Novel photo-induced oxidative cyclization of 1,3-dimethyl-5-(1- arylmethylidene)pyrimidine-2,4,6(1,3,5H)-triones: Synthesis and properties of areno[5,6]pyrano[2,3-d]pyrimidine-2,4(1,3H)-dionylium ions and their photo-induced autorecycling oxidizing reacti

Article abstract of DOI:10.1016/j.tet.2005.03.052

Novel photo-induced oxidative cyclization was accomplished to synthesize areno[b]pyrimido[5,4-e]pyran-2,4(1,3H)-dionylium ions 13a-c⁺· ClO₄^-. Furthermore, 13a-c⁺·BF ₄^- and their phenyl-subs

Full text of DOI:10.1016/j.tet.2005.03.052

Tetrahedron 61 (2005) 4919–4930
Novel photo-induced oxidative cyclization of 1,3-dimethyl-5-
(1-arylmethylidene)pyrimidine-2,4,6(1,3,5H)-triones:
synthesis and properties of areno[5,6]pyrano[2,3-d]pyrimidine-
2,4(1,3H)-dionylium ions and their photo-induced autorecycling
oxidizing reaction toward some amines
*
Shin-ichi Naya, Masashi Miyagawa and Makoto Nitta
Department of Chemistry, Advanced Research Center of Science and Engineering, Waseda University, Shinjuku-ku, Tokyo 169-8555, Japan
Received 10 February 2005; revised 14 March 2005; accepted 14 March 2005
Available online 12 April 2005
Abstract—Novel photo-induced oxidative cyclization was accomplished to synthesize areno[b]pyrimido[5,4-e]pyran-2,4(1,3H)-dionylium
ions 13a–cC$ClO4K. Furthermore, 13a–cC$BF4K and their phenyl-substituted derivatives 19a,bC$BFK4 were alternatively synthesized by
the reaction of salicylaldehyde and its naphthyl derivatives with barbituric acids and subsequent treatment with aq. HBF4. Structural
characteristics of 13a–cC and 19a,bC were clarified on inspection of the UV–vis and NMR spectral data as well as X-ray crystal analyses.
The electrochemical properties were studied by the CV measurement. In a search for reactivity, reactions of 13a–cC$BF4K with some
nucleophiles, hydride, benzylamine, and H2O, were also carried out. The photo-induced autorecycling oxidation reactions of 13a–cC$BF4K
toward some amines under aerobic conditions were carried out to give the corresponding imines (isolated by converting to the corresponding
2,4-dinitrophenylhydrazones) in 643–3600% yield (recycling number of 13a–cC$BF4K: 6.4–36.0).
q 2005 Elsevier Ltd. All rights reserved.
1. Introduction
Flavins and flavinium ions are known to play an important
role as cofactors in a wide variety of biological redox
reactions.1,2 The flavin–redox systems have been investi-
gated extensively through synthetic model systems and
theoretical calculations.3 Among these, 5-deazaflavin 1a
(Fig. 1) has been studied extensively in both enzymatic4 and
model systems,5 in the hope of gaining mechanistic insight
into flavin-catalyzed reactions. In this relation, 5-deaza-10-
oxaflavin 1b (2H-chromeno[2,3-d]pyrimidine-2,4(3H)-
dione), in which the nitrogen atom is replaced by an
oxygen, has also been synthesized and found to possess a
strong function to oxidize alcohols to the corresponding
carbonyl compounds.6 On the basis of the above obser-
vations, we have previously studied the preparation of
3,10-disubstituted cyclohepta[4,5]pyrro[2,3-d]pyrimidin-
2,4(3H)-diones (2a)7 and 3-substituted cyclohepta[4,5]-
furo[2,3-d]pyrimidin-2,4(3H)-diones (2b),8,9 which are
Keywords: Benzo[5,6]pyrano[2,3-d]pyrimidine-2,4(1,3H)-dionylium tetra-
fluoroborate; Photo-induced oxidative cyclization; X-ray analysis; Photo-
induced autorecycling oxidation.
*
Corresponding author. Tel.: C81 3 5286 3236; fax: C81 3 3208 2735;
e-mail: nitta@waseda.jp
Figure 1.
0040–4020/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2005.03.052

4920
S. Naya et al. / Tetrahedron 61 (2005) 4919–4930
photooxidation processes can be usually carried out in air
using catalytic amounts of the triphenylpyrylium ion. Thus,
pyrylium ions are good oxidants in the photo-excited state
and can act as efficient photosensitizers. Recently, a steady-
state and laser flash photolysis studies of the pyrylium
ion-photosensitized oxidation of benzyl alcohol have
been reported.16 Thus, the uracil-annulated pyrylium ions
13a–cC$BFK4 (Scheme 1) are interesting from the view-
point of functions of both the pyrylium ions and the
flavinium ions. From this viewpoint, we studied a novel
photo-induced oxidative cyclization of 1,3-dimethyl-5-(1-
arylmethylidene)pyrimidine-2,4,6(1,3,5H)-triones (12a–c),
which derived from the reaction of barbituric acid with
easily available aromatic aldehydes, to explore the method-
ology for synthesizing the benzo[5,6]pyrano[2,3-d]pyrimi-
dine-2,4(1,3H)-dionylium ion (13aC$BF4K) and related
compounds 13b,cC$BF4K (Scheme 1). Furthermore,
alternative synthesis of 13a–cC$BF4K was also accom-
plished by the reaction of salicylaldehyde 14a and its
derivatives 14b,c with dimethylbarbituric acid 11 and
subsequent treatment with aq. HBF4. The structural details
and chemical properties as well as the photo-induced
oxidizing reaction of 13a–cC$BF4K toward some amines
were investigated as well. We report herein the results in
detail.
2. Results and discussion
2.1. Photo-induced oxidative cyclization
Since compound 12a has been synthesized by the reaction
of benzaldehyde (10a) with dimethylbarbituric acid (11),17
the method was applied to prepare naphthyl derivatives
12b,c (Scheme 1). The acid-catalyzed reactions of 10b,c
with 11 in EtOH were carried out to give 12b,c in 94 and
95% yields, respectively. Compounds 12b,c were fully
characterized on the basis of the NMR, IR, UV–vis, mass
spectral data, and elemental analyses. Unlike the case of 4,14
a thermal oxidative cyclization of compound 12a,b by using
DDQ and Sc(OTf)3 in xylene did not afford 13a,bC, and the
reactions were complicated. We have reported that the
photo-induced oxidative cyclization of 4 afforded 5C$BF4K
in better yield (100%) as compared with the thermal
oxidative cyclization by using DDQ and Sc(OTf)3 (20%).14
Thus, photo-irradiation of 12a–c was carried out under
aerobic and acidic conditions. The results are summarized in
Table 1 (Runs 1–4). While a trace amount of 13aC$ClO4K
was obtained in the photo-reaction of 12a (Run 1), a
solution of 12b in Ac2O in the presence of 42% aq. HBF4
afforded 13bC$BF4K in 47% yield (Run 2). A similar
reaction by using 60% aq. HClO4 as additive proceeded
smoothly to give 13bC$ClOK4 in 90% yield (Run 3). The
cyclization of 12c proceeded at the C1 to give cation
13cC$ClOK4 as a single product in good yield (Run 4).
Alternative formation of cation 13dC$ClO4K, which is
expected from the cyclization at the C3 of 12c, was not
obtained. Compounds 13a–cC$ClO4K and 13bC$BFK4
(vide infra) were fully characterized on the basis of the
spectral data and mass spectral data as well as elemental
analyses. During recrystallization, hydrolysis of
13cC$ClOK4 with stray water in the solvent proceeded
gradually due to its lability. Thus, satisfactory elemental
Scheme 1. Reagents and conditions: (i) H2SO4, EtOH, reflux, 1 h; (ii) hv,
Ac2O, 60% aq. HClO4 or 42% aq. HBF4, aerobic, rt.
structural isomers of 1a and 1b, respectively. In this context,
1,3-disubstituted cyclohepta[4,5]furo[2,3-d]pyrimidin-
2,4(1,3H)-dionylium tetrafluoroborate (3aC$BF4K)10,11
and its sulfur and nitrogen analogues 3bC$BF4K and
3c,dC$BF4K have been synthesized,12,13 and photo-induced
autorecycling oxidizing reaction of 3a–dC$BF4K toward
some alcohols and amines was studied as well.11–13 In
addition, oxidative cyclization of heptafulvene (4) by using
DDQ/Sc(OTf)3 or photo-irradiation in acidic media to give
1,3-dimethylbenzocyclohepta[70,60:4,5]furo[2,3-d]pyrimi-
din-2,4(1,3H)-dionylium tetrafluoroborate (5C$BF4K),
which has also exhibited oxidizing ability toward some
alcohols,14 has been studied.
On the other hand, the photosensitizing ability of 2,4,6-
triarylpyrylium ions has been widely applied in photo-
induced electron transfer processes. Among these salts, the
2,4,6-tripheny-pyrylium ion is a strong oxidant in both the
singlet and triplet excited states to oxidize several organic
donors to the corresponding radical cations with concomi-
tant formation of a triphenylpyranyl radical.15 Since the
2,4,6-tripheny-pyrylium ion was regenerated through the
reaction of the triphenylpyranyl radical with O2,

