Concave imidazolinium salts as precursors to concave N-heterocyclic carbenes

Article abstract of DOI:10.1002/ejoc.200600843

Concave bimacrocyclic imidazolinium ions 8 have been synthesized as precursors for N-heterocyclic carbenes 9 (NHC) in 13 to 29 % overall yields based on 2-nitroresorcinol (1). As bridgeheads, 2,6-bis(ω-alkenyloxy) anilines 3 have been synthesized from 1.

Full text of DOI:10.1002/ejoc.200600843

FULL PAPER
DOI: 10.1002/ejoc.200600843
Concave Imidazolinium Salts as Precursors to Concave N-Heterocyclic
Carbenes[‡]
Ole Winkelmann,[a] Christian Näther,[b] and Ulrich Lüning*[a]
Keywords: Betaines / Carbenes / Heterocycles / Macrocycles / Supramolecular chemistry
Concave bimacrocyclic imidazolinium ions 8 have been syn-
thesized as precursors for N-heterocyclic carbenes 9 (NHC)
in 13 to 29% overall yields based on 2-nitroresorcinol (1).
As bridgeheads, 2,6-bis(ω-alkenyloxy)anilines 3 have been
synthesized from 1. Reaction of 3 with oxalyl chloride, re-
duction to respective diamines 5, and ring closure with tri-
ethyl orthoformate gave N,N-diaryl-substituted imidazolin-
ium ions 6. The terminal vinyl groups were connected by
ring-closing metathesis to give bimacrocyclic imidazolinium
ions 7, whose alkene functions were hydrogenated to give
saturated bimacrocyles 8. The structure of 8a was elucidated
by X-ray analysis. The respective NHC 9 was generated by
deprotonation with potassium tert-butoxide, and 9 was scav-
enged with CS2 to give adduct 10.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
Introduction
In 1958, Breslow[1] elucidated the nature of the “active
aldehyde” in thiamine-dependent biochemical transforma-
tions[2] and suggested nucleophilic catalysis. He postulated
that by deprotonation of thiamineЈs thiazolium unit in the
2-position, a betaine was formed which acted as the nucleo-
phile. Later, Wanzlick[3,4] and Arduengo[5] synthesized nu-
cleophilic stable carbenes derived from imidazolinium or
imidazolium ions. Their activity in nucleophilic catalysis
was also shown and has been reviewed recently.[6,7] All reac-
tive species have in common that their nature can be de-
scribed by two mesomeric forms, a betaine, as published by
Breslow, or a carbene, as described by Wanzlick and
Arduengo. Triazols can also be used as precursors to nucleo-
philic catalysts.[7]
Figure 1. N-Heterocycles are the precursors for N-heterocyclic
carbenes (NHC) which are also drawn in their mesomeric betaine
form.[8] Examples: thiazolium: X = S, Y = Z = CRЈ, imidazolium:
X = NRЈЈ, Y = Z = CRЈ, imidazolinium: X = NRЈЈ, Y = Z =
CRЈ2, triazolium: X = NRЈЈ, Y = N, Z = CRЈ.
In enzymes, the thiamine unit is embedded into the cavity
of an enzyme. This geometry is responsible for the selectiv-
ity of the enzymatic reaction. In principle, an N-heterocy-
clic carbene (NHC), or its precursor, respectively, can also
be embedded in a suitable shielding which in return shall
be responsible for enhanced selectivities in the reactions cat-
alyzed by the NHC. By applying the concept of concave
reagents, we envisaged a bimacrocyclic NHC as depicted
in Figure 2 and developed a synthetic route to respective
substituted imidazolinium[22] ions.
Besides their catalytic power as nucleophilic organocata-
lysts,[6,9–18] the carbenes of Figure 1 may also be employed
as ligands for transition metal catalysis,[8,19,20] the 2nd gen-
eration of Grubbs’ catalyst being a prominent example.[21]
[‡] Concave Reagents 52. Part 51: Ref.[25]
[a] Otto-Diels-Institut für Organische Chemie, Christian-Al-
brechts-Universität zu Kiel,
Figure 2. Schematic representation of a bimacrocyclic concave N-
heterocyclic carbene which may be obtained from respective imid-
azolinium ions.
Olshausenstr. 40, 24098 Kiel, Germany
Fax: +49-431-880-1558
Several strategies are conceivable to construct a concave
bimacrocycle which contains an imidazolium or an imid-
azolinium moiety as a precursor for an N-heterocyclic car-
bene as shown in Figure 2. All strategies must provide (1)
access to the trisubstituted aryl bridgeheads, (2) a bimacro-
E-mail: luening@oc.uni-kiel.de
[b] Institut für Anorganische Chemie der Christian-Albrechts-Uni-
versität zu Kiel,
Olshausenstr. 40, 24098 Kiel, Germany
Fax: +49-431-880-1520
E-mail: cnaether@ac.uni-kiel.de
Eur. J. Org. Chem. 2007, 981–987
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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O. Winkelmann, C. Näther, U. Lüning
FULL PAPER
cyclization strategy, and (3) a suitable synthesis of the het- with (E) and (Z) configurations. To simplify the products,
erocycle. We have selected ruthenium catalyzed metathesis the double bonds were subsequently hydrogenated in 91%
for the ring closure to provide the bimacrocycle because and 88% yield, respectively. Bimacrocyclic concave imid-
such bimacrocyclizations have proven to be very successful azolinium salts 8 were characterized, and the structure of
for the synthesis of a number of concave reagents.[23–25] 8a was proven by X-ray analysis.
Thus a precursor is demanded which contains the aryl
bridgeheads and the heterocycle. Prominent strategies[26–29]
for the synthesis of imidazolium and imidazolinium ions
start from anilines which are condensed with a C2 and a C1
unit ending up in the heterocycle as carbon atoms 4 and 5,
and carbon atom 2, respectively.
Thus, the first task was to synthesize respective bis-ortho-
substituted anilines 3. In a two-step reaction, 3a and 3b can
be obtained from commercially available 2-nitroresorcinol
(1) in 67% and 47% overall yield, respectively. The reaction
sequence first uses the Mitsunobu coupling of the phenol
OH groups of 1 with the respective ω-alkenols. Resulting
nitroarenes 2 can then be reduced to anilines 3 by tin(II)
chloride.
Figure 3 shows that the imidazolinium ion of 8a adopts
a C2 symmetrical structure in the solid state. This contrasts
the data in solution. As apparent in the time-averaged
NMR spectra, the cation of 8a possesses two mirror planes:
one mirror plane is identical with the averaged plane of the
imidazolinium heterocycle, the other mirror plane is orthog-
onal to it cutting the first plane through C1 and in the mid-
dle of the bond between C2 and C2A (for numbering see
Figure 3). In the crystal structure, however, the ion is dis-
torted: (1) the imidazolinium ring is not planar, (2) the twist
angles between the aryl bridgeheads and the plane through
N1–C1–N1A are not 90° as expected from NMR but 54°.
