A novel route to 2-imidazolin-5-one derivatives via oxidative cyclization of aryl-substituted (Z)-N-acetyl-α-dehydroalanines having a dialkylamino group

Article abstract of DOI:10.1016/j.tet.2004.07.068

It was found that the reaction of the title compounds [(Z)-1] with oxygen in methanol proceeds according to the first-order kinetics to give (Z)-2-imidazolin-5-one derivatives and hydrogen peroxide in quantitative yields. Analysis of substituent and solve

Full text of DOI:10.1016/j.tet.2004.07.068

Tetrahedron 60 (2004) 9517–9524
A novel route to 2-imidazolin-5-one derivatives via oxidative
cyclization of aryl-substituted (Z)-N-acetyl-a-dehydroalanines
having a dialkylamino group
Atsushi Kawasaki,a Kei Maekawa,a Kanji Kubo,b Tetsutaro Igarashia and Tadamitsu Sakuraia,
*
aDepartment of Applied Chemistry, Faculty of Engineering, Kanagawa University, Kanagawa-ku, Yokohama 221-8686, Japan
bInstitute for Materials Chemistry and Engineering, Kyushu University, Kasugakoen, Kasuga 816-8580, Japan
Received 9 June 2004; accepted 14 July 2004
Abstract—It was found that the reaction of the title compounds [(Z)-1] with oxygen in methanol proceeds according to the first-
order kinetics to give (Z)-2-imidazolin-5-one derivatives and hydrogen peroxide in quantitative yields. Analysis of substituent and
solvent effects on the rate constant for this oxidative cyclization led us to propose that electron transfer from the dialkylamino
nitrogen in (Z)-1 to oxygen, amide-proton abstraction by superoxide and the subsequent intramolecular electron transfer are all rate-
determining steps. The synthetic utility of the novel cyclization reaction of aryl-substituted (Z)-N-acetyl-a-dehydroalanine
derivatives was discussed.
q 2004 Elsevier Ltd. All rights reserved.
1. Introduction
complexes with oxygen in nonpolar solvents,5 it is possible
that the presence of oxygen in polar solvents thermally
activates the tertiary amino nitrogen introduced into aryl-
substituted a-dehydroalanine derivatives, thus allowing
us to expect that the oxidatively activated amino nitrogen
may induce a novel cyclization reaction. In a previous
communication,6 we found that the reaction of some
aryl-substituted (Z)-N-acetyl-a-dehydroalanines having a
dialkylamino group with oxygen in methanol gives the
corresponding (Z)-2-imidazolin-5-one derivatives in quan-
titative yields. In order to expand the study of this
fascinating oxidative cyclization reaction, we designed
and synthesized aryl-substituted (Z)-N-acyl-a-dehydro-
alanines [(Z)-1a–k] having a 2-(dialkylamino)ethyl or a
3-(dimethylamino)propyl group attached to the carbox-
amide nitrogen, and investigated the substituent and solvent
effects on the reactivity of (Z)-1 in the presence of oxygen,
hoping to shed much light on the mechanism of the novel
oxidative cyclization reaction found by us.
In recent years much attention is being devoted to the
synthetic application of photoinduced electron transfer
reactions, owing to the fact that many of these reactions
enable the construction of various heterocyclic rings.1,2
In the course of our systematic study toward the charac-
terization of the excited-state reactivities of substituted
a-dehydroamino acids, we discovered an interesting photo-
cyclization of N-acyl-a-dehydrophenylalanine derivatives,3
as well as photoinduced reductive cyclization of substituted
N-acyl-a-dehydro(1-naphthyl)alanines.4 The former photo-
cyclization afforded isoquinoline, 1-azetine and/or quinoli-
none derivatives in relatively good yields, depending on the
steric bulkiness and electronic properties of the substituents
introduced into the phenylalanines. The highly efficient and
selective formation of dihydrobenzoquinolinone derivatives
was observed through the latter electron transfer-initiated
cyclization, demonstrating that N-acyl-a-dehydroamino
acids containing a dialkylamino group or in the presence
of a tertiary amine readily undergo one electron reduction to
afford a radical ion pair intermediate.
Since tertiary amines are able to form charge-transfer
Keywords: a-Dehydroamino acid derivatives; Oxidative cyclization; 2-
Imidazolin-5-ones; Kinetics.
* Corresponding author. Fax: C81-45-491-7915;
e-mail: sakurt01@kanagawa-u.ac.jp
0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2004.07.068

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A. Kawasaki et al. / Tetrahedron 60 (2004) 9517–9524
structure, an oxygen-saturated methanol solution of
(Z)-1a (100 mL, 5.0!10K3 mol dmK3
[O2]Z1.02!
;
10K2 mol dmK3)8 was heated at 80 8C for 48 h in a sealed
tube. The reaction mixture obtained was subjected to short
column chromatography over silica gel, which allowed
us to isolate 1-[2-(dimethylamino)ethyl]-2-methyl-4-(1-
naphthylmethylene)-2-imidazolin-5-one (2a) in 95% yield.
The reactions of 1b–j with oxygen under the same
conditions gave the corresponding 2-imidazolin-5-one
derivatives (2b–j) in greater than 80% isolated yields.
As shown in Figure 2, a 1H NMR spectral analysis of
the mixture derived from the reaction of 1c (2.0!
10K3 mol dmK3) with oxygen in methanol confirmed that
the cyclization reaction proceeds cleanly to give only
2c. The structure of 2a–j was determined based on
their spectroscopic and physical properties including
1H–1H COSY, 13C–1H COSY and HMBC spectra. In
addition, the crystal structure of 2c provided conclusive
evidence for the imidazolinone ring as well as for the
(Z)-configuration of 2 (Fig. 3),9 indicating no occur-
rence of geometrical isomerization during the cycliza-
tion process of the starting (Z)-isomer. On the other
2. Results and discussion
2.1. Product analysis
The starting (Z)-isomers were prepared in good yields by
the ring-opening reactions of aryl-substituted oxazolones
with 2-(dimethylamino)ethylamine (1a, 1c, 1e–i and 1k),
2-(diethylamino)ethylamine (1b and 1d), or 3-(dimethyl-
amino)propylamine (1j).7 Each methanol solution of (Z)-1
(10 mL, 1.0!10K4 mol dmK3) was purged with air for
10 min and then heated at 80 8C in a sealed tube for a given
period of time. As typically shown in Figure 1, on heating
the solution in an atmosphere of air, the UV absorption of
the starting 1a at 312 nm decreased gradually with
appearance of the 378 nm absorption, while there were
three isosbestic points at 252, 276 and 334 nm during the
reaction. Similar UV spectral changes were observed for the
other derivatives, except for 1k which exhibited a negligible
change in its UV absorption under the same reaction
conditions. In order to isolate the product and determine its
Figure 2. 1H NMR spectra of dimethyl sulfoxide-d6 solutions of the
reaction mixtures obtained by heating an oxygen-saturated methanol
solution of (Z)-1c (2.0!10K3 mol dmK3) for 0 h (a), 5 h (b) and 32 h (c) at
80 8C, followed by evaporating the methanol solution to dryness.