S. Naya et al. / Tetrahedron 61 (2005) 4919–4930
Table 1. Results for the photo-induced oxidative cyclization of 12a–ca
4921
Run
12
Additive
Solvent
Time/h
Product
Yield/%
1
2
3
4
12a
12b
12b
12c
HClO4
HBF4
HClO4
HClO4
Ac2O
Ac2O
Ac2O
Ac2O
7
96
2
13aC$ClOK4
13bC$BFK4
13bC$ClOK4
13cC$ClOK4
Trace
47
90
2
99
a Reaction was carried out under photo-irradiation (RPR-100, 350 nm lamps).
Table 2. Redox potentials of 12a–c, 13a–cC$BF4K, and 19a,bC$BFK4 and reference compounds 1b and 4
Compd.
Redox potentiala
Compd.
Redox potentiala
E1red
E1ox
E1red
E1ox
12a
12b
12c
4b
K1.36
K1.29
K1.29
K1.11
K1.11
C1.91
C1.37
C1.37
C1.20
—
13aC$BFK4
13bC$BFK4
13cC$BFK4
19aC$BFK4
19bC$BFK4
K0.49
K0.46
K0.44
K0.47
K0.47
—
—
—
—
—
1bc
a V vs Ag/AgNO3; cathodic and anodic peak potentials.
b Ref. 14.
c This work.
analysis of 13cC$ClO4K was not obtained; however,
satisfactory 1H and 13C NMR and HRMS data were
obtained. In a search for details of the oxidative cyclization,
the characteristics of 12a–c were studied by an inspection of
their redox potentials and UV–vis spectra. The redox
property of 12a–c was determined by cyclic voltammetry
(CV) in CH3CN. The oxidation and reduction waves of
12a–c were irreversible under the conditions of the CV
measurements, and thus, the peak potentials are summarized
in Table 2, together with those of the reference compound
4.14 The first reduction potentials (E1red) of 12a–c are more
negative than that of 4,14 and the order is 12aO12bZ12c,
and the first oxidation potentials (E1ox) are more positive in
the order 12a[12bZ12cO4.14 Thus, the feature suggests
the difficulty of oxidative cyclization of 12a,b by using
DDQ and Sc(OTf)3 (vide supra). On the other hand,
the UV–vis spectra of 12a–c are shown in Figure 2, and
the longest wavelength absorption maxima (lmax) of 12b,c
(382 and 346 nm) appear at longer wavelength than that of
12a (323 nm). The visible region of the spectra of 12a–c
was not changed by adding 60% aq. HClO4. Thus,
protonation of 12a–c does not seem to occur in their ground
state, and the postulated mechanistic pathway for the
present photo-induced oxidative cyclization is depicted in
Scheme 2. The photo-induced 6p-cyclization of 12a–c
gives intermediate 14a–c, which would undergo 1,3-
hydrogen shift in acidic media and oxidation under aerobic
conditions to give 13a–cC$ClOK4 . Concerning the selec-
tivity of cyclization of 12c, the cyclization at the C1 giving
14c, which retains a benzene ring and affords 13c, would be
preferable as compared with the cyclization at the 3-position
giving 14d, which has a quinoid structure. Although the
E1ox of 12a is more positive and photo-induced oxidative
cyclization affords a trace of 13aC$ClO4K, the feature
would be attributable to an intrinsic inertness of the benzene
ring.
Scheme 2.
2.2. Alternative synthetic method
Although the reaction of salicylaldehyde (15a) with 11 has
been shown to give 16a in modest yield (Scheme 3),18
a
modified reaction of 15a–c with 2 M equiv amounts of 11
afforded 16a–c in good yields as summarized in Table 3
(Runs 1–3). Upon treatment with 42% aq. HBF4, 16a–c
Figure 2. UV–vis spectra of 12a–c in CH3CN.

4922
S. Naya et al. / Tetrahedron 61 (2005) 4919–4930
1
characterized on the basis of the H and 13C NMR, IR,
UV–vis, and mass spectral data, as well as elemental
analyses. Similarly to compound 13cC$ClO4K, satisfactory
elemental analysis of 13cC$BF4K was not obtained;
1
however, satisfactory H and 13C NMR and HRMS data
were obtained. In contrast, 13bC$BF4K is relatively stable as
compared with 13cC$BF4K. Mass spectra of 13a–cC$BF4K
and 19a,bC$BF4K exhibited the correct MCKBFK4 ion
peak, which is indicative of the cationic structure of the
compounds. The characteristic absorption band for the
counter ion of BFK4 was observed at 1084 cmK1 in the IR
spectra of 13a–cC$BF4K and 19a,bC$BFK4 . The UV–vis
spectra of 13a–cC$BF4K in CH3CN are shown in Figure 3.
The longest wavelength absorption maximum (lmax) of
13bC$BFK4 shows a red-shift by 70 nm as compared with
that of 13aC$BFK4 , suggesting the elongated p-conjugation
of 13bC$BF4K. The spectrum of 13cC$BFK4 is similar to
both 13aC$BF4K and 13bC$BFK4 , suggesting both contri-
butions of the elongated p-conjugation similar to
13bC$BFK4 and the structural feature similar to
13aC$BFK4 .
Scheme 3. Reagents and conditions: (i) EtOH, reflux, 2 h; (ii) 42% aq.
HBF4, Ac2O, 0 8C, 1 h.
underwent elimination reaction of barbituric acid to give
13a–cC$BFK4 in good yields. In order to obtain a single
crystal for X-ray analysis, similar reactions of 15a,b with
diphenylbarbituric acid (17) were also carried out to give
18a,b, respectively, which were converted to 19a,bC$BF4K
by treatment with 42% aq. HBF4 (Table 3, Runs 4 and 5).
Compound 16a was identified on the basis of a comparison
of the physical data with those reported in the literature.18
New compounds 16b,c and 18a,b were fully characterized
on the basis of the 1H and 13C NMR, IR, and mass spectral
data as well as elemental analyses.
Figure 3. UV–vis spectra of 13a–cC in CH3CN.
The 13C NMR spectral data of 13a–cC$BFK4 were fully
assigned by using the H–C Cosy spectra (HMQC and
HMBC) as summarized in Table 4. Delocalization of the
positive charge is affected by benzo-annulation. Concerning
the benzene-ring of 13aC$BFK4 and the naphthalene-ring of
13b,cC$BFK4 , the chemical shift of the labeled carbons
(Figure 4. Ca and Cb) appears at lower field (13aC: dC
154.7, 142.3; 13bC: dC 157.0, 145.7; 13cC: dC 154.6, 139.8)
as compared with those of other carbons (13aC: dC 119.4–
134.1; 13bC: dC 117.4–132.8; 13cC: dC 119.8–135.2),
suggesting that the positive charge is localized partially at
these positions. The chemical shift of the Cc carbon of
13bC$BFK4 (Fig. 4) appears at higher field than those
2.3. Properties of pyrylium ions 13a–cC$BF4K and
19a,bC$BFK4
Compounds 13a–cC$BF4K and 19a,bC$BFK4 were fully
Table 3. Results for the preparation of 17a–c and 19b and cation 13a–cC$BF4K and 19a,bC$BFK4
Run
Compd.
Barbituric acid
Condensation
Cation
Product
Yield (%)
Product
Yield (%)
1
2
3
4
5
15a
15b
15c
15a
15b
11
11
11
17
17
16a
16b
16c
18a
18b
96
100
97
85
96
13aC$BFK4
13bC$BFK4
13cC$BFK4
19aC$BFK4
19bC$BFK4
95
94
93
88
85

S. Naya et al. / Tetrahedron 61 (2005) 4919–4930
Table 4. 13C NMR chemical shifts (d) of 13a–cC$BF4K
4923
Compd.
Ca
Cb
Benzene and naphthalene ring
Cc
Remaining carbons
13aC
154.7 (C9a)
142.3 (C8)
119.4 (C9), 121.5 (C5a), 131.1 (C7), 134.1 156.8 (C5)
(C6)
117.4 (C6), 119.2 (C12a), 125.0 (C1), 129. 151.2 (C12)
8 (C12b), 130.9 (C3), 131.3 (C4), 132.6
(C2), 132.8 (C4a)
30.0 (N3Me), 32.0 (N1Me), 111.7 (C4a),
148.9 (C2), 157.7 (C4), 163.8 (C10a)
30.0 (N10Me), 31.7 (N8Me), 110.3 (C11a),
149.1 (C9), 157.9 (C11), 162.7 (C7a)
13bC
157.0 (C6a)
145.7 (C5)
13cC
154.6 (C11a)
139.8 (C4a)
119.8 (C6a), 122.6 (C12b), 124.8 (C1),
125.9 (C5), 130.3 (C4), 130.9 (C2), 131.5
(C6), 135.2 (C3)
155.9 (C7)
30.0 (N9Me), 31.9 (N11Me), 111.2 (C7a),
149.0 (C10), 157.8 (C8), 162.8 (C11a)
recrystallization from CH3CN–AcOEt. Thus, in order to
clarify the structural details, X-ray crystal analyses of
19a,bC$BFK4 were performed and the ORTEP drawings are
shown in Figure 5. The p-system of 19aC$BF4K has a
nearly planar structure, and the planes of the N1- and
N2-phenyl groups are twisted 65.68 and 69.18, respectively,
against the plane of the p-system. For compound
19bC$BFK4 , a small deformation of the p-system from
planarity is observed, and the planes of N1 and N2-phenyl
groups are twisted 73.78 and 72.48, respectively, against the
plane of the p-system. In both compounds 19a,bC$BF4K,
the bond length of O1–C11 is shorter than that of O1–C10,
suggesting that the former bond has a larger bond order.
In addition, the bond length of C9–C10 is shorter than those
of C5–C6 and C7–C8. Furthermore, for compound
19aC$BFK4 , the bond length of C6–C7 is shorter than
those of C8–C9. These facts suggest the existence of bond
alternation as shown in the canonical structures of 19a,bC-
A, 19a,bC-B, and 19a,bC-C (Fig. 6). Furthermore,
contribution of the canonical structure 19a,bC-D seems to
be less important.
Figure 4.
of 13a,cC$BFK4 , suggesting that the positive charge of
13bC$BFK4 is delocalized more effectively as compared
with those of 13a,cC$BFK4 . The feature supports the
relatively larger stability of 13bC$BF4K.
Single crystals of 19a,bC$BF4K were obtained by
Figure 5. ORTEP drawing of 19a,bC$BF4K with thermal ellipsoid plot (50% probability). Selected bond lengths (A) of 19aC$BFK4 ; N1–C11 1.336(2),
˚
O1–C10 1.388(2), O1–C11 1.316(2), C3–C11 1.404(2), C3–C4 1.360(2), C4–C5 1.416(2), C5–C6 1.409(2), C5–C10 1.403(2), C6–C7 1.377(2), C7–C8
1.402(2), C8–C9 1.386(2), C9–C10 1.382 (2). Selected bond lengths (A) of 19bC$BF4K; N1–C11 1.336(2), O1–C10 1.383(2), O1–C11 1.325(2), C3–C11
˚
1.395(3), C3–C4 1.363(2), C4–C5 1.409(2), C5–C6 1.448(2), C5–C10 1.388(3), C6–C7 1.418(3), C7–C8 1.418(3), C8–C9 1.355(3), C9–C10 1.397(3),
C6–C24 1.408(3), C24–C25 1.372(3), C25–C26 1.403(3), C26–C27 1.363(3), C7–C27 1.413(3).

