Synthesis of new benzosubstituted dioxaphosphonines containing quinoxaline subunit

Article abstract of DOI:10.1080/10426500903530891

A simple and efficient synthesis of previously unknown benzosubstituted dioxaphosphonines containing a quinoxaline subunit is described. Reasonably good yields of the products, mild reaction conditions, and convenient work-up are the advantages of this me

Full text of DOI:10.1080/10426500903530891

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Synthesis of New Benzosubstituted
Dioxaphosphonines Containing
Quinoxaline Subunit
Pallavi Singh a , Rakesh Tripathi a , Rajiv K. Verma a , Ganesh C.
Nandi a , Ashutosh Gupta b & Maya S. Singh a
a Department of Chemistry , Faculty of Science, Banaras Hindu
University , Varanasi, India
b Department of Chemistry , Udai Pratap Autonomous College ,
Varanasi, India
Published online: 24 Sep 2010.
To cite this article: Pallavi Singh , Rakesh Tripathi , Rajiv K. Verma , Ganesh C. Nandi , Ashutosh
Gupta & Maya S. Singh (2010) Synthesis of New Benzosubstituted Dioxaphosphonines Containing
Quinoxaline Subunit, Phosphorus, Sulfur, and Silicon and the Related Elements, 185:10, 2142-2151,
DOI: 10.1080/10426500903530891
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Phosphorus, Sulfur, and Silicon, 185:2142–2151, 2010
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500903530891
SYNTHESIS OF NEW BENZOSUBSTITUTED
DIOXAPHOSPHONINES CONTAINING QUINOXALINE
SUBUNIT
Pallavi Singh,1 Rakesh Tripathi,1 Rajiv K. Verma,1
Ganesh C. Nandi,1 Ashutosh Gupta,2 and Maya S. Singh1
1Department of Chemistry, Faculty of Science, Banaras Hindu University,
Varanasi, India
2Department of Chemistry, Udai Pratap Autonomous College, Varanasi, India
A simple and efficient synthesis of previously unknown benzosubstituted dioxaphosphonines
containing a quinoxaline subunit is described. Reasonably good yields of the products,
mild reaction conditions, and convenient work-up are the advantages of this method. The
procedure does not require any catalyst or activator and can be efficiently achieved via
dianion cyclization. All the synthesized compounds have been characterized by satisfactory
elemental analyses and spectral (IR, 1H, 13C, 31P NMR, and mass) studies.
Supplemental materials are available for this article. Go to the publisher’s online edition of
Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental
file.
Keywords Aldimine coupling; dianion cyclization; phosphorus heterocycles; quinoxaline;
Schiff base
INTRODUCTION
Organophosphorus1 compounds continue to be popular targets due to their ubiquity
in biological systems2 and their potential to serve as novel pharmaceutical,3 agricultural,4
and chemical agents.5 The formation of a phosphorus–oxygen bond is one of the most fun-
damental and important processes for producing useful natural and unnatural compounds
in organic synthesis. Quinoxalines have been found to show a wide range of biologi-
cal activities,6 such as antiviral, anti-inflammatory, antiprotozoal, anthelmintic, anticancer,
antimalarial, antidepressant, and anti-HIV activity.7 These benzoheterocycles are useful
intermediates in organic synthesis, and they can be important structural components in
combinatorial drug discovery libraries.8 Among the various methods available for the syn-
thesis of substituted quinoxalines,9 we have used the cyanide mediated aldimine coupling
reaction10 to convert the starting Schiff base to quinoxaline derivatives. To the best of our
Received 30 September 2009; accepted 27 November 2009.
The research grants from Department of Science and Technology (DST) and Council of Scientific and
Industrial Research (CSIR), New Delhi, are gratefully acknowledged.
Address correspondence to Maya S. Singh, Department of Chemistry, Faculty of Science, Banaras Hindu
University, Varanasi, India. E-mail: mssinghbhu@yahoo.co.in
2142

SYNTHESIS OF NEW BENZOSUBSTITUTED DIOXAPHOSPHONINES
2143
knowledge, no example of a quinoxaline-fused, benzosubstituted, nine-membered phospho-
rus heterocycle has been reported. In continuation of our previous reports on the synthesis
of heterocycles via dianion chemistry,11,12 in this article we report some well-defined exam-
ples of dioxaphosphonines containing a quinoxaline subunit via dianion cyclization with
the aim that they may have high biological activities and opto-electronic properties.