Figure 1. UV absorption spectra of air-saturated methanol solutions of
(Z)-1a (1.0!10K4 mol dmK3) heated for 0 h (curve a), 0.6 h (curve b),
1.8 h (curve c) and 24 h (curve d) at 80 8C.
Figure 3. ORTEP drawing of (Z)-2c.

A. Kawasaki et al. / Tetrahedron 60 (2004) 9517–9524
9519
electron transfer from the tertiary amino nitrogen to oxygen
in the reaction, as already suggested. Based on the
simplified Weller equation (Eq. 1),10 where Eox and
Ered are the oxidation potential of triethylamine (0.76 V
versus SCE in MeCN)11 and the reduction potential of
oxygen (K0.94 V versus SCE in MeCN),12 respectively,
free energy change in this electron transfer (DGet) was
estimated
DGet=kJ molK1 Z 96:5 ðEox KEred
Þ
(1)
to be 164 kJ molK1. Thus, the thermally-activated electron
transfer is thermodynamically unfavorable process, allow-
ing us to propose Scheme 2 in which reverse electron
transfer affording the starting dehydroamino acids and
oxygen should proceed preferentially, namely, the electron
transfer equilibrium should lie greatly to the left. It is likely
that the presence of the oxidized dialkylamino (–NC%R2)
and amide carbonyl groups having strong electron-
withdrawing abilities in the 1-derived cation radical enables
basic superoxide to abstract the amide proton affording the
amido anion and the hydroperoxyl radical.13 Intramolecular
electron transfer in the former intermediate should give the
amidyl radical. The final product (Z)-2 may be obtained by
dehydration of the amino alcohol formed via the cyclization
of this amidyl radical and the subsequent hydrogen
abstraction from methanol.
Scheme 1.
hand, the finding that two amide hydrogens in 1
disappear on generating 2 in the presence of oxygen
strongly suggests the appearance of hydrogen peroxide
as an oxygen-derived product (Scheme 1). After an
oxygen-saturated methanol solution of (Z)-1a (100 mL,
5.0!10K3 mol dmK3) was heated at 80 8C for 48 h in a
sealed tube, 10 mL aliquot of the reaction mixture was
diluted with an aqueous solution of KCl (10 mL,
0.20 mol dmK3) and subjected to voltammetric analysis.
The formation of 2a and hydrogen peroxide in
comparable yields to each other was confirmed by a
comparison of oxidation currents of this sample solution
(2.4 mA) and the reference solution (3.2 mA) containing
2a and hydrogen peroxide (2.5!10K3 mol dmK3) at
0.70 V.
Fortunately, the reaction of (Z)-1 (1.0!10K4 mol dmK3) in
2.2. Substituent and solvent effects on the rate constant
for the reaction
air-saturated methanol ([O2]Z2.1!10K3 mol dmK3 8
) at
80 8C proceeded according to the first-order kinetics in 1, as
typically shown in Figure 4. In addition, the reaction in any
air-saturated solvents examined was first order in 1 (Fig. 5),
so that we are able to scrutinize the substituent and solvent
effects on the rate for the reaction. In Table 1 are
The findings that no reaction occurs in an atmosphere of
argon and also without the dialkylamino group, like 1l, even
in oxygen-saturated methanol suggest the participation of
Scheme 2.

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A. Kawasaki et al. / Tetrahedron 60 (2004) 9517–9524
the solvents. Furthermore, the use of acetonitrile (having
almost the same polarity as methanol) as a solvent decreased
the reaction rate by a factor of about 3–4.14 The former
observation is consistent with the fact that an increase in
solvent polarity accelerates electron transfer reaction, and
the latter observation reveals that the solvation of –NC%R2
by the hydroxy oxygen of methanol plays a critical role in
determining the reaction rate. The considerations described
above, therefore, allow us to propose that electron transfer
from the dialkylamino nitrogen to oxygen is a rate-
determining step in the reaction sequence.
As already proposed, the combined action of the electron-
withdrawing amide carbonyl and oxidized dialkylamino
groups may enable basic superoxide to abstract the amide
proton affording an amido anion intermediate (Scheme 2). It
is, thus, predicted that addition of one more methylene
spacer chain to 1f slows down the reaction rate, owing to the
increased interatomic distance between the amide and
dimethylamino nitrogens. A comparison of the rate
constants for 1f and 1j reveals that the oxidative cyclization
rate of the latter is less than that of the former by a factor of
12 (Table 1). This finding is consistent with our prediction
and, hence, amide-proton abstraction by superoxide,
proceeding reversibly, is also a rate-determining step, as
shown in Scheme 2. Interestingly, a comparison of the rate
constants for 1c and 1e–i confirms that an increase in the
electron-withdrawing ability of the substituent R has a clear
tendency to decrease the reaction rate. This increase in
electron-withdrawing ability is considered to accelerate
amide-proton abstraction by superoxide and, in contrast, to
slow down intramolecular electron transfer in an amido
anion intermediate. Thus the finding that the replacement of
methoxy group by electron-withdrawing trifluoromethyl or
nitro group reduces the rate constant by only half strongly
suggests that the effects of the substituent R on the proton
abstraction and the subsequent electron transfer are
compensated each other and both of these two processes
are rate-determining steps. On the other hand, we previously
showed that as compared to N-acetyl group, N-benzoyl
group exerts a much greater steric effect on the cyclization
process of substituted (Z)-N-acyl-a-dehydrophenylalanines
Figure 4. First-order plots for the reactions of (Z)-1a (C), (Z)-1c (-),
(Z)-1d (:) and (Z)-1h (;, 1.0!10K4 mol dmK3) with oxygen in air-
saturated methanol at 80 8C. AN, A0 and At refer to as the final absorbance,
the initial absorbance and the absorbance after time, t, of the corresponding
reaction mixture at a given wavelength, respectively.
