A configurationally stable chiral concave imidazolinium salt

Article abstract of DOI:10.1002/ejoc.201001367

Starting from symmetric bis-ortho-alkenyl-substituted aniline 11 and unsymmetric bis-alkenyl-substituted aminonaphthalene 12, imidazolinium salt 17 has been prepared. Salt 17 was cyclized by ring-closing metathesis, and hydrogenation gave axially chiral N

Full text of DOI:10.1002/ejoc.201001367

FULL PAPER
DOI: 10.1002/ejoc.201001367
A Configurationally Stable Chiral Concave Imidazolinium Salt[‡]
Tim Reimers,[a] Christian Näther,[b] and Ulrich Lüning*[a]
Keywords: Carbenes / Concave reagents / Chirality / Configurational stability / Macrocycles
Starting from symmetric bis-ortho-alkenyl-substituted anil-
ine 11 and unsymmetric bis-alkenyl-substituted amino-
naphthalene 12, imidazolinium salt 17 has been prepared.
sor 19. The configurational stability of 19 was proven by tem-
perature-dependent NMR studies and also by the use of Λ-
BINPHAT as a chiral shift reagent. Compound 19 was also
Salt 17 was cyclized by ring-closing metathesis, and hydro- characterized by single-crystal X-ray diffraction.
genation gave axially chiral N-heterocyclic carbene precur-
planar chirality, that is, 5.[21] Moreover, carbene precursors
Introduction
containing chiral centers within the N-heterocycle, like
imidazolinium salt 4,[22] were created.
Since Arduengo et al. crystallized an N-heterocyclic carb-
ene (NHC) for the first time in 1991,[1] this class of com-
pounds has gained enormous interest. Because of the high
versatility with respect to the NHC core on one hand and
to the N-substituents on the other hand, a large number of
different NHCs has been synthesized to date. They are
widely applied in organocatalysis[2,3] but are also used as
ligands for transition metals, resulting in complexes with
remarkable new properties.[4] The most famous example
might be the second generation Grubbs catalyst used for
olefin metathesis.[5,6] Moreover, due to their antimicrobial
and antitumor properties, NHC noble metal complexes may
have medicinal applicabilities.[7]
Since many biologically active molecules are chiral, there
will always be a demand for asymmetric synthesis, and pref-
erentially asymmetric catalysis. Thus, chiral NHCs[8] have
been synthesized and investigated in both organocata-
lysis[2,9–11] and transition-metal catalysis.[12–16] Figure 1
shows some representative examples of chiral NHC precur-
Figure 1. Examples of chiral NHC precursors.
The properties of the NHCs can be influenced by varia-
tion of the N-substituents. Especially size and shape of
these groups can have a big influence on catalyzed reactions
because of their proximity to the reactive carbene unit. By
changing the residue R of NHC precursor 5, for example,
both reactivity and stereoselectivity has been tuned.[21]
Another concept of changing the steric properties of an
NHC is its incorporation into a concave system. We real-
ized this idea for the first time in 2007 by synthesizing con-
sors with different concepts of chirality: N-Heterocycles 1–
3 are examples for different types of NHCs, and all of them
have N-substituents containing centers of chirality: imid-
azolinium 1,[17] triazolium 2,[18] and imidazolium ions 3[19]
are shown here. Furthermore, there are NHCs with N-sub-
stituents containing axial chirality, that is, 6,[20] as well as
[‡] Concave Reagents, 59. Part 58: F. Eggers, U. Lüning, Eur. J.
Org. Chem. 2009, 2328–2341.
[a] Otto-Diels-Institut für Organische Chemie, Christian-Al-
brechts-Universität zu Kiel,
Olshausenstraße 40, 24098 Kiel, Germany
Fax: +49-431-8801558
E-mail: luening@oc.uni-kiel.de
[b] Institut für Anorganische Chemie, Christian-Albrechts-Uni-
versität zu Kiel,
Olshausenstraße 40, 24098 Kiel, Germany
Fax: +49-431-880-1520
E-mail: cnaether@ac.uni-kiel.de
1040
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2011, 1040–1046

A Configurationally Stable Chiral Concave Imidazolinium Salt
cave imidazolinium salt 7.[23] In this NHC precursor, the
Thus, a new synthetic route had to be found. In 2008,
N-heterocycle is part of a bimacrocycle with two phenyl Chung and Grubbs described the synthesis of asymmetric
bridgeheads that are connected by oxyalkyl chains.
N-substituted imidazolinium salts bearing two methyl
Upon deprotonation, the respective NHC was formed groups in the 4-position of the N-heterocycle[26] by starting
and used as an organocatalyst in the reaction of aldehydes from 2-bromo-2-methylpropionyl bromide (13) and anilines.
with enals.[24] Remarkably, the product distribution de-
pended strongly on the ring size. Whereas smaller bimacro-
cycle 7a formed lactones as described for other NHCs, the
larger concave NHC derived from 7b led to the formation
Results and Discussion
of an unexpected hemiacetal. This is proof for the special
influence of the concave shape. Interestingly, with shorter
alkyl chains, 8 methylene groups in 7a instead of 10 in 7b,
the formation of a hemiacetal was not observed, nor was a
hemiacetal found when standard NHCs such as IMes were
used. This fact shows that apparently small changes in the
environment of the reactive center can have a big influence
on the selectivity of the catalyst.
For the construction of an axially chiral NHC related to
10, two different bridgeheads had to be treated with dibro-
mide 13. The phenyl bridgehead was introduced by amide
formation between 13 and 2,6-bis(pent-4-enyloxy)aniline
(11). Resulting bromoamide 14 could be isolated in 93%
yield. Then, nucleophilic substitution of the remaining bro-
mide with 2,7-bis(pent-4-enyloxy)naphthylamine (12) led to
aminoamide 15 in 79% yield (Figure 2, Scheme 2).
Moreover, by exchanging one phenyl bridgehead for a
naphthalene unit, axially chiral concave bimacrocycle 10
was also prepared (Scheme 1).[25] However, this NHC pre-
cursor proved to be configurationally unstable. At room
temperature, rotation along the N–CAr bonds was observed
by NMR spectroscopy, which resulted in interconversion of
the enantiomers.
Figure 2. Structures of the arylamines that are used as bridgeheads
for the concave bimacrocycles.
