Synthesis and properties of novel 5-(cyclohepta-2′, 4′,6′-trienylidene)pyrimidine-2(1H),4(3H),6(5H)-triones: Methodology for synthesizing cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborates

Article abstract of DOI:10.1016/S0040-4020(03)00543-X

Novel condensation reaction of tropone with N-substituted and N,N′-disubstitued barbituric acids in Ac₂O afforded 5-(cyclohepta-2′,4′,6′-trienylidene)pyrimidine-2(1H), 4(3H),6(5H)-trione derivatives (8a-f) in moderate to good yields. The ¹³C NMR spectral study of 8a-f revealed that the contribution of zwitterionic resonance structures is less important as compared with that of 8,8-dicyanoheptafulvene. The rotational barriers (ΔG^?) around the exocyclic double bond of mono-substituted derivatives 8a-c were obtained to be 14.51-15.03kcalmol^-1 by the variable temperature ¹H NMR measurements. The electrochemical properties of 8a-f were also studied by CV measurement. Upon treatment with DDQ, 8a-c underwent oxidative cyclization to give two products, 7 and 9-substituted cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborates (11a-c·BF₄^- and 12a-c·BF₄^-) in various ratios, while that of disubstituted derivatives 8d-f afforded 7,9-disubstituted cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborate (11d-f·BF₄^-) in good yields. Similarly, preparation of known 5-(1′-oxocycloheptatrien-2′-yl)- pyrimidine-2(1H),4(3H),6(5H)-trione derivatives (14a-d) and novel derivatives 14e,f was carried out. Treatment of 14a-c with aq. HBF₄/Ac₂O afforded two kinds of novel products 11a-c·BF₄^- and 12a,c·BF₄^- in various ratios, respectively, while that of 14d-f afforded 11d-f. The product ratios of 11a-c·BF₄^- and 12a-c·BF₄^- observed in two kinds of cyclization reactions were rationalized on the basis of MO calculations of model compounds 20a and 21a. The spectroscopic and electrochemical properties of 11a-f·BF₄^- and 12a-c·BF₄^- were studied, and structural characterization of 11c·BF₄^- based on the X-ray crystal analysis and MO calculation was also performed.

Full text of DOI:10.1016/S0040-4020(03)00543-X

Tetrahedron 59 (2003) 3709–3718
Synthesis and properties of novel 5-(cyclohepta-20,40,60-
trienylidene)pyrimidine-2(1H),4(3H),6(5H)-triones: methodology
for synthesizing cyclohepta[b]pyrimido[5,4-d]furan-
8(7H),10(9H)-dionylium tetrafluoroborates
*
Shin-ichi Naya and Makoto Nitta
Department of Chemistry, School of Science and Engineering, Waseda University, Shinjuku-ku, Tokyo 169-8555, Japan
Received 19 February 2003; revised 1 April 2003; accepted 3 April 2003
Abstract—Novel condensation reaction of tropone with N-substituted and N,N0-disubstitued barbituric acids in Ac2O afforded
5-(cyclohepta-20,40,60-trienylidene)pyrimidine-2(1H),4(3H),6(5H)-trione derivatives (8a–f) in moderate to good yields. The 13C NMR
spectral study of 8a–f revealed that the contribution of zwitterionic resonance structures is less important as compared with that of 8,8-
dicyanoheptafulvene. The rotational barriers (DG ‡) around the exocyclic double bond of mono-substituted derivatives 8a–c were obtained
to be 14.51–15.03 kcal mol21 by the variable temperature 1H NMR measurements. The electrochemical properties of 8a–f were also studied
by CV measurement. Upon treatment with DDQ, 8a–c underwent oxidative cyclization to give two products, 7 and 9-substituted
cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborates (11a–c·BF24 and 12a–c·BF42) in various ratios, while that of
disubstituted derivatives 8d–f afforded 7,9-disubstituted cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium tetrafluoroborate
(11d–f·BF24 ) in good yields. Similarly, preparation of known 5-(10-oxocycloheptatrien-20-yl)-pyrimidine-2(1H),4(3H),6(5H)-trione
derivatives (14a–d) and novel derivatives 14e,f was carried out. Treatment of 14a–c with aq. HBF4/Ac2O afforded two kinds of novel
products 11a–c·BF24 and 12a,c·BF42 in various ratios, respectively, while that of 14d–f afforded 11d–f. The product ratios of 11a–c·BF42
and 12a–c·BF24 observed in two kinds of cyclization reactions were rationalized on the basis of MO calculations of model compounds 20a
and 21a. The spectroscopic and electrochemical properties of 11a–f·BF24 and 12a–c·BF42 were studied, and structural characterization of
11c·BF24 based on the X-ray crystal analysis and MO calculation was also performed. q 2003 Elsevier Science Ltd. All rights reserved.
1. Introduction
gated to evaluate the steric effect between the C2 or C7-
substituents and C8 substituents as well as the contribution
Heptafulvenes have intrigued chemists for several decades,
especially in the context of the concept of aromaticity.1–3
The properties and chemical behavior of substituted
heptafulvenes are usually rationalized in terms of the
differing contribution of the zwitterionic resonance struc-
tures. The relative contribution of such canonicical
structures depends on the electronegativity of the sub-
stituents at the 8-position, which modulates the aromaticity
of the ring. Thus, 8,8-dicyanoheptafulvene (1a) (Fig. 1) and
its derivatives have been synthesized by the reaction of
tropone (6) with active-methylene compounds, such as
malononitrile,4 and their properties and X-ray structure
analysis have been studied.5 The seven-membered ring of
1a is nearly planar,5 while that of 1b is puckered.6 Thus, the
rotational barrier around the exocyclic double bond of
heptafulvenes 2a–c and their derivatives has been investi-
Keywords: 5-(cyclohepta-20,40,60-trienylidene)pyrimidine-2(1H),4(3H),
6(5H)-trione; cyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-dionylium
tetrafluoroborate; uracil-annulated heteroazulene; redox potential.
*
Corresponding author. Tel.: þ81-3-5286-3236; fax: þ81-3-3208-2735;
e-mail: nitta@waseda.jp
Figure 1.
