Synthesis of 1,2,4-Triazine Compounds via Two Distinct One-Pot Domino Protocols

Article abstract of DOI:10.1002/cjoc.201600922

1,2,4-Triazine compounds were synthesized via two coupled domino strategies employing simple and readily available arylacetaldehydes/arylethyl alcohols as starting materials. The reactions proceed smoothly in one pot with the advantages of high functional

Full text of DOI:10.1002/cjoc.201600922

COMMUNICATION
DOI: 10.1002/cjoc.201600922
Synthesis of 1,2,4-Triazine Compounds via Two Distinct
One-Pot Domino Protocols
a
a
b
a
a
a
,a
Yafeng Liu, Xin Guo, Dong Tang, Jing Wang, Ping Wu, Jianwei Han, and Baohua Chen*
a
State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou, Gansu 730000, China
b
Department of Chemistry, Lishui University, Lishui, Zhejiang 323000, China
1
,2,4-Triazine compounds were synthesized via two coupled domino strategies employing simple and readily
available arylacetaldehydes/arylethyl alcohols as starting materials. The reactions proceed smoothly in one pot with
the advantages of high functional groups tolerance, being transition metal-free, and employing environmentally
friendly oxidants such as I and IBX, providing access to the desired 1,2,4-triazine products in excellent yields.
2
Keywords triazines, aldehydes, alcohols, N-aminobenzamidines, domino
Introduction
Experimental
The synthesis of 1,2,4-triazines has garnered signif-
icant attention due to the potential applications of
Typical procedure for the reaction between hyacin-
thins/2-phenylethanols and N-aminobenzamidines:
[
12]
synthesis of 3,5-diphenyl-1,2,4-triazine (3aa)
1
,2,4-triazines in organic materials and medicinal
Procedure A The reaction was performed in a
round-bottom sidearm flask (10 mL). Compound 2 (0.2
mmol), I (0.24 mmol) and DMSO (2 mL) were added
2
chemistry. The 1,2,4-triazine motif is frequently found
in natural products and bioactive molecules exhibiting
[
1]
[2]
[3]
antihypertensive,
analgesic,
anti-inflammatory,
to the 10 mL-flask containing a magnetic stirring bar
under air. After stirring for 2 h at 100 ℃, 1 (0.2 mmol)
was introduced into the catalyst system and the reaction
was stirred for an additional hour. After cooling to room
temperature, the mixture was washed with 20 mL water
and extracted with ethyl acetate (10 mL×3). The or-
ganic-layers were combined and concentrated under
reduced pressure to obtain the crude product, which was
further purified by silica gel chromatography
[
4]
[5]
[6]
antimalarial, anticancer, anticonvulsant and an-
[7]
tiepileptic properties. Some common methods for as-
sembling 1,2,4-triazines include direct condensation of
N-aminobenzamidines and 1,2-dicarbonyl compounds
to offer 3,5-disubstituted-1,2,4-triazines, or replacing
N-aminobenzamidines with ammonium acetate and
benzhydrazide to construct 3,5,6-trisubstituted-1,2,4-
[8]
[
9]
triazine. However, these current approaches require an
excess amount of acid or base, toxic oxidants, and com-
plex synthetic precursors. Consequently, developing
efficient protocols involving simple substrates and mild
conditions to obtain 1,2,4-triazine derivatives remains a
synthetic challenge.
[
V(petroleum)/V(ethyl acetate)＝5/1 as eluent] to obtain
product 3.
Procedure B The reaction was performed in a
round-bottom sidearm flask (10 mL). Compound 4
0.24 mmol), IBX (0.26 mmol), and DMSO (2 mL)
(
were added to the flask containing a magnetic stirring
bar under air. After stirring for 2 h at 100 ℃, 1 (0.2
mmol) was added into the catalyst system and the rea-
tion was stirred for an additional hour. The following
processing method was referred to procedure A.
Recently, domino reactions have gained increasing
interest in synthetic organic chemistry due to the high
[
10]
efficiency and low consumption.
Previously, our
group demonstrated the power and potential of dom-
ino-based strategy to construct triazoles, imidazoles,
etc. Inspired by the above strategy, we have designed
Results and Discussion
[11]
To develop an iodine-mediated domino strategy for
construction of 3,5-disubstituted-1,2,4-triazine, we first
began optimizing the reaction employing N-aminoben-
2
two simple, metal-free, domino pathways to construct
1
,2,4-triazine compounds using simple and readily
available aryl acetaldehydes and aryl ethyl alcohols.
zamidine and 2-phenylacetaldehyde. I and CuO af-
*
E-mail: chbh@lzu.edu.cn
Received December 26, 2016; accepted March 12, 2017; published online XXXX, 2017.
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cjoc. 201600922 or from the author.
Chin. J. Chem. 2017, XX, 1—5
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1

