Hydrochloric Acid → 4-Hydroxy-1,1-dioxo-N-phenyl-1,2-dihydro-1-benzothiopyran-3-carboxamide

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Reaction Steps

Preparation from the enamine-acid chloride. -- To 28.5 g. of a 12.5% solution of phosgene in benzene was added 30 ml. of tetrahydrofuran. The temperature of the solution was maintained at -10° to -15° and a solution of 7.5 g. (0.03 mole) of 4-(1-pyrrolidinyl)-2H-1-benzothiopyran 1,1-dioxide and 5 ml. (0.036 mole) of triethylamine in 125 ml. of tetrahydrofuran was added with stirring over a period of 20 minutes. After stirring at room temperature for 2 hr., a solution of 3.1 g. (0.033 mole) of aniline and 5 ml. of triethylamine in 25 ml. of tetrahydrofuran was added, the mixture was refluxed for 2 hr., and about a third of the solvent was distilled off. The remaining mixture was poured into ice-water and extracted with dichloromethane. The organic layer washed well with water, dried (MgSO4) and evaporated to give 12.3 g. of a dark syrup. This crude enamine-amide was dissolved in 100 ml. of methanol, treated successively with 10 ml. of water and 2 ml. of concentrated hydrochloric acid, and heated on a steam bath for 20 minutes. The mixture was cooled and filtered to yield 6 g. (64%) of product, m.p. 204°-208°.

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