Synthetic studies on a series of functionalized pyrylium salts, 4-chloro- and 4-bromophosphinines

Article abstract of DOI:10.1016/j.tet.2018.02.053

A series of new pyrylium salts that bear sulfonate and phosphonate groups were obtained from the reactions between 2,6-diphenyl-4H-pyran-4-one, sulfonic anhydride, and chlorophosphates, and analyzed spectroscopically. Furthermore, treatment of 2,6-diphenyl-4H-pyran-4-one with phosphoryl chloride or bromide afforded the corresponding 4-chloro- and 4-bromopyrylium tetrafluoroborates in good yield. Subsequently, the synthesis of the corresponding 4-chloro- and 4-bromophosphinines was accomplished by treating the respective chloro- and bromopyrylium tetrafluoroborates with tris(trimethylsilyl)phosphine.

Full text of DOI:10.1016/j.tet.2018.02.053

Accepted Manuscript
Synthetic studies on a series of functionalized pyrylium salts, 4-chloro- and 4-
bromophosphinines
Noriyoshi Nagahora, Hiroshi Tokumaru, Shinpei Ikaga, Takuya Hanada, Kosei Shioji,
Kentaro Okuma
PII:
S0040-4020(18)30211-4
10.1016/j.tet.2018.02.053
TET 29324
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 23 January 2018
Revised Date: 19 February 2018
Accepted Date: 21 February 2018
Please cite this article as: Nagahora N, Tokumaru H, Ikaga S, Hanada T, Shioji K, Okuma K, Synthetic
studies on a series of functionalized pyrylium salts, 4-chloro- and 4-bromophosphinines, Tetrahedron
(2018), doi: 10.1016/j.tet.2018.02.053.
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ACCEPTED MANUSCRIPT
Graphical Abstract
Synthetic Studies on a Series of Functionalized Pyrylium Salts, 4-Chloro- and
4-Bromophosphinines
N. Nagahora,* H. Tokumaru, S. Ikaga, T. Hanada, K. Shioji, and K. Okuma
The reactions of a pyranone with sulfonic anhydride or chlorophosphate resulted in the formation of
a series of new pyrylium salts that bear sulfonate and phosphonate groups, respectively, which were
characterized spectroscopically. Moreover, the reactions of 4-chloro- and 4-bromopyrylium
tetrafluoroborates with tris(trimethylsilyl)phosphine afforded the corresponding chloro- and
bromophosphinines.
1

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Synthetic Studies on a Series of Functionalized Pyrylium Salts, 4-Chloro- and
4-Bromophosphinines
Noriyoshi Nagahora,* Hiroshi Tokumaru, Shinpei Ikaga, Takuya Hanada, Kosei Shioji, and Kentaro
Okuma
Department of Chemistry, Faculty of Science, Fukuoka University, Jonan-ku, Fukuoka 814-0180,
Japan
E-mail: nagahora@fukuoka-u.ac.jp
Abstract
A series of new pyrylium salts that bear sulfonate and phosphonate groups were obtained from
the reactions between 2,6-diphenyl-4H-pyran-4-one, sulfonic anhydride, and chlorophosphates, and
analyzed spectroscopically. Furthermore, treatment of 2,6-diphenyl-4H-pyran-4-one with
phosphoryl chloride or bromide afforded the corresponding 4-chloro- and 4-bromopyrylium
tetrafluoroborates in good yield. Subsequently, the synthesis of the corresponding 4-chloro- and
4-bromophosphinines was accomplished by treating the respective chloro- and bromopyrylium
tetrafluoroborates with tris(trimethylsilyl)phosphine.
Key words
Pyrylium salt, Phosphinine, Chlorination, Bromination, Tris(trimethylsilyl)phosphine
1

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Introduction
Since the pioneering synthesis of 2,4,6-triphenylphosphinine as the first stable phosphinine by
Märkl,1 the chemistry of heavier congeners of pyridine has been studied extensively over the last 50
years.2 The chemistry of phosphinines has received much attention, as these compounds not only
represent fascinating synthetic building blocks for phosphorus heterocycles, but potentially also
offer fundamental insights into phosphorous-containing aromatics.3 To date, it is known that
phosphinines exhibit unique properties such as relatively low-lying π* orbitals and a narrow
HOMO–LUMO gap.2 Phosphinine molecules are thus ideal prospectives for the development of
functional materials such as organic electronic devices, and the development of advanced synthetic
methods.
Meanwhile, chloro- and bromophosphinines are of interest due to their unique electronic
structures and as potential new building blocks for phosphorous-containing aromatics. For example,
3-chloro- and 3-bromo-2-phenylphosphinine were synthesized by Märkl and Hock.4 In 1990, the
group of Mathey reported a [4+2] cycloaddition between dibromo(dibromomethyl)phosphine and
buta-1,3-diene, which afforded 2-bromophosphinine after a dehydrobromination.5 Thereafter, the
synthesis of other 2-bromophosphinines has also been achieved.6 Keglevich and co-workers
reported the synthesis of 4-chlorophosphinines by taking advantage of ring expansion reactions of
phosphabicyclo[3.1.0]hexane derivatives.7 Although these reports describe synthetic routes to
chloro- and bromophosphinines, the procedures involved are usually complicated and do not easily
provide halogen-containing phosphinines.
Meanwhile, Ni-catalyzed Suzuki-Miyaura coupling reactions of aryl sulfonamides or
phosphonates have been developed,8 and these results inspired us to explore the synthesis of new
phosphinines bearing OSO2NEt2 or OP(O)(OEt)2 groups in order to develop coupling reactions
involving phosphinines. Although synthetic investigations into phosphinines that carry a
sulfonamide or phosphonate group have not yet been conducted, they would represent an attractive
research target. Therefore, we have designed a plausible synthetic route to a series of phosphinines
(3, 6, 9, and 10) based on reactions of the corresponding pyrylium salts with
tris(trimethylsilyl)phosphine (Scheme 1).
2

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Scheme 1. Synthetic route to phosphinines 3, 6, 9, and 10 via the corresponding pyrylium salts.
3

