One-pot preparation of ternary and quaternary iminium salts from aldehydes and ketones

Article abstract of DOI:10.3184/030823408X338387

A facile, high-yielding, one-step procedure is described for the preparation of a wide range of stable iminium salts by direct combination of an aldehyde or a ketone with a secondary free amine in the presence of an ammonium salt. The broad scope of the method is illustrated by the preparation of iminium ions derived from aldehydes, cyclic/ acyclic ketones, and cyclic/acyclic secondary amines.

Full text of DOI:10.3184/030823408X338387

JOURNAL OF CHEMICAL RESEARCH 2008
JUNE, 301–304
RESEARCH PAPER 301
One-pot preparation of ternary and quaternary iminium salts from
aldehydes and ketones
Shahrokh Saba*, Diane Vrkic, Clair Cascella, Ida DaSilva, Kristine Carta and Adeline Kojtari
Department of Chemistry, Fordham University, Bronx, NY 10458, USA
A facile, high-yielding, one-step procedure is described for the preparation of a wide range of stable iminium salts
by direct combination of an aldehyde or a ketone with a secondary free amine in the presence of an ammonium
salt. The broad scope of the method is illustrated by the preparation of iminium ions derived from aldehydes, cyclic/
acyclic ketones, and cyclic/acyclic secondary amines.
Keywords: iminium salts, aldehydes, ketones, ammonium salts, amine salt
R2
Previously, we reported a convenient one-pot procedure for
the preparation of cyclic amidinium salts from orthoesters,
primary or secondary a,w-diamines and ammonium
tetrafluoroborate or ammonium hexafluorophosphate. The
resulting amidinium salts 1, 2 and 3 were isolated in high
yields and contained counterions with low nucleophilicity
(Scheme 1).1
R1
R1
R1
R1
NH
HN
N
N
A
+
R2C(OR)3
+
NH4
A
+
( )n
( )n
1 n = 0 A = BF4, PF6
2 n = 1
In the course of a related study on the preparation of acyclic
amidinium salts2 by application of the above procedure,
we observed that treatment of primary or secondary
monoamine free bases with ammonium tetrafluoroborate or
hexafluorophosphate in refluxing toluene afforded nearly
quantitative yields of 1° and 2° amine tetrafluoroborate and
hexafluorophosphate salts within about 0.5 h. These findings
led us to envision that synthetic transformations in which amine
salts are requisite starting materials may well be accomplished
using the corresponding amine free bases along with an
added ammonium salt. Therefore, we decided to explore the
preparation of iminium salts 4 by a direct, one-step procedure:
heating a mixture of an aldehyde or a ketone with a 2° free
amine in the presence of an ammonium salt (Scheme 2). The
iminium function, [R2C=NR2]+, is of enormous importance
in organic chemistry3-6 and preformed iminium salts 4 have
been extensively used in various synthetic applications within
the last three decades. In contrast to the existing methods
that frequently start with an aldehyde or ketone derivative or
require initial treatment of an amine with an acid and isolation
of the formed salt in a previous step,7 the procedure described
here involves direct treatment of these compounds in the
presence of an ammonium salt.
3 n = 2
Scheme 1
iminium salts. A wide range of iminium salts was prepared
and isolated in very high yields by this method (Table 1). This
reaction worked well with substrates containing acid labile
acetal groups (entries 4d and 4m) and was unaffected by the
counterions (entries 4e and 4f; 4s and 4t; 4u and 4v; 4y and
4z; 4aa, 4bb and 4cc).
All products were characterised by their H and 13C NMR
1
spectra. The most diagnostic absorption in the 13C NMR
spectra of the salts prepared is a downfield signal representing
the alkylidene carbon. For aliphatic ketones and aromatic
aldehydes, this absorption appears in the range d 184–201 and
d 161–166, respectively.
Although we have not investigated the detailed mechanism
of this reaction, it is most likely driven by initial proton transfer
from the ammonium ion to the secondary amine free base
with release of ammonia, leading to the secondary amine salt.
Proton transfer from the secondary amine salt to the carbonyl
oxygen and subsequent condensation affords iminium salts 4.