Figure 5. First-order plots for the reactions of (Z)-1c (1.0!10K4 mol dmK3
)
with oxygen in air-saturated methanol(C), ethanol (-), 2-propanol (:)
and acetonitrile (;) at 80 8C. AN, A0 and At refer to as the final absorbance,
the initial absorbance and the absorbance after time, t, of the reaction
mixture at 348 nm, respectively.
Table 1. Rate constants (k) for the reactions of (Z)-1 (1.0!10K4 mol dmK3
with oxygen at 80 8C
)
summarized the rate constants estimated from the slopes of
linear first-order plots. An inspection of the N-alkyl and aryl
substituent effects on the reaction rate confirms that the rate
constant is not much different between 1a and 1b and also
between 1c and 1d. An increase in the steric bulkiness of N-
alkyl substituent is considered to suppress attack of oxygen
at the amino nitrogen and, in contrast, to enhance the
stability of a cation radical intermediate (–NC%R2). Because
the former effect lowers the reaction rate which is increased
by the latter effect, the result of N-alkyl substituent effect
makes it highly probable that these two effects are
compensated each other. On the other hand, the replacement
of 1-naphthyl group (1a,b) by phenyl group (1c,d) exerts
only a small effect on the rate constant for the reaction.
Interestingly, the change in the polarity of protic solvents
affects the reaction rates for both 1a and 1c to a much
greater extent, as compared to that in the substituent R: the
rate constants decrease markedly with decreasing polarity of
Com-
pound
Solvent (3)a
[O2]b/10K3 mol dmK3
k/10K4 sK1
1a
1b
1c
1d
1a
1a
1a
1c
1c
1c
1e
1f
MeOH (32.66)
MeOH
MeOH
2.1
1.3
1.5
1.1
2.3
0.12
0.026
0.52
0.059
0.012
0.26
1.3
MeOH
EtOH (24.55)
i-PrOH (19.92)
MeCN (35.94)
EtOH (24.55)
i-PrOH (19.92)
MeCN (35.94)
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
2.1
2.1
1.9
1.2
1g
1h
1i
0.74
0.59
0.71
0.10
1j
a
Relative permittivity at 25 8C. See Ref. 13.
See Ref. 7.
b

A. Kawasaki et al. / Tetrahedron 60 (2004) 9517–9524
9521
to completely inhibit the formation of isoquinoline deriva-
tives.3 This result allows us to speculate that the negligible
formation of 2-imidazolin-5-one derivative in the reaction
between 1k and oxygen is due to a large steric hindrance of
the N-benzoyl phenyl group to the intramolecular attack of
amidyl radical on the benzoyl carbonyl moiety.
Physical and spectroscopic properties of (Z)-2-methyl-4-(4-
methoxybenzylidene)-5(4H)-oxazolone, (Z)-2-methyl-4-(4-
methybenzylidene)-5(4H)-oxazolone, (Z)-2-methyl-4-benzyl-
idene-5(4H)-oxazolone, (Z)-2-methyl-4-(4-chlorobenzyli-
dene)-5(4H)-oxazolone, (Z)-2-methyl-4-[4-(trifluoromethyl)
benzylidene]-5(4H)-oxazolone, (Z)-2-methyl-4-(1-naphthyl-
methylene)-5(4H)-oxazolone and (Z)-2-phenyl-4-(1-naphthyl-
methylene)-5(4H)-oxazolone were consistent with those of the
previously prepared samples.3c,4d
2.3. Synthetic utility of the reaction
Although many synthetic routes to 2-imidazolin-5-one
derivatives are known,15 there is no synthetic method (of
these derivatives) which employs the cyclization of aryl-
substituted N-acetyl-a-dehydroalanines activated by elec-
tron transfer to oxygen. The procedure for preparing the
starting (Z)-a-dehydroamino acids [(Z)-1] is simple and
easily applicable to its related compounds, as demonstrated
in the preceding sections. In addition, the cyclodehydration
reaction of (Z)-1 proceeds without any dehydrating agent to
quantitatively afford the corresponding (Z)-2-imidazolin-5-
one derivatives [(Z)-2] and, hence, provides a novel and
clean route to (Z)-2. Pretreatment of the concentrated
reaction mixtures with a short column of silica gel is
effective for obtaining (Z)-2a–j in high purities as well as in
high isolated yields.
3.2.1. (Z)-2-Methyl-4-(4-nitrobenzylidene)-5(4H)-oxazo-
lone. Mp 182.0–183.0 8C. IR (KBr): 1822, 1794, 1664,
1
1520, 1344, 1270 cmK1. H NMR (500 MHz, CDCl3): d
2.46 (3H, s), 7.14 (1H, s), 8.25 (2H, d, JZ9.2 Hz), 8.28 (2H,
d, JZ9.2 Hz).
3.3. General procedure for the synthesis of (Z)-2-
acetylamino-N-dialkylaminoalkyl-3-aryl-2-
propenamides [(Z)-1a–j], (Z)-2-benzoylamino-N-
dimethylaminoethyl-3-(1-naphthyl)-2-propenamide
[(Z)-1k] and (Z)-2-acetylamino-N-butyl-3-(1-naphthyl)-
2-propenamide [(Z)-1l]
(Z)-2-Methyl-4-(4-substituted benzylidene)-5(4H)-oxazo-
lone (for 1c–j), (Z)-2-methyl-4-(1-naphthylmethylene)-
5(4H)-oxazolone (for 1a, 1b and 1l), or (Z)-2-phenyl-4-(1-
naphthylmethylene)-5(4H)-oxazolone (for 1k, 0.020 mol)
was added to dry chloroform (200 mL) containing N,N-
dialkylaminoalkylamine (for 1a–k) or butylamine (for 1l,
0.021 mol) and the resulting solution was allowed to stand
for 1.0 h with stirring in an ice bath. The reaction mixture
was concentrated to dryness and the resulting residue was
dissolved in ethanol (50 mL) and then treated with activated
charcoal powder. After removal of the solvent under
reduced pressure, the crystalline solid obtained was
recrystallized twice from ethanol–hexane affording color-
less crystals (40–70%). Physical and spectroscopic proper-
ties of (Z)-1l were consistent with those of the previously
prepared sample.4c
3. Experimental
3.1. General
1H and 13C NMR and IR spectra were taken with a JEOL
JNM-A500 spectrometer and a Hitachi 270–30 infrared
spectrometer, respectively. Chemical shifts were deter-
mined using tetramethylsilane as an internal standard. UV
absorption spectra were recorded on a Hitachi UV-3300
spectrophotometer. A cell with a 10-mm pathlength was
used. Elemental analyses were performed on a Perkin–
Elmer PE2400 series II CHNS/O analyzer. X-ray crystal
data collection was performed with Mo Ka radiation (lZ
˚
0.71069 A) on a Rigaku RAXIS-RAPID equipped with an
imaging plate. Oxidation current-potential curves were
measured with a Yanaco P-1100 polarographic analyzer.
