NMR of enaminones part 3 ? - 1H, 13C and 17O NMR spectroscopic studies of acyclic and cyclic N-aryl enaminones: Substituent effects and intramolecular hydrogen bonding

Article abstract of DOI:10.1002/(SICI)1097-458X(199705)35:5<311::AID-OMR94>3.0.CO;2-M

¹⁷O, ¹³C and ¹H NMR spectra for para-and meta-substituted 4-arylaminopent-3-en-2-ones (acyclic enaminones, 1 and 2) and 3-arylaminocyclohex-2-en-1-ones (cyclic enaminones, 3 and 4) are reported. The ¹⁷O, ¹³C and ¹H shift values of these enaminones correlate well with σ_m⁰ and σ_p^- constants in the correlations for meta and para derivatives, and with pK_a values of the corresponding anilines. Dual substituent parameters analyses were also performed. Correlations of ¹⁷O and ¹³C chemical shifts of the carbonyl groups with those of the corresponding N-acylanilines indicate that the enaminone moiety as a whole has electronic properties similar to those of the RCONH group. The ¹⁷O shift values of the carbonyl O atoms of enaminones correlate well with their ¹H and ¹³C data. Shieldings of 33-45 ppm for O atoms are observed for 1 and 2 compared with 3 and 4, respectively. This is attributed to intramolecular hydrogen bonding.

Full text of DOI:10.1002/(SICI)1097-458X(199705)35:5<311::AID-OMR94>3.0.CO;2-M

MAGNETIC RESONANCE IN CHEMISTRY, VOL. 35, 311È322 (1997)
NMR of Enaminones Part 3¤È1H, 13C and 17O
NMR Spectroscopic Studies of Acyclic and Cyclic
N-Aryl Enaminones: Substituent E†ects and
Intramolecular Hydrogen Bonding
Jin-Cong Zhuo
Institute of Organic Chemistry, University of Lausanne, BCH, CH-1015 Lausanne-Dorigny, Switzerland
17O, 13C and 1H NMR spectra for para- and meta-substituted 4-arylaminopent-3-en-2-ones (acyclic enaminones,
1 and 2) and 3-arylaminocyclohex-2-en-1-ones (cyclic enaminones, 3 and 4) are reported. The 17O, 13C and 1H
shift values of these enaminones correlate well with r 0 and r — constants in the correlations for meta and para
m
p
derivatives, and with pK values of the corresponding anilines. Dual substituent parameters analyses were also
a
performed. Correlations of 17O and 13C chemical shifts of the carbonyl groups with those of the corresponding
N-acylanilines indicate that the enaminone moiety as a whole has electronic properties similar to those of the
RCONH group. The 17O shift values of the carbonyl O atoms of enaminones correlate well with their 1H and 13C
data. Shieldings of 33–45 ppm for O atoms are observed for 1 and 2 compared with 3 and 4, respectively. This is
attributed to intramolecular hydrogen bonding. ( 1997 by John Wiley & Sons, Ltd.
Magn. Reson. Chem. 35, 311È322 (1997) No. of Figures: 1 No. of Tables: 14 No. of References: 32
Keywords: NMR; 1H NMR; 13C NMR; 17O NMR; enaminones; substituent e†ects; linear correlations; intramolecular
hydrogen bonding
Received 27 August 1996; revised 5 November 1996; accepted 30 November 1996
d \ d0 ] o p ] o p
(2)
(3)
in
INTRODUCTION
I I
R R
d \ d0 ] o p ] o p 0/(1 [ ep 0)
I I
of
R R
substituent
R
Enaminones are important organic intermediates2 and
have been reported to have potential biological activ-
ity.3 Recently, the 17O NMR spectra of some enam-
inones have been reported1,4 in which the 17O chemical
shifts were shown to be sensitive to the nature, number
and position of the substituents and intramolecular
hydrogen bonding. The shielding of O by the intramole-
cular hydrogen bonding components, ranging from 14
to 47 ppm, depends on the nature of the substituents.4
The 17O, 13C-2 and 1H-2 data for enaminones have
been shown to correlate with each other and with the
The
transmission
e†ects
XC H ZCHxCH (Z \ O, S, Se or Te)9 and
6 4
2
XC H ZC(R)xO (Z \ O or NH)10 series have been
6 4
investigated. However, the SCS for enaminone systems
XC H NHCRxCHC(R@)xO, which can be considered
6 4
as a combination of the two series mentioned, have not
been systematically examined so far.
In order to examine the transmission of N-aryl sub-
stituent e†ects to enaminone moiety and to evaluate the
sensitivity of the 17O shift values of carbonyl groups on
the CxOÉÉÉHÈN type of hydrogen bonding, the 17O,
13C and 1H NMR spectra of para- and meta-substituted
4-(N-arylamino)pent-3-en-2-ones (acyclic enaminones
1aÈj and 2aÈj) and 3-(N-arylamino)cyclohex-2-en-1-ones
(cyclic enaminones 3aÈj and 4aÈj) have been investi-
gated.
pK values of the amines.1,4
a
NMR substituent-induced chemical shifts (SCS) have
been much investigated in aromatic systems.5,6 The
SCS values of various nuclei have been analyzed by
using Hammett substituent constants7 [Eqn (1)] and/or
dual substituent parameter (DSP)8 [Eqn (2)] and
DSP-NLR (DSP-nonlinear resonance e†ect)6b [Eqn
(3)]:
RESULTS AND DISCUSSION
d \ d0 ] op
(1)
The 17O SCS for acyclic (1 and 2) and cyclic enam-
inones (3 and 4), recorded in acetonitrile solution at
natural abundance are listed in Table 1. The carbonyl
17O signals of enaminones (1È4) appear in the region
Correspondence to: J.-C. Zhuo.
¤ For Part 2, see Ref. 1.
Contract grant sponsor: Swiss National Science Foundation.
( 1997 by John Wiley & Sons, Ltd.
CCC 0749È1581/97/050311È12 $17.50

312
J.-C. ZHUO
reported for enaminones.4 The substituent e†ects on
17O chemical shifts of the carbonyl O atoms parallel
those reported previously for the corresponding N-
arylacetamides10m and benzanilides:10n electron-
donatinggroupscauseshieldingandelectron-withdrawing
groups cause deshielding. The temperature dependence
of the 17O data is not signiÐcant. A slight deshielding at
higher temperature (70 ¡C) was noted only for 1j (1.1
ppm), 2j (1.4 ppm) and 3b (1.0 ppm).
The 13C NMR data for the acyclic (1 and 2) and
acyclic enaminones series (3 and 4) in CDCl solution
3
are summarized in Tables 2 and 3, respectively. The
peak assignments for the enaminone moieties are in
agreement with those reported for the corresponding
analogs.2 The trend of the substituent e†ects on 13C
chemical shifts of C-1 and C-2 is similar to that noted
for 17O, but it is reverse for C-3. The assignments of the
signals of the aromatic carbon nuclei were achieved by
considering peak intensity, peak multiplicity under o†-
resonance decoupling conditions, SCS for mono-
substituted benzenes6b and nJ
values for
CF
Ñuorine-containing enaminones.
The 1H NMR spectra of several enaminones have
been recorded previously.2,11 The present 1H data for
H-2 and H-N (Table 1) are in agreement with available
literature values measured under similar conditions.
