3-Trifloxy-3-(trifluoromethyl)prop-2-ene 1-Iminium Salts as Precursors for Elusive 3-(Trifluoromethyl)prop-2-yne 1-Iminium Salts

Article abstract of DOI:10.1002/ejoc.202100567

Abstract: 3-(Trifluoromethyl)prop-2-yne 1-iminium triflate salts were generated from 3-trifloxy-3-(trifluoromethyl)prop-2-ene 1-iminium salts by triethylamine-assisted elimination of triflic acid and trapped in situ in various cycloaddition reactions. The

Full text of DOI:10.1002/ejoc.202100567

European Journal of Organic Chemistry
Accepted Article
Accepted Article
Title: 3-Trifloxy-3-(trifluoromethyl)prop-2-ene 1-Iminium Salts as
Precursors for Elusive 3-(Trifluoromethyl)prop-2-yne 1-Iminium
Salts
Authors: Michael Keim, Katharina Konetzke, Angelika Freytag, and
Gerhard Maas
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of the final Version of Record (VoR). This work is currently citable by
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To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.202100567
Link to VoR: https://doi.org/10.1002/ejoc.202100567
01/2020

10.1002/ejoc.202100567
European Journal of Organic Chemistry
FULL PAPER
3-Trifloxy-3-(trifluoromethyl)prop-2-ene 1-Iminium Salts as
Precursors for Elusive 3-(Trifluoromethyl)prop-2-yne 1-Iminium
Salts
Michael Keim, Katharina Konetzke, Angelika Freytag, and Gerhard Maas*a]
Dedication ((optional))
[a]
Dr. M. Keim, K. Konetzke, A. Freytag, Prof. Dr. G. Maas
Institute of Organic Chemistry I
Ulm University
Albert-Einstein-Allee 11, 89081 Ulm, Germany
E-mail: gerhard.maas@uni-ulm.de
Supporting information for this article is given via a link at the end of the document.
Abstract: 3-(Trifluoromethyl)prop-2-yne 1-iminium triflate salts were
generated from 3-trifloxy-3-(trifluoromethyl)prop-2-ene 1-iminium
salts by triethylamine-assisted elimination of triflic acid and trapped in
situ in various cycloaddition reactions. These included Diels-Alder
reactions with 1,3-dienes, [2+2] cycloaddition with 1,4-diphenylbuta-
1,3-diene, and [3+2] cycloaddition with organoazides. All these
reactions revealed the excellent dienophilic and dipolarophilic
reactivity of the electrophilic C,C triple bond of the novel 3-CF3-
propyniminium salts.
molecular frameworks were obtained from salts 1 and 1,3-dienes
and styrenes[8a] or with the mesoionic Nitron.[8b]
So far unknown 3-CF3-substituted prop-2-yne 1-iminium salts 2
can be expected to exhibit some noticeable reactivity changes
compared to salts 1. By attachment of the CF3 group, the
acetylenic bond will become more electrophilic and therefore will
undergo faster cycloaddition reactions with sufficiently electron-
rich 1,3-dienes or 1,3-dipoles. At the same time, absence of the
CF3 group from the iminium carbon atom will lower the
electrophilicity of the iminium function and intramolecular SEAr
reactions (aminoalkylations), which followed cycloaddition
reactions of salts 1 and some 1,3-dienes and styrenes,[8a] will be
less likely.
Introduction
In this paper we report that acetylenic iminium salts 2 can be
generated from 3-trifloxy-3-(trifluoromethyl)prop-2-ene 1-iminium
salts by base-assisted elimination of triflic acid and can be trapped
in situ in diverse cycloaddition reactions. In this manner, salts 2
can serve as novel CF3-containing building blocks for the
construction of various trifluoromethylated carbo- and
heterocyclic ring systems.
The specific properties of the C‒F bond[1] are the basis of the
ongoing profound interest in fluorinated organic compounds with
potential applications in medicinal chemistry, agricultural
chemistry and diverse functional materials.[2] According to recent
estimates, 20‒25% of marketed drugs[3] contain at least one
fluorine atom. The percentage of commercial pesticides is also
steadily increasing and amounted to over 50% for the years
2010‒2016.[4] Quite often, a trifluoromethyl group is present in
those compounds. Several synthetic strategies allow the
introduction of a CF3 group into a molecular framework, such as
direct trifluoromethylation by electrophilic, nucleophilic or radical
methods, and the use of trifluoromethyl-containing building
blocks.[2,5,6] The latter strategy comprises simple CF3-substituted
C1 molecules as well as a great variety of more advanced building
blocks.[3,5,6]
Results and Discussion
Preparation of 3-trifloxy-3-(trifluoromethyl)propeniminium salts
Propyniminium salts 1 (NR2 = NMe2) can be prepared by C,C-
coupling of a terminal alkyne and imidoyl chloride CF3C(Cl)=NMe
followed by N-methylation of the resulting alkynyl imine with
methyl triflate.[7a] An analogous synthesis of propyniminium salts
2 appears not to be convenient, because it would require 3,3,3-
trifluoroprop-1-yne, which is a flammable gas (boiling point: ~-
48 °C) and is rather expensive if purchased. Therefore, we
considered an alternative approach, which had also been used to
prepare salts of type 1, namely O-sulfonylation of enaminones
with triflic anhydride to obtain 3-trifloxyprop-2-ene 1-iminium
triflates, which were transformed into the desired alkynes 1 by
thermal or base-assisted elimination of triflic acid.[9] 3-CF3-
substituted enaminones 4 can be prepared from readily available
trifluoromethylated starting materials, ethyl trifluoroacetate and
Figure 1. Two CF3-substituted propyniminium triflate salts.
Recently, we have introduced 1-CF3-substituted propyniminium
salts 1 as novel CF3-substituted acetylenic building blocks, which
could be used for the synthesis of -CF3-substituted pyrroles[7a]
and 4-CF3-quinolines[7b] and for [2+2] or [2+3] anellation of furans,
thiophenes and pyrroles.[7c] Various other CF3-substituted
1
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10.1002/ejoc.202100567
European Journal of Organic Chemistry
FULL PAPER
trifluoroacetic anhydride, as is shown in Scheme 1. In method A,
acetylenic ketone 3a was prepared from ethyl trifluoroacetate and
phenylethynyl lithium[10] and converted into enaminones 4a‒d by
conjugate addition of dialkylamines, as was already reported for
4c.[11] In method B, trimethylsilyl-substituted alkynone 3b was
prepared in the same manner as 3a;[12] it reacted with a
methanolic solution of diethylamine by conjugate addition and
desilylation to provide enaminone 4e. The corresponding 4-
(dimethylamino)but-3-en-2-one 4f was assembled from
trifluoroacetic anhydride, ethyl vinyl ether and dimethylamine as
reported by Balenkova et al.[13a] (method C, developed by Hoyo et
al.[14]).
The reaction of enaminones 4a‒f with a small excess (1.05
equiv.) of triflic anhydride in dry dichloromethane was fast even at
low temperatures and afforded 3-trifloxy-3-(trifluoromethyl)prop-
2-ene 1-iminium triflate salts 5a‒f in high yields (Scheme 1). Salt
5f has been prepared earlier on pathway C; it was identified by
the NMR data and in situ exposed to electron-rich aromatics or
aromatic amines for further transformations.[13] All iminium salts 5
are hygroscopic solids that deliquesce to form yellow to orange
oils on exposure to atmospheric moisture, but they can be stored
in a dry inert atmosphere.
a mixture of unknown fluorine-containing species, as indicated by
several new 19F NMR signals. In the mixture obtained from
vacuum thermolysis, a prominent 19F NMR signal at (CDCl3) = -
52.0 ppm at least pointed to the presence of the desired
acetylenic iminium salt 2 (compare: F = -52.3 ppm for CF3-C≡C-
COOEt[16] and -53.87 ppm for CF3-C≡C-PO(OEt)2[17]). Workup of
these mixtures was unpromising in view of the anticipated high
reactivity of alkynes 2 and the difficulty to separate a mixture of
ionic and potentially hydrolytically labile products.
On the other hand, the following observations indicated the
intended generation of a propyniminium salt 2. When salt 5b was
dissolved in dry CH2Cl2 and one equivalent of anhydrous
triethylamine was added at 20 or -78 °C, the yellowish color of the
solution changed to dark red. The 19F NMR spectra of the reaction
mixture showed a strong anionic triflate signal beside a multitude
of low-intensity signals, and the 1H NMR spectrum displayed the
prevailing signals of the triethylammonium ion. These
observations suggested that propyniminium salts 2 have a
fleeting existence but it might be possible to trap them in situ by
cycloaddition reactions with suitable 1,3-dienes or 1,3-dipolar
compounds (Scheme 2). As we show in the following, this concept
was successful indeed.
All enaminones 4 and ketiminium salts 5a‒d were obtained as
single configurational isomers according to the NMR spectra. For
aldimine salts 5e,f, a set of minor 1H NMR signals close to those
of the main product was detected, which we attribute to the O-
protonated enaminones that result from unavoidable hydrolysis of
the two iminium salts. The E(C=C) configuration of 4a‒f can be
assumed as the more stable one for steric reasons; it is supported
Scheme 2. Trapping reactions of in situ generated propyniminium salt 2.
1
by H NMR data (NOE correlations observed for 4c[11] and the
large 3JH,H coupling constant (12.2‒12.4 Hz) of the olefinic protons
in 4e[15] and 4f). For the propeniminium salts 5, the Z(C=C),s-
trans(C1-C2) configuration is proposed based on steric
considerations (planarity of the C=C‒C=N+Me2 moiety and lowest
steric strain), but is not readily evident from the NMR data.
Trapping reactions with 1,3-dienes
As was already stated in the Introduction, the very electrophilic
acetylenic bond of CF3-substituted propyniminium ions 2 is
expected to be
a highly reactive dienophile for [4+2]
cycloadditions (Diels-Alder reactions) with normal electron
demand. This was confirmed by reactions of in situ generated
salts 2 with cyclopentadiene, acyclic 1,3-dienes, and anthracene.
Various other CF3-substituted alkynes have been used before as
electron-deficient dienophiles in inter- and intramolecular Diels-
Alder reactions.[18] An interesting analogy to our work is 3,3,3-
trifluoro-1-(phenylsulfonyl)propyne, which „decomposed to
a
significant extent even at low temperature“ and was therefore
generated from 2-bromo-1-phenylsulfonyl-3,3,3-trifluoroprop-1-
ene and NEt3 and trapped in situ by Diels-Alder reactions with 1,3-
dienes.[19]
The 3-trifloxypropeniminium salts
5b,e reacted with
cyclopentadiene in the presence of an equimolar amount of
triethylamine at room temperature within a few minutes to afford
norbornadienyl iminium salts 6b,e, which likely result from a Diels-
Alder reaction involving the transient propyniminium salts 2b,e
(Scheme 3). As a successful and effective separation of the
iminium salts 6 from the by-product, triethylammonium triflate, is
very unlikely, they were directly converted into neutral products.
Thus, alkaline hydrolysis furnished ketone 7a and aldehyde 7b,
and the reaction with excess cyclopentadiene/NEt3 led to
pentafulvene 7c, all obtained in high overall yield. The latter was
isolated as an oil, which soon solidified, obviously as a result of
an oligomerization event (according to the 1H NMR spectra).
Concerning the formation of norbornadienes 7a and 7b, the
Scheme 1. Synthesis of 3-trifloxy-3-CF3-prop-2-ene 1-iminium triflates 5. Yields
of 4 (%): 91‒99 (4a‒c), 60 (4d), 67 (4e), 75 (4f); yields for 4 → 5: 91‒95%. Tf =
CF3SO2.
3-Trifloxy-3-CF3-propeniminium salts 5 as masked 3-CF3-prop-2-
yne 1-iminium salts 2
Our initial efforts to convert 3-CF3-trifloxypropeniminium salts 5
into 3-CF3-propyniminium salts 2 by base-assisted or thermal
elimination of triflic acid[9] led to disappointing results. Thus, both
a vacuum thermolysis (e.g., 120 °C/0.07 mbar, 15 min for 5b) and
the reaction with triethylamine or other tertiary amines generated
presumably involved 3-CF3-propyniminium salts
2 can be
2
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10.1002/ejoc.202100567
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FULL PAPER
considered as synthetic equivalents of the respective
trifluoromethylated acetylenic ketone or aldehyde. It has been
reported that the [4+2] cycloaddition of 1,1,1-trifluorodec-2-yn-4-
one and cyclopentadiene was almost complete (> 5 half-lives)
after 40 min at room temperature.[20] A qualitative comparison
indicates the even better reactivity of iminium salts 2 compared to
neutral CF3-ethynyl ketones.
Scheme 4. Synthesis of 2-trifluoromethylated benzophenone 9a and
benzaldehyde 9b.
anthracene(s) as the 1,3-diene component require significant
thermal activation (see below for some examples).[21] Therefore,
we were delighted to find that 3-CF3-propeniminium salts 5b,d‒f
reacted with anthracene and some substituted anthracenes in the
presence of triethylamine at room temperature almost
immediately to form dibenzobarrelenes 10 (Scheme 5). As no
reaction was observed at room temperature in the absence of
NEt3, the intermediacy of highly dienophilic 3-CF3-propyniminium
salts 2b,d‒f is likely. In situ derivatization of the Diels-Alder
adducts 10 by hydrolysis, Knoevenagel reaction, hydride
reduction or reductive alkylation of the iminium group afforded a
variety of novel CF3-substituted dibenzobarrelenes 11‒14
(Scheme 5, Table 1). The reaction of propeniminium salt 5d with
anthracene deviates in two aspects from all other reactions. First,
an increased reaction time (one hour) was required for the
cycloaddition step, probably because of the steric influence of the
bulky dialkylamino group; second, on basic hydrolysis at
moderately elevated temperature, instead of ketone formation a
dealkylation of the iminium group took place and imine 11g
(mixture of Z(C=N) and E(C=N) diastereomers) was isolated. In
summary, Scheme 5 shows that a variety of new CF3-
dibenzobarrelenes can be prepared by in situ trapping of 3-CF3-
prop-2-yne 1-iminium salts 2 and, in a one-pot procedure,
consecutive reactions at the reactive iminium functional group of
Diels-Alder adducts 10. Only a few other CF3-dibenzobarrelenes
have been reported so far.[17,22,23]
Scheme 3. Synthesis and derivatization of norbornadienyl iminium salts 6b (R1
= Ph) and 6e (R1 = H). Conditions: a) 6b, aq. K2CO3, r.t., 5 min, 86% yield; b)
6e (from equimolar amounts of 5e and cyclopentadiene), aq. K2CO3, r.t., 10 min,
94%; c) 5e (1 equiv.), 1,3-cyclopentadiene (4 equiv.), NEt3 (3 equiv.), r.t., 10
min, 89%, oligomerization of neat 7c at r.t. All yields were calculated based on
5b,e.
2,3-Dimethylbuta-1,3-diene is also known as a reactive diene
substrate in [4+2] cycloaddition reactions, although it is not locked
in the s-cis conformation that is required for a concerted
cycloaddition. When 3-trifloxypropeniminium salts 5b,e were
exposed to this diene in the presence of triethylamine, smooth
Diels-Alder reactions took place at room temperature, which was
almost complete when the dropwise addition of the diene/NEt3
mixture was finished. The resulting cyclohexadienyl iminium salts
1
8a,b were confirmed by their H NMR spectra but not isolated;
subsequent dehydrogenation and basic hydrolysis afforded the 2-
trifluoromethyl-benzophenone 9a and -benzaldehyde 9b in high
yields (Scheme 4).
We expected that propyniminium salts 2 can also be trapped in
Diels-Alder reactions with anthracenes leading to CF3-substituted
dibenzobarrelenes. Most [4+2] cycloaddition reactions with
Scheme 5. Synthesis of Diels-Alder adducts 10 and their in-situ derivatization. For conditions, products and yields, see Table 1.
3
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Table 1. In situ derivatization of the Diels-Alder adducts 10.a
Entry
Adduct 10b
NR2
R1
R2
R3
Conditions
Product
Yield (%)c
1
2
3
4
5
6
7
8
b
NEt2
Ph
H
H
H
K2CO3, H2O, r.t.
H2O, r.t.
