Chloroform → Ethyl 4-chloro-5-formyl-6,7-dihydro-3-methylthiobenzo[c]thiophene-1-carboxylate

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Reaction Steps

Ethyl 4,5,6,7-tetrahydro-3-methylthio-4-oxobenzo[c]thiophene-1-carboxylate (5.47 g) was dissolved in chloroform (130 ml) and added dropwise to a solution of phosphorus oxychloride (50.71 g) in N,N-dimethylformamide (40 ml) at 0° C. This mixture was stirred at room temperature, after which it was refluxed under heating in a nitrogen stream for 4.5 hours. The reaction mixture was poured over ice water and extracted with ethyl acetate. The organic layer was washed with water and dried (MgSO4), after which the solvent was distilled off to yield ethyl 4-chloro-5-formyl-6,7-dihydro-3-methylthiobenzo[c]thiophene-1-carboxylate (4.72 g, 73.8%), which was then recrystallized from ethyl acetate. Yellow prisms. Melting point 79-80° C.

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