The preparation of new enantiopure imidazolinium salts and their evaluation as catalysts and shift reagents

Article abstract of DOI:10.1016/j.tetasy.2006.02.021

A series of new chiral imidazolinium salts were prepared and tested as catalysts. It was possible to show that bis-imidazolinium salts had a higher reactivity than mono-imidazolinium salts. In addition a chiral discrimination of the bis-imidazolinium salt

Full text of DOI:10.1016/j.tetasy.2006.02.021

Tetrahedron: Asymmetry 17 (2006) 801–810
The preparation of new enantiopure imidazolinium salts and
their evaluation as catalysts and shift reagents
*
´
ˇ´
´
Vaclav Jurcık and Rene Wilhelm
Institute of Organic Chemistry, Clausthal University of Technology, Leibnizstr. 6, 38678 Clausthal-Zellerfeld, Germany
Received 18 January 2006; accepted 22 February 2006
Abstract—A series of new chiral imidazolinium salts were prepared and tested as catalysts. It was possible to show that bis-imidazolin-
ium salts had a higher reactivity than mono-imidazolinium salts. In addition a chiral discrimination of the bis-imidazolinium salts with
the potassium salt of racemic Mosher’s acid was proven by NMR studies.
ꢀ 2006 Elsevier Ltd. All rights reserved.
1. Introduction
2. Results and discussion
Recently, a few examples of chiral imidazolinium based
ionic liquids have been reported.1,2 However, the number
of examples of this class of chiral ionic liquid remains small
compared to other types of chiral ionic liquid.3–5 Further-
more, we have shown that an achiral imidazolinium based
ionic liquid is an inert medium for reactions involving
medium and strong bases.6 Chiral imidazolinium salts,
which have a hydrogen atom on the C-2 position and a hydr-
oxyl group incorporated were shown to be shift reagents
for the racemic potassium salt of Mosher’s acid.2
2.1. Preparation
The first step was preparation of the appropriate enantio-
pure imidazolidines, which were used as the precursors of
the desired chiral imidazolinium salts. The imidazolidines,
bearing different substituents on the C-2 atom, were
formed from chiral diamines and aldehydes (Table 1,
Scheme 1). A convenient method to prepare aminals is
the use of water as a solvent without the presence of a cat-
alyst, which has recently been described by our group.17
However, we found that some of the more complex chiral
aminals were not formed by applying this procedure, prob-
ably due to a certain level of steric hindrance in the chiral
diamines.
Due to the positive charge delocalized between the two
nitrogen atoms and the C-2 carbon atom, the imidazolin-
ium cation can act as a mild Lewis acid. It has been demons-
trated that achiral imidazolinium salts are able to catalyze
an aza Diels–Alder reaction or inverse electron demand aza
Diels–Alder reaction,7 which is one of the few examples of
carbocation based Lewis acids in catalysis.8–13 Due to the
absence of a metal, these salts can contribute to the field
of organocatalysis, which has attracted much interest in
recent years.14,15
Therefore, we initially used a standard procedure, Dean–
Stark/benzene/reflux,18 in order to obtain the desired imi-
dazolinium precursors (Table 1, entries 1, 2, 4 and 5). Over
the course of our investigation we found that it was also
possible to react the diamines with aldehydes under neat
conditions in a sealed vessel at 120 ꢁC, without the presence
of a catalyst. The aminals were obtained in good to excellent
yields (Table 1, entries 3 and 6). Moreover, it was possible
to prepare bis-aminals from (ꢀ)-(1S,2S)-N,N0-dimethyl-
1,2-diphenyl-1,2-ethylendiamine19 or (+)-(1R,2R)-N,N0-
dimethylcyclohexane-1,2-diamine19 with phthaldialdehyde
in excellent yields (Table 1, entries 7 and 8) under these con-
ditions. However, when (1S,2S)-1,2-di-tert-butyl-N,N0-
bis((R)-1-phenylethyl)ethane-1,2-diamine20 was treated
with phthaldialdehyde under neat conditions, no product
Herein, we report the preparation of a series of new chiral
imidazolinium salts and their investigation as chiral metal-
free Lewis acids and chiral shift reagents. In addition some
of the salts presented also qualify as ionic liquids.16
*
Corresponding author. Tel.: +49 5323 723886; fax: +49 5323 722834;
e-mail: rene.wilhelm@tu-clausthal.de
0957-4166/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2006.02.021

802
V. Jurcˇı´k, R. Wilhelm / Tetrahedron: Asymmetry 17 (2006) 801–810
Table 1. Preparation of aminals
Entry
Diamine
Aldehyde
Methoda
A
Aminal
Yield (%)
93
Ph
N
1
R1 = Me, (R,R)-R2 = Ph
2-Chlorobenzaldehyde
1
N
Ph
Cl
Ph
N
2
3
R1 = Me, (S,S)-R2 = Ph
4-Chlorobenzaldehyde
2-Hydroxybenzaldehyde
A
B
91
95
Cl
2
N
Ph
HO
Ph
Ph
N
3
4
N
Ph
Ph
N
N
4
5
6
R1 = (R)-MeBn, (S,S)-R2 = Ph
Pyridine-2-carbaldehyde
2-Chlorobenzaldehyde
4-Chlorobenzaldehyde
A
A
B
95
50
77
N
Ph
Ph
Ph
Ph
N
5
N
Ph
Cl
Ph
Ph
Ph
N
Cl
6
7
N
Ph
Ph
7
R1 = Me, (S,S)-R2 = Ph
Phthaldialdehyde
B
87
N
N
N
N
Ph
Ph
Ph
Ph
R1 = Me, (R,R)-R2 = (CH2)4
R1 = (R)-MeBn, (S,S)-R2 = tBu
Phthaldialdehyde
Phthaldialdehyde
B
B
99
0
N
N
8
9
8
N
N
—
9
a Method A: Dean–Stark/benzene/reflux/24 h; method B: neat, 120 ꢁC, 3 h.
cedure.21 The imidazolidines were oxidized with N-bromo-
acetamide (NBA) to the imidazolinium bromide salts
(Scheme 2, Table 2), which were used directly in a counter
anion exchange. In some cases, the bromide salts were
isolated to confirm by NMR, that the bromide salt was
O
R2
N
R2
R2
R2
Ar
R1
R1
R1 NH HN R1
N
Ar
1 - 8
Scheme 1. Preparation of aminals.
R2
N
R2
R2
N
R2
i. NBA, glyme, r.t., 1 h
N R1
R1
X–
R1
could be isolated (Table 1, entry 9). This may be due to the
bulky t-butyl groups that are incorporated in the diamine.
R1
N
ii. MX, H2O/CHCl3, r.t., 1 h
Ar
1 - 8
Ar
1b-8d
The aminals were then transformed into the corresponding
imidazolinium salts by applying a modified literature pro-
Scheme 2. Preparation of imidazolinium salts.

V. Jurcˇı´k, R. Wilhelm / Tetrahedron: Asymmetry 17 (2006) 801–810
Table 2. Oxidation of aminals and counter anion exchange Table 3. Aza Diels–Alder reaction
803
Entry
Aminal
Anion
Salt
Yield (%)
Entry
Catalyst
R
T (ꢁC)
Yield (%)
ꢀ
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
ent-1
PF6
ent-1b
1c
88
58
99
82
71
96
86
57
89
94
72
80
80
75
87
1
2
3
4a
5b
5b
4b
4b
Ph
Ph
Ph
Ts
0
rt
0
76
82
78
35
ꢀ
1
2
2
2
4
4
4
5
5
6
7
7
8
8
NTf2
Brꢀ
NTf2
B½3;5-ðCF3Þ2-C6H3ꢁ4
2a
2c
ꢀ
rt
ꢀ
2d
4a
4b
4c
a Reaction was performed in DCM.
Brꢀ
PF6
ꢀ
ꢀ
NTf2
Brꢀ
5a
5b
6b
7c
was present on the imine nitrogen atom, a lower reactivity
was observed, and no enantioselectivity was found (Table
3, entry 4).
ꢀ
PF6ꢀ
PF6
ꢀ
NTf2
ꢀ
ꢀ
B½3;5-ðCF3Þ2-C6H3ꢁ4
7d
8b
8d
2.2.2. Inverse electron demand aza Diels–Alder reaction.
We then explored the enantiopure salts in the inverse elec-
tron demand aza Diels–Alder reaction of N-benzylidenean-
iline 10 and dihydropyran 12 (Scheme 4).
ꢀ
PF6
B½3;5-ðCF3Þ2-C6H3ꢁ4
obtained in good purity and that all aminal was consumed
(Table 2, entries 3, 6 and 9). The bromide salts were diffi-
cult to handle, due to their considerable hygroscopic
behaviour. Bis-imidazolinium salts were prepared from
the bis-aminals 7 and 8 in very good yields (Table 2, entries
12–15).
O
catalyst
Ph
O
N
+
N
H
DCM, r.t.
Ph
10
12
cis-14a, trans-14b
The counter anion exchange was performed by vigorous
stirring of the imidazolinium bromide salt with the metal
salt of the new desired anion in a CHCl3/H2O mixture.