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Results and Discussion
Attempted Synthesis of 3-Bromopyrylium Tetrafluoroborate 2. Initially, we attempted the
synthesis of 3-bromopyrylium tetrafluoroborate 2 via 2-bromo-1,5-diphenylpentane-1,5-dione (1)
(Scheme 2). A Friedel-Crafts reaction of glutaryl chloride with benzene in the presence of
aluminum chloride afforded 1,5-diphenylpentane-1,5-dione (11) in 93% yield. A subsequent
bromination of 11 in tetrachloromethane using Br2 at room temperature furnished
2-bromo-1,5-diphenylpentane-1,5-dione (1) in 44% yield. Prior to inducing the formation of the
pyrylium framework in 2-bromopentane-1,5-dione 1 with ammonium salts, we confirmed the
formation of a pyridine ring according to previously reported methods.9 Treating
2-bromopentane-1,5-dione 1 with ammonium acetate in glacial acetic acid at 50 °C for 24 h did not
afford 3-bromo-2,6-diphenylpyridine but 3-amino-2,6-diphenylpyridine (12) in 6% yield together
with 2-amino-2,5-diphenylpentane-2,5-dione (13) in 63% yield (Scheme 3). Treating an ethanol
solution
of
1
with
ammonia
resulted
in
the
unexpected
formation
of
trans-1,2-dibenzoylcyclopropane (14) in 93% yield. These results indicate that a nucleophilic
substitution of 1 occurs in favor of the formation of a pyridine ring. Then, we investigated the
formation of a 3-bromopyrylium ring from 1. The reaction of 1 with H[BF4] and Ph3C[BF4], which
was prepared from H[BF4] and Ph3COH, followed by the decantation using cold ether afforded
2,6-diphenylpyrylium tetrafluoroborate (15) in 15% yield together with a large amount of a
complicated product mixture. These results indicate that a debromination of 1 occurred during the
formation of the pyrylium ring. In order to synthesize 2,6-diphenylphosphinine, we attempted a
reaction between pyrylium salt 15 and tris(trimethylsilyl)phosphine, which is efficient method for
the synthesis of phosphinines.10 Treatment of 15 with P(SiMe3)3 in acetonitrile/benzene (1:1, v/v)
furnished the corresponding 2,6-diphenyl-4H-pyran (16) in 60% yield. One of the plausible reaction
mechanism for the formation of 16 is shown in Scheme 4. Unfortunately, the formation of
2,6-diphenylphosphinine was not confirmed, which is comparable with the results in the literature.11
These results indicate that a nucleophilic attack of P(SiMe3)3 to pyrylium tetrafluoroborate 15 is
unlikely, and that an electron transfer from P(SiMe3)3 to 15 might occur, followed by abstraction of
a hydrogen atom to afford 16 (Scheme 4).
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Scheme 2. Synthesis of 2-bromo-1,5-diphenylpentane-1,5-dione (1).
Scheme 3. Reactions of 2-bromopentane-1,5-dione 1.
5

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Scheme 4. Plausible reaction mechanism for the formation of 4H-pyran 16.
6

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Reactions of 2,6-Diphenyl-4H-pyran-4-one (4) with Sulfonic Acid, Sulfonic Anhydride,
Chlorosulfonamide, and Chlorophosphate. In order to synthesize 2,6-diphenylpyrylium salts
5a–e, we treated 2,6-diphenyl-4H-pyran-4-one (4) with sulfonic acid, sulfonic anhydrides,
chlorosulfonamide, and chlorophosphate (Table 1). Treatment of 1,5-diphenylpentane-1,3,5-trione
(18) with concentrated sulfuric acid at 0 °C afforded 2,6-diphenyl-4H-pyran-4-one (4) in 91% yield.
The reaction of diphenylpyranone 4 with trifluoromethanesulfonic anhydride in dichloromethane
did not afford the corresponding TfO-substituted pyrylium trifluoromethanesulfonate (5a), but
HO-substituted pyrylium trifluoromethanesulfonate 5b as yellow crystals in 84% yield (entry 1).
This result can be rationalized in terms of a hydrolysis of 5a during the purification, which would
afford 5b. The results stand in sharp contrast to the formation of a bipyrylium ether derivative
during the reaction between 2,6-dimethyl-4H-pyran-4-one and Tf2O reported by Stang and
co-workers.12 The reaction between pyranone 4 and TfOH also generated pyrylium
trifluoromethanesulfonate 5b (entry 2). Crystalline 5b does not show any signs of decomposition
under atmospheric conditions, and is moreover thermally stable (m.p. = 202.6–202.9 °C) under an
atmosphere of argon. The molecular structure of 5b was confirmed by a single-crystal X-ray
diffraction analysis (Figure 1). The C(2)–C(3) and C(3)–C(4) bond lengths showed 1.406(4) and
1.403(4) Å, respectively, which are shorter than those of previously reported 4H-pyrans (1.50–1.52
Å)13 and comparable to those of reported pyrylium salts (1.40–1.41 Å).10b,14 The O–C bond lengths
of 5b fall in the range of 1.356(3)–1.360(3) Å, which is quite similar to those of reported pyrylium
salts (1.35–1.36 Å).10b,14 Subsequently, the reaction of 4 with p-toluenesulfonyl chloride and
p-toluenesulfonic anhydride was examined (entries 3 and 4). Preliminarily, we confirmed that
pyranone 4 did not react with TsCl at room temperature (entry 3). Upon treating 4 with Ts2O at
1
room temperature for 2 h, the signals for 4 disappeared in the H NMR spectrum. Then, five
equivalents of sodium tetrafluoroborate were added to the reaction mixture, which afforded
pyrylium tetrafluoroborate 5c as yellow crystals in 81% yield (entry 4). Under atmospheric
conditions, crystalline pyrylium tetrafluoroborate 5f did not show any decomposition or hygroscopy.
An attempted reaction of 4 with chlorosulfonamide in the presence of aluminum chloride did not
proceed, and exclusively the substrate was recovered (entry 5). 4-(Diethylphosphoryloxy)pyrylium
salts 5d and 5e were also synthesized (entries 6–8). Although the reaction of 4 with
7

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diethylchlorophosphate did not proceed (entry 6), pyranone 4 formed pyrylium salt 5d, which bears
a phosphoyloxy group, upon treatment with diethylchlorophosphate in the presence of aluminum
chloride (entry 7). However, 5d gradually decomposed in CDCl3 to afford pyranone 4. In order to
exchange the counter anion to tetrafluoroborate, sodium tetrafluoroborate was added to the reaction
mixture after the formation of 5d (entry 8). Accordingly, pyrylium tetrafluoroborate 5e was
successfully obtained as pale yellow crystals that were relatively robust in solution and in the solid
state.
8