11a
11b
12
87
80
26
75
27
15
30
51
f
NMe2
H
H
f
NMe2
H
H
H
H2C(COOMe)2, NEt3, r.t.
H2O, r.t.
fa
fb
fc
fd
d
NMe2
H
Me
Br
H
H
11c
11d
11ed
11f
NMe2
H
H
H2O, r.t.
NMe2
H
N(Me)Ac
H2O, r.t.
NMe2
H
H
N3
H
H2O, r.t.
N((S)-CHMePh)2
Ph
H
K2CO3, H2O, r.t.
11g
Reactions with [Met]‒Nu
Adduct 10b
NR2
R1 = R2 = R3 = H
Nu‒[Met]e
LiAlH4
Product
13a
Yield (%)c
9
e
f
NEt2
46
42
81
78
65
80
10
11
12
13
14
NMe2
NMe2
NMe2
NMe2
NMe2
LiAlH4
13b
f
MeMgBr
14a
f
EtMgBr
14b
f
CH2=CH-MgBr
14c
f
Me3Si-C≡C-MgBr
14d
[a] See Scheme 5; iminium-substituted Diels-Alder adducts 10 were transformed without isolation (i.e., an equimolar amount of by-product HN+Et3 TfO- was present
in the reaction mixture) into neutral products 11‒14. [b] Adduct 10b was prepared from 5b, 10d from 5d, 10e from 5e, all others from 5f. [c] Overall yields based on
salts 5 (two steps) are given. [d] Mixture of two regioisomers (1:0.45); see text. [e] An excess of Nu‒[Met] was used in order to neutralize HN+Et3‧TfO-.
The excellent dienophilic reactivity of 3-CF3-propyniminium salts
2 becomes evident by comparison with data reported for Diels-
Alder reactions of anthracene and some other electrophilic
dienophiles (Table 2). As many Diels-Alder reactions involving
anthracene require strong thermal activation, it represents kind of
regioisomeric transition states (TS-10A and TS-10B, Scheme 6)
are conceivable. They result from a highly asynchronous
cycloaddition, where a sigma bond between the electrophilic atom
C-3 of the propyniminium ion and the anthracene is formed first
and the developing partial charges are stabilized by  conjugation.
a benchmark diene to assess the reactivity of different dienophiles. In the extreme case, this [4+2] cycloaddition would proceed
Although no experimental kinetic data exist and the reported
reaction conditions data allow only a qualitative comparison, it is
evident that 3-CF3-substituted prop-2-yne ketiminium salt 2a and
aldiminium salt 2f (entry 1) are by far the most reactive
dienophiles in this list, certainly due to the two strongly electron-
withdrawing substituents and the polarized acetylenic bond. Only
terminal acetylenic iminium salts come close to this reactivity
(entries 3 and 4), probably due to monosubstitution of the
acetylenic bond, which reduces the contribution of steric factors
to the activation barrier. TCNE also reacts at room temperature
(entry 10), but more slowly than the listed acetylenic iminium
salts.[28] Other disubstituted electrophilic alkynes with and without
CF3 substitution (entries 5‒9) require much stronger thermal
activation.
The mechanism of Diels-Alder reactions has been studied by
Domingo and coworkers based on conceptual Density Functional
Theory and a scale of electrophilicity/nucleophilicity indices has
been established.[29] Assuming that acetylenic iminium ions 2
have a similar global electrophilicity as TCNE ( = 5.96,
compared to 2.27 for DMAD[29a, 29c]), one can expect a very polar
Diels-Alder reaction with quite a low activation barrier. Thus, for
the reactions of propyniminium salt 5f with 2-substituted
anthracenes leading to Diels-Alder adducts 10e,f two
stepwise through intermediates featuring an aminoallene and a
benzyl cation-type moiety. The extent of positive charge
stabilization in a benzyl cation depends on the type and position
of a substituent at the aromatic ring. In the cases of 10e and 10f,
both substituents R3 are strongly electron-donating by

conjugation and suited to stabilize a developing positive charge at
the benzylic carbon atom in TS-10A (Hammett constants for
+
NHCOMe: p = -0.65[30b], value for N(Me)COMe should be
similar; N3: p+ = -0.54[30c]). On the other hand, the combination of
resonance and polar effects renders substituents R3 overall
inductively electron-withdrawing, i.e. less suited to effectively
stabilize the positive charge (Hammett  constants, N(Me)COMe:
m 0.31, p 0.26; N3: m 0.37, p 0.08.[30a]) These data are
reflected in the experimental results. Thus, after hydrolysis of the
iminium function in 10e, a mixture of 11eA/11eB (1.0 : 0.45) was
obtained, as could be expected because the  constants are
rather similar in TS-10A (p) and in TS-10B (m).[31] On the other
hand, a benzyl cation is much less destabilized by an azido
substituent in para (TS-10A, weakly positive p parameter) than
in meta (TS-10B) position; in fact, isomer 11fA was obtained in
90% purity (the remainder being the other regioisomer or an
unknown impurity).
4
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10.1002/ejoc.202100567
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Scheme 6. Suggested transition-state structures leading to regioisomeric Diels-
Alder adducts 10e and 10f derived from 2-substituted anthracenes.
When (E,E)-1,4-diphenylbuta-1,3-diene was used to trap the
acetylenic iminium salt 2b, generated from propeniminium salt 5b
and triethylamine, no [4+2] cycloadduct was formed. After alkaline
hydrolytic workup or reaction with LiAlH4, 1,3,5-hexatrienes 16 or
17 were isolated in good yields (Scheme 7). The reaction course
likely includes the intermediate cyclobutene 15A, which results
Scheme 7. Reaction of iminium salt 5b with (E,E)-1,4-diphenylbuta-1,3-diene in
the presence of triethylamine.
from
a formal, probably stepwise, [2+2] cycloaddition of
propyniminium salt 2b and the 1,3-diene. An electroyclic
conrotatory ring-opening of 15A leads to 1,3,5-hexatrienyl
iminium salt 15B, which can be further transformed into neutral
products 16 and 17. The structure of the hydrobromide of 17 was
established by an XRD analysis (Fig. 2). It confirms the Z-
configuration at the CF3-substituted olefinic bond and reveals that
the CF3-substituted C=C bond is strongly tilted against the
coplanar butadiene moiety.[32] We have observed earlier an
analogous reaction pathway, when acetylenic iminium salt 1 (Fig.
1, R = Ph) was combined with the same 1,3-diene; in that case,
however, the reaction was less clean and only a product which
probably resulted from an intramolecular iminium cyclization of
the hexatriene intermediate analogous to 15B (CF3 and iminium-
substituted Ph interchanged) could be isolated in low yield.[8a]
Figure 2. Solid-state structure of 17‧HBr (ORTEP plot). Torsion angles: C13‒
C12‒C2‒C1 74.5(5), C13‒C12‒C2‒C3 -114.0(4), C12‒C2‒C1‒N1 78.8, C3‒
C4‒C5‒C6 -178.6(3)°.
Table 2. A comparison of the dienophilic reactivity of acetylenic iminium salts and other dienophiles toward anthracene.
Entry
Dienophile
Conditions
Yield (%)
Ref.
R = Et, R1 = Ph (2a)
R = Me, R1 = H (2f)
r.t., 5‒10 min
r.t., 5‒10 min
87a
80a
1
This work
2
3
r.t. → 55 °C, 14 h
95
[8a]
[24]
R = Me
R = H
-20 °C → r.t., 4 h
92
75
r.t., 2 h
4
r.t., 1 h
98b
[24]
5
6
200 °C, 2 h
71
79
[22]
[23]
120 °C, 52 h
5
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7
80 °C, 10 h
80 °C, 6 h
82
72
[17]
[25]
8
9
170–180 °C, 1 h
80
[26]
[27]
(DMAD)
10
tetracyanoethylene (TCNE)
r.t., 12 h
100
[a] Yield after hydrolysis of the iminium group. [b] Yield after reduction to amine with LiAlH4.
Trapping reactions with organoazides
Taking into account our initial attempts to isolate acetylenic
iminium salts 2 (see above), the reduced yields may be due in
part to their limited stability, which becomes a problem, when the
cycloaddition step is not fast enough (as is the case with PhN3,
entries 2 and 3).
In preceding papers we have shown, that a variety of 3-
substituted and terminal prop-2-yne 1-iminium salts and
organoazides undergo HOMOdipole‒LUMOdipolarophile controlled
[3+2] cycloadditions to give 1H-1,2,3-triazoles.[33] In general, the
iminium functional group was directed to the 4-position of the
triazole ring with complete regioselectivity; only with
propyniminium salts bearing a sterically demanding substituent (t-
Bu, SiMe3) at the acetylenic bond, a mixture of regioisomers was
obtained. Although the cycloaddition reactions of disubstituted
acetylenic propyniminium salts with aryl- or alkylazides
proceeded slowly even at 90 °C, we saw a chance that the more
electrophilic CF3-substituted salts 2 would react under much
milder conditions. These expectations were confirmed by the
results shown in Scheme 8 and Table 3. 3-Trifloxypropeniminium
salts 5b and 5e reacted with benzyl azides in the presence of
triethylamine already at room temperature to form (5-CF3-1,2,3-
triazol-4-yl)-substituted iminium salts 18; as for the Diels-Alder
reactions presented above, intermediate formation of 3-CF3-prop-
2-yne 1-iminium salts 2 can be assumed. Reactions with benzyl
azide were complete after 10‒30 min (entries 1,3‒5), whereas the
cycloaddition of less nucleophilic phenyl azide was much slower
(entries 2 and 3) and gave no defined product in the case of 5d.
The triazolyl-iminium salts 18 were not isolated but converted
directly into other 4-CF3-triazoles by alkaline hydrolysis (19),
reaction with a Grignard reagent (20) or Knoevenagel reaction
(21). Table 2 shows that the yields of these one-pot three-step
reactions (HOTf elimination, cycloaddition, iminium derivatization)
under the chosen conditions are not satisfactory in most cases.
Scheme 8. Synthesis of 1,2,3-triazoles 19‒21 from propene iminium salts 5;
see Table 2 for conditions, products and yields.
In the 13C NMR spectra of triazoles 19‒21 the following signals
are characteristic:  = 54.1±0.7 ppm (4JC,F = 2.1±0.3 Hz, NCH2 in
19a,d, 20, 21), 123.8‒129.0 ppm (2J = 40.9‒44.0 Hz, C-4), 145.0‒
151.1 (slightly broadened, C-4). The presence of a 4JC,F coupling
between NCH2 and CF3 hereby confirms the proposed orientation
of the [3+2] cycloaddition, which is the same as observed for a
Table 3. 1,2,3-Triazoles 19‒21 prepared by [3+2] cyloaddition of in situ generated 3-CF3-propyniminium salts 2 and organoazides.
Entry
R1
Ph
Ph
H
NR2
R2
Conditions,
step 1
Conditions,
step 2
Product
19a
19b
19c
19d
20
Yield (%)
1
2
3
4
5
6
NEt2
NEt2
NEt2
NEt2
NEt2
NEt2
CH2Ph
Ph
5b, CH3CN,
r.t., 30 min
5b, CH3CN,
r.t., 4 h
NaHCO3, H2O
83
40
0
NaHCO3, H2O
K2CO3, H2O
K2CO3, H2O
Ph
5e, CH3CN,
r.t., 6 ha
H
CH2Ph
5e, CH3CN,
r.t., 30 min
5e, CH2Cl2,
r.t., 10 min
5e, CH2Cl2,
r.t., 30 min
68
55
23
H
CH2-C6H4-
4-Cl
MeMgBr,
r.t., 20 min
H
CH2-C6H4-
4-Cl
H2C(COOEt)2,
NEt3, 30 min, then
SiO2
21
a Phenyl azide (3 equiv.) was dissolved in dry acetonitrile and solutions of 5e (1 equiv.) and NEt3 (1 equiv.) in the same solvent were added simultaneously from two
dropping funnels during 6 h. After workup, traces of 19c were observed by NMR but could not be isolated.
6
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10.1002/ejoc.202100567
European Journal of Organic Chemistry
FULL PAPER
(CH3CN) = 1.94; 13C NMR: (CDCl3) 77.16, (CD2Cl2) = 53.84, (CD3CN)
= 1.32 and 118.26], for 19F NMR spectra hexafluorobenzene was used
((C6F6) -162.90). 13C and 19F NMR spectra were recorded in the proton-
decoupled mode. When necessary, 13C signals were assigned by means
of HSQC and HMBC spectra. IR spectra of solid samples prepared as KBr
pellets or of oils between NaCl plates were recorded on a Bruker Vector
22 FT-IR instrument. 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, 63‒200 m, Macherey-Nagel). Preparative HPLC: Varian
Prostar 210, column Varian Dynamax 250×21.4 mm, microsorb 100-5 Si;
in general, a solution of the compound was first subjected to a flash
chromatography over dry siliga gel (40‒63 m, Macherey-Nagel) in order
to remove polymeric or ionic impurities.
variety of other acetylenic iminium salts.[33] Several other
syntheses of C-trifluoromethyl-substituted 1,2,3-triazoles have
been reported. In most of them, [3+2] cycloaddition reactions of
-dialkylamino--CF3-acrylic acid esters and organoazides were
involved and 5-CF3-1,2,3-triazole-4-carboxylic esters were
obtained.[34‒36] A series of ethyl 1-alkyl-5-trifluoromethyl-1,2,3-
triazole-4-carboxylates were obtained in good yields from ethyl -
monoalkylamino--CF3-acrylates and methanesulfonyl azide; in
this case, only the terminal N=N fragment of the azide was
incorporated in the triazole.[35] The thermal reaction of ethyl 4,4,4-
trifluorobutynoate and benzyl azide, on the other hand, provided
a ~1:1 mixture of the regioisomeric 5-CF3- and 4-CF3-1,2,3-
triazoles.[38] A 1-aryl-4-CF3-1,2,3-triazole was prepared either by
a late-stage trifluoromethylation of the corresponding 1-aryl-4-
iodo-1,2,3-triazole or by decarboxylative Cu(I)-catalyzed [3+2]
cycloaddition from ethyl 4,4,4-trifluorobut-2-ynoate/LiOH and an
aryl azide.[39] Characteristic features of our method are: mild
reaction conditions of the 1,3-dipolar cycloaddition, complete
regioselectivity, and introduction of an aldiminium or ketiminium
functional group at the C-4 position of the triazole ring, followed
by in situ transformation of the iminium group into a variety of
other substituents.
2. Synthesis of enaminones 4
2.1. E-4-(Dimethylamino)-1,1,1-trifluoro-4-phenylbut-3-en-2-one (4a):
1,1,1-Trifluoro-4-phenylbut-3-yn-2-one[10] (3a, 1.80 g, 9.08 mmol) was
dissolved in THF (6 mL) and dimethylamine (40% in H2O, 2.0 mL, 15.8
mmol) was added. The solution was stirred for 30 min, then extracted with
CH2Cl2 (2 × 100 mL), and the organic phase was washed with brine and
dried (Na2SO4). After evaporation of the volatiles in vacuo, the product was
obtained as an orange solid (2.00 g, 8.22 mmol, 91% yield). M.p. 53.1‒
54.7 °C. 1H NMR (CDCl3, 500 MHz):  = 2.82 (s, 3H, NCH3), 3.17 (s, 3H,
NCH3), 5.39 (s, 1H, CH), 7.16–7.18 (m, 2H, HPh), 7.44–7.47 (m, 3H, HPh).
