Terminal Acetylenic Iminium Salts: Cycloaddition Reactions with Azides Leading to 1,2,3-Triazoles and Bicyclic 1,2,3-Triazolium Salts

Article abstract of DOI:10.1002/ejoc.201801749

Terminal acetylenic iminium triflate salts [HC≡C-C(R)=N⁺Me₂ TfO^–] represent very potent dipolarophiles which undergo [3+2] cycloadditions with aryl and benzyl azides at very mild and uncatalyzed conditions, yielding 1,4-disubstituted 1,2,3-triazoles with complete regioselectivity. Addition of nucleophiles at the iminium group of the cycloadducts leads to diverse 1-aryl-(or benzyl-)-4-dimethylaminomethyl-1,2,3-triazoles. The first formed cycloaddition adducts subsequently react with a second molecule of the acetylenic iminium salt by a consecutive Michael addition/1,5-cyclization to form 2,4-dihydropyrrolo[1,2-c][1,2,3]triazol-7-ium triflates. Further transformations of the latter salts are described, among them the conversion into a mesoionic carbene, isolated as a monomeric silver(I) complex.

Full text of DOI:10.1002/ejoc.201801749

A Journal of
Accepted Article
Title: Terminal Acetylenic Iminium Salts: Cycloaddition Reactions with
Azides leading to 1,2,3-Triazoles and Bicyclic 1,2,3-Triazolium
Salts Michael Keim[a] and Gerhard Maas*[a]
Authors: Michael Keim and Gerhard Maas
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10.1002/ejoc.201801749
European Journal of Organic Chemistry
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Terminal Acetylenic Iminium Salts: Cycloaddition Reactions with
Azides leading to 1,2,3-Triazoles and Bicyclic 1,2,3-Triazolium
Salts
Michael Keim[a] and Gerhard Maas*[a]
Abstract: Terminal acetylenic iminium triflate salts [HC≡C-
C(R)=N+Me2 TfO–] represent very potent dipolarophiles which
undergo [3+2] cycloadditions with aryl and benzyl azides at very mild
and uncatalyzed conditions, yielding 1,4-disubstituted 1,2,3-triazoles
with complete regioselectivity. Addition of nucleophiles at the
iminium group of the cycloadducts leads to diverse 1-aryl-(or benzyl-
copper-catalyzed (CuAAC)[12,13] and the ruthenium(II)-catalyzed
(RuAAC)[14] versions of these “click” reactions are nowadays
widely used in the chemical community because of their
regioselectivity, mild reaction conditions, efficiency, and
tolerance of various functional groups. While the CuAAC
reaction is applicable to terminal alkynes only, Ru-catalysis also
accelerates the cycloaddition to internal alkynes. The control of
regioselectivity in these reactions is remarkable: copper-
catalyzed cycloadditions of azides and terminal alkynes provide
1,4-disubstituted 1,2,3-triazoles, while ruthenium catalysis leads
to 1,5-disubstituted triazoles.
)-4-dimethylaminomethyl-1,2,3-triazoles.
The
first
formed
cycloaddition adducts subsequently react with a second molecule of
the acetylenic iminium salt by a consecutive Michael addition/1,5-
cyclization to form 2,4-dihydropyrrolo[1,2-c][1,2,3]triazol-7-ium
triflates. Further transformations of the latter salts are described,
among them the conversion into a mesoionic carbene, isolated as a
monomeric silver(I) complex.
Given the ongoing interest in functionalized 1,2,3-triazoles, we
set out to study the preparation of iminium-substituted triazoles
by a [3+2] cycloaddition method. Acetylenic iminium salts are
expected to react more rapidly with sufficiently electron-rich
organoazides than related electron-deficient dipolarophiles such
as acetylenic esters and carboxamides; in terms of the frontier
orbital concept applied to these cycloadditions, an iminium group
lowers the acetylenic LUMO compared with a carbonyl function.
In fact, triazole formation by [3+2] cycloaddition reactions of
benzyl azide with N,N-dimethyl-propiolcarboxamidinium[15] and
acetylene-1,2-bis(carboxamidinium)[16] salts have been reported
and a certain acceleration as compared to corresponding
carboxamides was noted. On the other hand, we have just
reported that terminal acetylenic iminium salts HC≡C-
Introduction
The synthesis and potential applications of 1,2,3-triazoles have
attracted much attention during the last two decades. In
particular, these five-membered heterocycles own a rigid and
chemically rather stable scaffold, which renders substituted and
functionalized 1,2,3-triazoles as molecular entities of interest in
bioorganic and medicinal, supramolecular and material
chemistry. Among other things, they have been and still are
research objects as bioactive compounds[1,2] and drug-like
candidates.[1,3]
The 1,2,3-triazole ring system can be assembled by various
metal-free cycloaddition routes,[4] among them the now classical
Huisgen reaction from alkynes and azides.[5,6] Although this
[3+2] cycloaddition reaction can be completely atom-economic,
the regioselectivity is often not satisfactory and the kinetics
strongly depend on the electronic properties of the reaction
partners. For example, phenyl azide reacts quickly with
ynamines[7] and enamines (which can serve as masked
ynamines on the way to 1,2,3-triazoles[4d,8]), but only at
significant thermal activation with electron-deficient or
unactivated alkynes.[9–11] These drawbacks can be overcome by
metal-catalyzed azidealkyne cycloadditions, which have been
developed by the Meldal, Sharpless and Fokin groups. The
C(R)=N+Me2·TfO– (R
= aryl, H) are extremely reactive
dienophiles in [4+2] cycloaddition (Diels-Alder) reactions,[17] by
far better than related acetylenic iminium salts with an internal
C,C triple bond.[18] This high reactivity is considered to result
from
the
synergy
of
electronic
factors
(lowered
HOMOdipoleLUMOdipolarophile gap, polar effects) and steric factors
(less steric hindrance in the transition state).
It can be expected that terminal acetylenic iminium salts are not
only excellent electron-deficient dienophiles for [4+2]
cycloaddition reactions, but also highly reactive dipolarophiles in
[3+2] cycloaddition reactions with sufficiently electron-rich 1,3-
dipoles. This is confirmed by their reactions with organoazides
leading to 1,2,3-triazol-4-yl iminium and bicyclic triazolium salts,
which we present in this paper.
Results and Discussion
[a]
Dr. M. Keim, Prof. Dr. G. Maas
Institute of Organic Chemistry I, Ulm University
Albert-Einstein-Allee 11, 89081 Ulm
E-mail: gerhard.maas@uni-ulm.de
The 1,3-dipolar cycloaddition of phenyl azide and propyne
iminium triflate 1a was investigated first and furnished an
unexpected result (Scheme 1). Remarkably enough, the reaction
took place already at room temperature with a moderate rate.
With a slight excess of the azide, a product mixture was
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Supporting information for this article is given via a link at the end of
the document.
1
obtained, the H NMR spectra of which suggested the presence
1
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10.1002/ejoc.201801749
European Journal of Organic Chemistry
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of two iminium salts ((NMe) between 3.4 and 4.2 ppm). The
minor component of that mixture was the expected (1,2,3-triazol-
4-yl)methaniminium salt 2, which was confirmed by alkaline
hydrolysis yielding triazolyl ketone 4 and by hydride reduction
with lithium alanate yielding (triazolylmethyl)amine 5, both in low
yield. The major component of the product mixture could be
enriched by partial extractive removal of 2 with chloroform, but
due to its extreme lability toward hydrolysis, it could not be
isolated in pure form. Based on the assumption that the
unknown compound was still an iminium salt, potassium cyanide
was added to obtain a monocationic species with an -
dimethylaminonitrile moiety. An ESI mass spectrum showed a
basis peak corresponding to [C29H29N6]+, in agreement with an
adduct of two acetylene, one azide and one cyanide units.