Table 1. 17O and 1H NMR chemical shifts (ppm) for enaminones (1–4)
Compound
X
17Oa
1H-2b
1H-Nb
Dd(O)
c
Compound
17Oa
1H-2b
1H-Nb
HB
1a ¼2a
1b
1c
1d
1e
1f
H
435.3d
432.7
431.1f
429.1
434.9
437.8
437.5
444.3
448.0
451.4h,i
433.6
435.3k
440.0
440.0
441.7
443.5
444.5m,n
5.19
5.17
5.16
5.13
5.19
5.22
5.21
5.26
5.30
5.34
5.17
5.19
5.22
5.22
5.25
5.27
5.30
12.48
12.40
12.29
12.25
12.35
12.44
12.43
12.62
12.69
12.79
12.43
12.48
12.50
12.47
12.57
12.56
12.66
É35.9
É34.5
É33.2
É34.3
É36.6
É39.8
É42.0
É40.0
É45.1
É42.1
É36.6
É36.3
É38.0
É38.7
É38.3
É38.3
É41.1
3a ¼2a
3b
3c
3d
3e
3f
471.2d
467.2e
464.3g
463.4
471.5
477.6
479.5
484.3
493.1
493.5j
470.2
471.6l
478.0
478.7
480.0
481.8
485.6o
5.59
5.51
5.37
5.36
5.39
5.53
5.54
5.71
5.79
5.87
5.59
5.63
5.63
5.60
5.58
5.57
5.62
6.27
6.21
6.25
6.10
6.48
6.20
6.26
6.23
6.44
6.38
6.25
6.19
6.51
6.27
6.28
6.84
6.83
Me
MeO
NMe
F
2
Cl
1g
1h
1i
Br
3g
3h
3i
CF
3
CN
1j
NO
2
Me
3j
2b
2c
2e
2f
4b
4c
4e
4f
OMe
F
Cl
2h
2i
CF
3
CN
4h
4i
2j
NO
4j
2
a Natural abundance measurements of 0.25–0.5 M CH CN solution at 40 ¡C for series 1 and 2 and 70 ¡C for
series 3 and 4 unless stated otherwise; linewidths at half-height are 190–490 Hz.
3
b Relative to internal TMS in CDCl at 20 ¡C, singlet.
3
c Dd(O) ¼d(O)(1 or 2) Éd(O)(3 or 4).
HB
d Taken from Ref. 1.
e Measured at 40 ¡C: d ¼466.2 ppm.
0
f d
g d
h d
¼50.6 ppm.
¼46.3 ppm.
¼563.6 ppm.
OMe
OMe
NO2
i Measured at 70 ¡C: d ¼452.5 ppm and d
¼565.2 ppm.
0
NO2
jd
k d
l d
¼565.1 ppm.
¼48.8 ppm.
NO2
OMe
¼49.7 ppm.
¼573.9 ppm.
OMe
m d
NO2
n Measured at 70 ¡C: d ¼445.9 ppm and d
¼575.3 ppm.
0
NO2
o d
NO2
¼574.3 ppm.
( 1997 by John Wiley & Sons, Ltd.
MAGNETIC RESONANCE IN CHEMISTRY, VOL. 35, 311È322 (1997)

17O NMR OF ENAMINONES
313
Table 2. 13C chemical shifts (ppm) for 4-anilinopent-3-en-2-ones (1 and 2)a
Compound
C-1
C-2
C-3
C-4
C-5
C-1¾
13C-2¾
C-3¾
C-4¾
C-5¾
C-6¾
X
1a ¼2a
1b
196.08
195.90
195.78
195.34
196.33
97.62
97.21
96.84
96.33
97.55
160.30
160.80
161.31
161.85
160.55
19.82
19.77
19.63
19.65
19.64
29.13
29.07
29.04
29.01
29.14
138.67
136.02
131.47
127.68
134.73
(3.0)b
124.67
124.86
126.65
126.43
126.83
(8.4)
129.09
129.67
114.25
112.55
115.93
(22.6)
129.22
132.16
126.40
(3.7)
125.55
135.51
157.73
148.85
160.64
(246.0)
130.99
116.68
126.78
(32.8)
107.23
143.47
126.34
111.05
112.13
(21.1)
125.41
121.88
(3.3)
—
20.91
55.43
40.65
—
1c
1d
1e
1f
196.53
196.54
197.15
98.13
98.22
99.34
159.72
159.62
158.70
19.79
19.80
20.13
29.23
29.21
29.41
137.37
137.83
142.24
(0.7)
125.85
126.08
123.59
—
—
1g
1h
124.07
(271.7)
118.72
—
1i
197.55
197.90
195.92
196.13
196.72
100.49
101.22
97.47
97.76
98.47
157.55
157.04
160.36
160.19
159.37
20.41
20.62
19.83
19.90
19.96
29.54
29.65
29.11
29.14
29.29
143.33
145.34
139.03
139.87
140.49
(9.8)
122.83
121.86
125.35
110.35
111.50
(23.5)
124.43
121.07
(3.3)
133.30
125.19
138.61
160.16
162.90
(246.9)
134.62
131.70
(32.6)
113.28
148.72
1j
2b
2c
2e
128.85
129.77
130.27
(9.4)
121.70
116.89
119.99
(2.0)
21.31
55.28
—
2f
196.69
197.01
98.48
98.81
159.42
159.16
19.89
19.88
29.25
29.35
140.08
139.56
130.09
129.78
122.57
127.53
—
2h
123.70
(272.4)
118.15
—
2i
2j
197.28
197.44
99.34
99.62
158.50
158.36
19.94
20.01
29.40
29.45
139.96
140.33
126.99
118.32
128.48
119.56
130.18
130.03
128.48
129.66
a Relative to internal TMS in CDCl at 20 ¡C.
b Values in parentheses are C–F coupling constants (Hz).
3
The 19F data for Ñuorine-containing compounds are
are similar to those previously observed for N-
acylanilines.10 Good correlations of 17O values of the
carbonyl groups in series 1 and 3 were observed with
those in N-(4-substituted phenyl)acetamides (5)10m and
N-(4-substituted phenyl)benzamides (6)10n (Table 5,
lines 1È4). The results suggest that the substituent e†ects
on enaminone systems are similar to those in acet-
amides and benzamides. The slopes of ca. 0.9 (Table 5,
listed in Table 4.