4924
S. Naya et al. / Tetrahedron 61 (2005) 4919–4930
Figure 6.
Although the pKRC values of 13a–cC and 19a,bC could not
be determined due to irreversible ring-opening reaction
(vide infra), the reduction potential of 13a–cC and 19a,bC
was determined by cyclic voltammentry (CV) in CH3CN.
The reduction wave was irreversible under the conditions of
the CV measurements; the peak potential is summarized in
Table 2, together with that of the reference compound 1b.
The values of 13a–cC and 19a,bC are less negative than
that of 1b, suggesting that 13a–cC and 19a,bC have lower
LUMO, and thus, they are expected to have strong oxidizing
ability. Furthermore, the first reduction potentials (E1red) are
less negative in the order 13aCO13bCO13cC. The feature
is rationalized on the basis of the elongated conjugation of
13b,cC. We have recently clarified that perturbations
derived from benzo-annulation onto the cyclohepta[a]azu-
lenylium ion are highly dependent on the annulating
positions.19 While the benzo-annulation on the double
bond having a large bond order of the parent cation causes
smaller perturbation, the benzo-annulation on the double
bond having a small bond order significantly perturbs both
the original p-system and the annulating benzene ring.
Regarding cation 19aC, the X-ray crystal analysis revealed
Scheme 4. Reagents and conditions: (i) benzylamine or aq. NaHCO3,
CH3CN, rt, 1 h; (ii) 3% HCl, CH3CN, rt, 1 min; (iii) 42% aq. HBF4, Ac2O,
0 8C, 1 h; (iv) DDQ, CH2Cl2, rt, 1 h; (v) NaBH4, CH3CN, rt, 1 h.
of 11, 15a, 16a, and 22a. The retro-aldol reaction of 22a
afforded compounds 15a and 11, which would react with
remaining 13aC$BF4K to afford 16a. Thus, under acidic
conditions, the addition reaction of 13aC$BF4K with H2O
afforded C9a-adduct, which underwent a ring-opening
reaction to give 22a. Since the ring-opening reaction was
irreversible, the pKRC values of 13a–cC$BF4K could not be
determined (vide supra). Upon treatment with 42% aq.
HBF4 in Ac2O, compounds 20a and 21a regenerated
13aC$BFK4 in quantitative yields, respectively. Further-
more, an oxidizing reaction of 21a by using DDQ afforded
23a in 86% yield. On the other hand, the reaction of
13a–cC$BF4K with NaBH4 afforded single isomers 20a–23a
and 24a–c in good yields (Scheme 4). Compounds 24a–c
˚
that the bond length of the C8–C9 (1.386 A) is longer than
˚
that of the C6–C7 (1.377 A) (vide supra), suggesting that the
1
were fully characterized on the basis of the H and 13C
NMR, IR, and mass spectral data, as well as elemental
analyses. Furthermore, the DDQ-oxidation reaction of 24a
in CH2Cl2 afforded 23a in quantitative yield: the inter-
mediate 13aC, generated by the oxidative hydrogen
abstraction of 24a with DDQ, reacts with contaminated
H2O to give 21a, hydrogen abstraction of which with
another DDQ gives 23a.
former bond has a smaller bond order. Thus, the benzo-
annulation onto 13aC at the C8–C9 giving 13cC would
cause a larger perturbation than the benzo-annulation onto
13aC at the C6–C7 giving 13bC. Thus, the cation 13cC
would exhibit a less negative E1red as compared with that of
13bC.
2.4. Reactivity
2.5. Autorecycling oxidation
In order to clarify the reactivity of the pyrylium cation,
several reactions of 13a–cC$BF4K were carried out. The
reaction of 13aC$BF4K with benzylamine proceeded at the
C5 to afford a single isomer 20a in 97% yield (Scheme 4).
Similarly, a reaction of 13aC$BF4K with H2O under basic
conditions (aq. NaHCO3) proceeded at the C5 to give 21a in
92% yield. In contrast, a reaction of 13aC$BF4K with H2O
under acidic conditions (0.6% HCl) afforded a mixture
The photo-induced oxidizing reaction of benzyl alcohol by
using pyrylium salts has been reported.15 Furthermore, we
have previously reported that compounds 3a–dC$BF4K
undergo autorecycling oxidation of some alcohols to give
the corresponding carbonyl compounds under photo-
irradiation.11–13 In addition, compounds 2a and
3a–dC$BFK4 have also been reported to undergo

S. Naya et al. / Tetrahedron 61 (2005) 4919–4930
4925
Table 5. Autorecycling oxidation of some amines by 13a–cC$BF4 and 1b under photo-irradiationa
K
Run
Compd.
Amine
Yieldb/%
Recycling
no.c
Run
Compd.
Amine
Yieldb/%
Recycling
no.c
1
2
3
4
5
6
7
8
13aC$BFK4
13aC$BFK4
13aC$BFK4
13aC$BFK4
13bC$BFK4
13bC$BFK4
13bC$BFK4
13bC$BFK4
PhCH2NH2
PhCH(Me)NH2
Hexylamine
Cyclohexylamine
PhCH2NH2
PhCH(Me)NH2
Hexylamine
Cyclohexylamine
909
1133
643
9.1
11.3
6.4
9
13cC$BFK4
13cC$BFK4
13cC$BFK4
13cC$BFK4
1b
1b
1b
1b
PhCH2NH2
PhCH(Me)NH2
Hexylamine
Cyclohexylamine
PhCH2NH2
PhCH(Me)NH2
Hexylamine
Cyclohexylamine
1189
2067
3357
647
699
67
11.9
20.7
33.6
6.5
7.0
0.7
10
11
12
13
14
15
16
0d
0
2098
3600
2857
791
21.0
36.0
28.6
7.9
929
72
9.3
0.7
a CH3CN solution was irradiated by RPR-100, 350 nm lamps under aerobic conditions.
b Based on 13a–cC$BFK4 and 1b used; the yield is calculated by subtraction of the ‘blank’ yield from the total yield of carbonyl compound in the presence of
13a–cC$BFK4 and 1b.
c Isolated by converting to the corresponding 2,4-dinitrophenylhydrazone.
d The ‘blank’ yield was higher than the yield in the presence of 13a–cC$BFK4 and 1b.
autorecycling oxidation toward some amines under photo-
irradiation.9,20 In this context, we examined the oxidation of
some amines by using 13a–cC$BF4K as well as reference
compound 1b under aerobic and photo-irradiation con-
ditions (RPR-100, 350 nm lamps). We found that com-
pounds 13a–cC$BF4K have an oxidizing ability toward
benzylamine, 1-phenylethylamine, hexylamine, and cyclo-
hexylamine to give the corresponding imines. Imine
R1R2C]NH is produced at first; however, it reacts with
another amine to result in the formation of R1R2C]N–
CHR1R2. The results are summarized in Table 5. Direct
irradiation of the amines in the absence of 13a–cC$BF4K
and 1b (named ‘blank’) gives the imines in low to modest
yields. Thus, the yields of imines are calculated by
subtraction of the ‘blank’ yield from the yields obtained in
the presence of 13a–cC$BFK4 and 1b. More than 100%
yields are obtained (based on compounds 13a–cC$BF4K and
1b) (Table 5), and thus, autorecycling oxidation clearly
proceeds; however, cyclohexylamine was not oxidized
effectively by 13aC$BFK4 and 1b (Table 5, Runs 4 and
16). In order to clarify the time dependency of the oxidizing
reaction, 1H NMR monitoring of the photo-oxidation
reactions of 13a–cC$BF4K toward benzylamine was carried
out. By using mesitylene as the internal standard, the yield
monitoring was continued to 54 h, and the yield of
benzaldimine was increased linearly to be 20057%. These
features suggest that 13a–cC$BF4K would be stable under
these conditions. Attempted detection of the intermediate
such as a reduced radical species and 24a–c, in the oxidation
reaction of amines is unsuccessful at this stage. We propose
that the present autorecycling oxidation proceeds via a
radical species derived from the electron-transfer from
amines to the excited cations 13a–cC$BF4K or from the
homolysis of amine-adduct such as 20a by photo-
irradiation.9,15,20
3. Conclusion
Novel photo-induced oxidative cyclization of 12a–c, which
derived from the reaction of barbituric acid with easily
available aromatic aldehydes, was accomplished to syn-
thesize areno[b]pyrimido[5,4-e]pyran-2,4(1,3H)-dionylium
ions (13a–cC$ClO4K). Furthermore, 13a–cC$BFK4 and
19a,bC$BFK4 were also synthesized by the reaction of
salicylaldehyde 14a and related naphthyl derivative 14b,c
with dimethylbarbituric acid and subsequent treatment with
aq. HBF4. Structural characteristics of 13a–cC$ClO4K,
13a–cC$BF4K, and 19a,bC$BFK4 were investigated on the
basis of the inspection of the UV–vis and NMR spectral data
as well as X-ray crystal analyses. The electrochemical
properties were also clarified by the CV measurement. In a
search for reactivity, reactions of 13a–cC$BF4K with some
nucleophiles, hydride, benzylamine, and H2O, were carried
out. The photo-induced autorecycling oxidation reactions
of 13a–cC$BFK4 toward some amines under aerobic
conditions were carried out to give the corresponding
imines (isolated by converting to the corresponding 2,4-
dinitrophenylhydrazones) in 643–3600% yield (recycling
number of 13a–cC$BFK4 : 6.4–36.0).
1
of imine is recorded by using the H spectra at selected
intervals. The results are summarized in Figure 7, and
the yield of benzaldimine was increased linearly as the
irradiation time was prolonged to 16 h. Concerning the
photo-oxidation reaction by using 13bC$BF4K, H NMR
1
4. Experimental
4.1. General
IR spectra were recorded on a HORIBA FT-710 spectro-
meter. Mass spectra and high-resolution mass spectra were
run on JMS-AUTOMASS 150 and JMS-SX102A spectro-
meters. Unless otherwise specified, 1H and 13C NMR
spectra were recorded on JNM-lambda500 and
Figure 7. Time dependency of autorecycling oxidation of benzylamine by
using 13a–cC$BFK4
.

