Synthesis of 2,3-bis(halomethyl)quinoxaline derivatives and evaluation of their antibacterial and antifungal activities

Article abstract of DOI:10.1248/cpb.c12-01061

Quinoxaline derivatives having bis(fluoromethyl), bis(chloromethyl), or bis(iodomethyl) groups at the 2- and 3-positions, and various electron-donating/withdrawing substituents at the 6- and/or 7-positions, were synthesized. Their antibacterial and antifu

Full text of DOI:10.1248/cpb.c12-01061

438
Regular Article
Chem. Pharm. Bull. 61(4) 438–444 (2013)
Vol. 61, No. 4
Synthesis of 2,3-Bis(halomethyl)quinoxaline Derivatives and Evaluation
of Their Antibacterial and Antifungal Activities
,a
Hisato Ishikawa,a Takayuki Sugiyama,b and Akihiro Yokoyama*
a Department of Materials and Life Science, Faculty of Science and Technology, Seikei University; 3–3–1 Kichijoji-
b
kitamachi, Musashino, Tokyo 180–8633, Japan: and Japan EnviroChemicals, Ltd.; 5–11–61 Torishima, Konohana-
ku, Osaka 554–0051, Japan.
Received December 12, 2012; accepted January 11, 2013
Quinoxaline derivatives having bis(fluoromethyl), bis(chloromethyl), or bis(iodomethyl) groups at the
2- and 3-positions, and various electron-donating/withdrawing substituents at the 6- and/or 7-positions,
were synthesized. Their antibacterial and antifungal activities were evaluated by means of minimum inhibi-
tory concentration assays. The relationships between the substituents and the antimicrobial activities of the
quinoxaline derivatives indicate that the electrophilicity of the halomethyl units plays an important role in
generating the antimicrobial activity.
Key words quinoxaline; antibacterial activity; antifungal activity; halomethyl
Bacteria and fungi are responsible for a variety of problems, having a hydrophilic group such as CO2H or OH at the
including infectious diseases, food spoilage, and corrosion of 6-position exhibited almost no antimicrobial activity. How-
industrial materials. To counter this, many antimicrobial ever, an assessment of antifungal activity was less clear, with
agents have been developed, such as penicillin,1) gentamicin,2) the introduction of strong electron-releasing/withdrawing sub-
nalidixic acid,3) 3-iodo-2-propynyl N-butylcarbamate (IPBC),4) stituents (e.g., F, CF3, NO2, CN, and OCH3) resulting in a wide
and 5-chloro-2-methyl-4-isothiazolin-3-one (CMIT).5) How- antifungal spectrum. These results prompted us to study the
ever, because bacteria can develop resistance to all commonly effect of introducing various halomethyl groups at the 2- and
used antimicrobial agents, drug-resistant bacteria such as 3-positions of these quinoxaline compounds on their antimi-
methicillin-resistant Staphylococcus aureus (MRSA), vanco- crobial activity.
mycin-resistant Enterococci (VRE) and vancomycin-resistant
In this paper, we synthesized quinoxaline derivatives with
Staphylococcus aureus (VRSA) have appeared,6–8) and so the bis(fluoromethyl), bis(chloromethyl), and bis(iodomethyl) units
development of new antimicrobial agents is critically required. at the 2- and 3-positions, as well as various substituents at the
Nitrogen-containing heterocycles form the main component 6- and/or 7-positions (Fig. 1). Their antibacterial and antifun-
of many essential biomolecules, from DNA and RNA to co- gal activities were evaluated by means of minimum inhibitory
enzymes. They are thought to have high biocompatibility, and concentration assays, and relationships between the substitu-
have been used as structural units within many pharmaceuti- ents and the antimicrobial activities were studied.
cal products.9) Among the various classes of heterocyclic units,
the quinoxaline ring is one of the components involved in a
variety of antibiotic molecules such as hinomycin, levomycin,
Results and Discussion
Chemistry The 2,3-bis(fluoromethyl)quinoxalines 2a–8a
and actinoleutin.10–12) Furthermore, many quinoxaline deriva- were synthesized by the reaction of the corresponding bro-
tives have been reported to possess anticancer, antibacterial, momethyl compounds 2c–8c with potassium fluoride in the
antifungal, antiviral, and antiprotozoal activities.13–23)
presence of 18-crown-6 in acetone, giving 18–84% yields25)
In
a previous paper, we reported that the 2,3-bis- (Chart 1). The fluorination of quinoxaline derivatives bearing
(bromomethyl)quinoxaline framework is a good candidate a strong electron-withdrawing group at the 6-position, such
for a novel industrial antimicrobial agent, and that the lipo- as 2c–4c, gave many by-products and so the yields of the tar-
philicity and electrical properties of its substituents affect the get compounds were low. In particular, the fluorination of 1c
antimicrobial activity.24) For example, we found compounds (6-NO2) afforded a complex mixture from which 1a could not
with the strong electron-withdrawing and highly lipophilic be extracted.26)
trifluoromethyl group at the 6-position showed the highest ef-
The similar reactions of 1c–8c with potassium chloride gave
fectiveness against Gram-positive bacteria, while quinoxalines 2,3-bis(chloromethyl)quinoxalines 1b–8b in good yields27,28)
Fig. 1. Structure of the 2,3-Bis(halomethyl)quinoxaline Derivatives
The authors declare no conflict of interest.
