the sub-
stantial improvement of the selectivity (94% ee)2 as well as the case
of (S)-prolinol14 and (S)-diphenylprolinol4 (44 and 97% ee, re-
spectively), we expected that the modification of the 2-(anilino-
methyl)pyrrolidine skeleton would produce more efficient chiral
1,2-diamines. Here we report the preparation of chiral 2-(anilino-
phenylmethyl)pyrrolidines (1 and 2) and 2-(anilinodiphe-
nylmethyl)pyrrolidine (3) from N-(tert-butoxycarbonyl)pyrrolidine
or (S)-proline, respectively, and the enantioselective borane re-
duction of prochiral ketones using them (Scheme 1). Diamines 1e3
showed high selectivity in the reaction and various secondary al-
cohols were obtained in good yields with 62e98% ee.
We have been working on asymmetric syntheses using chiral
1,2-diamines prepared from (S)-proline11,12 or (S)-indoline-2-
carboxylic acid.12,13 In our previous study, it was found that a dia-
zaborolidine prepared from borane and (S)-2-(anilinomethyl)pyr-
rolidine served as an efficient catalyst for the enantioselective
borane reduction of prochiral ketones and corresponding chiral
secondary alcohols were obtained with moderate to high
Ph
Ph
Ph
Ph
N
H
N Ph
H
N
H
N Ph
H
N
H
N Ph
H
1
2
3
BH -Me S,
3
2
O
HO H
catalytic amount of 1-3
2
2
1
1
R
* R
R
R
* Corresponding author. Tel./fax: þ81 45 339 3968; e-mail address: m-asami@
Scheme 1. Catalytic enantioselective borane reduction of prochiral ketones using 1e3.
ynu.ac.jp (M. Asami).
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2012.12.024

1740
N. Hosoda et al. / Tetrahedron 69 (2013) 1739e1746
2. Results and discussion
(entry 1). The yield of major isomer 7 was improved when the re-
action was carried out at 0 ꢁC (66%, entry 2) and 20 ꢁC (71%, entry 3).
Furthermore, the enantioselectivities of 7 and 8 were increased to 93
and 91% ee, respectively, when the ether solution of 6 was added to
the ether solution of (S)-5 at ꢀ78 ꢁC and the reaction was carried out
at 20 ꢁC (entry 4). The stereochemistry of 7 and 8 was determined as
follows. Recrystallization of each of them fromethyl acetateafforded
crystalline 7 (52% from 4) and 8 (6% from 4), which were found to be
optically pure (>99% ee) by HPLC analyses. The X-ray crystallo-
graphic analysesof 7and 8 showed therelative configurationsof two
The chiral diamines, 2-(anilinophenylmethyl)pyrrolidines (1 and
2), were synthesized as shown in Scheme 2. Beak et al. reported that
asymmetric deprotonation of N-(tert-butoxycarbonyl)pyrrolidine
(4) with sec-butyllithium and (ꢀ)-sparteine gave chiral organo-
lithium reagent (S)-5, which was treated with electrophiles to give
enantiomerically enriched products.15 According to the method, the
reaction of (S)-5 and N-benzylideneaniline (6) was examined.
Namely, an ether solution of (S)-5 generated in situ by the reaction of
4 (1.0 equiv) and sec-butyllithium (1.2 equiv) in the presence of
chiral centers to be (4S
*
,5R
*
) and (4R
*
,5R
*
), respectively (Fig. 1).
Ph
Ph
Ph
Red-Al
THF,
reflux,
1 h
H2SO4
MeOH,
reflux,
15 h
N
N
N N
N
H
N Ph
H
Ph
Ph
s-BuLi,
O
Ph
H
(4S,5R)-7
(4S,5R)-9
(2R,1'S)-1
N
H
N
Ph
N
52%
76%
27%
6
Li
(>99% ee)
(>99% ee)
N
N
Et2O, 20 oC,
4 h
Et2O, -78 oC, 4 h
t-BuO
O
t-BuO
O
(S)-5
4
Ph
Ph
Ph
Red-Al
THF,
reflux,
1 h
H2SO4
MeOH,
reflux,
15 h
N
N
N N
N
H
N Ph
Ph
Ph
H
O
(4R,5R)-8
(4R,5R)-10
(2R,1'R)-2
6%
89%
40%
(>99% ee)
(>99% ee)
Scheme 2. Preparation of (2R,10S)-1 and (2R,10R)-2.
(ꢀ)-sparteine (1.3 equiv) at ꢀ78 ꢁC was added to an ether solution of
6 (1.5 equiv) at ꢀ20, 0, and 20 ꢁC, respectively, and the resulting
mixture was stirred for 4 h at the same temperature. The results are
shown in Table 1. When the reaction was carried out at ꢀ20 ꢁC,
Therefore, the absolute configurations of 7 and 8 were assigned to be
(4S,5R) and (4R,5R), respectively, by comparing with the literature.15
We assume the diastereoselectivity of the reaction of (S)-5 and 6 as
follows (Scheme 3). The nucleophilic addition of (S)-5 to 6 from its
Re-face gives (4S,5R)-7 and the addition from its Si-face gives
(4R,5R)-8. A steric repulsion between the pyrrolidine ring of (S)-5
and the phenyl group of 6 arises in the Si-face attack, while the re-
pulsion is avoided in the Re-face attack to yield (4S,5R)-7, prefer-
entially. Next, enantiopure (4S,5R)-7 was converted to (2R,10S)-2-
(anilinophenylmethyl)pyrrolidine ((2R,10S)-1) as follows (Scheme
2). The reduction of (4S,5R)-7 with sodium bis(2-methoxyethoxy)
aluminum hydride (Red-AlÒ) gave a chiral aminal, (4S,5R)-3,4-
diphenyl-1,3-diazabicyclo[3.3.0]octane ((4S,5R)-9), in 76% yield.
Then, (4S,5R)-9 was converted to (2R,10S)-1 in 27% yield by acidic
treatment in methanol. Enantiopure (2R,10R)-2 was also obtained
from (4R,5R)-8 in the same manner as the preparation of (2R,10S)-1.
The enantiomeric excesses of (2R,10S)-1 and (2R,10R)-2 were de-
termined to be >99% by HPLC analyses of (4S,5R)-7 and (4R,5R)-8
derived from (2R,10S)-1 and (2R,10R)-2 by the reaction with di-tert-
butyl dicarbonate in the presence of sodium hydroxide followed by
the treatment of resulting 1-Boc-protected 1 and 2 with butyl-
lithium, respectively.
a
diastereomer mixture of 3,4-diphenyl-1,3-diazabicyclo[3.3.0]
octan-2-one (7 was more polar than 8) was obtained in 37% yield.
