3-Trifloxypropene iminium and propyne iminium salts derived from N-Allyl-, N-Homoallyl-, and N-Benzyl-substituted semicyclic enaminones

Article abstract of DOI:10.1002/(SICI)1521-3897(199902)341:2<121::AID-PRAC121>3.0.CO;2-D

The novel semicyclic enaminoketones 3a-n, featuring N-allyl, N-homoallyl, N-benzyl, and N-4-chlorobenzyl substitution, have been prepared. Their reaction with triflic anhydride leads to 3-trifloxypropene iminium triflates 4 which are transformed into semicyclic propyne iminium triflates 5 by thermal β-elimination of triflic acid (HOTf). If a 4-chlorophenyl group is attached to the TfO-substituted carbon atom, salts 4 can be isolated (4a,d,g,h,k,m) and converted into propyne iminium triflates 5 at 120°C. The presence of a 2-thienyl or 3-thienyl group adjacent to the trifloxy group prevents the isolation of 4 since HOTf elimination occurs already below room temperature. Thus, salts 5b,c,e,f,i,j,l,m,n are obtained directly from enaminoketones 3 and triflic anhydride. Wiley-VCH Verlag GmbH, 1999.

Full text of DOI:10.1002/(SICI)1521-3897(199902)341:2<121::AID-PRAC121>3.0.CO;2-D

______________________________________________________________________________ FULL PAPER
3-Trifloxypropene Iminium and Propyne Iminium Salts Derived from N-Allyl-,
N-Homoallyl-, and N-Benzyl-Substituted Semicyclic Enaminones
R. Neumann, H. G. Herz, and G. Maas*
Ulm, Abteilung Organische Chemie I der Universität
Received October 19th, 1998, respectively November 30th, 1998
Keywords: Alkynes, Nitrogen heterocycles, Enaminoketones, Iminium salts, Sulfonylation
Abstract. The novel semicyclic enaminoketones 3a–n, fea-
turing N-allyl, N-homoallyl, N-benzyl, and N-4-chloroben-
zyl substitution, have been prepared. Their reaction with tri-
flic anhydride leads to 3-trifloxypropene iminium triflates 4
which are transformed into semicyclic propyne iminium tri-
flates 5 by thermal β-elimination of triflic acid (HOTf). If a
4-chlorophenyl group is attached to the TfO-substituted car-
bon atom, salts 4 can be isolated (4a,d,g,h,k,m) and con-
verted into propyne iminium triflates 5 at 120 °C. The pres-
ence of a 2-thienyl or 3-thienyl group adjacent to the trifloxy
group prevents the isolation of 4 since HOTf elimination
occurs already below room temperature. Thus, salts
5b,c,e,f,i,j,l,m,n are obtained directly from enaminoketones
3 and triflic anhydride.
the exocyclic N-substituent. This is the case in N-allyl,
N-homoallyl, and N-benzyl-substituted semicyclic imi-
nium salts II and III. We describe here the synthesis
and spectroscopic characterization of such salts.
Propyne iminium salts have been recognized as useful
synthetic building blocks in organic synthesis. Most im-
portantly, they can be transformed into functionalized
and highly substituted propargylamines, aminoallenes,
and amino-1,3-butadienes [1–4]. In earlier papers [5–
7], we have described that propyne iminium salts III
are easily available by O-sulfonylation of enaminoke-
tones I with triflic anhydride (Tf2O), followed by elim-
ination of triflic acid (HOTf) from the resulting 3-tri-
floxypropene iminium triflates II (Scheme 1). Elimina-
tion of HOTf from salts II is achieved by heating them
in acetonitrile solution, by vacuum thermolysis, or with
the help of tertiary amines.
O
( )n
( )n
( )n
OEt
OEt
a,b
c
O
N
N
H2CR
2
N
H2CR
3
Ar
Ar
H2CR
1
( )n
OTf
( )n
Tf2O
(∆)
-HOTf
+
+
N
Ar
N
-
-
H2CR
H2CR
TfO
TfO
R1
R1
R1
4
5
OTf
Tf2O
∆
Ar
CHCOAr
CH
+
N
R3
-HOTf
+
R2
N
1-5
n
R
Ar
R2
R2
Ar
-
N
R3
R3
-
TfO
TfO
1
1
1
2
2
2
2
2
2
2
2
2
3
3
CH=CH2
CH=CH2
phenyl
4-chlorophenyl
2-thienyl
a
b
c
d
e
f
III
I
II
2-thienyl
Scheme 1
CH=CH2
CH=CH2
CH=CH2
4-chlorophenyl
3-thienyl
2-thienyl
The enaminoketone route described above provides
access to both acyclic and semicyclic propyne iminium
salts III. In the acyclic salts, the NR2R3 moiety so far
was either a dialkylamino, morpholino, pyrrolidino or
piperidino group, whereas in the semicyclic salts, the
iminium function was part of a five-, six-, or seven-
membered ring and had an exocyclic methyl substitu-
ent [i.e. R1–R2 = (CH2)n, n = 3,4,5 and R3 = Me]. For
various synthetic studies with semicyclic 3-trifloxypro-
pene iminium and propyne iminium salts, we had a need
of derivatives in which a π system was incorporated in
CH2-CH=CH2
4-chlorophenyl
g
h
i
4-chlorophenyl 4-chlorophenyl
4-chlorophenyl
4-chlorophenyl
phenyl
3-thienyl
2-thienyl
j
4-chlorophenyl
2-thienyl
k
l
phenyl
CH=CH2
4-chlorophenyl
2-thienyl
m
n
CH=CH2
Scheme 2 Conditions: a) (MeO)2SO2, 80 °C; b) NaOEt
(2 equiv.); c) H3C–CO–Ar, 80 °C
J. Prakt. Chem. 1999, 341, No. 2
© WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1999 1436-9966/99/3410X-121 $ 17.50 + .50/0
121

R. Neumann et al.
FULL PAPER __________________________________________________________________________
(Table 3). In order to avoid deprotonation of salt 4 by
an excess of enaminoketone 3, a solution of the latter in
CH2Cl2 was added to Tf2O in order to keep the station-
ary concentration of 3 low.
Results
Semicyclic enaminoketones 3 (R = allyl, homoallyl, ben-
zyl, 4-chlorobenzyl) were prepared, by analogy to a pub-
lished procedure [8], in two steps from the correspond-
ing N-alkyllactams 1. The synthesis of the latter from
their NH precursors and an alkyl halide has been de-
scribed [9–13] except for 1-(4-chlorobenzyl)-2-piperid-
inone which was prepared analogously. O-Alkylation
of 1a–n with dimethyl sulfate followed by addition of
NaOEt delivered lactam acetals 2, which were con-
densed with an (het)aryl methyl ketone to give enami-
noketones 3a–n (Scheme 2 and Table 1).
