Synthesis of cyclic nitrone and 1,2-oxazine from 1,2,4-triaryl-but-2-ene-1, 4-dione and hydroxylamine

Article abstract of DOI:10.1007/s12039-012-0276-7

The reaction of hydroxylamine hydrochloride with differently substituted phenyldibenzoylethylene has been investigated. Both cyclic nitrone and 1,2-oxazine have been isolated and characterized by one- and two-dimensional NMR data and also by single crysta

Full text of DOI:10.1007/s12039-012-0276-7

c
J. Chem. Sci. Vol. 124, No. 4, July 2012, pp. 913–919. ꢀ Indian Academy of Sciences.
Synthesis of cyclic nitrone and 1,2-oxazine from
1,2,4-triaryl-but-2-ene-1,4-dione and hydroxylamine
MUTHUPANDI NAGARAJa, MURUGAN INIYAa, MUTHUSAMY BOOMINATHANa,
SHANMUGAM MUTHUSUBRAMANIANa,∗ and NATTAMAI BHUVANESHb
aDepartment of Organic Chemistry, School of Chemistry, Madurai Kamaraj University,
Madurai 625 021, India
bX-ray Diffraction Laboratory, Department of Chemistry, Texas A & M University,
College Station, TX 77842, USA
e-mail: muthumanian2001@yahoo.com
MS received 1 November 2011; revised 20 January 2012; accepted 29 February 2012
Abstract. The reaction of hydroxylamine hydrochloride with differently substituted phenyldibenzoylethylene
has been investigated. Both cyclic nitrone and 1,2-oxazine have been isolated and characterized by one- and
two-dimensional NMR data and also by single crystal X-ray analysis.
Keywords. 1,2,-Oxazines; cyclic nitrones; 1,4-diketones; regioselectivity; two-dimensional NMR.
1. Introduction
with hydroxylamine hydrochloride. A few references12
are available in which the reaction of unsubstituted
phenyldibenzoylethylene with hydroxylamine hydro-
chloride has been mentioned, but a systematic study
has now been carried out in order to (i) analyse the
structure of the products unambiguously, (ii) look upon
the regioselectivity, if any, in the case of substituted
phenyldibenzoylethylene and (iii) ascertain the mecha-
nism of the reaction.
Cyclic nitrones have drawn special attention due to their
successful application as building blocks in the syn-
thesis of various natural and biologically active com-
pounds.1 They are commonly used as precursors2 in
the synthesis of a variety of heterocycles, as spin-
trapping reagents in the identification of transient radi-
cals3 and as therapeutic agents.4 Nitrones possess one
of the largest dipole moments known for any functional
group type (3.37-3.47 D) making them potentially use-
ful for NLO applications and control of molecular
orientation. They offer a simple route to stable radicals
via one-electron electrochemical reduction.5 Anneala-
tion of imidazolidinyl-based nitronyl nitroxides leads
to stable planar spin delocalized radicals, the ben-
zonitronyl nitroxides, which exhibit strong magnetic
exchange through efficient π-π stacking interactions in
the solid state.6
1,2-Oxazines have gained interest in organic syn-
thesis as useful intermediates7 in the synthesis of
natural products8 and unnatural cyclic amino acids.9
1,2-Oxazines exhibit a broad spectrum of biological
activities.10
We are interested in the reactions of different nucleo-
philes with diketones in the process of generating new
heterocycles.11 In this connection, it has been planned
to investigate the reaction of phenyldibenzoylethylene
2. Experimental
2.1 General
Nuclear Magnetic Resonance (1H and 13C NMR) spec-
tra were recorded on a Bruker 300 MHz spectro-
meter in CDCl3 using TMS as an internal standard.
Chemical shifts are reported in parts per million (δ),
coupling constants (J values) are reported in Hertz
(Hz). 13C NMR spectra were routinely run with broad-
band decoupling. Infrared spectra were recorded on
a Shimatzu FT-IR instrument (in KBr pellet). Band
positions are reported in reciprocal centimeters (cm−1).