Table 1
Yields and enantiomeric excesses of 7 and 8 in nucleophilic addition of (S)-5 to 6a
Entry
Temp (ꢁC)
Yieldb (%) [eec (%)]
7
8
1
2
ꢀ20
0
20
20
23[84]
66[82]
71[82]
60[93]
14[81]
18[81]
16[82]
13[91]
3
4d
a
An ether solution of (S)-5 generated in situ by the reaction of 4 (1.0 equiv) and
sec-butyllithium (1.2 equiv) in the presence of (ꢀ)-sparteine (1.3 equiv) at ꢀ78 ꢁC
was added to an ether solution of 6 (1.5 equiv) at ꢀ20, 0, and 20 ꢁC, respectively, and
the resulting mixture was stirred for 4 h at the same temperature.
b
The products were isolated as a diastereomer mixture of 7 and 8. The yields
were determined by 1H NMR analysis of the diastereomer mixture.
c
ee was determined by HPLC analysis.
The ether solution of 6 was added to the ether solution of (S)-5 at ꢀ78 ꢁC, and
d
the resulting mixture was stirred for 4 h at 20 ꢁC.
Next, the synthesis of (R)-2-(anilinodiphenylmethyl)pyrrolidine
((R)-3) was attempted in the same manner as Scheme 2 using N-
(diphenylmethylene)aniline in place of 6. However no reaction
proceeded and starting material 4 was recovered quantitatively.
Thus, a synthesis of (S)-3 was examined using (S)-proline ((S)-11) as
a starting material (Scheme 4). At first, penultimate intermediate
(S)-17 was prepared according to the procedure reported by
Olivares-Romero and Juaristi.16 Namely, the treatment of (S)-
The yields of 7 and 8 were determined to be 23 and 14%, respectively,
by 1H NMR analysis of the diastereomer mixture. After separation of
the diastereomers by preparative thin-layer chromatography, the
enantiomeric excesses of 7 and 8 were determined to be 84 and 81%
ee, respectively, by HPLC analyses using a Daicel Chiralcel OD-H

N. Hosoda et al. / Tetrahedron 69 (2013) 1739e1746
1741
Fig. 1. ORTEP drawings of (4S,5R)-7 (left) and (4R,5R)-8 (right) with thermal ellipsoids drawn at the 50% probability level. All hydrogen atoms except on 4- and 5-positions are
omitted for clarity (black¼carbon, red¼oxygen, blue¼nitrogen, and green¼hydrogen).
proline methyl ester hydrochloride ((S)-12), which was prepared
from (S)-11 quantitatively, with benzyl bromide and the sub-
sequent reaction of methyl ester (S)-13 and phenylmagnesium
H
Li
Ph
Re-face
bromide afforded amino alcohol (S)-14 in good yield. In the azi-
dation of (S)-14, we encountered a problem that the reaction hardly
proceeded under the condition described in the literature.16 After
examinations of the reaction conditions in detail, it became ap-
parent that azide (S)-15 was obtained in 86% yield when the re-
action was conducted with 5 equiv of trifluoroacetic acid in
addition to an excess of sulfuric acid under reflux for 6 h. The re-
duction of (S)-15 and the subsequent hydrogenolysis of (S)-16 gave
(S)-17 in good yield. Next, diamine (S)-17 was coupled with iodo-
benzene in the presence of copper(I) iodide and cesium acetate17 to
afford (S)-3 in 46% yield.
N
attack
t-BuO
N
N
N
O
Ph
O
(4S,5R)-7
major product
Ph
Si-face
attack
H
Li
steric
repulsion
N
N
N
Ph
t-BuO
N
As (2R,10S)-1, (2R,10R)-2, and (S)-3 were obtained, the enantio-
selective borane reduction of acetophenone was carried out using
them as the catalysts. After refluxing a mixture of boraneedimethyl
sulfide complex (1.25 equiv) and the diamine (0.25 equiv) in THF for
45 min, acetophenone (1.00 equiv) was added to the resulting so-
lution over 2 h at room temperature, and stirring was continued for
2 h. The results are summarized in Table 2. (S)-1-Phenylethanol was
O
O
(4R,5R)-8
minor product
Scheme 3. Stereochemical model for diastereoselective nucleophilic addition of (S)-5
to 6.
NaN ,
3
BnBr,
3
CF CO H,
Ph
Ph
3
2
2
4
Ph
OH
Ph
PhMgBr
SOCl
Et N
H SO
2
+
COOH
COOMe
COOMe
N
H
N
H
N
Bn
N
N
N
3
THF,
rt, 12 h
CH Cl ,
MeOH,
reflux, 1 h
CHCl -H O,
2
2
3
2
2
-
Cl
rt, 4 h
Bn
Bn
reflux, 6 h
(S)-11
(S)-12
quant.
(S)-13
(S)-14
(S)-15
85%
86%
96%
PhI,
CuI,
H (1.5 MPa),
LiAlH
Ph
2
4
Ph
Ph
Ph
Ph
NH
Ph
CsOAc
Pd-C
N
NH
2
N
N
H
N Ph
H
THF,
rt, overnight
DMF,
2
MeOH-AcOH,
rt, 3 d
H
o
Bn
90 C, 12 h
(S)-16
(S)-17
(S)-3
46%
quant.
90%
Scheme 4. Preparation of (S)-3.

1742
N. Hosoda et al. / Tetrahedron 69 (2013) 1739e1746
Table 2
Table 4
Catalytic enantioselective borane reduction of acetophenone using 1e3
Catalytic enantioselective borane reduction of prochiral ketones using (S)-3
BH3-Me2S (1.25 equiv),
diamine (0.25 equiv)
THF, rt, 2 h
BH3-Me2S (1.30 equiv),
O
HO H
O
HO H
R1 R2
(S)-3 (0.30 equiv)
R1 R2
Ph Me
Ph * Me
THF, rt, 2 h
Entry
Diamine
Yielda (%)
eeb (%) (Config.)
Entry
Ketone
Yielda (%)
96
eeb (%) (Config.)
1
2
3
(2R,10S)-1
(2R,10R)-2
(S)-3
82
86
93
84 (S)
95 (S)
93 (R)
O
1
2
94 (R)
Cl
Ph
a
Isolated yield.
b
ee was determined by HPLC analysis, and the absolute configuration was de-
O
termined by specific rotation.18
93
92 (R)
obtained in 82% yield with 84% ee when (2R,10S)-1 was used (entry
1). On the other hand, the enantioselectivity was improved to 95% ee
when the reaction was carried out using (2R,10R)-2 (entry 2). Fur-
thermore, the reduction using (S)-3 afforded (R)-1-phenylethanol in
high yield with high ee (93% yield, 93% ee, entry 3).