Similar twists between aromatic rings and the heterocycles
of imidazolium or imidazolinium ions or even NHCs de-
rived therefrom have been observed frequently.[30–32] In 8a,
the torque is rather large. A view of the whole structure,
including counterion and solvent molecules, shows that the
chloroform molecules fit nicely into the octamethylene
chains only with the existing twist. This complementarity
is probably responsible for the unusual torque between the
heterocycle and the aryl rings.
Next, 2 equiv. of anilines 3 were connected by oxalyl
chloride to give diamides 4a and 4b in 87% and 52% yield,
respectively. Reduction with lithium aluminium hydride af-
forded diamines 5a and 5b in 80% and 90% yield, respec-
tively. In the final step towards imidazolinium ions 6, the
nitrogen atoms of 5 were connected with triethyl orthofor-
mate. Resulting salts 6a and 6b were isolated in 83% and
73% yield, respectively.
Finally, imidazolinium salt 8a was treated with potas-
sium tert-butoxide in THF to generate N-heterocyclic
carbene 9. As proof of its existence, the reaction mixture
was treated with carbon disulfide and adduct 10 was iso-
lated. The 13C-NMR signals for C-2 and CS2 appear at δ =
166.0 and 221.3 ppm, respectively. The composition
(C32H42N2O4S2) was determined from an ESI mass spec-
trum (deviation from calculated values 0.2 to 1.5 ppm, see
Experimental Section). According to 1H NMR spectro-
scopic analysis, the product contained approximately
0.5 equiv. of THF.
In imidazolinium ions 6, two functionalized aryl bridge-
heads are now bound to the central heterocycle. With the
use of the well-established reaction conditions for macro-
cyclizations of concave reagents by ring-closing metathe-
Conclusions
Two concave imidazolinium salts, 8a and 8b, have been
sis,[23–25] the ω-alkene units were now connected by adding synthesized in seven steps starting from 2-nitroresorcinol in
Grubbs’ catalyst. In 81% and 92% yield, respectively, bi- 29% and 13% (nonoptimized) overall yield. By deproton-
macrocycles 7a and 7b could be isolated. As with other re- ation, the respective N-heterocyclic carbenes can be gener-
lated macrocycles,[23–25] the new double bonds are formed ated, which was proven for 9 by scavenging it with CS2.
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Eur. J. Org. Chem. 2007, 981–987

Imidazolinium Salts as Precursors to N-Heterocyclic Carbenes
FULL PAPER
Because of concave shielding, these modified NHCs should
be able to enhance selectivities in reactions that are cata-
lyzed by NHCs as organocatalysts, but also in metal-cata-
lyzed reactions in which NHCs can be used as ligands. With
8a and 8b, chemo-, regio-, and diastereoselectivity can be
expected. In order to tackle enantioselectivity, the synthesis
of chiral concave NHCs is underway.
Experimental Section
General Remarks: The following chemicals were obtained commer-
cially and used without further purification: benzylidenebis(tricy-
clohexylphosphane)dichlororuthenium (Aldrich), carbon disulfide
(Fluka), diisopropylazodicarboxylate (Fluka), 5-hexen-1-ol
(Merck), lithium aluminium hydride (Merck), 2-nitroresorcinol
(Alfa Aesar), oxalyl chloride (Fluka), palladium/charcoal (10% Pd)
(Merck), 4-penten-1-ol (Alfa Aesar), potassium tert-butoxide
(Acros), stannous chloride dihydrate (Fluka), triethyl orthoformate
(Merck), triphenylphosphane (Fluka). Tetrahydrofuran was dried
by heating at reflux with lithium aluminium hydride. Dichloro-
methane was dried by heating at reflux with calcium hydride. All
syntheses except hydrogenations were carried out under an atmo-
sphere of dry nitrogen. Column chromatography was carried out
with silica gel (Macherey–Nagel) or neutral alumina (Macherey–
1
Nagel, activity I). H- and 13C-NMR spectra were recorded with a
Bruker ARX 300, DRX 500, or AV 600 instrument. IR spectra
were recorded with a Perkin–Elmer Paragon 1000. Mass spectra
were recorded with a Finnigan MAT 8200 or MAT 8230. ESI mass
spectra were recorded with an Applied Biosystems Mariner Spec-
trometry Workstation. Elemental analyses were carried out with an
EuroEA 3000 Elemental Analyzer from Euro Vector or VarioEL
from Elementaranalysensysteme. As alternative proof of composi-
tion, high resolution mass spectra were recorded for samples which
were pure according to NMR spectra.
General Procedure A – Synthesis of Nitrobenzenes 2: 2-Nitroresor-
cinol (1, 1 equiv.), the respective alkenol (3 equiv.), and tri-
phenylphosphane (2 equiv.) were dissolved in tetrahydrofuran. At
0 °C, diisopropylazodicarboxylate (3 equiv.) was slowly added, and
the mixture was stirred at room temp. for 20 h. Sodium hydroxide
solution (0.5 ) was added, the layers were separated, and the aque-
ous layer was extracted with diethyl ether. The organic layer was
dried with magnesium sulfate and concentrated, keeping the tri-
phenylphosphane oxide in solution. The product was purified by
column chromatography on silica gel.
General Procedure B – Synthesis of Anilines 3: Nitrobenzene 2 was
heated at reflux in ethanol with stannous chloride dihydrate
(7 equiv.) for 3 h. After cooling to room temp., the mixture was
poured into ice water and potassium hydroxide was added. After
extraction with dichloromethane, the organic layer was dried with
magnesium sulfate and the solvents evaporated to dryness. The
product was purified by column chromatography on silica gel.
Figure 3. Crystal structure of 8a. Top: View into the cavity from
below showing the bimacrocyclic structure of the cation. The chlo-
ride counterion is omitted. Middle: View of the cation along an axis
bridgehead 1–imidazolinium unit–bridgehead 2. The C2 symmetry
and the 54° twist of the aryl rings with respect to the N1–C1–N1A
plane are clearly visible. The position of the chloride counterion
next to C1 becomes visible. Bottom: view of the imidazolinium ion
along an axis through the middle of the C2–C2A bond and atom
C1. This structure also shows the positions of two additional chlo-
roform molecules. They are in contact with the chloride counterion
which obscures C1. Again the C2 symmetry and the twist within
the molecule can clearly be detected.
General Procedure C – Synthesis of Oxalamides 4: Aniline 3 was
dissolved in tetrahydrofuran and cooled to 0 °C. Oxalyl chloride
(0.5 equiv.) was slowly added, the mixture was warmed to room
temp., and stirred for 1 h. After addition of water, the layers were
separated, and the aqueous layer was extracted with dichlorometh-
ane. The organic layer was dried with magnesium sulfate, and the
solvents evaporated to dryness. The product was purified by col-
umn chromatography on silica gel.