RESULTS AND DISCUSSION
The adopted strategy for the synthesis of dioxaphosphonines depends on the conden-
sation between o-phenylenediamine and the appropriate aldehydes, to give the correspond-
ing Schiff base (1) followed by aldimine coupling10 to give a 2,3-disubstituted quinoxaline
(2). Alternatively, quinoxaline 2b has also been synthesized by microwave irradiation using
cyanide as a catalyst in DMF. The reaction was completed in 10 min at 90◦C. The crude
product was recrystallized from dichloromethane to afford 2b in good yield (78%). The
structures of compounds 2a and 2b were established by comparing their spectral data with
the literature values.10 We initially aimed to form a quinoxaline moiety into dibasic Schiff
base ligands fused with two benzene units, which was confirmed by the disappearance of
1
a peak for azomethine protons in their H NMR spectrum that was present in salophen
Schiff base ligands at 8.63 ppm in 1a and at 8.62 ppm in 1b. The reaction of quinoxalines
(2) with sodium in dry isopropanol or with triethyl amine in dry toluene generated the
corresponding dianion A. The reaction of dianion A with the appropriate phosphorus(V)
and phosphorus(III) dielectrophiles afforded the nine-membered phosphorus heterocycles
Figure 1 The ORTEP drawing of 3.

2144
P. SINGH ET AL.
3–12. The reaction proceeds via intermolecular cyclization of the dianion A with the phos-
phorus dielectrophiles. The beauty of the reaction procedure lies in the in situ formation of
a remote dianion followed by cyclization so that the multistep reaction sequence occurs in
one pot. The synthetic route to novel phosphorus heterocycles is outlined in Scheme 1.
CHO H2N
NaCN, DMF
NaCN, DMF, MW
10 min 90°C
MeOH
+
N
N
N
N
N
N
OH H2N
R
R
R
OH
R
OCH3
R
OH
HO
HO
H3CO
OH
HO
1
2
1b
1a, R=H
2a, R=H,
1b, R=OMe
2b, R=OMe,
Na / i-PrOH
N
N
R
ONa
R
NaO
[A]
PSCl3
PCl3
(C6H5O)P(O)Cl2
POCl3
(OCH3)P(O)Cl2
N
N
N
N
N
N
N
N
N
N
O
S
O
O
O
O
O
O
O
O
O
O
O
O
P
P
P
P
P
R
R
R
R
R
R
R
R
R
R
Cl
Cl
OCH3
OPh
Cl
5, 10
3, 8
7, 12
4, 9
6, 11
3, 4, 5, 6, 7; R=H
8, 9, 10, 11, 12; R=OCH3
Scheme 1 Synthesis of ligands and phosphorus heterocycles.
1H NMR spectra of all the compounds (3–12) indicate the absence of phenolic protons,
which was also supported by the absence of characteristic υ (OH) bands in their IR spectra.
The proton signals were unambiguously assigned on the basis of their multiplicity, position,
and intensity in the 1H NMR spectra. 13C NMR exhibits new signals at 50.3 and 50.7 ppm
for methoxy carbons attached to phosphorus in compounds 4 and 9. The formation of P O
bonds was suggested by the appearance of new bands in the region 1195–1289, 1010–1060,
and 950–1000 cm−1, which may be assigned to P O, P O C, and P O Ar stretching
bands, respectively. 31P NMR spectra of 3–12 show phosphorus resonance signals in the
region −10.5 to 32.6 ppm, which supports the insertion of phosphorus in the synthesized
compounds. The P Cl band appears in between 550–500 cm−1, and P S appears in the
region 710–670 cm−1. The mass spectra of these compounds displayed molecular ion peaks
at appropriate m/z values.