Efforts to crystallize the salt were unsuccessful and an anion
exchange, tetraphenylborate for triflate, was also in vain. The
structure of this salt as a bicyclic 2,4-dihydro-pyrrolo[1,2-
c][1,2,3]triazol-7-ium triflate was finally established, when single
crystals of 6b suited for an XRD analysis were obtained by
replacing phenyl azide with 4-bromophenyl azide (Figure 1).
Thus, the formerly unknown product 3 is the 2:1 addition product
of acetylenic iminium salt 1a and phenyl azide, which results
The following structural aspects of triazolium salts 6a,b are of
interest: a) According to the NMR spectra, only one of two
possible diastereomers was formed, the relative configuration of
which can be seen in Figure 1. b) The 1H NMR spectra (500
MHz) indicate that the molecule is in the coalescence region at
ambient temperature; the slow exchange regime is observed at
-40 °C (see Figure 2, Supporting Information). It is obvious that
the dynamics are caused by hindered rotation around bonds at
the two closely positioned and sterically overloaded chiral
centers.
Benzyl azide, as anticipated, adds to terminal acetylenic iminium
salts faster than phenyl azide, but again, the final result depends
on the stoichiometry of the reactants (Scheme 2). With a 1:1
molar ratio, the cycloaddition was complete after 30 minutes and
yielded the 1,4-disubstituted triazole 7 almost quantitatively
beside traces of triazolium salt 9. When a 2:1 molar ratio and an
extended reaction time were applied, the product ratios were
reversed and 9 was obtained in high yield. This very moisture-
sensitive salt could be isolated in pure form and fully
characterized by its NMR and HRMS data.
Alkaline hydrolysis of triazolyl-methaniminium salt 7 yielded the
1,4-disubstituted triazolyl ketone 8 in good yield. This result
clearly highlights the effect of the iminium activation of the
acetylenic bond, since the direct [3+2] cycloaddition of benzyl
azide to the corresponding alkynyl ketone requires harsh
from
a
[3+2] cycloaddition/Michael addition/1,5-cyclization
cascade. When the 2:1 stoichiometry of the reactants was
applied, salt 3 could be produced indeed selectively at the
expense of the 1:1 cycloaddition product 2.
conditions and yields
8 in moderate yield and with low
regioselectivity (refluxing benzene, 40 hours, 48% yield, 69:31
ratio of 1,4- and 1,5-regioisomers).[19] On the other hand, ketone
8 and similar acyltriazoles can be prepared regioselectively and
in good yields by CuAAC reactions.[20,21] Under optimized
conditions (catalyst, additives), mild reaction conditions (r.t., 5 h)
could be achieved.[21]
Scheme 1. Cycloadducts and their derivatives obtained from propyne iminium
salt 1a and aryl azides.
Scheme 2. Reactions of acetylenic iminium salt 1a with benzyl azide.
As it was described above for the cycloaddition products
obtained from aryl azides (see Scheme 1), triazoles such as 7
and the bicyclic triazolium salt 9 can be submitted to further
transformations without isolation in a two-step one-pot reaction
sequence. By variation of the propyne iminium salt, the
organoazide and the nucleophile that adds to the iminium unit,
diverse 1,4-disubstituted 1,2,3-triazoles are readily accessible.
Two examples are shown in Scheme 3. The acetylenic
aldiminium salt 1b underwent
a
very fast 1,3-dipolar
cycloaddition with 4-chlorobenzyl azide at room temperature; the
resulting iminium-substituted triazole was converted in situ by
Figure 1. Molecular structure of triazolium salt 6b in the solid state (ORTEP
plot). The numbering scheme is arbitrary. Bond distances (Å): N1N2 1.335(3),
N2N3 1.319(3), N3C4 1.361(3), N3C1 1.414(3), C4C5 1.369(4), C5N1
1.370(3).
very mild hydride reduction into
a
(1,2,3-triazol-4-yl-
methyl)amine, which was isolated as the hydrobromide 10. In a
2
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10.1002/ejoc.201801749
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Scheme 4. In-situ derivatization of the bicyclic triazolium salt 9 the arrows
indicate strong NOE interactions (irradiation at the CHO proton resonance for
both isomers of 14). a) See Scheme 2.
similar manner, bis(phenylethynyl)iminium salt 1c could be
converted into triazole 11 with phenylethynyl lithium as the
nucleophile.
The thermal stability of the bicyclic triazolium salts reported in
this study is only moderate. As Scheme 5 shows, triazolium salt
9 and cyclopentadiene underwent a slow reaction when heated
at a moderately elevated temperature; 1H NMR spectra indicated
the selective formation of triazole 7 and norbornadienyl iminium
salt 15[17] in a 1.0:0.9 ratio beside small amounts of side
products. Obviously, the formation of 9 from triazole 7 and
propyne iminium ion 1a by a formal [3+2] cycloaddition is
reversible, i.e., 9 is thermally cleaved into its components, of
which triazole 7 is observed directly and alkyne 1a is trapped by
cyclopentadiene in a fast Diels-Alder reaction. The cyclo-
reversion reaction of the cation could also be observed in an ESI
mass spectrum.
Scheme 3. Triazoles 10 and 11 obtained from propyne iminium salts 1b,c in a
two-step one-pot reaction.
In a similar manner, salt 9 was generated from propyne iminium
salt 1a and benzyl azide in a 1:(0.420.45) molar ratio and was
transformed in situ as shown in Scheme 4. Hydride reduction
with LiAlH4 leading to the monocationic salt 12 had to be
performed at very low temperature, in order to avoid the
complete decomposition which was observed at “harsher”
conditions. N-debenzylation of 12 with NaH/DMSO provided the
neutral pyrrolo[1,2-c]triazole 13.
Scheme 5. Transfer of a propyne iminium unit (1a) from bicyclic dication salt 9
to cyclopentadiene. Bn = PhCH2.
Hydrolysis of 9 with aqueous potassium carbonate unexpectedly
led to a product mixture, from which triazolyl ketone 8 and the -
ketoaldehydes Z-14 and E-14 could be isolated separately by
HPLC. The double bond configuration could be assigned by
NOESY NMR spectra (see Scheme 4). We assume that the
latter compounds, which at first glance could be regarded as
Knoevenagel products derived from ketone 8 and 3-phenyl-3-
oxopropanal or a synthetic equivalent thereof, are formed by a
somewhat complex mechanism, which starts with a rupture of
the bicyclic structure of 9, triggered by Michael addition of OH
at the olefinic iminium unit (see the Supporting Information for a
formula scheme).
In contrast to the large number of known 1,3-disubstituted and
1,3,4- or 1,3,5-trisubstituted 1,2,3-triazolium salts, C,N-
annelated congeners are still rare. They can be synthesized by
an intramolecular N-alkylation of appropriate 1,2,3-triazoles.[22] In
one paper, salts 16 were presented which showed some
potential for the nucleophilic organocatalysis of the base-
assisted oxidative esterification of certain aldehydes.[22c] It is
obvious that these triazolium salts are precursors of catalytically
active mesoionic 1,2,3-triazolyl-5-ylidenes, as was evidenced by
proving the relative acidity of the triazolium CH bond in a H/D
exchange experiment. In accordance with lit. 22c, we were able
to observe the deuterium incorporation by 1H NMR monitoring of
the triazolium 5-H proton ( = 9.18 ppm) under the conditions
given in Scheme 6. The exchange reaction turned out to be
relatively slow; a steady equilibrium was reached within two
days (the integration of triazolium-H was 0.78 after 2 hours, 0.73
after 2 days).