General Procedure D – Synthesis of Ethane-1,2-diamines 5: Oxal-
amide 4 was dissolved in tetrahydrofuran and added slowly to a
Eur. J. Org. Chem. 2007, 981–987
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O. Winkelmann, C. Näther, U. Lüning
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suspension of lithium aluminium hydride (10 equiv.) in tetra-
hydrofuran at 0 °C. The mixture was then heated at reflux for 5 h.
After cooling to 0 °C, water was added, the layers were separated,
and the aqueous layer was extracted with diethyl ether. The organic
layer was dried with magnesium sulfate, and the solvents evapo-
rated to dryness. The product was purified by column chromatog-
raphy on alumina.
1466, 1375, 1262, 1105, 994, 912, 852, 778, 733 cm–1. MS (EI,
70 eV): m/z (%) = 319 (1) [M]+, 273 (67), 155 (39), 137 (52), 109
(53), 81 (100), 67 (81). MS (CI): m/z (%) = 320 (4) [M + H]+.
2,6-Bis(pent-4-enyloxy)aniline (3a): General procedure B: 2-Nitro-
1,3-bis(pent-4-enyloxy)benzene (2a, 4.42 g, 15.2 mmol), stannous
chloride dihydrate (23.9 g, 106 mmol) in ethanol (60 mL). Work up:
Potassium hydroxide (100 g), extraction with dichloromethane
(2ϫ200 mL). Column chromatography [silica gel, cyclohexane/
ethyl acetate (10:1), Rf = 0.43] yielded crystalline colorless product
3a (3.25 g, 82%). M.p. 34 °C. 1H NMR (500 MHz, CDCl3, 25 °C):
General Procedure E – Synthesis of Imidazolinium Chlorides 6: Eth-
ane-1,2-diamine 5 was heated to 110 °C with ammonium chloride
(1.2 equiv.) in triethyl orthoformate (10 equiv.) for 3 h under a ni-
trogen flow to remove ethanol. After cooling to room temp., the
product was filtered off and purified by column chromatography
on silica gel.
3
3
δ = 6.64 (t, J = 8.2 Hz, 1 H, 4-H), 6.51 (d, J = 8.2 Hz, 2 H, 3-H,
5-H), 5.87 (ddt, 3J = 17.1 Hz, 3J = 10.2 Hz, 3J = 6.6 Hz, 2 H,
=CH), 5.08 (ddt, 3J = 17.1 Hz, 2J = 1.9 Hz, 4J = 1.6 Hz, 2 H,
3
2
4
HZHC=), 5.01 (ddt, J = 10.2 Hz, J = 1.9 Hz, J = 1.2 Hz, 2 H,
HEHC=), 4.02 (t, 3J = 6.4 Hz, 4 H, OCH2), 3.84 (br. s, 2 H, NH2),
2.26 (mc, 4 H, =CHCH2), 1.92 (mc, 4 H, OCH2CH2) ppm. 13C
NMR (125 MHz, CDCl3, 25 °C): δ = 146.9 (C-2,6), 137.9 (=CH),
125.9 (C-1), 116.8 (C-4), 115.1 (H2C=), 105.1 (C-3,5), 67.8 (OCH2),
General Procedure F – Synthesis of Imidazoliniumabicyclophan
Chlorides 7: Imidazolinium chloride 6 was stirred with benzyliden-
bis(tricyclohexylphosphane)dichlororuthenium
(10 mol-%)
in
dichloromethane at room temp. for 24 h. After evaporation to dry-
ness, the product was purified by column chromatography on silica
gel.
30.3 (=CHCH ), 28.6 (OCH CH ) ppm. IR (KBr): ν = 3461, 3371,
˜
2
2
2
3073, 2951, 2872, 1640, 1609, 1507, 1469, 1397, 1294, 1269, 1181,
1140, 1060, 999, 913, 757, 714 cm–1. MS (EI, 70 eV): m/z (%) = 261
(100) [M]+, 193 (25), 125 (84), 69 (31). MS (CI): m/z (%) = 262 (14)
[M + H]+. C16H23NO2 (261.36): calcd. C 73.53, H 8.87, N 5.36;
found C 73.48, H 9.00, N 5.46.
General Procedure G – Synthesis of Imidazoliniumabicyclophan
Chlorides 8: Imidazolinium chloride 7 was stirred with palladium/
charcoal (10% Pd) in methanol under an atmosphere of hydrogen
at room temp. for 24 h. After filtration and evaporation to dryness,
the product was purified by column chromatography on silica gel.
2,6-Bis(hex-5-enyloxy)aniline (3b): General procedure B: 1,3-Bis-
(hex-5-enyloxy)-2-nitrobenzene (2b, 2.50 g, 7.84 mmol), stannous
chloride dihydrate (14 g, 63 mmol) in ethanol (30 mL). Work up:
Potassium hydroxide (50 g), extraction with dichloromethane
(3ϫ100 mL). Column chromatography [silica gel, cyclohexane/
ethyl acetate (20:1), Rf = 0.18] yielded oily colorless product 3b
2-Nitro-1,3-bis(pent-4-enyloxy)benzene (2a): General procedure A:
2-Nitroresorcinol (1, 3.00 g, 19.4 mmol), 4-penten-1-ol (5.00 g,
58.0 mmol), triphenylphosphane (10.2 g, 38.8 mmol), DIAD
(11 mL, 58 mmol) in tetrahydrofuran (100 mL). Work up: Sodium
hydroxide solution (0.5 , 75 mL), extraction with diethyl ether
(2ϫ100 mL). Column chromatography [silica gel, cyclohexane/
ethyl acetate (7:1), Rf = 0.36] yielded oily colorless product 2a
(4.70 g, 82%). H NMR (600 MHz, CDCl3, 25 °C): δ = 7.27 (t, J
= 8.5 Hz, 1 H, 5-H), 6.58 (d, 3J = 8.6 Hz, 2 H, 4-H, 6-H), 5.80
(ddt, 3J = 17.0 Hz, 3J = 10.3 Hz, 3J = 6.7 Hz, 2 H, =CH), 5.05
1
3
(1.37 g, 60%). H NMR (500 MHz, CDCl3, 25 °C): δ = 6.63 (t, J
= 8.2 Hz, 1 H, 4-H), 6.49 (d, 3J = 8.2 Hz, 2 H, 3-H, 5-H), 5.82
(ddt, 3J = 17.0 Hz, 3J = 10.2 Hz, 3J = 6.7 Hz, 2 H, =CH), 5.03
1
3
3
2
4
(ddt, J = 17.1 Hz, J = 2.0 Hz, J = 1.6 Hz, 2 H, HZHC=), 4.97
3
2
4
3
2
4
(ddt, J = 10.2 Hz, J = 2.0 Hz, J = 1.2 Hz, 2 H, HEHC=), 3.99
(ddt, J = 17.1 Hz, J = 1.8 Hz, J = 1.6 Hz, 2 H, HZHC=), 4.99
3
3
2
4
(t, J = 6.5 Hz, 4 H, OCH2), 3.81 (br. s, 2 H, NH2) 2.13 (mc, 4 H,
(ddt, J = 10.2 Hz, J = 1.9 Hz, J = 1.2 Hz, 2 H, HEHC=), 4.04
(t, 3J = 6.4 Hz, 4 H, OCH2), 2.19 (mc, 4 H, =CHCH2), 1.86 (mc, 4
H, OCH2CH2) ppm. 13C NMR (150 MHz, CDCl3, 25 °C): δ =
151.2 (C-1,3), 137.4 (=CH), 132.5 (C-2), 130.9 (C-5), 115.5 (H2C=),
105.2 (C-4,6), 68.5 (OCH2), 29.8 (=CHCH2), 27.9 (OCH2CH2)
=CHCH2), 1.82 (mc,
4 H, OCH2CH2), 1.58 (mc, 4 H,
OCH2CH2CH2) ppm. 13C NMR (125 MHz, CDCl3, 25 °C): δ =
146.9 (C-2,6), 138.5 (=CH), 125.8 (C-1), 116.8 (C-4), 114.7 (H2C=),
105.0 (C-3,5), 69.3 (OCH2), 33.4 (=CHCH2), 28.9 (OCH2CH2),
25.4 (OCH CH CH ) ppm. IR (KBr): ν = 3482, 3386, 3076, 2938,
˜
2
2
2
ppm. IR (KBr): ν = 3078, 2945, 1641, 1611, 1586, 1536, 1483, 1466,
˜
1375, 1263, 1105, 995, 916, 851, 778, 733 cm–1. MS (EI, 70 eV): m/z
(%) = 245 (70), 203 (8), 189 (7), 177 (15), 155 (15), 137 (36), 109
(44), 69 (100). MS (CI): m/z (%) = 292 (9) [M + H]+.
