Preparation of 1,6-naphthyridine-2,5(1H,6H)-diones

Article abstract of DOI:10.1002/jhet.5570380123

Novel method for the synthesis of 3-acyl-1,6-dialkyl-7-methyl-1,6-naphthyridine-2,5(1H,6H)-diones (2) was developed. The reaction of 2-acyl-1-alkylamino-1-ethoxyethylenes (1) with acetyl chloride or β-keto amide 3 with acetyl chloride in the presence of p

Full text of DOI:10.1002/jhet.5570380123

Jan-Feb 2001
Preparation of 1,6-Naphthyridine-2,5(1H,6H)-diones
159
Tetsuo Ohta, Hironori Fujisawa, Mitsuru Kawazome,
Yasuto Nakai and Isao Furukawa*
Department of Molecular Science and Technology, Faculty of Engineering, Doshisha University, Kyotanabe, Kyoto 610-0394, Japan
Received March 3, 2000
Novel method for the synthesis of 3-acyl-1,6-dialkyl-7-methyl-1,6-naphthyridine-2,5(1H,6H)-diones (2)
was developed. The reaction of 2-acyl-1-alkylamino-1-ethoxyethylenes (1) with acetyl chloride or β-keto
amide 3 with acetyl chloride in the presence of p-toluenesulfonic acid gave 2 in moderate yield (14–59% yield).
J. Heterocyclic Chem., 38, 159 (2001).
Introduction.
reaction of 1e, its structure was confirmed as 3-benzoyl-7-
methyl-4-phenyl-1,6-dipropyl-1,6-naphthyridine-
2,5(1H,6H)-dione (2e) (see Experimental section). Using
dichloromethane, benzene, or dimethyl formamide (DMF)
as a solvent, lowering the temperature, and/or extending
the reaction time resulted in lower yields of the desired
products. The representative results using various 1 with
acyl chloride are listed in Table 1.
Employing 3-ethoxy-3-methylamino-1-phenyl-2-
propen-1-one (1e) resulted in the formation of 2e with a
benzoyl substituent on the 3-position of the 1,6-naphthy-
ridine-2,5(1H,6H)-dione framework and a phenyl
substituent on the 4-position. The reaction using propionyl
chloride instead of acetyl chloride gave 1,6-naphthyridine-
2,5(1H,6H)-dione derivative (2f), which has an ethyl
group on the 7-position and a methyl substituent on the
8-position. Although their yields were low, these products
demonstrated that the 3- and 4-substituents of 2 came from
the starting material 1 and the 7- and 8-substituents came
from acyl chloride.
In continuing our studies [1,2] on the utilization of
2-acyl-1-alkylamino-1-ethoxyethylenes (α-oxoketene
O,N-acetals, 1 [3,4]), prepared easily from CS2 via β-oxo
thionoesters, we are interested in the reaction of 1 with
acetyl chloride as an electrophile and found that the
reaction of 2-acyl-1-alkylamino-1-ethoxyethylenes (1)
with acetyl chloride gave 1,6-naphthyridine-2,5(1H,6H)-
diones (2). Compound 2 has scarcely been reported in the
literature thus far. Herein we wish to describe the
preparation of 2 in a single step.
In reaction product 2, the ethyl group of the ethoxy
moiety in 1 was not incorporated. Therefore the use of
3-oxobutanamide 3 was examined (equation 2). The
reaction of 3 with acetyl chloride gave 2 in low yield. On
the other hand, the reaction of 3 with acetyl chloride in the
presence of p-toluenesulfonic acid gave 2 in similar or
better yields to that of the reaction of 1 with acetyl chloride
(Table 1). For example, N-propyl-3-oxobutanamide 3b
afforded 2b in 59% yield.
Results and Discussion.
