Heterocycle Syntheses with Anionic N-Heterocyclic Carbenes: Ring Transformations of Sydnone Imine Anions

Article abstract of DOI:10.1002/ejoc.201800028

Sydnone imines were deprotonated at the C4 position to give lithium-stabilized anions, which proved to be stable for several months in solution. These anions are elements of the intersection of the substance classes of N-heterocyclic carbenes and mesomeric betaines. They can be formulated as anionic N-heterocyclic carbenes. The negative charge translates into high-field shifts of the ¹³C NMR resonance frequencies of C4 in comparison to other NHCs. Similar to the chemistry of N-heterocyclic carbenes, reactions with isocyanates and isothiocyanates gave 4-(N-carbamoyl)-benzoylsydnone imines in trapping reactions. As a result of ring transformations involving the characteristic π-architecture of the mesoionic framework, imidazolidine-2,4-dithiones, imidazolin-2,4-diones and 1,2,4-triazol-5-ones were formed depending on the substitution pattern of the starting materials and the reaction conditions.

Full text of DOI:10.1002/ejoc.201800028

A Journal of
Accepted Article
Title: Heterocycle syntheses with anionic N-heterocyclic carbenes.
Ring transformations of sydnone imine anions
Authors: Tyll Freese, Ana-Luiza Lücke, Jan C. Namyslo, Martin Nieger,
and Andreas Schmidt
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10.1002/ejoc.201800028
European Journal of Organic Chemistry
FULL PAPER
Heterocycle syntheses with anionic N-heterocyclic carbenes.
Ring transformations of sydnone imine anions
Tyll Freese,[a] Ana-Luiza Lücke,[a] Jan C. Namyslo,[a] Martin Nieger,[b] and Andreas Schmidt*[a]
Abstract: Sydnone imines were deprotonated at C4 to give lithium-
stabilized anions which proved to be stable for several months in
solution. These anions are elements of the intersection of the
substance classes of N-heterocyclic carbenes and mesomeric
betaines and can be formulated as anionic N-heterocyclic carbenes.
The negative charge translates into high-field shifts of the 13C NMR
resonance frequencies of C4 in comparison to other NHCs. Similar
to the chemistry of N-heterocyclic carbenes reactions with
the high degree of positive charge on N3, whereas the negative
partial charge on the exocyclic nitrogen atom is reflected in its
basicity.[7] The electron density on C4 is thought to determine the
mode of electrophilic substitution reactions.[7]
isocyanates
and
isothiocyanates
gave
4-(N-carbamoyl)-
benzoylsydnone imines in trapping reactions. As a result of ring
transformations involving the characteristic -architecture of the
mesoionic
framework,
however,
imidazolidine-2,4-dithiones,
imidazolin-2,4-diones and 1,2,4-triazol-5-ones were formed
depending on the substitution pattern of the starting materials and
the reaction conditions.
Scheme 1. Some canonical formulae of sydnones 1 and of sydnone imines 2.
In view of the current interest in anionic heterocyclic carbenes[8]
we became interested in studying the anions of sydnones 3 and
of O-ethyl sydnones 4.[3] Similar to the parent compound, the
anions have to be described by several mesomeric forms.
Concerning 3, the structures of anionic NHCs and of abnormal
anionic NHCs are among the canonical formulae as shown
(Scheme 2). By contrast, the deprotonated O-ethylsydnone 4
can be defined as abnormal N-heterocyclic carbene. The fact
that the delocalization of the negative charge of 3 include the
site of deprotonation, i.e. C4, sets these systems apart from
most known anionic N-heterocyclic carbenes. Connectivity
analyses[2] of sydnone anions reveal that C4 is a starred (active)
position and, correspondingly, large atomic orbital coefficients of
the highest occupied molecular orbitals (HOMO) were calculated
to be located on C4, resulting in an ESP partial charge of -0.94
and considerable high-field shifts of the 13C NMR signals.
Introduction
Sydnones 1 (1,2,3-oxadiazolium-5-olates) represent the most
prominent structural type of 228 theoretically predicted
mesoionic compounds.[1] They are members of the class of
conjugated mesomeric betaines (CMB) and belong to class 1B
according to a recent classification of heterocyclic mesomeric
betaines.[2] The term mesomeric betaine summarizes all
molecules which can exclusively be described by a number of
dipolar or tetrapolar resonance forms which delocalize the
positive and negative charges within a common -electron
system. As examples, sydnones can be described by canonical
forms such as 1(I), 1(II) and 1(III). The latter two are in
agreement with the bond lengths of the exocyclic C-O bond
which corresponds to a double bond.[3] Sydnones have proven
to be versatile 1,3-dipoles for cycloaddition reactions[4] and have
displayed various biological activities.[5] In contrast to sydnones,
the much lesser examined class of sydnone imines 2 (1,2,3-
oxadiazolium-5-aminides) formally possess an exocyclic imine
bond as analogously represented by the canonical forms 2(II)
and 2(III).[6] The chemistry of sydnone imines such as their
hydrolytic or thermal decomposition has been associated with
[a]
Tyll Freese, Ana-Luiza Lücke, Jan C. Namyslo, Andreas Schmidt
Institute of Organic Chemistry
Clausthal University of Technology
Leibnizstrasse 6, D-38678 Clausthal-Zellerfeld, Germany
E-mail: schmidt@ioc.tu-clausthal.de
https://www.ioc.tu-clausthal.de
Scheme 2. Sydnone anions 3 and the NHC of O-ethyl sydnone 4. Charge
distribution according to the resonance forms (I) and connectivity analysis (II).
[b]
Martin Nieger
Department of Chemistry, University of Helsinki
P.O Box 55, Fin-00014 University of Helsinki, Finland
Supporting information for this article is given via a link at the end of
the document.
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10.1002/ejoc.201800028
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The anions of sydnones form palladium complexes which are
catalytically active in cross-coupling reactions.[3],[9] These
derivatives of mesoionic compounds are elements of the
interesting intersection of the substance classes of mesomeric
betaines and N-heterocyclic carbenes.
A first review is
available.[10] Very recently, a quantitative analysis of factors
influencing the ease of formation and -bonding strength of N-
heterocyclic carbenes, including those derived from mesomeric
betaines, was developed.[11] According to this analysis, N-
phenylsydnone has CREF factor (carbene relative energy of
formation) of 0.572 which means that deprotonation occurs
easier than in diphenylimidazolium-4-olate (CREF = 0.600).[11] In
continuation of our interest in mesomeric betaines,[12] N-
heterocyclic carbenes[13] and the combination of both classes[14]
we report here on new and unexpected reactions of sydnone
imine anions which prove their Janus-type character.
Figure 1. Molecular drawing of 7a (displacement parameters are drawn at
50% probability level). Selected bond lengths [pm] (crystallographic
numbering): N2-N3: 129.71 (13), N3-C4: 134.70 (13), C4-C5: 138.63 (15), C5-
N6: 131.56 (14), C7-O7: 123.75(13), O7-H4: 238.3 pm.
Next we performed a base screening to obtain the anions of
sydnone imines for further examinations. The CREF index of 5-
(acetylimino)-3-methyl-sydnone as a model compound was
calculated to be 0.574.[11] Ring cleavages of sydnone imines are
known to occur under basic conditions[18] or in water to give N-
nitrosoaminoacetamides
and
-(N-
nitrosobenzylamino)acrylonitrile, respectively.[19] In addition, N-
acyl-substituted sydnone imines form 4-hydroxy-1,2,3-
triazoles[20] or pyrazolinones[21] on treatment with hydroxide or
aqueous ammonia by means of ring transformations. In the past,
nBuLi has been used to initiate several electrophilic attacks at
C4,[22] however, these reactions suffer from rapid
decompositions at elevated temperatures.[23] In the course of our
Results and Discussion
The sydnone imine hydrochlorides 6a,b were prepared from the
amines 5a,b by nucleophilic substitution with haloacetonitriles in
reasonable yields according to modified literature procedures
concerning the cyclohexyl derivative,[15] followed by N-nitrosation
and ring closure reaction on treatment with gaseous hydrochloric
acid. Final benzoylation gave the sydnone imines 7a,b as stable,
brownish to yellow-colored compounds which we used as
starting materials for further syntheses. The sydnone imine 7c
was prepared by a slightly different method which we described
in an earlier paper.[16]
base
screenings
we
found
that
1M
lithium
bis(trimethylsilyl)amide in THF at rt is the best base to
accomplish quantitative deprotonations at C4 of sydnone imines
(Scheme 4). Again, several canonical formulae describe the
systems, among those mesomeric forms of anionic NHCs,
anionic abnormal NHCs as well as by a structure which displays
two negative charges on C4. According to the understanding of
mesomerism concerning the distribution of charges in
conjugated systems, one of these two negative charges at C4 is
due to the exocyclic sp2 orbital, and the other represents the
delocalized negative charge within the -conjugated system.