Next, the effect of the amounts of borane was examined using
(S)-3 due to its ease of preparation from natural amino acid (S)-11
and high ability as an asymmetric catalyst. Borane was added in the
range of 1.15e1.40 equiv and (S)-3 was added in the range of
0.15e0.40 equiv based on acetophenone. The results are summa-
rized in Table 3. The enantioselectivity was improved by increasing
the amounts of borane and (S)-3 (entries 1e4). The best result (96%
yield, 94% ee) was obtained when 1.30 equiv of borane and
0.30 equiv of (S)-3 were employed (entry 4), which was superior to
the best result using (S)-2-(anilinomethyl)pyrrolidine (86% yield,
93% ee).11e The selectivity was not further improved even when
0.35 or 0.40 equiv of (S)-3 was used with 1.35 or 1.40 equiv of bo-
rane, respectively (entries 5 and 6).
O
3
4
97
97
98 (S)
80 (R)
Ph Me
O
Ph
Et
O
Me
5
6
99
99
82 (R)
89 (R)
O
Table 3
Effect of amounts of borane and (S)-3 on enantioselectivity
O
HO H
Ph Me
BH3-Me2S, (S)-3
O
Ph Me
THF, rt, 2 h
7
8
94
99
83 (R)
62 (R)
Me
Entry
BH3 (equiv)
(S)-3 (equiv)
Yielda (%)
eeb (%)
Br
O
1
2
3
4
5
6
1.15
1.20
1.25
1.30
1.35
1.40
0.15
0.20
0.25
0.30
0.35
0.40
94
98
93
96
93
94
83
90
93
94
94
94
Ph
Isolated yield.
Me
a
b
ee was determined by HPLC analysis, and the absolute configuration was de-
termined by specific rotation.18
a
Isolated yield.
ee was determined by HPLC analysis.
b
Then, the reaction was applied to various prochiral ketones
previous study.11e Next, another borane is chelated with the more
Lewis basic nitrogen atom of the pyrrolidine ring of 18. The car-
bonyl oxygen atom of the prochiral ketone approaches the boron
atom of the diazaborolidine ring of 18 to form six-membered chair
conformation 19. The ketone is reduced via 19, in which the larger
substituent (RL) of the ketone occupies the equatorial position of
the chair conformation to yield the major enantiomer with high ee.
From the results of the reduction using 1e3 (Table 2), we assume
that one phenyl group at 10-position which is located at trans-
position to the pyrrolidine ring (Ph1) is important rather than the
other phenyl group (Ph2) to achieve high enantioselectivity because
less preferred six-membered boat conformation 20 becomes less
stable by a steric repulsion between Ph1 and the smaller substituent
(RS) of the ketone (Scheme 5). By applying the similar explanation
to (2R,10S)-1 and (2R,10R)-2, which have R-configuration at 2-
position, it is rationalized that (S)-1-phenylethanol was obtained
from both (2R,10S)-1 and (2R,10R)-2 and the selectivity slightly de-
creased when (2R,10S)-1 in which Ph1 is lacking was used.
using the optimized reaction conditions in order to examine the
usefulness of (S)-3 as the catalyst. As shown in Table 4, good to
excellent enantioselectivities were achieved for aromatic ketones
(80e98% ee, entries 1e7). In particular, the reduction of phenacyl
chloride showed excellent selectivity (98% ee, entry 3). Moderate
selectivity was obtained in the case of an aliphatic ketone, 4-
phenyl-2-butanone (62% ee, entry 8). Furthermore, it is notewor-
thy that most of yields and enantioselectivities for the reduction of
these prochiral ketones were improved compared with the results
using (S)-2-(anilinomethyl)pyrrolidine,11e which indicates that the
two phenyl groups at 10-position of (S)-3 are effective to improve
yields and enantioselectivities.
The assumed stereochemical model to explain the enantiose-
lective borane reduction with (S)-3 is shown in Scheme 5. Initially,
cis-fused five-membered bicyclic diazaborolidine 18 is generated
by the reaction of (S)-3 and borane. The formation of diazabor-
olidine is important to achieve high selectivity as reported in our

N. Hosoda et al. / Tetrahedron 69 (2013) 1739e1746
1743
Ph1
Ph1
spectra were obtained on a JEOL JNM-EX270 or a Bruker biospin
DRX300 spectrometer using CDCl3 as a solvent. 1H and 13C NMR
chemical shift values are given in parts per million (ppm) relative to
Me4Si. Elemental analyses were carried out on a Vario EL III Ele-
mental analyzer. High-resolution mass spectra (HRMS) were
recorded on a Hitachi Nano Frontier LD spectrometer. High per-
formance liquid chromatography (HPLC) analyses were carried out
with JASCO instruments (pump, PU-2080 Plus; detector, UV-2075
Plus). Thin-layer chromatography (TLC) analyses were carried out
on silica-gel 60 F254-coated plates (Merck). Column chromatogra-
phy was carried out with Wakogel C-200 with indicated eluent
unless otherwise described. Preparative TLC was performed on
silica-gel-coated plates (Wakogel B-5F, 20 cmꢂ20 cm). A syringe
pump (Furue Science Co. Ltd., Micro Feeder JP-V) was used for the
enantioselective borane reduction of prochiral ketones.
Ph2
Ph2
BH3
N
N Ph
N
N Ph
H
H
B
H
(S)-3
18
BH3
O
RL
RS
Ph2
H
N
N
H2
Ph
RS
RL
B
Ph1
H2BO
H
RS
RL
B
O
H
4.2. Preparation of (4S,5R)- and (4R,5R)-3,4-diphenyl-
1,3-diazabicyclo[3.3.0]octan-2-one ((4S,5R)-7 and (4R,5R)-8):
typical procedure (Table 1, entry 4)
(major)
19 (favored)
To an ether (5.0 mL) solution of (ꢀ)-sparteine (660 mg,
2.8 mmol) was added sec-butyllithium (0.99 mol dmꢀ3 cyclohex-
ane/hexane solution, 2.7 mL, 2.7 mmol) at ꢀ78 ꢁC and the mixture
was stirred for 15 min at ꢀ78 ꢁC. The resulting mixture was added
dropwise to an ether (5.0 mL) solution of N-(tert-butoxycarbonyl)
pyrrolidine (4) (373 mg, 2.18 mmol) at ꢀ78 ꢁC, and the mixture was
stirred at ꢀ78 ꢁC for 4 h. An ether (20 mL) solution of N-benzyli-
deneaniline (6) (593 mg, 3.27 mmol) was added dropwise to the
mixture at ꢀ78 ꢁC, and the resulting mixture was stirred at 20 ꢁC for
4 h. After the reaction was quenched with water, the aqueous layer
was extracted with ethyl acetate, and the combined organic layers
were washed with 1 mol dmꢀ3 aqueous HCl, water, and brine,
successively. The organic layer was dried over anhydrous sodium
sulfate, and the solvent was removed under reduced pressure. The
crude product was purified by column chromatography (silica-gel,
ether/hexane¼1:1) to give a diastereomer mixture of (4S,5R)-7 and
(4R,5R)-8 as a white solid (442 mg, 1.59 mmol, 73%). The ratio of
(4S,5R)-7 and (4R,5R)-8 was determined to be 60:13 by 1H NMR
analysis. The enantiomeric excesses of (4S,5R)-7 and (4R,5R)-8 were
determined as follows. Diastereopure (4S,5R)-7 and (4R,5R)-8 were
obtained by preparative TLC (silica-gel, ether/hexane¼1:1) using
a portion of the diastereomer mixture. Using these diastereopure
samples, the enantiomeric excesses of (4S,5R)-7 and (4R,5R)-8 were
determined to be 93 and 91% ee, respectively, by HPLC analyses. For
comparison of the retention times, the racemic 7 and 8 were pre-
pared by the same manner as mentioned above using N,N,N0,N0-
tetramethylethylenediamine in place of (ꢀ)-sparteine. (4S,5R)-7:
Daicel Chiralcel OD-H (25ꢂ0.46 cm i.d.); eluent, 20% 2-propanol in
hexane; flow rate, 0.5 mL/min; tR,19.2 min for minor peak, 26.6 min
for major peak; (4R,5R)-8: Daicel Chiralcel OD-H (25ꢂ0.46 cm i.d.);
eluent, 20% 2-propanol in hexane; flow rate, 0.5 mL/min; tR,
15.0 min for major peak, 19.0 min for minor peak.