Heating a solution of 4-ethoxy-4-methylamino-3-buten-
2-one (1a) in acetyl chloride for 6 hours followed by
recrystallization of the chromatographically isolated
product gave a white powder. Spectroscopic analyses
indicated the formation of 3-acetyl-1,4,6,7-tetramethyl-
1,6-naphthyridine-2,5(1H,6H)-dione (2a). By single
crystal X-ray structure analysis of the product from the
Table 1
Synthesis of 3-Acyl-1,6-dialkyl-7-methyl-1,6-naphthyridine-2,5(1H,6H)-diones (2) from α-Oxoketene O,N-acetals (1) or β-Ketoamides (3)[a]
substrate
R
product 2
1
2
3
entry
R
R
Yield [b] from
Yield [b] from
1
3
1
2
3
4
5
6
1a
1b
1c
1d
1e
1a
3a
3b
3c
3d
CH
CH
CH
CH
CH
H
H
H
H
H
2a
2b
2c
2d
2e
2f
46
46
8 (34)
14
14
15
33
59
4(44)
30
3
3
3
3
3
n-C H
3 7
i-C H
3 7
CH C H
2 6 5
C H
n-C H
3 7
6 5
CH
CH
CH
3
3
3
[a] Reaction conditions: α-oxoketene O,N-acetals (1) (4.0 mmol) in acyl chloride (10.0 mL) for 6 hours at reflux temperature or N-alkyl-3-oxobu-
tanamide (3) (2.0 mmol) and p-TsOH (3.0 mmol) in acetyl chloride (10.0 mL) for 6 hours at reflux temperature. [b] Isolated yield based on 1 or 3. Figures
in parentheses show the yield of 4.

160
T. Ohta, H. Fujisawa, M. Kawazome, Y. Nakai and I. Furukawa
Vol. 38
Table 2
Crystallographic Data of 2e and 4
2e
4
chemical formula
formula weight
crystal
size, mm
crystal system
space group
a, Å
C
H
N O
C H NO
11 15
209.24
colorless, prismatic
0.2 x 0.1 x 1.0
monoclinic
29 32
2
4
3
472.58
colorless, prismatic
0.5 x 0.5 x 0.2
monoclinic
1,6-Naphthyridine-2,5(1H,6H)-diones are rare
compounds in the literature, and there are only few reports
dealing with their preparation [5]. For example,
1,6-dimethyl-1,6-naphthyridine-2,5(1H,6H)-dione was
synthesized by the Skraup reaction, alkylation, and then
oxidation,[6] while the reaction of ethyl N-benzylacetimi-
date with diketene was demonstrated to give 1,6-naph-
thyridine-2,5(1H,6H)-diones in moderate yields [7].
4-Hydroxy derivatives were also produced from
(alkylamino)pyridones [8] or from ethyl β-(alkylamino)-
crotonate [9]. Thus, this method for the preparation of 3
may be an alternative.
P2 /c
P2 /c
1
1
13.561(3)
14.460(3)
13.626(2)
108.08(1)
2540.2(8)
4
9.771(4)
6.972(3)
16.626(3)
94.03(2)
1129.7(6)
4
b, Å
c, Å
β, deg
3
V, Å
Z
D
3
, g/cm
1.236
0.82
1.230
0.89
calc
-1
µ (MoKa), cm
radiation, (Å)
scan type
Mo, 0.71069 (graphite monochromated)
ω-2θ
ω-2θ
scan rate, °/min
scan width, deg
2θmax, deg
16
16
1.89 + 0.30 tanθ
55.0
1.78 + 0.30 tanθ
55.0
no of unique data
no of obsd.(I > 3σ(I))
R
6065
2965
0.077
0.069
4.68
2814
1352
0.064
0.055
4.52
R
W
Goodness of Fit
Max Shift/Error
0.03
0.00
pyrone derivatives.[10] Our results also agree with the
tendency observed in the literature. That is, in the case of
substrate 1c, the only substrate having a sterically hindered
isopropyl group, a pyrone derivative was the main product,
and a pyrone was not obtained from any other substrates.
