BF3·Et2O-mediated intramolecular cyclization of unsaturated amides: Convenient synthesis of dihydroquinolin-2-one-BF 2 complexes

Article abstract of DOI:10.1039/c4ra06151a

A facile and efficient synthesis of substituted dihydropyridone-BF ₂ complexes is developed via intramolecular cyclization of α-acyl acrylamides and α-acyl cinnamamides mediated by BF ₃·Et₂O. This journal is the Partner Or

Full text of DOI:10.1039/c4ra06151a

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BF3$Et2O-mediated intramolecular cyclization of
unsaturated amides: convenient synthesis of
dihydroquinolin-2-one-BF2 complexes†
Cite this: RSC Adv., 2014, 4, 36234
*
Xu Liu, Qian Zhang, Xiaoqing Xin, Rui Zhang, Ning Zhang, Yongjiu Liang
Received 24th June 2014
Accepted 7th August 2014
*
and Dewen Dong
DOI: 10.1039/c4ra06151a
A
facile and efficient synthesis of substituted dihydropyridone–BF2 complexes is developed via
www.rsc.org/advances
intramolecular cyclization of a-acyl acrylamides and a-acyl cinnamamides mediated by BF3$Et2O.
During the course of our studies on the synthesis of
heterocycles based on b-oxo amide derivatives, we developed
Introduction
the synthesis of a variety of substituted pyridin-2(1H)-ones
under Vilsmeier conditions.18 Most recently, we achieved the
synthesis of indeno[2,1-c]quinolin-6(7H)-ones from a-acyl cin-
namamides mediated by PPA (eqn (1), Scheme 1),19 divergent
synthesis of quinolin-2(1H)-ones (eqn (2), Scheme 1)20 and
pyridin-2(3H)-ones (eqn (3), Scheme 1) from 2-acyl penta-2,4-
dienamides.21 Encouraged by the previous work, we are inter-
ested to examine the reaction behaviors of unsaturated amides
toward BF3$Et2O. By this research, we developed a facile and
convenient synthesis of dihydropyridone–BF2 complexes under
very mild conditions. Herein, we will report our experimental
results and present a proposed mechanism involved in the
cyclization reactions.
Over the past decades, pyridin-2(1H)-ones and their analogues
have attracted considerable attention in chemical and biolog-
ical elds.1,2 These structural motifs can serve as efficient
catalysts in a variety of proton-dependent reactions3 and as
valuable ligands in coordination chemistry.4 Furthermore, pyr-
idin-2(1H)-ones are versatile intermediates in the synthesis of a
wide range of aza-heterocycles, such as pyridines, piperidines,
indolizidines, quinolines and quinolizidines.5,6 In particular,
pyridin-2(1H)-one is a key unit in numerous natural products
and synthetic organic compounds such as elfamycin, cerpegin
and camptothecin,7 along with diverse bio-, physio- and phar-
macological activities. To date, a variety of synthetic approaches
have been well established to access pyridin-2(1H)-ones and
their analogues, which comprise the modication of the pre-
constructed heterocyclic ring by pyridinium salt chemistry8
and N-alkylation,9 the construction of heterocyclic skeletons
from appropriately substituted open-chain precursors via
metal-catalyzed sp2 C–H bond amination,10 ring closing
metathesis,11 and Diels–Alder reaction.12
On the other hand, organoboron compounds have emerged
as one of the most important class of organic complexes for
their excellent photophysical properties and potential use in
molecular sensors,13 biomolecular probes14 and optoelectronic
devices.15 Among those reported work, b-dicarbonyl compounds
are most used ligands, and the boron diuoride b-diketonates
have been extensively investigated and their promising lumi-
nescence make them good candidates for optical imaging and
sensing applications.16,17
Results and discussion
The substrates, unsaturated amides, were prepared by Knoe-
venagel condensation of commercially available b-oxo amides
with aryl aldehydes in the presence of piperidine and acetic acid
Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun,
130022, China. E-mail: ning.zhang@ciac.ac.cn; dwdong@ciac.ac.cn; Fax: +86 431
85262740; Tel: +86 431 85262676
† Electronic supplementary information (ESI) available: Experimental details,
spectral and analytical data, copies of 1H NMR and 13C NMR spectra for new
compounds 1–3 and 5, and CIF les for 2g and 5d. CCDC 922666 and 938933.
For ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c4ra06151a
Scheme 1 Reactions of a,b-unsaturated amides.
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in good yields according to reported procedures.19–22 Then, we
Table
2
Synthesis of dihydropyridin-2(3H)-one-BF2 complexes 5
from 2-acyl penta-2,4-dienamidesa
selected 2-benzylidene-3-oxo-N-phenylbutanamide 1a as
a
model compound to investigate its reaction behavior in the
presence of BF3$Et2O (1.0 equiv.) in CH2Cl2 at room tempera-
ture. The reaction could proceed and furnished a product,
which was characterized as 2,2-diuoro-4-methyl-5-phenyl-5,10-
dihydro-2H-[1,3,2]dioxa-borinino[4,5-b]quinolin-1-ium-2-uide
2a (in 76% yield) on the basis of its spectral and analytical data.
A series of experiments revealed that the optimal results were
obtained when the reaction of 1a was performed with BF3$Et2O
(2.0 equiv.) in CH2Cl2 at room temperature, in which the yield of
2a reached 88% (Table 1, entry 1).
Under the identical conditions as for 2a, a range of reactions
of a-acyl N-arylcinnamamides 1b–n were carried out and some
of the results are summarized in Table 2. All the reactions of 1b–
g bearing various electron-donating and electron-withdrawing
substituents R1 on the aryl amides proceeded smoothly to
afford the corresponding dihydropyridone–BF2 complexes 2b–g
in high yields (Table 1, entries 2–9). In the case of 1d, 2,2-
diuoro-4,8-dimethyl-5-phenyl-5,10-dihydro-2H-[1,3,2]dioxa-
borinino-[4,5-b]quinolin-1-ium-2-uide 2d was exclusively
obtained in 79% yield, which suggests that 1d underwent the
cyclization reaction in a regioselective manner (Table 1, entry 4).
