One-pot synthesis of a-monosubstituted pyridiniums from corresponding pyrylium salts

Article abstract of DOI:10.1080/00397911.2010.525775

α-monosubstituted pyridiniums were readily prepared by the one-pot reaction oftheir corresponding pyrylium salts and primary amines. This result shows that such kindof pyridiniums can be prepared via this route. It was proved that the number of phenyl gro

Full text of DOI:10.1080/00397911.2010.525775

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One-Pot Synthesis of α-Monosubstituted
Pyridiniums from Corresponding
Pyrylium Salts
Gang Li a , Wei-Tao Gong a , Jun-Wei Ye a , Yuan Lin a & Gui-Ling Ning
a
a State Key Laboratory of Fine Chemicals, Dalian University of
Technology , Dalian , China
Accepted author version posted online: 29 Jul 2011.Published
online: 17 Oct 2011.
To cite this article: Gang Li , Wei-Tao Gong , Jun-Wei Ye , Yuan Lin & Gui-Ling Ning (2012) One-
Pot Synthesis of α-Monosubstituted Pyridiniums from Corresponding Pyrylium Salts, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry,
42:4, 480-486, DOI: 10.1080/00397911.2010.525775
To link to this article: http://dx.doi.org/10.1080/00397911.2010.525775
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Synthetic Communications1, 42: 480–486, 2012
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.525775
ONE-POT SYNTHESIS OF a-MONOSUBSTITUTED
PYRIDINIUMS FROM CORRESPONDING PYRYLIUM
SALTS
Gang Li, Wei-Tao Gong, Jun-Wei Ye, Yuan Lin, and
Gui-Ling Ning
State Key Laboratory of Fine Chemicals, Dalian University
of Technology, Dalian, China
GRAPHICAL ABSTRACT
Abstract a-monosubstituted pyridiniums were readily prepared by the one-pot reaction of
their corresponding pyrylium salts and primary amines. This result shows that such kind
of pyridiniums can be prepared via this route. It was proved that the number of phenyl
groups at the pyrylium ring had a crucial effect on this one-pot synthetic route.
Keywords a-Monosubstituted pyridiniums; one-pot synthesis; primary amines; pyrylium
salts
INTRODUCTION
Pyridiniums have wide applications in many fields, including chemistry,
biology, and materials science.[1] Accordingly, their synthesis is always the focus
for many organic chemists. Until now, several synthetic routes to various pyridi-
niums have been developed, including the well-known Menschutkin reaction and
Zincke reaction.[2] Additionally, the reaction of pyrylium salts with primary amines
is an important and widely used synthetic method to corresponding pyridiniums,
which allows a wide variation of pyrylium salts and primary amine structures.[3]
Received January 21, 2010.
Address correspondence to Gui-Ling Ning and Wei-Tao Gong, State Key Laboratory of Fine
Chemicals, Dalian University of Technology, Dalian 116012, China. E-mail: ninggl@dlut.edu.cn;
wtgong@dlut.edu.cn
480

a-MONOSUBSTITUTED PYRIDINIUMS
481
Scheme 1. Complex two-step synthetic route to a-monosubstituted pyridiniums.
In this field, Katritzky and coworkers did systematic studies of the factors affecting the
conversion of pyrylium to pyridinium salts and the detailed mechanism kinetics.[4]
However, when they tried the reaction of a-monosubstituted pyrylium salts (2,4-
diphenylsubstituted pyrylium salt) with primary amines, only ring-opened products
were formed and no expected a-monosubstituted pyridiniums were obtained.[5]
Accordingly, they concluded that such kind of pyridiniums could not be prepared
directly from their pyrylium precursors and successful conversion must require the pres-
ence of a,a0-substituents simultaneously.[6] As a result, to prepare a-monosubstituted
pyridiniums, a more complex synthetic route will have to be utilized (Scheme 1).
In our studies on pyrylium salts, we have successfully prepared two novel a-
monosubstituted pyrylium salts, namely 2,4,5-triphenyl pyrylium salts and
2,3,4,5-tetraphenyl pyrylium salts, from aerobic oxidation of multiphenyl substituted
cyclopentadienes.[7] To test the possibility of converting them to their corresponding
a-unsubstituted pyridiniums, we tried to react them with various primary amines
(Scheme 2). Surprisingly, in our case, a-monosubstituted pyridiniums were obtained
smoothly in excellent yields, which is in contrast to Katritzky’s conclusion.[5] The
biggest difference between our case and Katritzky’s case is the number of phenyl
groups on the pyrylium ring, indicating some positively steric and electronic effects
for the transformation we reported here. Detailed studies of this issue are ongoing in
our laboratory. Anyway, the realization of this transformation provided an efficient
one-pot synthetic route to a-monosubstituted pyridiniums.
All results, including primary amines selected, reaction times, and the yields of
pyridiniums, are summarized in Table 1.
Scheme 2. One-pot synthetic route to a-monosubstituted pyridiniums from pyrylium precursors.

