Synthetic method of dorzolamide hydrochloride intermediate

The invention relates to a synthetic method of a dorzolamide hydrochloride intermediate Ia (4-ethylamino-5,6-dihydro-6-methyl-4H-thieno[2,3-b] thiapyran-2-sulfamide-7,7-dioxide) and Ib (4-ethylamino-5,6-dihydro-6-methyl-4H-thieno[2,3-b] thiapyran-2-sulfamide-7,7-dioxide) used for treating glaucoma. The preparation method of the Ia comprises the steps that IIa (4-ethylamino-5,6-dihydro-6-methyl-4H-thieno[2,3-b] thiapyran-2-sulfamide-7,7-dioxide) reacts in a solvent under the condition of the existence of sodium borohydride and iodine, and acetamido is reduced into ethylamino in a synthesis mode. The preparation method of the Ib comprises the steps that IIb ((4s,6s)-4-ethylamino-5,6-dihydro-6-methyl-4H-thieno[2,3-b] thiapyran-2-sulfamide-7,7-dioxide) reacts in a solvent under the condition of the existence of sodium borohydride and iodine, and acetamido is reduced into ethylamino in a synthesis mode. Compared with existing methods, the synthetic method of the dorzolamide hydrochloride intermediate is high in yield, eliminates highly toxic raw materials, is mild in reaction condition, is free of intense heat release or intensely released gas in postprocessing, and reduces operating dangers.