The constitution of salts 4 was indicated by an IR
absorption at ν/cm–1 = 1413–1433 which is typical for
the covalently bonded triflate group and represents the
νas(SO2) stretching vibration appearing at particularly
high wavenumbers [14] due to the attachment of the
electron-withdrawing CF3 group. Furthermore, the
13C NMR spectra show two quartets at δ/ppm = 119.1–
120.1 (anionic triflate) and at δ/ppm = 121.9–122.2
(covalent triflate) (Table 4). The configuration of the
salts 4h,k was determined exemplarily by selective
ROESY NMR experiments (Figure 1). In both salts, the
propene iminium unit adopts the Z, s-trans configura-
tion which was already established for related systems
[7]. Due to the similar substitution pattern, the same
geometry should also apply for all other salts 4.
Table 1 Yields, melting points, and elemental analyses of enami-
noketones 3a–n
Com- Yield m.p.
pound (%) (°C)
Formula
(g/mol)
Elemental Analysis
Calcd./Found
C
H
N
3a
3b
3c
3d
3e
3f
79
74
77
81
69
74
78
79
74
76
65
87
66
63
76
C15H16ClNO
(261.75)
C13H15NOS
(233.33)
C17H17NOS
(283.34)
C16H18ClNO
(275.78)
C14H17NOS
(247.36)
C14H17NOS
(247.36)
C17H20ClNO
(289.80)
C20H14Cl2NO
(360.28)
C18H18ClNOS 65.15
(331.86) 65.01
C18H18ClNOS 65.15
(331.86)
C20H20ClNO
(325.84)
C18H19NOS
(297.41)
68.83
68.80
66.92
67.10
72.05
71.86
69.69
69.67
67.98
67.81
67.98
68.00
70.46
70.29
66.68
66.68
6.16
6.14
6.48
6.58
6.05
5.79
6.58
6.69
6.93
6.87
6.93
6.92
6.96
6.78
5.32
5.28
5.47
5.69
5.47
5.49
6.19
6.15
6.44
6.38
6.98
7.08
7.33
7.38
5.35
5.44
6.00
5.96
4.94
4.73
5.08
5.19
5.66
5.64
5.66
5.76
4.83
4.75
3.89
3.95
4.22
4.52
4.52
4.29
4.30
4.19
4.71
4.71
4.83
4.84
5.36
5.27
63
OTf
110–112
81
+
N
Ar'
H
RCH2
H
35
-
TfO
53
4
3g
3h
3i
84
Fig. 1 NOE 1H signal intensity enhancement for 3-trifloxy-
propene iminium triflates 4
112
106–107
111–112
96-97
110–111
59
In contrast to the results mentioned above, 3-trifloxy-
propene iminium triflates 4 with a thienyl ring adjacent
to the trifloxy function could not be isolated. They elim-
inate HOTf already under the condition of their synthe-
sis (i.e. at temperatures between –60 and 0 °C) to give
propyne iminium salts 5. Possible reasons for the ac-
celeration of the β-elimination by electron-donating sub-
stituents at the trifloxy-substituted carbon atom have
been discussed [7]. In those cases where HOTf elimi-
nation from 4 occurs already during the synthesis of 4,
fast addition of the enaminoketone 3 to Tf2O is required.
Otherwise, the eliminated triflic acid is trapped by un-
consumed enaminoketone.
As an example, slow addition of 3i during 90 min-
utes to Tf2O in dichloromethane at 0 °C gave a mixture
of propyne iminium salt 5i (51%) and iminium salt 6
(12%) resulting from C-protonation of 3i (Scheme 3).
Elimination of triflic acid from salts 4 bearing a
4-chlorophenyl substituent adjacent to the trifloxy func-
tion requires a higher thermal activation. All of these
salts (4a,d,g,h,k,m) could be transformed in high yields
into the propyne iminium salts 5 by heating them in
acetonitrile solution at 120 °C for several hours (Table
5, Table 6).
3j
65.08
73.72
73.78
72.69
72.75
70.46
70.31
68.93
68.61
3k
3l
3m
3n
C17H20ClNO
(289.90)
C15H19NOS
70
(261.38)
Enaminoketones 3 were fully characterized by NMR
and IR spectroscopy (Table 2). In all cases, only one
diastereomer was detected by NMR. Selective ROESY
and NOESY experiments on 3c,h–l, with irradiation at
δ(=CH) showed an intensity enhancement for the exo-
cyclic NCH2 signal, which is indicative of the E config-
uration at the enaminic C=C bond. As the chemical shifts
for the olefinic proton in all enaminoketones are very
similar (δ = 5.57–5.79 ppm), the E configuration is also
assumed for all other enaminoketones 3.
The reaction of semicyclic enaminoketones 3a,d,g,h,
k,m, all of which have the electron-withdrawing 4-chlo-
rophenyl substituent bonded to the carbonyl group, with
triflic anhydride in CH2Cl2 yielded the 3-trifloxypro-
pene iminium triflates 4 as colorless solids in high yields
122
J. Prakt. Chem. 1999, 341, No. 2

3-Trifloxypropene Iminium and Propyne Iminium Salts
_____________________________________________________________________________ FULL PAPER
Table 2 1H and 13C NMR and IR data of enaminoketones 3a–n
Com- 1H NMR a)
pound
13C NMR b)
3a
2.02 (quin, 2H), 3.41 (t, 2H), 3.45 (t, 2H), 3.91 (d, 2H), 5.18 (dd, 3J =
20.6 (t), 33.7 (t), 48.9 (t), 52.5 (t), 86.1 (t), 117.6 (t),
128.0 (d, 2C), 128.5 (d, 2C), 130.2 (d), 136.0 (s),
140.2 (s), 167.2 (s), 185.9 (s)
17.2 Hz, 2J = 1.2 Hz, 1H), 5.24 (dd, 3J = 10.3 Hz, 2J = 1.2 Hz, 1H), 5.67
(s, 1H), 5.78 (mc, 1H), 7.33/7.80 (AA'BB', 4H)
3b
1.99 (quin, 2H), 3.38 (t, 2H), 3.42 (t, 2H), 3.90 (d, 2H), 5.14–5.28
(m, 2H), 5.65 (s, 1H), 5.78 (mc, 1H), 7.03 (dd, 3J = 5.0 Hz, 3J = 1.1 Hz,
1H), 7.38 (dd, 3J = 5.0 Hz, 4J = 1.1 Hz, 1H), 7.53 (dd, 3J = 3.8 Hz, 4J =