An alternative plausible mechanism involves initial formation
of an enamine intermediate that, upon protonation by the
ammonium ion, may yield the iminium species. To ascertain
the possible involvement of enamines, several enamines were
treated with ammonium salts. All attempts failed to afford
the corresponding iminium salts and led to dark intractable
materials. The likelihood of an enamine intermediate is further
lessened since nonenolisable aromatic aldehydes, unable to
form enamine intermediates, yielded iminium salts by direct
combination with a secondary amine and an ammonium salt,
as described here.
Herein we report the preparation and characterisation of
a series of ternary and quaternary iminium perchlorates,
tetrafluoroborates and hexafluorophosphates by this one-step
procedure.
Results and discussion
Typically, to prepare compound 4, a mixture of an aldehyde
or a ketone (5), a secondary amine (6) and an ammonium
salt (7) was heated in toluene or benzene in a Dean–Stark
apparatus. After cooling the mixture, the product precipitated
and was separated by suction filtration, affording nearly pure
R3
R1
R3
R1
R2
toluene/benzene
+
O
+
A
reflux
+
NH3 + H2O
HN
NH4
+
A
N
+
R2
R4
R4
5
6
4
7
Scheme 2
* Correspondent. E-mail: saba@fordham.edu

302 JOURNAL OF CHEMICAL RESEARCH 2008
Table 1 One-pot preparation of iminium salts (4)
Entry
R1
R2
R3
R4
A–
Yield/%a
Solvent
Reaction time/h
–
4a
4b
4c
4-MeOC6H4
4-Me2NC6H4
1-naphthyl
O
H
H
H
–(CH2)4-
–(CH2)4-
–(CH2)4-
PF6–
PF6–
PF6
88
90
81
Benzene
Benzene
Benzene
3
3
3
–
4d
4e
H
–(CH2)4-
–(CH2)4-
PF6
84
89
Benzene
Toluene
2
O
–
HC
CH
PF6
0.75
–
HC
HC
HC
CH
CH
CH
4f
–(CH2)4-
BF4
92
Toluene
0.75
–
4g
4h
–(CH2)6-
ClO4
88
75
Toluene
Toluene
0.75
3
–
–(CH2)3CH(CH3)CH2-
PF6
CH2
CH2
CH2
–
HC
4i
4j
–(CH2)3CH(CH3)CH2-
–(CH2)4-
PF6
87
91
Toluene
Toluene
3
2
HC
HC
–
PF6
–
4k
4l
–(CH2)6-
–(CH2)4-
ClO4
90
78
Toluene
Toluene
1.75
2.75
–
–CH2CH(CH3)(CH2)3–
PF6
O
(CH2)2-
–
4m
–(CH2)4-
PF6
92
Toluene
2
(CH2)2-
O
–
4n
4o
4p
4q
4r
Me
Et
Me
Et
–(CH2)4-
–(CH2)4-
–(CH2)4-
ClO4–
88
89
89
89
94
88
90
91
93
91
92
91
88
90
87
90
80
Benzene
Toluene
Toluene
Benzene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Benzene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
0.25
2.75
0.75
2
ClO4
–
–(CH2)4-
PF6
–
–(CH2)4-
–(CH2)4-
–(CH2)4-
–(CH2)4-
–(CH2)4-
–(CH2)4-
–(CH2)4-
–(CH2)4-
–(CH2)5-
–(CH2)5-
–(CH2)6-
–(CH2)6-
–(CH2)6-
–(CH2)6-
Et
Pr
Et
Pr
ClO4–
ClO4–
ClO4
3
4s
–(CH2)4-
–(CH2)4-
1
–
4t
4u
4v
4w
4x
4y
4z
4aa
4bb
4cc
4dd
BF4–
0.75
1.5
1.5
0.75
2.5
1.5
0.5
1.5
0.5
1.5
4
–(CH2)5-
PF6
–
–(CH2)5-
ClO4–
–(CH2)6-
ClO4
–
–(CH2)3CH(CH3)CH2-
–(CH2)4-
PF6–
PF6
–
–(CH2)4-
ClO4
–
–(CH2)4-
BF4
–
–(CH2)4-
ClO4
–
–(CH2)4-
PF6
–
–(CH2)6-
ClO4
aIsolated yields.
