Dichloromethane → 7-chloro-4-(4-chlorophenyl)-2-[(2,3-dimethyl-1-oxopentoxy)methyl]-5H-pyrido[3,4-b][1,4]benzothiazin-3(2H)-one

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Reaction Steps

A mixture of 2.06 g. of 2,3-dimethylvaleric acid (15.8 mmol). in 30 ml. of methylene chloride was cooled in a cold water bath and treated with 2.0 g. of oxalyl chloride (15.8 mmol.). The resulting solution was stirred at room temperature for 2 hours, then the methylene chloride was removed under reduced pressure. The resulting residue was added dropwise to a cold, stirred suspension of 1.2 g. of 7-chloro-4-(4-chlorophenyl)-2-(hydroxymethyl)-5H-pyrido[3,4-b][1,4]benzothiazin-3(2H)-one (3.1 mmol.) in 25 ml. of pyridine. After stirring for 35 minutes, the mixture was poured onto ice-water and allowed to stand for 16 hours at room temperature, resulting in the formation of a yellow precipitate, which was collected, washed with water, air-dried, then purified using flash chromatography on silica gel, employing a mixture of 5% ethyl acetate: 95% methylene chloride as the eluent. Fractions containing the product were combined and triturated with ether to yield 7-chloro-4-(4-chlorophenyl)-2-[(2,3-dimethyl-1-oxopentoxy)methyl]-5H-pyrido[3,4-b][1,4]benzothiazin-3(2H)-one as a pale yellow crystalline solid (1.18 g; 76% yield) having the structural formula, ##STR22## a melting point in the range of 165°-173° C. and the following elemental analysis:

Provenance & Evidence