Iron-catalyzed oxidative synthesis of N-heterocycles from primary alcohols

Article abstract of DOI:10.1039/c3ra46363j

An iron-catalyzed one-pot one-step oxidative system has been successfully developed in the conversion of primary alcohols into nitrogen-containing heterocycles, such as quinazolinone, quinazoline and 3,4-dihydro-2H-1,2,4- benzothiadiazine 1,1-dioxide derivatives.

Full text of DOI:10.1039/c3ra46363j

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Iron-catalyzed oxidative synthesis of
N-heterocycles from primary alcohols†
Cite this: RSC Adv., 2014, 4, 6486
*
Dan Zhao, Yu-Ren Zhou, Qi Shen and Jian-Xin Li
Received 3rd November 2013
Accepted 24th December 2013
An iron-catalyzed one-pot one-step oxidative system has been successfully developed in the conversion of
primary alcohols into nitrogen-containing heterocycles, such as quinazolinone, quinazoline and 3,4-
dihydro-2H-1,2,4-benzothiadiazine 1,1-dioxide derivatives.
DOI: 10.1039/c3ra46363j
www.rsc.org/advances
Quinazolinone as a building block occurs widely in natural alcohols to carbonyl compounds, obviously, alcohols could be
products that exhibit a broad range of useful biological and substrates in this transformation. In 2011, Zhou described an
pharmacological activities.1 It is assigned as a privileged skel- oxidative cyclization of primary alcohols with o-amino-
eton in drug discovery and many synthetic efforts have been benzamides to quinazolinones catalyzed by iridium complex
made for its construction.2 Transition metals have been exten- under hydrogen transfer conditions.10a Later, ruthenium-
sively utilized in the syntheses of quinazolinones, for example catalyzed hydrogen transfer was also applied (Scheme 1,
ruthenium and platinum complexes were involved in their method A).10b Thinking about high temperature and long
preparations via reductive N-heterocyclization.3 Multicompo- reaction time in method A, an oxidation protocol, which
nent reactions catalyzed by transition metals, such as galliu- involved inexpensive and less toxic catalysts with green
m(III) triate4a or cerium(IV) ammonium nitrate,4b were also oxidants was an alternative choice. Very recently, Wei group
described. Since 2000, Alper and co-authors have reported reported I2-catalyzed two-step oxidative system for synthesis of
methods via tandem reactions, in which palladium-catalyzed quinazolinones using DMSO as a mild oxidant (Scheme 1,
cyclocarbonylation of 2-iodoanilines or their derivatives was the method B).11 Due to the importance of quinazolinone skeleton,
key step.5 Later, Zhu group developed a palladium-catalyzed development of simple and environmentally benign protocols
intramolecular C(sp2)–H carboxamidation of N-arylamidines, using convenient catalysts is still highly desired. Considering
providing
a
more efficient approach to quinazolinones.6 iron complexes as inexpensive and nontoxic catalysts were
Recently, copper or iron-catalyzed C–N couplings have made used for the oxidation of alcohols to the corresponding
great achievements, and were applied in synthesis of quinazo- carbonyl compounds in the presence of peroxide,12 we
linones using 2-halobenzoic acid derivatives and ammonia hypothesize that, in an iron-catalyzed domino sequence as
sources as starting materials.7 However, stoichiometric shown in Scheme 1, oxidation of alcohol 1 to aldehyde fol-
amounts of bases were essential for the reactions, and in some lowed by condensation with o-aminobenzamide 2 might
cases ligands were also necessary.
provide quinazolinone 3 via the oxidation of the generated
As shown in Scheme 1, one of the typical synthetic methods aminal intermediate. This synthetic route is a one-pot one-step
is to utilize a condensation reaction between aldehyde and o- oxidative system, and has an additional advantage of opera-
aminobenzamide 2 followed by oxidation of the aminal inter- tional convenience.
mediate. For this oxidation, stoichiometric or large excess
amounts of toxic oxidants, such as KMnO4,8a MnO2,8b DDQ,8c
CuCl2,8d were required. Some molecules that can be oxidized to
aldehydes might be also used as starting materials. Very
recently, Wu converted aromatic ketones into corresponding
aldehydes via Kornblum oxidation, and used these to react
with o-aminobenzamide for synthesis of quinazolinones.9
Because many strategies have been devised for oxidation of
State Key lab of Analytical Chemistry for Life Science, School of Chemistry and
Chemical Engineering, Nanjing University, Nanjing, 210093, P. R. China. E-mail:
lijxnju@nju.edu.cn; Fax: +86-25-83686419; Tel: +86-25-83686419
† Electronic supplementary information (ESI) available: Experimental section,
spectral data and other information. See DOI: 10.1039/c3ra46363j
Scheme 1 Synthesis of quinazolinones from primary alcohols.