After reduction of amide 15 with lithium aluminum hy-
dride, respective diamine 16 was isolated (80% yield). Treat-
ment with hydrogen chloride dissolved in 1,4-dioxane con-
verted it into the diamino dihydrochloride. After reaction of
the salt with triethyl orthoformate at 140 °C, imidazolinium
chloride 17 was obtained in 96% yield.
For the generation of bimacrocycle 18, ring-closing me-
tathesis of 17 with Grubbs first generation catalyst was car-
ried out under high dilution conditions. Because of the two
remaining double bonds, a mixture of four E and Z isomers
[(E,E), (E,Z), (Z,E), and (Z,Z)] was formed in a yield of
88%. Conversion to saturated bimacrocyclic imidazolinium
salt 19 was successfully performed by catalytic hydrogena-
tion with palladium on charcoal in 87% yield.
Single crystals were grown from a mixture of CDCl3 and
cyclohexane, and the crystal structure (Figure 3) was deter-
mined by X-ray structure analysis. A comparison with the
crystal structure of related but configurationally unstable
chiral macrocycle 10 reveals distinct differences (Figure 4).
Before the two structures can be discussed, 10 and 19
have to be inspected closely: The main change is the intro-
duction of two methyl groups in imidazolinium chloride 19
Scheme 1. Synthesis of configurationally unstable axially chiral
NHC precursors 10, n = 3, 4; X = (CH2)n+6. Reagents and condi-
tions: (i) Bis(alkenyloxy)aniline, NEt3, (ii) KOH, (iii) (COCl)2,
(iv) bis(alkenyloxy)naphthylamine,
(v) LiAlH4,
(vi) NH4Cl,
HC(OEt)3, (vii) benzylidenebis(tricyclohexylphosphane)dichloro-
ruthenium, (viii) Pd/C, H2.
For stabilization of the configuration, rotation along the that do not exist in 10. Moreover, the alkyl chains of the
N–CAr bonds has to be prevented. This can be realized by two bimacrocycles differ by one methylene group [(CH2)8
installation of stoppers, for example, alkyl substituents, at in 19, but (CH2)9 in 10]. Furthermore, the crystals were
the backbone of the N-heterocycle. However, the used strat- grown in different ways, and 19 crystallized by including
egy to build up axially chiral bimacrocyclic NHC precur- one equivalent of chloroform, whereas the crystals of 10 are
sors 10 (Scheme 1) does not allow this. Reduction of an solvent free.
oxalyl diamide starting material by lithium aluminum hy-
The most striking differences in the crystal structures are
dride leads to methylene-substituted amines and thus can- the twists between the aromatic bridgeheads and the N-het-
not introduce substituents in the 4- or 5-position of the erocycle in methylated compound 19 when compared to 10.
imidazolinium ring.
The naphthyl ring in 19 is as orthogonal to the imidazolin-
Eur. J. Org. Chem. 2011, 1040–1046
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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T. Reimers, C. Näther, U. Lüning
FULL PAPER
Figure 4. Comparison of the crystal structures of two imidazolin-
ium ions: dimethyl-substituted 19 (top) and unsubstituted 10[25]
(bottom; n = 4, see Scheme 1). For clarity, only carbon, nitrogen,
and oxygen atoms are shown.
groups. In unmethylated case 10, there is a twist of ca. 6°
out of orthogonality and no distortion of the naphthalene
plane is observable.
The other bridgehead, the phenyl ring, is twisted out of
orthogonality in both cases, but this twist is much larger in
the unmethylated and larger bimacrocycle: 29° in 10 versus
ca. 15° in 19. In 10, the twist of the two bridgeheads is
disrotatory so that the overall “helicity” in the crystals is
considerably larger in the wider and unmethylated case 10.
If one is allowed to sum up the twist angles, this sum is ca.
15° for dimethylated 19 but ca. 35° for larger and unsubsti-
tuted 10.
If both bimacrocycles are looked at from the side (i.e.,
with the imidazolinium ring in the paper plane), the angle
defined by the two aryl heterocycle bonds between the imid-
azolinium nitrogen atoms and the bridgehead carbon atoms
seems to be considerably larger for dimethylated compound
19 than for unmethylated wider bimacrocycle 10. In such a
projection, this angle is 133° for unmethylated 10 in con-
trast to 143° for dimethylated salt 19. To understand this
difference, several dihedral and bond angles have to be in-
spected. There are the following differences: Of course, the
steric requirements of the methyl groups in 19 lead to a
larger dihedral angle along the C4–C5 bond of the imid-
azolinium unit by minimizing ecliptic interactions (18 vs.
10° for 10). With this twist, the heterocycle in 19 is less
planar. The C4–C5 bond is rotated with respect to the N–
C2–N moiety. This and the geminal dimethyl effect results
in altered angles within the five-membered ring (angular
sum of the inner angles in the pentagons: 539° for 10, 536°
for 19). Consequently, the wings of the aryl–heterocycle–
aryl unit are a bit more open. In addition, the twist of the
Scheme 2. Synthesis of configurationally stable axially chiral NHC
precursor 19, X1 = (CH2)3HC=CH(CH2)3, X2 = (CH2)8. Reagents
and conditions: (i) 11, NEt3 (93%), (ii) 12, NaH (79%), (iii) LiAlH4
(80%), (iv) HCl in 1,4-dioxane, (v) HC(OEt)3, [96% over steps (iv)
and (v)], (vi) benzylidenebis(tricyclohexylphosphane)dichlororu-
thenium (88%), (vii) Pd/C, H2 (87%). Total yield over six steps:
43%.
Figure 3. Crystal structure of imidazolinium chloride 19. Only one
enantiomer is shown; the chloroform molecule is omitted for clar- C4–C5 bond versus the N–C2–N unit results in a move-
ity.
ment of one aryl ring out of the paper plane towards the
observer and the other one is pushed behind the paper
ium ring as possible, with the naphthalene unit being bent plane. This movement adds to the opening of the wings
by ca. 3° out of plane by interaction with the two methyl and leads to the observed differences in the above discussed
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A Configurationally Stable Chiral Concave Imidazolinium Salt
angles observed in the side projection: 133° for 10 and 143°
for 19. The visible differences seem to be even larger be-
cause the bridgeheads are not perfectly planar. In wider
methylated 19, the aromatic bridgeheads themselves are dis-
torted a bit to the exo side, whereas they adopt a more endo
shape in unmethylated 10.