482
G. LI ET AL.
Table 1. One-pot synthesis of a-monosubstituted pyridiniums from pyrylium precursors and various
primary amines
Entry
R1
R2
Time (h)
Product
Yield (%)
1
2
H
H
p-(NH2)C6H4
p-[4-(NH2)C6H4]C6H4
p-(Cl)C6H4
6
18
4
3a
3b
3c
3d
3e
3f
89
87
74
70
88
86
81
70
68
84
3
H
4
H
p-(Br)C6H4
p-C5H3N
5
5
H
4.5
8
6
C6H5
C6H5
C6H5
C6H5
C6H5
p-(NH2)C6H4
p-[4-(NH2)C6H4]C6H4
p-(Cl)C6H4
7
24
6
3g
3h
3i
8
9
10
p-(Br)C6H4
p-C5H3N
9
7.5
3j
We should mention that this synthetic route shows a wide variation of primary
amine structures from electron-withdrawing halogen substituents to electron-
donating pyridinyl and aminophenyl substituents. Most of investigated primary
amines gave rather satisfactory yields just as shown in Table 1. More important,
all of the selected primary amines have been modified with various functional groups
to be readily transferred into other functional compounds. We can do coupling reac-
tion with halogen substituents,[8] condensation with amino moiety,[9] and coordi-
nation with metal using pyridine fragment.[10]
In summary, 10 a-monosubstituted pyridiniums modified with reactive amino-,
pyridinyl-, and halogen functional groups were prepared by one-pot reactions of pyr-
ylium precursors with primary amines. This route was thought to be impossible and
our result proved otherwise. In fact, the number of phenyl groups on the pyrylium
ring played a crucial role in this one-pot transformation. Undoubtedly, the realiza-
tion of this one-pot transformation provided a more efficient and mild synthetic
route to a-monosubstituted pyridiniums.
EXPERIMENTAL
Infrared (IR) spectra were recorded on a Jasco Fourier transform (FT)–IR-460
Plus spectrometer. 1H and 13C NMR spectra were performed on a Varian Inova 400
spectrometer using tetramethylsilane (TMS) as internal standard. API mass spectra
were recorded on HP1100 high performance liquid chromatography=mass selective
detector (HPLC=MSD) spectrometer. High-resolution mass spectra (HRMS) elec-
trospray ionization (ESI) was carried out on a UPLC-Q-ToF MS spectrometer.
Elemental analyses were meaured on a Vario EL III elemental analyzer.
2,4,5-Triphenylpyrylium and 2,3,4,5-tetraphenylpyrylium perchlorate were
synthesized according to our previously reported paper.[7b] Other chemical reagents
were used as received without further purification.
General Procedure
A solution of pyrylium perchlorate 1 (0.49 mmol), primary amine 2
(0.59 mmol), and triethylamine (50 mg, 0.49 mmol) in 15 mL dichloromethane was