1.1 Hz, 1H)
20.7 (t), 33.6 (t), 48.9 (t), 52.4 (t), 86.0 (d), 117.6 (t),
127.0 (d), 127.2 (d), 129.2 (d), 130.3 (d), 149.0 (s),
166.5 (s), 179.9 (s)
3c
3d
3e
1.99 (quin, 2 H), 3.24–3.48 (2 t, 4H), 4.48 (s, 2H), 5.79 (s, 1H), 6.99 (dd,
1H, 3J = 5.0 Hz, 3J = 3.7 Hz), 7.22 (m, 2H), 7.28 (m, 1H), 7.34 (t, 2H),
7.35 (dd, 1H), 7.46 (dd, 3J = 3.7 Hz, 4J = 1.2 Hz, 1H)
1.71 (mc, 2H), 1.82 (mc, 2H), 3.32 (t, 2H), 3.35 (t, 2H), 3.92 (d, 2H),
5.19 (d, 3J = 17.2 Hz, 1H), 5.27 (d, 3J = 10.4 Hz, 1H), 5.67 (s, 1H), 5.82
(mc, 1H), 7.31/7.74 (AA'BB', 4H)
1.69 (mc, 2H), 1.78 (mc, 2H), 3.28 (mc, 2H), 3.33 (mc, 2H), 3.90 (d, 2H),
5.19 (dd, 3J = 10.3 Hz, 2J = 1.3 Hz, 1H), 5.25 (dd, 3J = 17.2 Hz, 2J = 1.3 Hz,
1H), 5.65 (s, 1H), 5.81 (mc, 1H), 7.21 (dd, 3J = 5.0 Hz, 4J = 3.0 Hz, 1H),
7.44 (dd, 3J = 5.0 Hz, 4J = 1.2 Hz, 1H), 7.75 (dd, 4J = 3.0 Hz, 4J = 1.2 Hz,
1H)
20.8 (t), 33.6 (t), 50.2 (t), 52.6 (t), 86.3 (d), 127.1 (d,
2C), 127.2 (d), 127.3 (d), 127.6 (d), 128.8 (d, 2C),
129.3 (d), 135.4 (s), 149.1 (s), 167.0 (s), 180.1 (s)
19.2 (t), 22.8 (t), 28.3 (t), 50.0 (t), 54.9 (t), 90.3 (t),
117.2 (t), 127.9 (d), 128.5 (d), 130.2 (d), 135.8 (s),
141.4 (s), 164.8 (s), 185.8 (s)
19.1 (t), 22.7 (t), 28.0 (t), 49.7 (t), 54.6 (t), 91.1 (t),
116.9 (t), 124.7 (d), 126.4 (d), 126.9 (d), 130.4 (t),
147.0 (s), 163.9 (s), 181.5 (s)
3f
1.69 (mc, 2H), 1.79 (mc, 2H), 3.31 (t, 2H), 3.34 (t, 2H), 3.92 (d, 2H), 5.21
(dd, 3J = 17.2 Hz, 2J = 1.3 Hz, 1H), 5.27 (dd, 3J = 10.3 Hz, 2J = 1.3 Hz, 1H),
5.70 (s, 1H), 5.83 (mc, 1H), 7.01 (dd, 3J = 4.8 Hz, 3J = 3.8 Hz, 1H), 7.36
(dd, 3J = 4.9 Hz, 4J = 0.8 Hz, 1H), 7.47 (dd, 3J = 3.8 Hz, 4J = 0.8 Hz, 1H)
1.68 (mc, 2H), 1.79 (mc, 2H), 2.44 (q, 2H), 3.29–3.42 (m, 6H), 5.08–5.16
(m, 2H), 5.66 (s, 1H), 5.81 (mc, 1H), 7.33/7.76 (AA'BB', 4H)
19.2 (t), 22.9 (t), 28.2 (t), 49.9 (t), 54.9 (t), 90.0 (d),
117.3 (t), 126.8 (d), 127.2 (d), 128.9 (d), 130.4 (d),
150.1 (s), 164.2 (s), 179.6 (s)
3g
3h
19.0 (t), 22.7 (t), 28.1 (t), 29.9 (t), 50.4 (t), 52.0 (t),
89.7 (d), 117.3 (t), 128.0 (d, 2C), 128.4 (d, 2C), 134.3
(t), 135.7 (s), 141.6 (s), 164.6 (s), 185.6 (s)
19.3 (t), 23.1 (t), 28.4 (t), 50.8 (t), 55.4 (t), 91.2 (d),
127.8 (d, 2C), 128.1 (d, 2C), 128.5 (d, 2C), 129.1 (d,
2C), 133.3 (s), 134.0 (s), 136.1 (s), 141.2 (s), 165.0 (s),
186.4 (s)
1.70 (quin, 2H), 1.80 (quin, 2H), 3.31–3.35 (m, 4H), 4.44 (s, 2H), 5.57
(s, 1H), 7.08/7.27 (AA'BB', 4H), 7.19/7.48 (AA'BB', 4H)
3i
3j
1.67 (dt, 2H), 1.76 (dt, 2H), 3.27–3.33 (m, 4H), 4.41 (s, 2H), 5.54 (s, 1H),
7.07 (d, 3H), 7.20 (dd, 3J = 5.0 Hz, 4J = 0.5 Hz, 1H), 7.25 (d, 2H), 7.49
(d, 4J = 3.0 Hz, 4J = 1.2, 1H)
1.64 (quin, 2H), 1.74 (quin, 2H), 3.26–3.31 (m, 4H), 4.40 (s, 2H), 5.58
(s, 1H), 6.85 (dd, 1H, 3J = 4.9 Hz, 3J = 3.7 Hz), 7.07/7.23 (AA'BB', 4H),
7.18 (dd, 1H, 3J = 3.8 Hz, 4J = 1.1 Hz), 7.23 (m, 1H)
19.3 (t), 23.0 (t), 28.2 (t), 50.6 (t), 55.2 (t), 92.0 (d),
125.0 (d), 126.9 (d), 127.0 (d), 127.7 (d, 2 C), 129.0 (d,
2 C), 133.1 (s), 134.2 (s), 146.8 (s), 164.2 (s), 182.0 (s)
19.1 (t), 22.9 (t), 28.1 (t), 50.6 (t), 55.2 (t), 90.7 (d),
126.9 (d), 127.3 (d), 127.7 (d, 2C), 128.9 (d, 2C),
129.2 (d), 133.0 (s), 134.1 (s), 149.7 (s), 164.2 (s),
179.7 (s)
3k
1.71 (quin, 2H), 1.78 (mc, 2H), 3.33–3.36 (m, 4H), 4.47 (s, 2H), 5.61
(s, 1H), 7.14 (d, 2H), 7.17 (t, 1H), 7.29 (t, 2H), 7.16/7.47 (AA'BB', 4H)
19.3 (t), 23.0 (t), 28.4 (t), 50.8 (t), 56.0 (t), 91.2 (d),
126.4 (d, 2C), 127.5 (d), 128.0 (d, 2C), 128.5 (d, 2C),
128.9 (d, 2C), 135.5 (s), 135.9 (s), 141.3 (s), 165.1 (s),
186.2 (s)
3l
1.63–1.68 (mc, 2H), 1.72–1.77 (mc, 2H), 3.28–3.33 (m, 4H), 4.45 (s, 2H),
5.65 (s, 1H), 6.84 (dd,3J = 5.0 Hz, 3J = 3.7 Hz, 1H), 7.16 (d, 2H), 7.17–
7.22 (m, 3H), 7.26 (t, 2H)
1.57–1.65 (m, 2H), 1.68–1.79 (m, 4H), 3.42–3.54 (m, 4H), 3.95 (mc, 2H),
5.19 (dd, 3J = 17.2 Hz, 2J = 1.3 Hz, 1H), 5.25 (dd, 3J = 10.4 Hz, 2J = 1.3 Hz,
1H), 5.59 (s, 1H), 5.83 (mc, 1H), 5.95 (s, 1H), 7.32/7.76 (AA'BB', 4H)
1.53–1.61 (m, 2H), 1.63–1.75 (m, 2H), 3.42 (mc, 2H), 3.45–3.53 (m, 2H),
3.94 (d, 2H), 5.17–5.26 (m, 2H), 5.62 (s, 1H), 5.83 (mc, 1H), 7.00 (dd,
3J = 5.0 Hz, 4J = 3.7 Hz, 1H), 7.37 (dd, 3J = 5.0 Hz, 4J = 1.1 Hz, 1H), 7.48
(dd, 3J = 3.7 Hz, 4J = 1.1 Hz, 1H)
19.2 (t), 22.9 (t), 28.1 (t), 50.6 (t), 55.9 (t), 90.7 (d),
126.3 (d, 2 C), 126.8 (d), 127.2 (d), 127.4 (d), 128.8 (d,
2C), 129.1 (d), 135.6 (s), 150.0 (s), 164.5 (s), 179.8 (s)
25.3 (t), 27.8 (2 t), 29.4 (t), 52.5 (t), 55.7 (t), 91.4 (d),
116.9 (t), 127.9 (d, 2C), 128.6 (d, 2C), 131.1 (d),
135.9 (s), 141.2 (s), 169.7 (s), 186.4 (s)
25.2 (t), 27.6 (t), 27.7 (t), 29.2 (t), 52.6 (t), 55.6 (t),
90.8 (d), 116.8 (t), 126.8 (d), 127.1 (d), 129.1 (d),
131.1 (t), 150.0 (s), 168.9 (s), 179.7 (s)
3m
3n
a) CDCl3 as solvent, 500.14 MHz, δ values in ppm. b) Solvent CDCl3, 125.77 MHz, δ values in ppm; signal multiplicities of proton-coupled spectra are given
in parentheses.