Scheme 3. Reaction conditions starting from 5a: A) 1.1 eq. of ClCH2CN, 2.2
eq. of K2CO3, MeCN, 20 h, reflux (79 %)[39]; B) 2.4 eq. of amyl nitrite, Et2O, 20
h, rt, then HCl(g), 1.5 h, rt (88 %); C) 1.2 eq. of PhCOCl, CH2Cl2, -10 °C, then
2.4 eq. of NEt3 (96 %). Reaction conditions starting from 5b: A) 1.2 eq. of
BrCH2CN, 1.2 eq. of NaOAc, EtOH, 24 h, reflux (73 %); B) 2.4 eq. of amyl
nitrite, Et2O, 20 h, rt, then HCl(g), 1.5 h, rt (82 %); C) 1.2 eq. of PhCOCl,
CH2Cl2, -10 °C, then 2.4 NEt3 (76 %). Reaction conditions starting from 5c: D)
BrCH2CN, NaOAc, EtOH, reflux (83%); E) NaNO2, HCl, 0 °C (92%); F) HCl(g),
Et2O, 20 °C (99%); G) PhCOCl, CH2Cl2, -10 °C, then NEt3 (80%).
Sydnone imines are known to be photochemically and thermally
sensitive.[17] Nevertheless we obtained single crystals of sydnone
imine 7a by slow evaporation of a chloroform-ethyl acetate
mixture in the dark and subjected them to a single crystal X-ray
analysis. The exocyclic C-N bond was found to be 131.56(14)
pm which resembles the C(sp2)=N double bond length of oximes
and imines (128 pm) rather than the C(sp2)-N single bond length
of formamide (138 pm).
Scheme 4. Sydnone imine anions and their canonical forms.
The deprotonated sydnone imines 8a-c are stable in THF
solutions for several months in the absence of water. 13C NMR
spectra show a down field shift at the C4 position (8a: 152.0
ppm, 8b: 154.8 ppm, 8c: 159.8 ppm) in comparison to the
starting materials. These values, however, are considerably
shifted high-field in comparison to other N-heterocyclic
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10.1002/ejoc.201800028
European Journal of Organic Chemistry
FULL PAPER
carbenes.[10] The role of the lithium cation is crucial for the
stabilization of the anions, as potassium ions trigger
decomposition. According to a DFT calculation at the B3LYP/6-
31G(d,p) level the lithium cation is located between the carbene
carbon atom and the carbonyl oxygen atom. The 2-
methoxyphenyl substituent is twisted out of planarity. We
calculated the HOMO-1, HOMO and LUMO energies of 8c to be
-6.39 eV, -5.46 eV and -1.85 eV, respectively. The HOMO-1
includes the  lone pair, whereas the HOMO and LUMO are 
orbitals, respectively (Fig. 2).
Scheme 5. Amides and thioamides from sydnone imine 7a.
When starting from the 3-aryl substituted sydnone imines 7b,c,
however, the 5-arylhydrazono-imidazolidine-2,4-diones or
-
dithiones 12 - 17 and the triazoles 18,19 were formed in
moderate yields on reaction with the aforementioned
iso(thio)cyanates (Scheme 6). The outcome of the reactions is
dependent on the substitution patterns of the substrates, the
iso(thio)cyanates, the stoichiometry, and the reaction
temperature. Details are summarized in Table 1. The yellow
hydrazones 12 and 14 can be isolated when performing the
reaction at -30 °C with subsequent quenching with water,
whereas the corresponding triazoles 18 and 19 were formed
slowly while warming the reaction mixture to rt. Thus, the p-
chlorophenyl-substituted sydnone 7b reacted with isocyanates
to give the triazoles 18 and 19 (Table 1, entries 7,8), whereas
the less reactive isothiocyanate gave the hydrazone 17 (Table 1,
entry 6).
Figure 2. HOMO-1 (above left), HOMO (above right) and LUMO (below) of 8c.
In order to study the covalent bond character of the C-Li bond,
we performed 7Li NMR measurements of 8c. Literature suggests
a
rising covalent C-Li bonding character with increasing
downfield shifts in the Li NMR spectra.[24] The Li NMR shift of
8c was determined to be +0.6 ppm (THF-[D]8, rt), whereas the
chemical shift for LHMDS is +0.1 ppm (THF-[D]8, rt, ext. ref.
LiBr). Comparison of literature known chemical shifts in THF
(nBuLi: +1.2 ppm at rt;[25] tBuLi: + 0.3 ppm at -95 °C;[26] LiAlH4: -
0.2 ppm at rt[27]) indicates a covalent bond character between
tBuLi and nBuLi for the Li-C bond of the carbene 8c. Sydnone
imine anions form gold and palladium complexes[16] and undergo
reactions with S[28] and Se.[16] To the best of our knowledge,
however, the trapping reaction with CO2, isocyanates and
isothiocyanates have not yet been described. They are trapping
reactions of N-heterocyclic carbenes such as imidazole-2-
ylidene,[29] pyrazol-3-ylidene,[30] indazol-3-ylidene[31] as well as
several organo lithium compounds. Thus phenyl lithium reacts
with isocyanates,[32] isothiocyanates,[33] and carbon dioxide[34]
similarly; the non-complexed phenyl anion was calculated to
have a significant carbene character.[35] To study the behavior of
sydnone imine anions toward heterocumulenes we reacted
freshly prepared samples of deprotonated sydnone imines with
tolyl isocyanate, tolyl isothiocyanate and p-chlorophenyl
isocyanate. Starting from sydnone imine 7a the anticipated
amides 9,11 and the thioamide 10 were formed at rt in high
yields (Scheme 5). Higher temperatures (< 50 °C) gave identical
products in similar yields.
7
7
Scheme 6. Formation von arylhydrazones from sydnone imines 7b,c.
Table 1. Substitution pattern of compounds 12
– 19, reaction times,
temperatures and yields.
Entry
educt
7b
product
12
R1
H
R2
Cl
Cl
Cl
H
R3
Me
Me
Cl
X
O
S
O
O
S
O
-
t
T
yield
30%
47%
26%
36%
43%
40%
26%
26%
1
2
3
4
5
6
7
8
8 h
5 h
8 h
5 h
5 h
5 h
5 h
5 h
-30°C
7b
13
H
rt
7b
14
H
-30°C
7c
15
OMe
OMe
OMe
H
Me
Me
Cl
rt
rt
rt
rt
rt
7c
16
H
7c
17
H
7b
18
Cl
Cl
Me
Cl
7b
19
H
-
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10.1002/ejoc.201800028
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A single crystal X-ray study of 15 helped to determine the
structure (Fig. 3) and displays hydrogen bondings between O4-
N7-H and O14-N7-H, resulting in a planar conformation between
the o-methoxyphenyl and the imidazolidine ring fragments. The
NH-proton is localized at the N7-nitrogenatom in the crystal
structure and this is also true in solutions and can be proven by
HMBC NMR spectra at rt. The hydrazones show intense yellow
(diones) to violet colors (dithiones) with extinction coefficients
from 15500 (13) to 33900 (10) L/mol*cm.