The efficiency of the cyclization proved to be suitable for 1j–m
bearing various electron-donating and electron-withdrawing
substituents R2 on the benzene ring affording the correspond-
ing substituted dihydropyridone–BF2 complexes 2j–m in very
good yields (Table 1, entries 10–13). In the same fashion, the
validity of this dihydropyridone–BF2 complex synthesis was
further evaluated by performing 1n bearing secondary amide, in
Entry
4
R1
R2
5
Yieldb (%)
1
2
3
4
5
6
4a
4b
4c
4d
4e
4f
4-Me
4-MeO
4-Cl
2-Cl
2-Me
4-Me
H
H
H
4-MeO
4-MeO
4-Me
5a
5b
5c
5d
5e
5f
70
72
68
71
63
65
a
Reaction conditions: 1 (1.0 mmol), KOH (6.0 mmol), t-BuOH (10 mL),
b
80 ꢀC. 1.0–2.0 h. Isolated yields.
which dihydroquinolin-2-one-BF2 complex 2n was obtained in
high yield (Table 1, entry 14). The structure of 2g was further
conrmed by the X-ray single crystal analysis (Fig. 1). The
results shown above demonstrate the efficiency and synthetic
interest of the cyclization reaction of variable a-acyl N-aryl cin-
namamides 1.
It should be mentioned that when dihydropyridone–BF2
complex 2h was treated with 2,3-dichloro-5,6-dicyano-1,4-
benzoquinone (DDQ, 1.0 equiv.) in CH2Cl2 at room tempera-
ture for 1.0 h, 3-acyl-6-methoxy-4-phenylquinolin-2(1H)-one 3h
could be obtained in 80% yield (Scheme 2). Therefore, we
provided a novel and convenient synthesis of dihydropyridone–
Table
1 Synthesis of substituted dihydroquinolin-2-one-BF2
complexes 2 from a-Acyl N-arylcinnamamides 1a
BF2 complexes
2
and an alternative synthesis of
dihydroquinolin-2-ones 3 as well.
Entry
1
R1
R2
R3
R4
2
Yieldb (%)
1
2
3
4
5
6
7
8
1a
1b
1c
1d
1e
1f
1g
1h
1i
1j
1k
1l
1m
1n
H
H
H
H
H
H
H
H
H
Me
Me
Me
Me
Me
Me
Me
Me
Ph
Me
Me
Me
Me
Me
H
H
H
H
H
H
H
H
H
H
H
H
H
Et
2a
2b
2c
2d
2e
2f
2g
2h
2i
2j
2k
2l
2m
2n
88
81
82
79
80
83
96
94
75
87
86
85
83
81
4-Me
2-Me
3-Me
2,4-Me2
4-Cl
4-MeO
2-MeO
H
H
H
H
H
Fig. 1 ORTEP drawing of 2g.
9
H
10
11
12
13
14
4-Me
2-Me
2-MeO
4-Cl
H
H
a
Scheme
complex 2h with DDQ.
2 Reaction of substituted dihydroquinolin-2-one-BF2
Reagents and conditions: 1 (2.0 mmol), BF3$Et2O (4.0 mmol), CH2Cl2
(5.0 mL), rt, 2.0–3.0 h. b Isolated yield.
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Encouraged by the above results, we intended to explore the found to undergo a distinct intramolecular cyclization in which
reaction of 2-acyl penta-2,4-dienamides under identical reaction the nucleophilic addition site was on the b-carbon of the a,b-
conditions as for 2a. However, when 2-acyl-5-phenyl-N-(p-tolyl) unsaturated carbonyl compounds 1 instead of their a-acyl
penta-2,4-dienamide 4a was subjected to CH2Cl2 in the pres- groups. On the basis of the results obtained above and the
ence of BF3$Et2O at room temperature for 2.0 h, no reaction was reported literatures, a plausible mechanism for the synthesis of
observed. Then, the reaction of 4a was performed in (CH2)2Cl2 dihydroquinolin-2-one-BF2 complexes
2 is presented in
under reux for 1.0 h and furnished a product, which was Scheme 3. Mediated by BF3$Et2O, a-acyl N-arylcinnamamide 1 is
characterized as 2,2-diuoro-4-methyl-7-phenyl-8-(p-tolyl)-7,8- activated by the formation of BF2-complex intermediate A,17d,e
dihydro-2H-[1,3,2]dioxaborinino[4,5-b]pyridin-1-ium-2-uide 5a followed by an intramolecular Friedel–Cras reaction to afford
(Table 2, entry 1).
dihydropyridin-2(3H)-one-BF2 complex 2.24 It is most possible
Under the identical conditions as for 4a in Table 2 entry 1, a that the BF2-complex moiety could not provide enough activa-
series of reactions of 2-acyl penta-2,4-dienamides 4b–f were tion to promote further intramolecular cyclization for 2 under
carried out in the presence of BF3$Et2O, and some of the results the investigated conditions. As for 2-acyl penta-2,4-dienamides
are summarized in Table 2. All the reactions of 4b–f bearing 4, a BF2-complex intermediate B is formed in the same way
different aryl amide groups for R1 and aryl groups for R2 could (Scheme 3). Here, it is worth noting that BF2-complex inter-
proceed smoothly to afford the corresponding dihydropyridin- mediate B contains a 1-azatriene moiety, which under the
2(3H)-one-BF2 complexes 5b–f in good yields (Table 2, entries investigated conditions may undergo a 6p-azaelectrocyclization
2–7). The structure of 5d was elucidated by NMR (1H, 13C) reaction21 instead of the Friedel–Cras reaction as a-acyl N-aryl
spectra and further conrmed by means of the X-ray single cinnamamide 1 did. Just like the role of hydrogen bond did in
crystal analysis (Fig. 2).
our previous work, the BF2-complex structure provides the
In contrast to the conventional acid-catalyzed Knorr quino- driving force to keep the azadiene N]C–C]C of B in a cis
lin-2(1H)-one synthesis,23 a-acyl N-aryl cinnamamides 1 were conformation that may favor the subsequent 6p-azaelectro-
cyclization, and also stabilize the structure of product 5.