General procedure for one-pot preparation of iminium salts (4a–4dd)
To a solution of an aldehyde or a ketone (13 mmol) and a 2° amine
(13 mmol) in benzene or toluene (20 ml) was added an ammonium
salt (10 mmol). The magnetically stirred mixture was heated at reflux
with continuous removal of the water formed (Dean–Stark trap).
The mixture was then cooled in an ice-water bath and the precipitated
product was collected by suction filtration, washed with ether
(3¥10 ml), and air dried. Alternatively, the separated oily product
was rapidly stirred while cooling until it solidified prior to isolation
by suction filtration. The product was crystallised using the solvent
system below.
Other ammonium salts such as ammonium triflate also afforded
the corresponding iminium salts, but we report here a sampling
of those that could easily be purified by crystallisation, affording
nonhygroscopic crystalline products. In conclusion, a one-pot
high-yielding, facile, and direct procedure for the preparation
of iminium salts was developed using commercially available
and inexpensive bulk chemicals.
Experimental
All solvents and reagents were obtained from commercial suppliers
and were used without further purification. Benzene and toluene
which are used as solvents in this work are both flammable and toxic
with benzene being a carcinogen. Melting points are uncorrected and
were determined using a Mel-Temp capillary melting point apparatus.
1H (300 MHz) and 13C (75 MHz) NMR spectra were recorded on
a Bruker Avance DPX 300 spectrometer in DMSO-d6 with TMS as
the internal standard. Chemical shifts are reported in ppm (d) and
J values are in Hz. Elemental analyses were performed by Quantitative
Technologies Inc., Whitehouse, NJ, USA.
1-(4-Methoxybenzylidene)pyrrolidinium hexafluorophosphate (4a):
Pale yellow plates (ethanol–acetonitrile), m.p. 146–147°C. 1H NMR
(300 MHz, DMSO-d6): d 1.99–2.08 (m, 2H), 2.14–2.23 (m, 2H),
3.95 (s, 3H, OCH3), 4.17–4.25 (m, 4H, NCH2), 7.29 (d, J = 9.0 Hz,
2H, ArH), 8.04 (d, J = 9.0 Hz, 2H, ArH), 9.09 (s, 1H, N=CH). 13
C
NMR (75 MHz, DMSO-d6): d 23.2, 25.4, 53.1, 56.2, 59.5, 115.5,
120.3, 136.7, 164.7, 165.6. Anal. Calcd for C12H16F6NOP: C, 42.99;
H, 4.81, N, 4.18. Found: C, 43.1; H, 4.8; N, 4.2%.

JOURNAL OF CHEMICAL RESEARCH 2008 303
1-(4-Dimethylaminobenzylidene)pyrrolidinium hexafluorophosphate
(4b): Orange needles (ethanol–acetonitrile), m.p. 169–171°C. 1H NMR
(300 MHz, DMSO-d6): d 1.93-2.02 (m, 2H), 2.11-2.20 (m, 2H), 3.16
(s, 6H, NCH3), 4.01-4.11 (m, 4H, NCH2), 6.93 (d, J = 9.2 Hz, 2H,
ArH), 7.82 (d, J = 9.2 Hz, 2H, ArH), 8.67 (s, 1H, N=CH). 13C NMR
(75 MHz, DMSO-d6): d 23.4, 25.6, 39.7, 52.1, 58.3, 112.1, 113.8,
136.5, 154.9, 161.2. Anal. Calcd for C13H19F6N2P: C, 44.83; H, 5.50;
N, 8.04. Found: C, 44.5; H, 5.3; N, 7.9%.
