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small amounts of trimers 3d-3e among several unidentified There are no conflicts to declare.
oligomeric compounds while only 1b gave the corresponding trimer
DOI: 10.1039/C9CC01755K
in a good yield (Scheme 7). The chemical shift around 70-75 ppm is
characteristic of the bridgehead carbon connected to two nitrogen
Notes and references
atoms. The corresponding trimer of 1c has never been observed in
the spectra of decomposition products. For 1d, the trimeric
compound was also obtained when the corresponding ketone, a
saturated solution of ammonia in methanol and molecular sieves
were stirred for one day at room temperature. In similar conditions,
only small amounts of imine 1e,1f and the corresponding ketone
‡
https://chem.pg.edu.pl/documents/175230/54717567/8.%20IR.pdf.
C=O: C : 1785, C : 1748, C : 1715, C : 1705, C : 1700 cm .
4 5 6 7 8
-1
§
5
Cyclobutanimine 1b. 1/2 = 10 min (248 K, 5% in CD
1% in the presence of butyronitrile (7%). Removing of butyronitrile
by selective trapping of 1b at -43°C under 0 .1 mbar is difficult and
2 2
Cl ). Yield:
were observed after one day starting from cycloheptanone and leads to an important loss of product even on an analytical sample.
cyclooctanone, respectively. The trimer 3d diluted in methanol with 1H NMR (CD
, 400 MHz, 183 K) 1.85 (quint, 2H, JHH = 8.2 Hz,
3
2
Cl
2
potassium cyanide and trimethylamine hydrochloride (to generate CH ) ; 2.85 (t, 2H, J = 8.2 Hz, CH ) ; 2.87 (td, 2H, J = 8.2 Hz, 3JHH
3
3
2
HH
2
HH
1
3
HCN in situ) gave the aminonitrile 2d in a 30% yield demonstrating = 2.6 Hz, CH ) ; 8.85 (s brd, 1H, NH). C NMR (CD Cl , 100 MHz, 183
2
2
2
the reversibility of the trimerisation. However, trimers 3b, 3d
thermolyzed at 800°C gave only traces of 1b, 1d, respectively, and
thereby, they cannot be considered as efficient precursors of the
corresponding imine in these conditions.
K) 11.7 (1JCH = 139.3 Hz (t), CH
) ; 38.1 (1JCH = 135.4 Hz (t), CH
2
) ;
2
9.5 (1JCH = 135.2 Hz (t), CH
3
2
) ; 185.7 (s, C=N). Coalescence was
observed around 213 K. 13C NMR spectrum at 243K: 11.7; 38.6;
-1
1
1
85.1. IR ( cm , film): 3137 (m, NH), 2980 (s), 2961(s), 2923 (s),
703 (m, C=N), 1353 (s), 1019(s).
Tautomerism between such enolizable cycloalkylimines and the
corresponding enamines was easily evidenced recording the NMR
Cyclopentanimine 1c. 1/2 = 1h (296 K, 5% in CD
NMR (CD Cl , 400 MHz, 183 K) 1.72 (m, 4H, CH
CH CH Cl
CN) ; 8.94 (s brd, 1H, NH). 13C NMR (CD
CN) ; 35.2 (1JCH ≈ 130.0 Hz (t),
2
Cl
C=N) ; 2.19 (m, 4H,
, 100 MHz, 183 K)
). Yield: 80 %.1H
2
spectra of the kinetically stable 1e-1f in CD
3
OD. At room
2
2
2
temperature, the 2,2,7,7- or 2,2,8,8-tetradeutero derivative,
respectively, was slowly formed (1e-d : C2 = 39.0 ppm (q), JCD =
4
2
2
2
2
: C2 = 37.3 ppm (q), JCD = 21.2 Hz) (Scheme 8). The 25.5 (1JCH = 131.6 Hz (t), CH
1
9.6 Hz, 1f-d
4
2
CH
2
1
exchange can be accelerated by the presence of a base (DBU). Such CH CN), 37.0 ( J ≈ 130.0 Hz (t), CH CN) ; 185.7 (s, C=N).
2
CH
2
a tautomerism between an imine and the corresponding enamine is
usually challenging to demonstrate with N-H derivatives. At room
temperature in methanol, the decomposition of imines 1b-1d was
faster than tautomerism.
