Merging Visible-Light Photoredox and Lewis Acid Catalysis for the Intramolecular Aza-Diels–Alder Reaction: Synthesis of Substituted Chromeno[4,3-b]quinolines and [1,6]Naphthyridines

Article abstract of DOI:10.1002/cctc.201800192

Substituted chromeno[4,3-b]quinolines and [1,6]naphthyridines were achieved by tandem intramolecular aza-Diels–Alder reaction using a strategy of combination of visible-light photoredox and Lewis-acid-catalysis. This intramolecular aza-Diels–Alder cycloaddition took place between the in situ generated benzylidene anilines derived from arylamines and salicylaldehyde or 2-aminoaryl aldehydes bearing a tethered alkene partner, followed by oxidative aromatization to give the target products. The study on the oxidative aromatization step revealed that it is much faster than the cyclization step; both the combination of imine and Lewis acid, and the combination of photocatalyst and Lewis acid under aerobic condition with the irradiation of visible light are efficient to achieve the transformation. This method provided a new access to the synthesis of important heterocycles under mild reaction conditions.

Full text of DOI:10.1002/cctc.201800192

Accepted Article
Title: Merging Visible-Light-Photoredox and LewisAcid-Catalysis for the
Intramolecular Aza-Diels-Alder Reaction: Synthesis of Substituted
Chromeno[4,3-b]quinolines and [1,6]Naphthyridines
Authors: Wuheng Dong, Yao Yuan, Xiaoshuang Gao, Bei Hu, Xiaomin
Xie, and Zhao-Guo Zhang
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10.1002/cctc.201800192
ChemCatChem
FULL PAPER
Merging Visible-Light-Photoredox and Lewis-Acid-Catalysis for
the Intramolecular Aza-Diels-Alder Reaction: Synthesis of
Substituted Chromeno[4,3-b]quinolines and [1,6]Naphthyridines
Wuheng Dong[a], Yao Yuan[a], Xiaoshuang Gao[a], Bei Hu[a], Xiaomin Xie[a], and Zhaoguo Zhang* [a], [b]
Dedication ((optional))
Abstract:
Substituted
chromeno[4,3-b]quinolines
and
further oxidation of the corresponding tetrahydro
/
[1,6]naphthyridines was achieved by tandem intramolecular aza-
Diels-Alder reaction using a strategy of combination of visible-light-
photoredox and Lewis-acid-catalysis. This intramolecular aza-Diels-
Alder cycloaddition took place between the in situ generated
benzylidene anilines derived from arylamines and salicylaldehyde or
2-aminoaryl aldehydes bearing a tethered alkene partner, followed
by oxidative aromatization to give the target products. The study on
the oxidative aromatization step reaveled that it is much faster than
the cyclization step; both the combination of imine and Lewis acid,
and the combination of photocatalyst and Lewis acid under aerobic
condition with the irridation of visible light are efficient to achieve the
transformation. This method provided a new access to the synthesis
of important heterocycles under mild reaction conditions.
dihydroquinoline was usually conducted under harsh reaction
conditions and toxic oxidants were often used.[6] Recently,
chromenoquinoline skeleton have been synthesized, involving
the copper-catalyzed aza-Diels-Alder reaction / aromatization
cascade (Scheme 1a,[7] 1b[8]), and the reaction of diaryliodonium
triflates and arylpropynyloxy-benzonitriles.[9] In addition, the 5,6-
dihydrodibenzo[b,h][1,6]naphthyridines
have
also
been
synthesized by the copper-catalyzed aza-Diels-Alder reaction /
aromatization cascade reaction (Scheme 1c).[10] It is noteworthy
that the above-mentioned reactions involve an alkyne group as
dienophile. Given the importance of chromenoquinolines and
5,6-dihydrodibenzo[b,h][1,6]naphthyridines, developing a simple
and efficient protocol for the acquisition of them from readily
available starting materials under mild conditions is highly
desirable.
(a) Rajagopal Nagarajan and co-workers
Introduction
O
O
R1
CuI / La(OTf)3
CH3CN, reflux
R2
R1
+
N
Substituted
chromenoquinolines
and
5,6-
R2
NH2
O
dihydrodibenzo[b,h][1,6]naphthyridines
are
biologically
significant compounds, which widely occur in natural products,
pharmaceuticals and bioactive materials.[1] For examples, 6H-
chromeno[4,3-b]quinolines have been used as estrogen receptor
β-selective ligands[1b] and as bioimaging reagents,[1e,1f] the spiro
analogues of benzothiazolylchromeno derivatives have shown
cytotoxic activity against breast cancer cells,[2] and
dibenzo[b,h][1,6]naphthyridines have found applications in
fluorescent DNA labelling due to their fluorescent properties.[3]
Because of their biological importance, the development of
methods for the preparation of them has attracted much
attention from organic chemists.[1b,1e,3-4] One of the most efficient
methods for their preparation was the aza-Diels-Alder reaction of
N-aryl imines derived from aldehydes and anilines with electron-
rich olefins or alkynes.[5] To furnish the quinolone structure,
(b) Vellaisamy Sridharan and co-workers
X
Cu2O
O
R1
chloranil or bromanil
DME, 80 o
O
R1
N
R2
C
N
R2
(c) Vellaisamy Sridharan and co-workers
R3
N
R3
Ts
N
NTs
R1
CuBr2
R2
R1
+
toluene, rt - 70 o
C
R2
NH2
O
Scheme
1.
One-pot
access
to
chromenoquinolines
and
dibenzo[b,h][1,6]naphthyridines
[a]
Wuheng Dong, Yao Yuan, Bei Hu, Xiaoshuang Gao, Xiaomin Xie,
and Zhaoguo Zhang * [a]
Visible light photoredox reaction has revealed its power in
organic synthesis,[11] especially in the oxidation reaction of
amines to iminium ions followed by further functionalization.[12]
Recently, we have reported the synthesis of substituted
indolizino[1,2-b]quinolin-9(11H)-ones by merging visible-light-
photoredox and Lewis acid catalysis.[13] In this work, the
intramolecular aza-Diels-Alder cycloaddition between the in situ
generated benzylidene anilines derived from arylamines and 6-
Shanghai Key Laboratory for Molecular Engineering of Chiral Drugs,
School of Chemistry and Chemical Engineering
Shanghai Jiao Tong University
800 Dongchuan Road, Shanghai 200240, China
E-mail: zhaoguo@sjtu.edu.cn
Shanghai Institute of Organic Chemistry
Chinese Academy of Sciences
345 Lingling Road, Shanghai 200032, China
[b]
Supporting information for this article is given via a link at the end of
the document.((Please delete this text if not appropriate))
oxo-1,6-dihydropyridine-2-carbaldehyde bearing
a
tethered
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10.1002/cctc.201800192
ChemCatChem
FULL PAPER
alkene partner, followed by a visible-light-induced photocatalytic
aerobic oxidative aromatization to give the target products
(Scheme 2a). Base on this work, we speculated that
salicylaldehyde or 2-aminoaryl aldehydes could replace the 6-
oxo-1,6-dihydropyridine-2-carbaldehyde to give the substituted
chromeno[4,3-b]quinolines and [1,6]naphthyridines (Scheme
2b). Herein, we disclose the preparation of substituted
chromeno[4,3-b]quinolines and [1,6]naphthyridines from readily
available starting materials by merging visible-light-photoredox
and Lewis acid catalysis.
Table 1. Optimization of the reaction conditionsa
23 W flurescent bulb
photosensitizer
Ph
catalyst
O
O
+
solvent, air
NH2
N
O
1a
2a
3aa
Entry
Photosensitizer
Catalyst
Solvent
Yieldb
(%)
(a) Visble light-promoted synthesis of substituted indolizino[1,2-b]quinolin-9(11H)-ones:
(ref.[13]
our previous work
)
1
Ru(bpy)3(PF6)2
Ru(bpy)3(PF6)2
Ru(bpy)3(PF6)2
Ru(bpy)3(PF6)2
Ru(bpy)3(PF6)2
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
MeOH
DMSO
DCM
0
R2
R1
R1
O
R1
O
2
Zn(OTf)2
FeCl3
72
O
NH2
photocatalyst
R2
N
N
N
H
R2
H+
, MeOH, rt
3
41
N
H
O
N
4
TsOH.H2O
BF3.Et2O
BF3.Et2O
BF3.Et2O
BF3.Et2O
BF3.Et2O
BF3.Et2O
BF3.Et2O
BF3.Et2O
BF3.Et2O
BF3.Et2O
BF3.Et2O
BF3.Et2O
BF3.Et2O
41
(b) Visble light-promoted synthesis of Chromenoquinolines and 5,6-dihydrodibenzo[b,h][1,6]naphthyridines:
this work
5
87 (85 c)
58
R3
R3
.
Lewis acid / Photo cat.
6
Ru(bpy)3Cl2 6H2O
R1
X
+
X
R1
R2
CH3CN, rt
NH2
O
N
R2
7
[Ir(ppy)2bpy]PF6
[Ir(ppy)2dtb-bpy]PF6
EosinY
78
X= O, NTs
8
72
Scheme 2. Visible light-promoted synthesis of N-containing heterocycles
9
71
skeleton.