0040–4020/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0040-4020(03)00543-X

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S. Naya, M. Nitta / Tetrahedron 59 (2003) 3709–3718
of the zwitterionic structure.7 The chemistry of the extended
cyclic cross-conjugated compounds derived by insertion of
more complex conjugated p-systems instead of the exo-
double bond of heptafulvene has also been studied relative
to the molecular design of organic dyes, highly polarized
compounds, and electron acceptors or electron donors.8
Recently, the synthesis and photochemical properties of
compound 3, which is a more conjugated p-system of 1,
have been studied to demonstrate that compound 3
possesses a remarkable property of multimode-switching
arising from the ring-closure and ring-opening process: a
very fast photoreversible switch and a thermal switch.9
Thus, the heptafulvenes having variety of conjugated
functional groups seem to be interesting from the viewpoint
of molecular function. We have previously studied con-
venient preparations of 6,9-disubstituted cyclohepta[b]-
pyrimido[5,4-d]pyrrole-8(6H),10(9H)-diones (4) and
9-substituted cyclohepta[b]pyrimido[5,4-d]furan-8,10(9H)-
dione (5a–c), which are structural isomers of 5-deaza-
flavin10–12 and 5-deaza-10-oxaflavin, respectively,13 and
their functions in oxidizing some alcohols to the corre-
sponding carbonyl compounds.14,15 In relation to these
studies, we have previously studied the synthesis and
properties of heteroazulene-substituted methyl cations16–19
and tropylium ions.20 The reduction potentials and pKRþ
values of these cations clarified that heteroazulenes stabilize
not only cations but also radical species. In this context, we
have recently reported the synthesis and reactivity of 7,9-
dimethylcyclohepta[b]pyrimido[5,4-d]furan-8(7H),10(9H)-
dionylium tetrafluoroborate (11d·BF24 ) (Scheme 3) as well
as its photo-induced autorecycling oxidizing reactions
toward some alcohols.21 Thus, the uracil-annulated hetero-
azulenes are highly interesting from the viewpoint of
oxidizing functions as in the case of 5-deazaflavin10–12
and 5-deaza-10-oxaflavin,13 and exploration of method-
ology for synthesizing various cyclohepta[b]pyrimido[5,4-
d]furan-8(7H),10(9H)-dionylium tetrafluoroborate deriva-
tives of 11d·BF24 is required. We studied the synthesis and
properties of a novel type of heptafulvenes, 5-(cyclohepta-
20,40,60-trienylidene)pyrimidine-2(1H),4(3H),6(5H)-trione
(8a–f), which are converted to 11a–c·BF24 , 12a–c·BF42,
and 11d–f·BF24 , respectively, upon treatment with DDQ.
Similarly, synthesis of known 5-(10-oxocycloheptatrien-20-
yl)-pyrimidine-2(1H),4(3H),6(5H)-trione derivatives (14a–
c15) and novel derivative 14e,f in addition to known 14d21
was performed, and they were treated with aq. HBF4/Ac2O
to afford two kinds of products, 11a–f·BF24 and 12a,c·BF42.
The product ratios of 11a–c·BF24 and 12a–c·BF42 in both
reactions of 8a–c and 14a–c are rationalized on the basis of
MO calculations of the model compounds 20a and 21a as
well. The spectroscopic and electrochemical properties of
cations 11a–f and 12a–c are studied, and structural
characterization of 11c·BF24 based on the X-ray crystal
analysis and MO calculation is also performed. We report
herein the results in detail.
reddish needles in moderate to good yields (Scheme 1). The
results are summarized in Table 1. The heptafulvenes 8a–f
1
were fully characterized on the basis of the H and 13C
NMR, IR, UV–vis, and mass spectral data as well as
elemental analyses.
In the 13C NMR spectra, signals of carbon atoms (C-5 of the
barbituric acid moiety) of 8a–f appeared at dC 101.7–
103.1. Since these signals are shifted to higher field as
compared with those of 1a and 2a–c (1a: dC 70.1, 2a: dC
87.5, 2b: dC 89.0, and 2c: dC 79.2),7 the contributions of the
zwitterionic canonical structure B (Scheme 1) seems to be
less important than the canonical structure A, unlike in the
1
cases of 1a and 2a–c. In the H NMR spectra of 8a–c at
room temperature, the signals of H-20 and H-70 (Scheme 1)
appear as two broad signals. These signals become
equivalent at high-temperature (558C), while they appear
as two sharp doublets at low-temperature (2608C). Thus,
Scheme 1. Reagents and conditions: i, Ac2O, reflux, 0.5 h.
Table 1. Results for the preparation of heptafulvenes 8a–f and their
rotational barriers and redox potentials
Run Barbituric Condensation
acid 7a–f
Rotational
barriera
(DG ‡, kcal mol21
)
Redox
potentials b
product
(yield, %)
Elox
Elred
1
2
3
4
5
6
7a
7b
7c
7d
7e
7f
8a (77)
8b (74)
8c (62)
8d (80)
8e (83)
8f (99)
14.51
14.70
15.03
–
–
–
þ1.08 21.15
þ1.09 21.19
þ1.11 21.13
þ1.07 21.23
þ1.07 21.25
þ1.10 21.18
2. Results and discussion
2.1. Synthesis and properties of 8a–d
a
The rotation around the double bond between barbituric acid-moiety and
cycloheptatrienylidene-moiety. Determined by the 1H NMR signals of
H-20 and H-70 of cycloheptatrienylidene-moiety.
Condensation reactions of tropone (6) with barbituric acids
7a–f in Ac2O22 under reflux afforded heptafulvenes 8a–f as
b
Peak potentials in V vs Ag/AgNO3.

S. Naya, M. Nitta / Tetrahedron 59 (2003) 3709–3718
3711
rotation around the exocyclic double bonds of 8a–c clearly
occurs slowly on the NMR time scale at room temperature.
1
Through variable temperature H NMR measurements of
8a–c, the coalescence temperatures were determined to be
300, 308, and 315 K, respectively. In addition, the chemical
shift differences between H-20 and H-70 of 8a–c were 78 Hz,
105 Hz, and 108 Hz, respectively. Consequently, rotational
barriers (DG ‡) around the exocyclic double bond for 8a–c
were determined to be 14.1–15.03 kcal mol21 (Table 1).
The values (DG ‡) of 8a–c are in the order of 8a,8b,8c
and these are smaller than those of 2a–c (16.32–
23.30 kcal mol21); however, the contribution of the zwit-
terionic canonical structure B for 8a–c is smaller than that
of 2a–c. This feat0ure suggests that the steric hindrance
between the H-20, 7 and two carbonyl-oxygens for 8a–c is
larger than that for 2a–c. UV–vis spectra of 8a–f in
acetonitrile are shown in Figures 2 and 3. The spectra
resemble each other and the longest wavelength absorption
maxima of 8a–f are similar (8a: 432 nm, 8b: 432 nm, 8c:
434 nm, 8d: 431 nm, 8f, 431 nm, and 8f, 434 nm). In
addition, the absorption maxima of 8a–f appear at longer
wavelength than that of 1 (384 nm).23
Scheme 2.
of 8a–f are depicted in Scheme 2. At the first oxidation
potentials (E1ox) of 8a–d, radical cations 9a–f would be
generated, and radical anions 10a–f seemed to be generated
at the first reduction potentials (E1red), respectively. After
the first cycle of CV measurements of 8d–f, other reduction
waves were recorded at 20.58, 20.61, and 20.58 V,
respectively. These waves are suggested to be the reduction
waves of 11d–f, which are generated by oxidative
cyclization reactions of 9d–f under CV measurement
(vide infra).