1-(Naphthalen-1-ylmethylene)pyrrolidinium hexafluorophosphate
(4c): Yellow prisms (precipitation by addition of anhydrous ether
from methylene chloride-acetonitrile solution), m.p. 206–208°C. 1H
NMR (300 MHz, DMSO-d6): d 2.11–2.18 (m, 4H), 4.27 (bs, 2H,
NCH2), 4.47–4.51 (m, 2H, NCH2), 7.73–8.42 (m, 7H, ArH), 10.06
(s, 1H, N=CH). 13C NMR (75 MHz, DMSO-d6): d 22.9, 24.7, 54.3,
59.2, 124.0, 124.7, 125.2, 127.5, 128.6, 129.2, 130.3, 131.2, 132.9,
135.7, 166.8. Anal. Calcd for C15H16F6NP: C, 50.71; H, 4.54; N,
3.94. Found: C, 50.5; H, 4.4; N, 4.0%.
1-(1,3-Benzodioxol-5-ylmethylene)pyrrolidinium hexafluorophosphate
(4d): Pale yellow prisms (ethanol–acetonitrile), m.p. 169–172°C.
1H NMR (300 MHz, DMSO-d6): d 1.98–2.20 (m, 4H), 4.18–4.24
(m, 4H, NCH2), 6.30 (s, 2H, OCH2), 7.32 (d, J = 8.2 Hz, 1H, ArH),
7.62–7.67 (m, 2H, ArH), 9.04 (s, 1H, N=CH). 13C NMR (75 MHz,
DMSO-d6): d 23.2, 25.3, 53.1, 59.6, 103.4, 109.5, 110.3, 121.7,
134.2, 148.8, 154.4, 164.9. Anal. Calcd for C12H14F6NO2P: C, 41.27;
H, 4.04; N, 4.01. Found: C, 41.1; H, 3.9; N, 4.1%.
1-(Adamantan-2-ylidene)pyrrolidinium hexafluorophosphate (4e):
White needles (ethanol), m.p. 214–218°C (dec). 1H NMR (300 MHz,
DMSO-d6): d 1.86–2.12 (m, 16H), 3.17 (bs, 2H), 3.94–3.98 (m, 4H,
NCH2). 13C NMR (75 MHz, DMSO-d6): d 23.8, 25.9, 34.6, 38.0,
38.2, 53.0, 193.5. Anal. Calcd for C14H22F6NP: C, 48.14; H, 6.35; N,
4.01. Found: C, 48.1; H, 6.3; N, 4.0%.
(m, 8H), 2.21–2.30 (m, 1H), 2.45–2.57 (m, 1H), 2.83, 2.92 (m, 2H), 3.87–
4.00 (m, 4H, NCH2). 13C NMR (75 MHz, DMSO-d6): d 21.4, 23.6, 23.9,
31.2, 32.0, 32.9, 40.8, 53.4, 53.5, 188.3. Anal. Calcd for C11H20F6NP: C,
42.45; H, 6.48; N, 4.50. Found: C, 42.4; H, 6.6; N, 4.3%.
1-(1,4-Dioxaspiro[4.5]dec-8-ylidene)pyrrolidinium
hexafluoro-
phosphate (4m): White needles (ethanol–acetonitrile), m.p. 211–213°C.
1H NMR (300 MHz, DMSO-d6): d 1.92 (t, J = 6.7 Hz, 4H), 2.00–2.05
(m, 4H), 2.83–2.88 (m, 4H), 3.85–3.93 (m, 4H, NCH2), 3.95 (s, 4H,
OCH2). 13C NMR (75 MHz, DMSO-d6): d 24.0, 30.8, 31.1, 53.7, 64.1,
105.9, 186.3. Anal. Calcd for C12H20F6NO2P: C, 40.57; H, 5.67; N,
3.94. Found: C, 40.7; H, 5.5; N, 3.9%.
1-Isopropylidenepyrrolidinium perchlorate (4n): Off white plates
(ethanol–acetonitrile), m.p. 228–230°C (lit.9 m.p. 232–233°C).
1H NMR (300 MHz, DMSO-d6): d 2.00–2.05 (m, 4H), 2.42–2.43
(m, 6H), 3.85–3.90 (m, 4H, NCH2). 13C NMR (75 MHz, DMSO-d6):
d 24.2, 25.1, 53.8, 184.8.
1-(Pent-3-ylidene)pyrrolidinium perchlorate (4o): White plates
(ethanol), m.p. 210–212°C(lit.9 m.p. 213–214°C).1HNMR(300MHz,
DMSO-d6): d 1.18 (t, J = 7.6 Hz, 6H, CH3), 2.00–2.05 (m, 4H), 2.70
(q, J = 7.6 Hz, 4H), 3.93–3.97 (m, 4H). 13C NMR (75 MHz, DMSO-
d6): d 8.8, 24.0, 28.5, 53.5, 191.0.