Conclusions
In summary, a facile and convenient synthesis of substituted
dihydropyridone–BF2 complexes 3 and 5 is developed via
intramolecular cyclization of unsaturated amides, a-acyl N-ary
lcinnamamides 1 and 2-acyl penta-2,4-dienamides 4, mediated
by BF3$Et2O, respectively. The simple execution, readily avail-
able substrates, very mild conditions, good yields and wide
range of synthetic potential of the products make this protocol
much attractive. The extension of the scope of the methodology
Fig. 2 ORTEP drawing of 5d.
and its further applications are currently under investigation in
our laboratory.
Experimental section
General
All reagents were purchased from commercial sources and used
without treatment, unless otherwise indicated. The products
were puried by column chromatography over silica gel. 1H
13
ꢀ
NMR and C NMR spectra were recorded at 25 C at 300 MHz
and 100 MHz, respectively, with TMS as internal standard. IR
spectra (KBr) were recorded on FTIR-spectrometer in the range
of 400–4000 cmꢁ1. All melting points were determined in open
capillary tubes in a Thiele apparatus and are uncorrected.
Typical procedure for the synthesis of substituted unsaturated
amides 1 (1a as an example)
To a 100 mL round-bottomed ask was added 3-oxo-N-phenyl-
butanamide (0.89 g, 5.0 mmol), 4-methylbenzaldehyde (0.60 g,
5.0 mmol), piperidine (0.5 mmol), acetic acid (0.5 mmol) and
ethanol (30 mL). Then the mixture was stirred for 8.0 h at room
temperature. The resulting mixture was slowly poured into
Scheme
amides mediated by BF3$Et2O.
3 Plausible mechanism for the reaction of unsaturated
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saturated aqueous NaCl (100 mL), and extracted with 1493, 1333, 1119, 762, 706; Anal. calcd for C17H14BF2NO2: C,
dichloromethane (3 ꢂ 30 mL). The combined organic phase 65.21; H, 4.51; N, 4.47. Found: C, 65.52; H, 4.48; N, 4.54.
was washed with water (3 ꢂ 30 mL) and dried over anhydrous
2,2-Diuoro-4,7-dimethyl-5-phenyl-5,10-dihydro-2H-[1,3,2]-
Na2SO4. The solvent was removed under reduced pressure, and dioxaborinino[4,5-b]quinolin-1-ium-2-uide (2b). Yellow solid:
the crude product was puried by ash chromatography (silica mp 210–212 ꢀC; 1H NMR (300 MHz, DMSO): d 2.03 (s, 3H), 2.17
gel, petroleum ether : ethyl acetate10 : 1) to give 1a as a color- (s, 3H), 5.26 (s, 1H), 6.98 (d, J ¼ 9.9 Hz, 1H), 7.03 (d, J ¼ 9.9 Hz,
less solid (1.20 g, 86%).
2H), 7.18 (t, J ¼ 6.9 Hz, 1H), 7.25 (d, J ¼ 6.9 Hz, 2H), 7.30 (t, J ¼
Substrates 1a–k and 1n are known compounds (1a and 1j: J. 7.5 Hz, 2H), 12.01 (s, 1H); 13C NMR (100 MHz, DMSO): d 20.4,
Indian Chem. Soc., 1981, 58, 168, 1c and 1d: Comptes Rendus 41.7, 96.7, 117.1, 126.3, 126.8 (1), 126.8 (2), 128.4, 129.0, 129.8,
Hebdomadaires des Seances de I0Academie des Sciences, 1949, 228, 130.0, 134.9, 146.4, 163.5, 178.9; Anal. calcd for C18H16BF2NO2:
576, 1b, 1e–k and 1n: Org. Lett., 2013, 15, 776.)
C, 66.09; H, 4.93; N, 4.28. Found: C, 65.87; H, 4.90; N, 4.22.
2-(4-Methoxybenzylidene)-3-oxo-N-phenylbutanamide (1l)
2,2-Diuoro-4,9-dimethyl-5-phenyl-5,10-dihydro-2H-[1,3,2]-
[E/Z ¼ 4 : 25]. Colorless solid: mp 91–96 ꢀC; 1H NMR (300 MHz, dioxaborinino[4,5-b]quinolin-1-ium-2-uide (2c). Colorless solid:
1
ꢀ
CDCl3) (minor E-isomer): d 2.45 (s, 3H), 3.86 (s, 3H), 6.94 (d, J ¼ mp 246–247 C; H NMR (300 MHz, DMSO): 2.09 (s, 3H), 2.34
6.0 Hz, 2H), 7.14–7.16 (m, 1H), 7.28–7.33 (m, 2H), 7.57–7.63 (m, (s, 3H), 5.31 (s, 1H), 6.99 (t, J ¼ 7.5 Hz, 1H), 7.06 (d, J ¼ 7.5 Hz,
4H), 8.21 (s, 1H), 9.39 (s, 1H); (major Z-isomer): d 2.45 (s, 3H), 1H), 7.12 (d, J ¼ 7.5 Hz, 1H), 7.16–7.21 (m, 1H), 7.24–7.28
3.81 (s, 3H), 6.86 (d, J ¼ 6.0 Hz, 2H), 7.16 (t, J ¼ 6.0 Hz, 1H), 7.35 (m, 3H), 7.32 (d, J ¼ 7.5 Hz, 1H), 11.22 (s, 1H); 13C NMR (100
(t, J ¼ 6.0 Hz, 2H), 7.53–7.57 (m, 5H), 7.88 (s, 1H); 13C NMR (100 MHz, DMSO): d 17.8, 20.5, 41.8, 97.0, 125.4, 126.1, 126.8, 127.0,
MHz, CDCl3): d 13.7, 20.5, 22.2, 26.4, 30.9, 54.8, 59.9, 114.0, 127.4, 128.1, 128.9, 129.2, 129.8, 130.9, 146.5, 164.6, 179.9; Anal.
