Betaine-carbene interconversions. from N-ylides to zwitterionic n-heterocyclic carbene-borane adducts

Article abstract of DOI:10.1021/jo302479p

In the presence of NBS 3-methylindole reacted with various imidazoles to give the (indol-2-yl)imidazolium salts 21a-f, which were converted in aqueous solution into the 2-(imidazolium-3-yl)-3-methylindolates 22a-f by base. These conjugated ylides - which represent a subclass of mesomeric betaines - are the exclusively detectable form in the NMR spectra taken in DMSO-d₆. A DFT calculation revealed that the betaine 22a is -9.3 kJ/mol more stable than the tautomeric N-heterocyclic carbene 23a and that the energy for the betaine-carbene interconversion is ΔG^a?§§ = 66.4 kJ/mol. The N-heterocyclic carbenes (3-methyl-indol-2-yl)imidazol-2-ylidenes, however, can be trapped by sulfur, triethylborane, and triphenylborane. Whereas the first trapping reaction yielded the expected imidazolethiones, the borates gave the first representatives of new zwitterionic borane adducts, imidazo[2′,1′:3,4][1,4,2]diazaborolo[1,5-a]indolium-11-ides 26a-h. We performed DFT calculations on the structures of mesomeric betaine 22a, the carbene 23a, and the mechanisms of the borane adduct formation to 26a-h, NMR spectroscopic investigations including ¹⁵N, ⁷Li, and ¹¹B NMR spectroscopy, and an X-ray single-crystal analysis of one of the borane adducts.

Full text of DOI:10.1021/jo302479p

Article
pubs.acs.org/joc
Betaine−Carbene Interconversions. From N‑Ylides to Zwitterionic
N‑Heterocyclic Carbene−Borane Adducts
Nazar Pidlypnyi,† Jan C. Namyslo,† Martin H. H. Drafz,† Martin Nieger,‡ and Andreas Schmidt†,*
†Institute of Organic Chemistry, Clausthal University of Technology, Leibnizstrasse 6, D-38678 Clausthal-Zellerfeld, Germany
‡Laboratory of Inorganic Chemistry, Department of Chemistry, University of Helsinki, P.O. Box 55 (A.I. Virtasen aukio 1),
FIN-00014 University of Helsinki, Finland
S
* Supporting Information
ABSTRACT: In the presence of NBS 3-methylindole reacted
with various imidazoles to give the (indol-2-yl)imidazolium
salts 21a−f, which were converted in aqueous solution into the
2-(imidazolium-3-yl)-3-methylindolates 22a−f by base. These
conjugated ylideswhich represent a subclass of mesomeric
betainesare the exclusively detectable form in the NMR
spectra taken in DMSO-d6. A DFT calculation revealed that the betaine 22a is −9.3 kJ/mol more stable than the tautomeric N-
heterocyclic carbene 23a and that the energy for the betaine−carbene interconversion is ΔG⧧ = 66.4 kJ/mol. The N-heterocyclic
carbenes (3-methyl-indol-2-yl)imidazol-2-ylidenes, however, can be trapped by sulfur, triethylborane, and triphenylborane.
Whereas the first trapping reaction yielded the expected imidazolethiones, the borates gave the first representatives of new
zwitterionic borane adducts, imidazo[2′,1′:3,4][1,4,2]diazaborolo[1,5-a]indolium-11-ides 26a−h. We performed DFT
calculations on the structures of mesomeric betaine 22a, the carbene 23a, and the mechanisms of the borane adduct formation
to 26a−h, NMR spectroscopic investigations including 15N, 7Li, and 11B NMR spectroscopy, and an X-ray single-crystal analysis
of one of the borane adducts.
INTRODUCTION
■
1
2
3
̈
Since pioneering work by Breslow, Wanzlick, and Ofele and
the isolation of the first stable carbenes by Bertrand4
((phosphine)(silyl)carbene) and Arduengo5 (N-heterocyclic
carbene (NHC)) the class of N-heterocyclic carbenes has
developed remarkably. Among other motivations,6 numerous
structural variations have been performed aiming at enhancing
the electron density at the carbene center and thus influencing
the σ-donor capacity in catalytically active metal complexes.
Figure 1 presents the isomers imidazol-2-ylidene 1 as a
“classical” NHC,7 imidazol-4-ylidene 2 as a member of the
class of abnormal N-heterocyclic carbenes (aNHC)8 and
pyrazol-4-ylidene 3. The latter has inter alia been described
as structure 3A, which was termed a remote N-heterocyclic
carbene (rNHC)9 or aromatic zwitterion.10 Its representation
as cyclic bent allene 3B11 or as dipolar electron-sextet structure
3C12 reflects the sensitivity of this compound toward
substituent effects, which has been calculated in detail.11,12
The term “mesoionic carbene” (MIC) has been suggested by
Bertrand for certain aNHCs and rNHCs, because no
reasonable canonical resonance form containing a carbene
can be drawn.13 In cyclic alkyl(amino)carbenes 4 (CAAC) a
nitrogen is replaced by the strongly σ-donating carbon.14 In
contrast, the amino−phosphorus−ylide−carbenes 515 and
amino−sulfur−ylide carbenes 616 possess ylides as partial
structures.
Figure 1. Distinct types of N-heterocyclic carbenes.
(1955),20 and munchnone (1963)21 are milestones in the
̈
development of this class of compounds. Mesomeric betaines
are defined as neutral compounds which can exclusively be
represented by dipolar canonical formulas in which the positive
and negative charges are delocalized within a common π-
electron system.22 A comprehensive classification was recog-
Heterocyclic mesomeric betaines (MB) have constituted a
classical subject of research to date. The first mesoion (1882),17
mesomeric betaine (1891),18 sydnone (1935),19 classification
Received: November 14, 2012
Published: January 10, 2013
© 2013 American Chemical Society
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nized in 1985, and since then four distinct main classes of
heterocyclic mesomeric betaines have been distinguished.23
These are conjugated (CMB), cross-conjugated (CCMB), and
pseudo-cross-conjugated mesomeric betaines (PCCMB), in
addition to ylides which are closely related to CMB. Mesoionic
compounds have been defined as five-membered representa-
tives of CMB.22 Numerous examples of 144 theoretically
predicted type A and of 84 type B mesoionic compounds23
have been described to date.
Scheme 2. Architecture of a Negatively Charged N-
Heterocyclic Carbene Derived from a Mesomeric Betaine
A review analyzing the relationship between the two classes
of compounds, N-heterocyclic carbenes and mesomeric
betaines, has been published, as far as the chemistry of
pyrazoles and indazoles is concerned.24 However, the relation-
ship of the distinct classes of N-heterocyclic carbenes
(especially NHC, rNHC, aNHC, and MIC) and mesomeric
betaines (CMB, CCMB, PCCMB, ylides) with respect to
structures, properties, and reactions has not been examined
systematically to date. Results of a few scattered reports and
some own thoughts on the structures are as follows. Nitrone 7
(Busch’s reagent, a CMB, subclass mesoionic compounds) is in
equilibrium with its N-heterocyclic carbene 8 (Scheme 1).
Scheme 1. Classical Mesoionic Compounds and Their
Conversions into N-Heterocyclic Carbenes
Figure 2. Remote (rNHC) and abnormal N-heterocyclic carbenes
(aNHC) and their relationship to cross-conjugated mesomeric
betaines (CCMB).
is joined through union bonds (“u”) to the nodal position of
the HOMO (cf. III and V). The generation of carbenes from
these types of mesomeric betaines is seemingly limited due to
harsh reaction conditions. The formation of pyrazol-4-ylidene
by thermal decarboxylation of 15 was examined mass
spectrometrically,31 whereas imidazol-4-ylidene generated
from 16 was trapped by isocyanates.31
Thus, obviously NHCs have unknowingly been commercially
available for more than 100 years.25 The mesoionic compound
imidazolium-4-aminide 9 and its isomer, the NHC 10, show a
similar behavior.26 The mesoionic compound imidazolium-4-
olate 11 has been converted into the anionic N-heterocyclic
carbene 12.27 We believe that these very recent results are only
the first examples of numerous betaine−carbene interconver-
sions which await recognition and application.
A very small number of reports have dealt with conversions
of cross-conjugated mesomeric betaines (CCMB) into N-
heterocyclic carbenes. Thus, the CCMB 13 was recently
transformed into the stable anionic N-heterocyclic carbene 1428
(Scheme 2). Characteristic of CCMB, in the canonical formulas
the charges are strictly delocalized in separate parts of the
molecule.22 This translates into the MO theory in such a way
that the N atoms of the cationic partial structure are joined to
the anionic fragment of the molecule through nodal positions
of the highest occupied molecular orbital (HOMO) I.29,30 As a
consequence, in the anionic NHC 14 a diaminocarbene
fragment is bridged by union bonds (“u”) through nodal,
inactive positions of the HOMO of a 3-oxopropanolate anion.
The CCMBs pyrazolium-4-carboxylate 15 and imidazolium-
4-carboxylate 16 are formal 1:1 adducts II and IV of
heterocumulenes (such as CO2) of the remote NHC pyrazol-
4-ylidene and the abnormal NHC imidazol-4-ylidene, respec-
tively31 (Figure 2). Again, the anionic fragment of the betaines
In contrast, the thermal generation of N-heterocyclic
carbenes from pseudo-cross-conjugated mesomeric betaines
(PCCMB) proceeds under smooth conditions. PCCMBs have
been defined on the basis of their characteristic dipole types32
and their mesomeric structures, which include forms with an
electron-sextet structure without internal octet stabilization.22,30
Pyrazolium-3-carboxylates, -amidates, and -thioamidates 17 and
their isomeric imidazoles 18 are precursors of N-heterocyclic
carbenes which form thermally on extrusion of heterocumu-
lenes such as CO2, isocyanates, and thioisocyanates, respec-
tively33 (Figure 3, VI and VII). Vice versa, numerous examples
of trapping reactions of NHC with heterocumulenes to give
PCCMBs have been described.34 Among these trapping
reactions, adduct formations with boranes have been
reported,35 including those starting from PCCMBs.36 A review
on NHC−borane adducts appeared recently.37 This reflects the
remarkable development of the class of NHC−borane adducts
which was considered rare, perhaps even exotic,37 prior to 2008.