Mass spectra were recorded on a JEOL 01SG-2 spectro-
meter. MeOH, EtOH, i-PrOH and MeCN were purified
according to the standard procedures.14 All other reagents
used were obtained from commercial sources and of the
highest grade available.
3.3.1. (Z)-2-Acetylamino-N-dimethylaminoethyl-3-(1-
naphthyl)-2-propenamide [(Z)-1a]. Mp 157.5–158.5 8C.
IR (KBr): 3298, 3196, 2938, 1620 cmK1 1H NMR
.
(500 MHz, DMSO-d6): d 1.84 (3H, s,), 2.19 (6H, s), 2.37
(2H, t, JZ7.0 Hz), 3.28 (2H, dt, JZ6.1, 6.7 Hz), 7.51–7.58
(5H, m), 7.90–7.96 (4H, m), 9.25 (1H, s). 13C NMR
(125.7 MHz, DMSO-d6): d 22.6, 37.3, 45.2 (2C), 58.0,
124.1, 124.2, 125.5, 126.0, 126.2,126.3, 128.35, 128.42,
131.0, 131.3, 132.5, 133.2, 164.6, 169.4. Anal. Calcd
(Found) for C19H23N3O2: C, 70.13 (70.35); H, 7.12 (7.06);
N, 12.91% (12.85%).
3.2. General procedure for the synthesis of (Z)-2-methyl-
4-(4-substituted benzylidene)-5(4H)-oxazolones,
(Z)-2-methyl-4-(1-naphthylmethylene)-5(4H)-oxazolone
and (Z)-2-phenyl-4-(1-naphthylmethylene)-5(4H)-
oxazolone
3.3.2. (Z)-2-Acetylamino-N-diethylaminoethyl-3-(1-
naphthyl)-2-propenamide [(Z)-1b]. Mp 155.0–156.0 8C.
N-Acylglycine (0.13 mol), 1-arylaldehyde (0.15 mol) and
sodium acetate (0.10 mol) were added to acetic anhydride
(100 mL) and the resulting mixture was heated at 75–85 8C
for 2–7 h with stirring. The mixture was cooled with ice
and the solid separated out was collected by filtration with
suction and washed with water, small amounts of cold
EtOH and then with dry hexane. After the crude product had
been air-dried at room temperature, it was recrystallized
from hexane–CHCl3 to give yellow crystals (30–60%).
IR (KBr): 3298, 3118, 2968, 1623 cmK1 1H NMR
.
(500 MHz, DMSO-d6): d 0.99 (6H, t, JZ7.0 Hz), 1.84
(3H, s,), 2.49–2.53 (6H, m), 3.24 (2H, dt, JZ6.4, 7.0 Hz),
7.51–7.58 (5H, m), 7.90–7.95 (4H, m), 9.27 (1H, s). 13C
NMR (125.7 MHz, DMSO-d6): d 12.0 (2C), 22.6, 37.4, 46.7
(2C), 51.3, 124.1, 124.3, 125.5, 126.0, 126.2, 126.3, 128.35,
128.44, 131.0, 131.3, 132.5, 133.2, 164.5, 169.4. Anal.
Calcd (Found) for C21H27N3O2: C, 71.36 (71.13); H, 7.70
(7.73); N, 11.89% (11.58%).

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A. Kawasaki et al. / Tetrahedron 60 (2004) 9517–9524
3.3.3. (Z)-2-Acetylamino-N-dimethylaminoethyl-3-phenyl-
2-propenamide [(Z)-1c]. Mp 129.0–130.0 8C. IR (KBr):
3220, 2980, 1611 cmK1. 1H NMR (500 MHz, DMSO-d6): d
1.98 (3H, s,), 2.14 (6H, s), 2.31 (2H, t, JZ6.7 Hz), 3.20 (2H,
dt, JZ6.1, 6.7 Hz), 7.02 (1H, s), 7.30 (1H, dd, JZ7.3,
7.3 Hz), 7.37 (2H, dd, JZ7.3, 7.3 Hz), 7.51 (2H, d, JZ
7.3 Hz), 7.83 (1H, t, JZ6.1 Hz), 9.38 (1H, s). 13C NMR
(125.7 MHz, DMSO-d6): d 22.9, 37.4, 45.2 (2C), 58.0,
127.7, 128.6 (3C), 129.3 (2C), 130.2, 134.2, 164.9, 169.5.
Anal. Calcd (Found) for C15H21N3O2: C, 65.43 (65.50); H,
7.69 (7.42); N, 15.26% (15.47%).
132.0 8C. IR (KBr): 3400, 2980, 1659 cmK1 1H NMR
.
(500 MHz, DMSO-d6): d 1.99 (3H, s,), 2.16 (6H, s), 2.33
(2H, t, JZ6.7 Hz), 3.23 (2H, dt, JZ6.1, 6.7 Hz), 7.01 (1H, s),
7.70 (2H, d, JZ7.9 Hz), 7.74 (2H, d, JZ7.9 Hz), 7.99 (1H, t,
JZ6.1 Hz), 9.51 (1H, s). 13C NMR (125.7 MHz, DMSO-d6):
d 22.8, 37.2, 45.2 (2C), 57.9, 124.1 (1C, q, JZ272 Hz), 124.9,
125.2 (2C, q, JZ4 Hz), 128.0 (1C, q, JZ31 Hz), 129.6 (2C),
132.3, 138.5, 164.5, 169.2. Anal. Calcd (Found) for
C16H20F3N3O2: C, 55.97 (55.79); H, 5.87 (6.10); N, 12.24%
(12.61%).