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Table 1. Reactions of 4H-pyran-4-one 4 with electrophiles.
entry
1
reagent(s)
solvent
CH2Cl2
conditions
rt, 1.5 h
results or product
pyrylium salt 5b
(84%, R = H, X = TfO)
Tf2O
2
3
TfOH
TsCl
CH2Cl2
CH2Cl2
rt, 2 h
pyrylium salt 5b (79%)
reflux, 48 h
no reaction
pyrylium salt 5c
(81%, R = Ts, X = BF4)
4
5
(1) Ts2O, (2) Na[BF4]
Me2NSO2Cl, AlCl3
CH2Cl2
rt, 2 h
CH3NO2
70 ºC, 24 h
no reaction
6
7
8
(EtO)2P(O)Cl
CH3NO2
CH3NO2
CH3NO2
rt, 24 h
rt, 1.5 h
rt, 1.5 h
no reaction
pyrylium salt 5d*
(R = P(O)(OEt)2, X = Cl or AlCl4)
(EtO)2P(O)Cl, AlCl3
(1) (EtO)2P(O)Cl, AlCl3,
(2) Na[BF4]
pyrylium salt 5e
(72%, R = P(O)(OEt)2, X = BF4)
* Pyrylium salt 5d gradually decomposed to afford 4H-pyran-4-one 4.
9

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Fig. 1. Molecular structure of 4-hydroxypyrylium trifluoromethanesulfonate 5b monohydrate with
thermal ellipsoids set to 50% probability. One molecule of water was omitted for clarity. Selected
bond lengths [Å] and angles [°] of 5b: O(1)–C(5) 1.356(3), O(1)–C(1) 1.360(3), C(3)–O(2)
1.309(3), C(1)–C(7) 1.474(3), C(1)–C(2) 1.352(4), C(2)–C(3) 1.406(4), C(3)–C(4) 1.403(4),
C(4)–C(5) 1.363(4), C(5)–O(1)–C(1) 121.8(2), O(2)–C(3)–C(2) 117.7(3), C(2)–C(1)–O(1) 120.0(3),
C(1)–C(2)–C(3) 120.2(3), C(4)–C(3)–C(2) 118.3(3).
10

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Finally, we attempted the synthesis of novel phosphinines from the stable pyrylium
tetrafluoroborates 5c and 5e, which bear p-toluenesulfonate and phosphoyloxy groups, respectively
(Scheme 5). After treating 5c or 5e for 12 h with P(SiMe3)3 at room temperature, an NMR
spectroscopic analysis of the reaction mixtures revealed that the formation of the corresponding
phosphinines had not occurred. Under these conditions, even the synthesis of phosphinines bearing
a p-toluenesulfonate or phosphoyloxy group from the reaction of the corresponding pyrylium
tetrafluoroborates with P(SiMe3)3 was found to be difficult.
R
R
O
O
O
P
BF4
Ph
P(SiMe3)3
CH3CN, C6H6
rt, 12 h
Ph
Ph
Ph
5c (R = Ts)
5e (R = P(O)(OEt)2)
6c (not detected)
6e (not detected)
Scheme 5. Attempted reaction of 5c or 5e with P(SiMe3)3.
11

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Synthesis of 4-Chloro- and 4-Bromopyrylium Tetrafluoroborates. The first synthesis of
4-chloropyrylium perchlorate and hexachloroantimonate was accomplished by the reaction of
4H-pyran-4-one with phosgene, reported by Föhlisch and Krockenberger.15 Later on, Razus and
co-workers synthesized 4-chloropyrylium perchlorate from the reaction of pyranone with PCl5 or
POCl3 followed by treatment with HClO4.16 Following to the literature reports for the synthesis of
chloropyrylium salts, we initially tried to synthesize 4-chloro- and 4-bromopyrylium
tetrafluoroborates via the synthetic route shown in Scheme 6. Treating pyranone 4 for 1 h with
phosphoryl chloride at room temperature, followed by the addition of H[BF4] afforded
4-chloro-2,6-diphenylpyrylium tetrafluoroborate (7) as yellow crystals in 65% yield. Similarly,
4-bromopyrylium tetrafluoroborate 8 was obtained from the reaction of 4 with phosphoryl bromide
followed by the addition of H[BF4]. Purification by decantation of the reaction mixture afforded
pure yellow crystalline of 8 in 96% isolated yield. However, we did not detect any formation of
4-bromopyrylium tetrafluoroborate 8 in the reaction between 4 and phosphorus tribromide instead
of phosphoryl bromide. Pyrylium salts 7 and 8 are thermally stable (7: m.p. = 167 °C (decomp.); 8:
m.p. = 181 °C (decomp.)) under atmospheric conditions.
12

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Scheme 6. Synthesis of 4-chloro- (7) and 4-bromopyrylium tetrafluoroborates (8).
13

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Reactions of 4-Chloro- and 4-Bromopyrylium Tetrafluoroborates. In order to examine their
reactivity, we treated 4-chloro and 4-bromopyrylium salts with nucleophiles that contain a nitrogen
or phosphorus atom (Scheme 7). The reaction of 4-chloropyrylium tetrafluoroborate 7 with an
ethanolic solution of ammonia furnished 4-aminopyridine 19 and 4H-pyran-4-one 4 in 53% and
18% yield, respectively. These results are comparable with the formation of 3-aminopyridine 12
from the reaction of 2-bromopentane-1,5-dione 1 with ammonia, which can be rationalized in terms
of a nucleophilic substitution of the chlorine atom in 7. In the case of 4-bromopyrylium
tetrafluoroborate 8, the reaction with ammonia afforded 4-aminopyridine 19 in 23%, together with
4H-pyran-4-one 4 (52%) and 4-ethoxypyridine 20 (14%), which should be the hydrolysis and
solvolysis product, respectively. Also, the formation of a 4-bromopyridine derivative could be
detected in the reaction mixture. It should be noted that chloro- and bromopyrylium
tetrafluoroborates 7 and 8 exhibit high reactivity toward ammonia, water, and ethanol.
14

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O
Cl
NH2
BF4
Ph
NH4OH
EtOH
–60 °C–rt, 4 h
Ph
O
Ph
Ph
Ph
O
Ph
Ph
N
Ph
Ph
4
(18%)
7
19
19
(53%)
Br
NH2
O
OEt
BF4
Ph
NH4OH
EtOH
–60 °C–rt, 4 h
O
N
Ph
O
Ph
Ph
N
Ph
8
4
20
(14%)
(23%)
(52%)
Scheme 7. Reactions of chloro- and bromopyrylium tetrafluoroborates 7 and 8 with ammonia.
15

