N. Dorostkar-Ahmadi et al. / Spectrochimica Acta Part A 79 (2011) 1375–1380
1377
Table 1
Characterization data of newly prepared compounds 6a, 7a, and 8a.
Compound
Formula
Mr
wi(calc.)/% wi(found)/%
Yield
M.p.
C
H
N
%
◦C
6a
7a
8a
C10H7N3O3
C12H12N2O5
217
264
285
55.30
55.84
54.55
54.55
42.13
42.04
3.25
3.87
4.58
4.63
3.18
3.24
19.35
19.05
10.60
10.56
9.83
81
161–163
88
85
130–132
166–168
C
10H9BrN2O3
9.86
Table 3
4.1. General procedure for the synthesis of cycloadducts
The comparison of theoretical 13C NMR chemical shifts data (ꢂ, ppm) of C-1 and C-2
of each pair of regioisomers with those obtained from the experimental 13C NMR
spectroscopy.
To a mixture of 1 mmol of oxime and 1.5 mmol of dipolarophile
in tetrahydrofuran (THF) (25 mL) was added aqueous NaOCl (11%
Cl2 content, 1.62 mL, 2.50 mmol) at 5 ◦C. The reaction was stirred
for 10 min, then at r.t. for 24 h. After that, H2O (30 mL) was added,
the organic layer separated and remaining product extracted from
the aqueous layer using CHCl3 (15 mL). The combined organic layers
were washed with H2O (20 mL), dried (Na2SO4) and the solvent was
removed under reduced pressure. The crude product was purified
by precipitation with cold Et2O to afford cycloadducts as yellow
crystals.
Compound
Atom number
Calculated
chemical shift
Experimental
chemical shift
C-1
C-2
C-1
C-2
C-1
C-2
C-1
C-2
C-1
C-2
C-1
C-2
41.3
68.5
56.4
21.3
44.6
90.8
64.5
39.9
79.7
39.4
35.1
72.6
40.6
67.3
6a
6b
7a
7b
8a
8b
44.1
87.3
80.6
39.0
5. Results and discussion
Nitrile oxide (2) was generated in situ from the oxime (1) in
a mixture of aqueous NaClO in THF. 1,3-DC of nitrile oxide (2)
with the dipolarophiles proceeded smoothly in a selective man-
ner to give a single regioisomer of each pair 6a-b, 7a-b, and 8a-b
the nitrile absorption band in the IR spectrum of the cycloadduct
6a, is the reminiscent of the previously reported observations with
the aliphatic nitriles which are activated by a nitrogen or an oxygen
atom in their -position [32–34]. The assignment of the regiochem-
istry of these products was based upon (i) comparing the theoretical
13C NMR spectral data obtained by GIAO method with the observed
(i) For further cycloadduct characterization, we obtained the
theoretical 13C chemical shifts values for the products through the
GIAO method and compared it with the observed values. As it can
be seen in Table 3, the observed values for C1 and C2 in each of
the isolated products (40.6, 67.3;44.1, 87.3 and 80.6,39.0 ppm in
compounds 6, 7 and 8 respectively) are in close proximity to the
theoretical values for compounds 6a, 7a, and 8a. It seems likely
that the isolated regioisomers are structurally similar to 6a, 7a and
Table 2
Spectral data of newly prepared compounds 6a, 7a and 8a.
Table 4
Energies of reactives, transition states and cycloadducts 6, 7 and 8, E (a.u.), relative
activation energies ꢂEa (kcal mol−1) and relative energies between products and
reactives, ꢂEr (kcal mol−1).
Compound
6a
Spectral data
IR, ꢁ˜/cm−1: 1599 (C N), 1515 (NO2)as, 1347 (NO2)s
1H NMR (CDCl3), ı/ppm: 3.79(1H, dd, CHAHB, J = 6.80 Hz,
*
*
E
ꢂEa
ꢂEr
J
10.0 Hz), 3.86 (1H, dd, CHAHB, J = 6.00 Hz, J = 11.20 Hz),
5.56 (1H, dd, CH, J = 6.40 Hz, J = 6.80 Hz), 7.88 (2H, d, CH–Ar,
J = 9.60 Hz), 8.34 (2H, d, CH–Ar, J = 8.80 Hz)
13C NMR (CDCl3), ı/ppm: 40.6 (CH2), 67.3(CH), 116.5
(C N), 124.3, 128.0, 133.3, 149.2 (CPh), 154.8 (C N)
MS, m/z: 217 (M+)
Reaction a
Nitrilie oxide 2
Acrylonitrile 3
TS 6a
TS 6b
6a
−604.1384
−170.8316
−774.9500
−774.9485
−775.0274
−775.0259
12.5
13.5
7a
IR, ꢁ˜/cm−1: 1728(C O), 1599(C N), 1513 (NO2)as, 1347
(NO2)s
−36.0
−35.1
6b
1H NMR (CDCl3), ı/ppm: 1.77 (3H, s, CH3), 3.27 (1H, d,
CHAHB, J = 17.20 Hz), 3.84 (3H, s, OCH3), 3.95 (1H, d, CHAHB,
J = 16.80 Hz), 7.84 (2H, d, CH–Ar, J = 8.80 Hz), 8.28 (2H, d,
CH–Ar, J = 8.80 Hz).
Reaction b
Nitrilie oxide 2
Methyl methacrylate 4
TS 7a
TS 7b
7a
−604.1384
−345.7980
−949.9068
−949.8991
−949.9877
−949.9768
13C NMR (CDCl3), ı/ppm: 23.6 (CH3), 44.1 (CH2), 53.2
(OCH3), 87.3 (C), 124.0, 127.5, 135.1, 148.6, 154.8 (C N),
172.0 (C O)
18.6
23.4
−32.2
−25.3
MS, m/z: 264 (M+)
7b
8a
IR, ꢁ˜/cm−1: 1607 (C N), 1518 (NO2)as, 1350 (NO2)s
1H NMR (CDCl3), ı/ppm: 3.39 (1H, dd, CHAHB, J = 6.40 Hz,
J = 10.40 Hz), 3.49 1H, dd, CHAHB, J = 8.00 Hz, J = 2.40 Hz),
3.57 (1H, dd, CHAHB, J = 6.00 Hz, J = 10.80 Hz), 3.64 (1H, dd,
CHAHB, J = 4.00 Hz, J = 6.80 Hz), 5.20 (1H, m, CH), 7.87 (2H,
d, CH–Ar, J = 8.80 Hz), 8.30 (2H, d, CH–Ar, J = 8.80 Hz).
13C NMR (CDCl3), ı/ppm: 32.9 (CH2Br), 39.0 (CH), 80.6
(CH2), 124.1, 127.5, 135.1, 148.7 (CPh), 154.6 (C N).
MS, m/z: 284 (M+), 286 (M++2).
Reaction c
Nitrilie oxide 2
Allyl bromide 5
TS 8a
TS 8b
8a
−604.1384
−2689.0054
−3293.1311
−3293.1262
−3293.2201
−3293.2137
7.9
11.0
−47.9
−43.9
8b
*
To reactives.