Ph2
H
N
Ph
RL
RS
B
Ph1
N
H2BO
H
B
H2
O
RS
H
RL
20 (disfavored)
(minor)
Scheme 5. Stereochemical model for catalytic enantioselective borane reduction using
(S)-3.
3. Conclusion
Chiral diamines, 2-(anilinophenylmethyl)pyrrolidines ((2R,10S)-
1 and (2R,10R)-2) and 2-(anilinodiphenylmethyl)pyrrolidine ((S)-3),
were prepared. The catalytic enantioselective borane reduction of
prochiral ketones was studied using them. It became apparent that
the stereochemistry of products was exceedingly controlled by the
chirality at 2-position rather than 10-position of the diamines.
Chiral secondary alcohols were obtained in high yields with good to
excellent enantiomeric excesses from prochiral ketones under the
optimized reaction condition using (S)-3. Furthermore, our result
demonstrates that the aniline moiety of (S)-3 is also necessary to
achieve easy formation of diazaborolidine under the mild reaction
conditions and high enantioselectivity in the borane reduction as
Juaristi et al. reported that a diazaborolidine prepared from (S)-2-
(aminodiphenylmethyl)pyrrolidine ((S)-17) and borane under mi-
crowave irradiation at 75 ꢁC in toluene afforded (R)-1-
phenylethanol with 84% ee in the reduction of acetophenone.16
4. Experimental section
4.1. General
4.3. Preparation of enantiopure (4S,5R)- and (4R,5R)-
3,4-diphenyl-1,3-diazabicyclo[3.3.0]octan-2-one ((4S,5R)-7
and (4R,5R)-8)
Most manipulations were carried out under an atmosphere of
argon. Solvents were dried and purified in the usual manner. N-
(tert-Butoxycarbonyl)pyrrolidine (4),15b N-benzylideneaniline (6),19
and N-(diphenylmethylene)aniline20 were prepared according to
literature.
Melting points were determined on a Stuart melting point ap-
paratus SMP3 and are uncorrected. Specific rotations were mea-
sured on a JASCO P-1010 polarimeter. Infrared spectra were
recorded on a HORIBA FT-730 spectrometer. 1H and 13C NMR
The same procedure as mentioned above was carried out using
(ꢀ)-sparteine (7.14 g, 30.5 mmol), sec-butyllithium (0.99 mol dmꢀ3
cyclohexane/hexane solution, 28.0 mL, 28 mmol), N-(tert-butox-
ycarbonyl)pyrrolidine (4) (4.00 g, 23.4 mmol), and N-benzylide-
neaniline (6) (6.35 g, 35.0 mmol). The recrystallization of the crude
product from ethyl acetate gave crystalline (4S,5R)-7 (3.38 g,
12.1 mmol, 52%). The ee of (4S,5R)-7 was determined to be >99% by
HPLC analysis. Furthermore, the residue obtained from the mother
liquor after the recrystallization was purified by column

1744
N. Hosoda et al. / Tetrahedron 69 (2013) 1739e1746
chromatography (silica-gel, ether/hexane¼1:3) to give diaster-
eopure (4R,5R)-8 (0.74 g, 2.6 mmol, 11%), which was recrystallized
from ethyl acetate to give crystalline (4R,5R)-8 (0.37 g,1.3 mmol, 6%).
The ee of (4R,5R)-8 was determined to be >99% by HPLC analysis.
C18H20N2: C, 81.78; H, 7.63; N, 10.60%. Found: C, 81.77; H, 7.68; N,
10.53%.
4.6. Preparation of (2R,10S)-2-(anilinophenylmethyl)pyrroli-
dine ((2R,10S)-1)
4.3.1. (4S,5R)-7. White solid; mp 180.5e181.2 ꢁC; ½a D22
þ133.2 (c
ꢃ
1.02, CHCl3); IR (KBr) cmꢀ1: 2965, 2898,1680,1597,1495,1453,1389,
To a methanol (10 mL) solution of (4S,5R)-9 (779 mg, 2.95 mmol)
was added sulfuric acid (1.0 mL), and the solution was refluxed for
15 h. After the solutionwas cooled to room temperature, 6 mol dmꢀ3
aqueous NaOH was added to basify the solution. The mixture was
extracted with ether and the combined organic layers were washed
with water and brine. The organic layer was dried over anhydrous
sodium sulfate, and the solvent was removed under reduced pres-
sure. The crude product was purified by column chromatography
(silica-gel, ethyl acetate/triethylamine¼70:1) to give (2R,10S)-1
(199 mg, 0.79 mmol, 27%). The ee of (2R,10S)-1 was determined to be
>99% by HPLC analysis of (4S,5R)-7, which was derived from
(2R,10S)-1 by the reaction with di-tert-butyl dicarbonate in the
presence of sodium hydroxide followed by the treatment of result-
ing 1-Boc-protected (2R,10S)-1 with butyllithium.
771; 1H NMR (270 MHz, CDCl3)
d: 1.05e1.32 (m, 2H), 1.65e1.94 (m,
2H), 3.23(ddd, J¼4.0, 8.6,11.2Hz,1H), 3.75 (dt, J¼8.2,11.2Hz,1H), 4.11
(dt, J¼5.9, 8.6Hz,1H), 5.48 (d, J¼8.6Hz,1H), 6.97 (tt, J¼1.3, 7.3Hz,1H),
7.13e7.32 (m, 7H), 7.43 (d, J¼7.9 Hz, 2H); 13C NMR (67.8 MHz, CDCl3)
d: 24.9, 27.5, 46.0, 60.0, 60.8, 119.9, 122.9, 126.5, 127.6, 128.3, 128.5,
136.5, 138.9, 160.9; Anal. Calcd for C18H18N2O: C, 77.67; H, 6.52; N,
10.06%. Found: C, 77.65; H, 6.53; N, 10.09%.