119.7, 124.0, 128.5, 131.2, 131.9, 137.3, 140.5, 145.1, 161.3, calcd for C18H16BF2NO2: C, 66.09; H, 4.93; N, 4.28. Found: C,
165.8, 195.4; Anal. calcd for C18H17NO3: C, 73.20; H, 5.80; N, 66.35; H, 4.88; N, 4.31.
4.74. Found: C, 72.81; H, 5.85; N, 4.69.
2,2-Diuoro-4,8-dimethyl-5-phenyl-5,10-dihydro-2H-[1,3,2]-
2-(4-Chlorobenzylidene)-3-oxo-N-phenylbutanamide
(1m) dioxaborinino[4,5-b]quinolin-1-ium-2-uide (2d). Yellow solid:
[E/Z ¼ 2 : 5]. Colorless solid: mp 122–127 ꢀC; 1H NMR (300 MHz, mp 261–263 ꢀC; 1H NMR (300 MHz, DMSO): d 2.04 (s, 3H), 2.33
CDCl3) (minor E-isomer): d 2.17 (s, 3H), 7.11–7.18 (m, 2H), 7.27– (s, 3H), 5.27 (s, 1H), 5.76 (s, 1H), 6.90 (d, J ¼ 7.8 Hz, 2H), 7.13 (d,
7.35 (m, 2H), 7.47–7.50 (m, 2H), 7.52 (s, 2H), 7.58 (d, J ¼ 6.0 Hz, J ¼ 7.8 Hz, 1H), 7.19 (d, J ¼ 7.5 Hz, 1H), 7.24 (d, J ¼ 7.5 Hz, 2H),
2H), 9.28 (s, 1H); (major Z-isomer): d 2.43 (s, 3H), 7.11–7.18 (m, 7.30 (d, J ¼ 7.5 Hz, 2H), 12.02 (s, 1H); 13C NMR (100 MHz,
1H), 7.20 (d, J ¼ 12.0 Hz, 1H), 7.27–7.35 (m, 4H), 7.40 (d, J ¼ 9.0 DMSO): d 20.4, 20.5, 41.2, 54.8, 96.7, 117.4, 123.5, 126.2, 126.7,
Hz, 1H), 7.45 (s, 1H), 7.47–7.50 (m, 2H), 8.11 (d, J ¼ 4.0 Hz, 1H); 129.0, 129.3, 132.1, 137.3, 146.5, 163.8, 179.2; Anal. calcd for
13C NMR (100 MHz, CDCl3): d 26.4, 31.1, 119.5, 119.9, 124.2,
C
18H16BF2NO2: C, 66.09; H, 4.93; N, 4.28. Found: C, 66.42; H,
128.6, 130.5, 135.8, 136.8, 143.1, 160.3, 165.1, 195.4, 206.3; Anal. 5.00; N, 4.22.
calcd for C17H14ClNO2: C, 68.12; H, 4.71; N, 4.67. Found: C,
68.44; H, 4.75; N, 4.62.
2,2-Diuoro-4,7,9-trimethyl-5-phenyl-5,10-dihydro-2H-[1,3,2]-
dioxaborinino[4,5-b]quinolin-1-ium-2-uide (2e). Yellow solid:
mp 291–293 ꢀC; 1H NMR (300 MHz, DMSO): d 2.08 (s, 3H), 2.14
(s, 3H), 2.30 (s, 3H), 5.24(s, 1H), 6.87 (s, 1H), 6.91 (s, 1H), 7.16–
7.33 (m, 5H), 11.19 (s, 1H); 13C NMR (100 MHz, DMSO): d 17.5,
20.2, 20.4, 41.8, 96.9, 125.8, 126.6, 126.7, 126.8, 127.6, 128.4,
129.0, 130.3, 134.4, 146.4, 164.2, 179.3; IR (KBr, cmꢁ1): 3337,
Typical procedure for the synthesis of dihydropyridone–BF2
complexes 2 (2a as an example)
To a 50 mL round bottomed ask was added 1a (530.0 mg, 2.0 1626, 1601, 1526, 1485, 1327, 1146, 731, 706; Anal. calcd for
mmol), BF3$Et2O (5.0 mmol) and CH2Cl2 (10 mL). The mixture 19H18BF2NO2: C, 66.89; H, 5.32; N, 4.11. Found: C, 66.52; H,
was stirred at room temperature for 1.0 h. Aer the substrate 1a 5.39; N, 4.17.
C
was consumed completely as indicated by TLC, the mixture was
7-Chloro-2,2-diuoro-4-methyl-5-phenyl-5,10-dihydro-2H-
poured into ice water, and then extracted with dichloromethane [1,3,2]dioxaborinino[4,5-b]quinolin-1-ium-2-uide (2f). Yellow
(3 ꢂ 20 mL), the combined organic phase was washed with solid: mp 218–219 ꢀC; 1H NMR (300 MHz, DMSO): d 2.05 (s, 3H),
water (3 ꢂ 20 mL), and dried over anhydrous Na2SO4. The 5.37 (s, 1H), 7.11 (d, J ¼ 6.0 Hz, 1H), 7.20–7.24 (m, 1H), 7.28–7.36
solvent was removed under reduced pressure, and the crude (m, 6H), 12.20 (s, 1H); 13C NMR (100 MHz, DMSO): d 20.5, 41.3,
product was puried by ash chromatography (silica gel, 96.1, 119.0, 126.8, 127.1, 127.8, 128.5, 129.0, 129.2, 131.5, 145.8,
petroleum ether : ethyl acetate 5 : 1) to give 2a as colorless solid 163.8, 179.9; IR (KBr, cmꢁ1): 3348, 3333, 1622, 1609, 1593, 1520,
(551.1 mg, 88%).