According to a DFT calculation at the B3LYP/6-31G(d,p) level
the HOMO and LUMO of intermediate 7cB are separated. The
HOMO has indeed a large atomic orbital coefficient at the
negatively charged nitrogen atom of the northern carbamoyl)(2-
methoxyphenyl)amidate moiety, whereas the LUMO has a large
coefficient at C4 of the sydnone imine moiety. This step
therefore resembles intramolecular charge neutralizations of
cross-conjugated mesomeric betaines.[36] Likewise, the HOMO
of intermediate 7cC has large coefficients at the enolate carbon
atom, whereas at the azo group large coefficients of the LUMO
were calculated.
Figure 3. Molecular drawing of 15 (displacement parameters are drawn at
50% probability level). Selected bond lengths [pm] (crystallographic
numbering): N1-C2: 137.98(14), N1-C5: 141.06(13), C2-O2: 121.33(13), C2-
N3: 141.04(14), N3-C4: 138.98(14), C4-O4: 121.92(14), C4-C5: 146.93(15),
C5-N6: 128.63(14), N6-N7: 134.11(13), O4-H7: 212(1), O14-H7: 227(1) pm.
We propose the following mechanism for the formation of 12 -
17 (Scheme 7). The sydnone imine carbenes 7b,c are
subsequently trapped by two molecules of isocyanates (A → B).
The negative charge of the isocyanate residue of B induce a ring
cleavage of the sydnone imine to give C, the enolate moiety of
which attacks the azo group to give D. Formation of benzoyl
isocyanate yielded the isolated products 12 - 17.
Figure 4. Frontier orbital profile of the intermediates 7cB and 7cC.
Further investigation showed the possibility to directly react the
hydrazone 12 into the triazole 18 starting from the anion of 12
(Scheme 8). This is generated by LHMDS at rt and undergoes a
[2+3]-cycloaddition with isocyanate and subsequent ring
cleavage of the imidazoledione moiety. Extrusion of one
molecule of isocyanate gave the triazole 18 after quenching the
reaction mixture. A blind probe was also carried out without
addition of isocyanate. Under these conditions, reaction
temperatures up to 50 °C induced no reaction at all.
Scheme 7. Proposed mechanism for the formation of 12
- 17 by ring
transformation.
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10.1002/ejoc.201800028
European Journal of Organic Chemistry
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a DSC 6 apparatus (Perkin Elmer). The electrospray ionization
mass spectra (ESIMS) were taken with an Agilent LCMSD
series HP 1100 with APIES at a fragmentor voltage of 30 V
unless otherwise noted. Samples were dissolved in MeOH and
sprayed from MeCN at 4000 V capillary voltage. The HR-MS
spectra were measured on a Bruker Daltonik Tesla-Fourier
transform-ion cyclotron resonance mass spectrometer with
electrospray ionisation. Yields are not optimized.
Crystal structure determination
The single-crystal X-ray diffraction study was carried out on a
Bruker D8 Venture diffractometer with Photon100 detector at
123(2) K using Cu-Ka radiation ( = 1.54178 Å) (7a) or Mo-Ka
radiation ( = 0.71073 Å) (15). Direct Methods (SHELXS-97)[37]
were used for structure solution and refinement was carried out
using SHELXL-2014 (full-matrix least-squares on F2).[38]
Hydrogen atoms were localized by difference electron density
determination and refined using a riding model (H(N) free).
Semi-empirical absorption corrections and extinction corrections
were applied (see cif-file for details).
Scheme 8. Transformation of the hydrazone 12 into triazole 18.
Conclusions
Sydnone imine anions are elements of the intersection between
mesomeric betaines and N-heterocyclic carbenes. They have to
be represented by several canonical formulae, among those the
structures of anionic NHCs and abnormal anionic NHCs. The sp2
hybrid orbital at C4 containing the pair of electrons governs its
carbene character, whereas the architecture of -electrons
translates into a mesomeric betaine-like chemical behavior. A
large atomic orbital coefficient of the HOMO at C4 leads to
considerable high-field shifts of the 13C NMR resonance
frequencies. Sydnone imine anions were generated by LHMDS
in THF at rt. They proved to be stable under exclusion of light
and moisture. Depending on the substitution pattern they
reacted with isocyanates and isothiocyanates to give
(arylcarbamoyl)-3-cyclohexyl-sydnone imines, 1,3-diaryl-5-(2-
7a: colorless crystals, C15H17N3O2, M = 271.32, crystal size
0.32 × 0.16 × 0.08 mm, monoclinic, space group P21/c (no. 14),
a = 9.7085(4) Å, b = 17.9600(7) Å, c = 7.7222(3) Å,  =
103.236(1)°, V = 1310.71(9) Å3, Z = 4, (calc) = 1.375 Mg m-3,
F(000) = 576, (CuK) = 0.76 mm-1, 11915 reflections (max
=
72.2°), 2559 unique [Rint = 0.020], 182 parameters, R1 (for 2449
I > 2(I)) = 0.033, wR2 (all data) = 0.086, S = 1.05, largest diff.
peak and hole 0.29 and -0.19 e Å-3.
15: yellow crystals, C24H22N4O3, M = 414.45, crystal size
0.24 × 0.20 × 0.12 mm, triclinic, space group P-1 (no. 2), a =
7.7786(4) Å, b = 12.1357(8) Å, c = 12.5091(8) Å,  =
117.631(2)°,  = 99.457(2)°,  = 92.632(2)°, V = 1021.83(11) Å3,
Z = 2, (calc) = 1.347 Mg m-3, F(000) = 436, (MoK) = 0.09
mm-1, 41247 reflections (max = 27.5°), 4695 unique [Rint = 0.030],
287 parameters, 1 restraint, R1 (for 4117 I > 2(I)) = 0.038, wR2
(all data) = 0.101, S = 1.03, largest diff. peak and hole 0.40 and -
0.29 e Å-3.
arylhydrazono)-imidazolidine-2,4-diones
or
1-aryl-3-(N-
arylcarbamoyl)-4-aryl-4,5-dihydro-1,2,4-triazol-5-ones as a result
of the symphony of  (carbene) and  electrons (mesomeric
betaine).
Experimental Section
General consideration
CCDC 1588012 (7a), and 1588013 (15) contain the
supplementary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge
Flash-chromatography was performed with silica gel 60 (0.040-
0.063 mm). Nuclear magnetic resonance (NMR) spectra were
obtained with a Bruker Avance 400 and Bruker Avance III 600
Crystallographic
Data
Centre
via
www.ccdc.cam.ac.uk/data_request/cif.
1
MHz. H NMR spectra were recorded at 400 MHz or 600 MHz
and 13C NMR spectra were measured at 100 MHz or 150 MHz,
with the solvent peak or tetramethylsilane used as the internal
reference. Multiplicities are described by using the following
abbreviations: s = singlet, d = doublet, t = triplet, q = quartet, and
m = multiplet. Signal orientations in DEPT experiments were
described as follows: o = no signal; + = up (CH, CH3); - = down
(CH2). The numbering of the compounds is not necessarily in
accordance with IUPAC rules to allow comparisons
(“spectroscopic numbering”). FT-IR spectra were obtained on a
Bruker Vector 22 in the range of 400 to 4000 cm-1. Melting points
were measured by differential scanning calorimetry (DSC) using
Calculations.
All density-functional theory (DFT)-calculations were carried out
by using the current Spartan Software (Spartan’16,
Wavefunction,
http://www.wavefun.com) running on an Intel® CoreTM i7-6950X
deca-core system equipped with 64 GB RAM main memory and
sufficient solid-state disc space. MMFF optimized structures
were used as starting geometries. Then, the B3LYP density
functional and the 6-31G(d,p) basis set was used. All final
structures were proven to be true minima by the absence of
Inc.,
Irvine,
CA.
Available
from:
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10.1002/ejoc.201800028
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imaginary frequencies or transition states by the occurrence of a
negative frequency.
General prodecure for the benzoylation of sydnone imine
hydrochlorides 6a-c: A suspension of the sydnone imine
hydrochloride, 1.2 eq. of benzoyl chloride and DCM (abs.) was
cooled to -10 °C. Then under vigorous stirring a solution of 2.4
eq. of triethylamine in 5 mL of DCM (abs.) was added slowly.