1-Cyclopentylidenepyrrolidinium hexafluorophosphate (4p): Off
white needles (ethanol), m.p. 236–239°C (dec). 1H NMR (300 MHz,
DMSO-d6): d 1.89–1.93 (m, 4H), 2.02–2.07 (m, 4H), 2.78 (bs, 4H),
3.82 (bs, 4H, NCH2). 13C NMR (75 MHz, DMSO-d6): d 24.3, 35.4,
54.3, 195.8. Anal. Calcd for C9H16F6NP: C, 38.17; H, 5.69; N, 4.95.
Found: C, 38.3; H, 5.6; N, 5.0%.
N-Cyclopentylidenediethylaminium perchlorate (4q): White
needles (ethanol), m.p. 203–204°C (lit.10 m.p. 200–202°C). 1H NMR
(300 MHz, DMSO-d6): d 1.29 (t, J = 7.3 Hz, 6H, CH3), 1.88–1.93 (m,
4H), 2.87–2.92 (m, 4H), 3.79 (q, J = 7.3 Hz 4H, NCH2). 13C NMR
(75 MHz, DMSO-d6): d 11.9, 24.6, 35.0, 50.6, 200.5.
N-Cyclopentylidenedipropylaminium perchlorate (4r): White
needles (ethanol), m.p. 251–253°C (dec). (lit.10 m.p. 255–256°C).
1H NMR (300 MHz, DMSO-d6): d 0.93 (t, J = 7.4 Hz, 6H, CH3),
1.67–1.80 (m, 4H), 1.88–1.93 (m, 4H), 2.90–2.95 (m, 4H), 3.71 (t,
J = 8.0 Hz, 4H, NCH2). 13C NMR (75 MHz, DMSO-d6): d 10.8, 19.6,
24.2, 35.0, 56.8, 201.0.
1-Cyclopentylidenepyrrolidinium perchlorate (4s): Off white
plates (ethanol–acetonitrile), m.p. 229–231°C (dec). (lit.11 m.p. 231–
233°C (dec.)). 1H NMR (300 MHz, DMSO-d6): d 1.89–1.93 (m, 4H),
2.03–2.07 (m, 4H), 2.78 (bs, 4H), 3.83 (bs, 4H, NCH2). 13C NMR
(75 MHz, DMSO-d6): d 24.3, 35.5, 54.4, 195.8.
1-(Adamantan-2-ylidene)pyrrolidinium tetrafluoroborate (4f):
1
Light tan plates (ethanol), m.p. 233–235°C. H NMR (300 MHz,
DMSO-d6): d 1.86–2.12 (m, 16H), 3.17 (bs, 2H), 3.94–3.98 (m, 4H,
NCH2). 13C NMR (75 MHz, DMSO-d6): d 23.8, 25.9, 34.6, 38.0,
38.2, 53.0, 193.4. Anal. Calcd for C14H22BF4N: C, 57.76; H, 7.62; N,
4.81. Found: C, 57.6; H, 7.8; N, 4.8%.
1-(Adamantan-2-ylidene)azepanium perchlorate (4g): White plates
1
(ethanol), m.p. 350–354°C (dec). H NMR (300 MHz, DMSO-d6): d
1.58–2.19 (m, 20H), 3.46 (bs, 2H), 4.14 (t, J = 6.2 Hz, 4H, NCH2).
13C NMR (75 MHz, DMSO-d6): d 24.6, 25.7, 26.3, 34.4, 36.4, 39.0,
55.6, 197.9. Anal. Calcd for C16H26ClNO4: C, 57.91; H, 7.90; N, 4.22.
Found: C, 57.9; H, 7.9; N, 4.1%.