The new imidazolinium salts remained in the organic
phase, while the metal bromide salts were removed by
washing the organic phase with water. Also, bis-imid-
azolinium salts 7c and 8b could be prepared in good yields
following this procedure (Table 2, entries 12 and 15).
Salts 6b and 7d could qualify as ionic liquids, since their
melting points were below 100 ꢁC.16 Salts 1c, 4a and 4c
could qualify as room temperature ionic liquids.
Scheme 4. Inverse electron demand aza Diels–Alder reaction.
The reaction with dihydropyran 12 and 10 was not suffi-
ciently catalyzed by the mono-imidazolinium salts. For
example, when 10 mol % of salt 6b was used as the catalyst,
only traces of the desired product were obtained after 72 h
at rt. Bis-imidazolinium salt 7c revealed a poor reactivity
and 14a and 14b were isolated in 6% yield in a ratio
of 58:42 after 112 h at rt. However, when salt 7d, which
incorporated the very lipophilic and large anion
B½3;5-ðCF3Þ2-C6H3ꢁ4ꢀ, was applied, the reactivity increased
dramatically and 14a and 14b were obtained in 64% yield
with a ratio of 54:46 after 16 h at rt. Both diastereomers
were obtained as racemates. In addition, the bis-imidazo-
linium salt 8d resulted in a yield of 67% after 96 h at 0 ꢁC
in a diastereomeric ratio of 60:40 for 14a and 14b. No
enantiomeric excess was found.
2.2. Investigation of catalytic behaviour
2.2.1. Aza Diels–Alder reaction. Chiral salts ent-1b–8d
were tested in the aza Diels–Alder reaction (Scheme 3). A
few selected examples are presented in Table 3. In general,
the salts showed good catalytic activity, however, no asym-
metric induction was observed. When a tosyl substituent
2.3. Use as a shift reagent
OMe
Mono-imidazolinium salts bearing a hydrogen atom at the
C-2 position and a hydroxy group on the side chain have
been shown to be shift reagents for a racemate of potas-
sium Mosher’s carboxylate.2 To the best of our knowledge,
no imidazolinium salts with an aryl substituent at the C-2
position have been investigated as shift reagents. When
R
R
10 mol% catalyst
MeCN, 16 h
N
N
+
O
Ph
Ph
TMSO
10
9
11
Scheme 3. Aza Diels–Alder reaction.
Table 4. Chemical shifts of Mosher’s carboxylate in ppm and Dd in Hz on a 400 MHz NMR
Entry
Salt
1H d(S)
1H d(R)
19F d(S)
19F d(R)
1H Dd
19F Dd
1
2
3
4
8b
8d
7d
7c
3.59
3.57
3.58
3.57
3.57
3.57
3.60
3.57
ꢀ71.50
ꢀ71.67
ꢀ71.57
ꢀ71.84
ꢀ71.64
ꢀ71.72
ꢀ71.49
ꢀ71.88
6.3
0
4.3
0
53.0
18.8
27.1
13.0

804
V. Jurcˇı´k, R. Wilhelm / Tetrahedron: Asymmetry 17 (2006) 801–810
Figure 1. 19F NMR spectra on a 400 MHz NMR measured at 375 MHz.
the mono-imidazolinium salts were applied, no splitting of
either the 1H or 19F signal of Mosher’s carboxylate was ob-
served. However, the bis-imidazolinium salts 8b, 8d, 7d and
7c were able to divide the 19F signal of the two enantiomers
as shown in Table 4. Only 8b and 7d were also able to split
the 1H signal. The best result for an 19F NMR with salt 8b
is depicted in Figure 1. In this example, an enantioenriched
sample of 50% ee of Mosher’s carboxylate was used, in or-
der to assign the individual NMR signals to either the (R)-
or (S)-enantiomer through integration.
400 and a Bruker AC 200F and, if not otherwise stated,
measured in CDCl3. Mass spectra were recorded on
Hewlett–Packard 5898B (at 70 eV). Electron spray mass
spectrometry was performed directly on a MS LC/MSD
1100 MSD from Hewlett–Packard. High resolution mass
spectra were recorded at the Institute of Organic Chemis-
try, University of Hanover. Melting points are uncorrected.
Reactions were performed under a nitrogen atmosphere.
All solvents were dried using standard procedures, before
using in the reactions. Sodium tetrakis(3,5-bis(trifluoro-
methyl)phenyl)borate,23 (1S,2S)-1,2-diphenyl-N,N0-bis((R)-
1-phenylethyl)ethane-1,2-diamine,24 (+)-(1R,2R)-, (ꢀ)-
(1S,2S)-N,N0-dimethyl-1,2-diphenyl-1,2-ethylendiamine19
and (+)-(1R,2R)-N,N0-dimethylcyclohexane-1,2-diamine19
were prepared according to the literature procedures.
N-Bromoacetamide and racemic Mosher’s acid were pur-
chased from Lancaster. LiNTf2 and KPF6 were purchased
from Aldrich.
3. Conclusion
In conclusion, we have prepared a range of new chiral
mono- and bis-imidazolinium salts. It was shown that the
bis-imidazolinium salts were far more active catalysts,
however, no asymmetric induction was found in the test
reactions. In addition, it was demonstrated that the bis-
imidazolinium salts can be used as a shift reagent for the
potassium salt of Mosher’s acid.
4.2. Preparation of aminals
4.2.1. General procedure for the preparation of aminals
(method A). A diamine (1 mmol), p-toluenesulfonic acid
(5 mg) and an aldehyde (1 mmol) were dissolved in benzene
(25 mL). The reaction mixture was refluxed on a Dean–
Stark for 24 h. Benzene was removed under reduced pres-
sure to give the crude product, which was purified by
FCC (petroleum ether/ethyl acetate/Et3N, 95/5/0.5) to give
the desired aminal.
4. Experimental
4.1. General experimental
Flash column chromatography22 (FCC) was performed on
Sorbisil C-60. The reactions were monitored by TLC with
Merck Silica gel 60 F254 plates. Elemental analyses were
carried out by the Microanalytical Laboratory of the Insti-
4.2.2. General procedure for the preparation of aminals
under solvent free conditions (method B). A diamine
(1 mmol) and an aldehyde (1 mmol) were placed in a pres-
sure vessel equipped with a magnetic stirrer. The vessel was
flushed with nitrogen, sealed and the reaction mixture
tut fur Pharmazeutische Chemie der Technischen Univer-
¨
sita¨t Braunschweig. Infrared spectra were recorded on a
Bruker Vector 22 FTIR instrument. NMR spectra were
performed at ambient temperature on a Bruker AMX

V. Jurcˇı´k, R. Wilhelm / Tetrahedron: Asymmetry 17 (2006) 801–810
805
heated up to 120 ꢁC for 16 h. After cooling to rt, the glassy
solid formed was dissolved in DCM and dried over
Na2SO4. The solvent was removed under reduced pressure
and the remaining solid was dried under vacuum to give the
corresponding aminal.
(30), 134 (30), 120 (25), 91 (30); IR (KBr) 2850w, 1619vs,
1
1480m, 1454m, 1261s, 1152m, 756s, 699s cmꢀ1; H NMR
(200 MHz): d 7.40–7.13 (m, 12H), 6.94–6.84 (m, 2H), 4.84
(s, 1H, NCHN), 4.09 (d, J = 8.7 Hz, 2H, CHPh), 3.61 (d,
J = 8.7 Hz, 2H, CHPh), 2.22 (s, 3H, NCH3), 2.02 (s, 3H,
NCH3); 13C NMR (50 MHz): d 158.5 (COH), 139.5, 137.2,
131.2, 130.2, 128.7, 128.3, 128.2, 128.1, 127.8, 127.7, 120.7,
119.1, 89.4 (NCHN), 36.9 (CHPh), 35.6 (NCH3); HRMS
(ESI) calculated for C23H24N2O+: 345.1967, found:
345.1981.
4.2.3.