Substituent e†ects on the enaminone moiety
The trends of the 17O and 13C SCS of the carbonyl
groups for the para-substituted enaminones (1 and 3)
Table 3. 13C chemical shifts (ppm) for 3-anilinocyclohex-2-en-1-ones (3 and 4)a
Compound
C-1
C-2
C-3
C-4
C-5
C-6
C-1¾
C-2¾
C-3¾
C-4¾
C-5¾
C-6¾
X
3a ¼4a
3b
198.50
198.26
198.08
197.81
198.36
99.15 163.18 29.55 21.84 36.47 138.24
98.96 163.36 29.55 21.87 36.48 135.53
98.62 164.06 29.43 21.90 36.46 130.83
98.12 164.68 29.34 21.95 36.46 127.16
99.02 163.55 29.45 21.83 36.47 134.05
(2.6)b
123.93
124.08
126.19
125.97
126.30
(8.1)
129.23
129.78
114.43
112.78
116.10
125.42
135.29
157.56
148.80
160.34
—
20.95
55.47
40.68
—
3c
3d
3e
(22.7) (245.7)
3f
198.50
198.50
99.65 162.60 29.56 21.79 36.48 136.79
99.82 162.32 29.59 21.78 36.48 137.31
125.15
125.37
122.79
129.38
132.36
126.51
(3.3)
130.72
118.37
126.53
(32.9)
107.16
143.25
—
—
3g
3h
198.85 100.83 161.55 29.69 21.73 36.53 141.76
(0.5)
123.90
(271.7)
118.62
—
3i
198.87 102.30 160.14 29.77 21.66 36.55 143.01
199.14 102.92 160.23 29.75 21.64 36.58 145.04
122.14
121.34
124.52
109.71
110.79
133.47
125.30
138.19
160.26
163.04
3j
4b
4c
4e
198.47
198.54
98.94 163.49 29.53 21.86 36.49 139.12
99.36 163.26 29.52 21.84 36.51 139.54
126.21 128.99 120.96
110.81 129.91 116.11
112.10 130.48 119.12
21.33
55.27
—
198.71 100.15 162.22 29.61 21.78 36.51 139.98
(9.9)
(23.9) (246.7)
(21.1)
(9.3)
(2.0)
4f
198.68 100.14 162.21 29.62 21.78 36.50 139.54
198.66 100.28 161.92 29.66 21.76 36.54 138.94
123.76
120.37
(3.3)
134.86
131.90
(32.7)
113.42
148.85
125.44 130.30 121.81
121.92 129.92 126.89
(3.3)
—
4h
123.61
(272.6)
118.08
—
4i
4j
198.77 100.60 161.64 29.57 21.71 36.51 139.43
198.81 100.94 161.35 29.64 21.70 36.56 139.73
126.49
118.01
127.83 130.35 128.51
119.7
130.21 129.12
a Relative to internal TMS in CDCl at 20 ¡C.
b Values in parentheses are C–F coupling constants (Hz).
3
( 1997 by John Wiley & Sons Ltd.
MAGNETIC RESONANCE IN CHEMISTRY, VOL. 35, 311È322 (1997)

314
J.-C. ZHUO
Table 4. 19F Chemical shifts (ppm) for
Ñuorine-containing compounds
Compound
19Fa
Compound
19Fa
1e
2e
3e
4e
É3.29
1.47
1h
2h
3h
4h
50.87
50.25
50.84
50.28
É2.58
1.99
a Relative to internal fluorobenzene which
is 113.59 ppm from FCCl in CDCl .
Downfield is positive.
3
3
Scheme 1
lines 1 and 2) for series 1 and ca. 1.3 (Table 5, lines 3
and 4) for series 3 indicate that the substituent e†ects
were only slightly diminished in the former case and
increased in the latter. This result is not consistent with
that the substituent e†ects are reduced by approx-
imately 50% when a CxC double bond is inserted
between a substituted aromatic ring and a functional
group,12 indicating that the transmission of substituent
e†ects through CxC double bond is efficient. The
transmission efficiency of the CxC bond can be
explained in terms of the resonance structures AÈD
(Scheme 1) and reÑects the extended delocalization in
the molecule. The correlations of 13C SCS values of the
carbonyl carbons for acyclic series (1 and 2) and cyclic
series (3 and 4) with those for N-acylanilines (5 and 8)
show that the transmission of the substituent e†ects is
enhanced in acyclic enaminones and diminished in
cyclic enaminones, as shown by the slopes of more than
unity (Table 5, lines 5 and 6) and less than unity (Table
5, lines 7 and 8), respectively.
13C-3 data between 1 and 3 were observed with near-
unity slopes (Table 6, lines 4 and 5), indicating that the
substituent e†ects in both series are qualitatively identi-
cal. The slopes of the correlations between 1 and 3, 0.47
for 13C-1 and 1.47 for 17O, show the di†erence in sub-
stituent e†ects for the two nuclei. This may be owing to
the inÑuence of intramolecular hydrogen bonding and
to the enhanced delocalization and n,n interaction in
acyclic enaminones (1 and 2).
In previous papers,1,4 it has been shown that the
1H-2, 13C-2 and 17O chemical shifts of enaminones can
correlate well with each other, and these data can be
used to reÑect the polarization and the degree of n,n
conjugation. In present study, the 17O data of carbonyl
O atoms are correlated with the 1H-2, 1H-N, 13C-1,
13C-2 and 13C-3 SCS values (Table 7). These relation-
ships show that 17O, 13C and 1H shieldings are govern-
ed by the same e†ects. It is obvious that 17O values is
very sensitive to reÑect the polarization and the degree
of n,n conjugation in the NÈCxCÈCxO system.
As has been noted in a previous paper,4 excellent
correlations of the 13C chemical shifts di†erence
Correlations of the 1H, 13C and 17O SCS values
between 1 and 3 and between 2 and 4 were also exam-
ined (Table 6). Linear relationships of the 13C-2 and
Table 5. Correlations of 13C and 17O SCS for series 1–4 with those for
series 5–8
Line
SCSa
Series
Series
Slope
Intercept
rb
nc
SDd
1
2
3
4
5
6
7
8
O
1
5e
6g
5e
6g
5i
0.89
0.94
1.29
1.38
1.28
4.01
0.59
0.84
0.40
1.95
1.54
3.93
0.28
0.05
É0.07
0.01
0.991
0.965
0.986
0.940
0.960
0.972
0.983
0.978
6f
1.06
1.98
1.96
3.88
0.22
0.13
0.07
0.03
O
1
3
3
1
2
3
4
9h
6f
O
O
9h
9h
7k
9h
6l
C-1
C-1
C-1
C-1
8j
5i
8j
a SCS ¼d(X) Éd(H).
b Correlation coefficient.
c Number of points in the correlation.
d Standard deviation in ppm.
e Taken from Ref. 10m.
f Regression analysis was performed for p-H, p-Me, p-OMe, p-Cl, p-Br and
p-NO derivatives.
2
g Taken from Ref. 10n.
h Point for p-NMe derivative was not included owing to lack of 17O data for
6d.
2
i Taken from Ref. 10e.
jTaken from Ref. 10d.
k Point for m-NO derivative was excluded.
2
l Points for m-F and m-NO derivatives were excluded.
2
( 1997 by John Wiley & Sons, Ltd.