10
11
12
13
14 d
15 e
16 e
17 f
a
EosinY Na
67
Ru(bpy)3(PF6)2
Ru(bpy)3(PF6)2
Ru(bpy)3(PF6)2
Ru(bpy)3(PF6)2
Ru(bpy)3(PF6)2
------
70
Results and Discussion
47
Initially,
we
tested
the
reaction
of
2-
45
(cinnamyloxy)benzaldehyde (1a) and p-toluidine (2a) using
Ru(bpy)3(PF6)2 (2 mol %) as photosensitizer and CH3CN as
solvent under the irradiation of a 23 W household compact
fluorescent lamp (CFL) at room temperature. Unfortunately, no
desired compound was detected (Table 1, entry 1). We believe
that the Lewis acid might play an important role in the formation
of an imine intermediate and aza-Diels-Alder cycloaddition. [5a, 5h,
CH3CN
CH3CN
CH3CN
CH3CN
24
30
33
------
62
12d]
When Zn(OTf)2 (10 mol %) was employed as a catalyst to
Conditions: 1a (71.6 mg, 0.3 mmol), 2a (33.6 mg, 0.3 mmol),
photosensitizer (2 mol %), acid catalyst (10 mol %), solvent (3 mL),
irradiation with a 23 W household light bulb at rt for 24 h. b 1HNMR yield was
trigger this transformation, the reaction occurred in 72% yield
(Table 1, entry 2). Other acid, such as FeCl3, TsOH, and
BF3.Et2O, were also tested for this transformation, to our delight,
BF3.Et2O was the most effective and an 85% isolated yield was
obtained (Table 1, entries 3-5). Next, some commonly-used
photosensitizer were investigated, and Ru(bpy)3(PF6)2 was
proved superior to others (Table 1, entries 6-10). Besides, we
tested the solvents in this reaction, and acetonitrile was found to
be the best solvent (Table 1, entries 11-13). Control
experiments showed that both oxygen and visible light were
essential for this reaction, only 24% of desired product was
obtained when oxygen was absent, and only 30% yield was
obtained when the reaction was conducted in the dark (Table 1,
entries 14 and 15). Interestingly, the product 3aa was obtained
in 62% yield, even if the photosensitizer was absent (Table 1,
entry 17).
c
reported using 4,4'-ditertbutylbiphenyl as an internal standard. Isolated
d
yield.
Reaction mixture was degassed and carried out under N2
atmosphere. e Reaction was carried out in the dark. f Without photosensitizer.
Under the optimized reaction conditions, we explored the
substrate scope. As shown in Scheme 3, a variety of arylamines
efficiently coupled with 2-(cinnamyloxy)benzaldehyde (1a) under
standard reaction conditions to produce the corresponding
chromenoquinolines 3 in good yields. Anilines with an electron-
donating or weak electron-withdrawing group on the para-
position of the benzene ring afforded the desired products in
moderate to good yields (Scheme 3, 3ab-3ag). Interestingly,
hydroxyl, chloro, and bromo groups on the phenyl ring were well
tolerated, which enable potential applications in further
functionalization (Scheme 3, 3ae-3ag). It is noteworthy that
substrate with strong electron-withdrawing group such as cyano,
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10.1002/cctc.201800192
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alkoxycarbonyl, and carbonyl group could also work well, and
the corresponding products were isolated in good yields (3ah-
3aj). However, no products were obtained when pyridine-2-
amine and pyridine-3-amine were used as substrates. It seemed
that steric hindrance did not play any significant role in the
reaction, 3ak-3an were obtained in moderate yields.
corresponding product 3jo in good yield, which may have a
potential application as a biologically significant molecule.[14]
Scheme 4. Substrate scope-IIa
R3
2 mol % Ru(bpy)
3(PF6)2
10 mol % BF3.Et2O
R3
Scheme 3. Substrate scope-Ia
O
+
O
R2
NH2 CH3CN, air, hv, 24 h
O
N
R2
1
2 a
3
Ph
2 mol % Ru(bpy)
3(PF6)2
10 mol % BF3.Et2O
O
R1
R1
O
Ph
+
NH2
CH3CN, air, hv, 24 h
N
O
O
O
O
O
1 a
2
3
N
N
N
N
Ph
N
Ph
Ph
Ph
R
HO
O
O
O
O
CH3
OCH3
Cl
N
N
N
3ba
, 80%
3ca
, 67%
3da
, 76%
3ea
, 81%
3aa
, 85 %
3ab
3ac
, R=OMe, 74%
3ae
, 84%
, 63 %
R'
3ad
, R=t-Bu, 68%
S
H3C
Ph
N
Ph
N
O
Ph
O
Ph
N
O
X
NC
O
O
Br
O
O
O
O
O
O
N
N
N
N
N
Cl
3ka
, 64%
3fa
R'=F, 87%
3ia
, 82%
, 83%
,
3ga
3ha R'=OMe,
3af
3ah
3ai
3aj
, X=Cl, 55%
, 76%
, 64%
, 82%
85%
,
3ag
, X=Br, 61%
Ph
Ph
Ph
Ph
N
a Conditions: 1 (0.3 mmol), 2a (33.6 mg, 0.3 mmol), Ru(bpy)3(PF6)2 (5.3 mg, 2
mol %), BF3 Et2O (10 mol %), MeCN (3 mL), irradiation with 23 W household
O
Br
O
O
O
.
N
N
N
light bulb at rt for 24 h.
Br
CN
CH3
Ph
3ak
, 60%
3al
3am
3an
, 57%
, 69%
, 73%
a Conditions: 1a (71.6 mg, 0.3 mmol), 2 (0.3 mmol), Ru(bpy)3(PF6)2 (5.3 mg, 2
mol %), BF3 Et2O (10 mol %), MeCN (3 mL), irradiation with 23 W household
Scheme 5. Substrate scope-IIIa
.
light bulb at rt for 24 h.
Ph
2 mol % Ru(bpy)
3(PF6)2
10 mol % BF3.Et2O
Ts
NTs
R1
R1
N
Ph
+
NH2
NTs
CH3CN, air, hv, 24 h
N
O
Next, we extended this cyclization of 2-(cinnamyloxy)-
benzaldehyde with substituents on the benzene ring and allyl
counterpart (Scheme 4). The substrates bearing alkyl, methoxyl,
and halo groups on the salicylaldehyde moiety afforded the
corresponding products 3ba, 3ea, 3ca, and 3da in moderate to
good yields. In addition, various R3-substituted aryl groups, such
as p-fluoro-, p-methoxy-, and o-methylphenyls showed that the
electronic nature of the substituents has hardly any effect on
chemical yields, affording the products (3ga, 3ha, and 3ia) in
good yields. Finally, the product 3ka could be obtained in 64%
yield when the heterocyclic substrate 1k was introduced.
1j
2
3
Ph
N
Ph
Ph
Ph
N
H3C
H3CO
Cl
NTs
NTs
NTs
N
N
,
57%
,
67%
, 80%
, 60%
3jf
3jb
3ja
3jc
Ph
Ph
N
Ph
N
Ph
N
Br
NC
NTs
NTs
NTs
NTs
N
OH
CN
, 82%
3jl
, 76%
, 68%
, 69%
3jh
3jo
3jg
When 2-(cinnamyloxy)benzaldehyde (1a) was replaced by
N-cinnamyl-N-(2-formylphenyl)-4-methylbenzenesulfonamide
a Conditions: 1j (117.5 mg, 0.3 mmol), 2 (0.3 mmol), Ru(bpy)3(PF6)2 (5.3 mg, 2
mol %), BF3 Et2O (10 mol %), MeCN (3 mL), irradiation with a 23 W household
.
(1j),
the
corresponding
5,6-
light bulb at rt for 24 h.
dihydrodibenzo[b,h][1,6]naphthyridines products could be
obtained (Scheme 5). Compound 1j react with 2b to afford the
desired product 3jb in 57% yield under the same reaction
conditions. Anilines bearing an electron-donating or electron-
withdrawing substituent also afforded the target products in good
to excellent yields (3ja-3jo). It is noteworthy that the 2-
aminophenol could react with 1j smoothly to give the
To gain insight into the reaction, a time-concentration profile
of the reaction of 2-(cinnamyloxy)benzaldehyde (1a) and p-
toluidine (2a) under the optimized conditions was recorded by 1H
NMR spectroscopy. As shown in Figure 1, reaction of 1a and 2a
afforded imine 4aa in 45% yields within 15 min, along with the
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10.1002/cctc.201800192
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desired product 3aa and a secondary amine 5aa in 15% and
33% yields, respectively. It is evident that the rates of formation
of imine 4aa and the oxidation of I by 4aa to give 3aa are fast.
The consumption of 4aa and 5aa was fast at the first 4 hours
and then was slow. To our surprise, the Diels-Alder adduct I was
not observed, indicating that the oxidation rate of cycloadduct I
by the imine 4aa or the photocatalytic oxidation was much faster
than the rate of its formation by Diels-Alder cycloaddition.
2a, followed by aza-Diels-Alder reaction to give the intermediate
I. Then, the intermediate I was oxidized by the imine 4aa in the
presence of a Lewis acid to give the target product 3aa and the
amine 5aa (path a). Subsequent the amine 5aa was oxidized by
the excited RuII* to give the radical amine cation 5aa' and the
reduced species RuI, which could be oxidized by oxygen to
regenerate the RuII catalyst. The intermediate 5aa' was
converted to the imine 4aa by the O2 or O2•− under the influence
of the Lewis acid catalyst. Notably the peroxide was could be
detected by the starch / KI test paper. It is also possible that the
intermediate I was oxidized by the photocatalyst and Lewis acid
under the irradiation of visible light to give the target product 3aa
(path b).
Ph
O
Ph
standard
O
Ph
+
O
conditions
+
N
O
0-30 h
NH2
N
3 aa
O
1 a
2 a
4 aa
Ph
Ph
H
N
O
+
Ph
N
H
Ph
O
5 aa
I
(1)
O
CH3CN, N2, rt
5 h
N
N
4aa
3aa
3aa
, trace
Ph
O
O
+
, trace
(2)
(3)
N
N
H
I
CH3CN, N2, rt
5 h
A
10 mol % BF3.Et2O
O
3aa
, 54% yield
N
CH3CN, N2, rt
5 h
A
Ph
2 mol % Ru(bpy)
3(PF6)2
10 mol % BF3.Et2O
O
(4)
CH3CN, air, rt
N
hv, 5 h
Ph
3aa
3aa
, 61% yield
O
2 mol % Ru(bpy)
3(PF6)2
, 10% yield
(5)
(6)
N
H
I
CH3CN, air, rt
hv, 5 h
10 mol % BF3.Et2O
3aa
, 27% yield
CH3CN, air, rt
hv, 5 h
Figure 1. The time-concentration profile of the model reaction
Scheme 6. Verification experiments
To further clarify the product-forming profile, a series of
verification experiments were performed as shown in Scheme 2.
