Phosphorus oxychloride → Ethyl 4,5-dihydro-2-methyl-8-methylthiothieno[3,4-g]benzoxazole-6-carboxylate

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Reaction Steps

A mixture of ethyl 5-acetylamino-4,5,6,7-tetrahydro-3-methylthio-4-oxobenzo[c]thiophene-1-carboxylate (2.46 g), phosphorus oxychloride (3.46 g) and toluene (80 ml) was refluxed under heating for 1.5 hours; the solution obtained was concentrated under reduced pressure, diluted with a saturated aqueous solution of sodium hydrogen carbonate (200 ml) 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 4,5-dihydro-2-methyl-8-methylthiothieno[3,4-g]benzoxazole-6-carboxylate (2.18 g, 94.0%), which was then recrystallized from ethyl acetate-hexane. Light-yellow needles. Melting point 131-132° C.

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