The redox property of heptafulvene 8a–f was determined
by cyclic voltammetry (CV) in acetonitrile. The oxidation
and reduction waves of 8a–f were irreversible under the
conditions of CV measurements, and thus, the peak
potentials are summarized in Table 1. The redox processes
2.2. Synthesis and properties of 11a–f·BF24 and
12a–c·BF24
Reactions of 8a–c and 8d–f with DDQ in CH2Cl2 at room
Figure 2. UV–vis spectra of 8a–c in CH3CN.
Scheme 3. Reagents and conditions: i, (a) DDQ, CH2Cl2, rt, 1 h (b) 42% aq.
HBF4, Ac2O, 08C, 1 h; ii, aq. K2CO3, EtOH, 808C, 12 h; iii, 42% aq. HBF4,
Ac2O, 08C, 1 h; iv, (a) ButNH2, rt, 16 h (b) 3% HCl.
Figure 3. UV–vis spectra of 8d–f in CH3CN.

3712
S. Naya, M. Nitta / Tetrahedron 59 (2003) 3709–3718
were converted to 5a–c.15 Upon treatment with aq. HBF4 in
Ac2O, however, 14d was converted to 11d·BF24 in 96%
yield.21 Thus, 14e,f was prepared in a similar fashion, and
compounds 14a–c and 14e,f were treated with aq. HBF4 in
Ac2O to afford a mixture of 11a·BF24 and 12a·BF42, 11b·BF42,
a mixture of 11c·BF42 and 12cBF42, and 11e,f·BF24 , respect-
ively (Scheme 3, Table 2). Contrary to the reactions of 8a–c
with DDQ, 14a–c afforded compounds 11a–c·BF42
preferentially. A mixture of two products 11a·BF24 and
12a·BF24 was not separated; however, pure samples of
11b,c·BF24 were obtained by recrystallization. Furthermore,
compounds 12a–c·BF24 were obtained by protonation of
5a–c with aq. HBF4 in Ac2O (Scheme 3, Table 2), and thus,
assignment of the 1H NMR spectrum of a mixture of
11a·BF24 and 12a·BF24 was performed. Thus, a mixture of
11a·BF24 and 12a·BF42 as well as compounds 11b,c·BF24 ,
and 11e,f·BF24 , and 12a–c·BF24 were fully characterized on
1
the basis of H and 13C NMR, IR, mass spectral data and
elemental analyses. Mass spectra of these compounds
exhibited the correct Mþ2BF24 ion peaks, which are
indicative of the cationic structures of these compounds.
The characteristic absorption bands for the counter ion of
BF24 were observed at 1084–1085 cm21 in the IR spectra of
these compounds, respectively. In the 1H NMR spectra, the
proton signals on the seven-membered ring of 11a–c·BF42
(11a: d 8.67–9.44; 11b: d: 8.70–9.43; 11c: d 8.69–9.53),
12a–c·BF24 (12a: d 8.67–9.50: 12b: d 8.71–9.52; 12c: d
8.71–9.45), and 11e,f·BF42 (11e: d 8.70–9.52: 11f: d 8.73–
9.58) appeared in lower field than those of 5a–c (5a: d
7.70–8.89; 5b: d 7.67–8.87; 5c: d 7.72–8.85).15 These
features also support the cationic nature of the compounds.
UV–vis spectra of a mixture of 11a and 12a, 11b,c, 12a–c,
and 11d–f in acetonitrile are similar and the absorption
maxima are summarized in Table 3. In the UV–vis spectra
of 12a–c, two absorption maxima were observed in the
visible region, respectively. The longer wavelength absorp-
tion maxima are due to the generation of 5a–c (5a: 439 nm;
5b: 439 nm; 5c: 445 nm), respectively, by a slight amount of
deprotonation of 12a–c under measurement conditions of
UV–vis spectra and CV (vide infra). Upon addition of a
drop of 42% aq. HBF4 to the solutions of 12a–c,
respectively, the absorption of 5a–c in the UV–vis spectra
disappeared. In contrast, 1H NMR measurements of 12a–c
did not exhibit proton signals of 5a–c, respectively. In
addition, upon treatment of the mixtures of 11a–c·BF24 and
12a–c·BF24 with aqueous K2CO3 solution at 808C, ring-
opening reaction occurs to afford 14a–c, respectively
(Scheme 3).
Scheme 4.
temperature and subsequent anion exchange reaction using
aq. HBF4 in Ac2O afforded mixtures of two products
11a–c·BF24 and 12a–c·BF24 and single products
11d–f·BF24 , respectively (Scheme 3). Product ratios,
1
which were determined by H NMR as being preferential
formation of 12a–c·BF24 , and/or yields are summarized in
Table 2. Mixtures of 11a–c·BF24 and 12a–c·BF42 could not
be separated by recrystallization. On the other hand, we
have reported previously that compounds 14a–d can be
obtained by the reactions of 2-chlorotropone 13 with 7a–d
(Scheme 3). Upon treatment with TFA, compounds 14a–c
The selectivity of two types of cyclization reactions,
oxidative cyclization of 8a–c and acid-catalyzed cyclization
Table 2. Results for the preparation of cation 11a–f·BF24 and 12a–c·BF42
Run
Oxidative cyclization of 8a–f
Product (yield, %) Ratio of 11/12
Acidic dehydration of 14a–f
Product (yield, %) Ratio of 11/12
Protonation of 5a–c
Product (yield, %)
1
2
3
4
5
6
11a (43), 12a (47)
11b (27), 12b (67)
11c (23), 12c (77)
11d (86)
11e (100)
11f (99)
1:1.1
1:2.5
1:3.3
-
-
–
11a (62), 12a (38)
11b (80)
11c (58), 12c (6)
11d (96)
11e (100)
1:0.6
1:0.0
1:0.1
-
-
–
12a (88)
12b (97)
12c (99)
-
-
–
11f (100)

S. Naya, M. Nitta / Tetrahedron 59 (2003) 3709–3718
3713
Table 3. UV–vis spectral data (in acetonitrile) of cations 11a–f and 12a–c
(salts 11a–f·BF24 and 12a–c·BF24 were used for the measurements)
At the carbonyl-oxygen, the charge density of 20a and 21a as
well as the coefficients of SOMO of 20a and those of HOMO
of 21a are depicted in Figure 4. Regarding the charge density
and the coefficients of SOMO for radical cation 20a, both
values are larger for the oxygen atom of –CONH– than those
of –CONMe–, suggesting that cyclization of the former
moiety occurs preferentially to that of the latter moiety,
whether cyclization occurs charge-controlled or frontier
orbital-controlled. Thus, the intermediates 9a–c are postu-
latedtohaveatendencysimilar to20a;theformationof16a–c
would be preferable to that of 15a–c to result in the formation
of compounds 12a–c·BF24 . On the contrary, regarding the
charge density and the coefficients of HOMO for cation 21a,
both values are larger for the oxygen atom of the –CONMe–
moiety than those of the –CONH– moiety. Consequently,
18a–c would be generated mainly to result in the preferable
formation of 11a–c·BF24 as compared with 12a–c·BF24
(formation of 12b·BF24 is not observed). Thus, the selectivity
of oxidative cyclization of unsymmetrical heptafulvene 8a–c
and acid-catalyzed cyclization of 14a–c seems to be
rationalized.