It will be interesting to see the influence of this altered
geometry of 19 not only in enantioselective reactions with
enantiopure 19 but also with racemic material in organocat-
alytic reactions as carried out already.[24] Note, however,
that the geometrical differences have been found in the solid
state. In solution, the molecules are flexible, and 10 inverts
to its enantiomer quickly.[25]
1
Figure 6. Expanded section of the H NMR spectrum of the dia-
stereomeric imidazolium Λ-BINPHAT salt. Zooms on representa-
tive signals show the equal intensities of the respective signals.
For investigation of the configurational stability of new
dimethylated axially chiral concave bimacrocycle 19, two
NMR experiments were carried out: First, racemic imid-
azolinium chloride 19 was converted into a diastereomeric
salt with enantiopure Λ-BINPHAT[27] (Figure 5). We
showed that in case of the 4,5-nonsubstituted chiral imid-
azolinium salt 10, the use of enantiopure Λ-BINPHAT (20)
as a counterion led to NMR spectra with two sets of signals
with different intensities.[25] The rational is that one enan-
tiomeric imidazolium ion interacts more strongly with the
chiral counterion than the other and is stabilized by this
ion pair formation. Noteworthy is that the amplification of
one species can only happen by rotation along the N–CAr
bonds (Scheme 1) and only if the energy of the rotation
barrier is low.
Figure 7. 1H NMR spectra (500 MHz) of chiral concave imid-
azolium chloride 19 in C2D2Cl4 at various temperatures.
on the contrary, a slight separation of the signals is observ-
able. The doublet at δ = 4.5 ppm, attributable to one proton
in the 5-position of the N-heterocycle, shows the same ten-
dency. Moreover, by changing the temperature, a shift in
the imidazolium proton in the 2-positon (δ = 7.85 ppm) was
clearly detectable.
It is possible to estimate the energy of a rotational barrier
ΔG‡ with Equation (1).[28]
C
Figure 5. Structure of the chiral Λ-BINPHAT ion (20).
(1)
Thus, if the two methyl groups in the 4-postion of chiral
imidazolinium chloride 19 are able to stop the interconver-
sion by rotation, no amplification of one of the dia-
stereomeric ion pairs should be observed. Indeed, the inten-
sities of the isolated signals like H-5nap, H-4ph, and H-8nap
(Figure 6) are equal for both diastereomeric species over
time.
where TC is the coalescence temperature and Δυ is the dis-
tance between the separated signals at low temperature.
Moreover, for physical separation of atropisomers, the need
of an energy barrier ΔG‡298 Ն90 kJ/mol is postulated.[29] In
this case, with Δν = 4.8 Hz, the coalescence temperature
should be at least 398 K for a rotation barrier of 90 kJ/mol
or more. Measurement at this temperature was not possible
but until 368 K no tendency of coalescence was observable.
Because of the diastereotopicity of the methyl groups in
the 4-position of N-heterocycle 19, two different singlets are
1
detected by H NMR spectroscopy at 298 K. If there were
fast rotation along the N–CAr bonds, the methyl groups
would become indistinguishable and they would appear as
one singlet in the spectrum. To study the height of the rota-
tional barrier, NMR spectra were recorded at different tem-
peratures. Three of them are shown in Figure 7.
Conclusions
Starting from a bromoalkanoyl bromide 13 and amino-
arenes 11 and 12, chiral concave NHC precursor 19 was
In the case of a low rotational barrier, coalescence of the synthesized in 43% total yield over six synthetic steps. By
two singlets of the methyl groups at δ = 1.65 ppm would dimethylation in the 4-position of the imidazolinium ring,
have been observed when increasing the temperature, but, the configurational stability of chiral bimacrocycle 19 was
Eur. J. Org. Chem. 2011, 1040–1046
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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1043

T. Reimers, C. Näther, U. Lüning
FULL PAPER
2 H, CH=), 5.05 (ddt, 3J = 17.1 Hz, 2J = 1.8 Hz, 4J = 1.6 Hz, 2 H,
enhanced. Reaction with enantiopure Λ-BINPHAT re-
sulted in a 1:1 mixture of two diastereomers, which were
stable. This now allows the deracemization of 19 to be tack-
led, for instance, by chromatography on chiral columns or
by separation of diastereomeric salts such as 19·Λ-
BINPHAT. Because of its potential in enantioselective ca-
talyses, the enantiopure NHC shall be tested, for instance,
as an organocatalyst in the asymmetric reaction of alde-
hydes with enals,[19,24] or could be employed as a chiral li-
gand for transition metals.
Moreover, analysis of the crystal structures showed that
the naphthyl unit in 19 is positioned orthogonally with re-
spect to the N-heterocycle and that the overall structure of
the bimacrocycle is different to that of 10. This may result
in altered selectivities for instance in organocatalytic reac-
tions[24] even with racemic 19.
3
2
4
=CHEHZ), 4.98 (ddt, J = 10.2 Hz, J = 1.8 Hz, J = 1.2 Hz, 2 H,
=CHEHZ), 3.98 (t, 3J = 6.2 Hz, 4 H, OCH2), 2.24 (mc, 4 H,
CH2CH=), 2.06 (s, 6 H, CH3), 1.86 (mc, 4 H, OCH2CH2) ppm. 13
C
NMR (125 MHz, CDCl3, 300 K): δ = 170.0 (s, C=O), 154.8 (s, C-
2, C-6), 137.9 (d, CH=), 127.7 (d, C-4), 115.2 (t, =CH2), 114.4 (s,
C-1), 105.1 (d, C-3, C-5), 67.8 (t, OCH2), 63.1 (s, C-Br), 32.7 (q,
CH ), 30.1 (t, CH CH=), 28.6 (t, OCH CH ) ppm. IR (ATR): ν =
˜
3
2
2
2
3398 (N–H), 3076 (=C–H), 2976, 2934, 2872 (aliph. C–H), 1687
(C=O), 1596, 1508 (arom. C=C), 1257 (=C–O), 1100 (O–CH2), 909
(alkenyl = C–H), 767 (1,2,3-trisubs. ph C–H) cm–1. MS (ESI,
CHCl3/CH3OH): m/z (%) = 432 (83) [C20H2879BrNO3 + Na]+, 434
(100) [C20H2881BrNO3 + Na]+. (C20H28BrNO3) (410.35): calcd. C
58.54, H 6.88, N 3.41; found C 58.73, H 7.11, N 3.48.