3.3.9. (Z)-2-Acetylamino-N-dimethylaminoethyl-3-(4-
nitrophenyl)-2-propenamide [(Z)-1i]. Mp 147.5–
3.3.4. (Z)-2-Acetylamino-N-diethylaminoethyl-3-phenyl-
2-propenamide [(Z)-1d]. Mp 122.0–123.5 8C. IR (KBr):
3208, 2968, 1620 cmK1. 1H NMR (500 MHz, DMSO-d6): d
0.97 (6H, t, JZ7.3 Hz), 1.99 (3H, s,), 2.47 (2H, t, JZ
7.6 Hz), 2.49 (4H, q, JZ7.3 Hz), 3.19 (2H, dt, JZ6.1,
7.6 Hz), 7.05 (1H, s), 7.32 (1H, dd, JZ7.3, 7.3 Hz), 7.39
(2H, dd, JZ7.3, 7.3 Hz), 7.52 (2H, d, JZ7.3 Hz), 7.78 (1H,
t, JZ6.1 Hz), 9.40 (1H, s). 13C NMR (125.7 MHz, DMSO-
d6): d 11.9 (2C), 22.8, 37.3, 46.7 (2C), 51.3, 127.7, 128.5
(3C), 129.3 (2C), 130.1, 134.2, 164.6, 169.3. Anal. Calcd
(Found) for C17H25N3O2: C, 67.30 (67.04); H, 8.30 (7.96);
N, 13.85% (14.02%).
148.0 8C. IR (KBr): 3228, 2952, 1658, 1512, 1342 cmK1
.
1H NMR (500 MHz, DMSO-d6): d 2.00 (3H, s,), 2.16 (6H,
s), 2.33 (2H, t, JZ6.7 Hz), 3.24 (2H, dt, JZ6.4, 6.7 Hz),
7.00 (1H, s), 7.74 (2H, d, JZ8.9 Hz), 8.05 (1H, t, JZ
6.4 Hz), 8.22 (2H, d, JZ8.9 Hz), 9.60 (1H, s). 13C NMR
(125.7 MHz, DMSO-d6): d 22.9, 37.4, 45.2 (2C), 57.9,
123.5 (2C), 128.7, 130.1 (2C), 133.4, 141.5, 145.4, 164.5,
169.2. Anal. Calcd (Found) for C15H20N4O4: C, 56.24
(56.02); H, 6.29 (6.34); N, 17.49% (17.50%).
3.3.10. (Z)-2-Acetylamino-N-dimethylaminopropyl-3-(4-
methylphenyl)-2-propenamide [(Z)-1j]. Mp 125.0–
126.0 8C. IR (KBr): 3220, 2944, 1650 cmK1 1H NMR
.
3.3.5. (Z)-2-Acetylamino-N-dimethylaminoethyl-3-(4-
methoxyphenyl)-2-propenamide [(Z)-1e]. Mp 133.5–
(500 MHz, DMSO-d6): d 1.57 (2H, tt, JZ6.7, 7.3 Hz), ?.98
(3H, s,),2.12(6H, s), 2.22(2H, t, JZ7.3 Hz), 2.31(3H, s), 3.15
(2H, dt, JZ6.1, 6.7 Hz), 7.01 (1H, s), 7.19 (2H, d, JZ7.9 Hz),
7.42 (2H, d, JZ7.9 Hz), 8.00 (1H, t, JZ6.1 Hz), 9.29 (1H, s).
13C NMR (125.7 MHz, DMSO-d6): d 20.8, 22.8, 26.7, 37.9,
45.1 (2C), 57.1, 127.6, 129.0 (2C), 129.2 (2C), 129.4, 131.3,
138.0, 164.7, 169.1. Anal. Calcd (Found) for C17H25N3O2: C,
67.30 (67.42); H, 8.30 (8.27); N, 13.85% (13.92%).
134.5 8C. IR (KBr): 3328, 2944, 1653 cmK1 1H NMR
.
(500 MHz, DMSO-d6): d 2.00 (3H, s,), 2.15 (6H, s), 2.31
(2H, t, JZ6.7 Hz), 3.21 (2H, dt, JZ6.1, 6.7 Hz), 3.77 (3H,
s), 6.95 (2H, d, JZ8.6 Hz), 7.04 (1H, s), 7.50 (2H, d, JZ
8.6 Hz), 7.77 (1H, t, JZ6.1 Hz), 9.32 (1H, s). 13C NMR
(125.7 MHz, DMSO-d6): d 22.9, 37.3, 45.2 (2C), 55.2, 58.1,
114.0 (2C), 126.6, 127.9, 128.0, 131.0 (2C), 159.5, 165.0,
169.4. Anal. Calcd (Found) for C16H23N3O3: C, 62.93
(63.20); H, 7.59 (7.45); N, 13.76% (13.64%).
3.3.11. (Z)-2-Benzoylamino-N-dimethylaminoethyl-3-(1-
naphthyl)-2-propenamide [(Z)-1k]. Mp 176.0–177.0 8C.
IR (KBr): 3244, 3064, 2938, 1620 cmK1. 1H NMR (500 MHz,
DMSO-d6): d 2.16 (6H, s), 2.38 (2H, t, JZ6.7 Hz), 3.29 (2H,
dt, JZ5.5, 6.7 Hz), 7.42 (2H, dd, JZ7.3, 7.9 Hz), 7.42 (1H,
dd, JZ7.3, 7.9 Hz), 7.51 (1H, dd, JZ7.9, 7.9 Hz), 7.55 (1H,
dd, JZ7.3, 7.9 Hz), 7.56(1H, dd, JZ7.3, 7.9 Hz), 7.61 (1H, d,
JZ7.3 Hz), 7.75 (1H, s), 7.81 (2H, d, JZ7.3 Hz), 7.85 (1H, d,
JZ7.9 Hz), 7.92 (1H, d, JZ7.3 Hz), 8.02 (1H, d, JZ7.9 Hz),
8.09 (1H, t, JZ5.5 Hz), 9.75 (1H, s). 13C NMR (125.7 MHz,
DMSO-d6): d 37.4, 45.2 (2C), 58.0, 124.2, 125.3, 125.98,
126.03, 126.1, 126.4, 127.7 (2C), 128.1 (2C), 128.40, 128.43,
131.1, 131.4, 131.5, 132.3, 133.1, 133.8, 164.6, 166.2. Anal.
Calcd (Found) for C24H25N3O2: C, 74.39 (74.28); H, 6.50
(6.44); N, 10.84% (10.86%).
3.3.6. (Z)-2-Acetylamino-N-dimethylaminoethyl-3-(4-
methylphenyl)-2-propenamide [(Z)-1f]. Mp 130.5–
131.5 8C. IR (KBr): 3214, 2986, 1671 cmK1 1H NMR
.