Compound
l )
max (nm) (log 1, dm3 mol21 cm21
11aa
11b
11c
11db
11e
11f
12a
12b
12c
395 (4.38), 269 (4.42), 223 (4.41)
399 (4.67), 268 (4.41), 225 (4.42)
398 (4.50), 264 (4.43), 257 (4.45), 222 (4.51)
397 (4.47), 267 (4.45), 224 (4.41)
399 (4.49), 267 (4.43), 224 (4.41)
396 (4.49), 262 (4.48), 224 (4.51)
391 (4.44), 267 (4.45), 222 (4.35)
392 (4.36), 267 (4.47), 222 (4.38)
390 (4.44), 267 (4.40), 222 (4.46)
A mixture of 11a·BF24 and 12a·BF24 was used for the measurement.
Ref. 21.
a
b
The reduction property of cations 11a–c, 11e,f, and 12a–c
was determined by cyclic voltammetry (CV) in acetonitrile.
The reduction waves of 11a–c, 11e,f, and 12a–c were
irreversible under the conditions of CV measurements, and
thus, the peak potentials are summarized in Table 4, along
with that of compound 11d.21 Since a mixture of 11a·BF42
and 12a·BF24 was not isolated, a mixture of 11a·BF24 and
12a·BF24 is used for the measurement of 11a. The
irreversible nature would be due to the formation of a
tropyl radical and its dimerization. This reduction behavior
seems to be a typical property of tropylium ions.25 The E1red
of cations 11a–f and 12a–c are similar to each other. In the
CV measurement of 12a–c, the reduction waves of 5a–c,
which derives from deprotonation of 12a–c, were also
observed. This feature is similar to that observed in the
measurement of UV–vis spectra of 12a–c (vide supra).
Figure 4.
of 14a–c, affording 11a–c and 12a–c is explained as follows.
According to the redox properties of 8a–f under CV
measurement (vide supra), we propose the former reaction
pathway as outlined in Scheme 4. The radical cations 9a–f,
which are generated by oxidation of 8a–f with DDQ, undergo
cyclization reactions to give two kinds of intermediates 15a–f
and16a–c. Thehydrogenabstractionsofradicalcations15a–f
and 16a–c by DDQ-radical anion give cations 11a–f and
12a–c, respectively. Thus, the ratios of 11a–c/12a–c seem
to depend on the selectivity of the intramolecular O-radical
addition to the tropylium moiety in 9a–c. On the other hand,
the latter acid-catalyzed cyclization reaction of 14a–f
would proceed as shown also in Scheme 4. By using
3,5,7-trideuterio-2-chlorotropone, we have clarified that the
cyclization reaction of 14d giving 11d·BF24 proceeds via
C-1 attack on the tropone nucleus.21 The cations 17a–f,
which are generated by protonation of 14a–f with HBF4,
undergo cyclization reaction to give 18a–f and 19a–c. The
dehydration from cations 18a–f and 19a–c gives cations
11a–f and 12a–c, respectively. Thus, the ratio of 11a–c/
12a–c is considered to depend on the selectivity of
the intramolecular addition of barbituric acid-oxygen to the
hydroxytropylium moiety in 17a–c. In order to investigate
the reactivity of the intermediates 9a–c and 17a–c,
compounds 20a and 21a are selected as model compounds
of 9a and 17a, respectively (Fig. 4), and their MO calculations
were carried out by the 6-31G* basis set of the MP2 levels.24
A single crystal of 11c·BF24 was obtained by recrystalliza-
tion from CH3CN/Et2O. Thus, X-ray structure analysis was
carried out, and the ORTEP drawing of 11c·BF24 is shown in
Figure 5. The selected bond lengths are summarized in
Table 5 (The numbering is shown in Figure 6). The bond
lengths of C1–C2, C3–C4, and C5–C5a are shorter than
those of C2–C3, C4–C5, C5a–C10b, and C10b–C1. This
fact indicates the existence of bond alternation in the seven-
membered ring as shown in canonical structures 11c-B and
11c-C. In addition, since the bond length of C5a–O6 is
longer than that of O6–C6a, the contribution of 11c-D
Table 4. Reduction potentials (peak potential in V vs Ag/AgNO3) of
cations 11a–f and 12a–c (salts 11a–f·BF24 and 12a–c·BF4 were used for
the measurements)
Compound
E1red
Compound
E1red
11aa
11b
11c
11db
11e
11f
20.58
20.59
20.57
20.58
20.61
20.58
12a
12b
12c
20.56
20.57
20.55
A mixture of 11a·BF24 and 12a·BF24 was used for the measurement.
Ref. 21.
a
b

3714
S. Naya, M. Nitta / Tetrahedron 59 (2003) 3709–3718
oxidative cyclization of 8a–c and acid-catalyzed cycliza-
tion of 14a–c giving 11a–c·BF24 and 12a–c·BF42 was
rationalized based on MO calculations of model compounds
20a and 21a. The structural characteristics of 11c·BF24 were
clarified for the first time by X-ray crystal analysis and MO
calculations. Further studies0concerning exploration of the
functions of 5-(cyclohepta-2 ,40,60-trienylidene)pyrimidine-
2(1H),4(3H),6(5H)-trione derivatives and uracil-annulated
heteroazulenylium ions are underway.
4. Experimental
4.1. General
IR spectra were recorded on a HORIBA FT-710 spec-
trometer. Mass spectra and high-resolution mass spectra
were run on JMS-AUTOMASS 150 and JMS-SX102A
spectrometers. The 1H and 13C NMR spectra were recorded
Figure 5. An ORTEP drawing of 11c with thermal ellipsoid plot (50%
probability).
Table 5. Bond lengths of 11c·BF4 obtained by X-ray structure analysis and MO calculation
Cation
Method
Bond lengtha
C1–C2 C2–C3 C3–C4 C4–C5 C5–C5a C5a–C10b C10b–C1 C5a–O6 O6–C6a C6a–N7 C6a–c10a C10a–C10b
11c
11c
X-Ray 1.38
MP2/6-3lG* 1.38
1.40
1.41
1.38
1.39
1.39
1.41
1.36
1.37
1.43
1.43
1.40
1.41
1.38
1.38
1.34
1.35
1.34
1.33
1.37
1.38
1.42
1.41
a
The numbering is shown in Figure 6.
on a JNM-lambda 500 and an AVANCE 600 spectrometers,
and the chemical shifts are given relative to internal SiMe4
standard: J-values are given in Hz. Mps are recorded on a
Yamato MP-21 apparatus and are uncorrected. Compound
7d is commercially available, and desired compounds 7a,26a
7b,c,26b 7e,f,26c 14a–c,15 and 14d21 were prepared as
described in the literature.
