Efficient construction of N-heterocycles from benzylic ethers/alcohols and o-substituted anilines without using any catalyst and additive

Article abstract of DOI:10.3987/COM-16-13587

A novel method for the synthesis of N-heterocycles from benzylic ethers/alcohols with o-substituted aniline without using any catalyst and additive is developed. This protocol involves C-O bond cleavage of benzylic ethers, N-benzylation, and benzylic C-H amidation in one pot, the tandem oxidation-cyclization transformation may open the door for the easy generation of N-heterocycles.

Full text of DOI:10.3987/COM-16-13587

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HETEROCYCLES, Vol. 94, No. 1, 2017
HETEROCYCLES, Vol. 94, No. 1, 2017, pp. 86 - 94. © 2017 The Japan Institute of Heterocyclic Chemistry
Received, 28th September, 2016, Accepted, 11th November, 2016, Published online, 2nd December, 2016
DOI: 10.3987/COM-16-13587
EFFICIENT CONSTRUCTION OF N-HETEROCYCLES FROM
BENZYLIC ETHERS/ALCOHOLS AND o-SUBSTITUTED ANILINES
WITHOUT USING ANY CATALYST AND ADDITIVE§
§
§
Xiuling Chen, Hongxue Qi, Shaofeng Wu, Leng Liu,* Jianhui Wen, Wanxi
Li, Fang Guo, Yongjun Bian, and Jun Li*
College of Chemistry and Chemical Engineering, Jinzhong University, Jingzhong,
030619, People’s Republic of China
Fax: (+86)-051-3985576; e-mail: hxx406@126.com
Abstract — A novel method for the synthesis of N-heterocycles from benzylic
ethers/alcohols with o-substituted aniline without using any catalyst and additive is
developed. This protocol involves C-O bond cleavage of benzylic ethers,
N-benzylation, and benzylic C-H amidation in one pot, the tandem
oxidation-cyclization transformation may open the door for the easy generation of
N-heterocycles.
N-Heterocyclic compounds are key units with physiological significance and pharmaceutical utility.1
Especially for the quinazolinones core, has shown important biological activities such as anticancer,2
3
4
5
6
7
antibacterial, antidiabetic, antihypertensive, antiinflammatory, antitussive activity. In addition,
benzimidazoles and benzothiazoles are also very useful building blocks for the development of
8
pharmaceutical or biological molecules. Generally, there are two methods for the synthesis of
N-heterocyclic compounds. One is a multi-step process to construct N-heterocycles from simple starting
9
materials, however, time consuming, tedious and often low yielding hinder their wide application. The
other method is direct cross-coupling of o-substituted anilines with aldehydes (ketones) or in situ aldehydes
generation from alcohols, amines, carboxylic acid (or carboxylic acid derivative).10-15 Although the second
approaches provided more efficient, more straightforward and attractive method to produce N-heterocycles,
transition metals, hazardous peroxides, and other additives are generally required. A metal-free conditions
especially in the drug and pharmaceutical industry are highly desirable, due to transition metal catalysts are
toxic and they must be removed from the products. Therefore, the development of a transition metal-free
and environment friendly method for the synthesis of N-heterocycles using readily available starting
materials is highly desirable.

