1076 Mohan et al.
Asian J. Chem.
dialkyl azodicaboxylate (4 mmol) in dichloromethane (DCM) in
the presence of triphenylphosphine (4 mmol) at room tempera-
ture for 15 min under argon atmosphere (Scheme-I). The product
was isolated from the mixture with the help of column chromato-
graphy using hexane and ethyl acetate (95:5) as eluent. The
reaction was found general for a number of diphenyl cyclpropen-
ones prepared from dibenzyl ketones as shown in Table-1.
2-Ethoxy-4,5-bis(4-chlorophenyl)-6H-1,3-oxazin-6-one
(5): White solid; IR (KBr, νmax, cm-1): 1753, 1611, 1311 and
1091; 1H NMR (500 MHz, CDCl3): δ 7.11-7.31 (m, 8H), 4.53-
4.60 (q, 2H, J = 7.5 Hz), 1.47-1.5 (t, 3H, J = 7.5 Hz); 13C NMR
(75.47 MHz, CDCl3): δ159.7, 157.7, 136.5, 134.5, 134.2, 132.1,
131.2, 128.9, 128.4, 112.3, 66.6, 14.1 ppm. LRMS (+FAB) m/z
calcd for C18H13NO3Cl2 (M+H)+: 362.03; Found: 362.38.
2-(Benzyloxy)-4,5-bis(4-chlorophenyl)-6H-1,3-oxazin-
6-one (6): White solid; IR (KBr, νmax, cm-1): 1741and 1611;
1H NMR (500 MHz, CDCl3): δ 7.41-7.10 (m, 13H), 5.50 (s, 2H);
13C NMR (75.47 MHz, CDCl3): δ 161.0, 160.1, 157.4,136.3,
134.3, 132.8, 130.8, 130, 129.9, 129, 128.5, 127.9, 113.5, 71.5
ppm. LRMS (+FAB) m/z calcd for C23H15NO3Cl2 (M+H)+: 425.28;
Found: 425.69.
O
O
O
Ar
Ar
DCM; Argon
O
N
N
OR
15 min,
Room temp. RO
RO
N
Ar
Ar
O
Scheme-I
2-Isopropoxy-4,5-bis(3-nitrophenyl)- 6H-1,3-oxazin-6-
one (7): White solid; IR (KBr, νmax, cm-1): 1759, 1609, 1096
and 1295; 1H NMR (300 MHz, CDCl3): δ 7.8-7.2 (m, 10H),
5.18-5.14 (m, 1H), 1.35 (d, 6H, J = 6.5 Hz); 13C NMR (125 MHz,
CDCl3): δ 162, 150, 148, 147.9, 136, 129.7, 125, 120, 72.4, 21.6,
21.5 ppm. LRMS (+FAB) m/z calcd for C19H17N3O5 (M+H)+:
397.09; Found: 397.5.
2-Ethoxy-4,5-bis(3-nitrophenyl)- 6H-1,3-oxazin-6-one
(8): White solid; IR (KBr, νmax, cm-1): 1761, 1614, 1311 and
1091; 1H NMR (500 MHz, CDCl3): δ 7.64-7.15 (m, 8H), 4.2-4.02
(q, 2H, J = 7 Hz), 1.27-1.22 (t, 3H, J = 7 Hz); 13C NMR (75.47
MHz, CDCl3): δ162.2, 133.1, 132.8, 132.3, 132.1, 129.8, 128.7,
128.6, 123.3, 61.2, 61.1, 14.7 ppm. LRMS (+FAB) m/z calcd
for C18H13N3O5 (M+H)+: 383.08; Found: 383.51.
TABLE-1
REACTIONS OF DIARYL CYCLOPROPENONES
WITH DIALKYL AZODICARBOXYLATES
Compound
Ar group
Phenyl
Phenyl
R group
Yield (%)
1
2
3
4
5
6
7
8
9
Isopropyl
Ethyl
63
68
65
56
65
85
75
50
75
70
Phenyl
Benzyl
Isopropyl
Ethyl
Isopropyl
Ethyl
Benzyl
Ethyl
Isopropyl
m-Nitro phenyl
m-Nitro phenyl
p-Chloro phenyl
p-Chloro phenyl
p-Chloro phenyl
m-Bromo phenyl
m-Bromo phenyl
10
2-(Isopropoxy)-4,5-bis(3-bromophenyl)-6H-1,3-
oxazin-6-one (9): White solid; IR (KBr, νmax, cm-1): 1759 and
1609; 1H NMR (300 MHz, CDCl3): δ 7.92-7.18 (m, 8H), 5.180-
5.091 (m, 1H), 1.35 (d, 6H, J = 6.5 Hz); 13C NMR (125 MHz,
CDCl3): δ 162.4, 150, 139, 131, 130, 125, 124.6, 120.6, 64, 23
ppm. LRMS (+FAB) m/z calcd for C19H15NO3Br2 (M+H)+: 462.94;
Found: 462.85.