N-[2,6-Bis(pent-4-enyloxy)phenyl]-2-[2,7-bis(pent-4-enyloxy)naphth-
ylamino]-2-methylpropanamide (15): A dispersion of sodium hy-
dride (60%) in mineral oil (332 mg, 8.30 mmol) was added to a
solution of naphthylamine 12 (1.33 g, 4.30 mmol) in dry tetra-
hydrofuran (50 mL). Over a period of 2 h, a solution of bromo
propanamide 14 (1.65 g, 4.00 mmol) in dry tetrahydrofuran
(100 mL) was added dropwise while stirring. Then, the mixture was
stirred for 16 h at room temperature. Saturated aqueous solution
of ammonium chloride (100 mL) was added, and the aqueous layer
was extracted with tert-butyl methyl ether (3ϫ100 mL). The or-
ganic layer was dried with magnesium sulfate, the solvent was evap-
orated, and the product was purified by column chromatography
[silica gel, cyclohexane/ethyl acetate (20:1), Rf = 0.05]. A colorless
oil (2.04 g, 3.18 mmol, 79%) was obtained. 1H NMR (500 MHz,
Experimental Section
General Remarks: The following chemicals were obtained commer-
cially and used without further purification: benzylidenebis(tricy-
clohexylphosphane)dichlororuthenium (Aldrich), (Λ,R)-BIN-
PHAT tetrabutylammonium salt (Aldrich), 2-bromo-2-methylpro-
pionyl bromide (ABCR), Celite (Fluka), ethyl vinyl ether (Acros),
hydrogen chloride (4 m in 1,4-dioxane, Lancester), lithium alumi-
num hydride (Merck), palladium/charcoal (10% Pd, Merck), so-
dium hydride (Acros), and triethyl orthoformate (Merck). 2,6-
Bis(pent-4-enyloxy)aniline[23] and 2,7-bis(pent-4-enyloxy)naph-
thylamine[25] were synthesized according to literature procedures.
Tetrahydrofuran was dried by heating at reflux with lithium alumi-
num hydride. Dichloromethane was dried by heating at reflux with
calcium hydride. All syntheses except hydrogenations were carried
out under an atmosphere of dry nitrogen. Column chromatography
was carried out with silica gel (Macherey–Nagel). NMR spectra
were recorded with a Bruker DRX 500 instrument. Assignments
are supported by COSY, HSQC, and HMBC. Even when obtained
by DEPT, the type of 13C signal is always listed as singlet, doublet,
etc. All chemical shifts are referenced to TMS. For a definite desig-
nation, “im” for imidazolium, “nap” for naphthyl, and “ph” for
phenyl were used as indices. Mass spectra were recorded with a
Finnigan MAT 8200 or MAT 8230. ESI mass spectra were re-
corded with an Applied Biosystems Mariner Spectrometry Work-
station. IR spectra were recorded with a Perkin–Elmer Spectrum
100 equipped with an MKII Golden GateTM Single Reflection
ATR unit. Elemental analyses were carried out with a Euro EA
3000 Elemental Analyzer from Euro Vector.
3
CDCl3, 300 K): δ = 9.67 (s, 1 H, CONH), 7.60 (d, J = 8.9 Hz, 1
H, 5naph-H), 7.47 (d, 3J = 8.9 Hz, 1 H, 4naph-H), 7.44 (d, 2J =
3
3
2.4 Hz, 1 H, 8naph-H), 7.10 (t, J = 8.4 Hz, 1 H, 4ph-H), 7.07 (d, J
3
4
= 8.9 Hz, 1 H, 3naph-H), 6.98 (dd, J = 8.9 Hz, J = 2.4 Hz, 1 H,
6
naph-H), 6.58 (d, 3J = 8.4 Hz, 2 H, 3ph-H, 5ph-H), 5.86 [ddt, 3JZ
=
3
3
17.0 Hz, JE = 10.3 Hz, J = 6.7 Hz, 1 H, 2naph-O(CH2)3CH], 5.72
[ddt, 3JZ = 17.0 Hz, 3JE = 10.3 Hz, 3J = 6.7 Hz, 1 H, 7naph-O(CH2)3-
CH], 5.64 [ddt, 3JZ = 17.0 Hz, 3JE = 10.3 Hz, 3J = 6.8 Hz, 2 H,
2
ph-O(CH2)3CH, 6ph-O(CH2)3CH], 5.07 [ddt, 3J = 17.1 Hz, 4J =
2
3
1.8 Hz, J = 1.6 Hz, 1 H, 2naph-O(CH2)3CHCHEHZ], 5.02 [ddt, J
= 10.2 Hz, 2J = 1.8 Hz, 4J = 1.2 Hz, 1 H, 2naph-O(CH2)3-
3
4
2
CHCHEHZ], 4.92 [ddt, J = 17.1 Hz, J = 1.8 Hz, J = 1.6 Hz, 1
H, 7naph-O(CH2)3CHCHEHZ], 4.88 [ddt, 3J = 10.2 Hz, 2J = 1.8 Hz,
4J = 1.2 Hz, 1 H, 7naph-O(CH2)3CHCHEHZ], 4.87–4.82 [m, 4 H,
2ph-O(CH2)3CHCH2, 6Ph-O(CH2)3CHCH2], 4.36 [s, 1 H, C(CH3)2-
NH], 4.13 (t, J = 6.5 Hz, 2 H, 2naph-OCH2), 3.89 (t, J = 6.4 Hz,
4 H, 2ph-OCH2, 6ph-OCH2), 3.85 (t, 3J = 6.5 Hz, 2 H, 7naph-OCH2),