SYNTHESIS OF NEW BENZOSUBSTITUTED DIOXAPHOSPHONINES
2145
Table I Crystal structure and data refinement parameters
Compound
3
Empirical formula
Formula weight
C26 H17 N2 O4 P
452.39
Crystal system/space group
a/Å
b/Å
Monoclinic/P21/n
15.3750(7)
9.0273(3)
16.9486(3)
90◦
c/Å
α/◦
β/◦
116.872(3)◦
90◦
γ /◦
V/Å3
2098.36(14)
4
1.432
Z
D calc (g/cm3)
µ (mm−1
)
0.169
Crystal size (mm)
Color/shape
Temp (K)
0.28 × 0.21 × 0.18 mm
Golden yellow, block
150
Theta range for collection
Reflections collected
Goodness of fit on F2
Final R indices [I > 2σ(I)]
R indices (all data)
0.954, 0.970
3672
0.999
0.046(2556)
0.1155(3672)
Dibenzodioxaphosphoninoquinoxaline-6-oxide 3 was purified by crystallization from
isopropanol, and its structure was confirmed by single crystal X-ray diffraction analysis
(Figure 1, Table I).13 The various crystal stabilizing factors, i.e., intermolecular hydrogen
bonding and short contacts, present in the molecule are N(1). . . H(22)C(22) = 2.57Å,
N(2). . . H(10)C(10) = 2.60Å, N(2). . . H(18)C(18) = 2.67Å, O(1). . . H(6)C(6) = 2.63Å,
O(1). . . H(25)C(25) = 2.48Å, O(2). . . H(8)C(8) = 2.59Å, C(4)H(4). . . Cg(C(24)) = 3.88Å,
C(15)H(15). . . Cg(C(11)) = 3.61 Å, Cg(C(14)). . . Cg(C(16)) = 3.62 Å. These contacts and
interactions provide a rigid 3D arrangement to the molecule. Packing diagrams are shown
in Figures S1 and S2 (Supplemental Materials, available online). The structures proposed
for these new compounds are consistent with the data obtained from their IR, 1H, 13C, 31
P
NMR, and mass spectrometry. A supplemental file of bond lengths and angles is included
(Tables S1 and S2, available online).
In order to gain an insight into the possible use of the synthesized compounds as opto-
electronic devices, the first excited state energies (S1) and oscillator strength (f) of some
compounds are reported (Table II). It is observed that compounds have first excited singlet
energy in the visible range exhibiting possibility of fluorescence and phosphorescence,
suggesting that such compounds could be used as opto-electronic devices.
Table II First excited state energies (S1) and oscillator strength (f) of compounds
Compound No.
2a
2b
3
7
8
12
(S1) eV
(f)
410
0.06
445
0.01
367
0.01
444
0.01
371
0.01
369
0.01

2146
P. SINGH ET AL.
CONCLUSIONS
In summary, an efficient and convenient method for the synthesis of nine-membered
benzo-substituted phosphorus heterocycles containing quinoxaline moiety has been estab-
lished. It is noteworthy that the procedure does not require any catalyst and can be efficiently
achieved via dianion cyclization. Also, their first excited state singlet energy values infer
reasonable assumption that such compounds may be used as opto-electronic devices, since
they would fluoresce in the visible region. So, this article makes a useful contribution in
the field of the interesting family of dioxaphosphonine scaffolds.
EXPERIMENTAL
All the chemicals were obtained from Sigma-Aldrich, Merck, Fluka, and Lancaster,
and are used as such without further purification. All solvents (AR or extra pure grade)
used for spectroscopic and other physical studies were further purified by methods in
the literature.14 All operations were performed under a nitrogen atmosphere using standard
glassware. Microwave study was done in a Discover BenchMate System, Make CEM, USA.
IR spectra were recorded as KBr discs on a Jasco FT/IR-5300 spectrophotometer. NMR
(1H, 13C, and 31P) spectra were recorded on a JEOL AL 300 FT NMR spectrometer using
CDCl3 as solvent. All chemical shifts were reported in parts per million (δ) relative to TMS
as an internal standard in CDCl3. Mass spectra were recorded at 70 eV ionizing voltage on a
JEOL-D300 MS instrument. Combustion analyses were performed on a CE-440 elemental
analyzer from Exeter Analytical, Inc. Single crystal X-ray study was performed on an
Oxford Diffraction XCalibur-S from National Single Crystal X-ray Diffraction Laboratory,
IIT Powai, Bombay, India.