MAGNETIC RESONANCE IN CHEMISTRY, VOL. 35, 311È322 (1997)

17O NMR OF ENAMINONES
315
Table 6. Correlations of 1H, 13C and 17O SCS for series 3 or 4 with those
for series 1 or 2
Line
SCS
Series
Series
Slope
Intercept
r
n
SD
1
2
3
4
5
6
7
8
9
O
3
3
3
3
3
3
3
3
3
1
1
1
1
1
1
1
1
1
1.47
2.55
0.47
1.00
0.97
1.02
1.02
1.00
0.99
1.09
É0.09
É0.22
0.11
0.983
0.944
0.968
0.996
0.993
1.000
0.997
1.000
0.999
10
10
10
10
10
10
10
10
10
2.14
0.06
0.10
0.14
0.19
0.09
0.13
0.04
0.58
H-2
C-1
C-2
C-3
C-1¾
C-2¾
C-3¾
C-4¾
É0.07
É0.05
É0.09
0.01
0.27
10
11
12
13
14
15
16
17
18
19
O
4
4
4
4
4
4
4
4
4
4
2
2
2
2
2
2
2
2
2
2
1.35
0.21
0.89
1.01
0.95
1.00
1.00
0.99
1.04
1.04
0.51
0.02
0.987
0.964
0.985
0.982
0.986
1.000
1.000
0.999
0.999
0.999
8
8
8
8
0.99
0.04
0.13
0.16
0.10
0.17
0.22
0.25
0.02
0.23
C-1
C-2
C-3
C-1¾
C-2¾
C-3¾
C-4¾
C-5¾
C-6¾
0.06
1.08
É0.02
0.09
7a
8
8
8
8
8
É0.05
É0.04
0.00
0.14
a Point for Me derivatives was excluded.
between the two oleÐnic carbons, d(C-3ÈC-2) \ d(C-3)
[ d(C-2), with the 17O data were observed (Table 7,
lines 17È20). This further supports that the shielding of
the carbonyl O atoms depends on the polarization and
the degree of n,n conjugation. The 13C-1 SCS values
also correlate well with d(C-3ÈC-2) (Table 7, lines
21È24).
Hammett-type correlations
The results of Hammett correlations [Eqn (1)] of the
17O, 13C and 1H SCS data for the four series of enam-
inones are listed in Table 8. The 17O SCS of a variety of
substituted benzoyl compounds and a,b-unsaturated
Table 7. Correlations of 17O with 1H and with 13C SCS for series 1–4
Line
Series
SCS
SCS
Slope
Intercept
r
n
SD
1
2
3
4
5
1
O
O
O
O
O
C-1
9.03
É0.97
É0.22
0.31
0.992
0.997
0.995
0.996
0.979
10
10
10
10
10
1.01
0.56
0.80
0.69
1.61
C-2
C-3
H-2
H-N
4.64
É4.68
112.61
41.17
É0.13
3.20
6
7
8
9
2
3
4
O
O
O
O
C-1
C-2
C-3
H-2
7.10
5.07
É0.17
É0.25
É0.39
0.71
0.997
0.989
0.987
0.970
8
8
8
8
0.35
0.64
0.71
1.07
É5.13
88.93
10
11
12
13
O
O
O
O
C-1
C-2
C-3
H-2
26.38
6.74
5.70
0.04
1.00
6.75
0.942
0.973
0.987
0.928
10
10
10
10
3.93
2.68
1.89
4.40
É7.11
57.88
14
15
16
O
O
O
C-1
C-2
C-3
43.09
7.44
É0.20
É0.22
0.61
0.971
0.993
0.993
8
8
8
1.44
0.72
0.71
É6.91
17
18
19
20
1
2
3
4
O
O
O
O
C-3–C-2a
C-3–C-2
C-3–C-2
C-3–C-2
É2.33
É2.55
É3.49
É3.67
146.37
159.77
224.08
235.04
0.997
0.989
0.984
0.995
10
8
0.60
0.66
2.06
0.60
10
8
21
22
23
24
1
2
3
4
C-1
C-1
C-1
C-1
C-3–C-2
C-3–C-2
C-3–C-2
C-3–C-2
É0.25
É0.36
É0.12
É0.08
16.08
22.60
7.49
0.991
0.995
0.946
0.980
10
8
0.11
0.06
0.14
0.03
10
8
5.23
a d(C-3–C-2) ¼d(C-3) Éd(C-2).
( 1997 by John Wiley & Sons Ltd.
MAGNETIC RESONANCE IN CHEMISTRY, VOL. 35, 311È322 (1997)

316
J.-C. ZHUO
Table 8. Correlations for 1H, 13C and 17O SCS for series 1–4 with Hammett
constants
Line
Series
da
sb
r
d0
r
n
SD
1
2
3
4
5
6
1
O
s É
p
13.145
0.114
0.30
434.99
5.19
0.998
0.996
0.968
0.993
0.999
0.996
9
0.51
0.006
0.04
0.09
0.07
0.13
H-2
H-N
C-1
C-2
C-3
s É
p
9
9
9
9
9
s É
p
12.40
196.20
97.60
160.39
s É
p
1.373
2.826
É2.73
s É
p
s É
p
7
8
1
O
s É
p
12.90
0.114
0.30
435.14
5.19
0.998
0.997
0.975
0.993
0.999
0.997
0.956
0.993
10
10
10
10
10
10
10
10
0.55
0.005
0.04
0.10
0.09
0.12
0.11
0.03
H-2
H-N
C-1
C-2
C-3
C-4
C-5
s É
p
9
s É
p
12.40
196.17
97.63
160.40
19.79
29.15
10
11
12
13
14
s É
p
1.41
s É
p
2.78
s É
p
É2.74
0.58
s É
p
s É
p
0.38
15
16
17
18
19
20
2
3
O
s 0
14.18
0.15
434.88
5.18
0.995
0.972
0.995
0.995
0.994
0.986
8
8
8
8
8
8
0.43
0.01
0.06
0.08
0.09
0.02
m
H-2
C-1
C-2
C-3
C-5
s 0
m
s 0
1.99
196.05
97.59
160.29
29.13
m
s 0
m
2.77
s 0
É2.72
0.45
m
s 0
m
21
22
23
24
25
26
27
28
O
s É
p
19.01
0.29
472.04
5.50
0.984
0.951
0.965
0.993
0.986
0.945
0.992
0.961
10
10
10
10
10
10
10
10
2.10
0.06
0.11c
0.21
0.27
0.05
0.01
0.01
H-2
C-1
C-2
C-3
C-4
C-5
C-6
s É
p
s É
p
0.67
198.33
97.28
163.20
29.51
21.85
36.48
s É
p
2.77
s É
p
É2.64
0.23
s É
p
s 0
É0.25
0.071
p
s É
p
29
30
31
32
33
4
O
s 0
21.08
0.43
472.65
198.51
99.18
0.989
0.982
0.995
0.992
0.994
8
8
8
8
8
0.95
0.03
0.08
0.11d
0.01
m
C-1
C-2
C-3
C-5
s 0
m
s 0
2.50
m
s 0
m
É2.79
É0.21
163.27
21.85
s 0
m
a d¼d0 ½sr.
b s , s É and s were taken from Ref. 16a and s 0 from Ref. 16b. A s É value of
É0.52 was used for p-NMe , estimated from lines 1–6 in which the point for 1d
p
p
m
m
p
2
was excluded.
c Correlation with s gives o ¼0.80; r ¼0.977; SD ¼0.09.
p
d Correlation with s gives o ¼2.62; r ¼0.996; SD ¼0.07.
m
carbonyl compounds have been obtained the best corre-
lation with Hammett p` values,13 and acetanilides10m
and benzanilides10n with Hammett p values. The 13C
SCS of the carbonyl carbons of chalcones have been
correlated with Hammett p values.14 In a,b-unsaturated
carbonyl compounds, the 1H chemical shifts of the eth-
ylenic protons H-a and H-b were found to correlate
with p` and p0 values,15 respectively. The 1H chemical
shifts of the H-b protons in aryl vinyl ethers and sulÐdes
were previously correlated with the p value.9a In enam-
inone cases, the best correlations of the 1H-2, 13CxO,
13C-2, 13C-3 and 17O NMR SCS values of para-
were observed with p ~. In the meta series 2 and 4, the
p
correlations were observed only for C-5. The p ~ con-
p
stant ([0.52) for the NMe group was statistically esti-
2
mated from the 1H, 13C and 17O NMR data for 1d and
the corresponding correlation equations (Table 8, lines
1È6) in which the point for the -NMe group (1d) was
2
excluded.
