NMR of enaminones: Part 4 - 17O NMR study of 2,2-diacylenamines

Article abstract of DOI:10.1002/(SICI)1097-458X(199707)35:7<432::AID-OMR107>3.0.CO;2-F

Natural abundance ¹⁷O NMR spectra of 41 2,2-diacylenamines (enamino diketones and enamino diesters), recorded in acetonitrile solution, are reported. Tertiary enamino diketones show only one ¹⁷O signal; primary and secondary derivati

Full text of DOI:10.1002/(SICI)1097-458X(199707)35:7<432::AID-OMR107>3.0.CO;2-F

MAGNETIC RESONANCE IN CHEMISTRY, VOL. 35, 432È440 (1997)
NMR of Enaminones
Part 4¤È17O NMR Study of 2,2-Diacylenamines
Jin-Cong Zhuo*
Institute of Organic Chemistry, University of Lausanne, BCH, CH-1015 Lausanne-Dorigny, Switzerland
Natural abundance 17O NMR spectra of 41 2,2-diacylenamines (enamino diketones and enamino diesters), record-
ed in acetonitrile solution, are reported. Tertiary enamino diketones show only one 17O signal; primary and
secondary derivatives show two 17O signals. The shift di†erence (Dd ) between the two carbonyl groups is mainly
HB
attributed to intramolecular hydrogen bonding and depends on the donor property of the amino group and the
structure of the enamino diketone. The d(17O) values correlate well with the pK values of amines. Correlations of
a
d(17O-1) values for the chelated carbonyl group with their d(13C-1) and d(13C-2) values are observed. ( 1997 by
John Wiley & Sons, Ltd.
Magn. Reson. Chem. 35, 432È440 (1997) No. of Figures: 4 No. of Tables: 5 No. of References: 32
Keywords: NMR; 17O NMR; enamino diketones; enamino diesters; intramolecular hydrogen bonding
Received 21 October 1996; accepted 10 January 1997
kcal \ 4.184 kJ)],12 as compared with that in enam-
INTRODUCTION
inones (9È16 kcal mol~1)13 and enamines (ca. 7 kcal
mol~1),14 and is consistent with the results of x-ray
analyses. The x-ray crystallographic studies show that
in diacylenamines15 the CÈN bond (1.30È1.32 Ó) is
shorter and the CxC bond (1.39È1.41 Ó) is longer than
those in enaminones (CÈN, 1.32È1.36 Ó; CxC, 1.37È
1.39 Ó)16 and those in enamines (CÈN, 1.38È1.41 Ó;
CxC, 1.33È1.37 Ó).17
Enaminones are important organic intermediates,2 and
have been reported as potentially biologically active.3
Enaminone derivatives, diacylenamines,2a are useful
starting materials for the synthesis of heterocyclic com-
pounds,2a the antimalarial drug choroquine and similar
products of medicinal interest.4 The diacylvinyl groups
have been used to protect the amino group of amino
acids during the synthesis of peptides and penicillin
derivatives5 and amino sugars during Fischer glycosida-
tion.6 The properties of diacylenamines have been
investigated by UV,7 IR8 and 1H,8a,9 13C9c,10 and 15N
NMR spectroscopy.9c,11 These studies conÐrmed that
the resonance structures (B, C and D) are important in
the ground state of the molecule (Scheme 1).
The resonance interaction of the amino group with
the CxC bond, as in enaminones, enamines and
amides, reduces the CxC bond order and increases the
CÈN bond order. The increased CÈN bond order in
diacylenamines parallels the high barrier of rotation
around the CÈN bond [13È20 kcal mol~1 (1
17O NMR is a particularly useful tool for studying
electron distributions18 and intramolecular hydrogen
bonding in molecules.18,19 Recently, the 17O NMR
spectra of enaminones have been investigated.20 The
17O chemical shifts of enaminones correlated well with
their vinylic 13C-2 shifts and with the pK values of the
a
amines. As the chemical shift of 13C-2 serves as a char-
acteristic of the electron density, the shielding of the
O-atom in enaminones depends on the electron density
at the O-atom and reÑect the polarization and the
degree of n,n-conjugation in the NÈCxCÈCxO
system.20 In hydrogen-bonded primary and secondary
enaminones, the inÑuence of substituents on 17O shift
value of the carbonyl O-atom is additive.20b The shield-
Scheme 1
* Correspondence to: J.-C. Zhuo.
¤ For Part 3, see Ref. 1.
Contract grant sponsor: Swiss National Science Foundation.
( 1997 by John Wiley & Sons, Ltd.
CCC 0749È1581/97/070432È09 $17.50

17O NMR STUDY OF 2,2-DIACYLENAMINES
433
Scheme 3
vinyl proton 1H-3 at d7.7È8.6 ppm, as a doublet
( J \ 11È14 Hz), show that the iminoenol forms (I and
II) are not present. The non-equivalence of the two
methyl groups and the presence of the strong intramole-
cular hydrogen bond evidenced by the d(NH) values
(9È13 ppm) indicate that the oxoimino form is not
present either. Hence these enamino diketones exist in
solution in the ketamino form. In contrast, the struc-
tures of enamino diketones with a primary amino group
(3b, 4b, and 7a) were previously assigned as the imin-
oenol form I based on the UV, IR and NMR spectra.21
In the present case, the 1H NMR spectra of 3b, 4b and
7a show that the vinyl protons (H-3) have a doubletÈ
doublet splitting with coupling constants of 15.6 and 8.7
Hz, and that N-H protons show two broad signals at
5.8È7.3 and 10.3È10.5 ppm, attributed to the non-
bonded and bonded N-H, respectively. These data
clearly indicate that the enamino diketones (3b, 4b and
7a) exist in solution in the ketamino form. This is
further supported by their 17O NMR data. The 17O
signals of the two carbonyls of primary enamino dike-
tones (3a, 4b and 7a: 445È505 ppm) appear in the region
observed for secondary enamino diketones which are
known to exist in ketamino form,7 and there is no
signal corresponding to an OH group. The 17O NMR
signal for the OH chelated with a CxO group appears
at 62È124 ppm,19,22 and chelated with a CxN (azine)
group at ca. 95 ppm.22b The 17O signals of OH in 2-
acylcyclohexane-1,3-diones and 2-acylindan-1,3-diones,
in which the structures of the enol forms are very
similar to the iminoenol forms I and II, appear at 120È
248 ppm.22d Thus the two signals found in compounds
3b, 4b and 7a must belong to the carbonyl groups. This
conÐrms the results of the 1H NMR data, i.e. that
primary enamino diketones exist in solution in a keta-
mino form.
Scheme 2
ing of the carbonyl O-atom by intramolecular hydrogen
bonding (*d ), ranging from [14 to [47 ppm, was
HB
sensitive to the nature, number and position of the sub-
stituents.20b It has been demonstrated that the 17O
NMR parameters are sensitive to electronic e†ects, tor-
sional angles, steric interactions and intramolecular
hydrogen bonding.18,19 Therefore, to evaluate the *d
HB
values these factors should be taken into account.