13C NMR (CDCl3, 126 MHz):  = 40.5 (NCH3), 41.5 (NCH3), 87.7 (C-3),
117.9 (q, 1JC,F = 293 Hz, CF3); 127.2, 129.1, 129.3, 135.4 (all CPh); 168.6
Conclusion
2
(C-4), 174.9 (q, JC,F = 31.2 Hz, C=O). 19F NMR (CDCl3):  = -78.3. IR
Acetylenic iminium salts with the general constitution CF3-C≡C-
C(R1)=N+R2‧X-, where X- is a weakly nucleophilic anion such as
triflate, have never been reported in the literature, in contrast to
many other CF3-free acetylenic iminium salts with an internal or
terminal C,C triple bond. Our present study aiming at preparation
of these salts by established methods was unsuccessful in so far,
as they could not be isolated. However, we successfully applied
a strategy to generate them by triethylamine-assisted elimination
of triflic acid from the propyniminium ion and in situ cycloaddition
with sufficiently electron-rich dienes and organoazides. The very
mild reaction conditions indicate the high electrophilicity of CF3-
substituted acetylenic iminium salts. Beside their cycloaddition
qualities, several methods of subsequent in situ transformation of
the reactive iminium group, that is still present in the cycloadducts,
characterize the usefulness of these novel CF3-containing
acetylenic building blocks. Along these lines, we have developed
practical one-pot three-step procedures, which convert 3-CF3-3-
(KBr): 휈̃ = 1648 (vs), 1542 (s), 1379 (s), 1282 (s), 1180 (s), 1129 (s), 1072
(s), 934 (s), 773 (s), 705 (s) cm-1. MS (CI, 100 eV): m/z (%) = 244 (100)
[M+H]+. Analysis calcd. for C12H12F3NO (243.23): C 59.26, H 4.97, N 5.76;
found: C 59.34, H 5.06, N 5.68.
2.2. E-4-(Diethylamino)-1,1,1-trifluoro-4-phenylbut-3-en-2-one (4b
42b): Prepared from alkynone 3a (8.53 g, 43.1 mmol) and diethylamine
(3.18 g, 43.5 mmol) in CH2Cl2 (20 mL) as described for 4a. Yellowish solid
1
(11.5 g, 42.4 mmol, 99% yield), m.p. 92.8‒93.7 °C (lit.[14]: 93‒94 °C). H
NMR (CDCl3, 400 MHz):  = 1.04 (t, 3JH,H = 7.1 Hz, 3H, CH3), 1.36 (t, 3JH,H
= 7.2 Hz, 3H, CH3), 3.10 (q, 3JH,H = 7.1 Hz, 2H, NCH2), 3.52 (q, 3JH,H = 7.2
Hz, 2H, NCH2), 5.43 (s, 1H, CH=), 7.16–7.18 (m, 2H, HPh), 7.41–7.48 (m,
3H, HPh). 13C NMR (CDCl3, 100 MHz):  = 11.4 (CH3), 14.4 (CH3), 44.3
1
(NCH2), 45.7 (NCH2), 86.9 (3-H), 118.0 (q, JC,F = 293 Hz, CF3), 126.9
2
(CPh), 128.9 (4CPh), 135.6 (CPh), 167.2 (C-4), 174.6 (q, JC,F = 31.2 Hz,
C=O). 19F NMR (CDCl3):  = -78.2. IR (KBr): 휈̃ = 1655 (m), 1525 (s), 1293
(m), 1174 (m), 1132 (s), 776 (m), 700 (m) cm-1. Analysis calcd. for
C14H16F3NO (271.28): C 61.98, H 5.95, N 5.16; found: C 62.06, H 6.10, N
5.20.
trifloxyprop-2-ene 1-iminium triflates into
a
variety of
trifluoromethylated compounds by sequence of HOTf-
a
2.3. (E)-1,1,1-Trifluoro-4-phenyl-4-(pyrrolidin-1-yl)but-3-en-2-one (4c):
Prepared from alkynone 3a (3.52 g, 17.8 mmol) and pyrrolidine (1.28 g,
18.0 mmol) in dry CH2Cl2 (10 mL) at -20 °C. After stirring at this
temperature for 30 min, the solution was brought to r.t. and the volatiles
were evaporated in vacuo. The residual oil was diluted with a small volume
of CH2Cl2 and cooled at -78 °C. By addition of n-pentane, an orange
precipitate was obtained, which was isolated by filtration and dried. Yield:
4.68 g (17.4 mmol, 98%); m.p. 58.4‒66.6 °C (lit.[11]: 52 °C). 1H NMR (CDCl3,
500 MHz):  = 1.86 (p, 3JH,H = 6.9 Hz, 2H, CH2), 2.08 (p, 3JH,H = 6.9 Hz, 2H,
CH2), 3.16 (t, 3JH,H = 6.9 Hz, 2H, NCH2), 3.50 (t, 3JH,H = 7.1 Hz, 2H, NCH2),
5.31 (s, 1H, CH=), 7.21–7.22 (m, 2H, HPh), 7.40–7.47 (m, 3H, HPh). 13C
NMR (CDCl3, 126 MHz):  = 25.0 (CH2), 25.3 (CH2), 49.2 (NCH2), 50.8
(NCH2), 87.8 (C-3), 118.0 (q, 1JC,F = 293 Hz, CF3); 126.6, 128.98, 129.01,
elimination, cycloaddition and iminium group transformation.
Experimental Section
1. 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) and under argon. Triflic
anhydride was prepared from triflic acid and, if necessary, freshly distilled
from P2O5 before use. Melting points were determined in open capillaries
with a Büchi B-540 instrument at a heating rate of 2 °C/min. NMR spectra
were recorded on Bruker spectrometers (Avance 400 operating at 400.13
MHz for 1H, 100.61 MHz for 13C and 376.47 MHz for 19F; Avance 500
operating at 500.14 MHz for 1H and 125.77 MHz for 13C). NMR chemical
shifts () are reported in ppm; for the 1H and 13C spectra the solvent signal
served for internal calibration [1H NMR: (CHCl3) 7.26, (CH2Cl2) = 5.32,
2
136.5 (all CPh); 165.7 (C-4), 174.5 (q, JC,F = 31.0 Hz, C=O). 19F NMR
(CDCl3):  = -78.2. IR (KBr): 휈̃ = 1654 (s), 1526 (s), 1451 (s), 1276 (s),
1179 (s), 1130 (s), 1075 (s), 938 (s), 771 (s), 698 (m) cm-1. Analysis calcd.
for C14H14F3NO (269.27): C 62.45, H 5.24, N 5.20; found: C 62.43, H 5.19,
N 5.19.
7
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10.1002/ejoc.202100567
European Journal of Organic Chemistry
FULL PAPER
2.4. (E)-4-(Bis((S)-1-phenylethyl)amino)-1,1,1-trifluoro-4-phenylbut-3-
en-2-one (4d): Alkynone 3a (2.26 g, 11.39 mmol) and bis((S)-1-
phenylethyl)amine (2.57 g, 11.39 mmol) were dissolved in dry CH2Cl2 (25
mL) and the solution was kept with stirring at 40 °C for 14 days. The solvent
was evaporated in vacuo and the residue was triturated with cyclohexane‒
EtOAc (10:1, 20 mL) in an ultrasonic bath. The resulting solid was isolated
by filtration and washed with cyclohexane. Off-white solid (2.88 g, 6.79
mmol, 60% yield), m.p. 155‒156 °C. [푎]2퐷0 = -342 ( = 0.3; CHCl3). 1H NMR
All iminium salts 5 are hygroscopic and hydrolytically rather labile.
However, they can be stored in a dry argon atmosphere at -25 °C for
several months.
3.1. N-Methyl-N-(4,4,4-trifluoro-1-phenyl-3-(((trifluoromethyl)sulfonyl)
3
3
(CDCl3, 400 MHz):  = 1.63 (d, JH,H = 7.1 Hz, 3H, CH3), 2.00 (d, JH,H
=
oxy)but-2-en-1-ylidene)methanaminium
Triflate
(5a);
typical
7.1 Hz, 3H, CH3), 5.00 (q, 3JH,H = 7.1 Hz, 1H, NCH), 5.15 (q, 3JH,H = 7.0 Hz,
1H, NCH), 5.18 (q, 4JH,F = 0.8 Hz, 1H, 3-H), 6.83–6.85 (m, 2H, HPh), 7.15–
7.17 (m, 3H, HPh), 7.28–7.37 (m, 6H, HPh), 7.39–7.41 (m, 1H, HPh), 7.48–
7.55 (m, 2H, HPh), 7.58–7.62 (m, 1H, HPh). 13C NMR (CDCl3, 100 MHz): 
= 17.0 (CH3), 18.1 (CH3), 53.5 (NCH), 58.5 (NCH), 92.2 (C-3), 117.6 (q,
1JC,F = 293 Hz, CF3); 125.7, 126.3 127.2, 127.6, 128.4, 128.5, 128.77,
128.97, 129.06, 129.4, 129.6, 136.7, 138.4, 138.9 (all CPh); 164.7 (C-4),
174.4 (q, 2JC,F = 31.1 Hz, C=O). 19F NMR (CDCl3):  = -79.1. IR (KBr): 휈̃ =
1663 (s), 1523 (s), 1443 (s), 1310 (s), 1178 (s), 1120 (s), 1062 (s), 898 (m),
697 (s) cm-1. Analysis calcd. for C26H24F3NO (423.48): C 73.74, H 5.71, N
3.31; found: C 73.49, H 5.78, N 3.08.
procedure (TP1): The solution of triflic anhydride (1.38 mL, 8.2 mmol, 1.05
equiv.) in anhydrous CH2Cl2 (8 mL) was cooled at -78 °C and the solution
of enaminone 4a (1.90 g, 7.8 mmol, 1 equiv.) in anhyd. CH2Cl2 (3 mL) was
added dropwise. The mixture was stirred at this temperature for 30 min,
then at room temperature for 30 min. Under vigorous stirring, anhyd. Et2O
was added until an oil separated. This oil was separated from the organic
phase by decantation and rinced with several portions of Et2O. Solvent
traces were removed at 20 °C /0.01 mbar to obtain an orange oil, which
could not be crystallized. Yield: 3.78 g (7.2 mmol, 92%). 1H NMR (CD3CN):
 = 3.78 (s, 3H, NCH3), 3.85 (s, 3H, NCH3), 7.67–7.76 (m, 4H, HPh), 7.81–
7.85 (m, 1H, HPh), 7.88 (s, 1H, 2-H). 13C NMR (CD3CN, 100 MHz):  = 48.8
(NCH3), 48.8 (NCH3), 118.5 (q, 1JC,F = 275 Hz, CF3), 118.9 (q, 1JC,F = 321
Hz, 3-OTf), 121.9 (q, 1JC,F = 320 Hz, -OTf), 123.9 (q, 3JC,F = 3.7 Hz, C-2),
129.1 (CPh), 130.5 (CPh), 132.0 (CPh), 136.5 (CPh), 142.4 (q, 2JC,F = 40.9 Hz,
C-3), 173.7 (C=N+). 19F NMR (CD3CN):  = -69.0 (q, JF,F = 5.9 Hz, CF3), -
70.9 (q, JF,F = 5.8 Hz, 3-OTf), -77.8 (s, -OTf). IR (NaCl): 휈̃ = 1686 (m), 1640
(m), 1597 (m), 1445 (s), 1260 (s, br), 1221 (s), 1162 (s), 1032 (s), 910 (m),
701 (s) cm-1. Analysis calcd. for C14H12F9NO6S2 (525.36): C 32.01, H 2.30,
N 2.67; found: C 31.78, H 2.50, N 2.76.
2.5. (E)-4-(Diethylamino)-1,1,1-trifluorobut-3-en-2-one (4e): Based on
a
published procedure[12]
, 1,1,1-trifluoro-4-trimethylsilyl-but-3-yn-2-one
(3b) was prepared as follows: A solution of trimethylsilyl-acetylene (7.48 g,
76.2 mmol) in anhydrous THF (200 mL) was cooled at -78 °C and n-BuLi
in hexane (2.5 M, 30.5 mL, 76.2 mmol) was added drop by drop. After
stirring at this temperature for 30 min, ethyl trifluoroacetate (91 mL, 76.2
mmol) and BF3‧OEt2 (9.7 mL, 76.5 mmol) dissolved in anh. THF (20 mL)
were added. The mixture was stirred at -78 °C for 30 min and at r.t. for 30
min. After addition of a saturated aqueous solution of NH4Cl (200 mL) and
extraction with diethyl ether (2 × 100 mL), the organic phase containing 3b
was collected. A solution of diethylamine (7.85 mL, 76.2 mmol) in MeOH
(10 mL) was added. After stirring at r.t. for two hours, the solution was
concentrated, the residue was dissolved in CHCl3 (200 mL) and extracted
with water. The organic phase was dried (Na2SO4) and concentrated, and
the residual oil was subjected to bulb-to-bulb distillation at 90 °C/0.05 mbar.
3.2. N-Ethyl-N-(4,4,4-trifluoro-1-phenyl-3-(((trifluoromethyl)sulfonyl)
oxy)but-2-en-1-ylidene)ethanaminium Triflate (5b): Prepared from
enaminone 4b (11.5 g, 42.4 mmol) and triflic anhydride (13.2 g, 46.7 mmol)
according to TP1. Colorless solid (21.6 g, 39.0 mmol, 92% yield), m.p.
3
74.8–76.1 °C. H NMR (CDCl3, 500 MHz):  = 1.54 (t, JH,H = 7.3 Hz, 3H,
3
CH3), 1.61 (t, 3JH,H = 7.4 Hz, 3H, CH3), 4.17 (q, JH,H = 7.3 Hz, 2H, CH2),
3
4.28 (q, JH,H = 7.4 Hz, 2H, CH2), 7.61–7.64 (m, 2H, HPh), 7.66–7.68 (m,
1
Orange oil (10.0 g, 51.2 mmol, 67% yield). H NMR (CDCl3, 400 MHz): 
2H, HPh), 7.72–7.73 (m, 1H, HPh), 8.33 (s, 1H, CH). 13C NMR (CDCl3, 126
MHz):  = 12.4 (CH3), 13.2 (CH3), 52.5 (NCH2), 53.4 (NCH2), 117.5 (q, 1JC,F
= 276 Hz, CF3), 118.2 (q, 1JC,F = 322 Hz, 3-OTf), 120.7 (q, 1JC,F = 320 Hz,
3
= 1.20 (t, JH,H = 7.3 Hz, 3H, CH3), 1.25 (t, 3JH,H = 7.2 Hz, 3H, CH3), 3.29
(q, 3JH,H = 7.3 Hz, 2H, NCH2), 3.38 (q, 3JH,H = 7.2 Hz, 2H, NCH2), 5.30 (d,
3
3JH,H = 12.4 Hz, 1H, 3-H), 7.85 (d, JH,H = 12.4 Hz, 1H, 4-H). 13C NMR
3
-OTf), 123.4 (q, JC,F = 3.5 Hz, C-3); 129.1, 129.9, 129.9, 135.0 (all CPh);
(CDCl3, 100 MHz):  = 11.6 (CH3), 14.6 (CH3), 43.5 (NCH2), 51.3 (NCH2),
87.0 (C-3), 117.94 (q, 1JC,F = 291 Hz, CF3), 155.07 (C-4), 177.24 (q, 2JC,F
= 32.3 Hz, C=O). 19F NMR (CDCl3):  = -78.2. IR (NaCl): 휈̃ = 1667 (m),
1576 (s), 1468 (m), 1450 (m), 1265 (s), 1183 (s) 1135 (s), 1084 (s), 880
(m), 774 (m), 710 (m) cm-1. Analysis calcd. for C8H12F3NO (195.19): C
49.23, H 6.20, N 7.18; found: C 49.04, H 6.01, N 7.29.
141.9 (q, 2JC,F = 41.0 Hz, C-2), 174.8 (C=N+). 19F NMR (CDCl3):  = -71.2
-
(q, JF,F = 6.1 Hz, CF3), -72.7 (q, JF,F = 6.0 Hz, 3-OTf), -78.2 (s, OTf). IR
(KBr): 휈̃ = 1629 (m), 1444 (s), 1280‒1225 (s, br), 1155 (s), 1033 (s), 905
(m), 698 (s), 641 (s) cm-1. Analysis calcd. for C16H16F9NO6S2 (553.41): C
34.73, H 2.91, N 2.53; found: C 34.68, H 2.98, N 2.67.
3.3. 1-(4,4,4-Trifluoro-1-phenyl-3-(((trifluoromethyl)sulfonyl)oxy)but-
2-en-1-ylidene)pyrrolidin-1-ium Triflate (5c): Prepared from enaminone
4c (4.42 g, 16.4 mmol) and triflic anhydride (2.8 ml, 16.6 mmol) according
to TP1. Colorless solid (8.50 g, 15.4 mmol, 94% yield), m.p. 98.6–99.9 °C.