Scheme 6. H/D exchange in triazolium salt 12.
3
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10.1002/ejoc.201801749
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1,2,3-Triazolylidenes belong to the family of “abnormal” or
“mesoionic” carbenes;[23] they have been isolated in pure form[24]
and have recently become quite popular as novel nucleophilic
heterocyclic carbene (NHC) ligands in late-transition metal
complexes, some of which proved useful catalysts for diverse
chemical transformations.[25,26] AgNHC complexes have been
widely used for transmetalation reactions to obtain other
transition metalNHC complexes.[25,26] For this purpose, they are
typically generated in situ by treating the azolium salt with basic
silver compounds such as Ag2O or Ag2CO3 or from preformed
free NHCs.[27] Only a few (1,2,3-triazolylidene)silver complexes
have been characterized structurally and spectroscopically, and
the diversity of coordination motifs became evident.[25] Very
recently, two monomolecular complexes of the type (trz)AgX (X
= CN, I), derived from a monocyclic 1,3,4-trisubstituted-1,2,3-
triazolium ion, have been described.[28] With all these facts in
mind, we briefly checked the possibility to obtain a stable
(bicyclic 1,2,3-triazolylidene)silver complex (“Ag(btrz)”) derived
from the bicyclic triazolium salt 12.
When triazolium triflate 12 was allowed to react with Ag2O in
CH3CN, NMR spectra showed the disappearance of the
triazolium-H signal, but a pure product could not be isolated. On
the other hand, when 12 was treated briefly with potassium
butoxide in THF followed by addition of AgOTf, monitoring of the
reaction indicated complete conversion after 18 h and formation
of a major product (1H NMR). However, this product could not be
obtained in pure form, because most efforts (chromatography,
precipitation, selective crystallization) ended in decomposition
and formation of undefined product mixtures. However, when
the crude reaction product was dissolved in warm di-n-butyl
ether/chloroform and the mixture was brought back to room
temperature, a dark-grey, sticky oil separated, which was at
most sparingly soluble in common organic solvents and
appeared to contain elemental silver. The organic phase
contained at least three compounds: unconsumed triazolium salt
12, an unknown compound (1H NMR: broad signals, no
triazolium proton) and a silver complex which could be isolated
in low yield by crystallization. These crystals were identified as
Figure 3. Molecular structure (top ORTEP presentation) and unit cell content
of silver complex 17 in the crystal. The numbering scheme is arbitrary. The n-
butyl chain is disordered. Selected bond distances (Å) and angles (deg):
Ag1C1 2.054(3), Ag1O1 2.095(3), C30O1 1.267(6), C30O2 1.209(6),
C1Ag1O1 178.9(1), C30O1Ag1 109.1(3).
The molecular structure of 17 exhibits an almost planar
arrangement of bicyclic triazolylideneAgOOC and a linear
geometry which is typical for dicoordinated silver complexes.
Notably, the carboxylate ligand is monocoordinated to the silver
atom, whereas silver(I) carboxylates frequently form dimeric,
oligomeric and polymeric structures with the general formula
[Ag2(carboxylato-O,O’)2]n
featuring
bridging
carboxylate
ligands.[29] Obviously, the presence of an NHC ligand breaks
down the common coordination pattern of Ag(I) carboxylates.
This has been noted before for PR3 ligands. Thus, the complex
[Ag(P(n-Bu)3)(C(CH3)3COO)] forms a dimer made up from two
monomers in which the carboxylate ligand is unsymmetrically
dicoordinated to the silver atom.[30] Furthermore, the compound
the
(1,2,3-triazol-5-ylidene)silver
complex
17,
[(btrz)Ag(C3H7COO)], by X-ray diffraction analysis (Scheme 7,
Figure 3). Notably, a butyrate ligand is present, which must
result from cleavage of an ether CO bond and oxidation.
Further studies are necessary in order to clarify the mechanism
of this transformation, which seems to involve a novel oxidative
cleavage of an ether CO bond. Interestingly, a MALDI mass
spectrum of 17 showed prominent peaks which can be assigned
to [Ag(btrz)2]+ and [btrz + H]+ (see Experimental Section).
[Ag(P(C6H4-2-CH2NMe2)3)(CF3COO)] is
shaped monomeric complex containing
a
tricoordinated, T-
monocordinated
a
trifluoroacetato ligand.[31] The AgO and CO bond lengths in
the latter complex [AgO1 2.183(2), CO1 1.222(3), CO2
1.206(3) Å] show significant differences compared to 17: the
AgO distance is much longer than in 17 and the CO single
and double bonds are less localized. The bond length AgCbtrz
(2.054(3) Å) in 17 is at the lower side of the so far known range
(2.0642.105 Å[25]); specifically, it is shorter than in comparable
structures [2.087 Å in (trz)AgX (X = CN, I);[28] 2.084 Å in a (1,2,4-
trisubstituted 1,2,3-triazol-5-ylidene)AgCl complex, a “normal
NHC” complex[32]]. In the crystal, the unit cell of 17 contains two
centrosymmetrically related molecules. With a distance of 4.661
Å for Ag···Ag(1-x, 1-y,1-z), an argentophilic interaction[33] can be
excluded.
Scheme 7. Formation of the (1,2,3-triazolylidene)silver complex 17.
Conditions: 1. KO-t-Bu, THF, 0 °C, 5 min; 2. AgOTf, rt, 18 h, 3. Crystallization:
(n-Bu)2O, CHCl3, 70 °C, 45 min, then pentane; yield: 6%.
4
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N,N-Dimethyl-1-phenyl-1-(1-phenyl-1H-1,2,3-triazol-4-
Conclusions
yl)methanamine (5): To a solution of propyne iminium salt 1a (628 mg,
2.04 mmol) in CH2Cl2 (4.5 mL), phenyl azide (255 mg, 2.15 mmol) was
added and the mixture was stirred for 20 h. Thereafter LiAlH4 (2.5 mL,
6.0 mmol, 2.4 M in THF) was added at -20 °C and stirring was continued
for 1 h. The reaction was quenched with EtOAc and extracted wich 1 N
HCl. The aqueous phase was separated and NaOHaq was added (pH
12). After extraction with EtOAc, the organic layer was separated, dried
(Na2SO4), and the volatiles were removed at 200 mbar/40 °C. The black
residue was purified via column chromatography (SiO2, cyclo-
hexane/EtOAc/NEt3 = 1:3:0.05, Rf = 0.52) which gave 5 (113 mg, 0.41
mmol, 20%) as an orange oil. 1H NMR (CDCl3, 400 MHz):  [ppm] = 2.29
(s, 6 H, N(CH3)2), 4.66 (s, 1 H, CH), 7.25–7.29 (m, 1 H, HPh), 7.33–7.37
(m, 2 H, HPh), 7.39–7.43 (m, 1 H, HPh), 7.48–7.53 (m, 4 H, HPh), 7.70–
7.72 (m, 2 H, HPh), 7.91 (s, 1 H, 5-H). 13C NMR (CDCl3, 100 MHz): 
[ppm] = 44.16 (N(CH3)2), 68.71 (PhCH), 119.97, 120.53, 127.68, 128.29,
128.76, 129.81, 137.22, 140.97, 150.36. IR (KBr): 휈̃ [cm-1] = 3061 (m),
2987 (m), 2951 (m), 2864 (m), 2820 (m), 2775 (s), 1599 (s), 1502 (s),
1453 (s), 1258 (m), 1231 (s), 1178 (m), 1076 (m), 1039 (s), 803 (m), 756
(s), 695 (s). MS ((+)-ESI): m/z (%) = 279.1589 (calcd. 279.16097 for
C17H19N4+, [M + H]+). C17H18N4 (278.36 g/mol): calcd. C 73.35, H 6.52, N
20.13; found C 72.66, H 6.72, N 18.53. The elemental analysis could not
be improved.