The presence of an intramolecular CxOÉÉÉHN bond
in primary and secondary diacylenamines has been
clearly indicated by IR8a and 1H NMR spectroscopy8a
and x-ray crystallography.15 It has been shown that the
hydrogen-bonded diacylenamine systems are essentially
planar and that the electron delocalization a†ects both
carbonyl groups almost equally.15 This makes dia-
cylenamine systems suitable for evaluating the contribu-
tion of intramolecular hydrogen bonding in 17O NMR
data. 17O NMR investigations of diacylenamines have
not been reported. This paper reports the 17O chemical
shifts for a variety of 2,2-diacylenamines (1È10, Scheme
2) in which the e†ects of the CxOÉÉÉHÈN type of
intramolecular hydrogen bonds on the 17O chemical
shifts of the hydrogen bonded carbonyl are evaluated.
RESULTS AND DISCUSSION
Enamino diketones in the ketamine form can exist in
several isomeric forms owing to restricted rotation
around the CÈCO and CÈN single bonds and the
CxC double bond. The presence of strong intramolecu-
lar hydrogen bonds in enamino diketones with a
primary or secondary amino group favours two confor-
mations, the EZE and ZZE forms (Scheme 4). The 1H
chemical shift di†erences between the two COMe
groups in 7 are 0.19È0.24 ppm (Table 4), which is much
larger than those (0.04 ppm, Table 2) found between the
Structure of enamino diketones
The tautomeric equilibrium of enamino diketones with
a primary or secondary amino group is shown in
Scheme 3.
The tautomeric iminoenols (I and II), oxoimino and
ketamino forms can be easily distinguished by their 1H
NMR data. In the spectra of enaminodiones with a sec-
ondary amino group (see Tables 2 and 4), the signals of
( 1997 by John Wiley & Sons Ltd.
MAGNETIC RESONANCE IN CHEMISTRY, VOL. 35, 432È440 (1997)

434
J.-C. ZHUO
bond order of the CxO bond due to the second
electron-withdrawing carbonyl group which shares the
electronic e†ect coming from the amino group.
Considerable shielding of 62È84 ppm is observed for
cyclic enaminone diketones (3a, 4a and 5a) compared
with 1a. The same e†ect has been reported previously in
enaminone system; 2-(dimethylaminomethylene)cyclo-
hexanone (432 ppm)20a and 2-(dimethylaminomethyl-
ene)cyclopentanone (410 ppm)20a are shielded by 24 and
45 ppm, respectively, relative to 4-dimethylaminobut-3-
en-2-one (456 ppm).20a The high shielding may be
attributed to the reduced double bond character of the
carbonyls due to the increased bond polarization and
Scheme 4
two COCH in the Ðxed ZZE conformation 3 and 4.
This can be explained in terms of the anisotropy e†ect
2
of the non-bonded carbonyl group, which exists in an
s-trans conformation and causes a deshielding of 1H-4.
Therefore, compounds 7 exist in solution in the EZE
conformation. This is consistent with previous IR,
Raman and 1H NMR spectroscopic8a and the x-ray
crystallographic studies,15 which show that the chelated
enamino diketone systems are essentially planar and
that the open-chain enamino diketones adopt the EZE
conformation and the cyclic enamino diketones the
Ðxed ZZE conformation.
n,n-conjugation of the NÈCxCÈ(CxO) system. It
2
has been shown that the 13C shift di†erence between the
two oleÐnic carbons, which reÑects the bond polariza-
tion and the degree of the n,n-conjugation, correlated
well with the shielding of O in of enaminones.20a The
13C shift di†erences between the C-3 and C-2 for 3a, 4a
and 5a (ca. 51 ppm) are much larger than that for 1a (40
ppm).
The existence of only one signal for this type of com-
pound (except for 1e, 2 and 6a) can be attributed to the
low barriers of rotation around the CxC bond, which
makes the isomerization about the CxC double bond
fast on the NMR time-scale. The barrier to isomer-
ization about the CxC bond for 1a is ca. 10 kcal
mol~1.12 This result suggests that the dipolar resonance
structures BÈD (Scheme 1) are the main contributors to
the ground state of the molecule.
The cyclic compound 2, with a Ðxed conÐguration of
the CxC bond, shows two carbonyl 17O signals at 455
and 533 ppm. The former can be assigned to the cyclic
carbonyl O-1@, as compared with 3-pyrrolidinylcyclo-
hex-2-en-1-one (443 ppm).20a The lower Ðeld signals of 2
corresponds to the acetyl O-1. The considerable
deshielding of O-1 (79 ppm) relative to the cyclic car-
bonyl O-1@ can be attributed to the strong steric inter-
action between the acetyl group and both the cyclic
carbonyl group and pyrrolidinyl ring, which twist the
acetyl group out of the plane of the enaminone system.
The 17O chemical shift of the acetyl O-1 is close to
those for ketones (ca. 550 ppm),18 indicating that there
is a lack of conjugation between the acetyl group and
enaminone system.
Two carbonyl signals (at 424 and 456 ppm) are also
observed for compound 6a. Molecular mechanics calcu-
lations show that the molecule 6a is essentially planar
and that the bond angle of O-1ÈC-1ÈC-2 (128.6¡) is
larger than that of O-1@ÈC-1@ÈC-2 (125.6¡). It has been
reported that in planar molecules a bond angle distor-
tion causes deshielding of O.18,20a Therefore, the high
Ðeld signal was assigned to the trans-carbonyl O-1@ and
the low Ðeld signal to the cis-carbonyl O-1.
A similar result is observed for compound 1e, which
shows two 17O signals at 502 and 585 ppm. As dis-
cussed above, the former is assigned to the trans-
carbonyl O-1@ which is conjugated with the enamine
system, and the latter corresponds to the cis-carbonyl
O-1 which is twisted out of the plane of the enaminone
system due to steric repulsion with the amino group.
The 17O spectra of enamino diesters (8, 9 and 10) are
summarized in Table 5. One signal at 293 ppm was
observed for cyclic enamino diester 10a. In the acyclic
Tertiary enamino diketones
The 17O NMR chemical shifts for a series of enamino
diketones with tertiary amino groups (1aÈ1k, 2, 3aÈ6a)
were recorded at natural abundance in acetonitrile
(Table 1). With the exception of the non-symmetric
amino group 1e, the 17O spectra of compounds 1 show
only one signal at ca. 525 ppm (Table 1). They are
shifted to lower Ðeld by ca. 75 ppm relative to those
noted for enaminones (450 ppm).20a Similar deshielding
was observed for imides (ca. 370 ppm)18 vs. amides (ca.
330 ppm)18 and for anhydrides (ca. 400 ppm)18 vs. esters
(ca. 350 ppm).18 This may result from increased the
Table 1. 17O and 13C data (ppm) for tertiary enamino dike-
tones (1–6)
Compound
R1
R2
17Oa,b
13C-2
13C-3
1a
1b
1c
1d
1e
1f
1g
1h
1i
Me
Et
Me
Et
524.5
526.3
525.2
536.5
501.7c
524.0
521.1
525.9
526.6
526.5d
525.3
454.6e
457.9
462.5
440.6f
424.5g
115.10
115.02
114.28
116.78
117.04
115.68
113.67
115.01
115.41
114.63
114.63
113.64
109.36
108.22
106.72
103.10
156.59
152.85
149.26
153.01
151.10
152.06
155.60
155.35
153.99
154.47
154.80
167.01
162.28
161.75
156.36
152.97
i-Pr
i-Pr
PhCH
Ph
PhCH
Me
2
2
(CH )
2 4
(CH )
2 5
(CH )
2 6
(CH )
2 7
(CH ) O(CH )
2 2 2 2
(CH ) NMe(CH )
1j
1k
2
2 2
2 2
—
—
3a
4a
5a
6a
Me
Me
Me
Me
Me
Me
Me
Me
a 0.5
indicated otherwise.
