3H, ester CH3), 5.00 (d, 1H, J 11 Hz, 3-H), 5.05 (d, 1H, J 11 Hz,
3-H), 6.40 (s, 1H, 1-H), 7.57 (d, 2H, J 10 Hz, Ar-H) and 8.02 (d,
2H, J 10 Hz, Ar-H); δC (CDCl3) 11.8 (CH3), 51.6 (CH3 ester),
51.8 (CH3 ester), 63.7 (CH2), 66.9 (CH), 112.8, 115.5, 129.3,
129.7 (2 × CH), 130.6 (2 × CH), 133.7, 133.9, 141.8, 162.7
(C᎐O ester), 164.5 (C᎐O ester) and 187.8 (C᎐O ketone); m/z 425
(s, 3H, 7-CH3), 3.85 (s, 3H, ester CH3), 3.86 (s, 3H, ester CH3),
5.66 (s, 2H, CH2), 6.96 (s, 1H, CH), 7.33–7.44 and 7.68–7.71 (m,
5H, Ar-H); δC (CDCl3) 10.0 (CH3), 51.4 (CH3 ester), 51.5 (CH3
ester), 72.9 (CH2), 95.2 (CH), 108.6, 114.6, 124.9 (2 × CH),
128.5 (2 × CH), 129.5 (CH), 130.8, 132.4, 152.1, 164.6 (C᎐O
᎐
ester) and 165.5 (C᎐O ester); m/z 327 (Mϩ, 60%), 295 (35), 237
᎐
᎐
᎐
᎐
(Mϩ, 2%), 361 (2), 243 (3), 139 (100). Accurate mass: 425.0338,
C18H16ClNO7S requires 425.0331.
(20), 209 (100), 105 (57), 77 (58). Accurate mass: 327.1106,
C18H17NO5 requires 327.1107.
Method B (solution pyrolysis). A suspension of dimethyl 1-
benzoyl-2,2-dioxo-5-methyl-1H,3H-pyrrolo[1,2-c][1,3]thiazole-
6,7-dicarboxylate (0.2 g, 0.5 mmol) in 1,2,4-trichlorobenzene
(2 mL) was heated at reflux under dry nitrogen for 4 h. After
cooling to room temperature the mixture was purified by
flash chromatography [SiO2, petroleum ether] to remove the
1,2,4-trichlorobenzene followed by elution with [ethyl acetate–
petroleum ether (1 : 1)] to yield pure dimethyl 7-methyl-3-
phenyl-1H-pyrrolo[1,2-c][1,3]oxazine-5,6-dicarboxylate (0.14
g, 86%) as a yellowish oil, which had identical physical and
spectral properties to the product isolated in method A.
Dimethyl 1-(3,4-difluorobenzoyl)-2,2-dioxo-5-methyl-1H,3H-
pyrrolo[1,2-c][1,3]thiazole-6,7-dicarboxylate (30, R ؍
3,4-F2C6-
H4). Yellowish crystals (0.76 g, 51%), mp 152–154 ЊC (Found:
C, 50.4; H, 3.3; N, 3.2. C18H15F2NO7S requires C, 50.6; H, 3.5;
N, 3.3%); νmax (Nujol) 1740, 1715 and 1693 (C᎐O) cmϪ1
;
᎐
δH (CDCl3) 2.45 (s, 3H, 5-CH3), 3.64 (s, 3H, ester CH3), 3.86
(s, 3H, ester CH3), 5.02 (s, 2H, 3,3-H), 6.36 (s, 1H, 1-H), 7.35–
7.44 and 7.89–7.95 (m, 3H, Ar-H); δC (CDCl3) 11.7 (CH3), 51.7
(CH3 ester), 51.8 (CH3 ester), 63.8 (CH2), 66.9 (CH), 113.0,
115.6, 118.2 (CH), 118.5 (CH), 118.6, 118.8, 126.7, 126.8, 129.2,
133.9 (CH), 163.0 (C᎐O ester), 164.6 (C᎐O ester) and 186.8
᎐
᎐
(C᎐O ketone); m/z 427 (Mϩ, 0.2%), 363 (1), 141 (100), 113 (15).
᎐
Accurate mass: 427.0531, C18H15F2NO7S requires 427.0537.