The magnitude of the o values for these correlations
illustrates their relative sensitivity to the substituents. In
the four series of enaminones, the slopes of the corre-
lations of pÏs with the d values of 13C-2 and 13C-3 show
similar absolute values, but with opposite signs. The
opposite sign has been previously observed for aryl
vinyl ethers and sulÐdes,9b it probably reÑects the polar-
ization of the C-2xC-3 double bond, as described in
the resonance structures B and C (Scheme 1). The o
value for 17O shows that the SCS values of acyclic
enaminones (1 and 2) are less sensitive to the substit-
uents than those of cyclic derivatives (3 and 4), but it is
reverse for 13C-1. The sensitivity of the 1H-2 in cyclic
substituted enaminones (1 and 3) are obtained with p ~
p
constants (Table 8, lines 7È14 and 21È28, respectively)
by using the p ~ constant for the NMe group ( [ 0.52)
p
2
instead of [ 0.12,16a whereas those of meta-substituted
enaminones (2 and 4) with constants p 0 (Table 8, lines
m
15È20 and 29È33, respectively). The correlations of the
13C chemical shifts of carbons at side chain in the para
series, i.e. C-4 and C-5 in 1 and C-4, C-5 and C-6 in 3,
( 1997 by John Wiley & Sons, Ltd.
MAGNETIC RESONANCE IN CHEMISTRY, VOL. 35, 311È322 (1997)

17O NMR OF ENAMINONES
317
derivatives (3 and 4) may come from the anisotropic
e†ects of the aryl ring. The chemical shift di†erences of
1H-2 between acyclic enaminones (1 and 2) and cyclic
derivatives (3 and 4) for an N-aryl substituent, ca. 0.5
ppm, are much larger than that for an N-alkyl group,
ca. 0.2 ppm.1 The deshielding of the 1H-2 in 3 and 4 can
be attributed to the anisotropic e†ects of the N-aryl
rings and suggests that the aryl rings are located at the
H-2 side. This is consistent with the previous analysis of
cyclic enaminones.17
eters, whereas for 13C-1, 13C-3 and 17O with p 0
R
parameters. These results suggest that the contribution
of resonance structure C is more important in series 1
and the resonance structure B is more important in
series 3. An electron donor substituent decreases the
ability of the nitrogen lone pair delocalization with the
aromatic ring and increases the contribution of the
resonance structures B and C, whereas an electron
acceptor substituent leads to increased contribution of
resonance structure D (Scheme 1), and to enhanced the
n,n-interaction between the nitrogen lone pair and the
aromatic ring, resulting in decreased electron densities
at the O, H-2 and C-2 atoms with concomitant
deshielding. This result is consistent with that pre-
viously noted for acetanilides.10e,k DSP analysis for
meta-substituted enaminones (2 and 4) shows that the
correlations of 1H-N in series 2, and 1H-2 in series 4 are
poor (Table 9, lines 11 and 26, respectively).
DSP correlations
The results of the DSP treatment [Eqn (2)] for the
1H-2, 13C-1, 13C-2, 13C-3 and 17O NMR SCS are listed
in Table 9. In order to achieve the best Ðt, p 0, p , p ~
R
R
R
and p ` were used along with p . In series 1, for 1H-2,
The results of DSP treatment also show that the
inductive e†ects are greater in series 2 and 4, and the
resonance e†ects are greater in series 3, whereas both
e†ects (inductive and resonance e†ects) are similar in
series 1 except for 1H-N (Table 9, line 3), which shows
R
I
1H-N, 13C-2 and 17O SCS values the best correlations
are with p ~ parameters,7b whereas for 13C-1 and 13C-3
R
with p 0 parameters.7b In series 3, for 1H-2 and 13C-2
R
SCS values the best correlations are with p ~ param-
R
Table 9. DSP analysis of 1H, 13C and 17O SCS for series 1–4
Line
Series
da
Scaleb
r
r
d0
SD
r
n
fc
I
R
1
2
3
4
5
6
7
8
1
O
s É
R
15.47
0.14
0.22
2.55
3.34
É4.52
0.49
0.48
15.89
0.14
0.44
2.29
3.42
É4.83
0.84
0.46
435.14
5.19
0.61
0.01
0.02
0.04
0.08
0.15
0.06
0.02
0.996
0.996
0.995
0.998
0.999
0.995
0.984
0.997
10
10
10
10
10
10
10
10
0.08
0.08
0.10
0.05
0.05
0.09
0.18
0.07
H-2
H-N
C-1
C-2
C-3
C-4
C-5
s É
R
s É
R
12.46
196.14
97.63
160.22
19.88
29.14
s 0
R
s É
R
s 0
R
s É
R
s É
R
9
10
11
12
13
14
15
16
2
3
4
O
s
13.88
0.13
0.17
1.92
2.95
É2.89
0.23
0.43
6.28
0.07
435.06
5.19
0.32
0.004
0.02
0.04
0.03
0.08
0.02
0.02
0.996
0.995
0.933
0.998
0.999
0.994
0.923
0.990
8
8
8
8
8
8
8
8
0.06
0.07
0.30
0.05
0.02d
0.07
0.22
0.10
R
H-2
H-N
C-1
C-2
C-3
C-4
C-5
s É
R
s É
R
0.13
12.47
196.09
97.65
160.25
19.82
29.14
s
0.93
R
s 0
1.50
R
s 0
R
É1.44
É0.016
0.22
s
R
s
R
17
18
19
20
21
22
23
24
O
s 0
33.98
0.16
31.53
0.47
471.80
5.58
1.60
0.02
0.06
0.13
0.23
0.03
0.01
0.03
0.988
0.991
0.988
0.996
0.987
0.981
0.996
0.857
10
10
10
10
10
10
10
10
0.14
0.14
0.15
0.08
0.16
0.20
0.08
0.60
R
H-2
C-1
C-2
C-3
C-4
C-5
C-6
s É
R
s
0.69
0.96
198.46
99.32
162.92
29.58
21.84
36.48
R
s É
R
3.24
3.47
s 0
É4.18
0.29
É4.85
0.50
R
s 0
R
s É
R
É0.30
0.071
É0.29
0.13
s É
R
25
26
27
28
29
30
31
32
O
s
R
19.16
0.03
8.37
É0.06
0.11
471.33
5.58
0.56
0.01
0.02
0.04
0.08
0.03
0.005
0.02
0.994
0.784
0.991
0.999
0.994
0.756
0.996
0.802
8
8
8
8
8
8
8
8
0.07
0.52
0.08
0.03e
0.08
0.61
0.06
0.48
H-2
C-1
C-2
C-3
C-4
C-5
C-6
s
R
s
R
0.47
198.49
99.12
163.23
29.55
21.84
36.49
s
R
2.58
0.86
s
R
É2.73
0.13
É1.25
0.071
É0.12
0.024
s
R
s 0
É0.22
0.075
R
s É
R
a d¼d0 ½r s ½r s .
