Ring-Expansion Rearrangement
1721
Ethyl 8-(4-bromophenyl)-8-hydroxy-3-oxo-8H[1,2,4]oxadiazolo[3,4-c][1,4]
thiazine-5-carboxylate (5e): Red solid, yield 50%, mp 205–2068C; IR
1
(KBr) ncm21: 1727(C55O, ester), 1795 (C55O, lactone), 3335 (br, OH); H
NMR (300 MHz, CDCl3) d: 8.37 (d, J ¼ 8.0 Hz, 2H, ArH), 8.08 (s, 1H, C6-
H), 7.63 (d, J ¼ 8.2 Hz, 2H, ArH), 4.49 (q, J ¼ 7.1 Hz, 2H, CH2 of ester),
1.68 (br s, 1H, D2O exchangeable, OH), 1.42 (t, J ¼ 7.1 Hz, 3H, CH3 of
ester); 13C NMR (75 MHz, CDCl3) d: 186.0, 178.2, 157.7, 151.0, 132.2,
131.8, 130.0, 125.5, 122.4, 120.0, 63.4, 14.5. Anal. calcd. for
C14H11BrN2O5S: C, 42.10; H, 2.75; N, 7.01. Found: C, 42.53; H, 2.66; N,
7.16%. MS (m/z): Mþ (398) and Mþþ2 (400).
Ethyl 8-(2-thienyl)-8-hydroxy-3-oxo-8H[1,2,4]oxadiazolo[3,4-c][1,4]
thiazine-5-carboxylate (5f): Red solid, yield 46%, mp 210–2118C; IR
1
(KBr) ncm21: 1720 (C55O, ester), 1787 (C55O, lactone), 3328 (br, OH); H
NMR (300 MHz, CDCl3) d: 8.10 (s, 1H, C6-H), 6.90–6.60 (m, 3H,
thienyl), 4.50 (q, J ¼ 6.8 Hz, 2H, CH2 of ester), 1.58 (br s, 1H, D2O exchange-
able, OH), 1.32 (t, J ¼ 7.0 Hz 3H, CH3 of ester). Anal. calcd. for
C12H10N2O5S2: C, 44.17; H, 3.06; N, 8.58. Found: C, 44.40; H, 3.12; N,
8.65%.
Ethyl 8-(3-coumarinyl)-8-hydroxy-3-oxo-8H[1,2,4]oxadiazolo[3,4-c][1,4]
thiazine-5-carboxylate (5g): Red solid, yield 42%, mp 196–1988C; IR
(KBr) ncm21: 1721 (C55O, ester), 1790, 1750 (C55O, lactone), 3330 (br,
1
OH); H NMR (300 MHz, CDCl3) d: 8.56 (s, 1H, coumarinyl C4-H), 8.30
(s, 1H, C6-H), 8.16–7.69 (m, 4H, coumarinyl), 4.35 (q, J ¼ 6.8 Hz, 2H,
CH2 of ester), 1.55 (br s, 1H, D2O exchangeable, OH), 1.35 (t, J ¼ 6.8 Hz,
3H, CH3 of ester). Anal. calcd. for C17H12N2O7S: C, 56.35; H, 3.31; N,
7.73. Found: C, 56.99; H, 3.62; N, 7.44%.
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