From this reaction we have found the formation of a
small amount of 2-pyridone derivative 5. This compound
was considered to be formed from the reaction of 1 with
acid generated acetyl chloride and commented in a
separate paper.
In the case of 1c, 2,6-dimethyl-3-isopropylamino-
carbonyl-4H-pyran-4-one (4) was obtained in 34% yield
accompanied with 2c in 8% yield. Spectroscopic and
X-ray crystallographic analyses revealed the structure of 4.
Kato et al. reported that the reaction of amines with
diketene gave N-alkyl-3-oxobutanamide, pyridone, or
pyrone derivatives [10]. In this report, the alkyl
substituents on the nitrogen atom affected the type of
products, and the substrates with a sterically hindered
substituent, such as isopropyl and cyclohexyl, converted to
Plausible way of formation of 3-acyl-1,6-dialkyl-7-methyl-1,6-naphthyridine-2,5(1H,6H)-diones (2).

Jan-Feb 2001
Preparation of 1,6-Naphthyridine-2,5(1H,6H)-diones
161
Plausible way of formation of 3-acyl-1,6-dialkyl-7-methyl-1,6-naphthyridine-2,5(1H,6H)-diones (2).
Figure 1. X-Ray structure of 3-Benzoyl-4,7-dimethyl-1,6-dipropyl-1,6-naphthyridine-2,5(1H,6H)-dione (2e).
Figure 2. X-Ray structure of 2,6-dimethyl-3-isopropylcarbamoyl-4H-pyran-4-one (4).

162
T. Ohta, H. Fujisawa, M. Kawazome, Y. Nakai and I. Furukawa
Vol. 38
Table 3
Selected Bond Distances and Angles for 2e
Intramolecular Distances, Å (standard deviation)
O(1)—C(1)
N(1)—C(8)
C(1)—C(2)
C(4)—C(5)
C(7)—C(8)
1.225(5)
1.384(5)
1.437(6)
1.453(5)
1.429(5)
O(2)—C(5)
N(2)—C(5)
C(2)—C(3)
C(4)—C(8)
1.222(5)
1.399(5)
1.358(5)
1.380(5)
N(1)—C(1)
N(2)—C(6)
C(3)—C(4)
C(6)—C(7)
1.412(5)
1.363(5)
1.450(5)
1.353(5)
Selected Bond Angles, deg (standard deviation)
C(1)—N(1)—C(8)
N(1)—C(1)—C(2)
C(2)—C(3)—C(4)
C(3)—C(4)—C(8)
N(2)—C(5)—C(4)
C(6)—C(7)—C(8)
N(1)—C(8)—C(7)
122.6(4)
C(5)—N(2)—C(6)
C(1)—C(2)—C(3)
C(3)—C(4)—C(5)
C(5)—C(4)—C(8)
N(2)—C(6)—C(7)
N(1)—C(8)—C(4)
C(4)—C(8)—C(7)
123.0(4)
123.9(4)
120.6(4)
120.3(4)
120.6(4)
120.7(4)
119.5(4)
115.0(4)
118.5(4)
119.1(4)
116.1(4)
120.1(4)
119.7(4)
Table 4
Selected Bond Distances and Angles for 4
Intramolecular Distances, Å (standard deviation)
O(1)—C(2)
C(2)—C(3)
C(5)—C(6)
1.364(3)
1.350(4)
1.319(5)
O(1)—C(6)
C(3)—C(4)
1.368(4)
1.469(4)
O(9)—C(4)
C(4)—C(5)
1.237(4)
1.439(4)
Selected Bond Angles, deg (standard deviation)
C(2)—O(1)—C(6)
C(2)—C(3)—C(4)
C(4)—C(5)—C(6)
120.2(3)
118.5(3)
122.2(3)
O(1)—C(2)—C(3)
C(3)—C(4)—C(5)
O(1)—C(6)—C(5)
122.7(3)
115.4(3)
120.9(3)
A plausible way of formation for 2 is postulated as
follows. First, nucleophilic attack of 1 to acetyl chloride
occurs to give a monoacetylated intermediate 6. Self-
condensation of intermediate 6 may yield the product 2
(Scheme 1). In the reaction of ethyl N-benzylacetimidate
with diketene,[7] the condensation of two ethyl N-benzyl-
acetimidates occurred first, and then the condensed product
reacts with diketene. In our system, GC-MS analysis of the
reaction mixture during the course of the reaction indicated
that monoacetylated and diacetylated intermediates were
formed, before the product was formed, while dimeric
compounds of 1 were not observed by GC-MS.