When Diels-Alder adduct product I and the imine (4aa or A, 2.5
equiv.) were treated in CH3CN at room temperature for 5 h
under N2 atmosphere, trace of the corresponding quinoline 3aa
was observed (Scheme 6, eq. 1 and 2). However, in the
presence of 10 mol % BF3.Et2O, under albeit the same reaction
conditions as shown in eq. 2, the target product 3aa could be
obtained in 54% yield (Scheme 6, eq. 3), revealing that
BF3.Et2O plays the key role in accelerating the oxidation. Then,
Ph
O
+
1a 2a
N
O2
4aa
[RuII
]
H
2O2
visible light
[RuI]
[O2
]
[RuII]*
Ph
N
N
H
H
Ph
O
5aa'
O
5aa
the reaction of the Diels-Alder adduct
I
under standard
Ph
path a
Ph
Lewis acid
4aa
O
Lewis acid
O
conditions to yield product 3aa (61%) for 5 h (Scheme 6, eq. 4).
It is noteworthy that only 10% of desired product was obtained
when BF3.Et2O was absent, and 27% yield was obtained when
Ru(bpy)3(PF6)2 was absent (Scheme 5, eq. 5 and 6). These
results indicated that the adduct product I could also be
efficiently oxidized in the presence of both photocatalyst and
Lewis acid.
4aa
N
H
I
N
3aa
[RuII]*
visible light
[RuII
]
[O]
path b
O2
[RuI]
O
Ph
Ph
[O2]
O
N
H
II
N
On the basis of the above experiments and previous reports,
H
2O2
III
[12d]
a plausible mechanism for the reaction is proposed in
Scheme 7. The imine 4aa is formed via condensation of 1a and
Scheme 7. Proposed mechanism
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10.1002/cctc.201800192
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2-(Cinnamyloxy)-5-methoxybenzaldehyde[15b] (1c): Rf=0.5 (PE/EA
10:1); white solid, 1.20 g, yield: 87%, m.p. 105.3–107.2 oC; 1H NMR (400
MHz, CDCl3) δ 10.53 (s, 1H), 7.43 – 7.40 (m, 2H), 7.37 – 7.32 (m, 3H),
7.30 – 7.27 (m, 1H), 7.13 (dd, J = 9.2, 3.2 Hz, 1H), 7.00 (d, J = 8.8 Hz,
1H), 6.75 (dt, J = 15.6, 1.6 Hz, 1H), 6.42 (dt, J = 16.0, 5.6 Hz, 1H), 4.79
(dd, J = 6.0, 1.6 Hz, 2H), 3.81 (s, 3H); 13C NMR (100 MHz, CDCl3) δ
189.8, 156.0, 154.0, 136.4, 133.7, 128.9, 128.4, 126.8, 125.6, 123.9,
123.7, 115.2, 110.5, 70.1, 56.0.
Conclusions
In conclusion, we have developed a photocatalytic aerobic aza-
Diels-Alder cycloaddition strategy under visible light to construct
chromenoquinolines
dihydrodibenzo[b,h][1,6]naphthyridines, which are important
skeletons of biologically active molecules. The applicability of
readily available starting materials and the use of air as the sole
oxidant under the mild reaction conditions make this process
very attractive. Further applications of this transformation toward
other heterocyclic product are underway.
and
5,6-
5-Chloro-2-(cinnamyloxy)benzaldehyde[15b] (1d): Rf=0.5 (PE/EA 10:1);
white solid, 1.20 g, yield: 90%, m.p. 95.3–97.1 oC; 1H NMR (400 MHz,
CDCl3) δ 10.49 (s, 1H), 7.81 (d, J = 2.8 Hz, 1H), 7.48 (dd, J = 8.8, 2.8 Hz,
1H), 7.44 – 7.41 (m, 2H), 7.38 – 7.33 (m, 2H), 7.31 – 7.27 (m, 1H), 7.00
(d, J = 9.2 Hz, 1H), 6.75 (dd, J = 16.0, 1.6 Hz, 1H), 6.41 (dt, J = 16.0, 5.6
Hz, 1H), 4.82 (dd, J = 5.6, 1.2 Hz, 2H); 13C NMR (100 MHz, CDCl3) δ
188.6, 159.6, 136.2, 135.6, 134.2, 129.0, 128.6, 128.1, 126.9, 126.7,
126.1, 123.1, 114.9, 69.8.
Experimental Section
General Procedures. Unless otherwise noted, all reactions were carried
out under an atmosphere of nitrogen using standard Schlenk techniques.
Materials were purchased from commercial suppliers and were used
without further purification. 1H NMR and 13C NMR spectra were recorded
on a 400 MHz or 500 MHz spectrometer. The chemical shifts for 1H NMR
were recorded in ppm downfield from tetramethylsilane (TMS) with the
solvent resonance as the internal standard. The chemical shifts for 13C
NMR were recorded in ppm downfield using the central peak of
deuterochloroform (77.16 ppm) or dimethyl sulfoxide-d (39.52 ppm) as
the internal standard. Coupling constants (J) are reported in Hz and refer
to apparent peak multiplications. HRMS were obtained on an ESI-TOF
mass spectrometer. Flash column chromatography was performed on
silica gel (300-400 mesh).
3,5-Di-tert-butyl-2-(cinnamyloxy)benzaldehyde (1e): Rf=0.4 (PE/EA
5:1); white solid, 1.60 g, yield: 89%, m.p. 124.8–125.7 oC; 1H NMR (400
MHz, CDCl3) δ 10.36 (s, 1H), 7.73 (dd, J = 2.4, 0.4 Hz, 1H), 7.65 (d, J =
2.4 Hz, 1H), 7.47 – 7.44 (m, 2H), 7.38 – 7.34 (m, 2H), 7.31 – 7.26 (m,
1H), 6.84 – 6.80 (m, 1H), 6.48 (dt, J = 16.0, 5.6 Hz, 1H), 4.65 (dd, J = 5.6,
1.6 Hz, 2H), 1.46 (s, 9H), 1.34 (s, 9H); 13C NMR (100 MHz, CDCl3) δ
191.0, 160.0, 146.8, 143.3, 136.6, 133.2, 131.1, 129.7, 128.9, 128.3,
126.9, 124.3, 124.3, 79.5, 35.7, 35.0, 31.6, 31.2. HRMS (ESI-TOF) (m/z):
(M + Na)+ Calcd. for C24H30O2Na 373.2143; Found 373.2155.
3-Bromo-5-chloro-2-(cinnamyloxy)benzaldehyde (1f): Rf=0.5 (PE/EA
10:1); white solid, 1.60 g, yield: 90%, m.p. 85.2–86.3 oC; 1H NMR (400
MHz, CDCl3) δ 10.32 (s, 1H), 7.82 (d, J = 2.8 Hz, 1H), 7.76 (d, J = 2.8 Hz,
1H), 7.41 – 7.38 (m, 2H), 7.37 – 7.32 (m, 2H), 7.31 – 7.27 (m, 1H), 6.70
(d, J = 16.0 Hz, 1H), 6.44 (dt, J = 16.0, 6.4 Hz, 1H), 4.77 (dd, J = 6.4, 1.2
Hz, 2H); 13C NMR (100 MHz, CDCl3) δ 188.2, 157.5, 138.8, 136.0, 131.9,
131.2, 128.9, 128.7, 127.7, 127.0, 122.6, 119.6, 77.2. HRMS (ESI-TOF)
(m/z): (M + Na)+ Calcd. for C16H12BrClO2Na 372.9607; Found 372.9607.
General procedure for the synthesis of substrate (1a-1j)
The synthetic experimental procedures were based on the literature.[5h,15]
A 250 mL round-bottom flask was charged with cinnamyl bromide (9.47 g,
48 mmol), K2CO3 (7.19 g, 52 mmol), 2-hydroxybenzaldehyde (4.89 g, 40
mmol), and acetone (60 mL). The mixture was stirred at room
temperature under a nitrogen atmosphere for 14 h. After completion, the
mixture was filtered and washed with acetone (20 mL× 3). The solvent
was removed under reduced pressure, the crude product was purified by
(E)-2-((3-(4-Fluorophenyl)allyl)oxy)benzaldehyde[15b]
(1g): Rf=0.2
(PE/EA 10:1); white solid, 1.10 g, yield: 88%, m.p. 57.3–59.0 oC; 1H NMR
(400 MHz, CDCl3) δ 10.56 (d, J = 0.8 Hz, 1H), 7.86 (dd, J = 8.0, 2.0 Hz,
1H), 7.55 (ddd, J = 8.4, 7.2, 1.6 Hz, 1H), 7.42 – 7.37 (m, 2H), 7.07 – 7.01
(m, 4H), 6.73 (dt, J = 16.0, 1.6 Hz, 1H), 6.35 (ddd, J = 11.6, 6.4, 5.6 Hz,
1H), 4.82 (dd, J = 6.0, 1.6 Hz, 2H); 13C NMR (100 MHz, CDCl3) δ 189.9,
162.8 (d, JC-F = 245.9 Hz), 161.1, 136.2, 132.5, 128.7, 128.4 (d, JC-F = 8.1
Hz), 125.3, 123.4, 121.2, 115.8 (d, JC-F = 21.6 Hz), 113.1, 69.2; 19F NMR
(376 MHz, CDCl3) δ = -35.7 (s, 1F).
silica-gel column chromatography (PE/EA
=
20:1) to give 2-
(cinnamyloxy)benzaldehyde as a white solid (8.90 g, 93% yield).
2-(Cinnamyloxy)benzaldehyde[5h] (1a): Rf=0.6 (PE/EA 10:1); white solid,
8.90 g, yield: 93%, m.p. 51.1–52.4 oC; 1H NMR (400 MHz, CDCl3) δ
10.58 (d, J = 0.8 Hz, 1H), 7.87 (dd, J = 8.0, 2.0 Hz, 1H), 7.55 (ddd, J =
8.4, 7.6, 2.0 Hz, 1H), 7.44 – 7.41 (m, 2H), 7.37 – 7.33 (m, 2H), 7.31 –
7.26 (m, 1H), 7.07 – 7.03 (m, 2H), 6.77 (dt, J = 16.0, 1.6 Hz, 1H), 6.44 (dt,
J = 16.0, 5.6 Hz, 1H), 4.83 (dd, J = 5.6, 1.6 Hz, 2H); 13C NMR (100 MHz,
CDCl3) δ 189.9, 161.2, 136.4, 136.2, 133.7, 129.0, 128.8, 128.7, 128.4,
126.9, 125.4, 123.7, 121.2, 113.2, 69.4.