Terminal acetylenic iminium salts are not only among the most
reactive electron-deficient dienophiles in Diels-Alder reactions,
as we have reported earlier, but perform equally well as
dipolarophiles in [3+2] cycloaddition reactions with sufficiently
electron-rich organoazides. With (ring-substituted) phenyl and
benzyl azide, the 1,3-dipolar cycloaddition leading to 1,4-
disubstituted 1,2,3-triazoles is considerably faster than with
neutral
acetylenic
carbonyl
compounds,
high-yielding,
completely regioselective, and does not require metal catalysis.
The high electrophilicity of the propyne iminium ion unit paves
the way to little known bicyclic 1,2,3-triazolium salts in a [3+2]
cycloaddition/Michael addition/1,5-cyclization cascade. The
presence of the iminium function in the triazole and triazolium
products allows for further transformation into neutral products,
as is exemplified by hydride reduction, addition of carbon
nucleophiles (cyanide, phenylacetylenide), and alkaline ring-
opening reaction of a bicyclic triazolium salt. Finally, bicyclic
triazolium salts 12 are ligand precursors for transition metal
complexes, as was demonstrated by the formation of an isolable
AgNHC complex.
5-(Cyano(dimethylamino)(phenyl)methyl)-4-(dimethylamino)-2,4-
diphenyl-2,4-dihydropyrrolo[1,2-c][1,2,3]triazol-7-ium Triflate (6a):
To a solution of propyne iminium salt 1a (1.64 g, 5.34 mmol) in CH2Cl2 (8
mL), phenyl azide (318 mg, 2.67 mmol, 0.5 equiv.) was added and the
mixture was stirred for 23 h. The volatile components were removed at
0.02 mbar, and the residue was dissolved in CH3CN (2 mL) and added
dropwise to a suspension of KCN (452 mg, 6.94 mmol, 1.3 equiv.) in
CH3CN (20 mL). After complete addition stirring was continued for 1 h.
Then Et2O and n-pentane were added, until a purple oil separated. The
upper layer was collected by decantation (the purple residue was
discarded), the solvents were evaporated and the residue was dissolved
in CH2Cl2 (4 mL) and filtered. To the filtrate Et2O was added until the
solution became turbid. n-Pentane was added whereupon an oil
separated. Decantation, washing of the residue with Et2O and drying at
0.01 mbar gave 6a (998 mg, 1.63 mmol, 61%) as a dark violet solid
(decomposition starting at 102 °C). 1H NMR (CD2Cl2, 500 MHz, 220 K): 
[ppm] = 1.73, 2.27, 2.45, 2.59 (each s, 3H, NMe); 5.96 (d, J = 8.3 Hz, 1
H, HPh), 6.48 (td, J = 7.7, 1.4 Hz, 1 H, HPh), 6.81 (td, J = 7.7, 1.5 Hz, 1 H,
HPh), 6.90 (d, J = 8.5 Hz, 1 H, HPh), 7.27 (td, J = 7.8, 1.4 Hz, 1 H, HPh),
7.58–7.63 (m, 3 H, HPh), 8.01 (d, J = 8.1 Hz, 1 H, HPh), 8.05–8.07 (m, 2
H, HPh), 8.36 (s, 1 H, C=CH), 9.17 (s, 1 H, 3-H). 13C NMR (CD2Cl2, 125
MHz, 220 K):  [ppm] = 40.25 (2 NMe), 42.19 (NMe), 42.23 (NMe) 70.08
Experimental Section
Methods and materials. All reactions involving moisture-sensitive
compounds were carried out in rigorously dried glassware under an
argon atmosphere. Solvents were dried by established procedures and
stored over molecular sieves (4 Å; 3 Å for acetonitrile). All chemicals,
except where stated, were purchased from commercial sources and used
without further purification. Propyne iminium salts 1a–c[17] were prepared
by published methods. Melting points were determined in open capillaries
with a Büchi B-540 instrument at a heating rate of 2 °C/min. IR spectra of
solid samples prepared as KBr pellets or oils between NaCl plates were
recorded on a Bruker Vector 22 FT-IR instrument. NMR spectra were
recorded on a Bruker DRX 400 spectrometer operating at 400.13 MHz
1
for H and 100.61 MHz for 13C and on a Bruker AMX 500 spectrometer
operating at 500.14 MHz for 1H and 125.79 MHz for 13C and were
referenced to the residual proton signal of the solvent. If necessary, 13C
signals were assigned by means of DEPT-135, HMBC and HSQC
experiments. Mass spectra were recorded with the following instruments:
Finnigan-MAT SSQ-7000 (CI, 100 eV) and SolariX (HRMS, ESI).
Elemental analyses were carried out with an elementar Hanau vario
MICRO cube analyser. Column chromatography was performed on silica
gel (Silica 60, Macherey-Nagel, 63-200 mesh).
1
(Csp3), 78.94 (C-CN), 111.94 (CN), 120.53 (q, JC,F = 320.2 Hz, TfO–),
121.53 (CPh), 123.85 (HCTrz), 124.28 (HC=C), 124.94–135.14 (15 CPh),
144.64 (CTrz), 151.99 (HC=C). IR (KBr): 휈̃ [cm-1] = 3066 (m), 3004 (m),
2963 (m), 2877 (m), 2836 (m), 2793 (m), 1632 (m), 1596 (m), 1564 (m),
1496 (s), 1452 (s), 1388 (m), 1260 (s), 1223 (s), 1154 (s), 1031 (s), 1002
(m), 830 (m), 764 (m), 747 (m), 696 (s), 636 (s). HRMS ((+)-ESI): m/z =
461.24497 (calcd. 461.24482 for C29H29N6+, [M - OTf]+). C30H29F3N6O3S
(610.66 g/mol): calcd. C 59.01, H 4.79, N 13.76; found C 59.00, H 4.88,
N 13.46.
Phenyl(1-phenyl-1H-1,2,3-triazol-4-yl)methanone (4): To a solution of
propyne iminium salt 1a (1.64 g, 5.34 mmol) in CH2Cl2 (8 mL), phenyl
azide (635 mg, 5.34 mmol) was added, and the mixture was stirred for 20
h. Thereafter aqueous NaHCO3 was added, the organic layer was
separated, dried (Na2SO4), and the volatiles were removed at 800
mbar/40 °C. The black residue was purified via column chromatography
(SiO2, cyclohexane/EtOAc = 5:1, Rf = 0.38) which gave 4 (150 mg, 0.602
2-(4-Bromophenyl)-5-(cyano(dimethylamino)(phenyl)methyl)-4-
(dimethylamino)-4-phenyl-2,4-dihydropyrrolo[1,2-c][1,2,3]triazol-7-
ium Triflate (6b): Prepared from 1a (1.28 g, 4.17 mmol) and 4-
bromophenyl azide (413 mg, 2.09 mmol) according to 6a. Yield: 1.04 g
(1.51 mmol, 72%), beige solid (decomposition starting at 122 °C). 1H
NMR (CD2Cl2, 500 MHz, 220 K):  [ppm] = 1.73, 2.27, 2.45, 2.59 (each s,
3 H, NMe), 5.95 (d, J = 7.8 Hz, 1 H, HPh), 6.47 (t, J = 7.6 Hz, 1 H, HPh),
6.81 (t, J = 7.5 Hz, 1 H, HPh), 6.90 (d, J = 7.9 Hz, 1 H, HPh), 6.96 (d, J =
7.6 Hz, 1 H, HPh), 6.99 (d, J = 7.9 Hz, 1 H, HPh), 7.04 (t, J = 7.6 Hz, 1 H,
HPh), 7.20 (d, J = 7.9 Hz, 1 H, HPh), 7.27 (t, J = 7.7 Hz, 1 H, HPh), 7.74 (d,
J = 8.8 Hz, 2 H, HPh), 7.98–8.02 (m, 3 H, HPh), 8.32 (s, 1 H, C=CH), 9.18
(s, 1 H, HTrz). 13C NMR (CD2Cl2, 125 MHz, 220 K):  [ppm] = 40.28 (2
1
mmol, 11%) as a colorless solid. M.p. 128.7–130.1 °C. H NMR (CDCl3,
400 MHz):  [ppm] = 7.47–7.57 (m, 5 H, HPh), 7.61–7.65 (m, 1 H, HPh),
7.79–7.82 (m, 2 H, HPh), 8.46–8.49 (m, 2 H, HPh), 8.73 (s, 1 H, 5-H). 13C
NMR (CDCl3, 100 MHz):  [ppm] = 120.85, 126.50, 128.53, 129.59,
130.04, 130.72, 133.52, 136.43 (all CPh); 136.50 (CTrz), 148.61 (C-5),
185.60 (C=O). IR (KBr): 휈̃ [cm-1] = 3139 (m), 1643 (s), 1597 (m), 1574
(m), 1525 (s), 1347 (m), 1268 (s), 991 (m), 905 (m), 760 (m), 719 (s), 685
(s). MS (CI, 100 eV): m/z (%) = 277 (100) [M + C2H4]+. C15H11N3O
(249.27 g/mol): calcd. C 72.28, H 4.45, N 16.86; found C 72.21, H 4.51,
N 16.89.