Melting points were determined on a melting point
apparatus (Inlab Pvt Ltd, India) equipped with a ther-
mometer and were uncorrected. Column chromatogra-
phy was carried out in silica gel (60-120 mesh) using
petroleum ether-ethyl acetate as eluent. Elemental ana-
lyses were performed on a Perkin Elmer 2400 series II
Elemental CHNS analyzer.
∗For correspondence
913

914
Muthupandi Nagaraj et al.
8.1, s
H
8.61, d, J =7.8Hz
8.30, s
HO
H
7.7, d, J =7.8Hz
H
137.7
H
103.9
N
O
161.7
CH3
O
H
7.52, dd
H
Figure 1. HMBC-NMR spectra of 7e and some selected correlation diagram.
2.2 General procedure
154◦C; IR (KBr): 3095, 2939, 2840, 1665, 1598, 1531,
1
1438, 1213, 780 cm−1; H NMR (300 MHz, CDCl3):
A mixture of 1,2-diphenyl-4-arylbut-2-ene-1,4-dione (2)
(3.61 mmol), hydroxylamine hydrochloride (7.22 mmol)
and sodium acetate (7.22 mmol) in ethanol was heated
under reflux for 2 h. After completion of the reaction,
the reaction mixture was poured into crushed ice and fil-
tered. The crude product was purified by column chro-
matography using petroleum ether-ethyl acetate mix-
ture as eluent to yield 7 and 4/8.
δ = 6.81 (s, 1H), 7.25–7.55 (m, 13H) 8.12 (d, J =
7.2 Hz, 2H); 13C NMR (75 MHz, CDCl3): δ = 103.1,
117.2, 126.0, 126.5, 127.2, 127.9 128.0, 128.3, 128.7,
128.9, 129.0, 129.6, 131.2, 136.9, 140.4, 144.5; Anal.
Calcd. for C22H16ClNO2 (%): C, 73.03; H, 4.46; N,
3.87. Found (%): C, 72.92; H, 4.35; N, 3.76.
2.2d 5-(4-Bromophenyl)-2-hydroxy-2,3-diphenyl-2H-
pyrrole-1-oxide (7c): Yellow colour solid; m.p. 171–
173◦C; IR (KBr) 3075, 3028, 2846, 1671, 1591, 1524,
2.2a 4-(5-Bromothiophen-2-yl)-4-(hydroxyimino)-1,2-
diphenylbut-2-en-1-one (4f): Yellow colour solid; m.p.
156–158◦C; IR (KBr) 3625, 1654, 1632, 1210 cm−1;
1H NMR (300 MHz, CDCl3): δ = 7.10 (d, J = 4.2 Hz,
1H), 7.25–7.29 (m, 3H), 7.39–7.43 (m, 3H), 7.46
(s, 1H), 7.57 (d, J = 4.2 Hz, 1H), 7.58–7.66 (m, 4H),
8.44 (s, 1H); 13C NMR (75 MHz, CDCl3): δ = 120.5,
123.0, 126.4, 127.2, 128.5, 129.2, 129.6, 130.6, 131.3,
131.9, 133.7, 135.2, 147.2, 149.0, 156.9, 179.3; Anal.
Calcd. for C20H14BrNO2S (%): C, 58.26; H, 3.42; N,
3.40; S, 7.78. Found (%): C, 58.02; H, 3.26; N, 3.24;
S, 7.62.
1
1438, 1213, 688 cm−1; H NMR (300 MHz, DMSO-
d6): δ = 7.11–7.24 (m, 6H), 7.38–7.41 (m, 2H),
7.54 (d, J = 7.5 Hz, 2H), 7.64 (d, J = 8.7 Hz, 2H),
8.02 (s, 1H), 8.32 (s, 1H), 8.42 (d, J = 8.7 Hz, 2H);
13C NMR (75 MHz, DMSO-d6): δ = 104.7, 121.0,
124.3, 126.8, 127.2, 128.4, 129.4, 129.6, 129.7, 129.8,
130.0, 132.6, 132.9, 137.4, 138.5, 143.8; Anal. Calcd.
for C22H16BrNO2 (%): C, 65.04; H, 3.97; N, 3.45.