In continuation of our interest in mesomeric betaines,38
organic polycations,39 and N-heterocyclic carbenes40 we
describe here a series of imidazolium indolates which belong
to the class of N-ylides related to conjugated mesomeric
betaines (CMB). These are in equilibrium with their N-
heterocyclic carbenes. The NHCs of imidazolium indolates, i.e.
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Scheme 3. Trapping of N-Heterocyclic Carbenes 23a−f,
Which Are in Equilibrium with N-Ylides 22a−f, and
Formation of the Anionic N-Heterocyclic Carbene 25a
Figure 3. Heterocumulene adducts of N-heterocyclic carbenes forming
a special class of mesomeric betaines, namely PCCMB.
1-(indol-2-yl)imidazol-2-ylidenes, undergo trapping reactions
with sulfur. Triethylborane and triphenylborane proved to be
suitable reagents to trap both forms, N-ylide as well as NHC, as
the first representatives of a new boron-containing zwitterionic
1
7
heterocyclic ring system. We present results of H, 13C, Li,
15N, and 11B NMR spectroscopic examinations and a single-
crystal X-ray structure analysis.
RESULTS AND DISCUSSION
■
The (indol-2-yl)imidazolium salts 21a−f were prepared in good
to quantitative yields on addition of NBS to a slightly cooled
dioxane solution of 3-methylindole 19 and the imidazoles 20a−
f, respectively. After 30 min precipitates of the salts were
filtered off (Scheme 3). Deprotonation of the salts 21a−f to the
mesomeric betaines 22a−f was best accomplished by an
ethanolic NaOH solution. The mesomeric betaines are stable,
colorless to yellowish compounds and were obtained in high
yields. On deprotonation, the NH resonance frequencies of
21a−f, detectable between δ 12.04 and 12.16 ppm, disappear
and the 15N NMR signals are shifted considerably. Thus, the
signals of 21a at −251.8 (Nindole), −206.9 (N1imidazolium) bearing
the indolyl substituent, and −193.5 ppm (N3imidazolium) adjacent
to the benzyl group shift to −210.1 (Nindole), −196.2
(N1imidazolium), and −195.0 ppm (N3imidazolium) on conversion
to 22a.
The betaine 22a was calculated to be ΔG = −9.3 kJ/mol
more stable than the corresponding carbene 23a. In DMSO-d6
solution only the mesomeric betaines 22a−f can be detected in
the NMR spectra. Assuming an unimolecular mechanism, the
betaine−carbene interconversion possesses a computed activa-
tion barrier of ΔG⧧ = 66.4 kJ/mol. The carbenes could be
trapped by sulfur in boiling xylene, whereupon the thiones
24a−f were formed in high to quantitative yields.
heterocyclic carbene possessing a bridging Li cation as the
most stable form (cf. the Supporting Information).
The betaines 22a−f are members of the class of N-ylides
which are closely related to conjugated heterocyclic mesomeric
betaines (CMB) (Figure 4). Characteristic canonical formulas
such as B can be drawn, and common atoms for either charge
can be dissected from mesomeric structures such as A and C. It
should be noted here that the negative charge is delocalized in
Treatment of 21a with excess nBuLi in MeCN-d3 led to the
formation of lithium salts of the anionic N-heterocyclic carbene
25a, three mesomeric structures of which are shown in Scheme
3. The sample was prepared at −40 °C under an inert
atmosphere from freshly dried salt 21a and proved to be stable
under these conditions for a few hours. The carbene resonance
frequency is detectable by NMR spectroscopy. Thus, the
carbene atom of 25a can be measured as an Li adduct at δ
181.4 ppm in the 13C NMR spectra. The Li signal appears at δ
0.40 ppm in 7Li NMR spectroscopy. In high-resolution
electrospray ionization mass spectrometry, the anionic N-
heterocyclic carbene 25a is clearly detectable as a prominent
peak in the anion detection mode (calcd 286.1344, found
286.1337). A DFT calculation predicts an anionic N-
Figure 4. Mesomeric structures of the target N-ylides 22 (A−C) and
their tautomeric carbenes 23 (D−F).
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the π-electron system according to the definition of mesomeric
betaines, and a negative charge can be drawn on the potential
carbene center C2 of the imidazolium ring (C). Canonical
structures of the tautomeric carbene includes the usual
zwitterionic representation D, the electron sextet structure E,
and a tetrapolar structure F with two negative charges located
on C2 of the imidazole.
rescent crystals (Scheme 4). These compounds are the first
examples of a new heterocyclic ring system. On reaction of 22a
Scheme 4. Borane Adduct Formation Starting from the N-
Ylide−NHC Equilibrium
As the distinct classes of mesomeric betaines differ in their
frontier orbital profiles (see above), we were interested in
calculating changes of the highest occupied (HOMO) and
lowest unoccupied molecular orbital (LUMO) on betaine−
carbene conversion. The frontier orbital profile is shown in
Figure 5. The bond between N1imidazolium and C2indolate was
with triphenylborane, 26g was formed. Perfluorophenylborane
failed to undergo the reaction to 26h under the conditions
applied.
Figure 5. Frontier orbital profile of 22a.
The structure of these compounds in solution was elucidated
by detailed NMR investigations, including 1H, 13C, and 1H,15N-
HMBC measurements (cf. the Supporting Information). The
boron atoms give singlets between δ −1.6 and 0.0 ppm in 11B
NMR spectroscopy. Related structures are extremely rare.
4,4,8,8-Tetraethyl-1,5-dimethylimidazabole,41 B,B,B′,B′-tetrae-
thylthiazabole,42 and its triazabole derivative43 also possess
N−B(Et)2−Ccarbene structure elements which we compared to
our molecules; their 11B NMR resonance frequencies are at δ
−6.3 (1JCB = 54 Hz), −2.5 , and −6.1 ppm (s), respectively. As
the ring system is not planar, the diastereotopic ethyl groups
split into two sets of signals. Despite the often observed
quadrupole broadening and spin−spin coupling to the
neighboring boron atom in NHC−borane adducts which
prevent the detection of the carbene carbon atoms, the C2
atom of the imidazole moiety gives a resonance frequency at δ
175.8 ppm (26a) in the 13C NMR spectrum taken in CDCl3.
This chemical shift proves the formation of a single bond
between the boron atom and the C2 carbon, which was
additionally detected by an HMBC cross-peak originating from
calculated to have a bond length of 142.1 pm (22a), which
corresponds to a 33% double-bond character according to the
Pauling−Brockway equation. The same DFT calculation
predicts a torsion angle of 4.6° between the two partial
structures in vacuo.
On conversion into the carbene form, the π-type HOMO
changes only slightly according to the calculations (Figure 6).
3
a JC,H coupling of the C2 carbon with the methylene protons
of the alkyl borate. The corresponding signals of the
aforementioned imidazabole and thiazabole are δ 164 (br,
C6d6) and 195 ppm (br, C6d6), respectively. The N atoms of
26a give resonance frequencies at δ −218.7 (Nindole), −182.3
(N1imidazolium), and −199.8 ppm (N3imidazolium). The last atom
mentioned, benzyl-substituted nitrogen, was identified by its
1H,15N-HMBC signal with the benzylic protons, whereas the
indole nitrogen was assigned on the basis of a coupling with the
ortho proton of the annelated phenyl ring and, additionally, by
means of a cross-peak with the BCH2 protons. Thus, the
combination of both cross-peaks from these methylene protons
proves the formation of the central diazaborolium-type five-
membered ring in 26a. The benzylic protons of 26a cannot be
removed either by Proton Sponge in CDCl3 or by NaOD in
Figure 6. Frontier orbital profile and the σ-type HOMO-2 of 23a.
The HOMO-2 is mainly a σ-type molecular orbital. On
conversion from the ylide into the carbene form, the permanent
dipole moment decreases dramatically. Thus, ylide 22a has a
calculated dipole moment of 11.99 D, which changes to 3.67 D
on carbene formation.
We the found that BEt3 and BPh3 are suitable trapping
reagents for both forms, N-ylide and N-heterocyclic carbene, as
treatment of suspensions of the betaines 22a−f with
triethylborane in hexane under an inert atmosphere at 150
°C in a sealed tube resulted in the formation of the
imidazodiazaboroloindoles 26a−f as colorless, slightly fluo-
1
THD-d8, as evidenced by H NMR spectroscopy, so that an
imidazolium ylide partial structure in equilibrium can be
excluded from consideration.
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Single crystals of 26a, obtained from p-xylene/hexane, were
subjected to an X-ray analysis. The compound crystallized in
the monoclinic system. The crystallographically determined B−
Ccarbene bond is longer (165.2(2) pm) than the B−Cethyl bonds
(162.3(2)/161.5(2) pm). The boron−nitrogen bond was
measured to be 158.7(2) pm. Thus, in 26a the B−Ccarbene
bond is slightly longer than the B−C bonds in structures with
sterically hindered groups. As example, the corresponding bond
in the IDipp/B(C6F5)3 adduct was found to be 166.3(5) pm,43
and those in adducts of 2,3,4,5-tetramethyl-1,3-imidazol-2-
ylidene/B(C6F5)3 were found to be 164.07(18)44 and 159.2(2)
pm.45 The angle N−Ccarbene−N was determined to be
105.54(11)°, and this value characteristically is between the
angles of free carbenes (101°) and imidazolium salts (108°).37
The torsion angle between the imidazolium moiety and the
indole ring was determined to be −4.0(2)°.