1H NMR (CD3CN, 400 MHz):  = 2.10–2.17 (m, 2H, CH2), 2.26–2.33 (m,
2H, CH2), 4.22–4.27 (m, 4H, NCH2), 7.67–7.71 (m, 2H, HPh), 7.79–7.85 (m,
3H, HPh, 2-H). 13C NMR (CD3CN, 100 MHz):  = 25.2 (CH2), 25.8 (CH2),
2.6. (E)-4-(Dimethylamino)-1,1,1-trifluorobut-3-en-2-one (4f): Prepared
as described in lit.[13a] from trifluoroacetic anhyride (28.2 mL, 200 mmol),
ethyl vinyl ether (14.4 g, 200 mmol) and dimethylamine (40% in H2O, 55.5
ml, 438 mmol). The product obtained after extractive workup was purified
by bulb-to-bulb distillation at 80 °C/0.02 mbar). Light yellow solid (24.9 g,
1
149 mmol, 75% yield), m.p. 57.3 °C (lit.[13a]: 57‒58 °C]. H NMR (CDCl3,
400 MHz):  = 2.91 (s, 3H, NCH3), 3.17 (s, 3H, NCH3), 5.22 (d, 3JH,H = 12.2
59.0 (NCH2), 60.1 (NCH2), 118.6 (q, 1JC,F = 275 Hz, CF3), 118.9 (q, 1JC,F
=
3
Hz, 1H, 3-H), 7.82 (d, JH,H = 12.2 Hz, 1H, 4-H). 13C NMR (CDCl3, 100
321 Hz,3- OTf), 120.4 (q, 1JC,F = 321 Hz, -OTf), 123.6 (q, 3JC,F = 3.7 Hz, C-
MHz):  = 37.6 (NCH3), 45.7 (NCH3), 87.4 (C-3), 117.8 (q, 1JC,F = 291 Hz,
CF3), 156.8 (C-4), 177.1 (q, 2JC,F = 32.4 Hz, C=O). 19F NMR (CDCl3):  = -
78.3. IR (KBr): 휈̃ = 1663 (m), 1588 (s), 1272 (m), 1176 (m), 1136 (s), 1086
(s), 902 (m), 767 (m), 710 (m) cm-1. Analysis calcd. for C6H8F3NO (167.13):
C 43.12, H 4.82, N 8.38; found: C 43.28, H 4.72, N 8.31.
2
2); 129.9, 130.5, 131.7, 136.5 (all CPh); 142.0 (q, JC,F = 40.8 Hz, C-3),
169.4 (C=N+). 19F NMR (CD3CN):  = -68.9 (q, JF,F = 5.9 Hz, CF3), -71.1
(q, JF,F = 5.9 Hz, 3-OTf), -77.8 (-OTf). IR (KBr): 휈̃ = 1626 (m), 1598 (w),
1449 (m), 1424 (m), 1333 (m), 1266 (s, br), 1160 (s), 1032 (s), 909 (m),
697 (m), 638 (s), 604 (m) cm-1. Analysis calcd. for C16H14F9NO6S2
(551.39): C 34.85, H 2.56, N 2.54; found: C 34.77, H 2.66, N 2.57.
3. Synthesis of 3-CF3-3-trifloxypropene iminium salts 5
8
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10.1002/ejoc.202100567
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FULL PAPER
3.4. (S)-1-Phenyl-N-((S)-1-phenylethyl)-N-(4,4,4-trifluoro-1-phenyl-3-
(((trifluoromethyl)sulfonyl)oxy)but-2-en-1-ylidene)ethan-1-aminium
Triflate (5d): Prepared from enaminone 4d (2.34 g, 5.53 mmol) and triflic
anhydride (0.94 mL, 5.58 mmol) according to TP1. When the reaction was
completed, the solvent was evaporated at 0.02 mbar. The residue was
exposed to anhyd. Et2O/anhyd. pentane (1:1) in an ultrasonic bath. The
supernatant liquid phase was decanted off and the remaining oil was kept
at 0.03 mbar to remove residual volatiles, whereby the product was
obtained as a very moisture-sensitive yellow solid (3.70 g, 5.25 mmol, 95%
yield), m.p. 57.1–58.5 °C. On contact to atmospheric moisture, the solid
quickly changed to a sticky resin. 1H NMR (CD2Cl2, 400 MHz):  = 2.12 (d,
thermally cracked cyclopentadiene (266 mg, 4.03 mmol) and anhydrous
NEt3 (0.56 mL, 4.03 mmol) in dry CH3CN (3 mL) was added gradually. The
solution was stirred for 15 min, brought to r.t., and saturated aqueous
K2CO3 (10 mL) was added. After 5 min, the mixture was extracted with
Et2O and the organic phase was separated and dried (Na2SO4). After
solvent evaporation an orange oil remained, which was dissolved in a
small volume of cyclohexane‒EtOAc (40:1 v/v) and passed over a short
column (~10 × 2 cm) filled with silica gel. The product was obtained as a
yellowish oil (768 mg, 2.90 mmol, 86% yield). 1H NMR (CDCl3, 400 MHz):
 = 2.16 (dq, JH,H = 6.8 and 1.3 Hz, 1H, CH2), 2.47 (dt, JH,H = 6.8 and 1.7
Hz, 1H, CH2), 3.86–3.89 (m, 1H, Hbridgehead), 3.92–3.95 (m, 1H, Hbridgehead),
7.00–7.02 (m, 1H) and 7.03–7.06 (m, 1H) (HC=CH), 7.44–7.49 (m, 2H,
HPh), 7.57–7.61 (m, 1H, HPh), 7.74–7.76 (m, 2H, HPh). 13C NMR (CDCl3,
101 MHz):  = 51.3 (m, CH), 55.8 (CH), 73.0 (CH2), 123.0 (q, 1JC,F = 269
Hz, CF3); 128.8, 129.1, 134.1, 135.9 (all CPh); 142.4 (m, HC=C), 142.5
(HC=C), 143.6 (q, 2JC,F = 35.1 Hz, C=C-CF3), 157.5 (q, 3JC,F = 4.8 Hz, C=C-
CF3), 194.2 (C=O). 19F NMR (CDCl3):  = -64.3. IR (NaCl): 휈̃ = 1661 (s),
1271 (s), 1174 (s), 1151 (s), 1118 (s), 700 (m) cm-1. HRMS ((+)-ESI): m/z
= 303.03943 (calcd.: 303.03936 for C15H11F3KO+, [M+K]+). Analysis calcd.
for C15H11F3O (264.25): C 68.18, H 4.20; found: C 67.91, H 4.15.
3JH,H = 7.2 Hz, 3H, CH3), 2.17 (d, 3JH,H = 7.2 Hz, 3H, CH3), 5.88 (q, 3JH,H
=
3
7.2 Hz, 1H, NCH), 6.34 (q, JH,H = 7.1 Hz, 1H, NCH), 6.69–6.71 (m, 2H,
HPh), 7.24 (s, 1H, 2-H), 7.29–7.54 (m, 10H, HPh), 7.73–7.74 (m, 3H, HPh).
13C NMR (CD2Cl2, 126 MHz):  = 18.4 (CH3), 19.5 (CH3), 65.0 (NCH2),
69.1 (NCH2); 127.8, 129.5, 129.90, 129.94, 130.4, 130.56, 130.76, 130.78,
131.80, 131.89, 132.9, 135.7 (all CPh); 172.8 (C=N+); CF3 not clearly
identified due to the low signal intensity. 19F NMR (CD2Cl2):  = -70.2 (q,
JF,F = 5.9 Hz, CF3), -71.6 (q, JF,F = 5.9 Hz, 3-OTf), -78.9 (s, -OTf). IR (KBr):
휈̃ = 1623 (w), 1452 (w), 1278 (s), 1170 (s, br), 1030 (s), 700 (m), 640 (m)
cm-1. Analysis calcd. for C28H24F9NO6S2 (705.61): C 47.66, H 3.43, N 1.99;
found: C 46.24, H 3.86, N 1.82. The moisture sensitivity of 5d prevented
correct analytical values.
4.2. 3-(Trifluoromethyl)bicyclo[2.2.1]hepta-2,5-diene-2-carbaldehyde
(7b): Prepared from propeniminium salt 5e (1.15 g, 2.41 mmol),
cyclopentadiene (0.20 mL, 2.41 mmol) and anhyd. NEt3 (0.33 mL, 2.41
mmol) as described for 7a. The crude oily product was purified by column
chromatography (silica gel, n-pentane‒Et2O (5:1), Rf = 0.3) to obtain a
rather volatile redish oil (426 mg, 2.27 mmol, 94% yield). 1H NMR (CDCl3,
400 MHz):  = 2.12–2.15 (m, 1H, CH2), 2.20 (dt, JH,H = 7.1 and 1.6 Hz, 1H,
CH2), 3.87 (dq, J = 2.8 and 1.6 Hz, 1H, Hbridgehead), 4.13–4.16 (m, 1H,
Hbridgehead), 6.85–6.88 (m, 2H, HC=CH), 10.07–10.08 (q, 5JH,F = 0.7 Hz, 1H,
CHO). 13C NMR (CDCl3, 101 MHz):  = 49.2 (Cbridgehead), 52.4 (q, 3JCF = 1.9
Hz, Cbridgehead), 72.7 (CH2), 123.2 (q, 1JCF = 270 Hz, CF3), 141.8–141.9 (m)
3.5. N-Ethyl-N-(4,4,4-trifluoro-3-(((trifluoromethyl)sulfonyl)oxy)but-2-
en-1-ylidene)ethanaminium Triflate (5e): Prepared from enaminone 4e
(9.73 g, 49.9 mmol) and triflic anhydride (8.80 ml, 52.3 mmol) according to
1
TP1. Colorless solid (22.6 g, 47.4 mmol, 95% yield), m.p. 67–69 °C. H
NMR (CD3CN, 500 MHz):  = 1.42 (tt, J = 7.4 and 2.2 Hz, 3H, CH3), 1.49
(tt, J = 7.2 and 2.2 Hz, 3H, CH3), 4.12–4.17 (m, 4H, NCH2), 7.69 (d, 3JH,H
= 9.6 Hz, 1H, 2-H), 8.59 (d, 3JH,H = 9.6 Hz, 1H, CH=N+). 13C NMR (CD3CN,
3
126 MHz):  = 13.2 (CH3), 13.7 (CH3), 52.2 (t, J13C,14N = 3.0 Hz, NCH2),
57.9 (t, 3JCN = 3.5 Hz, NCH2), 117.7 (q, 3JC,F = 3.3 Hz, C-2), 118.6 (q, 1JC,F
= 275 Hz, CF3), 119.2 (q, 1JC,F = 321 Hz, 3-OTf), 121.8 (q, 1JC,F = 320 Hz,
-OTf), 146.62 (qt, J = 41.5 and 2.7 Hz, C-3), 162.0 (t, 1JC,N = 14.2 Hz, C=N+).
19F NMR (CD3CN):  = -68.7 (q, JF,F = 4.0 Hz, CF3), -70.6 (q, JF,F = 4.0 Hz,
3-OTf), -77.8 (-OTf). IR (KBr): 휈̃ = 1681 (w), 1265 (s, br), 1184 (s), 1152
(s), 1033 (s), 641 (s) cm-1. HRMS ((+)-ESI): m/z = 328.04429; calcd.
328.04366 (C9H12F6NO3S+, [M - OTf]+). Analysis calcd. for C10H12F9NO6S2
(477.31): C 25.16, H 2.53, N 2.93; found: C 25.25, H 2.55, N 2.94.
and 143.0 (q, JC,F = 1.4 Hz) (HC=CH), 156.4 (q, JC,F = 35.7 Hz, C=C-
4
2
CF3), 157.18 (q, JC,F = 4.0 Hz, C=C-CF3), 185.47–185.48 (m, C=O). 19F
3
NMR (CDCl3):  = -63.4. IR (NaCl): 휈̃ = 1677 (s), 1639 (m), 1337 (m), 1294
(m), 1265 (m), 1171 (s), 1126 (s), 709 (m), 665 (m) cm-1. MS (CI, 100 eV):
m/z (%) = 189 (20) [M+H]+,188 (13) [M]+, 92 (42). C9H7F3O (188.15 g/mol).
3.6. N-Methyl-N-(4,4,4-trifluoro-3-(((trifluoromethyl)sulfonyl)oxy)but-
2-en-1-ylidene)methanaminium Triflate (5f): Prepared from enaminone
4f (8.99 g, 53.8 mmol) and triflic anhydride (9.00 mL, 53.8 mmol) according
to TP1. The crude product was precipitated from the reaction solution by
addition of anhyd. Et2O and anhyd. n-pentane. Colorless solid (22.1 g, 49.2
mmol, 91% yield), m.p. 94.5‒95.8 °C. A mixture of two components was
obtained (1:0.09 ratio according to 1H NMR). 1H NMR (CD3CN, 400 MHz):
 = 3.72 (s, 3H, NCH3), 3.86 (s, 3H, NCH3), 7.57 (d, 3JH,H = 9.7 Hz, 1H, 2-
H), 8.57 (d, 3JH,H = 9.7 Hz, 1H, 1-H); minor component: 3.64 (s, 3H, NCH3),
3.84 (s, 3H, NCH3), 7.34 (d, JH,H = 9.9 Hz, 1H), 7.90 (broad, 1H, OH?),
8.73–8.75 (d , 1H, JH,H = 9.9 Hz). 13C NMR (CD3CN, 100 MHz):  = 45.4 (t,
3JC,N = 4.6 Hz, NCH3), 52.9 (t, 3JC,N = 5.0 Hz, NCH3), 118.6 (q, 1JC,F = 275
Hz, CF3), 119.2 (q, 1JC,F = 321 Hz, 3-OTf), 121.8 (q, 1JC,F = 320 Hz, -OTf),
146.4 (qt, J = 41.4 and 3.3 Hz, C-3), 163.1 (t, 1JC,N = 14.7 Hz, C=N+); C-2
probably covered by solvent signal at ~118 ppm. 19F NMR (CD3CN):  = -
68.7 (q, JF,F = 4.1 Hz, CF3), -70.6 (q, JF,F = 4.1 Hz, 3-OTf), -77.8 (-OTf). IR
(KBr): 휈̃ = 1679 (w), 1443 (m), 1261 (s), 1227 (s), 1156 (s), 1032 (s), 641
(m) cm-1. HRMS ((+)-ESI): m/z (%) = 300.01267, 748.98278; calcd.
300.01964 (C7H8F6NO3S+, [cation]+), 748.99185 (C15H16F15N2O9S3+, [2
4.3.
2-(Cyclopenta-2,4-dien-1-ylidenemethyl)-3-(trifluoromethyl)
bicyclo[2.2.1]hepta-2,5-diene (7c): Prepared from propeniminium salt 5e
(456 mg, 0.96 mmol), cyclopentadiene (0.32 mL, 3.84 mmol) and anhyd.
NEt3 (0.40 ml, 2.88 mmol) as described for 7a. The crude product was
dissolved in n-pentane and passed over a short column (~10 × 2 mL) filled
with silica gel. The product was obtained as a yellowish oil (202 mg, 0.85
mmol, 89% yield), which after a short time oligomerized to form a yellow
solid. H NMR (CDCl3, 400 MHz):  = 2.16 (d, JH,H = 6.8 Hz, 1H, CH2),
2.21 (dt, JH,H = 6.8 and 1.7 Hz, 1H, CH2), 3.81–3.84 (m, 1H, Hbridgehead),
4.19 (s, 1H, Hbridgehead); 6.25 (dt, JH,H = 5.2, 1.8 Hz, 1H), 6.49–6.51 (m, 1H),
6.63–6.65 (m, 1H), 6.66–6.68 (m, 1H), 6.87–6.89 (m, 1H), 6.95 (dd, J =
5.0 and 3.0 Hz, 1H) (all CHolef.), 7.19 (s, 1H, Ccp=CH). 13C NMR (CDCl3,
1
2
3
101 MHz):  = 51.1 (q, JCF = 1.8 Hz, Cbridgehead), 55.7 (Cbridgehead), 71.4
(CH2), 119.7 (C=CH), 124.3 (q, 1JC,F = 269 Hz, CF3); 127.6, 127.7, 131.9,
136.1, 140.9 (q, JC,F = 1.7 Hz), 142.7 (broadened) (all CHolef.); 145.3 (q,
2JC,F = 33.1 Hz, C=C-CF3), 146.8 (q, JC,F = 1.7 Hz, C=CH), 156.5 (q, 3JC,F
= 5.0 Hz, C=C-CF3). 19F NMR (CDCl3):  = -62.9. MS (CI, 100 eV): m/z (%)
= 237 (46) [M+H]+, 217 (44) [M - F]+. C14H11F3 (236.24 g/mol).