M
acetonitrile solution at 40 ¡C, d(O-1) ¼d(O-1¾), unless
b Linewidth at half-height: 250–630 Hz (880 Hz for 1f).
c Signal for O-1¾ ; d(O-1) ¼584.7 ppm.
d d(—O—) ¼1.2 (100) ppm.
e Signal for O-1¾ ; d(O-1) ¼533.3 ppm.
f Recorded at 70 ¡C.
g Signal for O-1¾ ; d(O-1) ¼456.3 ppm; measurement at 70 ¡C
gives d(O-1) ¼457.8 ppm and d(O-1¾) ¼426.0 ppm.
( 1997 by John Wiley & Sons, Ltd.
MAGNETIC RESONANCE IN CHEMISTRY, VOL. 35, 432È440 (1997)

17O NMR STUDY OF 2,2-DIACYLENAMINES
435
enamino diester 8a, two carbonyl oxygen signals are
observed at 372 and 304 ppm; and two ether oxygens
are at 149 and 119 ppm. The higher Ðeld signals for the
carbonyl and methoxy oxygen (304 and 119 ppm) can
be assigned to the trans-carbonyl group, as compared
with methyl 3-dimethylaminoprop-2-enoate (295 and
119 ppm).20a The lower Ðeld signals (372 and 147 ppm)
corresponds to the cis-carbonyl group, which is close to
those found in methyl acetate (359 and 140 ppm, in ace-
tonitrile solution, new measurement). The deshielding of
the cis-carbonyl group can be attributed to steric repul-
sion between the amino and cis-carbonyl groups. Pre-
vious x-ray studies showed that the cis-carbonyl group
is twisted out of the enamino ester plane by 67¡.15d
exhibit two carbonyl 17O signals: those at higher Ðeld
are assigned to the intramolecular hydrogen-bonded
carbonyl groups O-1 and the lower Ðeld signals to the
free carbonyl O-1@. The e†ects of substituents in these
compounds are similar to those noted for the corre-
sponding N-substituted enaminones.20b It has been
shown that the inÑuence of the substituents on 17O
chemical shifts of the carbonyl groups in various enam-
inone systems is additive:20b
d(17O) \ 462.2 ] ;* (R )
(1)
i
i
where * is the increment value of substituent R at the
i
i-position. The additivity relationship also exists in
enamino diketones 7. The increment value of the hydro-
gen bonded 2-acetyl group (*
) is assigned a value
of 53.6 ppm deshielding, and the increment value of
Zv2vAc
non-bonded 2-acetyl group (*
) is assigned a value
Ev2vAc
Primary and secondary enamino diketones
of 22.6 ppm deshielding. The calculated 17O chemical
shifts for the both carbonyl O-atoms are included in
Table 3. The di†erences between the calculated and the
experimental data, *d \ d(17O) [ d(17O)calc., are less
The 17O spectra of enamino diketones (3È7) with
primary or secondary amino groups (Table 2 and 3)
Table 2. 17O, 1H and 13C data (ppm) for primary and secondary enamino diketones 3–6
Compound
R1
R2
17O-1a
17O-1¾a
Dd
HB
b
1H-Nc
1H-3
H-4d
H-6d
13C-1
13C-1¾
13C-2
13C-3
3b
3c
3d
4b
4c
4d
5b
5c
6b
H
H
H
H
H
H
H
H
H
H
444.5
451.1
É6.6 10.50
É3.9 11.07
8.24 (dd, 15.6, 8.7)
8.12 (dq, 14.0, 0.7)
2.47 2.51 200.64
197.57
109.70 158.41
Me 436.9e 440.8
2.46 2.48 199.75f 196.60g 108.77 160.25
Ph
H
451.7
449.8
457.3
454.8
444.8
462.9
É5.6 12.93h 8.65 (d, 14.0)
2.54 2.58 200.56
2.36 2.40 200.00
2.33 2.37 199.04
2.43 2.47 199.97
2.52 2.52 206.00
2.63 2.63 206.28
196.79
197.09
196.02
196.35
202.03
202.27
188.99
110.07 151.02
108.41 157.92
107.52 159.71
108.84 150.46
107.73 156.13
108.94 146.66
104.45 153.27
É5.0 10.45
É4.1 11.01
É4.3 12.88i
8.21 (dd, 15.6, 8.7)
Me 440.7
Ph 458.6
8.10 (d, 14.0)
8.62 (d, 13.8)
7.73 (d, 14.0)
8.24 (d, 11.5)
7.69 (d, 14.0)
Me 430.4j 430.4
Ph 446.0k 446.0
Me 434.4l 434.4
0.0
0.0
0.0
10.19
11.94
9.10
—
—
193.84
a 0.5 M acetonitrile solution at 40 ¡C, unless indicated otherwise; linewidth at half-height: 190–410 Hz.
b Dd ¼d(17O-1) Éd(17O-1¾).
HB
c Singlet, unless indicated otherwise.
d Triplet for 3b, 3c and 3d, J ¼6.5 Hz; singlet for 4b, 4c and 4d; multiplet for 5b and 5c.
e Measurement at 70 ¡C gives d(O-1¾) ¼442.9 ppm and d(O-1) ¼437.4 ppm.
f 3J
g 3J
¼7.2 Hz.
¼3.0 Hz.
CO, Hv3
CO, Hv3
h Broad doublet, J ¼14.0 Hz.
i Broad doublet, J ¼13.8 Hz.
jRecorded at 70 ¡C.
k 0.1 M acetonitrile solution at 70 ¡C.
l 0.2 M acetonitrile solution at 70 ¡C.
Table 3. 17O data (ppm) for 7
Compound
R
17O-1a
17O-1calc. b
Ddc
17O-1¾a
17O-1¾calc. b
Ddc
Dd
HB
d
7a
7b
7c
7d
7e
7f
7g
7h
7i
H
484.7
468.5
469.6
469.1
466.5
472.8
468.0
468.5
483.9
479.2
484.8
467.3
469.1
469.3
467.1
474.5
466.9
468.8
491.9
—
É0.1
0.8
504.5
498.1
498.5
499.5
499.8
502.6
500.3
500.0
518.2
511.3
515.8
498.3
500.1
500.3
498.1
505.5
497.8
499.8
522.9
—
É11.3
É0.2
É1.6
É0.8
1.7
É19.8
É29.6
É28.9
É30.4
É33.3
É29.8
É31.7
É31.5
É34.3
É32.1
Me
Et
0.5
i-Pr
t-Bu
É0.2
É0.6
É1.7
1.2
CH Ph
2
i-Bu
É2.9
2.5
Cyclohexyl
Ph
É0.3
É8.0
—
0.2
É4.7
—
7j
2,6-Me C H
2
6 3
a 0.5 M acetonitrile solution at 40 ¡C; linewidth at half-height: 150–360 Hz.
b D values were taken from Ref. 20b; for cyclohexylamino group, D ¼ É16.0 ppm; for hydrogen-
N
N
bonded 2-acetyl group, D
c Dd ¼ d(17O) Éd(17O)calc.
d Dd ¼d(17O-1) Éd(17O-1¾).