a-MONOSUBSTITUTED PYRIDINIUMS
483
stirred at room temperature. After 20 min, acetic acid (59 mg, 0.98 mmol) was added
into this solution. When thin-layer chromatography (TLC) showed the complete
conversion of 1, dichloromethane was concentrated under reduced pressure to
2–3 mL. To this solution, 30 mL diethyl ether was poured and the precipitate was
formed. The filtered precipitate was washed by diethyl ether (3 ꢀ 10 mL) and dried
to give pure target a-monosubstituted pyridiniums.
Spectral Data
1-(4-Aminophenyl)-2,4,5-triphenylpyridinium perchlorate (3a). IR (KBr)
v: 3468, 3377 (NH2), 1623 (C N), 1092, 621 (ClO4 ) cmꢁ1; H NMR (400 MHz,
1
ꢁ
=
CD3CN): d ¼ 8.72 (s, 1H, PyH), 8.09 (s, 1H, PyH), 7.31–7.56 (m, 15H, ArH), 7.11
(d, 2H, J ¼ 8.8 Hz, ArH), 6.59 (d, 2H, J ¼ 8.8 Hz, ArH), 4.64 (s, 2H, NH2); 13C
NMR (100 MHz, CD3CN): d ¼ 157.9, 154.9, 151.1, 147.8, 139.6, 136.45, 134.8,
133.2, 131.9, 131.8, 131.6, 131.2, 130.8, 130.5, 130.2, 129.8, 129.7, 129.6, 128.4,
114.5; MS (API-ES) m=z: 399.1 (Mþ); HRMS (ESI) calcd. for C29H23N2 (Mþ)
399.1816; found 399.1876.; Anal. calcd. for C29H23N2O4Cl: C, 69.81; H, 4.65; N,
5.61. Found: C, 69.71; H, 4.53; N, 5.78.
1-(4’-Amino-4-biphenylyl)-2,4,5-triphenylpyridinium perchlorate (3b). IR
ꢁ1
;
1H NMR
ꢁ
=
(KBr) v: 3464, 3368 (NH2), 1623 (C N), 1095, 623 (ClO4 ) cm
(400 MHz, CD3CN): d ¼ 8.83 (s, 1H, PyH), 8.18 (s, 1H, PyH), 7.63 (d, 2H,
J ¼ 8.4 Hz, ArH), 7.30–7.54 (m, 19H, ArH), 6.70 (d, 2H, J ¼ 8.4 Hz, ArH), 4.38 (s,
2H, NH2); 13C NMR (100 MHz, CD3CN): d ¼ 158.7, 154.9, 149.9, 147.6, 144.4,
140.3, 139.8, 136.4, 134.7, 132.8, 132.0, 131.9, 131.6, 131.4, 130.9, 130.8, 130.7,
130.6, 130.3, 129.9, 129.8, 129.5, 129.2, 129.1, 128.8, 128.5, 127.9, 127.7, 127.4,
127.1, 116.1, 115.7; MS (API-ES) m=z: 475.1 (Mþ); HRMS (ESI) calcd. for
C35H27N2 (Mþ) 475.2174; found 475.2182. Anal. calcd. for C35H27N2O4Cl: C,
73.10; H, 4.73; N, 4.87. Found: C, 72.92; H, 4.88; N, 4.72.
1-(4-Chlorophenyl)-2,4,5-triphenylpꢁyridinium perchlorate (3c). IR (KBr)
v: 1621 (C N), 1016 (Ar-Cl), 1095, 620 (ClO4 ) cmꢁ1; 1H NMR (400 MHz, CD3CN):
=
d ¼ 8.78 (s, 1H, PyH), 8.17 (s, 1H, PyH), 7.30–7.56 (m, 19H, ArH); 13C NMR
(100 MHz, CD3CN): d ¼ 159.4, 155.0, 147.5, 141.2, 140.0, 137.5, 136.4, 134.8,
132.5, 132.1, 132.0, 131.5, 131.1, 131.0, 130.9, 130.7, 130.5, 130.0, 129.9, 129.6;
MS (API-ES) m=z: 418.0 (Mþ); HRMS (ESI) calcd. for C29H21NCl (Mþ)
418.1363; found 418.1372. Anal. calcd. for C29H21NO4Cl2: C, 67.19; H, 4.08; N,
2.70. Found: C, 67.42; H, 3.92; N, 2.84.
1-(4-Bromophenyl)-2,4,5-triphenylpyridinium
perchlorate
(3d). IR
(KBr) v: 1623 (C N), 1013 (Ar-Br), 1096, 621 (ClO4 ) cmꢁ1; H NMR (400 MHz,
CD3CN): d ¼ 8.781 (s, 1H, PyH), 8.164 (s, 1H, PyH), 7.24–7.70 (m, 19H, ArH);
13C NMR (100 MHz, CD3CN): d ¼ 159.0, 154.8, 147.3, 141.5, 139.7, 136.2, 134.5,
133.8, 132.3, 132.0, 131.5, 131.0, 130.8, 130.6, 130.4, 130.0, 129.9, 129.8, 129.6,
125.5; MS (API-ES) m=z: 464.0 (Mþ); HRMS (ESI) calcd. for C29H21NBr (Mþ)
462.0857; found 462.0873. Anal. calcd. for C29H21NO4ClBr: C, 61.88; H, 3.76; N,
2.49. Found: C,62.05; H, 3.62; N, 2.35.
1
ꢁ
=