2,2-Diuoro-4-methyl-5-phenyl-5,10-dihydro-2H-[1,3,2]diox- 58.75; H, 3.77; N, 4.03. Found: C, 59.10; H, 3.69; N, 4.06.
aborinino[4,5-b]quinolin-1-ium-2-uide (2a). Yellow solid: mp
2,2-Diuoro-7-methoxy-4-methyl-5-phenyl-5,10-dihydro-2H-
1489, 1140, 746, 710, 696; Anal. calcd for C17H13BClF2NO2: C,
239–240 ꢀC; 1H NMR (300 MHz, DMSO): d 2.05 (s, 3H), 5.33 [1,3,2]dioxaborinino[4,5-b]quinolin-1-ium-2-uide (2g). Yellow
(s, 1H), 7.07 (d, J ¼ 6.0 Hz, 1H), 7.11 (s, 1H), 7.17–7.22 (m, 2H), solid: mp 226–228 ꢀC; 1H NMR (400 MHz, DMSO): d 2.03 (s, 3H),
7.25 (s, 1H), 7.28 (d, J ¼ 2.4 Hz, 3H), 7.32 (d, J ¼ 7.5 Hz, 1H), 3.66 (s, 3H), 5.29 (s, 1H), 6.82–6.85 (m, 2H), 7.02–7.05 (m, 1H),
12.08 (s, 1H); 13C NMR (100 MHz, DMSO): d 20.4, 41.5, 96.6, 7.17–7.22 (m, 1H), 7.25–7.29 (m, 3H), 7.32 (d, J ¼ 7.5 Hz, 1H),
117.2, 125.5, 126.4, 126.7, 126.9, 127.8, 129.0, 129.5, 132.4, 11.99 (s, 1H); 13C NMR (100 MHz, DMSO): d 21.2, 43.5, 55.5,
146.3, 163.8, 179.4; IR (KBr, cmꢁ1): 3352, 1624, 1610, 1593, 1526, 96.1, 113.2, 115.2, 118.0, 124.8, 126.9, 127.3, 129.2, 145.2, 157.5,
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163.3, 181.0; IR (KBr, cmꢁ1): 3348, 1703, 1647, 1620, 1597, 1529, (d, J ¼ 7.6 Hz, 2H), 7.09–7.19 (m, 5H), 7.26 (t, J ¼ 7.6 Hz, 1H),
1499, 1269, 1130, 733, 698; Anal. calcd for C18H16BF2NO3: C, 7.37 (d, J ¼ 7.6 Hz, 1H), 7.45–7.50 (m, 4H), 7.56 (t, J ¼ 6.8 Hz,
63.01; H, 4.70; N, 4.08. Found: C, 63.18; H, 4.69; N, 4.10.
1H), 12.41 (s, 1H); 13C NMR (100 MHz, DMSO): d 41.4, 97.2,
Crystal data for 2g: C18H16BF2NO3, colorless crystal, M ¼ 117.1, 125.7, 126.1, 126.3, 126.7, 127.8, 127.9, 128.6, 128.7,
343.13, monoclinic, C2/c , a ¼ 26.916(3) A, b ¼ 8.0515(9) A, c ¼ 129.4, 131.2, 132.4, 133.6, 145.6, 165.1, 174.8; IR (KBr, cmꢁ1):
0
ꢀ
˚
˚
ꢀ
ꢀ
˚
17.954(2) A, a ¼ 90.00 , b ¼ 123.571(2) , g ¼ 90.00 , V ¼ 3312, 1628, 1589, 1580, 1522, 1489, 1132, 762, 702; Anal. calcd
3
˚
3241.9(6) A , Z ¼ 8, T ¼ 293(2) K, F000 ¼ 1512, R ¼ 0.0474.
for C22H16BF2NO2: C, 70.43; H, 4.30; N, 3.73. Found: C, 70.01; H,
2,2-Diuoro-9-methoxy-4-methyl-5-phenyl-5,10-dihydro-2H- 4.19; N, 3.81.
[1,3,2]dioxaborinino[4,5-b]quinolin-1-ium-2-uide (2h). Color-
10-Ethyl-2,2-diuoro-4-methyl-5-phenyl-5,10-dihydro-2H-
less solid: mp 239–240 ꢀC; 1H NMR (300 MHz, DMSO): d 2.06 (s, [1,3,2]dioxaborinino[4,5-b]quinolin-1-ium-2-uide (2n). Color-
3H), 3.83 (s, 3H), 5.28 (s, 1H), 6.84 (d, J ¼ 8.1 Hz, 1H), 6.90 (d, J ¼ less solid: mp 189–191 ꢀC; 1H NMR (400 MHz, DMSO): d 1.31 (t, J
8.1 Hz, 1H), 7.04 (t, J ¼ 8.1 Hz, 1H), 7.15–7.23 (m, 1H), 7.25–7.31 ¼ 6.9 Hz, 3H), 2.12 (s, 1H), 4.14–4.24 (m, 2H), 5.34 (s, 1H), 7.16–
(m, 4H), 11.50 (s, 1H); 13C NMR (100 MHz, DMSO): d 20.5, 41.5, 7.23 (m, 3H), 7.25–7.32 (m, 4H), 7.36 (d, J ¼ 7.8 Hz, 1H), 7.39 (t, J
56.1, 96.7, 110.2, 121.0, 121.6, 125.8, 126.7, 126.9, 127.4, 129.0, ¼ 7.8 Hz, 1H), 7.45 (d, J ¼ 7.8 Hz, 1H); 13C NMR (100 MHz,
146.2, 147.8, 164.0, 179.5; IR (KBr, cmꢁ1): 3319, 1608, 1593, DMSO): d 13.0, 20.8, 39.1, 41.4, 97.5, 116.9, 126.3, 127.0, 127.4,
1543, 1495, 1271, 1103, 750; Anal. calcd for C18H16BF2NO3: C, 128.5, 129.5, 130.4, 133.8, 146.2, 163.6, 179.3; IR (KBr, cmꢁ1):
63.01; H, 4.70; N, 4.08. Found: C, 62.82; H, 4.74; N, 3.99.