(+)-(4R,5R)-2-(2-Chlorophenyl)-1,3-dimethyl-4,5-
diphenylimidazolidine 1. (+)-(4R,5R)-2-(2-Chlorophenyl)-
1,3-dimethyl-4,5-diphenylimidazolidine 1 was prepared
from
(+)-(R,R)-N,N0-dimethyl-1,2-diphenylethylenedi-
amine (500 mg, 2.08 mmol) and o-chlorobenzaldehyde
(246 lL, 2.18 mmol) in benzene (50 mL) according to
4.2.7. (+)-(4S,5S)-2-(2-Pyridinyl)-4,5-diphenyl-1,3-bis((R)-
1-phenylethyl)imidazolidine 4. (+)-(4S,5S)-2-(2-Pyridin-
yl)-4,5-diphenyl-1,3-bis((R)-1-phenylethyl)imidazolidine 4
was prepared from (1S,2S)-1,2-diphenyl-N,N0-bis((R)-
1-phenylethyl)ethane-1,2-diamine (1.50 g, 3.57 mmol),
2-pyridinecarbaldehyde (340 lL, 3.57 mmol) and p-toluene-
sulfonic acid (10 mg) in benzene (100 mL) according to
method A. The reaction mixture was refluxed for 48 h.
method A. FCC gave the title compound (+)-1 as a white
22
solid (700 mg, 93%). Mp 128 ꢁC. ½aꢁD ¼ 107:6 (c 0.59,
CHCl3); MS (EI), m/e 361 (M+ꢀH, 30%), 244 (40), 243
(100), 208 (40), 152 (25); IR (KBr) 2792s, 1452s, 1263s,
1
1011s, 756vs, 699vs cmꢀ1; H NMR (200 MHz): d 8.02–
7.98 (m, 1H), 7.43–7.16 (m, 13H), 5.38 (s, 1H, NCHN),
3.84 (d, J = 8.5 Hz, 2H, CHPh), 3.63 (d, J = 8.5 Hz, 2H,
CHPh), 2.16 (s, 3H, NCH3), 1.91 (s, 3H, NCH3); 13C
NMR (50 MHz): d 139.8, 139.3, 137.5, 130.9, 129.6,
129.1, 128.3, 128.2, 128.1, 128.0, 127.5, 127.4, 126.7, 83.2
(NCHN), 37.6 (CHPh), 35.6 (NCH3). Anal. Calcd for
C23H23ClN2: C, 76.12; H, 6.39; N, 7.72. Found: C, 76.36;
H, 6.26, N, 7.49.
FCC gave the title compound (+)-4 as a white solid
22
(1.73 g, 95%). Mp 105–108 ꢁC; ½aꢁD ¼ þ115:0 (c 0.32,
CHCl3); MS (CI), m/e 432 (M+ꢀpyridinyl, 50%), 299
(60), 105 (100); IR (KBr) 3451vs, 1492s, 1453s, 1431s,
1104s, 760s, 699vs cmꢀ1 1H NMR (400 MHz): d 8.57–
;
8.54 (m, 1H), 7.40–7.00 (m, 20H), 6.80–6.70 (m, 3H),
5.34 (s, 1H, NCHN), 4.65 (d, J = 7.9 Hz, 1H, NCHPh),
4.18 (d, J = 7.9 Hz, 1H, NCHPh), 3.98 (q, J = 7.0 Hz,
1H, CHCH3), 3.67 (q, J = 7.0 Hz, 1H, CHCH3), 1.07 (d,
J = 7.1 Hz, 3H, CHCH3), 0.88 (d, J = 7.1 Hz, 3H,
CHCH3); 13C NMR (100 MHz): d 165.4, 148.5, 145.4,
143.2, 142.9, 142.5, 135.3, 128.9, 128.6, 128.34, 128.30,
128.28, 128.20, 128.0, 127.4, 127.3, 127.2, 127.1, 127.05,
124.6, 122.0, 83.2 (NCHN), 76.6 (CHPh), 73.6 (CHPh),
61.5 (CHCH3), 57.3 (CHCH3), 23.1 (CHCH3), 22þ.5
4.2.4. (ꢀ)-(4S,5S)-2-(2-Chlorophenyl)-1,3-dimethyl-4,5-di-
phenylimidazolidine ent-1. (ꢀ)-(4S,5S)-2-(2-Chlorophenyl)-
1,3-dimethyl-4,5-diphenylimidazolidine ent-1 was prepared
in the same way as the enantiomer above. The spectral data
were consistent with the data of 1.
4.2.5. (ꢀ)-(4S,5S)-2-(4-Chlorophenyl)-1,3-dimethyl-4,5-di-
phenylimidazolidine 2. (ꢀ)-(4S,5S)-2-(4-Chlorophenyl)-
1,3-dimethyl-4,5-diphenylimidazolidine 2 was prepared
(CHCH3); HRMS (ESI) calculated for C36H35N3
:
from
(+)-(S,S)-N,N0-dimethyl-1,2-diphenylethylenedi-
510.2909, found: 510.2912.
amine (750 mg, 3.13 mmol) and 4-chlorobenzaldehyde
(483 mg, 3.44 mmol) in benzene (50 mL) according to
4.2.8.
bis((R)-1-phenylethyl)imidazolidine
(ꢀ)-(4S,5S)-2-(2-Chlorophenyl)-4,5-diphenyl-1,3-
method A. FCC gave the title compound (ꢀ)-2 as a white
5. (ꢀ)-(4S,5S)-2-
22
solid (1.029 g, 91%). Mp = 98 ꢁC; ½aꢁD ¼ ꢀ35:5 (c 0.32,
(2-Chlorophenyl)-4,5-diphenyl-1,3-bis((R)-1-phenylethyl)-
imidazolidine 5 was prepared from (1S,2S)-1,2-diphenyl-
CHCl3); MS (EI), m/e 360 (M+, 40%), 244 (40), 243
(100), 165 (45), 152 (60), 139 (40), 118 (40), 91 (50), 77
(60), 69 (50), 51 (40); IR (KBr) 3425s, 2789s, 1599s,
N,N0-bis((R)-1-phenylethyl)ethane-1,2-diamine
(1.00 g,
2.39 mmol), 2-chlorobenzaldehyde (336 mg, 2.39 mmol)
and p-toluenesulfonic acid (50 mg) in benzene (75 mL)
according to method A. The reaction mixture was refluxed
1490s, 1451s, 1088s, 1009s, 841s, 759s, 698vs, 511s cmꢀ1
;
1H NMR (400 MHz): d 7.61 (d, J = 8.6 Hz, 2H), 7.44 (d,
J = 8.4 Hz, 2H) 7.37–7.19 (m, 10H), 4.78 (s, 1H, NCHN),
3.91 (d, J = 8.3 Hz, 1H, CHPh), 3.68 (d, J = 8.3 Hz, 1H,
CHPh), 2.20 (s, 3H, NCH3), 1.88 (s, 3H, NCH3); 13C
NMR (100 MHz): d 140.1, 139.78, 139.73, 134.4, 131.1,
128.8, 128.7, 128.5, 128.3, 127.96, 127.92, 88.2 (NCHN),
77.9 (CHPh), 37.9 (NCH3), 36.2 (NCH3). Anal. Calcd for
C23H23ClN2: C, 76.12; H, 6.39; N, 7.72. Found: C, 76.26;
H, 6.41; N, 7.73.
for 48 h. FCC gave the title compound (ꢀ)-5 as a white
22
solid (640 mg, 50%). Mp 57–58 ꢁC; ½aꢁD ¼ ꢀ99:9 (c 1.6,
CHCl3) MS (ESI, 0 V), m/e 541.2 (M+ꢀH, 100%); IR
(KBr) 3027m, 1492s, 1453vs, 1222s, 1133s, 1027s, 756vs,
1
700vs cmꢀ1; H NMR (400 MHz): d 8.02 (d, J = 7.7 Hz,
1H), 7.40–6.70 (m, 23H), 6.00 (s, 1H, NCHN), 4.38 (d,
J = 8 Hz, 1H, NCHPh), 4.10 (d, J = 8 Hz, 1H, NCHPh),
3.92–3.89 (m, 1H, CHCH3), 3.70–3.67 (m, 1H, CHCH3),
1.16 (d, J = 8.1 Hz, 3H, CHCH3), 0.78 (d, J = 7.0 Hz,
3H, CHCH3); 13C NMR (100 MHz): d 145.5, 142.7,
142.4, 140.6, 140.5, 134.8, 132.3, 129.2, 128.5, 128.4,
128.3, 128.1, 127.8, 127.75, 127.73, 127.67, 127.2, 127.0,
126.97, 126.93, 126.3, 126.0, 76.2 (NCHN), 74.7 (CHPh),
72.4 (CHPh), 58.6 (CHCH3), 56.5 (CHCH3), 21.7
(CHCH3), 20.1 (CHCH3). Anal. Calcd for C37H35ClN2:
C, 81.82; H, 6.50; 6.53; N, 5.16. Found: C, 81.78; H,
6.91; N, 5.05.
4.2.6.
idin-2-yl)phenol 3. (ꢀ)-2-((4S,5S)-1,3-Dimethyl-4,5-diphen-
(ꢀ)-2-((4S,5S)-1,3-Dimethyl-4,5-diphenylimidazol-
ylimidazolidin-2-yl)phenol
3 was prepared from (+)-
(S,S)-N,N0-dimethyl-1,2-diphenylethylenediamine (608 mg,
2.53 mmol) and salicyl aldehyde (0.264 mL, 2.53 mmol)
according to method B as a yellow oil which solidified
22
(830 mg, 95%). Mp 40–42 ꢁC; ½aꢁD ¼ ꢀ38:9 (c 0.18,
CHCl3); MS (EI), m/e 343 (M+ꢀH, 30%), 224 (100), 208

806
V. Jurcˇı´k, R. Wilhelm / Tetrahedron: Asymmetry 17 (2006) 801–810
4.2.9.
bis((R)-1-phenylethyl)imidazolidine
(ꢀ)-(4S,5S)-2-(4-Chlorophenyl)-4,5-diphenyl-1,3-
(CH2). HRMS calculated for C24H39N4þ: 383.3169; found:
383.3171.
