Mendeleev Commun., 2009, 19, 42–44
the imidazole ring, finally giving carbene intermediate D (the
stable imidazole carbenes of such a type are well known ). The
1
3
6
14
15
3
N
12
1
4
3
,2-migration of the functionalized 1,3-butadienyl group in
16
1
14'
15'
2
13'
12'
5
these intermediates affords 2-(1,3-butadienyl)imidazoles 4a–c.
Note that zwitterions of the type A are well-established
intermediates in the reactions of nucleophiles with electron-
deficient systems.7
1
N
6
11'
7
1
6'
R
8
NC10
9
H
NC10'
In one case (R = Me), molar ratio 1a:2 = 1:2 (20–25 °C, Et O,
2
1
20 h), imidazole 4a has been isolated as an individual com-
Z-4a–c
pound (10% yield).
Figure 1 Labeling hydrogen and carbon atoms in adducts 4.
Apparently, no limitations for further elongation of the
conjugation polyene chain at the 2-position of the imidazole
nucleus using excess acetylene 2 are envisaged.
Imidazoles 4a–c have been identified and exhaustively charac-
belonging to adducts 4a–c. This conclusion follows from that
9
the proton H is spin-coupled over three bonds not with imidazole
2
7
C , but with carbon C of the second double bond (Figure 1).
1
13
15
terized in the mixture with imidazoles 3 by H, C, N NMR
The configuration of imidazoles 4a–c has been assigned
1
1
1
13
3
9
spectroscopy and using H– H homonuclear and H– C hetero-
based on the vicinal J values for the proton H and carbon
CH
7
3
11'
nuclear 2D (COSY, NOESY, HSQC and HMBC) techniques.
C ( J
C7,H9
10.1–10.3 Hz) as well as C of phenyl substituents
4.8–5.0 Hz). As is evident from the J values, the
proton H is in the trans position with respect to the imidazole
cycle and, consequently, in the cis position relative to the phenyl
group, that corresponds to the (Z)-configuration of this olefinic
moiety (Figure 1).
The H NMR spectra of adducts 4a–c show the signals of
protons H and H of the imidazole ring, whereas the signals
of protons H are absent. In the C NMR spectra the signals of
carbons C and C remain unchanged, while the signal of carbon
1
3
3
In the H NMR spectrum of compounds 4a–c, the singlets
( J
C11',H9
CH
9
13
9
of the H protons appear at 5.60–5.72 ppm. In the C NMR
spectra of the mixtures 3 + 4, along with the signals of vinyl-
imidazoles 3a–c, there are signals of two other olefinic moieties
6
7
at 151.60–152.10 (C ), 110.09–111.03 (C ), 157.04–157.43
C ), 96.99–97.45 ppm (C ) as well as those of two CN groups
8
9
1
(
4
5
2
13
1
3
4
b: H NMR, d: 1.13 (t, 3H, N–CH Me, J
7.1 Hz), 3.50 (q, 2H,
2
MeCH2
4
5
3
9
5
3
N–CH , J
7.1 Hz), 5.65 (s, 1H, H ), 7.00 (d, 1H, H , J 1.1 Hz),
2
MeCH2
5,4
2
4
3
14'
14
atom C is shifted low-field from 136–137 ppm to 142–143 ppm.
In addition, in the N NMR spectra the nitrogen atoms N and
N resonate in different regions (from –195 to –220 ppm and
7
(
H
1
(
1
(
.06 (d, 1H, H , J 1.1 Hz), 7.47 (m, 1H, H ), 7.50 (m, 1H, H ), 7.50
4,5
1
3',15'
), 7.52 (m, 2H, H13,15), 7.55 (m, 2H, H12,16), 7.65 (m, 2H,
15
1
m, 2H, H
1
2',16' 13
9
3
). C NMR, d: 14.64 (N–CH Me), 42.42 (N–CH ), 97.36 (C ),
2
10
2
7
10'
5
14
11.03 (C ), 116.52 (C ), 116.71 (C ), 121.92 (C ), 127.40 (C ), 128.15
2',16'
from –109 to –111 ppm, respectively). These facts are indicative
1
13',15'
12,16
13,15
4
C
), 129.18 (C
14'
), 129.50 (C
), 129.70 (C
), 130.29 (C ),
2
of substitution of the hydrogen atom at C and confirm that
31.50 (C ), 135.27 (C11'), 135.92 (C ), 142.46 (C ), 151.70 (C ), 157.24
11
2
6
1
,3-butadienyl fragment is located at second carbon atom of the
8
15
1
10'
3
C ). N NMR, d: –203.40 (N ), –116.70 (C N), –108.50 (N ).
imidazole ring.
(
Z)-1-Phenyl-2-(2-cyano-1-phenylethenyl)imidazole 3c and (Z)-1-phenyl-
Alternatively, zwitterionic 1:2 intermediate C could undergo
cyclization to yield fused heterocyclic system 5 (two tautomers)
2
8
-(2,4-dicyano-1,3-diphenyl-1,3-butadienyl)imidazole 4c: (1c:2, 1:1,
0 h). Analogously, from 1-phenylimidazole 1c (144 mg, 1 mmol) and
(Scheme 2).
acetylene 2 (127 mg, 1 mmol) in MeCN (1 ml), 101 mg of crimson oil
containing imidazoles 3c (22%) and 4c (20%) in the ratio of 3:2
1
–1
Ph
N
Ph
N
(
H NMR), were prepared. IR (microlayer of 3c and 4c mixture, n/cm ):
CN
Ph
CN
Ph
5
1
1
34, 647, 673, 697, 732, 764, 833, 906, 1003, 1030, 1059, 1078, 1108,
160, 1180, 1263, 1295, 1365, 1389, 1402, 1446, 1492, 1509, 1570,
596, 1656, 1686, 2217, 2894, 2923, 3061, 3155.
