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To a stirred solution of 6-bromo-2-hydroxy-3-methoxybenzaldehyde (0.33 g, 1.43 mmol) and triethylamine (0.17 g, 1.71 mmol) in dichloromethane (5 mL) was added methanesulfonyl chloride (0.19 g, 2.3 mmol) at 0° C., the reaction was stirred at 0° C. for 10 minutes and then at room temperature for 30 minutes, by which time a brown colour had developed. Water (20 mL) was added, the mixture was extracted with ethyl acetate (2×20 mL). The combined extract was washed with brine, dried over MgSO4, filtered and evaporated to give a crude solid (0.42 g). Flash chromatography over silica gel (60 g), eluting with hexane-ethyl acetate (3:1), gave 3-bromo-2-formyl-6-methoxyphenyl methanesulfonate (320 mg, 72%) and 5-bromo-8-methoxybenzo[e][1,2]oxathiine 2,2-dioxide (90 mg, 22%) as white solids. The 3-bromo-2-formyl-6-methoxyphenyl methanesulfonate had m.p. 95-97° C.; NMR Spectrum δH (300 MHz, CDCl3) 10.30 (1H, s, CHO), 7.58 (1H, d, J 8.9 Hz, 4-H), 7.11 (1H, d, J 8.9 Hz, 5-H), 3.95 (3H, s, OCH3), 3.57 (3H, s, SCH3); NMR Spectrum δC (75 MHz, CDCl3) 40.4, 57.1, 115.5, 118.3, 129.2, 133.2, 138.9, 152.9, 190.0; νmax/cm−1 (thin film) 1705, 1565, 1468, 1399, 1363, 1293, 1219, 1165, 1130, 971, 878, 800; m/z (ES) 374/372 (MNa2H2O+, 100%), 333/331 (MNa+, 80); Rf (hexane-ethyl acetate 1:1) 0.35. The 5-bromo-8-methoxybenzo[e][1,2]oxathiine 2,2-dioxide had m.p. 186-188° C.; Elemental Analysis Found: C, 37.3; H, 2.2; S, 10.9; Br, 27.2 (C9H7BrO4S requires C, 37.13; H, 2.42; S, 11.01; Br, 27.45%); NMR Spectrum δH (300 MHz, CDCl3) 7.62 (1H, d, J 10.5 Hz, 4-H), 7.47 (1H, d, J 10.5 Hz, 6-H), 6.96 (1H, d, J 10.5 Hz, 7-H), 6.88 (1H, d, J 10.5 Hz, 3-H), 3.88 (3H, s, OCH3); NMR Spectrum δC (75 MHz, CDCl3) 57.0, 113.7, 116.2, 120.3; 123.9, 129.9, 135.8, 142.0, 149.1; νmax/cm−1 (nujol mull) 3091, 2959, 2924, 2854, 1608, 1569, 1468, 1367, 1309, 1270, 1169, 1080, 909; Rf(hexane-ethyl acetate 1:1) 0.60.

1. waitat room temperature for 30 minutes
2. extractionthe mixture was extracted with ethyl acetate (2×20 mL)
3. extractionThe combined extract
4. washwas washed with brine
5. dry with materialdried over MgSO4
6. filtrationfiltered
7. customevaporated
8. customto give a crude solid (0.42 g)
9. washFlash chromatography over silica gel (60 g), eluting with hexane-ethyl acetate (3:1)