4.2. General synthetic procedure for 5-(cyclohepta-
20,40,60-trienylidene)pyrimidine-2(1H),4(3H),6(5H)-
trione derivatives (8a–f)
A solution of 6 (106 mg, 1 mmol) and 7a–f (1 mmol) in
Ac2O (2 mL) was heated under reflux for 0.5 h. After the
reaction completed, the mixture was concentrated in vacuo
and the resulting residue was purified by column chroma-
tography on SiO2 using AcOEt as the eluent to give the
products 8a–f. The results are summarized in Table 1.
Figure 6.
seems to be less important. MO calculation of 11c was
carried out by the 6-31G* basis set of the MP2 levels23 and
the selected bond lengths are also summarized in Table 5.
Concerning the seven-membered ring of 11c, the bond
lengths of C1–C2, C3–C4, and C5–C5a are shorter than
those of C2–C3, C4–C5, C5a–C10b, and C10b–C1. The
bond length alternation obtained by MO calculation for 11c
is very similar to that obtained by X-ray analysis.
4.2.1. Compound 8a. Reddish needles; mp 226–2288C
1
(from CH2Cl2/EtOH); H NMR (500 MHz, CDCl3) d 3.34
(3H, s, CH3), 7.32–7.36 (2H, m, H-30, 60), 7.43–7.50 (2H,
m, H-40, 50), 7.65 (1H, br, s, NH), 9.31 (1H, br, s, H-20 or 70),
9.33 (1H, br, s, H-20 or 70); 13C NMR (125.7 MHz, CDCl3) d
27.6, 101.7, 140.0, 140.2, 140.5, 150.0, 162.8, 164.4, 165.2;
IR (CHCl3) n 3408, 1714, 1662, 1623, 1387 cm21; MS (rel.
int) m/z 230 (Mþ, 100%); HRMS calcd for C12H10N2O3:
231.0770 (MþH). Found: 231.0806 (Mþ þH). Anal. calcd
for C12H10N2O3þ1/5H2O: C, 61.64; H, 4.48; N, 11.98.
Found: C, 61.3; H, 4.3; N, 12.1.
3. Conclusion
The synthesis and properties of a novel type of hepta-
fulvenes 8a–f were investigated. The rotational barriers
around the exocyclic double bond of 8a–c were determined
by variable temperature 1H NMR measurements. Moreover,
two types of synthetic methodology of 11a–f·BF24 and
12a–c·BF24 were established, and their spectroscopic and
electrochemical properties were studied. The selectivity of
4.2.2. Compound 8b. Reddish needles; mp 141–1428C
1
from (EtOH); H NMR (500 MHz, CDCl3) d 0.95 (3H, t,
J¼7.4 Hz, Bu-4), 1.39 (2H, tq, J¼7.6, 7.4 Hz, Bu-3), 1.63
(2H, quint., J¼7.6 Hz, Bu-2), 3.92 (2H, t, J¼7.6 Hz, Bu-1),

S. Naya, M. Nitta / Tetrahedron 59 (2003) 3709–3718
3715
7.36–7.40 (2H, m, H-30, 60), 7.47–7.54 (2H, m, H-40, 50),
8.31 (1H, br s, NH), 9.28 (1H, br s, H-20 or 70), 9.39 (1H, br
s, H-20 or 70); 13C NMR (125.7 MHz, CDCl3) d 13.7, 20.2,
30.3, 41.0, 102.2, 139.5, 139.9, 149.9, 162.9, 164.1, 164.8;
IR (CHCl3) n 3403, 1713, 1664, 1622, 1393 cm21; MS (rel.
int.) m/z 272 (Mþ, 68), 255 (3), 215 (50), 57 (100%). Anal.
calcd for C15H16N2O3: C, 66.16; H, 5.92; N, 10.29. Found:
C, 66.0, H, 5.7; N, 10.1.
filtration and washed with ether to give mixtures of
11a–c·BF24 and 12a–c·BF42 and 11d–f·BF24 . The results
are summarized in Table 2. The cation 11d·BF24 was
identical with the authentic specimen.21
4.4. General synthetic procedure for 5-(10-oxocyclo-
heptatrien-20-yl)-pyrimidine-2(1H),4(3H),6(5H)-trione
derivatives (14a–c and 14e,f)
4.2.3. Compound 8c. Reddish needles; mp 243–2468C
(from EtOH, decomp.); 1H NMR (500 MHz, CDCl3) d
7.24–7.26 (4H, m, H-30, 60, o-Ph), 7.38–7.41 (2H, m, H-40,
50), 7.41 (1H, t, J¼7.4 Hz, p-Ph), 7.48 (2H, dd, J¼7.9,
7.4 Hz, m-Ph), 7.78 (1H, br s, NH), 9.40 (2H, br s, H-20, 70);
13C NMR (125.7 MHz, CDCl3) d 101.2, 128.7, 128.8,
129.3, 135.0, 140.5, 140.7, 141.1, 149.5, 162.9, 164.5,
A solution of 2-chlorotropone (13) (422 g, 3 mmol),
2(1H),4(3H),6(5H)-pyrimidinetrione derivatives (7a–c
and 7e,f) (3 mmol), and ButNH2 (548 g, 7.5 mmol) in
MeOH (30 mL) was stirred at rt for 24 h. After evaporation
of the MeOH and ButNH2, the residue was filtered and
washed with Et2O. The crystals were dissolved in 3% HC1
and extracted with CH2C12. The extract was dried over
Na2SO4 and concentrated in vacuo to give 14a–c and 14e,f
(14a: 716 mg, 97%, 14b: 868 mg, 91%, 14c: 924 mg, 100%,
14e: 864 mg, 100%, 14f: 1152 mg, 100%).
165.8; IR (CHCl3) n 3396, 1718, 1669, 1635, 1380 cm21
;
MS (rel. int.) m/z 292 (Mþ, 100%); HRMS cacld for
C17H12N2O3: 293.0926 (MþH). Found: 293.0948 (MþþH).
Anal. calcd for C17H12N2O3þ1/2H2O: C, 67.77; H, 4.35; N,
9.30. Found: C, 67.4; H, 4.1; N, 8.9.
4.4.1. Compound 14a. Colorless powder; mp 202–2048C
1
(from AcOEt, decomp.); H NMR (400 MHz, CD3OD) d
4.2.4. Compound 8d. Reddish needles; mp 207–2088C
1
3.25 (3H, s, CH3), 7.11 (1H, d, J¼12.0 Hz, H-7), 7.27–7.35
(2H, m), 7.44–7.50 (1H, m), 7.70–7.78 (1H, m); 13C NMR
(150.9 MHz, CDC13) d 28.1, 56.9, 133.7, 135.6, 137.4,
140.4, 141.2, 148.1, 150.0, 165.6, 167.1, 185.1; IR (CHC13)
n 1722, 1691, 1574 cm21; MS (FAB) m/z 247 (MþþH).