Synthesis of 2,3-Di(2-hydroxyphenyl)quinoxaline (2a)
N,Nꢁ-Bis(salicylidene)-o-phenylenediamine10 1a (2.00g, 6.3 mmol), NaCN (0.124 g,
2.5 mmol), and DMF (27.5 mL) were stirred in a 100 mL round bottom flask for 48 h
at room temperature. After completion of the reaction (monitored by TLC), the reaction
mixture was poured onto ice-cold water. The resulting yellow solid was filtered, dissolved
in dichloromethane (DCM), and washed with water. The organic layer was dried over anhy-
drous sodium sulfate and evaporated in vacuo to give 2,3-di(2-hydroxyphenyl)quinoxaline
2a (1.66 g, 83.8%) as yellow powder; mp 184–186◦C; IR (KBr): ν = 3510, 1450 cm−1;1H
NMR (300 MHz, CDCl3): δ = 6.69–6.65 (m, 2H, ArH), 7.15–7.11 (m, 2H, ArH), 7.28–7.25
(m, 4H, ArH), 7.83–7.78 (m, 2H, ArH), 8.08–8.02 (m, 2H, ArH), 9.91 (s, 2H, OH); 13C
NMR (75 MHz, CDCl3): δ = 157.1, 151.7, 137.9, 132.2, 131.8, 131.0, 127.9, 120.7, 119.3,
118.6; MS (ESI) m/z: 315 [M+H]+; Anal. Calcd for C20H14N2O2 (314.34): C, 76.42; H,
4.49; N, 8.91%, Found: C, 76.51; H, 4.39; N, 8.79%.
Synthesis of 2,3-Di(2-hydroxy-3-methoxyphenyl)quinoxaline (2b)
Method A. N,Nꢁ-Bis(o-vanillidene)-o-phenylenediamine10 1b (2.00g, 5.3 mmol),
NaCN (0.145 g, 2.9 mmol), and DMF (27.5 mL) were stirred in a 100 mL round bottom flask
for 98 h at 60◦C. After completion of the reaction (monitored by TLC), the reaction mixture
was poured onto ice-cold water. The resulting yellow solid was filtered, dissolved in DCM,

SYNTHESIS OF NEW BENZOSUBSTITUTED DIOXAPHOSPHONINES
2147
and washed with water. The organic layer was dried over anhydrous sodium sulfate and
evaporated in vacuo to give crude product, which was further purified by recrystallization
in methanol to obtain 2b (1.22 g, 61%), mp 213–215◦C.
Method B. Compound 2,3-di(2-hydroxy-3-methoxyphenyl)quinoxaline 2b has
also been synthesized under microwave irradiation. A mixture of N,Nꢁ-bis(o-vanillidene)-
o-phenylenediamine 1b (1.00 g, 2.6 mmol) and NaCN (0.068 g, 1.4 mmol) in DMF (10
mL) was irradiated in a microwave oven for 10 min. After completion of the reaction
(monitored by TLC), reaction mixture was poured onto ice-cold water and extracted
using DCM. The organic layer was washed with water, dried over anhydrous sodium
sulfate, and evaporated in vacuo to obtain 2b (0.408 g, 78%); mp 214–216◦C; IR (KBr)
1
ν 3519, 1464 cm−1; H NMR (300 MHz, CDCl3): δ = 3.86 (s, 6H, OCH3), 6.66–6.61
(t, 2H, J = 8.0 Hz, ArH), 6.88–6.82 (m, 4H, ArH), 7.73–7.70 (m, 2H, ArH), 8.02–7.99
(m, 2H, ArH), 9.99 (s, 2H, OH); 13C NMR (75 MHz, CDCl3): δ = 152.1, 148.3, 146.5,
138.9, 130.6, 128.3, 122.9, 122.5, 119.0, 112.8, 56.3; MS (ESI) m/z: 375 [M+H]+; Anal.
Calcd for C22H18N2O4 (374.39): C, 70.58; H, 4.85; N, 7.48%, Found: C, 70.35; H, 4.81;
N, 7.62%.