Liu et al.
COMMUNICATION
forded the desired product in a low yield at 100 ℃ in
DMSO (Table 1, entry 1). To improve the reactivity,
other additives such as TBHP, KI, NIS and IBX, were
screened, and NIS furnished superior yields (Table 1,
entries 2－5). Surprisingly, during the control experi-
scope of the reaction employing a diversity of both aryl
acetaldehydes and N-aminoarylamidines. First, the sub-
strate scope with respect to N-aminoarylamidines with
various aryl substituents was examined (Scheme 1).
N-Aminoarylamidines bearing electron-donating groups
were well-tolerated, affording the desired products in
satisfactory yields (3ab－3ad). Electrophilic functional
groups, such as bromine, chlorine and fluorine, were
also compatible in the reaction to furnish the corre-
sponding halogenated products in 55%－90% yields
(3ae － 3ag). Notably, N-aminoarylamidines bearing
electron-donating moieties showed superior reactivity
and produced higher yields than N-aminoarylamidines
bearing electron-withdrawing substituents.
The reaction scope was also evaluated with respect
to coupling partner 2 (Scheme 1). The electronic and
steric properties of the aryl acetaldehydes exhibited a
pronounced effect on the reactions. For example, elec-
tron-rich derivatives containing methyl, ethyl and
methoxy functional groups, afforded the corresponding
products in good yields (3ba－3bg); however, elec-
tron-deficient substrates, such as 3bh and 3bi, were less
reactive in the reactions. N-Aminobenzamidine with
substituents in the para-position provided the higher
yields than ortho-substituted reactants (3ba and 3bc,
ments, using 1.2 equiv. I
product in a good yield of 86% in the absence of addi-
tives (Table 1, entry 6). Replacing I with other oxidants,
such as NIS, CuI, H , failed to improve reaction
2
alone afforded the desired
2
2
O
2
yields (Table 1, entries 7－9). Further optimization also
showed that altering key operating parameters, such as
increasing the amount of iodine, or adjusting the tem-
perature, had a negligible effect on the yields (Table 1,
entries 10－13). Notably, the production of 3aa did not
decrease under nitrogen atmosphere, which indicated
that oxygen did not participate in the reaction (Table 1,
entry 14). Next, different types of solvents such as tolu-
ene and DMF were also investigated, and DMSO was
the most efficient media for the domino reaction (Table
1
1
, entries 15－16). A complete optimization identified
.2 equiv. of I at 100 ℃ in DMSO as the optimal re-
2
action conditions (Table 1, entry 6).
Table 1 Reaction optimization for the domino reaction between
hyacinthin and benzimidohydrazide
3
bd and 3bg), which was a result of steric interactions
possibly. These results revealed that the steric hindrance
from the ortho-position of phenylacetaldehydes showed
an adverse effect in the domino reaction.
We subsequently explored the feasibility of the reac-
tion using N-aminobenzamidine 1a and phenethyl alco-
hol 4a as model substrates. The desired product 3aa was
isolated in a 40% yield by the use of above-mentioned I2
as the catalyst in DMSO at 100 ℃ (Table 2, entry 1).
To improve the yield, various oxidants were screened
Entry Oxidant/equiv.
Additive/equiv. Solvent Yield/%
1
2
3
4
5
6
7
8
9
I
I
2
2
(0.1)
(0.1)
CuO (1.0)
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMF
34
72
82
74
67
86
30
84
83
81
85
81
81
86
30
trace
KI (1.0)
I2 (0.1)
I2 (0.1)
I2 (0.1)
NIS (1.0)
2 2 4
including MnO , CuO, SeO , KMnO , NIS and IBX
IBX (1.0)
(Table 2, entries 2－7). To our surprise, a 76% yield of
TBHP (1.0)
product was obtained using 1.2 equiv. of IBX as an ox-
idant. We then investigated the effect of IBX loading on
reactivity. For example, the yield of 3aa was improved
by increasing the amount of IBX. Using 1.3 equiv. of
IBX, 84% yield of the desired product was observed;
however, higher loading failed to further improve yields
I
2
(1.2)
－
－
－
－
－
－
－
－
－
－
－
CuI (1.2)
IBX (1.2)
NIS (1.2)
I2 (1.2)
b
c
1
0
(
Table 2, entries 8－9). Furthermore, the effect of tem-
1
1
I2 (1.2)
perature was examined, and it was found that lower
temperature produced lower yields for 3aa and that no
yield change was observed for higher temperature such
as 110 ℃ (Table 2, entries 10－11). Subsequently, only
1
2
3
2
I (1.3)
1
I2 (1.1)
I2 (1.2)
I2 (1.2)
I2 (1.2)
d
1
4
3
0% of 3aa was detected in the presence of nitrogen,
1
1
5
6
which indicated oxygen was crucial to the reaction (Ta-
ble 2, entry 12). Finally, we explored other polar and
non-polar solvents, such as DMF, toluene and dioxane;
however, no improvement in yields was observed (Table
toluene
a
Reaction conditions: 2a (0.24 mmol), oxidant (0.24 mmol), and
additive were heated at 100 ℃ for 2 h, then 1a (0.2 mmol) was
b
added in DMSO for another 1 h. Reaction conditions: tempera-
2
, entries 13－15).
c
ture was 90 ℃. Reaction conditions: temperature was 110 ℃.
Considering the easier availability of alcohols com-
d
Reaction conditions: under nitrogen atmosphere.
pared to the corresponding aldehydes, the reaction of
phenyl ethyl alcohols with benzimidohydrazides was
investigated using optimized reaction conditions and the
Using the optimized conditions, we explored the
2
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Chin. J. Chem. 2017, XX, 1—5