C
H
N
R
N
R
1
7
12,16
), 7.41 (d, 1H, H5,
4
c: H NMR, d: 5.72 (s, 1H, H ), 7.36 (m, 2H, H
H
CN
CN
3J
13,15
14'
1.0 Hz), 7.41 (m, 2H, H
), 7.41 (m, 1H, H ), 7.43 (m, 1H,
5
,4
5
1
4
13',15'
H ), 7.45 (m, 2H, o-H from N–Ph), 7.45 (m, 2H, H
H
), 7.48 (m, 2H,
1
2',16'
4
3
Scheme 2
), 7.50 (m, 1H, p-H from N–Ph), 7.53 (d, 1H, H , J 1.0 Hz),
4,5
13
9
7
7.62 (m, 2H, m-H from N–Ph). C NMR, d: 97.29 (C ), 110.09 (C ),
10'
10
5
However, no cyclic adducts have been detected (NMR) in the
reaction mixtures. First, this is proved by the 15N NMR spectra
116.50 (C ), 116.89 (C ), 123.05 (C ), 124.90 (o-C from N–Ph), 126.62
1
4
12',16'
(
C ), 128.07 (C
), 128.21 (p-C from N–Ph), 128.77 (m-C from
1
3',15'
12,16
13,15
4
N–Ph), 129.00 (C
), 129.51 (C ), 129.74 (C ), 130.24 (C ), 131.48
of compounds 3a–c and 4a–c, where there are both ‘pyrrole’
1
4'
11'
11
2
1
3
(
C
), 135.10 (C ), 135.62 (C ), 136.00 (i-C from N–Ph), 142.03 (C ),
(N ) and ‘pyridinic’ (N ) nitrogen atoms (from –195 to –220
6
8
15
1
10'
151.60 (C ), 157.43 (C ). N NMR, d: –205.90 (N ), –115.70 (C N),
and from –107 to –111 ppm, respectively), while in cyclic
3
–108.20 (N ).
1
3
adducts 5, both nitrogen atoms (N and N ) should have a
(
Z)-1-Methyl-2-(2,4-dicyano-1,3-diphenyl-1,3-butadienyl)imidazole 4a:
A mixture of 1-methylimidazole 1a (42 mg, 0.5 mmol) and acetylene 2
127 mg, 1 mmol) in dry diethyl ether (0.3 ml) was stirred at 20–25 °C
similar character.
3
9
Second, the vicinal J values between the proton H and
CH
(
1
1'
ipso-carbon C in compounds 4a–c are discernible over three
for 120 h. The solvent was removed, viscous residue was passed through
3
bonds ( J
C11',H9
4.8–5.0 Hz), whereas in the cyclic six-membered
a column (40×1 cm) and 1,3-butadienylimidazole 4a (17 mg, 10%) was
3
2
–1
structures 5 the J values between H atom and ipso-carbon
isolated, mp 166–168 °C (acetone). IR (KBr, n/cm ): 461, 499, 584, 642,
CH
of the phenyl group would be transmitted over four bonds and
are to be expected lesser than 1 Hz.
6
94, 732, 765, 827, 893, 929, 1030, 1077, 1152, 1183, 1281, 1329, 1436,
1
1471, 1578, 1632, 2205, 2852, 2920, 2954, 3058, 3096, 3136. H NMR,
9
5
3
Third, practically equal values of cis- and trans-vicinal 3JCH
in compounds 3a–c and 4a–c (4.8–5.4 and 10.1–11.0 Hz, respec-
tively) are also indicative of their similar structure.
The absence of cyclic adducts 5 from the reaction mixtures is
in agreement with the configuration of intermediate zwitterions
C (Scheme 1), where carbanionic site is trans-position with
respect to the imidazolic cycle, that is unfavourable for the ring
closing.
d: 3.11 (s, 3H, N–Me), 5.62 (s, 1H, H ), 6.93 (d, 1H, H , J 1.2 Hz),
5
,4
4
3
14'
13',15'
7
7
2
.03 (d, 1H, H , J 1.2 Hz), 7.48 (m, 1H, H ), 7.48 (m, 2H, H
.49 (m, 1H, H ), 7.51 (m, 2H, H
),
4
,5
1
4
13,15
12,16
), 7.57 (m, 2H, H
), 7.66 (m,
1
2',16' 13
9
7
H, H
). C NMR, d: 34.76 (N–Me), 96.99 (C ), 110.68 (C ), 116.70
1
0'
10
5
14
12',16'
(
C
), 116.90 (C ), 125.16 (C ), 126.90 (C ), 128.27 (C
), 129.40 (C
), 129.00
), 129.84 (C ), 131.30 (C ), 134.96
1
3',15'
12,16
13,15
4
14'
(
(
C
), 129.70 (C
C11'), 135.50 (C ), 142.72 (C ), 152.10 (C ), 157.40 (C ). 15N NMR, d:
11
2
6
8
1
10'
3
–217.60 (N ), –116.90 (C N), –107.10 (N ). Found (%): C, 78.20; H, 4.62;
N, 16.54. Calc. for C H N (%): C, 78.55; H, 4.79; N, 16.66.
22
16
4
–
43 –