¼53.6 ppm; for non-bonded 2-acetyl group, D
Ev2vAc
¼22.6 ppm.
Zv2vAc
HB
( 1997 by John Wiley & Sons Ltd.
MAGNETIC RESONANCE IN CHEMISTRY, VOL. 35, 432È440 (1997)

436
J.-C. ZHUO
Table 4. 1H and 13C data (ppm) for 7
Compound
1H-Na
1H-3
H-4a
H-5¾a
13C-1
13C-1¾
13C-2
13C-3
7a
7b
7c
7d
7e
7f
7g
7h
7i
10.32
10.95
11.04
11.07
11.42
11.33
11.15
11.15
12.76b
12.31b
7.89 (dd, 8.6, 15.6)
7.74 (d, 13.2)
7.76 (d, 13.4)
7.80 (d, 13.5)
7.88 (d, 13.7)
7.81 (d, 13.3)
7.71 (d, 13.2)
7.81 (d, 13.2)
8.24 (d, 12.8)
7.82 (d, 12.8)
2.50
2.48
2.47
2.47
2.47
2.50
2.49
2.48
2.56
2.58
2.28
2.28
2.26
2.27
2.27
2.26
2.27
2.27
2.38
2.27
201.26
200.30
200.26
200.15
200.01
200.51
200.30
200.14
201.12c
201.30
195.33
194.31
194.35
194.41
194.44
194.42
194.39
194.36
194.83d
194.65
112.75
111.50
111.30
111.10
111.06
111.86
111.19
111.14
113.27
112.12
158.40
161.33
159.56
157.79
155.36
159.83
160.38
157.90
151.86
159.14
7j
a Singlet, unless indicated otherwise.
b Doublet, J ¼12.8 Hz.
c 3J
d 3J
¼7.0 Hz.
¼4.0 Hz.
CO, Hv3
CO, Hv3
than ^3 ppm (Table 3) except for 7a and 7i. The experi-
mental chemical shift of the non-bonded carbonyl O-1@
of 7a is much smaller than the calculated value, indicat-
ing that there is an additional shielding arising from the
contribution of intermolecular hydrogen bonding. The
large *d values ([8.0 ppm for O-1 and [4.7 ppm for
O-1@) for 7i indicate that the N-Ph ring is twisted out of
the plane of enamino diketone system owing to steric
repulsion between N-Ph and H-3. Introducing alkyl
groups in the two ortho positions of 7i, as in compound
7j, creates an e†ect of angular torsion. The slight shield-
ing of the two carbonyl in 7j, as compared with those in
7i, demonstrates that the N-Ph ring in 7i is not copla-
nar with the enamino diketone moiety. The crystal
structure of N-(2,2-diacetylvinyl)-o-phenylenediamine
shows that the aryl ring is rotated out of the plane of
enamino diketone by [145¡.15a
primary amino group was excluded owing to the inÑu-
ence of intermolecular hydrogen bonding].
In the previous paper,1 the 17O shift values of enam-
inones correlated well with their d(13C-2). In enamino
diketones 7, the d(17O-1) values of the hydrogen-bonded
carbonyls also correlate with their d(13C-1) and d(13C-2)
values:
d(17O-1) \ 15.46 d(13C-1) [ 2626.7
(r \ 0.985, SD \ 1.3, n \ 9) (4)
d(17O-1) \ 8.40 d(13C-2) [ 465.5
(r \ 0.967, SD \ 1.9, n \ 9) (5)
(the point for 7j was excluded). This indicates that the
shielding of C-1, C-2 and O-1 is inÑuenced by the same
factors.
The 17O chemical shifts of enaminones have been
shown to depend on the donor quality of the amino
Intramolecular hydrogen bonding
nitrogen1,20 and to correlate well with the pK values23
a
of the corresponding amines. This type of relationship is
IR8a and x-ray15 analyses show that hydrogen-bonded
open-chain enamino diketone systems exist both in
solid form and in solution in the EZE-conformation,
that the conjugated system is essentially planar and that
electron delocalization a†ects both carbonyl groups
almost equally. This demonstrates that the electronic
and torsional e†ects do not contribute to the observed
chemical shifts. Therefore, the 17O chemical shift di†er-
also found in enamino diketones 7:
d(O-1) \ 496.0 [ 2.60 pK
a
(r \ 0.983, SD \ 1.1, n \ 8) (2)
d(O-1@) \ 532.7 [ 3.14 pK
a
(r \ 0.993, SD \ 0.8, n \ 9) (3)
The point for 7j was excluded owing to strong steric
interaction [in Eqn (2), the enamino diketone 7a with a
ences (*d ) between the carbonyl groups O-1@ and O-1
HB
in enamino diketones with primary or secondary amino
Table 5. 17O, 1H and 13C data (ppm) for enamino diesters (8, 9 and 10)
Compound
R1
R2
17O-1a
17O-1¾
17O-2
17O-2¾
Dd
HB
b
1H-N
1H-3
13C-1
13C-1¾
13C-2
13C-3
8a
8b
Me Me 372.3
303.9 147.8 118.7
—
—
7.56 (s)
167.78 167.78 92.04 154.18
H
Ph
322.3 328.0 134.6 125.4
É5.7 11.04 (d, 13.9) 8.54 (d, 13.9) 169.36 165.95 92.81 152.27
É6.5
323.1c 329.6 135.9 124.1
9a
9b
Me Me 372.5 305.9 178.2 151.1
—
—
7.50 (s)
167.57 167.48 93.06 153.41
H
Ph
321.5 327.0 165.4 154.8
É5.5 11.02 (d, 13.8) 8.54 (d, 13.8) 169.06 165.73 93.49 151.92
É6.4
323.2c 329.6 165.0 155.8
10a
10b
Me Me 293.2 293.2 188.9 188.9
0.0
—
8.13 (s)
165.9d 165.9d 84.02 160.99
H
Ph 314.0 325.5 188.4 188.4 É11.5 11.24 (d, 14.2) 8.65 (d, 14.2) 165.51 163.52 87.23 152.62
a 0.5 M acetonitrile solution at 40 ¡C, unless indicated otherwise; linewidth at half-height: 220–490 Hz.
b Dd ¼d(17O-1) Éd(17O-1¾).
HB
c Measurements at 70 ¡C.
d Broad signal.
( 1997 by John Wiley & Sons, Ltd.
MAGNETIC RESONANCE IN CHEMISTRY, VOL. 35, 432È440 (1997)

17O NMR STUDY OF 2,2-DIACYLENAMINES
437
groups can be mainly attributed to the intramolecular
hydrogen bonding.
the chelated carbonyl group is ca. 30 ppm more shield-
values). Addi-
tivity relationships demonstrate that common factors
inÑuence the shielding of O-atoms in enaminones and
enamino diketones.
ed than the non-chelated group (*d
HB
The *d values (Tables 2 and 3), are sensitive to the
HB
donor ability of the N-substituent and the structure of
the compounds. The *d values, ca. [30 ppm for N-
HB
alkylenamino diketones (7), are in good agreement with
those obtained previously for the corresponding 4-
alkylaminopent-3-en-2-ones 11.20b This indicates that
EXPERIMENTAL
the previous *d values evaluated for primary and sec-
HB
ondary enaminones 11 from the comparison of 17O
chemical shifts of the hydrogen-bonded compounds
with those non-hydrogen-bonded cyclic analogues are
reasonable and acceptable.