-
cations + OTf]+). Analysis calcd. for C8H8F9NO6S2 (449.26): C 21.39, H
1.79, N 3.12, S 14.27; found: C 21.52, H 2.08, N 3.20, S 14.09.
4.4. (4,5-Dimethyl-2-(trifluoromethyl)phenyl)(phenyl)methanone (9a):
To a solution of propeniminium salt 5b (1.58 g, 2.85 mmol) in dry CH2Cl2
(5 mL) a solution of 2,3-dimethylbuta-1,3-diene (246 mg, 2.99 mmol) and
anhyd. NEt3 (0.42 mL, 2.99 mmol) in CH2Cl2 (3 mL) was added gradually
at r.t. and the mixture was stirred for 30 min. After addition of o-chloranil
(701 mg, 2.85 mmol), stirring was continued for 18 h, followed by short
4. Cycloaddition reactions with 1,3-dienes
4.1.
Phenyl(3-(trifluoromethyl)bicyclo[2.2.1]hepta-2,5-dien-2-
yl)methanone (7a): A solution of propeniminium salt 5b (1.86 g, 3.36
mmol) in dry acetonitrile (7 mL) was cooled at -12 °C and a solution of
9
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10.1002/ejoc.202100567
European Journal of Organic Chemistry
FULL PAPER
treatment with satd. aqueous K2CO3 (10 mL). The mixture was extracted
with Et2O (2 × 50 mL) and the organic phase was extracted with brine (100
mL), finally dried with Na2SO4. After evaporation of the solvent, an orange
oil was obtained, which was purified by column chromatography (silica gel
(200 g), eluent cyclohexane‒EtOAc (20:1), Rf = 0.24) to obtain the product
4.7.
12-(Trifluoromethyl)-9,10-dihydro-9,10-ethenoanthracene-11-
carbaldehyde (11b); typical procedure (TP2): To
a solution of
propeniminium salt 5f (831 mg, 1.85 mmol) in anhyd. CH2Cl2 (30 mL) and
anthracene (329 mg, 1.85 mmol) was added anhyd. NEt3 (0.26 mL, 1.85
mmol) dissolved in anhyd. CH2Cl2 (3 mL). After stirring at room
temperature for 10 min, water (50 mL) was added and the mixture was
extracted with CH2Cl2. The organic solvent was evaporated and the
residue re-dissolved in cyclohexane‒EtOAc (99:1) and submitted to flash
column chromatography (silica gel (100 g)). The crude product was
purified by HPLC (elution with cyclohexane‒EtOAc; continuous increase
of the EtOAc gradient, until the product was eluted). Colorless solid (444
mg, 1.48 mmol, 80% yield), m.p. 146.2–149.8 °C. 1H NMR (CDCl3, 400
MHz):  = 5.42 (s, 1H, Hbridgehead), 5.96 (s, 1H, Hbridgehead), 7.05–7.08 (m,
4H, HAr), 7.41–7.44 (m, 4H, HAr), 10.31 (q, JH,F = 0.9 Hz, 1H, CHO). 13C
1
as a yellowish oil (680 mg, 2.44 mmol, 86% yield). H NMR (CDCl3, 400
MHz):  = 2.33 (s, 3H, CH3), 2.38 (s, 3H, CH3), 7.14 (s, 1H, HPh), 7.43–
7.47 (m, 2H, HPh), 7.52 (s, 1H, HPh), 7.57–7.61 (m, 1H, HPh), 7.77–7.80 (m,
2H, HPh). 13C NMR (CDCl3, 101 MHz):  = 19.82 (CH3), 19.84 (CH3), 123.9
(q, 1JC,F = 274 Hz, CF3), 125.8 (q, 2JC,F = 32.1 Hz, C-CF3), 127.8 (q, 3JC,F
= 4.5 Hz, C=C-CF3); 128.6, 129.4, 130.3, 133.7 (all CPh); 135.9 (q, 3JC,F
1.9 Hz, C=C-CF3), 136.8 (CPh), 139.0 (CPh), 140.6 (CPh), 196.1 (C=O). 19
=
F
NMR (CDCl3):  = -58.8. IR (NaCl): 휈̃ = 1676 (s), 1450 (s), 1393 (s), 1320
(s), 1268 (s), 1126 (s), 993 (s), 881 (s), 712 (s) cm-1. HRMS ((+)-ESI): m/z
= 301.08092, 317.05484, 579.17255; calcd. 301.08107 (C16H13F3NaO+,
NMR (CDCl3, 101 MHz):  = 48.0 (Cbridgehead), 51.4 (q, JC,F = 2.7 Hz,
Cbridgehead), 123.6 (q, 1JC,F = 273 Hz, CF3); 124.0, 124.4, 125.8, 126.1, 142.8,
3
+
[M+Na]+), 317.05501 (C16H13F3KO+, [M+K]+), 579.17292 (C32H26F6NaO2
,
[2M+Na]+). Analysis calcd. for C16H13F3O (278.27): C 69.06, H 4.71; found:
C 68.99, H 4.81.
143.4 (all CAr); 150.1 (q, JC,F = 34.6 Hz, C=C-CF3), 151.5 (q, JC,F = 3.3
Hz, C=C-CF3), 185.4 (q, 4JC,F = 3.2 Hz, CHO). 19F NMR (CDCl3):  = -61.8.
IR (KBr): 휈̃ = 1677 (s), 1249 (m), 1188 (m), 1148 (m), 1119 (s), 750 (m)
cm-1. MS (CI, 100 eV): m/z (%) = 301 (100) [M+H]+, 281 (22) [M - F]+, 271
(5) [M - CHO]+. Analysis calcd. for C18H11F3O (300.28): C 72.00, H 3.69;
found: C 71.91, H 3.92.
2
3
4.5. 4,5-Dimethyl-2-(trifluoromethyl)benzaldehyde (9b): Prepared from
salt 5d (999 mg, 2.09 mmol), 2,3-dimethyl-1,3-butadiene (0.26 mL, 2.30
mmol) and anhyd. NEt3 (0.32 mmol, 2.30 mmol) as described for 9a.
Chromatographic purification using n-pentane‒Et2O (5:1 v/v) as the eluent.
Yellow solid (397 mg, 1.96 mmol, 94% yield), m.p. 48.3–51.2 °C. 1H NMR
(CDCl3, 400 MHz):  = 2.38 (s, 3H, CH3), 2.39 (s, 3H, CH3), 7.53 (s, 1H,
HPh), 7.89 (s, 1H, HPh), 10.33 (q, JH,F = 2.1 Hz, 1H, CHO). 13C NMR (CDCl3,
101 MHz):  = 19.8 (CH3), 20.3 (CH3), 124.1 (q, 1JC,F = 274 Hz, CF3), 127.4
4.8. 10-Methyl-12-(trifluoromethyl)-9,10-dihydro-9,10-ethenoanthra
cene-11-carbaldehyde (11c): Prepared from iminium salt 5f (396 mg,
0.88 mmol), 9-methylanthracene (169 mg, 0.88 mmol) and anhyd.
triethylamine (0.11 mL, 0.88 mmol) according to TP2. Purification by flash
chromatography (elution with cyclohexane to remove residual anthracene,
followed by cyclohexane‒EtOAc (5:1)). Yellowish solid (208 mg, 0.66
3
2
(q, JC,F = 5.7 Hz, C=C-CF3), 128.8 (q, JC,F = 32.2 Hz, C=C-CF3), 130.2
(CPh), 131.50 (m, CPh), 141.6 (m, CPh), 143.7 (CPh), 189.3 (q, 4JC,F = 2.4 Hz,
C=O). 19F NMR (CDCl3):  = -56.3. IR (KBr): 휈̃ = 1696 (s), 1608 (m), 1315
(s), 1158 (s), 1133 (s), 1101 (s), 1021 (m), 988 (m), 889 (m) cm-1. MS (CI,
100 eV): m/z (%) = 405 (4) [2M+H]+, 231 (36) [M+H+C2H4]+, 203 (85)
[M+H]+, 183 (100) [M-F]+. Analysis calcd. for C10H9F3O (202.18): C 59.41,
H 4.49; found: C 55.96, H 4.22. The measured values indicate extensive
1
mmol, 75% yield), m.p. 172.0–173.5 °C. H NMR (CDCl3, 400 MHz):  =
2.40 (s, 3H, CH3), 5.35 (s, 1H, Hbridgehead), 7.05–7.13 (m, 4H, HPh), 7.37–
7.41 (m, 4H, HAr), 10.11 (q, JH,F = 2.1 Hz, 1H, CHO). 13C NMR (CDCl3, 101
MHz):  = 14.3 (CH3), 50.5 (q, 3JCF = 2.6 Hz, Cbridgehead), 51.9 (Cbridgehead),
121.8, 123.7, 123.6 (q, 1JC,F = 273 Hz, CF3), 125.6, 125.8, 143.77, 146.29,
150.4 (q, JC,F = 34.0 Hz, C=C-CF3), 152.4 (q, JC,F = 3.7 Hz, C=C-CF3),
188.9 (q, 4JC,F = 2.6 Hz, CHO). 19F NMR (CDCl3):  = -60.7. IR (KBr): 휈̃ =
1691 (s), 1633 (m), 1456 (m), 1245 (m), 1189 (s), 1162 (s), 1119 (s), 1087
(m) cm-1. MS (CI, 100 eV): m/z (%) = 315 (100) [M+H]+, 295 (35) [M - F]+,
285 (10) [M - CHO]. Analysis calcd. for C19H13F3O (314.31): C 72.61, H
4.17; found: C 72.86, H 4.01.
2
3
oxidation (CHO
→
COOH); C10H9F3O
+
3.5·C10H9F3O2 (202.18 +
3.5·218.18) requires: C 55.96, H 4.23.
4.6. Phenyl(12-(trifluoromethyl)-9,10-dihydro-9,10-ethenoanthracen-
11-yl)methanone (11a): Propeniminium salt 5b (1.55 g, 2.80 mmol) and
anthracene (500 mg, 2.80 mmol) were dissolved in dry CH3CN (15 mL),
and triethylamine (0.39 mL, 2.80 mmol) dissolved in dry CH3CN (3 mL)
was gradually added. The solution was stirred at r.t. for 10 min, then
treated with a saturated aqueous solution of K2CO3 (10 mL) for 5 min,
extracted with Et2O (2×50 mL), and the organic phase was collected and
dried (Na2SO4). The solvent was evaporated in vacuo and the solid residue
was purified by column chromatography (silica gel (300 g), eluent
cyclohexane‒CH2Cl2 (1:1), Rf = 0.23). A yellowish oil was obtained (916
mg, 2.44 mmol, 87% yield), which could be crystallized from CH2Cl2
solution, m.p. 127.0–129.1 °C. 1H NMR (CDCl3, 400 MHz):  = 5.25 (s, 1H,
Hbridgehead), 5.43 (s, 1H, Hbridgehead), 7.07–7.15 (m, 4H, HAr), 7.36–7.40 (m,
4H, HAr), 7.47–7.50 (m, 2H, HAr), 7.52–7.54 (m, 2H, HAr), 7.56–7.59 (m, 1H,
HAr). 13C NMR (CDCl3, 101 MHz):  = 50.0 (Cbridgehead), 54.2 (Cbridgehead),
4.9. 10-Bromo-12-(trifluoromethyl)-9,10-dihydro-9,10-ethenoanthra
cene-11-carbaldehyde (11d): Prepared from iminium salt 5f (813 mg,
1.81 mmol), 9-bromoanthracene (465 mg, 1.81 mmol) and anhyd. NEt3
(0.25 mL, 1.81 mmol) according to TP2. The crude product from extractive
workup was dissolved in cyclohexane and purified by flash
chromatography (elution with cyclohexane to remove residual anthracene,
then cyclohexane‒EtOAc (1:1)). Yellowish solid (185 mg, 0.49 mmol, 27%),
m.p. 139.5 °C. 1H NMR (CDCl3, 400 MHz):  = 5.38 (s, 1H, Hbridgehead),
7.12–7.20 (m, 4H, HAr), 7.39–7.42 (m, 2H, HAr), 7.78–7.80 (m, 2H, HAr),
10.05 (q, JH,F = 2.1 Hz, 1H, CHO). 13C NMR (CDCl3, 101 MHz):  = 49.9
1
123.2 (q, JC,F = 271 Hz, CF3); 123.7, 124.1, 125.7, 125.8, 128.8, 129.4,
2
134.3, 135.3 (all CAr); 139.0 (q, JC,F = 34.2 Hz, C-CF3), 143.3 (m, CAr),
3
143.8 (CAr), 153.0 (q, JC,F = 4.4 Hz, C=C-CF3), 194.0 (C=O). 19F NMR
(CDCl3):  = -64.7. IR (KBr): 휈̃ = 1664 (s), 1265 (s), 1172 (s), 1118 (s) cm-
1. HRMS ((+)-ESI): m/z = 399.09698, 415.07087; calcd. 399.09672
(C24H15F3NaO+, [M+Na]+), 415.07066 (C24H15F3KO+, [M+K]+). Analysis
calcd. for C24H15F3O (376.38): C 76.59, H 4.02; found: C 74.65, H 3.83;
calcd. for C24H15F3O·0.14 CH2Cl2 (376.38 + 0.14·84.93): C 74.68, H 3.79.
3
1
(q, JC,F = 2.1 Hz, Cbridgehead), 65.0 (Cbridgehead), 122.5 (q, JC,F = 273 Hz,
2
CF3); 123.4, 124.4, 126.2, 126.9, 141.5, 142.7 (all CAr); 143.1 (q, JC,F
38.4 Hz, C=C-CF3), 150.8 (q, 3JC,F = 3.7 Hz, C=C-CF3), 189.2 (CHO). 19
NMR (CDCl3):  = -63.3. IR (KBr): 휈̃ = 1702 (s), 1641 (w), 1454 (m), 1325
(m), 1292 (m), 1242 (m), 1179 (s), 1129 (s) cm-1. MS (CI, 100 eV): m/z (%)
= 299 (100) [M - Br]+, 300 (31) [M - Br+H]+.
=
F
10
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10.1002/ejoc.202100567
European Journal of Organic Chemistry
FULL PAPER
4.10.
N-(11-Formyl-12-(trifluoromethyl)-9,10-dihydro-9,10-etheno
cyclohexane was added until a lilac precipitate appeared. It was separated
by decantation of the liquid phase, dissolved in CH3CN and treated with a
satd. aqueous K2CO3 solution (10 mL) at 45 °C for 5 min. The mixture was
extracted with Et2O (2 × 100 mL), the organic phase was dried (Na2SO4)
and concentrated, and the orange residue was submitted to filtration over
dry silica gel (elution with cyclohexane‒CH2Cl2 (1:1)) to furnish the product
as a yellow oil (388 mg), which was a mixture of two diastereomers (Z- and
E(C=N)). They could be separated by HPLC (eluent: n-hexane‒CH2Cl2
(2:1)), but underwent an E/Z equilibration in solution at 40 °C within a short
time. Colorless solid (350 mg, 0.73 mmol, 51% yield), m.p. 168.2–169.5 °C
(2:1 diastereomeric mixture). 1H NMR (CDCl3, 400 MHz), Z-11g (major
isomer)  = 1.44 (d, 3JH,H = 6.5 Hz, 3H, CH3), 3.90 (q, 3JH,H = 6.7 Hz, NCH),
5.11 (s, 1H, Hbridgehead), 5.40 (s, 1H, Hbridgehead), 6.99–7.52 (m, 18H, HAr); E-
anthracen-2-yl)-N-methylacetamide (11e) (and N-(12-formyl-11-
(trifluoromethyl)-...): Prepared from iminium salt 5f (930 mg, 2.07 mmol),
N-(anthracen-2-yl)-N-methylacetamide (517 mg, 2.07 mmol) and anhyd.