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We also attempted the formation of a phosphinine framework using P(SiMe3)3 as a phosphorus
source. The reactions of 7 and 8 with P(SiMe3)3 in acetonitrile/benzene (1:1, v/v) proceeded at room
temperature, and furnished 4-chloro- (9) and 4-bromophosphines (10) in 35% and 16% isolated
yield, respectively, after chromatographic purification (Scheme 8). The 1H NMR spectra of 9 and 10
in CDCl3 showed doublet signals at 7.98 (3JPH = 5.2 Hz) and 8.12 (3JPH = 5.8 Hz) ppm, respectively,
which can be feasibly attributed to hydrogen atoms at the 3-position of the phosphinine rings. The
31P NMR spectra of 9 and 10 exhibited signals at +184.2 and +186.1 ppm, respectively, which are
slightly up-field shifted relative to those of previously reported 2,4,6-triarylphosphinines (171–172
ppm),2d,10b reflecting the electronic perturbations when connecting the halogens of 9 and 10. These
results should be of great interest for the synthesis of chloro- and bromophosphinines 9 and 10 from
the reaction of chloro- and bromopyrylium tetrafluoroborates 7 and 8 with P(SiMe)3, as compared
to more traditional synthetic methods.4–7 Cl- and Br-containing 9 and 10 thus represent fascinating
potential synthetic building blocks for new phosphorous-containing aromatics.
16

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Scheme 8. Reactions of 7 and 8 with P(SiMe3)3.
17

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Conclusions
A series of new pyrylium salts was obtained from the reactions of 2,6-diphenylpyranone 4.
Pyrylium salts bearing sulfonate and phosphonate groups were synthesized by the reactions of
pyranone 4 with sulfonic anhydride and chlorophosphate, respectively. We found that the
consecutive treatment of pyranone 4 with phosphoryl chloride or bromide and sodium
tetrafluoroborate afforded the corresponding 4-chloro- and 4-bromopyrylium tetrafluoroborates as
stable crystalline solids in good yield. Furthermore, we succeeded in synthesizing 4-chloro- and
4-bromo-2,6-diphenylphosphinines from the reactions of the corresponding chloro- and
bromopyrylium tetrafluoroborates with P(SiMe3)3. The unprecedented formation of 4-chloro- and
4-bromo-2,6-diphenylphosphinines is noteworthy not only with respect to the construction of
phosphinine frameworks from pyrylium salts and P(SiMe3)3, but also with regard to the
development of synthetic methods for halogenated phosphinines.
18

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Experimental section
General Comments. All experiments were performed under an argon atmosphere unless
otherwise noted. All solvents were purified by standard methods. Preparative thin-layer
chromatography (PTLC) was performed with Merck Kieselgel 60 PF254. 1H NMR (400 MHz) and
13C NMR (101 Hz) spectra were measured in CDCl3 or CD3CN with a Varian Mercury 400 plus or a
Bruker Avance III spectrometer using CHCl3 (δΗ = 7.26) and CDCl3 (δC = 77.0), or CHD2CN (δH
=
1
13
31
1.94) and CD3CN (δC = 1.32) as internal standards for H and C NMR spectra, respectively. P
NMR (161 MHz) and 19F NMR (376 MHz) spectra were measured in CDCl3 or CD3CN with a
Varian Mercury 400 plus or a Bruker Avance III spectrometer using 85% H3PO4 in water (δP = 0.00)
and CFCl3 (δF = 0.00) as an external standard, respectively. An assignment of the signals was
usually used by 1D (homodecoupling and DEPT) and 2D (COSY, HMQC, and HMBC) NMR
techniques. All 13C, 19F, and 31P NMR experiments were performed with broad-band 1H decoupling
unless otherwise noted. EI and ESI-TOF mass spectral data were obtained on a JEOL
JMS-GCmateII and a JEOL JMS-T100CS spectrometer, respectively. Elemental analyses were
performed by a Yanaco MT-5 CHN corder. All melting points were determined on a Yanaco micro
melting point apparatus or a Mettler Toledo MP90 melting point system, and were uncorrected.
Materials. All materials were purchased from chemical suppliers and used without further
purification
unless
otherwise
noted.
1,5-Diphenylpentane-1,3,5-trione
(18)
and
2,6-diphenyl-4H-pyran-4-one (4) were prepared according to the procedures reported in the
literatures.17
Preparation of 1,5-Diphenylpentane-1,5-dione (11). To a solution of glutaryl chloride (6.704
g, 39.67 mmol) in benzene (300 mL) was added aluminum chloride (11.54 g, 79.42 mmol) at room
temperature. After the solution was stirred at 40 ºC for 20 h, saturated ammonium chloride solution
was added to the solution. An organic layer was extracted with hexane, dried over anhydrous
sodium sulfate, filtered, evaporated to afford 1,5-diphenylpentane-1,5-dione (9.347 g, 37.05 mmol,
93%) as orange solid. 11: 1H NMR (400 MHz, CDCl3)
ArH), 7.49–7.43 (m, 4H, ArH), 3.13 (t, J = 7.0 Hz, 4H, CH3), 2.21 (quint, J = 7.0 Hz, 2H, CH3); 13C
NMR (101 MHz, CDCl3)
199.8, 136.8, 133.0, 128.6, 128.0, 37.5, 18.7; MS (EI+) m/z 252 (M+).
Bromination of
δ 8.00–7.96 (m, 4H, ArH), 7.58–7.52 (m, 2H,
δ
1,5-Diphenylpentane-1,5-dione
(11).
To
a
solution
of
19

