A. Hoz, I. Alkorta and J. Elguero
Tetrahedron 97 (2021) 132413
4.5. 2-N-(3-oxo-3-phenyl-1-p-tolyl)thiosemicarbazide (12c)
1H NMR (DMSO‑d
J ¼ 7.3 Hz, 2H), 7.31 (d, 2H), 7.09 (d, J ¼ 7.7 Hz, 2H), 5.33 (bd, 1H),
.42 (dq, 1H), 4.41 (bs, 1H), 2.27 (s, 3H). Very impure, it contains a
large amount of chalcone 3.
):
d
7.88 (d, 2H), 7.62 (t, J ¼ 7.6 Hz, 1H), 7.50 (t,
6
4
4.6. (1Z)-1-((E)-1-phenyl-3-p-tolylallylidene)thiosemicarbazide
(6c) and (1E)-1-((E)-1-phenyl-3-p-tolylallylidene)
thiosemicarbazide (7c). Compound 6c was reported in Ref. [27] but
1
only its H NMR data
A
solution of 3-p-methylphenyl-1-phenylpropenone (3)
149 mg, 0.67 mmol), thiosemicarbazide (4c) (61 mg, 0.67 mmol)
and acetic acid (335 L) in ethanol (10 mL) were heated to reflux for
4 h. The solvent was removed in vacuo and the crude product was
(
m
2
chromatographed on silica gel using hexane: ethyl acetate 4:1 as
the eluent to give 82 mg (43%) of a 65%: 35% mixture of Z/E and E/E
thiosemicarbazones that evolves to 86%: 14% within time.
(
1Z)-1-((E)-1-phenyl-3-p-tolylallylidene)thiosemicarbazide 6c.
1
H NMR (CDCl
J ¼ 8.0 Hz, 2H), 7.43 (t, J ¼ 7.9 Hz, 2H), 1H) 7.25 (dd, J ¼ 8.0 Hz, 2H),
.13 (d, J ¼ 8.0 Hz, 2H), 7.02 (d, J ¼ 16.2 Hz, 1H), 6.53 and 6.55 (bs,
H), 6.41 (d, J ¼ 16.2 Hz, 1H), 2.34 (s, 3H).
3
):
d
8.50 (bs, 1H), 7.56 (t, J ¼ 7.6 Hz, 2H), 7.28 (d,
7
2
1
3
C NMR (CDCl
29.99, 129.57, 128.34, 127.64, 128.85, 127.09, 21.39.
1E)-1-((E)-1-phenyl-3-p-tolylallylidene)thiosemicarbazide 7c.
3
): d 178.39, 152.70, 139.32, 139.03, 133.09, 130.31,
1
(
1
3
H NMR (CDCl ): d 9.27 (bs, 1H), 7.38 (bs, 2H), 7.60 (m, 2H), 7.21
(
(
d, J ¼ 8.0 Hz, 2H), 7.46e7.41 (m, 4H), 6.99 (d, J ¼ 16.3 Hz, 1H), 6.90
d, J ¼ 16.3 Hz, 1H), 2.38 s (3H).
1
3
3
C NMR (CDCl ): d 179.04, 150.53, 142.73, 140.51, 136.49, 132.13,
130.09, 129.76, 128.99, 128.48, 127.63, 115.20, 21.49.
5. NMR experiments
NMR experiments were recorded in Bruker Avance Neo in-
1
struments working at 500.16 and 399.77 MHz for H and at 125.76
13
and 100.52 MHz for C using the standard Bruker pulse sequences
1
13
for H, C, COSY, NOESY and HSQC experiments. Typically, 16
1
transits and a 30-degree flip angle was used for H, 1024 transits
13
and a 90-degree flip angle was used for C. For 2D experiments the
following parameters were used: 1 transit and 128 increments for
COSY, and 4 transits and 256 increments for NOESY and HSQC.
6. Computational details
All the calculations have been carried out using the Gaussian-16
package [50]. In all cases, we have used the B3LYP/6e311þþG (d,p)
method [51]; frequency calculations were carried out to verify that
the structures obtained correspond to energetic minima (I ¼ 0) or
to transition states (TS, I ¼ 1). These geometries have been used for
the calculation of the absolute chemical shieldings with the GIAO
method [52,53].
Equations 4-6 have been used to transform absolute shieldings
into chemical shifts:
1
1
d
H ¼ 31.0e0.97 x
s H, (reference TMS, 0.00 ppm) (Eq. (4)) [54]
13
13
d
C ¼ 175.7e0.963 x
s
C, (reference TMS, 0.00 ppm) (Eq. (5))
[
55]
d
15
15N, (reference TMS, 0.00 ppm) (Eq.
N ¼ ꢀ152.0e0.946 x
s
(
6)) [55].
In order to locate the intermediates at either sites of the TS point
we followed the vibrational mode of the imaginary frequency e
forward and backward e along the intrinsic reaction coordinate
(
(
IRC) [56,57] and relaxed the geometry for searching an energy
local) minimum.
17