2869, 1640, 1607, 1566, 1504, 1469, 1390, 1293, 1180, 1145, 1073,
995, 910, 759, 713 cm–1. MS (EI, 70 eV): m/z (%) = 289 (80) [M]+,
207 (17), 125 (100). MS (CI): m/z (%) = 290 (100) [M + H]+.
HRMS: calcd. for C18H27NO2 289.20419; found 289.20416
(0.1 ppm); calcd. for C1713CH27NO2 290.20752; found 290.20752
(0 ppm).
1,3-Bis(hex-5-enyloxy)-2-nitrobenzene (2b): General procedure A: 2-
Nitroresorcinol (1, 4.00 g, 25.8 mmol), 5-hexen-1-ol (7.7 g,
77 mmol), triphenylphosphane (13.5 g, 51.6 mmol), DIAD (15 mL,
77 mmol) in tetrahydrofuran (100 mL). Work up: Sodium hydrox-
ide solution (0.5 , 100 mL), extraction with diethyl ether
(2ϫ100 mL). Column chromatography [silica gel, cyclohexane/
N,NЈ-Bis[2,6-bis(pent-4-enyloxy)phenyl]oxaldiamide (4a): General
procedure
C:
2,6-Bis(pent-4-enyloxy)aniline
(3a,
2.33 g,
8.90 mmol), oxalyl chloride (0.36 mL, 4.3 mmol) in tetrahydrofuran
ethyl acetate (7:1), Rf = 0.44] yielded oily colorless product 2b (10 mL). Work up: Water (8 mL), extraction with dichloromethane
1
3
(6.37 g, 78%). H NMR (300 MHz, CDCl3, 25 °C): δ = 7.26 (t, J (3ϫ30 mL). Column chromatography [silica gel, cyclohexane/ethyl
= 8.5 Hz, 1 H, 5-H), 6.58 (d, 3J = 8.5 Hz, 2 H, 4-H, 6-H), 5.80 acetate (3:1), Rf = 0.49] yielded colorless crystalline product 4a
(ddt, 3J = 17.0 Hz, 3J = 10.2 Hz, 3J = 6.7 Hz, 2 H, =CH), 5.02
(2.15 g, 87%). M.p. 111 °C. 1H NMR (600 MHz, CDCl3, 25 °C): δ
3
2
4
3
3
(ddt, J = 17.1 Hz, J = 2.0 Hz, J = 1.6 Hz, 2 H, HZHC=), 4.96
= 8.75 (s, 2 H, NH), 7.17 (t, J = 8.4 Hz, 2 H, 4-H), 6.58 (d, J =
3
2
4
3
3
3
(ddt, J = 10.1 Hz, J = 2.1 Hz, J = 1.2 Hz, 2 H, HEHC=), 4.04
8.5 Hz, 4 H, 3-H, 5-H), 5.82 (ddt, J = 17.0 Hz, J = 10.3 Hz, J
(t, 3J = 6.4 Hz, 4 H, OCH2), 2.09 (mc, 4 H, =CHCH2), 1.77 (mc, 4 = 6.7 Hz, 4 H, =CH), 5.04 (ddt, 3J = 17.1 Hz, J = 1.9 Hz, J =
2
4
H, OCH2CH2), 1.52 (mc, 4 H, OCH2CH2CH2) ppm. 13C NMR 1.6 Hz, 4 H, HZHC=), 5.01 (ddt, J = 10.3 Hz, J = 1.9 Hz, J =
3
2
4
3
(75 MHz, CDCl3, 25 °C): δ = 151.3 (C-1,3), 138.3 (=CH), 130.8 1.1 Hz, 4 H, HEHC=), 4.01 (t, J = 6.5 Hz, 8 H, OCH2), 2.21 (mc,
(C-5), 114.9 (H2C=), 105.2 (C-4,6), 69.3 (OCH2), 33.2 (=CHCH2),
28.3 (OCH2CH2), 25.0 (OCH2CH2CH2) ppm. C-2 was not ob- (150 MHz, CDCl3, 25 °C): δ = 157.8 (C=O), 154.5 (C-2,6), 137.8
served. IR (KBr): ν = 3077, 2942, 1640, 1612, 1586, 1537, 1483, (=CH), 127.9 (C-4), 115.2 (H2C=), 113.2 (C-1), 105.1 (C-3,5), 67.9
8 H, =CHCH2), 1.87 (mc, 8 H, OCH2CH2) ppm. 13C NMR
˜
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Eur. J. Org. Chem. 2007, 981–987

Imidazolinium Salts as Precursors to N-Heterocyclic Carbenes
(OCH ), 30.0 (=CHCH ), 28.3 (OCH CH ) ppm. IR (KBr): ν =
3273, 3073, 2944, 2864, 1680, 1639, 1600, 1513, 1450, 1393, 1261,
1106, 910, 802, 758, 715 cm–1. MS (EI, 70 eV): m/z (%) = 576 (42)
[M]+, 491 (8), 261 (100). MS (CI): m/z (%) = 577 (100) [M + H]+.