4926
S. Naya et al. / Tetrahedron 61 (2005) 4919–4930
AVANCE600 spectrometers using CD3CN as a solvent, and
the chemical shifts are given relative to internal SiMe4
standard; J-values are given in Hz. Mps were recorded on a
Yamato MP-21 apparatus and were uncorrected.
were collected by filtration to give 13a–cC$ClO4K or
13bC$BFK4 . The results are summarized in Table 1.
4.4.1. 1,3-Dimethylbenzo[5,6]pyrano[2,3-d]pyrimidine-
2,4(1,3H)-dionylium perchlorate (13a–cC$ClO4K). Color-
less powder; mp 269–272 8C dec (from CH3CN–AcOEt);
1H NMR (400 MHz, CD3CN) d 3.46 (3H, s, N3Me), 3.85
(3H, s, N1Me), 7.97 (1H, dd, JZ7.9, 7.3 Hz, H-7), 8.16 (1H,
d, JZ8.6 Hz, H-9), 8.34 (1H, dd, JZ8.6, 7.3 Hz, H-8), 8.37
(1H, d, JZ7.9 Hz, H-6), 9.70 (1H, s, H-5); IR (KBr) n 1754,
1694, 1637, 1251, 1229, 1106, 1087 cmK1; MS (FAB) m/z
243 (MCKClO4); HRMS calcd for C13H11N2O7Cl:
243.0770 (MKClO4). Found: 243.0761 (MCKClO4).
Anal. Calcd for C13H11N2O7Cl: C, 45.56; H, 3.24; N,
8.17. Found: C, 45.45; H, 3.31; N, 8.00.
4.2. Preparation of 12a–c
A solution of 10a–c (10 mmol) and 11 (1.56 g, 10 mmol) in
EtOH (50 mL) in the presence of H2SO4 (three drops) was
heated under reflux for 1 h. After the reaction was
completed, the resulting mixture was cooled to rt, and the
precipitates were collected by filtration to give products
12a–c (12a: 2.20 g, 84%, 12b: 2.76 g, 94%, 12c: 2.79 g,
95%). Compound 12a was identified on the basis of a
comparison of the physical data with those reported in the
literature.17
4.4.2. 8,10-Dimethylnaphto[10,20:5,6]pyrano[2,3-d]-
pyrimidine-9,11(8,10H)-dionylium perchlorate (13bC$
ClOK4 ). Orange needles; mp 281–284 8C dec (from
CH3CN–AcOEt); 1H NMR (400 MHz, CD3CN) d 3.50
(3H, s, N10Me), 3.89 (3H, s, N8Me), 7.98 (1H, dd, JZ8.1,
7.1 Hz, H-3), 8.09 (1H, dd, JZ8.5, 7.1 Hz, H-2), 8.18 (1H,
d, JZ9.3 Hz, H-6), 8.32 (1H, d, JZ8.1 Hz, H-4), 8.86 (1H,
d, JZ9.3 Hz, H-5), 8.92 (1H, d, JZ8.5 Hz, H-1), 10.30 (1H,
s, H-12); IR (KBr) n 1744, 1695, 1629, 1289, 1209,
1091 cmK1; MS (FAB) m/z 293 (MCKClO4); HRMS
calcd for C17H13N2 O7Cl: 293.0926 (MKClO4). Found:
293.0957 (MCKClO4). Anal. Calcd for C17H13N2O7Cl: C,
51.99; H, 3.34; N, 7.13. Found: C, 51.92; H, 3.40; N, 6.99.
4.2.1. 1,3-Dimethyl-5-(1-naphthylmethylidene)pyrimi-
dine-2,4,6(1,3,5H)-trione (12b). Yellow needles; mp
1
195–196 8C (from AcOEt); H NMR (400 MHz, CDCl3) d
3.32 (3H, s, NMe), 3.48 (3H, s, NMe), 7.51–7.60 (3H, m),
7.84–7.94 (2H, m), 7.96 (1H, d, JZ7.3 Hz), 7.99 (1H, d, JZ
8.3 Hz), 9.24 (1H, s); 13C NMR (150.9 MHz, CDCl3) d 28.4,
29.0, 119.7, 124.1, 124.7, 126.4, 127.3, 129.1, 129.2, 130.3,
131.5, 132.2, 133.1, 151.3, 157.7, 159.9, 162.1; IR (CHCl3)
n 1738, 1684, 1676, 1458, 1420, 1376 cmK1; MS (FAB) m/z
295 (MCCH); HRMS calcd for C17H14N2O3: 295.1082
(MCH). Found: 295.1105 (MCCH). Anal. Calcd for
C17H14N2O3: C, 69.38; H, 4.79; N, 9.52. Found: C, 69.25;
H, 4.84; N, 9.60.
4.4.3. 9,11-Dimethylnaphto[10,20:6,5]pyrano[2,3-d]pyrimi-
dine-8,10(9,11H)-dionylium perchlorate (13cC$ClO4K).
Yellow needles; mp 291–294 8C dec (from CH3CN–Et2O);
1H NMR (400 MHz, CD3CN) d 3.49 (3H, s, N9Me),
4.01 (3H, s, N11Me), 8.03 (1H, dd, JZ8.4, 6.9 Hz, H-2),
8.12 (1H, dd, JZ8.2, 6.9 Hz, H-3), 8.15 (1H, d, JZ8.7 Hz,
H-5), 8.29 (1H, d, JZ8.2 Hz, H-4), 8.32 (1H, d, JZ8.7 Hz,
H-6), 8.83 (1H, d, JZ8.4 Hz, H-1), 9.77 (1H, s, H-7); IR
(KBr) n 1751, 1700, 1653, 1294, 1249, 1091 cmK1; MS
(FAB) m/z 293 (MCKClO4); HRMS calcd for
C17H13N2O7Cl: 293.0926 (MKClO4). Found: 293.0954
(MCKClO4).
4.2.2. 1,3-Dimethyl-5-(2-naphthylmethylidene)pyrimi-
dine-2,4,6(1,3,5H)-trione (12c). Yellow needles; mp 201–
1
202 8C (from AcOEt); H NMR (400 MHz, CDCl3) d 3.41
(3H, s, NMe), 3.45 (3H, s, NMe), 7.54 (1H, dd, JZ8.1,
7.1 Hz, H-6), 7.61 (1H, dd, JZ8.1, 7.1 Hz, H-7), 7.86 (1H,
d, JZ8.1 Hz, H-8), 7.87 (1H, d, JZ8.8 Hz, H-3), 7.95 (1H,
d, JZ8.1 Hz, H-4), 8.15 (1H, d, JZ8.8 Hz, H-5), 8.61 (1H,
s, H-1), 8.74 (1H, s, C]CH); 13C NMR (150,9 MHz,
CDCl3) d 28.5, 29.1, 117.3, 126.8, 127.7, 127.7, 128.7,
129.0, 129.7, 130.4, 132.6, 135.4, 136.4, 151.3, 159.3,
160.5, 162.6; IR (CHCl3) n 1733, 1674, 1580, 1380, 1215,
1087 cmK1; MS (FAB) m/z 295 (MCCH); HRMS calcd for
C17H14N2O3: 295.1082 (MCH). Found: 295.1071 (MCC
H). Anal. Calcd for C17H14N2O3: C, 69.38; H, 4.79; N, 9.52.
Found: C, 69.16; H, 4.68; N, 9.51.
4.5. Preparation of 16a–c and 18a,b
A solution of 15a–c (10 mmol) and 11 (3.12 g, 20 mmol) or
17 (5.64 g, 20 mmol) in EtOH (50 mL) was heated under
reflux for 2 h. After the reaction was completed, the
resulting mixture was cooled to rt, and the precipitates
were collected by filtration to give products 16a–c and
18a,b. The results are summarized in Table 3. Compound
16a was identified on the basis of the comparison of the
physical data with those reported in the literature.18
4.3. Attempted oxidative cyclization of 12a,b with DDQ
and Sc(OTf)3
To stirred solutions of 12a,b (0.2 mmol) in xylene (10 mL)
was added DDQ (150 mg, 0.66 mmol) and Sc(OTf)3
(324 mg, 0.66 mmol) and the mixtures were heated under
reflux for 72 h; however, the reactions were complicated.
4.5.1. 8,10-Dimethyl-12-(1,3-dimethyl-2,4,6(1,3,5H)-
trioxopyrimidin-5-yl)naphto[10,20:5,6]pyrano[2,3-d]-
pyrimidine-9,11(8,10H)-dione (16b). Yellow prisms; mp
4.4. Photo-induced oxidative cyclization of 12a–c
1
A solution of 12a–c (0.25 mmol) and 60% aq. HClO4
(1 mL) or 42% aq. HBF4 (1 mL) or NaBF4 (28 mg,
0.25 mmol) in a solvent (8 mL) in a Pyrex tube was
irradiated by RPR-100, 350 nm lamps under aerobic
condition until the reaction completed (Table 1). To the
mixture was added Et2O (50 mL) and the precipitates
244–247 8C dec (from CHCl3–Et2O); H NMR (400 MHz,
CDCl3) d 3.05 (3H, s, NMe), 3.34 (6H, s, NMe), 3.59 (3H, s,
NMe), 3.95 (1H, d, JZ1.2 Hz, CH), 5.67 (1H, d, JZ1.2 Hz,
H-12), 7.33 (1H, d, JZ9.0 Hz, H-6), 7.55 (1H, dd, JZ8.1,
6.8 Hz, H-3), 7.71 (1H, dd, JZ8.5, 6.8 Hz, H-2), 7.87 (1H,
d, JZ9.0 Hz, H-5), 7.91 (1H, d, JZ8.1 Hz, H-4), 8.55 (1H,