Synthesis of 1,2,4-Triazine Compounds
Scheme 1 Reactions scopes for the domino reaction between substituted benzimidohydrazides and various benzaldehydes
Table 2 Optimization of reaction conditions of phenethyl alco-
hol and benzimidohydrazide
Continued
Yield/%
Entry
Oxidant/equiv.
IBX (1.3)
Solvent
DMSO
DMF
d
1
1
1
2
3
4
5
30
IBX (1.3)
17
IBX (1.3)
toluene
dioxane
trance
19
1
IBX (1.3)
a
Reaction conditions: 4a (0.24 mmol) and oxidant (0.26 mmol)
Entry
Oxidant/equiv.
(1.2)
MnO (1.2)
Solvent
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
Yield/%
40
were heated at 100 ℃ in solvent (2 mL) for 2 h, then 1a (0.2
b
mmol) was added for another 1 h. Reaction conditions: temper-
1
2
3
4
5
6
7
8
I
2
c
ature was 90 ℃. Reaction conditions: temperature was 110 ℃.
2
trace
trace
40
d
Reaction conditions: under nitrogen atmosphere.
CuO (1.2)
results are presented in Scheme 2. Much to our delight,
a wide range of functional groups for benzimidohydra-
zide partner furnished the desired products in moderate
to good yields, which include methyl-, methoxyl-, chlo-
ro-, fluoro-, bromo- groups, etc. (Scheme 2, 3aa－3ag).
Similarly, higher yields were obtained for 4-substitued
triazines such as 3ad containing electron-rich groups
SeO (1.2)
2
KMnO (1.2)
trace
40
4
NIS (1.2)
IBX (1.2)
IBX (1.3)
IBX (1.4)
IBX (1.3)
IBX (1.3)
76
84
9
81
(
Scheme 2, 3ad) compared to electron-deficient sub-
b
strates (Scheme 2, 3ae－3ag).
To further explore the generality and scope of this
protocol, a variety of the substitution patterns on the
1
0
1
70
c
1
84
Chin. J. Chem. 2017, XX, 1—5
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3