The mixture was then slowly warmed to rt and stirred for 16 h.
Afterwards 100 mL of water were added. The aqueous phase
was extracted with dichloromethane three times. The combined
organic phases were dried over MgSO4 and the solvent was
finally removed under reduced pressure.
Synthesis
of
sydnone
imine
hydrochloride
6a:
Cyclohexylamine (5a) (5.00 g, 50.4 mmol), chloroacetonitrile
(4.19 g, 55.5 mmol), potassium carbonate (13.94 g, 101 mmol)
and 50 mL of acetonitrile were combined in a 100 mL flask and
refluxed for 20 h. Afterwards the reaction mixtures were poured
into 250 mL of water. The aqueous phase was extracted with
dichloromethane three times, respectively. The combined
organic phases were dried over MgSO4 and the solvent was
removed under reduced pressure. Further purification of the
black liquid was not necessary for the follow-up reaction. Yield:
5.50 g (79%) of a black oil of N-cyclohexyl-aminoacetonitrile. 1H
NMR (400 MHz, CDCl3): 훿 = 3.63 (s, 2H, 5-H), 2.68 (tt, JH,H1 =
10.2 Hz, JH,H2 = 3.8 Hz, 1H, 1-H), 1.83-1.88 (m, 2H, 2/2’-H),
1.72-1.78 (m, 2H, 3/3’-H), 1.60-1.67 (m, 1H, 4-H), 1.25-1.36 (m,
2H, 3/3’-H), 1.14-1.23 (m, 1H, 4-H),1.04-1.14 (m, 2H, 2/2’-H)
ppm. Spectroscopic data are in agreement with those reported
in the literature.[39] A solution of N-cyclohexyl-aminoacetonitrile
thus prepared (5.50 g, 39.8 mmol) in 35 mL Et2O (abs.) in a two-
necked flask was treated with isopentyl nitrite (12.9 mL, 95.5
mmol) and stirred at rt for 20 hours. Afterwards the solution was
treated with gaseous hydrochloric acid for 90 minutes. The
resulting precipitation was filtered off and washed generously
with Et2O and DCM. Yield: 7.13 g (88%) of a white solid. 1H
NMR (400 MHz, DMSO-d6): 9.87 (s, 2H, 6-H), 8.17 (s, 1H, 4-H),
4.88 (tt, JH,H1 = 11.3 Hz, JH,H2 = 3.8 Hz, 1H, 7-H), 2.17-2.20 (m,
2H, 8/8’-H), 1.81-1.91 (m, 4H, 8/8’-H + 9/9’-H), 1.62-1.65 (m, 1H,
10-H), 1.36-1.47 (m, 2H, 9/9’-H), 1.19-1.30 (m, 1H, 10-H) ppm.
Spectroscopic data are in agreement with those reported in the
literature.[40]
3-Cyclohexyl-6-benzoylsydnone imine 7a: N-Cyclohexyl-
sydnone imine hydrochloride (2.00 g, 9.82 mmol), benzoyl
chloride (1.37 mL, 11.78 mmol), triethylamine (3.28 mL, 23.57
mmol) and 30 mL of DCM (abs.) were used. Purification was
achieved by column chromatography (silica gel, DCM:MeOH =
30:1). Yield: 2.55 g (96%) of a brownish solid. 1H NMR (400
MHz, CDCl3): 훿 = 8.27-8.29 (m, 2H, 9/9’-H), 8.20 (s, 1H, 4-H),
7.46-7.51 (m, 1H, 11-H), 7.41-7.45 (m, 2H, 10/10’-H), 4.52 (tt,
JH,H1 = 11.8 Hz, JH,H2 = 3.9 Hz, 1H, 12-H), 2.27-2.31 (m, 2H,
13/13’-H), 1.96-2.01 (m, 2H, 14/14’-H) 1.83-1.94 (m, 2H, 13/13’-
H), 1.76-1.81 (m, 1H, 15-H), 1.41-1.52 (m, 2H, 14/14’-H), 1.24-
1.35 (m, 1H, 15-H) ppm; 13C NMR (100 MHz, CDCl3): 훿 = 174.4
(o, C-5), 174.2 (o, C-7), 137.1 (o, C-8), 129.3 (+, C-11), 129.3 (+,
C-9/9’), 127.9 (+, C-10/10’), 104.0 (+, C-4), 64.6 (+, C-12), 32.2
(-, C-13/13’), 24.6 (-, C-14/14’), 24.5 (-, C-15) ppm.
Spectroscopic data are in agreement with those reported in the
literature.[15]
3-(p-Chlorophenyl)-6-benzoylsydnone imine 7b: N-(p-
Chlorophenyl)-sydnone imine hydrochloride (0.30 g, 1.29 mmol),
benzoyl chloride (0.18 mL, 1.55 mmol), triethylamine (0.43 mL,
3.10 mmol) and 10 mL DCM (abs.) were used. Purification was
achieved by column chromatography (silica gel, DCM:MeOH =
30:1). Yield: 0.29 g (76%) of a yellow solid, mp: 191 °C
Synthesis of sydnone imine hydrochloride 6b: p-
Chloroaniline (10.00 g, 78.4 mmol), bromoacetonitrile (11.28 g,
94.1 mmol), sodium acetate trihydrate (12.80 g, 94.1 mmol) and
40 mL of ethanol were combined in a 100 mL flask and refluxed
for 24 h. Afterwards the reaction mixture was poured into 250
mL of iced water. The resulting precipitate was filtered off,
washed with water and dried in vacuo. Purification was achieved
by recrystallization from EtOH. Yield: 9.53 g (73%) of a white
solid consistent of N-(p-chlorophenyl)-aminoacetronitrile. 1H
NMR (400 MHz, CDCl3): 훿 = 7.19-7.23 (m, 2H, 2/2’-H), 6.60-6.64
(m, 2H, 3/3’-H), 4.06 (s, 3H, 4-H + 5-H) ppm. Spectroscopic data
1
(decomposition). H NMR (400 MHz, CDCl3): 휹 = 8.65 (s, 1H, 4-
H), 8.26-8.29 (m, 2H, 9/9’-H), 7.79-7.84 (m, 2H, 13/13’-H), 7.58-
7.61 (m, 2H, 14/14’-H), 7.48-7.52 (m, 1H, 11-H), 7.41-7.45 (m,
2H, 10/10’-H) ppm; 13C NMR (100 MHz, CDCl3): 휹 = 174.5 (o,
C-5), 174.3 (o, C-7), 139.5 (o, C-15), 136.8 (o, C-8), 132.2 (o, C-
12), 131.7 (+, C-11), 130.8 (+, C-14/14‘), 129.5 (+, C-9/9‘), 128.0
(+, C-10/10‘),122.8 (+, C-13/13‘), 104.3 (+, C-4) ppm; IR (ATR):
3187, 3066, 1627, 1553, 1489, 1432, 1314, 1293, 1093, 1067,
1011, 971, 946, 832, 729, 707, 690, 681, 662, 642, 516, 497 cm-
1; MS (ESI 30 V) m/z (%) = 300.0 (30) [M+H+]. HR-ESI-MS:
calcd for C15H11N3O2Cl1+ 300.0540. Found 300.0540.
are in agreement with those reported in the literature.[41]
A
solution of N-cyclohexyl-aminoacetonitrile thus prepared (3.76 g,
22.5 mmol) in 35 mL of Et2O (abs.) in a two-necked flask was
treated with isopentyl nitrite (7.3 mL, 54.1 mmol) and stirred at rt
for 20 hours. Afterwards the solution was treated with gaseous
hydrochloric acid for 90 minutes. The precipitation was filtered
off and washed generously with Et2O. Yield: 4.28 g (82%) of a
General procedure for the sydnone imine deprotonations:
Under an inert atmosphere a dry sample of the sydnone imine in
an NMR tube was dissolved in anhydrous THF-d8. Then 1.2 eq.
of a 2M solution of LHMDS in THF was added to give the lithium
adduct in quantitative yields.