484
G. LI ET AL.
1-(4-Pyridyl)-2,4,5-triphenylpyridinium perchlorate (3e). IR (KBr) v:
1
1626 (C N), 1578, 1521, 1483, 1454 (C5H4N), 1096, 621 (ClO4 ) cmꢁ1; H NMR
(400 MHz, CD3CN): d ¼ 8.79 (s, 1H, PyH), 8.71 (d, 2H, J ¼ 6.0 Hz, PyH), 8.22 (s,
1H, PyH), 7.38–7.58 (m, 17H, ArH & PyH); 13C NMR (100 MHz, CD3CN):
d ¼ 159.8, 154.6, 152.7, 149.3, 147.0, 140.2, 136.4, 134.7, 132.3, 132.2, 132.1, 131.6,
131.2, 131.0, 130.7, 130.5, 130.0, 129.9, 122.5; MS (API-ES) m=z: 385.1 (Mþ);
HRMS (ESI) calcd. for C28H21N2 (Mþ) 385.1705; found 385.1722. Anal. calcd.
for C28H21N2O4Cl: C, 69.35; H, 4.36; N, 5.78. Found: C, 69.12; H, 4.48; N, 5.92.
ꢁ
=
1-(4-Aminophenyl)-2,3,4,5-tetraphenylpyridinium perchloꢁra1 te (3f). IR
;
1H NMR
ꢁ
=
(KBr) v: 3463, 3370 (NH2), 1628 (C N), 1089, 622 (ClO4 ) cm
(400 MHz, CD3CN): d ¼ 8.82 (s, 1H, PyH), 6.78–7.45 (m, 22H, ArH), 6.52 (d, 2H,
J ¼ 8.8 Hz, ArH), 4.55 (s, 2H, NH2); 13C NMR (100 MHz, CD3CN): d ¼ 158.6,
155.2, 150.8, 145.9, 143.3, 141.1, 136.3, 135.9, 135.3, 132.8, 131.5, 131.4, 130.9,
130.5, 130.3, 129.9, 129.5, 129.3, 129.1, 128.7, 128.5, 128.4, 117.9, 114.5; MS
(API-ES) m=z: 475.2 (Mþ); HRMS (ESI) calcd. for C35H27N2 (Mþ) 475.2174; found
475.2155. Anal. calcd. for C35H27N2O4Cl: C,73.10; H, 4.73; N, 4.87. Found: C,72.92;
H, 4.86; N, 4.70.
1-(4’-Amino-4-biphenylyl)-2,3,4,5-tetraphenylpyridinium
=
(3g). IR (KBr) v: 3470, 3371(NH2), 1623 (C N), 1093, 621 (ClO4 ) cm
perchlorate
ꢁ1
;
1H
ꢁ
NMR(400 MHz, CD3CN): d ¼ 8.89 (s, 1H, PyH), 6.90–7.66 (m, H, ArH), 6.68 (d,
2H, J ¼ 8.4 Hz, ArH), 4.36 (s, 2H, NH2); 13C NMR (100 MHz, CD3CN):
d ¼ 159.6, 154.8, 149.8, 145.5, 145.3, 144.1, 143.5, 141.3, 141.0, 136.2, 135.7, 135.3,
132.4, 131.7, 131.5, 131.2, 131.0, 130.8, 130.7, 130.6, 130.4, 130.0, 129.8, 129.5,
129.4, 128.8, 128.7, 128.5, 128.0, 127.7, 127.1, 126.2, 115.7, 115.6; MS (API-ES)
m=z: 551.2 (Mþ); HRMS (ESI) calcd. for C41H31N2 (Mþ) 551.2487; found
551.2470. Anal. calcd. for C41H31N2O4Cl: C, 75.63; H, 4.80; N, 4.30. Found: C,
75.89; H, 4.67; N, 4.12.
1-(4-Chlorophenyl)-2,3,4,5-tetraphenylpyridinium perchlorate (3h). IR
1
(KBr) v: 1610 (C N), 1022 (Ar-Cl), 1090, 622 (ClO4 ) cmꢁ1; H NMR (400 MHz,
ꢁ
=
CD3CN): d ¼ 8.85 (s, 1H, PyH), 6.86–7.62 (m, 24H, ArH); 13C NMR(100 MHz,
CD3CN): d ¼ 159.5, 154.5, 145.3, 143.3, 141.7, 141.2, 136.9, 136.2, 135.6, 135.2,
132.1, 131.4, 130.9, 130.5, 130.4, 130.3, 129.8, 129.5, 129.4, 129.3, 128.8, 128.7,
128.6, 128.5; MS (API-ES) m=z: 494.2 (Mþ); HRMS (ESI) calcd. for C35H25NCl
(Mþ) 494.1676; found 494.1659. Anal. calcd. for C35H25NO4Cl: C, 70.71; H, 4.24;
N, 2.36. Found: C, 70.42; H, 4.41; N, 2.24.
1-(4-Bromophenyl)-2,3,4,5-tetraphenylpyridinium perchlorate (3i). IR
1
(KBr) v: 1608 (C N), 1018 (Ar-Br), 1086, 622 (ClO4 ) cmꢁ1; H NMR (400 MHz,
ꢁ
=
CD3CN): d ¼ 8.85 (s, 1H, PyH), 6.80–7.63 (m, 24H, ArH); 13C NMR (100 MHz,
CD3CN): d ¼ 159.7, 154.6, 145.3, 143.5, 142.3, 141.3, 136.2, 135.7, 135.3, 133.5,
132.2, 131.5, 131.0, 130.6, 130.0, 129.8, 129.4, 129.3, 128.9, 128.8, 128.7, 128.5,
125.1,; MS (API-ES) m=z: 538.0 (Mþ); HRMS (ESI) calcd for C35H25NBr (Mþ)
538.1170; found 538.1149. Anal. calcd. for C35H25NO4ClBr: C, 65.79; H, 3.94; N,
2.19. Found: C, 66.01; H, 3.78; N, 2.36.