6-Phenoxydibenzo[3,4:8,9][1,3,2]dioxaphosphonino-
[6,7-b]quinoxaline-6-oxide (3)
2,3-Di(2-hydroxyphenyl)quinoxaline 2a (0.314 g, 1 mmol) dissolved in dry iso-
propanol (50 mL) was added to a solution of sodium isopropoxide (generated from 0.046g
Na and 2 mL dry isopropanol) in dry isopropanol (10 mL) at −4◦C. The reaction mixture
was stirred for 4 h at the same temperature. After complete consumption of 2a, phenyl
dichlorophosphate (0.15 mL, 1 mmol) dissolved in dry isopropanol (2 mL) was added
slowly at −20◦C, and the reaction mixture was stirred for 30 min. The reaction mixture
was further stirred at room temperature for 4 h. The precipitate that formed was filtered on
a sintered glass crucible (G4), and the solvent was evaporated under reduced pressure. The
resulting solid was washed with diethyl ether and recrystallized from isopropanol to give
the yellow colored compound, 3 (0.29 g, 64%); IR (KBr): ν = 1642, 1612, 1252, 1181,
1
978 cm−1; H NMR (300 MHz, CDCl3): δ = 8.18–6.74 (m, 17H, ArH); 13C NMR (75
MHz, CDCl3): δ = 151.8, 147.6, 147.5, 141.2, 130.7, 129.6, 129.4, 129.0, 126.1, 125.3,
122.2, 121.9, 119.8, 119.7; 31P NMR (121.5 MHz, CDCl3): δ = −18.5; MS (ESI) m/z: 453
[M+H]+; Anal. Calcd for C26H17N2O4P (452.40): C, 69.03; H, 3.79; N, 6.19%, Found: C,
69.23; H, 3.91; N, 6.05%.
6-Methoxydibenzo[3,4:8,9][1,3,2]dioxaphosphonino-
[6,7-b]quinoxaline-6-oxide (4)
Following the procedure described above, 2,3-di(2-hydroxyphenyl)quinoxaline (2a)
(0.314 g, 1 mmol) and methyl dichlorophosphate (0.1 mL, 1 mmol) afforded 4 (0.265 g,
68%); IR (KBr): ν = 1638, 1602, 1259, 1175, 988 cm−1; 1H NMR (300 MHz, CDCl3): δ =
3.82 (s, 3H, POCH3), 8.25–7.17 (m, 12H, ArH); 13C NMR (75 MHz, CDCl3): δ = 152.6,
147.1, 146.5, 141.2, 131.6, 129.1, 129.0, 126.1, 122.2, 119.7, 50.3; 31P NMR (121.5 MHz,
CDCl3): δ = −21.7; MS (ESI) m/z: 391 [M+H]+; Anal. Calcd for C21H15N2O4P (390.33):
C, 64.62; H, 3.87; N, 7.18%, Found: C, 64.42; H, 3.49; N, 6.91%.

2148
P. SINGH ET AL.
6-Chlorodibenzo[3,4:8,9][1,3,2]dioxaphosphonino[6,7-b]-
quinoxaline-6-oxide (5)
Following the procedure described above, 2,3-di(2-hydroxyphenyl)quinoxaline (2a)
(0.314 g, 1 mmol) and POCl3 (0.1 mL, 1 mmol) gave 5 (0.24 g, 61%); IR (KBr): ν = 1634,
1598, 1273, 1190, 966 cm−1; 1H NMR (300 MHz, CDCl3): δ = 8.32–6.77 (m, 12H, ArH);
13C NMR (75 MHz, CDCl3): δ = 153.6, 146.1, 145.5, 143.2, 130.6, 129.9, 129.0, 126.1,
121.2, 117.7; 31P NMR (121.5 MHz, CDCl3): δ = −17.8; MS (ESI) m/z: 395 [M+H]+;
Anal. Calcd for C20H12ClN2O3P (394.75): C, 60.85; H, 3.06; N, 7.10%, Found: C, 61.08;
H, 3.31; N, 6.92%.