2.28 [mc, 2 H, 2naph-O(CH2)2CH2], 2.09 [mc, 4 H, 2ph-O(CH2)2CH2,
3
3
7ph-O(CH2)2CH2], 1.99–1.91 [m, 4 H, 2naph-OCH2CH2, 7naph
O(CH2)2CH2], 1.75–1.63 (m, 6 H, 2ph-OCH2CH2, 6ph-OCH2CH2,
N-[2,6-Bis(pent-4-enyloxy)phenyl]-2-bromo-2-methylpropanamide 7naph-OCH2CH2), 1.47 (s, 6 H, CH3) ppm. 13C NMR (125 MHz,
-
(14): Aniline 11 (1.97 g, 7.54 mmol) and triethylamine (1.53 g,
15.1 mmol) were dissolved in dry dichloromethane (25 mL). At
0 °C, bromopropionyl bromide 13 (1.91 g, 8.29 mmol) was added
slowly to the solution. After a few minutes, a white solid precipi-
tated. The mixture was stirred for 1.5 h. Then, dichloromethane
(25 mL) and a saturated aqueous solution of ammonium chloride
(50 mL) were added. The aqueous layer was extracted with dichlo-
romethane (3ϫ50 mL), and the organic layer was dried with mag-
nesium sulfate. After evaporation of the solvent, the product was
purified by column chromatography [silica gel, cyclohexane/ethyl
acetate (10:1), Rf = 0.13]. A colorless oil (2.88 g, 7.02 mmol, 93%)
CDCl3, 300 K): δ = 175.3 (s, C=O), 157.2 (s, C-7naph), 154.1 (s, C-
2naph), 149.5 (s, C-2ph, C-6ph), 138.2 [d, =CH(CH2)3OC-7naph],
137.9 [d, =CH(CH2)3OC-2ph
, =CH(CH2)3OC-6ph], 137.6 [d,
=CH(CH2)3OC-2naph], 132.5 (s, C-8anaph), 129.4 (d, C-5naph), 127.8
(s, C-1naph), 126.3 (d, C-4ph), 124.9 (s, C-4anaph), 123.9 (d, C-4naph),
117.1 (d, C-6naph), 115.5 (s, C-1ph), 115.4 [t, CH2CH(CH2)3OC-
2naph], 114.8 [t, CH2CH(CH2)3OC-2ph, CH2CH(CH2)3OC-6ph],
114.6 [t, CH2CH(CH2)3OC-7naph], 110.8 (d, C-3naph), 105.1 (d, C-
3ph, C-5ph), 103.6 (d, C-8naph), 68.4 (t, CH2OC-2naph), 67.8 (t,
CH2OC-2ph
C(CH3)2], 30.3 [t, CH2(CH2)2OC-2naph], 30.1 [t, CH2(CH2)2OC-2ph
CH2(CH2)2OC-6ph], 30.0 [t, CH2(CH2)2OC-7naph], 28.8 (t,
, CH2OC-6ph), 67.2 (t, CH2OC-7naph), 61.7 [s,
,
1
was obtained. H NMR (500 MHz, CDCl3, 300 K): δ = 7.90 (s, 1
3
3
H, N-H), 7.13 (t, J = 8.4 Hz, 1 H, 4-H), 6.54 (d, J = 8.4 Hz, 2 CH2CH2OC-7naph), 28.6 (t, CH2CH2OC-2naph), 28.5 (t,
3
3
3
H, 3-H, 5-H), 5.83 (ddt, J = 17.0 Hz, J = 10.2 Hz, J = 6.7 Hz,
CH2CH2OC-2ph, CH2CH2OC-6ph), 26.9 (q, CH3) ppm. IR (ATR):
1044
www.eurjoc.org
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2011, 1040–1046

A Configurationally Stable Chiral Concave Imidazolinium Salt
ν = 3344 (N–H), 3076 (=C–H), 2933, 2872 (aliph. C–H), 1696
triethyl orthoformate (5 mL) and stirred for 1 h at 140 °C. After
evaporation of the solvent, the product was purified by column
chromatography [silica gel, dichloromethane/methanol (10:1), Rf =
0.36]. A white solid (614 mg, 952 μmol, 96%) was obtained. M.p.
153–154 °C. 1H NMR (500 MHz, CDCl3, 300 K): δ = 8.21 (s, 1 H,
2-Him), 7.96 (d, J = 9.0 Hz, 1 H, 5-Hnaph), 7.80 (d, J = 9.0 Hz, 1
H, 4-Hnaph), 7.37 (t, 3J = 8.5 Hz, 1 H, 4-Hph), 7.23 (d, 3J = 9.0 Hz,
1 H, 3-Hnaph), 7.14 (dd, 3J = 9.0 Hz, 4J = 2.3 Hz, 1 H, 6-Hnaph),
˜
(C=O), 1628, 1598, 1505 (arom. C=C), 1257, 1213 (=C–O), 1097,
1056 (O–CH2), 992, 909 (alkenyl = C–H), 825 (1,2,7-trisubst. naph
C–H) cm–1. MS (EI, 70 eV): m/z (%) = 640 (13) [M]+, 352 (100)
[C23H30NO2]+. MS (CI, isobutane): m/z (%) = 641 (83) [M]+, 352
(35) [C23H30NO2]+, 332 (100) [C20H30NO3]+, 312 (76) [C20H26-
NO2]+, 352 (35) [C23H30NO2]+, 352 (35) [C23H30NO2]+.
C40H54N2O4 (640.85): calcd. C 74.48, H 8.18, N 4.44; found C
74.66, H 8.61, N 4.14.
3
3
4
3
7.09 (d, J = 2.3 Hz, 1 H, 8-Hnaph), 6.68 (d, J = 8.5 Hz, 2 H, 3-
3
3
3
H
ph, 5-Hph), 5.86 [ddt, JZ = 17.0 Hz, JE = 10.3 Hz, J = 6.7 Hz,
2-[2,7-Bis(pent-4-enyloxy)naphthylamino]-3-[2,6-bis(pent-4-enyloxy)-
phenylamino]-2-methylpropane (16): Lithium aluminum hydride
(604 mg, 15.9 mmol) was suspended in dry tetrahydrofuran
(40 mL). At 0 °C, a solution of amino propanamide 15 (2.04 g,
3.18 mmol) in dry tetrahydrofuran (60 mL) was added slowly.