(E)-2-((3-(4-Methoxyphenyl)allyl)oxy)benzaldehyde[15b] (1h): Rf=0.2
(PE/EA 10:1); white solid, 1.10 g, yield: 84%, m.p. 75.0–78.0 oC; 1H NMR
(400 MHz, CDCl3) δ 10.56 (d, J = 0.8 Hz, 1H), 7.86 (dd, J = 8.4, 2.0 Hz,
1H), 7.54 (ddd, J = 8.0, 7.2, 1.6 Hz, 1H), 7.38 – 7.35 (m, 2H), 7.06 – 7.02
(m, 2H), 6.90 – 6.86 (m, 2H), 6.73 – 6.68 (m, 1H), 6.29 (dt, J = 16.0, 5.6
Hz, 1H), 4.80 (dd, J = 6.0, 1.6 Hz, 2H), 3.82 (s, 3H); 13C NMR (100 MHz,
CDCl3) δ 190.1, 161.3, 159.9, 136.1, 133.5, 129.1, 128.6, 128.1, 125.3,
121.3, 121.0, 114.3, 113.2, 69.6, 55.5.
2-(Cinnamyloxy)-5-methylbenzaldehyde[15b] (1b): Rf=0.5 (PE/EA 10:1);
yellow solid, 1.10 g, yield: 84%, m.p. 59.5–61.2 oC; 1H NMR (400 MHz,
CDCl3) δ 10.54 (s, 1H), 7.66 – 7.65 (m, 1H), 7.44 – 7.41 (m, 2H), 7.37 –
7.32 (m, 3H), 7.30 – 7.26 (m, 1H), 6.94 (d, J = 8.4 Hz, 1H), 6.76 (dt, J =
16.0, 1.6 Hz, 1H), 6.42 (dt, J = 16.0, 6.0 Hz, 1H), 4.80 (dd, J = 5.6, 1.6
Hz, 2H), 2.32 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 189.8, 159.0, 136.5,
136.1, 133.2, 130.2, 128.6, 128.3, 128.1, 126.6, 124.7, 123.6, 113.0,
69.1, 20.2.
(E)-2-((3-(o-Tolyl)allyl)oxy)benzaldehyde (1i): Rf=0.5 (PE/EA 10:1);
white solid, 1.00 g, yield: 82%, m.p. 69.6–70.5 oC; 1H NMR (400 MHz,
CDCl3) δ 10.57 (d, J = 0.8 Hz, 1H), 7.86 (dd, J = 8.0, 2.0 Hz, 1H), 7.58 –
7.53 (m, 1H), 7.49 – 7.46 (m, 1H), 7.21 – 7.15 (m, 3H), 7.07 – 6.97 (m,
3H), 6.31 (dt, J = 16.0, 5.6 Hz, 1H), 4.85 (dd, J = 5.6, 1.6 Hz, 2H), 2.35 (s,
3H); 13C NMR (100 MHz, CDCl3) δ 190.0, 161.2, 136.1, 135.9, 135.5,
131.7, 130.6, 128.7, 128.3, 126.5, 126.0, 125.4, 124.9, 121.1, 113.2,
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10.1002/cctc.201800192
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69.5, 20.0. HRMS (ESI-TOF) (m/z): (M + Na)+ Calcd. for C17H16O2Na
275.1048; Found 275.1048.
122.5, 121.5, 117.1, 104.5, 66.9, 55.4. HRMS (ESI-TOF) (m/z): (M + H)+
Calcd. for C23H18NO2 340.1338; Found 340.1338.
N-Cinnamyl-N-(2-formylphenyl)-4-methylbenzenesulfonamide[15a]
(1j): Rf=0.4 (PE/EA 10:1); white solid, 3.60 g, yield: 70%, m.p. 115.8–118
oC; 1H NMR (400 MHz, CDCl3) δ 10.41 (d, J = 0.8 Hz, 1H), 7.97 (dd, J =
7.6, 1.6 Hz, 1H), 7.53 – 7.41 (m, 4H), 7.31 – 7.18 (m, 9H), 6.80 (dd, J =
7.6, 1.6 Hz, 1H), 6.33 (d, J = 15.6 Hz, 1H), 6.09 (dt, J = 15.6, 6.8 Hz, 1H),
4.69 (s, 1H), 4.08 (s, 1H), 2.46 (s, 3H); 13C NMR (100 MHz, CDCl3) δ
190.3, 144.5, 141.7, 136.2, 136.0, 135.6, 134.8, 134.4, 130.0, 128.9,
128.8, 128.7, 128.4, 128.3, 128.2, 126.7, 122.7, 54.4, 21.9.
9-(Tert-butyl)-7-phenyl-6H-chromeno[4,3-b]quinoline (3ad): Rf=0.71
(PE/EA 10:1); white solid, 73.6 mg, yield: 68%, m.p. 186.7–189.1 oC; 1H
NMR (400 MHz, CDCl3) δ 8.52 (dd, J = 7.6, 1.6 Hz, 1H), 8.11 (dd, J = 8.8,
0.4 Hz, 1H), 7.78 (dd, J = 8.8, 2.0 Hz, 1H), 7.59 – 7.50 (m, 3H), 7.41 –
7.36 (m, 2H), 7.34 – 7.31 (m, 2H), 7.18 (ddd, J = 7.6, 7.2, 1.2 Hz, 1H),
6.98 (dd, J = 8.4, 1.2 Hz, 1H), 5.11 (s, 2H), 1.28 (s, 9H); 13C NMR (100
MHz, CDCl3) δ 157.4, 149.2, 148.3, 146.8, 143.8, 135.3, 131.8, 129.5,
129.4, 128.9, 128.7, 128.4, 126.8, 125.9, 124.0, 123.0, 122.7, 121.3,
117.3, 67.1, 35.2, 31.3. HRMS (ESI-TOF) (m/z): (M + H)+ Calcd. for
C26H25NO 366.1858; Found 366.1858.
(E)-2-((3-(Thiophen-2-yl)allyl)oxy)benzaldehyde (1k): Rf=0.4 (PE/EA
20:1); light yellow solid, 1.82 g, yield: 60%, m.p. 77.0–78.9 oC; 1H NMR
(400 MHz, CDCl3) δ 10.56 (s, 1H), 7.86 (dd, J = 7.6, 2.0 Hz, 1H), 7.57 –
7.52 (m, 1H), 7.21 (d, J = 4.8 Hz, 1H), 7.07 – 6.97 (m, 4H), 6.89 (d, J =
16.0 Hz, 1H), 6.26 (dt, J = 16.0, 6.0 Hz, 1H), 4.79 (dd, J = 5.6, 1.6 Hz,
2H).; 13C NMR (100 MHz, CDCl3) δ 190.0, 161.1, 141.3, 136.2, 128.7,
127.8, 126.9, 125.3, 123.0, 121.2, 113.1, 69.0. HRMS (ESI-TOF) (m/z):
(M + Na)+ Calcd. for C14H12O2SNa 267.0456; Found 267.0465.
7-Phenyl-6H-chromeno[4,3-b]quinolin-9-ol (3ae): Rf=0.13 (PE/EA
10:1); gray solid, 82.3 mg, yield: 84%, m.p. 246.0–248.0 oC; 1H NMR
(400 MHz, DMSO) δ 9.98 (s, 1H), 8.35 (dd, J = 7.6, 1.6 Hz, 1H), 7.97 (d,
J = 8.8 Hz, 1H), 7.65 – 7.55 (m, 3H), 7.40 – 7.36 (m, 3H), 7.30 (dd, J =
8.8, 2.4 Hz, 1H), 7.17 (td, J = 7.2, 1.2 Hz, 1H), 7.00 (dd, J = 8.0, 0.8 Hz,
1H), 6.70 (d, J = 2.8 Hz, 1H), 5.06 (s, 2H); 13C NMR (100 MHz, DMSO) δ
156.9, 156.5, 145.3, 143.1, 141.9, 135.1, 131.9, 131.4, 129.7, 129.4,
129.1, 128.5, 125.4, 123.8, 123.0, 122.8, 122.6, 117.6, 107.4, 66.8.
HRMS (ESI-TOF) (m/z): (M + H)+ Calcd. for C22H16NO2 326.1181; Found
326.1181.
Typical Procedure: Preparation of 9-Methyl-7-phenyl-6H-chromeno
[4,3-b]quinoline (3aa)
Caution! The reaction is run in a sealed vessel under O2. Though no
incidents have been encountered in the submitters' laboratory, it is
nonetheless recommended that a blast shield be used as a precaution.
9-Chloro-7-phenyl-6H-chromeno[4,3-b]quinoline[9]
(3af):
Rf=0.74
(PE/EA 10:1); yellow solid, 56.7 mg, yield: 55%, m.p. 174.5–175.2 oC; 1H
NMR (400 MHz, CDCl3) δ 8.50 (ddd, J = 8.0, 2.0, 0.4 Hz, 1H), 8.11 (dd, J
= 9.2, 0.8 Hz, 1H), 7.63 – 7.55 (m, 4H), 7.44 (d, J = 2.0 Hz, 1H), 7.38
(ddd, J = 9.2, 7.2, 1.6 Hz, 1H), 7.31 – 7.28 (m, 2H), 7.18 (ddd, J = 8.4,
7.2, 1.2 Hz, 1H), 7.00 – 6.97 (m, 1H), 5.10 (s, 2H); 13C NMR (100 MHz,
CDCl3) δ 157.5, 149.2, 146.6, 143.1, 134.4, 132.3, 132.2, 131.4, 130.4,
129.3, 129.2, 129.1, 128.0, 125.9, 125.1, 123.9, 123.4, 122.8, 117.4,
66.8.
A solution of 2-(cinnamyloxy)benzaldehyde (1a, 0.3 mmol, 71.5 mg), p-
toluidine (2a, 0.3 mmol, 33.6 mg), Ru(bpy)3(PF6)2 (0.006 mol, 5.3 mg) in
.
CH3CN (3 mL) was mixed and then BF3 Et2O (0.03 mol, 9.0 mg) was
added. The reaction solution was irradiated with a 23 W fluorescent light
(distance app. 5 cm) under air atmosphere at room temperature for 24 h.