Liu et al.
COMMUNICATION
Scheme 2 Reactions of substituted benzimidohydrazides with various phenyl ethanol
R2
R1
NH
NH2
OH
N
N
N
IBX (1.3 equiv.)
H
o
N
DMSO, 100 C
R1
R2
1
4
3
O
N
N
N
N
N
N
N
N
N
N
N
N
3
ad
3
aa
3ab
71%
3ac
70%
80%
84%
Cl
F
Br
N
N
N
N
N
N
N
N
N
N
N
N
3
ae
3
af
3ag
76%
3ba
75%
Br
77%
72%
F
Cl
O
N
N
N
N
N
N
N
N
N
N
F
N
N
N
N
N
3
8
bl
8%
3
bd
2%
3bh
70%
3bi
75%
3bk
82%
7
aryl ethyl alcohols were also investigated. As summa-
rized in Scheme 2, various aryl ethyl alcohols bearing
both electron-donating and electron-withdrawing groups
smoothly underwent the cyclization reaction with 1,
delivering a series of triazines in moderate to good
yields. Electron-donating substituents provided desired
products in the yields of 72%－75% (Scheme 2, 3ba,
proposed in Scheme 3. Initially, 2-phenylacetaldehyde
(
2a) is iodinated to 2-iodo-2-phenylacetaldehyde A in
[14]
the presence of I
2
(path 1). Correspondingly,
phenethyl alcohol 4a is first oxidized to hyacinthin by
[15]
oxygen and then is converted into A in the presence
[16]
of IBX (path 2). Subsequently, A is further converted
into 2-oxo-2-phenylacetaldehyde B through a Komblum
3
bd), which were lower than those of electron-with-
[
17]
oxidation in DMSO.
N-aminobenzamidine 1a and (Z)-N'-aminobenzamidine
a' can be converted into each other. Then, B is reacted
with 1a' via a condensation reaction affording the de-
To the best of our knowledge,
drawing substitution (Scheme 2, 3bh－3bl). Steric hin-
drance from the 2-position of phenyl ethyl alcohols
produced a slightly lower yield.
1
[
13]
Inspired by the previous similar reactions, a pos-
sible reaction mechanism for this domino reaction is
[18]
sired products 3,5-diphenyl-1,2,4-triazine (3aa).
Scheme 3 Proposed mechanism
4
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Chin. J. Chem. 2017, XX, 1—5

Synthesis of 1,2,4-Triazine Compounds
Conclusions
(b) Maheshwari, V.; Bhattacharyya, D.; Fronczek, F. R.; Marzilli, P.
A.; Marzilli, L. G. Inorg. Chem. 2006, 45, 7182.
In conclusion, we have developed a novel method
for the synthesis of 3,5-diaryl-1,2,4-triazines using sim-
ple and readily available 2-arylacetaldehyde and
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Rong, L.; Li, X.; Wang, H.; Shi, D. Synth. Commun. 2007, 37, 173;
(b) Phucho, T.; Nongpiur, A.; Tumtin, S.; Nongrum, R.; Myrboh, B.;
Nongkhlaw, R. L. Arkivoc 2008, (xv), 79; (c) Shi, B.; Lewis, W.;
Campbell, L. B.; Moody, C. J. Org. Lett. 2009, 11, 3686; (d) Ramin,
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G.; Du, B. Chin. J. Chem. 2016, 34, 901; (b) Viswanadham, K. D. R.;
Reddy, M. P.; Sathyanarayana, P.; Ravi, O.; Kant, R.; Bathula, S. R.
Chem. Commun. 2014, 50, 13517; (c) Wang, C. H.; Guan, Z.; He, Y.
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2
-arylethanols with N-aminobenzamidine in the pres-
ence of iodine sources. Notably, for both the I and IBX
2
systems, no transition-metals are required, the reaction
is environmentally friendly and excellent yields were
obtained. In addition, the protocols eliminate the need to
prepare 1,2-dicarbonyl precursors. Further studies on
the application of this strategy will be reported in due
course.
[
8
19.
Acknowledgement
[
11] (a) Zhang, Y. Q.; Li, X. L.; Li, J. H.; Chen, J. Y.; Meng, X.; Zhao, M.
M.; Chen, B. H. Org. Lett. 2012, 14, 26; (b) Tang, D.; Wu, P.; Liu,
X.; Chen, Y. X.; Guo, S. B.; Chen, W. L.; Li, J. G.; Chen, B. H. J.
Org. Chem. 2013, 78, 2746; (c) Tang, D.; Li, X. L.; Guo, X.; Wu, P.;
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We are sincerely grateful for sponsorship of this pro-
ject by the National Natural Science Foundation of
China (No. 21372102).
4
038; (d) Wu, P.; Qu, J. P.; Li, Y. X.; Guo, X.; Tang, D.; Meng, X.;
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