Sodium triacetoxyborohydride → 3-(3-Benzyloxy-cyclobutylamino)-5-(3,3-dimethyl-but-1-ynyl)-thiophene-2-carboxylic acid methyl ester

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A mixture of 3-amino-5-(3,3-dimethyl-but-1-ynyl)-thiophene-2-carboxylic acid methyl ester, hydrochloride salt (750 mg, 2.74 mmol) and 3-benzyloxy-cyclobutanone (2.5 g, 14.3 mmol) in DCM (40 mL) was treated with sodium triacetoxyborohydride (3.34 g, 15.8 mmol) portionwise. The mixture was stirred at room temperature for 3 hours. The solution was diluted with ethyl acetate, washed sequentially with saturated aqueous sodium bicarbonate, water, and brine. The organic phase was dried over magnesium sulfate, filtered and concentrated. The residue was purified by silica gel chromatography (0-10% ethyl acetate:hexanes). This resulted in 1.26 g (quant. yield) of 3-(3-benzyloxy-cyclobutylamino)-5-(3,3-dimethyl-but-1-ynyl)-thiophene-2-carboxylic acid methyl ester as a mixture of cis- and trans-isomers.

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