After the completion of the reaction, the mixture was concentrated in
vacuum and the pure product was obtained by flash column
chromatography on silica gel (PE/EA = 50:1) to give the product 3aa.
9-Bromo-7-phenyl-6H-chromeno[4,3-b]quinoline[9] (3ag): Rf=0.72
(PE/EA 10:1); yellow solid, 70.3 mg, yield: 61%, m.p. 196.5–198.0 oC; 1H
NMR (400 MHz, CDCl3) δ 8.50 (dd, J = 8.0, 1.6 Hz, 1H), 8.03 (d, J = 9.2
Hz, 1H), 7.74 (dd, J = 8.8, 2.2 Hz, 1H), 7.61 – 7.55 (m, 4H), 7.39 (ddd, J
= 9.2, 7.6, 2.0 Hz, 1H), 7.31 – 7.28 (m, 2H), 7.20 – 7.16 (m, 2H), 6.98 (dd,
J = 8.4, 1.2 Hz, 1H), 5.10 (s, 2H); 13C NMR (100 MHz, CDCl3) δ 157.5,
149.3, 146.8, 143.1, 134.3, 133.0, 132.4, 131.5, 129.4, 129.2, 129.1,
128.5, 126.0, 123.9, 123.4, 122.8, 120.5, 117.5, 66.8.
9-Methyl-7-phenyl-6H-chromeno[4,3-b]quinoline[9] (3aa): Rf=0.63
(PE/EA 10:1); yellow solid, 82.0 mg, yield: 85%, m.p. 192.0–194.1 oC; 1H
NMR (400 MHz, CDCl3) δ 8.51 (dd, J = 8.0, 1.6 Hz, 1H), 8.07 (d, J = 8.4
Hz, 1H), 7.59 – 7.51 (m, 4H), 7.38 – 7.29 (m, 3H), 7.22 – 7.16 (m, 2H),
6.98 (dd, J = 8.4, 1.2 Hz, 1H), 5.09 (s, 2H), 2.41 (s, 3H); 13C NMR (100
MHz, CDCl3) δ 156.9, 147.6, 146.4, 142.8, 135.9, 134.8, 131.3, 129.1,
129.0, 128.5, 128.2, 126.7, 125.4, 124.7, 123.4, 122.6, 122.2, 116.9,
66.6, 21.6.
7-Phenyl-6H-chromeno[4,3-b]quinoline-9-carbonitrile (3ah): Rf=0.61
(PE/EA 10:1); yellow solid, 75.8 mg, yield: 76%, m.p. 190.0–191.4 oC; 1H
NMR (400 MHz, CDCl3) δ 8.52 (dd, J = 8.0, 5.6 Hz, 1H), 8.23 (d, J = 8.8
Hz, 1H), 7.87 – 7.80 (m, 2H), 7.64 – 7.59 (m, 3H), 7.45 – 7.41 (m, 1H),
7.30 – 7.28 (m, 2H), 7.20 (td, J = 8.0, 1.2 Hz, 1H), 7.01 – 6.99 (m, 1H),
5.14 (s, 2H); 13C NMR (100 MHz, CDCl3) δ 157.7, 151.6, 149.1, 144.2,
133.4, 133.0, 132.6, 131.0, 130.1, 129.4, 129.3, 129.1, 126.7, 126.2,
124.5, 122.8, 119.0, 117.5, 109.5, 66.5. HRMS (ESI-TOF) (m/z): (M + H)+
Calcd. for C23H15N2O 335.1184; Found 335.1164.
7-Phenyl-6H-chromeno[4,3-b]quinoline[9] (3ab): Rf=0.79 (PE/EA 10:1);
white solid, 58.8 mg, yield: 63%, m.p. 155.0–157.3 oC; 1H NMR (400
MHz, CDCl3) δ 8.54 (dd, J = 8.0, 1.6 Hz, 1H), 8.18 (ddd, J = 8.4, 1.2, 0.8
Hz, 1H), 7.71 – 7.67 (m, 1H), 7.59 – 7.48 (m, 4H), 7.42 – 7.36 (m, 2H),
7.33 – 7.31 (m, 2H), 7.21 – 7.17 (m, 1H), 6.99 (dd, J = 8.4, 1.2 Hz, 1H),
5.12 (s, 2H); 13C NMR (100 MHz, CDCl3) δ 157.4, 148.8, 148.2, 143.8,
135.0, 132.0, 129.7, 129.4, 129.3, 128.9, 128.7, 127.2, 126.3, 126.2,
125.9, 123.7, 122.9, 122.6, 117.3, 66.9.
Methyl-7-phenyl-6H-chromeno[4,3-b]quinoline-9-carboxylate (3ai):
Rf=0.62 (PE/EA 10:1); yellow solid, 70.8 mg, yield: 64%, m.p. 198.0–
200.0 oC; 1H NMR (400 MHz, CDCl3) δ 8.55 – 8.52 (m, 1H), 8.28 – 8.19
(m, 3H), 7.62 – 7.56 (m, 3H), 7.43 – 7.38 (m, 1H), 7.33 – 7.31 (m, 2H),
7.21 – 7.17 (m, 1H), 7.00 – 6.98 (m, 1H), 5.12 (s, 2H), 3.89 (s, 3H); 13C
NMR (100 MHz, CDCl3) δ 167.0, 157.8, 150.9, 150.2, 145.2, 134.3,
132.7, 130.1, 129.4, 129.21, 129.15, 129.1, 127.7, 126.5, 126.3, 123.8,
123.3, 122.8, 117.5, 66.9, 52.5. HRMS (ESI-TOF) (m/z): (M + H)+ Calcd.
for C24H18NO3 368.1287; Found 368.1281.
9-Methoxy-7-phenyl-6H-chromeno[4,3-b]quinoline (3ac): Rf=0.41
(PE/EA 10:1); yellow solid, 75.6 mg, yield: 74%, m.p. 163.5–165.0 oC; 1H
NMR (400 MHz, CDCl3) δ 8.48 (dd, J = 7.6, 1.6 Hz, 1H), 8.09 (d, J = 9.2
Hz, 1H), 7.59 – 7.50 (m, 3H), 7.37 – 7.31 (m, 4H), 7.20 – 7.15 (m, 1H),
6.97 (dd, J = 8.4, 1.2 Hz, 1H), 6.75 (d, J = 2.8 Hz, 1H), 5.09 (s, 2H), 3.72
(s, 3H); 13C NMR (100 MHz, CDCl3) δ 157.7, 156.9, 146.5, 144.2, 142.4,
135.2, 131.3, 131.2, 129.2, 128.9, 128.6, 128.0, 125.4, 123.8, 123.1,
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10.1002/cctc.201800192
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1-(7-Phenyl-6H-chromeno[4,3-b]quinolin-9-yl)ethan-1-one
(3aj):
2-Methoxy-9-methyl-7-phenyl-6H-chromeno[4,3-b]quinoline
(3ca):
Rf=0.52 (PE/EA 10:1); yellow solid, 86.5 mg, yield: 82%, m.p. 223.7–
225.2 oC; 1H NMR (400 MHz, CDCl3) δ 8.54 (dd, J = 7.6, 1.6 Hz, 1H),
8.25 – 8.20 (m, 2H), 8.11 – 8.10 (m, 1H), 7.63 – 7.57 (m, 3H), 7.43 –
7.39 (m, 1H), 7.34 – 7.32 (m, 2H), 7.22 – 7.18 (m, 1H), 7.00 (dd, J = 8.0,
1.2 Hz, 1H), 5.14 (s, 2H), 2.55 (s, 3H); 13C NMR (100 MHz, CDCl3) δ
197.6, 157.7, 151.0, 150.1, 145.3, 134.5, 134.2, 132.7, 130.2, 129.3,
129.1, 128.3, 127.8, 126.4, 126.2, 123.8, 123.2, 122.8, 117.4, 66.7, 26.8.
HRMS (ESI-TOF) (m/z): (M + H)+ Calcd. for C24H18NO2 352.1338; Found
352.1351.
Rf=0.43 (PE/EA 10:1); yellow solid, 70.5 mg, yield: 67%, m.p. 224.6–
227.1 oC; 1H NMR (400 MHz, CDCl3) δ 8.09 – 8.01 (m, 2H), 7.59 – 7.51
(m, 4H), 7.32 – 7.28 (m, 2H), 7.22 (s, 1H), 6.96 – 6.90 (m, 2H), 5.04 (s,
2H), 3.96 (s, 3H), 2.41 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 155.3,
151.6, 148.1, 146.7, 143.3, 136.4, 135.3, 131.8, 129.5, 129.0, 128.7,
127.3, 125.2, 124.2, 123.3, 119.5, 118.4, 108.3, 67.1, 56.2, 22.0. HRMS
(ESI-TOF) (m/z): (M + H)+ Calcd. for C24H21NO2 354.1494; Found
354.1494.
2-Chloro-9-methyl-7-phenyl-6H-chromeno[4,3-b]quinoline
(3da):
11-Bromo-7-phenyl-6H-chromeno[4,3-b]quinoline
(3ak):
Rf=0.73
Rf=0.68 (PE/EA 10:1); yellow solid, 81.6 mg, yield: 76%, m.p. 247.1–
249.3 oC; 1H NMR (400 MHz, CDCl3) δ 8.48 (d, J = 2.8 Hz, 1H), 8.07 (d,
J = 8.4 Hz, 1H), 7.59 – 7.52 (m, 4H), 7.31 – 7.27 (m, 3H), 7.23 – 7.22 (m,
1H), 6.91 (d, J = 8.4 Hz, 1H), 5.08 (s, 2H), 2.42 (s, 3H); 13C NMR (100
MHz, CDCl3) δ 155.8, 146.8, 143.5, 136.8, 135.1, 132.0, 131.5, 129.6,
129.4, 129.0, 128.8, 127.9, 127.4, 125.4, 125.2, 122.6, 118.8, 67.1, 22.0.
HRMS (ESI-TOF) (m/z): (M + H)+ Calcd. for C23H18ClNO 358.0999;
Found 358.0999.