Coalescence was observed around 190 K. 13C NMR spectrum at 296
K: 25.5, 36.4 (1JCH = 128.7 Hz (t), CH CN), 185.7 (C=N). IR ( cm-1,
film): 3180 (m, NH), 2957(s), 2869(s), 1675 (m, C=N), 1418(m), 1182
m), 952.
2
(
Cyclohexanimine 1d. 1/2 = 2h (296 K, 5% in CD
NMR (CD Cl , 400 MHz, 193 K) 1.50 (m, 2H, CH
CH
) ; 2.20 (t, 4H, 3JHH = 6.7 Hz, CH CN) ; 8.64 (s brd, 1H, NH). 13
NMR (CD Cl ) ; 27.4
, 100 MHz, 193 K) 25.3 (1JCH = 128.3 Hz (t), CH
CH = 129.5 Hz (t), CH
) ; 37.5 (1JCH ≈ 127.2 Hz (t), CH CN), 41.5 (1JCH
126.8 Hz (t), CH CN) ; 184.4 (s, C=N). Coalescence was observed
2
Cl
2
). Yield: 77 %. 1H
2
) ; 1.60 (m, 4H, 2
2
2
2
2
C
2
2
2
(1
=
J
2
2
2
Scheme 8 Imine-enamine tautomerism of imines 1e,1f demonstra-
ted by deuteration
around 240 K. 13C NMR spectrum at 296 K: 25.4, 27.4, 39.6 (1JCH
=
-1
1
2
26.4 Hz (t), CH
2
), 183.1 (s, C=N). IR ( cm , film): 3182 (m, NH),
930(s), 2852(s), 1660 (m, C=N), 1449(m), 1401 (m), 1248 (m), 1178
To summarize, unsubstituted cycloalkylimines with a 4 to 8
membered ring have been prepared on gram scale through the
dehydrocyanation of cyclic -aminonitriles. The kinetic stability of
these imines is strongly dependent on the size of the ring. The use
of these imines in chemistry and particularly in the preparation of
polycyclic compounds is currently under progress in our lab.
(m), 1011 (m).
1
Cycloheptanimine 1e. Yield: 73 %. H NMR (CD
1.50 (s brd, 4H, CH ) ; 1.57 (s brd, 4H, 2 CH
) ; 2.38 (t, 4H, 3JHH = 6.1
Hz, CH Cl , 100 MHz, 183 K)
CN) ; 8.75 (s brd, 1H, NH). 13C NMR (CD
26.2 (1JCH = 128.3 Hz (t), CH ) ; 30.3 (1JCH = 126.4 Hz (t), CH
) ; 39.0
1JCH ≈ 127.2 Hz (t), CH CN), 41.7 (1JCH = 126.8 Hz (t), CH
CN) ; 184.4
s, C=N). Coalescence was observed around 190K. 13C NMR
), 187.5
s, C=N). IR ( cm , film): 3177 (m, NH), 2924(s), 2849(s), 1637 (s,
2 2
Cl , 400 MHz, 183K)
2
2
2
2
2
(
(
2
2
2
2
Funding support was received from the Centre National d’Etudes
Spatiales (CNES), the French Programme National “Physique et
Chimie du Milieu Interstellaire”, the Institut National de Chimie du
CNRS. W. N. thanks the Ecole Nationale Supérieure de Chimie de
Rennes for a fellowship.
spectrum at 296 K: 26.2, 30.3, 40.3 (1JCH = 126.4 Hz (t), CH
2
-1
(
C=N), 1453(m), 1390(m), 1135(m), 834(m).
1
Cyclooctanimine 1f. Yield: 68 %. H NMR (CD
2
Cl
) ; 1.67 (s brd, 4H, CH
CN) ; 8.92 (s brd, 1H, NH). 13C NMR (CD
Cl , 100
) ; 26.1 (brd, 1JCH
2
, 400 MHz , 183 K)
1.32 (s brd, 2H, CH
.24 (s brd, 4H, CH
2
) ; 1.42 (s brd, 4H, CH
2
2
) ;
Conflicts of interest
2
2
2
2
MHz, 183 K) 24.2 (1JCH = 126.4 Hz (t), 1 CH
=
2
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