Found (%): C, 64.92; H, 3.84; N, 3.29.
2.2e 2-Hydroxy-2,3-diphenyl-5-p-tolyl-2H-pyrrole-1-
oxide (7d): Yellow colour solid; m.p. 151–153◦C;
IR (KBr) 3067, 2938, 2825, 1662, 1596, 1529,
2.2b 2-Hydroxy-2,4,5-triphenyl-2H-pyrrole-1-oxide (7a):
Yellow colour solid; m.p. 179–181◦C (lit. m.p.
179◦C);12a IR (KBr) 3088, 3061, 2850, 1674, 1593,
1
1438 cm−1; H NMR (300 MHz, DMSO-d6): δ = 2.39
1
1523, 1485, 1371, 1205 cm−1; H NMR (300 MHz,
(s, 3H), 7.24–7.53 (m, 10H), 7.66 (d, J = 7.2 Hz,
2H), 7.90 (s, 1H), 8.30 (s, 1H), 8.44 (d, J = 7.2 Hz,
2H); 13C NMR (75 MHz, DMSO-d6): δ = 19.5, 101.4,
118.0, 123.6, 123.8, 124.3, 125.1, 126.3, 126.4, 126.6,
126.8, 127.4, 129.7, 135.4, 135.7, 138.3, 141.3; Anal.
Calcd. for C23H19NO2 (%): C, 80.92; H, 5.61; N, 4.10.
Found (%): C, 80.79; H, 5.54; N, 3.96.
CDCl3): δ = 6.75 (s, 1H), 7.24–7.63 (m, 13H), 8.09 (dd,
J = 7.8 Hz, 1.2 Hz, 2H); 13C NMR (75 MHz, CDCl3):
δ = 103.9, 117.6, 125.7, 126.5, 127.2,* 127.9, 128.3,
128.5, 128.6, 128.9, 129.2, 130.9, 136.7, 140.5, 146.9;
Anal. Calcd. for C22H17NO2 (%): C, 80.71; H, 5.23;
N, 4.28. Found (%): C, 80.59; H, 5.12; N, 4.09. * two
carbons are merged together.
2.2f 2-Hydroxy-5-(4-methoxyphenyl)-2,3-diphenyl-
2H-pyrrole-1-oxide (7e): Yellow colour solid; m.p.
163–165◦C; IR (KBr): 3088, 3022, 2927, 2816, 1657,
2.2c 5-(4-Chlorophenyl)-2-hydroxy-2,4-diphenyl-2H-
pyrrole-1-oxide (7b): Yellow colour solid; m.p. 152–

Reaction of hydroxylamine with 1,4-diketones
915
1
1589, 1531, 1438 cm−1; H NMR (300 MHz, DMSO- NMR (300 MHz, DMSO-d6): δ = 4.01 (bs, 1H), 6.75
d6): δ = 3.48 (s, 3H), 7.13 (d, J = 8.7 Hz, 2H), (s, 1H), 7.15–7.55 (m, 12H), 7.80 (d, J = 7.2 Hz,
7.23–7.37 (m, 6H), 7.51–7.53 (m, 2H), 7.70 (d, J = 2H); 13C NMR (75 MHz, DMSO-d6): δ = 97.6, 112.9,
7.5 Hz, 2H), 8.11 (s, 1H), 8.30 (s, 1H), 8.61 (d, J = 126.4, 127.5, 127.8, 127.9, 128.2, 128.5, 128.7, 128.9,
8.7 Hz, 2H); 13C NMR (75 MHz, DMSO-d6): δ = 56.6, 130.0, 133.2, 135.4, 139.5, 143.5, 152.1; Anal. Calcd.
103.9, 115.3, 121.5, 122.1, 126.9, 127.1, 129.2, 129.5, for C22H16ClNO2 (%): C, 73.03; H, 4.46; N, 3.87.