HETEROCYCLES, Vol. 94, No. 1, 2017
87
In view of the drawbacks of existing routes and the importance of green chemistry, improvements are
focused towards the development of synthetic models which use a “green” oxidant, such as readily
3
available and nontoxic O
2
or air. Herein, we communicate a novel metal-free and acid-free sp C-H bonds
oxidation, C-O bond cleavage of benzylic ethers with o-substituted anilines to construct N-heterocycles
Scheme 1). Compared to conventional methods, this procedure is distinguished by using biofriendly
(
clean dioxygen oxidant without metal catalyst. This new method provides a general and environmentally
friendly access to N-heterocyclic compounds.
X
XH
Ar
N
Ar = Ph, substituted-Ph
R = Me
Ar
O
R
NH2
O2
X = S, NH
+
or
R2
X
N
DMSO
R2
X
Ar
OH
N
H
1
2
R = Cl, R = Me
R1
N
Ar
NH2
R1
X = CO, CH2
ꢀ
We began our study with the reaction of o-aminobenzamide 1a and benzyl methyl ether 2a for the
optimization of the present oxidation-cyclization strategy to construct quinazolin-4(3H)-one 3aꢀand the
o
results were compiled in Table 1. When the reaction mixture was heated in DMF for 12 h at 120 C, this
aerobic oxidation reaction take place to produce the corresponding 2-phenylquinazolin-4(3H)-one
compound 3a in 30% isolated yield (Table 1, entry 1). To improve the yield of this reaction, 1,4-dioxane
was used as solvent, affording 3a in 55% yield (Table 1, entry 2). When DMSO was used as solvent, the
reaction gave 3a in 88% isolated yield (Table 1, entry 3). Other solvents such as toluene, benzene, hexane,
1,2-dichloroethane and MeCN were not effective to the present oxidation-cyclization reaction (Table 1,
entries 4-8).
Table 1. Optimization of the reaction conditions in the reaction of 1a with 2aa
Entry
Solvent
DMF
Yield of 3ab
Entry
6
Solvent
hexane
Yield of 3ab
1
2
3
4
30
55
88
--
--
1,4-dioxane
DMSO
7
1,2-dichloroethane --
8
9c
10d
MeCN
DMSO
DMSO
--
toluene
benzene
--
5
--
89
a
Reaction conditions: 1a (0.2 mmol), 2a (0.6 mmol), sovent (1 mL), O
2
(1 atm) in a sealed glass tube (25
mL) at 120 C, 12 h. GC yields based on 1a using dodecane as an internal standard. 100 C or N
. d
o
b
c
o
2
o
1
30 C.

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HETEROCYCLES, Vol. 94, No. 1, 2017
o
Interestingly, the temperature also plays an important role, and 120 C serves as the suitable temperature.
o
For example, the reaction does not occur at 100 C or N
2
in DMSO (Table 1, entry 9), while further
o
increase of reaction temperature to 130 C leads to no evident improvement on product yield (Table 1,
entry 10). Thus, the optimal set of conditions was determined as described in entry 3.
Under these optimized reaction conditions, the scope of substrates that could be used and the versatility of
the reaction were investigated. As shown in Table 2, o-substituted anilines with substituted benzyl methyl
ethers were employed in this reaction to synthesize a variety of N-heterocycles derivatives in good yields
(Table 2, entries 1-3). In addition to benzyl methylꢀ ether, the symmetric ether such as ether,
substituted-benzyl ether also served as efficient substrates under the current reaction conditions and
converted to the corresponding substituted quinazolin-4(3H)-one in 70%-91% yield (Table 2, entries 4-7).
The reaction of N-methyl or 5-chloro substituted 2-aminobenzamides with substituted benzyl methyl
ethers proceeded smoothly to give the corresponding product in good yield (Table 2, entries 8-9). To our
delight, 2-phenylquinazoline has also been efficiently synthesized under the present aerobic
oxidation-cyclization strategy (Table 2, entry 10). Using the current strategy, the protocol can also be
applied to preparation of the five-membered compounds (Table 2, entries 11-12). The reaction of
o-phenylenediamine and o-aminothiophenol with substituted benzyl methyl ethers provided
benzimidazole and benzothiazole in good yield.
Table 2. Metal-free aerobic oxidation of benzylic ethers and o-substituted anilines for the synthesis of
N-heterocyclesa
XH
NH2
O2
R3
O
R
+
N-heterocycles
R2
DMSO
X
N
H
NH2
R = Me
R1
X = CO, CH2
1
2
R = Cl, R = Me
3
R = Me, Ph, substituted Ph

HETEROCYCLES, Vol. 94, No. 1, 2017
89
O
NH
NH
OMe
2
1
1
a
a
2b
N
O
MeO
3b,88%
OMe
OMe
3
2
c
N
Br
3
c, 81%
O
Br
NH
4c
EtOEt
1a
3
d, 70%
N
Me
2
d
O
3a, 91%
5
6
1
a
2
e
3
3
b, 88%
c, 85%
O
1a
1a
2
f
MeO
Br
OMe
Br
O
7
8
2
g
O
O
NHMe
NMe
2
c
NH2
O
N
O
3
e,78%
1
b
Br
Cl
Cl
9
NH2
NH2
NH
N
2
2
b
a
N
3
f, 81%
1
c
d
OMe
NH2
1
0
N
NH2
3
g, 70%
1
H
N
NH2
1
1
2b
2c
OMe
N
NH2
3
h, 73%
1
e
NH2
N
S
1
2
Br
SH
3
i, 68%
1
f
a
Reaction conditions: 1a-1f (0.2 mmol), 2a-2g (0.6 mmol), DMSO (1 mL), O (1 atm) in a sealed glass
2
o
b
c
tube (25 mL) at 120 C, 12 h. Isolated yields. Et O (0.3 mL).
2
After success in the elaboration of benzyl ether, we moved our attention to investigate a variety of
alcohols as coupling partners. To our delight, most alcohols underwent smooth transformation to afford