4.3.2. (4R,5R)-8. White solid; mp 193.1e193.4 ꢁC; ½a D21
þ40.0 (c
ꢃ
1.02, CHCl3); IR (KBr) cmꢀ1: 2979, 2894, 1690, 1600, 1502, 1458,
1397, 754; 1H NMR (270 MHz, CDCl3)
d: 1.51e1.66 (m,1H), 1.74e1.92
(m, 1H), 1.97e2.10 (m, 1H), 2.13e2.23 (m, 1H), 3.15 (ddd, J¼4.0, 9.1,
11.6 Hz, 1H), 3.54 (ddd, J¼2.6, 6.3, 9.2 Hz, 1H), 3.84 (dt, J¼7.9,
11.6 Hz, 1H), 5.06 (d, J¼2.6 Hz, 1H), 6.95 (t, J¼7.3 Hz, 1H), 7.18e7.33
Viscous light yellow oil; ½a D27
ꢃ
þ11.8 (c 1.01, CHCl3); IR (neat) cmꢀ1
:
(m, 7H), 7.46 (d, J¼7.9 Hz, 2H); 13C NMR (67.8 MHz, CDCl3)
d
: 24.6,
3338, 2966, 2872,1614,1515,1316, 909, 732, 703; 1H NMR (270 MHz,
31.3, 45.5, 63.6, 65.4, 119.7, 122.9, 126.0, 127.9, 128.5, 129.0, 138.8,
140.7, 161.3; Anal. Calcd for C18H18N2O: C, 77.67; H, 6.52; N, 10.06%.
Found: C, 77.37; H, 6.59; N, 9.94%.
CDCl3) d: 1.56e1.75 (m, 5H), 2.80e2.89 (m, 1H), 2.95e3.03 (m, 1H),
3.33e3.41 (m, 1H), 4.30 (d, J¼5.9 Hz, 1H), 4.60 (br, 1H), 6.51 (d,
J¼7.9 Hz, 2H), 6.62 (t, J¼7.3 Hz, 1H), 7.05 (dd, J¼7.3, 7.9 Hz, 2H),
7.19e7.39 (m, 5H); 13C NMR (67.8 MHz, CDCl3)
d: 24.8, 27.4, 46.5, 61.2,
4.4. Preparation of (4S,5R)-3,4-diphenyl-1,3-diazabicyclo
[3.3.0]octane ((4S,5R)-9)
64.0,113.8, 117.3, 127.0 (ꢂ2), 128.4, 128.9, 141.5, 147.6; HRMS-ESI (m/
z): [MþH]þ Calcd for C17H21N2: 253.1699. Found: 253.1704.
To a THF (40 mL) solution of (4S,5R)-7 (1.19 g, 4.27 mmol) was
added sodium bis(2-methoxyethoxy)aluminum hydride (70% tol-
uene solution, 3.6 mL, 13 mmol) at room temperature, and the re-
action mixture was refluxed for 1 h. After the reaction was
quenched with water, the aqueous layer was extracted with ethyl
acetate, and the combined organic layers were washed with water
and brine. The organic layer was dried over anhydrous sodium
sulfate, and the solvent was removed under reduced pressure. The
crude product was purified by column chromatography (ethyl ac-
etate/hexane¼1:5) using Chromatorex NH-DM1020 (Fuji Silysia
Chemical Ltd.) to give (4S,5R)-9 (0.86 g, 3.3 mmol, 76%).
4.7. Preparation of (2R,10R)-2-(anilinophenylmethyl)pyrroli-
dine ((2R,10R)-2)
Diamine (2R,10R)-2 was prepared from (4R,5R)-10 (913 mg,
3.45 mmol) in the same manner as the preparation of (2R,10S)-1. The
crude product was purified bycolumn chromatography (chloroform/
hexane¼1:2) using Chromatorex NH-DM1020 (Fuji Silysia Chemical
Ltd.) to give (2R,10R)-2 (350 mg,1.39 mmol, 40%). The ee of (2R,10R)-2
was determinedto be >99% by HPLCanalysis of (4R,5R)-8, which was
derived from (2R,10R)-2 by the reaction with di-tert-butyl dicar-
bonate in the presence of sodium hydroxide followed by the treat-
ment of resulting 1-Boc-protected (2R,10R)-2 with butyllithium.
White solid; mp 84.0e84.7 ꢁC; ½a D21
þ77.8 (c 1.01, CHCl3); IR
ꢃ
(KBr) cmꢀ1: 2900, 1601, 1502, 1322, 1126, 752, 695; 1H NMR
Viscous light yellowoil; ½a D27
ꢃ
ꢀ46.0 (c 1.08, CHCl3); IR (KBr) cmꢀ1
:
(270 MHz, CDCl3)
d: 1.31e1.54 (m, 2H), 1.59e1.83 (m, 2H), 2.88 (q,
3377, 2961, 2862,1601,1505,1318, 869, 748, 699; 1H NMR (270 MHz,
J¼8.6 Hz, 1H), 3.23 (dt, J¼3.7, 8.6 Hz, 1H), 4.07 (dt, J¼3.7, 8.6 Hz, 1H),
4.36 (d, J¼7.3 Hz, 1H), 4.54 (d, J¼8.6 Hz, 1H), 4.70 (d, J¼7.3 Hz, 1H),
6.50 (d, J¼7.9 Hz, 2H), 6.71 (t, J¼7.3 Hz, 1H), 7.13 (dd, J¼7.3, 7.9 Hz,
CDCl3) d: 1.66e1.85 (m, 5H), 2.79e2.88 (m, 1H), 2.96e3.04 (m, 1H),
3.32e3.39 (m, 1H), 4.21 (d, J¼4.6 Hz, 1H), 5.14 (br, 1H), 6.51 (d,
J¼7.9 Hz, 2H), 6.58 (t, J¼7.3 Hz, 1H), 7.04 (dd, J¼7.3, 7.9 Hz, 2H),
2H), 7.19e7.33 (m, 5H); 13C NMR (67.8 MHz, CDCl3)
d
: 24.9, 27.2,
7.17e7.36 (m, 5H); 13C NMR (67.8 MHz, CDCl3)
d: 25.5, 28.9, 46.6,
54.9, 65.7, 69.0, 72.2, 114.5, 117.6, 126.7, 127.0, 128.4, 128.8, 140.9,
146.7; Anal. Calcd for C18H20N2: C, 81.78; H, 7.63; N, 10.60%. Found:
C, 81.78; H, 7.66; N, 10.62%.