Scheme 6. Model Compounds
described above. Deprotonation of 29, however, with nBuLi in
cyclohexane in MeCN-d3 at −40 °C resulted in the formation
of the free carbene and its Li adduct. The carbene can
unambiguously be detected by a carbon NMR signal at δ 201.8
ppm, whereas the Li adduct shows a characteristic resonance
frequency at δ 184.2 ppm. Then, excess BEt3 in MeCN-d3 was
added to the mixture and the borane formation was monitored
by NMR spectrometry. The formation of new signals was
observed while the original signals disappeared over a period of
24 h at room temperature. Attempts to isolate 30, however,
failed due to decomposition of the material during the workup
procedure.
The frontier orbital profile of 26a is presented in the
Supporting Information. As expected, the HOMO and LUMO
are π orbitals.
To gain insight into the mechanism, we monitored the
reaction of ylide 22a with BEt3 by NMR spectroscopy in
MeCN-d3 at room temperature. Surprisingly, no adduct
formation between Nindole and BEt3 was detectable under
these conditions, although a DFT calculation predicted that the
initial coordination of triethylborane to the indolate nitrogen of
22a to G is energetically slightly more favored by 19.7 kJ/mol
than the coordination to the carbene carbon atom of 23a to H
(Scheme 5). Instead, a 1H,15N-HMBC spectrum of a mixture of
CONCLUSIONS
■
The chemistry of mesomeric betaines and the chemistry of N-
heterocyclic carbenes have an area of overlap which has not yet
been examined in detail. In this report, examples of N-ylides,
which form a class of mesomeric betaines of its own, are in
equilibrium with N-heterocyclic carbenes. Thus, the equili-
brium of the N-ylides 2-(imidazolium-3-yl)-3-methylindolates
and their tautomeric N-heterocyclic carbenes (3-methylindol-2-
yl)imidazol-2-ylidenes (NHC) can be shifted by trapping of the
carbene by sulfur with formation of imidazolethiones.
Triethylborane and triphenylborane proved to be suitable
reagents to trap either form with formation of a new ring
system. Thus, we describe the first representatives of new
zwitterionic borane adducts, imidazo[2′,1′:3,4][1,4,2]-
diazaborolo[1,5-a]indolium-11-ides. In these compounds, the
boron atom bridges the carbene center with the former
negatively charged ylide N atom. DFT calculations reveal that
HOMO and LUMO of the N-ylide as well as of the N-
heterocyclic carbene are π-type orbitals; the HOMO-2 of the
carbene was found to be a σ-type orbital. Characteristic 11B and
15N NMR resonance frequencies were identified, which allowed
an NMR monitoring of the reaction.
Scheme 5. Initial Borane Adduct Formation According to
NMR Investigations
22a and BEt3 clearly showed a signal at δ −250.2 ppm, which is
characteristic of an NH group. Fortunately, this 2D hetero
correlation spectrum additionally showed a one-bond coupling
N−H cross-peak of this indole nitrogen with the slightly
broadened proton singlet at approximately 9.35 ppm. Thus, the
former N-ylide nitrogen is reprotonated, whereas the
trialkylborane attacks the imidazolium carbene atom to give
the corresponding NHC−-borane adduct H. The formation of
the B−Ccarbene bond is confirmed by a 11B shift of −12.7 ppm.
The N1imidazolium and N3imidazolium signals of H were
unambiguously assigned to resonance frequencies at δ −194.3
and −202.8 ppm in the 15N NMR spectra.
To prove these results, we prepared the methylated
derivatives 27 and 29 as model compounds (Scheme 6). On
addition of triethylborane to 27 in MeCN-d3 at room
temperature, we were not able to observe any shift changes
in the 1H NMR spectra, in accordance with the results
We believe that a closer inspection of the characteristic
features of mesomeric betaines is a stimulus for the develop-
ment of the ever-growing chemistry of N-heterocyclic carbenes
and their relatives.
EXPERIMENTAL SECTION
■
1
General Remarks. The H, 13C, 15N, and 11B NMR spectra were
recorded in DMSO-d6, CDCl3, or CD3CN at 400 MHz (1H NMR)
and 600 MHz (1H NMR), respectively. The chemical shifts are
reported in ppm relative to internal standard tetramethylsilane (δ 0.00
ppm), nitromethane, and boron trifluoride etherate, respectively.
Multiplicities are described by using the following abbreviations: s =
singlet, d = doublet, t = triplet, q = quartet, sep = septet, m = multiplet,
br = broad. Peak assignments were accomplished by results of HMBC-
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NMR, HSQC-NMR, and HH-NOESY measurements. FT-IR spectra
were obtained in the range 400−4000 cm−1 (2.5% pellets in KBr).
Samples for ESI mass spectrometry were sprayed from methanol at 0
V fragmentor voltage unless otherwise noted. The melting points were
measured by differential scanning calorimetry and are not corrected.
Yields are not optimized. All density functional theory (DFT)
calculations were carried out by using the Jaguar 7.7.107 software
running on Linux 2.6.18−238.el5 SMP (x86_64) on two AMD
Phenom II X6 1090T processor workstations (Beowulf-cluster)
parallelized with OpenMPI 1.3.4. MM2 optimized structures were
used as starting geometries. Complete geometry optimizations were
carried out on the implemented LACVP* (Hay−Wadt effective core
potential (ECP) basis on heavy atoms, N31G6* for all other atoms)
basis set and with the B3LYP density functional. All calculated
structures were proven to be true minima or first-order saddle points
by the absence of imaginary frequencies or occurrence of one
imaginary frequency, respectively. Plots were obtained using Maestro
9.1.207, the graphical interface of Jaguar. Thermodynamic corrections
were estimated from unscaled frequencies, using standard formulas in
the ideal gas harmonic oscillator approximation as implemented in
Jaguar, and refer to a standard state of 298.15 K and 1 mol/dm3
concentration. Charges were obtained using the natural atomic orbital
and natural bond orbital analysis which is included in Jaguar NBO
5.0.46 Calculations of the reactions in the solution phase (toluene)
displayed essentially no energy differences (<2 kJ/mol), in comparison
to the calculations performed for reactions in the gas phase.
(KBr): ν 2961, 1568, 1446, 1332, 1238, 1118, 1084, 867, 744, 727,
+
626, 562, 445, 437 cm−1. HR-ESI-MS: calcd for C20H20N3 302.1657,
found 302.1654.
3-(3-Methyl-1H-indol-2-yl)-1-(naphthalen-2-ylmethyl)-
imidazolium Bromide (21d). 1-(Naphthalen-2-ylmethyl)imidazole
(277 mg) was used. Salt 21d was isolated as colorless crystals, mp
1
262 °C, yield 381 mg (91%). H NMR (DMSO-d6, 400 MHz): 2.32
(s, 3 H, Me), 5.80 (s, 2 H, CH2), 7.16 (ddd, 1 H, J = 8.0 Hz, J = 7.0
Hz, J = 0.8 Hz), 7.28 (ddd, 1 H, J = 8.2 Hz, J = 7.0 Hz, J = 1.1 Hz),
7.46 (d, 1 H, J = 8.2 Hz), 7.58−7.61 (m, 2 H), 7.66 (d, 1 H, J = 8.0
Hz), 7.69 (dd, 1 H, J = 8.6 Hz, J = 1.7 Hz), 7.96−7.99 (m, 2 H), 8.03
(d, 1 H, J = 8.6 Hz), 8.12 (s, 1 H), 8.22−8.24 (m, 2 H), 10.06 (dd, 1
H, J1 ≈ J2 = 1.6 Hz), 12.05 ppm (s, 1 H, NH). 13C NMR (DMSO-d6,
100 MHz): δ 7.7, 52.6, 104.2, 111.7, 119.5, 120.0, 123.1, 123.5, 123.9,
125.1, 125.8, 126.8, 126.8, 126.9, 127.7, 127.8, 127.9, 128.8, 131.9,
132.7, 132.8, 133.4, 137.3 ppm. ESI-MS: m/z (%) 338.1 (100) [M+].
IR (KBr): ν 3053, 1632, 1566, 1544, 1454, 1329, 1122, 1079, 856, 819,
775, 739, 689, 646, 623, 611, 263, 472, 409 cm−1. HR-ESI-MS: calcd
+
for C23H20N3 338.1657, found 338.1656.
1-Benzhydryl-3-(3-methyl-1H-indol-2-yl)-1H-imidazolium Bro-
mide (21e). A 256 mg portion of 1-benzhydrylimidazole was used.
Salt 21e was isolated as white crystals, mp 188 °C, yield 320 mg
(72%). 1H NMR (DMSO-d6, 400 MHz): δ 2.29 (s, 3 H, Me), 3.37 (s,
2 H, CH2), 7.15 (ddd, 1 H, J = 7.8 Hz, J = 7.0 Hz, J = 0.8 Hz), 7.27
(ddd, 1 H, J = 8.2 Hz, J = 7.0 Hz, J = 1.0 Hz), 7.41−7.54 (m, 12 H),
7.65 (d, 1 H, J = 7.8 Hz), 8.16 (dd, 1 H, J1 ≈ J2 = 1.8 Hz), 8.33 (dd, 1
H, J1 ≈ J2 = 1.8 Hz), 9.87 (s, 1 H), 12.04 ppm (s, 1 H, NH). 13C NMR
(DMSO-d6, 100 MHz): δ 7.7, 66.2, 104.3, 111.7, 119.4, 120.0, 122.7,
123.6, 124.4, 125.0, 126.8, 128.3, 129.0, 129.2, 133.4, 136.8, 137.3
ppm. ESI-MS: m/z (%) 364.0 (100) [M − 80]. IR (KBr): ν 3016,
1739, 1632, 1555, 1494, 1446, 1336, 1218, 1121, 1076, 743, 714, 696,
General Procedure for the Synthesis of the Salts 21a−f. A
solution of 3-methylindole (145 mg, 1.0 mmol) and the corresponding
imidazoles (1.3 mmol) in 3 mL of dioxane was stirred at 12−15 °C
while NBS (179 mg, 1.0 mmol) was added over a period of 5 min.
After stirring for an additional 30 min the precipitates were filtered off,
washed with a small amount of dioxane, and dried in vacuo.