© 2013 The Pharmaceutical Society of Japan
*To whom correspondence should be addressed. e-mail: ayokoyama@st.seikei.ac.jp

April 2013
439
Chart 1. Synthesis of the 2,3-Bis(fluoromethyl)quinoxaline Derivatives
2a–8a
Chart 2. Synthesis of the 2,3-Bis(chloromethyl)quinoxaline Derivatives
1b–8b
(Chart 2). Unlike in the fluorination reactions, the compounds
having electron-withdrawing substituents at the 6-position
could be chlorinated without serious side reactions. The prog-
ress of the reaction was monitored with HPLC, because TLC
analysis exhibited that the Rf value of the product was almost
the same as that of the starting material.
The 2,3-bis(iodomethyl)quinoxalines 2d–8d were syn-
thesized from 2c–8c by the Finkelstein reaction,29,30) and
obtained in 36–94% yields (Chart 3). These reactions were
also monitored with HPLC. As with some of the fluorination
reactions, the reactions of 2d and 3d, which had the strong
electron-withdrawing substituents CN and CF3 respectively
at the 6-position, were accompanied by many side reactions,
resulting in low yields for the target compounds, and the io-
Chart 3. Synthesis of the 2,3-Bis(iodomethyl)quinoxaline Derivatives
2d–8d
dination of 1c having a nitro group at the 6-position did not A similar trend (–CH2I≈–CH2Br>–CH2Cl) was observed in
afford 1d at all.26)
compounds containing 6-F (4b, 4c, 4d), 6-Br (6b, 6c, 6d),
Antibacterial Activity The antibacterial activities of the and 6-OCH3 (8b, 8c, 8d) substituents. In these cases, the
newly-synthesized quinoxaline derivatives (2a–8a, 1b–8b, compounds that exhibited the highest activity possessed io-
2d–8d), as well as those of previously reported compounds domethyl, the halomethyl group of highest electrophilicity.
(1c–8c),24) were evaluated by means of minimum inhibitory In contrast, the activities of 6-CF3-substituted quinoxalines
concentration (MIC) assays; the results are summarized in (3b, 3c, 3d) ranked as 3c (–CH2Br)>3b (–CH2Cl), with
Table 1. All compounds were inactive against Gram-negative 2,3-bis(iodomethyl)quinoxaline (3d) being completely inac-
bacteria. The outer membrane of Gram-negative bacteria is tive. These results seem to be caused by heightened electro-
covered by many lipopolysaccharides, which consist mainly philicity as well, although in this case it becomes excessive:
of hydrophilic polysaccharides.31) Therefore, the lipophilic the electron-withdrawing trifluoromethyl group at the 6-posi-
materials are hard to reach the surface of the outer membrane. tion of 3d increases the electrophilicity of the iodomethyl
We think that the synthesized 2,3-bis(halomethyl)quinoxaline group so much that 3d undergoes decomposition under the
derivatives are too lipophilic to come close to the outer mem- MIC assay conditions before it can exert its antibacterial ac-
brane of Gram-negative bacteria.
tivity. A similar relationship between electron-withdrawing
For Gram-positive bacteria, while 2,3-bis(fluoromethyl)- substituents at the 6-position and antibacterial activity was
quinoxalines 2a–8a exhibited no antibacterial activ- also observed in the case of 6-NO2 substituted quinoxalines
ity, four 2,3-bis(chloromethyl)quinoxalines (1b–3b, 8b), five (1b, 1c), whose activity became the highest when the sub-
2,3-bis(iodomethyl)quinoxalines (2d, 4d–6d, 8d), and all stituents at the 2- and 3-positions were chloromethyl, a less
eight 2,3-bis(bromomethyl)quinoxalines (1c–8c) did. Among reactive substituent than bromomethyl. As with the 6-CF3-
them, 2,3-bis(chloromethyl)-6-nitroquinoxaline (1b) showed substituted quinoxalines, the strong electron-withdrawing
the highest activity. The relationships between the substituents nitro group at the 6-position increases the electrophilicity of
and the activities of quinoxaline derivatives suggest that the halomethyl groups, which would result in adequate reactiv-
electrophilicity of halomethyl groups plays an important role ity for the chloromethyl group of 1b, but extend too far and
in their antibacterial activity. That is, the lower electrophilic- induce instability for the bromomethyl group of 1c. The no-
ity of the fluoromethyl group compared with the other halo- tion of electron-withdrawing group-induced destabilization of
methyl groups can be interpreted as directly responsible for halomethyl groups seems to also be supported by the fact that
the inactivity of 2,3-bis(fluoromethyl) derivatives.
the reaction of 2,3-bis(bromomethyl)-6-nitroquinoxaline 1c
When the activities of the quinoxaline derivatives with with sodium iodide afforded complex mixtures of by-products,
6-CN (2b, 2c, 2d) and 6-Cl (5b, 5c, 5d) substituents were instead of forming the desired iodinated compounds.