5
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201801749
European Journal of Organic Chemistry
FULL PAPER
NMe), 42.19 (NMe), 42.28 (NMe), 70.11 (Csp3), 79.00 (C-CN), 111.91
3.52 (s, 3 H, NMe), 5.98 (s, 2 H, PhCH2), 7.35 (d, J = 7.2 Hz, 2 H, HPh),
7.53–7.57 (m, 5 H, HPh), 7.59–7.63 (m, 3 H, HPh), 7.69–7.73 (m, 2 H,
HPh), 7.76–7.79 (m, 3 H, HPh), 8.45 (s, 1 H, C=CH), 8.80 (s, 1 H, HTrz).
13C NMR (CD3CN, 125 MHz):  [ppm] = 40.54 (NMe), 47.49 (NMe), 48.56
1
(CN), 120.48 (q, JC,F = 320.1 Hz, TfO–), 123.16 (CPh), 123.93 (HCTrz),
124.16 (HC=C), 124.89–134.74 (14 CPh signals), 144.81 (CTrz), 152.45
(HC=C). IR (KBr): 휈̃ [cm-1] = 3067 (m), 3004 (m), 2963 (m), 2876 (m),
2836 (m), 2793 (m), 1632 (m), 1564 (m), 1493 (s), 1452 (s), 1403 (m),
1260 (s), 1223 (s), 1070 (m), 1032 (s), 997 (m), 832 (m), 750 (m), 712
(m), 697 (m), 637 (s). HRMS ((+)-ESI): m/z = 541.15309 (calcd.
541.15329 for C29H2881BrN6+), 539.15513 (calcd. 539.15533 for
C29H2879BrN6+, [M - OTf]+). C30H28BrF3N6O3S (689.55 g/mol): calcd. C
1
(NMe), 59.53 (PhCH2), 84.22 (C-4), 122.04 (q, JCF = 320.8 Hz, TfO–),
127.90 (HC=C), 128.84 (HCTrz); 130.09, 130.36, 130.44, 130.53, 130.90,
131.48, 132.04, 132.36, 132.57, 134.63 (all CPh); 139.25 (HC=C), 142.42
(Cq,Trz), 176.27 (C=N). IR (KBr): 휈̃ [cm-1] = 3091 (m), 1658 (m), 1454 (m),
1283 (s), 1258 (s), 1225 (s), 1161 (s), 1030 (s), 752 (m), 700 (m), 638
52.26,
H
4.09,
N
12.19; found
C
52.77,
H
4.42,
N
11.97;
(s). HRMS ((+)-ESI): m/z
=
1345.40641 (calcd. 1345.37142 for
+
C30H28BrF3N6O3S·0.35 Et2O (689.55 + 0.3574.12 g/mol): calcd. C
52.71, H 4.44, N 11.75.
C61H62F9N10O9S3
,
[2M
-
OTf]+), 598.21645 (calcd. 598.20942 for
OTf]+), 421.20663 (calcd. 421.20229 for
C30H31F3N5O3S+, [M
-
C27H25N4O+, [M + H2O - H2NMe2OTf]+), 291.16099 (calcd. 291.16042 for
C18H19N4+, [cation of 7]+). C31H31F6N5O6S2 (747.73 g/mol): calcd. C
N-((1-Benzyl-1H-1,2,3-triazol-4-yl)(phenyl)methylene)-N-
49.80,
H
4.18,
N
9.37; found
C
49.28,
H
4.22,
N
9.33;
methylmethanaminium Triflate (7): To a solution of propyne iminium
salt 1a (885 mg, 2.88 mmol) in CH2Cl2 (8 mL), benzyl azide (539 µL, 4.32
mmol, 1.5 equiv.) was added. After stirring for 0.5 h at ambient
temperature, the solvent was evaporated at 0.02 mbar and the residue
was washed with several portions of ether. Drying of the residue at 0.02
mbar gave 7 (1.22 g, 2.76 mmol, 96%) as a brownish solid, which was
slighly contaminated with triazolium salt 9. M.p. 93 °C (decomposition
starting at 70 °C). 1H NMR (CD3CN, 500 MHz):  [ppm] = 3.51 (s, 3 H,
NMe), 4.12 (s, 3 H, NMe), 5.63 (s, 2 H, PhCH2), 7.35–7.40 (m, 5 H, HPh),
7.52–7.53 (m, 2 H, HPh), 7.64–7.67 (m, 2 H, HPh), 7.74–7.77 (m, 1 H,
HPh), 8.19 (s, 1 H, HTrz). 13C NMR (CD3CN, 125 MHz):  [ppm] = 48.18
C31H31F6N5O6S2·0.43 H2O (689.55 + 0.4318.02 g/mol): calcd. C 49.28,
H 4.25, N 9.27.
1-(1-(4-Chlorobenzyl)-1H-1,2,3-triazol-4-yl)-N,N-
dimethylmethanaminium bromide (10): To a solution of propyne
iminium salt 1b (326 mg, 1.41 mmol) in CH2Cl2 (8 mL) and CH3CN (2
mL), 4-Chlorobenzyl azide (354 mg, 2.12 mmol, 1.5 equiv.) was added
and the mixture was stirred for 0.5 h. Thereafter the solution was cooled
to -78 °C and LiAlH4 (588 µL, 1.41 mmol, 2.4 M in THF) was added
dropwise. After stirring for 5 min the reaction was quenched at this
temperature by adding acetone followed by extraction with ether and
brine. The organic layer was dried (Na2SO4) and the volatile components
were evaporated. The residue was dissolved in EtOAc/MeOH (10:1) and
filtered through flash silica gel. The filtrate was collected, the solvents
were removed, and the residue was dissolved in ether. Conc. HBr was
added dropwise until pH 1 was reached. The resulting oil was separated,
washed with ether and dried at 0.02 mbar to obtain 10 (351 mg, 1.06
mmol, 75%) as a yellow oil, which could not be purified further. 1H NMR
(CD3CN, 400 MHz):  [ppm] = 2.72 (d, J = 5.2 Hz, 6 H, N(CH3)2), 4.32 (d,
J = 4.9 Hz, 2 H, NCH2), 5.59 (s, 2 H, PhCH2), 7.31–7.33 (m, 2 H, HPh),
7.39–7.41 (m, 2 H, HPh), 8.26 (s, 1 H, HTrz), 10.84 (s, br, 1 H, NH). 13C
NMR (CDCl3, 100 MHz):  [ppm] = 42.91 (N(CH3)2), 49.53 (NCH2), 55.72
(PhCH2), 129.99 (CPh), 131.05 (HCTrz), 131.59 (CPh), 133.07 (CPh),
134.89 (CPh), 135.47 (CTrz). IR (KBr): 휈̃ [cm-1] = 2954 (s), 2680 (s), 2469
(m), 1624 (m), 1492 (s), 1469 (s), 1438 (m), 1411 (m), 1275 (s), 1230
(m), 1162 (m), 1053 (m), 1030 (m), 1015 (m), 951 (m), 812 (m), 639 (m).