129.7, 129.8, 130.9, 132.7, 137.7, 138.9, 143.9, 161.7; Found (%): C, 72.92; H, 4.35; N, 3.75.
Anal. Calcd. for C23H19NO3 (%): C, 77.29; H, 5.36; N,
3.92. Found (%): C, 77.18; H, 5.28; N, 3.80.
2.2j 3-(4-Bromophenyl)-5,6-diphenyl-6H-1,2-oxazin-
6-ol (8c): Yellow colour solid; m.p. 172–174◦C;
IR (KBr): 3201, 1629, 1496, 1205, 1002, 682 cm−1;
1H NMR (300 MHz, DMSO-d6): δ = 6.95 (s, 1H),
7.11–7.16 (m, 6H), 7.34–7.41 (m, 4H), 7.61 (d, J =
8.1 Hz, 2H), 7.79 (d, J = 8.1 Hz, 2H), 8.06 (s, 1H); 13C
NMR (75 MHz, DMSO-d6): δ = 96.2, 111.6, 122.7,
126.8, 127.0, 127.4, 127.8, 127.9, 128.4, 131.2, 131.7,
132.6, 135.1, 140.5, 141.2, 151.1; Anal. Calcd. for
C22H16BrNO2 (%): C, 65.04; H, 3.97; N, 3.45. Found
(%): C, 64.91; H, 4.02; N, 3.34.
2.2g 5-(5-Bromothiophen-2-yl)-2-hydroxy-2,3-diphenyl-
2H-pyrrole 1-oxide (7f): Yellow colour solid; m.p.
144–146◦C; IR (KBr): 3068, 2929, 2847, 1669,
1
1592 cm−1; H NMR (300 MHz, CDCl3): δ = 6.77
(s, 1H), 7.05 (d, J = 4.2 Hz, 1H), 7.10 (d, J = 4.2 Hz,
1H). 7.25–7.35 (m, 6H), 7.59–7.62 (m, 5H); 13C NMR
(75 MHz, CDCl3): δ = 102.7, 114.8, 119.2, 125.8,
126.9, 128.6, 128.7, 129.4,* 129.5,* 130.2, 130.6,
136.2, 137.9, 148.6; Anal. Calcd. for C20H14BrNO2S
(%): C, 58.26; H, 3.42; N, 3.40; S, 7.78. Found (%):
C, 58.08; H, 3.34; N, 3.31; S, 7.65. * two carbons are
merged together.
2.2k 5,6-Diphenyl-3-p-tolyl-6H-1,2-oxazin-6-ol (8d):
Yellow colour solid; m.p. 146–148◦C; IR (KBr): 3192,
1641, 1497, 1222, 1011, 656 cm−1; 1H NMR (300 MHz,
CDCl3): δ = 2.39 (s, 3H), 4.10 (s, 1H), 6.71 (s, 1H),
7.19–7.51 (m, 12H), 7.68 (d, J = 7.5 Hz, 2H); 13C
NMR (75 MHz, CDCl3): δ = 21.3, 97.2, 113.0, 126.0,
127.3, 127.7, 128.0, 128.1, 128.5, 128.7, 129.4, 130.9,
135.6, 139.7, 140.1, 143.2, 153.2; Anal. Calcd. for
C23H19NO2 (%): C, 80.92; H, 5.61; N, 4.10. Found (%):
C, 80.85; H, 5.57; N, 4.04.
2.2h 3,5,6-Triphenyl-6H-1,2-oxazin-6-ol (8a): Yel-
low colour solid; m.p. 159–160◦C; IR (KBr): 3198,
1624, 1491, 1209, 1008, 692 cm−1; 1H NMR (300 MHz,
CDCl3): δ = 3.99 (bs, 1H), 6.75 (s, 1H), 7.15–7.55
(m, 13H), 7.80 (dd, J = 7.8 Hz, 1.2 Hz, 2H); 13C
NMR (75 MHz, CDCl3): δ = 97.4, 113.0, 126.2, 127.3,
127.8,* 128.1, 128.2, 128.6, 128.8, 129.9, 133.8, 135.6,
139.7, 143.2, 153.3; Anal. Calcd. for C22H17NO2 (%):
C, 80.71; H, 5.23; N, 4.28. Found (%): C, 80.58; H,
5.17; N, 4.23. * two carbons are merged together.