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HETEROCYCLES, Vol. 94, No. 1, 2017
the corresponding 2-substituted quinazolin-4(3H)-one in excellent yields, and the results are summarized
in Table 3. For different substituted benzyl alcohols holding both electron-donating groups and
electron-withdrawing groups on the aromatic cycles work well to give the corresponding quinazolines.
The electronic properties of the substituents in the aromatic ring had not influence on the reaction rate.
Table 3. Substituted alcohols with o-substituted anilines for the synthesis of N-heterocyclesa
Entry
1
Substrate 1
Substrate 2
Products and yieldb
O
O
NH2
NH2
OH
NH
2h
N
O
3a, 88%
1a
OH
NH
2
3
4
5
6
MeO
Br
2i
1
a
N
O
OMe
3b, 83%
OH
NH
1a
2j
N
O
Br
3c, 79%
OH
NH
1a
1a
1a
2k
O N
2
N
O
NO2
NH
3j, 89%
S
N
OH
S
2
l
O
3k, 77%
NH
N
OH
2m
3l, 72%
a
Reaction conditions: 1a (0.1 mmol), alcohol 2h-2n (0.6 mmol), DMSO (1 mL), O (1 atm) in a sealed
2
o
b
glass tube (25 mL) at 120 C, 12 h, recharging oxygen after 6 h. Isolated yields.
3
In conclusion, we have demonstrated an efficient aerobic sp C-H bonds oxidation-cyclization strategy to
construct N-heterocycles from benzylic ethers/alcohols with o-substituted anilines. In the present system,
3
metal-free sp C-H bond oxidation, C-O bond cleavage and C-N bond formation was achieved in one pot.
This tandem reaction provides an environmentally friendly protocol to N-heterocyclic compounds with
wide substrate scope.