General procedure for the preparation of dimethyl 3-substituted-
7-methyl-1H-pyrrolo[1,2-c][1,3]oxazine-5,6-dicarboxylates
Dimethyl
1-(2-furoyl)-2,2-dioxo-5-methyl-1H,3H-pyrrolo-
Using method B (solution pyrolysis) described above the
following pyrrolo[1,2-c]oxazines were obtained:
[1,2-c][1,3]thiazole-6,7-dicarboxylate (30, R ؍
2-furyl). Colour-
less crystals (0.85 g, 64%), mp dec. 210–212 ЊC (Found: C, 50.4;
H, 3.7; N, 3.5. C16H15NO8S requires C, 50.4; H, 3.9; N, 3.7%);
Dimethyl
3,7-dimethyl-1H-pyrrolo[1,2-c][1,3]oxazine-5,6-
νmax (KBr) 1735, 1715 and 1677 (C᎐O) cmϪ1; δH (CDCl3) 2.46 (s,
᎐
dicarboxylate (32, R ؍
Me). Yellowish oil (0.1 g, 52%) (Found:
C, 58.7; H, 5.8; N, 5.3. C13H15NO5 requires C, 58.9; H, 5.7;
N, 5.3%); δH (CDCl3) 2.00 (s, 3H, 3-CH3), 2.35 (s, 3H, 7-CH3),
3.81 (s, 3H, ester CH3), 3.83 (s, 3H, ester CH3), 5.48 (s, 2H,
CH2) and 6.20 (s, 1H, CH); δC (CDCl3) 9.9 (CH3), 19.0 (CH3),
51.2 (CH3 ester), 51.5 (CH3 ester), 72.4 (CH2), 96.5 (CH), 113.4,
3H, 5-CH3), 3.64 (s, 3H, ester CH3), 3.86 (s, 3H, ester CH3), 4.98
(d, 1H, J 11 Hz, 3-H), 5.03 (d, 1H, J 11 Hz, 3-H), 6.31 (s, 1H,
1-H), 6.70–6.73 (m, 1H, J 2, 5 Hz, Ar-H), 7.50 (d, 1H, J 5 Hz,
Ar-H) and 7.79 (d, 1H, J 2 Hz, Ar-H); δC (CDCl3) 11.6 (CH3),
51.6 (CH3 ester), 51.8 (CH3 ester), 63.7 (CH2), 67.4 (CH), 113.1,
113.8 (CH), 115.5, 120.9 (CH), 128.6, 133.9, 148.9 (CH), 151.4,
117.0, 130.0, 130.9, 153.7, 162.2 (C᎐O ester) and 162.9 (C᎐O
᎐
᎐
162.5 (C᎐O ester), 164.5 (C᎐O ester) and 176.3 (C᎐O ketone);
᎐
᎐
᎐
ester); m/z 265 (Mϩ, 59%), 233 (65), 175 (50), 147 (100) and 43
m/z 381 (Mϩ, 12%), 317 (100), 285 (28), 199 (34), 81 (32).
(27). Accurate mass: 265.0951, C13H15NO5 requires 265.0950.
Accurate mass: 381.0522, C16H15NO8S requires 381.0513.
Dimethyl 7-methyl-3-(4-methylphenyl)-1H-pyrrolo[1,2-c][1,3]-
oxazine-5,6-dicarboxylate (32, R ؍
4-MeC6H4). Yellowish solid
(0.14 g, 85%), mp 108–110 ЊC (Found: C, 66.5; H, 5.8; N, 4.3.
C19H19NO5 requires C, 66.8; H, 5.6; N, 4.1%); νmax (KBr) 1711
Dimethyl 1-cyclohexanoyl-2,2-dioxo-5-methyl-1H,3H-pyrrolo-
[1,2-c][1,3]thiazole-6,7-dicarboxylate (30, R ؍
cyclohexyl).
Colourless needles (1.22 g, 88%), mp 141–142 ЊC (Found: C,
54.4; H, 5.7; N, 3.5. C18H23NO7S requires C, 54.4; H, 5.8; N,
and 1693 (C᎐O) cmϪ1; δH (CDCl3) 2.38 (s, 3H, C6H4CH3), 2.41
᎐
3.5%); νmax (KBr) 1721 and 1693 (C᎐O) cmϪ1; δH (CDCl3) 1.22–
᎐
(s, 3H, 7-CH3), 3.85 (s, 3H, ester CH3), 3.86 (s, 3H, ester CH3),
5.65 (s, 2H, CH2), 6.92 (s, 1H, CH), 7.21 (d, 2H, J 12 Hz, Ar-H)
and 7.59 (d, 2H, J 12 Hz, Ar-H); δC (CDCl3) 10.0 (CH3),
21.4 (CH3), 51.4 (CH3 ester), 51.6 (CH3 ester), 72.8 (CH2),
94.4 (CH), 108.2, 114.4, 124.9 (2 × CH), 129.3 (2 × CH),
1.54, 1.70–1.74, 1.85–1.88, 2.04–2.07 (m, 10H, cyclohexyl ring-
H), 2.41 (s, 3H, 5-CH3), 2.74–2.81 (m, 1H), 3.79 (s, 3H, ester
CH3), 3.85 (ester CH3), 4.90 (d, 1H, J 11 Hz, 3-H), 4.93 (d, 1H,
J 11 Hz, 3-H) and 5.74 (s, 1H, 1-H); δC (CDCl3) 11.7 (CH3), 25.3
(CH2), 25.4 (CH2), 25.6 (CH2), 27.2 (CH2), 27.5 (CH2), 51.7
(CH3 ester), 51.8 (CH3 ester), 51.9 (CH), 63.2 (CH2), 69.0 (CH),
129.6, 130.6, 131.1, 139.8, 152.4, 164.7 (C᎐O ester) and 165.6
᎐
(C᎐O ester); m/z 341 (Mϩ, 100%), 310 (21), 223 (57), 105 (31).