+
655, 593, 572, 410 cm−1. HR-ESI-MS: calcd for C25H22N3 364.1814,
found 364.1806.
1-Benzyl-3-(3-methyl-1H-indol-2-yl)imidazolium Bromide (21a).
1-Benzylimidazole (211 mg, 1.3 mmol) was used. Recrystallization
from i-PrOH/H2O gave colorless crystals, yield 280 mg (76%), mp
1-(4-(Dimethylamino)phenyl)-3-(3-methyl-1H-indol-2-yl)-1H-imi-
dazolium Bromide (21f). A sample of 249 mg of 1-(4-
dimethylamino)phenylimidazole was used. Salt 21f was isolated as
white crystals, mp 262 °C, yield 397 mg (100%). 1H NMR (DMSO-d6,
400 MHz): δ 2.37 (s, 3 H, 3-Me), 3.01 (s, 6 H, NMe2), 6.94 (d, 2 H,
H-o-PhNMe2, J = 9.2 Hz), 7.17 (ddd, 1 H, H-5, J = 7.9 Hz, J = 7.0 Hz,
J = 0.8 Hz), 7.30 (ddd, 1 H, H-6, J = 8.2 Hz, J = 7.0 Hz, J = 1.1 Hz),
7.49 (d, 1 H, H-7, J = 8.2 Hz), 7.67 (d, 1 H, H-4, J = 7.9 Hz), 7.73 (d,
2 H, H-m-PhNMe2, J = 9.2 Hz), 8.40 (dd, 1 H, Himidazole, J ≈ J4 = 1.8
Hz), 8.55 (dd, 1 H, Himidazole, J ≈ J4 = 1.8 Hz), 10.20 (dd, 1 H,
Himidazole, J4 = 1.6 Hz), 12.07 ppm (br s, 1 H, NH). 13C NMR (DMSO-
d6, 100 MHz): δ 7.7, 40.0, 104.4, 111.7, 112.3, 119.5, 120.0, 121.8,
122.9, 123.3, 123.6, 124.0, 125.1, 126.9, 133.4, 134.9, 151.0 ppm. ESI-
MS: m/z (%) 317.1 (100) [M − 80]. IR (KBr): ν 3059, 1608, 1527,
1441, 1373, 1325, 1192, 1116, 1066, 815, 781, 754, 666, 631, 607, 510,
1
>300 °C. H NMR (DMSO-d6, 600 MHz): δ 2.32 (s, 3 H, Me), 5.71
(s, 2 H, CH2), 7.15 (ddd, 1 H, J = 8.0 Hz, J = 7.0 Hz, J = 0.8 Hz), 7.27
(ddd, 1 H, J = 8.2 Hz, J = 7.0 Hz, J = 1.0 Hz), 7.40−7.48 (m, 4 H),
7.63−7.66 (m, 3 H), 8.25 (dd, 1 H, J1 ≈ J2 = 1.8 Hz), 8.26 (dd, 1 H, J1
≈ J2 = 1.8 Hz), 10.23 (m, 1 H), 12.16 (br s, 1H, NH) ppm. 13C NMR
(DMSO-d6, 150 MHz): δ 8.2, 52.7, 104.6, 112.2, 119.9, 120.5, 123.5,
124.0, 124.3, 125.5, 127.4, 129.1, 129.4, 129.5, 133.9, 135.1, 137.5
ppm. 15N NMR (DMSO-d6, 61 MHz): δ −251.8, −206.9, −193.5
ppm. ESI-MS: m/z (%) 288.1 (100) [M+]. IR (KBr): ν 3062, 1737,
1632, 1566, 1543, 1495, 1454, 1330, 1228, 1170, 1124, 1101, 1079,
888, 740, 709, 646, 626, 563, 464 cm−1. HR-ESI-MS: calcd for
+
C19H18N3 288.1501, found 288.1500.
1-(2-Chlorobenzyl)-3-(3-methyl-1H-indol-2-yl)imidazolium Bro-
mide (21b). 2-Chlorobenzylimidazole (256 mg; 1.3 mmol) was
used. The salt 21b was isolated as colorless crystals, mp 210 °C, yield
289 mg (72%). 1H NMR (DMSO-d6, 400 MHz): δ 2.29 (s, 3 H, Me),
5.72 (s, 2 H, CH2), 7.16 (dd, 1 H, J1 ≈ J2 = 7.6 Hz), 7.28 (dd, 1 H, J1
≈ J2 = 7.6 Hz), 7.45−7.67 (m, 6 H), 8.09 (s, 1 H), 8.25 (s, 1 H), 9.94
(s, 1 H), 12.04 (s, 1 H, NH) ppm. 13C NMR (DMSO-d6, 100 MHz): δ
7.6, 50.5, 104.4, 111.7, 119.5, 120.0, 123.3, 123.6, 124.0, 124.9, 126.8,
128.0, 129.9, 131.0, 131.0, 131.6, 132.9, 133.4, 137.8 ppm. ESI-MS: m/
z (%) 322.0 (100) [M+]. IR (KBr): ν 2923, 1629, 1562, 1439, 1329,
1123, 1079, 1050, 776, 739, 681, 646, 624, 563, 444, 411 cm−1. HR-
+
444 cm−1. HR-ESI-MS: calcd for C20H21N4 317.1766, found
317.1765.
General Procedure for the Formation of Ylides 22a−f. The
corresponding salt (1.0 mmol) was dissolved in 10 mL of aqueous
EtOH (50%). Then, 1.5 equiv of a 3 M solution of NaOH was added.
The resulting precipitate was filtered off, washed two times with water,
and dried in vacuo.
2-(1-Benzyl-1H-imidazolium-3-yl)-3-methylindolate (22a). A
sample of the salt 21a (367 mg, 1.0 mmol) was used. The ylide 22a
1
was obtained as white crystals, mp 106 °C, yield 178 mg (62%). H
+
NMR (DMSO-d6, 600 MHz): δ 2.37 (s, 3 H, Me), 5.47 (s, 2 H, CH2),
6.72 (ddd, 1 H, J = 7.9 Hz, J = 6.8 Hz, J = 1.1 Hz), 6.78 (ddd, 1 H, J =
8.0 Hz, J = 6.8 Hz, J = 1.4 Hz), 7.26 (d, 1 H, J = 8.0 Hz), 7.33 (d, 1 H,
J = 7.9 Hz), 7.38−7.51 (m, 5 H, Ph), 7.86 (s, 1 H), 8.08 (s, 1 H), 9.73
(s, 1 H) ppm. 13C NMR (DMSO-d6, 150 MHz): δ 9.7, 52.4, 93.8,
115.4, 116.9, 117.6, 117.8, 122.2, 122.4, 128.7, 129.2, 129.5, 131.2,
134.1, 135.7, 137.0, 143.0 ppm. 15N NMR (DMSO-d6, 61 MHz): δ
−195.0, −196.2, −210.1 ppm. ESI-MS: m/z (%) 288.1 (100) [M −
80]. IR (KBr): ν 1633, 1566, 1543, 1496, 1454, 1383, 1333, 1231,
1170, 1124, 1102, 1079, 1006, 888, 821, 778, 757, 709, 647, 629, 564,
ESI-MS: calcd for C19H17ClN3 322.1106, found 322.1111.
3-(3-Methyl-1H-indol-2-yl)-1-(3-methylbenzyl)imidazolium Bro-
mide (21c). 3-Methylbenzylimidazole (229 mg, 1.3 mmol) was used.
Salt 21c was isolated as colorless crystals, mp 236 °C, yield 298 mg
(78%). 1H NMR (DMSO-d6, 400 MHz): δ 2.31 (s, 3 H, Me), 2.34 (s,
3 H, Me), 5.57 (s, 2 H, CH2), 7.14−7.18 (m, 1 H), 7.23−7.30 (m, 2
H), 7.35−7.36 (m, 2 H), 7.39 (s, 1 H), 7.46 (d, 1 H, J = 8.2 Hz), 7.65
(d, 1 H, J = 8.0 Hz), 8.16 (dd, 1 H, J1 ≈ J2 = 1.7 Hz), 8.21 (dd, 1 H, J1
≈ J2 = 1.7 Hz), 8.21 (s, 1 H), 12.04 (s, 1 H, NH) ppm. 13C NMR
(DMSO-d6, 100 MHz): δ 7.6, 20.9, 52.3, 104.2, 111.7, 119.5, 120.0,
123.0, 123.5, 123.9, 125.0, 125.6, 126.8, 128.9, 129.1, 129.5, 133.4,
134.4, 137.1, 138.3 ppm. ESI-MS: m/z (%) 302.2 (100) [M+]. IR
+
464, 407 cm−1. HR-ESI-MS: calcd for C19H18N3 288.1501, found
288.1501.
1075
dx.doi.org/10.1021/jo302479p | J. Org. Chem. 2013, 78, 1070−1079

The Journal of Organic Chemistry
Article
2-(1-(2-Chlorobenzyl)-1H-imidazolium-3-yl)-3-methylindolate
1-Benzyl-3-(3-methyl-1H-indol-2-yl)-1H-imidazole-2(3H)-thione
(24a). A sample of the betaine 22a (144 mg, 0.5 mmol) was used. The
thione 24a was isolated in 96% yield (153 mg), mp 154 °C. 1H NMR
(CDCl3, 400 MHz): 2.31 (s, 3 H, Me), 5.31 (s, 2 H, CH2), 6.69 (d, 1
H, Himidazole, J = 2.5 Hz), 6.92 (d, 1 H, Himidazole, J = 2.5 Hz), 7.15 (ddd,
1 H, 5-H, J = 7.9 Hz, J = 7.0 Hz, J = 1.0 Hz), 7.24 (ddd, 1H, 6-H, J =
8.2 Hz, J = 7.0 Hz, J = 1.2 Hz), 7.35−7.40 (m, 6 H, Ar), 7.56 (d, 1 H,
H-4, J = 7.9 Hz), 9.56 (br s, 1 H, NH) ppm. 13C NMR (CDCl3, 150
MHz): δ 8.8, 51.3, 104.6, 111.5, 117.3, 118.3, 119.0, 119.9, 123.1,
127.7, 128.4, 128.4, 128.5, 129.0, 133.7, 135.2, 163.5 ppm. ESI-MS: m/
z (%) 320.0 (100) [M + 1]. IR (KBr): ν 3356, 3091, 2918, 1629, 1494,
1471, 1399, 1325, 1299, 1241, 745, 714, 670, 470, 433 cm−1. HR-ESI-
MS: calcd for C19H18N3S+ 320.1221, found 320.1217.