compared, we found the halomethyl groups exhibited high
Antifungal Activity The MIC values of 2,3-bis-
)
activity in the descending order –CH2I>–CH2Br>–CH2Cl. (halomethyl)quinoxaline derivatives (2a–8a, 1b–8b, 1c–8c,24

440
Vol. 61, No. 4
Table 1. Antibacterial Activities of 2a–8a, 1b–8b, 1c–8c, and 2d–8d
MIC (µg/mL)
R1
R2
X
Gram-positive
B. s.a) S. a.b)
0.4 6.3
25 50
Gram-negative
P. a.d)
E. c.c)
S. m.e)
1b
1c
2a
2b
2c
2d
3a
3b
3c
3d
4a
4b
4c
4d
5a
5b
5c
5d
6a
6b
6c
6d
7a
7b
7c
7d
8a
8b
8c
8d
NO2
NO2
CN
CN
CN
CN
CF3
CF3
CF3
CF3
F
F
F
F
Cl
Cl
Cl
Cl
Br
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
Cl
Br
F
Cl
Br
I
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
50
>100
>100
25
25
6.3
6.3
F
>100
>100
Cl
Br
I
25
25
12.5
12.5
>100
>100
>100
25
>100
>100
>100
50
F
Cl
Br
I
25
25
F
>100
>100
50
>100
>100
50
Cl
Br
I
H
H
H
H
12.5
25
F
>100
>100
25
>100
>100
50
Br
Br
Br
Cl
Br
I
H
25
>100
>100
>100
50
CH3
CH3
CH3
CH3
OCH3
OCH3
OCH3
OCH3
CH3
CH3
CH3
CH3
H
H
H
H
F
>100
>100
50
Cl
Br
I
>100
>100
100
>100
>100
100
F
Cl
Br
I
25
50
25
100
a) Bacillus subtilis. b) Staphylococcus aureus. c) Escherichia coli. d) Pseudomonas aeruginosa. e) Serratia marcescens.
2d–8d) against fungi are listed in Table 2. All 2,3-bis(fluoro- This suggests that the greater the electron-withdrawing ability
methyl)quinoxalines (2a–8a) were inactive, as was the case of the substituent at the 6-position, the wider the antifungal
for the antibacterial assays, while five 2,3-bis(chloromethyl)- spectrum, due to the increase in electrophilicity at the chloro-
quinoxalines (1b–4b, 8b), four 2,3-bis(iodomethyl)quinoxalines methyl moiety.
(2d, 4d, 5d, 8d), and seven 2,3-bis(bromomethyl)quinoxalines
As for the quinoxaline derivatives having iodomethyl (2d–
(1c–6c, 8c) exhibited antifungal activities. These results in- 8d) and bromomethyl groups (1c–8c), the compounds with
dicate that, similarly to antibacterial activities, quinoxaline the highest and the widest-ranging activities were electron-
derivatives having highly electrophilic halomethyl groups tend withdrawing cyano group-substituted 2d and 2c, followed by
to exhibit antifungal activities.
fluoro-substituted 4d and 4c. In contrast, the compound 3d
Detailed analyses of the relationships between the sub- bearing the strong electron-withdrawing trifluoromethyl group
stituents at the 6-position and the antifungal activities of was inactive against fungi, similar to its effectiveness against
2,3-bis(halomethyl)quinoxalines indicate that the compounds bacteria. This result corroborates the notion of destabilization
having an electron-withdrawing group at the 6-position of iodomethyl and bromomethyl groups induced by the strong
showed the greatest antifungal activity. Among them, 1b electron-withdrawing trifluoromethyl unit, which leads to the
(6-NO2), 2b (6-CN), 2d (6-CN), and 4d (6-Cl) showed the decomposition of compounds before any antifungal activ-
highest activity (12.5µg/mL) against Aspergillus niger, Clado- ity can be exerted. We think that the moderate activity of 1c
sporium cladosporioides, and Mucor spinescens. In contrast, (6-NO2) and 3c (6-CF3) may also be caused by similar destabi-
introduction of the moderate electron-withdrawing bromo lization of their bromomethyl groups.
group or strong electron-donating methoxy group at the 6-po-
sition, and of the moderate electron-donating methyl group
at the 6- and 7-positions resulted in low and/or no antifungal
activities.
Conclusion
Quinoxaline derivatives bearing fluoromethyl, chloromethyl,
or iodomethyl groups at the 2- and 3-positions were synthe-
Among the 2,3-bis(chloromethyl)quinoxalines (1b–8b), sized by the reaction of corresponding 2,3-bis(bromomethyl)-
the compound with the widest antifungal spectrum was 1b quinoxaline derivatives with a metal halide (KF, KCl, or
(6-NO2), followed by 2b (6-CN), 3b (6-CF3), and 4b (6-F). NaI). No compounds were active against Gram-negative

April 2013
441
Table 2. Antifungal Activities of 2a–8a, 1b–8b, 1c–8c, and 2d–8d
MIC (µg/mL)
R1
R2
X
Mold
Yeast
A. n.a)
P. c.b)
C. c.c)
A. p.d)
A. s.e)
M. s.f)
G. v.g)
R. r.h)
S. c.i)
1b
1c
2a
2b
2c
2d
3a
3b
3c
3d
4a
4b
4c
4d
5a
5b
5c
5d
6a
6b
6c
6d
7a
7b
7c
7d
8a
8b
8c
8d
NO2
NO2
CN
CN
CN
CN
CF3
CF3
CF3
CF3
F
F
F
F
Cl
Cl
Cl
Cl
Br
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
Cl
Br
F
Cl
Br
I
12.5
100
>100
25
50
25
>100
50
50
100
>100
>100
25
25
>100
50
100
50
>100
12.5
25
12.5
>100
50
50
100
>100
50
50
25
>100
50
50
25
>100
>100
25
25
50
>100
12.5
25
25
>100
25
100
100
100
>100
>100
100
50
50
>100
>100
50
25
>100
100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
100
50
>100
>100
>100
100
>100
>100
>100
100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
F
>100
>100
100
>100
>100
>100
50
Cl
Br
I
50
50
100
50
25
50
>100
>100
100
>100
>100
>100
50
>100
>100
25
>100
>100
100
100
100
>100
>100
50
>100
>100
>100
50
F
Cl
Br
I
50
50
50
25
25
25
100
50
25
F
>100
>100
50
>100
>100
>100
100
>100
>100
>100
>100
>100
>100
>100
50
>100
>100
100
>100
>100
>100
100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
25
12.5
>100
>100
50
>100
>100
>100
>100
>100
>100
50
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
100
>100
>100
50
>100
>100
>100
50
>100
>100
>100
>100
>100
>100
50
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
100
Cl
Br
I
H
H
H
H
F
Br
Br
Br
Cl
Br
I
H
CH3
CH3
CH3
CH3
OCH3
OCH3
OCH3
OCH3
CH3
CH3
CH3
CH3
H
H
H
H
F
Cl
Br
I
F
Cl
Br
I
50
>100
50
>100
>100
>100
50
>100
a) Aspergillus niger. b) Penicillium citrinum. c) Cladosporium cladosporioides. d) Aureobasidium pullulans. e) Alternaria sp. f ) Mucor spinescens. g) Gliocladium virens.