HRMS ((+)-ESI): m/z = 251.10613 (calcd. 251.10580 for C12H16ClN4+, [M
– Br]+). C12H16BrClN4 (331.64 g/mol).
1
(NMe), 48.71 (NMe), 54.80 (Cbenzyl), 121.81 (q, JC,F = 321.0 Hz, TfO–);
129.05, 129.50, 129.53, 129.71, 129.90, 132.58 133.46, 135.06 (all CPh);
136.55 (CTrz), 142.04 (CTrz), 169.91 (C=N). IR (KBr): 휈̃ [cm-1] = 3130 (m),
1641 (m), 1537 (m), 1263 (s), 1224 (m), 1154 (s), 1031 (s), 771 (m), 733
(m), 637 (s). HRMS ((+)-ESI): m/z = 291.16056 (calcd. 291.16042 for
C18H19N4, [M - OTf]+). C19H19F3N4O3S (440.44 g/mol): calcd. C 51.81, H
4.35, N 12.72; found C 51.89, H 4.41, N 12.73.
(1-Benzyl-1H-1,2,3-triazol-4-yl)(phenyl)methanone (8): To a solution of
propyne iminium salt 1a (420 mg, 1.37 mmol) in CH2Cl2 (8 mL), benzyl
azide (364 mg, 2.73 mmol, 2.0 equiv.) was added. After stirring for 1 h at
ambient temperature n-pentane was added, whereupon an orange oil
separated. The upper layer was removed and the residue was washed
with several portions of ether, then dissolved in CH2Cl2, and saturated
aqueous NaHCO3 was added. After stirring for 5 min, the mixture was
extracted with ether and brine, the organic layer was dried over Na2SO4,
and the volatiles were evaporated. The residue was taken up in n-
hexane/CHCl3 (9:1) and the mixture was filtered through silica gel.
Solvent evaporation furnished 8 (313 mg, 1.19 mmol, 87%) as a white
solid; m.p. 114.3–115.2 °C. (lit.[19]: 115–116 °C). 1H NMR (CDCl3, 400
MHz):  [ppm] = 5.60 (s, 2 H, PhCH2), 7.32–7.35 (m, 2 H, HPh), 7.37–7.43
(m, 3 H, HPh), 7.48–7.53 (m, 2 H, HPh), 7.58–7.62 (m, 1 H, HPh), 8.17 (s, 1
H, HTrz), 8.40–8.42 (m, 2 H, HPh). 13C NMR (CDCl3, 100 MHz):  [ppm] =
54.55 (PhCH2); 128.39, 128.48, 129.26, 129.42, 130.67, 133.37, 133.79
(all CPh); 136.57 (CTrz), 148.44 (CTrz), 185.75 (C=O). IR (KBr): 휈̃ [cm-1] =
3119 (s), 1635 (s), 1598 (m), 1573 (m), 1518 (s), 1346 (m), 1232 (s),
1048 (m), 901 (s), 713 (s), 692 (s). HRMS ((+)-ESI): m/z = 549.20044
(calcd. 549.20095 for C32H26N6NaO2+, [2M + Na]+), 286.09492 (calcd.
286.09508 for C16H13N3NaO+, [M + Na]+). C16H13N3O (263.30 g/mol):
calcd. C 72.99, H 4.98, N 15.96; found C 72.93, H 4.99, N 16.09.
3-(1-(4-Chlorobenzyl)-1H-1,2,3-triazol-4-yl)-N,N-dimethyl-1,5-
diphenylpenta-1,4-diyn-3-amine (11): To a solution of propyne iminium
salt 1c (617 mg, 1.86 mmol) in CH2Cl2 (30 mL), 4-chlorobenzyl azide
(467 mg, 2.79 mmol, 1.5 equiv.) was added. After stirring for 2 h at
ambient temperature, the mixture was cooled to -40 °C and
phenylethynyl lithium [prepared from phenylacetylene (300 mg, 2.94
mmol) and n-BuLi (1.18 mL, 2.94 mmol, 2.5 M in hexane) in THF (10 mL)
at -40 °C] was added dropwise. After stirring for 0.5 h at ambient
temperature the reaction was quenched by addition of water followed by
extraction with ether. The organic layer was dried (Na2SO4) and the
volatile components were evaporated. The residue was dissolved in
EtOAc and filtered through flash silica gel. The filtrate was submitted to
HPLC (cyclohexane/EtOAc) which gave 11 (403 mg, 0.89 mmol, 48%) as
an orange oil, which could not be fully purified. 1H NMR (CDCl3, 400
MHz):  [ppm] = 2.47 (s, 6 H, N(CH3)2), 5.50 (s, 2 H, PhCH2), 7.20–7.22
(m, 2 H, HPh), 7.27–7.34 (m, 8 H, HPh), 7.48–7.50 (m, 4 H, HPh), 7.68 (s, 1
H, 5-H). 13C NMR (CDCl3, 100 MHz):  [ppm] = 40.13 (N(CH3)2), 53.26
(PhCH2), 56.36 (Cq), 85.03 and 122.01 (C≡C), 122.47 (C-5); 128.00,
128.40, 129.08, 129.17, 131.72, 132.81, 134.52 (all CPh); 148.97 (CTrz).
IR (NaCl): 휈̃ [cm-1] = 2953 (s), 2864 (m), 1491 (s), 1447 (m), 1211 (m),
1044 (m), 1012 (m), 757 (s), 692 (s). HRMS ((+)-ESI): m/z = 901.33451
(calcd. 901.32953 for C56H47Cl2N8+, [2M + H]+), 451.16993 (calcd.
451.16840 for C28H24ClN4+, [M + H]+), 406.1115 (calcd. 406.11055 for
C26H17ClN3+, [M - NMe2]+). C28H23ClN4 (450.97 g/mol).