HRMS: calcd. for C34H44N2O6 576.31995; found 576.32021
(0.5 ppm); calcd for C3313CH44N2O6 577.32330; found 577.32317
(0.2 ppm). C34H44N2O6 (576.73): calcd. C 70.81, H 7.69, N 4.86;
found C 70.81, H 7.84, N 4.98.
FULL PAPER
2 H, 4-H), 6.50 (d, 3J = 8.3 Hz, 4 H, 3-H, 5-H), 5.78 (ddt, 3J =
˜
2
2
2
2
16.9 Hz, 3J = 10.2 Hz, 3J = 6.7 Hz, 4 H, =CH), 5.00 (ddt, 3J =
2
4
3
17.1 Hz, J = 2.0 Hz, J = 1.6 Hz, 4 H, HZHC=), 4.94 (ddt, J =
2
4
10.2 Hz, J = 2.1 Hz, J = 1.2 Hz, 4 H, HEHC=), 4.23 (br. s, 2 H,
NH), 3.95 (t, J = 6.7 Hz, 8 H, OCH2), 3.34 (s, 4 H, NCH2), 2.08
(mc, 8 H, =CHCH2), 1.78 (mc, 8 H, OCH2CH2), 1.52 (mc, 8 H,
OCH2CH2CH2) ppm. 13C NMR (150 MHz, CDCl3, 25 °C): δ =
150.5 (C-2,6), 138.5 (=CH), 127.5 (C-1), 119.5 (C-4), 114.7 (H2C=),
105.5 (C-3,5), 68.5 (OCH2), 47.4 (NCH2), 33.4 (=CHCH2), 28.8
3
N,NЈ-Bis[2,6-bis(hex-5-enyloxy)phenyl]oxaldiamide (4b): General
procedure C: 2,6-Bis(hex-5-enyloxy)aniline (3b, 1.59 g, 5.51 mmol),
oxalyl chloride (0.23 mL, 2.7 mmol) in tetrahydrofuran (5 mL).
Work up: Water (6 mL), extraction with dichloromethane
(3ϫ20 mL). Column chromatography [silica gel, cyclohexane/ethyl
acetate (2:1), Rf = 0.69] yielded colorless crystalline product 4b
(891 mg, 52%). M.p. 97 °C. 1H NMR (500 MHz, CDCl3, 25 °C): δ
= 8.72 (s, 2 H, NH), 7.16 (t, J = 8.4 Hz, 2 H, 4-H), 6.58 (d, J =
8.4 Hz, 4 H, 3-H, 5-H), 5.79 (ddt, 3J = 17.0 Hz, 3J = 10.2, 3J =
6.6 Hz, 4 H, =CH), 5.00 (ddt, 3J = 17.1 Hz, 2J = 2.0 Hz, 4J =
(OCH CH ), 25.3 (OCH CH CH ) ppm. IR (KBr): ν = 3436, 3410,
˜
2
2
2
2
2
3074, 2924, 2855, 1641, 1602, 1502, 1446, 1393, 1292, 1234, 1213,
1174, 1104, 993, 908, 757, 738, 711 cm–1. MS (EI, 70 eV): m/z (%)
= 604 (30) [M]+, 303 (100).
1,3-Bis[2Ј,6Ј-bis(pent-4-enyloxy)phenyl]imidazolinium Chloride (6a):
General procedure E: N,NЈ-Bis[2,6-bis(pent-4-enyloxy)phenyl]eth-
ane-1,2-diamine (5a, 1.05 g, 1.91 mmol), ammonium chloride
(123 mg, 2.30 mmol) in triethyl orthoformate (30.0 mL, 180 mmol).
Column chromatography [silica gel, dichloromethane/methanol
(10:1), Rf = 0.17] yielded crystalline colorless product 6a (940 mg,
3
3
3
2
4
1.6 Hz, 4 H, HZHC=), 4.93 (ddt, J = 10.2 Hz, J = 2.0 Hz, J =
3
1
1.2 Hz, 4 H, HEHC=), 4.01 (t, J = 6.6 Hz, 8 H, OCH2), 2.09 (mc,
83%). M.p. 203 °C. H NMR (500 MHz, CDCl3, 25 °C): δ = 8.14
8 H, =CHCH2), 1.79 (mc, 8 H, OCH2CH2), 1.54 (mc, 8 H, (s, 1 H, 2-H), 7.37 (t, 3J = 8.6 Hz, 2 H, 4Ј-H), 6.68 (d, J = 8.6 Hz,
3
OCH2CH2CH2) ppm. 13C NMR (125 MHz, CDCl3, 25 °C): δ =
4 H, 3Ј-H, 5Ј-H), 5.80 (ddt, 3J = 17.0 Hz, 3J = 10.2 Hz, 3J = 6.6 Hz,
157.8 (C=O), 154.6 (C-2,6), 138.5 (=CH), 127.8 (C-4), 114.7 4 H, =CH), 5.03–4.97 (m, 8 H, H2C=), 4.59 (s, 4 H, 4-H, 5-H),
3
(H2C=), 113.5 (C-1), 105.2 (C-3,5), 68.5 (OCH2), 33.3 (=CHCH2),
4.10 (t, J = 6.7 Hz, 8 H, OCH2), 2.19 (mc, 8 H, =CHCH2), 1.93
28.6 (OCH CH ), 25.1 (OCH CH CH ) ppm. IR (KBr): ν = 3266, (mc, 8 H, OCH2CH2) ppm. 13C NMR (125 MHz, CDCl3, 25 °C):
˜
2
2
2
2
2
3076, 2944, 2866, 1679, 1641, 1607, 1590, 1513, 1454, 1394, 1262,
1107, 908, 798, 762, 709 cm–1. MS (EI, 70 eV): m/z (%) = 632 (38)
[M]+, 289 (100). HRMS: calcd. for C38H52N2O6 632.38251; found
632.38281 (0.5 ppm); calcd. for C3713CH52N2O6 633.38586; found
633.38604 (0.3 ppm). C38H52N2O6 (632.84): calcd. H 72.12, H 8.28,
N 4.43; found C 72.09, H 8.45, N 4.43.
δ = 160.4 (C-2), 154.3 (C-2Ј,6Ј), 136.9 (=CH), 131.3 (C-4Ј), 115.5
(H2C=), 112.2 (C-1Ј), 105.0 (C-3Ј,5Ј), 68.3 (OCH2), 51.3 (C-4,5),
29.7 (=CHCH ), 27.9 (OCH CH ) ppm. IR (KBr): ν = 3075, 2946,
˜
2
2
2
1618, 1481, 1462, 1392, 1256, 1107, 991, 907, 775, 731, 643 cm–1.
ESI-MS (MeOH): m/z (%) = 559.36 (100) [C35H47N2O4]+. HRMS:
calcd. for C35H47N2O4 559.35358; found 559.34896 (8.3 ppm);
calcd. for C3413CH47N2O4 560.35693; found 560.35345 (6.2 ppm).