Compounds
For the cyclic enamino diketones 3 and 4, the *d
HB
Compounds 1 and 7 were prepared by a known procedure9a from a
solution of 3-ethoxymethylenepentane-2,4-dione (10 mmol) and the
appropriate amine (10 mmol) (in cases of gaseous amines, ammonia or
methylamine ethanolic solution or ethylamine aqueous solution was
applied) in acetonitrile (10 ml). Enamino diketones 2,25 3a,26 3d,27
4a,26 4d,27 5a,26 5c,28 6a,26 8a,12c 8b,9a 9a,29 9b,30 10a8a and 10b8a
were prepared according to literature methods. Transamination8a of
3d, 4d, 5c and 2-anilinomethyleneindan-1,3-dione29 (5 mmol) with an
excess of ethanol solution of ammonia (33%, 3 ml) or methylamine
(33%, 2 ml) gave 3b21 and 4b21 or 3c,8a 4c,8a 5b and 6b,31 respectively.
The spectroscopic data (not included in Tables 1È4) of enamino
diketones synthesized by the above-mentioned methods are listed
below (chemical shifts in ppm; J in Hz; IR in cm~1; m/z with relative
intensity as % of base peak).
values are much smaller than those of the acyclic deriv-
atives 7. The presence of intramolecular hydrogen
bonding in 3 and 4 is clearly indicated by their 1H
NMR spectra. The small *d values for 3 and 4 are
HB
consistent with smaller 13C shift di†erences between the
two carbonyl carbons in 3 and 4 (ca. 3 ppm), compared
with those in 7 (ca. 6 ppm). However, this contrasts with
the results of x-ray analyses, which show that the conju-
gated enamino diketone system is strictly planar and
that electron delocalization a†ects both carbonyl
groups almost equally.15b This may indicate that the
conformations of 3 and 4 in solution are not the same
as in solid state. In the Ðve-membered ring derivatives 5
and 6, there is no di†erence between the two carbonyls;
the reasons for this observations are not clear.
1a. M.p. 58.6È59.8 ¡C (lit.:26 59È61 ¡C). 1H NMR (CDCl ): 7.44 (s,
3
1H, H-3), 3.00 (br, 6H, NMe ), 2.33 (s, 6H, 2 COMe). 13C NMR
2
(CDCl ): 197.71 (2 CxO), 156.59, 115.10, 44.84 (NMe ), 29.94 (2
3
2
COMe).
1b. IR (Ðlm): 1666, 1620, 1580. 1H NMR (CDCl ): 7.38 (s, 1H, H-3),
Interestingly, the above ring e†ect was not observed
3
3.33 (q, J \ 7.0, 4H, 2 NCH ), 2.33 (s, 6H, 2 COMe), 1.17 (t, J \ 7.0,
2
in the cyclic enamino diester 10b (*d \ [11.5 ppm).
6H, 2 Me). 13C NMR (CDCl ): 198.24 (2 CxO), 152.85, 115.02, 52.1
HB
3
It is well known that ester carbonyl groups are less
and 47.4 (2 NCH ), 29.72 (2 COMe), 13.27 (2 Me).). MS: 184
2
(M ] H`, 4), 183 (M`, 11), 168 (26), 140 (11), 136 (16), 127 (14), 126
basic than ketones carbonyls,24 and consequently ester
(100), 124 (30), 112 (12), 108 (14), 98 (42), 96 (21), 94 (14), 84 (31), 82
(19), 72 (14), 70 (22), 69 (22), 68 (24), 56 (66), 53 (22).
carbonyls are expected to be poorer hydrogen bond
acceptors than ketone carbonyls. The *d values for
1c. IR (Ðlm): 1681, 1621, 1574. 1H NMR (CDCl ): 7.48 (s, 1H, H-3),
HB
3
acyclic enamino diesters 8b and 9b, ca. [6 ppm, are
3.72 (m, 2H, 2 NCH), 2.33 (s, 6H, 2 COMe), 1.28 (d, J \ 6.5, 12H, 4
much smaller than that for the corresponding acyclic
Me). 13C NMR (CDCl ): 198.89 (CxO), 149.26, 114.28, 52.5 and 47.7
3
(2 NCH), 29.87 (2 COMe), 23.41 (2 Me), 20.36 (2 Me). MS: 212
enamino diketone 7i (34 ppm). This is consistent with
(M ] H`, 15), 211 (M`, 17), 196 (42), 168 (12), 150 (15), 136 (44), 127
(13), 126 (88), 112 (60), 110 (36), 108 (50), 100 (13), 98 (13), 96 (23), 94
(22), 85 (43), 84 (100), 82 (19), 70 (81), 69 (32), 68 (40), 58 (29), 56 (16),
53 (25).
the lower basicity of the ester carbonyl groups. *d
HB
values of [4 to [13 ppm have been noted previously
for hydroxypyridine carboxy esters and benzoates.719k
1d. M.p. 82.4È84.7 ¡C. IR (Ðlm): 1670, 1624, 1590, 1578. 1H NMR
(CDCl ): 7.65 (s, 1H, H-3), 7.30È7.40 (m, 6H, 2 Ph), 7.10È7.20 (m, 4H,
3
2 Ph), 4.44 (br, 4H, 2 NCH ), 2.10 (s, 6H, 2 COMe). 13C NMR
2
CONCLUSION
(CDCl ): 198.42 (2 CxO), 153.01, 134.76 (2 C, Ph), 128.98 (4 CH, Ph),
3
128.17 (2 CH, Ph), 127.56 (4 CH, Ph), 116.78, 61.8 and 55.7 (2 NCH ),
2
29.46 (2 COMe). MS: 308 (M ] H`, 2), 307 (M`, 4), 292 (15), 264 (6),
216 (34), 198 (3), 131 (3), 130 (3), 126 (3), 112 (27), 106 (11), 91 (100), 77
(9), 70 (18), 69 (3), 68 (2), 65 (38), 51 (8).
The results of this work conÐrm that enamino diketones
exist in solution in a ketamino form. The 17O spectra of
the tertiary enamino diketones show only one signal
which is essentially insensitive to substituents (ca. 525
ppm). This is attributed to the low barrier of rotation
around the CxC double bond and suggests that the
dipolar resonance structures (B, C and D) are the main
contributors to the ground state of the molecule. The
17O chemical shifts of the two carbonyls in primary and
secondary enamino diketones are sensitive to the basic-
ity of the amino groups and depend on the intramolecu-
lar hydrogen bonding. Their d(17O) values can be
calculated by the sum of substituent increments. The
large di†erences between the experimental and calcu-
lated data are explained in terms of steric interactions
and intermolecular hydrogen bonding. The existence of
the strong intramolecular hydrogen bonds in enamino
diketones is well evidenced: in alkylamino compounds 7
1e. IR (Ðlm): 1674, 1631, 1604, 1576. 1H NMR (CDCl ): 7.63 (s, 1H,
3
H-3), 7.38È7.44 (m, 2H, Ph), 7.24È7.29 (m, 1H, Ph), 7.18È7.23 (m, 2H,
Ph), 3.25 (s, 3H, NMe), 2.32 (s, 6H, 2 COMe). 13C NMR (CDCl ):
3
201.6 and 195.56 (2 CxO), 151.10, 147.08 (C, Ph), 129.71 (2 CH, Ph),
126.48 (CH, Ph), 122.26 (2 CH, Ph), 117.04, 42.07 (NMe), 32.2 and 27.1
(2 COMe). MS: 218 (M ] H`, 24), 217 (M`, 35), 202 (49), 184 (46),
174 (64), 160 (75), 140 (3), 132 (86), 130 (40), 126 (43), 117 (55), 106 (26),
104 (46), 103 (20), 102 (10), 91 (47), 90 (22), 84 (23), 77 (100), 65 (18), 63
(18), 55 (10), 53 (18), 51 (60).