NEt3 (0.29 mL, 2.07 mmol) according to TP2. The crude product from
extractive workup was submitted to flash chromatography (silica gel,
CH2Cl2 as eluent), the filtrate was concentrated and further purified by
HPLC (cyclohexane‒EtOAc, see TP2). Orange solid (120 mg, 0.32 mmol,
15% yield), m.p. 62‒63 °C, mixture of isomers (A:B = 1.0 : 0.45), which
could not be separated.[31] Because of overlap of almost all signals, no
efforts were made to assign the two species. 1H NMR (CDCl3, 400 MHz),
isomer A:  = 1.81 (s, 3H, CH3C=O), 3.19 (s, 3H, NCH3), 5.40 (s, 1H, 10-
Hbridgehead), 5.98 (s, 1H, 5-Hbridgehead), 6.88–6.90 (m, 1H, HAr), 7.09–7.11 (m,
2H, HAr), 7.24 (m, 1H, HAr), 7.41–7.45 (m, 3H, HAr), 10.13 (unresolved m,
1H, CHO); isomer B:  = 5.44 and 5.94 (bridgehead-H’s), all other signals
coincide with those of A. 13C NMR (CDCl3, 101 MHz), isomer A:  = 22.6
11g (minor isomer):  = 1.34 (d, 3JH,H = 6.3 Hz, 3H, CH3), 3.94 (q, 3JH,H
=
6.4 Hz, NCH), 4.77 (s, 1H, Hbridgehead), 5.45 (s, 1H, Hbridgehead), 6.73 (d, 3JH,H
= 7.2 Hz, 1H, HAr), 6.94–6.98 (m, 1H, HAr), 6.99–7.52 (m, 16H, HAr). The
configuration (Z and E) was assigned based on NOE NMR spectra. 13C
NMR (CDCl3, 101 MHz), both isomers:  = 25.1 (CH3, Z), 25.9 (CH3, E),
50.11 and 50.15 (2NCH); 55.2 (Z), 55.9 (E), 62.4 (Z), 62.6 (E) (4 Cbridgehead);
3
(CH3C=O), 37.4 (NCH3), 47.6 (C-5bridgehead), 51.1 (q, JC,F = 2.8 Hz, C-
10bridgehead), 122.7 (CAr), 123.5 (q, 1JC,F = 273 Hz, CF3); 124.2, 124.6, 124.8,
125.3, 126.0, 126.4, 142.2, 142.3, 142.95, 142.99, 144.8 (all CAr); 149.8
2
3
(q, JC,F = 34.8 Hz, C=C-CF3), 151.4 (q, JC,F = 3.2 Hz, C=C-CF3), 170.6
123.36‒136.98 (see spectrum, Supporting Information), 137.72 (q, 2JC,F
33.1 Hz, C-CF3), 137.80 (q, 2JC,F = 32.9 Hz, C-CF3), 142.67‒146.15 (see
=
4
(NC=O), 185.2 (q, JC,F = 3.3 Hz, CHO); isomer B:  = 47.8 and 50.9
(bridgehead-C’s); signals of CH3C=O and NCH3 coincide with A. 19F NMR
(CDCl3):  = -61.91 (A), -61.87 (B). IR (KBr): 휈̃ = 1659 (s), 1604 (shoulder),
1274 (m), 1189 (m), 1158 (s), 1125 (s) cm-1. HRMS ((+)-ESI): m/z (%) =
Supp. Information), 150.8 (q, JC,F = 4.9 Hz, C=C-CF3), 151.1 (q, JC,F =
3
3
4.9 Hz, C=C-CF3), 161.0 (C=N). 19F NMR (CDCl3):  = -65.9 (E), -66.3 (Z).
IR (KBr): 휈̃ = 1671 (w), 1622 (m), 1457 (m), 1350 (m), 1262 (m), 1171 (s),
1110 (s), 769 (m), 753 (s) cm-1. MS (CI, 100 eV): m/z (%) = 480 (100)
[M+H]+, 460 (17) [M - F]+, 402 (12) [M - Ph]+. C32H24F3N (479.55 g/mol).
394.10303, 743.23578, 765.21747; calcd. 394.10253 (C21H16F3NO2Na+,
[M+Na+]),
743.23390
(C42H33F6N2O4
,
[2M+H+]),
765.21585
+
(C42H32F6N2O4Na+, [2M+Na+]). C21H16F3NO2 (371.36 g/mol).
4.13.
Dimethyl
2-((12-(trifluoromethyl)-9,10-dihydro-9,10-etheno
4.11.
2-Azido-12-(trifluoromethyl)-9,10-dihydro-9,10-ethenoanthra
anthracen-11-yl)methylene)malonate (12): To a solution of iminium salt
5f (508 mg, 1.13 mmol) and anthracene (202 mg, 1.13 mmol) in anhyd.
CH2Cl2 (30 mL), anhyd. NEt3 dissolved in anhyd. CH2Cl2 (3 mL) was added.
After 10 min, dimethyl malonate (0.13 mL, 1.13 mmol) and NEt3 (0.30 mL,
2.27 mmol) were added and the mixture was stirred for 30 min. After
removal of the solvent, the residue was re-dissolved in cyclohexane‒
EtOAc (5:1). Flash chromatography over silica gel followed by HPLC
(cyclohexane‒EtOAc, see TP2) furnished a yellowish solid (124 mg, 0.30
mmol, 26%), m.p. 126‒127 °C. 1H NMR (CDCl3, 400 MHz):  = 3.59 (s, 3H,
OMe), 3.83 (s, 3H, OMe), 5.25 (s, 1H, Hbridgehead), 5.34 (s, 1H, Hbridgehead),
cene-11-carbaldehyde (11f): Prepared from iminium salt 5f (553 mg, 1.23
mmol), 2-azidoanthracene (286 mg, 1.30 mmol) and anhyd. NEt3 (0.17 mL,
1.23 mmol) as described for 11e. Purification by flash column
chromatography (eluent: cyclohexane, then cyclohexane‒EtOAc (5:1)).
Orange solid (123 mg, 0.36 mmol, 30% yield), m.p. 63.2–64.8 °C; An
impurity B (19F NMR: 11f (= A) : B = 1.00 : 0.10) could not be removed.
The constitution of 11f was derived mainly from HSQC and HMBC NMR
1
spectra (see Supporting Information). H NMR (CDCl3, 400 MHz), A:  =
5.37 (s, 1H, 10-Hbridgehead), 5.92 (s, 1H, 5-Hbridgehead), 6.71 (dd, JH,H = 7.9
and 2.2 Hz, 1H, HAr), 7.06–7.09 (m, 2H, HAr), 7.10 (d, 4JH,H = 2.2 Hz, 1H,
HAr), 7.36 (d, 3JH,H = 7.9 Hz, 1H, HAr), 7.39–7.43 (m, 2H, HAr), 10.12 (q, JH,F
5
7.05–7.07 (m, 4H, HAr), 7.34–7.40 (m, 4H, HAr), 7.71–7.73 (q, JH,F = 2.7
Hz, CH). 13C NMR (CDCl3, 101 MHz):  = 50.6 (q, 3JC,F = 2.3 Hz, Cbridgehead),
52.7 (Cbridgehead), 53.0 (OMe), 54.6 (OMe), 123.5), 123.7 (q, 1JC,F = 272 Hz,
CF3), 124.0, 125.6, 125.8, 128.6 (q, 5JC,F = 1.8 Hz), 136.9, 140.3 (q, 2JC,F
= 0.9 Hz, 1H, CHO); signals of B could not be identified without doubt. 13
C
NMR (CDCl3, 101 MHz), A:  = 47.4 (C-10bridgehead), 51.2 (q, 3JC,F = 2.8 Hz,
C-5bridgehead), 115.3 (CAr), 116.3 (CAr), 123.4 (q, 1JCF = 273 Hz, CF3); 124.2,
124.4, 125.3, 125.9, 126.4, 137.8, 140.3, 142.2, 143.3, 145.0 (all CAr);
4
= 32.6 Hz, C=C-CF3), 143.4 (q, JC,F = 1.4 Hz, HC=C), 143.5, 148.2 (q,
3JC,F = 4.3 Hz, C=C-CF3), 163.8 (C=O), 165.5 (C=O). 19F NMR (CDCl3): 
= -63.4. IR (KBr): 휈̃ = 1731 (s), 1629 (m), 1595 (m), 1460 (m), 1438 (m),
1155 (m), 1112 (m), 753 (m) cm-1. HRMS ((+)-ESI): m/z (%) = 437.09713,
851.20419; calcd. 437.09711 (C23H17F3O4Na+, [M+Na]+), 851.20501
(C46H34F6O8Na+, [2M+Na]+). Analysis calcd. for C23H17F3O4 (414.38): C
66.67, H 4.14; found: C 66.64, H 4.17.
2
3
149.6 (q, JC,F = 34.8 Hz, C=C-CF3), 151.6 (q, JC,F = 3.6 Hz, C=C-CF3),
185.2 (CHO); B:  = 37.8, 53.6 (bridgehead-C’s). 19F NMR (CDCl3):  = -
61.85 (B), -61.75 (A). IR (KBr): 휈̃ = 2113 (s), 1678 (s), 1125 (s) cm-1. MS
(CI, 100 eV): m/z (%) = 342 (100) [M+H]+, 322 (10) [M - F]+. Analysis calcd.
for C18H10F3N3O (341.29): C 63.35, H 2.95, N 12.31; found: C 63.32, H
3.35, N 11.75.
4.14. N-Ethyl-N-((12-(trifluoromethyl)-9,10-dihydro-9,10-ethenoanthra
cen-11-yl)methyl)ethanamine (13a): The cycloaddition product 10e was
prepared from iminium salt 5e (1.09 g, 2.28 mmol), anthracene (406 mg,
2.28 mmol) and anhyd. NEt3 (0.41 mL (2.96 mmol) in anhyd. CH2Cl2 as
described in TP2 (section 4.7). The mixture was stirred at room
temperature for 1.5 h, then cooled at 0 °C and, after addition of LiAlH4 in
THF (2.4 M, 2.0 mL, 4.80 mmol), stirred for another 30 min at this
temperature. Water (100 mL) was added and the mixture was extracted
with Et2O (300 mL). The organic phase was washed with brine (3×50 mL),
dried (Na2SO4) and concentrated. The oily residue was dissolved in Et2O
(50 mL) and gaseous HCl was introduced to obtain 13b‧HCl as a brown
precipitate, which was isolated by filtration, washed with Et2O (50 mL), re-
4.12.
1-Phenyl-N-((S)-1-phenylethyl)-1-(12-(trifluoromethyl)-9,10-
dihydro-9,10-ethenoanthracen-11-yl)methanimine (11g): Iminium salt
10d (1.015 g, 1.44 mmol) and anthracene (256 mg, 1.44 mmol) were
dissolved in anhyd. CH2Cl2 (25 mL) and anhyd. NEt3 (0.20 mL, 1.44 mmol)
dissolved in anhyd. CH2Cl2 (3 mL) was added gradually. After stirring at r.t.
for one hour, the solution was concentrated to a small volume and
11
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10.1002/ejoc.202100567
European Journal of Organic Chemistry
FULL PAPER
dissolved in CH2Cl2 (100 mL) and converted into 13b by addition of
aqueous K2CO3 (50 mL). The biphasic mixture was extracted with ether
(200 mL) and the organic phase was separated, dried (Na2SO4) and
evaporated to dryness. Beige solid (379 mg, 1.05 mmol, 46%), m.p. 82.1–
84.4 °C. 1H NMR (CDCl3, 400 MHz):  = 0.99 (t, 3JH,H = 7.1 Hz, 6H, CH3),
2.32 (q, 3JH,H = 7.1 Hz, 4H, NCH2CH3), 3.35 (q, JH,F = 1.9 Hz, 2H, NCH2C=),
5.26 (s, 1H, Hbridgehead), 5.56 (s, 1H, Hbridgehead), 6.98–7.05 (m, 4H, HAr),
7.33–7.38 (m, 4H, HAr). 13C NMR (CDCl3, 101 MHz):  = 11.9 (CH3), 47.0
mg, 1.00 mmol) and anhyd. NEt3 (0.14 mL (1.00 mmol) in anhyd. CH2Cl2
as described in TP2 (section 4.7). After stirring the reaction solution for 10
min, EtMgBr (1 M in Et2O, 5.0 mL, 5.0 mmol) in anhyd. CH2Cl3 (30 mL)
was added. The product was isolated from the reaction mixture by flash
chromatography (first run: elution with EtOAc, second run: elution with
EtOAc‒cyclohexane (10:1)). Brownish solid (278 mg, 0.78 mmol 78%
yield), m.p. 95‒96 °C. 1H NMR (CDCl3, 400 MHz):  = 0.24–0.29 (m, 3H,
CH2CH3), 1.49–1.59 (m, 1H, CH2CH3), 1.83–1.94 (m, 1H, CH2CH3), 2.07
(s, 6H, NMe2), 3.15–3.20 (m, 1H, NCH), 5.29 (s, 1H, Hbridgehead), 5.57 (s,
1H, Hbridgehead), 6.98–7.05 (m, 4H, HAr), 7.30–7.44 (m, 4H, HAr). 13C NMR
(CDCl3, 101 MHz):  = 10.3 (CH2CH3), 23.5 (CH2CH3), 44.6 (NMe2), 50.4
3
(CH2CH3), 50.4 (q, JC,F = 2.5 Hz, Cbridgehead), 52.2 (m, Cbridgehead), 54.2
1
(NCH2C=), 123.0, 123.6, 125.0 (q, JC,F = 271 Hz, CF3), 125.1, 125.2,
134.8 (q, 2JC,F = 32.4 Hz, C=C-CF3), 144.98, 145.01–145.02 (broadened),
156.4 (q, 3JC,F = 4.0 Hz, C=C-CF3). 19F NMR (CDCl3:  = -61.7. IR (KBr): 휈̃
= 1663 (w), 1460 (m), 1349 (m), 1295 (m), 1234 (m), 1179 (m), 1145 (m),
1099 (s), 747 (m) cm-1. HRMS ((+)-ESI): m/z (%) = 358.17764; calcd.
358.17771 (C22H23F3N+, [M+H]+). Analysis calcd. for C22H22F3N (357.42):
C 73.93, H 6.20, N 3.92; found: C 74.22, H 6.19, N 3.79.
3
(q, JC,F = 2.7 Hz, Cbridgehead), 51.5 (Cbridgehead), 67.1 (CH); 122.9, 123.0,
123.4, 123.7, 123.8 (all CAr); 125.1 (q, 1JC,F = 272 Hz, CF3), 125.13 (CAr),
125.18 (CAr), 125.2 (CAr), 135.6 (q, 2JC,F = 31.9 Hz, C=C-CF3); 144.5, 145.0,
145.0, 145.1 (all CAr); 157.3 (q, 3JC,F = 4.0 Hz, C=C-CF3). 19F NMR (CDCl3):
 = -60.7. IR (KBr): 휈̃ [cm-1] = 1658 (w), 1461 (m), 1345 (m), 1296 (m),
1238 (m), 1178 (m), 1142 (m), 1111 (s), 741 (m) cm-1. Analysis calcd. for
C22H22F3N (357.42): C 73.93, H 6.20, N 3.92; found: C 74.02, H 6.08, N
3.90.
4.15. N,N-Dimethyl-1-(12-(trifluoromethyl)-9,10-dihydro-9,10-etheno
anthracen-11-yl)methanamine (13b): The cycloaddition product 10f was
prepared from iminium salt 5f (491 mg, 1.09 mmol), anthracene (195 mg,
1.09 mmol) and anhyd. NEt3 (0.15 mL (1.09 mmol) in anhyd. CH2Cl2 (see
section 4.8). The product solution was cooled at -78 °C, LiAlH4 in THF (2.4
M, 0.96 mmol) was added dropwise, and excess LiAlH4 was quenched with
acetone after five minutes. After warming to r.t., brine (100 mL) was added
and the reaction mixture was extracted with Et2O (200 mL) and the organic
phase was extracted with brine (2 × 50 mL) followed by 1 M hydrochloric
acid (200 mL). The HClaq extract was collected, brought to pH 11 by the
addition of solid K2CO3 and extracted with ether (2 × 100 mL). The ether
phase was dried (Na2SO4) and concentrated. A brownish solid was
obtained (150 mg, 0.46 mmol, 42%), m.p. 145.2‒147.9 °C. 1H NMR (CDCl3,
400 MHz):  = 2.08 (s, 6H, CH3), 3.24 (q, 3JH,H = 2.3 Hz, 2H, NCH2), 5.26
(s, 1H, Hbridgehead), 5.51 (s, 1H, Hbridgehead), 7.00–7.02 (m, 4H, HAr), 7.33–
7.35 (m, 2H, HAr), 7.38–7.40 (m, 2H, HAr). 13C NMR (CDCl3, 101 MHz): 
4.18. N,N-Dimethyl-1-(12-(trifluoromethyl)-9,10-dihydro-9,10-etheno
anthracen-11-yl)prop-2-en-1-amine (14c): The cycloaddition product 10f
was prepared from iminium salt 5f (716 mg, 1.59 mmol), anthracene (284
mg, 1.59 mmol) and anhyd. NEt3 (0.22 mL (1.59 mmol) in anhyd. CH2Cl2
as described in TP2 (section 4.7). After stirring the reaction solution for 10
min, vinylmagnesium bromide (1.08 M in THF, 10 mL, 10.8 mmol) in anhyd.