h) Rhodotorula rubra. i) Saccharomyces cerevisiae.
bacteria. All fluoromethyl derivatives were inactive against
Experimental
Gram-positive bacteria and fungi, while the antibacterial and
General All common reagents and solvents were ob-
antifungal properties of chloromethyl, bromomethyl, and io- tained from Wako Pure Chemical Industries, Tokyo Chemi-
domethyl quinoxalines were dependent upon the substituents cal Industry, and Sigma-Aldrich, and used without further
at the 6-position. We propose that the antimicrobial activities purification. Column chromatography was carried out using
of 2,3-bis(halomethyl)quinoxaline derivatives largely depend silica gel (Silica Gel 60N, 63–210µm, Kanto Chemical). Thin
on the electrophilicity of halomethyl groups, which is in turn layer chromatography (TLC) was conducted on Merck Silica
affected by the electrical properties of the substituent at the Gel 60 F254. Melting points were determined on an SMP3
6-position. When moderate electron-withdrawing substituents melting point apparatus (Bibby Scientific Limited) and were
were introduced at the 6-position, the relative strengths of the uncorrected. 1H- and 13C-NMR spectra were recorded on
antibacterial and antifungal activities of the halomethyl com- JEOL JNM-LA400D and JNM-ECA-500, respectively, using
pounds became –CH2I≥–CH2Br>–CH2Cl: almost in the order DMSO-d6 and CDCl3 as solvents. Chemical shifts (δ) were
of descending electrophilicity of the halomethyl groups. In reported as parts per million (ppm) relative to tetramethyl-
1
contrast, introduction of strong electron-withdrawing groups, silane (TMS) as an internal standard for H-NMR, and as the
such as nitro and trifluoromethyl groups, at the 6-position midpoint of CDCl3 (77.16ppm) for 13C-NMR. IR spectra were
induced the destabilization of iodomethyl groups, leading to recorded with a JASCO FT/IR-470. Elemental analyses for C,
low antimicrobial activities. To confirm the effects of substitu- H and N were performed using a Perkin Elmer 2400 analyzer
ent electrophilicity at the 2- and 3-positions on antibacterial series II and EURO EA 3000 Series. All compounds were
and antifungal efficacy, synthesis of quinoxaline derivatives characterized by the above techniques. Syntheses of 1c–8c
containing other electrophilic substituents at the 2- and 3-po- and evaluation of antimicrobial activities by means of mini-
sitions and evaluation of their antimicrobial activities is in mum inhibitory concentration assay were carried out as has
progress.
been described previously.24)
General Procedure for 2,3-Bis(fluoromethyl)quinoxalines
(2a–8a) A mixture of 2c–8c (1.0mmol), KF (10.0mmol), and

442
Vol. 61, No. 4
18-crown-6 (4.0mmol) in dry acetone (15mL) was refluxed for
2,3-Bis(fluoromethyl)-6,7-dimethylquinoxaline (7a): White
8h under an argon atmosphere. Then, the solvent was evapo- powder, yield: 84%, mp 130–131°C. 1H-NMR (400MHz,
rated, and the residue was dissolved in CHCl3 (50mL). The CDCl3) δ: 2.52 (6H, s), 5.79 (4H, d, J=47Hz), 7.88 (2H,
CHCl3 layer was washed with H2O (50mL×3) and dried over s). 13C-NMR (126MHz, CDCl3) δ: 20.6 (CH3), 83.9 (d,
anhydrous Na2SO4. The crude product was purified by col- JCF=168Hz, CH2), 128.4 (CH), 140.5 (C), 142.0 (C), 148.3 (d,
umn chromatography on silica gel with CHCl3–acetone–EtOH JCF=19Hz, C). IR (KBr) cm−1: 3000, 2926, 1625, 1559, 1456,
(200:5:1).
1361, 1205, 1017, 874. Anal. Calcd for C12H12N2F2: C, 64.85; H,
6-Cyano-2,3-Bis(fluoromethyl)quinoxaline (2a): White pow- 5.44; N, 12.61. Found: C, 64.83; H, 5.50; N, 12.49.