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1,5-diphenylpentane-1,5-dione (0.503 g, 1.99 mmol) in carbon tetrachloride (15 mL) was added
molecular bromine (0.317 g, 1.98 mmol) at room temperature. After the solution was stirred at room
temperature for 1 h, water was added to the reaction mixture. An organic layer was extracted with
dichloromethane, dried over anhydrous sodium sulfate, filtered, evaporated to give orange oil.
Purification of the reaction mixture by column chromatography on silicagel (eluting with
hexane:dichloromethane = 1:1) afforded 2-bromo-1,5-diphenylpentane-1,5-dione (0.287 g, 0.857
mmol, 44%) as orange oil. 1: 1H NMR (400 MHz, CDCl3)
δ 8.07–8.05 (m, 2H, ArH), 8.01–7.98 (m,
2H, ArH), 7.63–7.55 (m, 2H, ArH), 7.52–7.46 (m, 4H, ArH), 5.49 (q, J = 7.2 Hz, 1H, CH),
3.41–3.33 (m, 1H, CH), 3.26–3.19 (m, 1H, CH), 2.70–2.63 (m, 1H, CH), 2.61–2.49 (m, 1H, CH);
13C NMR (101 MHz, CDCl3)
δ 198.8, 193.2, 136.5, 134.2, 133.8, 133.4, 129.0, 128.8, 128.7, 128.0,
47.1, 35.6, 27.8; HRMS (ESI+) m/z found 330.0248 [M+], calcd for C17H1579BrO2: 330.0255.
Reaction of 2-Bromo-1,5-diphenylpentane-1,5-dione (1) with Ammonium Acetate. To a
solution of 2-bromopentane-1,5-dione 1 (0.089 g, 0.27 mmol) in glacial acetic acid (10 mL) was
added ammonium acetate (0.042 g, 0.54 mmol) at room temperature. The solution was stirred at 50
ºC for 24 h, and cooled to room temperature. An organic layer was extracted with ether, dried over
anhydrous sodium sulfate, filtered, and evaporated under reduced pressure. Separation of the
reaction mixture by column chromatography on silicagel (eluent with dichloromethane) gave
2-amino-1,5-diphenylpentane-1,5-dione (13) (0.054 g, 0.20 mmol, 63%) as orange oil and
1
3-amino-2,6-diphenylpyridine (12) (0.010 g, 0.025 mmol, 6%) as yellow solid. 13: orange oil; H
NMR (400 MHz, CDCl3)
δ 8.14 (d, J = 7.2 Hz, 2H, ArH), 7.86 (d, J = 7.6 Hz, 2H, ArH), 7.67–7.63
(m, 1H, ArH), 7.59–7.53 (m, 3H, ArH), 7.49–7.43 (m, 2H, ArH), 5.23–5.18 (m, 1H, CH), 3.51–3.42
(m, 1H, CH2), 3.13–3.06 (m, 1H, CH2), 2.55–2.47 (m, 1H, CH2), 1.78–1.69 (m, 1H, CH2); HRMS
1
(EI+) m/z found 267.1246 [M+], calcd for C17H17NO2: 267.1259. 12: yellow solid; H NMR (400
MHz, CDCl3)
1H, CH), 7.56–7.52 (m, 2H, ArH), 7.48–7.43 (m, 3H, ArH), 7.38–7.36 (m, 1H, ArH), 7.33 (d, J =
8.4 Hz, 1H, CH) 5.47 (s, 1H, NH2); 13C NMR (101 MHz, CDCl3)
149.4, 149.3, 138.9, 136.7,
δ 8.01 (d, J = 6.8 Hz, 2H, ArH), 7.86 (d, J = 6.8 Hz, 2H, ArH), 7.64 (d, J = 7.64 Hz,
δ
129.0, 128.55, 128.52, 128.48, 128.08, 126.6, 124.7, 120.6; HRMS (EI+) m/z found 246.1142 [M+],
calcd for C17H14N2: 246.1157.
Reaction of 2-Bromo-1,5-diphenylpentane-1,5-dione (1) with Ammonia. To a solution of
20

ACCEPTED MANUSCRIPT
2-bromopentane-1,5-dione 1 (0.105 g, 0.319 mmol) in ethanol (10 mL) was added a solution of
26% ammonia (13.8 mol/L, 0.23 mL, 3.2 mmol) at 0 ºC. The solution was stirred at room
temperature for 24 h, and then an organic layer was extracted with ethyl acetate. The solution was
washed with calcium chloride solution, dried over anhydrous sodium sulfate, filtered, and
evaporated under reduced pressure to afford trans-1,2-dibenzoylcyclopropane18 (14) (0.075 g, 0.30
1
mmol, 93%) as pale red solid. 14: H NMR (400 MHz, CDCl3)
δ 8.07–8.04 (m, 2H, ArH),
7.62–7.57 (m, 4H, ArH), 7.51–7.45 (m, 2H, ArH), 3.43 (t, J = 7.2 Hz, 1H, CH), 1.82 (t, J = 7.2 Hz,
2H, CH); HRMS (EI+) m/z found 250.0980 [M+], calcd for C17H14O2: 250.0994.
Reaction of 2-Bromo-1,5-diphenylpentane-1,5-dione (1) with Tetrafluoroboric Acid and
Triphenylmethanol. To a solution of 2-bromopentane-1,5-dione 1 (0.808 g, 2.44 mmol) in acetic
anhydride (80 mL) was added a solution of tetrafluoroboric acid (1.930 g, 10.98 mmol) in acetic
anhydride (30 mL) at room temperature. The solution was stirred at 80 ºC for 24 h, and cooled to
room temperature. The reaction mixture was slowly added to a solution of cooled ether, green
precipitate generated in the cooled etheral solution. After supernatant of the suspension was
separated, the resulting brown precipitate was dried under reduced pressure to afford
1
2,6-diphenylpyrylium tetrafluoroborate (0.112 g, 0.34 mmol, 15%) as brown solids. 15: H NMR
(400 MHz, CD3CN) δ 8.94 (t, J = 8.4 Hz, 2H, CH), 8.49 (d, J = 8.4 Hz, 2H, CH), 8.36–8.34 (m, 4H,
ArH), 7.89–7.86 (m, 2H, ArH), 7.79–7.75 (m, 4H, ArH); 19F NMR (376 MHz, CD3CN)
δ
–152.3;
HRMS (ESI+) m/z 233.0982 ([M–BF4]+), calcd for C17H13O: 233.0961.
Reaction
of
2,6-Diphenylpyrylium
Tetrafluoroborate
(15)
with
Tris(trimethylsilyl)phosphine. To a solution of 2,6-diphenylpyrylium tetrafluoroborate (0.261 g,
0.815 mmol) in acetonitrile (5 mL) was added a solution of tris(trimethylsilyl)phosphine (0.205 g,
0.818 mmol) in benzene (3 mL) at room temperature. The solution was stirred at 60 ºC for 16 h, and
then cooled to room temperature. After the solution was evaporated under reduced pressure,
separation of the reaction mixture by column chromatography on silica gel (eluting with
dichloromethane) afforded 2,6-diphenyl-4H-pyran (0.114 g, 0.459 mmol, 60%) as brown solids.
16: 1H NMR (400 MHz, CDCl3)
2H, ArH), 5.43 (t, J = 3.6 Hz, 2H, CH), 3.09 (t, J = 3.6 Hz 2H, CH2); 13C NMR (101 MHz, CDCl3)
δ 7.68–7.66 (m, 4H, ArH), 7.40–7.37 (m, 4H, ArH), 7.34–7.32 (m,
δ
149.2, 134.7, 128.26, 128.14, 124.3, 96.5, 21.8; HRMS (EI+) m/z 234.1060 (M+), calcd for
21