Anal. calcd for C12H10N2O4: C, 58.54; H, 4.09; N, 11.38.
Found: C, 58.4; H, 3.9; N, 11.6.
(from CH2Cl2/EtOH); H NMR (500 MHz, CDCl3) d 3.38
(6H, s, CH3), 7.31–7.33 (2H, m, H-40, 50), 7.40–7.44 (2H,
m, H-30, 60), 9.20 (2H, d, J¼11.6 Hz, H-20, 70); 13C NMR
(125.7 MHz, CDCl3) d 28.4, 102.7, 138.9, 139.3, 139.6,
151.5, 163.4, 164.5; IR (CHCl3) n 1707, 1640, 1387,
1244 cm21; MS (rel. int.) m/z 244 (Mþ, 100%). Anal. cacld
for C13H12N2O3: C, 63.93; H, 4.95; N, 11.47. Found: C,
63.9; H, 4.8; N, 11.2.
4.4.2. Compound 14b. Colorless powder; mp 179–1818C
1
(from AcOEt, decomp.); H NMR (400 MHz, CD3OD) d
4.2.5. Compound 8e. Reddish needles; mp 141–1428C
1
(from AcOEt); H NMR (500 MHz, CDCl3) d 1.24 (6H, t,
0.95 (3H, t, J¼7.1 Hz, Bu-4), 1.37 (2H, sex, J¼7.1 Hz,
Bu-3), 1.59 (2H, quint, J¼7.1 Hz, Bu-2), 3.85 (2H, t,
J¼7.1 Hz, Bu-1), 7.11 (1H, d, J¼12.0 Hz, H-7), 7.26–7.36
(2H, m), 7.43–7.50 (1H, m), 7.69–7.77 (1H, m); 13C NMR
(150.9 MHz, CDC13) d 13.6, 20.0, 29.8, 41.6, 57.0, 133.6,
135.5, 137.3, 140.4, 141.2, 148.2, 150.0, 166.0, 166.9,
185.1; IR (CHC13) n 1724, 1688, 1574 cm21; MS (FAB)
m/z 289 (MþþH). Anal. calcd for C15H16N2O4: C, 62.49; H,
5.59; N, 9.72. Found: C, 62.2; H, 5.7; N, 9.8.
J¼7.1 Hz, Et-20), 4.03 (4H, q, J¼7.1 Hz,0 Et-1), 7.24–7.30
(2H, m, H-40, 5 ), 7.34–7.41 (2H, m, H-3 , 60), 9.14 (2H, d,
J¼11.2 Hz, H-20, 70); 13C NMR (125.7 MHz) d 13.4, 36.8,
103.1, 138.4, 138.9, 139.2, 150.6, 162.9, 164.2; IR (CHCl3)
n 1705, 1635, 1398, 1296 cm21; MS (ESI) m/z (MþþH).
Anal. calcd for C15H16N2O3; C, 66.16; H, 5.92; N, 10.29.
Found: C, 66.1; H, 6.0; N, 10.4.
4.2.6. Compound 8f. Reddish needles; mp 264–2658C
1
4.4.3. Compound 14c. Colorless powder; mp 201–2038C
1
(from AcOEt, decomp.); H NMR (400 MHz, CD3OD) d
(from AcOEt); H NMR (500 MHz, CDCl3) d 7.32 (4H, d,
J¼11.4 Hz, o-Ph), 7.38–7.42 (4H, m, p-Ph, H-40, 50), 7.45–
7.50 (6H, m, m-Ph, H-30, 60), 9.38 (2H, d, J¼11.4 Hz, H-20,
70); 13C NMR (125.7 MHz) d 101.9, 128.5, 128.8, 129.2,
135.6, 139.9, 140.1, 140.8, 150.7, 163.6, 165.7; IR (CHCl3)
n 1718, 1653, 1375, 1258 cm21; MS (ESI) m/z 369
(MþþH); HRMS calcd for C23H16N2O3: 369.1239
(MþH). Found: 369.1217 (MþþH). Anal. calcd for
C23H16N2O3þ1/5H2O: C, 74.26; H, 4.44; N, 7.53. Found:
C, 74.5; H, 4.2; N, 7.5.
7.16 (1H, d, J¼12.0 Hz, H-7), 7.24–7.33 (4H, m), 7.38–
7.52 (4H, m), 7.72–7.79 (1H, m); 13C NMR (150.9 MHz,
CD3OD) d 97.2, 129.8, 129.9, 130.2, 135.7, 136.1, 137.2,
139.9, 141.5, 142.9, 150.1, 152.6, 169.1, 169.8, 187.3; IR
(CHC13) n 1721, 1704, 1572 cm21; MS (FAB) m/z 309
(MþþH); HRMS calcd for C17H12N2O4: 309.0875 (MþH).
Found: 309.0870 (MþþH). Anal. calcd for C17H12N2O4þ1/
5H2O: C, 65.47; H, 4.01; N, 8.98. Found: C, 65.7; H, 3.9; N,
8.9.
4.3. General oxidative cyclization of 8a–f with DDQ
4.4.4. Compound 14e. Colorless prisms; mp 164–1658C
1
(from AcOEt); H NMR (500 MHz, CDCl3) d 1.23 (6H, t,
To a stirred solution of 8a–f (0.20 mmol) in CH2C12
(10 mL) was added DDQ (70 mg, 0.3 mmol) and the
mixture was stirred at rt for 1 h until the reaction completed.
After evaporation of the CH2C12, the residue was dissolved
in a mixture of Ac2O (2 mL) and 42% aq. HBF4 (0.4 mL) at
08C and the mixture was stirred for 1 h. To the mixture was
added Et2O (40 mL) and the precipitates were collected by
J¼7.1 Hz, Et-2), 3.96–4.00 (4H, m, Et-1), 4.13 (1H, s, CH),
7.07–7.14 (3H, m), 7.22–7.28 (1H, m), 7.46–7.53 (1H, m);
13C NMR (125.7 MHz) d 13.0, 37.6, 57.3, 133.6, 135.2,
137.1, 140.1, 141.3, 148.9, 150.8, 166.1, 185.2; IR (CHCl3)
n 1679, 1576 cm21; MS (ESI) m/z 289 (MþþH). Anal.
calcd for C15H16N2O4: C, 62.49; H, 5.59; N, 9.72. Found: C,
62.6; H, 5.6; N, 9.8.

3716
S. Naya, M. Nitta / Tetrahedron 59 (2003) 3709–3718
4.4.5. Compound 14f. Colorless prisms; mp 212–2138C
(from CH2Cl2/AcOEt); 1H NMR (500 MHz, CDCl3) d 4.49
(1H, s, CH), 7.05–7.10 (3H, m), 7.14–7.21 (1H, m), 7.32
(4H, d, J¼7.5 Hz, o-Ph), 7.40 (2H, t, J¼7.3 Hz, p-Ph), 7.45
(4H, dd, J¼7.5, 7.3 Hz, m-Ph), 7.52–7.59 (1H, m); 13C
NMR (125.7 MHz) d 57.7, 128.5, 128.9, 133.7, 134.6,
135.5, 137.3, 140.3, 141.3, 148.8, 151.0, 166.3, 185.5; IR
(CHCl3) n 1700, 1570 cm21; MS (ESI) m/z 385 (MþþH).
