Sodium Hydroxide → Carbamic acid, [2-chloro-2-(3-thienyl)ethyl]-, 1,1-dimethylethyl ester

To a solution of 12.2 g of 2-t-butoxycarbonylamino-1-(3-thienyl)ethanol [prepared as described in step (a) above] in 100 ml of absolute methylene chloride was added a solution of 10.4 g of phosphorus pentachloride in 200 ml of absolute methylene chloride at 0° to -5° C. After the addition, the reaction mixture was stirred for 10 minutes. To the reaction mixture was added a 4N aqueous solution of sodium hydroxide, and the mixture was stirred for 5 minutes. The methylene chloride layer was separated, washed with large amount of water and dried over anhydrous magnesium sulfate, and the solvent was evaporated off. The residue was subjected to silica gel column chromatography using a 1:4 by volume mixture of ethyl acetate and cyclohexane as eluent, to yield 7.3 g of the title compound melting at 63°-65° C.