In summary, we have reported, for the first time, the
O
OTf
+
N
+
Tf2O, CH2Cl2, 0 °C
preparation of 3-trifloxypropene iminium and proypne
iminium salts with an exocyclic alkenyl or benzyl sub-
stituent at the nitrogen atom. As we will show in future
papers, the presence of such substituents in the conju-
gated iminium salts offer opportunities for novel syn-
thetic transformations.
N
N
S
slow
addition
S
S
-
TfO–
TfO
Cl
Cl
Cl
TfO
-
HOTf
–
TfO
4i
5i
3i
+
3i
O
+
N
S
This work was supported financially by the Deutsche For-
schungsgemeinschaft and the Fonds der Chemischen Indus-
trie.
Cl
-
–
TfO
TfO
6
Scheme 3
J. Prakt. Chem. 1999, 341, No. 2
123

R. Neumann et al.
FULL PAPER __________________________________________________________________________
Table 3 Synthesis, melting points, and elemental analyses of 3-trifloxypropene iminium triflates 4
Com- Reaction Temp. Yield
m.p.
(°C)
Formula
(g/mol)
Elemental Analysis
Calcd./Found
pound (°C)
(%)
C
H
N
4a
4d
4g
4h
4k
4m
– 60
– 60
– 60
– 5
85
87
91
88
92
86
71
C17H16ClF6NO6S2
(543.90)
C18H18ClF6NO6S2
(557.91)
C19H20ClF6NO6S2
(571.93)
C22H19Cl2F6NO6S2
(642.41)
C22H20ClF6NO6S2
(607.97)
37.54
37.72
38.75
38.65
39.90
39.92
41.13
41.11
43.46
43.58
39.90
2.96
2.86
3.25
3.34
3.52
3.60
2.98
3.10
3.32
3.41
3.52
2.58
2.66
2.51
2.60
2.45
2.36
2.18
2.30
2.30
2.46
2.45
72
70
122
103
102
– 5
– 60
C19H20ClF6NO6S2
(571.93)
39.85
3.45
2.36
Table 4 1H and 13C NMR data of 3-trifloxypropene iminium triflates 4
Com-
pound
1H NMR a)
13C NMR b)
4a
2.29 (quin, 2H), 3.51 (t, 2H), 4.17 (t, 2H), 4.56 (d, 2H),
5.43 (d, 3J = 10.2 Hz, 1H), 5.47 (d, 3J = 17.1 Hz, 1H), 6.91
(s, 1H), 7.55/7.73 (AA'BB', 4H)
20.0 (t), 39.0 (t), 54.7 (t), 60.6 (t), 109.8 (d), 119.1 (q, JC,F = 320.7),
122.1 (q, JC,F = 321.9 Hz), 123.1 (t), 128.9 (d), 130.5 (d, 2C), 130.7 (d,
2C), 140.2 (s), 159.3 (s), 179.3 (s)
4d
1.85–1.93 (m, 2H), 1.97–2.04 (m, 2H), 3.14 (mc, 2H), 3.89
(mc, 2H), 4.62 (d, 2H), 5.54 (d, 3J = 10.2 Hz, 1H), 5.58 (d,
17.1 Hz, 1H), 5.96 (mc, 1H), 7.08 (s, 1H), 7.58/7.75
(AA'BB', 4H)
17.4 (t), 21.1 (t), 33.8 (t), 54.1 (t), 62.4 (t), 114.8 (d), 119.2 (q, JC,F =
320.0 Hz), 122.2 (q, JC,F = 320.7 Hz), 124.7 (t), 128.5 (d), 129.8 (d, 3J =
2C), 130.0 (s), 130.5 (d, 2C), 139.4 (s), 151.9 (s), 181.9 (s)
4g
1.84–1.91 (m, 2H), 1.96–2.02 (m, 2H), 2.62 (q, 2H), 3.11
(mc, 2H), 3.92 (mc, 2H), 4.04 (t, 2H), 5.19 (dd, 3J =
10.2 Hz, 2J = 1.5 Hz, 1H), 5.26 (dd, 3J = 17.2 Hz, 2J =
1.5 Hz, 1H), 5.84 (mc, 1H), 7.02 (s, 1H), 7.59/7.75 (AA'
BB', 4H)
17.4 (t), 21.1 (t), 31.7 (t), 33.7 (t), 54.6 (t), 59.3 (t), 114.7 (d), 119.2 (q,
JC,F = 320.3 Hz), 119.9 (t), 122.0 (q, JC,F = 320.6 Hz), 129.9 (d, 2C),
130.1 (s), 130.5 (d, 2C), 133.7 (d), 139.5 (s), 152.0 (s), 181.5 (s)
4h
4k
4m
1.85–1.89 (m, 2H), 1.92–1.97 (m, 2H), 3.18–3.20 (m, 2H),
3.75–3.77 (t, 2H), 5.19 (s, 2H), 7.13 (t, 1H, 4J = 1.6 Hz),
7.44/7.48 (AA'BB', 4H), 7.59/7.75 (AA'BB', 4H)
1.86–1.97 (m, 4H), 3.21 (t, 2H), 3.76 (t, 2H), 5.22 (s, 1H),
7.19 (s, 1H), 7.44–7.48 (m, 5H), 7.58/7.75 (AA'BB', 4H)
17.4 (t), 21.2 (t), 34.1 (t), 54.5 (t), 62.4 (t), 114.8 (d), 119.1 (q), 122.1
(q), 129.9 (d, 2C), 130.4 (d, 2C), 130.5 (s), 130.5 (d, 2C), 132.2 (d, 2C),
136.2 (s) 139.6 (s), 152.3 (s), 182.8 (s, C-6') c)
17.4 (t), 21.2 (t), 34.0 (t), 54.5 (t), 63.2 (t), 114.9 (d), 120.1 (q), 121.9
(q), 129.9 (d, 2C), 130.0 (d, 2C), 130.4 (3 d), 130.5 (d, 2C), 130.7 (s),
131.7 (s), 139.5 (s), 152.2 (s), 182.3 (s)
22.5 (t), 24.4 (t), 29.4 (t), 37.4 (t), 58.3 (t), 63.6 (t), 116.2 (d), 119.2 (q,
JC,F = 320.3 Hz), 122.0 (q, JC,F = 320.1 Hz), 125.2 (t), 128.3 (d), 129.9
(d, 2 C), 130.2 (s), 130.5 (d, 2 C), 139.6 (s), 153.2 (s), 186.7 (s)
1.78–1.96 (m, 6H), 3.29 (mc, 2H), 4.15 (mc, 2H), 4.66 (d,
2H), 5.55 (dd, 3J = 10.2 Hz, 2J = 1.0 Hz, 1H), 5.62 (dd, 3J =
17.3 Hz, 2J = 1.0 Hz, 1H), 5.96 (mc, 1H), 7.30 (s, 1H),
7.58/7.79 (AA'´BB', 4 H)