Furthermore the reaction of 1 with diketene did not yield
any condensation product. Accordingly, we consider
N-acylation to be the first and key step for this reaction.
Usually the nucleophilic character of an enamine is
located on the β-carbon as well as on the nitrogen. In the
case of 1c, a sterically hindered isopropyl group is attached
on the nitrogen atom and, therefore, acylation takes place
on the β-carbon to give 7 as the major intermediate.
Intermediate 7 is then acylated on oxygen of the acetyl
group, followed by an intramolecular cyclization to yield
4. This is the reason why 1c underwent conversion to form
4 as the major product and 2c was formed in low yield.
Conclusions.
2-Acyl-1-alkylamino-1-ethoxyethylenes 1 act as nucleo-
philes. In the presence of acyl chloride, the nucleophilic
nitrogen attacked acyl chloride first, followed by the self-
condensation of the acylated intermediate to give
1,6-naphthyridine-2,5(1H,6H)-diones 2. In contrast, the
sterically hindered isopropyl group on nitrogen underwent
reaction with the β-carbon of acyl chloride to give the
pyrone derivative 4. N-Alkyl-3-oxobutanamides 3 were
used as alternative starting materials for the preparation of 2.
Acknowledgment.
We thank Dr. Takayuki Yamashita for helpful discus-
sions during the course of this work. This work was
partially supported by a research fund from Kyoeisha
Chemical Co., Ltd., and by a grant to RCAST at Doshisha
University from the Ministry of Education, Japan.

Jan-Feb 2001
Instrumentation.
Preparation of 1,6-Naphthyridine-2,5(1H,6H)-diones
163
EXPERIMENTAL
Anal. Calcd for C H N O : C, 64.60; H, 6.20; N, 10.76%.
14 16 2 3
Found: C, 64.67; H, 6.14; N, 10.59%..
3-Acetyl-4,7-dimethyl-1,6-dipropyl-1,6-naphthyridine-
2,5(1H,6H)-dione (2b).
1
Proton nuclear magnetic resonance ( H NMR) spectra were
measured on a JEOL JNM A-400 (400 MHz) spectrometer using
tetramethylsilane as an internal standard. IR spectra were
measured on a Shimadzu IR-408 spectrometer. Mass spectra
(GC-MS) were recorded on a Shimadzu GP2000A instrument.
Elemental analyses were performed at the Microanalytical Center
of Kyoto University. X-Ray analyses were conducted on a
Rigaku RASA-7R four-circle diffractometer. Melting points were
measured on a Yanako Model MP and were not corrected.
All solvents were dried by standard methods [11].
Commercially available compounds were used without
purification. 2-Acyl-1-alkylamino-1-ethoxyethylenes (1) [1] and
N-alkyl-3-oxobutanamides (3) [4,12] were prepared according to
literature methods.
