To a stirred solution of 0.540 g (1.45 mmol) of (5S)-1-amino-5-[(trityloxy)methyl]pyrrolidin-2-one from step A above in 5 mL of anhydrous DMF was added 0.327 g (7.25 mmol) of formamide followed by 0.050 g (0.36 mmol) of zinc(II) chloride. The resulting mixture was heated to 160° C. for 48 h, cooled to ambient temperature and diluted with 25 mL of ethyl acetate. The solution was washed sequentially with an aqueous sodium bicarbonate solution, water and then brine and the organic layer dried over magnesium sulfate. The mixture was then filtered, evaporated to dryness in vacuo and purified by silica gel chromatography eluting with a 0-100% ethyl acetatae in hexanes gradient to afford the title compound (0.27 g, 49%). LC-MS: m/z (ES) 382 (MH)+.