1603, 1580, 1518, 1487, 1337, 1138, 756, 700; Anal. calcd for
C19H18BF2NO2: C, 66.89; H, 5.32; N, 4.11. Found: C, 67.23; H,
2,2-Diuoro-4-methyl-5-(p-tolyl)-5,10-dihydro-2H-[1,3,2]dioxa-
borinino[4,5-b]quinolin-1-ium-2-uide (2i). Yellow solid: mp 5.26; N, 4.17.
192–194 ꢀC; 1H NMR (300 MHz, DMSO): d 2.04 (s, 3H), 2.22
(s, 3H), 5.27 (s, 1H), 7.05–7.11 (m, 4H), 7.15 (d, J ¼ 8.1 Hz, 2H),
The procedure for the synthesis of substituted quinolin-2(1H)-
one 3h
(2), 132.3, 136.0, 143.5, 163.7, 179.2; IR (KBr, cmꢁ1): 3344, 1628, To a 50 mL round bottomed ask was added 2 h (686.3 mg, 2.0
7.19–7.25 (m, 2H), 12.04 (s, 1H); 13C NMR (100 MHz, DMSO): d
20.5, 41.2, 54.8, 96.6, 117.1, 125.4, 126.6, 127.7, 129.5 (1), 129.5
1595, 1526, 1491, 1329, 810, 762; Anal. calcd for C18H16BF2NO2: mmol), DDQ (3.0 mmol) and CH2Cl2 (10 mL). The mixture was
C, 66.09; H, 4.93; N, 4.28. Found: C, 65.79; H, 5.01; N, 4.33.
stirred at room temperature for 1.0 h. Aer the substrate 2g was
2,2-Diuoro-4-methyl-5-(o-tolyl)-5,10-dihydro-2H-[1,3,2]dioxa- consumed completely as indicated by TLC, the mixture was
borinino[4,5-b]quinolin-1-ium-2-uide (2j). Yellow solid: mp poured into ice water, and then extracted with dichloromethane
251–253 ꢀC; 1H NMR (300 MHz, DMSO): d 1.92 (s, 3H), 2.34 (3 ꢂ 20 mL), the combined organic phase was washed with
(s, 3H), 5.52 (s, 1H), 7.03–7.08 (m, 3H), 7.12–7.18 (m, 3H), 7.20– water (3 ꢂ 20 mL), and dried over anhydrous Na2SO4. The
7.26 (m, 2H), 12.08 (s, 1H); 13C NMR (100 MHz, DMSO): d 19.0, solvent was removed under reduced pressure, and the crude
20.8, 96.5, 117.0, 125.5, 125.8, 126.6, 126.9, 127.8, 129.3, 131.4, product was puried by ash chromatography (silica gel,
132.3, 134.2, 144.4, 163.6, 179.0; IR (KBr, cmꢁ1): 3354, 1622, petroleum ether : ethyl acetate 4 : 1) to give 3h as colorless solid
1591, 1521, 1493, 1047, 764; Anal. calcd for C18H16BF2NO2: C, (469.3 mg, 80%).
66.09; H, 4.93; N, 4.28. Found: C, 66.41; H, 4.89; N, 4.32.
3-Acetyl-6-methoxy-4-phenylquinolin-2(1H)-one (3h). Yellow
2,2-Diuoro-5-(4-methoxyphenyl)-4-methyl-5,10-dihydro-2H- solid: mp 260–261 ꢀC; 1H NMR (400 MHz, DMSO): d 2.21 (s, 3H),
[1,3,2]dioxaborinino[4,5-b]quinolin-1-ium-2-uide (2k). Yellow 3.57 (s, 3H), 6.64 (d, J ¼ 2.4 Hz, 1H), 7.24–7.27 (dd, J1 ¼ 9.2 Hz,
solid: mp 204–206 ꢀC; 1H NMR (300 MHz, DMSO): d 2.04 (s, 3H), J2 ¼ 2.4 Hz, 1H), 7.31 (s, 1H), 7.33 (d, J ¼ 2.4 Hz, 1H), 7.37 (d, J ¼
3.68 (s, 3H), 5.26 (s, 1H), 6.86 (d, J ¼ 9.0 Hz, 2H), 7.08 (t, J ¼ 9.0 9.2 Hz, 1H), 7.48–7.53 (m, 3H), 12.14 (s, 1H); 13C NMR (100
Hz, 2H), 7.17 (d, J ¼ 9.0 Hz, 2H), 7.21–7.25 (m, 2H), 12.03 (s, 1H); MHz, CDCl3): d 31.4, 55.2, 109.0, 117.0, 119.5, 119.8, 128.5,
13C NMR (100 MHz, DMSO): d 20.8, 41.0, 55.4, 97.1, 114.7, 117.5, 128.7, 133.0, 133.7, 134.2, 146.4, 154.2, 158.8, 201.7; IR (KBr,
125.8, 127.2, 128.0, 128.2, 129.9, 132.6, 139.0, 158.4, 164.1, cmꢁ1): 3446, 1703, 1647, 1597, 1497, 1281, 733, 702; Anal. calcd
179.7; Anal. calcd for C18H16BF2NO3: C, 63.01; H, 4.70; N, 4.08. for C18H15NO3: C, 73.71; H, 5.15; N, 4.78. Found: C, 74.16; H,
Found: C, 63.39; H, 4.77; N, 4.16.
5.20; N, 4.83.