6. (ꢀ)-(4S,5S)-2-(4-
Chlorophenyl)-4,5-diphenyl-1,3-bis((R)-1-phenylethyl)imi-
dazolidine 6 was prepared from (1S,2S)-1,2-diphenyl-N,N0-
bis((R)-1-phenylethyl)ethane-1,2-diamine (821 mg, 2.00
mmol) and 4-chlorobenzaldehyde (290 mg, 2.00 mmol)
according to method B. FCC gave the title compound
4.3. Preparation of salts
4.3.1. General procedure for the preparation of imidazoli-
nium bromide salts. Imidazolidine (1 mmol) was dissolved
in a minimal amount of 1,2-dimethoxyethane. N-Bromo-
acetamide (1 mmol) was added in two portions (0.5 mmol
each) in an interval of 15 min. After the addition of the sec-
ond portion, the reaction mixture was stirred for an addi-
tional hour. Diethyl ether (5 mL) was added and an oily
solid formed. The solvent was decanted and the remaining
solid was washed with diethyl ether (3 mL) and dried under
high vacuum to give the corresponding bromide salt.
(ꢀ)-6 as a white solid (833 mg, 77%). Mp 53 ꢁC;
22
½aꢁD ¼ ꢀ12:8 (c 0.2, CHCl3); MS (ESI, 0 V), m/e 541.3
(M+ꢀH, 10%); IR (KBr) 3026m, 1490s, 1452s, 1225m,
1088m, 832m, 765s, 700vs cmꢀ1; H NMR (200 MHz): d
1
7.30–6.80 (m, 24H), 5.11 (s, 1H, NCHN), 4.31 (d, J =
8.3 Hz, 1H, NCHPh), 4.14 (d, J = 8.3 Hz, 1H, NCHPh),
3.90 (q, J = 7.0 Hz, 1H, CHCH3), 3.44 (q, J = 7.0 Hz,
1H, CHCH3), 0.99 (d, J = 7.0 Hz, 3H, CHCH3), 0.67 (d,
J = 7.0 Hz, 3H, CHCH3); 13C NMR (50 MHz): d 145.6,
143.4, 143.3, 141.5, 140.9, 132.5, 130.9, 128.3, 128.25,
128.1, 128.0, 127.9, 127.8, 127.6, 127.3, 127.13, 127.06,
126.9, 126.6, 126.2, 81.6 (NCHN), 75.8 (CHPh), 73.2
4.3.2. General procedure for the counter anion exchange with
potassium hexafluorophosphate, lithium bis(trifluoromethyl-
sulfonyl)imide or sodium tetrakis(3,5-bis(trifluoromethyl)-
phenyl)borate. Imidazolinium bromide salt (1 mmol) was
dissolved in CHCl3 (3 mL) and stirred vigorously with
1 equiv of KPF6, LiNTf2 or NaB[3,5-(CF3)2-C6H3]4 in
water (3 mL) for 30 min. The organic phase was separated,
washed with water (3 · 3 mL) and dried over molecular
(CHPh), 60.4 (CHCH3), 58.3 (CHCH3), 24.7 (CHCH3),
21.6 (CHCH3). HRMS calculated for C37H36ClN2
543.2562; found: 543.2563.
þ
:
4.2.10.
(ꢀ)-(4S,5S)-1,3-Dimethyl-2-(2-((4S,5S)-1,3-
˚
dimethyl-4,5-diphenylimidazolidin-2-yl)phenyl)-4,5-diphenyl-
imidazolidine 7. (ꢀ)-(4S,5S)-1,3-Dimethyl-2-(2-((4S,5S)-
1,3-dimethyl-4,5-diphenylimidazolidin-2-yl)phenyl)-4,5-
diphenylimidazolidine 7 was prepared from (1S,2S)-N,N0-
dimethyl-1,2-diphenylethane-1,2-diamine (960 mg, 4 mmol)
and phthaldialdehyde (269 mg, 2 mmol) according to
sieves 3 A. The solvent was evaporated and the product
further dried overnight under high vacuum to give the
corresponding imidazolinium hexafluorophosphate, bis-
(trifluoromethylsulfonyl)imide or tetrakis(3,5-bis(trifluoro-
methyl)phenyl)borate salt.
method B as a yellow solid (1.01 g, 87%). Mp 83–85 ꢁC;
4.3.3.
(ꢀ)-(4S,5S)-2-(2-Chlorophenyl)-1,3-dimethyl-4,5-
22
½aꢁD ¼ ꢀ89:8 (c 0.44, CHCl3); MS (EI), m/e 578 (M+,
diphenylimidazolinium hexafluorophosphate ent-1b. (ꢀ)-
(4S,5S)-2-(2-Chlorophenyl)-1,3-dimethyl-4,5-diphenylimi-
dazolinium hexafluorophosphate ent-1b was prepared from
(ꢀ)-(4S,5S)-2-(2-chlorophenyl)-1,3-dimethyl-4,5-diphenyl-
imidazolidine ent-1 (200 mg, 0.55 mmol) and NBA (80 mg,
0.55 mmol) in glyme (2 mL), followed by a counter anion
exchange with KPF6 (103 mg, 0.55 mmol) in a mixture of
1%), 368 (100), 180 (20), 142 (10), 118 (20), 91 (10), 77
(10), 52 (10); IR (KBr) 3452vs, 1631m, 1451m, 1264m,
1
1161m, 1103m, 755s, 699s cmꢀ1; H NMR (400 MHz): d
8.13–8.11 (m, 2H), 7.57–7.50 (m, 2H), 7.48–7.27 (m,
20H), 5.52 (s, 2H, NCHN), 3.92 (d, J = 8.4 Hz, 2H,
CHPh), 3.59 (s, 2H, CHPh), 2.18 (s, 6H, NCH3), 2.07 (s,
6H, NCH3); 13C NMR (100 MHz): d 141.8, 140.3, 138.9,
129.6, 128.9, 128.8, 128.5, 128.4, 128.3, 128.0, 127.6, 83.7
(NCHN), 78.8 (CHPh), 38.9 (NCH3), 38.0 (NCH3);
DCM (3 mL) and water (3 mL) as a white solid (245 mg,
22
88%). Mp 277 ꢁC; ½aꢁD ¼ ꢀ116:7 (c 0.36, CHCl3); MS
(ESI, 0 V), m/e 361.1 (M+, 100%); IR (KBr) 3453s,
HRMS calculated for C40H43N4
579.3466.
:
579.3488; found:
1608vs, 837vs, 754s, 702s, 557s cmꢀ1 1H NMR
;
þ
(200 MHz): d 8.20–8.10 (m, 1H), 7.56–7.32 (m, 13H),
5.42 (d, J = 12.2 Hz, 1H, CH), 5.00 (d, J = 12.2 Hz, 1H,
CHPh) 2.87 (s, 3H, NCH3), 2.78 (s, 3H, NCH3); 13C
NMR (50 MHz): d 164.3 (NC+N), 134.5, 134.3, 132.7,
131.6, 131.0, 130.4, 130.3, 130.2, 129.9, 129.8, 129.2,
128.5, 127.9, 121.5, 75.8 (CHPh), 74.4 (CHPh), 32.8
(NCH3), 32.6 (NCH3). HRMS (ESI) calculated for
C23H22N2Cl+: 361.1472, found: 361.1458.
4.2.11.
(+)-(3aR,7aR)-Octahydro-2-(2-((3aR,7aR)-octa-
hydro-1,3-dimethyl-1H-benzo[d]imidazol-2-yl)phenyl)-1,3-di-
methyl-1H-benzo[d]imidazole 8. (+)-(3aR,7aR)-Octahy-
dro-2-(2-((3aR,7aR)-octahydro-1,3-dimethyl-1H-benzo[d]-
imidazol-2-yl)phenyl)-1,3-dimethyl-1H-benzo[d]imidazole
8 was prepared from (1R,2R)-N,N0-dimethylcyclohexane-
1,2-diamine (119 mg, 0.84 mmol) and phthaldialdehyde
(56 mg, 0.42 mmol) according to method B as a yellow
4.3.4.
(+)-(4R,5R)-2-(2-Chlorophenyl)-1,3-dimethyl-4,5-
22
solid (159 mg, 99%). Mp 98 ꢁC; ½aꢁD ¼ þ103:6 (c 1.48,
diphenylimidazolinium bis(trifluoromethylsulfonyl)imide 1c.