2-Benzyl-4-(dimethylamino)-5-((dimethyliminio)(phenyl)methyl)-4-
phenyl-2,4-dihydropyrrolo[1,2-c][1,2,3]triazol-7-ium Triflate (9): To a
solution of propyne iminium salt 1a (450 mg, 1.46 mmol) in CH2Cl2 (8
mL), benzyl azide (97.5 mg, 0.732 mmol, 0.5 equiv.) was added. After
stirring for 3 h at ambient temperature, ether was added whereupon an
oil precipitated. The upper layer was decanted and the oily residue was
washed with several portions of ether and dried at 0.02 mbar. The
resulting brown solid was dissolved in a minimum amount of CH2Cl2,
cooled to -78 °C, and ether was added until a solid precipitated. Filtration
under argon and washing with cold CHCl3 gave 9 (478 mg, 0.639 mmol,
87%) as a colorless, very hygroscopic, solid; m.p. 144 °C (dec.). 1H NMR
(CD3CN, 500 MHz):  [ppm] = 1.76 (s, 6 H, NMe), 2.80 (s, 3 H, NMe),
6
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201801749
European Journal of Organic Chemistry
FULL PAPER
2-Benzyl-4-(dimethylamino)-5-((dimethylamino)(phenyl)methyl)-4-
phenyl-2,4-dihydropyrrolo[1,2-c][1,2,3]triazol-7-ium Triflate (12): To a
solution of propyne iminium salt 1a (460 mg, 1.50 mmol) in CH2Cl2 (8
mL), benzyl azide (85 mg, 0.64 mmol, 0.42 equiv.) was added. After
stirring for 4 h at ambient temperature, the solution was cooled to -95 °C
and LiAlH4 (310 µL, 0.745 mmol, 2.4 M in THF, 0.5 equiv.) was added
dropwise. After 5 min the reaction was quenched at this temperature by
addition of acetone, the suspension was warmed to ambient temperature
and water was added. The mixture was extracted with ether and brine,
the organic layer was dried (Na2SO4), and the volatile components were
removed at 800 mbar/40 °C. The resulting brownish solid was dissolved
in a minimum amount of CH2Cl2 and ether, and n-pentane was added
until the solution became turbid. Then the mixture was cooled to -78 °C,
whereupon a voluminous precipitate appeared. Filtration and washing
with ether gave 12 (299 mg, 0.49 mmol, 78%) as a slightly violet solid;
m.p. 159.3–160.5 °C. 1H NMR (CDCl3, 500 MHz):  [ppm] = 2.14 (s, 6 H,
NMe), 2.27 (s, 6 H, NMe), 4.20 (d, J = 1.1 Hz, 1 H, CH), 6.02 (d, J = 14.3
Hz, 1 H, PhCH), 6.08 (d, J = 14.3 Hz, 1 H, PhCH), 6.68–6.70 (m, 2 H,
HPh), 6.76–6.79 (m, 4 H, HPh), 6.83–6.87 (m, 3 H, HPh), 6.90–6.93 (m, 1
H, HPh), 7.40–7.45 (m, 3 H, HPh), 7.62–7.64 (m, 2 H, HPh), 7.76 (s, 1 H,
HC=C), 9.09 (s, 1 H, HTrz). 13C NMR (CDCl3, 125 MHz):  [ppm] = 40.76
(NMe), 44.25 (NMe), 58.19 (PhCH2), 67.60 (CH), 79.58 (Csp3, ring), 120.81
7.13–7.21 (m, 5 H, HPh), 7.25–7.29 (m, 4 H, HPh), 7.35–7.42 (m, 5 H, HPh
and HTrz), 7.74–7.76 (m, 2 H, HPh), 10.41 (s, 1 H, CHO). 13C NMR
(CDCl3, 100 MHz): Z-14:  [ppm] = 54.17 (PhCH2), 126.47 (HCTrz);
127.86, 128.74, 128.79, 128.88, 129.12, 129.17, 130.42, 130.68, 133.49,
133.99, 134.42, 136.63 (all CPh), 137.54 (C=C-CHO), 145.65 (Cq, Trz),
147.84 (C=C-CHO), 191.18 (CHO), 196.11 (C=O); E-14:  [ppm] = 54.60
(PhCH2), 126.94 (HCTrz); 128.14137.34 (12 CPh), 139.61 (C=C-CHO),
145.99 (Cq, Trz), 146.24 (C=C-CHO), 191.73 (CHO), 195.94 (C=O). IR
(KBr): Z-14: 휈̃ [cm-1] = 1681 (s), 1653 (s), 1593 (s), 1450 (m), 1377 (m),
1270 (s), 1240 (m), 1165 (m), 1050 (m), 966 (m), 911 (m), 782 (m), 730
(s); E-14: 휈̃ [cm-1] = 1678 (s), 1653 (s), 1593 (s), 1450 (m), 1368 (m),
1315 (m), 1266 (m), 1233 (m), 1166 (m), 1052 (m), 963 (m), 912 (m), 728
(s), 695 (s). HRMS ((+)-ESI): Z-14: m/z = 809.28419 (calcd. 809.28467
for C50H38N6NaO4+, [2M + Na]+), 416.13683 (calcd. 416.13695 for
C25H19N3NaO2+, [M + Na]+); E-14: m/z = 809.28444 (calcd. 809.28467 for
+
C50H38N6NaO4
,
[2M
+
Na]+), 416.13694 (calcd. 416.13695 for
C25H19N3NaO2+, [M + Na]+).
(2-Benzyl-4-(dimethylamino)-5-((dimethylamino)(phenyl)methyl)-4-
phenyl-2,4-dihydropyrrolo[1,2-c][1,2,3]triazol-7-ium-3-
yl)(butyryloxy)argentate(I) (17): To a solution of triazolium salt 12 (565
mg, 0.94 mmol) in THF (15 mL), potassium tert-butoxide (108 mg, 0.96
mmol, 1.02 equiv.) was added at -20 °C. After stirring for 5 min, AgOTf
(242 mg, 0.94 mmol, 1.0 equiv.) was added and stirring was continued
1
(q, JCF = 320.2 Hz, TfO–), 121.21 (HC=C), 126.97 (CPh), 127.06 (HCTrz);
127.57, 127.88, 128.67, 128.93, 129.18, 129.54, 129.77, 129.93, 132.10,
133.03, 135.90 (all CPh); 143.59 (Cq, Trz), 157.80 (HC=C). IR (KBr): 휈̃ [cm-
1] = 1455 (m), 1276 (s), 1259 (s), 1225 (m), 1154 (s), 1031 (s), 702 (m),
637 (s). HRMS ((+)-ESI): m/z = 450.26480 (calcd. 450.26522 for
C29H32N5+, [M - OTf]+). C30H32F3N5O3S (599.67 g/mol): calcd. C 60.09, H
5.38, N 11.68; found C 60.27, H 5.41, N 11.67.
for 18
h at ambient temperature. The volatile components were
evaporated at 0.01 mbar, and the residue was dissolved in a minimum
amount of CH2Cl2 and filtered through a paper filter under an argon
atmosphere. The filtrate was collected and the solvent was removed. The
solid residue was dissolved in n-butyl ether/CHCl3 at 60 °C. After cooling
to ambient temperature
a dark-grey, sticky oil separated. The
5-((Dimethylamino)(phenyl)methyl)-N,N-dimethyl-4-phenyl-4H-
pyrrolo[1,2-c][1,2,3]triazol-4-amine (13): To a solution of triazolium salt
12 (136 mg, 0.227 mmol) in THF (5 mL), NaH (6.8 mg, 0.227 mmol, 80%
in mineral oil, 1.0 equiv.) and DMSO (0.5 µL, 7.2 µmol, 0.03 equiv.) was
added. After stirring for 18 h at ambient temperature, the volatile
components were evaporated. The residue was dissolved in EtOAc and
filtered through flash silica gel. The filtrate was collected and evaporated
to dryness to obtain 13 (71 mg, 0.197 mmol, 87%) as a slightly violet
solid; m.p. 173.8–174.5 °C. 1H NMR (CDCl3, 400 MHz):  [ppm] = 2.20
(s, 6 H, HC-N(CH3)2), 2.24 (s, 6 H, N(CH3)2), 4.12 (d, J = 1.4 Hz, 1 H,
PhCH), 6.75–6.92 (m, 10 H, HPh), 7.53 (d, J = 0.7 Hz, 1 H, HTrz), 7.71–
7.72 (m, 1 H, C=CH). 13C NMR (CDCl3, 100 MHz):  [ppm] = 40.54
(NMe2), 44.39 (HC-NMe2), 67.38 (PhCH), 76.15 (C-4), 122.39 (HC=C);
126.96, 127.49, 127.55, 127.91, 127.98, 129.07 (all CPh); 129.73 (HCTrz),
136.77 (CPh), 137.65 (CPh), 140.60 (CTrz), 147.77 HC=C). IR (KBr): 휈̃ [cm-
1] = 3091 (s), 2938 (m), 2862 (m), 2826 (m), 2786 (s), 1641 (m), 1490
(m), 1452 (s), 1431 (m), 1199 (m), 1183 (m), 1041 (s), 1017 (m), 835 (m),
724 (m), 699 (s), 633 (m). HRMS ((+)-ESI): m/z = 719.43920 (calcd.