(PE/EA 10:1); yellow solid, 72.0 mg, yield: 60%, m.p. 184.8–186.1 oC; 1H
NMR (400 MHz, CDCl3) δ 8.66 (dd, J = 7.6, 1.6 Hz, 1H), 8.01 (dd, J = 7.6,
1.6 Hz, 1H), 7.59 – 7.53 (m, 3H), 7.45 – 7.37 (m, 2H), 7.31 – 7.28 (m,
2H), 7.24 – 7.18 (m, 2H), 6.97 (dd, J = 8.0, 0.8 Hz, 1H), 5.12 (s, 2H); 13C
NMR (100 MHz, CDCl3) δ 157.6, 149.6, 145.1, 144.4, 134.8, 133.3,
132.5, 129.5, 129.4, 129.1, 129.0, 128.7, 126.6, 126.5, 126.3, 125.8,
123.8, 123.5, 122.9, 117.3, 66.8. HRMS (ESI-TOF) (m/z): (M + H)+ Calcd.
for C22H15BrNO 388.0337; Found 388.0337.
2,4-Di-tert-butyl-9-methyl-7-phenyl-6H-chromeno[4,3-b]quinoline
(3ea): Rf=0.76 (PE/EA 10:1); yellow solid, 105.9 mg, yield: 81%, m.p.
278.1–280.0 oC; 1H NMR (400 MHz, CDCl3) δ 8.41 (d, J = 2.4 Hz, 1H),
8.11 (d, J = 8.4 Hz, 1H), 7.59 – 7.50 (m, 5H), 7.42 (d, J = 2.4 Hz, 1H),
7.34 – 7.31 (m, 2H), 7.25 – 7.23 (m, 1H), 5.03 (s, 2H), 2.41 (s, 3H), 1.43
(s, 9H), 1.39 (s, 9H); 13C NMR (100 MHz, CDCl3) δ 154.1, 149.2, 146.9,
144.5, 142.7, 138.1, 136.0, 135.6, 131.5, 129.8, 129.7, 129.0, 128.6,
126.9, 126.5, 125.1, 124.2, 123.7, 120.3, 66.3, 35.1, 31.9, 30.2, 22.0.
HRMS (ESI-TOF) (m/z): (M + H)+ Calcd. for C31H34NO 436.2640; Found
436.2650.
7-Phenyl-6H-chromeno[4,3-b]quinoline-11-carbonitrile (3al): Rf=0.6
(PE/EA 10:1); yellow solid, 69.3 mg, yield: 69%, m.p. 215.6–217.4 oC; 1H
NMR (400 MHz, CDCl3) δ 8.68 (ddd, J = 7.6, 1.6, 0.4 Hz, 1H), 8.07 (dd, J
= 7.2, 1.6 Hz, 1H), 7.71 (dd, J = 8.4, 1.2 Hz, 1H), 7.62 – 7.56 (m, 3H),
7.44 – 7.40 (m, 2H), 7.31 – 7.28 (m, 2H), 7.22 – 7.18 (m, 1H), 6.99 –
6.97 (m, 1H), 5.14 (s, 2H); 13C NMR (100 MHz, CDCl3) δ 157.7, 150.8,
147.5, 144.4, 135.5, 133.9, 133.1, 131.4, 129.4, 129.3, 129.2, 127.3,
126.8, 125.4, 124.5, 122.9, 122.7, 117.7, 117.3, 113.1, 66.6. HRMS (ESI-
TOF) (m/z): (M + H)+ Calcd. for C23H15N2O 335.1184; Found 335.1184.
7-Phenyl-11-(phenylethynyl)-6H-chromeno[4,3-b]quinoline
(3am):
4-Bromo-2-chloro-9-methyl-7-phenyl-6H-chromeno[4,3-b]quinoline
(3fa): Rf=0.81 (PE/EA 10:1); yellow solid, 108.7 mg, yield: 83%, m.p.
231.1–234.0 oC; 1H NMR (400 MHz, CDCl3) δ 8.47 (d, J = 2.8 Hz, 1H),
8.06 (d, J = 8.4 Hz, 1H), 7.59 – 7.53 (m, 5H), 7.30 – 7.28 (m, 2H), 7.25 –
7.24 (m, 1H), 5.19 (s, 2H), 2.42 (s, 3H); 13C NMR (100 MHz, CDCl3) δ
152.5, 146.8, 146.0, 143.8, 137.3, 134.8, 134.2, 132.3, 129.6, 129.3,
129.1, 128.9, 128.1, 127.5, 126.0, 125.2, 124.8, 122.0, 111.8, 67.7, 22.1.
HRMS (ESI-TOF) (m/z): (M + H)+ Calcd. for C23H16BrClNO 436.0104;
Found 436.0104.
Rf=0.71 (PE/EA 10:1); yellow solid, 89.6 mg, yield: 73%, m.p. 175.4–
177.1 oC; 1H NMR (400 MHz, CDCl3) δ 8.70 (dd, J = 7.6, 1.6 Hz, 1H),
7.94 (dd, J = 7.2, 1.6 Hz, 1H), 7.77 – 7.75 (m, 2H), 7.59 – 7.53 (m, 3H),
7.47 – 7.44 (m, 2H), 7.43 – 7.36 (m, 4H), 7.33 – 7.30 (m, 2H), 7.20 (td, J
= 7.6, 1.2 Hz, 1H), 6.98 (dd, J = 8.0, 1.2 Hz, 1H), 5.13 (s, 2H); 13C NMR
(100 MHz, CDCl3) δ 157.6, 149.1, 148.1, 144.3, 134.9, 133.7, 132.3,
132.1, 129.5, 129.1, 128.9, 128.7, 128.6, 127.4, 126.9, 126.4, 125.9,
124.2, 123.8, 123.6, 123.4, 122.8, 117.4, 95.8, 88.1, 66.9. HRMS (ESI-
TOF) (m/z): (M + H)+ Calcd. for C30H20NO 410.1545; Found 410.1545.
7-(4-Fluorophenyl)-9-methyl-6H-chromeno[4,3-b]quinoline
(3ga):
9-Bromo-11-methyl-7-phenyl-6H-chromeno[4,3-b]quinoline
(3an):
Rf=0.52 (PE/EA 10:1); yellow solid, 89.5 mg, yield: 87%, m.p. 131.4–
133.7 oC; 1H NMR (400 MHz, CDCl3) δ 8.50 (dd, J = 8.0, 2.0 Hz, 1H),
8.07 (d, J = 8.8 Hz, 1H), 7.53 (dd, J = 8.8, 2.0 Hz, 1H), 7.39 – 7.34 (m,
1H), 7.31 – 7.27 (m, 4H), 7.20 – 7.16 (m, 2H), 7.00 – 6.97 (m, 1H), 5.08
(s, 2H), 2.42 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 163.0 (d, JC-F = 246.7
Hz), 157.3, 148.1, 146.8, 142.2, 136.6, 131.9, 131.3 (d, JC-F = 8.0 Hz),
131.1, 129.7, 127.2, 125.8, 124.9, 123.8, 123.2, 122.8, 117.3, 116.2 (d,
JC-F = 21.4 Hz), 66.9, 22.0; 19F NMR (376 MHz, CDCl3) δ = -35.1 (s, 1F).
HRMS (ESI-TOF) (m/z): (M + H)+ Calcd. for C23H17FNO 342.1294; Found
342.1295.
Rf=0.85 (PE/EA 10:1); yellow solid, 68.3 mg, yield: 57%, m.p. 175.4–
177.8 oC; 1H NMR (400 MHz, CDCl3) δ 8.55 (dd, J = 8.0, 1.6 Hz, 1H),
7.63 (dd, J = 2.4, 1.2 Hz, 1H), 7.60 – 7.53 (m, 3H), 7.44 (d, J = 2.0 Hz,
1H), 7.40 – 7.35 (m, 3H), 7.28 – 7.26 (m, 2H), 7.17 (td, J = 7.6, 1.2 Hz,
1H), 6.97 (dd, J = 8.0, 1.2 Hz, 1H), 5.09 (s, 2H), 2.89 (s, 3H); 13C NMR
(100 MHz, CDCl3) δ 157.4, 147.7, 145.8, 143.1, 140.1, 134.8, 132.8,
132.1, 129.4, 129.1, 128.9, 128.3, 126.3, 125.9, 123.7, 123.4, 122.6,
120.2, 117.4, 66.9, 18.1. HRMS (ESI-TOF) (m/z): (M + Na)+ Calcd. for
C23H16BrNONa 424.0313; Found 424.0313.
2,9-Dimethyl-7-phenyl-6H-chromeno[4,3-b]quinoline (3ba): Rf=0.62
(PE/EA 10:1); yellow solid, 79.8 mg, yield: 80%, m.p. 177.0–179.4 oC; 1H
NMR (400 MHz, CDCl3) δ 8.30 (s, 1H), 8.07 (d, J = 8.4 Hz, 1H), 7.59 –
7.51 (m, 4H), 7.31 (dd, J = 7.6, 1.6 Hz, 2H), 7.22 (s, 1H), 7.17 (dd, J =
8.0, 2.0 Hz, 1H), 6.88 (d, J = 8.4 Hz, 1H), 5.05 (s, 2H), 2.43 (s, 3H), 2.41
(s, 3H);13C NMR (100 MHz, CDCl3) δ 155.3, 148.3, 146.8, 143.2, 136.3,
135.4, 132.6, 132.0, 131.8, 129.5, 129.0, 128.7, 127.2, 125.8, 125.2,
123.5, 123.3, 117.1, 67.0, 22.0, 21.1. HRMS (ESI-TOF) (m/z): (M + H)+
Calcd. for C24H21NO 338.1545; Found 338.1545.