᎐
112.5, 115.3, 129.2, 133.4, 163.0 (C᎐O ester), 164.6 (C᎐O ester)
᎐
᎐
Accurate mass: 341.1267, C19H19NO5 requires 341.1257.
and 201.4 (C᎐O ketone); m/z 397 (Mϩ, 2%), 366 (2), 333 (1), 255
᎐
(15), 111 (45), 83 (100). Accurate mass 397.1199, C18H23NO7S
requires 397.1188.
Dimethyl 3-(4-chlorophenyl)-7-methyl-1H-pyrrolo[1,2-c][1,3]-
oxazine-5,6-dicarboxylate (32, R ؍
4-ClC6H4). Yellowish solid
(0.13 g, 76%), mp dec. 130–132 ЊC (Found: C, 59.7; H, 4.6; N,
4.1. C18H16ClNO5 requires C, 59.8; H, 4.4; N, 3.9%); νmax (KBr)
Dimethyl 7-methyl-3-phenyl-1H-pyrrolo[1,2-c][1,3]oxazine-5,6-
dicarboxylate (32, R ؍
Ph)
1719 and 1699 (C᎐O) cmϪ1; δH (CDCl3) 2.41 (s, 3H, 7-CH3),
᎐
3.85 (s, 3H, ester CH3), 3.86 (s, 3H, ester CH3), 5.66 (s, 2H,
CH2), 6.94 (s, 1H, CH), 7.36 (d, 2H, J 10 Hz, Ar-H) and 7.62
(d, 2H, J 10 Hz, Ar-H); δC (CDCl3) 10.0 (CH3), 51.6 (CH3
ester), 51.8 (CH3 ester), 72.9 (CH2), 95.5 (CH), 108.9, 114.6,
126.1 (2 × CH), 128.9 (2 × CH), 130.8, 131.8, 131.9, 135.3,
150.9, 164.6 (C᎐O ester) and 165.5 (C᎐O ester); m/z 361 (Mϩ,
Method A (flash pyrolysis). Pyrolysis of dimethyl 1-benz-
oyl-2,2-dioxo-5-methyl-1H,3H-pyrrolo[1,2-c][1,3]thiazole-6,7-
dicarboxylate (0.2 g, 0.5 mmol) at 600 ЊC/1 × 10Ϫ3 Torr onto
a surface cooled at Ϫ196 ЊC over a 2 h period gave a yellowish
pyrolysate. The pyrolysate was allowed to warm to room
temperature under a positive flow of dry nitrogen and removed
from the cold finger with dichloromethane. The solvent was
removed in vacuo and the residue purified by flash chroma-
tography [SiO2, ethyl acetate–petroleum ether (1 : 1)] to give
dimethyl 7-methyl-3-phenyl-1H-pyrrolo[1,2-c][1,3]oxazine-5,6-
dicarboxylate 32 (R = Ph) (0.13 g, 75%) as a yellowish oil
(Found: C, 65.8; H, 5.1; N, 4.2. C18H17NO5 requires C, 66.1; H,
᎐
᎐
100%), 329 (42), 271 (19), 243 (77), 139 (24). Accurate mass:
361.0713, C18H16ClNO5 requires 361.0713.
Dimethyl 3-(3,4-difluorophenyl)-7-methyl-1H-pyrrolo[1,2-c]-
[1,3]oxazine-5,6-dicarboxylate (32, R ؍
3,4-F2C6H4). Yellowish
oil (0.1 g, 60%) (Found: C, 59.3; H, 3.9; N, 3.6. C18H15F2NO5
requires C, 59.5; H, 4.1; N, 3.9%); δH (CDCl3) 2.41 (s, 3H,
5.2; N, 4.3%); νmax (Nujol) 1711 (C᎐O) cmϪ1; δH (CDCl3) 2.41
᎐
1804
J. Chem. Soc., Perkin Trans. 1, 2001, 1795–1806