S. Naya et al. / Tetrahedron 61 (2005) 4919–4930
4927
d, JZ8.5 Hz, H-1); 13C NMR (150,9 MHz, CDCl3) d 28.1,
28.2, 28.7, 29.2, 35.5, 54.0, 85.6, 114.5, 116.2, 122.8, 125.9,
128.4, 129.2, 130.1, 130.4, 131.9, 147.9, 150.4, 151.3,
154.7, 162.3, 167.4, 167.7; IR (KBr) n 1712, 1691, 1672,
1662, 1637, 1491, 1454, 1375, 1240 cmK1; MS (FAB) m/z
449 (MCCH); HRMS calcd for C23H20N4O6: 449.1461
(MCH). Found: 449.1448 (MCCH). Anal. Calcd for
C23H20N4O6: C, 61.60; H, 4.50; N, 12.49. Found: C,
61.32; H, 4.43; N, 12.48.
C43H28N4O6: 697.2087 (MCH). Found: 697.2104 (MCC
H). Anal. Calcd for C43H28N4O6C1/4CHCl3: C, 71.50; H,
3.92; N, 7.71. Found: C, 71.59; H, 4.09; N, 7.74.
4.6. Preparation of 13a–cC$BF4K and 19a,bC$BFK4
A solution of 16a–c (1 mmol) or 18a,b (1 mmol) in Ac2O
(10 mL) and 42% aq. HBF4 (2 mL) was stirred at 0 8C for
1 h. To the mixture was added Et2O (50 mL) and the
precipitates were collected by filtration to give 13a–cC$
BFK4 or 19a,bC$BFK4 . The results are summarized in
Table 3.
4.5.2. 9,11-Dimethyl-7-(1,3-dimethyl-2,4,6(1,3,5H)-tri-
oxopyrimidin-5-yl)naphto[10,20:6,5]pyrano[2,3-d]pyri-
midine-8,10(9,11H)-dione (16c). Colorless needles; mp
1
256–259 8C dec (from CHCl3–Et2O); H NMR (400 MHz,
4.6.1. 1,3-Dimethylbenzo[5,6]pyrano[2,3-d]pyrimidine-
2,4(1,3H)-dionylium tetrafluoroborate (13aC$BF4K).
Colorless powder; mp 225–228 8C dec (from CH3CN–
AcOEt); 1H NMR (500 MHz, CD3CN) d 3.46 (3H, s,
N3Me), 3.85 (3H, s, N1Me), 7.97 (1H, dd, JZ7.9, 7.3 Hz,
H-7), 8.16 (1H, d, JZ8.6 Hz, H-9), 8.34 (1H, dd, JZ8.6,
7.3 Hz, H-8), 8.37 (1H, d, JZ7.9 Hz, H-6), 9.70 (1H, s,
H-5); 13C NMR (150.9 MHz, CD3CN) d 30.0, 32.0, 111.7,
119.4, 121.5, 131.1, 134.1, 142.3, 148.9, 154.7, 156.8,
CDCl3) d 3.01 (3H, s, NMe), 3.28 (3H, s, NMe), 3.40 (3H, s,
NMe), 3.74 (3H, s, NMe), 4.17 (1H, d, JZ2.2 Hz, CH), 5.27
(1H, d, JZ2.2 Hz, H-7), 7.21 (1H, d, JZ8.5 Hz, H-6), 7.55–
7.67 (2H, m, H-2 and H-3), 7.66 (1H, d, JZ8.5 Hz, H-5),
7.85 (1H, d, JZ7.6 Hz, H-4), 8.14 (1H, d, JZ8.1 Hz, H-1);
13C NMR (150,9 MHz, CDCl3) d 28.2, 28.3, 28.5, 29.3,
37.0, 54.1, 86.5, 115.1, 120.6, 123.2, 124.0, 126.0, 127.4,
127.4, 128.0, 133.7, 145.0, 150.6, 151.2, 154.6, 162.1,
167.0, 167.1; IR (KBr) n 1701, 1687, 1678, 1668, 1637,
1491, 1458, 1383, 1244, 1213 cmK1; MS (FAB) m/z 449
(MCCH); HRMS calcd for C23H20N4O6: 449.1461 (MC
H). Found: 449.1473 (MCCH). Anal. Calcd for
C23H20N4O6: C, 61.60; H, 4.50; N, 12.49. Found: C,
61.42; H, 4.45; N, 12.48.
157.7, 163.8; IR(KBr)n1752, 1696, 1640, 1250, 1084 cmK1
;
MS (FAB) m/z 243 (MCKBF4); HRMS calcd for
C13H11BF4N2O3: 243.0770 (MKBF4). Found: 243.0790
(MCKBF4). Anal. Calcd for C13H11BF4N2O3: C, 47.31; H,
3.36; N, 8.49. Found: C, 47.30; H, 3.44; N, 8.48.
4.6.2. 8,10-Dimethylnaphto[10,20:5,6]pyrano[2,3-d]-
pyrimidine-9,11(8,10H)-dionylium tetrafluoroborate
(13bC$BFK4 ). Yellow plates; mp 239–241 8C dec (from
CH3CN–AcOEt); 1H NMR (500 MHz, CD3CN) d 3.50 (3H,
s, N10Me), 3.89 (3H, s, N8Me), 7.98 (1H, dd, JZ8.1,
7.1 Hz, H-3), 8.09 (1H, dd, JZ8.5, 7.1 Hz, H-2), 8.18 (1H,
d, JZ9.3 Hz, H-6), 8.32 (1H, d, JZ8.1 Hz, H-4), 8.86 (1H,
d, JZ9.3 Hz, H-5), 8.93 (1H, d, JZ8.5 Hz, H-1), 10.31 (1H,
s, H-12); 13C NMR (150.9 MHz, CD3CN) d 30.0, 31.7,
110.3, 117.4, 119.2, 125.0, 129.8, 130.9, 131.3, 132.6,
132.8, 145.7, 149.1, 151.2, 157.0, 157.9, 162.7; IR (KBr) n
1700, 1684, 1654, 1214, 1084 cmK1; MS (FAB) m/z 293
(MCKBF4); HRMS calcd for C17H13BF4N2O3: 293.0950
(MKBF4). Found: 293.0938 (MCKBF4). Anal. Calcd for
C17H13BF4N2O3: C, 53.72; H, 3.45; N, 7.37. Found: C,
53.66; H, 3.50; N, 7.21.
4.5.3. 1,3-Diphenyl-5-(1,3-diphenyl-2,4,6(1,3,5H)-trioxo-
pyrimidin-5-yl)benzo[5,6]pyrano[2,3-d]pyrimidine-2,
4(1,3H)-dione (18a). Colorless needles; mp 189–192 8C
dec (from EtOH); 1H NMR (500 MHz, CDCl3) d 4.47 (1H,
d, JZ2.7 Hz, CH), 5.35 (1H, d, JZ2.7 Hz, H-5), 6.82–6.85
(1H, m), 7.01 (2H, bs), 7.17 (2H, d), 7.28–7.32 (4H, m),
7.37–7.41 (3H, m), 7.41–7.51 (12H, m); 13C NMR
(150,9 MHz, CDCl3) d 37.5, 55.0, 86.5, 117.1, 120.3,
126.4, 128.1, 128.2, 128.4, 128.8, 128.9, 129.0, 129.1,
129.1, 129.2, 129.3, 129.3, 129.4, 129.7, 129.7, 133.2,
133.9, 134.0, 134.5, 149.7, 150.0, 150.5, 155.0, 162.3,
166.7, 166.8; IR (KBr) n 1707, 1693, 1655, 1491, 1448,
1396, 1367, 1273 cmK1; MS (FAB) m/z 647 (MCCH);
HRMS calcd for C39H26N4O6: 647.1895 (MCH). Found:
647.1913 (MCCH). Anal. Calcd for C39H26N4O6CEtOH:
C, 71.09; H, 4.66; N, 8.09. Found: C, 70.68; H, 4.69; N,
8.12.
4.6.3. 9,11-Dimethylnaphto[10,20:6,5]pyrano[2,3-d]-
pyrimidine-8,10(9,11H)-dionylium tetrafluoroborate
(13cC$BFK4 ). Yellow plates; mp 233–236 8C dec (from
CH3CN–Et2O); 1H NMR (600 MHz, CD3CN) d 3.49 (3H, s,
N9Me), 4.00 (3H, s, N11Me), 8.03 (1H, dd, JZ8.4, 6.9 Hz,
H-2), 8.12 (1H, dd, JZ8.2, 6.9 Hz, H-3), 8.15 (1H, d, JZ
8.7 Hz, H-5), 8.29 (1H, d, JZ8.2 Hz, H-4), 8.32 (1H, d, JZ
8.7 Hz, H-6), 8.83 (1H, d, JZ8.4 Hz, H-1), 9.77 (1H, s, H-
7); 13C NMR (150.9 MHz, CD3CN) d 30.0, 31.9, 111.2,
119.8, 122.6, 124.8, 125.9, 130.3, 130.9, 131.5, 135.2,
139.8, 149.0, 154.6, 155.9, 157.8, 162.8; IR (KBr) n
1774, 1700, 1648, 1250, 1084 cmK1; MS (FAB) m/z 293
(MCKBF4); HRMS calcd for C17H13BF4N2O3: 293.0950
(MKBF4). Found: 293.0938 (MCKBF4).
4.5.4. 8,10-Diphenyl-12-(1,3-diphenyl-2,4,6(1,3,5H)-
trioxopyrimidin-5-yl)naphto[10,20:5,6]pyrano[2,3-d]pyri-
midine-9,11(8,10H)-dione (18b). Colorless needles; mp
1
272–275 8C dec (from CHCl3–Et2O); H NMR (400 MHz,
CDCl3) d 4.34 (1H, d, JZ1.2 Hz, CH), 5.88 (1H, d, JZ
1.2 Hz, H-12), 6.88 (1H, d, JZ8.8 Hz, H-5), 7.11 (2H, d,
JZ6.8 Hz, NPh-o), 7.28–7.57 (19H, m, H-8 and NPh-o, m,
p), 7.68 (1H, dd, JZ7.0, 8.4 Hz, H-2), 7.75 (1H, d, JZ
8.8 Hz, H-5), 7.87 (1H, d, JZ8.0 Hz, H-4), 8.68 (1H, d, JZ
8.4 Hz, H-1); 13C NMR (150,9 MHz, CDCl3) d 36.5, 54.7,
85.9, 114.4, 116.3, 122.9, 126.0, 128.1, 128.4, 128.4, 128.5,
128.6, 128.7, 128.7, 128.9, 129.0, 129.2, 129.2, 129.3,
129.3, 129.4, 129.5, 129.7, 129.9, 130.4, 132.0, 133.1,
134.1, 134.4, 134.5, 147.9, 149.9, 150.8, 155.3, 162.7,
167.6, 167.7; IR (KBr) n 1697, 1662, 1446, 1390, 1363,
1240 cmK1; MS (FAB) m/z 697 (MCCH); HRMS calcd for
4.6.4. 1,3-Diphenylbenzo[5,6]pyrano[2,3-d]pyrimidine-
2,4(1,3H)-dionylium tetrafluoroborate (19aC$BF4K).
Pale yellow prisms; mp 256–259 8C dec (from CH3CN–