1f. M.p. 53.3È54.9 ¡C. IR (Ðlm): 1660, 1620, 1574. 1H NMR
(CDCl ): 7.61 (s, 1H, H-3), 3.65 (br, 2H, NCH ), 2.97 (br, 2H, NCH ),
3
2
2
2.34 (s, 6H, 2 COMe), 1.97 (m, 4H, 2 CH ). 13C NMR (CDCl ): 197.55
2
3
(2 CxO), 152.06, 115.68, 55.48 and 51.33 (2 NCH ), 29.77 (2 COMe),
2
25.87 and 24.59 (2 CH ). MS: 182 (M ] H`, 10), 181 (M`, 35), 166
2
(31), 138 (33), 124 (100), 122 (25), 110 (21), 106 (14), 96 (32), 94 (17), 83
(13), 82 (28), 80 (14), 70 (82), 69 (36), 68 (38), 55 (40), 54 (31), 53 (38).
1g. IR (Ðlm): 1660, 1621, 1574. 1H NMR (CDCl ): 7.49 (s, 1H, H-3),
3
3.29 (br, 4H, 2 NCH ), 2.30 (s, 6H, 2 COMe), 1.69 (m, 6H, 3 CH ). 13C
2
2
NMR (CDCl ): 197.99 (2 CxO), 155.60, 113.67, 53.8 (2 NCH ), 30.00
3
2
(2 COMe), 25.80 (2 CH ), 23.10 (CH ). MS: 196 (M ] H`, 5), 195
2
2
( 1997 by John Wiley & Sons Ltd.
MAGNETIC RESONANCE IN CHEMISTRY, VOL. 35, 432È440 (1997)

438
J.-C. ZHUO
(M`, 22), 180 (44), 152 (7), 138 (100), 136 (46), 124 (9), 120 (4), 100 (20),
108 (8), 97 (8), 96 (14), 94 (10), 84 (69), 83 (70), 82 (42), 69 (28), 68 (16),
67 (17), 56 (26), 55 (76), 54 (26), 53 (35).
(CDCl ): 138.39 (C, Ph), 129.96 (2 CH, Ph), 126.46 (CH, Ph), 118.11 (2
CH, Ph), 51.65 (C-6), 51.29 (C-4), 31.16 (C-5), 28.56 (2 Me).
3
5a. M.p. 91.8È92.6 ¡C (lit.:26 94 ¡C). 1H NMR (CDCl ): 7.46 (s, 1H,
3
1h. M.p. 63.5È65.3 ¡C. IR (KBr): 1663, 1610, 1577. IR (Ðlm): 1660,
H-3), 3.73 (s, 3H, NMe), 3.37 (s, 3H, NMe), 2.52 (s, 4H, 2 CH ). 13C
2
1615, 1574, 1H NMR (CDCl ): 7.50 (s, 1H, H-3), 3.45 (br, 2H, NCH ),
NMR (CDCl ): 204.1 (br, CO), 200.7 (br, CO), 48.47 and 33.94 (2
3
2
3
3.08 (br, 2H, NCH ), 2.34 (s, 6H, 2 COMe), 1.78 (m, 4H, 2 CH ), 1.59
CH ), 44.36 (NMe ).
2
2
2
2
(m, 4H, 2 CH ). 13C NMR (CDCl ): 198.18 (2 CxO), 155.35, 115.01,
5b. M.p. 205 ¡C (decomp.). 1H NMR (CDCl ): 3.25 (d, J \ 4.5, 3H,
2
3
3
56.64 and 53.11 (2 NCH ), 29.94 (2 COMe), 27.34 (3 CH ), 26.47
NMe). 13C NMR (CDCl ): 33.78 and 33.14 (2 CH ), 36.70 (NMe).
2
2
3
2
(CH ). MS: 210 (M ] H`, 13), 209 (M`, 25), 194 (100), 166 (18), 152
5c. M.p. 175.6È177.5 ¡C (lit.:28 170 ¡C). 1H NMR (CDCl ): 7.42È
2
3
(74), 150 (14), 138 (12), 134 (6), 126 (29), 124 (28), 122 (14), 112 (19), 110
7.48 (m, 2H), 7.26È7.32 (m, 3H), 2.58È2.68 (m, 4H, 2 CH ). 13C NMR
2
(26), 111 (7), 109 (17), 108 (8), 98 (29), 97 (22), 96 (37), 94 (24), 84 (26),
83 (18), 82 (52), 81 (19), 80 (27), 70 (38), 69 (52), 68 (62), 67 (27), 56 (37),
55 (96), 54 (33), 53 (51).
(CDCl ): 137.67 (C, Ph), 130.15 (2 CH, Ph), 127.08 (CH, Ph), 118.00 (2
3
CH, Ph), 33.98 and 33.40 (2 CH ).
2
6a. M.p. 141.9È143.2 ¡C (lit.:26 147 ¡C). 1H NMR (CDCl ): 7.72È
3
1i. M.p. 126.0È126.8 ¡C. IR (KBr): 1661, 1610, 1583. 1H NMR
7.78 (m, 2H), 7.58È7.64 (m, 2H), 7.49 (s, 1H, H-3), 3.79 (s, 3H, NMe),
(CDCl ): 7.45 (s, 1H, H-3), 3.39 (br, 4H, 2 NCH ), 2.34 (s, 6H, 2
3.37 (s, 3H NMe). 13C NMR (CDCl ): 192.67 (C-1), 188.43 (C-3),
3
2
3
COMe), 1.50È1.85 (m, 10H, 5 CH ). 13C NMR (CDCl ): 197.86 (2
140.81 and 138.66 (2 C, Ar), 133.21, 132.88, 121.51 and 121.34 (4 CH,
2
3
CxO), 153.99, 115.41, 58.39 and 50.77 (2 NCH ), 29.79 (2 COMe),
Ar), 48.00 and 43.69 (NMe ).
2
2
27.80 (CH ), 25.51 (3 CH ), 23.98 (CH ). MS: 224 (M ] H`, 8), 223
6b. M.p. 250 ¡C (decomp.). 1H NMR (CDCl ): 7.70È7.78 (m, 2H),
2
2
2
3
7.58È7.64 (m, 2H), 3.25 (d, J \ 5.0, 3H, NMe). 13C NMR (CDCl ):
3
(M`, 14), 208 (59), 180 (7), 166 (10), 164 (4), 152 (5), 140 (7), 139 (8), 138
(18), 136 (8), 126 (19), 124 (41), 122 (11), 112 (23), 110 (21), 98 (18), 97
(12), 96 (30), 84 (35), 83 (38), 82 (54), 81 (12), 80 (23), 70 (42), 69 (42), 68
(36), 67 (23), 56 (35), 55 (100), 54 (24), 53 (40).
139.74 (2 C, Ar), 133.29, 133.18, 121.88 and 121.24 (4 CH, Ar), 36.42
(NMe).