C35H47ClN2O4 (595.22): calcd. C 70.63, H 7.96, N 4.71; found C
70.27, H 8.04, N 4.80.
N,NЈ-Bis[2,6-bis(pent-4-enyloxy)phenyl]ethane-1,2-diamine (5a):
General procedure D: N,NЈ-Bis[2,6-bis(pent-4-enyloxy)phenyl]oxal-
diamide (4a, 2.06 g, 3.56 mmol), lithium aluminium hydride
(1.33 g, 35.0 mmol) in tetrahydrofuran (100 mL). Work up: Water 1,3-Bis[2Ј,6Ј-bis(hex-5-enyloxy)phenyl]imidazolinium Chloride (6b):
(60 mL), extraction with diethyl ether (2 ϫ 100 mL). Column
chromatography [alumina, cyclohexane/ethyl acetate (3:1), Rf =
0.83] yielded crystalline colorless product 5a (1.57 g, 80%). M.p.
62 °C. 1H NMR (500 MHz, CDCl3, 25 °C): δ = 6.73 (t, 3J = 8.2 Hz,
2 H, 4-H), 6.50 (d, 3J = 8.3 Hz, 4 H, 3-H, 5-H), 5.81 (ddt, 3J =
17.0 Hz, 3J = 10.3 Hz, 3J = 6.6 Hz, 4 H, =CH), 5.02 (ddt, 3J =
General procedure E: N,NЈ-Bis[2,6-bis(hex-5-enyloxy)phenyl]eth-
ane-1,2-diamine (5b, 194 mg, 320 µmol), ammonium chloride
(20 mg, 0.37 mmol) in triethyl orthoformate (5.0 mL, 30 mmol).
Column chromatography [silica gel, dichloromethane/methanol
(10:1), Rf = 0.16] yielded crystalline colorless product 6b (152 mg,
1
73%). M.p. 206 °C. H NMR (600 MHz, CDCl3, 25 °C): δ = 8.02
2
4
3
3
17.1 Hz, J = 1.9 Hz, J = 1.6 Hz, 4 H, HZHC=), 4.96 (ddt, J =
(s, 1 H, 2-H), 7.34 (t, 3J = 8.5 Hz, 2 H, 4Ј-H), 6.65 (d, J = 8.6 Hz,
2
4
10.2 Hz, J = 2.0 Hz, J = 1.2 Hz, 4 H, HEHC=), 4.21 (br. s, 2 H, 4 H, 3Ј-H, 5Ј-H), 5.74 (ddt, 3J = 17.0 Hz, 3J = 10.2 Hz, 3J = 6.6 Hz,
3
NH), 3.96 (t, J = 6.6 Hz, 8 H, OCH2), 3.37 (s, 4 H, NCH2), 2.19
4 H, =CH), 4.98 (ddt, 3J = 17.1 Hz, 2J = 1.7 Hz, 4J = 1.6 Hz, 4 H,
(mc, 8 H, =CHCH2), 1.86 (mc, 8 H, OCH2CH2) ppm. 13C NMR HZHC=), 4.94 (ddt, J = 10.2 Hz, J = 1.7 Hz, J = 1.2 Hz, 4 H,
3
2
4
(125 MHz, CDCl3, 25 °C): δ = 150.4 (C-2,6), 137.9 (=CH), 127.7 HEHC=), 4.60 (s, 4 H, 4-H, 5-H), 4.08 (t, 3J = 6.8 Hz, 8 H, OCH2),
(C-1), 119.4 (C-4), 115.1 (H2C=), 105.7 (C-3,5), 68.0 (OCH2), 47.5
2.01 (mc, 8 H, =CHCH2), 1.84 (mc, 8 H, OCH2CH2), 1.51 (mc, 8
H, OCH2CH2CH2) ppm. 13C NMR (150 MHz, CDCl3, 25 °C): δ
= 160.3 (C-2), 154.5 (C-2Ј,6Ј), 138.0 (=CH), 131.3 (C-4Ј), 115.1
(NCH ), 30.2 (=CHCH ), 28.6 (OCH CH ) ppm. IR (KBr): ν =
˜
2
2
2
2
3435, 3409, 3074, 2941, 2861, 1640, 1595, 1502, 1446, 1392, 1292,
1233, 1212, 1101, 996, 910, 755, 731, 718 cm–1. MS (EI, 70 eV): m/z (H2C=), 112.5 (C-1Ј), 105.1 (C-3Ј,5Ј), 69.0 (OCH2), 51.6 (C-4,5),
(%) = 548 (20), 275 (100). HRMS: calcd. for C34H48N2O4
548.36139; found 548.36294 (2.8 ppm); calcd. for C3313CH48N2O4
549.36475; found 549.36797 (5.9 ppm). C34H48N2O4 (548.76):
calcd. C 74.42, H 8.82, N 5.10; found C 74.53, H 9.04, N 5.14.
33.1 (=CHCH2), 28.8 (OCH2CH2), 25.0 (OCH2CH2CH2) ppm. IR
(KBr): ν = 3076, 2944, 1618, 1482, 1463, 1396, 1257, 1108, 992,
˜
907, 774, 730, 649 cm–1. ESI-MS (MeOH): m/z (%) = 615.41 (100)
[C39H55N2O4]+. HRMS: calcd. for C39H55N2O4 615.4162; found
615.41635 (0.2 ppm); calcd. for C3813CH55N2O4 616.41956; found
616.41938 (0.3 ppm). C39H55ClN2O4 (651.33): calcd. C 71.92, H
8.51 N 4.30, C39H55ClN2O4·0.25H2O calcd. C 71.42, H 8.53, N
4.27; found C 71.24, H 8.67,N 4.40.
N,NЈ-Bis[2,6-bis(hex-5-enyloxy)phenyl]ethane-1,2-diamine (5b):
General procedure D: N,NЈ-Bis[2,6-bis(hex-5-enyloxy)phenyl]oxal-
diamide (4b, 500 mg, 0.790 mmol), lithium aluminium hydride
(316 mg, 8.32 mmol) in tetrahydrofuran (30 mL). Work up: Water
(15 mL), extraction with diethyl ether (2 ϫ 30 mL). Column
chromatography [alumina, cyclohexane/ethyl acetate (4:1), Rf =
0.87] yielded crystalline colorless product 5b (430 mg, 90%). M.p.