Compound 2b has mp 136.5-136.8 °C; IR (KBr) 1615 (br),
1699; MS (m/z) 316; H NMR (deuteriochloroform): δ 1.01
1
(3H, t, J = 7.2 Hz, CH CH CH ), 1.02 (3H, t, J = 6.8 Hz,
2
2
3
CH CH CH ), 1.66-1.77 (4H, m, CH CH CH ), 2.48
2
2
3
2
2
3
(3H, s, CH ), 2.50 (3H, s, CH ), 2.61 (3H, s, CH ), 3.94 (2H, t,
3
3
3
J = 8.0 Hz, NCH CH CH ), 4.09 (2H, t, J = 7.8 Hz,
2
2
3
NCH CH CH ), 6.04 (1H, s, -CH=).
2
2
3
Anal Calcd. for C18H24N2O3: C, 68.33; H, 7.65; N, 8.85%.
Found: C, 68.39; H, 7.58; N, 8.94%.
3-Acetyl-1,6-diisopropyl-4,7-dimethyl-1,6-naphthyridine-
2,5(1H,6H)-dione (2c).
Compound 2c has mp 173.0-173.5 °C; IR (KBr) 1600 (br),
1698; MS (m/z) 316; H NMR (deuteriochloroform): δ 1.59
Preparation of 1,6-Naphthyridine-2,5(1H,6H)-diones (2).
1
(6H, d, J = 7.2 Hz, CH(CH ) ), 1.65 (6H, d, J = 6.8 Hz,
3 2
Method A. From 4-Ethoxy-4-methylamino-3-buten-2-one (1a)
with Acetyl Chloride.
CH(CH ) ), 2.47 (3H, s, CH ), 2.49 (3H, s, CH ), 2.56
3 2
3
3
(3H, s, CH ), 4.54 (1H, br, NCH(CH ) ), 6.18 (1H, s, -CH=).
3
3 2
This is a typical procedure for the reaction of 2-acyl-1-alkyl-
amino-1-ethoxyethylenes (1) with acyl chloride. In a 25–mL
flask equipped with a reflux condenser were introduced
4-ethoxy-4-methylamino-3-buten-2-one (1a, 0.57 g, 4.0 mmol)
and acetyl chloride (10 mL). The mixture was stirred under reflux
for 6 hours and then diluted with ethyl acetate (20 mL). Methanol
was added dropwise to this mixture, which was cooled in an ice-
water bath to avoid decomposition of acetyl chloride, and then
the solvent was removed under reduced pressure. To the resulting
mixture was added saturated aqueous sodium hydrogen
carbonate (10 mL) and chloroform (30 mL) and the resulting
layers were separated. The organic layer was dried over
anhydrous sodium sulfate and concentrated in vacuo. The residue
was purified by column chromatography (silica gel; hexane/ethyl
acetate = 2: 3 followed by 1:3) and by recrystallization from
methanol to give white solids (2a, 0.48 g, 1.8 mmol, 46 % yield).
Anal. Calcd for C H N O : C, 68.33; H, 7.65; N, 8.85%.
Found: C, 68.04; H, 7.57; N, 8.88%.
18 24
2 3
3-Isopropylcarbamoyl-2,6-dimethyl-4H-pyran-4-one (4).
-1
Compound 4 has mp 93.5-94.0 °C; IR (KBr) 1682, 1639 cm ;
1
MS (m/z) 209; H NMR (deuteriochloroform): δ 1.23 (6H, d, J = 6.8
Hz, CH(CH ) ), 2.29 (3H, s, CH ), 2.80 (3H, s, CH ), 4.17 (1H,
3 2
3
3
octet, J = 6.8 Hz, CH(CH ) ), 6.21 (1H, s, -CH=), 9.56 (1H, br, NH).
3 2
Anal. Calcd. for C H NO : C, 63.15; H, 7.18 ; N, 6.70%.
11 15
3
Found: C, 63.12; H, 7.10; N, 6.67%.
3-Benzoyl-7-methyl-4-phenyl-1,6-dipropyl-1,6-naphthyridine-
2,5(1H,6H)-dione (2e).