(+)-(4R,5R)-2-(2-Chlorophenyl)-1,3-dimethyl-4,5-diphenyl-
imidazolinium bis(trifluoromethylsulfonyl)imide 1c was
prepared from aminal 1 (61 mg, 0.169 mmol) and NBA
(24.5 mg, 0.17 mmol) in glyme (1 mL), followed by a coun-
ter anion exchange with LiNTf2 (50 mg 97%, 0.17 mmol) in
CHCl3); MS (ESI, 0 V), m/e 383.3 (M++H, 100%); IR
(KBr) 3441s, 2972s, 2931vs, 2455s, 2791s, 1452s, 1360s,
1190s, 1009s, 758s cmꢀ1 1H NMR (200 MHz): d 7.80–
;
7.60 (m, 2H), 7.32–7.27 (m, 2H), 4.85 (s, 2H, NCHN),
2.18 (s, 6H, NCH3), 1.93 (s, 6H, NCH3) 2.50–2.00 (m,
4H, NCHCH2), 2.10–1.80 (m, 8H), 1.40–1.10 (m, 8H);
13C NMR (50 MHz): d 139.0,, 129.1, 127.4, 84.0 (NCHN),
69.8 (NCHCH2), 68.98 (NCHCH2), 37.3 (NCH3), 37.0
(NCH3), 29.4 (CH2), 29.0 (CH2), 24.7 (CCH2), 24.4
a mixture of CHCl3 (3 mL) and water (3 mL) as a colour-
22
less oil (63 mg, 58%). ½aꢁD ¼ þ86:5 (c 0.28, CHCl3); MS
(ESI, 0 V), m/e 361.0 (M+, 100%); IR (KBr) 1607s,
1352s, 1195vs, 1135s, 1058s, 760m, 653m cmꢀ1; H NMR
1

V. Jurcˇı´k, R. Wilhelm / Tetrahedron: Asymmetry 17 (2006) 801–810
807
(400 MHz): d 8.18–8.12 (m, 1H), 7.75–7.65 (m, 3H), 7.55–
7.45 (m, 8H), 7.40–7.32 (m, 2H), 5.43 (d, J = 12.1 Hz, 1H,
CHPh), 4.99 (d, J = 11.8 Hz, 1H, CHPh), 2.88 (s, 3H,
NCH3), 2.80 (s, 3H, NCH3); 13C NMR (100 MHz): d
164.9 (NC+N), 135.1, 134.7, 133.1, 131.9, 131.8, 131.0,
130.7, 130.65, 130.4, 130.3, 129.8, 128.8, 128.3, 121.9,
121.88, 76.5 (CHPh), 75.1 (CHPh), 33.6 (NHCH3), 33.1
(NHCH3). HRMS (ESI) calculated for C23H22N2Cl+:
361.1472, found: 361.1458.
CCF3), 118.9, 117.95 (CHCCF3), 75.5 (NCHPh), 34.2
(NCH3). Anal. Calcd for C55H34BClF24: C, 53.92; H,
2.80; N, 2.29. Found: C, 53.72; H, 2.84; N, 2.20; HRMS
(ESI) calculated for C23H22N2Cl+: 361.1472, found:
361.1483.
4.3.8. (ꢀ)-(4S,5S)-2-(2-Pyridinyl)-4,5-diphenyl-1,3-bis((R)-
1-phenylethyl)imidazolinium bromide 4a. (ꢀ)-(4S,5S)-
2-(2-Pyridinyl)-4,5-diphenyl-1,3-bis((R)-1-phenylethyl)imi-
dazolinium bromide 4a was prepared from (4S,5S)-2-
(pyridinyl)-4,5-diphenyl-1,3-bis((R)-1-phenylethyl)imidazo-
lidine 4 (1.13 g, 2.23 mmol) and NBA (308 mg, 2.23 mmol)
4.3.5.
(ꢀ)-(4S,5S)-2-(4-Chlorophenyl)-1,3-dimethyl-4,5-
diphenylimidazolinium bromide 2a. (ꢀ)-(4S,5S)-2-(4-
Chlorophenyl)-1,3-dimethyl-4,5-diphenylimidazolinium bro-
mide 2a was prepared from (4S,5S)-2-(4-chlorophenyl)-1,3-
dimethyl-4,5-diphenylimidazolidine 2 (359 mg, 0.99 mmol)
in Et2O (5 mL) as a yellow oil (1.26 g, 96%). Hygroscopic.
22
½aꢁD ¼ ꢀ85:9 (c 0.67, CHCl3); 1H NMR (200 MHz): d 9.57
(d, J = 7.7 Hz, 1H), 8.90 (d, J = 3.8 Hz, 1H), 8.32 (t,
J = 7.7 Hz, 1H), 7.80–7.70 (8m, 1H), 7.30–6.90 (m, 20H),
5.20–4.90 (m, 4H, NCHPh, PhCHCH3), 1.65 (br s, 6H,
CHCH3); 13C NMR (50 MHz): d 164.2 (NC+N), 150.3,
143.1, 139.4, 136.4, 135.1, 129.3, 129.2, 128.4, 128.3,
127.9, 127.6, 127.4, 72.1 (CHPh), 57.8 (NCHCH3), 18þ.1
and NBA (144 mg, 0.99 mmol) in glyme (3 mL) as a white
22
solid (446 mg, 99%). Hygroscopic. Mp 98 ꢁC; ½aꢁD ¼ ꢀ56:5
(c 0.35, CHCl3); MS (ESI, 0 V), m/z 361 (M+, 100%); IR
(KBr) 1605s, 1345s, 1327s, 1199vs, 1138s, 1058s, 616s
1
cmꢀ1; H NMR (200 MHz): d 8.08 (d, J = 8.34 Hz, 2H),
7.58–7.55 (m, 6H), 7.38–7.35 9 (m, 6H), 5.33 (s, 2H,
CHPh), 2.87 (s, 6H, CH3); 13C NMR (50 MHz3): d 166.6
(NC+N), 139.9, 133.4, 130.43, 130.38, 130.1, 129.7, 128.3,
120.3, 75.2 (CHPh), 33.6 (NCH3); HRMS (ESI) calculated
for C23H22N2Cl+: 361.1472, found: 361.1482.
(CHCH3); HRMS (ESI) calculated for C36H34N3
:
508.2753, found: 508.2758.
4.3.9. (ꢀ)-(4S,5S)-2-(2-Pyridinyl)-4,5-diphenyl-1,3-bis((R)-
1-phenylethyl)imidazolinium hexafluorophosphate 4b. (ꢀ)-
(4S,5S)-2-(2-Pyridinyl)-4,5-diphenyl-1,3-bis((R)-1-phenyl-
ethyl)imidazolinium hexafluorophosphate 4b was prepared
from (4S,5S)-2-(2-pyridyl)-4,5-diphenyl-1,3-bis((R)-1-phen-
ylethyl)imidazolinium bromide 4a (105 mg, 0.18 mmol)
and KPF6 (36 mg, 0.20 mmol) in a mixture of CHCl3
4.3.6.
(ꢀ)-(4S,5S)-2-(4-Chlorophenyl)-1,3-dimethyl-4,5-
diphenylimidazolinium bis(trifluoromethylsulfonyl)imide 2c.
(ꢀ)-(4S,5S)-2-(4-Chlorophenyl)-1,3-dimethyl-4,5-diphenyl-
imidazolinium bis(trifluoromethylsulfonyl)imide 2c was
prepared from (4S,5S)-2-(4-chlorophenyl)-1,3-dimethyl-
4,5-diphenylimidazoliniumbromide 2a (330 mg, 0.75 mmol)
and LiNTf2 (236 mg, 0.82 mmol) in a mixture of CHCl3
(3 mL) and water (3 mL) as a white solid (100 mg, 86%).
22
Mp 87 ꢁC; ½aꢁD ¼ ꢀ65:4 (c 0.48, CHCl3); MS (ESI, 0 V),
m/e 508 (M+); IR (KBr) 3423w, 1556s, 1456m, 1278m,
(2 mL) and water (2 mL) as a white solid (347 mg, 82%).
838vs, 757m, 696s, 557s cmꢀ1 1H NMR (200 MHz): d
;
22
Mp 102 ꢁC; ½aꢁD ¼ ꢀ62:4 (c 0.34, CHCl3); MS (EI), m/e
360 (M+ꢀH, 100%), 327 (5), 283 (5), 152 (10), 78 (5), 69
9.00 (d, J = 4.2 Hz, 1H) 8.58 (d, J = 7.8 Hz, 1H), 8.34–
8.30 (m, 1H), 7.79–7.73 (m, 1H), 7.26–6.99 (m, 20H),
5.00–4.80 (m, 4H, CHPh, CHCH3), 1.56 (d, J = 6.8 Hz,
6H, NCH3); 13C NMR (50 MHz): d 164.1 (NC+N),
151.4, 142.7, 139.4, 136.0, 135.2, 129.5, 129.4, 128.7,
128.5, 127.9, 127.7, 126.6, 126.4, 71.4 (CHPh), 57.8
(NCHCH3), 17.9 (CHCH3); HRMS (ESI) calculated for
C36H34N3þ: 508.2753, found: 508.2752.
(30); IR (KBr) 1604vs, 1346vs, 1199vs, 1138s, 1158s,
1
616s, 512s cmꢀ1; H NMR (200 MHz): d 7.70–7.59 (m,
4H), 7.43–7.31 (m, 10H), 5.05 (s, 2H, CHPh), 4.64 (s,
6H, NCH3); 13C NMR (50 MHz): d 166.6 (NC+N),
140.2, 133.3, 130.5, 130.3, 130.2, 129.8, 128.1, 120.0, 75.2
(CHPh), 33.6 (NCH3). HRMS (ESI) calculated for
C23H22N2Cl+: 361.1472, found: 361.1470.