ACCEPTED MANUSCRIPT
C17H14O: 234.1045.
Preparation of 1,5-Diphenylpentane-1,3,5-trione (18). To a solution of benzoylacetone (0.505
g, 3.08 mmol) in 1,2-dimethoxyethane (18 mL) was added sodium hydride (0.592 g, 14.8 mmol) at
room temperature. Methyl benzoate (0.540 g, 3.70 mmol) was added to the mixture at room
temperature, the solution was refluxed for 48 h, and then allowed to be cool to room temperature.
After saturated ammonium chloride solution was added to the solution, an organic layer was
extracted with ether. The layer was dried over anhydrous sodium sulfate, filtered, and dried under
reduced pressure to afford 1,5-diphenylpentane-1,3,5-trione (0.812 g, 3.05 mmol, 99%) as yellow
1
crystals. 18: mp 106–108 ºC; H NMR (400 MHz, CDCl3)
δ 14.8 (br, 1H), 7.87–7.84 (dd, J = 7.2,
1.2 Hz, 4H), 7.51–7.43 (m, 6H), 6.02 (s, 2H), 4.11 (s, 1H); MS (EI+) m/z 266 (M+).
Preparation of 2,6-Diphenyl-4H-pyran-4-one (4). 1,5-Diphenylpentane-1,3,5-trione (18) was
added to concentrated sulfuric acid at 0 ºC, the solution was stirred at 0 ºC for 20 min. The solution
was poured into a mixture of crushed ice and water. The resulting precipitate were filtered and dried
under reduced pressure to afford 2,6-diphenyl-4H-pyran-4-one (0.340 g, 1.37 mmol, 91%) as
1
colorless crystals. 4: mp 138.0–140.8 ºC (lit.17 mp 139–140 ºC); H NMR (400 MHz, CDCl3)
δ
13
7.89–7.86 (m, 4H), 7.56–7.52 (m, 6H), 6.84 (s, 2H); C NMR (101 MHz, CDCl3)
δ 180.2, 163.4,
131.4, 129.1, 125.9, 111.3, 29.6; MS (EI+) m/z 248 (M+).
Reaction of 4H-Pyran-4-one 4 with Trifluoromethanesulfonic Anhydride (Tf2O). To a
solution of 4H-pyran-4-one 4 (0.829 g, 3.34 mmol) in dichloromethane (30 mL) was added Tf2O
(1.09 g, 3.86 mmol) at room temperature. The solution was stirred at room temperature for 1.5 h,
volatile substances were removed under reduced pressure. The resulting yellow solid was washed
with ether, and the ethereal solution was dried under reduced pressure to afford 4-hydroxypyrylium
trifluoromethanesulfonate 5b (1.44 g, 2.71 mmol, 84%) as yellow solid. 5b: mp 202.6–202.9 ºC; 1H
NMR (400 MHz, CD3CN)
δ 8.19 (d, J = 8.4 Hz, 4H, ArH), 7.80–7.67 (m, 6H, ArH), 7.76 (s, 2H,
pyrylium ring); 13C NMR (101 MHz, CD3CN)
δ
179.7, 171.4, 134.8, 130.1, 129.2, 128.1, 120.3
–
19
(quartet, JFC = 157.4 Hz, CF3SO3 ), 117.6, 107.4; F NMR (376 MHz, CD3CN)
δ –79.82 (s); MS
(ESI+) m/z 249 ([M–TfO]+); Anal. Calcd for C18H13F3O5S: C, 54.27; H, 3.29%. Found C, 54.09; H,
3.56%.
Reaction of 4H-Pyran-4-one 4 with p-Toluenesulfonic Anhydride (Ts2O) and Sodium
22

ACCEPTED MANUSCRIPT
Tetrafluoroborate. To a solution of 4H-pyran-4-one 4 (0.504 g, 2.03 mmol) in dichloromethane
(15 mL) was added Ts2O (0.796 g, 2.44 mmol) at room temperature. After the reaction mixture was
stirred at room temperature for 2 h, sodium tetrafluoroborate (1.115 g, 10.15 mmol) was added to
the reaction mixture. The suspension was stirred for 1 h, and then volatile materials were removed
under reduced pressure. The resulting yellow solid was washed with ether, then the ethereal solution
was dried under reduced pressure to afford 4-(p-toluenesulfonyloxy)pyrylium tetrafluoroborate 5c
(0.673 g, 1.64 mmol, 81%) as pale yellow solid. 5c: 1H NMR (400 MHz, CDCl3)
δ 8.06 (d, J = 7.2
Hz, 4H, ArH), 7.86 (d, J = 8.4 Hz, 2H, ArH), 7.85 (s, 2H, ArH), 7.70 (t, J = 7.2 Hz, 2H, ArH), 7.66
(t, J = 7.2 Hz, 4H, ArH), 7.22 (d, J = 8.4, 2H, ArH), 2.37 (s, 3H, CH3); 13C NMR (101 MHz,
CDCl3)
δ
180.8 (C), 169.7 (C), 141.5 (C), 139.6 (C), 134.1 (CH), 129.9 (CH), 129.0 (CH), 129.0
19
(C), 127.3 (CH), 126.3 (CH), 107.8 (CH), 21.38 (CH3); F NMR (376 MHz, CDCl3)
δ –150.3 (s);
HRMS (ESI+) m/z 403.1013 ([M–BF4]+), calcd for C24H19O4S: 403.0999; Anal. Calcd for
C24H19BF4O4S: C, 58.80; H, 3.91%. Found C, 59.12; H, 4.10%.
Reaction of 4H-Pyran-4-one 4 with Diethyl Chlorophosphate and Sodium
Tetrafluoroborate. To a solution of 4H-pyran-4-one 4 (0.504 g, 2.03 mmol) in nitromethane (15
mL) was added diethyl chlorophosphate (0.720 g, 4.17 mmol) and aluminum chloride (0.544 g,
4.08 mmol) at room temperature. After the solution was stirred at room temperature for 1.5 h,
1
signals for 4H-pyran-4-one 4 disappeared in the H NMR spectrum. Sodium tetrafluoroborate
(0.890 g, 8.11 mmol) was added to the reaction mixture at room temperature. The solution was
stirred at room temperature for 24 h, and then volatile materials were removed under reduced
pressure. After the resulting yellow solid was washed with ether, the ethereal solution was dried
under reduced pressure to afford 4-(diethylphosphoryloxy)pyrylium tetrafluoroborate 5e (0.689 g,
1
1.46 mmol, 72%) as pale yellow solid. 5e: mp 97.5–99.0 ºC; H NMR (400 MHz, CD3CN)
δ 8.15
(d, J = 8.0 Hz, 4H, ArH), 7.75 (t, J = 7.2 Hz, 2H, ArH), 7.68 (t, J = 7.2, 4H, ArH), 7.61 (s, 2H, ArH),
13
4.27–4.23 (m, 4H, CH2), 2.45 (td, J = 7.6 Hz, 6H, CH3); C NMR (101 MHz, CD3CN)
δ 171.1,
19
134.9, 130.8, 130.5, 130.1, 128.5, 109.6, 67.4 (d, JPC = 7.1 Hz), 16.0 (d, JPC = 7.0 Hz); F NMR
(376 MHz, CD3CN)
–152.5 (s); 31P NMR (162 MHz, CD3CN) 3.50 (s); HRMS (ESI+) m/z
385.1189 ([M–BF4]+), calcd for C21H22O5P: 385.1199.
δ
δ
Preparation of 4-Chloropyrylium Tetrafluoroborate 7. To a solution of 4H-pyran-4-one 4 (1.036
23