I I R R
b s and s were taken from Ref. 18 and s 0 and s É from Ref. 7b.
I
R
R
R
cf ¼SD/rms.
d Correlation with s É: r ¼2.49; r ¼1.00; SD ¼0.06; r ¼0.997; f ¼0.05.
e Correlation with s É: r ¼2.47; r ¼0.61; SD ¼0.10; r ¼0.990; f ¼0.09.
R
I
R
R
I
R
( 1997 by John Wiley & Sons Ltd.
MAGNETIC RESONANCE IN CHEMISTRY, VOL. 35, 311È322 (1997)

318
J.-C. ZHUO
that the contribution of the resonance e†ect is more
important.
SD \ 2.3) for benzaniles 6 and [5.77 (r \ 0.989, n \ 8,
SD \ 1.7) for intramolecular hydrogen-bonded sali-
cylanilides (calculated from the published data).10n The
slopes of the correlations of 13C data of the carbonyl
carbons, [0.50 for 1, [0.24 for 3 and [0.36 for acet-
amides 5 (calculated from the published data),10e are
slightly diminished in cyclic enaminone systems relative
to those in acyclic system and the acetamides.
The o and o values for 13C-3 have the opposite sign
I
R
to those for 1H-2, 13C-2 and 17O. The negative sign
reÑects the reverse nature of the 13C-3 shifts. The fact
that the p 0 or p scale is preferred for the C-3 and C-1,
R
R
and the p ~ scale for O, C-2 and H-2 indicates the con-
R
tribution of the resonance structure C.
Correlations with the pK values of anilines
Intramolecular hydrogen bonding
a
The 1H-2, 13C-2 and 17O NMR data of enaminones
The 17O chemical shifts for the carbonyl O atoms in 1
appear at higher Ðeld than those in 3. The shielding
e†ects in acyclic enaminones can be attributed to the
intramolecular hydrogen-bonding. The 1H NMR
spectra show that the N-H signals appear at ca. 6.5 ppm
for 3 and ca. 12.5 ppm for 1, indicating the presence of
intramolecular hydrogen bonding in 1. Comparison of
the 17O chemical shifts for the cyclic with acyclic
systems allows calculation of the chemical shift change
coming from the intramolecular hydrogen bonding
[*d(O) ]. The values of *d(O) range from [33 to
have been found to depend on the donor quality of the
amino group and previously correlate with the pK
a
values of the corresponding amines.1,4 In present paper,
the correlations of the 1H-2, 1H-N, 13C-1, 13C-2, 13C-3
and 17O NMR SCS values with the pK values of
a
anilines19 are good to excellent (Table 10). This indi-
cates that the e†ects of substituents on the chemical
shifts for enaminone moiety are parallel to those on the
basic strength of the amines. The slope of the corre-
lation of 17O data is ca. [6.7 for the cyclic enaminones
and [4.7 for acyclic enaminones. The results are in
good agreement with those previously noted for the cor-
responding enaminone systems.1 These data can be
compared with the slopes of [4.92 (r \ 0.963, n \ 10,
HB
HB
[45 ppm, which are slightly larger than those in N-
alkylenaminones1 [*d(O) \ [27 ^ 2 ppm]. The
HB
shielding e†ects [*d(O) ] of intramolecular hydrogen
HB
bonding of the type of NHÉ É ÉCxO, ranging from [4
to [29 ppm have been reported previously for 2-
amino-acetophenones,20a
1-aminoanthraquinones20b
and 1-aminoÑuorenones.20b It is generally accepted that
Table 10. Correlations of 1H, 13C and 17O SCS for series 1–4
*d(O) values indicate the strength of the hydrogen
with pK a
HB
a
bond.21a The high values of *d(O) ([33 to [45 ppm)
Line
Series
db
a
d0
r
n
SD
HB
found in acylic enaminones 1 and 2 indicate a strong
1
2
3
4
5
6
7
8
1
O
É4.58
456.03
0.998 10 0.46
hydrogen bond.
H-2
É0.040
5.374 0.995 10 0.007
H-N É0.106
12.89
198.46
102.12
155.96
20.72
0.972 10 0.04
0.995 10 0.08
0.996 10 0.15
0.996 10 0.15
0.948 10 0.12
0.993 10 0.03
C-1
C-2
C-3
C-4
C-5
É0.50
É0.98
0.97
Substituent e†ects on the benzene rings
The results of the correlations of the 13C SCS values for
the nuclei of the benzene ring in enaminones (1È4) with
the SCS values of the corresponding carbon nuclei for
the monosubstituted benzene6b are listed in Table 11.
The slopes of the correlations are all close to unity, indi-
cating that the chemical shifts of the aromatic carbons
are a†ected little by the enaminone moiety as a whole
and mainly by the electronic e†ects of the substituents.
However, a slope of 0.89 for C-1@ was observed for the
É0.20
É0.14
29.77
9
10
11
12
13
14
2
3
O
É4.90
É0.053
É0.69
É0.97
0.95
457.20
5.42
0.977
0.965
0.980
0.989
0.988
0.970
8
8
8
8
8
8
0.93
0.01
0.12
0.12
0.13
0.03
H-2
C-1
C-2
C-3
C-5
199.19
102.00
155.97
29.84
É0.16
15
16
17
18
19
20
21
22
O
É6.77
É0.10
É0.24
É0.98
0.94
502.88
5.97
0.987 10 1.90
0.947 10 0.06
0.967 10 0.11
0.988 10 0.27
0.986 10 0.28
0.946 10 0.05
0.991 10 0.01
0.961 10 0.01
series
4-XC H NHCOCH Ph,10d
0.86
for
4-
H-2
C-1
C-2
C-3
C-4
C-5
C-6
6 4
2
XC H NHAc10e and 1.26 for 4-XC H NHSO Me.22
199.41
103.74
158.92
29.89
21.56
36.48
6 4
6 4
2
DSP analyses and DSP-NLR [Eqn (3)]6b treatments
for the para carbon to X, i.e. C-1@ in 1 and 3 or C-6@ in 2
and 4, are summarized in Table 12, in which DSP
analyses for the meta carbon to X, i.e. C-2@ in 1 and 3 or
C-1@ and C-5@ in 2 and 4, are included. The results show
that both Ðeld and resonance e†ects of the substituent X
contribute to changes in chemical shifts at C-1@ or C-6@.
The o and o values for the para series (1 and 3), ca. 5.0
É0.082
0.062
0.071
23
24
25
26
27
4
O
É6.75
É0.15
É0.87
0.96
501.87
199.20
103.14
158.89
21.52
0.979
0.984
0.989
0.971
0.986
8
8
8
8
8
1.22
0.02
0.12
0.21
0.01
C-1
C-2
C-3
C-5
I
R
and 21.0, respectively, can be compared with those for
0.073
C-4 of 4-substituted anilines (o \ 5.0; o \ 17.8)6b and
I
R
7 (o \ 4.5; o \ 19.5).10d In the meta series 2 and 4, the
a Taken from Ref. 19. A pK value of 6.05 was used for p-NMe ,
estimated from the correlation of the pK values of para-
I
R
a
2
o and o values are close to those of 3-substituted
a
I
R
substituted anilines with s É values (pK ¼4.56–2.81 s É,
r ¼0.998, SD ¼0.10) by using a s É value of É0.52 for p-NMe .
anilines6b and 8.10d According to electron demand (e),
small positive values of e for C-1@ in the para series (1
and 3), as noted for 1,4-disubstituted benzenes6b and
p
a
p
p
2
b d¼d0 ½a pK
.
a
( 1997 by John Wiley & Sons, Ltd.