35 °C. 1H NMR (600 MHz, CDCl3, 25 °C): δ = 6.74 (t, 3J = 8.3 Hz,
2,11,13,22-Tetraoxa-1,12(1,3,2)-dibenzena-23(1,3)-imidazoliniuma-
bicyclo[10.10.1]tricosaphan-6,17-diene Chloride (7a): General pro-
cedure F: 1,3-Bis[2Ј,6Ј-bis(pent-4-enyloxy)phenyl]imidazolinium
chloride (6a, 600 mg, 1.09 mmol), benzylidenbis(tricyclohexylphos-
Eur. J. Org. Chem. 2007, 981–987
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
985

O. Winkelmann, C. Näther, U. Lüning
FULL PAPER
phane)dichlororuthenium (90 mg, 0.11 mmol) in dichloromethane
(600 mL). Column chromatography [silica gel, dichloromethane/
methanol (10:1), Rf = 0.19] yielded crystalline colorless product 7a
(447 mg, 81 %). M.p. 212 °C. 1H NMR[33] (500 MHz, CDCl3,
25 °C): δ = 8.07 (s, 1 H, 2-H), 7.36 (mc, 2 H, 4Ј-H), 6.65 (mc, 4 H,
form. Empirical formula C31H43ClN2O4·2CHCl3, Fw = 781.86 g/
mol, a = 24.435(2) Å, b = 12.4936(9) Å, c = 16.5068(9) Å, β =
129.063(5)°, V = 3912.7(4) Å3, T = 220(2) K, ρcalcd. = 1.327 g/cm3,
µ = 0.544 mm–1, monoclinic, space group C2/c, Z = 4, STOE Im-
aging Plate Diffraction System (IPDS-1), Mo-Kα (λ = 0.71073 Å),
3Ј-H, 5Ј-H), 5.59 (mc, 0.7 H, =CHZ*), 5.50 (mc, 3.3 H, =CHE*), 14905 measured reflections in the range of 6°Յ2θՅ56°, 4554 inde-
4.64 (mc, 4 H, 4-H, 5-H), 4.15–4.05 (m, 8 H, OCH2), 2.41 (mc, 4 pendent reflections used for refinement. Rint = 0.0363. The struc-
H, CH2#), 2.17 (mc, 4 H, CH2#), 1.94 (mc, 4 H, CH2#), 1.76 (mc, ture was solved with SHELXS-97. Structure refinement was per-
4 H, CH2#) ppm. 13C NMR[33] (125 MHz, CDCl3, 25 °C): δ = formed against F2 using SHELXL-97; 210 parameters, R1 for all
161.0, 160.6 (C-2), 154.9, 154.3 (C-2Ј,6Ј), 131.7, 131.6 (C-4Ј), 130.8, reflections with 3609 Fo Ͼ 4σ(Fo) = 0.0551, wR2 for all 4554 reflec-
130.6 (=CHZ*), 129.5, 129.5 (=CHE*), 112.4, 111.9 (C-1Ј), 105.3,
104.9 (C-3Ј,5Ј), 68.8, 67.9 (OCH2), 51.6, 50.4 (C-4,5), 30.1, 28.9,
tions = 0.1473, GoF = 1.057, residual electron density 0.63/
–0.75 [e/Å3]. All non-hydrogen atoms were refined by using aniso-
tropic displacement parameters. The hydrogen atoms were posi-
28.8, 27.4, 23.7, 23.6 (CH ) ppm. IR (KBr): ν = 3030, 2938, 1628,
˜
2
1599, 1480, 1459, 1299, 1259, 1102, 925, 777, 722 cm–1. ESI-MS tioned with idealized geometry and refined isotropically by using a
(MeOH): m/z (%) = 503.29 (100) [C31H39N2O4]+. HRMS: calcd.
for C31H39N2O4 503.29016; found 503.28646 (7.4 ppm); calcd. for
C3013CH39N2O6 504.29434; found 504.28966 (9.3 ppm).
riding model. CCDC-625523 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.
2,13,15,26-Tetraoxa-1,14(1,3,2)-dibenzena-27(1,3)-imidazoliniuma-
bicyclo[12.12.1]heptacosaphan-7,20-diene Chloride (7b): General
procedure F: 1,3-Bis[2Ј,6Ј-bis(hex-5-enyloxy)phenyl]imidazolinium
chloride (6b, 80 mg, 0.12 mmol), benzylidenbis(tricyclohexylphos-
phane)dichlororuthenium (10 mg, 12 µmol) in dichloromethane
(100 mL). Column chromatography [silica gel, dichloromethane/
methanol (10:1), Rf = 0.17] yielded crystalline colorless product 7b
(65 mg, 92%). M.p. 217 °C. 1H NMR[33] (500 MHz, CDCl3, 25 °C):
δ = 7.72 (s, 1 H, 2-H), 7.31 (mc, 2 H, 4Ј-H), 6.61 (mc, 4 H, 3Ј-H,
2,13,15,26-Tetraoxa-1,14(1,3,2)-dibenzena-27(1,3)-imidazoliniuma-
bicyclo[12.12.1]heptacosaphane Chloride (8b): General procedure G:
2,13,15,26-Tetraoxa-1,14(1,3,2)-dibenzena-27(1,3)-imidazol-
iniumabicyclo[12.12.1]heptacosaphan-7,20-diene chloride (7b,
45 mg, 0.76 mmol), palladium/charcoal (5 mg) in methanol (5 mL).
Column chromatography [silica gel, dichloromethane/methanol
(10:1), Rf = 0.18] yielded crystalline colorless product 8b (40 mg,
1
88%). M.p. 209 °C. H NMR (500 MHz, CDCl3, 25 °C): δ = 8.24
3
(s, 1 H, 2-H), 7.33 (t, 3J = 8.4 Hz, 2 H, 4Ј-H), 6.66 (d, 3J = 8.4 Hz,
5Ј-H), 5.36 (mc, 4 H, =CH), 4.58 (s, 4 H, 4-H, 5-H), 3.98 (t, J =
3
8.0 Hz, 8 H, OCH2), 2.16 (mc, 8 H, =CHCH2), 1.80 (mc, 8 H,
OCH2CH2), 1.48 (mc, 8 H, OCH2CH2CH2) ppm. 13C NMR[33]
(125 MHz, CDCl3, 25 °C): δ = 159.2, 159.1 (C-2), 155.3, 155.3 (C-
2Ј,6Ј), 131.5, 131.5 (C-4Ј), 131.1 (=CHZ*), 130.3, 130.3 (=CHE*),
112.0, 111.9 (C-1Ј), 104.9, 104.7 (C-3Ј,5Ј), 69.5, 69.4 (OCH2), 51.9,
51.8 (C-4,5), 31.8, 31.7, 28.6, 27.7, 27.7, 26.8, 24.9, 24.1, 24.0 (CH2)
4 H, 3Ј-H, 5Ј-H), 4.63 (s, 4 H, 4-H, 5-H), 4.13 (t, J = 6.2 Hz, 8 H,
OCH2), 1.82 (mc, 8 H, OCH2CH2), 1.46 (mc, 8 H, OCH2CH2CH2),
1.39 (mc, 16 H, CH2) ppm. 13C NMR (125 MHz, CDCl3, 25 °C):
δ = 160.7 (C-2), 154.5 (C-2Ј,6Ј), 131.1 (C-4Ј), 112.9 (C-1Ј), 105.3
(C-3Ј,5Ј), 69.4 (OCH2), 51.9 (C-4,5), 28.5, 26.5, 26.3, 24.9 (CH2)
ppm. IR (KBr): ν = 2932, 1617, 1480, 1459, 1390, 1301, 1257, 1101,
˜
774, 728, 648 cm–1. ESI-MS (MeOH): m/z (%) = 563.39 (100)
[C35H51N2O4]+. HRMS: calcd. for C35H51N2O4 563.38489; found
563.38357 (2.3 ppm); calcd. for C3413CH51N2O4 564.38824; found
564.38928 (1.8 ppm).
