Stannous chloride dihydrate → methyl 3-amino-2-(((2'-(1-(4-methoxybenzyl)-1H-tetrazol-5-yl)-[1,1'-biphenyl]-4-yl)methyl)amino)benzoate

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A mixture of methyl 2-[({2′-[1-(p-methoxybenzyl)-1H-tetrazol-5-yl]biphenyl-4-yl}methyl)amino]-3-nitrobenzoate (compound 21a, 2.73 g, 4.96 mmol) and tin(II) chloride dihydrate (4.48 g, 19.9 mmol) in methanol (60 mL) was heated under reflux for 2 hr. The reaction mixture was concentrated under reduced pressure, and to the concentrated residue were added saturated aqueous sodium hydrogen carbonate and ethyl acetate. The mixture was stirred for 1 hr, and filtered, and the insoluble material was washed with ethyl acetate. The filtrate and washing were combined, and concentrated under reduced pressure. The concentrated solution was extracted with ethyl acetate. The ethyl acetate solution of the resultant product was dried magnesium sulfate, and filtered. The filtrate was concentrated under reduced pressure, and the concentrated residue was purified by silica gel column (hexane→hexane:AcOEt=4:1→2:1→3:2) to give methyl 2-[({2′-[1-(p-methoxybenzyl)-1H-tetrazol-5-yl]biphenyl-4-yl}methyl)amino]-3-aminobenzoate (compound 22a) (1.96 g, 70%) as a brown amorphous solid.

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