Then, the mixture was heated at reflux for 16 h. After cooling to
room temperature, the suspension was poured into ice water
(100 mL), and the aqueous layer was extracted with tert-butyl
methyl ether (3ϫ80 mL). After evaporation of the solvent, the
product was purified by column chromatography [silica gel, cyclo-
hexane/ethyl acetate (14:1), Rf = 0.37]. A reddish oil (1.59 g,
2.54 mmol, 80%) was obtained. 1H NMR (500 MHz, CDCl3,
300 K): δ = 7.76 (d, 4J = 2.2 Hz, 1 H, 8naph-H), 7.60 (d, 3J = 8.9 Hz,
1 H, 5naph-H), 7.48 (d, 3J = 8.9 Hz, 1 H, 4naph-H), 7.06 (d, 3J =
8.9 Hz, 1 H, 3naph-H), 6.93 (dd, 3J = 8.9 Hz, 4J = 2.2 Hz, 1 H,
3
3
1 H, 7naph-O(CH2)3CH], 5.79 [ddt, JZ = 17.0 Hz, JE = 10.3 Hz,
3J = 6.7 Hz, 1 H, 2naph-O(CH2)3CH], 5.76 [ddt, 3JZ = 17.6 Hz, JE
3
= 9.7 Hz, 3J = 6.6 Hz, 2 H, 2ph-O(CH2)3CH, 6ph-O(CH2)3CH], 5.07
3
2
4
[ddt, JZ = 17.0 Hz, J = 1.8 Hz, J = 1.6 Hz, 1 H, 7naph-O(CH2)3-
CHCHEHZ], 5.03–4.94 [m, 7 H, 2naph-O(CH2)3CHCH2, 7naph
O(CH2)3CHCHEHZ, 2ph-O(CH2)3CHCH2, 6ph-O(CH2)3CHCH2],
-
3
3
4.64 (d, J = 11.4 Hz, 1 H, 5-Him,a), 4.35 (d, J = 11.4 Hz, 1 H, 5-
Him,b), 4.22 (mc, 2 H, 2naph-OCH2), 4.16–4.05 (m, 6 H, 7naph-OCH2,
2ph-OCH2, 6ph-OCH2), 2.29 [dt, 3J = 7.9 Hz, 3J = 6.7 Hz, 2 H,
2
naph-O(CH2)2CH2], 2.23–2.17 [m, 6 H, 7naph-O(CH2)2CH2, 2ph
-
-
O(CH2)2CH2, 6ph-O(CH2)2CH2], 2.00–1.90 (m, H, 2naph
8
OCH2CH2, 7naph-OCH2CH2, 2ph-OCH2CH2, 6ph-OCH2CH2), 1.74
(s, 3 H, CH3), 1.67 (s, 3 H, CH3) ppm. 13C NMR (125 MHz,
CDCl3, 300 K): δ = 161.3 (d, C-2im), 159.3 (s, C-7naph), 154.5 (s,
C-2ph, C-6ph, C-2naph),* 137.6 [d, =CH(CH2)3OC-7naph], 137.0 [d,
=CH(CH2)3OC-2naph], 136.9 [d, =CH(CH2)3OC-2ph, =CH(CH2)3-
OC-6ph], 133.7 (s, C-8anaph), 132.8 (d, C-5naph), 131.6 (d, C-4ph),
130.6 (d, C-4naph), 124.5 (s, C-4anaph), 116.7 (d, C-6naph), 115.8 [t,
3
3
6
naph-H), 6.71 (t, J = 8.2 Hz, 1 H, 4ph-H), 6.53 (d, J = 8.2 Hz, 2
H, 3ph-H, 5ph-H), 5.89–5.76 [m, 2 H, 2naph-O(CH2)3CH, 7naph-O-
3
3
3
(CH2)3CH], 5.73 [ddt, JZ = 17.0 Hz, JE = 10.3 Hz, J = 6.8 Hz,
2 H, 2ph-O(CH2)3CH, 6ph-O(CH2)3CH], 5.08–4.93 [m, 4 H, 2naph
-
CH2CH(CH2)3OC-2ph
,
CH2CH(CH2)3OC-6ph],
115.8
[t,
O(CH2)3CHCH2, 7naph-O(CH2)3CHCH2], 4.90 [mc, 4 H, 2ph
-
CH2CH(CH2)3OC-2naph], 115.4 [t, CH2CH(CH2)3OC-7naph], 112.6
(s, C-1naph), 112.2 (s, C-1ph), 110.6 (d, C-3naph), 105.3 (d, C-3ph, C-
3
O(CH2)3CHCH2, 6ph-O(CH2)3CHCH2], 4.08 (t, J = 6.5 Hz, 2 H,
2naph-OCH2), 3.98 (t, 3J = 6.4 Hz, 4 H, 2ph-OCH2, 6ph-OCH2), 3.92
5
ph), 102.0 (d, C-8naph), 72.1 (s, C-4im), 68.9 (t, CH2OC-2naph), 68.5
(t, CH2OC-2ph, CH2OC-6ph), 67.5 (t, CH2OC-7naph), 63.6 (t, C-
5im), 30.1 [t, CH2(CH2)2OC-7naph], 30.0 [t, CH2(CH2)2OC-2ph
CH2(CH2)2OC-6ph], 30.0 [t, CH2(CH2)2OC-2naph], 28.4 (t,
CH2CH2OC-7naph), 28.3 (t, CH2CH2OC-2naph, CH2CH2OC-2ph
CH2CH2OC-6ph),* 27.3 (q, CH3), 25.9 (q, CH3) ppm; *signals
3
3
(t, J = 6.4 Hz, 2 H, 7naph-OCH2), 3.45 (s, 2 H, NCH2), 2.27 [q, J
3
= 7.1 Hz, 2 H, 2naph-O(CH2)2CH2], 2.19 [q, J = 7.2 Hz, 4 H, 2ph
O(CH2)2CH2, 6ph-O(CH2)2CH2], 2.08 [q, J = 7.2 Hz, 2 H, 7naph
O(CH2)2CH2], 1.84 (quint., J = 6.9 Hz, 4 H, 2ph-OCH2CH2, 6ph
OCH2CH2), 1.94 (quint., J = 6.9 Hz, 2 H, 2naph-OCH2CH2), 1.73
(quint., 3J = 6.9 Hz, 2 H, 7naph-OCH2CH2), 1.16 (s, 6 H, CH3)
ppm; no NH signals observed. 13C NMR (125 MHz, CDCl3,
300 K): δ = 157.3 (s, C-7naph), 152.0 (s, C-2naph), 150.1 (s, C-2ph),
-
-
-
,
3
3
,
3
overlaid respectively. IR (ATR): ν = 3077 (=C–H), 2977, 2938,
˜
2873, 2841 (aliph. C–H), 1625, 1599 (arom. C=C), 1259, 1217 (=C–
O), 1096, 1060 (O–CH2), 990, 906 (alkenyl = C–H), 830 (1,2,7-
trisubst. naph C–H), 779 (1,2,3-trisubst. ph C–H) cm–1. MS (ESI,
CHCl3/MeOH): m/z (%) = 637 (100) [M – Cl]+. C41H53ClN2O4
138.5 [d, =CH(CH2)3OC-7naph], 138.2 [d, =CH(CH2)3OC-2ph
,
=CH(CH2)3OC-6ph], 138.1 [d, =CH(CH2)3OC-2naph], 135.2 (s, C-
8anaph), 129.6 (s, C-1ph), 129.3 (d, C-4naph), 128.9 (s, C-1naph), 125.3
(s, C-4anaph), 124.6 (d, C-5naph), 118.8 (d, C-4ph), 117.2 (d, C-6naph),
(673.32): calcd.