(22b). A sample of 401 mg of 21b was used. The ylide 22b was
1
isolated as a yellowish powder, mp 95 °C, yield 254 mg (79%). H
NMR (DMSO-d6, 400 MHz): δ 2.36 (s, 3 H, Me), 5.64 (s, 2 H, CH2),
6.66 (dd, 1 H, J = 7.4 Hz, J = 7.0 Hz), 6.72 (dd, 1 H, J = 7.9 Hz, J = 7.0
Hz), 7.21 (d, 1 H, J = 8.0 Hz), 7.28 (d, 1 H, J = 7.6 Hz), 7.42−7.50
(m, 3 H), 7.58−7.61 (m, 1 H), 7.81 (s, 1 H), 8.12 (s, 1 H), 9.63 ppm
(s, 1 H). 13C NMR (DMSO-d6, 100 MHz): δ 9.3, 49.9, 92.9, 114.7,
116.5, 116.9, 117.0, 121.7, 122.1, 127.7, 128.0, 129.5, 129.8, 130.4,
130.7, 130.8, 132.5, 132.6, 134.0, 136.8, 142.8 ppm. ESI-MS: m/z (%)
322.1 (100) [M + 1]. IR (KBr): ν 1546, 1442, 1321, 1161, 1113, 1055,
+
821, 737, 680, 625, 452 cm−1. HR-ESI-MS: calcd for C19H17ClN3
322.1111, found 322.1106.
1-(2-Chlorobenzyl)-3-(3-methyl-1H-indol-2-yl)-1H-imidazole-
3-Methyl-2-(1-(3-methylbenzyl)-1H-imidazolium-3-yl)indolate
2(3H)-thione (24b). A sample of 161 mg of 22b was used. Thione 24b
(22c). A sample of 381 mg of 21c was used. The ylide 22c was isolated
1
1
was isolated in 95% yield (168 mg), mp 142 °C. H NMR (CDCl3,
as a yellowish powder, mp 93 °C, yield 211 mg (70%). H NMR
400 MHz): δ 2.31 (s, 3 H, Me), 5.44 (s, 2 H, CH2), 6.79 (d, 1 H, J =
2.5 Hz), 6.94 (d, 1 H, J = 2.5 Hz), 7.13−7.17 (m, 1 H), 7.22−7.33 (m,
3 H), 7.36 (d, 1 H, J = 8.1 Hz), 7.43−7.47 (m, 2 H), 7.56 (d, 1 H, J =
7.9 Hz), 9.55 (s, 1 H, NH) ppm. 13C NMR (CDCl3, 100 MHz): δ 8.8,
48.7, 104.8, 111.5, 117.6, 118.4, 119.1, 120.0, 123.2, 127.5, 127.8,
128.4, 129.9, 129.9, 130.8, 133.0, 133.8, 133.8, 163.9 ppm. GC-MS: m/
z (%) 353.0 (25) [M+]. IR (KBr): ν 3159, 1628, 1469, 1399, 1311,
1237, 1054, 744, 135, 705, 673, 588, 239, 451, 426 cm−1. HR-ESI-MS:
calcd for C19H16N3NaSCl+ 376.0651, found 376.0651.
(DMSO-d6, 400 MHz): δ 2.33 (s, 3 H, Me), 2.36 (s, 3 H, Me), 5.44 (s,
2 H, CH2), 6.66−6.76 (m, 2 H), 7.21−7.23 (m, 2 H), 7.28−7.35 (m, 4
H), 7.88 (s, 1 H), 8.08 (s, 1 H), 9.70 (s, 1 H) ppm. 13C NMR
(DMSO-d6, 100 MHz): δ 9.3, 20.9, 51.9, 92.8, 114.7, 116.4, 116.9,
117.0, 121.6, 121.9, 125.3, 128.8, 128.9, 129.3, 130.8, 133.4, 135.1,
136.8, 138.3, 142.7 ppm. ESI-MS: m/z (%) 302.1 (100) [M + 1]. IR
(KBr): ν 1442, 1321, 1161, 1113, 1055, 821, 737, 680, 625, 452 cm−1.
+
HR-ESI-MS: calcd for C20H20N3 302.1657, found 302.1654.
3-Methyl-2-(1-(naphthalen-2-ylmethyl)-1H-imidazolium-3-yl)-
indolate (22d). A sample of 417 mg of 21d was used. The ylide 22d
was isolated as a yellowish powder, mp 212 °C, yield 317 mg (94%).
1H NMR (DMSO-d6, 400 MHz): δ 2.38 (s, 3 H, Me), 5.66 (s, 2 H,
1-(3-Methyl-1H-indol-2-yl)-3-(3-methylbenzyl)-1H-imidazole-
2(3H)-thione (24c). A sample of 151 mg of 22c was used. Thione 24c
1
was isolated in 90% yield (150 mg), mp 156 °C. H NMR (CDCl3,
400 MHz): δ 2.31 (s, 3 H, Me), 2.37 (s, 3 H, Me), 5.26 (s, 2 H, CH2),
6.68 (d, 1 H, J = 2.5 Hz), 6.92 (d, 1 H, J = 2.5 Hz), 7.13−7.30 (m, 6
H), 7.37 (d, 1 H, J = 8.2 Hz), 7.56 (d, 1 H, J = 7.9 Hz), 9.59 (br.s., 1
H, NH) ppm. 13C NMR (CDCl3, 100 MHz): δ 8.8, 21.5, 51.4, 104.7,
111.5, 117.4, 118.3, 119.1, 120.0, 123.2, 125.7, 127.8, 128.5, 129.0,
129.3, 129.3, 133.8, 135.2, 138.9, 163.5 ppm. GC-MS: m/z (%) 333.1
(65) [M+]. IR (KBr): ν 3158, 1567, 1454, 1391, 1329, 1237, 1122,
729, 693, 673, 589, 539, 519, 432 cm−1. HR-ESI-MS: calcd for
C20H19N3NaS+ 356.1197, found 356.1194.
1-(3-Methyl-1H-indol-2-yl)-3-(naphthalen-2-ylmethyl)-1H-imida-
zole-2(3H)-thione (24d). A sample of 169 mg of 22d was used.
Thione 24d was isolated in 94% yield (174 mg), mp 205 °C. 1H NMR
(DMSO-d6, 400 MHz): δ 2.13 (s, 3 H, Me), 5.49 (s, 2 H, CH2), 7.07
(ddd, 1 H, J = 7.9 Hz, J = 7.0 Hz, J = 1.0 Hz), 7.17 (ddd, 1 H, J = 8.2
Hz, J = 7.0 Hz, J = 1.1 Hz), 7.33−7.35 (m, 2 H), 7.44 (d, 1 H, J = 2.5
Hz), 7.50−7.56 (m, 3 H), 7.60 (dd, 1 H, J = 8.2 Hz, J = 1.6 Hz), 7.89−
7.95 (m, 4 H), 11.43 ppm (s, 1 H, NH). 13C NMR (DMSO-d6, 100
MHz): δ 8.1, 50.3, 105.2, 111.3, 118.5, 118.7, 118.8, 119.6, 122.1,
125.9, 126.1, 126.4, 126.6, 127.0, 127.6, 127.7, 128.2 (2 C), 132.4,
132.7, 133.6, 134.2, 164.4 ppm. GC-MS: m/z (%) 369.4 (80) [M+]. IR
(KBr): ν 3166, 1602, 1493, 1472, 1403, 1328, 1298, 1242, 1122, 956,
811, 776, 758, 738, 710, 670, 603, 541, 521, 477, 442 cm−1. HR-ESI-
MS: calcd for C23H20N3S+ 370.1378, found 370.1375.
CH2), 6.67 (ddd, 1 H, J = 7.6 Hz, J = 6.7 Hz, J = 1.0 Hz), 6.74 (ddd, 1
H, J = 7.9 Hz, J = 6.7 Hz, J = 1.3 Hz), 7.23 (d, 1 H, J = 7.9 Hz), 7.29
(s, 1 H, J = 7.6 Hz), 7.54−7.59 (m, 2 H), 7.63 (dd, 1 H, J = 8.5 Hz, J =
1.7 Hz), 7.92−7.96 (m, 3 H), 7.99 (d, 1 H, J = 8.5 Hz), 8.03 (s, 1 H),
8.10 (s, 1 H), 9.77 ppm (s, 1 H). 13C NMR (DMSO-d6, 100 MHz): δ
9.4, 52.0, 92.7, 114.6, 116.6, 116.9 (2 C), 121.6, 122.0, 125.6, 126.7 (2
C), 127.4, 127.7, 127.9, 128.8, 130.9, 132.7, 132.7, 133.5, 137.1, 142.9
ppm. ESI-MS: m/z (%) 338.1 (100) [M − 80]. IR (KBr): ν 1549,
1443, 1318, 1292, 1161, 1115, 863, 821, 777, 737, 614, 476 cm−1. HR-
+
ESI-MS: calcd for C23H20N3 338.1657, found 338.1656.