4928
S. Naya et al. / Tetrahedron 61 (2005) 4919–4930
AcOEt); 1H NMR (400 MHz, CD3CN) d 7.44–7.49 (2H, m,
NPh-o), 7.57–7.68 (5H, m, NPh-m and p and o), 7.72 (1H, d,
JZ8.8 Hz, H-9), 7.72–7.78 (3H, m, NPh-m and p), 7.96
(1H, dd, JZ8.1, 7.3 Hz, H-7), 8.26 (1H, dd, JZ8.8, 7.3 Hz,
H-8), 8.41 (1H, d, JZ8.1 Hz, H-6), 9.83 (1H, s, H-5); 13C
NMR (150, 9 MHz, CD3CN) d 112.2, 116.9, 119.4, 121.9,
128.7, 129.1, 129.8, 130.0, 130.2, 130.9, 131.0, 131.3,
131.4, 132.1, 132.5, 134.1, 134.8, 142.7, 148.9, 154.8,
157.9, 158.1, 163.9; IR (KBr) n 1761, 1709, 1606, 1548,
1387, 1261, 1084 cmK1; MS (FAB) m/z 367 (MCKBF4);
HRMS calcd for C23H15BF4N2O3: 367.1083 (MKBF4).
Found: 367.1060 (MCKBF4). Anal. Calcd for
C23H15BF4N2O3: C: 60.82; H: 3.33;N: 6.17. Found: C:
60.66; H: 3.29; N: 6.09.
DcZ1.485 g mLK1, crystal dimensions 0.80!0.40!
0.30 mm. Data were measured on a Rigaku RAXIS-
RAPID radiation diffractomater with graphite monochro-
mated Mo Ka radiation. Total 19,651 reflections were
collected, using the u–2q scan technique to a maximum 2q
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,21 with 313 variables and
3309 observed reflections [IO3.00s(I)]. The non-hydrogen
atoms were refined anisotropically. The weighting scheme
wZ[0.5000sc(F20)C0.0030F20]K1 gave satisfactory agree-
ment analysis. The final R and Rw values were 0.0390 and
0.0620. The maximum peak and minimum peak in the final
K
3
˚
difference map were 0.34 and K0.18 e /A .
4.6.5. 8,10-Diphenylnaphto[10,20:5,6]pyrano[2,3-d]-
pyrimidine-9,11(8,10H)-dionylium tetrafluoroborate
(19bC$BFK4 ). Yellow prisms; mp 231–234 8C dec (from
CH3CN–AcOEt); 1H NMR (500 MHz, CD3CN) d 7.47–7.51
(2H, m, NPh-o), 7.57–7.65 (3H, m, NPh-m and p), 7.68–
7.72 (3H, m, H-6 and NPh-o), 7.75–7.79 (3H, m, NPh-m and
p), 7.99 (1H, dd, JZ8.1, 7.1 Hz, H-3), 8.11 (1H, dd, JZ8.5,
7.1 Hz, H-2), 8.30 (1H, d, JZ8.1 Hz, H-4), 8.78 (1H, d, JZ
9.3 Hz, H-5), 8.95 (1H, d, JZ8.5 Hz, H-1), 10.44 (1H, s,
H-12); 13C NMR (150,9 MHz, CD3CN) d 110.9, 117.3,
119.9, 125.1, 129.0, 129.2, 129.7, 129.9, 130.9, 131.0,
131.1, 131.4, 131.5, 132.3, 132.5, 132.8, 132.8, 135.1,
146.3, 149.2, 152.2, 152.2, 157.4, 158.3, 162.8; IR (KBr) n
1715, 1705, 1626, 1204, 1084 cmK1; MS (FAB) m/z 417
(MCKBF4); HRMS calcd for C27H17BF4N2O3: 417.1239
(MKBF4). Found: 417.1260 (MCKBF4). Anal. Calcd for
C27H17BF4N2O3: C, 64.31; H, 3.40; N, 5.56. Found: C,
64.09; H, 3.24; N, 5.50.
4.9. X-ray structure determination of 19bC$BF4K‡
Yellow prisms, C27H17N2O3BF4, MZ504.25, monoclinic,
space group P21/c, aZ10.78(1), bZ18.02(1), cZ
3
˚
˚
11.96(1) A, bZ100.83(2)8, VZ2281(3) A , ZZ4, DcZ
1.468 g mLK1, crystal dimensions 0.80!0.40!0.20 mm.
Data were measured on a Rigaku RAXIS-RAPID radiation
diffractometer with graphite monochromated Mo Ka
radiation. Total 21,709 reflections were collected, using
the u–2q scan technique to a maximum 2q 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,21 with 351 variables and 2741 observed
reflections [IO3.00s(I)]. The non-hydrogen atoms were
refined anisotropically. The weighting scheme wZ
[0.9000sc(F20)C0.0005F20]K1 gave satisfactory agreement
analysis. The final R and Rw values were 0.0330 and 0.0380.
The maximum peak and minimum peak in the final
K
3
˚
4.7. Cyclic voltammetry of 12a–c, 13a–cC$BF4K, and
19a,bC$BFK4
difference map were 0.32 and K0.23 e /A .
4.10. Reaction of 13aC$BFK4 with benzylamine
The reduction potential of 12a–c, 13a–cC$BF4K, and
19a,bC$BFK4 was determined by means of CV-27 volt-
ammetry controller (BAS Co). A three-electrode cell was
used, consisting of Pt working and counter electrodes and a
reference Ag/AgNO3 electrode. Nitrogen was bubbled
through an acetonitrile solution (4 mL) of 12a–c,
13a–cC$BFK4 , and 19a,bC$BF4K (0.5 mmol dmK3) and
Bu4NClO4 (0.1 mol dmK3) to deaerate it. The measure-
ments were made at a scan rate of 0.1 V sK1 and the
voltammograms were recorded on a WX-1000-UM-019
(Graphtec Co) X-Y recorder. Immediately after the
measurements, ferrocene (0.1 mmol) (E1/2ZC0.083) was
added as the internal standard, and the observed peak
potential was corrected with reference to this standard.
Compounds 12a–c exhibited one irreversible oxidation
wave and one irreversible reduction wave. Compounds
13a–cC$BF4K and 19a,bC$BFK4 exhibited one irreversible
reduction wave. The results are summarized in Table 2.
To a solution of 13aC$BF4K (33 mg, 0.1 mmol) in CH3CN
(5 mL) was added benzylamine (21.4 mg, 0.20 mmol), and
the mixture was stirred at rt for 1 h. To the mixture was
added saturated aq. NH4Cl solution, and the mixture was
extracted with CH2Cl2. The extract was dried over Na2SO4
and concentrated in vacuo to give 20a (34 mg, 97%).
4.10.1. 5-Benzylamino-1,3-dimethylbenzo[5,6]pyrano-
[2,3-d]pyrimidine-2,4(1,3H)-dione (20a). Colorless
prisms; mp 192–194 8C (from CHCl3–Et2O); 1H NMR
(500 MHz, CDCl3) d 3.33 (3H, s, NMe), 3.40 (2H, s,
PhCH2), 3.49 (3H, s, NMe), 5.27 (1H, s, H-5), 7.12–7.24
(6H, m, H-9 and Ph), 7.28 (1H, t, JZ7.5 Hz, H-8), 7.34 (1H,
dd, JZ7.7, 7.5 Hz, H-7), 7.64 (1H, d, JZ7.7 Hz, H-6); 13C
NMR (150,9 MHz, CDCl3) d 28.0, 28.9, 47.6, 48.1, 88.2,
116.1, 121.8, 125.9, 126.6, 127.8, 128.0, 128.9, 130.4,
140.7, 150.0, 150.6, 153.3, 162.6; IR (KBr) n 3417, 1709,
1664, 1645, 1581, 1479, 1456, 1240 cmK1; MS (FAB) m/z
350 (MCCH); HRMS calcd for C20H19N3O3: 350.1515
(MCH). Found: 350.1528 (MCCH). Anal. Calcd for
C20H19N3O3: C, 68.75; H, 5.48; N, 12.03. Found: C,
69.87; H, 5.39; N, 12.11.
4.8. X-ray structure determination of 19aC$BF4K†
Yellow prisms, C23H15N2O3BF4, MZ454.19, monoclinic,
space group P21/c, aZ11.1093(4), bZ9.7258(3), cZ
3
˚
˚
19.1523(7) A, bZ100.998(2)8, VZ2031.3(1) A , ZZ4,
† CCDC reference number 262897.
‡ CCDC reference number 262898.