4.3.7.
(ꢀ)-(4S,5S)-2-(4-Chlorophenyl)-1,3-dimethyl-4,5-
4.3.10. (ꢀ)-(4S,5S)-2-(2-Pyridinyl)-4,5-diphenyl-1,3-bis((R)-
diphenylimidazolinium tetrakis(3,5-bis(trifluoromethyl)phen-
yl)borate 2d. (ꢀ)-(4S,5S)-2-(4-Chlorophenyl)-1,3-dimethyl-
4,5-diphenylimidazolinium tetrakis(3,5-bis(trifluoromethyl)-
phenyl)borate 2d was prepared from (4S,5S)-2-(4-chloro-
phenyl)-1,3-dimethyl-4,5-diphenylimidazolinium bromide 2a
(150 mg, 0.34 mmol) and NaB[3,5-(CF3)2-C6H3]4 (300 mg,
0.34 mmol) in a mixture of CHCl3 (3 mL) and water
1-phenylethyl)imidazolinium
imide
bis(trifluoromethylsulfonyl)-
4c. (ꢀ)-(4S,5S)-2-(2-Pyridinyl)-4,5-diphenyl-1,3-
bis((R)-1-phenylethyl)imidazolinium bis(trifluoromethyl-
sulfonyl)imide 4c was prepared from (4S,5S)-2-(2-pyrid-
yl)-4,5-diphenyl-1,3-bis((R)-1-phenylethyl)imidazolinium
bromide 4a (300 mg, 0.51 mmol) and LiNTf2 (176 mg,
0.61 mmol) in a mixture of DCM (3 mL) and water
22
(3 mL) as a white solid (48 mg, 71%). mp 114 ꢁC;
(3 mL) as a colourless liquid (230 mg, 57%). ½aꢁD ¼ ꢀ50:0
22
½aꢁD ¼ ꢀ39:4 (c 0.31, CHCl3); MS (EI), m/e 361 (M+,
(c 0.46, CHCl3); MS (ESI, 0 V), m/e 508.3 (M+); IR
20%), 243 (100), 228 (20), 165 (20), 152 (20), 118 (25); IR
(KBr) 3426m, 1604s, 1356vs, 1278vs, 1127vs, 839s, 713s,
(KBr) 1556m, 1353s, 1196vs, 1135m, 1058s, 696m cmꢀ1
;
1H NMR (200 MHz): d 8.95–8.87 (m, 1H) 8.50 (d,
J = 6.8 Hz, 1H), 8.27 (td, J = 7.7, 1.7 Hz, 1H), 7.75–7.60
(m, 1H), 7.25–6.70 (m, 20H), 4.90–4.70 (m, 4H, CHPh,
CHCH3), 1.50 (d, J = 7.0 Hz, 6H, NCH3); 13C NMR
(50 MHz): d 163.1 (NC+N), 150.1, 141.7, 138.5, 135.1,
134.2, 129.9, 128.4, 127.8, 127.5, 126.9, 126.7, 125.6,
125.4, 119.0 (q, J = 64.9 Hz, CF3), 70.5 (CHPh), 56.8
682s, 669m cmꢀ1; H NMR (400 MHz): d 7.80–7.69 (m,
1
10H), 7.59–7.46 (m, 12H), 7.26–7.25 (m, 4H), 4.98 (s, 2H,
CH), 2.92 (s, 6H, CH3); 13C NMR (50 MHz) 166.4
(NC+N), 162.1 (q, J = 49.6 Hz, BC), 142.3, 135.2
(BCCH), 133.8, 131.7, 131.5, 130.9, 129.5, 129.3 (q,
J = 28.4 Hz, CCF3), 126.9, 126.3, 125.0 (q, J = 271 Hz,

808
V. Jurcˇı´k, R. Wilhelm / Tetrahedron: Asymmetry 17 (2006) 801–810
(NCHCH3), 12.0 (CHCH3). HRMS (ESI) calculated for
bromide salt. The solvent was removed by filtration and the
remaining solid washed with Et2O (2 · 3 mL). The solid
was dissolved in CHCl3 (3 mL) and an aqueous solution
of KPF6 (68 mg, 0.368 mmol) was added. The mixture
was stirred vigorously for 30 min and the aqueous phase
removed. The organic phase was washed with water
C36H34N3þ: 508.2753, found: 508.2767.
4.3.11.
(ꢀ)-(4S,5S)-2-(2-Chlorophenyl)-4,5-diphenyl-1,3-
bis((R)-1-phenylethyl)imidazolinium bromide 5a. (ꢀ)-
(4S,5S)-2-(2-Chlorophenyl)-4,5-diphenyl-1,3-bis((R)-1-phen-
ylethyl)imidazolinium bromide 5a was prepared from
(4S,5S)-2-(2-chlorophenyl)-4,5-diphenyl-1,3-bis((R)-1-phen-
ylethyl)imidazolidine 5 (100 mg, 0.18 mmol) and NBA
˚
(3 · 3 mL), dried (3 A MS) and the solvent was removed
under reduced pressure to give the title compound 6b as a
22
yellow solid (183 mg, 72%). Mp 87 ꢁC; ½aꢁD ¼ þ5:7 (c
(26.8 mg, 0.18 mmol) in glyme (1 mL) as a white solid
0.39, CHCl3); MS (ESI, 0 V), m/e 541.0 (M+, 100%); IR
22
1
(102 mg, 89%). Hygroscopic. ½aꢁD ¼ ꢀ131:6 (c 0.29,
(KBr) 3441s, 1543m, 848vs, 696s, 557s cmꢀ1; H NMR
CHCl3); 1H NMR (400 MHz): d 9.41 (d, J = 7.2, 1H),
7.90 (t, J = 7.2 Hz, 1H), 7.70 (t, J = 7 Hz, 1H), 7.55–6.90
(m, 18H), 6.65–6.58 (m, 2H), 6.63 (d, J = 10.3 Hz, 1H,
CHPh), 5.34 (q, J = 7.2 Hz, 1H, CHCH3), 5.08 (d, J =
10.3 Hz, 1H, CHPh), 4.83 (q, J = 7.2 Hz, 1H, CHCH3),
1.75 (d, J = 7.1 Hz, 6H, CHCH3); 13C NMR (100 MHz):
d 165.3 (NC+N), 138.03, 138.0, 136.0, 134.7, 134.2, 137.7,
132.8, 130.6, 129.95, 129.87, 129.7, 129.6, 129.5, 128.9,
128.7, 128.6, 128.5, 128.4, 128.2, 127.7, 123.5, 73.4 (CHPh),
72.9 (CHPh), 60.7 (NCHCH3), 57.2 (NCHCH3), 19.8
(CHCH3), 17.0 (CHCH3). This compound was used di-
rectly in the subsequent step.
(200 MHz): d 7.85 (dd, J = 27.8, 8.6 Hz, 4H), 7.40–6.75
(m, 20H), 4.97 (s, 2H, NCHPh), 5.00–4.85 (m, 2H,
NCHMe), 1.60 (d, J = 7.2 Hz, 6H, CHCH3); 13C NMR
(50 MHz): d 166.7 (NC+N), 140.1, 136.1, 135.5, 131.0,
130.2, 129.6, 129.5, 128.7, 128.6, 126.6, 120.9, 71.7 (2C,
NCHPh), 58.0 (2C, NCHCH3), 17.9 (2C, CHCH3); HRMS
(ESI) calculated for C37H34N2Cl: 541.2411, found:
541.2418.
4.3.14. (ꢀ)-(4S,5S)-1,3-Dimethyl-2-(2-((4S,5S)-1,3-dimethyl-
4,5-diphenylimidazolidin-2-yl)phenyl)-4,5-diphenylimidazo-
linium bis-bis(trifluoromethylsulfonyl)imide 7c. (4S,5S)-
1,3-Dimethyl-2-(2-((4S,5S)-1,3-dimethyl-4,5-diphenylimid-
azolidin-2-yl)phenyl)-4,5-diphenylimidazolidine 7 (500 mg,
0.864 mmol) was dissolved in glyme (3 mL) and NBA
(128 mg, 0.864 mmol) was added. After 15 min, a second
portion of NBA (128 mg, 0.864 mmol) was added. The
reaction mixture was stirred overnight and Et2O (5 mL)
was added in order to precipitate the bromide salt formed.
