Methanesulfonic Acid → Ethyl 5-methyl-4-oxo-2,3,7,8-tetrahydro-4H-1-benzothiopyran-6-carboxylate

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Reaction Conditions

Reaction Steps

A mixture of ethyl-4-β-carboxyethylthio-2-methyl-1,3-cyclohexadiene-1-carboxylate (121.3 g, 0.449 mole) in toluene is stirred at 20° C., treated sequentially with 5.0 ml methanesulfonic acid and portionwise over a 5 minute period with trifluoroacetic anhydride (94.3 g, 0.449 mole) and allowed to stir at ambient temperatures for 18 hours. The resultant reaction mixture is quenched with a 1:1 mixture of ethyl acetate and water and stirred for 15 minutes. The phases are separated. The organic phase is washed with water and concentrated in vacuo to give a residue. Crystallization of the residue from isopropanol/heptane affords the title product as a yellow solid, 90.1 g, (79.5% yield), mp 99°-100° C., identified by 1HNMR and mass spectral analyses.

Provenance & Evidence