1-(Adamantan-2-ylidiene)-3-methylpiperidinium hexafluorophosphate
(4h): White plates (ethanol–acetonitrile), m.p. 299–305°C (dec).1H NMR
(300 MHz, DMSO-d6): d 0.97 (d, J = 6.5 Hz, 3H), 1.37–2.20 (m, 17H),
3.32–3.44 (m, 1H), 3.59–3.68 (m, 3H), 4.42–4.51 (m, 2H). 13C NMR (75
MHz, DMSO-d6): d 18.1, 25.7, 25.9, 26.1, 31.1, 33.1, 34.5, 36.1, 36.3,
38.3, 38.4, 39.4, 53.0, 58.4, 195.4.Anal. Calcd for C16H26F6NP: C, 50.93;
H, 6.94; N, 3.71. Found: C, 51.0; H, 7.15; N, 3.7%.
1-(Bicyclo[2.2.1]hept-2-ylidene)-3-methylpiperidinium hexafluoro-
phosphate (4i): Colourless plates (ethanol–acetonitrile), m.p. 255–
260°C (dec). Complex NMR spectra due to mixture of diastereomers.
1H NMR (300 MHz, DMSO-d6): d 0.92–0.98 (m), 1.27–1.47 (m),
1.56–2.00 (m), 2.45–2.79 (m), 3.20–3.91 (m), 4.19–4.34 (m). 13C
NMR (75 MHz, DMSO-d6): d 17.90, 18.01, 18.05, 18.08, 24.15,
24.19, 24.42, 24.55, 24.65, 25.04, 25.66, 30.31, 30.36, 30.45, 31.32,
31.54, 31.63, 32.14, 35.36, 38.54, 38.59, 40.45, 40.60, 40.62, 40.85,
44.33, 44.44, 44.50, 44.60, 53.51, 53.56, 53.88, 54.07, 59.14, 59.19,
59.48, 59.62, 195.24 and 195.37. Anal. Calcd for C13H22F6NP: C,
46.29; H, 6.57; N, 4.15. Found: C, 46.3; H, 6.6; N, 4.1%.
1-Cyclopentylidenepyrrolidinium tetrafluoroborate (4t): White
plates (ethyl acetate–acetonitrile), m.p. 206–208°C (dec). 1H NMR
(300 MHz, DMSO-d6): d 1.88–1.93 (m, 4H), 2.02–2.07 (m, 4H),
2.78 (bs, 4H), 3.82 (bs, 4H, NCH2). 13C NMR (75 MHz, DMSO-d6):
d 24.3, 35.4, 54.3, 195.8. Anal. Calcd for C9H16BF4N: C, 48.04; H,
7.17; N, 6.22. Found: C, 48.1; H, 7.1; N, 6.2%.
1-Cyclopentylidenepiperidinium hexafluorophosphate (4u): White
prisms (ethanol–acetonitrile), m.p. 225–227°C (dec). 1H NMR (300
MHz, DMSO-d6): d 1.67–1.92 (m, 10H), 2.84–2.89 (m, 4H), 3.82–
3.86 (m, 4H, NCH2). 13C NMR (75 MHz, DMSO-d6): d 22.0, 24.2,
25.4, 34.6, 54.8, 197.3. Anal. Calcd for C10H18F6NP: C, 40.41; H,
6.10; N, 4.71. Found: C, 40.5; H, 6.1; N, 4.7%.
1-Cyclopentylidenepiperidinium perchlorate (4v): White plates
(ethanol–acetonitrile), m.p. 231–233°C (dec). (lit.8 m.p. 232.5–
235.5°C). 1H NMR (300 MHz, DMSO-d6): d 1.67–1.92 (m, 10H),
2.84–2.89 (m, 4H), 3.82–3.86 (m, 4H, NCH2). 13C NMR (75 MHz,
DMSO-d6): d 22.0, 24.2, 25.4, 34.6, 54.8, 197.3.
1-Cyclopentylideneazepanium perchlorate (4w): White plates
(ethanol), m.p. 218–221°C (dec). (lit.12 m.p. 212–213°C dec.).
1H NMR (300 MHz, DMSO-d6): d 1.56–1.63 (m, 4H), 1.84–1.93 (m,
8H), 2.86–2.91 (m, 4H), 3.90 (t, J = 5.8 Hz, 4H, NCH2). 13C NMR
(75 MHz, DMSO-d6): d 24.1, 25.3, 26.0.0, 35.0, 55.8, 200.5.