The precipitate was washed with Et2O (2 · 5 mL) and dried
in vacuo for 30 min. The bromide salt was dissolved in
CHCl3 (3 mL) and a solution of LiNTf2 (574.16 mg,
2 mmol) in H2O (2 mL) added. The mixture was stirred vig-
orously for 30 min, during which a white precipitate
formed. The latter was filtered off, washed with CHCl3
(3 mL), water (3 mL) and dried in vacuo to give the
4.3.12.
bis((R)-1-phenylethyl)imidazolinium
(ꢀ)-(4S,5S)-2-(2-Chlorophenyl)-4,5-diphenyl-1,3-
hexafluorophosphate
5b. (ꢀ)-(4S,5S)-2-(2-Chlorophenyl)-4,5-diphenyl-1,3-bis-
((R)-1-phenylethyl)imidazolinium hexafluorophosphate 5b
was prepared from (4R,5R)-2-(2-chlorophenyl)-4,5-diphen-
yl-1,3-bis((S)-1-phenylethyl)imidazolinium bromide 5a
(88 mg, 0.14 mmol) and KPF6 (29 mg, 0.16 mmol) in a
mixture of CHCl3 (3 mL) and water (3 mL) as a white solid
22
(92 mg, 94%). Mp = 160 ꢁC; ½aꢁD ¼ ꢀ82:7 (c 2.75, CHCl3);
MS (ESI, 0 V), m/e 541.3 (M+, 100%); IR (Kbr) 2360m,
1
2341m, 1533s, 1456m, 840vs, 697s, 558s cmꢀ1; H NMR
(400 MHz): d 8.49 (dd, J = 7.7, 1.4 Hz, 1H), 8.01–7.95
(m, 1H), 7.78 (td, J = 5.6, 1.5 Hz, 1H), 7.64 (d, J =
8.0 Hz, 1H), 7.40–6.95 (m, 16H), 6.85–6.80 (m, 2H), 6.65
(d, J = 7.4 Hz, 2H), 5.19 (d, J = 8.4 Hz, 1H, CHPh), 5.00
(d, J = 8.4 Hz, 1H, CHPh), 4.98 (q, J = 7.1 Hz, 1H,
CHCH3), 4.88 (q, J = 7.1 Hz, 1H, CHCH3), 1.74 (d, J =
7.1 Hz, 3H, CHCH3), 1.68 (d, J = 7.1 Hz, 3H, CHCH3);
13C NMR (100 MHz): d 164.9 (NC+N), 137.8, 136.6,
135.5, 135.2, 132.5, 132.4, 131.1, 130.5, 130.0, 129.9,
129.87, 129.8, 128.9, 128.7, 128.3, 127.8, 127.7, 127.65,
123.0, 72.6 (CHPh), 72.6 (CHPh), 59.8 (NCHCH3), 57.7
(NCHCH3), 18.4 (CHCH3), 17.6 (CHCH3); HRMS (ESI)
calculated for C37H24N2Cl+: 541.2421, found: 541.2421.
title compound 7c as a white solid (622 mg, 80%). Mp
22
165 ꢁC; ½aꢁD ¼ ꢀ21 (c 0.2, acetone); MS (ESI, 0 V), m/e
288 (M2+, 100%), 856 (M++NTf2, 20); IR (KBr) 3425m,
1602s, 1350vs, 1197vs, 1058s, 616s cmꢀ1
;
1H NMR
(400 MHz, DMSO-d6): d 8.40–8.20 (m, 4H), 7.80–7.30
(m, 20H), 5.82 (d, J = 14.0 Hz, 2H, CHPh), 5.39 (d,
J = 14.0 Hz, 2H, CHPh), 3.00–2.80 (m, 12H, NCH3); 13C
NMR (100 MHz, DMSO-d6): d 164.9 (NC+N), 135.5,
134.6, 132.0, 133.2, 131.2, 130.8, 130.4, 130.2, 129.9,
129.85, 121.9, 120.4 (q, J = 314.3 Hz, CF3), 76.4 (CHPh),
72.0 (CHPh), 35.4 (NCH3), 34.9 (NCH3). HRMS (ESI) cal-
culated for C40H40N42þ: 288.1626, found: 288.1621.
4.3.13.
bis((R)-1-phenylethyl)imidazolinium
(+)-(4S,5S)-2-(4-Chlorophenyl)-4,5-diphenyl-1,3-
hexafluorophosphate
4.3.15. (ꢀ)-(4S,5S)-1,3-Dimethyl-2-(2-((4S,5S)-1,3-dimethyl-
6b. (+)-(4S,5S)-2-(4-Chlorophenyl)-4,5-diphenyl-1,3-bis-
((R)-1-phenylethyl)imidazolinium hexafluorophosphate 6b
was prepared when (4S,5S)-2-(4-chlorophenyl)-4,5-diphen-
yl-1,3-bis((R)-1-phenylethyl)imidazolidine 6 (200 mg, 0.368
mmol) was dissolved in glyme (1 mL) and NBA (27 mg,
0.18 mmol) added. The reaction mixture was stirred at rt
for 15 min and a second portion of NBA (27 mg,
0.18 mmol) added. The reaction mixture was stirred for
an additional 30 min, during which a yellow solid precipi-
tated. Et2O (3 mL) was added and the mixture stirred for
15 min in order to precipitate the rest of the imidazolinium
4,5-diphenylimidazolidin-2-yl)phenyl)-4,5-diphenylimidazol-
inium
bis-tetrakis(3,5-bis(trifluoromethyl)phenyl)borate
7d. (4S,5S)-1,3-Dimethyl-2-(2-((4S,5S)-1,3-dimethyl-4,5-
diphenylimidazolidin-2-yl)phenyl)-4,5-diphenylimidazolidine
7 (250 mg, 0.43 mmol) was dissolved in a minimal amount
of glyme (2 mL) and NBA (62 mg, 0.43 mmol) was added.
After 15 min stirring at rt, a second portion of NBA
(62 mg, 0.43 mmol) was added. The reaction mixture
was stirred overnight and Et2O (5 mL) was added in order
to precipitate the formed bromide salt. The precipitate was
washed with Et2O (2 · 5 mL) and dried in vacuo for

V. Jurcˇı´k, R. Wilhelm / Tetrahedron: Asymmetry 17 (2006) 801–810
809
30 min. The bromide salt was then dissolved in DCM
(5 mL), followed by the addition of NaB[3,5-(CF3)2-
C6H3]4 (765.8 mg, 0.86 mmol) and water (3 mL). The mix-
ture was stirred vigorously for 30 min. The organic phase
was separated, washed with water (3 · 5 mL), dried (3 A
MS) and the solvent removed under reduced pressure.
The remaining solid was further dried under high vacuum
itate was washed with Et2O (2 · 5 mL) and dried in vacuo
for 30 min. The bromide salt was dissolved in DCM (3 mL)
and NaB[3,5-(CF3)2-C6H3]4 (672.5 mg, 0.759 mmol) and
water (3 mL) were added. The mixture was vigorously stir-
red for 30 min and the organic phase separated, washed
˚
˚
with water (3 · 5 mL), dried (3 A MS) and the solvent re-
moved under reduced pressure. The remaining solid was
to give the title compound 7d as a light brown solid
further dried under high vacuum to give the title compound
22
22
(792 mg, 80%). Mp 66–68 ꢁC; ½aꢁD ¼ ꢀ25 (c 0.45, ace-
8d as a brown solid (677 mg, 87%). Mp 115 ꢁC; ½aꢁD ¼
tone); MS (ESI, 0 V), m/e 288.2 (M2+, 100%); IR (KBr)
ꢀ5:9 (c 0.67, acetone); MS (ESI, 20 V), m/e 190.1 (M2+
;
cmꢀ1 1H NMR (400 MHz, DMSO): d 8.10–7.95 (m,
,
1605m, 1356s, 1279vs, 1126s, 682m cmꢀ1
;
1H NMR
100%); IR (KBr) 1612w, 1357s, 1280vs, 1125vs, 713m
(400 MHz, DMSO-d6): d 8.30–8.20 (m, 4H), 7.60–7.40
(m, 44H), 5.91 (d, J = 14.0 Hz, 2H, CHPh), 5.47 (d, J =
14.0 Hz, 2H, CHPh), 2.99 (d, J = 5.1 Hz, 12H, NCH3);
13C NMR (100 MHz, DMSO-d6): d 164.5 (NC+N), 161.5
(q, J = 49.6 Hz, BC), 135.1, 134.2 (b, BCCH), 134.4,
133.6, 132.8, 130.7, 130.3, 130.0, 129.7, 129.5, 129.4,
128.9 (q, J = 28.4 Hz, CHCCF3), 124.4 (q, J = 271.2 Hz,
CCF3), 121.6, 118.0 (CHCCF3), 79.6 (NCHPh), 71.6
(NCHPh), 35.0 (NCH3), 34.5 (NCH3). HRMS (ESI) cal-
4H), 7.70–7.50 (m, 24H), 3.60–3.50 (m, 4H, NCHCH2),
3.01 (s, 6H, NCH3), 2.83 (s, 6H, CH3), 2.40–2.20 (m, 4H,
CH2), 1.90–1.80 (m, 4H, CH2), 1.60–1.40 (m, 4H, CH2),
1.40–1.20 (m, 4H, CH2); 13C NMR (100 MHz, CDCl3): d
164.9 (NC+N), 160.0 (q, J = 49.6 Hz, BC), 134.0, 131.3,
128.4 (q, J = 62.4 Hz, CCF3), 123.9 (q, J = 271 Hz,
CCF3), 121.2, 117.3, 68.7 (NCHCH2), 67.1 (NCHCH2),
33.1 (CH3), 32.2 (CH3), 26.7 (CH2), 23.2 (CH2), 23.0
2þ
2þ
culated for C20H20N2 288.1626, found 288.1616.