1
der, yield: 18%, mp 157–159°C. H-NMR (400MHz, CDCl3)
2,3-Bis(fluoromethyl)-6-methoxyquinoxaline (8a): Pale yel-
1
δ: 5.83 and 5.84 (4H, two d, J=47Hz), 7.98 (1H, dd, J=1.7, low powder, yield: 78%, mp 103–104°C. H-NMR (400MHz,
8.5Hz), 8.25 (1H, d, J=8.5Hz), 8.52 (1H, d, J=1.7Hz). CDCl3) δ: 3.99 (3H, s), 5.80 and 5.81 (4H, two d, J=48Hz),
13C-NMR (126MHz, CDCl3) δ: 83.5 (d, JCF=169Hz, CH2), 7.41 (1H, d, J=2.7Hz), 7.47 (1H, dd, J=2.7, 9.2Hz), 8.00 (1H,
83.6 (d, JCF=169Hz, CH2), 114.7 (CN), 117.7 (C), 131.0 d, J=9.2Hz). 13C-NMR (126MHz, CDCl3) δ: 56.0 (OCH3),
(CH), 131.8 (CH), 135.3 (CH), 140.4 (C), 142.7 (C), 151.4 (d, 83.5 (d, JCF=169Hz, CH2), 83.6 (d, JCF=169Hz, CH2), 106.5
JCF=19Hz, C), 152.2 (d, JCF=19Hz, C). IR (KBr) cm−1: 3082, (CH), 124.6 (CH), 130.3 (CH), 137.7 (C), 143.4 (C), 146.4 (d,
2976, 2235, 1615, 1560, 1493, 1323, 1037, 899, 846. Anal. JCF=19Hz, C), 149.4 (d, JCF=19Hz, C), 161.8 (C). IR (KBr)
Calcd for C11H7N3F2: C, 60.28; H, 3.22; N, 19.17. Found: C, cm−1: 3016, 2973, 1620, 1498, 1335, 1242, 1146, 1020, 839, 797.
60.57; H, 3.44; N, 18.87.
Anal. Calcd for C11H10N2OF2∙0.5H2O: C, 56.65; H, 4.75; N,
2,3-Bis(fluoromethyl)-6-(trifluoromethyl)quinoxaline (3a): 12.01. Found: C, 56.85; H, 4.48; N, 11.89.
1
Brown oil, yield: 54%. H-NMR (400MHz, CDCl3) δ: 5.84
General Procedure for 2,3-Bis(chloromethyl)quinoxa-
and 5.85 (4H, two d, J=46Hz), 8.01 (1H, d, J=2.7Hz), 8.27 lines (1b–8b) A mixture of 1c–8c (1.0mmol), KCl (10.0
(1H, dd, J=2.7, 9.2Hz), 8.47 (1H, d, J=9.2Hz). 13C-NMR mmol), and 18-crown-6 (4.0mmol) in dry acetone (15mL) was
(126MHz, CDCl3) δ: 83.5 (d, JCF=169Hz, CH2), 123.5 (q, refluxed for 16h under an argon atmosphere. Then, the sol-
JCF=274Hz, CF3), 126.8 (q, JCF=2.4Hz, CH), 127.4 (q, vent was evaporated, and the residue was dissolved in CHCl3
JCF=3.6Hz, CH), 130.8 (CH), 132.7 (q, JCF=32Hz, C), 140.4 (50mL). The CHCl3 layer was washed with H2O (50mL×3)
(C), 142.4 (C), 150.8 (d, JCF=19Hz, C), 151.6 (d, JCF=18Hz, and dried over anhydrous Na2SO4. The crude product was
C). IR (KBr) cm−1: 3023, 2964, 1573, 1449, 1316, 1196, 1022, purified by column chromatography on silica gel with CHCl3.
906, 844. Anal. Calcd for C11H7N2F5∙0.8 H2O: C, 47.77; H,
3.13; N, 10.13. Found: C, 47.52; H, 3.08; N, 10.36.
2,3-Bis(chloromethyl)-6-nitroquinoxaline (1b): White pow-
der, yield: 89%, mp 97–99°C (decomp.). H-NMR (400MHz,
1
6-Fluoro-2,3-bis(fluoromethyl)quinoxaline (4a): White solid, CDCl3) δ: 5.08 (4H, s), 8.26 (1H, d, J=9.0Hz), 8.58 (1H, dd,
1
yield: 41%, mp 121–123°C. H-NMR (400MHz, CDCl3) δ: J=2.4, 9.0Hz), 9.01 (1H, d, J=2.4Hz). 13C-NMR (126MHz,
5.80 and 5.81 (4H, two d, J=47Hz), 7.62 (1H, dt, J=2.5, CDCl3) δ: 43.8 (CH2), 124.4 (CH), 125.5 (CH), 131.0 (CH),
9.0Hz), 7.77 (1H, dd, J=2.5, 8.8Hz), 8.15 (1H, dd, J=6.0, 140.5 (C), 143.9 (C), 148.6 (C), 153.0 (C), 153.8 (C). IR (KBr)
9.1Hz). 13C-NMR (126MHz, CDCl3) δ: 83.6 (d, JCF=169Hz, cm−1: 3027, 2977, 1618, 1526, 1482, 1347, 915, 849, 730. Anal.
CH2), 83.7 (d, JCF=169Hz, CH2), 113.0 (d, JCF=22Hz, CH), Calcd for C10H7N3O2Cl2∙0.7H2O: C, 42.19; H, 2.79; N, 14.76.
121.6 (d, JCF=25Hz, CH), 131.6 (d, JCF=11Hz, CH), 138.7 Found: C, 42.01; H, 3.02; N, 14.88.
