Thionyl Chloride → (1)-S-(3-Chloro-2-methyl-3-oxopropyl) benzenecarbothioate

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Reaction Steps

3-Benzoylthio-2-methylpropanoic acid (11.6 g) in toluene (78 ml) was treated with thionyl chloride (4.6 ml). The resulting solution was warmed to 80° for 2.5 hours and then evaporated to dryness under reduced pressure to yield 3-benzoylthio-2-methylpropanoyl chloride. A solution of (±)-1,2,3,4-tetrahydro-2-quinolinecarboxylic acid hydrochloride (10.7 g) in pyridine (65 ml) was treated dropwise with the crude 3-benzoylthio-2-methylpropanoyl chloride with vigorous stirring. After stirring overnight, the reaction mixture was added to ice (900 g), acidified with 20% hydrochloric acid (130 ml), and extracted with ether (700 ml). The ether layer was dried over sodium sulfate and activated charcoal, and then concentrated to dryness to yield a viscous oil (25 g) which was dissolved in acetonitrile (100 ml) and treated with dicyclohexylamine (13 ml). The crystalline product, (±) 1-(3-benzoyl-2-methyl-1-oxopropyl)-1,2,3,4-tetrahydro-2-quinolinecarboxylic acid dicyclohexylamine salt, was collected by filtration; yield 3.6 g, m.p. 170°-173°.

Provenance & Evidence