a) CD3CN as solvent, 500.14 MHz, δ values in ppm. b) Solvent CD3CN, 125.77 MHz, δ values in ppm; signal multiplicities of proton-coupled spectra are given
in parentheses. c) The signal of one carbon atom was not detected.
1-(4-Chlorobenzyl)-1-piperidinone
Experimental
A solution of 2-piperidinone (14.90 g, 0.15 mol) in toluene
(60 ml) was added during 2 h to a suspension of sodium (3.40
g, 0.15 mol) in boiling toluene (300 ml), and the mixture was
kept at reflux for 4 h. After addition of 4-chlorobenzyl chlo-
ride (24.2 g, 0.15 mol) in toluene (20 ml) at 20 °C, the mix-
ture was refluxed again for 2 h. After cooling the precipitate
was removed by centrifugation, and the solution was distilled
to give the product at 143–148 °C/0.02 mbar as a colorless
liquid; yield 22.15 g (66%). – IR (film): ν/cm–1= 3083 (w),
3045 (m), 2946 (vs), 2865 (s), 1644 (vs), 1491 (vs), 1466 (s),
1446 (s), 1410 (s), 1350 (vs), 1284 (s), 1174 (s), 1090 (vs),
The NMR spectra were taken on Bruker AMX 500 and AC
200 instruments. As the internal reference, Me4Si was used
for the proton spectra, and the solvent signal for the 13C NMR
spectra [δ (CDCl3) = 77.0 ppm, δ (CD3CN) = 1.3 ppm]. IR
spectra were recorded on a Perkin Elmer IR 883 spectrome-
ter. Microanalyses were carried out with analyzer systems
Elementar Vario E1 and Heraeus CHN rapid. Melting points
were determined in an apparatus after Dr. Tottoli (Buechi)
and are not calibrated. Solvents were dried by established
procedures. Triflic anhydride was distilled from phosphorus
pentoxide prior to use. Column chromatography was per-
formed under hydrostatic conditions (silica gel 60, Macherey-
Nagel, 70–230 mesh). Dimethylaminomethyl-polystyrene was
heated at 90 °C for 5 days to remove water. All reactions
were carried out in oven-dried glassware and under argon.
Lactams 1a,b,d,e,f,m,n [9], 1g [10,11], and 1c,j–l [12, 13]
were prepared by literature procedures.
1
1015 (s). – H NMR (CDCl3, 200.13 MHz): δ/ppm = 1.70–
1.84 (m, 4H), 2.40–2.44 (m, 2H), 3.14–3.18 (m, 2H), 4.54
(s, 2H), 7.19/7.22 (AA'BB', 4H). – 13C NMR (CDCl3, 50.32
MHz): δ/ppm = 20.6 (t), 22.6 (t), 31.9 (t), 46.9 (t), 48.9 (t),
128.1, 128.9, 132.5 (s), 135.5 (s), 169.3 (s).
C12H14ClNO
(223.70)
calcd.: C 64.43 H 6.31 N 6.26
found: C 64.10 H 6.56 N 6.32.
124
J. Prakt. Chem. 1999, 341, No. 2

3-Trifloxypropene Iminium and Propyne Iminium Salts
_____________________________________________________________________________ FULL PAPER
Table 5 Synthesis, yields, melting points, and elemental analyses of propyne iminium salts 5
Com-
pound
Reaction
Conditions
(°C/h)
Yield
(%)
m.p.
(°C)
Formula
(g/mol)
Elemental Analysis
Calcd./Found
C
H
N
5a
5b
5c
5d
5e
5f
120/5
85 a)
77 b)
54 b)
88 a)
69 b)
80 b)
93 a)
93 a)
58 b)
57 b)
91 a) c)
61 b)
84 a)
80 b)
79
C16H15ClF3NO3S
(393.81)
C14H14F3NO3S2
(365.38)
C18H16F3NO3S2
(415.46)
C17H17ClF3NO3S
(407.84)
C15H16F3NO3S2
(379.41)
C15H16F3NO3S2
(379.41)
C18H19ClF3NO3S
(421.86)
C21H18Cl2F3NO3S
(492.34)
C19H17ClF3NO3S2
(463.92)
C19H17ClF3NO3S2
(463.92)
C21H19ClF3NO3S
(457.89)
C19H18F3NO3S2
(429.47)
48.80
48.90
46.02
45.70
52.03
52.07
50.07
49.93
47.49
47.52
47.49
47.21
51.25
51.40
51.23
51.11
49.19
48.90
49.19
49.11
55.09
54.83
53.14
52.94
51.25
51.16
48.85
48.76
3.84
3.78
3.86
3.94
3.88
3.89
4.20
4.20
4.25
4.25
4.25
4.45
4.54
4.62
3.68
3.73
3.69
3.78
3.69
3.64
4.18
4.21
4.22
4.25
4.54
4.62
4.61
4.69
3.56
3.59
3.83
3.72
3.37
3.44
3.43
3.45
3.69
3.79
3.69
3.64
3.32
3.36
2.84
3.06
3.02
3.09
3.02
3.06
3.06
2.96
3.26
3.58
3.32
3.43
3.56
3.54
60/0.25
–10/0.5
120/1
68
101
122
–60/0.5
60/0.25
120/0.5
120/2.5
–15/0.5
–15/0.5
120/2.5
–15/0.5
120/1
76
58
5g
5h
5i
109
114
105–107
112
5j
5k
5l
103–105
110–111
88
5m
5n
C18H19ClF3NO3S
(421.86)
C16H18F3NO3S2
(393.44)
–60/0.5
79
a) Yields are based on salts 4. b) Yields are based on enaminoketones 3. c) A similar yield was obtained by bulb-to-bulb distillation (170 °C, 0.002 mbar, 8 min).