5-(4-Chlorophenyl)-2,2-diuoro-4-methyl-5,10-dihydro-2H-
[1,3,2]dioxaborinino[4,5-b]quinolin-1-ium-2-uide (2l). Yellow
solid: mp 218–220 ꢀC; 1H NMR (300 MHz, DMSO): d 2.07 (s, 3H),
5.40 (s, 1H), 7.10 (t, J ¼ 7.5 Hz, 2H), 7.24 (t, J ¼ 7.5 Hz, 2H), 7.31
Typical procedure for the synthesis of dihydropyridone–BF2
complexes 5 (5a as an example)
(d, J ¼ 8.4 Hz, 2H), 7.39 (d, J ¼ 8.4 Hz, 2H), 12.12 (s, 1H); 13C To a 50 mL round bottomed ask was added 4a (610.7 mg, 2.0
NMR (100 MHz, DMSO): d 20.5, 40.9, 96.3, 117.3, 125.6, 125.9, mmol), BF3$Et2O (3.0 mmol) and DCE (10 mL). The mixture was
ꢀ
128.0, 129.0, 129.5, 131.7, 132.4, 145.2, 163.7, 179.6; IR (KBr, stirred at 80 C for 2.0 h. Aer the substrate 4a was consumed
cmꢁ1): 3333, 1630, 1595, 1529, 1493, 1323, 1057, 760, 719; Anal. completely as indicated by TLC, the mixture was poured into ice
calcd for C17H13BClF2NO2: C, 58.75; H, 3.77; N, 4.03. Found: C, water, and then extracted with dichloromethane (3 ꢂ 20 mL),
58.44; H, 3.84; N, 4.12.
the combined organic phase was washed with water (3 ꢂ 20
2,2-Diuoro-4,5-diphenyl-5,10-dihydro-2H-[1,3,2]dioxabor- mL), and dried over anhydrous Na2SO4. The solvent was
inino[4,5-b]quinolin-1-ium-2-uide (2m). Colorless solid: mp removed under reduced pressure, and the crude product was
282–284 ꢀC; 1H NMR (400 MHz, DMSO): d 5.36 (s, 1H), 6.90 puried by ash chromatography (silica gel, petroleum
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ether : ethyl acetate 4 : 1) to give 5a as a colorless solid (494.4 (s, 3H), 2.31 (s, 3H), 3.79 (s, 3H), 4.62 (d, J ¼ 7.2 Hz, 1H), 5.94–
mg, 70%).
6.01 (dd, J1 ¼ 15.6 Hz, J2 ¼ 7.2 Hz, 1H), 6.30 (d, J ¼ 15.6 Hz, 1H),
2,2-Diuoro-4-methyl-7-phenyl-8-(p-tolyl)-7,8-dihydro-2H- 6.81 (d, J ¼ 8.7 Hz, 2H), 7.06–7.08 (m, 2H), 7.15–7.18 (m, 1H),
[1,3,2]dioxaborinino[4,5-b]pyridin-1-ium-2-uide (5a). Yellow 7.23 (s, 1H), 7.66 (s, 1H); 13C NMR (100 MHz, CDCl3): d 16.5,
solid: mp 189–192 ꢀC; 1H NMR (300 MHz, DMSO): d 2.21 (s, 3H), 20.7, 40.8, 55.3, 94.2, 114.0, 124.1, 124.4, 125.5, 127.4, 127.7,
2.27 (s, 3H), 4.55 (d, J ¼ 7.5 Hz, 1H), 6.04–6.11 (dd, J1 ¼ 15.6 Hz, 128.6, 128.7, 129.7, 130.4, 159.4, 164.3, 181.7; IR (KBr, cmꢁ1):
J2 ¼ 7.5 Hz, 1H), 6.34 (d, J ¼ 15.6 Hz, 1H), 6.84 (d, J ¼ 8.1 Hz, 1630, 1601, 1560, 1512, 1252, 1180, 827, 764; Anal. calcd for
1H), 6.99 (d, J ¼ 8.1 Hz, 1H), 7.04 (s, 1H), 7.18–7.29 (m, 5H), 8.20
C21H20BF2NO3: C, 65.82; H, 5.26; N, 3.66. Found: C, 66.03; H,
(s, 1H); 13C NMR (100 MHz, DMSO): d 20.1, 20.6, 94.2, 117.0, 5.31; N, 3.57.
124.5, 126.5, 127.6, 128.0, 128.6, 129.8, 130.5, 131.9, 134.9,
2,2-Diuoro-4-methyl-7,8-di-p-tolyl-7,8-dihydro-2H-[1,3,2]dioxa-
136.2, 163.5, 178.6; IR (KBr, cmꢁ1): 3346, 1622, 1595, 1529, 1501, borinino[4,5-b]pyridin-1-ium-2-uide (5f). Yellow solid: mp 219–
1
ꢀ
1167, 816, 770, 746, 689; Anal. calcd for C20H18BF2NO2: C, 68.02; 221 C; H NMR (300 MHz, CDCl3): d 2.24 (s, 3H), 2.30 (s, 3H),
H, 5.14; N, 3.97. Found: C, 67.83; H, 5.21; N, 4.07.
2,2-Diuoro-8-(4-methoxyphenyl)-4-methyl-7-phenyl-7,8-dihy- J2 ¼ 7.5 Hz, 1H), 6.34 (d, J ¼ 15.6 Hz, 1H), 6.85 (d, J ¼ 8.1 Hz,
dro-2H-[1,3,2]dioxaborinino[4,5-b]pyridin-1-ium-2-uide
2.31 (s, 3H), 4.57 (d, J ¼ 7.5 Hz, 1H), 6.02–6.10 (dd, J1 ¼ 15.6 Hz,
(5b). 1H), 7.03 (d, J ¼ 8.1 Hz, 1H), 7.09 (d, J ¼ 8.1 Hz, 3H), 7.21 (d, J ¼
Yellow solid: mp 210–211 ꢀC; 1H NMR (300 MHz, CDCl3): d 2.25 8.1 Hz, 2H), 8.02 (s, 1H); 13C NMR (100 MHz, CDCl3): d 20.6,
(s, 3H), 3.79 (s, 3H), 4.61 (d, J ¼ 7.5 Hz, 1H), 6.08–6.16 (dd, J1 ¼ 20.9, 21.1, 40.8, 94.4, 116.9, 124.0, 126.4, 128.9, 129.0, 129.2,
15.6 Hz, J2 ¼ 7.5 Hz, 1H), 6.38 (d, J ¼ 15.6 Hz, 1H), 6.76–6.79 (dd, 129.6, 129.7, 129.8, 133.3, 135.8, 137.7, 163.8, 180.4; IR (KBr,
J1 ¼ 8.7 Hz, J2 ¼ 2.7 Hz, 1H), 6.82 (d, J ¼ 2.7 Hz, 1H), 6.91 (d, J ¼ cmꢁ1): 3344, 1626, 1599, 1529, 1500, 1207, 1163, 814; Anal. calcd
8.7 Hz, 1H), 7.22–7.30 (m, 5H), 8.00 (s, 1H); 13C NMR (100 MHz, for C21H20BF2NO2: C, 68.69; H, 5.49; N, 3.81. Found: C, 68.36; H,
DMSO): d 19.9, 55.4, 93.8, 113.4, 114.6, 118.1, 126.0, 126.1, 5.54; N, 3.84.