6-Chlorodibenzo[3,4:8,9][1,3,2]dioxaphosphonino[6,7-b]-
quinoxaline-6-sulfide (6)
Following the procedure described above for the preparation of 5, 2,3-di(2-
hydroxyphenyl) quinoxaline (2a) (0.314 g, 1 mmol) and PSCl3 (0.1 mL, 1 mmol) afforded
6 (0.258 g, 63%); IR (KBr): ν = 1642, 1612, 1188, 978, 692 cm−1; 1H NMR (300 MHz,
CDCl3): δ = 8.05–6.69 (m, 12H, ArH); 13C NMR (75 MHz, CDCl3): δ = 152.4, 146.3,
144.9, 142.8, 130.2, 129.4, 128.8, 126.3, 121.7, 117.1; 31P NMR (121.5 MHz, CDCl3):
δ = −14.6; MS (ESI) m/z: 411 [M]+; Anal. Calcd for C20H12ClN2O2PS (410.81): C,
58.47; H, 2.94; N, 6.82%, Found: C, 58.65; H, 3.15; N, 6.61%.
6-Chlorodibenzo[3,4:8,9]dioxaphosphonino[6,7-b]quinoxaline (7)
Following the procedure described above for the preparation of 5, 2,3-di(2-
hydroxyphenyl) quinoxaline (2a) (0.314 g, 1 mmol) and PCl3 (0.09 mL, 1 mmol) yielded
1
7 (0.245 g, 65%); IR (KBr): ν = 1637, 1596, 1177, 992 cm−1; H NMR (300 MHz,
CDCl3): δ = 8.22–6.67 (m, 12H, ArH); 13C NMR (75 MHz, CDCl3): δ = 152.9, 145.8,
145.3, 144.0, 131.3, 129.1, 128.4, 125.1, 121.5, 117.9; 31P NMR (121.5 MHz, CDCl3):
δ = 29.8; MS (ESI) m/z: 380 [M+H]+; Anal. Calcd for C20H12ClN2O2P (378.75): C,
63.42; H, 3.19; N, 7.40%, Found: C, 63.61; H, 3.43; N, 7.21%.
6-Phenoxydiaryl[3,4:8,9][1,3,2]dioxaphosphonino[6,7-b]-
quinoxaline-6-oxide (8)
To a stirred solution of 2,3-di(2-hydroxy-3-methoxyphenyl) quinoxaline 2b (0.374 g,
1 mmol) in dry toluene (10 mL), triethyl amine (0.3 mL) was added slowly, and stirring was
continued for 1 h. A solution of phenyl dichlorophosphate (0.15 mL, 1 mmol) in toluene (1
mL) was added to reaction mixture and was refluxed for 4 h. The solvent was evaporated
in vacuo, and the residue was dissolved in DCM. The organic layer was washed with water
followed by brine and dried over anhydrous MgSO4. The solvent was evaporated to give
crude product, which was crystallized from ethanol to afford 8 (0.348 g, 68%); IR (KBr):
ν = 1638, 1604, 1260, 1176, 965 cm−1;1H NMR (300 MHz, CDCl3): δ = 3.88 (s, 6H,
OCH3), 8.18–6.81 (m, 15H, ArH); 13C NMR (75 MHz, CDCl3): δ = 152.2, 147.2, 147.1,
140.6, 131.1, 129.8, 122.7, 122.3, 121.9, 120.3, 119.7, 118.2, 117.5, 57.1; 31P NMR (121.5
MHz, CDCl3): δ = −17.6; MS (ESI) m/z: 513 [M+H]+; Anal. Calcd for C28H21N2O6P
(512.45): C, 65.63; H, 4.13; N, 5.47%, Found: C, 65.91; H, 4.33; N, 5.61%.

SYNTHESIS OF NEW BENZOSUBSTITUTED DIOXAPHOSPHONINES
2149
6-Methoxydiaryl[3,4:8,9][1,3,2]dioxaphosphonino[6,7-b]-
quinoxaline-6-oxide (9)
Following the procedure described above for the preparation of 8, 2,3-di(2-hydroxy-
3-methoxyphenyl)quinoxaline (2b) (0.374 g, 1 mmol) and methyl dichlorophosphate
(0.1 mL, 1 mmol) gave 9 (0.306 g, 68%); IR (KBr): ν = 1647, 1603, 1264, 1182, 948
cm−1;1H NMR (300 MHz, CDCl3): δ = 3.81 (s, 6H, OCH3), 3.93 (s, 3H, POCH3), 8.19–6.77
(m, 10H, ArH); 13C NMR (75 MHz, CDCl3): δ = 153.2, 147.8, 147.1, 142.2, 131.1, 129.8,
121.9, 121.7, 120.1, 119.3, 57.5, 50.7; 31P NMR (121.5 MHz, CDCl3): δ = −9.8; MS (ESI)
m/z: 451 [M+H]+; Anal. Calcd for C23H19N2O6P (450.38): C, 61.34; H, 4.25; N, 6.22%,
Found: C, 61.52; H, 4.33; N, 6.12%.