Anal. calcd for C23H16N2O4: C, 71.87; H, 4.20; N, 7.29.
Found: C, 71.7; H, 4.1; N, 7.3.
cald for C17H11N2O3BF4: C, 54.01; H, 2.93; N, 7.41. Found:
C, 53.7; H, 2.8; N, 7.4.
4.5.5. Compound 11e·BF24 . Yellow prisms; mp 204–2058C
1
(from CH3CN/Et2O); H NMR (500 MHz, CD3CN) d 1.27
(3H, t, J¼7.3 Hz, Et-2), 1.47 (3H, t, J¼7.3 Hz, Et-2), 4.10
(2H, q, J¼7.3 Hz, Et-1), 4.31 (2H, q, J¼7.3 Hz, Et-1),
8.70–8.76 (2H, m, H-3, 4), 8.79–8.85 (1H, m, H-2), 9.05–
9.09 (1H, m, H-5), 9.52 (1H, d, J¼10.1 Hz, H-1); 13C NMR
(150.9 MHz, CD3CN) d 12.9, 13.4, 38.3, 41.5, 98.4, 135.1,
139.5, 144.5, 147.9, 148.5, 149.1, 149.7, 157.5, 163.0,
165.9; IR (KBr) n 1724, 1675, 1272, 1085 cm21; MS (FAB)
m/z 271 (Mþ2BF4); HRMS calcd for C15H15N2O3BF4:
271.1083 (M2BF4). Found: 271.1094 (Mþ2BF4). Anal.
calcd for C15H15N2O3BF4: C, 50.31; H, 4.22; N, 7.8. Found:
C, 50.4; H, 4.0; N, 7.9.
4.5. General synthetic procedure for 11a–c·BF24 and
1e,f·BF24 from 14a–c and 14e,f
A solution of 14a–c and 14e,f (0.5 mmol) in Ac2O (2.5 mL)
and 42% aq. HBF4 (0.5 mL) was stirred at 08C for 1 h.
To the mixture was added Et2O (50 mL) and the
precipitates were collected by filtration to give 11a–c·BF42
and 12a,c·BF24 and 11e,f·BF24 . The results are summarized
in Table 2.
4.5.6. Compound 11f·BF24 . Orange prisms; mp 289–2918C
(from CH3CN/Et2O, decomp.); 1H NMR (500 MHz,
CD3CN) d 7.43–7.45 (4H, m, o-Ph), 7.56 (1H, t,
J¼7.3 Hz, p-Ph), 7.61 (1H, t, J¼7.3 Hz, p-Ph), 7.67–7.69
(2H, m, m-Ph), 7.71–7.74 (2H, m, m-Ph), 8.73 (1H, dd,
J¼10.2, 9.9 Hz, H-4), 8.80 (1H, dd, J¼10.2, 9.4 Hz, H-3),
8.88 (1H, dd, J¼10.2, 9.4 Hz, H-2), 8.96 (1H, d, J¼9.9 Hz,
H-5), 9.58 (1H, d, J¼10.2 Hz, H-1); 13C NMR (150.9 MHz,
CD3CN) d 98.8, 128.9, 129.5, 130.4, 130.6, 131.2, 132.1,
132.4, 135.5, 135.8, 140.3, 145.0, 148.7, 148.9, 148.9,
150.3, 157.8, 163.1, 165.6; IR (KBr) n 1705, 1640, 1265,
1084 cm21; MS (FAB) m/z 367 (Mþ2BF4); HRMS calcd
for C23H15N2O3BF4: 367.1083 (M2BF4). Found: 367.1076
(Mþ2BF4). Anal. calcd for C23H15N2O3BF4: C, 60.82; H,
3.33; N, 6.17. Found: C, 60.8; H, 3.2; N, 6.2.
4.5.1. A mixture of 11a·BF24 and 12a·BF42. Yellow
powder; mp 243–2468C (from CH3CN/Et2O, decomp.);
IR (KBr) n 3382, 2790, 1718, 1685, 1265, 1084 cm21; MS
(FAB) m/z 229 (Mþ2BF4; HRMS calcd for
C12H9N2O3BF4: 229.0613 (M2BF4). Found: 229.0617
(Mþ2BF4). Anal. calcd for C12H9N2O3BF4: C, 45.61; H,
2.87; N, 8.86. Found: C, 46.0; H, 2.9; N, 9.0.
1
4.5.2. Compound 11a·BF24 . H NMR (500 MHz, CD3CN)
d 3.67 (3H, s, Me), 8.67–8.75 (2H, m), 8.77–8.85 (1H, m),
9.04–9.09 (1H, m), 9.44 (1H, d, J¼10.4 Hz, H-1), 9.89 (1H,
br s, NH); 13C NMR (150.9 MHz, CD3CN) d 30.7, 98.9,
135.3, 136.5, 138.8, 139.7, 144.7, 148.1, 148.6, 149.0,
157.3, 163.1.
4.6. Protonation of 5a–c to give 12a–c·BF42
A solution of 5a–c (0.3 mmol) in Ac2O (2 cm3) and 42%
aq. HBF4 (0.4 cm3) was stirred at 08C for 1 h. To the
reaction mixture was added Et2O (30 cm3) and the
precipitates were collected by filtration to give 12a–c·BF24 .
The results are summarized in Table 2.
4.5.3. Compound 11b·BF24 . Yellow prisms; mp 238–
2398C (from CH3CN/Et2O, decomp.); 1H NMR (500 MHz,
CD3CN) d 1.00 (3H, t, J¼7.4 Hz, Bu-4), 1.47 (2H, tq,
J¼7.8, 7.4 Hz, Bu-3), 1.84 (2H, quint, J¼7.8 Hz, Bu-2),
4.21 (2H, t, J¼7.8 Hz, Bu-1), 8.70–8.76 (2H, m), 8.80–
8.84 (1H, m), 9.05–9.08 (1H, m), 9.43 (1H, d, J¼9.1 Hz,
H-1), 9.84 (1H, s, NH); 13C NMR (150.9 MHz, CD3CN) d
13.9, 20.5, 30.7, 45.3, 99.1, 135.4, 139.7, 144.7, 148.2,
148.7, 149.1, 149.5, 157.5, 163.4, 167.6; IR (KBr) n 3241,
2786, 1715, 1643, 1231, 1084 cm21; MS (FAB) m/z 271
(Mþ2BF4); HRMS calcd for C15H15N2O3BF4: 271.1083
(M–BF4). Found: 271.1065 (Mþ–BF4). Anal. calcd for
C15H15N2O3BF4: C, 50.31; H, 4.22; N, 7.8. Found: C, 50.1;
H, 4.2; N, 7.8.