a-MONOSUBSTITUTED PYRIDINIUMS
485
1-(4-Pyridyl)-2,3,4,5-tetraphenylpyridinium perchlorate (3j). IR (KBr) v:
1607 (C N), 1577, 1533, 1492, 1457 (C5H4N), 1094, 620 (ClO4 ) cmꢁ1; H NMR
1
ꢁ
=
(400 MHz, CD3CN): d ¼ 8.86 (s, 1H, PyH), 8.65 (d, 2H, J ¼ 6.0 Hz, PyH), 7.52 (d,
2H, J ¼ 6.0 Hz, PyH), 6.96–7.40 (m, 20H, ArH); 13C NMR (100 MHz, CD3CN):
d ¼ 160.0, 154.0, 152.3, 149.7, 144.7, 143.5, 141.5, 136.0, 135.4, 135.0, 131.6, 131.5,
131.4, 130.9, 130.4, 129.9, 129.4, 128.9, 128.8, 128.7, 128.5, 122.4; MS (API-ES)
m=z: 461.1 (Mþ); HRMS (ESI) calcd. for C34H25N2 (Mþ) 461.2018; found
461.2032. Anal. calcd. for C34H25N2O4Cl: C, 72.79; H, 4.49; N, 4.99. Found: C,
72.58; H, 4.62; N, 4.85.
ACKNOWLEDGMENTS
This research has been supported by the National Natural Science Foundation
of China (20772014 and 20923006) and the Fundamental Research Funds for the
Central Universities (1000-893116).
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