S. Naya et al. / Tetrahedron 61 (2005) 4919–4930
4929
4.11. Reaction of 13aC$BF4K with OHK
Na2SO4 and concentrated in vacuo. The resulting residue
was chromatographed on SiO2 using AcOEt as the eluent to
give 23a (11 mg, 86%).
To a solution of 13aC$BF4K (33 mg, 0.1 mmol) in CH3CN
(5 mL) was added saturated aq. NaHCO3 (1 mL), and the
mixture was stirred at rt for 1 h. The mixture was extracted
with CH2Cl2 and the extract was dried over Na2SO4. The
filtrate was concentrated in vacuo to give 21a (24 mg, 92%).
4.14.1. 1,3-Dimethylbenzo[5,6]pyrano[2,3-d]pyrimidine-
2,4,5(1,3H)-trione (23a). Colorless needles; mp 290–
293 8C dec (from CHCl3–Et2O); 1H NMR (400 MHz,
CDCl3) d 3.43 (3H, s, NMe), 3.72 (3H, s, NMe), 7.42–
7.53 (2H, m, H-7 and H-9), 7.72 (1H, dd, JZ8.3, 7.3 Hz,
H-8), 8.31 (1H, d, JZ7.8 Hz, H-6); 13C NMR (150,9 MHz,
CDCl3) d 28.3, 29.7, 96.0, 116.9, 123.2, 126.8, 127.2, 134.2,
149.6, 152.5, 158.1, 160.9, 172.2; IR (KBr) n 1727, 1719,
1677, 1673, 1617, 1566, 1270, 1226, 774, 754 cmK1; MS
(FAB) m/z 259 (MCCH); HRMS calcd for C13H10N2O4:
259.0719 (MCH). Found: 259.0709 (MCCH). Anal. Calcd
for C13H10N2O4: C, 60.47; H, 3.90; N, 10.85. Found: C,
60.06; H, 3.76; N, 10.73.
4.11.1. 1,3-Dimethyl-5-hydroxybenzo[5,6]pyrano[2,3-d]-
pyrimidine-2,4(1,3H)-dione (21a). Colorless prisms; mp
105–108 8C; H NMR (400 MHz, CDCl3) d 3.41 (3H, s,
1
NMe), 3.57 (3H, s, NMe), 3.81 (1H, d, JZ2.4 Hz, OH), 5.97
(1H, d, JZ2.4 Hz, H-5), 7.20 (1H, d, JZ8.4 Hz, H-9), 7.32
(1H, dd, JZ7.6, 7.2 Hz, H-7), 7.40 (1H, dd, JZ8.4, 7.2 Hz,
H-8), 7.60 (1H, d, JZ7.6 Hz, H-6); 13C NMR (150,9 MHz,
CDCl3) d 28.0, 29.1, 59.4, 89.7, 116.4, 121.5, 126.2, 129.8,
130.3, 148.4, 150.6, 152.7, 163.4; IR (CHCl3) n 3566, 3330,
1700, 1663, 1639, 1486, 1464, 1280 cmK1; MS (FAB) m/z
259 (MCKH); HRMS calcd for C13H12N2O4: 259.0719
(MCKH). Found: 259.0694 (MCKH).
4.15. Reaction of 13a–cC$BF4K with NaBH4
A solution of 13a–cC$BF4K (0.3 mmol) and NaBH4 (11 mg,
0.3 mmol) in CH3CN (15 mL) was stirred at rt for 1 h. To
the mixture was added saturated aq. NH4Cl solution, and the
mixture was extracted with CH2Cl2. The extract was dried
over Na2SO4 and concentrated in vacuo to give 24a–c (24a:
73 mg, 100%, 24b: 85 mg, 96%, 24c: 88 mg, 100%).
4.12. Reaction of 13aC$BF4K with H3OC
To a solution of 13aC$BFK4 (16.5 mg, 0.05 mmol) in
CH3CN (5 mL) was added 0.6% HCl (5 mL), and the
mixture was stirred at rt for 1 min. To the mixture was added
H2O, and the mixture was extracted with CH2Cl2. The
extract was dried over Na2SO4 and concentrated in vacuo to
give a mixture of 22a, 11, 15a, and 16a (12 mg, the ratio of
4.15.1. 1,5-Dihydro-1,3-dimethylbenzo[5,6]pyrano[2,3-d]-
pyrimidine-2,4(1,3H)-dione (24a). Colorless prisms; mp
190–192 8C (from CHCl3–Et2O); 1H NMR (600 MHz,
CDCl3) d 3.39 (3H, s, NMe), 3.53 (3H, s, NMe), 3.74
(2H, s, H-5), 7.07 (1H, d, JZ8.2 Hz, H-9), 7.16 (1H, dd, JZ
8.4, 7.4 Hz, H-7), 7.22–7.27 (2H, m, H-6 and H-8); 13C
NMR (150,9 MHz, CDCl3) d 21.8, 28.2, 29.0, 85.5, 116.5,
120.0, 125.7, 128.0, 130.0, 149.2, 150.9, 152.7, 162.7; IR
(CHCl3) n 1705, 1665, 1637, 1490, 1450, 1244 cmK1; MS
(FAB) m/z 245 (MCCH); HRMS calcd for C13H12N2O3:
245.0926 (MCH). Found: 245.0969 (MCCH). Anal. Calcd
for C13H12N2O3: C, 63.93; H, 4.95; N, 11.47. Found: C,
63.85; H, 4.80; N, 11.48.
1
22a, 11, 15a, and 16a was determined to be 9:2:2:1 by H
NMR).
4.12.1. 1,3-Dimethyl-5-[(20-hydroxyphenyl)methylide-
ne]pyrimidine-2,4,6(1,3,5H)-trione (22a). Yellow prisms;
mp 184–185 8C (from AcOEt); 1H NMR (400 MHz, CDCl3)
d 3.43 (3H, s, NMe), 3.45 (3H, s, NMe), 7.04 (1H, dd, JZ
7.8, 7.3 Hz, H-40), 7.08 (01H, d, JZ8.3 Hz, H-60), 7.49 (1H,
dd, JZ8.3, 7.3 Hz, H-5 ), 7.60 (1H, d, JZ7.8 Hz, H-30),
8.13 (1H, s, OH), 8.75 (1H, d, C]CH); 13C NMR
(150,9 MHz, CDCl3) d 28.8, 29.2, 115.9, 120.3, 121.0,
122.9, 135.5, 135.9, 150.7, 157.1, 158.9, 162.0, 163.9; IR
(KBr) n 3282, 1727, 1672, 1645, 1603, 1396, 1384, 1259,
1159 cmK1; MS (FAB) m/z 261 (MCCH); HRMS calcd for
C13H12N2O3: 261.0875 (MCH). Found: 261.0849 (MCC
H). Anal. Calcd for C13H12N2O3: C, 60.00; H, 4.65; N,
10.76. Found: C, 59.42; H, 4.49; N, 10.57.
4.15.2. 8,12-Dihydro-8,10-dimethylnaphto[10,20:5,6]-
pyrano[2,3-d]pyrimidine-9,11(8,10H)-dione (24b). Color-
1
less needles; mp 279–282 8C dec (from CHCl3–Et2O); H
NMR (600 MHz, CDCl3) d 3.42 (3H, s, NMe), 3.56 (3H, s,
NMe), 4.00 (2H, s, H-12), 7.24 (1H, d, JZ8.9 Hz, H-6),
7.53 (1H, dd, JZ8.0, 6.9 Hz, H-3), 7.63 (1H, dd, JZ8.5,
6.9 Hz, H-2), 7.77 (1H, d, JZ8.9 Hz, H-5), 7.85 (1H, d, JZ
8.0 Hz, H-4), 7.94 (1H, d, JZ8.5 Hz, H-1); 13C NMR
(150,9 MHz, CDCl3) d 19.9, 28.2, 29.0, 85.5, 113.1, 116.4,
123.3, 125.7, 127.5, 128.4, 128.9, 131.1, 131.7, 146.3,
150.8, 152.5, 162.9; IR (CHCl3) n 1704, 1674, 1638, 1490,
1465, 1233, 1213 cmK1; MS (FAB) m/z 295 (MCCH);
HRMS calcd for C17H14N2O3: 295.1083 (MCH). Found:
295.1096 (MCCH). Anal. Calcd for C17H14N2O3C1/
2H2O: C, 67.32; H, 4.98; N, 9.24. Found: C, 66.94; H,
4.80; N, 9.43.
4.13. Reactions of 20a or 21a with HBF4
To a solution of 20a (35 mg, 0.1 mmol) or 21a (24 mg,
0.1 mmol) in Ac2O (2 mL) was added 42% aq. HBF4
(0.4 mL) at 0 8C. The mixture was stirred for 1 h. To the
mixture was added Et2O (10 mL) and the precipitate was
collected by filtration to give 13aC$BF4K (33 mg, 100%
from 20a and 33 mg, 100% from 21a).
4.14. Reaction of 21a with DDQ
To a stirred solution of 21a (13 mg, 0.05 mmol) in CH2Cl2
(1 mL) was added DDQ (11.4 mg, 0.05 mmol) and the
mixture was stirred at rt for 1 h. After evaporation of the
solvent, the residue was dissolved in aq. NaHCO3 solution,
and extracted with CH2Cl2. The extract was dried over
4.15.3. 7,11-Dihyro-9,11-dimethylnaphto[10,20:6,5]-
pyrano[2,3-d]pyrimidine-8,10(9,11H)-dione (24c). Color-
1
less needles; mp 218–221 8C dec (from CHCl3–Et2O); H
NMR (600 MHz, CDCl3) d 3.42 (3H, s, NMe), 3.69 (3H, s,
NMe), 3.86 (2H, s, H-7), 7.29 (1H, d, JZ8.4 Hz, H-6), 7.54