1
white solid. H NMR (400 MHz, DMSO-d6): 훿 = 10.22 (s, 2H, 6-
H), 8.75 (s, 1H, 4-H), 8.10-8.13 (m, 2H, 8/8’-H), 7.85-7.87 (m, 2H,
9/9’-H) ppm. Spectroscopic data are in agreement with those
reported in the literature.[18b]
4-Lithium-3-cyclohexyl-6-benzoylsydnone imine 8a: 3-
Cyclohexyl-6-benzoylsydnone imine (0.021 g, 0.077 mmol) and
a 2M solution of LHMDS in THF (0.046 mL, 0.093 mL) were
used for the deprotonation experiment. 1H NMR (600 MHz, THF-
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201800028
European Journal of Organic Chemistry
FULL PAPER
d8): δ = 8.33-8.35 (m, 2H, 9/9’-H), 7.30-7.35 (m, 3H, 10/10’-H +
11-H), 4.45-4.50 (m, 1H, 12-H), 2.15-2.18 (m, 2H, Cy-H), 1.96-
2.03 (m, 2H, Cy-H) 1.88-1.92 (m, 2H, Cy-H), 1.73-1.78 (m, 1H,
Cy-H), 1.45-1.54 (m, 2H, Cy-H), 1.22-1.30 (m, 1H, Cy-H) ppm;
13C NMR (150 MHz, THF-d8): 휹 = 185.6 (o, C-5), 170.2 (o, C-7),
152.0 (o, C-4), 141.1 (o, C-8), 130.1 (+, C-11), 129.8 (+, C-9/9’),
127.8 (+, C-10/10’), 64.3 (+, C-12), 34.4 (-, C-Cy), 26.1 (-, C-Cy),
25.9 (-, C-Cy) ppm.
1.30-1.37 (m, 1H, 15-H) ppm; 13C NMR (150 MHz, CDCl3): 휹 =
172.1 (o, C-7), 165.5 (o, C-5), 153.8 (o, C-16), 136.7 (o, C-8),
134.9 (o, C-21), 134.8 (o, C-18), 132.2 (+, C-11), 129.9 (+, C-
20/20’), 129.4 (+, C-9/9’), 128.4 (+, C-10/10’), 120.2 (+, C-
19/19’), 107.4 (o, C-4), 65.8 (+, C-12), 32.6 (-, C-13/13’), 25.2 (-,
C-14/14’), 24.9 (-, C-15), 21.1 (+, C-22) ppm; IR (ATR): 3175,
3116, 3053, 2936, 2853, 1674, 1635, 1606, 1574, 1549, 1512,
1447, 1396, 1369, 1307, 1277, 1261, 1234, 1178, 1035, 1018,
902, 869, 828, 805, 741, 712, 693, 591, 536, 508 cm-1; MS (ESI
30 V) m/z (%) = 427.1 (30) [M+Na+], 831.5 (100) [2M+Na+]. HR-
ESI-MS: calcd for C23H25N4O3+ 405.1927. Found 405.1926.
4-Lithium-3-(p-chlorophenyl)-6-benzoylsydnone imine 8b: 3-
(p-Chlorophenyl)-6-benzoylsydnone imine (0.015 g, 0.050 mmol)
and 2M solution of LHMDS in THF (0.030 mL, 0.060 mL) were
used for the deprotonation experiment. 1H NMR (600 MHz, THF-
d8): δ = 8.29-8.31 (m, 2H, 9/9’-H), 8.14-8.16 (m, 2H, 13/13’-H),
7.53-7.56 (m, 2H, 14/14’-H), 7.29-7.32 (m, 1H, 11-H), 7.24-7.27
(m, 2H, 10/10’-H) ppm. 13C NMR (150 MHz, THF-d8): δ = 186.5
(o, C-5), 171.2 (o, C-7), 154.8 (+, C-4) 139.8 (o, C-15), 140.7 (o,
C-8), 136.4 (o, C-12), 130.4 (+, C-11), 130.2 (+, C-14/14‘), 130.0
(+, C-9/9‘), 127.9 (+, C-10/10‘),123.9 (+, C-13/13‘),ppm.
4-(N-(p-Methylphenyl)carbamothioyl)-3-cyclohexyl-6-
benzoylsydnone imine 10: 3-Cyclohexyl-6-benzoylsydnone
imine (0.271 g, 1.00 mmol), 2 M of LHMDS in THF (0.60 mL,
1.20 mmol), 4-tolyl isothiocyanate (0.328 g, 2.20 mmol) and 12
mL of THF (abs.) were used. Purification was achieved by
column chromatography (silica gel, DCM:PE = 10:1). Yield:
1
0.352 g (84%) of a yellow solid, mp: 171 °C (decomposition). H
NMR (400 MHz, CDCl3): 휹 = 13.47 (s, 1H, 17-H), 8.15-8.18 (m,
2H, 9/9’-H), 7.64-7.66 (m, 2H, 19/C19’-H), 7.49-7.54 (m, 1H, 11-
H), 7.40-7.46 (m, 2H, 10/10’-H), 7.24-7.26 (m, 2H, 20/20’-H),
6.97 (tt, JH,H1 = 11.4 Hz, JH,H2 = 3.5 Hz, 1H, 12-H), 2.44-2.47 (m,
2H, 13/13’-H), 2.39 (s. 3H, 22-H), 1.90-2.00 (m, 4H, 13/13’-H +
14/14’-H), 1.79-1.83 (m, 1H, 15-H), 1.50-1.62 (m, 2H, 14/14’-H),
1.28-1.38 (m, 1H, 15-H) ppm; 13C NMR (100 MHz, CDCl3): 휹 =
176.1 (o, C-16), 172.0 (o, C-7), 163.4 (o, C-5), 137.3 (o, C-21),
136.3 (o, C-8), 135.6 (o, C-18), 132.3 (+, C-11), 129.7 (+, C-
20/20’), 129.4 (+, C-9/9’), 128.4 (+, C-10/10’), 124.2 (+, C-
19/19’), 111.6 (o, C-4), 65.9 (+, C-12), 32.9 (-, C-13/13’), 25.2 (-,
C-14/14’), 24.9 (-, C-15), 21.3 (+, C-22) ppm; IR (ATR): 2936,
2855, 1640, 1600, 1564, 1506, 1448, 1392, 1307, 1253, 1231,
1045, 1020, 817, 756, 737, 708, 571, 505, 449 cm-1; MS (ESI 30
V) m/z (%) = 443.1 (100) [M+Na+], 863.5 (80) [2M+Na+]. HR-
ESI-MS: calcd for C23H25N4O2S1+ 421.1698. Found 421.1700.
4-Lithium-3-(o-methoxyphenyl)-6-benzoylsydnone imine 8c:
3-(o-Methoxyphenyl)-6-benzoylsydnone imine (0.022 g, 0.075
mmol) and 2M solution of LHMDS in THF (0.045 mL, 0.089 mL)
1
were used for the deprotonation experiment. H NMR (600 MHz,
THF-d8): δ = 8.25-8.24 (m, 2H, 9/9’-H), 7.48-7.51 (m, 1H, 15-H),
7.46-7.47 (m, 1H, 17-H), 7.22-7.25 (m, 1H, 11-H), 7.19-7.20 (m,
1H, 14-H), 7.13-7.16 (m, 2H, 10/10’-H), 7.05-7.07 (m, 1H, 16-H),
3.73 (s, 3H, 19-H) ppm.[16] 13C NMR (150 MHz, THF-d8): δ =
185.4 (o, C5), 170.4 (o, C7), 159.8 (o, C4), 154.9 (o, C13), 140.8
(o, C8), 131.8 (+, C15), 130.8 (o, C12), 130.1 (+, C11), 129.8 (+,
C9/C9‘), 128.2 (+, C17), 127.9 (+, C10/C10‘), 121.0 (+, C16),
113.4 (+, C14), 56.1 (+, C19) ppm. 7Li NMR (233 MHz, THF- d8):
δ = 0.58 ppm.