7-(4-Methoxyphenyl)-9-methyl-6H-chromeno[4,3-b]quinoline (3ha):
Rf=0.42 (PE/EA 10:1); white solid, 90.1 mg, yield: 85%, m.p. 198.3–199.7
oC; 1H NMR (400 MHz, CDCl3) δ 8.50 (dd, J = 7.6, 1.6 Hz, 1H), 8.06 (d, J
= 8.4 Hz, 1H), 7.51 (dd, J = 8.4, 1.6 Hz, 1H), 7.36 (ddd, J = 9.2, 7.2, 1.6
Hz, 1H), 7.27 (s, 1H), 7.24 – 7.21 (m, 2H), 7.17 (td, J = 7.6, 1.2 Hz, 1H),
7.11 – 7.07 (m, 2H), 6.98 (dd, J = 8.0, 1.2 Hz, 1H), 5.12 (s, 2H), 3.93 (s,
3H), 2.42 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 159.8, 157.3, 148.1,
146.9, 143.1, 136.3, 131.75, 131.71, 130.8, 129.6, 127.6, 127.2, 125.8,
125.3, 124.0, 123.3, 122.7, 117.3, 114.4, 67.1, 55.6, 22.1. HRMS (ESI-
TOF) (m/z): (M + H)+ Calcd. for C24H20NO2 354.1494; Found 354.1494.
This article is protected by copyright. All rights reserved.

10.1002/cctc.201800192
ChemCatChem
FULL PAPER
9-Methyl-7-(o-tolyl)-6H-chromeno[4,3-b]quinoline
(3ia):
Rf=0.64
143.7, 138.3, 134.5, 134.2, 132.6, 131.2, 131.0, 130.3, 129.4, 128.9,
128.0, 127.9, 127.4, 127.2, 126.5, 124.9, 123.9, 48.0, 21.3. HRMS (ESI-
TOF) (m/z): (M + H)+ Calcd. for C29H22ClN2O2S 497.1091; Found
497.1091.
(PE/EA 10:1); yellow solid, 83.1 mg, yield: 82%, m.p. 176.0–178.1 oC; 1H
NMR (400 MHz, CDCl3) δ 8.52 (dd, J = 8.0, 1.6 Hz, 1H), 8.07 (d, J = 8.4
Hz, 1H), 7.52 (dd, J = 8.4, 2.0 Hz, 1H), 7.46 – 7.34 (m, 4H), 7.20 – 7.12
(m, 2H), 7.03 – 7.02 (m, 1H), 6.97 (dd, J = 8.0, 0.8 Hz, 1H), 5.04 – 4.91
(m, 2H), 2.40 (s, 3H), 2.00 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 157.4,
148.2, 146.9, 142.9, 136.6, 136.3, 134.8, 131.9, 131.8, 130.7, 129.7,
129.3, 128.9, 127.1, 126.5, 125.8, 124.8, 123.9, 123.2, 122.7, 117.4,
66.9, 22.0, 19.9. HRMS (ESI-TOF) (m/z): (M + H)+ Calcd. for C24H20NO
338.1545; Found 338.1545.
9-Bromo-7-phenyl-5-tosyl-5,6-dihydrodibenzo[b,h][1,6]naphthyridine
(3jg): Rf=0.61 (PE/EA 10:1); white solid, 110.4 mg, yield: 68%, m.p.
217.5–218.6 oC; 1H NMR (400 MHz, CDCl3) δ 8.37 (dd, J = 7.6, 1.6 Hz,
1H), 7.89 (d, J = 9.2 Hz, 1H), 7.80 (dd, J = 8.0, 1.2 Hz, 1H), 7.71 (dd, J =
8.8, 2.0 Hz, 1H), 7.67 – 7.60 (m, 4H), 7.56 (td, J = 7.6, 1.6 Hz, 1H), 7.49
(td, J = 7.6, 1.2 Hz, 1H), 7.28 (d, J = 2.0 Hz, 1H), 6.98 (d, J = 8.4 Hz, 2H),
6.72 – 6.69 (m, 2H), 4.82 (s, 2H), 1.97 (s, 3H); 13C NMR (100 MHz,
CDCl3) δ 149.8, 146.3, 144.0, 143.6, 138.3, 134.5, 134.1, 132.9, 131.3,
131.1, 129.5, 129.4, 128.9, 128.2, 128.0, 127.9, 127.2, 126.5, 123.9,
9-Methyl-7-(thiophen-2-yl)-6H-chromeno[4,3-b]quinoline (3ka): Rf=0.70
(PE/EA 10:1); yellow solid, 63.4 mg, yield: 64%, m.p. 197.0–198.6 oC; 1H
NMR (400 MHz, CDCl3) δ 8.49 (d, J = 8.0 Hz, 1H), 8.06 (d, J = 8.8 Hz,
1H), 7.59 (d, J = 5.2 Hz, 1H), 7.53 (d, J = 8.4 Hz, 1H), 7.44 (s, 1H), 7.38
– 7.34 (m, 1H), 7.28 – 7.26 (m, 1H), 7.17 (t, J = 7.6 Hz, 1H), 7.10 (d, J =
3.2 Hz, 1H), 6.99 (d, J = 8.4 Hz, 1H), 5.21 (s, 2H), 2.46 (s, 3H); 13C NMR
(100 MHz, CDCl3) δ 157.3, 148.0, 146.8, 136.8, 136.0, 134.7, 132.0,
131.9, 129.6, 129.0, 128.0, 127.8, 127.6, 125.8, 125.0, 124.9, 123.7,
122.7, 117.3, 67.1, 22.1. HRMS (ESI-TOF) (m/z): (M + H)+ Calcd. for
C21H16NOS 330.0953; Found 330.0947.
120.8, 47.9, 21.3. HRMS (ESI-TOF) (m/z): (M
C29H22BrN2O2S 541.0585; Found 541.0585.
+
H)+ Calcd. for
7-Phenyl-5-tosyl-5,6-dihydrodibenzo[b,h][1,6]naphthyridine-9-
carbonitrile (3jh): Rf=0.55 (PE/EA 10:1); yellow solid, 100.4 mg, yield:
69%, m.p. 253.8–254.6 oC; 1H NMR (400 MHz, CDCl3) δ 8.40 (dd, J =
8.0, 2.0 Hz, 1H), 8.10 (d, J = 8.8 Hz, 1H), 7.86 (d, J = 2.0 Hz, 1H), 7.82 –
7.76 (m, 2H), 7.70 – 7.64 (m, 3H), 7.62 – 7.58 (m, 3H), 7.51 (td, J = 8.0,
1.6 Hz, 1H), 7.28 – 7.25 (m, 2H), 6.99 (d, J = 8.4 Hz, 2H), 6.70 (d, J = 8.0
Hz, 2H), 4.85 (s, 2H), 1.95 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 152.2,
148.6, 145.0, 144.1, 138.8, 134.4, 133.4, 132.6, 131.8, 130.9, 130.6,
130.1, 129.9, 129.7, 129.4, 129.0, 128.1, 128.0, 127.2, 126.9, 126.2,
124.8, 119.0, 110.0, 47.8, 21.3. HRMS (ESI-TOF) (m/z): (M + H)+ Calcd.
for C30H22N3O2S 488.1433; Found 488.1425.
7-Phenyl-5-tosyl-5,6-dihydrodibenzo[b,h][1,6]naphthyridine
(3jb):
Rf=0.51 (PE/EA 10:1); yellow solid, 78.8 mg, yield: 57%, m.p. 201.0–
202.7 oC; 1H NMR (400 MHz, CDCl3) δ 8.40 (dd, J = 7.6, 2.0 Hz, 1H),
8.04 – 8.02 (m, 1H), 7.80 (dd, J = 8.0, 1.6 Hz, 1H), 7.66 – 7.47 (m, 7H),
7.41 – 7.37 (m, 1H), 7.31 – 7.28 (m, 2H), 6.99 (d, J = 8.4 Hz, 2H), 6.67 (d,
J = 8.0 Hz, 2H), 4.84 (s, 2H), 1.92 (s, 3H); 13C NMR (100 MHz, CDCl3) δ
149.4, 147.7, 144.4, 143.9, 138.3, 134.8, 134.6, 131.4, 130.8, 129.6,
129.4, 129.2, 129.1, 128.9, 128.0, 127.9, 127.2, 126.7, 126.5, 126.1,
7-Phenyl-5-tosyl-5,6-dihydrodibenzo[b,h][1,6]naphthyridin-11-ol
(3jo): Rf=0.12 (PE/EA 10:1); white solid, 108.5 mg, yield: 76%, m.p.
196.9–198.1 oC; 1H NMR (400 MHz, CDCl3) δ 8.30 (dd, J = 7.6, 1.6 Hz,
1H), 8.21 (s, 1H), 7.79 (dd, J = 8.0, 1.2 Hz, 1H), 7.64 – 7.48 (m, 5H), 7.34
– 7.29 (m, 3H), 7.12 (dd, J = 7.6, 1.2 Hz, 1H), 6.99 – 6.92 (m, 3H), 6.63
(d, J = 8.0 Hz, 2H), 4.84 (s, 2H), 1.97 (s, 3H); 13C NMR (100 MHz,
CDCl3) δ 152.3, 147.3, 145.0, 144.1, 138.4, 137.4, 134.7, 134.2, 131.0,
130.9, 129.4, 129.2, 128.8, 128.1, 128.0, 127.8, 127.2, 127.1, 126.2,
123.6, 116.5, 109.8, 48.1, 21.2. HRMS (ESI-TOF) (m/z): (M + H)+ Calcd.
for C29H23N2O3S 479.1429; Found 479.1429.
122.9, 48.1, 21.2. HRMS (ESI-TOF) (m/z): (M
C29H23N2O2S 463.1480; Found 463.1472.
+
H)+ Calcd. for
9-Methyl-7-phenyl-5-tosyl-5,6-dihydrodibenzo[b,h][1,6]naphthyridine
(3ja): Rf=0.52 (PE/EA 10:1); white solid, 95.3 mg, yield: 67%, m.p.
244.6–245.8 oC; 1H NMR (400 MHz, CDCl3) δ 8.37 (dd, J = 7.2, 1.6 Hz,
1H), 7.92 (d, J = 8.4 Hz, 1H), 7.79 (dd, J = 8.0, 1.2 Hz, 1H), 7.65 – 7.56
(m, 3H), 7.55 – 7.45 (m, 3H), 7.30 – 7.27 (m, 2H), 7.20 (s, 1H), 6.99 (d, J
= 8.4 Hz, 2H), 6.68 (d, J = 8.0 Hz, 2H), 4.81 (s, 2H), 2.42 (s, 3H), 1.94 (s,
3H); 13C NMR (100 MHz, CDCl3) δ 148.5, 146.4, 143.8, 138.2, 136.7,
135.1, 134.6, 131.7, 131.5, 130.5, 129.6, 129.3, 129.2, 129.0, 128.9,
127.9, 127.8, 127.2, 126.6, 126.3, 124.8, 122.9, 48.1, 22.1, 21.3. HRMS
(ESI-TOF) (m/z): (M + H)+ Calcd. for C30H25N2O2S 477.1637; Found
477.1637.