2-(1-Benzhydryl-1H-imidazolium-3-yl)-3-methylindolate (22e). A
sample of 401 mg of 21e was used. The ylide 22e was isolated as a
yellowish powder, mp 229 °C, yield 287 mg (79%). 1H NMR
(DMSO-d6, 400 MHz): δ 2.36 (s, 3 H, Me), 5.64 (s, 2 H, CH2), 6.66
(dd, 1 H, J = 7.4 Hz, J = 7.0 Hz), 6.72 (dd, 1 H, J = 7.9 Hz, J = 7.0
Hz), 7.21 (d, 1 H, J = 8.0 Hz), 7.28 (d, 1 H, J = 7.6 Hz), 7.42−7.50
(m, 3 H), 7.58−7.61(m, 1 H), 7.81 (s, 1 H), 8.12 (s, 1 H), 9.63 ppm
(s, 1 H). 13C NMR (DMSO-d6, 100 MHz): δ 9.3, 49.9, 92.9, 114.7,
116.5, 116.9, 117.0, 121.7, 122.1, 127.7, 128.0, 129.5, 129.8, 130.4,
130.7, 130.8, 132.5, 132.6, 134.0, 136.8, 142.8 ppm. ESI-MS: m/z (%)
322.1 (100) [M + 1]. IR (KBr): ν 1536, 1392, 1324, 1291, 1239, 1152,
1111, 1073, 834, 752, 729, 701, 656, 641, 475, 411 cm−1. HR-ESI-MS:
+
calcd for C25H22N3 364.1814, found 364.1806.
1-Benzhydryl-3-(3-methyl-1H-indol-2-yl)-1H-imidazole-2(3H)-thi-
2-(1-(4-(Dimethylamino)phenyl)-1H-imidazolium-3-yl)-3-methyl-
one (24e). A sample of 182 mg of 22e was used. Thione 24e was
1
indolate (22f). A sample of 397 mg of 21f was used. The ylide 22f was
isolated in 62% yield (123 mg), mp 201 °C. H NMR (CDCl3, 400
1
isolated as a yellowish powder, mp 110 °C, yield 240 mg (76%). H
MHz): δ 2.33 (s, 3 H, Me), 6.69 (d, 1 H, J = 2.5 Hz), 6.95 (d, 1 H, J =
2.5 Hz), 7.12−7.16 (m, 1 H), 7.21−7.25 (m, 5 H), 7.33−7.42 (m, 7
H), 7.47 (s, 1 H), 7.56 (d, 1 H, J = 7.8 Hz), 9.59 (br s., 1 H, NH) ppm.
13C NMR (CDCl3, 100 MHz): δ 8.9, 64.0, 104.5, 111.5, 116.8, 118.0,
119.0, 120.0, 123.2, 127.8, 128.3, 128.5, 128.6, 128.9, 133.7, 138.3,
163.9 ppm. GC-MS: m/z (%) 395.2 (20) [M+]. IR (KBr): ν 1627,
1489, 1469, 1449, 1397, 1324, 1119, 1095, 1004, 750, 738, 716, 699,
673, 647, 582, 515, 463, 423 cm−1. HR-ESI-MS: calcd for C25H22N3S+
396.1534, found 396.1530.
NMR (DMSO-d6, 400 MHz): 2.42 (s, 3 H, Me), 2.99 (s, 6 H, NMe2),
6.69 (dd, 1 H, J = 7.4 Hz, J = 7.4 Hz), 6.76 (dd, 1 H, J = 7.6 Hz, J = 7.4
Hz), 6.88 (d, 2 H, 9.0 Hz), 7.26 (d, 1 H, J = 7.6 Hz), 7.32 (d, 1 H, J =
7.4 Hz), 7.70 (d, 2 H, 9.0 Hz), 8.24 (s, 1 H), 8.28 (s, 1 H), 9.86 ppm
(s, 1 H, NH). 13C NMR (DMSO-d6, 100 MHz): δ 9.2, 93.6, 112.3,
112.7, 114.8, 116.5, 117.0, 117.1, 120.4, 120.9, 122.2, 122.6, 122.8,
123.9, 125.5, 130.8, 131.3, 136.7, 142.6, 150.7 ppm. ESI-MS: m/z (%)
317.1 (25) [M + 1]. IR (KBr): ν 1606, 1519, 1442, 1332, 1298, 1236,
1092, 1055, 944, 810, 741, 625, 517 cm−1. HR-ESI-MS: calcd for
1-(4-(Dimethylamino)phenyl)-3-(3-methyl-1H-indol-2-yl)-1H-imi-
+
C20H21N4 317.1766, found 317.1765.
dazole-2(3H)-thione (24f). A sample of 158 mg of 22f was used.
1
General Procedure for the Formation of Thiones 24a−f. A
flask was charged with the ylide (0.5 mmol), sulfur (32 mg, 1.0 mmol),
and p-xylene (5 mL), and the mixture was stirred and boiled for 3 h.
After evaporation, the resulting precipitate was purified by column
chromatography (silica gel, ethyl acetate/petroleum ether).
Thione 24f was isolated in 54% yield (94 mg), mp 256 °C. H NMR
(CDCl3, 400 MHz): δ 2.30 (s, 3 H, Me), 2.94 (s, 6 H, Me2N), 6.71 (d,
2 H, J = 9.0 Hz), 6.87 (d, 1 H, J = 2.3 Hz), 6.96 (d, 1 H, J = 2.3 Hz),
7.06−7.10 (m, 1 H), 7.14−7.18 (m, 1 H), 7.29 (d, 1 H, J = 8.1 Hz),
7.34 (d, 2 H, J = 9.0 Hz), 7.50 (d, 1 H, J = 8.1 Hz), 9.60 (br s., 1 H,
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NH) ppm. 13C NMR (CDCl3, 100 MHz): δ 8.9, 40.5, 104.7, 111.6,
112.2, 118.3, 119.0, 119.5, 119.9, 123.1, 126.5, 127.0, 127.8, 128.7,
133.9, 150.5, 164.0 ppm. GC-MS: m/z (%) 348.2 (30) [M+]. IR
(KBr): ν 3294, 1738, 1611, 1520, 1489, 1472, 1351, 1330, 1310, 1226,
1194, 1099, 982, 936, 811, 741, 732, 671, 642, 599, 585, 566, 527, 504,
439 cm−1. HR-ESI-MS: calcd for C20H21N4S+ 349.1487, found
349.1488.
General Procedure for the Synthesis of the Borane Adducts
26a−g. The ylide (1.0 mmol) and a stirring bar were placed under a
nitrogen atmosphere (glovebox) in a bomb tube with 5 equiv excess of
50% triethylborane in hexane (1.5 mL). Then, the tube was closed
tightly and placed into a preheated oil bath at 150 °C. The reaction
mixture was stirred overnight at that temperature, cooled to room
temperature, diluted with THF, and subjected to column chromatog-
raphy (EtOAC/petroleum ether).
26d was isolated as white crystals, mp 181 °C, yield 272 mg (67%). 1H
NMR (CDCl3, 400 MHz): δ 7.39 (t, 6 H, Me), 0.67−0.76 (m, 2 H,
CH2), 0.85−0.95 (m, 2 H, CH2), 2.39 (s, 3 H, Me), 5.30 (s, 2 H,
CH2), 6.77 (d, 1 H, J = 1.9 Hz), 6.94 (ddd, 1 H, J = 7.9 Hz, J = 7.0 Hz,
J = 1.0 Hz), 7.02 (ddd, 1 H, J = 8.3 Hz, J = 7.0 Hz, J = 1.2 Hz), 7.27
(dd, 1 H, J = 8.3 Hz, J = 1.8 Hz), 7.35 (d, 1 H, J = 7.9 Hz), 7.39 (d, 1
H, J = 1.9 Hz), 7.44−7.48 (m, 3 H), 7.68 (s, 1 H), 4.74−7.81 (m, 3 H)
ppm. 13C NMR (CDCl3, 100 MHz): δ 8.2, 11.2, 14.3, 52.4, 66.1, 67.5,
67.7, 89.6, 106.4, 107.7, 112.3, 114.0, 117.3, 118.4, 120.1, 122.0, 125.2,
127.0 (2C), 127.7, 127.9, 128.0, 129.5, 131.6, 131.7, 133.3, 133.3,
136.0, 136.1, 175.7 ppm. 11B NMR (CDCl3, 128 MHz, BF3·Et2O): δ
−1.41 ppm. GC-MS: m/z (%) 405.3 (2) [M+]. IR (KBr): ν 2854,
1172, 1638, 1452, 1337, 1228, 1192, 1123, 1050, 860, 821, 775, 762,
746, 732, 475, 443 cm−1. HR-ESI-MS: calcd for C27H29BN3+ 406.2455,
found 406.2450.
1-Benzyl-11,11-diethyl-5-methyl-1,11-dihydroimidazo[2′,1′:3,4]-
[1,4,2]diazaborolo[1,5-a]indol-4-ium-11-ide (26a). A sample of the
ylide 22a (287 mg, 1.0 mmol) was used. Yield: 238 mg (67%), mp 157
°C. 1H NMR (CDCl3, 600 MHz): δ 0.55 (t, 6 H, Me), 0.78−0.84 (m,
2 H, CH2), 0.98−1.04 (m, 2 H, CH2), 2.53 (s, 3 H, Me), 5.28 (s, 2 H,
CH2), 6.88 (d, 1 H, J = 2.0 Hz), 7.08 (ddd, 1 H, J = 7.9 Hz, J = 6.9 Hz,
J = 1.1 Hz), 7.16 (ddd, 1 H, J = 8.0 Hz, J = 6.9 Hz, J = 1.2 Hz), 7.34−
7.35 (m, 2 H), 7.45−7.49 (m, 4 H), 7.51 (d, 1 H, J = 2.0 Hz), 7.60
ppm (ddd, 1 H, J = 7.9 Hz, J = 1.2 Hz, J = 0.7 Hz). 13C NMR (CDCl3,
150 MHz): δ 8.20, 11.1, 14.3, 52.2, 89.5 112.3, 114.0, 117.3, 118.4,
120.1, 122.0, 128.2, 129.1, 129.3, 131.6, 134.3, 136.0, 136.2, 175.8
ppm. 15N NMR (CDCl3, 60 MHz, MeNO2): δ −218.7, −199.8,
−182.3 ppm. 11B NMR (CDCl3, 128 MHz, BF3·Et2O): δ −1.33 ppm.