Synthesis of Enaminoketones 3
1-Allyl-5-{2-(4-chlorophenyl)-2-[(trifluoromethyl)sulfonyl-
oxy]-1-ethenyl}-3,4-dihydro-2H-pyrrolium Trifluorometh-
anesulfonate (4a)
The following procedure, carried out in analogy to a pub-
lished method [8], is typical. For yields and physical data, see
Table 1; for NMR data, see Table 2.
A solution of enaminoketone 3a (8.60 g, 35.6 mmol) in CH2Cl2
(50 ml) was added dropwise to a cooled (–60 °C) solution of
triflic anhydride [15] (6.50 ml, 39.6 mmol) in CH2Cl2 (100
ml). After stirring for 30 min, the red-brown solution was
concentrated by partial evaporation of the solvent in vacuo.
Addition of diethyl ether yielded 4a as a pale-yellow solid,
which was purified further by redissolving in CH2Cl2 and
precipitation with diethyl ether as a colorless powder; yield
16.46 g (85%). – IR (KBr): ν/cm–1 = 3098 (w), 3044 (w),
1643 (s), 1593 (m), 1431 (s), 1376 (m), 1282 (s), 1254 (vs),
1228 (s), 1163 (m), 1094 (m), 1031 (s), 1017 (m), 991 (m).
2-(1-Allyltetrahydro-1H-2-pyrrolylidene)-1-(4-chlorophe-
nyl)-1-ethanone (3a)
A two-phase mixture of 1-allylpyrrolidin-2-one (1a) (25.2 g,
0.20 mol) and of dimethyl sulfate (26.5 g, 0.21 mol) was heated
at 80 °C for 12 h. After cooling, the homogeneous oil was
washed with ether (50 ml), and residual solvent was removed
in vacuo. The residue was slowly added to a solution of NaOEt
[from sodium (9.2 g) in ethanol (200 ml)]. After
2 h, the precipitate was filtered off with suction under argon,
the solvent was evaporated, and the residue was destilled at
82 °C/10 mbar to give 1-allyl-2,2-diethoxypyrrolidine (2a,
yield 31.9 g, 0.16 mol), which was used immediately. A mix-
ture of this acetal (31.9 g, 0.16 mol) and of 4-chloroacetophe-
none (27.3 g, 0.175 mol) was heated at 80 °C for 8 h. The sol-
vent was removed in vacuo, and from the remaining dark oil,
3a was obtained as a yellow powder by crystallization with
CH2Cl2-petroleum ether (b.p. 40–60 °C). – IR (KBr):
ν/cm–1 = 3051 (w), 2963 (w), 1612 (s), 1581 (s), 1551 (s),
1482 (m), 1417 (m), 1352 (m), 1297 (m), 1217 (m), 1176
(m), 1109 (m), 1091 (m), 1009 (m).
Synthesis of Propyne Iminium Triflates 5a,d,g,h,m
The following procedure is typical. For yields and physical
data, see Table 5; for NMR data, see Table 6.
1-Allyl-5-[2-(4-chlorophenyl)-1-ethynyl]-3,4-dihydro-2H-
pyrrolium Trifluoromethanesulfonate (5a)
A solution of 4a (5.4 g, 10 mmol) in CH3CN (15 ml) was
placed in a thick-walled Schlenk tube; the tube was closed
and immersed in an oil bath. The solution was heated with
stirring at 120 °C for 5 h. After concentration of the solution
to half its volume and cooling at –30 °C, the product was
precipitated by addition of diethyl ether. The supernatant so-
lution was decanted, and the solid residue was washed with
diethyl ether (3 × 50 ml) to afford 5a as orange-yellow crys-
Synthesis of 3-Trifloxypropene Iminium Triflates 4
The following procedure is typical. For yields and physical
data, see Table 3; for NMR data, see Table 4.
J. Prakt. Chem. 1999, 341, No. 2
125

R. Neumann et al.
FULL PAPER __________________________________________________________________________
1
Table 6 H and 13C NMR data of propyne iminium triflates 5a–n
Com-
pound
1H NMR a)
13C NMR b)
5a
2.37 (quin, 2H), 3.39 (t, 2H), 4.22 (t, 2H), 4.66 (d, 2H),
5.51 (dd, 3J = 10.2 Hz, 2J = 1.0 Hz, 1H), 5.57 ( dd, 3J =
17.1 Hz, 2J = 1.0 Hz, 1H), 5.98 (mc, 1H), 7.56/7.78 (AA'
BB', 4H)
20.1 (t), 40.9 (t), 56.1 (t), 59.7 (t), 79.5 (s), 116.7 (s), 117.7 (s), 122.2
(q, JC,F = 321.1 Hz), 123.7 (t), 128.9 (d), 130.7 (d, 2C), 136.3 (d, 2C),
140.3 (s), 169.4 (s)
5b
2.35 (quin, 2H), 3.35 (t, 2H), 4.18 (t, 2H), 4.59 (d, 2H),
5.49 (dd, 3J = 10.2 Hz, 2J = 1.0 Hz, 1H), 5.55 (dd, 3J = 17.1
Hz, 2J = 1.0 Hz, 1H), 5.97 (mc, 1H), 7.28 (dd, 3J = 5.0 Hz,
3J = 3.8 Hz, 1H), 7.86 (dd, 3J = 3.8 Hz, 4J = 1.2 Hz, 1H),
7.99 (dd, 3J = 5.0 Hz, 4J = 1.2 Hz, 1H)
20.3 ( t), 40.6 (t), 55.8 (t), 59.5 (t), 84.2 (s), 112.9 (s), 118.4 (s), 123.5
(t), 129.1 (d), 130.2 (d), 138.4 (d), 141.7 (d), 168.5 (s) c)
5c
2.27 (quin, 2H), 3.36 (t, 2H), 4.07 (t, 2H), 5.17 (s, 2H),
7.28 (dd, 3J = 5.0 Hz, 3J = 3.9 Hz, 1H), 7.46 (m, 5H), 7.88
(dd, 3J = 3.9 Hz, 4J = 1.0 Hz, 1H), 7.99 (dd, 3J = 5.0 Hz,
4J = 0.6 Hz, 1H)
20.2 (t), 40.6 (t), 57.2 (t), 59.4 (t), 84.5 (s), 113.3 (s), 118.0 (s), 122.1
(q, JC,F = 320.3 Hz), 130.2 (d), 130.3 (4 d), 130.5 (d), 132.3 (s), 138.6