2-Ethoxy-4,5-bis(3-bromophenyl)- 6H-1,3-oxazin-6-
one (10): White solid; IR (KBr, νmax, cm-1): 1759, 1609 and
1611; 1H NMR (500 MHz, CDCl3): δ 7.8-7.2 (m, 8H), 5.180-5.14
(m, 1H, J= 6 Hz), 1.35 (d, 6H, J = 6.5 Hz); 13C NMR (75.47 MHz,
CDCl3): δ162.4, 149, 139, 131, 125, 123, 120, 55.16 ppm. LRMS
(+FAB) m/z calcd for C18H13NO3Br2 (M+H)+: 448.93; Found:
448.34.
Spectral data
2-Isopropoxy-4,5-diphenyl-6H-1,3-oxazin-6-one (1):
White solid; IR (KBr, νmax, cm-1): 1746, 1607, 1096 and 1295;
1H NMR (500 MHz CDCl3): δ 7.17-7.27 (m, 10H), 5.37-5.39
(m, 1H, J = 6 Hz), 1.47-1.48 (d, 6H, J = 6.5 Hz); 13C NMR (75.47
MHz,CDCl3): δ 161.2, 160.3, 157.1, 136.5, 133.0, 130.8, 128.3,
127.8, 113, 74.7, 21.6 ppm. LRMS (+FAB) m/z calcd for
C19H17NO3 (M+H)+: 308.12; Found: 308.58.
2-Ethoxy-4,5-diphenyl-6H-1,3-oxazin-6-one (2):White
solid; IR (KBr, νmax, cm-1): 1754, 1614, 1319 and 1096; H
1
NMR (500 MHz CDCl3): δ 7.18-7.33 (m, 10H), 4.56-4.57(q,
2H, J = 7 Hz), 1.47-1.5 (t, 3H, J = 6.5 Hz); 13C NMR (75.47
MHz, CDCl3): δ 161.11, 160.1, 157.5, 136.4, 132.9, 130.8, 130,
128.3, 127.9, 127.8, 66.3, 14.1 ppm. LRMS (+FAB) m/z calcd
for C18H15NO3 (M+H)+: 294.11; Found: 294.50.
RESULTS AND DISCUSSION
2-(Benzyloxy)-4,5-diphenyl-6H-1,3-oxazin-6-one (3):
White solid; IR (KBr, νmax, cm-1): 1752, 1612, 1305 and 1115;
1H NMR (500 MHz, CDCl3): δ 7.17-7.47 (m, 15H), 5.51 (s, 2H);
13C NMR (75.47 MHz, CDCl3): δ 160.9, 160.0, 157.5, 136.3,
134.3,132.8,130.8,130,129.9,129, 127.9,113.5,71.5 ppm.
LRMS (+FAB) m/z calcd for C23H17NO3 (M+H)+: 356.12; Found:
356.67.
2-Isopropoxy-4,5-bis(4-chlorophenyl)- 6H-1,3-oxazin-
6-one (4): White solid; IR (KBr, νmax, cm-1): 1759, 1608, 1091
and 1309; 1H NMR (300 MHz, CDCl3): δ 7.91-7.11 (m, 8H), 5.4-
5.25 (m, 1H, J = 6.3 Hz), 1.46-1.450 (d, 6H, J = 6.3 Hz); 13C NMR
(125 MHz, CDCl3): δ 160.3, 159.8, 157.3, 136.4, 134.6, 134.1,
1.32.1, 128.9, 128.3, 112, 21.59 ppm. LRMS (+FAB) m/z calcd
for C19H15NO3Cl2 (M+H)+: 376.04; Found: 376.34.
Despite their potential utility, zwitterions are rarely used
in synthetic organic chemistry when compared with other
reactive intermediates. However, we have employed the utility
of Huisgen zwitterion for the synthesis of various oxazinones
(1-10).
The mechanism of the reaction is explained by the nucleo-
philic attack of Huisgen zwitterion on cyclopropenone followed
by internal cyclization to yield corresponding oxazinone
(Scheme-II).
Conclusion
We have unravelled a facile and novel route for the synthesis
of oxazinones and successfully employed it for a series of diaryl
cyclopropenones with various dialkyl azodicarboxylates. It is