1-Cyclopentylidene-3-methylpiperidinium hexafluorophosphate (4x):
1-(Bicyclo[2.2.1]hept-2-ylidene)pyrrolidinium
hexafluoro-
1
phosphate (4j): White plates (ethanol), m.p. 213–217°C (dec). H
NMR (300 MHz, DMSO-d6): d 1.26–2.69 (m, 13H), 3.38–3.40 (m,
1H), 3.68–4.05 (m, 4H). 13C NMR (75 MHz, DMSO-d6): d 23.6,
24.0, 24.3, 25.5, 35.5, 39.1, 41.1, 45.8, 53.4, 54.0, 193.6. Anal. Calcd
for C11H18F6NP: C, 42.72; H, 5.87; N, 4.53. Found: C, 42.7; H, 5.7;
N, 4.5%.
1
Light tan plates (ethanol), m.p. 220–223°C (dec). H NMR (300 MHz,
DMSO-d6): d 0.96 (d, J = 6.7 Hz, 3H, CH3), 1.29–1.40 (m, 1H), 1.65–
1.92 (m, 8H), 2.80–2.96 (m, 4H), 3.29 (t, J = 11.8 Hz, 1H), 3.54 (t, J =
11.8 Hz, 1H), 4.05 (t, J = 11.7 Hz, 2H). 13C NMR (75 MHz, DMSO-d6):
d 18.1, 24.1, 24.4, 30.3, 31.5, 34.6, 34.7, 54.3, 59.9, 197.5. Anal. Calcd for
C11H20F6NP: C, 42.45; H, 6.48; N, 4.50. Found: C, 42.4; H, 6.4; N, 4.5%.
1-Cyclohexylidenepyrrolidinium hexafluorophosphate (4y): White
needles (ethanol–acetonitrile), m.p. 233–234°C (dec). 1H NMR
(300 MHz, DMSO-d6): d 1.56–1.64 (m, 2H), 1.75–1.84 (m, 4H),
1.99–2.04 (m, 4H), 2.71 (t, J = 6.4 Hz, 4H), 3.90 (bs, 4H, NCH2).
13C NMR (75 MHz, DMSO-d6): d 22.7, 23.9, 24.2, 33.2, 53.3, 188.3.
Anal. Calcd for C10H18F6NP: C, 40.41; H, 6.10; N, 4.71. Found: C,
40.3; H, 6.2; N, 4.7%.
1-(Bicyclo[2.2.1]hept-2-ylidene)azepanium perchlorate (4k): White
plates (ethanol), m.p. 300–302°C (dec). (lit.8 m.p. 301.5–302.5°C
1
(dec)). H NMR (300 MHz, DMSO-d6): d 1.33–2.05 (m, 14H),
2.46–2.81 (m, 3H), 3.62–3.63 (m, 1H), 3.79–3.83 (m, 2H, NCH2),
3.99–4.06 (m, 2H, NCH2). 13C NMR (75 MHz, DMSO-d6): d 24.5,
25.3, 25.5, 25.6, 26.1, 26.2, 35.4, 38.7, 40.6, 44.8, 55.28, 55.31, 198.2.
Anal. Calcd for C13H22ClNO4: C, 53.51; H, 7.60; N, 4.80. Found: C,
53.6; H, 7.7; N, 4.7%.
1-(3-Methylcyclohexylidene)pyrrolidinium hexafluorophosphate (4l):
White needles (ethanol), m.p. 221–224°C (dec). 1H NMR (300 MHz,
DMSO-d6): d 1.02 (d, J = 6.6 Hz, 3H, CH3), 1.18–1.30 (m, 1H), 1.59–2.08

304 JOURNAL OF CHEMICAL RESEARCH 2008
1-Cyclohexylidenepyrrolidinium perchlorate (4z): White prisms
Division of Undergraduate Education through Grant
DUE #9650684 for the NMR spectrometer at Fordham.
The authors also acknowledge helpful comments on this
manuscript by Profs. James A. Ciaccio and Amy M. Balija of
this department.