7a. M.p. 143.6È145.0 ¡C (lit.:21 146 ¡C). 1H NMR (CDCl ): 5.87 (br,
3
1j. M.p. 85.7È87.4 ¡C. IR (Ðlm): 1660, 1622, 1577. 1H NMR
1H, NH). 13C NMR (CDCl ): 32.22 (C-4), 27.14 (C-5).
3
(CDCl ): 7.38 (s, 1H, H-3), 3.77 (t, J \ 5.0, 4H, 2 OCH ), 3.33 (t,
7b. M.p. 107.6È109.2 ¡C (lit.:8a 110È111 ¡C). 1H NMR (CDCl ): 3.18
3
2
3
J \ 5.0, 4H, 2 NCH ), 2.32 (s, 6H, 2 COMe). 13C NMR (CDCl ):
(d, J \ 5.0, 3H, NMe). 13C NMR (CDCl ): 36.49 (NMe), 31.84 (C-4),
2
3
3
198.24 (2 CxO), 154.47, 114.63, 66.27 (2 OCH ), 52.36 (2 NCH ),
27.26 (C-5).
2
2
30.00 (2 COMe). MS: 198 (M ] H`, 7), 197 (M`, 36), 182 (100), 154
(7), 140 (84), 139 (32), 138 (25), 126 (8), 124 (50), 122 (17), 112 (21), 110
(21), 97 (19), 96 (43), 94 (20), 87 (33), 86 (31), 85 (34), 84 (14), 83 (21), 82
(70), 80 (18), 69 (42), 68 (22), 67 (26), 56 (36), 55 (100), 54 (48), 53 (56).
7c. M.p. 93.4È94.8 ¡C. IR (KBr): 3182, 1651, 1612, 1584. 1H NMR
(CDCl ): 3.41 (dq, J \ 7.3, 6.0, 2H, NCH ), 1.31 (t, J \ 7.3, 3H,
3
2
NCH Me). 13C NMR (CDCl ): 45.01 and 15.95 (NCH Me),31.89 (C-
2
3
2
4), 27.33 (C-4). MS: 156 (M ] H`, 7), 155 (M`, 28), 140 (62), 126 (59),
122 (12), 98 (100), 84 (24), 80 (38), 70 (32), 69 (28), 68 (26), 67 (17), 56
(26), 53 (27).
1k. IR (Ðlm): 1660, 1622, 1575. 1H NMR (CDCl ): 7.43 (s, 1H, H-3),
3
3.35 (t, J \ 5.0, 4H, 2 NCH ), 2.48 (t, J \ 5.0, 4H, 2 NCH ), 2.32 (s,
2
2
3H, NMe), 2.31 (s, 6H, 2 COMe). 13C NMR (CDCl ): 198.12 (2
7d. M.p. 71.4È73.1 ¡C. IR (KBr): 3183, 1658, 1613, 1581. 1H NMR
3
CxO), 154.80, 114.63, 54.45 (2 CH , CH NMe), 52.26 (2 NCH ),
(CDCl ): 3.49 (m, 1H, NCH), 1.32 (d, J \ 6.5, 6H, NCHMe ). 13C
2
2
2
3 2
NMR (CDCl ): 51.88 and 23.50 (NCHMe ), 31.91 (C-4), 27.36 (C-5).
45.92 (NMe), 30.01 (2 COMe). MS: 211 (M ] H`, 8), 210 (M`, 14),
138 (4), 124 (15), 100 (24), 98 (33), 97 (21), 96 (13), 86 (13), 83 (14), 82
(30), 71 (37), 70 (100), 69 (14), 68 (11), 67 (16), 58 (63), 57 (37), 56 (45),
55 (22), 54 (19), 53 (16).
3
2
MS: 170 (M ] H`, 1), 169 (M`, 14), 154 (18), 136 (25), 126 (94), 112
(77), 94 (14), 84 (29), 70 (100), 69 (20), 68 (18), 67 (12), 53 (16).
7e. M.p. 88.5È89.9 ¡C. IR (KBr): 3187, 1663, 1617, 1581. 1H NMR
(CDCl ): 1.37 (s, 9H, NCMe ). 13C NMR (CDCl ): 53.64 and 29.75
2. M.p. 130.8È131.5 ¡C. IR (KBr): 1662, 1600, 1508. 1H NMR
3
3
3
(CDCl ): 3.60 (br, 2H, NCH ), 2.99 (br, 2H, NCH ), 2.66 (t, J \ 6.6,
(NCMe ), 33.87 (C-4), 27.39 (C-5). MS: 184 (M ] H`, 4), 183 (M`,
3
2
2
3
2H, CH ), 2.53 (s, 3H, COMe), 2.32 (m, 2H, CH ), 1.97 (br, 4H, 2
13), 168 (6), 150 (5), 126 (82), 112 (100), 108 (14), 98 (8), 94 (10), 70 (81),
2
2
CH ), 1.87 (m, 2H, CH ). 13C NMR (CDCl ): 198.96 (CxO), 194.65
69 (22), 68 (18), 67 (12), 58 (24), 57 (77), 56 (16), 55 (17), 53 (16).
2
2
3
(CxO), 167.01, 113.64, 54.91 (NCH ), 50.45 (NCH ), 37.78, 31.38 and
7f. M.p. 100.5È101.6 ¡C (lit.:32 89È90 ¡C). IR (KBr): 3168, 1646,
2
2
19.15 (3 CH ), 24.73 (CH CH ). MS: 208 (M ] H`, 13), 207 (M`, 33),
1616, 1575. 1H NMR (CDCl ): 7.30È7.43 (m, 3H), 7.24È7.30 (m, 2H),
2
2
2
3
192 (100), 190 (34), 178 (15), 164 (20), 151 (8), 138 (11), 136 (34), 123
(48), 108 (45), 96 (17), 95 (13), 94 (19), 82 (29), 80 (28), 70 (96), 68 (31),
67 (33), 66 (28), 55 (55), 54 (19), 53 (32).
4.55 (d, J \ 6.0, 2H, NCH ). 13C NMR (CDCl ): 135.97 (C, Ph),
2
3
129.11 (2 CH, Ph), 128.35 (CH, Ph), 127.31 (2 CH, Ph), 53.72 (NCH ),
2
31.93 (C-4), 27.29 (C-5). MS: 218 (M ] H`, 3), 217 (M`, 5), 202 (18),
3a. M.p. 113.5È114.8 ¡C (lit.:26 118 ¡C). 1H NMR (CDCl ): 8.05 (s,
160 (2), 126 (68), 106 (9), 104 (9), 91 (100), 84 (11), 77 (7), 65 (37), 63 (9),
51 (11).
3
br, 1H, H-3), 3.39 (s, 3H, NMe), 3.17 (d, J \ 0.7, 3H, NMe), 2.46 (t,
J \ 6.5, 4H, 2 CH ), 1.95 (m, 2H, CH ). 13C NMR (CDCl ): 196.15 (2
7g. M.p. 54.2È56.0 ¡C. IR (KBr): 3187, 1653, 1618, 1588. 1H NMR
2
2
3
CxO), 162.28, 109.36, 48.53 and 44.66 (NMe ), 38.18 (C-4 and C-6),
(CDCl ): 3.18 (t, J \ 6.5, 2H, NCH ), 1.87 (m, 1H, CH), 0.97 (d,
2
3
2
19.56 (C-5).