4.6.1. Compound 12a·BF24 . Yellow powder; mp 255–
2588C (from CH3CN/Et2O, decomp.); 1H NMR (500 MHz,
CD3CN) d 3.37 (3H, s, Me), 8.67–8.75 (2H, m), 8.77–8.85
(1H, m), 9.01–9.04 (1H, m), 9.50 (1H, d, J¼9.6 Hz, H-1),
9.89 (1H, br s, NH); 13C NMR (150.9 MHz, CD3CN) d 28.2,
98.1, 134.8, 139.3, 144.5, 147.7, 148.4, 148.9, 150.3, 158.5,
163.3, 166.6; IR (KBr) n 3447, 2535, 1723, 1685, 1254,
1084 cm21; MS (FAB) m/z 229 (Mþ2BF4); HRMS
calcd for C12H9N2O3BF4: 229.0613 (M2BF4). Found:
229.0613 (Mþ2BF4). Anal. calcd for C12H9N2O3BF4þ1/
4HBF4: C, 42.65; H, 2.76; N, 8.29. Found: C, 42.5; H, 2.5;
N, 8.3.
4.5.4. Compound 11c·BF24 . Orange prisms; mp 241–2438C
(from CH3CN/Et2O, decomp.); 1H NMR (500 MHz,
CD3CN) d 7.59–7.62 (2H, m, o-Ph), 7.68–7.71 (3H, m,
m, p-Ph), 8.69 (1H, dd, J¼9.8, 9.6 Hz, H-4), 8.77 (1H, dd,
J¼10.2, 9.6 Hz, H-3), 8.86 (1H, dd, J¼10.3, 10.2 Hz, H-2),
8.90 (1H, d, J¼9.8 Hz, H-5), 9.53 (1H, d, J¼10.3 Hz, H-1),
10.03 (1H, br s, NH); 13C NMR (125.7 MHz, CD3CN) d
99.3, 129.0, 131.2, 132.0, 132.1, 135.8, 140.3, 145.0, 148.7,
148.8, 149.4, 157.5, 163.2, 166.9 (one carbon overlapping);
IR (KBr) n 3261, 1749, 1711, 1264, 1084 cm21; MS (FAB)
m/z 291 (Mþ2BF4); HRMS calcd for C17H11N2O3BF4:
291.0769 (M2BF4). Found: 291.0784 (Mþ2BF4). Anal.
4.6.2. Compound 12b·BF24 . Yellow powder; mp 205–
2068C (from CH3CN/Et2O); 1H NMR (500 MHz, CD3CN) d
0.96 (3H, t, J¼7.4 Hz, Bu-4), 1.40 (2H, quint., J¼7.4 Hz,
Bu-3), 1.65 (2H, quint, J¼7.4 Hz, Bu-2), 4.00 (2H, t,
J¼7.4 Hz, Bu-1), 5.20 (1H, br s, NH), 8.71–8.79 (2H, m),
8.82–8.87 (1H, m), 9.05–9.10 (1H, m), 9.52 (1H, d,
J¼9.1 Hz, H-1); 13C NMR (125.7 MHz, CD3CN) d 14.1,
20.8, 30.5, 42.1, 98.4, 135.3, 139.7, 144.9, 148.2, 148.7,
149.1, 149.8, 158.5, 163.4, 166.2; IR (KBr) n 3397, 2513,

S. Naya, M. Nitta / Tetrahedron 59 (2003) 3709–3718
3717
1734, 1678, 1261, 1084 cm21; MS (FAB) m/z 271
(Mþ2BF4); HRMS calcd for C15H15N2O3BF4: 271.1083
(M2BF4). Found: 271.1085 (Mþ2BF4). Anal. calcd for
C15H15N2O3BF4þ1/2HBF4: C, 44.82; H, 3.89; N, 6.97.
Found: C, 45.0; H, 3.6; N, 6.9.
total 13069 reflections were collected, using the v22u scan
technique to a maximum 2u value of 55.08. The structure
was solved by direct methods and refined by a full-matrix
least-squares method using SIR92 structure analysis
software,27 with 256 variables and 2019 observed
reflections [I.3.00s(I)]. The non-hydrogen atoms were
refined anisotropically. The weighing scheme
w¼[s2c(F0)þ0.0020£F20]21 gave satisfactory agreement
analysis. The final R and Rw values were 0.041 and 0.057.
The maximum peak and minimum peak in the final
4.6.3. Compound 12c·BF24 . Yellow powder; mp 203–
2048C (from CH3CN/Et2O); 1H NMR (500 MHz, CD3CN) d
4.28 (1H, br s, NH), 7.34–7.36 (2H, m, o-Ph), 7.49–7.60
(3H, m, m, p-Ph), 8.71–8.79 (2H, m), 8.79–8.84 (1H, m),
9.06–9.12 (1H, m), 9.45 (1H, d, J¼11.2 Hz, H-1); 13C
NMR (125.7 MHz, CD3CN) d 98.8, 129.8, 130.4, 130.6,
135.4, 139.7, 145.0, 148.3, 148.8, 149.1, 150.1, 158.6,
163.5, 166.7; IR (KBr) n 3421, 2539, 1748, 1707, 1263,
1084 cm21; MS (FAB) m/z 291 (Mþ2BF4); HRMS cacld
for C17H11N2O3BF4: 291.0769 (M2BF4). Found: 291.0776
(Mþ2BF4). Anal. calcd for C17H11N2O3BF4þ1/3HBF4: C,
50.12; H, 2.80; N, 6.88. Found: C, 50.6; H, 3.0, N, 7.0.
2
3
˚
difference map were 0.31 and 20.26e /A .
Acknowledgements
Financial support from a Waseda University Grant for
Special Research Project and 21COE ‘Practical Nano-
chemistry’ from MEXT, Japan is gratefully acknowledged.
We thank the Materials Characterization Central Labora-
tory, Waseda University for technical assistance with the
spectral data, elemental analyses and X-ray analysis.
4.7. Alkaline hydrolysis of mixtures of 11a–c·BF24 and
12a–c·BF24
To a stirred solution of mixtures 11a–c·BF24 and 12a–c·BF42
(0.3 mmol) in EtOH (6 cm3) was added saturated aq. K2CO3
(3 cm3) and the mixture was stirred at 808C for 12 h. After
evaporation of the solvent, the residue was dissolved in 3%
HCl and the mixture was stirred for 1 h. The mixture was
extracted with CH2Cl2 and the extract was dried over Na2SO4.
The residue was concentrated in vacuo to give 14a–c, which
were identified on the basis of the comparison of the physical
data with those reported in the literature.15
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˚
group P21/n, a¼7.3640(2), b¼12.5380(3), c¼17.0902(6) A,
3
23
˚
b¼97.190(1)8, V¼1565.53(8) A , Z¼4, Dc¼1.604 g cm
,
crystal dimensions 0.40£0.20£0.20 mm3. Data were
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†
CCDC reference number 202050.

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