(d), 141.9 (d), 168.6 (s)
5d
5e
1.83–1.90 (m, 2H), 1.97–2.04 (m, 2H), 3.10 (mc, 2H),
3.83 (mc, 2H), 4.74 (d, 2H), 5.49–5.59 (m, 2H), 6.01
(mc, 1H), 7.55/7.73 (AA'BB', 4H)
17.4 (t), 21.3 (t), 35.0 (t), 53.2 (t), 63.1 (t), 83.3 (s), 113.7 (s), 117.9 (s),
121.8 (q, JC,F = 320.3 Hz), 123.3 (t), 129.2 (d), 130.6 (d, 2C), 136.1 (d,
2 C), 139.9 (s), 167.9 (s)
1.80–2.04 (m, 4H), 3.06 (mc, 2H), 3.80 (mc, 2H), 4.69
(d, 2H), 5.47–5.57 (m, 2H), 5.99 (mc, 1H), 7.39 (dd,
3J = 5.1 Hz, 4J = 1.1 Hz, 1H), 7.60 (dd, 3J = 5.1 Hz, 4J =
2.9 Hz, 1H), 8.23 (dd, 4J = 2.9 Hz, 4J = 1.1 Hz, 1H)
1.81–1.87 (m, 2H), 1.92–2.02 (m, 2H), 3.06 (mc, 2H),
3.80 (mc, 2H), 4.66 (d, 2H), 5.47–5.56 (m, 2H), 5.99
(mc, 1H), 7.26 (dd, 3J = 5.1 Hz, 3J = 3.8 Hz, 1H), 7.81
(dd, 3J = 5.1 Hz, 4J = 1.2 Hz, 1H), 7.95 (dd, 3J = 3.8 Hz,
4J = 1.2 Hz, 1H)
17.5 (t), 21.3 (t), 34.9 (t), 53.0 (t), 62.8 (t), 83.2 (s), 111.2 (s), 118.5 (s),
123.2 (t), 129.1 (d), 129.3 (d), 131.1 (d), 139.4 (d), 167.8 (s) c)
5f
18.1 (t), 22.0 (t), 35.2 (t), 53.6 (t), 63.5 (t), 88.3 (s), 110.5 (s), 119.1 (s),
122.8 (q, JC,F = 321.2 Hz), 123.7 (t), 129.9 (d), 130.7 (d), 138.3 (d),
141.7 (s), 167.7 (s)
5g
1.77–1.86 (m, 2H), 1.90–2.00 (m, 2H), 2.63 (q, 2H),
3.05 (mc, 2H), 3.83 (mc, 2H), 4.15 (t, 2H), 5.16 (d, 3J =
10.2 Hz, 1H), 5.23 (d, 3J = 17.1 Hz, 1H), 5.87 (mc, 1H),
7.55/7.71 (AA'BB', 4 H)
17.4 (t), 21.2 (t), 32.2 (t), 34.8 (t), 53.6 (t), 60.3 (t), 83.3 (s), 113.6 (s),
118.0 (s), 119.6 (t), 130.6 (d, 2C), 134.0 (d), 136.0 (d, 2C), 139.9 (s),
167.5 (s), c)
5h
5i
1.82–1.85 (m, 2H), 1.90–1.95 (m, 2H), 3.15 (t, 2H),
3.71–3.74 (m, 2H), 5.31 (s, 2H), 7.47 (s, br, 4H),
7.54/7.73 (AA'BB', 4H)
1.80–1.85 (m, 2H), 1.90–1.94 (m, 2H), 3.12 (t, 2H),
3.71 (m, 2H), 5.28 (s, 2H), 7.39 (dd, 1H), 7.45–7.49
(m, 4H), 7.59 (dd, 1H), 8.23 (dd, 1H)
17.4 (t), 21.3 (t), 35.4 (t), 53.1 (t), 63.3 (t), 83.7 (s), 114.3 (s), 117.8 (s),
122.2 (q), 130.3 (d, 2C), 130.6 (d, 2C), 131.4 (s), 131.8 (d, 2C), 135.9
(s), 136.2 (d, 2C), 140.2 (s), 168.6 (s)
17.5 (t), 21.3 (t), 35.2 (t), 53.0 (t), 63.1 (t), 83.7 (s), 111.9 (s), 118.3 (s),
122.2 (q), 129.2 (d), 130.3 (d, 2C), 131.1 (d), 131.6 (s), 131.8 (d, 2C),
136.0 (s), 139.8 (d), 168.5 (s)
5j
1.81–1.85 (m, 2H), 1.90–1.94 (m, 2H), 3.12 (t, 2H),
3.73 (t, 2H), 5.25 (s, 2H), 7.24 (dd, 3J = 5.1 Hz, 3J =
3.8 Hz, 1H), 7.46 (s, br, 4H), 7.80 (dd, 3J = 3.8 Hz, 4J =
1.1 Hz, 1H), 7.94 (dd, 3J = 5.1 Hz, 4J = 1.1 Hz, 1H)
1.82–1.87 (m, 2H), 1.91–1.95 (m, 2H), 3.17 (t, 2H),
3.75 (m, 2H), 5.36 (s, 2H), 7.42–7.50 (m, 5H). 7.51/7.72
(AA'BB', 4H)
1.81–1.86 (m, 2H), 1.91–1.96 (m, 2H), 3.12 (t, 2H), 3.75
(t, 2H), 5.28 (s, 2H), 7.25 (dd, 3J = 5.1 Hz, 3J = 3.8 Hz,
1H), 7.45–7.48 (m, 5H), 7.81 (dd, 3J = 3.8 Hz, 4J = 0.9 Hz,
1H), 7.94 (dd, 3J = 5.1 Hz, 4J = 0.9 Hz, 1H)
17.5 (t), 21.4 (t), 34.9 (t), 53.1 (t), 63.1 (t), 88.2 (s), 110.6 (s), 118.3 (s),
122.2 (q), 130.1 (d), 130.3 (d, 2C), 131.7 (d, 2C), 131.7 (s), 135.8 (s),
138.1 (d), 141.4 (d), 167.8 (s)
5k
5l
17.5 (t), 21.3 (t), 35.3 (t), 53.1 (t), 64.1 (t), 83.8 (s), 113.8 (s), 117.8 (s),
122.2 (q), 129.9 (d, 2C), 130.3 (d, 2C), 130.4 (d), 130.5 (d, 2C), 132.6
(s), 136.1 (d, 2C), 139.9 (s) 168.2 (s)
17.5 (t), 21.4 (t), 34.8 (t), 53.0 (t), 63.9 (t), 88.2 (s), 110.2 (s), 118.3 (s),
122.2 (q), 129.9 (d, 2C), 130.1 (d), 130.3 (d, 2C), 130.4 (d), 132.9 (s),
138.0 (d), 141.3 (d), 167.4 (s)
5m
5n
1.73–1.91 (m, 6H), 3.23 (mc, 2H), 4.08 (mc, 2H), 4.78
(d, 2H), 5.50 (d, 3J = 10.3 Hz, 1H), 5.57 (d, 3J = 17.0 Hz,
1H), 5.98 (mc, 1H), 7.53/7.74 (AA'BB', 4H)
1.58–1.88 (m, 6H), 3.18 (mc, 2H); 4.05 (mc, 2H), 4.71
(d, 2H), 5.47 (dd, 3J = 10.2 Hz, 2J = 0.9 Hz, 1H), 5.54
(dd, 3J = 17.1 Hz, 2J = 1.0 Hz, 1H), 5.95 (mc, 1H), 7.26
(dd, 3J = 5.0 Hz, 3J = 3.8 Hz, 1H), 7.85 (dd, 3J = 3.8 Hz,
4J = 1.1 Hz, 1H), 8.00 (dd, 3J = 5.0 Hz, 4J = 1.1 Hz, 1H)
22.5 (t), 24.8 (t), 29.5 (t), 38.7 (t), 57.4 (t), 64.6 (t), 85.4 (s), 117.0 (s),
117.9 (s), 122.2 (q, JC,F = 320.7 Hz), 123.9 (t), 129.0 (d), 130.6 (d, 2C),
136.4 (d, 2C), 140.3 (s), 172.5 (s)
22.8 (t), 25.0 (t), 29.6 (t), 38.3 (t), 57.2 (t), 64.3 (t), 90.1 (s), 113.2 (s),
118.6 (s), 123.6 (t), 129.2 (d), 130.3 (d), 138.8 (d), 141.9 (s), 171.4 (s) c)
a) CD3CN as solvent, 500.14 MHz, δ values in ppm. b) Solvent CD3CN, 125.77 MHz, δ values in ppm; signal multiplicities of proton-coupled spectra are given
in parentheses. c) CF3SO3– not found.