IR (KBr): ν 3445, 2860, 1639, 1488, 1455, 1344, 1235, 1123, 747, 712
cm−1. GC-MS: m/z (%) 355.4 (3) [M+]. HR-ESI-MS: calcd for
1-Benzhydryl-11,11-diethyl-5-methyl-1,11-dihydroimidazo-
[2′,1′:3,4][1,4,2]diazaborolo[1,5-a]indol-4-ium-11-ide (26e). A sam-
ple of 321 mg of 22e was used. The boron adduct 26e was isolated as
white crystals, mp 33 °C, yield 362 mg (84%). 1H NMR (CDCl3, 400
MHz): δ 0.31 (t, 6 H, Me, J = 7.7 Hz), 0.58−0.67 (m, 2 H, CH2),
0.86−0.94 (m, 2 H, CH2), 2.47 (s, 3 H, Me), 6.86 (s, 1 H), 6.90 (d, 1
H, J = 2.0 Hz), 6.98−7.02 (m, 1 H), 7.06−7.10 (m, 1 H), 7.18−7.21
(m, 4 H), 7.35−7.42 (m, 7 H), 7.51−7.53 ppm (m, 2 H). 13C NMR
(CDCl3, 100 MHz): δ 8.2, 10.9, 14.2, 65.8, 89.6, 112.2, 113.7, 117.3,
118.4, 120.1, 121.4, 128.2, 128.9, 129.1, 131.6, 136.0, 136.1, 138.0
ppm. 11B NMR (CDCl3. 128 MHz, BF3·Et2O): δ −1.29 ppm. GC-MS:
m/z (%) 431.2 (1.5) [M+]. IR (KBr): ν 2858, 1635, 1452, 1341, 1209,
+
1030, 722, 695, 657 cm−1. HR-ESI-MS: calcd for C29H31BN3
432.2611, found 432.2602.
1-(4-(Dimethylamino)phenyl)-11,11-diethyl-5-methyl-1,11-
dihydroimidazo[2′,1′:3,4][1,4,2]diazaborolo[1,5-a]indol-4-ium-11-
ide (26f). A sample of 316 mg of 22f was used. The boron adduct 26f
+
C23H27BN3 356.2298, found 356.2298.
1-(2-Chlorobenzyl)-11,11-diethyl-5-methyl-1,11-dihydroimidazo-
[2′,1′:3,4][1,4,2]diazaborolo[1,5-a]indol-4-ium-11-ide (26b). A sam-
ple of 22b (321 mg) was used. The boron compound 26b was isolated
1
was isolated as white crystals, mp 192 °C, yield 300 mg (78%). H
NMR (CDCl3, 400 MHz): δ 0.37 (t, 6 H, J = 7.6 Hz), 0.50−0.60 (m, 2
H, CH2), 0.77−0.87 (m, 2 H, CH2), 3.03 (s, 6 H, NMe2), 6.77 (d, 2 H,
J = 9.0 Hz), 7.01 (ddd, 1 H, J = 7.8 Hz, J = 7.0 Hz, J = 1.1 Hz), 7.08
(ddd, 1 H, J = 8.0 Hz, J = 7.0 Hz, J = 1.3 Hz), 7.18 (d, 1 H, J = 1.8
Hz), 7.34 (d, 2 H, J = 9.0 Hz), 7.40 (d, 1 H, J = 8.0 Hz), 7.55 (d, 1 H, J
= 7.8 Hz), 7.59 ppm (d, 1 H, J = 1.8 Hz). 13C NMR (CDCl3, 100
MHz): δ 8.3, 10.9, 14.7, 40.4, 89.4, 112.2, 112.3, 113.4, 117.2, 118.4,
119.9, 123.6, 124.7, 125.8, 131.6, 135.8, 136.1, 150.8 ppm. 11B NMR
(CDCl3, 128 MHz, BF3·Et2O): δ −0.01 ppm. IR (KBr): ν 2858, 1739,
1640, 1612, 1521, 1451, 1335, 1227, 1138, 1035 884, 821, 742, 717,
1
as white crystals, mp 148 °C, yield 253 mg (65%). H NMR (CDCl3,
400 MHz): δ 0.38 (t, 6 H, Me, J = 7.4 Hz), 0.62 (q, 1 H, CH2, J = 7.4
Hz), 0.66 (q, 1 H, CH2, J = 7.4 Hz), 0.83 (q, 1 H, CH2, J = 7.4 Hz),
0.87 (q, 1 H, CH2, J = 7.4 Hz), 2.41 (s, 3 H, Me), 5.32 (s, 2 H, CH2),
6.86 (d, 1 H, Himidazole, J = 2.0 Hz), 6.94 (ddd, 1 H, J = 7.8 Hz, J = 6.9
Hz, J = 1.0 Hz), 7.02 (ddd, 1 H, J = 8.1 Hz, J = 6.9 Hz, J = 1.2 Hz),
7.12 (dd, 1 H, J = 7.6 Hz, J = 1.6 Hz), 7.23 (ddd, 1 H, J = 7.6 Hz, J =
7.6 Hz, J = 1.4 Hz), 7.28 (ddd, 1 H, J = 7.7 Hz, J = 7.6 Hz, J = 1.6 Hz),
7.33 (d, 1 H, J = 8.1 Hz), 7.41−7.43 (m, 2 H), 7.46 (d, 1 H, J = 7.8
Hz) ppm. 13C NMR (CDCl3, 100 MHz): δ 8.2, 11.1, 14.2, 49.6, 89.6,
112.3, 113.9, 117.3, 118.4, 120.1, 122.2, 127.8, 130.1, 130.2, 130.5,
131.5, 132.1, 133.7, 136.0, 136.0, 176.0 ppm. 11B NMR (CDCl3, 128
MHz, BF3·Et2O): δ −1.36 ppm. GC-MS: m/z (%) 360.2 (100) [M −
29]. IR (KBr): ν 2864, 1635, 1485, 1451, 1342, 1136, 1056, 875, 839,
774, 743, 730, 682, 643, 445 cm−1. HR-ESI-MS: calcd for
+
694, 670, 642, 564, 529, 443 cm−1. HR-ESI-MS: calcd for C24H30BN4
385.2564, found 385.2560.
1-Benzyl-5-methyl-11,11-diphenyl-1,11-dihydroimidazo-
[2′,1′:3,4][1,4,2]diazaborolo[1,5-a]indol-4-ium-11-ide (26g). A sam-
ple of 287 mg of 22a and 726 mg (3 equiv) of triphenylborane was
used. The boron adduct 26g was isolated as white crystals, mp 244 °C,
1
+
yield 190 mg (42%). H NMR (CDCl3, 400 MHz): δ 2.60 (s, 3 H,
C23H26BClN3 390.1908, found 390.1904.
Me), 5.21 (s, 2 H, CH2), 6.76−6.77 (m, 1 H), 6.91−6.93 (m, 2 H),
7.09−7.11 (m, 2 H), 7.26−7.49 (m, 16 H), 7.64−7.65 ppm (m, 1 H).
13C NMR (CDCl3, 100 MHz): δ 8.2, 52.5, 91.2, 112.9, 114.0, 117.9,
118.6, 121.0, 122.4, 126.1, 127.7, 128.7, 129.1, 129.2, 131.9, 133.6,
134.0, 135.4, 135.9, 147.0, 171.8 ppm. 15N NMR (CDCl3, 60 MHz,
MeNO2): −278.5, −204.2, −188.6 ppm. 11B NMR (CDCl3, 193 MHz,
BF3·Et2O): δ −2.60 ppm. GC-MS: m/z (%) 451.2 (30) [M+]. IR
(KBr): ν 1644, 1495, 1453, 1343, 1266, 1174, 992, 868, 745, 730, 703,
11,11-Diethyl-5-methyl-1-(3-methylbenzyl)-1,11-dihydro-
imidazo[2′,1′:3,4][1,4,2]diazaborolo[1,5-a]indol-4-ium-11-ide (26c).
A sample of 301 mg of 22c was used. The boron adduct 26c was
1
isolated as white crystals, mp 138 °C, yield 114 mg (31%). H NMR
(CDCl3, 400 MHz): δ 0.55 (t, 6 H, Me, J = 7.4 Hz), 0.79 (q, 2 H,
CH2, J = 7.4 Hz), 0.83 (q, 2 H, CH2, J = 7.4 Hz), 2.42 (s, 3 H, Me),
2.54 (s, 3 H, Me), 5.26 (s, 2 H, CH2), 6.91 (d,1 H, Himidazole, J = 1.9
Hz), 7.06−7.10 (m, 1 H), 7.15−7.18 (m, 3 H), 7.26 (d, 1 H, J = 7.8
Hz), 7.34−7.38 (m, 1 H), 7.48 (d, 1 H, J = 8.0 Hz), 7.53 (d, 1 H,
Himidazole, J = 1.9 Hz), 7.60 ppm (d, 1 H, J = 7.8 Hz). 13C NMR
(CDCl3, 100 MHz): δ 8.2, 11.1, 14.2, 21.4, 52.2, 89.5, 112.2, 113.9,
117.3, 118.4, 120.0, 122.0, 125.3, 128.9, 129.2, 129.8, 131.6, 134.3,
136.0, 136.2, 139.2, 175.6 ppm. 11B NMR (CDCl3, 128 MHz,
BF3·Et2O): δ −1.57 ppm. GC-MS: m/z (%) 369.3 (4) [M+]. IR
(KBr): ν 2864, 1639, 1453, 1343, 1234, 1194, 1122, 1050, 874, 788,
743, 712, 663, 431 cm−1. HR-ESI-MS: calcd for C24H29BN3+ 370.2455,
found 370.2452.
+
596, 442 cm−1. HR-ESI-MS: calcd for C31H27BN3 452.2298, found
452.2296.
2-(1-Benzyl-1H-imidazolium-3-yl)-3-methylindolate (27).