CH2Cl2 (30 mL) was added. The reaction mixture was quenched with satd.
aqueous NH4Cl (50 mL), extracted with CH2Cl2 (2×50 mL). The organic
extract was filtered through a pad of silica gel (50 g). The eluate was
concentrated, diluted with EtOAc and submitted to flash chromatography
(silica gel, elution with EtOAc). Brown solid (367 mg, 1.03 mmol, 65%
yield), m.p. 69‒70 °C. 1H NMR (CDCl3, 400 MHz):  = 2.04 (s, 6H, NMe2),
3
3.78 (d, JH,H = 8.4 Hz, 1H, NCH), 5.01–5.04 and 5.15–5.20 (2 m, 2H,
3
= 45.9 (NMe2), 50.4 (q, JC,F = 2.7 Hz, Cbridgehead), 54.2 (Cbridgehead), 58.1
H2C=), 5.26 (s, 1H, Hbridgehead), 5.64 (s, 1H, Hbridgehead), 5.83 (m, 1H, =CH),
(NCH2), 123.1, 123.7, 124.8 (q, 1JC,F = 271 Hz, CF3), 125.19, 125.24, 135.7
6.96–7.06 (m, 4H, HAr), 7.30–7.36 (m, 3H, HAr), 7.42–7.47 (m, 1H, HAr).
(q, 2JC,F = 32.7 Hz, C=C-CF3), 144.8, 145.9 (broadened), 155.2 (q, 3JC,F
=
13C NMR (CDCl3, 101 MHz):  = 44.5 (NMe2), 50.3 (q, JC,F = 3.0 Hz,
3
4.1 Hz, C=C-CF3). 19F NMR (CDCl3):  = -61.5. IR (KBr): 휈̃ = 1668 (w),
1460 (m), 1351 (m), 1236 (m), 1184 (m), 1146 (s), 1099 (s), 743 (m), cm-
1. HRMS ((+)-ESI): m/z (%) = 330.14703; calcd. 330.14641 (C20H19F3N+,
[M+H]+). C20H18F3N (329.37 g/mol).
Cbridgehead), 51.7 (Cbridgehead), 69.7 (NCH), 118.8 (HC=CH2), 122.9, 123.1,
1
123.4, 123.8 (all CAr); 124.8 (q, JC,F = 272 Hz, CF3); 125.08, 125.22,
2
125.27, 125.28 (all CPh); 134.2 (q, JC,F = 32.4 Hz, C=C-CF3), 135.8
(HC=CH2), 144.6 (CAr), 144.9 (CAr), 145.4 (2 CAr), 157.5 (q, 3JC,F = 3.9 Hz,
C=C-CF3). 19F NMR (CDCl3):  = -60.6. IR (KBr): 휈̃ = 1656 (w), 1460 (m),
1345 (m), 1237 (m), 1174 (m), 1147 (m), 1110 (s), 749 (m) cm-1. HRMS
((+)-ESI): m/z (%) = 356.16202; calcd. 356.16206 (C22H21F3N+, [M+H]+).
C22H20F3N (355.40 g/mol).
4.16. N,N-Dimethyl-1-(12-((trifluoromethyl)-9,10-dihydro-9,10-etheno
anthracen-11-yl)ethan-1-amine (14a): The cycloaddition product 10f was
prepared from iminium salt 5f 43e? (620 mg, 1.38 mmol), anthracene (246
mg, 1.38 mmol) and anhyd. NEt3 (0.19 mL (1.38 mmol) in anhyd. CH2Cl2
as described in TP2 (section 4.7). After stirring the reaction solution for 10
min, CH3MgBr (1 M in toluene/THF (3:1), 8.0 mL, 8.0 mmol) in anhyd.
CH2Cl2 (30 mL) was added. When the addition was completed, the solution
was passed over dry silica (200 g) to remove residual Grignard reagent,
the solvents were evaporated, and the residue was purified by flash
chromatography (silica gel, eluent: EtOAc). Brownish solid (351 mg, 1.03
mmol, 81% yield), m.p. 95.3–97.8 °C. 1H NMR (CDCl3, 400 MHz):  = 1.12
(d, 3JH,H = 6.5 Hz, 3H, CH3), 2.06 (s, 6H, NMe2), 3.36 (s, 1H, NCH), 5.25
(s, 1H, Hbridgehead), 5.60 (s, 1H, Hbridgehead), 7.00–7.02 (m, 4H, HAr), 7.31–
7.33 (m, 3H, HAr), 7.40–7.42 (m, 1H, HAr). 13C NMR (CDCl3, 101 MHz): 
4.19. N,N-Dimethyl-1-(12-(trifluoromethyl)-9,10-dihydro-9,10-etheno
anthracen-11-yl)-3-(trimethylsilyl)prop-2-yn-1-amine
(14d):
The
cycloaddition product 10f was prepared from iminium salt 5f (1.22 mg, 2.72
mmol), anthracene (484 mg, 2.72 mmol) and anhyd. NEt3 (0.38 mL (2.72
mmol) in anhyd. CH2Cl2 as described in TP2 (section 4.7). After stirring the
reaction solution for 10 min, (trimethylsilyl)ethynyl magnesium bromide
(1.0 M in Et2O, 10.0 mL, 10.0 mmol) in anhyd. CH2Cl2 (30 mL) was added.
The reaction mixture was passed through a pad of silica gel (50 g, EtOAc
as eluent). Subsequent purification by HPLC (elution with cyclohexane‒
EtOAc, see TP2) afforded the product as a yellow oil, which crystallized on
standing. Yellowish solid (926 mg, 2.18 mmol, 80% yield), m.p. 90.7–
91.1 °C. 1H NMR (CDCl3, 400 MHz):  = 0.16 (s, 9H, SiMe3), 2.12 (s, 6H,
NMe2), 4.16 (s, 1H, NCH), 5.26 (s, 1H, Hbridgehead), 5.63 (s, 1H, Hbridgehead),
6.99–7.02 (m, 4H, HAr), 7.32–7.34 (m, 2H, HAr), 7.37–7.41 (m, 2H, HAr).
3
= 18.2 (CH3), 44.5 (NMe2), 50.3 (q, JC,F = 2.8 Hz, Cbridgehead), 51.5
(Cbridgehead), 60.73 (NCH); 123.0, 123.2, 123.4, 123.9 (all CAr); 125.0 (q,
1JC,F = 272 Hz, CF3), 125.2 (CAr), 125.3 (CAr), 125.4 (2 CAr), 133.5 (q, 2JC,F
= 32.2 Hz, C=C-CF3); 144.6, 145.1, 145.3, 145.6 (all CAr); 160.1 (q, 3JC,F
=
4.1 Hz, C=C-CF3). 19F NMR (CDCl3):  = -60.6. IR (KBr): 휈̃ [cm-1] = 1658
(w), 1458 (m), 1346 (m), 1295 (m), 1240 (m), 1178 (m), 1144 (s), 1106 (s),
744 (m) cm-1. MS (CI, 100 eV): m/z (%) = 344 (100) [M+H]+, 324 (52) [M -
F]+. Analysis calcd. for C21H20F3N (343.39): C 73.45, H 5.87, N 4.08; found:
C 73.47, H 5.74, N 4.07.
13C NMR (CDCl3, 101 MHz):  = -0.1 (SiMe3), 43.6 (NMe2), 50.5 (q, 3JC,F
=
2.6 Hz, Cbridgehead), 53.1 (Cbridgehead), 57.5 (broadened, NCH), 91.5 (C≡C),
1
100.9 (C≡C), 122.9, 123.1, 123.9, 124.5 (q, JC,F = 272 Hz, CF3), 125.1,
125.25, 125.30, 125.33, 135.8 (q, 2JC,F = 32.5 Hz, C=C-CF3); 144.1, 144.6,
145.5, 145.5 (all CAr); 153.0 (q, 3JC,F = 4.0 Hz, C=C-CF3). 19F NMR (CDCl3):
 = -61.9. IR (NaCl): 휈̃ = 2176 (w), 1665 (w), 1460 (m), 1343 (m), 1297 (m),
1239 (m), 1165 (s), 1115 (s), 845 (s), 747 (m) cm-1. MS (CI, 100 eV): m/z
(%) = 427 (100) [M+H]+, 336 (57) [M - F]+. Analysis calcd. for C25H26F3NSi
(425.57): C 70.56, H 6.16, N 3.29; found: C 70.65, H 6.30, N 3.42.
4.17. N,N-Dimethyl-1-(12-(trifluoromethyl)-9,10-dihydro-9,10-etheno
anthracen-11-yl)propan-1-amine (14b): The cycloaddition product 10f
was prepared from iminium salt 5f (449 mg, 1.00 mmol), anthracene (178
12
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10.1002/ejoc.202100567
European Journal of Organic Chemistry
FULL PAPER
5. Reactions with E,E-1,4-diphenylbuta-1,3-diene
6. Cycloadditions with organoazides
5.1. (2Z,4E)-1,5-Diphenyl-2-((Z)-3,3,3-trifluoro-1-phenylprop-1-en-2-
yl)penta-2,4-dien-1-one (16): Prepared from iminium salt (325 mg, 0.59
mmol) 5b and E,E-1,4-diphenylbuta-1,3-diene (121 mg, 0.59 mmol) and
anhyd. NEt3 (85 L, 0.62 mmol) in anhyd. CH2Cl2 (10 mL) as described for
11a (section 4.6). The mixture was stirred for 4 h at room temp. Purification
of the crude product by column chromatography (silica gel (300 g), elution
with cyclohexane‒EtOAc (60:1), Rf = 0.17) afforded a yellowish oil (198
mg, 0.48 mmol, 82% yield). 1H NMR (CDCl3, 400 MHz):  = 6.92 (d, 3JH,H
= 14.8 Hz, 1H, 5-H), 7.00 (s, 1H, 2‘-H), 7.17 (d, 3JH,H = 11.1 Hz, 1H, 3-H),
7.23 (dd, JH,H = 14.7 and 11.1 Hz, 1H, 4-H), 7.30–7.50 (m, 10H, HPh), 7.55–
7.59 (m, 3H, HPh), 7.78–7.81 (m, 2H, HPh). 13C NMR (CDCl3, 101 MHz): 
6.1. (1-Benzyl-5-(trifluoromethyl)-1H-1,2,3-triazol-4-yl)(phenyl)meth
anone (19a), typical procedure (TP3): Iminium salt 5b (1.70 g, 3.10
mmol) was dissolved in dry CH3CN (10 mL) and benzyl azide (420 mg,
3.23 mmol) was added. A solution of anhyd. NEt3 (0.43 mL, 3.10 mmol) in
dry CH3CN (5 mL) was added dropwise and the mixture was stirred at r.t.
for 30 min. After addition of satd. aqueous NaHCO3 (50 mL) and stirring
for 5 min, the mixture was extracted with Et2O (2 × 100 mL). The ether
phase was dried (Na2SO4) and concentrated to leave an orange oil.
Purification by column chromatography (silica gel (300 g), elution with
cyclohexane‒EtOAc (5:1), Rf = 0.43) provided the product as a pale
orange powder (852 mg, 2.57 mmol, 83% yield), m.p. 68.3–69.5 °C. 1H
NMR (CDCl3, 400 MHz):  = 5.78 (s, 2H, PhCH2), 7.30–7.32 (m, 2H, HPh),
2
= 122.9 (q, 1JCF = 275 Hz, CF3), 123.8, 125.9 (q, JC,F = 32.2 Hz, C-CF3),
127.5, 128.47, 128.49, 129.02, 129.13, 129.14 (q, JC,F = 2.7 Hz), 129.53,
129.65, 132.2, 133.87¸ 135.88, 136.1 (q, JC,F = 2.1 Hz), 138.1, 142.5, 142.6
7.36–7.42 (m, 3H, HPh), 7.49–7.54 (m, 2H, HPh), 7.62–7.66 (m, 1H, HPh),
4
8.13–8.16 (m, 2H, HPh). 13C NMR (CDCl3, 101 MHz):  = 54.8 (q, JC,F
=
3
(q, JC,F = 3.3 Hz), 145.3, 195.9 (C=O). 19F NMR (CDCl3):  = -58.2. IR
2.4 Hz, PhCH2), 119.5 (q, 1JC,F = 271 Hz, CF3), 127.8 (CPh), 128.6 (q, 2JC,F
= 42.4 Hz, C-5Trz); 128.6, 129.2 (2C), 130.8, 133.3, 134.2, 135.9 (all CPh);
146.1 (m, C-4Trz), 185.3 (C=O). 19F NMR (CDCl3):  = -58.3. IR (KBr): 휈̃ =
1676 (s), 1452 (m), 1346 (m), 1231 (s), 1177 (s), 1151 (s), 1060 (m), 914
(m), 698 (m) cm-1. MS (CI, 100 eV): m/z (%) = 332 (100) [M+H]+. Analysis
calcd. for C17H12F3N3O (331.30): C 61.63, H 3.65, N 12.68; found: C 61.69,
H 3.68, N 12.64.
(NaCl): 휈̃ = 1647 (s), 1614 (s), 1581 (s), 1276 (s), 1235 (s), 1161 (s), 1124
(s), 730 (s), 694 (s) cm-1. Analysis calcd. C26H19F3O (404.43): C 77.22, H
4.74; found: C 77.23, H 4.77.
5.2.
(2Z,4E)-N,N-Diethyl-1,5-diphenyl-2-((Z)-3,3,3-trifluoro-1-phenyl
6.2.
Phenyl(1-phenyl-5-(trifluoromethyl)-1H-1,2,3-triazol-4-yl)meth
prop-1-en-2-yl)penta-2,4-dien-1-amine (Z-17): A solution of iminium salt
5b (1.147 g, 2.07 mmol) and E,E-1,4-diphenylbuta-1,3-diene (427 mg,
2.07 mmol) in anhyd. CH2Cl2 (25 mL) was prepared. Anhydrous NEt3 (0.31
mL, 2.17 mmol) dissolved in anhyd. CH2Cl2 (5 mL) was added dropwise
and the mixture was stirred for 4 h, whereby the solution color changed
from yellow to deep orange. After cooling at -78 °C, LiAlH4 (2.4 M in THF,
1.73 mL, 4.15 mL) was added, the mixture was stirred for 5 min, then
excess LiAlH4 was quenched with acetone. The mixture was brought to
room temp. and after addition of brine (100 mL) it was extracted with Et2O
(2 × 100 mL). The organic phase was dried (Na2SO4), concentrated, and
the residue was fractionated by flash chromatography (elution with
cyclohexane‒EtOAc (20:1)) to afford a yellow oil (Rf = 0.31, 688 mg, 1.49
mmol, 72% yield). 1H NMR (CDCl3, 400 MHz):  = 1.02 (t, 3JH,H = 7.0 Hz,
anone (19b): Prepared from iminium salt 5b (1.47 g, 2.65 mmol), phenyl
azide (319 mg, 2.68 mmol) and NEt3 (0.37 mL, 2.68 mmol) by TP3. The
reaction mixture was stirred at room temperature for 4 h. Workup as
described afforded a pale orange solid (340 mg, 1.07 mmol, 40% yield),
m.p. 74.8–77.0 °C. 1H NMR (CDCl3, 400 MHz):  = 7.46–7.57 (m, 7H, HPh),
7.58–7.62 (m, 1H, HPh), 8.11–8.14 (m, 2H, HPh). 13C NMR (CDCl3, 101
MHz):  = 119.2 (q, 1JC,F = 271 Hz, CF3), 125.8 (CPh), 128.8 (CPh), 129.0
2
(q, JC,F = 42.3 Hz, C-5Trz); 129.8, 130.9, 131.3, 134.4, 135.5, 135.9 (all
CPh); 146.0 (m, C-4Trz), 185.3 (C=O). 19F NMR (CDCl3):  = -57.3. IR (KBr):
휈̃ = 1673 (m), 1500 (m), 1359 (m), 1254 (s), 1236 (s), 1190 (s), 1165 (s),
1145 (s), 1099 (m), 913 (m), 771 (m), 693 (m) cm-1. HRMS ((+)-ESI): m/z
=
318.08538, 340.06723, 356.04075, 657.14569; calcd. 318.08487
(C16H11F3N3O+, [M+H]+), 340.06682 (C16H10F3N3NaO+, [M+Na]+),
6H, CH2CH3), 2.70–2.86 (m, 4H, NCH2), 4.57 (s, 1H, 1-H), 6.34 (d, 3JH,H
=
356.04075 (C16H10F3KN3O+, [M+K]+), 657.14441 (C32H20F6NaN6O2
,
+
3
[2M+Na]+). Analysis calcd. for C16H10F3N3O (317.27): C 60.57, H 3.18, N
13.24; found: C 60.57, H 3.31, N 13.04.