126.4, 127.6, 128.1, 128.6, 131.8, 136.2, 157.0, 178.1; Anal. calcd
for C20H18BF2NO3: C, 65.07; H, 4.91; N, 3.79. Found: C, 65.53; H,
4.85; N, 3.91.
Acknowledgements
8-(4-Chlorophenyl)-2,2-diuoro-4-methyl-7-phenyl-7,8-dihy- Financial support of this research by the National Natural
dro-2H-[1,3,2]dioxaborinino[4,5-b]pyridin-1-ium-2-uide
(5c). Science Foundation of China (21172211) and Department of
Yellow solid: mp 219–221 ꢀC; 1H NMR (300 MHz, CDCl3): d 2.28 Science and Technology of Jilin Province (201105030 and
(s, 3H), 5.43 (d, J ¼ 3.9 Hz, 1H), 5.49–5.54 (dd, J1 ¼ 10.2 Hz, J2 ¼ 201205027) are greatly acknowledged.
3.9 Hz, 1H), 6.46 (d, J ¼ 10.2 Hz, 1H), 6.84 (d, J ¼ 8.7 Hz, 1H),
7.06–7.10 (m, 2H), 7.26 (s, 1H), 7.27–7.31 (m, 1H), 7.32 (d, J ¼ 1.5
Notes and references
Hz, 1H), 7.34 (d, J ¼ 1.5 Hz, 1H); 13C NMR (100 MHz, CDCl3): d
19.6, 68.5, 95.2, 118.0, 118.5, 127.7, 128.5, 129.1, 129.2, 129.6,
134.8, 135.8, 137.8, 164.8, 174.0; Anal. calcd for C19H15BClF2-
NO2: C, 61.08; H, 4.05; N, 3.75. Found: C, 61.53; H, 4.16; N, 3.86.
8-(2-Chlorophenyl)-2,2-diuoro-7-(4-methoxyphenyl)-4-methyl-
7,8-dihydro-2H-[1,3,2]dioxaborinino[4,5-b]pyridin-1-ium-2-uide
(5d) (d/r ¼ 5 : 3). Yellow solid: mp 151–155 ꢀC; 1H NMR (major
isomer) (400 MHz, DMSO): d 2.29 (s, 3H), 3.73 (s, 3H), 5.50 (d, J
¼ 4.0 Hz, 1H), 5.62–5.66 (dd, J1 ¼ 12.0 Hz, J2 ¼ 4.0 Hz, 1H), 6.42
(d, J ¼ 8.0 Hz, 1H), 6.91 (d, J ¼ 12.0 Hz, 2H), 7.13 (d, J ¼ 8.0 Hz,
2H), 7.21 (t, J ¼ 8.0 Hz, 1H), 7.44 (t, J ¼ 8.0 Hz, 1H), 7.72 (d, J ¼
8.0 Hz, 1H); 1H NMR (minor isomer) (400 MHz, DMSO): d 2.27
(s, 3H), 3.68 (s, 3H), 5.57–5.60 (dd, J1 ¼ 12.0 Hz, J2 ¼ 4.0 Hz, 1H),
5.93 (s, 1H), 6.71 (d, J ¼ 12.0 Hz, 1H), 6.78 (d, J ¼ 12.0 Hz, 2H),
6.99 (d, J ¼ 8.0 Hz, 2H), 7.35–7.39 (m, 2H), 7.49–7.53 (m, 1H),
7.87 (d, J ¼ 8.0 Hz, 1H); 13C NMR (100 MHz, DMSO): d 19.7, 19.8,
55.4, 55.5, 66.0, 67.5, 95.2, 95.3, 113.8, 114.6, 118.0, 118.7, 119.2,
119.3, 128.1, 128.9, 130.4, 131.1, 134.4, 135.1, 159.9, 160.0,
163.8, 164.9, 173.3, 174.4; Anal. calcd for C20H17BClF2NO3: C,
59.52; H, 4.25; N, 3.47. Found: C, 59.91; H, 4.36; N, 3.40.
Crystal data for 5d: C20H17BClF2NO3, colorless crystal, M ¼
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˚
˚
˚
871.29, P-1, a ¼ 7.643(5) A, b ¼ 12.269(5) A, c ¼ 12.840(5) A, a ¼
3
ꢀ
ꢀ
ꢀ
˚
101.954(5) , b ¼ 104.028(5) , g ¼ 98.284(5) , V ¼ 1118.6(10) A ,
Z ¼ 1, T ¼ 293(2) K, F000 ¼ 450, R ¼ 0.0123.
2,2-Diuoro-7-(4-methoxyphenyl)-4-methyl-8-(o-tolyl)-7,8-dihy-
dro-2H-[1,3,2]dioxaborinino[4,5-b]pyridin-1-ium-2-uide
(5e).
Yellow solid: mp 182–183 ꢀC; 1H NMR (300 MHz, CDCl3): d 2.27
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