60.4, 64.4,113.3,116.6,126.7,126.8,128.4,128.9, 143.2, 147.7; HRMS-
ESI (m/z): [MþH]þ Calcd for C17H21N2: 253.1699. Found: 253.1704.
4.8. Preparation of (S)-2-azidodiphenylmethyl-1-
benzylpyrrolidine ((S)-15)
4.5. Preparation of (4R,5R)-3,4-diphenyl-1,3-diazabicyclo
[3.3.0]octane ((4R,5R)-10)
To a chloroform (50 mL) solution of (S)-(1-benzylpyrrolidin-2-
yl)diphenylmethanol ((S)-14)16 (5.24 g, 15.3 mmol) were added
trifluoroacetic acid (8.17 g, 71.6 mmol), sodium azide (3.75 g,
57.7 mmol), water (25 mL), and sulfuric acid (51 mL) at 0 ꢁC, and the
resulting mixture was refluxed for 6 h. After the mixture was cooled
to room temperature, the organic layer was separated and the
aqueous layer was extracted with dichloromethane. The combined
organic layers were washed with 5% aqueous sodium hydrogen
carbonate and brine. The organic layer was dried over anhydrous
sodium sulfate, and the solvent was removed under reduced
pressure. The crude product was purified by column chromatog-
raphy (silica-gel, ethyl acetate/hexane¼1:19) to give (S)-15 (4.82 g,
13.1 mmol, 86%).
Aminal (4R,5R)-10 was prepared from (4R,5R)-8 (1.10 g,
3.94 mmol) in the same manner as the preparation of (4S,5R)-9. The
crude product was purified by column chromatography (silica-gel,
ethyl acetate) to give (4R,5R)-10 (0.93 g, 3.5 mmol, 89%).
White solid; mp 124.7e125.3 ꢁC; ½a D22
ꢀ139.6 (c 1.06, CHCl3); IR
ꢃ
(KBr) cmꢀ1: 2922, 1601, 1505, 1360, 1126, 752, 693; 1H NMR
(270 MHz, CDCl3) d: 1.90e2.17 (m, 4H), 2.61e2.71 (m, 1H), 3.17 (ddd,
J¼3.3, 6.9, 10.2 Hz, 1H), 3.55 (dt, J¼2.2, 7.3 Hz, 1H), 4.27 (d, J¼7.3 Hz,
1H), 4.47(d, J¼7.9 Hz,1H), 4.83 (d, J¼7.9Hz,1H), 6.42(d, J¼7.9Hz,2H),
6.63 (t, J¼7.3 Hz, 1H), 7.10 (dd, J¼7.3, 7.9 Hz, 2H), 7.17e7.36 (m, 5H);
13C NMR (67.8 MHz, CDCl3)
d: 24.1, 28.1, 53.4, 66.6, 72.2, 75.1, 112.5,
116.3, 125.8, 127.0, 128.77, 128.83, 142.2, 146.1; Anal. Calcd for

N. Hosoda et al. / Tetrahedron 69 (2013) 1739e1746
1745
Colorless oil; ½a D27
ꢃ
ꢀ54.4 (c 0.98, CHCl3) {lit.16
½
a 2D5
ꢃ
ꢀ37.0 (c 1.0,
Indanol: eluent, 5% 2-propanol in hexane; flow rate, 0.5 mL/min;
tR, 18.9 min for minor peak, 21.0 min for major peak. 4-Phenyl-2-
butanol: eluent, 5% 2-propanol in hexane; flow rate, 0.5 mL/min;
tR, 21.2 min for major peak, 30.4 min for minor peak.
CHCl3)}; IR and NMR spectral data were consistent with those re-
ported in the literature.16
4.9. Preparation of (S)-2-(anilinodiphenylmethyl)pyrrolidine
((S)-3)
4.11. Experimental procedure for X-ray crystallography of
(4S,5R)-7 and (4R,5R)-8
To a DMF (3.0 mL) solution of cesium acetate (2.44 g, 12.7 mmol)
and copper(I) iodide (0.95 g, 5.0 mmol) were added a DMF (2.0 mL)
solution of iodobenzene (1.03 g, 5.05 mmol) and a DMF (2.0 mL)
solution of (S)-17 (1.26 g, 4.99 mmol) at room temperature, and the
resulting mixture was stirred at 90 ꢁC for 12 h. After the mixture
was cooled to room temperature, aqueous ammonia was added and
the mixture was extracted with ethyl acetate. The combined or-
ganic layers were washed with brine. The organic layer was dried
over anhydrous sodium sulfate, and the solvent was removed under
reduced pressure. The crude product was purified by column
chromatography (silica-gel, ethyl acetate/hexane¼1:4) to give (S)-3
(0.76 g, 2.3 mmol, 46%).
Suitable single crystals (4S,5R)-7 and (4R,5R)-8 were obtained
by recrystallization from ethyl acetate and were individually
mounted on glass fibers. All measurements were made on a Rigaku
Mercury70 diffractometer by using graphite monochromated Mo-
ꢀ
K
a
radiation (
l
¼0.71070 A). The data were collected at a tempera-
ture of ꢀ50ꢄ1 ꢁC to maximum 2
q
values of 61.3ꢁ and 55.0ꢁ, re-
spectively. A total of 744 oscillation images were collected for each
compound. The crystal-to-detector distance was 45.00 mm. Read-
out was performed in the 0.137 mm pixel mode. In the reduction of
the data, a numerical absorption correction was applied. The data
were corrected for Lorentz and polarization effects.
White solid; mp 95.7e96.4 ꢁC; ½a D19
þ31.9 (c 1.01, CHCl3); IR (KBr)
ꢃ
Crystallographic data and the results of measurements are
summarized in Table 5. The structure was solved by direct methods
(SIR2004)21 for all compounds, and expanded using Fourier tech-
niques. Least-square refinements were carried out using
SHELXL97.22 All of the non-hydrogen atoms were refined aniso-
tropically. Hydrogen atoms were introduced at the ideal positions
and refined using the riding model. All calculations were performed
using the CrystalStructure crystallographic software package.23
Crystal (4R,5R)-8 contained two independent molecules A and B.
In Fig. 1 (right), only molecule A is displayed, because molecule B
has a similar geometry to molecule A.
cmꢀ1: 3343, 2954, 2871, 1600, 1502, 1320, 751, 701; 1H NMR
(300 MHz, CDCl3) d: 1.33e1.42 (m,1H),1.53e1.74 (m, 4H), 2.84e2.92
(m,1H), 3.00e3.07 (m,1H), 3.85e3.90 (m,1H), 5.73 (br,1H), 6.32 (dd,
J¼0.9, 8.5 Hz, 2H), 6.53 (t, J¼7.3 Hz, 1H), 6.91 (dd, J¼7.3, 8.5 Hz, 2H),
7.17e7.35 (m, 6H), 7.56 (dd, J¼1.5, 8.5 Hz, 2H), 7.61 (dd, J¼1.5, 8.7 Hz,
2H); 13C NMR (75.5 MHz, CDCl3)
d: 24.8, 27.6, 46.5, 66.3, 69.3, 116.0,
116.5, 126.6, 126.7, 127.7, 127.9, 128.2, 128.7, 129.1, 141.6, 143.1, 147.0;
HRMS-ESI (m/z): [MþH]þ Calcd for C23H25N2: 329.2012. Found:
329.2014.