C 73.14, H 7.93, N 4.16; C41H53ClN2O4·
0.5CH3OH: calcd. C 72.31, H 8.04, N 4.06; found C 72.07, H 8.31,
N 4.40.
115.6 [t, CH2CH(CH2)3OC-2naph], 115.4 [t, CH2CH(CH2)3OC-2ph
,
CH2CH(CH2)3OC-6ph], 115.1 [t, CH2CH(CH2)3OC-7naph], 111.2
(d, C-3naph), 106.4 (d, C-3ph, C-5ph), 104.2 (d, C-8naph), 68.4 (t,
CH2OC-2naph, CH2OC-2ph, CH2OC-6ph)*, 67.4 (t, CH2OC-7naph),
58.6 [s, C(CH3)2], 58.3 (t, NCH2), 30.7 [t, CH2(CH2)2OC-2naph],
30.6 [t, CH2(CH2)2OC-2ph, CH2(CH2)2OC-6ph], 30.5 [t, CH2(CH2)2-
2,11,13,22-Tetraoxa-1(1,3,2)-benzena-12(2,7,1)-naphthalena-
23(1,3)-4,4-dimethylimidazoliuminabicyclo[10.10.1]tricosaphane-
6,17-diene Chloride (18): Tetraene 17 (433 mg, 643 μmol) and
benzylidenebis(tricyclohexylphosphane)dichlororuthenium
(52.9 mg, 64.3 μmol) were dissolved in dry dichloromethane
(500 mL), and the mixture was stirred for 24 h at room tempera-
ture. Then, ethyl vinyl ether (1 mL) was added, and the mixture
was stirred for 1 h. After evaporation of the solvent, the product
was purified twice by column chromatography [silica gel, dichloro-
methane/methanol (10:1), Rf = 0.42]. A white solid (350 mg,
567 μmol, 88%) was obtained. M.p. 147–150 °C. 1H NMR
(500 MHz, CDCl3, 300 K): δ = 8.22 (s, 0.2 H, 2-Him), 8.11 (s, 0.7
H, 2-Him), 8.02 (s, 0.1 H, 2-Him), 7.94 (d, 3J = 9.1 Hz, 1 H, 4-
Hnaph), 7.79 (d, 3J = 9.7 Hz, 1 H, 5-Hnaph), 7.36 (t, 3J = 8.5 Hz, 0.2
OC-7naph], 29.2 (t, CH2CH2OC-2naph), 29.1 (t, CH2CH2OC-2ph
,
CH2CH2OC-6ph), 28.9 (t, CH2CH2OC-7naph), 27.1 (q, CH3) ppm;
*signals overlaid. IR (ATR): ν = 3356 (N–H), 3076 (=C–H), 2937,
˜
2870 (aliph. C–H), 1627, 1597 (arom. C=C), 1255, 1214 (=C–O),
1095, 1055 (O–CH2), 991, 909 (alkenyl = C–H), 824 (1,2,7-trisubst.
naph C–H) cm–1. MS (ESI, CHCl3/MeOH): m/z (%) = 627 (100)
[M + H]+, 316 (35) [C20H30NO2]+. C40H54N2O4 (626.41): calcd. C
76.64, H 8.68, N 4.47. C40H54N2O4·0.25H2O: calcd. C 76.09, H
8.70, N 4.44; found C 76.05, H 8.56, N 4.63.
3-[2,7-Bis(pent-4-enyloxy)naphthyl]-1-[2,6-bis(pent-4-enyloxy)-
phenyl]-4,4-dimethyl-4,5-imidazolinium Chloride (17): To a solution
of diamine 16 (618 mg, 986 μmol) in dry dichloromethane (5 mL)
was added HCl (4 m in 1,4-dioxane, 1 mL). After stirring for
10 min, the solvent was evaporated. The residue was dissolved in
3
3
H, 4-Hph), 7.35 (t, J = 8.5 Hz, 0.1 H, 4-Hph), 7.34 (t, J = 8.5 Hz,
3
3
0.7 H, 4-Hph), 7.25 (d, J = 9.1 Hz, 0.2 H, 3-Hnaph), 7.24 (d, J =
9.1 Hz, 0.7 H, 3-Hnaph), 7.21 (d, 3J = 9.1 Hz, 0.1 H, 3-Hnaph), 7.14–
4
7.09 (m, 1.8 H, 6-Hnaph, 8-Hnaph), 7.05 (d, J = 2.4 Hz, 0.2 H, 8-
Eur. J. Org. Chem. 2011, 1040–1046
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
1045

T. Reimers, C. Näther, U. Lüning
FULL PAPER
Hnaph), 6.71–6.63 (m, 2 H, 3-Hph, 5-Hph), 5.7–5.4 (m, 4 H,
refinement was done using SHELXL-97. 488 parameters, R1 for all
2
CH=CH2), 4.76 (d, J = 11.6 Hz, 0.7 H, 5-Him,a), 4.4–3.9 (m, 9.3 reflections with IϾ2σ(I) = 0.0592, wR2 for all independent reflec-
H, 5-Him,b, OCH2), 2.6–1.7 (m, 22 H, CH3, OCH2CH2, CH2CH=) tions = 0.1867, largest diff. peak and hole 0.430 and –0.295 eÅ–3.
ppm. 13C NMR (125 MHz, CDCl3, 300 K): δ = 161.6 (s), 160.4 (s),
159.4 (s), 159.3 (s), 155.1 (s), 155.0 (s), 154.9 (s), 154.7 (s), 154.2
(s), 133.9 (s), 133.8 (s), 132.8 (d), 131.7 (s), 131.6 (d), 130.6 (d),
130.54 (d), 130.50 (d), 130.0 (d), 129.89 (d), 129.88 (d), 129.5 (d),
129.4 (d), 129.1 (d), 124.6 (s), 124.5 (s), 117.5 (d), 117.3 (d), 112.9
(s), 112.6 (s), 112.5 (s), 112.4 (s), 110.6 (d), 105.5 (d), 105.3 (d),
105.2 (d), 105.0 (d), 101.8 (d), 101.6 (d), 77.3 (d), 72.2 (s), 72.0 (s),
69.7 (t), 69.5 (t), 68.7 (t), 67.3 (s), 67.2 (t), 66.61 (t), 66.57 (t), 63.9
(t), 29.9 (t), 29.8 (t), 29.7 (t), 29.3 (t), 28.7 (d), 28.4 (t), 28.1 (t),
27.8 (t), 27.6 (t), 26.2 (d), 25.8 (d), 24.6 (t), 24.3 (s), 23.7 (s), 23.3
The chloroform molecule is disordered and was refined using a
split model.
