[C:1]([C:3]1[S:12][C:6]2[S:7][CH2:8][C:9](=[O:11])[NH:10][C:5]=2[CH:4]=1)#[N:2].CC(C)([O-])C.[K+].I[CH2:20][CH2:21][CH2:22][CH3:23].C(OCC)(=O)C>CN(C)C=O.O>[CH2:20]([N:10]1[C:9](=[O:11])[CH2:8][S:7][C:6]2[S:12][C:3]([C:1]#[N:2])=[CH:4][C:5]1=2)[CH2:21][CH2:22][CH3:23]
To a solution of 6-cyano-2,3-dihydro-2-oxo-1H-thieno[2,3-b][1,4]thiazine (13.6 g) in N,N-dimethylformamide (270 ml) was added potassium tert-butoxide (9.3 g) under ice cooling. After stirring for 10 minutes under ice cooling, to the reaction mixture was added 1-iodobutane (9.5 ml). After stirring for 8 hours at room temperature, the reaction mixture was poured into a mixture of ethyl acetate and water. The organic layer was successively washed with water and brine and dried over magnesium sulfate. The solvent was evaporated in vacuo and the residue was purified by column chromatography on silica gel eluting with chloroform. The fractions containing the object compounds were collected and evaporated in vacuo to give 1-n-butyl-6-cyano-2,3-dihydro-2-oxo-1H-thieno[2,3-b][1,4]thiazine (13.78 g).
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