ACCEPTED MANUSCRIPT
g, 4.17 mmol) in nitromethane (30 mL) was added phosphoryl chloride (0.76 mL, 8.2 mmol) at
room temperature. After the solution was stirred at room temperature for 1 h, tetrafluoroboric acid
in ether solution (1.18 g/mL, 1.30 mL, 10.3 mmol) was added to the reaction mixture. The solution
was stirred at room temperature for 1 h, and then dropwisely poured into cooled ether. The resulting
precipitate was filtered, washed with cooled ether, and dried under reduced pressure to afford
4-chloropyrylium tetrafluoroborate 7 (0.961 g, 2.71 mmol, 65%) as yellow crystals. 7: mp 166.9 ºC
(decomp.); 1H NMR (400 MHz, CD3CN)
δ
8.60 (s, 2H), 8.33 (d, J = 7.8 Hz, 4H), 7.90 (t, J = 7.6 Hz,
19
13
2H), 7.77 (t, J = 7.8 Hz, 4H); F NMR (376 MHz, CD3CN)
δ
–152.2 (s); C NMR (101 MHz,
CD3CN)
δ
172.74, 167.56, 137.4, 131.3, 130.1, 128.8, 121.1; MS (ESI+) m/z 267 ([M–BF4]+); Anal.
Calcd for C17H12BClF4O: C, 57.59; H, 3.41%. Found C, 57.35; H, 3.58%.
Preparation of 4-Bromopyrylium Tetrafluoroborate 8. To a solution of 4H-pyran-4-one 4
(0.202 g, 0.814 mmol) in nitromethane (15 mL) was added phosphoryl bromide (0.469 g, 1.64
mmol) at room temperature. After the solution was stirred at room temperature for 2 h,
tetrafluoroboric acid in ether solution (1.18 g/mL, 0.50 mL, 3.4 mmol) was added to the reaction
mixture. The solution was stirred at room temperature for 18 h, and then dropwisely poured into
cooled ether. The resulting precipitate was filtered, washed with cooled ether, and dried under
reduced pressure to afford 4-bromopyrylium tetrafluoroborate 8 (0.308 g, 0.772 mmol, 96%) as
1
yellow crystals. 8: mp 181 ºC (decomp.); H NMR (400 MHz, CD3CN) δ 8.81 (s, 2H, pyrylium
ring), 8.34 (d, J = 7.4 Hz, 4H, ArH), 7.89 (t, J = 7.4 Hz, 2H, ArH), 7.79 (t, J = 7.4 Hz, 4H, ArH);
19
13C NMR (101 MHz, DMSO-d6)
δ
179.0, 162.5, 131.5, 131.0, 129.2, 126.1, 110.9; F NMR (376
MHz, CD3CN)
331.0066.
δ
–152.2 (s); HRMS (ESI+) m/z 331.0055 ([M–BF4]+), calcd for C17H1279BrO:
Reaction of 4-Chloropyrylium Tetrafluoroborate 7 with Ammonia. To a solution of
4-chloropyrylium tetrafluoroborate 7 (0.300 g, 0.846 mmol) in ethanol (16 mL) was added 26%
ammonia solution (13.8 mol/L, 0.61 mL, 8.5 mmol) at –60 ºC. The solution was stirred at –60 ºC to
room temperature for 16 h. An organic layer was extracted with ethyl acetate, washed with brain,
dried over anhydrous sodium sulfate, and filtered. The layer was evaporated and purified by PTLC
(eluent with hexane and dichloromethane) to afford 4H-pyran-4-one 4 (0.038 g, 0.15 mmol, 18%)
1
and 4-aminopyridine 19 (0.111 g, 0.451 mmol, 53%). 19 (4-aminopyridine): H NMR (400 MHz,
24

