1-Cycloheptene-1-carboxylic acid, 2-mercapto-, ethyl ester → Ethyl 2-sulfo-1-cycloheptene-1-carboxylate

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Reaction Conditions

Reaction Steps

Sodium peroxyborate tetrahydrate (6.8 g) was admixed with acetic acid (37 ml) and heated to 50 to 55° C. and then a solution of ethyl 2-mercapto-1-cycloheptene-1-carboxylate (3.0 g, synthesized in accordance with Tetrahedron, Vol.30, p.3753 (1974)) in acetic acid (15 ml) was added dropwise over 1 hour. The mixture was stirred at 50 to 55° C. for 3 hours and then at 80 to 85° C. for 5 hours and concentrated under reduced pressure. The residue was combined with acetonitrile (100 ml) and stirred at room temperature for 3 hours and the resultant insolubles were filtered off. The insolubles were washed with acetonitrile (10 ml) and the filtrate and the washing were combined and concentrated under reduced pressure, and the resultant residue was dissolved in acetonitrile (70 ml) and stirred at room temperature for 1 hour. The resultant insolubles were filtered off, and the filtrate was concentrated under reduced pressure. The residue was combined with diisopropyl ether (100 ml) and the pellet which precipitated was isolated by a filtration to obtain ethyl 2-sulfo-1-cycloheptene-1-carboxylate as a white powder (3.4 g) containing inorganic substances. This (1.5 g) was dissolved in thionyl chloride (4 ml) and then stirred at 80 to 90° C. for 15 hours. The mixture was evaporated under reduced pressure to dryness and the residue was dissolved in ethyl acetate (30 ml). The solution obtained was washed with saturated brine (30 ml×2) and then dried over anhydrous sodium sulfate. The solvent was evaporated off to obtain a residue, which was purified by flash chromatography on silica gel column (eluent: ethyl acetate/hexane=1/8) to yield ethyl 2-chlorosulfonyl-1-cycloheptene-1-carboxylate (590 mg) as a brown oil.

Provenance & Evidence