2.2l 3-(4-Methoxyphenyl)-5,6-diphenyl-6H-1,2-oxazin-
6-ol (8e): Yellow colour solid; m.p.179–181◦C; IR
1
(KBr): 3209, 1632, 1498, 1213, 1012, 662 cm−1; H
NMR (300 MHz, DMSO-d6): δ = 3.42 (s, 3H), 7.13
2.2i 3-(4-Chlorophenyl)-5,6-diphenyl-6H-1,2-oxazin- (d, J = 7.5 Hz, 2H), 7.23–7.37 (m, 4H), 7.52 (m, 2H),
6-ol (8b): Yellow colour solid; m.p. 163–165◦C; IR 7.68 (d, J = 7.5 Hz, 2H), 7.70 (d, J = 7.2 Hz, 2H),
1
(KBr): 3192, 1632, 1497, 1212, 1012, 725 cm−1; H 8.02 (s, 1H), 8.30 (s, 1H), 8.61 (d, J = 8.1 Hz, 2H);
H
Ar
O
O
KOH / ethanol
O
Ar C CH3
O
O
1
2
a) Ar = Phenyl; b) Ar = 4-Chlorophenyl;
c) Ar = 4-Bromophenyl; d) Ar = 4-Methylphenyl;
e) Ar = 4-Methoxyphenyl; f) Ar = 5-Bromo-2-thienyl
Scheme 1. Preparation of differently substituted phenyldibenzoylethylene.

916
Muthupandi Nagaraj et al.
Ph
H
Ph
H
H
Ph
NH2OH.HCl
NaOAc
Ph
Ar
Ph
Ph
Ar
N
OH
O
O
N
O
OH
Ph
O
Ar
2
6
4
Ar = Ph, 4-Cl-Ph, 4-Br-Ph
4-Me-Ph, 4-OMe-Ph
5-Br-thienyl
H
H
Ar
Ph
HO
Ph
HO
Ar
N
O
N
O
8
Ph
7
Scheme 2. The reactions of hydroxylamine hydrochloride with differently substituted phenyldibenzoylethylene.
13C NMR could not be recorded due to poor solubility;
Anal. Calcd. for C23H19NO3 (%): C, 77.29; H, 5.36; N, (scheme 2). While 2a to 2e have yielded 7 and 8, 2f
The reaction has led to two products in all the case
3.92. Found (%): C, 77.08; H, 5.28; N, 3.88.
has led to 4f and 7f (table 1).
3. Results and discussion
The 1,2,4-Triaryl-but-2-ene-1,4-diones (2) can be pre-
pared by the condensation of benzil and the derivatives
of acetophenone/heteroaryl ketone13 (scheme 1). To the
best of our knowledge, the ketone 2f is not reported in
the literature.
1,2,4-Triaryl-but-2-ene-1,4-diones 2 were allowed to
react with hydroxylamine hydrochloride and sodium
acetate taken in 1:3:3 ratio. Excess hydroxylamine was
used to ascertain complete hydroxylation in order to
establish whether both the carbonyl groups are reactive
towards the nucleophile or not. The course of the reac-
tion was monitored by TLC. After 2 h, the diketone
vanished (TLC) and the products obtained were sep-
arated and analysed for their structures. The reaction
has been conducted in different protic solvents and it
was found that ethanol produced the best results.
Table 1. Isolated yields of the products 4, 7 and 8.
Entry
Aryl
Yield of 4 Yield of 7 Yield of 8
a
b
c
d
e
f
Phenyl
–
–
–
–
–
55
58
48
49
61
68
26
21
23
22
20
–
4-Chlorophenyl
4-Bromophenyl
4-Methylphenyl
4-Methoxyphenyl
5-Bromo-2-thienyl
11
Figure 2. ORTEP diagram of 7b.