General procedure for the sydnone imine carbene
generation and subsequent reaction with isocyanates /
isothiocyanates: Under an inert atmosphere the sydnone
imines were solved in THF (abs.) and treated with a 2M solution
of LHMDS in THF. After stirring for 10 minutes at rt the
isocyanates/isothiocyanates were added. An immediate change
of color was be observed. The reaction mixture was stirred for 5
h, then combined with silica gel and purified by column
chromatography.
4-(N-(p-Chlorophenyl)carbamoyl)-3-cyclohexyl-6-
benzoylsydnone imine 11: 3-Cyclohexyl-6-benzoylsydnone
imine (0.200 g, 0.74 mmol), 2 M of LHMDS in THF (0.44 mL,
0.89 mmol), 4-chlorophenyl-isocyanate (0.249 g, 1.62 mmol)
and 12 mL of THF (abs.) were used. Purification was achieved
by column chromatography (silica gel, DCM:PE = 10:1). Yield:
1
0.261 g (83%) of a white solid, mp: 182 °C (decomposition). H
NMR (400 MHz, CDCl3): 휹 = 11.33 (s, 1H, 17-H), 8.20-8.23 (m,
2H, 9/9’-H), 7.60-7.64 (m, 2H, 19/C19’-H), 7.54-7.58 (m, 1H, 11-
H), 7.46-7.50 (m, 2H, 10/10’-H), 7.33-7.36 (m, 2H, 20/20’-H),
5.89 (tt, JH,H1 = 11.5 Hz, JH,H2 = 3.6 Hz, 1H, 12-H), 2.37-2.39 (m,
2H, 13/13’-H), 1.92-2.00 (m, 4H, 13/13’-H + 14/14’-H), 1.81-1.84
(m, 1H, 15-H), 1.51-1.63 (m, 2H, 14/14’-H), 1.28-1.40 (m, 1H,
15-H) ppm; 13C NMR (100 MHz, CDCl3): 휹 = 172.0 (o, C-7),
165.4 (o, C-5), 153.9 (o, C-16), 136.6 (o, C-8), 136.0 (o, C-18),
132.4 (+, C-11), 130.2 (o, C-21), 129.5 (+, C-20/20’), 129.4 (+,
C-9/9’), 128.5 (+, C-10/10’), 121.4 (+, C-19/19’), 107.1 (o, C-4),
4-(N-(p-Methylphenyl)carbamoyl)-3-cyclohexyl-6-benzoyl-
sydnone imine 9: 3-Cyclohexyl-6-benzoylsydnone imine (0.271
g, 1.00 mmol), 2 M of LHMDS in THF (0.60 mL, 1.20 mmol), 4-
tolyl isocyanate (0.28 mL, 2.20 mmol) and 12 mL THF (abs.)
were used.
Purification was
achieved
by column
chromatography (silica gel, DCM:MeOH = 100:1). Yield: 0.399 g
(99 %) of a white solid, mp: 198 °C (decomposition). 1H-NMR
(600 MHz, CDCl3): 휹 = 11.21 (s, 1H, 17-H), 8.24-8.25 (m, 2H,
9/9’-H), 7.55-7.56 (m, 2H, 19/C19’-H), 7.53-7.57 (m, 1H, 11-H),
7.46-7.48 (m, 2H, 10/10’-H), 7.18-7.19 (m, 2H, 20/20’-H), 5.94 (tt, 66.0 (+, C-12), 32.6 (-, C-13/13’), 25.2 (-, C-14/14’), 24.9 (-, C-
JH,H1 = 11.6 Hz, JH,H2 = 3.6 Hz, 1H, 12-H), 2.37-2.39 (m, 2H,
13/13’-H), 2.35 (s. 3H, 22-H), 1.93-2.01 (m, 4H, 13/13’-H +
14/14’-H), 1.80-1.82 (m, 1H, 15-H), 1.54-1.61 (m, 2H, 14/14’-H),
15) ppm; IR (ATR): 3234, 3112, 3057, 2933, 2849, 1677, 1640,
1602, 1577, 1548, 1489, 1448, 1395, 1366, 1334, 1307, 1266,
1183, 1169, 1086, 1037, 1021, 898, 870, 825, 762, 708, 689,
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10.1002/ejoc.201800028
European Journal of Organic Chemistry
FULL PAPER
584, 507, 454, 439 cm-1; MS (ESI 30 V) m/z (%) = 447.1 (100)
[M+Na+], 871.3 (60) [2M+Na+]. HR-ESI-MS: calcd for
C22H21N4O3Cl1Na+ 447.1200. Found 447.1200.
2H, 7/7’-H), 7.50-7.52 (m, 2H, 8/8’-H) 7.50 (s, 4H, 11/11’/12/12’-
H), 7.22-7.25 (m, 2H, 18/18’-H), 6.97-6.99 (m, 2H, 17/17’-H)
ppm; 13C NMR (150 MHz, CDCl3): 훿 = 156.0 (o, C-4), 150.0 (o,
C-2), 141.5 (o, C-16), 134.8 (o, C-13), 133.8 (o, C-6), 130.5 (o,
C-9), 129.7 (+, C-11/11’), 129.6 (+, C-18/18’), 129.5 (+, C-7/7’),
129.0 (o, C-10), 127.5 (+, C8/8’), 127.3 (o, C-19), 127.2 (+, C-
12/12’), 125.3 (o, C-5), 114.5 (+, C-17/17’) ppm; IR (ATR): 3266,
3098, 1754, 1699, 1599, 1491, 1396, 1235, 1133, 1092, 1014,
941, 898, 816, 792, 759, 549, 506, 481 cm-1; MS (ESI 30 V) m/z
1,3-Di-(4-methylphenyl)-5-(2-(4-chlorophenyl)-hydrazono)-
imidazolidine-2,4-dione
12:
3-(4-Chlorophenyl)-6-
benzoylsydnone imine (0.300 g, 1.00 mmol), 2 M of LHMDS in
THF (0.60 mL, 1.20 mmol), 4-tolyl isocyanate (0.28 mL, 2.20
mmol) and 12 mL of THF (abs.) were used. The reaction was
stirred at -30 °C for 8 h and then quenched with 1 mL of water.
Purification was achieved by column chromatography (silica gel,
DCM). Yield: 0.127 g (30%) of a yellow solid, mp: 221 °C. 1H
NMR (400 MHz, CDCl3): 휹 = 11.07 (s, 1H, 17-H), 7.45-7.47 (m,
-
(%) = 459.0 (100) [M-H+]. HR-ESI-MS: calcd for C21H12N4O2Cl3
457.0026. Found 457.0023.
1,3-Di-(4-methylphenyl)-5-(2-(2-methoxyphenyl)-hydrazono)-
2H, 7/7’-H), 7.37-7.40 (m, 2H,12/12’-H) 7.31-7.33 (m, 2H, 8/8’-H), imidazolidine-2,4-dione
15:
3-(2-Methoxyphenyl)-6-
7.30-7.32 (m, 2H, 13/13’-H), 7.18-7.21 (m, 2H, 20/20’-H), 6.94-
6.98 (m, 2H, 19/19’-H), 2.43 (s, 3H, 10-H), 2.41 (s, 3H, 15-H)
ppm; 13C NMR (100 MHz, CDCl3): 휹 = 156.7 (o, C-4), 150.7 (o,
C-2), 141.9 (o, C-18), 138.9 (o, C-14), 138.0 (o, C-9), 130.0 (+,
C-8/8’), 129.9 (+, C-13/13’), 129.5 (o, C-6), 129.4 (+, C-20/20’),
127.9 (o, C-11), 126.7 (o, C-21), 126.3 (o, C-5), 126.2 (+, C7/7’),
125.9 (+, C-12/12’), 114.3 (+, C-19/19’), 21.4 (+, C-10 + C-15)
ppm; IR (ATR): 3297, 3037, 2921, 1761, 1699, 1616, 1600,
1502, 1406, 1235, 1136, 1093, 943, 898, 817, 806, 762, 736,
642, 582, 509, 420 cm-1; MS (ESI 30 V) m/z (%) = 471.1 (100)
[M-H+]. HR-ESI-MS: calcd for C23H19N4O2Cl1Na+ 441.1094.