CCDC-794911 (for 19) contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
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(t), 23.1 (t), 23.0 (t) ppm. IR (ATR): ν = 2936, 2879 (aliph. C–H),
˜
1615 (arom. C=C), 1256, 1221 (=C–O), 1096, 1065 (O–CH2), 832,
777, 741 (=C–H) cm–1. MS (ESI, CHCl3/MeOH): m/z (%) = 581
(100) [M – Cl]+. C37H45ClN2O4 (617.22): calcd. C 73.14, H 7.93,
N 4.16; C37H49ClN2O4·0.75CHCl3: calcd. C 64.15, H 6.52, N 3.96;
found C 64.48, H 6.77, N 4.22.
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2,11,13,22-Tetraoxa-1(1,3,2)-benzena-12(2,7,1)-naphthalena-
23(1,3)-4,4-dimethylimidazoliuminabicyclo[10.10.1]tricosaphane
Chloride (19): Diene 18 (370 mg, 600 μmol) and palladium (10%
on charcoal, 31.9 mg, 30 μmol) were dissolved in methanol
(30.0 mL), and the mixture was stirred under an atmosphere of
hydrogen at room temperature for 24 h. The mixture was filtered
through Celite, and after evaporation of the solvent, the product
was purified by column chromatography [silica gel, dichlorometh-
ane/methanol (10:1), Rf = 0.38]. A white solid (323 mg, 520 μmol,
87%) was obtained. M.p. 156–158 °C. 1H NMR (500 MHz, CDCl3,
300 K): δ = 8.09 (s, 1 H, 2-Him), 7.97 (d, 3J = 9.1 Hz, 1 H, H-4naph),
7.86 (d, 3J = 9.0 Hz, 1 H, H-5naph), 7.37 (t, 3J = 8.5 Hz, 1 H, 4-
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3
3
4
H
ph), 7.27 (d, J = 9.1 Hz, 1 H, 3-Hnaph), 7.20 (dd, J = 9.1 Hz, J
4
= 2.3 Hz, 1 H, 6-Hnaph), 7.16 (d, J = 2.3 Hz, 1 H, 8-Hnaph), 6.68
3
2
(d, J = 8.5 Hz, 2 H, 3-Hph, 5-Hph), 4.63 (d, J = 11.4 Hz, 1 H, 5-
Him,a), 4.28–4.00 (m, 9 H, 5-Him,b, OCH2), 2.0–1.4 [m, 30 H, CH3,
OCH2(CH2)6CH2O] ppm. 13C NMR (125 MHz, CDCl3, 300 K): δ
= 160.6 (s, C-2im), 159.2 (s, C-7naph), 155.18 (s, C-2naph)*, 155.15
(s, C-2ph)*, 154.6 (s, C-6ph)*, 133.9 (s, C-8anaph), 133.1 (d, C-4naph),
131.7 (d, C-4ph), 130.9 (d, C-5naph), 124.4 (s, C-4anaph), 114.2 (d,
C-6naph), 112.3 (s, C-1ph), 111.9 (s, C-1naph), 111.0 (d, C-3naph),
105.09 (d, C-3ph)*, 105.07 (d, C-5ph)*, 104.6 (d, C-8naph), 71.8 (s,
C-4im), 70.2 (t, OCH2), 70.0 (t, OCH2), 69.0 (t, OCH2), 68.7 (t,
OCH2), 63.8 (t, C-5im), 28.7 (t, CH2), 28.4 (t, CH2), 27.8 (q, CH3),
27.1 (t, CH2), 26.9 (t, CH2), 26.8 (t, CH2), 26.24 (t, CH2), 26.17 (t,
CH2), 26.14 (t, CH2), 25.9 (q, CH3), 24.7 (t, CH2), 24.4 (t, CH2),
24.3 (t, CH2) ppm; *assignments may be interchanged, respectively.
IR (ATR): ν = 2930, 2856 (aliph. C–H), 1616 (arom. C=C), 1257,
˜
[22] T. J. Seiders, D. W. Ward, R. H. Grubbs, Org. Lett. 2001, 3,
1221 (=C–O), 1093 (O–CH2), 832 (1,2,7-trisubst. naph. C–H), 773
(1,2,3-trisubst. phen. C–H) cm–1. MS (ESI, CHCl3/MeOH): m/z
(%) = 585 (100) [M – Cl]+. (C37H49ClN2O4) (621.25): calcd. C
71.53, H 7.95, N 4.51. C37H49ClN2O4·0.5CH3OH: calcd. C 70.68,
H 8.07, N 4.40; found C 70.70, H 8.14, N 4.40.
3225–3228.
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X-ray Structural Data: C37H49ClN2O4·CHCl3, formula weight
740.60 gmol–1, crystal size 0.4ϫ0.3ϫ0.3 mm, crystal system tri-
clinic, space group P1, unit cell dimensions: a = 9.7324(7) Å, b =
11.903(1) Å, c = 19.592(2) Å, α = 81.29(1)°, β = 80.67(1)°, γ =
84.77(1)°, V = 2208.6(3) Å3, Z = 2, Dcalcd. = 1.114 Mgm–3, absorp-
tion coefficient 0.303 mm–1, radiation: Mo-Kα (0.71073 Å), T =
200(2) K, 2θmax = 26.02°, 19062 reflections collected, 8320 indepen-
dent reflections and 5943 reflections with IϾ2σ(I). Rint = 0.0341,
structure solution was performed with SHELXS-97 and structure
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Bernardinelli, Org. Lett. 2000, 2, 4185–4188.
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4th ed., Wiley-VCH, Weinheim, 2006, pp. 317–321.
[29] M. Oki, Top. Stereochem. 1983, 14, 1–81.
Received: October 4, 2010
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Published Online: December 30, 2010
1046
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Eur. J. Org. Chem. 2011, 1040–1046