Benzylimidazole (211 mg; 1.3 mmol) and 3-methylindole (145 mg,
1.0 mmol) were used. 1-Benzyl-2-methyl-3-(3-methyl-1H-indol-2-
yl)imidazolium bromide was isolated as colorless crystals, mp 242.3
°C, yield 336 mg (88%). 1H NMR (DMSO-d6, 400 MHz): δ 2.18 (s, 3
H, Meindole), 2.59 (s, 3 H, Meimidazole), 5.60 (s, 2 H, CH2), 7.16 (dd, 1
H, J = 7.7 Hz, J = 7.3 Hz), 7.28 (dd, 1 H, J = 8.1 Hz, J = 7.3 Hz), 7.42
− 7.51 (m, 6 H), 7.66 (d, 1 H, J = 7.7 Hz), 8.09 (s, 1 H), 11.84 ppm
(br s, 1 H, NH). 13C NMR (DMSO-d6, 100 MHz): δ 7.5, 10.4, 51.3,
106.9, 111.8, 119.6, 119.8, 122.4, 123.6, 123.9, 123.9, 126.5, 128.0,
11,11-Diethyl-5-methyl-1-(naphthalen-2-ylmethyl)-1,11-
dihydroimidazo[2′,1′:3,4][1,4,2]diazaborolo[1,5-a]indol-4-ium-11-
ide (26d). A sample of 337 mg of 26d was used. The boron adduct
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Article
128.7, 129.1, 133.7, 134.1, 146.6 ppm. ESI-MS: m/z (%) 302.1 [M+].
IR (KBr): ν 3048, 1582, 1493, 1452, 1332, 1177, 1009, 743, 734, 699,
Cambridge, U.K., 2011. (b) Droge, T.; Glorius, F. Angew. Chem., Int.
Ed. 2010, 49, 6940. (c) Hahn, F. E.; Jahnke, M. C. Angew. Chem., Int.
Ed. 2008, 47, 3122.
̈
+
664, 631, 468, 428 cm−1. HR-ESI-MS: calcd for C20H20N3 302.1657,
found 302.1656.
(8) (a) Holschumacher, D.; Bannenberg, T.; Hrib, C. G.; Jones, P.
G.; Tamm, M. Angew. Chem., Int. Ed. 2008, 47, 7428. (b) Schmidt, A.;
Beutler, A.; Albrecht, M.; Ramírez, F. J. Org. Biomol. Chem. 2008, 6,
287.
(9) Han, Y.; Huynh, H. V. Dalton Trans. 2011, 40, 2141.
(10) Christl, M.; Engels, B. Angew. Chem., Int. Ed. 2009, 48, 1538.
(11) (a) Lavallo, V.; Dyker, C. A.; Donnadieu, B.; Bertrand, G.
Angew. Chem., Int. Ed. 2008, 47, 5411. (b) Lavallo, V.; Dyker, C. A.;
Donnadieu, B.; Bertrand, G. Angew. Chem., Int. Ed. 2009, 48, 1540.
(c) Fernandez, I.; Dyker, C. A.; DeHope, A.; Donnadieu, B.; Frenking,
́
G.; Bertrand, G. J. Am. Chem. Soc. 2009, 131, 11875.
(12) (a) Han, Y.; Huynh, H. V. Chem. Commun. 2007, 1089.
(b) Han, Y.; Huynh, H. V.; Tan, G. K. Organometallics 2007, 26, 6581.
(c) Han, Y.; Lee, L. J.; Huynh, H. V. Organometallics 2009, 28, 2778.
A sample of 382 mg of 1-benzyl-2-methyl-3-(3-methyl-1H-indol-2-
yl)imidazolium bromide was used to prepare the ylide as described
before. The ylide 27 was isolated as a yellowish powder, mp 98.0 °C,
yield 253 mg (84%). 1H NMR (DMSO-d6, 400 MHz): δ 2.14 (s, 3 H,
Meindole), 2.58 (s, 3 H, Meimidazole), 5.50 (s, 2 H, CH2), 6.74 (dd, 1 H, J1
≈ J2 = 7.4 Hz), 6.81 (dd, 1 H, J1 ≈ J2 = 7.4 Hz), 7.25 (d, 1 H, J = 8.0
Hz), 7.34 (d, 1 H, 7.8 Hz), 7.39−7.49 (m, 5 H), 7.80 (d, 1 H, J = 2.0
Hz), 7.84 ppm (d, 1 H, J = 2.0 Hz). 13C NMR (DMSO-d6, 100 MHz):
δ 8.7, 10.3, 50.8, 97.5, 115.2, 116.2, 117.3, 117.7, 121.2, 123.2, 127.8,
128.5, 129.1, 129.4, 134.5, 135.3, 142.0, 144.2 ppm. ESI-MS: m/z (%)
302.1 [M + H+]. IR (KBr): ν 3060, 1395, 1323, 1288, 733, 694, 440
+
cm−1. HR-ESI-MS: calcd for C20H20N3 302.1657, found 302.1658.
1-Benzyl-3-(1,3-dimethyl-1H-indol-2-yl)imidazolium Bro-
mide (29). Benzylimidazole (211 mg; 1.3 mmol) was used. The salt
29 was isolated as colorless crystals, mp 234.0 °C, yield 279 mg (73%).
1H NMR (DMSO-d6, 400 MHz): δ 2.20 (s, 3 H, Me), 3.60 (s, 3 H,
(d) Hanninen, M. M.; Peuronen, A.; Tuononen, H. M. Chem. Eur. J.
̈
2009, 15, 7287.
(13) Guisado-Barrios, G.; Bouffard, J.; Donnadieu, B.; Bertrand, G.
Angew. Chem., Int. Ed. 2010, 49, 4759.
(14) (a) Lavallo, V.; Canac, Y.; Prasang, C.; Donnadieu, B.; Bertrand,
NMe), 5.62 (s, 2 H, CH2), 7.20 (dd, 1 H, J1 ≈ J2 = 7.6 Hz), 7.36 (dd, 1
H, J1 ≈ J2 = 7.6 Hz), 7.42−7.51(m, 3 H), 7.55−7.60 (m, 3 H), 7.69 (d,
1 H, J = 8.0 Hz), 8.16−8.18 (m, 1 H), 8.21−8.23 (m, 1 H), 9.96 ppm
(br s, 1 H). 13C NMR (DMSO-d6, 100 MHz): δ 7.6, 29.4, 52.5, 106.5,
110.4, 119.6, 120.1, 123.3, 123.8, 125.1, 125.3, 125.8, 128.4, 128.9,
129.1, 134.3, 134.7, 138.9 ppm. ESI-MS: m/z (%) 302.1 [M+]. IR
(KBr): ν 2947, 1564, 1456, 1368, 1271, 1193, 1106, 908, 763, 752,
G. Angew. Chem., Int. Ed. 2005, 44, 5705. (b) Lavallo, V.; Canac, Y.;
Donnadieu, B.; Scholler, W. W.; Bertrand, G. Angew. Chem., Int. Ed.
̈
2006, 45, 3488.
(15) Nakafuji, S.-Y.; Kobayashi, J.; Kawashima, T. Angew. Chem., Int.
Ed. 2008, 47, 1141.
(16) Kobayashi, J.; Nakajuji, S.-Y.; Yatabe, A.; Kawashima, T. Chem.
Commun. 2008, 6233.
+
723, 662, 615, 549, 463, 411 cm−1. HR-ESI-MS: calcd for C20H20N3
302.1657, found 302.1655.
(17) (a) Fischer, E.; Besthorn, E. Ann 1882, 212, 316.
(b) Ramakrishna, R. S.; Irving, H. M. N. H. J. Chem. Soc. D: Chem.
Commun. 1969, 1356. (c) Kushi, Y.; Fernando, Q. J. Chem. Soc. D:
Chem. Commun. 1969, 1240. (d) Kushi, Y.; Fernando, Q. J. Am. Chem.
Soc. 1970, 92, 1965.
(18) Claus, A.; Howitz, H. J. Prakt. Chem. 1891, 43, 520.
(19) (a) Earl, J. C.; Mackney, A. W. J. Chem. Soc. 1935, 899.
(b) Eade, R. A.; Earl, J. C. J. Chem. Soc. 1946, 591. (c) Stewart, F. H.
C. Chem. Rev. 1964, 64, 129. (d) Gilchrist, T. L. Sci. Synth. 2004, 13,
109.
ASSOCIATED CONTENT
* Supporting Information
Text, figures, tables, and a CIF file giving additional compound
characterization data, X-ray data, results of calculations, and
NMR spectra. This material is available free of charge via the
Internet at http://pubs.acs.org.
■
S
AUTHOR INFORMATION
Corresponding Author
*E-mail: schmidt@ioc.tu-clausthal.de.
■
(20) Katritzky, A. R. Chem. Ind. 1955, 521.
(21) Huisgen, R.; Gotthardt, H.; Bayer, H. O. Angew. Chem., Int. Ed.
Notes
Engl. 1964, 3, 135.
(22) Ollis, W. D.; Stanforth, S. P.; Ramsden, C. A. Tetrahedron 1985,
41, 2239.
The authors declare no competing financial interest.
(23) (a) Ollis, W. D.; Ramsden, C. A. Adv. Heterocycl. Chem. 1976,
19, 1. (b) Ramsden, C. A. In Comprehensive Organic Chemistry;
Sammes, P. G., Ed.; Pergamon Press: Oxford, U.K., 1979; Vol. 4, p
1171.
ACKNOWLEDGMENTS
The Deutsche Forschungsgemeinschaft (DFG) is gratefully
acknowledged for financial support. Dr. Gerald Drager,
University of Hannover (Hannover, Germany) is gratefully
acknowledged for measuring the HRMS spectra.
■
̈
(24) Schmidt, A.; Guan, Z. Synthesis 2012, 3251.
(25) Farber, C.; Leibold, M.; Bruhn, C.; Maurer, M.; Siemeling, U.
̈
Chem. Commun. 2012, 48, 227.
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