719.42927 for C44H51N10+, [2M + H]+), 360.21923 (calcd. 360.21827 for
C22H25N5+, [M + H]+), 287.15576 (calcd. 287.15428 for C20H19N2+, [M -
NMe2 - N2]+). C22H25N5 (359.48 g/mol): C 73.51, H 7.01, N 19.48. A
correct elemental analysis could not be obtained.
supernatant solution was poured into n-pentane, whereupon a colorless
solid precipitated, which was filtered off to obtain 280 mg of a mixture of
12 and an unknown species (0.43:1). Further separation and
identification of the main species failed. By slow evaporation of the
mother liquor, crystals of 17 (35 mg, 54 µmol, 6%) were obtained. 1H
NMR (CDCl3, 500 MHz):  [ppm] = 0.92 (t, J = 7.4 Hz, 3 H, CH3), 1.61–
1.67 (m, 2 H, CH2), 2.18 (s, 6 H, N(CH3)2), 2.26 (t, J = 7.5 Hz, 2 H, CH2),
2.41 (s, 6 H, N(CH3)2), 4.29 (s, 1 H, CH), 5.81 (s, 2 H, PhCH2), 6.71–6.84
(m, 7 H, HPh), 6.86–6.89 (m, 2 H, HPh), 6.92–6.95 (m, 1 H, HPh), 7.38–
7.43 (m, 3 H, HPh), 7.58–7.59 (m, 2 H, HPh), 7.61 (s, 1 H, C=CH). 13C
NMR (CDCl3, 125 MHz):  [ppm] = 14.39 (CH3), 20.21 (CH2), 38.82
(CH2), 41.23 (N(CH3)2), 44.37 (CH-(N(CH3)2), 60.50 (PhCH2), 77.94
(Cq,sp3), 120.55 (C=CH, ring); 127.33, 127.70, 127.74, 128.24, 128.46,
128.92, 129.07, 129.13, 129.28, 134.80, 135.10, 136.82 (all CPh); 149.84
(CTrz), 155.76 (C=CH, ring), 161.44 (CAg), 181.04 (C=O). HRMS
(MALDI): m/z = 1007.41841 and 1005.41823 (calcd. 1007.42010 and
1005.42044 for [C58H64107/109AgN10]+, [Ag(btrz)2]+), 450.26476 (calcd.
450.26522 for C29H32N5+, [btrzH]+); btrz = bicyclic 1,2,3-triazolylidene.
C33H38AgN5O2 (644.57 g/mol): calcd. C 61.49, H 5.94, N 10.87.
X-ray Crystallography
Data collection was performed on an Oxford Diffraction Rigaku
instrument for 6b (SuperNova, Dual Source, Atlas CCD, Mo K radiation)
and a Bruker D8 Quest diffractometer (Mo K) for 17; T = 150 K.
Structure solution: SHELXT;[34] structure refinement: SHELXL-2014/7.[35]
Molecule plots: ORTEP-3 for Windows[36] and Mercury, version 3.10.1.[37]
2-Benzoyl-3-(1-benzyl-1H-1,2,3-triazol-4-yl)-3-phenylacrylaldehyde
(14): To a solution of propyne iminium salt 1a (484 mg, 1.58 mmol) in
CH2Cl2 (8 mL), benzyl azide (95 mg, 0.71 mmol, 0.45 equiv.) was added.
After stirring for 4 h at ambient temperature, saturated aqueous K2CO3
(400 µL) was added and the mixture was wamed to 40 °C for some
minutes. Na2SO4 was added to bind residual water, and after filtration the
volatiles were evaporated. The residue was dissolved in CHCl3 and
filtered through a pad of silica gel. The filtrate was submitted to HPLC (n-
hexane/CHCl3) which furnished 8 (51 mg, 0.19 mmol, 12%) as a
colorless solid, followed by Z-14 (69 mg, 0.18 mmol, 24%) and E-14 (47
mg, 0.12 mmol, 17%) as yellow solids. M.p. Z-14: 73.8–76.2 °C; m.p. E-
Selected data for 6b: Diffusion crystallization from CH2Cl2 and
diethylether/pentane. (C29H28BrN6)(CF3SO3), Mw = 689.55. Monoclinic
space group P21/c, a = 9.3632(2), b = 33.3632(5), c = 11.4279(2) Å, b =
109.754(2)o, V = 3359.84(2) Å3; Z = 4, Dx = 1.363 g cm-3, μ = 1.34 mm-1.
R = 0.0442 (5397 reflexions with I > 2(I)), wR2 = 0.1221 (all 6376 data).
Residual electron densities between 1.38 (close to Br) and -1.19 e Å-3.
1
14: 66.1–70.1 °C. H NMR (CDCl3, 400 MHz): Z-14:  [ppm] = 5.34 (s, 2
H, PhCH2), 7.03–7.05 (m, 2 H, HPh), 7.25–7.29 (m, 3 H, HPh), 7.31 (s, 1
H, HTrz), 7.38 (t, J = 7.6 Hz, 2 H, HPh), 7.46–7.53 (m, 6 H, HPh), 7.90–7.92
(m, 2 H, HPh), 9.58 (s, 1 H, CHO); E-14:  [ppm] = 5.56 (s, 2 H, PhCH2),
Selected data for 17: Crystals were obtained by slow evaporation of a
solution in CHCl3/di(n-butyl)ether and pentane. C33H38AgN5O2, Mw
=
7
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10.1002/ejoc.201801749
European Journal of Organic Chemistry
FULL PAPER
644.55. Triclinic space group P-1, a = 11.2877(7), b = 11.5726(7), c =
13.8670(7) Å,  = 69.899(2),  = 70.185 (2),  = 66.664(2)o; Z = 2, Dx =
1.410 g cm-3,  = 0.70 mm-1. R = 0.0456 (5772 reflexions with I > 2(I)),
wR2 = 0.1393 (all 7573 data). Maximal residual electron densities were
1.01 (close to C32a) and 0.88 Å-3 (close to Ag1). Due to disorder of the
alkyl chain, the two hydrogen atoms at C31 were not included and
restraints were imposed on the distances in the C31C32A/BC33
fragment.
Sustainability and Chemical Education (Eds.: V. S. Parmar, P. Malhotra,
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Entry for the Table of Contents
FULL PAPER
1,2,3-Triazoles
Michael Keim, Gerhard Maas*
Page No. – Page No.
Terminal Acetylenic Iminium Salts:
1,3-Dipolar Cycloaddition Reactions
with Azides leading to 1,2,3-Triazoles
and Bicyclic 1,2,3-Triazolium Salts
Terminal acetylenic iminium triflates are excellent dipolarophiles for [3+2] cyclo-
additions with (ring-substituted) benzyl and phenyl azide, yielding novel 1,2,3-
triazol-4-yl)methaniminium salts. The latter are readily converted into 2:1 adducts,
dicationic bicyclic 1,2,3-triazolium salts, which can be transformed into some
interesting compounds, among them a mesoionic carbene and a Ag(I) complex
thereof.
10
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