[BH4-].[Na+].[CH3:3][O:4][C:5]1[CH:17]=[CH:16][C:8]([CH:9]=[C:10]2[CH2:15][CH2:14][S:13][CH2:12][CH2:11]2)=[C:7]([N+:18]([O-])=O)[CH:6]=1.Cl>COCCOC.CO>[CH3:3][O:4][C:5]1[CH:17]=[CH:16][C:8]([CH2:9][CH:10]2[CH2:15][CH2:14][S:13][CH2:12][CH2:11]2)=[C:7]([CH:6]=1)[NH2:18]Sodium borohydride (63.58 mg; 1.68 mmol; 0.07 eq) is suspended in DME (6.5 mL) at room temperature. Borane-methyl sulfide complex (39.61 mL; 2 M; 79.22 mmol; 3.3 eq) is added dropwise. After 30 min stirring at room temperature, a solution of 4-(4-methoxy-2-nitrobenzylidene)tetrahydro-2H-thiopyran (6.37 g; 24.01 mmol; 1 eq) in DME (100 mL) is added dropwise over 30 min and the orange solution is stirred at room temperature for 30 min then heated up to reflux for 3.5 days. The reaction mixture is quenched with MeOH (40 mL) upon which a yellow-brownish solution is obtained. The solution is stirred at room temperature for 1 h prior to evaporation of the solvent. The oily brownish residue obtained is taken up in MeOH (10 mL) and 5 N HCl (10 mL˜2 eq) is added dropwise while cooling the solution to 0° C. with an ice bath. After addition of ⅔ of the HCl, precipitation starts. The suspension is stored at 4° C. for 30 min. The precipitate is filtered off then washed twice with cold EtOAc (10 mL) to afford 2.39 g (36%) of the title compound as a yellow powder. 1H NMR (DMSO-d6) δ 9.61 (br s, 2H), 7.09-7.06 (m, 1H), 9.95-6.87 (m, 1H), 6.83-6.79 (m, 1H), 3.72 (s, 3H), 2.54-2.47 (m, 6H), 1.87-1.81 (m, 2H), 1.68-1.59 (m, 1H), 1.33-1.20 (m, 2H). HPLC (max plot) 95%; Rt 2.57 min. LC/MS: (ES+): 238.1; (ES−): 236.1.
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