ACCEPTED MANUSCRIPT
CDCl3)
δ
8.06 (d, J = 7.2 Hz, 4H, ArH), 7.46 (t, J = 7.4 Hz, 4H, ArH), 7.40 (t, J = 7.4 Hz, 2H, ArH),
6.96 (s, 2H, ArH), 4.34 (br, 2H, NH2); 13C NMR (101 MHz, CDCl3)
δ 157.64, 154.13, 139.67,
128.76, 128.48, 126.95, 105.07; HRMS (EI+) m/z 246.1170 (M+), calcd for C17H14N2: 246.1162.
Reaction of 4-Bromopyrylium Tetrafluoroborate 8 with Ammonia. To a solution of
4-bromopyrylium tetrafluoroborate 8 (0.206 g, 0.516 mmol) in ethanol (10 mL) was added 26%
ammonia solution (13.8 mol/L, 0.18 mL, 2.5 mmol) at –60 ºC. The solution was stirred at –60 ºC to
room temperature for 24 h. An organic layer was extracted with ethyl acetate, washed with brain,
dried over anhydrous sodium sulfate, and filtered. The layer was evaporated and purified by PTLC
(eluent with hexane and dichloromethane) to afford 4-ethoxypyridine 20 (0.017 g, 0.073 mmol,
14%), 4H-pyran-4-one 4 (0.070 g, 0.27 mmol, 52%), and 4-aminopyridine 19 (0.029 g, 0.12 mmol,
23%). 20: brown crystals; mp 73.6–74.9 ºC; 1H NMR (400 MHz, CDCl3)
ArH), 7.49 (t, J = 7.2 Hz, 4H, ArH), 7.42 (t, J = 7.2 Hz, 2H, ArH), 7.21 (s, 2H, ArH), 4.23 (q, J =
7.2 Hz, 2H, OEt), 1.51 (t, J = 7.2 Hz, 3H, OEt); 13C NMR (101 MHz, CDCl3)
166.6 , 158.5, 139.7,
δ 8.12 (d, J = 6.8 Hz, 4H,
δ
128.9, 128.6, 127.0, 105.3, 63.58, 14.60; HRMS (EI+) m/z 275.1302 (M+), calcd for C19H17NO:
275.1310.
Preparation of Tris(trimethylsilyl)phosphine.19 Sodium (3.96 g, 172 mmol) and potassium
(5.26 g, 135 mmol) were added to 1,2-dimethoxyethane (200 mL) at room temperature, and the
suspension was refluxed for 1 h (Color of the suspension was changed to purple). After the
suspension allowed to be cool to room temperature, red phosphorus (3.12 g, 101 mmol) was added
to the suspension at room temperature. The reaction mixture was refluxed for 4.5 h, and then cooled
down to room temperature. After a solution of Me3SiCl (42.0 mL, 330 mmol) in
1,2-dimethoxyethane (50 mL) was added to the reaction mixture at room temperature (Color of the
suspension was changed to gray), the resulting suspension was refluxed for 1 h. After the
suspension allowed to cool to room temperature, volatile substances were removed under reduced
pressure. Hexane (3 x 50 mL) was added to the reaction mixture, and the hexane solution was
filtered through a pad of celite. Volatile substances was removed under reduced pressure to afford
1
3
P(SiMe3)3 (13.9 g, 55.5 mmol, 55%) as colorless oil. H NMR (400 MHz, C6D6)
δ 0.31 (d, JHP =
31
4.4 Hz, CH3); P NMR (162 MHz, C6D6)
δ –252.3 (s). Caution: P(SiMe3)3 ignites spontaneously
under atmospheric conditions.
25

ACCEPTED MANUSCRIPT
Preparation of 4-Chlorophosphinine 9. To a solution of 4-chloropyrylium tetrafluoroborate
7 (0.502 g, 1.42 mmol) in acetonitrile (50 mL) was added a solution of tris(trimethylsilyl)phosphine
(0.530 g, 2.12 mmol) in benzene (5 mL) at room temperature. The solution was stirred at room
temperature for 3 h. Purification of the reaction mixture by column chromatography on silicagel
(eluent with dichloromethane:hexane = 1:1) gave 4-chlorophosphinine 9 (0.014 g, 0.050 mmol,
1
35%) as yellow crystals. 9: mp 213–214 ºC; H NMR (400 MHz, CDCl3)
δ
7.98 (d, JPH = 5.2 Hz,
13
2H, phosphinine ring) 7.68 (d, JHH = 7.6 Hz, 4H, ArH) 7.50–7.43 (m, 6H, ArH); C NMR (101
MHz, CDCl3)
δ
172.8 (d, JPC = 54.3 Hz), 142.1 (d, JPC = 24.2 Hz), 137.1 (d, JPC = 15.1 Hz), 132.0
31
(d, JPC = 12.8 Hz), 129.0 (s), 128.4 (d, JPC = 1.0 Hz), 126.1 (s); P NMR (162 MHz, CDCl3)
184.2 (s); HRMS (EI+) m/z 282.0382 (M+), calcd for C17H12ClP: 282.0375.
δ
Preparation of 4-Bromophosphinine 10. To a solution of 4-bromopyrylium tetrafluoroborate 8
(0.213 g, 0.534 mmol) in acetonitrile (40 mL) was added a solution of tris(trimethylsilyl)phosphine
(0.251 g, 1.00 mmol) in benzene (5 mL) at room temperature. The solution was stirred at room
temperature for 3 h. Purification of the reaction mixture by column chromatography on silicagel
(eluent with dichloromethane) afforded 4-bromophosphinine 10 (0.028 g, 0.086 mmol, 16%) as
1
brown crystals. 10: 110.5 ºC (decomp.); H NMR (400 MHz, CDCl3)
δ 8.12 (d, JPH = 5.8 Hz, 2H,
phosphinine ring), 7.73 (d, JHH = 8.0 Hz, 4H, ArH), 7.54–7.49 (m, 4H, ArH), 7.47–7.44 (m, 2H,
ArH); 13C NMR (101 MHz, CDCl3)
172.2 (d, JPC = 52.3 Hz), 143.2 (d, JPC = 24.2 Hz), 142.9 (d,
JPC = 13.1 Hz), 131.3 (d, JPC = 12.1 Hz), 129.0 (s), 128.1 (d, JPC = 1.0 Hz), 126.1 (s); 31P NMR (162
MHz, CDCl3)
186.1 (s); HRMS (EI+) m/z 325.9869 (M+), calcd for C17H1279BrP: 325.9860.
δ
δ
X-Ray Crystallographic Analysis of 4-Hydroxypyrylium Trifluoromethanesulfonate 5b.
Single crystals of 4-hydroxypyrylium trifluoromethanesulfonate 5b were obtained by slow
recrystallization from dichloromethane solution at room temperature. The intensity data were
collected on a Rigaku Saturn CCD system with graphite-monochromated Mo Kα radiation (λ =
0.71070 Å). Selected structural parameters and crystal data of 5b are shown in Tables 2 and S1–S3
(in the Supplementary Data), respectively. The structure was solved by direct method
(SHELXS-97)20 and refined by full-matrix least-squares procedures on F2 for all reflections
(SHELXL-97).21 All non-hydrogen atoms were refined anisotropically. All hydrogen atoms were
placed using AFIX instructions. Crystallographic data reported in this manuscript have been
26

ACCEPTED MANUSCRIPT
deposited with Cambridge Crystallographic Data Centre as supplementary publication No.
CCDC-1532041. Copies of the data can be obtained free of charge via
www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data Centre,
12, Union Road, Cambridge, CB2 1EZ, UK; fax: +44 1223 336033; or deposit@ccdc.cam.ac.uk).
Acknowledgments
This work was partially supported by funds (no 161041) from the Central Research Institute of
Fukuoka University, the Collaborative Research Program of Institute for Chemical Research, Kyoto
University (grant Nos. 2016-96 and 2017-101), and Grant-in-Aid for Scientific Research (C) (No.
JP16K05709) from the Ministry of Education, Culture, Sports, Science and Technology, Japan.
Supplementary data
Supplementary data related to this article can be found at XXX.
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