HETEROCYCLES, Vol. 94, No. 1, 2017
91
EXPERIMENTAL
General
All manipulations were carried out under air atmosphere unless otherwise specified. The reactions were
1
13
monitored by GC and GC-MS. The H NMR and C NMR spectra were obtained from a solution in
CDCl or DMSO-d with tetramethylsilane (TMS) as internal standard on a Brucker ADVANCE III
3
6
spectrometer at 400 MHz and 100 MHz, respectively. Flash column chromatography was performed
using silica gel 300-400 mesh. o-Substituted anilines 1 were purchased from Energy Chemical, Alfa
Aesar, Aladdin or Maya Reagent, benzylic ethers/alcohols 2 were purchased from Energy Chemical,.
General procedure for the synthesis of N-heterocyclic compounds
A 25 mL Schlenk-type tube equipped with a magnetic stir bar was charged with o-substituted aniline
1
a-1f. The reaction tube was evacuated and back-filled with O . Under oxygen atmospheres, ethers or
2
alcohols 2a-2n and DMSO were added at room temperature, then the reaction mixture was stirred at 120
ºC for 12 h. The reaction was monitored by TLC. After completion of the reaction, the resulting solution
was cooled to room temperature, and neutralized with saturated NaHCO
3
aqueous solution. The product
was extracted with EtOAc or CHCl , dried over anhydrous Na SO and concentrated in vacuum. The
3
2
4
crude product was purified by flash column chromatography on silica gel to give N-heterocyclic
compounds 3.
1
6
1
2
1
9
1
2
-Phenylquinazolin-4(3H)-one (3a) : White solid, mp 236-238 ºC; H NMR (400 MHz, DMSO-d): δ
2.59 (s, br, 1H), 8.20 (t, J = 8.6 Hz, 3H), 7.84 (d, J = 7.2 Hz, 1H), 7.76 (d, J = 8.0 Hz, 1H), 7.57 (t, J =
1
3
.0 Hz, 4H); C NMR (100 MHz, DMSO-d): δ 162.8, 152.8, 149.1, 135.0, 133.2, 131.8, 129.1, 128.2,
27.9, 127.0, 126.3, 121.4. GC-MS: m/z = 222.
1
6
1
-(4-Methoxyphenyl)quinazolin-4(3H)-one (3b) : White solid, mp 248-251 ºC; H NMR (400 MHz,
DMSO-d ): δ 12.31 (s, br, 1H), 8.20 (d, J = 8.4 Hz, 2H), 8.14 (d, J = 7.6 Hz, 1H), 7.83 (t, J = 7.4 Hz, 1H),
1
3
7
.71 (d, J = 8.0 Hz, 1H), 7.50 (t, J = 7.2 Hz, 1H), 7.10 (d, J = 8.4 Hz, 1H), 3.84 (s, 3H); C NMR (100
MHz, DMSO-d): δ 162.8, 162.3, 152.3, 149.4, 135.0, 129.9, 127.8, 126.6, 126.3, 125.3, 121.1, 114.5,
5
5.9. GC-MS: m/z = 252.
1
6
1
2
-(4-Bromophenyl)quinazolin-4(3H)-one (3c) : white solid, mp 294-296 ºC; H NMR (400 MHz,
DMSO-d): δ 12.61 (s, br, 1H), 8.13 (t, J = 9.4 Hz, 3H), 7.82 (d, J = 6.8 Hz, 1H), 7.75 (d, J = 7.2 Hz, 3H),
1
3
7
1
2
1
7
1
.53 (d, J = 6.4 Hz, 1H); C NMR (100 MHz, DMSO-d): δ 162.7, 152.0, 149.1, 135.2, 132.4, 132.1,
30.3, 128.0, 127.3, 126.4, 125.7, 121.5. GC-MS: m/z = 299.
1
7
1
-Methylquinazolin-4(3H)-one (3d) : White solid, mp 235-239 ºC; H NMR (400 MHz, CDCl
3
): δ
2.20 (s, br, 1H), 8.26 (d, J = 8.0 Hz, 1H), 7.75 (t, J = 7.6 Hz, 1H), 7.65 (d, J = 8.0 Hz, 1H), 7.45 (t, J =
1
3
.6 Hz, 1H), 2.59 (s, 3H); C NMR (100 MHz, CDCl ): δ 164.6, 157.7, 153.5, 149.6, 135.1, 127.2, 126.6,
3
26.4, 120.4, 22.3. GC-MS: m/z = 160.