Compound 2e has mp 221.5-222.0 °C; IR (KBr) 1615 (br),
1
1675 (shoulder); H NMR (deuteriochloroform): δ 0.89 (3H, t,
J = 7.4 Hz, CH CH CH ), 1.05 (3H, t, J = 7.6 Hz, CH CH CH ),
2
2
3
2
2
3
Method B. From N-Propyl-3-oxobutanamide (3b) with Acetyl
Chloride in the Presence of p-Toluenesulfonic Acid.
1.61 (2H, sextet, J = 7.5 Hz, CH CH CH ), 1.81 (2H, sextet, J =
2
2
3
7.6 Hz, CH CH CH ), 2.50 (3H, s, CH ), 3.84 (2H, t, J = 7.8 Hz,
2
2
3
3
Typical procedure: In a 25–mL flask having a reflux condenser
were added N-propyl-3-oxobutanamide (3b, 0.29 g, 2.0 mmol),
acetyl chloride (10 mL), and p-toluenesulfonic acid hydrate
(0.57 g, 3.0 mmol). The mixture was heated at reflux for 6 hours.
The work-up of the mixture was the same as in the reaction of 1a
with acetyl chloride (vide ante). 3-Acetyl-4,7-dimethyl-1,6-
dipropyl-1,6-naphthyridine-2,5(1H,6H)-dione (2b) was obtained
as a white solid (0.38 g, 1.2 mmol, 59 %). 3-Acetyl-1,6-dibenzyl-
4,7-dimethyl-1,6-naphthyridine-2,5(1H,6H)-dione (2d) was
NCH CH CH ), 4.17 (2H, t, J = 8.0 Hz, NCH CH CH ), 6.16
2 2 3 2 2 3
(1H, s, -CH=), 7.08~7.70 (10H, m, Ar).
Anal. Calcd for C H N O •CH OH: C, 73.71; H, 6.83; N,
28 28
2
3
3
5.93%. Found: C, 73.98; H, 6.73; N, 5.97%.
3-Acetyl-7-ethyl-4,8-dimethyl-1,6-dipropyl-1,6-naphthyridine-
2,5(1H,6H)-dione (2f).
Compound 2f was obtained as an oily material: IR (neat)
-1
1
1620, 1692 cm : MS (m/z) 344: H-NMR (deuterio-
chloroform): δ 0.81 (3H, t, J = 7.4 Hz, CH CH CH ), 0.98
1
identified by comparison of its H NMR and IR spectral data
with that in literature.[7]
2
2
3
(3H, t, J = 7.4 Hz, CH CH CH ),1.24 (3H, t, J = 7.4 Hz,
2
2
3
3-Acetyl-1,4,6,7-tetramethyl-1,6-naphthyridine-2,5(1H,6H)-
dione (2a).
CH CH ), 1.63-1.76 (4H, m, CH CH CH ), 2.22 (3H, s, CH ),
2
3
2
2
3
3
2.50 (3H, s, CH ), 2.59 (3H, s, CH ), 2.77 (2H, q, J = 7.4 Hz,
3
3
CH CH ), 4.01 (2H, t, J = 7.8 Hz, CH CH CH ), 4.10 (2H, t,
2
3
2
2
3
Compound 2a has mp 239.0-240.5 °C; IR (KBr) 1595 (br),
1688; MS (m/z) 268; H NMR (deuteriochloroform): δ 2.47 (3H,
1
J = 7.6 Hz, CH CH CH ).
2
2
3
Anal. Calcd. for C H N O : C, 69.74; H, 8.19 ; N, 8.13%.
s, CH ), 2.51 (3H, s, CH ), 2.60 (3H, s, CH ), 3.51
20 28
2 3
3
3
3
Found: C, 68.44; H, 8.56; N, 7.57%.
(3H, s, NCH ), 3.58 (3H, s, NCH ), 7.42 (1H, s, -CH=).