11.1 Hz, 1H, 3-H), 6.50 (s, 1H, 2‘-H), 6.61 (d, JH,H = 15.7 Hz, 1H, 5-H),
7.20–7.40 (m, 3H, HPh), 7.26–7.34 (m, 6H, HPh), 7.38–7.43 (m, 4H, HPh),
7.47–7.49 m, 2H, HPh), 8.29 (dd, JH,H = 15.7 and 11.2 Hz, 1H, 4-H). 13C
NMR (CDCl3, 101 MHz):  = 10.5 (CH2CH3), 42.5 (NCH2), 70.3 (NCH = C-
1), 123.5 (q, 1JC,F = 276 Hz, CF3), 126.2 (C-4); 126.8, 127.2, 127.9, 128.15,
128.22, 128.29 (all CPh); 128.5 (q, 3JC,F = 2.6 Hz, C-2), 128.9 (CPh), 129.2
(CPh), 132.5 (C-3), 132.6 (q, 2JC,F = 29.8 Hz, C-1’), 135.0 (CPh), 135.5 (C-
6.3.
1-Benzyl-5-(trifluoromethyl)-1H-1,2,3-triazole-4-carbaldehyde
(19d): Prepared from iminium salt 5e (1.16 g, 2.43 mmol), benzyl azide
(324 mg, 2.40 mmol) and anhyd. NEt3 (0.35 mL, 2.52 mmol) by TP3. The
reaction mixture was stirred for 30 min, then processed as described.
Yellow oil (Rf = 0.28, 415 mg, 1.63 mmol, 68% yield), which solidifies at
~20 °C. 1H NMR (CDCl3, 400 MHz):  = 5.74 (s, 2H, H, PhCH2), 7.24–7.26
(m, 2H, HPh), 7.33–7.36 (m, 3H, HPh), 10.16 (s, 1H, CHO). 13C NMR (CDCl3,
3
5), 137.7 (CPh), 138.8 (broadened, CPh), 139.3 (q, JC,F = 3.5 Hz, C-2’),
140.8 (CPh); 1H and 13C assignments were made based on HSQC and
HMBC spectra. 19F NMR (CDCl3):  = -56.6. IR (KBr): 휈̃ = 1621 (w), 1168
(m), 1119 (m), 698 (w-m) cm-1. MS (CI, 100 eV): m/z (%) = 462 (100)
[M+H]+, 442 (37) [M - F]+, 389 (76) [M - HNEt2]+. C30H30F3N (461.57 g/mol).
1
101 MHz):  = 54.7 (q, JC,F = 2.1 Hz, PhCH2), 119.3 (q, JC,F = 271 Hz,
2
CF3), 127.8 (CPh), 128.0 (q, JC,F = 44.0 Hz, C-5Trz), 129.3 (CPh), 129.4
(CPh), 133.0 (CPh), 145.0 (C-4Trz), 182.2 (C=O). 19F NMR (CDCl3):  = -58.0.
IR (KBr): 휈̃ = 1715 (s), 1475 (m), 1439 (m), 1333 (m), 1187 (s), 1154 (s),
1052 (m), 837 (m) cm-1. HRMS ((+)-ESI): m/z = 278.05183, 533.11419;
The hydrobromide of 17 was obtained by addition of conc. hydrobromic
acid to a solution of 17 (120 mg, 0.26 mmol) in Et2O (4 mL); a white solid
(m.p. 120.1–121.9 °C) resulted, from which crystals suited for an XRD
analysis could be prepared by vapor diffusion crystallization from CH2Cl2‒
n-pentane at 4 °C. These crystals contained 1.54 CH2Cl2 solvate
molecules per formula unit. 1H NMR (CDCl3, 400 MHz):  = 1.36 (t, J = 7.2
Hz, 3H, CH3), 1.70 (t, J = 7.2 Hz, 3H, CH3), 3.18 (m, 2H, 2 NCH), 3.70 (dm,
J = 12.7 Hz, 1H, NCH), 3.90 (dm, J = 13.4 Hz, 1H, NCH), 5.17 (d, J = 10.2
Hz, 1-H), 6.70 (d, J = 11.6 Hz, 1H, 5-H), 7.06 (s, 1H, 2’-H), 7.32-7.50
(several signals, 12H), 7.82 (d, J = 7.6 Hz, 1H), 7.88 (d, J = 7.6 Hz, 1H),
11.25 (broadened s, NH). C30H31F3N·HBr (542.48 g/mol).
calcd.
278.05117
(C11H8F3N3NaO+,
[M+Na]+),
533.11311
(C22H16F6N6NaO2+, [2M+Na]+). Analysis calcd. for C11H8F3N3O (255.20): C
51.77, H 3.16, N 16.47; found: C 51.63, H 3.39, N 16.27.
6.4.
1-(1-(4-Chlorobenzyl)-5-(trifluoromethyl)-1H-1,2,3-triazol-4-yl)-
N,N-diethylethan-1-amine (20): To a solution of iminium salt 5e (810 mg,
1.70 mmol) and 4-chlorobenzyl azide (285 mg, 1.70 mmol) in anhyd.
13
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10.1002/ejoc.202100567
European Journal of Organic Chemistry
FULL PAPER
CH2Cl2 (5 mL), NEt3 (0.24 mL, 1.70 mmol) dissolved in CH2Cl2 (3 mL) was
gradually added. After stirring for 10 min, anhyd. Et2O and pentane was
added until an orange oil separated. The supernatant liquid was decanted
off, the residual oil was triturated with another portion of anhyd. Et2O. The
remaining oil was dissolved in dry THF (30 mL) and methylmagnesium
bromide (1.4 m in THF‒toluene (1:3), 2.43 mL, 3.40 mmol) was added.
After stirring for 20 min, satd. aqueous NaHCO3 (50 mL) was added, the
mixture was extracted with Et2O (2 × 100 mL), and the organic phase was
dried (Na2SO4) and concentrated. The residue was dissolved in EtOAc and
filtered through a pad of silica gel. The solvent of the filtrate was replaced
by Et2O, and this solution was acidified with gaseous HCl. An oil separated
(20 ‧ HCl), which was isolated and converted into free amine 20 by
treatment with aqueous K2CO3. After drying at 0.02 mbar, an orange-
(See footnote on the first page of this article): NMR (1H, 13C, 19F) and IR
spectra of all synthesized compounds, crystallographic data for compound
17‧HBr.
Acknowledgements
Financial support by the University of Ulm is gratefully
acknowledged. We thank Dr. M. Wunderlin for the mass spectra
and B. Müller for the XRD data collection.
Keywords: Alkynes • Cycloaddition • Iminium Salts •
Organofluorine Compounds • 1,2,3-Triazoles
1
brown oil (339 mg, 0.94 mmol, 55%) was obtained. H NMR (CDCl3, 500
MHz):  = 0.95 (t, 3JH,H = 7.1 Hz, 6H, CH2CH3), 1.46 (d, 3JH,H = 6.9 Hz, 3H,
CH3), 2.41–2.48 (m, 2H, NCH2), 2.54–2.61 (m, 2H, NCH2), 4.25 (q, 3JH,H
=
3
6.8 Hz, 1H, NCH), 5.60 (s, 2H, PhCH2), 7.16 (d, JH,H = 8.5 Hz, 2H, HPh),
7.30–7.33 (m, 2H, HPh). 13C NMR (CDCl3, 126 MHz):  = 13.9 (CH2CH3),
14.4 (CHCH3), 43.9 (NCH2), 50.5 (NCH), 53.3 (q, JC,F = 1.8 Hz, PhCH2),
[1] D. O’Hagan, Understanding organofluorine chemistry. An introduction to the
C–F bond, Chem. Soc. Rev. 2008, 37, 308–319.
1
2
120.6 (q, JC,F = 269 Hz, CF3), 123.8 (q, JC,F = 40.3 Hz, C-5Trz); 129.1,
129.2, 132.7, 134.9 (all CPh); 151.1 (C-4Trz). 19F NMR (CDCl3):  = -57.8.
[2] a) P. Kirsch, Modern Fluoroorganic Chemistry - Synthesis, Reactivity,
Applications, 2nd ed., Wiley-VCH, Weinheim, Germany, 2013; b) K.
Uneyama, Organofluorine Chemistry, Blackwell Publishing Ltd., Oxford,
UK, 2006; ch. 7: Methods for Introduction of Fluorine‐Functionality Into
Molecules.
IR (NaCl): 휈̃ = 1494 (m), 1340 (m), 1171 (s), 1148 (s), 1067 (m) cm-1.
+
HRMS ((+)-ESI): m/z = 361.14001; calcd. 361.14014 (C16H21ClF3N4
[M+H]+). C16H20ClF3N4 (360.81 g/mol).
,
[3] a) J. Wang, M. Sꢀnchez-Rosellꢁ, J. L. Aceꢂa, C. del Pozo, A. E. Sorochinsky,
S. Fustero, V. A. Soloshonok, H. Liu, Chem. Rev. 2014, 114, 2432−2506;
b) D. O’Hagan, J. Fluorine Chem. 2010, 131, 1071‒1081.
[4] a) P. Jeschke, ChemBioChem 2004, 5, 570–589; b) P. Jeschke, Pest Manag.
Sci. 2010, 66, 10–27; c) T. Fujiwara, D. O’Hagan, J. Fluorine Chem. 2014,
167, 16–29. d) P. Jeschke, Pest Manag. Sci., 2017, 73, 1053–1066.
[5] S. Caron, Org. Proc. Res. Dev. 2020, 24, 470–480. DOI:
10.1021/acs.oprd.0c00030.
6.5. Diethyl 2-((1-(4-chlorobenzyl)-5-(trifluoromethyl)-1H-1,2,3-triazol-
4-yl)methylene)malonate (21): To a solution of iminium salt 5e (817 mg,
1.71 mmol) and 4-chlorobenzyl azide (287 mg, 1.71 mmol) in anhyd.
CH2Cl2 (5 mL), NEt3 (0.24 mL, 1.71 mmol) dissolved in CH2Cl2 (3 mL) was
gradually added. After stirring for 30 min, diethyl malonate (274 mg, 1.71
mmol) and anhyd. NEt3 (0.24 mL, 1.71 mmol) were added and the mixture
was stirred for 90 min, then diluted with ether (20 mL). Pentane was added
until an oil separated. The supernatant layer was isolated by decantation,
the solvent was evaporated, and a solution of the residue was passed over
a pad of silica gel. The filtrate was concentrated and the residue was
filtered twice through a pad of dry silica gel (elution with n-pentane‒Et2O
(5:2)). After evaporation of the solvent, the residue was dried at 0.02 mbar
[6] a) J. M. Percy, Building Block Approaches to Aliphatic Organofluorine
Compounds, in Organofluorine Chemistry (Ed.: R. D. Chambers), Top.
Curr. Chem., Vol. 193, Springer, Berlin, Heidelberg, 1997, pp. 131‒195;
DOI: 10.1007/3-540-69197-9_4; b) J. M. Percy, Recent Advances in
Organofluorine Chemistry, Contemp. Org. Synth. 1995, 2, 251‒268. DOI:
10.1039/CO9950200251; c) L. V. Politanskaya et al., Russ. Chem. Rev.
2019, 88, 425–569. Organofluorine chemistry: promising growth areas
and challenges.
[7] a) T. Schneider, B. Seitz, M. Schiwek, G. Maas, J. Fluorine Chem. 2020, 235,
109567; b) T. Schneider, M. Fleischmann, D. Hergesell, N. Majstorović,
G. Maas, accepted, DOI: ejoc.202100378; c) T. Schneider, G. Heinrich,
R. Koch, G. Maas, Eur. J. Org. Chem. 2021, 1011–1025.
1
to leave an orange oil (170 mg, 0.39 mmol, 23%). H NMR (CDCl3, 400
MHz):  = 1.32 (t, 3JH,H = 7.1 Hz, 3H, CH3), 1.36 (t, 3JH,H = 7.2 Hz, 3H, CH3),
4.31 (q, 3JH,H = 7.1 Hz, 2H, OCH2), 4.43 (q, 3JH,H = 7.2 Hz, 2H, OCH2), 5.61
(s, 2H, PhCH2), 7.19–7.21 (m, 2H, HPh), 7.31–7.35 (m, 2H, HPh), 7.59 (m,
1H, CH). 13C NMR (CDCl3, 101 MHz):  = 14.0 (CH3), 14.2 (CH3), 53.6 (q,
[8] a) T. Schneider, M. Keim, B. Seitz, G. Maas, Beilstein J. Org. Chem. 2020,
16, 2064–2072; b) G. Maas, R. Koch, Z. Naturforsch. 2020, 75b, 1065–
1074.
1
4JC,F = 1.8 Hz, PhCH2), 62.1 (OCH2), 62.3 (OCH2), 119.9 (q, JC,F = 270
2
Hz, CF3), 124.8 (q, 4JC,F = 2.1 Hz, CH), 126.0 (q, JC,F = 40.9 Hz, C-5Trz),
[9] a) G. Maas, B. Singer, P. Wald, M. Gimmy, Chem. Ber. 1988, 121, 1847–
1854. b) R. Rahm, G. Maas, Synthesis 1994, 295–299. c) M. Reisser, G.
Maas, J. Org. Chem. 2004, 69, 4913–4924.
129.4 (CPh), 129.4 (CPh), 130.7 (CH=C), 131.7 (CPh), 135.4 (CPh), 141.2 (C-
4Trz), 163.3 (C=O), 165.6 (C=O) cm-1. 19F NMR (CDCl3):  = -58.0. IR
(NaCl): 휈̃ = 1733 (s), 1549 (m), 1492 (m), 1287 (s), 1241 (s), 1177 (s), 1146
(s), 1065 (s) cm-1. HRMS ((+)-ESI): m/z = 454.07504, 885.15957; calcd.
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14
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10.1002/ejoc.202100567
European Journal of Organic Chemistry
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15
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10.1002/ejoc.202100567
European Journal of Organic Chemistry
FULL PAPER
Entry for the Table of Contents
Layout 2:
FULL PAPER
Iminium Salts
Dr. Michael Keim, Katharina Konetzke,
Angelika Freytag, Prof. Dr. Gerhard
Maas*
Page No. – Page No.
3-Trifloxy-3-(trifluoromethyl)prop-2-
ene 1-iminium salts as precursors for
elusive 3-(trifluoromethyl)prop-2-yne
1-iminium salts
So far unknown 3-trifluoromethyl-prop-2-yne 1-iminium triflate salts were generated
by elimination of triflic acid from 3-trifloxy-3-CF3-prop-2-ene 1-iminium salts and
trapped in situ by cycloaddition to 1,3-dienes or organoazides. Hereby, these doubly
activated electrophilic alkynes were found to be more reactive than other CF3-
substituted alkynes and acetylenic iminium salts without 3-CF3 substitution.
16
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