J \ 6.5, 6H, 2 Me). 13C NMR (CDCl ): 58.04, 29.49 and 19.66
3
3b. M.p. 107.5È107.7 ¡C (lit.:21 110 ¡C). 1H NMR (CDCl ): 7.30 (br,
(NCH CHMe ), 31.88 (C-4), 27.31 (C-5). MS: 184 (M ] H`, 11), 183
3
2
2
1H, NH), 1.98 (m, 2H, CH ). 13C NMR (CDCl ): 38.09 (C-6), 37.51
(M`, 36), 168 (38), 150 (4), 140 (34), 126 (100), 122 (97), 112 (33), 108
(9), 98 (18), 95 (18), 94 (17), 86 (24), 84 (33), 80 (46), 70 (70), 69 (59), 68
(26), 67 (20), 57 (39), 56 (26), 55 (32), 53 (39).
2
3
(C-4) and 19.72 (C-5).
3c. M.p. 175.6È176.2 ¡C. IR (KBr): 3191, 1665, 1605, 1586. 1H NMR
(CDCl ): 3.21 (d, J \ 5.0, 3H, NMe), 1.96 (m, 2H, CH ). 13C NMR
7h. M.p. 76.5È78.2 ¡C. IR (KBr): 3291, 1654, 1619, 1586. 1H NMR
3
2
(CDCl ): 37.67 (C-6), 37.33 (C-4) and 19.98 (C-5), 36.60 (NMe). MS:
(CDCl ): 3.22 (m, 1H, NCH), 1.91È2.02 (m, 2H), 1.74È1.87 (m, 2H),
3
3
154 (M ] H`, 24), 153 (M`, 42), 138 (24), 136 (17), 125 (96), 112 (61),
1.59È1.70 (m, 1H), 1.25È1.50 (m, 5H). 13C NMR (CDCl ): 58.79
3
110 (75), 97 (92), 84 (78), 83 (100), 82 (42), 80 (28), 69 (83), 68 (72), 67
(22), 56 (14), 55 (95), 54 (80), 53 (68).
(NCH), 33.73 (2 CH ), 31.92 (C-4), 27.36 (C-5), 24.90 (CH ), 24.34 (2
2
2
CH ). MS: 213 (M ] H`, 3), 209 (M`, 11), 194 (14), 166 (3), 138 (5),
2
3d. M.p. 120.4È121.7 ¡C (lit.:27 120 ¡C). 1H NMR (CDCl ): 7.37È
126 (100), 112 (56), 110 (15), 96 (11), 86 (20), 70 (62), 69 (16), 68 (12), 67
3
7.47 (m, 2H), 7.20È7.30 (m, 3H), 2.00 (m, 2H, CH ). 13C NMR
(14), 55 (51), 53 (16).
2
(CDCl ): 138.37 (C, Ph), 129.96 (2 CH, Ph), 126.51 (CH, Ph), 118.16 (2
3
7i. M.p. 87.7È88.2 ¡C (lit.:8a 89È90 ¡C). 1H NMR (CDCl ): 7.38È7.44
3
(m, 2H), 7.20È7.26 (m, 1H), 7.16È7.20 (m, 2H). 13C NMR (CDCl ):
3
CH, Ph), 37.98 (C-6), 37.61 (C-4) and 19.70 (C-5).
4a. M.p. 87.0È88.3 ¡C (lit.:12a 83È87 ¡C; lit.:26 93 ¡C). 1H NMR
139.04 (C, Ph), 129.97 (2 CH, Ph), 125.79 (CH, Ph), 117.86 (2 CH, Ph),
(CDCl ): 8.01 (s, 1H, H-3), 3.39 (s, 3H, NMe), 3.19 (s, 3H, NMe), 2.36
32.04 (C-4), 27.34 (C-5).
3
(s, 4H, 2 CH ), 1.07 (s, 6H, 2 Me). 13C NMR (CDCl ): 195.60 (2
7j. M.p. 74.8È76.1 ¡C. 1H NMR (CDCl ): 7.14 (s, 3H), 2.33 (s, 6H, 2
2
3
3
Me). 13C NMR (CDCl ): 137.70 (C, Ar), 132.56 (2 C, Ar), 129.10 (2
3
CxO), 161.75, 108.22, 48.52 and 44.74 (NMe ), 52.16 (C-4 and C-6),
2
30.87 (C-5), 28.47 (2 Me).
CH, Ar), 127.35 (CH, Ar), 32.09 (C-4), 27.21 (C-5), 18.53 (2 Me).
4b. M.p. 133.4È134.9 ¡C (lit.:21 135 ¡C). 1H NMR (CDCl ): 6.76 (br,
3
1H, NH), 1.07 (s, 6H, 2 Me). 13C NMR (CDCl ):51.74 (C-6), 51.19 (C-
3
4), 31.09 (C-5), 28.49 (2 Me).
4c. M.p. 176.3È177.1 ¡C (lit.:8a 171È173 ¡C). 1H NMR (CDCl ): 3.21
Instrumentation
3
(d, J \ 5.0, 3H, NMe), 1.05 (s, 6H, 2 Me). 13C NMR (CDCl ): 51.34
3
(C-6), 51.01 (C-4), 36.55 (NMe), 31.16 (C-5), 28.52 (2 Me).
4d. M.p. 137.9È138.3 ¡C (lit.:8a 135È136 ¡C). 1H NMR (CDCl ):
The 17O NMR spectra were recorded on a Bruker-WH-
3
7.37È7.46 (m, 2H), 7.22È7.30 (m, 3H), 1.10 (s, 6H, 2 Me). 13C NMR
360 spectrometer, equipped with a 10 mm probe, at 48.8
( 1997 by John Wiley & Sons, Ltd.
MAGNETIC RESONANCE IN CHEMISTRY, VOL. 35, 432È440 (1997)

17O NMR STUDY OF 2,2-DIACYLENAMINES
439
MHz, in the Fourier transform (FT) mode without lock.
System control, data acquisition and data management
were performed by an Aspect-2000 microcomputer. The
instrumental settings were as follows: spectral width
50 000 Hz (1025 ppm), 2K data points, pulse width 33
ls, acquisition time 20 ms, preacquisition delay 5 ls,
150 000È300 000 scans (1 400 000 scans for 5c and 6b),
sample spinning (30 Hz). An even number (12È28) 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 FT. The chemical shifts d(17O), measured
in 0.5 M acetonitrile solution at 40 ¡C at natural isotopic
The 1H and 13C NMR spectra (d, in ppm relative to
internal TMS in CDCl solution at 20 ¡C) were record-
3
ed on Bruker WH-250 and Bruker Advance DPX-400
spectrometers, IR spectra on a Perkin-Elmer Paragon
1000 FT-IR spectrometer and electron impact mass
spectra on a Nermag R-10-10C spectrometer. Melting
points were observed under a microscope using a
Mettler FP-52 instrument.
Acknowledgements
abundance, are reported relative to d(17O)(H O) (\0.0
2
ppm); dioxane [d(17O) \ 0.0 ppm] was used as an
The author expresses his appreciation to Professor Hans Dahn for
valuable comments and to Professor Hugo Wyler for helpful dis-
cussions. The Swiss National Science Foundation is thanked for
Ðnancial support.
external standard; downÐeld shifts are positive. The
general reproducibility of chemical shifts values is ca.
^ 1 ppm (^0.2 ppm within the same series).
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