tals; yield 3.11 g (79%). – IR (KBr): ν/cm–1 = 3060 (w), 2968
(w), 2207 (s), 1648 (s), 1586 (s) 1461 (m), 1387 (s), 1276
(vs), 1174 (s), 1100 (m), 1090 (s), 1030 (vs).
(–60 °C) solution of triflic anhydride (5.54 ml, 33 mmol) in
CH2Cl2 (100 ml). After removing the solvent in vacuo, the
dark oil was dissolved in CH3CN and placed in a thick-walled
Schlenk tube. After 15 minutes at 60 °C, the elimination of
HOTf was complete. The solution was concentrated to half
its volume, and diethyl ether was added. After stirring at
0 °C, 5b could be isolated as a dark solid which was triturated
with diethyl ether (3×50 ml), then dissolved in CH3CN and
precipitated with diethyl ether to give a yellow powder; yield
8.44 g (77%). – IR (KBr): ν/cm–1 = 3071 (w), 2189 (s), 1628
Synthesis of Propyne Iminium Triflates 5b,f
1-Allyl-5-[2-(2-thienyl)-1-ethynyl]-3,4-dihydro-2H-pyrro-
lium Trifluoromethanesulfonate (5b); Typical Procedure
A solution of enaminoketone 3b (7.0 g, 30 mmol) in CH2Cl2
(50 ml) was added dropwise during 20 min to a cooled
126
J. Prakt. Chem. 1999, 341, No. 2

3-Trifloxypropene Iminium and Propyne Iminium Salts
_____________________________________________________________________________ FULL PAPER
[4] M. Reißer, G. Maas, Synthesis 1998, 1129
[5] G. Maas, B. Singer, P. Wald, M. Gimmy, Chem. Ber. 1988,
121, 1847
(m), 1508 (m), 1439 (m), 1321 (m), 1260 (s), 1222 (m), 1150
(m), 1048 (m), 1030 (s). See Table 6 for NMR data.
[6] R. Rahm, G. Maas, Synthesis 1994, 295
[7] R. Reinhard, G. Maas, J. Bohrisch, J. Liebscher, Liebigs Ann.
Chem. 1994, 429
Synthesis of Propyne Iminium Triflates 5c,e,i,j,l
1-Benzyl-5-[2-(2-thienyl)-1-ethynyl]-3,4-dihydro-2H-pyrro-
lium Trifluoromethanesulfonate (5c); Typical Procedure
[8] V. Virmani, M. B. Nigam, P. C. Jain, N. Anand, Indian J.
Chem. 1979, 17B, 472
A solution of enaminoketone 3c (8.5 g, 30 mmol) in CH2Cl2
(60 ml) was added dropwise to a cooled (–10 °C) solution of
triflic anhydride (5.54 ml, 33 mmol) in CH2Cl2 (100 ml). After
stirring at room temperature for 1 h, the solvent was removed
in vacuo. The brown solution was concentrated to half its
volume, and diethyl ether was added. After stirring at 0 °C,
5c was isolated as a dark solid, triturated with diethyl ether
(3×50 ml), dissolved in CH3CN and precipitated with die-
thyl ether to give a yellow solid; yield 6.73 g (54%). –
IR (KBr): ν/cm–1 = 3075 (w), 2186 (s), 1631 (m), 1260 (s),
1148 (s, sh), 1029 (s). See Table 6 for NMR data.
[9] N. G. Vepkhishvili, L. M. Khananashvili, D. Sh. Akhobadze,
Z. Sh. Lomtatidze, N. G. Makhoradze, N. G. Giorgobiani,
Pharm. Chem. J. (Engl. Transl.) 1991, 25, 548
[10] A. G. Shipov, Y. I. Bankov, J. Gen. Chem. USSR (Engl.
Transl.) 1991, 61, 1875
[11] S. F. Martin, C. P. Yang, W. L. Lasell, H. Rueeger, Tetrahed-
ron Lett. 1985, 51, 6685
[12] S. Sugasawa; T. Fujii, Chem. Pharm. Bull. 1958, 6, 587
[13] C. Raeth, Justus Liebigs Ann. Chem. 1931, 489, 107
[14] D. Lin-Vien, N. B. Colthup, W. G. Fately, J. G. Grasselli,
Infrared and Raman Characteristic Frequencies of Organic
Molecules, Academic Press, Boston 1991, p. 244
[15] P. J. Stang, T. Dueber, Org. Synth. 1974, 54, 79
Address for correspondence:
Prof. Dr. G. Maas
Abteilung Organische Chemie I
Universität Ulm
Albert-Einstein-Allee 11
D-89081 Ulm
FAX: Internat. code (0)731 502 2803
e-mail: gerhard.maas@chemie.uni-ulm.de
References
[1] T. Mayer, G. Maas, Synlett 1990, 399; G. Maas, T. Mayer,
Synthesis 1991, 1209
[2] G. Maas, R. Reinhard, R. Neumann, M. Glaser, J. prakt.
Chem. 1996, 338, 441
[3] M. Brunner, G. Maas, Synthesis 1995, 957
J. Prakt. Chem. 1999, 341, No. 2
127