C1(S)C=CC=CC=1.[OH-].[K+].[CH2:10]([N:12]([C@H:25]1[CH2:30][C@H:29]([CH3:31])[S:28][C:27]2[S:32][CH:33]=[CH:34][C:26]1=2)S(C1C=CC=CC=1[N+]([O-])=O)(=O)=O)[CH3:11]>C(#N)C.O>[CH2:10]([NH:12][C@H:25]1[CH2:30][C@H:29]([CH3:31])[S:28][C:27]2[S:32][CH:33]=[CH:34][C:26]1=2)[CH3:11]Benzenethiol (3.2 mL) is dissolved in acetonitrile (15 mL). It is cooled under 5° C. and a mixture of potassium hydroxide (1.73 g) in water (4.2 mL) is added, maintaining the temperature under 10° C. The temperature is allowed to rise to 20-25° C. and a solution of trans-4-[N-ethyl-N-(2-nitrobenzenesulfonyl)amino]-5,6-dihydro-6-methyl-4-H-thieno-[2,3-b]-thiopyran (4.9 g) in acetonitrile (10 mL) is added. The resulting mixture is heated at 50° C. and is maintained until completing the transformation. Water (80 mL) is added and it is vacuum distilled until the volatiles are removed. It is extracted with ethyl acetate (80 mL). The resulting organic phase is vacuum distilled to dryness and the obtained residue is chromatographed in a column (methylene chloride/methanol 94/6), obtaining 1.9 g of trans-4-(N-ethylamino)-5,6-dihydro-6-methyl-4-H-thieno-[2,3-b]-thiopyran.
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