(C), 142.3 (d, JCF=13Hz, C), 148.8 (d, JCF=19Hz, C), 150.3 (d,
2,3-Bis(chloromethyl)-6-cyanoquinoxaline (2b): White pow-
1
JCF=19Hz, C), 163.5 (d, JCF=254Hz, C). IR (KBr) cm−1: 3054, der, yield: 78%, mp 162–164°C. H-NMR (400MHz, CDCl3)
2977, 1622, 1570, 1493, 1331, 1210, 1146, 880, 821. Anal. Calcd δ: 5.05 (4H, s), 7.97 (1H, dd, J=1.3, 8.8Hz), 8.21 (1H, d,
for C10H7N2F3∙0.2H2O: C, 55.66; H, 3.46; N, 12.98. Found: C, J=8.8Hz), 8.48 (1H, d, J=1.3Hz). 13C-NMR (126MHz,
55.56; H, 3.32; N, 12.88.
CDCl3) δ: 43.9 (CH2), 114.6 (CN), 117.8 (C), 130.9 (CH), 131.8
6-Chloro-2,3-bis(fluoromethyl)quinoxaline (5a): White pow- (CH), 135.1 (CH), 140.6 (C), 142.9 (C), 152.8 (C), 153.4 (C).
1
der, yield: 71%, mp 100–101°C. H-NMR (400MHz, CDCl3) IR (KBr) cm−1: 3002, 2978, 2230, 1568, 1489, 1323, 899, 846,
δ: 5.81 and 5.82 (4H, two d, J=47Hz), 7.77 (1H, dd, J=2.0, 706. Anal. Calcd for C11H7N3Cl2: C, 52.41; H, 2.80; N, 16.67.
9.0Hz), 8.08 (1H, d, J=9.0Hz), 8.14 (1H, d, J=2.0Hz). Found: C, 52.52; H, 3.08; N, 16.94.
13C-NMR (126MHz, CDCl3) δ: 83.7 (d, JCF=169Hz, CH2),
2,3-Bis(chloromethyl)-6-(trifluoromethyl)quinoxaline (3b):
1
128.3 (CH), 130.6 (CH), 132.2 (CH), 137.1 (C), 140.0 (C), 141.7 Brown solid, yield: 76%, mp 61–62°C. H-NMR (400MHz,
(C), 149.5 (d, JCF=19Hz, C), 150.4 (d, JCF=19Hz, C). IR (KBr) CDCl3) δ: 5.06 (4H, s), 7.99 (1H, dd, J=2.0, 8.8Hz), 8.23 (1H,
cm−1: 3050, 2975, 1605, 1562, 1465, 1322, 1146, 884, 827, 739. d, J=8.8Hz), 8.43 (1H, d, J=2.0Hz). 13C-NMR (126MHz,
Anal. Calcd for C10H7N2F2Cl∙0.3H2O: C, 51.32; H, 3.27; N, CDCl3) δ: 44.0 (CH2), 123.5 (q, JCF=274Hz, CF3), 126.8 (q,
11.97. Found: C, 51.12; H, 3.10; N, 12.21.
JCF=2.4Hz, CH), 127.3 (q, JCF=4.8Hz, CH), 130.5 (CH), 132.7
6-Bromo-2,3-bis(fluoromethyl)quinoxaline (6a): White pow- (q, JCF=32Hz, C), 140.7 (C), 142.7 (C), 152.2 (C), 152.8 (C).
1
der, yield: 76%, mp 94–95°C. H-NMR (400MHz, CDCl3) δ: IR (KBr) cm−1: 3053, 2984, 1631, 1569, 1449, 1318, 1135, 905,
5.81 and 5.82 (4H, d, J=47Hz), 7.91 (1H, dd, J=2.2, 9.0Hz), 826, 707. Anal. Calcd for C11H7N2F3Cl2∙0.6H2O: C, 43.19; H,
8.01 (1H, d, J=9.0Hz), 8.33 (1H, d, J=2.2Hz). 13C-NMR 2.70; N, 9.16. Found: C, 43.13; H, 2.51; N, 9.41.
(126MHz, CDCl3) δ: 83.7 (d, JCF=169Hz, CH2), 125.3 (C),
2,3-Bis(chloromethyl)-6-fluoroquinoxaline (4b): White pow-
1
130.7 (CH), 131.7 (CH), 134.7 (CH), 140.2 (C), 141.9 (C), 149.7 der, yield: 97%, mp 141–142°C. H-NMR (400MHz, CDCl3) δ:
(d, JCF=19Hz, C), 150.3 (d, JCF=19Hz, C). IR (KBr) cm−1: 5.04 (4H, s), 7.60 (1H, dt, J=2.6, 9.1Hz), 7.73 (1H, dd, J=2.5,
3075, 2977, 1598, 1560, 1455, 1319, 1146, 880, 821, 583. Anal. 9.0Hz,), 8.11 (1H, dd, J=2.6, 9.1Hz). 13C-NMR (126MHz,
Calcd for C10H7N2F2Br∙0.4H2O: C, 42.85; H, 2.80; N, 9.99. CDCl3) δ: 44.1 (CH2), 44.2 (CH2), 112.8 (d, JCF=22Hz, CH),
Found: C, 42.76; H, 2.91; N, 10.16.
121.6 (d, JCF=25Hz, CH), 131.3 (d, JCF=11Hz, CH), 138.9

April 2013
443
(C), 142.8 (d, JCF=13Hz, C), 150.0 (C), 151.6 (C), 163.5 (d, d, J=8.8Hz), 8.33 (1H, d, J=1.5Hz). 13C-NMR (126MHz,
JCF=254Hz, C). IR (KBr) cm−1: 3019, 2975, 1620, 1567, 1497, CDCl3) δ: 1.8 (CH2), 123.6 (q, JCF=272Hz, CF3), 126.2 (q,
1334, 1217, 866, 841, 714. Anal. Calcd for C10H7N2FCl2∙0.3 JCF=3.6Hz, CH), 126.9 (q, JCF=4.8Hz, CH), 130.1 (CH), 132.2
H2O: C, 47.95; H, 3.06; N, 11.18. Found: C, 47.88; H, 3.20; N, (q, JCF=34Hz, C), 140.5 (C), 142.6 (C), 153.7 (C), 154.4 (C).