4.10. Catalytic enantioselective borane reduction of aceto-
phenone by using (S)-2-(anilinodiphenylmethyl)pyrrolidine
((S)-3): typical procedure (Table 3, entry 4)
Table 5
Summary of crystal data for compounds (4S,5R)-7 and (4R,5R)-8
(4S,5R)-7
(4R,5R)-8
To a THF (1.25 mL) solution of (S)-2-(anilinodiphenylmethyl)
pyrrolidine ((S)-3) (99 mg, 0.30 mmol) was added bor-
aneedimethyl sulfide complex (0.12 mL, 1.3 mmol) at 0 ꢁC, and the
mixture was refluxed for 45 min with stirring. After the mixture
was cooled to room temperature, acetophenone (0.33 mol dmꢀ3
THF solution, 3.0 mL, 1.0 mmol) was added dropwise via syringe
pump over 2 h, and stirring was continued for 2 h at room tem-
perature. Then 1 mol dmꢀ3 aqueous HCl was added at 0 ꢁC, and the
reaction mixture was stirred at room temperature for 30 min. The
aqueous layer was separated and extracted with ether, and the
combined organic layers were washed with 1 mol dmꢀ3 aqueous
HCl, water, and brine, successively. The organic layer was dried over
anhydrous sodium sulfate, and the solvent was removed under
reduced pressure. The resulting crude product was purified by
preparative TLC (chloroform) to give (R)-1-phenylethanol (118 mg,
0.96 mmol, 96%). The ee was determined to be 94% by HPLC analysis
using a chiral column (Daicel Chiralcel OD-H (25ꢂ0.46 cm i.d.));
eluent, 5% 2-propanol in hexane; flow rate, 0.5 mL/min; tR, 17.5 min
for major peak, 21.0 min for minor peak. Enantioselective reduction
of the other ketones was performed in a similar manner. The ees
Empirical formula
Formula weight
Crystal color, habit
Crystal size/mm3
Crystal system
C18H18N2O
278.35
Colorless, block
0.50ꢂ0.42ꢂ0.36
Orthorhombic
P212121 (no. 19)
C18H18N2O
278.35
Colorless, platelet
0.76ꢂ0.36ꢂ0.08
Orthorhombic
P212121 (no. 19)
Space group
Lattice parameters
ꢀ
a/A
10.026(3)
11.403(3)
12.798(3)
1463.2(6)
4
1.263
592.00
0.792
11,376
3326 (0.0301)
191
17.41
0.0456; 0.1039
0.0407
1.117
8.103(3)
12.380(4)
28.964(9)
2906(2)
8
1.273
1184.00
0.798
23,099
6651 (0.0613)
380
17.50
0.1039; 0.2037
0.0829
ꢀ
b/A
ꢀ
c/A
V/A
3
ꢀ
Z
Dcalcd/g cmꢀ3
F000
m
(Mo-K
a
)/cmꢀ1
Reflections measured
Independent reflections (Rint
No. of variables
Reflection/parameter ratio
Residuals: R; Rw
)
Residuals: R1 (I>2.00
Goodness-of-fit indicator
ꢀꢀ3
s(I))
1.087
Drmax
;
Drmin/e A
0.11; ꢀ0.14
0.26; ꢀ0.24
Flack parameter
0.0(14)
0(3)
were determined by HPLC using
a Daicel Chiralcel OD-H
(25ꢂ0.46 cm i.d.) column. 1-Phenyl-1-propanol: eluent, 5% 2-
propanol in hexane; flow rate, 0.5 mL/min; tR, 15.5 min for major
peak, 17.0 min for minor peak. 2-Chloro-1-phenylethanol: eluent,
3% 2-propanol in hexane; flow rate, 0.5 mL/min; tR, 33.7 min for
major peak, 38.8 min for minor peak. 1-(2-Bromophenyl)ethanol:
eluent, 2% 2-propanol in hexane; flow rate, 0.5 mL/min; tR, 24.7 min
for major peak, 27.7 min for minor peak. 1-(1-Naphthyl)ethanol:
eluent, 5% 2-propanol in hexane; flow rate, 0.5 mL/min; tR, 31.5 min
for minor peak, 57.0 min for major peak. 1,2,3,4-Tetrahydro-1-
naphthol: eluent, 2% 2-propanol in hexane; flow rate, 0.5 mL/
min; tR, 28.4 min for minor peak, 30.7 min for major peak. 1-
CCDC 878616 ((4S,5R)-7) and 878648 ((4R,5R)-8) contain the
supplementary crystallographic data for this paper. These data can
be obtained free of charge from the Cambridge Crystallographic
Data Centre via http://www.ccdc.cam.ac.uk/cgi-bin/catreq.cgi.
Acknowledgements
The authors are grateful to Mr. Shinji Ishihara (Instrumental
Analysis Center, Yokohama National University) for his technical

1746
N. Hosoda et al. / Tetrahedron 69 (2013) 1739e1746
5. Bolm, C.; Felder, M. Tetrahedron Lett. 1993, 34, 6041e6044.
6. (a) Li, K.; Zhou, Z.; Wang, L.; Chen, Q.; Zhao, G.; Zhou, Q.; Tang, C. Tetrahedron:
Asymmetry 2003, 14, 95e100; (b) Gamble, M. P.; Smith, A. R. C.; Wills, M. J. Org.
Chem. 1998, 63, 6068e6071.
7. Yang, T.-K.; Lee, D.-S. Tetrahedron: Asymmetry 1999, 10, 405e409.
8. (a) Li, G.-Q.; Yan, Z.-Y.; Niu, Y.-N.; Wu, L.-Y.; Wei, H.-L.; Liang, Y.-M. Tetrahedron:
Asymmetry 2008, 19, 816e821; (b) Yang, S.-D.; Shi, Y.; Sun, Z.-H.; Zhao, Y.-B.;
Liang, Y.-M. Tetrahedron: Asymmetry 2006, 17, 1895e1900; (c) Froelich, O.; Bo-
nin, M.; Quirion, J.-C.; Husson, H.-P. Tetrahedron: Asymmetry 1993, 4,
2335e2338.
assistance in the elemental analyses. The authors also acknowledge
Mr. Takeo Kaneko (Yokohama National University) and Dr. Hironari
Kurihara (Instrumental Analysis Center, Yokohama National Uni-
versity) for their technical assistance in the high-resolution mass
spectrometric analyses.