6486 | RSC Adv., 2014, 4, 6486–6489
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a
Table 2 Synthesis of quinazolin-4(3H)-ones catalyzed by FeCl3
Results and discussion
To exam our hypothesis, we chose benzyl alcohol 1a and o-
aminobenzamide 2 as model substrates (Table 1). Initially, FeCl3
(5 mol%) with TBHP (5.5 M in decane) was investigated for
detecting availability of the catalytic system. Fortunately, the
reaction gave the target product, 2-phenylquinazolin-4(3H)-one
3a in DMSO (entry 1). Some abundant and cheap catalysts were
also tested, while, the data indicated that FeCl3 was the most
effective one, giving the product in a moderate yield at 60 ꢀC for
12 h (entries 1–4). Among all the solvents screened, such as
DMSO, toluene, DMF, 1,4-dioxane, acetonitrile and water, DMSO
was the best one (entries 1, 5–9). It should be noted that
although several loadings of FeCl3 were tested, 2 mol% gave a
better result (entry 10), probably due to signicant unknown
byproduct formation with a relatively high catalyst loading. Aer
screening the effect of reaction temperature and time (entries
11–18), the appropriate yield was achieved with the reaction
conditions of 1a and 2 at 60 ꢀC for 7 h. Increasing or decreasing
the amount of TBHP did not improve the yield signicantly
(entries 19 and 20). In addition, when T-HYDRO was used as an
oxidant, a lower yield was obtained (entry 21). Aer examining
the reaction proles, we decided the conditions of entry 16 as the
optimal one for our next investigations of the substrate scope.
Entry
R
Product
Yieldb (%)
1
2
3
4
5
6
7
8
Ph
3a
3b
3c
3d
3e
3f
3g
3h
3i
93
57
66
37
40
45
84
67
76
42
60
Ndc
2-Me-C6H4
4-Me-C6H4
4-MeO-C6H4
4-F-C6H4
4-Cl-C6H4
2-Br-C6H4
2-I-C6H4
2-furyl
9
10
11
12
Me
Heptyl
1-Naphthyl
3j
3k
3l
a
Reaction conditions: 1 (1.5 mmol), 2 (0.5 mmol), FeCl3 (2 mol%), 5.5 M
TBHP in decane (1.5 mmol), DMSO (2 mL), sealed tube, under an air
atmosphere, at 60 ꢀC for 7 h. Isolated yield. c Not detected.
b
With the optimized conditions in hand, various primary
alcohols were investigated (Table 2). For different substituted
benzyl alcohols with electron donating and withdrawing groups
gave moderate to good yields. Notably, C–X (F, Cl, Br and I) bond
remained intact during the reaction (entries 5–8), which
provided an additional handle for further elaboration of prod-
ucts. Heteroaryl substrate like 2-furylmethanol was examined
and the corresponding product 3i was obtained in 76% yield
(entry 9). In order to demonstrate the broad synthetic utility of
this system, we investigated more challenging alkyl primary
alcohols such as ethanol and octanol, fortunately, the desired
products were also afforded with moderate yields (entries 10
and 11). However, 1-naphthalenemethanol produced an insep-
arable mixture of products (entry 12).
