C. Ramesh et al. / Tetrahedron 67 (2011) 1187e1192
1191
(Mþ) 197.0238 found 197.0247. C9H837ClNO2 (Mþ) 199.0209 found
199.0218.
NMR (400 MHz, CDCl3)
d
8.60 (br s,1H), 8.08 (d, J¼8.4 Hz,1H), 7.77 (d,
J¼8.1 Hz, 1H), 7.52e7.48 (m, 2H), 7.41 (t, J¼7.5 Hz, 1H), 7.02 (d,
J¼8.6 Hz, 1H), 4.81 (s, 2H). 13C NMR (100 MHz, CDCl3, and DMSO-d6)
4.3.13. 2-Methyl-2H-benzo[b][1,4]oxazin-3(4H)-one
(3m). White
d 164.4, 136.4, 129.8, 127.1, 125.6, 124.2, 123.9, 121.7, 121.5, 120.0, 116.1,
solid; mp: 140e142 ꢀC (EtOAcehexane); IR(KBr)
n
/cmꢁ1: 1679,
67.0. MS (EI) (m/z) (relative intensity) 199 (Mþ, 100). HRMS calcd for
1609, 1502. 1H NMR (400 MHz, CDCl3)
d
9.52 (br s, 1H), 6.97e6.86
C12H9NO2 (Mþ) 199.0628 found 199.0635.
(m, 4H), 4.67 (q, J¼6.8 Hz, 1H), 1.59 (d, J¼6.8 Hz, 3H). 13C NMR
(100 MHz, CDCl3)
d
169.3, 143.3, 126.7, 124.2, 122.7, 117.1, 116.1, 73.4,
4.3.21. 2-Ethyl-2H-benzo[b][1,4]oxazin-3(4H)-one (3u). White solid;
16.3. MS (EI) (m/z) (relative intensity) 163 (Mþ, 100), 120 (36).
mp: 80e82 ꢀC (EtOAcehexane); IR(KBr) /cmꢁ1: 1676, 1609, 1502. 1H
n
HRMS calcd for C9H9NO2 (Mþ) 163.0628 found 163.0636.
NMR (400 MHz, CDCl3) d 8.69 (br s,1H), 6.98e6.92 (m, 3H), 6.81e6.79
(m, 1H), 4.51 (dd, J¼8.1, 4.5 Hz, 1H), 1.98e1.88 (m, 2H), 1.09 (t,
4.3.14. 2,6-Dimethyl-2H-benzo[b][1,4]oxazin-3(4H)-one (3n). White
J¼7.4 Hz, 3H). 13C NMR (100 MHz, CDCl3)
d 168.8, 143.1, 126.5, 124.3,
solid; mp: 144e145 ꢀC (EtOAcehexane); IR (KBr)
n
/cmꢁ1: 1682,
122.6, 117.1, 116.0, 78.2, 24.0, 9.5. MS (EI) (m/z) (relative intensity) 177
(Mþ, 100), 149 (19), 120(23). HRMS calcd for C10H11NO2 (Mþ) 177.0784
found 177.0794.
1607, 1520. 1H NMR (400 MHz, CDCl3)
d 9.08 (br s, 1H), 6.86e6.65
(m, 3H), 4.63 (q, J¼6.8 Hz,1H), 2.28 (s, 3H),1.57 (d, J¼6.8 Hz, 3H). 13C
NMR (100 MHz, CDCl3) d 169.6,141.0,132.4,126.3,124.7,116.7,116.5,
73.3, 20.7, 16.3. MS (EI) (m/z) (relative intensity) 177 (Mþ, 100), 134
4.3.22. 4-(2-Oxo-2-phenylethyl)-2H-benzo[b][1,4] oxazin-3(4H)-one
(50). HRMS calcd for C10H11NO2 (Mþ) 177.0784 found 177.0793.
