(17) Crawford, M.; Rasburn, JW J. Chem. Soc., 1956, 2155. was added to a solution of 46 (3.3 g, 10 mmol) in DMF (5 mL). After standing at 20" C for 16 h, the cloudy solution was evaporated, and the gummy residue was crystallized to give 48 (3.4 g): NMR 6 1.2 (9 H, s), 3.1 (9 H, s), 4.8 (2 H, s), 4.25 (H, d, J= 2 Hz), 4.50 (H, d, J= 2 Hz).