MAGNETIC RESONANCE IN CHEMISTRY, VOL. 35, 311È322 (1997)

17O NMR OF ENAMINONES
319
values of para-substituted nitrobenzenes.20b The inÑu-
ences of the enaminone moiety in 1j (563.6 ppm) and 3j
(565.1 ppm) on the 17O chemical shifts of the nitro
groups are [8.8 and [8.7 ppm, respectively, compared
with nitrobenzene (572.4 ppm at 40 ¡C and 573.8 ppm at
70 ¡C, acetonitrile, new measurement). Using a o` value
Table 11. Correlations of 13C SCS for series 1–4 with those for
monosubstituted benzenes
Series
SCSa
SCSb
b
a
r
n
SD
1
C-1¾
C-3¾
C-4¾
SCS
0.98
1.03
1.06
0.36
0.16
0.999
0.998
0.998
10
10
10
0.24
0.47
1.11
p
SCS
o
of 14.3,23 the p ` value of ca. [0.61 is obtained for the
SCS
É1.24
i
p
enaminone moieties. Similarly, p and p values were
2
C-2¾
C-3¾
C-4¾
C-6¾
SCS
0.96
0.99
0.99
0.93
É0.64
0.01
0.996
1.000
0.998
0.998
8
8
8
8
0.63
0.25
0.47
0.29
m
p
o
estimated by using the correlations of the 13C SCS of
the CxN carbon in benzonitriles with p (o \ [3.21)
SCS
i
SCS
SCS
É0.44
É0.41
m
m
o
p
and p (o \ [2.39)24 and the chemical shift di†erences
p
p
between enaminones (1i, 2i, 3i and 4i) and unsubstituted
benzonitrile (118.81 ppm).24 From the relationships of
13C SCS values for the meta and para carbon atoms of
3
4
C-1¾
C-3¾
C-4¾
SCS
SCS
0.99
1.03
1.05
0.32
0.16
0.999
0.999
0.999
10
10
10
0.27
0.44
0.99
p
o
SCS
É0.96
i
monosubstituted benzene derivatives in CDCl [Eqns
3
C-2¾
C-3¾
C-4¾
C-6¾
SCS
0.96
0.99
0.98
0.97
É0.54
É0.04
É0.47
É0.28
0.998
1.000
0.998
0.997
8
8
8
8
0.47
0.29
0.49
0.41
(4) and (5)],6b the p and p 0 values for the enaminone
o
i
R
SCS
moiety were obtained by using the 13C data for 1a and
3a. Since the meta SCS data for monosubstituted ben-
zenes Ðtted poorly to substituent parameters by DSP
i
SCS
SCS
o
p
a SCS ¼d(X) Éd(H) ¼a ½b SCS
b SCS
i, o, p
.
¼SCS for monosubstituted benzenes (Ref. 6b).
[Eqn (5)], the estimated p should have a large devi-
i, o, p
I
ation. It has been shown that 19F SCS data of meta-
substituted Ñuorobenzenes correlate well with p values
I
[Eqn (6)].25 Therefore, more precise values of p and
I
p 0 for the enaminone moiety can be estimated by using
R
p-NHCOR groups,10d indicate that the enaminone
moiety is weak electron donor in presence of a strong
electron acceptor at the para position, whereas negative
values of e for C-6@ in the meta series (2 and 4) mean
that the enaminone moieties are weak electron accep-
tors. These results suggest that the electronic e†ects of
the enaminone moieties are very similar to those of
RCONH groups.
the corresponding 19F data and Eqns (4) and (6).
SCS(13C ) \ 4.6p ] 21.5p 0
(4)
(5)
(6)
para
I
R
SCS(13C ) \ 1.6p [ 1.3p 0
meta
I
R
SCS(19F ) \ 7.1p [ 0.6
meta
I
The p constants (Table 13) for both acyclic and cyclic
enaminone moieties are very close, indicating that they
have essentially identical electronic properties. Corre-
lations of 13C SCS for carbons at the aryl ring in the
cyclic series (3 and 4) with the those in acyclic series (1
and 2) further support the contention that the e†ects of
the two enaminone moieties on the chemical shifts at
these sites are identical, as evidenced by the near unity
slopes (Table 6, lines 6È9 and 14È19). Comparison of
r Values of enaminone moieties
In order to determine whether the enaminone moiety as
a whole is an electron donor or acceptor, its p values
were evaluated. The p ` values for the enaminone moi-
p
eties of 1 and 3 can be estimated from the 17O SCS
Table 12. DSP and DSP-NLR correlations of 13C chemical shifts for nuclei at the
benzene ring in series 1–4
Series
da
r
b
r 0 b
d0
SD
ec
r
n
fd
I
R
1
C-1¾
C-1¾
C-2¾
5.09
5.09
20.70
20.62
É6.56
138.76
138.76
124.06
0.14
0.14
0.76
0.00
É0.01
0.00
0.9996
0.9996
0.886
10
10
10
0.03
0.03
0.44
É0.13
2
C-6¾
C-6¾
C-1¾
C-5¾
3.48
3.62
2.45
2.10
20.40
19.77
É1.28
É0.66
124.57
124.56
138.77
128.97
0.16
0.15
0.12
0.12
0.00
É0.11
0.00
0.999
0.999
0.978
0.969
8
8
8
8
0.04
0.04
0.11
0.13
0.00
3
4
C-1¾
C-1¾
C-2¾
5.02
4.99
0.11
21.13
21.62
É7.01
138.35
138.34
123.28
0.19
0.19
0.70
0.00
0.06
0.00
0.999
0.999
0.908
10
10
10
0.04
0.03
0.38
C-6¾
C-6¾
C-1¾
C-5¾
3.79
3.89
1.78
2.15
21.13
20.72
É1.48
É0.77
123.90
123.89
138.55
129.10
0.34
0.34
0.24
0.11
0.00
É0.07
0.00
0.997
0.997
0.886
0.977
8
8
8
8
0.08
0.08
0.27
0.11
0.00
a d¼d0 ½r s ½r s 0 or d¼d0 ½r s ½r s 0/(1 Ées 0).
I I R R I I R R
R
b s and s 0 were taken from Ref. 6a.
c Demand parameter for C -SCS in 1,4- or 1,3-disubstituted benzenes (Refs 6b and c).
I
R
p
df ¼SD/rms.
( 1997 by John Wiley & Sons Ltd.