Reaction of hydroxylamine with 1,4-diketones
917
Br
H
H
7.61, d, J = 8.1Hz
7.79, d, J = 8.1Hz
H
H
151.1
6.95, s
H
N
O
96.2
OH
8.06, s
Figure 3. HMBC-NMR spectra of 8C and some selected correlation diagram.
1
The structure of nitrone 7 was established by H,
13C and 2D NMR spectral data, ruling out the pos-
sibility of the regioisomer 6, as illustrated for a rep-
resentative example 7e (figure 1). HMBC spectrum
of 7e has contours connecting deshielded doublet at
8.61 ppm with the carbons at 129.8 ppm, 137.7 ppm
and 161.7 ppm. Thus, it is clear that these hydrogens
are meta to methoxy group and this doublet is not
giving any contour with the saturated quaternary carbon
at 103.9 ppm.
But the doublet of doublet at 7.52 ppm due to two
hydrogen has HMBC connection with the carbon at
103.9 ppm. These informations helped to unambigu-
ously assign the regiochemistry of the product 7. Thus
the p-anisyl group is attached to azomethine carbon,
while the aryl is attached to the saturated quaternary
carbon. The structure of the cyclic nitrone 7b was con-
firmed by single crystal X-ray analysis also (figure 2).14
Similarly the structure of 1,2-oxazine 8 has been
1
established by H, 13C and 2D NMR spectral data as
illustrated for a representative example 8c (figure 3).
Here, it is noticed that the downfield two hydrogen
signal at 7.79 ppm is not a doublet of doublet, but a
perfect doublet, which gives HMBC contour with the
carbon at 151.1 ppm. Hence, the p-bromophenyl group
is attached to the azomethine carbon. The olefinic sin-
glet hydrogen at 6.95 ppm has HMBC contour with the
carbons at 96.2, 135.1, 140.5 and 151.1 ppm. The alco-
holic proton appears at 8.06 singlet giving an HMBC
contour with the carbon 96.2 ppm revealing two bond
connectivity, clearly establishing the structure of the
molecule. The structure of 8c has been confirmed by
single crystal X-ray analysis (figure 4).15
It can be noticed that in all the cases, the regioiso-
mer 7, is formed exclusively and not 6. As hydroxy-
lamine prefers to attack the less hindered carbonyl
group, the intermediate 3 would have been formed from
Figure 4. ORTEP diagram of 8c.

918
Muthupandi Nagaraj et al.
H
H
Ph
Ph
H
Ph
Ph
HO
NH2OH
OH
Ph
Ar
OH
O
Ph
Ar
Ar
HN
OH
HO
N
O
N
O
H
H
Ph
Ph
3
5
7
O
Ar
O
H
H
Ph
2
Ph
Ar
NH2OH
-H2O
Ph
Ar
HO
N
N
OH
O
O
Ph
4
8
Scheme 3. Proposed mechanism.
2 (scheme 3) easily. This can undergo water elimination
to give monooxime 4. But, the -NHOH group prefers
to attack the other free carbonyl and forms the inter-
mediate 5. Intermediate 5 can lose water molecule to
form cyclic nitrone 7. The oxygen of the oxime 4 can
attack the free carbonyl carbon to form 8. But in 4f, the
oxime has not undergone the subsequent cyclisation.
The above described steps are depicted in scheme 3.
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4. Conclusion
Reaction between differently substituted 1,4-diketones
with hydroxylamine hydrochloride has been investi-
gated. Cyclic nitrone, and 1,2-oxazine have been iso-
lated and characterized adequately by NMR and single
crystal X-ray analysis. Possible mechanism for the for-
mation of these products has been suggested accounting
for the observed regioselectivity.
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Supporting information
The electronic supporting information can be seen in
www.ias.ac.in/chemsci.
Acknowledgements
The authors thank the Department of Science and
Technology (DST), New Delhi for assistance under the
IRHPA program for providing funds for creating an
NMR facility. MN thanks the Council of Scientific and
Industrial Research (CSIR), New Delhi for JRF.
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