Supplementary data
9. Lin, Y.-M.; Fu, I.-P.; Uang, B.-J. Tetrahedron: Asymmetry 2001, 12, 3217e3221.
10. Wang, J.; Liu, H.; Du, D.-M. Tetrahedron: Asymmetry 2009, 20, 605e609.
11. (a) Asami, M. J. Synth. Org. Chem., Jpn. 1996, 54, 188e199 and references cited
therein; (b) Asami, M.; Inoue, S. Bull. Chem. Soc. Jpn. 1997, 70, 1687e1690; (c)
Asami, M.; Sato, S.; Honda, K.; Inoue, S. Heterocycles 2000, 52, 1029e1032; (d)
Seki, A.; Asami, M. Tetrahedron 2002, 58, 4655e4663; (e) Hosoda, N.; Iogawa, Y.;
Shimada, Y.; Asami, M. Bull. Chem. Soc. Jpn. 2008, 81, 274e277; (f) Hosoda, N.;
Ito, H.; Takimoto, T.; Asami, M. Bull. Chem. Soc. Jpn. 2012, 85, 1014e1022.
12. (a) Asami, M.; Sato, S.; Watanabe, H. Chem. Lett. 2000, 990e991; (b) Sato, S.;
Watanabe, H.; Asami, M. Tetrahedron: Asymmetry 2000, 11, 4329e4340.
13. (a) Asami, M.; Watanabe, H.; Honda, K.; Inoue, S. Tetrahedron: Asymmetry 1998,
9, 4165e4173; (b) Asami, M.; Wada, M.; Furuya, S. Chem. Lett. 2001, 1110e1111.
14. Hirao, A.; Itsuno, S.; Nakahama, S.; Yamazaki, N. J. Chem. Soc., Chem. Commun.
1981, 315e317.
Supplementary data associated with this article can be found in
the online version, at http://dx.doi.org/10.1016/j.tet.2012.12.024.
These data include MOL files and InChiKeys of the most important
compounds described in this article.
References and notes
1. For reviews: (a) Cho, B. T. Chem. Soc. Rev. 2009, 38, 443e452; (b) Cho, B. T.
Tetrahedron 2006, 62, 7621e7643; (c) Cho, B. T. Aldrichimica Acta 2002, 35,
3e16; (d) Itsuno, S. Org. React. 1998, 52, 395e576; (e) Corey, E. J.; Helal, C. J.
Angew. Chem., Int. Ed. 1998, 37, 1986e2012; (f) Deloux, L.; Srebnik, M. Chem. Rev.
1993, 93, 763e784; (g) Singh, V. K. Synthesis 1992, 605e617; (h) Wallbaum, S.;
Martens, J. Tetrahedron: Asymmetry 1992, 3, 1475e1504.
15. (a) Kerrick, S. T.; Beak, P. J. Am. Chem. Soc. 1991, 113, 9708e9710; (b) Nikolic, N.
A.; Beak, P. Org. Synth. 1997, 74, 23e32.
2. Itsuno, S.; Ito, K.; Hirao, A.; Nakahama, S. J. Chem. Soc., Chem. Commun. 1983,
16. Olivares-Romero, J. L.; Juaristi, E. Tetrahedron 2008, 64, 9992e9998.
17. Okano, K.; Tokuyama, H.; Fukuyama, T. Org. Lett. 2003, 5, 4987e4990.
18. (a) Kuwano, R.; Sawamura, M.; Shirai, J.; Takahashi, M.; Ito, Y. Bull. Chem. Soc.
Jpn. 2000, 73, 485e496; (b) Huang, W.-S.; Hu, Q.-S.; Pu, L. J. Org. Chem. 1999, 64,
7940e7956.
469e470.
ꢁ
ꢁ
ꢁ
3. For recent examples: (a) Krzeminski, M. P.; Cwiklinska, M. Tetrahedron Lett.
2011, 52, 3919e3921; (b) Xiao, J.; Wong, Z. Z.; Lu, Y. P.; Loh, T. P. Adv. Synth. Catal.
2010, 352, 1107e1112; (c) Xu, W.; Guo, H.; Zhu, Q.; Ke, X.; Hu, X. Catal. Lett.
2008, 125, 302e307; (d) Zhou, Y.; Wang, W.-H.; Dou, W.; Tang, X.-L.; Liu, W.-S.
Chirality 2008, 20, 110e114; (e) Hobuß, D.; Baro, A.; Laschat, S.; Frey, W. Tet-
rahedron 2008, 64, 1635e1640; (f) Goushi, S.; Funabiki, K.; Ohta, M.; Hatano, K.;
Matsui, M. Tetrahedron 2007, 63, 4061e4066; (g) Braun, M.; Sigloch, M.;
19. Rosa, J. N.; Santos, A. G.; Afonso, C. A. M. J. Mol. Catal. A: Chem. 2004, 214,
161e165.
ꢃ
20. Seno, M.; Shiraishi, S.; Suzuki, Y.; Asahara, T. Bull. Chem. Soc. Jpn. 1978, 51,
1413e1417.
ˇ
ꢁ
Cremer, J. Adv. Synth. Catal. 2007, 349, 337e342; (h) Krzeminski, M. P.; Wojtc-
zak, A. Tetrahedron Lett. 2005, 46, 8299e8302; (i) Lapis, A. A. M.; de Fatima, A.;
21. SIR2004: Burla, M. C.; Caliandro, R.; Camalli, M.; Carrozzini, B.; Cascarano, G. L.;
De Caro, L.; Giacovazzo, C.; Polidori, G.; Spagna, R. J. Appl. Crystallogr. 2005, 38,
381e388.
ꢁ
Martins, J. E. D.; Costa, V. E. U.; Pilli, R. A. Tetrahedron Lett. 2005, 46, 495e498;
€
(j) Zhang, Y.-X.; Du, D.-M.; Chen, X.; Lu, S.-F.; Hua, W.-T. Tetrahedron: Asymmetry
22. Sheldrick, G. M. Program for the Refinement of Crystal Structures SHELX97;
2004, 15, 177e182; (k) Jiang, B.; Feng, Y.; Hang, J.-F. Tetrahedron: Asymmetry
€
University of Gottingen: Germany, 1997.
ꢂ
2001, 12, 2323e2329; (l) Puigjaner, C.; Vidal-Ferran, A.; Moyano, A.; Pericas, M.
23. CrystalStructure 4.0: Crystal Structure Analysis Package; Rigaku Corporation:
A.; Riera, A. J. Org. Chem. 1999, 64, 7902e7911.
4. Corey, E. J.; Bakshi, R. K.; Shibata, S. J. Am. Chem. Soc. 1987, 109, 5551e5553.
Tokyo, Japan, 2000e2010.