3
3

164
T. Ohta, H. Fujisawa, M. Kawazome, Y. Nakai and I. Furukawa
Vol. 38
GC-MS Analysis of the Reaction Mixture in the Reaction of
4-Ethoxy-4-propylamino-3-buten-2-one (1b) with Acetyl
Chloride.
from a difference Fourier electron density map and the positions
of hydrogen atoms were determined by calculation, and then
refined anisotropically for non-hydrogen atoms and isotropically
for hydrogen atoms. All calculations were performed using the
teXsan crystallographic software packag [13]. Structure of 2e and
4 are shown in Figure 1 and 2, respectively. Selected bond dis-
tances and angles are summarized in Table 3 for 2e and Table 4
for 4.
In a 25–mL flask equipped with a reflux condenser were
introduced 4-ethoxy-4-propylamino-3-buten-2-one (1b, 0.69 g, 4.0
mmol) and acetyl chloride (10 mL). The mixture was stirred under
reflux for 1 hour and then diluted with ethyl acetate (20 mL).
Methanol was added dropwise to this mixture, which was cooled in
an ice-water bath to avoid decomposition of acetyl chloride, and
then the solvent was removed under reduced pressure. To the
resulting mixture was added saturated aqueous sodium hydrogen
carbonate (10 mL) and chloroform (30 mL) and the resulting layers
were separated. The organic layer was dried over anhydrous
sodium sulfate and then analyzed by GC-MS. GC-MS (initial
column temperature 100 °C for 3 minutes; heating to 280 °C at
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113, 573 (1982).
[9] M. Yamato, K. Sato, K. Hashigaki and M. Ninomiya,
Heterocycles, 19, 1263 (1982).
[10a] T. Kato and Y. Kubota, Yakugaku Zasshi, 89, 1477 (1969); [b]
T. Kato, Acc. Chem. Res., 7, 265 (1974).
[11] D. D. Perrin and W. L. F. Armarego, Purification of
Laboratory Chemicals, 3rd ed; Pergamon: Oxford, 1988.
[12] D. Bormann, Methoden der organischen Chemie (Houben-
Wetl-Müller), 4. Aufl., Thieme, Stuttgart, 1968, Bd. VII/4, S. 233.
[13] ”teXsan Crystal Structure Analysis Package,” Molecular
Structure Corporation (1985 and 1992).
+
20 °C/minute; hold 6 minutes at 280 °C) (m/z) 143 (8.8 min, M
+
for 1b - C H ), 171 (10.5 minutes, M for 1b), 184 (13 minutes,
(M - H) for 1b - C H + CH CO - H), 213 (17 minutes, M for
2
4
+
+
2
4
3
1b + CH CO - H), and 255 (18.5 min, M+ for 1b + 2CH CO - 2H).
3
3
Crystallographic Data Collections and Structure Determination
of 2e and 4.
The crystals of 2e and 4 suitable for X-ray diffraction studies
were prepared by recrystallization from methanol. Relevant
crystal and data statistics are summarized in Table 2. The unit cell
parameter at 20 °C was determined by a least-squares fit to 2θ
values of 10 strong higher reflections. Three standard reflections
were chosen and monitored every 150 reflections and showed no
significant intensity decay during the data collection (less than
2.5% for 2e and 3% for 4). The crystal structure was solved by
the direct method (Multan) and refined by the full-matrix least
squares method. Measured non-equivalent reflections with
I>3.0σ(I) were used for the structure determination. In the
2
subsequent refinement the function ∑ω(|Fo|-|Fc|) was
minimized, where |Fo| and |Fc| are the observed and calculated
structure factors amplitudes, respectively. The agreement indices
2
are defined as R = ∑||Fo|-|Fc||/∑|Fo| and Rw = [∑ω(|Fo|-|Fc|) /-
2 1/2
−1
2
2
2
2
∑ω(|Fo|) ] where ω = σ (Fo) = σ (Fo )/(4Fo ). For both 2e
and 4, the positions of all atoms except hydrogen were found