B. To an ice-cooled suspension of pyridinium halide 5-8 (33 mmol) in ethanol (15 ml), a solution of
triethylamine (15 mmol) in ethanol (5 ml) was added dropwise for 15 min with stirring. A solution of
p-nitrosodimethylaniline (12 mmol) in 5 ml of ethanol was added to the reaction mixture and the stirring was
continued for another 2 h at room temperature. The red precipitate was filtered off. Using the same procedure,
nitrones 9, 10 were obtained starting from tetrahydrothiophenium bromides 11, 12 or from S-(phenoxathiin-2-
carbonylmethyl)dimethylsulfonium chloride (13).
Phenoxathiinyl Glyoxal Hydrates 14, 15. To a suspension of nitrone 9, 10 (15 mmol) in water (2 ml),
H2SO4 5N (5 ml) was added. The reaction mixture was maintained at room temperature for 6 h with stirring and
then was extracted with ether (3 × 10 ml). After the ether was removed by evaporation, the obtained solid was
recrystallized from 80% AcOH giving crystals of 2-(2'-phenoxathiinyl)glyoxal hydrate (14) (mp 132-134°C;
24% yield) and 2-(2'-phenoxathiinyl-10,10-dioxide)glyoxal hydrate (15) (mp 128.5-129.5°C; 35% yield).
Furan Derivatives 16-18. To 2-ω-bromoacetylphenoxathiine (3) (2.5 mmol) a solution of aldehydes
19-21 (2.5 mmol) in ethanol (20 ml) and anhydrous K2CO3 (3.5 g) were added. The reaction mixture was
refluxed for 90 min (16, 18) and 4 h respectively (17). After removing the solvent by vacuum distillation, water
was poured over the residue and the resulting solid was filtered off, washed with water, and dried.
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