(4). White solid; mp: 131e132 ꢀC (EtOAcehexane); IR(KBr) /cmꢁ1
n :
1704, 1682, 1596, 1503. 1H NMR (400 MHz, CDCl3)
d 8.05e8.02 (m,
4.3.15. 6-Methoxy-2-methyl-2H-benzo[b][1,4]oxazin-3(4H)-one
2H), 7.67e7.63 (m, 1H), 7.55e7.51 (m, 2H), 7.03e6.91 (m, 3H),
(3o). White solid; mp: 139e141 ꢀC (EtOAcehexane); IR(KBr)
n/
6.63e6.60 (m, 1H), 5.35 (s, 2H), 4.73 (s, 2H). 13C NMR (100 MHz,
cmꢁ1: 1683, 1608, 1503. 1H NMR (400 MHz, CDCl3)
d
9.04 (br s, 1H),
CDCl3) d 192.0, 165.2, 145.3, 134.7, 134.2, 129.1, 128.9, 128.2, 124.2,
6.89e6.87 (m, 1H), 6.52e6.41 (m, 2H), 4.59 (q, J¼6.8 Hz,1H), 3.76 (s,
123.0, 117.2, 114.8, 67.6, 48.1. MS (EI) (m/z) (relative intensity) 267
(Mþ, 100), 162 (20), 105 (28). HRMS calcd for C16H13NO3 (Mþ)
267.0890 found 267.0900.
3H), 1.56 (d, J¼6.8 Hz, 3H). 13C NMR (100 MHz, CDCl3)
d 169.6, 155.3,
137.3, 127.4, 117.5, 108.8, 102.2, 73.4, 55.9, 16.2. MS (EI) (m/z) (rela-
tive intensity) 193 (Mþ, 100), 150 (35). HRMS calcd for C10H11NO3
(Mþ) 193.0733 found 193.0745.
4.4. Procedure for the preparation of starting material (4)
4.3.16. 2-Phenyl-2H-benzo[b][1,4]oxazin-3(4H)-one (3p). White solid;
mp: 160e162 ꢀC (EtOAcehexane); IR(KBr) /cmꢁ1: 1694, 1608, 1502,
n
In an oven dried round-bottom flask, under a nitrogen atmo-
sphere, 2H-benzo[b][1,4]oxazin-3(4H)-one 3a (2.0 mmol, 1 equiv)
was dissolved in dry acetone (5 mL) and stirred with anhydrous
K2CO3 (2.6 mmol, 1.3 equiv). 2-bromo-1-phenylethanone
(2.4 mmol, 1.2 equiv) was added to the reaction mixture and
refluxed fluxed for 3 h. The progress of the reaction was monitored
by TLC. After the completion of the reaction, the reaction mixture
was diluted with ethyl acetate (25 mL), washed with water
(3ꢂ10 mL), brine (2ꢂ10 mL), and dried over Na2SO4. The solvent
was evaporated and the crude product was purified by flash chro-
matography on silica gel (Yield 77%).
1387. 1H NMR (400 MHz, CDCl3)
7.40e7.33 (m, 3H), 7.04e6.91 (m, 3H), 6.82e6.80 (m, 1H), 5.70 (s, 1H).
13C NMR (100 MHz, CDCl3)
166.8, 143.0, 135.3, 129.0, 128.8, 127.2,
d 9.25 (br s, 1H), 7.50e7.45 (m, 2H),
d
126.0, 124.5, 122.8, 117.3, 116.3, 78.6. MS (EI) (m/z) (relative intensity)
225 (Mþ, 100), 118 (20). HRMS calcd for C14H11NO2 (Mþ) 225.0784
found 225.0793.
4.3.17. 2-Propyl-2H-benzo[b][1,4]oxazin-3(4H)-one (3q). White solid;
mp: 108e110 ꢀC (EtOAcehexane); IR(KBr) /cmꢁ1: 1682, 1609, 1502.
n
1H NMR (400 MHz, CDCl3)
d 9.30(br s, 1H), 6.97e6.92 (m, 3H),
6.85e6.83 (m, 1H), 4.58 (dd, J¼8.0, 4.8 Hz, 1H), 1.89e1.84 (m, 2H),
1.62e1.51 (m, 2H), 0.97 (t, J¼7.3 Hz, 3H). 13C NMR (100 MHz, DMSO-
d6) d 168.0, 142.9, 127.5, 124.4, 123.3, 117.3, 116.4, 76.6, 32.5, 18.3, 14.1.