MAGNETIC RESONANCE IN CHEMISTRY, VOL. 35, 311È322 (1997)

320
J.-C. ZHUO
Table 13. Estimated substituent constants for the enaminone moieties
Substituent
s
s
s ½
p
s
s 0
R
m
p
I
NH
2
AcNH
É0.16a
0.21a
É0.66a
0a
É1.30a
É0.60a
0.17b
0.28b
É0.51b
É0.35b
0.21
0.23
0.04
0.08
É0.62
É0.61
0.29c (0.33)d
0.36c (0.40)d
É0.19c (É0.20)d
É0.21c (É0.22)d
a Taken from Ref. 16a.
b Taken from Ref. 7b.
c Estimated from the 13C and 19F data.
d Estimated from the 13C data for 1a and 3a.
the p constants (Table 13) for the enaminone moieties
with those for the acetamino group shows that their
electronic properties are essentially similar. The slightly
width 33 ls, acquisition time 20 ms, preacquisition
delay 5 ls, 150 000È300 000 scans, sample spinning (28
Hz). An even number (28È32) left-shifts (LS) were
applied to the FID signal; the latter was zero Ðlled to
8K words and exponentially multiplied with a 100 Hz
line broadening factor (LB) before being subjected to
the FT. The chemical shifts d(17O), measured in 0.25È
0.5 M acetonitrile solution at 40 ¡C for series 1 and 2
and at 70 ¡C for series 3 and series 4 at natural isotopic
more positive p values reÑect that the nitrogens in
I
enaminone moieties are slightly more electronegative,
and the less negative p 0 values demonstrate than the
R
enaminone moieties are poorer n-donors that NHAc
group. This can be attributed to the delocalization of
the lone pair of the nitrogen into the enone moiety.
These results conÐrm that in presence of a strong accep-
tor the enaminone moiety, as acetamino group, is a
weak electron donor.
abundance, are reported relative to d(17O)(H O) (\0.0
2
ppm); dioxane [d(17O) \ 0 ppm] was used as an exter-
nal standard; downÐeld shifts are positive. The general
reproducibility of chemical shifts values is ca. ^1 ppm
(^0.2 ppm within the same series).
The 1H and 13C NMR spectra were measured at
400.13 and 100.62 MHz, respectively on a Bruker
DPX-400 spectrometer. The 1H and 13C chemical shifts,
CONCLUSION
Correlations of 17O, 13C and 1H chemical shifts for four
series of enaminones showed that there is transmission
of inductive (Ðeld) and resonance e†ects from N-aryl
ring to the enamonone moiety. The correlation of O,
H-2, C-2 with p ~, and C-1, C-3 with p 0 suggests that
measured in ca. 0.05 and 0.5 M CDCl solutions, respec-
3
tively, in a 5 mm o.d. tube at 20 ¡C, are reported relative
to TMS as an internal reference (d \ 0). The 1D proton
decoupling 13C NMR spectra were recorded using the
following conditions: 16K data points, spectral width
26 315 Hz, 200È1000 scans, acquisition time, 0.311 s pre-
acquisition delay 4.5 ls and pulse width 6.5 ls (90¡).
FID signals were zero Ðlled to 32K and an exponential
multiplier with LB of 3 Hz prior to FT. The accuracy of
the results is within ^0.03 ppm.
R
R
the resonance structures for enaminones can be
described as AÈD (Scheme 1). The e†ects of the enam-
inone moiety as a whole are very similar to those of the
acetamido group. The enaminone moiety as a whole is a
weak electron donor in the presence of the strong
electron-withdrawing group, as evidenced by its p con-
stants. The correlations of 17O, 13C and 1H chemical
The 19F NMR spectra were measured at 376.48 MHz
on a Bruker ARX-400 spectrometer under the following
conditions: 32K data points, spectral width 62 500 Hz, 8
scans, pulse width 16.9 ls (90¡), acquisition time 0.262 s
and preacquisition delay 4.5 ls. The proton decoupling
19F NMR spectra were recorded by using a frequency
of 7280 Hz at 300 K (27 ¡C). The samples were run as
shifts with the pK values of anilines suggests that the
nuclear shielding parameters depend on the strength of
a
the basicity of anilines.
EXPERIMENTAL
Spectra
ca. 0.05 M solutions in CDCl with 0.05 M Ñuorobenzene
3
as an internal reference (d \ 0).
Melting points were observed under a microscope
using a Mettler FP-52 instrument.
The 17O NMR spectra were recorded on a Bruker
WH-360 spectrometer, equipped with a 10 mm probe,
at 48.8 MHz, in the Fourier transform (FT) mode
without lock. System control, data acquisition and data
management were performed by an Aspect-2000 micro-
computer. The instrumental settings were as follows:
spectral width 50 kHz (1025 ppm), 2K data points, pulse
Materials
The general procedure for the preparation of 4-
arylaminopent-3-en-2-ones (1 and 2) was as follows. A
mixture of Na SO (5.0 g), the appropriate arylamine
(10 mmol) and pentane-2,4-dione (11 mmol) in a sealed
tube was heated at 120 ¡C for 1 h. After cooling, the
2
4
( 1997 by John Wiley & Sons, Ltd.
MAGNETIC RESONANCE IN CHEMISTRY, VOL. 35, 311È322 (1997)

17O NMR OF ENAMINONES
321
Table 14. Yields and melting points of enaminones (1–4)
Compound
Yield (%)
M.p. (¡C)a
Compound
Yield (%)
M.p. (¡C)
1a
1b
1c
1d
1e
1f
1g
1h
1i
86
88
80
73
81
89
83
86
78
82
90
83
80
79
71
85
77
45.3–46.5 (48)27
64.5–65.8 (65–67)3a
40.5–42.1 (41–43)3a
58.5–59.5 (59–61)28
oil (semisolid)29
58.6–60.3 (60–61)27
57.3–58.5 (58–60.5)3a
71.9–73
3a
3b
3c
3d
3e
3f
3g
3h
3i
91
85
83
81
83
86
80
82
61
50
87
83
78
81
75
76
73
174.9–175.3 (176–177)31
134.4–135.5 (140–141)31
164.5–165.0 (160–161)31
206.5–207.2
174–175.1
188.5–189.5 (190)32
184–185.5
203.5–204.5 (203–204)3a
214–215
86.5–87.5
1j
143.6–144.1 (144–145)3a
oil
3j
180.5–181.8 (178–80)31
142–142.8
2b
2c
2e
2f
2h
2i
4b
4c
4e
4f
4h
4i
oil
124–125
26.8–28.3b
175–177.3
40–42.7 (42)27
62.3–62.8
155–156
156.5–157.0 (158)32
142.1–142.8
87.3–88.0
2j
75.5–76.0 (78–80)30
4j
169.7–170.8
a Values in parentheses are taken from the References cited.
b Bulb-to-bulb distillation at 150 ¡C/0.05 Torr.
mixture was Ñash chromatographed on a silica gel
column (ethyl acetate) to a†ord the pure sample (71È
90%).
provided the pure sample (50È91%). The melting points
and yields of enaminones are given in Table 14.
The general procedure for the preparation of 3-
arylaminocyclohex-2-en-1-ones (3 and 4) followed the
modiÐed method.26 A mixture of the appropriate aryla-
mine (10 mmol) and cyclohexane-1,3-dione (10 mmol) in
a sealed tube was heated at 140 ¡C for 20 min. After
cooling, the solidiÐed product was crushed and washed
with ethyl acetate. Recrystallization from acetonitrile
Acknowledgements
The author is indebted to Professor Hugo Wyler for helpful dis-
cussions and Ðnancial support (from the Swiss National Science
Foundation).
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( 1997 by John Wiley & Sons, Ltd.
MAGNETIC RESONANCE IN CHEMISTRY, VOL. 35, 311È322 (1997)