Found 441.1092.
benzoylsydnone imine (0.295 g, 1.00 mmol), 2 M of LHMDS in
THF (0.60 mL, 1.20 mmol), 4-tolyl isocyanate (0.15 mL, 1.20
mmol) and 12 mL of THF (abs.) were used. Purification was
achieved by column chromatography (silica gel, DCM:MeOH =
1
300:1). Yield: 0.196 g (47%) of a yellow solid, mp: 230 °C. H
NMR (400 MHz, CDCl3):  = 11.35 (s, 1H, 17-H), 7.48-7.51 (m,
2H, 7/7’-H), 7.40-7.42 (m, 2H, 12/12’-H), 7.27-7.33 (m, 5H, 8/8’H
+ 13/13’-H + 23-H), 6.86-6.90 (m, 2H, 21-H + 22-H), 6.83-6.85
(m, 1H, 20-H), 3.88 (s, 3H, 25-H), 2.43 (s, 3H, 10-H), 2.40 (s, 3H,
15-H) ppm; 13C NMR (100 MHz, CDCl3): 휹 = 156.4 (o, C-4),
150.7 (o, C-2), 146.3 (o, C-19), 138.8 (o, C-14), 137.7 (o, C-9),
132.8 (o, C-18), 130.0 (+, C-13/13’), 129.8 (o, C-6), 129.8 (+, C-
8/8’), 128.1 (o, C-11), 126.4 (o, C-5), 126.3 (+, C-7/7’), 126.0 (+,
C12/12’), 121.5 (+, C-21), 121.5 (+, C-22), 112.1 (+, C-23),
110.5 (+, C-20), 55.8 (+, C-25), 21.4 (+, C-10 + C15) ppm; IR
(ATR): 3292, 2992, 2853, 1743, 1703, 1600, 1512, 1464, 1437,
1394, 1268, 1224, 1173, 1133, 1021, 938, 835, 804, 746, 606,
577, 507, 430 cm-1; MS (ESI 30 V) m/z (%) = 437.0 (100)
[M+Na+]. HR-ESI-MS: calcd for C24H22N4O3Na+ 437.1590. Found
437.1588.
1,3-Di-(4-methylphenyl)-5-(2-(4-chloroyphenyl)-hydrazono)-
imidazolidine-2,4-dithione
13:
3-(4-Chlorophenyl)-6-
benzoylsydnone imine (0.300 g, 1.00 mmol), 2 M of LHMDS in
THF (0.60 mL, 1.20 mmol), 4-tolyl isothiocyanate (0.328 g, 2.20
mmol) and 12 mL of THF (abs.) were used. Purification was
achieved by column chromatography (silica gel, DCM). Yield:
0.181 g (40%) of a red solid, mp: 273 °C (decomposition). 1H
NMR (600 MHz, CDCl3): 휹 = 14.41 (s, 1H, 17-H), 7.39-7.41 (m,
6H, 8/8’-H + 12/12’-H + 13/13’-H), 7.27-7.28 (m, 2H, 7/7’-H),
1,3-Di-(4-methylphenyl)-5-(2-(2-methoxyphenyl)-hydrazono)-
7.22-7.25 (m, 2H, 20/20’-H), 7.04-7.06 (m, 2H, 19/19’-H), 2.48 (s, imidazolidine-2,4-dithione
3H, 15-H), 2.46 (s, 3H, 10-H) ppm; 13C NMR (150 MHz, CDCl3):
benzoylsydnone imine (0.295 g, 1.00 mmol), 2 M of LHMDS in
휹 = 174.0 (o, C-4), 171.2 (o, C-2), 140.6 (o, C-18), 140.3 (o, C-9), THF (0.75 mL, 1.50 mmol), 4-tolyl isothiocyanate (0.328 g, 2.20
16:
3-(2-Methoxyphenyl)-6-
139.5 (o, C-14), 133.8 (o, C-5), 132.0 (o, C-6), 131.5 (o, C-11),
130.4 (+, C-8/8’), 130.1 (+, C-13/13’), 129.8 (+, C-20/20’), 129.4
(o, C-21), 128.6 (+, C7/7’), 128.4 (+, C-12), 116.4 (+, C-19), 21.6
(+, C-10) 21.6 (+, C-15) ppm; IR (ATR): 3038, 2961, 2919, 2856,
1564, 1511, 1479, 1422, 1389, 1320, 1258, 1218, 1145, 1082,
982, 884, 801, 761, 724, 632, 607, 574, 518, 508, 416 cm-1; MS
(ESI 30 V) m/z (%) = 473.0 (100) [M+Na+]. HR-ESI-MS: calcd for
C23H19N4S2Cl1Na+ 473.0637. Found 473.0641.
mmol) and 12 mL of THF (abs.) were used. Purification was
achieved by column chromatography (silica gel, DCM). Yield:
0.161 g (36%) of a violet solid, mp: 274 °C (decomposition). H
1
NMR (600 MHz, CDCl3): 휹 = 14.36 (s, 1H, 17-H), 7.42-7.43 (m,
2H, 7/7’-H), 7.39-7.41 (m, 2H, 13/13’-H), 7.38-7.40 (m, 2H,
8/8’H), 7.29-7.31 (m, 3H, 12/12’-H + 23-H), 7.03-7.05 (m, 1H,
21-H), 6.88-6.91 (m, 2H, 20-H + 22-H), 3.94 (s, 3H, 25-H), 2.48
(s, 3H, 10-H), 2.46 (s, 3H, 15-H) ppm; 13C NMR (150 MHz,
CDCl3): 휹 = 173.6 (o, C-4), 170.1 (o, C-2), 147.7 (o, C-19), 140.0
(o, C-14), 139.2 (o, C-9), 134.7 (o, C-5), 132.3 (o, C-11), 131.8
(o, C-6), 131.5 (o, C-18), 130.0 (+, C-13/13’), 129.8 (+, C-8/8’),
126.3 (+, C-12/12’), 126.0 (+, C7/7’), 121.5 (+, C-21), 121.5 (+,
C-22), 112.1 (+, C-23), 110.5 (+, C-20), 56.1 (+, C-25), 21.6 (+,
C-10) 21.6 (+, C-15) ppm; IR (ATR): 3041, 2943, 2842, 1596,
1549, 1511, 1477, 1417, 1391, 1318, 1298, 1255, 1208, 1180,
1151, 1111, 1090, 1040, 1022, 986, 869, 802, 782, 742, 725,
646, 630, 576, 551, 520 cm-1; MS (ESI 30 V) m/z (%) = 469.1
1,3-Di-(4-chlorophenyl)-5-(2-(4-chlorophenyl)-hydrazono)-
imidazolidine-2,4-dione 14: 3-(4-Chlorophenyl)-6-benzoyl-
sydnone imine (0.300 g, 1.00 mmol), 2 M of LHMDS in THF
(0.75 mL, 1.50 mmol), 4-chlorophenyl isocyanate (0.369 g, 2.40
mmol) and 12 mL of THF (abs.) were used. The reaction was
stirred at -30 °C for 8 h and then quenched with 1 mL of water.
Purification was achieved by column chromatography (silica gel,
1
DCM). Yield: 0.119 g (26%) of a yellow solid, mp: 261 °C. H
NMR (600 MHz, CDCl3): 훿 = 11.06 (s, 1H, 15-H), 7.54-7.57 (m,
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10.1002/ejoc.201800028
European Journal of Organic Chemistry
FULL PAPER
+
(100) [M+Na+]. HR-ESI-MS: calcd for C24H23N4O1S2 447.1313.
Found 447.1310.
