Iodine → (R)-methyl 2-((tert-butoxycarbonyl)amino)-3-(2-(2,4-dimethoxybenzyl)-1,1-dioxido-3,4-dihydro-2H-benzo[e][1,2]thiazin-6-yl)propanoate

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Iodine (0.11 g, 0.43 mmol) was added to a mixture of (R)-methyl 2-(tert-butoxycarbonylamino)-3-iodopropanoate (1.30 g, 3.58 mmol) and zinc (0.620 g, 9.75 mmol) in DMF (30 mL). The mixture was stirred for 10 min and another portion of iodine (0.11 g, 0.43 mmol) was added. The mixture was stirred for another 1 h. 6-Bromo-2-(2,4-dimethoxybenzyl)-3,4-dihydro-2H-benzo[e][1,2]thiazine 1,1-dioxide (1.34 g, 3.25 mmol), Pd2(dba)3 (0.08 g, 0.09 mmol) and S—Phos (0.070 g, 0.17 mmol) were added. The reaction mixture was stirred at 50° C. for 4 h and then cooled to ambient temperature. The mixture was filtered and the filtrate was poured into water (50 mL). The resulting mixture was extracted with EtOAc (100 mL×3). The organic extracts were combined, dried over anhydrous sodium sulfate, and concentrated. The residue was purified by flash column chromatography on silica gel (petroleum ether/EtOAc=15:1 to 3:1) to afford (R)-methyl 2-((tert-butoxycarbonyl)amino)-3-(2-(2,4-dimethoxybenzyl)-1,1-dioxido-3,4-dihydro-2H-benzo[e][1,2]thiazin-6-yl)propanoate (0.8 g, 46% yield) as a yellow oil.

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