Pyridine → 2-t-Butoxycarbonylamino-1-chloro-1-phenylethane

A mixture of 3.7 ml of pyridine and 2.2 ml of methanesulfonyl chloride was added dropwise to 35 ml of a solution of 3.5 g of 2-t-butoxycarbonylamino-1-phenylethanol [prepared as described in step (a) above] in methylene chloride and the reaction mixture was allowed to stand overnight at room temperature. The reaction mixture was condensed by evaporation under reduced pressure, and the residue was dissolved in a mixture of ethyl acetate and water. The ethyl acetate layer was separated, washed with water and then washed with an aqueous solution of potassium hydrogen sulfate and with an aqueous solution of sodium bicarbonate. The resulting solution was dried over anhydrous magnesium sulfate. The solvent was then distilled off. The residue was subjected to silica gel column chromatography using a 15:85 by volume mixture of ethyl acetate and cyclohexane as the eluent, to give 0.75 g of the title compound as crystals melting at 57°-59° C.