To a suspension of 3-amino-5-phenyl-thiophene-2-carboxylic acid methyl ester (987 mg, 4.23 mmol) in dry THF (1.0 ml), at room temperature, was added 1,4-cyclohexanedione monoethylene ketal (661 mg, 4.23 mmol), followed by dibutyltin dichloride (129 mg, 0.42 mmol). After 5 min, phenyl silane (575 μL, 4.65 mmol) was added and the reaction mixture was stirred at room temperature for 4 days when a clear solution resulted. It was then concentrated and the residue purified by flash chromatography (0% to 30% EtOAc/Hexane) to obtain 1.22 g (77%) of 3-(1,4-Dioxa-spiro[4.5]dec-8-ylamino)-5-phenyl-thiophene-2-carboxylic acid methyl ester.