4930
S. Naya et al. / Tetrahedron 61 (2005) 4919–4930
(1H, dd, JZ7.7, 6.9 Hz, H-3), 7.58(1H, dd, JZ8.2, 6.9 Hz, H-
2), 7.65 (1H, d, JZ8.4 Hz, H-5), 7.84 (1H, d, JZ7.7 Hz, H-4),
8.07 (1H, d, JZ8.2 Hz, H-1); 13C NMR (150,9 MHz, CDCl3)
d 22.4, 28.2, 29.1, 85.6, 115.1, 120.2, 123.5, 125.2, 126.4,
126.6, 127.0, 128.0, 133.4, 143.8, 150.9, 152.8, 162.7; IR
(CHCl3) n 1704, 1674, 1639, 1490, 1440, 1387, 1326, 1247,
1229 cmK1; MS (FAB) m/z 295 (MCCH); HRMS calcd for
C17H14N2O3: 295.1083 (MCH). Found: 295.1068 (MCCH).
Anal. Calcd for C17H14N2O3C 1/4H2O: C, 68.33; H, 4.89; N,
9.38. Found: C, 68.51; H, 4.71; N, 9.39.
References and notes
1. Muller, F. In Muller, F., Ed.; Chemistry and Biochemistry of
Flavoenzymes; CRC: Boca Raton, 1991; Vol. 1, pp 1–71; and
references cited therein.
2. Hamilton, G. A. In Kaiser, E. T., Kezdy, F. J., Eds.; Progress in
Bioorganic Chemistry; Wiley: New York, 1971; Vol. 1, p 83.
3. (a) Chiu, C. C.; Pan, K.; Jordan, F. J. Am. Chem. Soc. 1995,
117, 7027–7028. (b) Kim, J.; Hoegy, S. E.; Mariano, P. S.
J. Am. Chem. Soc. 1995, 117, 100–105. (c) Murahashi, S.;
Ono, S.; Imada, Y. Angew. Chem., Int. Ed. 2002, 41,
4.16. Reaction of 24a with DDQ
¨
2366–2368. (d) Bergstad, K.; Jonsson, S.; Bachvall, J. J. Am.
Chem. Soc. 1999, 121, 10424–10425. (e) Van Houten, K. A.;
Kim, J.; Bogdan, M. A.; Ferri, D. C.; Mariano, P. S. J. Am.
Chem. Soc. 1998, 120, 5864–5872. (f) Zheng, Y.; Ornstein,
R. L. J. Am. Chem. Soc. 1996, 118, 9402–9408.
(g) Breinlinger, E. C.; Keenan, C. J.; Rotello, V. M. J. Am.
Chem. Soc. 1998, 120, 8606–8609. (h) Hasford, J. J.; Rizzo,
C. J. J. Am. Chem. Soc. 1998, 120, 2251–2255. (i) Antony, J.;
Medvedev, D. M.; Stuchebrukhov, A. A. J. Am. Chem. Soc.
2000, 122, 1057–1065.
To a stirred solution of 24a (24.4 mg, 0.1 mmol) in CH2Cl2
(5 mL) was added DDQ (56.8 mg, 0.25 mmol) and the
mixture was stirred at rt for 1 h. After evaporation of the
solvent, the residue was dissolved in aq. NaHCO3 solution,
and extracted with CH2Cl2. The extract was dried over
Na2SO4 and concentrated in vacuo. The resulting residue
was chromatographed on SiO2 using AcOEt as the eluent to
give 23a (26 mg, 100%).
4. Walsh, C. Acc. Chem. Res. 1986, 19, 216–221 and references
cited therein.
4.17. General procedure for the autorecycling oxidation
of amines catalyzed by 13a–cC$BF4K and 1b under
photo-irradiation
5. Yoneda, F.; Tanaka, K. Med. Res. Rev. 1987, 4, 477–506 and
references cited therein.
A CH3CN (16 mL) solution each of compounds 13a–cC$
BFK4 and 1b (0.005 mmol) and amines (2.5 mmol, 500 equiv)
in a Pyrex tube was irradiated by RPR-100, 350 nm lamps
under aerobic conditions for the period indicated in Table 5.
The reaction mixture was concentrated in vacuo and diluted
6. Yoneda, F.; Hirayama, R.; Yamashita, M. Chem. Lett. 1980,
1157–1160.
7. Nitta, M.; Tajima, Y. Synthesis 2000, 651–654.
8. Takayasu, T.; Mizuta, Y.; Nitta, M. Heterocycles 2001, 54,
601–606.
1
with Et2O and filtered. The H NMR spectra of the filtrates
9. Naya, S.; Iida, Y.; Nitta, M. Tetrahedron 2004, 60, 459–467.
10. Naya, S.; Nitta, M. Tetrahedron 2003, 59, 3709–3718.
11. Naya, S.; Miyama, H.; Yasu, K.; Takayasu, T.; Nitta, M.
Tetrahedron 2003, 59, 1811–1821.
revealed the formation of the imines (Table 5). The filtrate was
treatedwithasaturatedsolutionof2,4-dinitrophenylhydrazine
in 6% HCl to give 2,4-dinitrophenylhydrazone. The results are
summarized in Table 5.
12. Naya, S.; Miyama, H.; Yasu, K.; Takayasu, T.; Nitta, M.
Tetrahedron 2003, 59, 4929–4938.
1
4.18. H NMR monitoring of the photo-oxidation of
13. Naya, S.; Nitta, M. Tetrahedron 2003, 59, 7291–7299.
14. Naya, S.; Tokunaka, T.; Nitta, M. J. Org. Chem. 2003, 68,
9317–9321.
benzylamine by using 13a–cC$BF4K
A CD3CN (0.5 mL) solution of each compound 13a–cC$
15. (a) Miranda, M. A.; Garcia, H. Chem. Rev. 1994, 94,
1063–1089. (b) Akaba, R.; Kamata, M.; Sakuragi, H.;
Tokumaru, K. Tetrahedron Lett. 1992, 33, 8105–8108.
(c) Akaba, R.; Sakuragi, H.; Tokumaru, K. J. Chem. Soc.,
Perkin Trans. 2 1992, 291–297.
BFK4
(0.0005 mmol),
benzylamine
(18.73 mg,
0.175 mmol), and mesitylene (internal standard; 3.6 mg,
0.03 mmol) in an NMR tube irradiated by RPR-100, 350 nm
lamps under aerobic conditions. The NMR measurement
was carried out at selected intervals, and the yield of
benzaldimine calculated by using the internal standard was
plotted against irradiated time (Fig. 7).
16. Branchi, B.; Bietti, M.; Ercolani, G.; Izquierdo, M. A.;
Miranda, M. A.; Stella, L. J. Org. Chem. 2004, 69, 8874–8885.
17. Sekiya, M.; Yanaihara, C. Chem. Pharm. Bull. 1969, 17,
747–751.
18. Akabori, S. Chem. Ber. 1933, 66B, 139.
Acknowledgements
19. Yamane, K.; Yamamoto, H.; Nitta, M. J. Org. Chem. 2002, 67,
8114–8122.
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 analyses.
20. Naya, S.; Nitta, M. Tetrahedron 2004, 60, 9139–9148.
21. Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, M.;
Giacovazzo, C.; Guagliardi, A.; Polidori, G. J. Appl. Crystal-
logr. 1994, 27, 435.