p-Toluenesulfonic acid → Ethyl 2-(4-methoxyphenylmethyl)-2H-thieno[3,2-e]-1,2-thiazine-3-carboxylate 1,1-dioxide

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Reaction Steps

A mixture of the product from Step A (3.91 g) and p-toluenesulfonic acid (0.2 g) in acetone (150 mL) was heated at reflux temperature for 3 h, cooled and a saturated solution of sodium bicarbonate (50 mL) was added and acetone evaporated. The aqueous mixture was extracted with ethyl acetate (2×10 mL) and the combined extracts were dried (MgSO4) and filtered. DBU (0.3 g) was added to the filtrate and this mixture was heated at reflux temperature for 2 h, cooled and acidified by the addition of 1N HCl. The organic layer was separated, dried (MgSO4) and evaporated to a residue which was purified by column chromatography (silica, 30% ethyl acetate/hexane) to give a viscous oil (1.80 g, 55%).

Provenance & Evidence