(500 MHz, DMSO-d6): d 1.99 (3H, s,), 2.16 (6H, s), 2.31
(3H, s), 2.32 (2H, t, JZ6.7 Hz), 3.22 (2H, dt, JZ6.1,
6.7 Hz), 7.01 (1H, s), 7.20 (2H, d, JZ7.9 Hz), 7.42 (2H, d,
JZ7.9 Hz), 7.82 (1H, t, JZ6.1 Hz), 9.35 (1H, s). 13C NMR
(125.7 MHz, DMSO-d6): d 20.9, 22.9, 37.3, 45.2 (2C), 58.0,
127.8, 129.1 (2C), 129.30 (2C), 129.34, 131.4, 138.1, 164.9,
169.3. Anal. Calcd (Found) for C16H23N3O2: C, 66.41
(66.08); H, 8.01 (7.98); N, 14.52% (14.64%).
3.3.7. (Z)-2-Acetylamino-N-dimethylaminoethyl-3-(4-
chlorophenyl)-2-propenamide [(Z)-1g]. Mp 132.0–
133.0 8C. IR (KBr): 3214, 2980, 1656 cmK1 1H NMR
.
3.4. General procedure for the reactions of (Z)-1 and
oxygen
(500 MHz, DMSO-d6): d 1.98 (3H, s,), 2.15 (6H, s), 2.31
(2H, t, JZ6.7 Hz), 3.22 (2H, dt, JZ5.5, 6.7 Hz), 6.99 (1H,
s), 7.49 (2H, d, JZ8.5 Hz), 7.53 (2H, d, JZ8.5 Hz), 7.91
(1H, t, JZ5.5 Hz), 9.43 (1H, s). 13C NMR (125.7 MHz,
DMSO-d6): d 22.9, 37.4, 45.2 (2C), 58.0, 125.9, 128.5 (2C),
130.8, 130.9 (2C), 132.8, 133.2, 164.6, 169.3. Anal. Calcd
(Found) for C15H20ClN3O2: C, 58.16 (58.27); H, 6.51
(6.76); N, 13.56% (13.71%).
In order to determine the rate constant for the pseudo-first
order reaction of (Z)-1 with oxygen in a given solvent, each
solution of (Z)-1 (10 mL, 1.0!10K4 mol dmK3) was
purged with air for 10 min and sealed into a Pyrex vessel,
which was immersed in an oil bath thermostated at 80 8C. At
appropriate time intervals, the vessels were taken out one by
one and cooled in an ice-water bath in order to stop the
reaction. By following a gradual increase in the first UV
absorption band of (Z)-2 which appeared in the
3.3.8. (Z)-2-Acetylamino-N-dimethylaminoethyl-3-[4-(tri-
fluoromethyl)phenyl]-2-propenamide [(Z)-1h]. Mp 131.0–

A. Kawasaki et al. / Tetrahedron 60 (2004) 9517–9524
9523
wavelength region of 350–380 nm, the rate constant for the
reaction was estimated. The UV absorption spectrum of a
given solution (measured after the reaction was completed)
was in nearly agreement with that of the corresponding
solution of (Z)-2 (1.0!10K4 mol dmK3) isolated. Simi-
larly, an oxygen-saturated MeOH solution of (Z)-1 (10 mL,
2.0!10K3 mol dmK3) was heated at 80 8C in a sealed tube
for a given period of time and then concentrated to dryness
in vacuo. The residue obtained was dissolved in DMSO-d6
(KBr): 2980, 1719, 1644 cmK1
.
1H NMR (500 MHz,
DMSO-d6): d 2.18 (6H, s), 2.40 (3H, s), 2.41 (2H, t, JZ
6.4 Hz), 3.65 (2H, t, JZ6.4 Hz), 6.96 (1H, s), 7.40 (1H, dd,
JZ7.0, 7.0 Hz), 7.45 (2H, dd, JZ7.0, 7.3 Hz), 8.20 (2H, d,
JZ7.3 Hz). 13C NMR (125.7 MHz, DMSO-d6): d 15.5,
38.1, 45.3 (2C), 57.4, 124.7, 128.6 (2C), 129.9, 131.8 (2C),
134.1, 138.7, 164.3, 169.8. Anal. Calcd (Found) for
C15H19N3O: C, 70.01 (69.94); H, 7.44 (7.35); N, 16.33%
(16.19%). HR FAB-MS m/z calcd for C15H20N3O:
258.1606. Found: 258.1609.
1
and subjected to the H NMR spectral analysis.
For isolating and identifying products, a MeOH solution of
(Z)-1 (100 mL, 5.0!10K3 mol dmK3) was saturated with
oxygen and sealed into a Pyrex vessel, which was immersed
in an oil bath thermostated at 80 8C. After completion of the
reaction was confirmed by measuring the UV absorption
spectrum of the mixture, 10 mL aliquot of this mixture was
diluted in a volumetric flask to 20 mL with water containing
0.2 mol dmK3 KCl. The resulting solution was subjected to
the voltammetric analysis using a glassy carbon electrode.
Oxidation potentials were determined with reference to the
Ag/AgCl electrode. The remaining reaction mixture was
concentrated to dryness under reduced pressure and the
resulting crystalline solid was subjected to short column
chromatography over silica gel (230 mesh, Merck) eluting
with EtOAc–MeOH (9:1 v/v) in order to obtain analytical-
grade (Z)-2, which was, if necessary, recrystallized from
EtOAc–hexane. Physical and spectroscopic properties of
(Z)-2-imidazolin-5-one derivatives (2a–j) thus obtained are
as follows.
3.4.4. (Z)-1-[2-(Diethylamino)ethyl]-2-methyl-4-benzyli-
dene-2-imidazolin-5-one [(Z)-2d]. Mp 39.5–40.5 8C. IR
(KBr): 2968, 1710, 1644 cmK1 1H NMR (500 MHz,
.
DMSO-d6): d 0.90 (6H, t, JZ7.3 Hz), 2.41 (3H, s,), 2.47
(4H, q, JZ7.3 Hz), 2.52 (2H, t, JZ6.1 Hz), 3.60 (2H, t, JZ
6.1 Hz), 6.95 (1H, s), 7.40 (1H, dd, JZ6.7, 6.7 Hz), 7.45
(2H, dd, JZ6.7, 7.3 Hz), 8.20 (2H, d, JZ7.3 Hz). 13C NMR
(125.7 MHz, DMSO-d6): d 11.9 (2C), 15.5, 39.0, 46.7 (2C),
50.8, 124.5, 128.6 (3C), 129.8, 131.8, 134.1, 138.8, 164.5,
169.9. Anal. Calcd (Found) for C17H23N3O: C, 71.55
(71.23); H, 8.12 (7.98); N, 14.72% (14.58%).