10.93.
IR (KBr) cm−1: 3022, 2961, 1554, 1496, 1449, 1317, 1282, 899,
6-Chloro-2,3-bis(chloromethyl)quinoxaline (5b): White 843. Anal. Calcd for C11H7N2F3I2: C, 27.64; H, 1.48; N, 5.86.
powder, yield: 92%, mp 142–143°C. 1H-NMR (400MHz, Found: C, 27.82; H, 1.51; N, 5.62.
CDCl3) δ: 5.03 (4H, s), 7.75 (1H, dd, J=2.2, 9.0Hz), 8.04 (1H,
6-Fluoro-2,3-bis(iodomethyl)quinoxaline (4d): Pale orange
d, J=9.0Hz), 8.10 (1H, d, J=2.2Hz). 13C-NMR (126MHz, powder, yield: 71%, mp 148–150°C. 1H-NMR (400MHz,
CDCl3) δ: 44.1 (CH2), 44.2 (CH2), 128.0 (CH), 130.3 (CH), CDCl3) δ: 4.81 (4H, s), 7.54 (1H, dt, J=2.2, 9.0Hz), 7.64
132.2 (CH), 137.0 (C), 140.2 (C), 141.9 (C), 150.8 (C), 151.6 (1H, dd, J=2.2, 8.8Hz), 8.02 (1H, dd, J=5.8, 9.0Hz,).
(C). IR (KBr) cm−1: 3020, 2921, 1605, 1558, 1479, 1323, 879, 13C-NMR (126MHz, CDCl3) δ: 2.2 (CH2), 2.3 (CH2), 112.6
805, 731, 711. Anal. Calcd for C10H7N2Cl3∙0.6 H2O: C, 44.10; (d, JCF=22Hz, CH), 121.2 (d, JCF=26Hz, CH), 131.1 (d,
H, 3.03; N, 10.29. Found: C, 44.09; H, 3.16; N, 10.11.
JCF=10Hz, CH), 138.8 (C), 142.5 (d, JCF=14Hz, C), 151.4 (C),
6-Bromo-2,3-bis(chloromethyl)quinoxaline (6b): White 153.1 (C), 163.2 (d, JCF=254Hz, C). IR (KBr) cm−1: 3042,
powder, yield: 86%, mp 137–138°C. 1H-NMR (400MHz, 2954, 1566, 1490, 1418, 1326, 1215, 894, 818. Anal. Calcd for
CDCl3) δ: 5.02 (4H, s), 7.88 (1H, dd, J=2.0, 9.0Hz), 7.97 (1H, C10H7N2FI2: C, 28.06; H, 1.65; N, 6.55. Found: C, 28.36; H,
d, J=9.0Hz), 8.29 (1H, d, J=2.0Hz). 13C-NMR (126MHz, 1.45; N, 6.39.
CDCl3) δ: 44.1 (CH2), 44.2 (CH2), 125.3 (C), 130.5 (CH), 131.5
6-Chloro-2,3-bis(iodomethyl)quinoxaline (5d): Orange pow-
1
(CH), 134.7 (CH), 140.4 (C), 142.1 (C), 150.9 (C), 151.6 (C). der, yield: 70%, mp 144–146°C. H-NMR (400MHz, CDCl3)
IR (KBr) cm−1: 3019, 2924, 1597, 1478, 1321, 880, 821, 727, δ: 4.80 (4H, s), 7.70 (1H, dd, J=2.4, 9.0Hz), 7.95 (1H, d,
583. Anal. Calcd for C10H7N2Cl2Br: C, 39.25; H, 2.31; N, 9.14. J=9.0Hz), 8.01 (1H, d, J=2.4Hz). 13C-NMR (126MHz,
Found: C, 39.53; H, 2.45; N, 9.09.
CDCl3) δ: 2.2 (CH2), 2.3 (CH2), 127.9 (CH), 130.1 (CH), 131.8
2,3-Bis(chloromethyl)-6,7-dimethylquinoxaline (7b): White (CH), 136.6 (C), 140.1 (C), 141.8 (C), 152.3 (C), 153.2 (C).
powder, yield: 98%, mp 148–149°C. 1H-NMR (400MHz, IR (KBr) cm−1: 3016, 2950, 1557, 1479, 1438, 1355, 893, 832,
CDCl3) δ: 2.51 (6H, s), 5.02 (4H, s), 7.84 (2H, s). 13C-NMR 735. Anal. Calcd for C10H7N2ClI2: C, 27.02; H, 1.59; N, 6.30.
(126MHz, CDCl3) δ: 20.6 (CH3), 44.5 (CH2), 128.2 (CH), Found: C, 27.19; H, 1.57; N, 6.38.
140.7 (C), 141.9 (C), 150.0 (C). IR (KBr) cm−1: 3013, 2917,
1621, 1556, 1484, 1359, 1022, 873, 733. Anal. Calcd for low powder, yield: 77%, mp 158–160°C. H-NMR (400MHz,
C12H12N2Cl2∙0.3H2O: C, 55.32; H, 4.87; N, 10.75. Found: C, CDCl3) δ: 4.80 (4H, s), 7.82 (1H, dd, J=1.7, 9.0Hz), 7.88 (1H,
55.37; H, 4.68; N, 10.72.