6-Chlorodiaryl[3,4:8,9][1,3,2]dioxaphosphonino[6,7-b]-
quinoxaline-6-oxide (10)
Following the procedure described above for the preparation of 8, 2,3-di(2-hydroxy-
3-methoxyphenyl)quinoxaline (2b) (0.374 g, 1 mmol) and POCl3 (0.1 mL, 1 mmol) af-
forded 10 (0.299 g, 65.9%); IR (KBr): ν = 1637, 1592, 1276, 1194, 973 cm−1; 1H NMR
(300 MHz, CDCl3): δ = 3.85 (s, 6H, OCH3), 8.23–6.85 (m, 10H, ArH); 13C NMR (75
MHz, CDCl3): δ = 151.8, 147.6, 147.5, 141.2, 130.7, 129.6, 122.2, 121.9, 119.8, 119.7,
57.3; 31P NMR (121.5 MHz, CDCl3): δ = -10.4; MS (ESI) m/z: 456 [M+H]+; Anal. Calcd
for C22H16ClN2O5P (454.80): C, 58.10; H, 3.55; N, 6.16%, Found: C, 58.45; H, 3.69; N,
5.98%.
6-Chlorodiaryl[3,4:8,9][1,3,2]dioxaphosphonino[6,7-b]-
quinoxaline-6-sulfide (11)
Following the procedure described above for the preparation of 8, 2,3-di(2-hydroxy-
3-methoxyphenyl)quinoxaline (2b) (0.374 g, 1 mmol) and PSCl3 (0.1 mL, 1 mmol) gave
11 (0.296 g, 63%); IR (KBr): ν = 1632, 1602, 1178, 988, 678 cm−1;1H NMR (300 MHz,
CDCl3): δ = 3.84 (s, 6H, OCH3), 8.26–6.76 (m, 10H, ArH); 13C NMR (75 MHz, CDCl3):
δ = 153.1, 147.2, 146.9, 141.2, 131.3, 128.8, 122.9, 121.3, 120.1, 119.5, 57.5; 31P
NMR (121.5 MHz, CDCl3): δ = −16.6; MS (ESI) m/z: 472 [M+H]+; Anal. Calcd for
C22H16ClN2O4PS (470.87): C, 56.12; H, 3.42; N, 5.95%, Found: C, 56.40; H, 3.61; N,
5.72%.
6-Chlorodiaryl[3,4:8,9]dioxaphosphonino[6,7-b]quinoxaline (12)
Following the procedure described above for the preparation of 8, 2,3-di(2-hydroxy-
3-methoxyphenyl)quinoxaline (2b) (0.374 g, 1 mmol) and PCl3 (0.09 mL, 1 mmol) yielded
12 (0.262 g, 60%); IR (KBr): ν = 1633, 1593, 1179, 964 cm−1;1H NMR (300 MHz, CDCl3):
δ = 3.86 (s, 6H, OCH3), 8.29–6.62 (m, 10H, ArH); 13C NMR (75 MHz, CDCl3): δ = 152.6,
147.5, 146.2, 140.2, 132.3, 127.8, 122.6, 121.3, 120.6, 119.1, 58.1; 31P NMR (121.5 MHz,
CDCl3): δ = 32.6; MS (ESI) m/z: 440 [M+H]+; Anal. Calcd for C22H16ClN2O4P (438.80):
C, 60.22; H, 3.68; N, 6.38%, Found: C, 60.41; H, 3.79; N, 6.52%.
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deposited with the Cambridge Crystallographic Data Centre as supplementary publication

SYNTHESIS OF NEW BENZOSUBSTITUTED DIOXAPHOSPHONINES
2151
number CCDC 703302. Copies of the data can be obtained free of charge upon an applica-
tion to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [fax: +44 (0) 1223 336033 or e-mail:
deposit@ccdc.cam.ac.uk or at www.ccdc.cam.ac.uk/conts/retrieving.html].
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