3.4.5. (Z)-1-[2-(Dimethylamino)ethyl]-2-methyl-4-(4-
methoxybenzylidene)-2-imidazolin-5-one [(Z)-2e]. Mp
74.0–74.5 8C. IR (KBr): 2938, 1707, 1644 cmK1 1H
.
NMR (500 MHz, DMSO-d6): d 2.18 (6H, s), 2.38 (3H, s),
2.40 (2H, t, JZ6.7 Hz), 3.64 (2H, t, JZ6.7 Hz), 3.82 (3H,
s), 6.93 (1H, s), 7.02 (2H, d, JZ8.6 Hz), 8.18 (2H, d, JZ
8.6 Hz). 13C NMR (125.7 MHz, DMSO-d6): d 15.4, 38.0,
45.3 (2C), 55.3, 57.5, 114.3 (2C), 124.9, 126.8, 133.8 (2C),
136.8, 160.7, 162.7, 169.8. Anal. Calcd (Found) for
C16H21N3O2: C, 66.88 (67.11); H, 7.37 (7.35); N, 14.62%
(14.73%).
3.4.1. (Z)-1-[2-(Dimethylamino)ethyl]-2-methyl-4-(1-
naphthylmethylene)-2-imidazolin-5-one [(Z)-2a]. Mp
88.0–89.0 8C. IR (KBr): 2956, 1719, 1644 cmK1 1H
.
NMR (500 MHz, DMSO-d6): d 2.20 (6H, s,), 2.43 (3H, s),
2.44 (2H, t, JZ6.4 Hz), 3.70 (2H, t, JZ6.4 Hz), 7.60 (1H,
dd, JZ7.3, 7.9 Hz), 7.63 (1H, dd, JZ7.9, 7.9 Hz), 7.66 (1H,
dd, JZ7.0, 7.3 Hz), 7.72 (1H, s), 8.00 (1H, d, JZ7.3 Hz),
8.02 (1H, d, JZ7.3 Hz), 8.31 (1H, d, JZ7.9 Hz), 8.88 (1H,
d, JZ7.0 Hz). 13C NMR (125.7 MHz, DMSO-d6): d 15.5,
38.1, 45.3 (2C), 57.5, 119.5, 122.8, 125.6, 126.1, 127.3,
128.9, 129.5, 130.4, 130.9, 131.7, 133.3, 139.6, 165.2,
169.8. Anal. Calcd (Found) for C19H21N3O: C, 74.24
(74.05); H, 6.89 (6.91); N, 13.67% (13.68%). HR EI-MS m/z
calcd for C19H21N3O: 307.1685. Found: 307.1685.
3.4.6. (Z)-1-[2-(Dimethylamino)ethyl]-2-methyl-4-(4-
methylbenzylidene)-2-imidazolin-5-one [(Z)-2f]. Mp
78.5–79.0 8C. IR (KBr): 2944, 1712, 1646 cmK1 1H
.
NMR (500 MHz, DMSO-d6): d 2.18 (6H, s), 2.34 (3H, s),
2.39 (3H, s), 2.40 (2H, t, JZ6.4 Hz), 3.65 (2H, t, JZ
6.4 Hz), 6.93 (1H, s), 7.26 (2H, d, JZ7.9 Hz), 8.10 (2H, d,
JZ7.9 Hz). 13C NMR (125.7 MHz, DMSO-d6): d 15.4,
21.1, 38.1, 45.3 (2C), 57.5, 124.9, 129.3 (2C), 131.4, 131.9
(2C), 138.0, 140.0, 163.6, 169.8. Anal. Calcd (Found) for
C16H21N3O: C, 70.82 (70.74); H, 7.80 (7.88); N, 15.49%
(15.49%).
3.4.2. (Z)-1-[2-(Diethylamino)ethyl]-2-methyl-4-(1-
naphthylmethylene)-2-imidazolin-5-one [(Z)-2b]. Mp
3.4.7. (Z)-1-[2-(Dimethylamino)ethyl]-2-methyl-4-(4-
chlorobenzylidene)-2-imidazolin-5-one [(Z)-2g]. Mp
88.0–88.5 8C. IR (KBr): 2962, 1701, 1632 cmK1 1H
.
115.5–116.5 8C. IR (KBr): 2980, 1713, 1644 cmK1 1H
.
NMR (500 MHz, DMSO-d6): d 0.92 (6H, t, JZ7.3 Hz),
2.44 (3H, s,), 2.50 (4H, q, JZ7.3 Hz), 2.56 (2H, t, JZ
6.1 Hz), 3.65 (2H, t, JZ6.1 Hz), 7.60 (1H, dd, JZ6.7,
7.9 Hz), 7.64 (1H, dd, JZ7.3, 7.3 Hz), 7.66 (1H, dd, JZ7.9,
8.5 Hz), 7.72 (1H, s), 8.00 (1H, d, JZ6.7 Hz), 8.01 (1H, d,
JZ7.3 Hz), 8.30 (1H, d, JZ8.5 Hz), 8.89 (1H, d, JZ
7.3 Hz). 13C NMR (125.7 MHz, DMSO-d6): d 11.9 (2C),
15.6, 39.1, 46.8 (2C), 50.9, 119.3, 122.8, 125.6, 126.2,
127.3, 128.9, 129.5, 130.4, 130.9, 131.7, 133.3, 139.7,
165.5, 169.9. Anal. Calcd (Found) for C21H25N3O: C, 75.19
(75.24); H, 7.51 (7.45); N, 12.53% (12.60%).
NMR (500 MHz, DMSO-d6): d 2.18 (6H, s), 2.40 (3H, s),
2.40 (2H, t, JZ6.1 Hz), 3.65 (2H, t, JZ6.1 Hz), 6.97 (1H,
s), 7.52 (2H, d, JZ8.5 Hz), 8.23 (2H, d, JZ8.5 Hz). 13C
NMR (125.7 MHz, DMSO-d6): d 15.4, 38.1, 45.2 (2C),
57.4, 123.1, 128.7 (2C), 132.9, 133.3 (2C), 134.4, 139.1,
164.8, 169.6. Anal. Calcd (Found) for C15H18ClN3O: C,
61.75 (62.01); H, 6.22 (6.35); N, 14.40% (14.70%).