17/17’-H) 7.48-7.51 (m, 2H, 12/12’-H), 7.45-7.48 (m, 2H, 12/12’-
H), 7.33-7.35 (m, 2H, 11/11’-H), 7.30-7.33 (m, 2H, 18/18’-H)
ppm; 13C NMR (150 MHz, CDCl3): 휹 = 153.0 (o, C-14), 151.4 (o,
C-3), 138.0 (o, C-5), 135.7 (o, C-13), 135.5 (o, C-6), 134.9 (o, C-
16), 132.4 (o, C-9), 131.2 (o, C-10), 130.7 (o, C-19), 129.7 (+, C-
12/12’), 129.5 (+, C-8/8’), 129.4 (+, C-18/18’), 128.7 (+, C11/11’),
121.4 (+, C-17/17’), 120.6 (+, C-7/7’) ppm; IR (ATR): 3387, 3100,
1731, 1703, 1593, 1532, 1489, 1398, 1372, 1302, 1240, 1180,
1,3-Di-(4-chlorophenyl)-5-(2-(2-methoxyphenyl)-hydrazono)-
imidazolidine-2,4-dione
17:
3-(2-Methoxyphenyl)-6-
benzoylsydnone imine (0.295 g, 1.00 mmol), 2 M of LHMDS in
THF (0.60 mL, 1.20 mmol), 4-chlorophenyl-isocyanate (0.338 g,
2.20 mmol) and of 12 mL THF (abs.) were used. Purification was
achieved by column chromatography (silica gel, DCM:PE = 10:1). 1089, 1002, 889, 842, 824, 789, 727, 601, 567, 500, 442 cm-1;
1
Yield: 0.195 g (43%) of a yellow solid, mp: 259 °C. H NMR (600
MHz, CDCl3): 휹 = 11.34 (s, 1H, 15-H), 7.57-7.59 (m, 2H, 12/12’-
H), 7.51-7.53 (m, 2H, 8/8’-H), 7.49-7.51 (m, 2H, 11/11’H), 7.48-
7.50 (m, 2H, 7/7’-H) 7.27-7.29 (m, 1H, 21-H), 6.91-6.93 (m, 2H,
19-H + 20-H), 6.86-6.87 (m, 1H, 18-H), 3.90 (s, 3H, 23-H) ppm;
13C NMR (150 MHz, CDCl3): 휹 = 155.7 (o, C-4), 150.0 (o, C-2),
146.4 (o, C-17), 134.5 (o, C-6), 133.5 (o, C-10), 132.3 (o, C-16),
130.8 (o, C-13), 129.6 (+, C-11/11’), 129.4 (+, C-7/7’), 129.2 (o,
C-9), 127.5 (+, C-12/12’), 127.2 (+, C8/8’), 125.4 (o, C-5), 122.2
(+, C-19), 121.6 (+, C-20), 112.2 (+, C-21), 110.6 (+, C-18), 55.9
(+, C-23) ppm; IR (ATR): 3275, 3099, 3060, 2942, 2838, 1749,
1704, 1594, 1523, 1493, 1401, 1248, 1215, 1175, 1138, 1091,
1017, 944, 821, 794, 759, 735, 671, 595, 508, 482 cm-1; MS
(ESI 30 V) m/z (%) = 477.0 (100) [M+Na+]. HR-ESI-MS: calcd for
C22H16N4O3Cl2Na+ 477.0497. Found 477.0492.
MS (ESI 30 V) m/z (%) = 457.0 (100) [M-H+]. HR-ESI-MS: calcd
for C21H12N4O2Cl3- 457.0026. Found 457.0026.
From
1,3-Di-(4-methylphenyl)-5-(2-(4-chlorophenyl)-
hydrazono)- imidazolidine-2,4-dione (12) to
1-(4-Chlorophenyl)-3-(N-(4-methylphenyl)carbamoyl)-4-(4-
methylphenyl)- 4,5-dihydro-1,2,4-triazol-5-on 18: Under an
inert atmosphere 1,3-di-(4-methylphenyl)-5-(2-(4-chlorophenyl)-
hydrazono)-imidazolidine-2,4-dione (0.035 g, 0.084 mmol) was
dissolved in 10 mL of THF (abs.), then 2 M LHMDS in THF (0.05
mL, 0.100 mmol) was added. The mixture was stirred for 10
minutes at rt, afterwards 4-tolyl isocyanate (0.01 mL, 0.092
mmol) was added dropwise. Purification was achieved by
column chromatography (silica gel, DCM). Yield: 0.024 g (69%)
of a white solid.
1-(4-Chlorophenyl)-3-(N-(4-methylphenyl)carbamoyl)-4-(4-
methylphenyl)-4,5-dihydro-1,2,4-triazol-5-on
18:
3-(4-
Chlorophenyl)-6-benzoylsydnone imine (0.300 g, 1.00 mmol), 2
M of LHMDS in THF (0.60 mL, 1.20 mmol), 4-tolyl isocyanate
(0.30 mL, 2.40 mmol) and 12 mL of THF (abs.) were used.
Purification was achieved by column chromatography (silica gel,
DCM, then again PE:EE 3:1). Yield: 0.109 g (26%) of a white
Acknowledgements
Dr. Gerald Dräger, University of Hannover (Germany) is
gratefully acknowledged for measuring the high resolution mass
spectra. The Deutsche Forschungsgemeinschaft DFG is
gratefully acknowledged for financial support.
1
solid, mp: 236 °C. H NMR (600 MHz, CDCl3): 휹 = 8.56 (s, 1H,
16-H), 7.99-8.02 (m, 2H, 7/7’-H), 7.45-7.47 (m, 2H, 18/18’-H)
7.42-7.45 (m, 2H, 8/8’-H), 7.29-7.31 (m, 2H, 12/12’-H), 7.25-7.27
(m, 2H, 11/11’-H), 7.11-7.13 (m, 2H, 19/19’-H), 2.41 (s, 3H, 14-
H), 2.31 (s, 3H, 21-H) ppm; 13C NMR (150 MHz, CDCl3): 휹 =
152.8 (o, C-15), 151.6 (o, C-3), 139.5 (o, C-13), 138.6 (o, C-5),
135.7 (o, C-6), 135.0 (o, C-20), 133.9 (o, C-17’), 131.8 (o, C-9),
130.1 (o, C-10), 129.9 (+, C-12/12’), 129.6 (+, C-19/19’), 129.2
(+, C-8/8’), 126.9 (+, C11/11’), 120.3 (+, C-7/7’), 119.9 (+, C-
18/18’), 21.3 (+, C-14) 20.9 (+, C-21) ppm; IR (ATR): 3387, 3039,
2922, 2859, 1717, 1699, 1595, 1533, 1516, 1490, 1443, 1403,
1370, 1298, 1238, 1176, 1090, 1010, 887, 837, 806, 728, 718,
594, 579, 511 cm-1; MS (ESI 30 V) m/z (%) = 441.0 (100)
[M+Na+]. HR-ESI-MS: calcd for C23H19N4O2Cl1Na+ 441.1094.
Found 441.1096.
Keywords: Betaines • Carbenes • Anions • 1,2,4-Triazolones •
Imidazolidine-2,4-diones
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1-(4-Chlorophenyl)-3-(N-(4-chlorophenyl)carbamoyl)-4-(4-
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3-(4-
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M of LHMDS in THF (0.75 mL, 1.50 mmol), 4-chlorophenyl
isocyanate (0.369 g, 2.40 mmol) and 12 mL of THF (abs.) were
used. Purification was achieved by column chromatography
(silica gel, DCM then again PE:EE 3:1). Yield: 0.121 g (26%) of
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10.1002/ejoc.201800028
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FULL PAPER
Anionic N-heterocyclic carbenes
Tyll Freese, Ana-Luiza Lücke, Jan C.
Namyslo, Martin Nieger, and Andreas
Schmidt*
Page No. – Page No.
Sydnone imine anions combine elements of anionic N-heterocyclic carbenes and
mesomeric betaines. Thus, reaction with isocyanates (X = O) or isothiocyanates (X
= S) give adducts of the carbene type  orbitals, whereas ring transformations to
give imidazolidine-2,4-dithiones, imidazolin-2,4-diones and 1,2,4-triazol-5-ons result
from their characteristic  architecture of betaines.
Heterocycle syntheses with anionic
N-heterocyclic carbenes. Ring
transformations of sydnone imine
anions
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