The success of above results encouraged us to further extend
the substrate scope beyond o-aminobenzamide. Because of the
structural similarity, we explored the possibility of using o-
aminobenzylamine as starting material for synthesis of quina-
zolines which exhibit important biological properties.13
Substituted quinazolines have been synthesized by a variety of
methods,14 one strategy is through the oxidative condensation
of o-aminobenzylamine with aldehydes mediated by strong
oxidants such as DDQ,15a MnO2 (ref. 15b) and NaClO.15c Later,
Cu/N-ligand/TEMPO16a and bi-metallic alloyed nanoclusters/
dimeric catechol catalytic systems16b were developed as more
environmentally benign methods. Very recently, an Ir-catalyzed
hydrogen transfer reaction was also applied in the synthesis of
substituted quinazolines starting from o-aminobenzylamine
and aldehydes.17 Encouraged by above results, we tested the
employment of primary alcohols instead of aldehydes, the
current synthetic strategy still worked well and the results were
listed in Table 3. As benzyl alcohols (entries 1–7), heteroaryl
Table 1 Optimization of reaction conditionsa
Entry Cat. (mol%) Solvent
Temp. (ꢀC) Time (h) Yieldb (%)
1
2
3
4
5
6
7
8
FeCl3 (5)
CuCl2 (5)
ZnCl2 (5)
NiCl2 (5)
FeCl3 (5)
FeCl3 (5)
FeCl3 (5)
FeCl3 (5)
FeCl3 (5)
FeCl3 (2)
FeCl3 (2)
FeCl3 (2)
FeCl3 (2)
FeCl3 (2)
FeCl3 (2)
FeCl3 (2)
FeCl3 (2)
FeCl3 (2)
FeCl3 (2)
FeCl3 (2)
FeCl3 (2)
DMSO
DMSO
DMSO
DMSO
Toluene
DMF
1,4-Dioxane 60
CH3CN
H2O
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
60
60
60
60
60
60
12
12
12
12
12
12
12
12
12
12
12
12
12
12
10
7
51ꢁ
24
26
42
40
Trace
Trace
46
44
93
86
90
84
86
92
93
85
75
60
60
60
70
50
80
40
60
60
60
60
60
60
60
9
10
11
12
13
14
15
16
17
18
19c
20d
21e
5
3
7
7
91
81
73
7
a
Reaction conditions: 1a (1.5 mmol), 2 (0.5 mmol), solvent (2 mL), 5.5 M
TBHP in decane (1.5 mmol), sealed tube, under an air atmosphere.
b
c
d
e
Isolated yield. TBHP (2 mmol). TBHP (1 mmol). T-HYDRO ¼
70% TBHP in water (1.5 mmol).
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a
Table 3 Synthesis of quinazolines catalyzed by FeCl3
benzothiadiazine derivatives by using o-aminobenzene-sulfon-
amide and primary alcohols as starting materials.19 Generally,
these compounds were prepared from o-amino-benzenesulfo-
namide by condensation with aldehydes or ethyl hemiacetals in
acidic medium.20 As shown in Table 4, using the present system,
the nal products, cyclic aminals (7) without C]N bond
formation were obtained. The result indicated the second
oxidation didn't occur in current conditions. Both aryl and alkyl
primary alcohols were tolerated in this transformation, and aryl
primary alcohols were more reactive.
Entry
R
Product
Yieldb (%)
1
2
3
4
5
6
7
8
9
Ph
5a
5b
5c
5d
5e
5f
5g
5h
5i
70
60
71
71
55
62
65
35
44
53
2-Me-C6H4
4-Me-C6H4
4-MeO-C6H4
4-F-C6H4
4-Cl-C6H4
1-Naphthyl
3-Pyridyl
2-Furyl
Conclusions
In summary, we have successfully developed an iron-catalyzed
one-pot one-step oxidative system for the synthesis of N-
heterocycles from the cyclization of primary alcohols 1 with
10
Me
5j
o-aminobenzamide 2, o-aminobenzylamine
4 or o-amino-
a
benzenesulfonamide 6 using similar conditions. Furthermore,
this environmentally friendly protocol displays good functional
group compatibility and both aromatic and alkyl primary alco-
hols were reactive. The present results provided an economic
and feasible way to prepare bioavailable skeletons, such as
quinazolinones, quinazolines and benzothiadiazine derivatives.
Reaction conditions: 1 (1.5 mmol), 4 (0.5 mmol), FeCl3 (2 mol%), 5.5 M
TBHP in decane (1.5 mmol), DMSO (2 mL), sealed tube, under N2
b
atmosphere, at 60 ꢀC for 6 h. Isolated yield.
primary alcohols (entries 8 and 9) and alkyl primary alcohol
(entry 10) were employed, the corresponding products were
obtained in moderate yields.
Acknowledgements
Having successfully achieved the synthesis of quinazoli-
nones and quinazolines, we tried to expand the current catalytic
system to the synthesis of 3,4-dihydro-2H-1,2,4-benzothiadia-
zine 1,1-dioxide derivatives. Benzothiadiazine derivatives, such
as cyclothiazide and 7-chloro-3-methyl-3,4-dihydro-2H-1,2,4-
benzothiadiazine 1,1-dioxide (IDRA-21) were the modulators of
AMPA receptor desensitization.18 Very recently, a Pd-catalyzed
synthetic route was developed for the preparation of
This work was supported by National Natural Science Founda-
tion of China (21272114, 90913023), and the National Natural
Science Fund for Creative Research Groups (21121091).
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Entry
R
Product
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1
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2-Br-C6H4
2-I-C6H4
1-Naphthyl
Me
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TBHP in decane (1.5 mmol), DMSO (2 mL), sealed tube, under an air
b
atmosphere, at 60 ꢀC for 12 h. Isolated yield.
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