(CH2). HRMS (ESI) calculated for C24H36N4 190.1470,
found: 190.1469.
4.3.16.
(ꢀ)-(4R,5R)-1,3-Dimethyl-2-(2-((4R,5R)-1,3-
dimethyl-4,5-diphenylimidazolidin-2-yl)phenyl)-4,5-diphenyl-
imidazolinium bis-hexafluorophosphate 8b. (3aR,7aR)-
Octahydro-2-(2-((3aR,7aR)-octahydro-1,3-dimethyl-1H-
benzo[d]imidazol-2-yl)phenyl)-1,3-dimethyl-1H- benzo[d]-
imidazole 8 (140 mg, 0.37 mmol) was dissolved in a
minimal amount of glyme (1.5 mL) and NBA (53 mg,
0.37 mmol) was added. After 15 min stirring at rt, a sec-
ond portion (53 mg, 0.37 mmol) was added. The reaction
mixture was stirred for 3 h during which a brown precipi-
tate formed. The solvent was decanted and the precipitate
washed with Et2O and dissolved in CHCl3 (2 mL). A solu-
tion of KPF6 (135 mg, 0.732 mmol) in water (3 mL) was
added and the mixture was vigorously stirred overnight
during which a brown precipitate formed. The solvents
were carefully removed and the rest was dried in vacuo
4.4. Imidazolinium salts as catalysts
4.4.1. General procedure for the imidazolinium salt catalyzed
aza Diels–Alder reaction in acetonitrile. An imine
(0.2 mmol) and catalyst (0.02 mmol, 10 mol %) were placed
into a dry Schlenk flask under a nitrogen atmosphere. The
reaction mixture was dissolved in dry acetonitrile (2 mL)
and Danishefsky’s diene (0.22 mmol, 43 lL) was added at
once. After 16 h stirring at rt, the mixture was quenched
with a saturated solution of potassium hydrogencarbonate
(2 mL) and extracted with ethyl acetate (3 · 5 mL). The
organic phases were combined, dried over Na2SO4 and
the solvent was evaporated under reduced pressure. FCC
(petroleum ether/ethyl acetate, 1/1) gave the desired product.
to give the title compound 8b as a brown solid (184 mg,
22
4.4.2. General procedure for the imidazolinium salt catalyzed
inverse electron demand aza Diels–Alder reaction for mono-
imidazolinium salts. Imine 10 (0.2 mmol) and the catalyst
(0.02 mmol) were placed into a dry Schlenk flask under a
nitrogen atmosphere. The reaction mixture was dissolved
in dry acetonitrile (2 mL) and the dienophile 3,4-dihydro-
2H-pyran 12 (0.4 mmol, 30.27 lL) or 3,4-dihydro-2H-
pyran 13 (0.4 mmol, 36.18 lL) was added at once. The
reaction mixture was stirred at rt between 16 and 112 h
and the solvent was evaporated under reduced pressure.
The products were isolated by FCC (petroleum ether/ethyl
acetate, 95/5) to give the corresponding quinolines.
75%). Mp 145–150 ꢁC; ½aꢁD ¼ ꢀ7:7 (c 0.3, acetone); MS
(ESI, 50 V), m/e 190.1 (M2+, 100%); IR (KBr) 2360m,
1
1589m, 839vs, 558s cmꢀ1; H NMR (400 MHz, DMSO):
d 8.20–8.10 (m, 2H), 8.10–7.95 (m, 2H), 3.65–3.50 (m,
4H, CH), 3.05 (s, 6H, CH3), 2.85 (s, 6H, CH3), 2.40–2.25
(m, 4H, CH2), 2.00–1.85 (m, 4H, CH2), 1.60–1.25 (m,
8H, CH2); 13C NMR (100 MHz, DMSO): d 165.3
(NC+N), 134.5, 131.8, 121.8, 69.2 (NCHCH2), 67.6
(NCHCH2), 33.7 (CH3), 32.8 (CH3), 27.4 (CH2), 27.3
(CH2), 23.9 (CH2), 23.7 (CH2). HRMS (ESI) calculated
2þ
for C24H36N4 190.1471, found: 190.1470.
4.3.17.
(ꢀ)-(4R,5R)-1,3-Dimethyl-2-(2-((4R,5R)-1,3-
dimethyl-4,5-diphenylimidazolidin-2-yl)phenyl)-4,5-diphenyl-
imidazolinium bis-tetrakis(3,5-bis(trifluoromethyl)phenyl)-
borate 8d. (3aR,7aR)-Octahydro-2-(2-((3aR,7aR)-octa-
hydro-1,3-dimethyl-1H-benzo[d]imidazol-2-yl)phenyl)-1,3-
4.4.3. In DCM, catalyzed by bis-imidazolinium salts. N-
Benzylidene aniline (54.3 mg, 0.3 mmol) and the catalyst
(0.03 mmol) were placed into a dry Schlenk flask under a
nitrogen atmosphere. The reaction mixture was dissolved
in dry DCM (1 mL) and 3,4-dihydro-2H-pyran (56 lL,
0.6 mmol) added at once. The reaction mixture was stirred
at rt (for different reaction times and temperatures see text
in Section 2.2). The solvent was removed and the crude
product purified by FCC (petroleum ether/ethyl acetate,
95/5) to give the corresponding quinolines.
dimethyl-1H-benzo[d]imidazole
8 (145 mg, 0.38 mmol)
was dissolved in a minimal amount of glyme (3 mL) and
NBA (55 mg, 0.19 mmol) was added. After 15 min stirring
at rt a second portion (55 mg, 0.19 mmol) was added and
the reaction mixture stirred for 3 h. Et2O (5 mL) was added
in order to precipitate the bromide salt formed. The precip-

810
V. Jurcˇı´k, R. Wilhelm / Tetrahedron: Asymmetry 17 (2006) 801–810
4.4.4. 2,3-Dihydro-1,2-diphenylpyridin-4(1H)-one 11 (R =
Ph). 2,3-Dihydro-1,2-diphenylpyridin-4(1H)-one 11 was
prepared from 9 and 10 (R = Ph) as yellow solid. The spec-
tral data were consistent with the literature values.25
author would like to thank Dr. Dra¨ger, for HRMS mea-
surements and Dr. Namyslo, for 19F NMR measurements.
References
4.4.5. 2-Phenyl-1-tosyl-2,3-dihydropyridin-4(1H)-one 11 (R =
Ts). From (E)-N-(benzylidene) tosylamine (52 mg, 0.20
mmol) and Danishefsky’s diene (43 lL, 0.22 mmol) in the
presence of imidazolinium catalyst (0.02 mmol) as a white
solid (23 mg, 35%). Spectral data were consistent with
literature values.26
´
´
1. Genisson, Y.; Lauth-de Viguerie, N.; Andre, C.; Baltas, M.;
Gorrichon, L. Tetrahedron: Asymmetry 2005, 16, 1017–1023.
2. Clavier, H.; Boulanger, L.; Audic, N.; Toupet, L.; Mauduit,
M.; Guillemin, J. C. Chem. Commun. 2004, 1224–1225.
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4.4.6. 3,4,4a,5,6,10b-Hexahydro-5-phenyl-2H-pyrano[3,2-c]-
quinoline 14a and 14b. 3,4,4a,5,6,10b-Hexahydro-5-phen-
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pyran (50 lL, 0.6 mmol) as a mixture of cis- and trans-dia-
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´
6. Jurcˇık, V.; Wilhelm, R. Green Chem. 2005, 7, 844–848.
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7. Jurcˇık, V.; Wilhelm, R. Org. Biomol. Chem. 2005, 3, 239–244.
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Cis-isomer as a white solid: The spectral data were consis-
tent with the literature values.27 HPLC conditions: AD-H
(2.5% i-PrOH/hexane, 0.3 mL/min) t1 = 71.2 min, t2 =
83.8 min.
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(2.5% i-PrOH/hexane, 0.4 mL/min) t1 = 38.5 min, t2 =
59.1 min.
4.5. NMR experiments with Mosher’s acid salt
4.5.1. Preparation of racemic potassium Mosher’s carbox-
ylate. Racemic Mosher’s acid (302 mg, 1.29 mmol) was
dissolved in water (1 mL) and a solution of KOH (72 mg,
1.29 mmol) in water (3 mL) was added. The mixture was
stirred at rt for 15 min and water was removed under
reduced pressure. The remaining solid was further dried
under high vacuum to give the potassium Mosher’s
carboxylate salt as a white solid (351 mg, quant.).
´
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4.5.2. NMR experiment with the racemic Mosher’s acid
salt. Mosher’s acid salt (1 mmol) and the corresponding
imidazolinium salt (1 mmol) were dissolved in acetone-d6
1
and the H NMR and 19F NMR spectra were recorded
at rt. For results see Table 4.
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Acknowledgements
Financial support by Fonds der Chemischen Industrie and
the DFG is gratefully acknowledged. In addition the
27. Yadav, J. S.; Reddy, B. V. S.; Madhuri, C. R.; Sabitha, G.
Synthesis 2001, 1065–1068.