7-Phenyl-5-tosyl-5,6-dihydrodibenzo[b,h][1,6]naphthyridine-11-
carbonitrile (3jl): Rf=0.52 (PE/EA 10:1); yellow solid, 121.0 mg, yield:
82%, m.p. 229.8–231.3 oC; 1H NMR (400 MHz, CDCl3) δ 8.56 (dd, J =
7.6, 1.6 Hz, 1H), 8.05 (dd, J = 6.8, 1.2 Hz, 1H), 7.78 (dd, J = 8.0, 1.2 Hz,
1H), 7.72 (dd, J = 8.8, 1.6 Hz, 1H), 7.67 – 7.57 (m, 4H), 7.52 (td, J = 7.6,
1.2 Hz, 1H), 7.44 (dd, J = 8.4, 7.2 Hz, 1H), 7.27 (dd, J = 8.0, 2.8 Hz, 2H),
6.95 (d, J = 8.4 Hz, 2H), 6.68 (d, J = 8.0 Hz, 2H), 4.85 (s, 2H), 2.00 (s,
3H); 13C NMR (100 MHz, CDCl3) δ 151.2, 146.9, 144.9, 144.2, 138.6,
135.4, 134.2, 133.7, 131.7, 131.2, 130.6, 129.7, 129.5, 129.4, 128.9,
128.2, 127.6, 127.4, 127.2, 126.7, 125.7, 124.6, 117.5, 113.1, 47.9, 21.3.
HRMS (ESI-TOF) (m/z): (M + H)+ Calcd. for C30H22N3O2S 488.1433;
Found 488.1433.
9-Methoxy-7-phenyl-5-tosyl-5,6-
dihydrodibenzo[b,h][1,6]naphthyridine (3jc): Rf=0.41 (PE/EA 10:1);
yellow solid, 117.5 mg, yield: 80%, m.p. 208.4–210.1 oC; 1H NMR (400
MHz, CDCl3) δ 8.34 (dd, J = 7.6, 2.0 Hz, 1H), 7.93 (d, J = 9.2 Hz, 1H),
7.78 (dd, J = 7.6, 1.6 Hz, 1H), 7.65 – 7.55 (m, 3H), 7.53 – 7.44 (m, 2H),
7.31 – 7.28 (m, 3H), 6.99 (d, J = 8.4 Hz, 2H), 6.74 – 6.68 (m, 3H), 4.81 (s,
2H), 3.73 (s, 3H), 1.96 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 158.0,
147.1, 143.8, 143.1, 137.9, 135.1, 134.6, 131.6, 131.1, 130.2, 129.4,
129.3, 129.1, 128.8, 127.9, 127.8, 127.7, 127.1, 126.1, 123.2, 121.6,
104.2, 55.6, 48.1, 21.3. HRMS (ESI-TOF) (m/z): (M + H)+ Calcd. for
C30H25N2O3S 493.1586; Found 493.1586.
(E)-1-(2-(cinnamyloxy)phenyl)-N-(p-tolyl)methanimine (4aa): Rf=0.66
(PE/EA 10:1); yellow oil; 1H NMR (400 MHz, CDCl3) δ 8.99 (s, 1H), 8.16
(d, J = 6.8 Hz, 1H), 7.44 – 7.40 (m, 3H), 7.33 (t, J = 7.6 Hz, 2H), 7.28 –
7.24 (m, 1H), 7.17 (q, J = 8.0 Hz, 4H), 7.05 (t, J = 7.2 Hz, 1H), 6.99 (d, J
= 8.4 Hz, 1H), 6.73 (d, J = 16.0 Hz, 1H), 6.42 (dt, J = 16.0, 5.6 Hz, 1H),
4.79 (d, J = 5.6 Hz, 1H), 2.36 (s, 3H); 13C NMR (100 MHz, CDCl3) δ
158.8, 156.0, 150.4, 136.5, 135.8, 133.5, 132.7, 130.0, 128.9, 128.3,
127.9, 126.9, 125.5, 124.3, 121.4, 121.3, 69.5 21.3. HRMS (ESI-TOF)
(m/z): (M + H)+ Calcd. for C23H22NO 328.1701; Found 328.1701.
9-Chloro-7-phenyl-5-tosyl-5,6-dihydrodibenzo[b,h][1,6]naphthyridine
(3jf): Rf=0.53 (PE/EA 10:1); white solid, 88.7 mg, yield: 60%, m.p. 229.7–
231.1 oC; 1H NMR (400 MHz, CDCl3) δ 8.37 (dd, J = 7.6, 1.6 Hz, 1H),
7.96 (d, J = 8.8 Hz, 1H), 7.80 (dd, J = 7.6, 1.2 Hz, 1H), 7.67 – 7.53 (m,
5H), 7.49 (td, J = 7.6, 1.6 Hz, 1H), 7.43 (d, J = 2.4 Hz, 1H), 7.28 (d, J =
1.6 Hz, 1H), 6.98 (d, J = 8.0 Hz, 2H), 6.70 (d, J = 8.0 Hz, 2H), 4.82 (s,
2H), 1.96 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 149.7, 146.1, 143.9,
This article is protected by copyright. All rights reserved.

10.1002/cctc.201800192
ChemCatChem
FULL PAPER
(E)-N-(2-(cinnamyloxy)benzyl)-4-methylaniline (5aa): Rf=0.51 (PE/EA
10:1); white solid; 1H NMR (400 MHz, CDCl3) δ 7.38 – 7.30 (m, 2H), 7.27
– 7.20 (m, 2H), 6.97 – 6.90 (m, 2H), 6.72 (d, J = 16.0 Hz, 1H), 6.58 (d, J
= 8.4 Hz, 2H), 6.41 (dt, J = 16.0, 5.2 Hz, 1H), 4.75 – 4.74 (m, 2H), 4.37 (s,
2H), 4.05 (s, 1H), 2.22 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 156.8,
146.6, 136.8, 132.9, 130.0, 129.4, 128.9, 128.5, 128.4, 128.2, 126.9,
126.8, 124.8, 121.2, 113.6, 112.1, 68.9, 44.3, 20.8. HRMS (ESI-TOF)
(m/z): (M + H)+ Calcd. for C23H24NO 330.1858; Found 330.1858.
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(6aRS,7SR,12aRS)-9-Methyl-7-phenyl-6a,7,12,12a-tetrahydro-6H-
chromeno[4,3-b]quinoline (I): The procedure was adopted from the
[16]
literature:
A 100 mL round-bottom flask was charged with 2-
(cinnamyloxy)benzaldehyde (1a, 0.95 g, 4 mmol), 4-nitrotoluene (0.55 g,
4 mmol), iron powder (0.89 g, 16 mmol), citric acid monohydrate (3.07 g,
16 mmol), montmorillonite K10 (600 mg), and water (30 mL). The mixture
was stirred at 80 °C under a nitrogen atmosphere for 4 h. After
completion, the mixture was filtered with suction and washed with water
(20 mL× 3) and then extracted with hot acetone (30 mL× 3). The solvent
was removed under reduced pressure, the crude product was purified by
silica-gel column chromatography (PE/DCM = 1:1) to give I as a white
solid (0.92 g, 70% yield). Rf=0.51 (PE/EA 10:1); white solid, m.p. 206.1–
207.8 oC; 1H NMR (500 MHz, CDCl3) δ 7.37 – 7.32 (m, 3H), 7.28 (t, J =
7.0 Hz, 1H), 7.22 – 7.17 (m, 3H), 6.99 (ddd, J = 7.5, 7.5, 1.5 Hz, 1H),
6.88 (dd, J = 8.0, 1.5 Hz, 1H), 6.82 (dd, J = 8.0, 1.0 Hz, 1H), 6.69 (d, J =
8.0 Hz, 1H), 6.44 (s, 1H), 4.44 (d, J = 10.5 Hz, 1H), 4.24 (s, 1H), 4.03 (dd,
J = 11.0, 4.0 Hz, 1H), 3.85 (t, J = 11.5 Hz, 1H), 3.80 (d, J = 12.0 Hz, 1H),
2.45 (dddd, J = 11.0, 11.0, 11.0, 3.5 Hz, 1H), 2.09 (s, 3H); 13C NMR (125
MHz, CDCl3) δ 154.2, 143.1, 142.1, 130.8, 129.2, 128.8, 128.7, 128.4,
128.2, 127.1, 125.6, 125.0, 122.9, 120.8, 117.1, 116.4, 67.7, 52.4, 47.1,
41.5, 20.7. HRMS (ESI-TOF) (m/z): (M + H)+ Calcd. for C23H22NO
328.1701; Found 328.1707.
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The authors acknowledge the financial support provided by the
National Natural Science Foundation of China (No. 21232003).
Keywords: chromeno[4,3-b]quinolines•[1,6]naphthyridines•aza-
Diels-Alder reaction•Lewis-acid-catalysis•visible-light-photoredox
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Wuheng Dong, Yao Yuan, Xiaoshuang
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Ar
X
Ar
X
Lewis acid
Photo cat
R1
R1
+
R2
Page No. – Page No.
O
NH2
N
R2
Merging Visible-Light-Photoredox
and Lewis-Acid-Catalysis for the
Intramolecular Aza-Diels-Alder
Reaction: Synthesis of Substituted
Chromeno[4,3-b]quinolines and
[1,6]Naphthyridines
30 examples
up to 87% yield
X= O, NR
Text for Table of Contents
A photocatalytic aerobic aza-Diels-Alder cycloaddition strategy under visible
light to construct chromenoquinolines and 5,6-dihydrodibenzo[b,h][1,6]naphthyridines,
which are important skeletons of biologically active molecules.
The applicability of readily available starting materials and the use of air as
the sole oxidant under the mild reaction conditions make this process very attractive.
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