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HETEROCYCLES, Vol. 94, No. 1, 2017
1
8
o
1
2
-(4-Bromophenyl)-3-methylquinazolin-4(3H)-one (3 HH ) : white solid, mp >300 C; H NMR (400
1
3
MHz, CDCl
3
): δ 8.22 (d, J = 7.2 Hz, 1H), 7.60-7.66 (m, 4H), 7.41 (d, J = 7.6 Hz, 3H), 3.42 (s, 3H); C
): δ 162.5, 155.0, 147.1, 134.4, 134.2, 132.1, 129.8, 127.4, 127.2, 126.6, 124.5,
20.4, 34.2. GC-MS: m/z = 315.
-Chloro-2-(4-methoxyphenyl)quinazolin-4(3H)-one (3I) : white solid, mp >300 C; H NMR (400
): 12.70 (s, br, 1H), 8.08 (s, 1H), 7.80 (d, J = 2.8 Hz, 4H), 7.45 (s, 1H), 7.16 (s, 1H), 3.86 (s,
NMR (100 MHz, CDCl
3
1
1
8
o
1
6
MHz, CDCl
3
1
3
3
1
2
H); C NMR (100 MHz, CDCl ): δ 162.5, 161.8, 152.8, 148.2, 135.1, 130.7, 130.0, 125.3, 124.9, 122.4,
3
14.5. GC-MS: m/z = 286.
1
9
o
1
-Phenylquinazoline (3g) : white solid, mp 98-100 C; H NMR (400 MHz, CDCl ): 9.38 (s, 1H), 8.61
3
1
3
(
d, J = 7.2 Hz, 2H), 8.03 (d, J = 8.4 Hz, 1H), 7.80 (d, J = 7.6 Hz, 2H), 7.51 (d, J = 7.2 Hz, 4H); C NMR
100 MHz, CDCl ): 161.0, 160.5, 150.7, 138.1, 134.1, 130.7, 128.7, 128.6, 127.3, 127.1, 123.6. GC-MS:
(
3
m/z = 206
2
0
o
1
2
-(4-Methoxyphenyl)-1H-benzo[d]imidazole (3h) : white solid, mp 223-225 C; H NMR (400 MHz,
DMSO-d): δ 12.94 (s, br, 1H), 7.77 (d, J = 7.2 Hz, 2H), 7.67 (s, 1H), 7.56 (s, J = 5.2 Hz, 1H), 7.47 (t, J
1
3
=
7.8 Hz, 1H), 7.22 (s, 2H), 7.06 (d, J = 8.0 Hz, 1H), 3.87 (s, 3H); C NMR (100 MHz, DMSO-d): δ
1
60.1, 151.5, 131.9, 130.6, 123.1, 122.2, 119.3, 119.2, 116.3, 111.8. GC-MS: m/z = 224.
1
8
o
1
2
-(4-Bromophenyl)benzo[d]thiazole (3i) : white solid, mp 129-131 C; H NMR (400 MHz, CDCl
3
): δ
7
.98 (d, J = 8.0 Hz, 1H), 7.87 (d, J = 8.4 Hz, 2H), 7.81 (J = 8.0 Hz, 1H), 7.54 (d, J = 8.4 Hz, 2H), 7.42 (t,
1
3
J = 7.6 Hz, 1H), 7.32 (t, J = 7.6 Hz, 1H); C NMR (100 MHz, CDCl
3
): δ 166.7, 154.1, 135.0, 132.5,
1
32.2, 128.9, 126.5, 125.5, 125.42, 125.39, 123.3, 121.6. GC-MS: m/z = 290.
1
6
1
2
-(4-Nitrophenyl)quinazolin-4(3H)-one (3j) : white solid, mp >300 ºC; H NMR (400 MHz,
DMSO-d): δ 12.84 (s, br, 1H), 8.40 (d, J = 1.6 Hz, 4H), 8.18 (d, J = 8.0 Hz, 1H), 7.88 (t, J = 7.2 Hz, 1H),
1
3
7
1
2
.80 (d, J = 8.0 Hz, 1H), 7.58 (t, J = 7.2 Hz, 1H); C NMR (100 MHz, DMSO-d): δ. 162.6, 151.9, 149.0,
35.1, 132.4, 132.1, 130.3, 127.9, 127.3, 126.4, 125.7, 121.5. GC-MS: m/z =267.
1
6
1
-(Thiophen-2-yl)quinazolin-4(3H)-one (3k) : white solid, mp 277-278 ºC; H NMR (400 MHz,
DMSO-d): δ 12.65 (s, br, 1H), 8.23 (d, J = 3.6 Hz, 1H), 8.12 (d, J = 8.0 Hz, 1H), 7.86 (d, J = 4.8 Hz, 1H),
13
7
.79 (t, J = 7.6 Hz, 1H), 7.65 (d, J = 8.4 Hz, 1H), 7.49 (t, J = 7.4 Hz, 1H), 7.24 (t, J = 4.2 Hz, 1H); C
NMR (100 MHz, DMSO-d): δ 162.3, 149.0, 148.3, 137.8, 135.2, 132.6, 129.9, 129.0, 127.4, 126.8, 126.5,
1
21.3. GC-MS: m/z = 228.
-(Naphthalen-2-yl)quinazolin-4(3H)-one (3l) : white solid, mp 213-215 C; H NMR (400 MHz,
1
8
o
1
2
DMSO-d): δ 12.70 (s, br, 1H), 8.23 (d, J = 8.0 Hz, 1H), 8.18 (d, J = 7.2 Hz, 1H), 8.13 (d, J = 8.4 Hz, 1H),
.05 (d, J = 7.2 Hz, 1H), 7.87 (t, J = 7.2 Hz, 1H), 7.81 (d, J = 6.8 Hz, 1H), 7.75 (d, J = 8.0 Hz, 1H), 7.66
8
1
3
(
t, J = 8.8 Hz, 1H), 7.60 (t, J = 8.8 Hz, 3H); C NMR (100 MHz, DMSO-d): δ 162.4, 154.1, 149.2, 135.0,

HETEROCYCLES, Vol. 94, No. 1, 2017
93
1
33.6, 132.1, 130.8, 130.7, 128.8, 128.1, 127.9, 127.5, 127.2, 126.8, 126.3, 125.6, 125.5, 121.7. GC-MS:
m/z = 272.
ACKNOWLEDGEMENTS
This work was supported by research fund for the doctoral program of Jinzhong University.
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§
These authors contributed equally to this work
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