6-Bromo-2,3-bis(iodomethyl)quinoxaline (6d): Pale yel-
1
d, J=9.0Hz), 8.20 (1H, d, J=1.7Hz). 13C-NMR (126MHz,
2,3-Bis(chloromethyl)-6-methoxyquinoxaline (8b): Pale yel- CDCl3) δ: 2.1 (CH2), 2.3 (CH2), 124.8 (CH), 130.2 (CH), 131.3
1
low powder, yield: 93%, mp 108–109°C. H-NMR (400MHz, (CH), 134.3 (C), 140.3 (C), 142.1 (C), 152.4 (C), 153.2 (C). IR
CDCl3) δ: 3.98 (3H, s), 5.01 and 5.02 (4H, two s), 7.37 (1H, d, (KBr) cm−1: 3026, 2964, 2922, 1547, 1470, 1436, 1351, 880,
J=2.7Hz), 7.46 (1H, dd, J=2.7, 9.2Hz), 7.97 (1H, d, J=9.2Hz). 830, 569. Anal. Calcd for C10H7N2BrI2: C, 24.57; H, 1.44; N,
13C-NMR (126MHz, CDCl3) δ: 44.3 (CH2), 44.4 (CH2), 56.1 5.73. Found: C, 24.57; H, 1.33; N, 5.84.
(OCH3), 106.5 (CH), 124.6 (CH), 130.2 (CH), 137.9 (C), 143.5
2,3-Bis(iodomethyl)-6,7-dimethylquinoxaline (7d): White
(C), 147.8 (C), 150.6 (C), 161.8 (C). IR (KBr, cm−1): 3004, powder, yield: 70%, mp 145–146°C. 1H-NMR (400MHz,
2963, 1613, 1445, 1327, 1224, 1020, 853, 836, 714. Anal. Calcd CDCl3) δ: 2.48 (6H, s), 4.81 (4H, s), 7.76 (2H, s). 13C-NMR
for C11H10N2OCl2∙0.2H2O: C, 50.67; H, 4.02; N, 10.74. Found: (126MHz, CDCl3) δ: 3.2 (CH2), 20.6 (CH3), 127.9 (CH), 140.6
C, 50.56; H, 4.28; N, 10.89.
(C), 141.6 (C), 150.0 (C). IR (KBr) cm−1: 3023, 2970, 2913,
General Procedure for 2,3-Bis(iodomethyl)quinoxalines 1623, 1481, 1442, 1358, 1019, 870. Anal. Calcd for C12H12N2I2:
(2d–8d) A mixture of 2c–8c (0.5mmol) and NaI (5.0mmol) C, 32.90; H, 2.76; N, 6.40. Found: C, 32.73; H, 2.73; N, 6.17.
in dry acetone (10mL) was refluxed for 2h under an argon
2,3-Bis(iodomethyl)-6-methoxyquinoxaline (8d): Pale yel-
1
atmosphere. Then, the solvent was evaporated, and the residue low powder, yield: 94%, mp 161–163°C. H-NMR (400MHz,
was dissolved in CHCl3 (40mL). The CHCl3 layer was washed CDCl3) δ: 3.96 (3H, s), 4.80 and 4.81 (4H, two s), 7.30 (1H, d,
with H2O (40mL×2) and dried over anhydrous Na2SO4. The J=2.7Hz), 7.40 (1H, dd, J=2.7, 9.3Hz), 7.90 (1H, d, J=9.3Hz).
crude product was purified by column chromatography on 13C-NMR (126MHz, CDCl3) δ: 2.7 (CH2), 3.1 (CH2), 56.0
silica gel with CHCl3.
(OCH3), 106.2 (CH), 124.3 (CH), 129.9 (CH), 137.8 (C), 143.3
6-Cyano-2,3-bis(iodomethyl)quinoxaline (2d): Brown pow- (C), 149.1 (C), 152.0 (C), 161.5 (C). IR (KBr) cm−1: 3021, 2959,
1
der, yield: 36%, mp 126–128°C. H-NMR (400MHz, CDCl3) 1617, 1492, 1443, 1354, 1226, 1020, 886, 819. Anal. Calcd for
δ: 4.82 and 4.84 (4H, two s), 7.90 (1H, dd, J=1.7, 8.8Hz), 8.11 C11H10N2OI2: C, 30.03; H, 2.29; N, 6.37. Found: C, 30.25; H,
(1H, d, J=8.8Hz), 8.39 (1H, d, J=1.7Hz). 13C-NMR (126MHz, 2.21; N, 6.18.
CDCl3) δ: 1.5 (CH2), 1.6 (CH2), 114.0 (CN), 117.9 (C), 130.5
(CH), 131.3 (CH), 134.7 (CH), 140.6 (C), 142.9 (C), 154.4 (C),
Acknowledgments This work was supported by a Grant
155.1 (C). IR (KBr) cm−1: 3034, 2957, 2227, 1554, 1489, 1441, from Seikei University.
1356, 916, 803. Anal. Calcd for C11H7N3I2: C, 30.37; H, 1.62;
N, 9.66. Found: C, 30.66; H, 1.57; N, 9.66.
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2,3-Bis(iodomethyl)-6-(trifluoromethyl)quinoxaline
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1
Brown solid, yield: 51%, mp 109–111°C. H-NMR (400MHz,
CDCl3) δ: 4.84 (4H, s), 7.92 (1H, dd, J=1.5, 8.8Hz), 8.12 (1H,

444
Vol. 61, No. 4
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