MS (EI) (m/z) (relative intensity) 191 (Mþ, 100), 149 (69). HRMS calcd
4.5. Procedure for the synthesis of 2-phenyl-4H-benzo[b]
imidazo[1,2-d][1,4]oxazine (5)
for C11H13NO2 (Mþ) 191.0941 found 191.0949.
4.3.18. N-(2-(3-cyanopropoxy)phenyl)acetamide (3r). White solid;
4-(2-oxo-2-phenylethyl)-2H-benzo[b][1,4]oxazin-(4H)-one (4,
1mmol) was weighed in a 10 mL Emrys reaction vial, and NH4OAc
(3 equiv) was then added. Subsequently, the reaction vial was
capped and then stirred for 15 s. The reaction mixture was irradi-
ated at 150 ꢀC (100 W) under neat reaction condition (solid phase)
until TLC (petroleum ether/ethyl acetate) showed the disappear-
ance of the starting material (30 min). The reaction mixture was
then cooled to room temperature and then diluted with water,
extracted with ethyl acetate followed by brine solution, and dried
over anhydrous MgSO4. The solvent was removed under reduced
pressure to obtain the crude product. The crude product was pu-
rified by column chromatography to furnish the pure product 5 as
a white solid in 91% yield.
mp: 92e94 ꢀC (EtOAcehexane); IR(KBr) /cmꢁ1: 2243, 1681, 1599,
n
1502. 1H NMR (400 MHz, CDCl3)
d 8.38e8.36 (m, 1H), 8.01 (br s, 1H),
7.01e6.95 (m, 2H), 6.84e6.8 (m, 1H), 4.15 (t, J¼5.5 Hz, 2H), 2.57 (t,
J¼6.3 Hz, 2H), 2.24e2.19 (m, 2H), 2.19 (s, 3H). 13C NMR (100 MHz,
DMSO-d6) d 168.3, 148.4, 127.5, 124.2, 121.9, 121.0, 120.4, 111.8, 66.6,
24.7, 23.9, 13.5. MS (EI) (m/z) (relative intensity) 218 (Mþ, 100), 176
(80), 108 (20). HRMS calcd for C12H14N2O2 (Mþ) 218.1050 found
218.1057.
4.3.19. 2H-pyrido[3,2-b][1,4]oxazin-3(4H)-one (3s). White solid;
mp: 190e192 ꢀC (EtOAcehexane); IR(KBr) /cmꢁ1: 1707, 1609, 1513,
n
1468. 1H NMR (400 MHz, CDCl3)
1H), 7.27 (d, J¼7.2 Hz, 1H), 6.97 (dd, J¼7.8, 5.0 Hz, 1H), 4.68 (s, 2H).
d
11.03 (br s, 1H), 8.06 (d, J¼4.4 Hz,
13C NMR (100 MHz, CDCl3)
d
165.8, 141.5, 141.0, 139.6, 124.0, 119.6,
4.5.1. 2-Phenyl-4H-benzo[b]imidazo[1,2-d][1,4]oxazine (5). White
67.3. MS (EI) (m/z) (relative intensity) 150 (Mþ, 100), 95 (15). HRMS
solid; mp: 117e119 ꢀC (EtOAcehexane); IR(KBr) /cmꢁ1: 1602, 1537,
n
calcd for C7H6N2O2 (Mþ) 150.0424 found 150.0432.
1507, 1427, 1242. 1H NMR (400 MHz, CDCl3)
7.63 (s, 1H), 7.43e7.39 (m, 2H), 7.34e7.29 (m, 2H), 7.16e7.09 (m,
3H), 5.33 (s, 2H). 13C NMR (100 MHz, CDCl3)
146.0, 143.1, 140.1,
133.5, 128.8, 127.5, 126.7, 125.1, 124.8, 122.9, 118.2, 115.6, 108.4, 64.3.
d 7.83e7.80 (m, 2H),
4.3.20. 2H-naphtho[1,2-b][1,4]oxazin-3(4H)-one (3t). Dark red solid;
d
mp: 247e249 ꢀC (EtOAcehexane); IR(KBr) /cmꢁ1: 1683, 1414. 1H
n