1
(ethanol) m.p. 231–233°C (dec). (lit.11 m.p. 230–231°C (dec.)). H
NMR (300 MHz, DMSO-d6): d 1.56–1.64 (m, 2H), 1.76–1.86 (m, 4H),
2.00–2.06 (m, 4H), 2.71 (t, J = 6.4 Hz, 4H), 3.91 (bs, 4H, NCH2). 13
NMR (75 MHz, DMSO-d6): d 22.7, 24.0, 24.2, 33.2, 53.3, 188.3.
C
1-Cycloheptylidenepyrrolidiniumtetrafluoroborate(4aa):Colourless
plates (ethanol), m.p. 210–213°C (dec). 1H NMR (300 MHz, DMSO-
d6): d 1.57–1.77 (m, 8H), 2.00–2.05 (m, 4H), 2.84 (t, J = 5.0 Hz, 4H,
N=CCH2), 3.89 (bs, 4H, NCH2). 13C NMR (75 MHz, DMSO-d6):
d 23.6, 24.3, 29.0, 36.4, 54.0, 191.3. Anal. Calcd for C11H20BF4N: C,
52.20; H, 7.97; N, 5.53. Found: C, 52.2; H, 8.1; N, 5.5%.
Received 19 February 2008; accepted 3 May 2008
Paper 08/5107 doi: 10.3184/030823408X338387
References
1-Cycloheptylidenepyrrolidinium perchlorate (4bb): Off white
plates (ethanol), m.p. 234–236°C (dec). (lit.11 m.p. 234–235°C (dec)).
1H NMR (300 MHz, DMSO-d6): d 1.57–1.84 (m, 8H), 2.00–2.05 (m,
1
S. Saba, A. Brescia and M.K. Kaloustian, Tetrahedron Lett., 1991, 32,
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2
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4H), 2.84 (t, J = 5.0 Hz, 4H, N=CCH2), 3.89 (bs, 4H, NCH2). 13
NMR (75 MHz, DMSO-d6): d 23.3, 24.0, 28.7, 36.1, 53.7, 191.0.
C
1-Cycloheptylidenepyrrolidinium hexafluorophosphate (4cc): White
plates(ethanol–acetonitrile), m.p. 233–236°C(dec).1HNMR(300MHz,
DMSO-d6): d 1.59–1.77 (m, 8H), 2.00–2.05 (m, 4H), 2.84 (t, J = 5.0 Hz,
4H, N=CCH2), 3.89 (bs, 4H, NCH2). 13C NMR (75 MHz, DMSO-d6):
d 23.3, 24.0, 28.7, 36.1, 53.7, 191.0. Anal. Calcd for C11H20F6NP: C,
42.45; H, 6.48; N, 4.50. Found: C, 42.5; H, 6.4; N, 4.5%.
3
4
5
6
1-Cycloheptylideneazepanium perchlorate (4dd): Off white prisms
1
(ethanol–acetnitrile), m.p. 284–288°C (dec). H NMR (300 MHz,
7
8
K.A. Tehrani and N. De Kimpe, Sci. Synth., 2004, 27, 313.
W. Dörscheln, H. Tiefenthaler, H. Göth, P. Cerutti and H. Schmid, Helv.
Chim. Acta, 1967, 50, 1759.
DMSO-d6): d 1.56–1.81 (m, 16H), 2.92–2.96 (m, 4H, N=CCH2),
4.02 (t, J = 6 Hz, 4H, NCH2). 13C NMR (75 MHz, DMSO-d6): d 23.5,
25.0, 25.7, 28.0, 34.3, 54.9, 195.1. Anal. Calcd for C13H24ClNO4: C,
53.15; H, 8.23; N, 4.77. Found: C, 53.2; H, 8.4; N, 4.8%.
9
N.J. Leonard and J.V. Paukstelis, J. Org. Chem., 1963, 28, 3021.
10 N.M. Libman, Zh. Org. Khim., 1967, 3, 1235.
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12 A.G. Cook, W.C. Meyer, K.E. Ungrodt and R.H. Mueller, J. Org. Chem.,
1966, 31, 14.
The authors gratefully acknowledge financial support from
Fordham University and the National Science Foundation’s