3.4.8. (Z)-1-[2-(Dimethylamino)ethyl]-2-methyl-4-[4-
(trifluoromethyl)benzylidene]-2-imidazolin-5-one [(Z)-
2h]. Mp 117.5–118.0 8C. IR (KBr): 2948, 1716,
1
3.4.3. (Z)-1-[2-(Dimethylamino)ethyl]-2-methyl-4-benzyl-
idene-2-imidazolin-5-one [(Z)-2c]. Mp 89.5–90.0 8C. IR
1650 cmK1. H NMR (500 MHz, DMSO-d6): d 2.17 (6H,
s), 2.40 (2H, t, JZ6.1 Hz), 2.41 (3H, s), 3.65 (2H, t, JZ

9524
A. Kawasaki et al. / Tetrahedron 60 (2004) 9517–9524
Kubo, K.; Igarashi, T.; Sakurai, T. Heterocycles 2000, 53,
2261–2274. (e) Maekawa, K.; Kajiwara, H.; Iseya, Y.;
Igarashi, T.; Sakurai, T. Heterocycles 2003, 60, 637–654.
(f) Hoshina, H.; Maekawa, K.; Taie, K.; Igarashi, T.; Sakurai,
T. Heterocycles 2003, 60, 1779–1786.
6.1 Hz), 7.02 (1H, s), 7.79 (2H, d, JZ8.5 Hz), 8.38 (2H, d,
JZ8.5 Hz). 13C NMR (125.7 MHz, DMSO-d6): d 15.6,
38.2, 45.3 (2C), 57.4, 122.4, 124.1 (1C, q, JZ273 Hz),
125.4 (2C, q, JZ4 Hz), 129.1 (1C, q, JZ31 Hz), 132.1
(2C), 138.0, 140.5, 166.2, 169.7. Anal. Calcd (Found) for
C16H18F3N3O: C, 59.07 (58.94); H, 5.58 (5.77); N, 12.92%
(12.87%).
4. (a) Kubo, K.; Ishii, Y.; Sakurai, T.; Makino, M. Tetrahedron
Lett. 1998, 39, 4083–4086. (b) Sakurai, T.; Morioka, Y.;
Maekawa, K.; Kubo, K. Heterocycles 2000, 53, 271–276.
(c) Maekawa, K.; Igarashi, T.; Kubo, K.; Sakurai, T.
Tetrahedron 2001, 57, 5515–5526. (d) Motohashi, T.;
Maekawa, K.; Kubo, K.; Igarashi, T.; Sakurai, T. Heterocycles
2002, 57, 269–292. (e) Maekawa, K.; Kubo, K.; Igarashi, T.;
Sakurai, T. Hterocycles 2002, 57, 1591–1597.
3.4.9. (Z)-1-[2-(Dimethylamino)ethyl]-2-methyl-4-(4-
nitrobenzylidene)-2-imidazolin-5-one [(Z)-2i]. Mp
137.0–138.0 8C. IR (KBr): 2980, 1716, 1641, 1508,
1
1340 cmK1. H NMR (500 MHz, DMSO-d6): d 2.18 (6H,
s), 2.42 (2H, t, JZ6.1 Hz), 2.45 (3H, s), 3.68 (2H, t, JZ
6.1 Hz), 7.08 (1H, s), 8.29 (2H, d, JZ8.5 Hz), 8.45 (2H, d,
JZ8.5 Hz). 13C NMR (125.7 MHz, DMSO-d6): d 15.7,
38.2, 45.3 (2C), 57.3, 121.4, 123.6 (2C), 132.5 (2C), 140.6
141.3, 147.2, 167.2, 169.7. Anal. Calcd (Found) for
C15H18N4O3: C, 59.59 (59.46); H, 6.00 (5.76); N, 18.53%
(18.41%).
5. (a) Tsubomura, H.; Yagishita, T.; Toi, H. Bull. Chem. Soc. Jpn
1973, 46, 3051–3055. (b) Maeda, K.; Nakane, A.; Tsubomura,
H. Bull. Chem. Soc. Jpn 1975, 48, 2448–2450.
6. Oshimi, K.; Kubo, K.; Kawasaki, A.; Maekawa, K.; Igarashi,
T.; Sakurai, T. Tetrahedron Lett. 2002, 43, 3291–3294.
7. (a) Rao, Y. S.; Filler, R. Synthesis 1975, 749–764.
(b) Rzeszotarska, B.; Karolak-Wojciechowska, J.; Broda,
M. A.; Galdecki, Z.; Trzezwinska, B.; Koziol, A. E. Int.
J. Pept. Protein Res. 1994, 44, 313–319.
3.4.10. (Z)-1-[2-(Dimethylamino)propyl]-2-methyl-4-(4-
methylbenzylidene)-2-imidazolin-5-one [(Z)-2j]. Oily
liquid. IR (neat): 2943, 1709, 1643 cmK1 1H NMR
.
8. Murov, S. L.; Carmichael, I.; Hug, G. L. Handbook of
Photochemistry. 2nd ed.; Marcel Dekker: New York, 1993
pp 289–293.
(500 MHz, DMSO-d6): d 1.69 (2H, tt, JZ6.9, 7.6 Hz),
2.12 (6H, s,), 2.20 (2H, t, JZ6.9 Hz), 2.34 (3H, s), 2.38 (3H,
s), 3.58 (2H, t, JZ7.6 Hz), 6.91 (1H, s), 7.26 (2H, d, JZ
8.2 Hz), 8.10 (2H, d, JZ8.2 Hz). 13C NMR (125.7 MHz,
DMSO-d6): d 15.3, 21.1, 26.3, 38.2, 45.0 (2C), 56.0, 124.8,
129.3 (2C), 131.4, 131.9 (2C), 138.0, 140.0, 163.5, 169.9.
Anal. Calcd (Found) for C17H23N3O: C, 71.55 (71.38); H,
8.12 (7.87); N, 14.72% (14.54%).
9. Crystallographic data of (Z)-2c have been deposited at the
CCDC 183850, 12 Union Road, Cambridge CB2 1EZ, UK
(fax: C44-1223-336033 or e-mail: deposit@ccdc.cam.ac.uk)
and copies can be obtained on request, free of charge, by
quoting our publication.
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(b) Rehm, D.; Weller, A. Z. Phys. Chem. 1970, 69, 183–200.
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12. Eriksen, J.; Foote, C. S. J. Am. Chem. Soc. 1980, 102,
6083–6088.
Acknowledgements
This research was partially supported by a ‘High-Tech
Research Project’ from the Ministry of Education, Sports,
Culture, Science and Technology, Japan.
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