ppm. IR (KBr): ν = 2944, 2853, 1619, 1600, 1468, 1256, 1103, 967,
˜
779, 733, 638 cm–1. ESI-MS (MeOH): m/z (%) = 559.35 (100)
[C35H47N2O4]+. HRMS: calcd. for C35H47N2O4 559.35358; found
559.35357 (0.0 ppm); calcd. for C3413CH47N2O4 560.35693; found
560.35689 (0.1 ppm).
2,11,13,22-Tetraoxa-1,12(1,3,2)-dibenzena-23(1,3)-imidazoliniuma-
bicyclo[10.10.1]tricosaphan-232-yldithiocarboxylate (10): 2,11,13,22-
Tetraoxa-1,12(1,3,2)-dibenzena-23(1,3)-imidazoliniumabicyclo-
[10.10.1]tricosaphane chloride (8a, 13 mg, 0.024 mmol) was stirred
at room temp. with potassium tert-butoxide (4 mg, 0.04 mmol) in
tetrahydrofuran (5 mL). After 15 min., carbon disulfide (0.05 mL,
0.8 mmol) was added, and the mixture was stirred for 16 h. The
solvent and excess carbon disulfide were evaporated and crude
product 10 was analyzed without purification. 1H NMR (300 MHz,
CDCl3, 25 °C): δ = 7.16 (t, J = 8.5 Hz, 2 H, 4Ј-H), 6.47 (d, J =
8.5 Hz, 4 H, 3Ј-H, 5Ј-H), 4.21 (s, 4 H, 4-H, 5-H), 4.00 (mc, 8 H,
OCH2), 1.95 (mc, 4 H, CH2), 1.80–1.50 (m, 20 H, CH2) ppm. 13C
NMR (150 MHz, CDCl3, 25 °C): δ = 221.3 (CS2), 166.0 (C-2),
156.6 (C-2Ј,6Ј), 130.4 (C-4Ј), 113.5 (C-1Ј), 104.1 (C-3Ј,5Ј), 68.4
(OCH2), 49.0 (C-4,5), 28.5, 26.0, 23.9 (CH2) ppm. ESI-MS
(MeOH): m/z (%) = 583.2650 (37) [C32H42N2O4S2 + H]+ (calcd.
583.2659, 1.5 ppm), 584.2686 (11) [C3113CH42N2O4S2 + H]+ (calcd.
584.2690, 0.7 ppm), 621.2196 (100) [C32H42N2O4S2 + K]+ (calcd.
621.2223, 4.3 ppm), 622.2255 (24) [C3113CH42N2O4S2 + K]+ (calcd.
622.2254, 0.2 ppm).
2,11,13,22-Tetraoxa-1,12(1,3,2)-dibenzena-23(1,3)-imidazoliniuma-
bicyclo[10.10.1]tricosaphane Chloride (8a): General procedure G:
2,11,13,22-Tetraoxa-1,12(1,3,2)-dibenzena-23(1,3)-imidazoliniuma-
bicyclo[10.10.1]tricosaphan-6,17-diene chloride (7a, 280 mg,
519 µmol), palladium/charcoal (10 mg) in methanol (40 mL). Col-
umn chromatography [silica gel, dichloromethane/methanol (10:1),
Rf = 0.18] yielded crystalline colorless product 8a (256 mg, 91%).
M.p. 199 °C. 1H NMR (500 MHz, CDCl3, 25 °C): δ = 8.14 (s, 1 H,
3
2-H), 7.34 (t, J = 8.5 Hz, 2 H, 4Ј-H), 6.64 (d, 3J = 8.6 Hz, 4 H,
3
3
2
3
3Ј-H, 5Ј-H), 4.62 (s, 4 H, 4-H, 5-H), 4.16 (ddd, J = 9.3 Hz, J =
3
2
3
7.5 Hz, J = 3.0 Hz, 4 H, OCHaHb), 4.10 (ddd, J = 9.3 Hz, J =
6.8 Hz, 3J = 3.2 Hz, 4 H, OCHaHb), 1.80 (mc, 8 H, CH2), 1.61 (mc,
4 H, CH2), 1.47 (mc, 12 H, CH2) ppm. 13C NMR (MHz, CDCl3):
δ = 160.4 (C-2), 155.0 (C-2Ј,6Ј), 131.4 (C-4Ј), 112.4 (C-1Ј), 104.9
(C-3Ј,5Ј), 69.0 (OCH2), 51.7 (C-4,5), 28.1, 26.6, 24.3 (CH2) ppm.
IR (KBr): ν = 3058, 2941, 2864, 1619, 1598, 1482, 1458, 1386, 1297,
˜
1257, 1101, 925, 777, 721, 640 cm–1. ESI-MS (MeOH): m/z (%) =
507.32 (100) [C31H43N2O4]+. HRMS: calcd. for C31H43N2O4
507.32230; found 507.32225 (0.1 ppm); calcd. for C3013CH43N2O4
508.32565; found 508.32563 (0.0 ppm). C31H43ClN2O4 (543.12):
calcd. C 68.55, H 7.98, N 5.16, C31H43ClN2O4·CH3OH calcd. C
66.82, H 8.24, N 4.87; found C 66.89, H 8.37, N 5.05.
[1] R. Breslow, J. Am. Chem. Soc. 1958, 80, 3719–3726.
[2] A recent review on thiamine-dependent enzymes: R. Duggleby,
Acc. Chem. Res. 2006, 39, 550–557.
X-ray Crystal Structure Determination of 8a: Suitable crystals were
grown by diffusion of diethyl ether into a solution of 8a in chloro-
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986
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Eur. J. Org. Chem. 2007, 981–987

Imidazolinium Salts as Precursors to N-Heterocyclic Carbenes
FULL PAPER
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[33] Because of the formation of (Z)- and (E)-double bonds in the
metathesis, three diastereomers may be formed: (Z,Z), (Z,E),
and (E,E). For 7a, two distinct signals are observed for the
protons at the double bond, for 7b one multiplet is observed.
*: assignments may be interchanged. #: exo- and endo-CH2, no
assignments possible.
Received: September 26, 2006
Published Online: December 12, 2006
Eur. J. Org. Chem. 2007, 981–987
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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